The present invention relates to an electrostatic protection circuit and a semiconductor integrated circuit using the same, particularly to an electrostatic protection circuit for an integrated circuit using an insulated gate field effect transistor (hereinafter referred to as a MOSFET).
FIG. 9 shows a typical electrostatic protection circuit having a commonly-used signal terminal 1509 and power supply terminals 1 and 2 of a MOS integrated circuit using a bulk substrate. In FIG. 9, there are two paths for absorbing static electricity charge applied between the signal terminal 1509 and the power supply terminals 1 and 2. One is a path in which discharge current flows from the signal terminal 1509 to the first power supply terminal 1 designated as potential +VDD through a diode 1503 and the other is a path in which discharge current flows from the second power supply terminal 2 designated as potential xe2x88x92VSS to the signal terminal through a diode 1504. There is another path in which discharge current flows from the second power supply terminal 2 through the diode 1501 to the first power supply terminal 1. To be more practical, an input signal from a pad terminal 1506 is fed to gate electrodes of a p-type MOSFET 1507 and an n-type MOSFET 1508 which form an internal circuit inverter, through a resistor 1505 and the connection of the terminals of the diodes 1503 and 1504, as shown in FIG. 9.
If the pad 1506 is directly connected to the gate of the p-type MOSFET 1507 or n-type MOSFET 1508 of the internal circuit in FIG. 9, the gate electrodes of the p-type MOSFET 1507 and the n-type MOSFET 1508 are often broken when static electricity is applied from the pad 1506. To prevent this, a resistor 1505 for buffering the shock of static electricity and the diodes 1503 and 1504 for absorbing the charge are used. In addition, the diode 1501 serves as a charge-absorbing path not only for static electricity applied between the first and second power supply terminals but also for static electricity applied to the above-described signal terminals as discussed later.
In the conventional electrostatic protection circuit, the above-mentioned diode element 1503 for absorbing charges is connected so as to conduct the charges to the first power supply terminal 1, and the diode element 1504 is connected so as to conduct the charges from the second power supply terminal 2 to the signal terminal 1509. Further, the diode 1501 is connected in a reverse direction between the first power supply terminal 1 and the second power supply terminal 2. This is because, if the diodes 1501, 1503, and 1504 are connected in a forward direction so as to conduct the current in the opposite direction to that shown in FIG. 9, leakage currents may flow through the forward-biased diodes when the integrated circuit is connected to a power supply.
Further, in integrated circuits using a silicon-on-insulator substrate (hereinafter abbreviated as xe2x80x9cSOI integrated circuitxe2x80x9d), there are no wells such as those in a bulk substrate, the bottom is insulated by a buried oxide film, and the side is also covered with a local oxide film formed by LOCOS (local oxidation of silicon) method. For this reason, there is generally no equivalent to the diode 1501 between the first and second power supply terminals shown in FIG. 9. In other words, there is no diode formed by a p well and an n well in a conventional substrate between the first and second power supply terminals as shown in FIG. 11. However, such a diode is required from the viewpoint of electrostatic protection as discussed later. Therefore, in an SOI integrated circuit, a diode 1801 is added between the first and second power supply terminals as shown in FIG. 12, or a MOSFET 1901 with the source and gate electrodes connected together is connected between the first and second power supply terminals for causing the MOSFET 1901 to perform the function of the reverse-biased diode as shown in FIG. 13. Alternatively, a p-type MOSFET 2001 and n-type MOSFET 2000 each having the source and gate electrodes connected together are connected in parallel between the first and second power supply terminals as shown in FIG. 14 to cause them perform the function of the reverse-biased diodes. SOI integrated circuits are thus provided with electrostatic protection based on the same principle as for bulk-substrate integrated circuits.
If static electricity is added between the power supply terminals or between the signal terminal and one of the power supply terminals, electrostatic breakdown may occur inside the integrated circuit. In the case where static electricity is added to signal terminals, the internal circuit to which the signal terminals are connected may frequently be damaged unless the charges are quickly absorbed by an electrostatic protection circuit. In FIG. 9, the gates of p-type MOSFET 1507 and n-type MOSFET 1508 may be broken down. The gate insulating film of a MOSFET is made of a very thin film from several hundred angstrom to several tens angstrom formed between the substrate and the gate electrode, and the substrate or the source electrode is finally connected to the power supply. As a result, a high voltage is applied across the thin gate silicon oxide film to produce a strong electric field, resulting in breakdown of the gate film. Therefore, when static electricity is added, the electrostatic protection circuit in FIG. 9 or a similar means is used to absorb the charges quickly. In the circuit of FIG. 9, the following four cases are possible for the flow of charges between the signal terminal 1509 and the first and second power supply terminals 1 and 2:
(A) Signal terminal: positive charges, First power supply terminal: negative charges
(B) Signal terminal: negative charges, First power supply terminal: positive charges
(C) Signal terminal: positive charges, Second power supply terminal: negative charges
(D) Signal terminal: negative charges, Second power supply terminal: positive charges
In the conventional circuit shown in FIG. 9, the diode 1503 or diode 1504 operates in a forward direction in the cases (A) and (D) above. Accordingly, electrostatic charges that comes in can be quickly absorbed, thereby preventing electrostatic destruction. In cases (B) and (C), the diodes 1503 and 1504 are both in a reverse direction with respect to the polarity of electrostatic charges. In case (B), negative charge forces its path through the diode 1503 in a reverse direction. Otherwise, the negative charges first flow through the diode 1504 in a forward direction, then flow from the second power supply terminal 2 to the first power supply terminal 1 through the reverse diode 1501 in the substrate. In case (C), positive charges force its path through the diode 1504 in a reverse direction. Alternatively, the positive charges first flow through the diode 1503 in a forward direction, then flow from the first power supply terminal 1 to the second power supply terminal 2 through the reverse diode 1501 in the substrate. Therefore, in cases (B) and (C), because charges must necessarily flow through a diode in a reverse direction, the circuit is vulnerable to static electricity and can be broken by even comparatively low voltages. A path through which electrostatic charges flow out in the case (C) is shown in FIG. 10 as an example.
The function of the reverse-biased diode between the power supplies in the case where static electricity is applied to the signal terminals has been described above. If static electricity is applied between the power supply terminals in the same polarity as the power supply voltage, the charges flow through the diode between the power supply terminals in a reverse direction. Since even this diode does not exist in SOI integrated circuits, electrostatic charges cannot be absorbed, and hence breakdown easily occurs at the most vulnerable part among the parts involved in the power supply lines.
Next, the mechanism why a diode is endurable in a forward direction and weak in a reverse direction will be briefly discussed referring to FIGS. 30 and 31. In FIG. 30, a p-type diffusion layer 131 and an n-type diffusion layer 132 join together at the boundary to form a pn diode. FIG. 30 shows the case in which the p-type diffusion layer 131 is at a positive potential and the n-type diffusion layer 132 is at a negative potential. In this case, since the diode is forward-biased and a current therefore can flow easily everywhere in the pn boundary, the current flows uniformly across the entire pn boundary. Accordingly, the diode as a whole allows easy flow of current and exhibits high charge-absorbing capability. Furthermore, because the current flows in the diode itself well dispersed and uniformly without extreme concentration, no destruction of the diode itself occurs due to flow of current.
On the other hand, FIG. 31 shows the state where a current flows in a reverse direction. In FIG. 31, a p-type diffusion layer 141 and an n-type diffusion layer 142 join together at the boundary to form a pn diode. FIG. 31 shows the case in which the p-type diffusion layer 141 is at a negative potential and the n-type diffusion layer 142 is at a positive potential.
In this case, since the diode is reverse-biased to the voltage applied, normally no current flows. However, if a high voltage is applied to the diode in order to force a current in a reverse direction, the current begins to flow at specific parts where the breakdown voltage is comparatively low and hence current can easily flow due to non-uniform pn boundaries. Therefore, even if the voltage goes over the breakdown voltage and a current begins to flow, this does not mean that the current is flowing uniformly across the entire boundary. The current tends to concentrate in the parts allowing easy flow thereof. The state of this current flow is shown in FIG. 31. Since current does not flow uniformly in the diode but tends to concentrate in specific parts when the current flows in a reverse direction in the diode, the capability of the diode to allow current to flow is small relative to the size of the pn boundary area of the diode. In other words, the diode exhibits only a small charge absorbing capability. In addition, since current concentrates in parts of the diode allowing easy flow of current, the current density in those parts extremely increases, there is a high risk for the diode to be unduly heated and broken down.
As described above, a diode exhibits high endurance to static electricity when acting in a forward direction, but exhibits so weak endurance when acting in a reverse direction that the diode may be damaged even by low static electricity depending on the manner in which the static electricity is applied.
In the conventional electrostatic protection circuit configuration, the above-described occurrence in which the diodes operate only in a reverse direction to the charges is unavoidable. To improve the electrostatic endurance in these cases, conventionally the size of the diode or MOSFET has been increased to cope with weakness in a reverse direction by increasing the areas of the diode or MOSFET. This increases the area occupied by the electrostatic protection circuit attached to each pad, resulting in a cost increase and limitation to the number of pads and pins which can be formed.
Furthermore, the increase in the diode area accompanies an increase in the parasitic electrostatic capacity acting as a capacitor, causing degradation of the high frequency characteristics of signal terminals for which the high frequency operation is required and an increase in power consumption.
In the case of SOI integrated circuits, as mentioned above there is a problem of very low electrostatic endurance due to absence of even the reverse-biased diode formed by p and n wells between the power supply terminals. Assume that an attempt is made, for example, to add a reverse-biased diode or equivalent device corresponding to the reverse-biased diode formed by p and n wells in a conventional bulk substrates between the power supply terminals by forming an additional diode or MOSFET. This method also cannot provide SOI integrated circuits with a sufficiently high electrostatic endurance because it is not possible to form a reverse-biased diode as large as the conventional reverse-biased diode formed by the p and n wells parasiting between power supply terminals with a very large area because of the limitation to the area.
The present invention has been completed in view of these problems, and has an objective of providing an improved electrostatic protection circuit which affords a sufficiently high electrostatic endurance between the power supply terminals or between one of the power supply terminals and the signal terminal, and a semiconductor integrated circuit using the electrostatic protection circuit. Another objective of the present invention is to provide an electrostatic protection circuit exhibiting high electrostatic endurance with a comparatively small area, and a semiconductor integrated circuit using this electrostatic protection circuit, which is sufficiently endurable to the static electricity and suitable for high-frequency operation because of very small parasitic electrostatic capacity due to the use of this protection circuit.
According to one aspect of the present invention, there is provided an electrostatic protection circuit comprising:
a first power supply terminal to which a first voltage is applied;
a second power supply terminal to which a second voltage lower than the first voltage is applied;
a first diode connected in a reverse direction between the first and second power supply terminals; and
a second diode connected in a forward direction between the first and second power supply terminals,
wherein a forward drop voltage of the second diode is set to be higher than a drive voltage supplied between the first and second power supply terminals.
According to this aspect of the present invention, either one of the first and second diodes always operates in a forward direction with respect to the static electricity applied between the first and second power supply terminals regardless of the polarity of the static electricity. Electrostatic charges therefore can be quickly absorbed through the diode in a forward direction.
Because the second diode is connected in a forward direction between the first and second power supply terminals in this embodiment, this second diode is forward-biased to the electric charges of the drive voltage applied between the first and second power supply terminals in the ordinary operations. However, the forward drop voltage of the second diode is set to be higher than the drive voltage supplied between the first and second power supply terminals. For this reason, a forward leakage current does not flow through the second diode during normal operation.
The second diode may have a pn junction structure formed by a p-type diffusion layer and an n-type diffusion layer joined together. In this case, the forward drop voltage of the second diode is defined by a contact potential (or contact potential difference) which is a potential difference generated at the boundary of the p-type diffusion layer and an n-type diffusion layer. Therefore, if the forward drop voltage of the second voltage is set to be higher than the drive voltage supplied between the first and second power supply terminals, a forward leakage current of the second diode can be prevented from flowing during normal operation.
The second diode may be formed from a plurality of diodes connected in series. Each of the plurality of diodes has a pn junction structure formed by a p-type diffusion layer and an n-type diffusion layer joined together. Assuming that the number of diodes connected in series is n, the forward drop voltage of the second diode becomes n times the contact potential of each diode. As a result, it is possible to use higher power supply voltages.
The second diode may include first p-type and n-type diffusion layers and a second p-type or n-type diffusion layer disposed between and connected to the first p-type and n-type diffusion layers. In this case, it is preferable that the diffusion concentration of the first p-type and n-type diffusion layers is set to be higher than the diffusion concentration of the second p-type or n-type diffusion layer. Because the contact potential of the second diode can be increased in this manner, it is possible to use higher power supply voltages.
The second diode may also be formed by a MOS transistor having a drain electrode and a gate electrode which are connected to each other. In this case, the forward drop voltage of the second diode is defined by the threshold voltage of the MOS transistor.
The second diode may also be formed by connecting a plurality of MOS transistors in series. In this case, a drain electrode and a gate electrode are connected to each other in each of the plurality of MOS transistors. Assuming the number of MOS transistors connected in series is n, the forward drop voltage of the second diode is n times the threshold voltage of each MOS transistor. As a result, it becomes possible to use higher power supply voltages.
The first diode may be formed by connecting in parallel a p-type MOS transistor having a source electrode and a gate electrode connected to the first power supply terminal, with an n-type MOS transistor having a source electrode and a gate electrode connected to the second power supply terminal. This configuration ensures the first diode to exhibit more stable characteristics.
The first and second diodes may be formed on a silicon-on-insulator (SOI) substrate. The first and second diodes are then surrounded by insulator layers, and therefore formation of superfluous parasitic diodes can be prevented.
According to another aspect of the present invention, there is provided an electrostatic protection circuit comprising:
a first power supply terminal to which a first voltage is applied;
a second power supply terminal to which a second voltage lower than the first voltage is applied;
a signal terminal to which a signal voltage equal to or lower than the first voltage and equal to or higher than the second voltage is applied;
a first diode connected in a forward direction between the first power supply terminal and the signal terminal;
a second diode connected in a forward direction between the signal terminal and the second power supply terminal;
a third diode connected in a reverse direction between the first power supply terminal and the signal terminal; and
a fourth diode connected in a reverse direction between the signal terminal and the second power supply terminal,
wherein a forward drop voltage of each of the first and second diodes is set to be higher than a drive voltage supplied between the first and second power supply terminals.
According to this aspect of the present invention, one of the first to fourth diodes certainly operates in a forward direction with respect to the static electricity applied between the signal terminals and the first/second power supply terminal regardless of the polarity of the static electricity. Electrostatic charges therefore can be quickly absorbed through the diode in a forward direction.
The first and second diodes are connected in a forward direction between the signal terminal and the first or second power supply terminal. Therefore, the first and second diodes are forward-biased to electric charges of the drive voltage applied between the signal terminal and the first/second power supply terminal in the ordinary operations. However, the forward drop voltage of each of the first and second diodes is set to be higher than the drive voltage supplied between the first and second power supply terminals. For this reason, a forward leakage current does not flow through the first and diode during normal operation.
The above-mentioned features can be applied to other aspects of the present invention.
According to still another aspect of the present invention, there is provided a semiconductor integrated circuit comprising:
a logic circuit formed by interconnecting a plurality of p-type MOS transistors and a plurality of n-type MOS transistors; and
an input/output circuit disposed around the logic circuit,
wherein the input/output circuit includes an electrostatic protection circuit which protects the logic circuit from static electricity and has elements of one aspect of the present invention.
According to this aspect of the present invention, the logic circuit can be protected from static electricity by the actions of the above-described electrostatic protection circuit.
Above-described features of the electrostatic protection circuit can be applied to the semiconductor integrated circuit of the present invention.
Particularly, the diffusion concentration of at least one of the p-type and n-type diffusion layers of the first diode may be set equal to or higher than the diffusion concentration of diffusion layers used for source electrodes of the plurality of p-type and n-type MOS transistors in the logic circuit. If the diffusion concentrations of the above diffusion layers are set to be equal, no forward leakage current occurs through the second diode during normal operation when the forward drop voltage (contact potential) of the second diode is set to be higher than the drive voltage supplied between the first and second power supply terminals. If the above diffusion concentrations are set to be higher, the contact potential of the second diode increases and higher power supply voltages can be used.
Similarly in the case that the threshold voltage of the MOS transistor which forms the second diode is set to be higher than the threshold voltage of each of the plurality of p-type and n-type MOS transistors in the logic circuit, higher power supply voltages can be used.
The semiconductor integrated circuit according to other aspects of the present invention includes the electrostatic protection circuit having the elements of the other aspects of the present invention.
The above described features of the electrostatic protection circuit can be applied to the semiconductor integrated circuit of the present invention.


Japanese Patent Application Laid-Open Publication No. 2008-118004 (Patent Document 1) describes a layout structure in which a power supply wiring connected to a diffusion layer is drawn onto boundary line between adjacent standard cells. More specifically, Patent Document 1 describes a layout structure in which a diffusion layer is shared between adjacent standard cells and a wiring is drawn from a power supply wiring onto boundary line between the adjacent standard cells. And, Patent Document 1 describes a structure in which the wiring drawn on the boundary line between the adjacent standard cells and the diffusion layer shared between the adjacent standard cells are electrically connected to each other via a plug.


Steam bath have been popular worldwide recently for health reasons. The only drawback of a steam bath is the high service charge due to the expensive associated facilities. As such, a relatively cheap portable sauna enclosure has been commercially available as shown in FIG. 1. The sauna enclosure comprises a frame 1 including a plurality of interconnected vertical and horizontal bars, a canopy 2 covered on the frame 1 and stretched by it for forming a space to allow a person to take a bath therein, canopy 2 having three holes 201 for the neck and two arms extending through and a zipper 202 for permitting a person to enter the sauna enclosure when it is unfastened, a steamer 3 outside the sauna enclosure, and a steam pipe 4 connected between the steamer 3 and the inside of the sauna enclosure for transferring steam from steamer 3 to the sauna enclosure. The user should add water into steamer 3 for heating. After bathing, the user should use a dry cloth to absorb the condensed steam (i.e., water) in the sauna enclosure in order to forestall the growth of micro-organisms on the canopy 2.
However, the previous design suffered from several disadvantages. For example, it is still possible for steam to pass through holes 201 and zipper 202 during bathing due to the gaps between human body (i.e., neck and arms) and holes 201 as well as the gaps in the zipper 202 itself. As such, the leaked steam may be subsequently carried from the bathroom to the other rooms in the house, resulting in a potential damage to the household appliances, furniture, and wall due to humidity. In addition, the assembly and disassembly of frame 1 and steam pipe 4 is a tedious job. Also, the efficiency of steamer 3 may be adversely affected if the packing between steam pipe 4 and steamer 3 is not well sealed. Furthermore, the bulky steamer 4 is not easy to store when not in use. In view of this, its portability is adversely affected. Thus, it is desirable to provide an improved portable sauna enclosure in order to overcome the above drawbacks of the prior art.


Brine is a concentrated salt solution (usually sodium chloride), which is used for preserving various foodstuffs, as well as in the refrigerant industry. Brine is also a by-product of some seawater desalination plants. However, the disposal of brine can be problematic. For example, the density of brine is greater than typical seawater, and if it was discharged into the sea, it would tend to sink towards the seabed and not disperse throughout the water column. This can result in a hypersaline layer of water forming on the seabed, which could damage sea habitats and organisms.


This invention relates to a cyclic or step feed drilling machine in which one drilling process is carried out, instead of being performed in a single stroke, by gradually deepening a bore-depth by means of repeating reciprocative movement of a tool for a plurality of times before completing the drilling process.
More particularly it relates to a cyclic drilling machine in which magnitude of a load applied on the tool is detected so that the tool is, when the detected load grows larger to a certain value, retreated backwards once for being advanced again.
As a prior art belonging to this category, a technological idea disclosed in the Japanese patent publication TOKU-K0-No. SHO 53(1978)-40745 can be cited, in which magnitude of a load applied on the tool is detected or measured by the fluctuation or variation of load current observed in a tool driving motor, and the tool, i.e. drill in this instance, is returned backwards once in response to an indication of reaching of the load current to a predetermined value.
In this kind of device a load current of a motor at a non-load status is memorized once as a minimum value (Io) in a memory circuit, and a load current of a motor corresponding to a cutting (drilling) torque within the maximum allowable limit, wherein the drill can not be broken, is set in advance on the other hand as a current set value ({ Is). Sum of the both values (Is (=Io+.DELTA.Is)) is regarded as a reference value. Comparing of this reference value (Is) with a load current (I) of a motor which is detected in the course of a cutting is executed in a comparing circuit or comparator, so that the drill in advancing movement may be instantly returned backwards as soon as the load current (I) reaches the reference value (Is), that is when a cutting torque of the maximum allowable limit is applied on the drill. When a certain predetermined period of time has elapsed after the motor was placed under a non-load condition due to the return of the drill, the then non-load current value is memorized in the memory circuit in place of the previous minimum value as a new minimum value (Io). The drill is advanced again so as to resume the cutting of a workpiece which has been halfway suspended. The then load current value (I) of the motor is compared in the comparator with the reference value (Is). When the drill receives a cutting torque of the maximum allowable limit again it is instantly returned backwards similarly to the previous instance. This type of operation is repeated until a bore of a predetermined depth is formed in the workpiece, so that the drill may be prevented from damage or breakage.
The cutting process is however finished in general within 1-3 minutes after a workpiece is placed on the drilling machine, and the motor is stopped between the finish of cutting on one workpiece and the beginning of cutting on another workpiece. In other words, the cutting is carried out in the prior art while the motor (in this instance AC motor is used, but DC motor is also permissible) is under an unstable status, as shown in FIG. 1, wherein the winding current gradually decreases from a large initial current value to a stable current value. It means that the aforesaid minimum value (Io) is set while the winding current is unstable in the course of falling as shown in FIG. 2 and the reference value (Is), on which the cutting process depends, is set according to this minimum value (Io). Comparison of the minimum value (Io) with a current value (Io1), which would have been attained if the minimum value had been set when the winding current reached the reference value (Is), will show that the current value (Io1) is smaller than the minimum value (Io) by an amount of (.DELTA.I.alpha.).
For preventing the drill from the breakage, the reference value (Is) must be made, therefore, smaller by the difference (.DELTA.I.alpha.) of the minimum value (Io) minus the current value (Io1), i.e., to (Iss (=Is-.DELTA.I.alpha.)). It signifies that for making the reference value (Is) smaller by .DELTA.I.alpha., the aforementioned current set value (.DELTA.Is) must be set smaller by that much. In practical machining lines, such as a machining factory, wherein power source is variable in voltage even when a motor itself is in a stable status, the winding current thereof varies a great detal so that mistaking of this variation for that owing to load variation will cause an error operation. External noise will also cause the error operation. Reducing of the current set value (.DELTA.Is) is therefore envisaged with a limit. The step feed type cutting (drilling) with a thin drill which requires setting of a small current set value (.DELTA.Is) is practically next to impossible.
Comparison of a characteristic curve Ip1 of the winding current in the initial stage of the motor driving starting from a sleeping status with those curves Ip2 and Ip3 in the initial stage of the motor driving at a repeatedly operated status will show that the time required for decreasing value is longer in the curve Ip1 than in the others Ip2, Ip3, due to variation in the motor itself such as internal resistance in the motor. And the difference (I.alpha.) is maintained in a larger state, in other words, a status where the difference (.DELTA.I.alpha.) is large is maintained for a long period of time in the drilling of the workpiece in the initial operation period. It means that the time with a large difference (.DELTA.I.alpha.) continues for a comparatively longer period, particularly in a colder region for quite a long time, before the motor enters a stabilized operation wherein the machining can be stably performed. It naturally deteriorates the operational efficiency, to the great disadvantage.
In the conventional devices variation of the load current, i.e. variation of the winding current of the motor which is caused by the load variation is the detection object. It is quite difficult to get true variation of the cutting torque in this method, because the variation obtained herewith is nothing but a sum of the true variation value of the cutting torque plus a torque produced in the transmission system from the motor to the drill. And the torque produced in the transmission system is variable in itself during operation thereof. It is, therefore, problematical in this connection whether the variation of the winding current can be truly regarded as the variation of the cutting torque.
Besides, the technology disclosed in the Japanese patent publication TOKU-SO-No. SHO 54(1979)-23158 attempts to raise in put impedance by means of an emitter follower with FET (field-effect-transistor) so as to minimize leakage of electric charge which is charged in a capacitor for the purpose of preventing the timewise variation of the minimum value (Io) in a memory circuit storing the minimum value (Io). It is however practically very difficult to prevent the leakage in the capacitor, so exact maintenance of the minimum value (Io) and subsequent setting as well as maintaining of an exact reference value (Io) is next to impossible, to the great problem.


Nipple drinker watering systems are commonly used to provide water to poultry and other small animals. These watering systems involve the use of several branching water supply lines extending the interior length of a house, such as a poultry house. The water supply lines have numerous nipple drinkers attached thereto so that the poultry may obtain water by pecking at the nipples. Stand-tubes are typically provided at various locations along the length of the water supply lines, typically proximate to pressure regulators. The stand-tubes are generally clear and provide a visual indication, with the assistance of a float provided in the stand-tube, of the water pressure level (via water column) in the water supply line at their locations. In order to be effective, the stand-tubes must be able to vent to the outside environment.
Periodically, it may be necessary to flush the nipple drinker watering systems in order to clean out the watering system as material may build up in the watering lines over time due to, for instance, the introduction of sediment from the water source itself or from growers adding material to the water source, such as chlorine or medication. Such build-up of material in the watering system can interfere with proper water flow along the water supply line and may eventually contribute to the malfunction of the nipple drinkers. It may also be necessary to flush the nipple drinker watering systems in order to remove warmer water from the watering system. Removal of warm water from the watering system in order to replace it with cooler water has been found to increase consumption of water by poultry.
Due to the need to flush the systems, the stand-tubes have been outfitted with caps designed to try and prevent leakage out of the stand-tubes during a flushing operation, as well as to prevent the floats from being blown out of the stand-tubes in view of the increased water pressure in the system caused by the flushing. One example of such a cap is shown and described in U.S. Pat. No. 5,136,983. This cap, as well as others, however, have had their own problems. For instance, some caps have had problems with air lock being caused by the seal being formed when it should be allowing air to pass. Other caps have had problems with still allowing leakage to occur after the seal is formed. Other caps have had problems with forming the seal at lower water pressures (e.g., the seal may be formed in caps provided closer to the water source, where the water pressure is typically higher, but not in caps provided distal from the water source, where the water pressure is typically lower). Other caps have designs which allow for air flow both in and out of the assembly, but which allows for unwanted particles to enter the assembly which can cause contamination of the water and which can creates blockages in the cap, thereby potentially causing it to malfunction.
In view of the foregoing, there is a need for a breather cap assembly which overcomes all of the disadvantages of the prior art caps.


The present invention relates to a stage apparatus used for, e.g., a fine moving stage for finely aligning a substrate such as a wafer or a master such as a reticle in an exposure apparatus or the like, an exposure apparatus, and a device manufacturing method.
Control techniques for industrial and information devices are increasing in precision and speed as such devices become complicated, advanced, and miniaturized. Exposure apparatuses for manufacturing xe2x80x9csemiconductor devicesxe2x80x9d which support various types of such devices are also rapidly increasing in speed and precision, and demands are arising for nm-order alignment precision and the like.
A generally known alignment mechanism for a wafer and reticle in an exposure apparatus is a stage apparatus constituted by a fine moving stage having a microtranslation mechanism and fine rotation mechanism, and a coarse moving stage having a large-stroke moving mechanism in the translational direction.
Such an exposure apparatus finely aligns, controls, and exposes a wafer or reticle on the fine moving stage so as to make it coincide with the image or object plane by the fine moving stage mounted on the coarse moving stage while the coarse moving stage makes large-stroke movement.
In general, both the coarse and fine moving stages often use linear motors, which utilize a Lorentz force, as the actuator of the alignment mechanism.
However, the fine moving stage of the exposure apparatus has recently been found to suffer from the following problems.
(1) As chips, wafers, and reticles increase in size, the fine moving stage also increases in size. Pushing up the fine moving stage by a linear motor using a Lorentz force consumes a large amount power.
Especially the actuator of the fine moving stage is often attached near a wafer or reticle. Compared to the coarse moving stage, the fine moving stage greatly influences the wafer or reticle to thermally deform it, resulting in very low final exposure precision.
(2) Demands are arising for a high-speed exposure apparatus, and the acceleration of the coarse moving stage is being increased. This means that the acceleration applied from the coarse moving stage to the fine moving stage also increases. When the coarse moving stage accelerates the fine moving stage, a moment force proportional to the acceleration of the coarse moving stage acts on the fine moving stage due to the difference between the barycenter of the fine moving stage and a xe2x80x9cpoint of applicationxe2x80x9d where the actuator of the coarse moving stage pushes the fine moving stage.
Hence, as the speed increases, the actuator of the fine moving stage becomes bulky in order to withstand the moment force, and the amount of heat generated by the actuator increases to adversely influence the exposure precision. In other words, a bulky actuator increases heat, which is a vicious cycle.
As a means for solving these problems, there is provided a method of compensating for the weight of the fine moving stage by using the repulsion and attraction forces of a magnet or electromagnet. In this case, it is difficult to hold the posture of the fine moving stage by compensation with only the magnet, so a spring is also used to hold the posture.
FIGS. 5A and 5B schematically show a conventional wafer stage for compensating for the weight by magnetic repulsion. This wafer stage comprises a fine moving stage 101 having a support surface 101a for supporting a wafer WO, a coarse moving stage 102 having a large-stroke moving mechanism (not shown), first to third spring members 103a to 103c for holding the posture of the fine moving stage 101 on the coarse moving stage 102, and first to third magnetic units 104a to 104c for compensating for the weight by a so-called magnetic repulsion force for supporting the weight of the fine moving stage 101. The magnetic units 104a to 104c are respectively made up of magnets 141a to 141c fixed to the upper surface of the coarse moving stage 102 and magnets 142a to 142c fixed to the lower surface of the fine moving stage 101 so as to face the corresponding magnets 141a to 141c.
The weight of the fine moving stage 101 is compensated for by the magnetic repulsion forces of the magnets 141a to 141c and 142a to 142c of the magnetic units 104a to 104c. When the wafer W0 is aligned near the image plane of a projection optical system (not shown), the weight of the fine moving stage 101 is canceled by the magnetic repulsion force.
The three spring members 103a to 103c for compensating for the posture of the fine moving stage 101 have the same spring constant, which is set to minimize the restoring forces of the springs while the wafer W0 is near the image plane.
The fine moving stage 101 has a pair of bar mirrors 110 for detecting the position of the fine moving stage 101 by a laser interferometer or the like. This wafer stage is equipped with a control system for feeding back the detected position information of the fine moving stage 101 to the actuator of the coarse moving stage 102.
The three posture compensation spring members 103a to 103c are generally arranged at positions Z1 to Z3 at equal intervals of 120xc2x0 on a circle of a radius r having a geometrical center O of the fine moving stage 101 as its center.
In this prior art, however, the barycenter of a structure formed from the members and fine moving stage is at a position different from the geometrical center of the fine moving stage, i.e., the geometrical centroid of a triangle formed by the support points Z1 to Z3 of the spring members 103a to 103c under the influence of the members such as the bar mirrors fixed to the fine moving stage for holding a wafer. The restoring forces of the three spring members necessary for pushing up the fine moving stage only in the +Z direction without rotating it and for keeping it at a predetermined pushed-up position and posture are different.
Accordingly, holding the posture by the three springs having the same spring constant causes the following problems even if the magnets compensate for the weight of the fine moving stage. Assume that the fine moving stage is vertically displaced in the xe2x88x92Z direction without rotating it, and the springs uniformly deflect. In this case, the sum of the restoring forces of the three springs not only translates the fine moving stage in the +Z direction but also rotates it.
More specifically, if an external force acts on the fine moving stage owing to some factor while position control by the actuator of the fine moving stage stops, or if position control stops due to an emergency stop caused by an accident while the fine moving stage is displaced in the xe2x88x92Z direction by the actuator, restoring motion of the fine moving stage in the +Z direction and tilt motion exceeding a moving stroke in the rotational direction occur, scoring or damaging the stage.
There is proposed a method of compensating for the weight of the fine moving stage by magnets, compensating for the posture by springs, and generating a uniform weight compensation force by the magnets in almost the entire range of the Z-direction stroke on the fine moving stage. Even this method requires a posture holding means using coil springs or leaf springs because compensation by only magnets is unstable. This method cannot solve the static unbalance.
There is also proposed a method of directly compensating for the weight of the fine moving stage by springs. Even this method cannot solve the above problems.
The present invention has been made to overcome the conventional drawbacks, and has as its object to provide a stage apparatus which uses at least three spring members in order to compensate for the weight of a stage for setting a wafer or reticle, can improve the stability of a compensation function by the spring members, and can effectively avoid scoring of or damage to the stage, to provide an exposure apparatus including the stage, and to provide a method of manufacturing a device by using the exposure apparatus.
To achieve the above object, according to the present invention, there is provided a stage apparatus comprising:
a stage;
a member fixed to said stage; and
a weight compensation mechanism having at least three spring members for compensating for a weight of a structure including said stage and said member, a barycentric position of the structure deviating from a centroid of a polygon formed by support points of the at least three spring members,
wherein spring constants of the at least three spring members are determined based on a relative position relationship between the barycentric position of the structure and the at least three spring members so as to set at least one spring constant different from the other spring constants.
According to a preferred embodiment of the present invention, it is preferable that the at least three spring members include coil springs.
According to a preferred embodiment of the present invention, it is preferable that the at least three spring members include air cylinders.
According to a preferred embodiment of the present invention, it is preferable that the at least three spring members include leaf springs.
According to a preferred embodiment of the present invention, it is preferable that the weight compensation mechanism further includes a magnet.
According to a preferred embodiment of the present invention, it is preferable that the apparatus further comprises an actuator for vertically driving said stage.
According to a preferred embodiment of the present invention, it is preferable that the actuator includes a linear motor.
According to a preferred embodiment of the present invention, it is preferable that the apparatus further comprises at least three actuators for vertically driving said stage, wherein a supporting force generated by each of the spring members and applied to said stage and a driving force generated by each of the actuators and applied to said stage are exerted on the same axis.
According to a preferred embodiment of the present invention, it is preferable that the member includes a mirror.
According to a preferred embodiment of the present invention, it is preferable that the at least three spring members are arranged at positions a constant distance from the geometrical center of said stage.
According to a preferred embodiment of the present invention, it is preferable that the at least three spring members include n spring members, and the n spring members are arranged at vertexes of a regular n-side polygon having the geometrical center of said stage as a center.
According to the present invention, there is provided a stage apparatus comprising:
a stage;
a member fixed to said stage; and
a weight compensation mechanism having at least three spring members for compensating for a weight of a structure including said stage and said member, a barycentric position of the structure deviating from a centroid of a polygon formed by support points of the at least three spring members,
wherein spring constants of the at least three spring members are determined to make application points of restoring forces of the at least three spring members coincide with the barycentric position of the structure when said stage is statically balanced.
According to the present invention, there is provided a stage apparatus comprising:
a coarse moving stage;
a fine moving stage mounted on said coarse moving stage;
a member fixed to said fine moving stage; and
a weight compensation mechanism which has at least three spring members for compensating for a weight of a structure including said fine moving stage and said member and is interposed between said coarse moving stage and said fine moving stage, a barycentric position of the structure deviating from a centroid of a polygon formed by support points of the at least three spring members,
wherein spring constants of the at least three spring members are determined based on a relative positional relationship between the barycentric position of the structure and the at least three spring members so as to set at least one spring constant different from the other spring constants.
According to the present invention, there is provided a stage apparatus comprising:
a coarse moving stage;
a fine moving stage mounted on said coarse moving stage;
a member fixed to said fine moving stage; and
a weight compensation mechanism which has at least three spring members for compensating for a weight of a structure including said fine moving stage and said member and is interposed between said coarse moving stage and said fine moving stage, a barycentric position of the structure deviating from a centroid of a polygon formed by support points of the at least three spring members,
wherein spring constants of the at least three spring members are determined to make application points of restoring forces of the at least three spring members coincide with the barycentric position of the structure when said stage is statically balanced.
According to the present invention, there is provided an exposure apparatus comprising:
an illumination system for illuminating a master;
a master stage apparatus which moves while supporting the master;
a projection optical system for projecting a pattern of the master onto a substrate; and
a substrate stage apparatus which moves while supporting the substrate,
at least one of said master and substrate stage apparatuses having
a stage,
a member fixed to said stage, and
a weight compensation mechanism having at least three spring members for compensating for a weight of a structure including said stage and said member, a barycentric position of the structure deviating from a centroid of a polygon formed by support points of the at least three spring members,
wherein spring constants of the at least three spring members are determined based on a relative positional relationship between the barycentric position of the structure and the at least three spring members so as to set at least one spring constant different from the other spring constants.
According to the present invention, there is provided an exposure apparatus comprising:
an illumination system for illuminating a master;
a master stage apparatus which moves while supporting the master;
a projection optical system for projecting a pattern of the master onto a substrate; and
a substrate stage apparatus which moves while supporting the substrate,
at least one of said master and substrate stage apparatuses having
a stage,
a member fixed to said stage, and
a weight compensation mechanism having at least three spring members for compensating for a weight of a structure including said stage and said member, a barycentric position of the structure deviating from a centroid of a polygon formed by support points of the at least three spring members,
wherein spring constants of the at least three spring members are determined to make application points of restoring forces of the at least three spring members coincide with the barycentric position of the structure when said stage is statically balanced.
According to the present invention, there is provided an exposure apparatus comprising:
a projection optical system for projecting an image onto a substrate; and
a substrate stage apparatus which moves while supporting the substrate,
said substrate stage apparatus having
a stage,
a member fixed to said stage, and
a weight compensation mechanism having at least three spring members for compensating for a weight of a structure including said stage and said member, a barycentric position of the structure deviating from a centroid of a polygon formed by support points of the at least three spring members,
wherein spring constants of the at least three spring members are determined based on a relative positional relationship between the barycentric position of the structure and the at least three spring members so as to set at least one spring constant different from the other spring constants.
According to the present invention, there is provided an exposure apparatus comprising:
a projection optical system for projecting an image onto a substrate; and
a substrate stage apparatus which moves while supporting the substrate,
said substrate stage apparatus having
a stage,
a member fixed to said stage, and
a weight compensation mechanism having at least three spring members for compensating for a weight of a structure including said stage and said member, a barycentric position of the structure deviating from a centroid of a polygon formed by support points of the at least three spring members,
wherein spring constants of the at least three spring members are determined to make application points of restoring forces of the at least three spring members coincide with the barycentric position of the structure when said stage is statically balanced.
According to the present invention, there is provided a device manufacturing method comprising the steps of:
exposing a photosensitive agent on a substrate by using an exposure apparatus; and
developing the photosensitive agent on the substrate,
the exposure apparatus having
an illumination system for illuminating a master,
a master stage apparatus which moves while supporting the master,
a projection optical system for projecting a pattern of the master onto a substrate, and
a substrate stage apparatus which moves while supporting the substrate,
at least one of the master and substrate stage apparatuses having
a stage,
a member fixed to the stage, and
a weight compensation mechanism having at least three spring members for compensating for a weight of a structure including the stage and the member, a barycentric position of the structure deviating from a centroid of a polygon formed by support points of the at least three spring members,
wherein spring constants of the at least three spring members are determined based on a relative position relationship between the barycentric position of the structure and the at least three spring members so as to set at least one spring constant different from other spring constants.
According to the present invention, there is provided a device manufacturing method comprising the steps of:
exposing a photosensitive agent on a substrate by using an exposure apparatus; and
developing the photosensitive agent on the substrate,
the exposure apparatus having
an illumination system for illuminating a master,
a master stage apparatus which moves while supporting the master,
a projection optical system for projecting a pattern of the master onto a substrate, and
a substrate stage apparatus which moves while supporting the substrate,
at least one of the master and substrate stage apparatuses having
a stage,
a member fixed to the stage, and
a weight compensation mechanism having at least three spring members for compensating for a weight of a structure including the stage and the member, a barycentric position of the structure deviating from a centroid of a polygon formed by support points of the at least three spring members,
wherein spring constants of the at least three spring members are determined to make application points of restoring forces of the at least three spring members coincide with the barycentric position of the structure when the stage is statically balanced.
According to the present invention, there is provided a device manufacturing method comprising the steps of:
exposing a photosensitive agent on a substrate by using an exposure apparatus; and
developing the photosensitive agent on the substrate,
the exposure apparatus having
a projection optical system for projecting an image onto a substrate, and
a substrate stage apparatus which moves while supporting the substrate,
the substrate stage apparatus having
a stage,
a member fixed to the stage, and
a weight compensation mechanism having at least three spring members for compensating for a weight of a structure including the stage and the member, a barycentric position of the structure deviating from a centroid of a polygon formed by support points of the at least three spring members,
wherein spring constants of the at least three spring members are determined based on a relative position relationship between the barycentric position of the structure and the at least three spring members so as to set at least one spring constant different from other spring constants.
According to the present invention, there is provided a device manufacturing method comprising the steps of:
exposing a photosensitive agent on a substrate by using an exposure apparatus; and
developing the photosensitive agent on the substrate,
the exposure apparatus having
a projection optical system for projecting an image onto a substrate, and
a substrate stage apparatus which moves while supporting the substrate,
the substrate stage apparatus having
a stage,
a member fixed to the stage, and
a weight compensation mechanism having at least three spring members for compensating for a weight of a structure including the stage and the member, a barycentric position of the structure deviating from a centroid of a polygon formed by support points of the at least three spring members,
wherein spring constants of the at least three spring members are determined to make application points of restoring forces of the at least three spring members coincide with the barycentric position of the structure when the stage is statically balanced.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.


Zeolites have been used extensively to catalyze a number of chemical reactions in refinery and petrochemical reactions, and catalysis, adsorption, separation, and chromatography. For example, both synthetic and natural zeolites and their use in promoting certain reactions, including conversion of methanol to olefins (MTO reactions) and the selective catalytic reduction (SCR) of nitrogen oxides with a reductant such as ammonia, urea or a hydrocarbon in the presence of oxygen, are well known in the art. Zeolites are crystalline materials having rather uniform pore sizes which, depending upon the type of zeolite and the type and amount of cations included in the zeolite lattice, range from about 3 to 10 Angstroms in diameter. Zeolites having 8-ring pore openings and double-six ring secondary building units, particularly those having cage-like structures, have recently been noted to be of interest for use as SCR catalysts. A specific type of zeolite having these properties is chabazite (CHA), which is a small pore zeolite with 8 member-ring pore openings (˜3.8 Angstroms) accessible through its 3-dimensional porosity. A cage like structure results from the connection of double six-ring building units by 4 rings.
Catalysts employed in the SCR process ideally should be able to retain good catalytic activity over the wide range of temperature conditions of use, for example, 200° C. to 600° C. or higher, under hydrothermal conditions. Hydrothermal conditions are often encountered in practice, such as during the regeneration of a soot filter, a component of the exhaust gas treatment system used for the removal of particles.
Metal-promoted zeolite catalysts including, among others, iron-promoted and copper-promoted zeolite catalysts, for the selective catalytic reduction of nitrogen oxides with ammonia are known. Iron-promoted zeolite beta (U.S. Pat. No. 4,961,917) has been an effective commercial catalyst for the selective reduction of nitrogen oxides with ammonia. Unfortunately, it has been found that under harsh hydrothermal conditions, for example, as exhibited during the regeneration of a soot filter with temperatures locally exceeding 700° C., the activity of many metal-promoted zeolites begins to decline. This decline is often attributed to dealumination of the zeolite and the consequent loss of metal-containing active centers within the zeolite.
The synthesis of a zeolite varies according to structure type of the zeolite, but usually, zeolites are synthesized using a structure directing agent (sometimes referred to as a template, e.g., an organic template) together with sources of silica and alumina. The structure directing agent can be in the form of an organic, e.g., tetraethylammonium hydroxide (TEAOH), or inorganic cation, e.g., Na+ or K+. During crystallization, the tetrahedral silica-alumina units organize around the structure directing agent to form the desired framework, and the structure directing agent is often embedded within the pore structure of the zeolite crystals.
Metal-promoted, particularly copper-promoted aluminosilicate zeolites having the CHA structure type and a silica to alumina molar ratio greater than 2, particularly those having a silica to alumina ratio greater than or equal to 5, 10, or 15 and less than about 1000, 500, 250, 100 and 50 have recently solicited a high degree of interest as catalysts for the selective catalytic reduction of oxides of nitrogen in lean burning engines using nitrogenous reductants. This is because of the wide temperature window coupled with the excellent hydrothermal durability of these materials, as described in U.S. Pat. No. 7,601,662. Prior to the discovery of metal-promoted zeolites, as described in U.S. Pat. No. 7,601,662, while the literature had indicated that a large number of metal-promoted zeolites had been proposed in the patent and scientific literature for use as SCR catalysts, each of the proposed materials suffered from one or both of the following defects: (1) poor conversion of oxides of nitrogen at low temperatures, for example 350° C. and lower; and (2) poor hydrothermal stability marked by a significant decline in catalytic activity in the conversion of oxides of nitrogen by SCR. Thus, the invention described in U.S. Pat. No. 7,601,662 addressed a compelling, unsolved need to provide a material that would provide conversion of oxides of nitrogen at low temperatures and retention of SCR catalytic activity after hydrothermal aging at temperatures in excess of 650° C.
In view of the considerable interest in molecular sieves having 8-ring pore openings and double-six ring secondary building units, particularly those having the CHA structure type, there is an on-going desire to improve the process of preparing such zeolites.


Discovery protocols are known as a technique for automatically acquiring service information of a network device connected on the same LAN. Discovery protocols are found in various forms. Examples of discovery protocols include UPnP (Universal Plug and Play), proposed by Microsoft, and Bonjour, proposed by Apple. There are various other ones, such as WS-Discovery and SLP (Service Location Protocol).
“Service information” refers to, for example, information (e.g., a service name) for identifying a service such as printing or file storing provided by a network device, and information required for connection, such as the network device name. A network device can easily implement connection with another network device by acquiring the service information of the other device.
In a discovery protocol, each device periodically broadcasts its service information over a network or inquires for the service information of a device at the other end, thereby managing a list of services on a LAN. In the case where an inquiry signal is sent to a device with service(s) that has once been found through a search and no response to the inquiry signal is detected, at the time of a service inquiry (search), it is determined that the device has left (disappeared from) the network and that provision of the service(s) in question by that device has stopped, and the connection with the service-providing-device at the other end is then disconnected.
Disconnecting a connection with a service-providing device is performed in a recognizable manner when the service-providing device has disappeared. The above-described service discovery is intended for a wired network. Accordingly, if there is no response to a service inquiry, it can be determined that the device at the other end has disappeared.
This causes a problem specific to wireless communication environments. Examples of such a problem include a temporary deterioration in radio wave conditions and various problems associated with movement of a device. If this kind of problem occurs, throughput decreases due to a temporary deterioration in radio wave condition at a wireless layer. However, connection with a device at the other end is still maintained, and a service-providing device is correctly performing processing.
In spite of this, if a service inquiry is sent, no response is obtained, at least temporarily, from the service-providing device. For this reason, a higher-level application which performs service discovery mistakenly determines that provision of a service has stopped and disconnects the lower-level (wireless layer) communication.


The market for portable devices, for example, mobile phones, smart watches, tablets, etc., is expanding with many more features and applications. As the number of applications on these devices increases, there also is an increasing demand to run multiple applications concurrently. More features and applications call for microprocessors to have high performance, but with low power consumption. Multithreading can contribute to high performance in this new realm of application. Keeping the power consumption for the microprocessor and related cores and integrated circuit chips near a minimum, given a set of performance requirements, is desirable, especially in portable device products.
Multithreading is the ability to pursue two or more threads of control in parallel within a microprocessor pipeline. Multithreading is motivated by low utilization of the hardware resource in a microprocessor. In comparison, multi-core is fairly wasteful of the hardware resource. Multithreading can, in general, provide the same performance as multicore without duplicating of resources.
Multithreading can be used in an effort to increase the utilization of microprocessor hardware and improve system performance. Multithreading is a process by which two or more independent programs, each called a “thread,” interleave execution in the same processor, which is not a simple problem. Each program or thread has its own register file, and context switching to another program or thread requires saving and restoring of data from a register file to a memory. This process can consume much time and power. These and other problems confront attempts in the art to provide efficient multithreading processors and methods.


1. Field of the Invention
The invention relates to an apparatus for extending the lip plate of a dock leveler for movement of the lip plate onto the bed of a truck or other vehicle located next to the dock.
2. Description of the Prior Art
Dock levelers generally employ a base member attached to the side of a dock, a bridge plate which is pivotally attached to the edge of the base member and a lip plate which is pivotally attached to the other edge of the bridge plate. The known manually operated dock levelers in use today place a large amount of strain on the operator when lifting the plates for proper positioning. Spring mechanisms are employeed on dock levelers to aid in lifting the plates; however, they do not provide,, the assistance needed.
U.S. Pat. Nos. 3,974,537 and 4,065,824 are directed to different types of mechanisms for assisting the operator in lifting the plates of a dock leveler for proper positioning.


1. Field of the Invention
The invention relates to chemical vapor deposition (CVD) systems and, more particularly, to temperature control apparatus, and a concomitant method, for controlling the temperature of the walls of a CVD reaction chamber.
2. Description of the Prior Art
In a conventional chemical vapor deposition (CVD) system, a reaction chamber envelopes a volume wherein the deposition process occurs. The chamber typically is fabricated of transparent quartz. As such, the reaction chamber is said to have quartz windows (accessible surfaces of the chamber) through which the temperature of the apparatus within the chamber can be optically monitored using optical pyrometers. In general, since the windows are integral with the walls of the chamber, the temperature of these windows is indicative of the chamber wall temperature. The temperature of the windows and the walls of the chamber vary depending upon the temperature of the workpiece within the chamber, the process presently being accomplished, the gases involved in the current process, and the run time of the process.
More specifically, it is desirable that during a deposition process, the quartz wall temperature be controlled within a narrow temperature range to minimize deposits on the chamber wall. Furthermore, it is desirable that, during cleaning steps, the quartz wall temperature be maintained at a different temperature to maximize the etch rate of any film that may have been deposited on the chamber walls. Such temperature maintenance minimizes particulate contamination problems.
Typically, the temperature of the walls of the chamber is maintained at a nominal value by a flow of air proximate the outer surface of the chamber. This air flow is fixed for each process performed within the chamber. Thus, the temperature of the chamber walls varies with conditions within the chamber, e.g., the wall temperature differs depending on whether the process in the chamber is depositing material or etching material from a workpiece.
Through empirical study, it has been shown that the processes performed within the chamber can be optimized when the chamber wall temperature is maintained at an optimum temperature for a particular process. However, prior art CVD systems contemplate maintaining the air flow past the chamber at a fixed flow rate. As such, these systems exhibit significant chamber wall temperature variations which preclude a high degree of temperature optimization.
Therefore, a need exists in the art for closed loop apparatus, and a concomitant method, for controlling the air flow proximate a reaction chamber such that the temperature of the chamber walls can be readily optimized for each of the processes accomplished within the chamber.


The scoring of test answer sheets involves complex problems. These test answer sheets typically include a series of response positions such as, for example, "bubbles," ovals, or rectangles. A person taking a test would, for example, darken in an appropriate oval with a pencil to answer a multiple choice question. These test answer sheets may also include handwritten answers, such as essay or short answer questions. Systems for scanning and scoring the bubbles on such answer sheets are known in the art. Increased difficulties are encountered, however, when such answer sheets either include other types of answers, such as handwritten answers, or cannot be machine graded. For example, if the student has failed to include his or her name on the test answer sheet, the system may be unable to machine score the test answer.
The goals in scoring test answers that cannot be machine scored include efficiency and consistency. These test answer sheets are typically scored by test resolvers either by manually scoring the physical test answer sheet or scoring an electronic representation of the test answer sheet on a computer. Ideally, the scores provided by the various test resolvers for a particular test question should be consistent, since the scores are used in comparing performance of the students against one another. In addition, a test resolver should ideally work efficiently so as to maintain consistently high scoring rates. The test resolver should not have such a high scoring rate that the consistency or quality of scoring significantly declines; likewise, the test resolver should not have such a low scoring rate that the too few answer sheets are being scored. This manual scoring of test answer sheets, however, makes it difficult to monitor the consistency of scoring among the various test resolvers.
In many situations, test resolvers actually travel to a particular location so that all test resolvers may simultaneously score test answer sheets. Requiring the test resolvers to travel to a given location is inconvenient for the resolvers and expensive for those who administer the tests. Furthermore, tracking the performance of test resolvers against both their own performance and the performance of other resolvers can be very difficult with a manual scoring environment.
The process of resolving test questions is currently done manually, and this presents problems. A resolver is manually presented with the actual test answer sheets for scoring. This process is relatively inefficient, since the resolvers must score the answer sheets one at a time and in the order in which they are presented. Also, manual scoring systems do not have the capability to efficiently gather and categorize the test answers for subsequent analysis. Therefore, with a manual system it is very difficult to determine how teaching methods should be changed to decrease, for example, the number of incorrect answers.
A need thus exists for a system that promotes and achieves consistency and efficiency in scoring or resolving of tests.


1. Technical Field
The present invention relates to wafer-to-wafer alignments, and more specifically, to wafer-to-wafer alignments using capacitive coupling structures.
2. Related Art
In the prior art, two wafers containing devices can be aligned and then bonded together so as to, among other purposes, double the device density. As a result, there is always a need for a structure (and methods for operating the same) that helps achieve good wafer-to-wafer alignments for subsequent wafer bonding process.


Electromagnetic sources used in geophysical surveying generally produce unfocused regions of subsurface excitation. Unfocused excitations result both from the diffusive nature of low frequency electromagnetic wave propagation in the earth and from the use of relatively simple source configurations in the surveys. Unfocused excitations are a severe disadvantage when a target-oriented survey is needed, such as when it is desirable to probe the electrical properties of a prospective formation in a location where a complex geologic background may be present.
To eliminate the disadvantages of unfocused surveys, a method of source focusing is disclosed in U.S. patent application Ser. No. 09/656,191, filed Sep. 6, 2000 (hereinafter referred to as “Srnka”). The method, referred to as the remote reservoir resistivity mapping method (“R3M”) uses a spatially extended grounded electromagnetic source array that is positioned on the earth's surface, or near the seafloor, to focus electromagnetic energy on the subsurface target. The source array consists of two concentric electrode rings whose radii are optimally determined from theoretical modeling to focus the subsurface excitation at the approximate depth of the subsurface target. A limitation of the Srnka method, however, is that for typical reservoir depths, which range from 500 meters to greater than 5000 meters, the total length of electrode wire that is required in the concentric electrode rings ranges from about 23.5 km to greater than 235 km.
These extreme lengths of electrode wire raise numerous operational challenges. For example, difficulties in handling and deploying the electrode wires, and problems in ensuring accurate positioning of the wires in the desired electrode ring locations may be involved, and there is the need to avoid obstacles in the area of the desired ring locations, and the requirement that the electrodes be uniformly grounded along their lengths. Other problems influence the economics of the survey, including the large cost of the electrode wire, some of which is likely to be damaged or lost in each survey, and the large labor and logistics costs associated with mobilization, demobilization, deployment, and recovery of the wire.
For these reasons, Srnka also disclosed an alternative method that reduces the required length of electrode wire by substituting a set of equally spaced radial electric bipoles, each having a length equal to the difference in the lengths of the radii of the two concentric rings. FIG. 1 depicts both the R3M concentric ring method and this radial bipole alternative. Concentric electrode rings 4 and 5 lie on surface 1 of earth 2 and have radii a and b, respectively, and a center 7 generally above reservoir 3. In the radial bipole alternative method these concentric rings are replaced by radial electrode bipole sources 6. Each bipole source 6 has a length L=b−a. Srnka discloses that a minimum of six radial bipole sources 6 is preferable. A signal equivalent to the signal that a receiver array would receive from the concentric ring source array is produced mathematically by summing the signals received by the receiver array from each of the bipole sources 6 (For convenience, FIG. 1 does not depict the location of the receiver array). This alternative method, which allows the simulation of a concentric ring source array, is referred to as the virtual concentric ring source method, or as the radial bipole method, and substantially reduces the required length of electrode wire as compared to the R3M physical concentric ring source method.
The virtual concentric ring source method nevertheless uses relatively long lengths of electrode wire and inherently retains many of the operational challenges of the R3M physical concentric ring source method. In addition, both methods have other inherent disadvantages, in particular for certain aspects of the subsurface resistivity-imaging problem. Specifically, both methods produce maximum responses near a pre-specified subsurface excitation focus depth (in other words, at the approximate depth of the target), but provide little differential sensitivity to features within an appreciable vertical range of that depth. More specifically, the ability to image separately features above or below the target a distance of less than five percent of the target's depth below the surface is limited. This limitation greatly hinders the imaging of stacked reservoirs. In addition, amplifier saturation effects can influence data quality and hinder analysis of such data. A third issue is that both methods produce primarily vertical subsurface currents in the region of the target. These currents are not adequate for imaging reservoir electrical macro-anisotropy (vertical electrical isotropy), such as exists in many reservoirs due to the presence of shale interbeds. Imaging this anisotropy is essential for estimating reservoir net and gross volumes, and for determining hydrocarbon pore volumes.
Accordingly, a method is desired which retains the advantageous electromagnetic responses of the R3M physical concentric ring source and radial bipole methods, but which reduces or eliminates the disadvantages of those methods. The present invention satisfies that desire.