Significance and Use
Division of the Co-60 Hardness Testing into Five Parts:
The equilibrium absorbed dose shall be measured with a dosimeter, such as a TLD, located adjacent to the device under test. Alternatively, a dosimeter may be irradiated in the position of the device before or after irradiation of the device.
This absorbed dose measured by the dosimeter shall be converted to the equilibrium absorbed dose in the material of interest within the critical region within the device under test, for example the SiO 2 gate oxide of an MOS device.
A correction for absorbed-dose enhancement effects shall be considered. This correction is dependent upon the photon energy that strikes the device under test.
A correlation should be made between the absorbed dose in the critical region (for example, the gate oxide mentioned in 4.1.2) and some electrically important effect (such as charge trapped at the Si/SiO2 interface as manifested by a shift in threshold voltage).
An extrapolation should then be made from the results of the test to the results that would be expected for the device under test under actual operating conditions.
1.1 This practice covers recommended procedures for the use of dosimeters, such as thermoluminescent dosimeters (TLD's), to determine the absorbed dose in a region of interest within an electronic device irradiated using a Co-60 source. Co-60 sources are commonly used for the absorbed dose testing of silicon electronic devices.
Note 1—This absorbed-dose testing is sometimes called “total dose testing” to distinguish it from “dose rate testing.”
Note 2—The effects of ionizing radiation on some types of electronic devices may depend on both the absorbed dose and the absorbed dose rate; that is, the effects may be different if the device is irradiated to the same absorbed-dose level at different absorbed-dose rates. Absorbed-dose rate effects are not covered in this practice but should be considered in radiation hardness testing.
1.2 The principal potential error for the measurement of absorbed dose in electronic devices arises from non-equilibrium energy deposition effects in the vicinity of material interfaces.
1.3 Information is given about absorbed-dose enhancement effects in the vicinity of material interfaces. The sensitivity of such effects to low energy components in the Co-60 photon energy spectrum is emphasized.
1.4 A brief description is given of typical Co-60 sources with special emphasis on the presence of low energy components in the photon energy spectrum output from such sources.
1.5 Procedures are given for minimizing the low energy components of the photon energy spectrum from Co-60 sources, using filtration. The use of a filter box to achieve such filtration is recommended.
1.6 Information is given on absorbed-dose enhancement effects that are dependent on the device orientation with respect to the Co-60 source.
1.7 The use of spectrum filtration and appropriate device orientation provides a radiation environment whereby the absorbed dose in the sensitive region of an electronic device can be calculated within defined error limits without detailed knowledge of either the device structure or of the photon energy spectrum of the source, and hence, without knowing the details of the absorbed-dose enhancement effects.
1.8 The recommendations of this practice are primarily applicable to piece-part testing of electronic devices. Electronic circuit board and electronic system testing may introduce problems that are not adequately treated by the methods recommended here.