In the semiconductor industry, lithography (often called “litho”) is the process of creating a microscopic pattern of the desired circuitry onto a wafer. The most common lithography processes (including “dry” optical lithography, immersion optical lithography, and Extreme Ultraviolet Lithography (EUVL)) use light to create the pattern, and thus are called photolithography processes. Some lithography processes, however, do not use light to create the pattern, including Nanoimprint Lithography (NIL) and electron beam maskless lithography.
The photolithography process involves several steps, including:
- Coating the wafer with a light-sensitive photoresist film
- Exposing the film with light projected through a mask that has the desired circuit pattern
- Developing the photoresist film to leave behind the required pattern on the wafer
As semiconductor technology progresses, not only do the photoresist critical dimensions (CDs) for each new technology node tend to decrease, but also the CD specification ranges become tighter, as well as the ranges for CD uniformity (CDU) across-die, across-wafer, wafer-to-wafer, and lot-to-lot. Metrology requirements for these CD measurements correspondingly become more difficult as well.
An electron beam-based measurement can shrink the photoresist during the exposure to the electrons, potentially affecting the measurement quality. Furthermore, photoresist profile metrology is also often needed, largely in the form of photoresist sidewall angle (SWA) metrology. For EUVL, SWA metrology is particularly difficult due to the thinness of the photoresist.
Non-optical-based lithography methods have challenges unique to them, including measurement of the Residual Layer Thickness (RLT) for NIL and stitching effects for electron beam maskless lithography.
Nova’s optical metrology technologies offer a wide range of application solutions for current and next-generation lithography challenges. Our stand-alone scatterometry platforms offer excellent precision, accuracy, and tool-to-tool matching with maximum application flexibility, including full profile information that current and next-generation lithography methods require. The high throughput of our optical metrology systems enables the sampling rates needed for both high volume manufacturing and high-spatial-sampling lithography development, without photoresist shrinkage effects.