Nonaqueous development of silsesquioxane electron beam resist

Abstract

While the primary use of hydrogen silsesquioxane (HSQ) is as a dielectric in microelectronics fabrication, this material is also capable of forming high resolution, negative-tone features with low roughness when patterned with an electron beam. Unfortunately, under common processing conditions HSQ is relatively insensitive to electron beam exposure; poor reproducibility has also been observed. HSQ postexposure processing typically consists of development via immersion in an industry-standard aqueous solution of base, followed by rinsing with water or isopropanol. While other resist materials have been specifically designed for compatibility with aqueous base processing, HSQ is known to be chemically unstable in the presence of base. We report that several organic solvents that are not reactive towards HSQ are less aggressive at removing the exposed regions of the film. As a result, it is possible to successfully image HSQ with markedly reduced exposure dose. The considerable difference in exposure dose can be largely attributed to the difference in reactivity toward HSQ between organic solvents and aqueous base, but other factors must also be considered. For example, HSQ structures can be formed at low doses when developed with isopropanol, but the structures are very rough and irregular. This paper reports an alternative approach to HSQ processing that provides insight into mechanistic phenomena while offering certain advantages over standard processing techniques.