Effects of Exposure Atmosphere and Ejected Electrons on PGMA Negative Resist Cross-Linking in X-Ray Lithography

The exposure atmosphere effect for poly (glycidyl methacrylate) (PGMA) in x-ray lithography using an A1 x-ray source has been studied with special reference to the interaction with electrons ejected from the gold film on the x-ray mask. The exposures were performed in a pressure-controlled exposure chamber, using a 1.7 kW stationary A1 source and a gap-controlled mask and wafer assembly. PGMA cross-linking distinctly increases, as the atmosphere pressure is increased from 6.7 to 2670 Pa, when using the x-ray masks with thin gold films. As the mask-to-wafer gap is increased from 6/~m to 1 ram, PGMA cross-linking markedly decreases when using these masks. An interpretation f the mechanism for the ob-served effects is also presented. Furthermore, protective films, such as Mylar, polyimide, and silicon nitride, have been examined to suppress electrons ejected from the gold film. X-ray l ithography is a promising technology for replicating very high resolution patterns. However, for replication of submicron-size f atures, problems such as the effects of photoelectrons and Auger electrons from the x-ray mask (1, 2) and exposure atmosphere effect (3, 4) should be elaborately investigated