SURFACE IMAGING LITHOGRAPHY AT 248 NM

This paper discusses the use of surface imaging lithography for deep UV step and repeat applications. In particular, results obtained using the DESIRE(R) process are presented. It is shown that surface imaging is a very attractive option for 248 nm lithography given the small depth of focus of steppers working at this wavelength and the lack of standard, commercially available, photoresists able to fulfill the requirements of deep UV lithography. First, the concept of surface imaging lithography and the DESIRE(R) process are reviewed. Next, results obtained using g-line resists exposed at 248 nm are presented. Although the results are acceptable, the exposure requirements are prohibitive. A deep UV formulation of the resist allows for higher silylation temperatures and the consequent reduction in exposure requirements to the 100 mJ/cm2 range. The focus latitude for 0.5 mu-m lines is approximately 1.5 mu-m, while the uniformity across the wafer, for the same lines, is 5%. The etch is done using a highly selective process in a parallel plate reactor. In addition, results obtained using a commercially available magnetically-enhanced ion etcher are discussed. Other characteristics of the process, as well as its drawbacks, are also presented. Finally, alternate surface imaging processes for deep UV applications are discussed.