Multilayer resist technique for submicron optical lithography

Abstract

Analysis has shown that the limiting factor in achieving 1 μ technology in optical lithography is mainly due to nonideal operating conditions such as surface topography, reflectivity, defocusing, etc. By using a multilayer resist process to eliminate these extraneous factors, we have demonstrated that optical lithography can be pushed beyond 1 μ into the submicron range. The advantages and problems encountered with the bilayer DUV flood exposure process were pointed out. One of the most serious problems, due to reflected light from surface topography, was corrected by using an antireflecting coating between the PMMA and AZ resist layers. This antireflection coating layer also eliminates the interface mixing between PMMA and AZ resists. A trilayer resist process was developed based on the highly directional RIE process. A new barrier film based on spin-on-glass was optimized to obtain defect free films. This spin-on barrier layer greatly simplifies the work flow and provides significant cost savings over the conventional vacuum deposited or CVD films. Submicron resolution capability and good dimension controls over severe wafer surface topography have been demonstrated. The trilayer resist process has been demonstrated to be capable of handling dimensions beyond the resolving power of currently available optical lithographic systems.