Process compatibility using high sensitivity resist for KrF excimer laser lithography-ASKA.

Abstract

The current state of the art g-line and i-line photolithography using conventional novolac based resists will be able to pattern 0.5-0.6micron devices adequately, however beyond 0.5micron, an alternative lithography will be required. KrF excimer laser lithography is one of the leading candidates for sub-half micron VLSI lithography. This technology will be able to take advantage of the higher resolution and wider depth of focus possible with the smaller wavelength. One of the major technical barriers for application of this technology to mass production is the low sensitivity of commercially available resists. New non-novolac based resist have been introduced with high sensitivity to meet this requirement. By using chemical means, Ito [1] was able to achieve quantum efficiencies much greater than one resulting in very sensitive resist systems. In this paper we describe our work to develop ASKA, Alkaline Soluble Kinetics using Acid Generator, positive resist. This resist has sensitivity greater than 25mJ/cm2 which is sufficient for a controllable manufacturing process. ASKA resist also has very good lithographic characteristics with resolution to 0.40micron and near vertical resist profiles. Process characterization of ASKA resist is also reported. Post exposure bake (PEB) is a critical step that controls performance of this resist. ASKA resist has excellent stability and linewidth control and is not dependent on the time between exposure and PEB. The resist has wide exposure latitude up to +-15% for 10% variation in linewidth. ASKA has mask linearity down to 0.40micron lines where at 0.35micron the linewidth begins to deviate from linearity. Depth of focus for 0.40micron lines is about +-1.0micron. Etch resistance is evaluated and reported for silicon dioxide, nitride and polysilicon layers. ASKA was successfully applied to actual device wafers. KrF excimer laser lithography using ASKA resist can fabricate sub-half micron patterns for 64M DRAM.