Advanced negative i-line resist development on metal surfaces for next-generation lithography mask fabrication

Abstract

Development of next generation mask technology (SCALPEL, X-ray. and EUVL) requires the use of several different metallic materials. As a result, it is necessary to develop resist processes which offer a combination of good resolution and adhesion for each surface. In this study, Ultra i-300, a high resolution, chemically amplified, negative i-line resist was evaluated for use with several metal substrate materials. The metal films in the evaluation include: Cr, TaSi, TaSiN, and TiW.Early tests with Ultra i-300 using a baseline process optimized for silicon, provided very poor adhesion on these metal films. Several approaches were used to solve this problem including pre-application dehydration bakes, modified processing bakes, surface pretreatments, and use of anti-reflective coatings. Adjustment of the soft bake/post bake temperatures greatly improved adhesion, but resulted in severe standing waves and/or poor processing latitude. Significant improvements were achieved using AR2-600, a DUV anti-reflective coating (ARC) with a modified bake process. This eliminated standing waves, improved adhesion, and provided the best resolution and processing latitude. Other ARCs were also evaluated in an attempt to further optimize the process.Although the goal of this study was to develop a resist process for next generation mask technology, the results are applicable wherever it is desirable to use a negative i-line resist on metallic substrates.