Electron-beam processing of deep-UV resist

Abstract

To advance production processing well beyond 0.30 micrometer design rules, it is considered necessary to introduce deep-UV photolithography. Currently, most deep-UV photoresist systems are based on poly(4-hydroxystyrene) (PHS) resins, which have good thermal properties. When combined with photo-acid generators (PAG) and dissolution inhibitors, the thermal properties of the resulting resists are severely reduced. Since the Tg of these types of advanced resists are in the 100 to 120 degree Celsius region, it is necessary to apply a stabilization process to the resists prior to processing at high temperatures. This study investigates the application of electron beam stabilization processing to deep-UV resist materials. A PHS based deep-UV resist, and a solution of the PHS resin material, have been evaluated to determine the nature of the reactions induced by electron beam exposure. Chemical changes induced in the resist, or resin, are evaluated via FTIR analysis. Changes in optical properties are evaluated using UV/visible reflectance as well as changes in index of refraction. Film shrinkage is determined for all processing conditions. Thermal properties are evaluated by DSC and TGA techniques. The Tg of the processed resist is presented as a function of electron beam exposure. Thermal flow properties are evaluated via SEM cross sections of resist features exposed to high temperatures after electron beam stabilization. Electron beam stabilized films are demonstrated to withstand temperatures in excess of 200 degrees Celsius. The resist or resin materials properties are evaluated as a function of electron beam dose level and stabilization process temperature. Trends in materials properties are evaluated and optimized process conditions are presented for a range of production processing applications.