George Joseph Hefferon

Resist Technology For Submicrometer Optical Lithography

This paper reviews the impact of advances in photoresists and processing on submicrometer imaging using optical lithography. Among the topics discussed for the extension of single-layer resists into the submicrometer regime are the use of dyes, the development of materials for the deep-UV region, image reversal, and contrast-enhancement layers. Approaches to dealing with substrate topographical effects, such as multilayer resists and antireflection coatings, are reviewed. Future directions to extend optical lithography further and address current problems are discussed.

Environmentally stable chemically amplified DUV resist based on diazoketone chemistry

This paper describes a resist that uses a polymer bound diazoacetoacetate as a photoacid generator in a two component system. The diazoacetoacetate is not used merely as a photoactive component, but its utility is extended to function as a photoacid generator for deprotection chemistry. The carboxylic acid generated upon exposure deprotects carboxylic acid-labile groups bound to another polymer backbone. This scheme has led to a resist with excellent performance like lithographically useful photospeed, resolution, environmental stability and aqueous base solubility combined with wide process latitudes. The resist does not require a topcoat or additives for stabilization towards airborne contaminants. The photo acid is a weak acid and hence allows fairly high concentrations of the acid generator to be used which helps in reducing contamination effects. Furthermore, being bound to a polymer backbone, diffusion into unexposed regions is limited and therefore exhibits greater stability towards PEB delay effects. Loss from surface due to volatility is also reduced in a polymeric acid generator compared to low molecular weight, monomeric compounds.

Improved reflectivity control of APEX-E positive tone deep-UV photoresist

A study optimizing the actinic absorbance of APEX-E positive deep UV photoresist was performed using a variety of dye additives. The selection of a dye and the optimization of dye content for APEX-E positive photoresist has led to substantial process enhancements in reduction of reflective notching and of thin film interference effects. The usual side effects as found in dyed I- line resists such as significant loss of photospeed, decreased focus latitude and sidewall angle decrease were not apparent with selected conjugated aromatic dyes. The benefit of added absorbance has allowed the direct use of dyed APEX-E to counteract the step interference (notching) problems over the severe topography of CMOS gate level and eliminate the reflective notching of surface strap level in the fabrication of 16 Mb devices. In addition, the depth of focus window was enhanced and process latitude was maintained. Geometries of 250nm were printed, with dyed APEX-E for optical densities ranging from 0.4 to 0.8 per micron with a DUV optical scanner.