Reduction of linewidth variation over reflective topography

Abstract

As device dimensions have shrunk well below the one micron level, linewidth control particularly over reflective topography has become a major problem in optical lithography. Other than reflective notching caused by light reflected into unwanted areas, thin-film interference is the major contributor to linewidth variations. Small changes in film thickness over steps cause significant changes in the amount of energy deposited into photoresist films. Various methods used to solve this problem are investigated to measure their relative effectiveness. Conventional photoresist, dyed-resist, bottom layer ARCs (antireflcctivc coatings; both inorganic and organic), TAR (top-antircflcctivc layer) and CEL (contrast enhancement layer) as a special case of TAR arc compared for their relative effectiveness as well as their advantages and disadvantages for use in manufacturing. Simulations and functional evaluation of film thickness effects on exposure requirement and on linewidths as well as imaging over topography are used as a means of comparison. The use of TAR is a relatively new approach to solving this problem in a simple, effective manner. Material choice depends on film refractive index and ease of processing. Several TAR materials have been investigated and will be discussed.