Christopher F. Lyons

Reduction of linewidth variation over reflective topography

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.

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.

Practicing the top antireflector process

Thickness variations in photoresist caused by substrate topography, and normal variations in deposited thin films, arc unavoidable sources of linewidth variation in optical lithography. Thin film interference effects cause exposure to vary by large amounts. A new approach to controlling these effects is the use of a top antircficctor (TAR) film on top of the photoresist. In this paper, the performance of a process using a water soluble TAR material is described. Simulation and experimental results arc given which show the effectiveness in controlling wafer reflectivity, and exposure dose in the presence of varying insulator and resist films. The effect of the TAR process on focus and exposure latitude is examined and initial results from device manufacturing are presented.

Novel DNQ PACs for high-resolution i-line lithography

The use of i-line lithography for the 16 to 64 Mbit DRAM device generations calls for increased performance of i-line resists. This paper reports on investigations on novel sensitizers for advanced i-line lithography, starting out with a discussion of general design criteria, then discussing methodology and results of a screening phase, and examining in greater detail a small number of selected candidates for which resolution, exposure latitude, and depth-of-focus data were obtained. Finally, a new advanced resist for i-line lithography, AZR 7500, is presented, and its performance is evaluated in terms of the above criteria as well as thermal flow resistance.

TAR processing for CD control in I-line and 248-nm lithography

The combination of dyed photoresist and top antireflection (TAR) coatings was applied to I- line and deep-UV lithography on polysilicon. Optimization of the resist layers absorption and application of the TAR process significantly improves CD control of submicron gate level lithography.

Formulation and modeling of dyed positive i-line resist for control of the reflective notching and CD variation

This study evaluates the effect of dyes, including photosensitive dyes, on resist performance such as: swing curve reduction, resist dissolution rate, resolution, dose and focus latitude, scumming, etc. The paper demonstrates good correlation between modeling of the dyed resist performance and experimental results.