Ryan M. Stamp

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Standing wave effects have been seen throughout the history of microlithography. Due to standing wave effects, the line width control of imaged lines in photoresist is compromised. A technology that has emerged as strong solution for the reduction of standing wave effects is a Bottom Antireflective Coating (BARC) that is deposited onto the wafer before the photoresist deposition. By reducing the substrate reflectivity, the standing wave effects can also be reduced dramatically.

The 193 nm photoresist and the bi-layer BARC films were characterized and then optimized to reduce standing wave effects within the 193 nm photoresist. A bi-layer BARC film configuration that reduces the reflectivity to less than 1% for both of the experimental numerical aperture settings of 1.05NA and 1.3NA is the goal of this project and was achieved in the RIT SMFL cleanroom. Also, a single-layer BARC system was designed to reduce substrate reflectivity to less than 1% at a setting of 1.05NA. This single-layer design was used as the control experiment or baseline to prove that a bi-layer BARC design is much more efficient than a single-layer BARC system. Simulations were conducted for the design of the multi-layer lithography systems using ILSim 1.0, an interferometric lithography simulation software as well as a simulation program on the JA Woolam Co., Inc. Variable Angle Spectroscopic Ellipsometer (VASE), which was also used to characterize the 193nm DUV resist. The simulations are run by utilizing the refractive indexes (n) and the extinction coefficients (k) of the films being used, which are the optical characteristics of the films.

Imaged lines and spaces were then exposed for each of the two designed film stacks and at the two NA settings as stated above. Imaged lines of 45 nm and 35 nm were obtained at 1.05 NA and 1.3NA, respectively, for the bi-layer system, while only 45 nm lines could be obtained with the single-layer BARC system. Since the project objectives and goals were reached, a brief proposal to push the limits of the bi-layer BARC system to 1.5NA is suggested.

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