Proceedings Article | 1 July 1991
Proc. SPIE. 1463, Optical/Laser Microlithography IV
KEYWORDS: Lithography, Phase shifting, Optical lithography, Deep ultraviolet, Lenses, Reflectivity, Absorbance, Chemical analysis, Photoresist processing, Chemically amplified resists
The simulation analysis of standing wave effects in deep-UV lithography, which is the most serious problem in 64 MDRAM fabrication, is studied. One lithographic problem for device fabrication is periodic linewidth variation due to multireflection light in the resist film. It was observed that the amplitude of linewidth variation was more than 0.1 micrometers for a 3- component chemically amplified negative resist using a KrF excimer laser stepper (NAequals0.42). So, we simulated the standing wave effect as a function of resist material, exposure tool, and process conditions in order to minimize periodic linewidth variation. The SAMPLE simulator was improved to calculate a series of pattern profiles automatically, to change simulation parameters, and to create a periodic linewidth curve from the simulated pattern profiles. The following discoveries were made: Increasing optical resistance slightly decreases linewidth variation, although the resist pattern profiles degrade significantly. High NA lenses can also decrease linewidth variation under best focus conditions, but, linewidth variation increases significantly under slight defocus. Also, an optimum lens NA value, that minimizes periodic linewidth error, was found. Finally the Anti-Reflecting-Coating (ARC) technique, which can diminish standing wave effects, also degrades pattern profiles. To summarize, in order to minimize linewidth variation due to standing wave effects, it is important to minimize reflectivity, to optimize lens NA and coherency factor by simulation analysis.
