30 July 2002 New method to determine optimal photolithography process conditions using scatterometry
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A quick, accurate, automatic and robust method to evaluate the best focus and lens quality of the advanced lithography tools is highly demanded when the optical lithography is pushed into 130 nm regimes and beyond. This paper presents how this tedious lithographer's daily job has been performed in Texas Instrument in a more pleasant way thanks to scatterometery. The widely used critical dimension (CD) SEM measurement and +/-10% golden rule have been experiencing in great difficulties to define the optimal process conditions. CD only is not capable to fully describe the resist profile. Lithographers must consider all resist profile parameters such as sidewall angle, resist height and linewidth of resist profile which can be quickly measured by scatterometer. Across exposure field variation, another key process sensitive parameter, has to be integrated into the decision-making loop of process optimization. A new parameter (DCAT ratio) has been introduced and defined as a function of those process sensitive parameters. It has a clear maximum and zero first derivative point (that is, a preferred parabolic bell shape) at the best process condition. The DCAT ratio has been used to find the true best focus offset for multiple scanners to guide tool-to-tool focus matching. It has been used to qualify scanners, optimize lithography process and determine the exposure latitude.
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Changan Wang, Changan Wang, Simon Chang, Simon Chang, Mark A. Boehm, Mark A. Boehm, } "New method to determine optimal photolithography process conditions using scatterometry", Proc. SPIE 4691, Optical Microlithography XV, (30 July 2002); doi: 10.1117/12.474578; https://doi.org/10.1117/12.474578

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