Mitsubishi Electric Corporation (MELCO) has developed an advanced microlithographic process for producing 0.1 micrometer contact holes (CH). A chemical shrink technology, RELACS^TM (Resolution Enhancement Lithography Assisted by Chemical Shrink), utilizes the crosslinking reaction catalyzed by the acid component existing in a predefined resist pattern. This 'RELACS^TM' process is a hole shrinking procedure that includes simple coating, baking, and rinse steps applied after conventional photolithography. This paper examines the process parameters affecting shrinkage of CH size. We subsequently evaluated the dependency of CH shrinkage on resist formulation. We conducted investigations of shrink magnitude dependency on each process parameter. (1) Photoresist lithography process: CH size, exposure dose, post development bake temperature. (2) AZ^R R200 [a product of Clariant (Japan) K.K.] RELACS^TM process: Soft bake temperature, film thickness, mixing bake temperature (diffusion bake temperature), etc. We found that the mixing bake condition (diffusion bake temperature) is one of most critical parameters to affect the amount of CH shrink. Additionally, the structural influence of photoacid generators on shrinkage performance was also investigated in both high and low activation energy resist systems. The shrinkage behavior by the photoacid generator of the resist is considered in terms of the structure (molecular volume) of the photogenerated acid and its acidity (pKa). The results of these studies are discussed in terms of base polymer influence on shrinkage performance and tendency. Process impact of the structure and acidity of the photogenerated acid is explored. Though the experimental acetal type KrF positive resist (low activation energy system) can achieve around 0.1 micrometer CH after RELACS^TM processing under the optimized condition, the experimental acrylate type positive resist (high activation energy system) showed less shrinkage under the same process condition. The shrinkage performance of RELACS^TM process largely depends on the resist chemistry used as the underlying layer. Further, shrinkage degree can be controlled by process optimization even for the high activation energy type photoresist.

Hatsuyuki Tanaka

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