Recently semiconductor manufacturers have strived to continuously introduce new products with smaller circuit designs. With this in mind, we are required to improve critical dimension (CD) control during development. Resist reacts with TMAH to swell and dissolve in developer solution. During this time, dissolution products are created in and around the exposed area. The behavior of dissolution products is a factor that varies CD in the development process. The dissolution products diffuse into the developer solution. As one of the developer methods to eliminate the influence of dissolution products, the authors substituted the dissolved resist with a large amount of unreacted, remaining developer solution. This “Optimized Spin-off Develop Method” lessened the influence of dissolved resist compared to other normal development methods. Detailed evaluations, however, revealed that dissolution products were not able to be completely removed. Moreover, the swelled resist dissolved again during static development. As a result, it was observed that dissolution of the residuals affected the development process. To remove the dissolution products completely we established a novel development method. Using this method, we were able to eliminate dissolution products, resulting in minimization of CD variation.
A loading effect in particular is accounting for an increasing percentage of factors responsible for CD variations. A multi-puddle method in development process therefore is considered a solution of this problem. However, the method consumes large amounts of developer solution. In this paper, we have studied the influence of loading effect on CD and evaluated several development methods to minimize the influence. In this paper, we evaluated the correlation between the width of exposed area and CD in the device area. Based on this result, we estimated the diffusion range of dissolution products. We also found another phenomenon that CD uniformity within a wafer became worse when each pattern was surrounded by an unexposed area. A novel development method we have evaluated in this study is as follows: (1) perform a puddle formation normally; (2) after a short static development, spin off developer solution from the puddle; and (3) after the puddle is decreased in volume, perform a rather long static development. This new method proved to have the capability of minimizing the influence of dissolution products.
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