Technique for the measurement of the in-situ development rate

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Title: Technique for the measurement of the in-situ development rate
Author: Drennan, Patrick; Smith, Bruce; Alexander, David
Abstract: In the past, a Perkin Elmer Development Rate Monitor (DRM) has been used to measure the development rate of photoresist. However, due to several limitations of the DRM, the development rates measured therein, are not truly representative of the resist processing on a production lire. Subtleties in the development system are not obtained through the DRM and hence an in-situ development rate is required. Using a Site Services Development Spray Monitor (DSM 100) and a post processing algorithm. the in-situ measured development rates were obtained. The interference signals for eight different wavelengths were simultaneously monitored on a pattemed wafer as it spun on the development module of a wafer track. Since the interference signal is generated from a circularly polarized light source, the DSM 100 has demonstrated robustness to the red cloud effect, developer spray, bubbles in the developer, and ambient light.' Two algorithms for the calculation of the in-situ development rate are proposed. After collecting the eight interference curves, these post processing algorithms used the Marquardt Levenberg non-linear regression algorithm and a linear regression approach to find the development rate as a function of development time. Although the standing wave effect was visible in the plots of development rate versus time using both techniques, the first approach generated the better curve. A plot of development rate versus depth was generated via numerical integration of the plot of development rate versus time. Since the only equation used in the post processing algorithm is the interference relationship, this technique is equally well suited for other types of exposure and resist chemistries. Possession of the in-situ development rate could provide further insight into resist development mechanisms, the development of better models, and the extraction of photolithography model parameters that are specific to the production process.
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Date: 1994-03

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