As semiconductor technologies move toward 90nm generation and below, it is more difficult to get high pattern fidelity by
248nm wavelength exposure and 193nm processes are turning into major production currently. However, in order to continue
KrF production life, research has paid attention to low k1 processes on KrF. There are a lot of resolution enhancement
technologies (RET) such as OPC, assistant features and double exposure technologies (DET) have been introduced. Sub-
Resolution Assists Features (SRAF) is a well know and well described method for process window improvement. The
introduction of such a technique is not always an easy task for two reasons. On one hand the SRAF placement rules must be
defined very well and on the other hand an empirical simulation model must be created, which describes the process. There
are sub-resolution features and make semi-isolated and isolated features to be imaged like dense feature as the illumination
conditions are always decided by most dense pitch. Assistant features have been helpful in extending the limit of optical
lithography. This study describes the improvement in contact-hole process window and resolution conspicuously. It also
indicates that the effect of contact-hole process with assistant features and FLEX, the process window is improved about
60% after bias fitting and it has been guided to production already.
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