Contact-hole process window improved by assistant features with FLEX function on KrF

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 kl 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.