Overlay modeling for proximity x-ray lithography

Abstract

Proximity x-ray lithography is one of the most promising manufacturing technologies for the fabrication of future electronics devices with ground rules of 100 nm and less because of its wide exposure latitude and processing simplicity. However, the ability to make 1× x-ray masks, with high pattern placement accuracy, has continued to be one of the main technical challenges preventing the wide use of this technology by the semiconductor industry. A model has recently been developed to examine the parameters affecting the overall lithographic system overlay performance, such as the mask pattern placement error as well as the error sources from the x-ray aligner. The model treats all of the error sources statistically. The major assumption of the model is that all the error sources are statistically independent. This is a fairly accurate assumption for the error sources under consideration. For example, the mask pattern placement error is and should be independent of the aligner wafer stage stepping errors. Furthermore, the model can simulate error sources that do not follow the normal statistics. The model has three major components: (1) the x-ray aligner machine model that simulates all the major aligner error sources such as mask and wafer alignments, (2) the application parameter component that considers any application-specific setup tool parameters such as the number of wafer alignment marks and the number and location of global alignment sites, and (3) the mask component that accounts for the effects of pattern placement accuracy on alignment marks and overlay metrology targets. A detailed description of the model and the experimental data used to verify its validity will be given. The relative impact of the various subcomponent error contributions on the overall overlay performance will be provided.