Overlay modeling for proximity x-ray lithography

Proximity x-ray lithography is one of the most promising manufacturing tech nologies for the fabrication of future electronics devices with ground rule s of 100 nm and less because of its wide exposure latitude and processing s implicity. However, the ability to make 1 x x-ray masks, with high pattern placement accuracy, has continued to be one of the main technical challenge s preventing the wide use of this technology by the semiconductor industry. A model has recently been developed to examine the parameters affecting th e overall lithographic system overlay performance, such as the mask pattern placement error as well as the error sources from the x-ray aligner. The m odel treats all of the error sources statistically. The major assumption of the model is that all the error sources are statistically independent. Thi s is a fairly accurate assumption for the error sources under consideration . For example, the mask pattern placement error is and should be independen t of the aligner wafer stage stepping errors. Furthermore, the model can si mulate error sources that do not follow the normal statistics. The model ha s three major components: (1) the x-ray aligner machine model that simulate s all the major aligner error sources such as mask and wafer alignments, (2 )the application parameter component that considers any application-specifi c 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 ma rks and overlay metrology targets. A detailed description of the model and the experimental data used to verify its validity will be given. The relati ve impact of the various subcomponent;error contributions on the overall ov erlay performance will be provided. (C) 1998 American Vacuum Society. [S073 4-211X(98)07406-X].