Advanced spectral engineering: a new way of process improvements by laser spectra optimization for optical lithography

Abstract

It is widely known that the spectral shapes of light sources, represented by FWHM or E95 conventionally, have great impacts on the optical lithography performances. On the other hand, modern optical lithography requires more precise control of Critical Dimension (CD). Of the many factors impact the CD, OPE and Process Window (PW) play important roles in optical lithography. The Gigaphoton’s Spectral Engineering (SE) technique introduced in its latest light sources, which can generate a variety of spectral shapes, such as, top-hat spectra, multi-peak spectra in addition to conventional broadband spectra, can have substantial contributions to both PW enhancements as well as OPE optimizations. In the last report, as an example, we have shown that the PW of CH/VIA will be improved by the introduction of SE technique. However, the PW improvement is realized mainly by expanding DOF at the cost of EL. As users are interested in CD Uniformity (CDU), not PW itself, and the CDU depends on both focus and dose accuracies, a question that is likely to arise is, will the CDU be improved by the SE? In this report, we are going to show that, by the introduction of SE, users can expect significant improvements of CDU for semi-isolated or isolated patterns, at trivial costs of CDU deteriorations for dense patterns. For the OPE, although it is widely known that spectral width can be used in OPE tunings, but it has rarely been used in FABs, as a tuning knob. We are going to show that the spectral width control with SE will greatly improve both qualities and chances of OPE tunings.