A novel X-ray mask for mix-and-match of optical and X-ray lithography applied in SOI device fabrication

This paper reports on an application of a novel X-ray mask with a back-side alignment mark for fabricating of 0.15-μm SOI p-MOSFETs in a mix-and-match process of optical and synchrotron radiation X-ray lithography. Optical alignment signals generated from the alignment marks on an X-ray mask and a wafer play an important role in obtaining high alignment accuracy. In this paper, a novel structure of the X-ray mask to improve the alignment signal of the mask and to minimize the optical interference effect on the SiN membrane is discussed. For Karl Suss XRS 200 X-ray stepper, the alignment result for synchrotron radiation lithography with the novel X-ray mask applied to fabricate SOI devices was σ _x = 0.023 μm and σ _y = 0.025 μm. The saturation drain current I _d,sat was about 100 μA/μm, and the threshold voltage V _T was about 0.4 V. The breakdown voltage BV _dss between the source and the drain was measured at V _G = 0 V and I _D = 10 nA was larger than 4 V.