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For AlGaN/GaN HEMT fabrication, an isolation mesa etch is needed. Dry etch is usually used because wet etch is a difficult process for GaN. It was found that CCl2F2 chemistry can etch GaN easily. However, CCl2F2 chemistry may have difficulty to etch AlGaN or AlN because AlF3 is not volatile and can form a layer which blocks further etching. This can be overcome by increasing the RF power. Higher RF power helps by sputtering away the non-volatile AlF3. In this way, CCl2F2 can be used to etch AlGaN/GaN. CCl2F2 chemistry with Ar can be used to etch GaN with slightly higher selectively over AlGaN or AlN. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A WSiN cap can improve the surface morphology of Ti/Al Ohmic contact to n-GaN significantly. This is because it is a conductive diffusion barrier which can help to suppress the decomposition of GaN. With WSiN cap, the edge is much sharper. However, the WSiN film may pick up Ar during the WSiN sputtering process, resulting in some surface morphology problem. This can be solved by lowering the Ar flow rate during sputtering. Auger electron spectroscopy results show that our best WSiN cap has a chemical composition of W0.62Si0.14N0.34. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A modified shift-and-ratio (MS&R) method of extracting the effective channel length (L eff) has been tested on metal oxide semiconductor (MOS) transistors fabricated by state-of-the-art CMOS technology. The value of L eff generated by this method is more reasonable than the original shift-and-ratio method with much less computation time involved. We show the correctness of the MS&R method by comparing the L eff extracted with the channel length obtained by cross-sectional scanning capacitance microscopy (SCM) measurement. In addition, we show that a higher off current corresponds to a smaller L eff measured by our method.