Comparative study of self-aligned and nonself-aligned SiGe p-metal-oxide-semiconductor modulation-doped field effect transistors with nanometer gate lengths

A self-aligned process used to fabricate p-type SiGe metal-oxide-semiconduc tor modulation-doped field effect transistors (MOS-MODFET) is described. Se lf- and nonself-aligned p-type Si0.2Ge0.8/Si0.7Ge0.3 MOS-MODFETs with gate- lengths from 1 mum down to 100 nm were fabricated. The de and microwave cha racteristics of these devices are presented. In comparison with nonself-ali gned devices, self-aligned devices exhibited higher extrinsic transconducta nces, lower threshold voltages, higher unity current gain cutoff frequencie s f(T), and maximum oscillation frequencies f(MAX). Self-aligned MOS-MODFET s with a gate length of 100 nm. exhibited an extrinsic transconductance of 320 mS/mm, an f(T) of 64 GHz, and an f(MAX) of 77 GHz. To our knowledge, th ese are the highest data ever reported for any MOS-type p-FETs with a SiGe channel. All these excellent performances were measured at very low drain a nd Sate biases. (C) 2000 American Vacuum Society. [S0734-211X(00)11806-2].