Ultra-thin high quality SOS films

Abstract

SOS films 0.2- mu m, 0.5- mu m, and 1.0- mu m thick have been grown at rates from 0.5 to 26 mu m/min in a single-wafer epitaxial reactor. Both p-channel and n-channel MOS transistors were fabricated, using n/sup +/ poly-Si as a gate material. The channel lengths and widths were 20 mu m and 250 mu m, respectively. The p-channel transistors were enhancement devices with threshold voltages around -1.2 V. The n-channel transistors were depletion devices with threshold voltages around 0 V. The 1.0- mu m-thick films produced transistors with values of mu /sub n/ around 700 cm/sup 2//V-s and mu /sub p/ around 275 cm/sup 2//V-s and almost independent of growth rate. The 0.5- mu m-thick films produced transistors with lower mobilities until the growth rate exceeded 8 mu m/min. Films grown at growth rates above 8 mu m/min produced n-channel and p-channel transistors with mobilities of 700 cm/sup 2//V-s and 250 cm/sup 2//V-s, respectively. The 0.2- mu m-thick films produced lower mobility transistors until the growth rates exceeded 8 mu m/min, at which time the mobilities also reached the above-quoted values. Several films 0.1- mu m-thick grown at growth rates above 10 mu m/min had equally high mobilities. The subthreshold characteristics of these transistors indicated surface-state densities of about 10/sup 11/ states/cm/sup 2/. Leakage currents were less than 10/sup -11/ A. The mobility dropped about 20% from the threshold voltage to gate voltages of 5 V. The mobilities in the saturation region were about 20% less than the mobilities in the linear region.<>