Ultra-thin high quality SOS films

SOS films 0.2-μm, 0.5-μm, and 1.0-μm thick have been grown at rates from 0.5 to 26 μm/min in a single-wafer epitaxial reactor. Both p-channel and n-channel MOS transistors were fabricated, using n⁺ poly-Si as a gate material. The channel lengths and widths were 20 μm and 250 μm, 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-μm-thick films produced transistors with values of μ_n around 700 cm²/V-s and μ_p around 275 cm²/V-s and almost independent of growth rate. The 0.5-μm-thick films produced transistors with lower mobilities until the growth rate exceeded 8 μm/min. Films grown at growth rates above 8 μm/min produced n-channel and p-channel transistors with mobilities of 700 cm²/V-s and 250 cm² /V-s, respectively. The 0.2-μm-thick films produced lower mobility transistors until the growth rates exceeded 8 μm/min, at which time the mobilities also reached the above-quoted values. Several films 0.1-μm-thick grown at growth rates above 10 μm/min had equally high mobilities. The subthreshold characteristics of these transistors indicated surface-state densities of about 10¹¹ states/cm². Leakage currents were less than 10^-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