Polysilicon films have been deposited at a low temperature by single and dual ion beam sputtering. The structural and electrical properties of as-deposited and annealed films have been characterized by x-ray diffraction, secondary ion mass spectroscopy, atomic force microscopy, and Hall mobility measurements. The films are microcrystalline with average grain size ranging from 200 to 400 Å. The films exposed to a low-energy secondary ion beam during sputtering from a silicon target have exhibited smoother surface topography and different electrical behavior than the films deposited without any secondary ion bombardment. Some preliminary studies on ion beam sputtered SiGe films using a compound target are also presented.
Microwave plasma oxidation of polycrystalline silicon has been carried out to grow thin polyoxide films at a low temperature in O 2 ambient. The electrical properties of grown oxides have been studied using a metal-oxide-semiconductor structure. The current-voltage characteristics of polyoxides have been studied for different poly doping and post-oxidation annealing conditions. It is found that the polyoxide on undoped poly-Si has lower leakage current and higher breakdown voltage, whereas the oxide on doped poly-Si has higher tunnelling efficiency at lower field. The oxide on boron doped poly-Si exhibits electron trapping behaviour.
Ion-assisted oxidation has been carried out at a substrate temperature of 150 • C for fabrication of metal-oxide-semiconductor capacitors using fully strained Si 1−x Ge x (x = 0.2 and 0.26) and partially strained Si 1−x−y Ge x C y (Ge:C = 20:1 and 40:1) films. The oxide thickness is designed to consume a part of the Si-cap layer, leading to the formation of a valence band quantum well for confining the carriers away from the Si-SiO 2 interface. The fixed oxide charge density and mid-gap interface trap density are found to be higher for the sample containing higher Ge and C concentration. The presence of hole-trapping centres is observed for all the samples. However, a decrease in the hole trap density is observed either with the reduction of Ge content or with the increase of carbon fraction in the film.
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