Electrical characterization of silicon and silicon dioxide materials

Graduation date: 1988The major goal of this research work was to develop better\ud electrical measurements for the evaluation of silicon material\ud quality.\ud The first approach investigated was the Zerbst generation\ud lifetime measurement technique. It was demonstrated that the\ud error in the estimation of the generation lifetime obtained with\ud this technique could be as high as two orders of magnitude due to\ud the neglect of lateral surface generation effects. A procedure\ud was developed to evaluate the generation lifetimes accurately.\ud It includes the use of oxide annealing to reduce surface\ud generation, the employment of an acid-free backside contact\ud process to minimize oxide surface irregularities, and the use of\ud devices of various sizes to extract the actual generation\ud lifetimes. Very high lifetimes of about 50 msec were obtained\ud using this procedure.\ud The second approach investigated was evaluation of the\ud dielectric strength of Si0₂ films thermally grown on silicon\ud material. It was found that oxide annealing did not affect the\ud measured dielectric strength results when the breakdown criterion\ud was set at the catastrophic breakdown current level in the\ud voltage ramp-up technique and when the electrons were injected\ud from the silicon/Si0₂ interface in the constant current\ud technique.\ud A supplemental goal of this research work was to use the\ud developed generation lifetime measurement procedure to\ud investigate the effect of pre-epitaxial deposition nucleation\ud cycles on the generation lifetimes of silicon wafers from\ud different parts of a silicon ingot. It was found that when a\ud 650°C nucleation heat treatment cycle was inserted before the\ud depositon of the epitaxial layer, followed by a typical intrinsic\ud gettering process, the generation lifetimes of wafers became\ud independent of their origin in the ingot and were very high,\ud about 35 msec.\ud A relationship between the dielectric strength of Si0₂ films\ud and the density of bulk microdefects was also investigated. The\ud dielectric strength of Si0₂ films was found to increase with the\ud bulk stacking fault density, not with the bulk precipitate\ud density. This indicates that the formation of bulk stacking\ud faults may be the key element responsible, for gettering heavy\ud metal contaminants away from the front surface of the wafer