Undoped LPCVD silicon films have been deposited at five temperatures between 560° and 620°C. The films were characterized as grown and after thermal annealing at 900°, 950°, and 1000°C. We used x‐ray diffraction, TEM, SEM, Raman and elastic light scattering, optical absorption and reflection, and other techniques in order to obtain information on the grain size, structure, structural perfection, and surface roughness. We found that polysilicon films of good structural perfection, low strain, and small surface roughness are obtained when the films are deposited in the amorphous phase and subsequently crystallized at 900°–1000°C. Such films are superior in all investigated material aspects to films grown in the crystalline phase.
Undoped and in situ phosphorus-doped low pressure chemical vapor deposited polysilicon films have been studied by various structural analysis and optical techniques as a function of deposition temperature. Polysilicon films of high quality can only be obtained by deposition in the amorphous phase and subsequent crystallization.
The influence of oxygen on the minority carrier lifetime of silicon is reported. Bulk annealed, oxygen‐rich crystals subsequently sliced into wafers show lifetime degradation with annealing time. Silicon oxide precipitates and punched out dislocation loops induced during annealing are identified as electrically active defects responsible for the observed lifetime degradation. Increase in device yields (diodes) and improved lifetime in epitaxial films obtained with oxygen‐rich wafers as substrates are a result of “intrinsic gettering” of oxygen‐rich wafers. It is shown that “external gettering” cannot improve minority carrier lifetime in silicon wafers if during processing “intrinsic gettering” is activated. It is also shown that “external gettering” such as impact sound stressing (ISS) is very effective in improving lifetime for wafers not containing “intrinsic gettering” sources.
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