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High oxygen wafers from 100 mm diam Si crystals grown by the Czochralski process, but subjected to three different thermal histories in an experimental puller, were examined by Wright etching, transmission electron microscopy, and Fourier transform infrared spectroscopy after wafer heat-treatments at 775 ~ 1050 ~ 775 ~ + 1050 ~ and 1320 ~ + 775 ~ + 1050~ Only wafers near the seed end of each ingot were used, thus minimizing differences in parameters other than thermal history. The observations show that defect morphology and O precipitate number density (not total O precipitation) after the one-and two-step heat-treatments depend on thermal history in the puller. In particular, 775~ heated wafers which spent less than an hour in the puller below 1000~ show number densities down by more than a factor of 100 from those which spent longer. On the other hand, the observations indicate that effects of puller thermal history are erased with a short 1320~ anneal, or typical VLSI multistep pretreatments which enhance bulk oxygen precipitation. In addition, the results suggest two possible complications for simple models of oxygen precipitation. These are that 500~ annealing can be much more effective than 775~ annealing for nucleating oxygen precipitates, contrary to model predictions, and that critical sizes for precipitate dissolution at 1050~ can be much larger than predicted by classical calculations.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.255.6.125 Downloaded on 2015-06-05 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.255.6.125 Downloaded on 2015-06-05 to IP

Transmission electron microscope studies of carbon-doped Czochralski silicon, when combined with previous infrared data on the same specimens, reveal a double peak in the carbon-sited oxygen-cluster size distribution after 64 h at 750 °C. The first peak, which represents most of the carbon and oxygen in the specimen, is comprised of clusters with an average of two oxygens per carbon atom. These clusters can survive 64 h at 1000 °C although they are not created by such an anneal, suggesting that carbon atoms have difficulty trapping a first oxygen atom at 1000 °C. The second peak in the distribution near 104 oxygen atoms in size is populated with regular {111}-octahedral precipitates having large dilatational strain fields. The two peaks in the size distribution, and their dependences on heat treatment, indicate roles for both seeding (creation of metastable clusters below critical size) and nucleation (achievement of energetic stability) in the formation of carbon-sited precipitates. The observations confirm a trend toward octahedral precipitate morphologies in carbon-doped specimens. However, the trend may result not from site differences but from effects of carbon or point defects on strain energy during precritical cluster growth. Finally, differences between secondary defects associated with precipitation in low- and high-carbon specimens suggest that substitutional carbon atoms at 1000 °C act as sites for silicon self-interstitial condensation near precipitates.

Reduction of the dislocation density in silicon-on-insulator layers produced by oxygen implantation has been achieved by sequentially implanting and annealing the wafers with oxygen doses less than a critical value of about 4×1017/cm2 at 150 keV between heat treatments. Anneals of 17 h duration at 1250 °C were employed. Dislocation densities of less than 103/cm2 were obtained by etching studies on thin epitaxial layers grown on these wafers, in comparison to values around 109/cm2 with single doses greater than the critical value. Since the dislocations in the epitaxial layer arise from those in the implanted silicon overlayer, we expect a six order of magnitude decrease in dislocations at the top of the overlayer as well. The absence of threading dislocations in transmission electron microscope cross sections and plan views reinforces this expectation.