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The spurious contribution of oxide precipitates to the infrared absorption of interstitial oxygen in silicon is determined from spectra collected at 7 K for samples with different initial interstitial oxygen O-i concentration subjected to a three-step thermal treatment. These data can be used to correct the residual O-i values determined at room temperature following the standard procedure from the intensity of the 1107 cm(-1) absorption band. The error in residual O-i is found to reach values on the order of 2x10(17) atoms/cm(3) for samples with initial O-i content higher than 6.5x10(17) atoms/cm(3). (C) 2001 American Institute of Physics

Gettering efficiencies and stabilities of internal gettering sites for metallic impurities in high and low carbon doped silicon have been compared with ramped and standard two-step pre-annealing conditions. This study was intended to compare two proposed techniques to shorten the long low temperature nucleation step in the standard Hi-Lo-Hi internal gettering site formation treatment. Specifically, we compare the affect of carbon and a ramped annealing sequence on oxygen precipitate formation and gettering effectiveness. Our results show both techniques accelerate oxygen precipitation, however, only the low carbon ramped materials produced efficient and stable gettering sites. The high carbon materials did not with either annealing treatment. This disparity in performance is due to a difference in the oxygen precipitate’s strain field. The precipitates in the low carbon material possessed a high strain field with strain-induced defects while in the high carbon material they were strain-free with no defects. These results indicate the strain stabilizes the gettered impurity such that the gettering rate is increased and stability is enhanced.

Using Czochralski‐grown silicon crystals with carbon concentrations from 1014 to 1016 cm−3, we studied the influence of oxygen precipitates on the mechanical strength of silicon crystals. Reducing carbon concentration from 1016 to 1014 cm−3 suppressed oxygen precipitation and thus, improved the strength. Carbon concentration reduction from 1015 to 1014 cm−3 did not, however, decrease oxygen precipitation as dramatically as reduction from 1016 to 1015 cm−3. Carbon impurities below 1014 cm−3 no longer affect oxygen precipitation. Therefore, we conclude that reducing carbon concentration below 1014 cm−3 no longer improves the mechanical strength of silicon crystals.

High-spatial resolution Fourier transform infrared spectroscopy permitted us to study the effects of incident light polarization on the absorption band related to aggregates of SiO2 disk-shaped precipitates present in annealed (100) Czochralski silicon samples. This is the first report documenting the strong dependence of such a band intensity on light polarization. Experimental results were compared with the simulation obtained using the effective medium theory. From this comparison we deduce that the precipitates only lie on the planes among {100} which are parallel to the wafer surface. This result can be related to the difference between the 〈100〉 direction and those crystallographically equivalent, introduced by the ingot growth process.

A generalized expression is derived describing the impact of intrinsic point defects and strain on the critical size of spheroidal incoherent precipitates. An important phenomenon that has been neglected so far is the incorporation of intrinsic point defects of the host matrix in the precipitate itself. It is shown that this can have an important impact both on the critical precipitate size, on the amount of emitted intrinsic point defects, and on the precipitated phase itself. The theoretical results are illustrated for the case of oxygen precipitation in silicon.

A procedure for reducing the interstitial oxygen content of virgin Czochralski silicon wafers is described. The process consists of oxidizing wafers in an HCl‐added dry oxygen ambient. The gettering action reduces the probability of oxygen precipitation throughout the bulk of the wafer and simultaneously provides a masking or passivating surface oxide. Since oxygen precipitates have been correlated with the nucleation of dislocations and stacking faults, which are known to adversely affect many devices, these gettering procedures may provide a means for overcoming some of the processing problems associated with large‐diameter high oxygen content Czochralski material.

It is shown that the energetically optimum shape of a precipitate which generates strains in the host lattice is a disc with a thickness that increases approximately with the square root of the size (disc radius). This relationship contravenes the two common assumptions that either the thickness or the aspect ratio stays unchanged during precipitate growth. From this relationship is derived a precipitate growth law of r∝t2/3. The results of the analysis are discussed with special reference to the growth of oxygen precipitates in silicon. The change in the morphology of oxygen precipitates with temperatures is also discussed.

The ability of SiO2 precipitates to act as a source of process‐induced defects which can either beneficially getter unwanted impurities, or deleteriously interact with surface devices, has led to some confusion in interpreting the role of wafer oxygen content in device processing. This report presents a composite model which explains the many variables involved in oxygen precipitation and gettering phenomena.

The suppression effect on oxygen precipitation by carbon was observed under a certain heat treatment condition. The amount of precipitate oxygen in a high carbon silicon crystal is less than that in a low carbon silicon crystal, when silicon crystals are heat treated by the two‐step thermal anneal (700 °C anneal+1000 °C anneal), whose first step annealing time is long. This is caused by the generation of too many precipitate nuclei during the first step thermal anneal. Growth rate for small precipitates is retarded. Carbon has the enhancement effect on oxygen precipitation during the first step anneal at 700 °C, but no enhancement effects during the second step anneal at 1000 °C.

Photoluminescence in the photon energy range 0.7–1.2 eV is investigated for commercial Czochralski‐grown Si crystals subjected to isothermal annealing at 650 °C for 1–450 h. A strong and sharp line appears at 0.903 eV at certain annealing stages, regardless of the sources and the conductivity type of starting materials. The intensity dependence of the 0.903‐eV line on the annealing time coincides with the concentration dependence expected for Si self‐interstitials emitted during the oxygen precipitation process. This is experimental evidence that microdefects responsible for this line are correlated with Si self‐interstitials.