SiO2precipitate strain relief in Czochralski Si: Self-interstitial emission versus prismatic dislocation loop punching
Formation of SiO2precipitates in Czochralski Si is associated with a volume expansion of more than 100%. The needed extra volume for precipitate growth to occur is primarily supplied by emission of Si self-interstitials (I) into the Si matrix, in balance with a compressive growth residual strain. During cooling after the anneal, an additional compressive cooling strain component also develops because of the different thermal expansion coefficients of SiO2and Si. For precipitates grown to a sufficiently large size, the growth residual strain and/or the cooling strain can be further relieved by punching interstitial type prismatic dislocation loops into the Si matrix. Otherwise, only I emission can occur. Up to now, there have been no quantitatively determined strain values, which constitute in a given experiment a measure of the I emission efficiency on the one hand, and a basis for determining whether prismatic punching can also occur on the other. In this study, we have calculated the strain values and obtained a quantitative criterion for prismatic punching to occur. In the order of ∼10-3-10-2, the growth residual strain component values indicate that I emission has attained an efficiency of relieving the precipitate growth strain by ∼90%-99%. Available experimental data on the precipitate size dependence of prismatic dislocation loop punching have been satisfactorily fitted using the obtained strain values and the punching criterion, indicating that these calculated values are in acceptable accuracy ranges.
Taylor, WJ; Gösele, U; Tan, TY
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