Dislocation glide and blocking kinetics in compositionally graded SiGe/Si
Dislocation glide and blocking kinetics in compositionally graded SiGe/Si
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成分梯度 SiGe/Si 中的位错滑移和阻挡动力学
DOI：
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发表时间：
2001
期刊：
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通讯作者：
M. Bulsara
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文献类型：
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作者：
C. Leitz;M. Currie;A. Kim;J. Lai;E. Robbins;E. Fitzgerald;M. Bulsara
探讨了生长温度、衬底边角料和位错堆积形成对成分梯度 SiGe 缓冲器中的穿透位错密度 (TDD) 的影响。为了研究这些结构中的位错滑移动力学，在 650 至 900°C 的温度下，在 (001)-、(001) 向面内<110>- 6° 切边和 (001) 向面内 <100> 取向的 Si 衬底上 6° 切边生长一系列相同的 30% Ge 样品。轴上样品中的场穿透位错密度（场 TDD）随温度呈指数变化，从 650°C 时的 3.7×106 cm−2 到 900°C 时的 9.3×104 cm−2。根据场 TDD 随生长温度的演化计算，该系列中位错滑移的活化能为 1.38 eV，远低于该成分的预期值。这种偏差表明，在低生长温度下的分级过程中累积的应变正在迫使位错进一步成核，从而导致与纯滑动限制弛豫的偏差。在切边衬底上生长的样品的 TDD 表现出更复杂的温度依赖性，可能是因为在切边衬底上生长的薄膜在高温下位错还原反应中趋于饱和。通过在 650°C 下开始成分分级至 15% Ge，并在 900°C 下继续分级至 30% Ge，进一步探索了位错减少过程。该生长的低温部分提供了过量浓度的穿透位错，这些位错随后可以在生长的高温部分期间被湮灭，从而能够比较不同衬底边角料的减少率。将这些结果与各种其他样品中的螺纹位错密度相结合，就可以得出成分梯度 SiGe/Si 中应变弛豫动力学的完整图像。一般来说，这些结构中的应变弛豫受到位错滑移的限制，并且穿透位错密度与最终的Ge含量无关。然而，我们推测位错堆积的形成抑制了应变弛豫过程，因此伴随着场穿透位错密度的增加。基于这些结果，我们现在拥有了在各种生长条件下成分分级的 SiGe/Si 的 TDD 预测模型。
The effects of growth temperature, substrate offcut, and dislocation pileup formation on threading dislocation density (TDD) in compositionally graded SiGe buffers are explored. To investigate dislocation glide kinetics in these structures, a series of identical samples graded to 30% Ge were grown at temperatures between 650 and 900 °C on (001)-, (001) offcut 6° towards an in-plane 〈110〉-, and (001) offcut 6° towards an in-plane 〈100〉-oriented Si substrates. The field threading dislocation density (field TDD) in the on-axis samples varied exponentially with temperature, from 3.7×106 cm−2 at 650 °C to 9.3×104 cm−2 at 900 °C. The activation energy for dislocation glide in this series, calculated from the evolution of field TDD with growth temperature, was 1.38 eV, much lower than the expected value for this composition. This deviation indicates that strain accumulating during the grading process at low growth temperatures is forcing further dislocation nucleation, resulting in a deviation from pure glide-limited relaxation. The TDD of samples grown on offcut substrates exhibited a more complicated temperature dependence, likely because films grown on offcut substrates have an increased tendency towards saturation in dislocation reduction reactions at high temperature. Dislocation reduction processes were further explored by initiating compositional grading up to 15% Ge at 650 °C and continuing the grade to 30% Ge at 900 °C. The low temperature portion of this growth provided an excess concentration of threading dislocations which could subsequently be annihilated during the high temperature portion of the growth, enabling a comparison of reduction rates for different substrate offcuts. Combining these results with threading dislocation densities in a variety of other samples, a complete picture of strain relaxation kinetics in compositionally graded SiGe/Si emerges. Generally, strain relaxation in these structures is limited by dislocation glide, and threading dislocation densities are independent of final Ge content. However, we theorize that dislocation pileup formation inhibits the strain relaxation process and is therefore accompanied by a rise in field threading dislocation density. Based on these results, we now have a predictive model for TDD in compositionally graded SiGe/Si over a wide range of growth conditions.