| 摘要 |
A semiconductor substrate having recesses filled with heteroepitaxial silicon-containing material with different portions having different impurity concentrations. Strained layers can fill recessed source/drain regions in a graded, bottom-up fashion. Layers can also line recess sidewalls with one concentration of strain-inducing impurity and fill the remainder to the recess with a lower concentration of the impurity. In the latter case, the sidewall liner can be tapered.
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