Selective etching in the formation of epitaxy regions in MOS devices

摘要

A method for forming a semiconductor structure includes forming a gate stack over a semiconductor substrate; forming a recess in the semiconductor substrate and adjacent the gate stack; and performing a selective epitaxial growth to grow a semiconductor material in the recess to form an epitaxy region. After the step of performing the selective epitaxial growth, a selective etch-back is performed to the epitaxy region. The selective etch-back is performed using process gases comprising a first gas for growing the semiconductor material, and a second gas for etching the epitaxy region.

主权项

1. A method for forming a semiconductor structure, the method comprising:
forming a gate stack over a semiconductor substrate, the semiconductor substrate having a first lattice constant; forming a recess in the semiconductor substrate and adjacent the gate stack; performing a first selective epitaxial growth to grow a first semiconductor material in the recess and adjoining a bottom-most surface of the recess, the first selective epitaxial growth substantially only growing the first semiconductor material from one or more crystalline surface, the bottom-most surface of the recess comprising a surface of the semiconductor substrate, the first semiconductor material having a second lattice constant; after the step of performing the first selective epitaxial growth, performing a selective etch-back on the first semiconductor material, wherein the selective etch-back is performed using process gases comprising a first gas for growing the first semiconductor material, and a second gas for etching the first semiconductor material, wherein after the selective etch-back is performed at least a portion of a top surface of the first semiconductor material is at or above a top surface of the semiconductor substrate; and performing a second selective epitaxial growth to grow a second semiconductor material adjoining the first semiconductor material to form a cap region, the second selective epitaxial growth substantially only growing the second semiconductor material from one or more crystalline surface, the second semiconductor material having a third lattice constant, a magnitude of a difference between the first lattice constant and the second lattice constant being greater than a magnitude of a difference between the first lattice constant and the third lattice constant.