Patent ID: 7776674

Claim:
A semiconductor structure fabrication method, comprising: providing a semiconductor structure which includes: (a) a substrate, (b) a first semiconductor region on top of the substrate, wherein the first semiconductor region comprises a first semiconductor material and a second semiconductor material, which is different from the first semiconductor material, and wherein the first semiconductor region has a first crystallographic orientation, and (c) a third semiconductor region on top of the substrate, wherein the third semiconductor region comprises the first and the second semiconductor materials, and wherein the third semiconductor region has a second crystallographic orientation different than the first crystallographic orientation; and forming a second semiconductor region and a fourth semiconductor region on top of the first and the third semiconductor regions respectively, wherein the second semiconductor region comprises the first and the second semiconductor materials, wherein the second semiconductor region has the first crystallographic orientation, wherein the fourth semiconductor region comprises the first and the second semiconductor materials, and wherein the fourth semiconductor region has the second crystallographic orientation, wherein a first ratio in number of atoms of the first semiconductor material to the second semiconductor material in the first semiconductor region is smaller than a second ratio in number of atoms of the first semiconductor material to the second semiconductor material in the second semiconductor region, and wherein a third ratio in number of atoms of the first semiconductor material to the second semiconductor material in the third semiconductor region is greater than a fourth ratio in number of atoms of the first semiconductor material to the second semiconductor material in the fourth semiconductor region.