Patent ID: 9698013
Date: 2017-07-04
CPC Classifications: H01L

Claim:
1. A combined trench for growing a selective epitaxial buffer material, the combined trench comprising: a first and a second shallow trench isolation (STI) region on a substrate surface, the first and second STI regions having first and second STI inner sidewalls defining first and second lower trench sidewalls of a lower trench, the lower trench having a bottom surface that is the substrate surface, the lower trench having a lower trench upper opening, wherein the first and second STI inner sidewalls form an inward angle of 55 degrees with respect to the substrate surface; and a third and a fourth STI region on the first and second STI regions, the third and fourth STI regions having third and fourth STI inner sidewalls defining third and fourth upper trench sidewalls of an upper trench, the upper trench exposing the lower trench upper opening and the substrate surface; the upper trench having an upper trench lower surface above and completely surrounding the lower trench upper opening.