Fabrication of a localized thick box with planar oxide/SOI interface on bulk silicon substrate for silicon photonics integration

A semiconductor structure comprising:

• a semiconductor oxide portion embedded within a semiconductor substrate, wherein said semiconductor substrate contiguously extends from a first portion underlying said semiconductor oxide portion to a second portion overlying a peripheral portion of said semiconductor oxide portion;
• a semiconductor material portion having a planar bottom surface that is in contact with a planar top surface of said semiconductor oxide portion and comprising a same semiconductor material as said second portion;
• a first line trench located on one side of said semiconductor material portion and extending into said semiconductor oxide portion;
• and
• a second line trench located on an opposite side of said semiconductor material portion and extending into said semiconductor oxide portion, wherein said semiconductor material portion laterally extends between a first sidewall of said first line trench and a second sidewall of said second line trench, and is laterally spaced from said second portion by one of said first line trench and said second line trench, and wherein each bottom surface of said first and second line trenches comprises a non-planar convex surface of said semiconductor oxide portion or a pair of grooves between which a portion said semiconductor oxide portion protrudes above bottommost surfaces of said grooves.