Patent ID: 9653477
Date: 2017-05-16
CPC Classifications: H01L

Claim:
1. A method comprising: forming a first set of openings in a precursor structure having: wherein the first set of openings each exposes the silicon substrate; undercut etching the silicon substrate in a direction perpendicular to the crystal direction of the silicon substrate to form a set of trenches corresponding with the first set of openings, respectively; passivating exposed surfaces of at least one of the SiGe layer and the silicon layer in the first set of openings; at least partially filling each trench with a dielectric layer to form air gaps in the set of trenches, respectively, each of the air gaps being surrounded by the dielectric layer; and forming a gate over the second oxide layer, wherein the dielectric layer forms a joint portion between adjacent ones of the air gaps, the joint portion being jointly disposed in adjacent trenches of the set of trenches, and wherein the gate directly overlies the joint portion.