Patent ID: 9583605
Date: 2017-02-28
CPC Classifications: H01L

Claim:
1. A method of forming a trench in a semi-conductor substrate, the method comprising the steps of: a) providing a semiconductor substrate with a planar surface with a first SiO2 layer disposed on the planar surface thereof, and a first Si3N4 layer on the first SiO2 layer, b) patterning the first SiO2 layer and the first Si3N4 layer by lithography and etching; c) etching a trench into the substrate using the first SiO2 layer and a first Si3N4 layer as an etching mask; d) depositing a second SiO2 conformal layer on the side of the substrate having the trench, e) depositing a second Si3N4 conformal layer on the side of the substrate having the trench, f) anisotropically etching the side of the substrate having the trench to remove the second Si3N4 layer and the second SiO2 layer on substrate surfaces that are parallel to the planar substrate surface wherein the trench sidewall retain at least a portion of the second Si3N4 layer and the second SiO2 layer, g) thermally oxidizing the side of the substrate having the trench to an extent necessary to grow thermal oxide in a trench bottom and at a trench top corner; h) removing all Si3N4 layers and SiO2 layers.