Method of forming shallow trench isolation structure

A method of forming a semiconductor structure, the method comprising:

• depositing a mask layer over a substrate;
• etching the substrate using the mask layer to define a first opening in the substrate;
• depositing a sacrificial material in a bottom surface of the first opening;
• depositing a dielectric liner along sidewalls of the first opening, wherein a bottom surface of the dielectric liner contacts the sacrificial material;
• removing the sacrificial material;
• etching the substrate exposed by the dielectric liner to enlarge the first opening to define a second opening, wherein the second opening comprises:
• a first portion extending a first depth from the dielectric material in a first direction perpendicular to a top surface of the substrate, and
• a second portion extending in a second direction, parallel to the top surface of the substrate, from the first portion;
• removing the dielectric liner;
• and
• filling the second opening with a dielectric material.

A method of forming a semiconductor structure, the method comprising:

• etching a substrate to define a first opening in the substrate, wherein the first opening has a first depth measured from a top surface of the substrate to a bottom surface of the first opening in a first direction perpendicular to the top surface of the substrate;
• depositing a sacrificial material in on the bottom surface of the first opening, wherein the sacrificial material exposes a portion of sidewalls of the substrate;
• depositing a dielectric liner along the portion of the sidewalls;
• removing the sacrificial material;
• etching the substrate through a space defined by the dielectric liner to enlarge the first opening to define a second opening, wherein the second opening comprises:
• a first portion extending a second depth greater than the first depth, wherein the second depth is measured from the top surface of the substrate to a bottom surface of the first opening in the first direction, and
• a second portion extending in a second direction, parallel to the top surface of the substrate, from the first portion, wherein the second portion defines a tip at a third depth in the substrate, and the third depth is measured from the top surface of the substrate to the tip in the first direction;
• removing the dielectric liner to expose the portions of the sidewalls of the substrate;
• and
• filling the second opening with a dielectric material.