Patent ID: 6551875
Filing Date: 2003-04-22
Classification: H01L

Abstract:
A method of forming a uniform collar oxide layer over an upper portion of a sidewall of a trench extending into a semiconductor substrate, comprising:providing a semiconductor substrate; forming a trench extending into the semiconductor substrate with a width of w; forming a conformal oxide layer and a conformal mask layer; forming a photoresist layer on the mask layer; removing a part of the photoresist layer to make the top surface of the photoresist layer lower than the top surface of the semiconductor substrate with a distance d; removing the mask layer and the oxide layer to expose an upper portion of the sidewall of the trench; removing the photoresist layer; performing an ion implantation process to reduce oxidation rate on (110) orientation with a dopant to make the oxidation rates on (110) and (100) orientations existing in the sidewall of the trench equal to each other; and performing local oxidation to form a collar oxide layer with a uniform thickness on the upper portion of the sidewall of the trench.