Method for preparing oxide film at bottom of trench

Abstract

The invention discloses a method for preparing an oxide film at the bottom of a trench. The method comprises the following steps of: after the trench is etched on a substrate, 1) growing a gasket oxide film in the trench; 2) depositing silicon nitride on the whole substrate to ensure that silicon nitride layers are deposited on both the upper surface of the substrate and the inner wall of the trench; 3) etching back the silicon nitride layers to remove the silicon nitride from the bottom of the trench, forming a silicon nitride side wall on the side wall of the trench, removing the gasket oxide film from the bottom of the trench by wet etching and etching the gasket oxide film positioned at the bottom of the silicon nitride side wall at the same time; 4) performing an oxidation process togrow a bottom oxide film at the bottom of the trench; and 5) completely removing the silicon nitride layers from the substrate, the silicon nitride side wall and the gasket oxide film from the side wall of the trench by using an etching process and performing an ordinary process of growing gate oxide and filling the trench. By the method, a thicker oxide film can be formed at the bottom of the trench to greatly reduce the grid-drain capacitance of a device, so that the switch characteristic of a trench power device is improved.

Description

technical field [0001] The invention relates to a method for preparing a dielectric film at the bottom of a trench, in particular to a method for preparing an oxide film at the bottom of the trench. Background technique [0002] In the existing trench fabrication technology, whether using photoresist to do mask protection or using dielectric film to do mask protection, after the trench etching is completed and the required trench shape is obtained (trench depth, width and shape), a thermal oxide film is grown to make the gate oxide film of the device. Then grow polysilicon to fill the trench, and remove the polysilicon on the silicon surface by etching back or chemical mechanical polishing, and then perform well implantation, source implantation and P+ region implantation to obtain the following: figure 1 The device structure shown. In this structure, the thickness of the oxide film at the bottom of the trench is basically the same as the thickness of the gate oxide film o...

AI Technical Summary

Problems solved by technology

However, the thickness uniformity of the bottom dielectric film obtained by this proposal is poor, and the oxide film on the side wall cannot be etched in the same plane as required, etc., which make it unable to meet the needs of mass production.

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