Method for manufacturing high-breakdown voltage semiconductor device.

摘要

A first silicon oxide film (11) is formed on the major surface of an n-type silicon substrate (10). A silicon nitride film is formed on the first silicon oxide film. The first silicon oxide film and the silicon nitride film are selectively etched to form an opening. Boron ions are implanted into the silicon substrate (10) using the first silicon oxide film (11) and the silicon nitride film as a mask. A second silicon oxide film (16) is formed on the silicon substrate (10) exposed by the opening. Gallium ions are implanted into the second silicon oxide film (16) using the silicon nitride film as a mask. Boron and gallium ions are simultaneously diffused in the silicon substrate. In this case, a diffusion rate of gallium in the silicon substrate is higher than that of boron in the silicon substrate (10), and the diffusion rate of gallium in the silicon oxide film (11) is higher than that in the silicon substrate (10). Therefore, a p-type second layer is formed in the substrate to surround a p<+>-type first layer in a self-aligned manner.