Method of manufacturing an LDMOS device having a well region below a groove

A method of making a LDMOS device, comprising:

• obtaining a wafer in which a first conductive type doped region is formed, a top buried layer is formed in the first conductive type doped region, and a field oxidation insulating layer structure is formed on the top buried layer;
• opening a groove on the first conductive type doped region, the groove extending to the top buried layer and the field oxidation insulating layer structure to remove a part of the top buried layer;
• injecting ions of a second conductive type to form a well region below the groove;
• and
• forming a source doped region in the well region;
• the first conductive type and the second conductive type being opposite conductive types,
• wherein the step of opening the groove on the first conductive type doped region is to etch using the field oxidation insulating layer structure as a hard mask.