Integrated lateral high voltage MOSFET

A process of forming an integrated circuit, comprising steps:

• providing a monolithic semiconductor substrate having a first conductivity type;
• and
• forming a dual drift layer extended drain MOS transistor, by a process including steps:
• forming a lower drift layer implant mask over said monolithic substrate so as to expose a top surface of said substrate in a lower drift layer area overlapping a drain section of said dual drift layer extended drain MOS transistor and in a lower drift extension area adjacent to said lower drift layer area;
• performing a lower drift layer ion implant operation which implants lower drift layer dopants of an opposite conductivity type from said substrate through said lower drift layer implant mask to form a lower drift layer implanted region in said monolithic substrate in said lower drift layer area at a desired depth and to form a lower drift extension implanted region in said monolithic substrate in said lower drift extension area at said desired depth;
• performing a lower drift layer anneal operation which heats said monolithic substrate so as to diffuse said lower drift layer dopants in said lower drift layer implanted region and in said lower drift extension implanted region to form a lower drift layer in the lower drift layer area and to form a lower drift extension in said lower drift extension area contacting said lower drift layer, said lower drift layer and said lower drift extension having said opposite conductivity type from said monolithic substrate;
• forming an upper drift layer implant mask over said monolithic substrate to expose a top surface of said monolithic substrate above said lower drift layer and in an isolation link area above said lower drift extension;
• performing an upper drift layer ion implant operation which implants upper drift layer dopants of said opposite conductivity type from said monolithic substrate through said upper drift layer implant mask to form an upper drift layer implanted region in said monolithic substrate over said lower drift layer area and to form an isolation link implanted region in said monolithic substrate in said lower drift extension area;
• performing an upper drift layer anneal operation to diffuse said upper drift layer dopants in said upper drift layer implanted region to form an upper drift layer which contacts an upper surface of said lower drift layer along at least 75 percent of a common length of said upper drift layer and said lower drift layer and to diffuse said upper drift layer dopants in said isolation link implanted region to form an isolation link which contacts said lower drift extension such that a body region of said dual drift layer extended drain MOS transistor is electrically isolated from said monolithic substrate outside of said dual drift layer extended drain MOS transistor, said body region having said first conductivity type, said upper drift layer and said isolation link having said opposite conductivity type from said monolithic substrate, so that an average doping density in said lower drift layer is between 2 and 10 times an average doping density in said upper drift layer;
• forming a gate dielectric layer on said body region and overlapping said upper drift layer;
• and
• forming a gate located on said gate dielectric layer above said body region and overlapping said upper drift layer.