High breakdown n-type buried layer

A method of forming a semiconductor device, comprising the steps:

• providing a first epitaxial layer of a substrate comprising p-type semiconductor material;
• implanting n-type dopants into the first epitaxial layer at a dose greater than 5×1014 cm−2, the n-type dopants being selected from the group consisting of arsenic and phosphorus;
• implanting phosphorus into the first epitaxial layer at a dose of 1×1013 cm−2 to 1×1014 cm−2 and at an energy above 100 keV;
• heating the first epitaxial layer in a first thermal drive process which heats the first epitaxial layer to a temperature of 1150° C. to 1225° C. for at least 30 minutes;
• and
• forming a p-type epitaxial layer of the substrate on the first epitaxial layer;
• wherein the implanted n-type dopants form a main layer of an n-type buried layer, the main layer being 2 microns to 10 microns thick, wherein at least 50 percent of n-type dopants in the main layer are selected from the group consisting of antimony and arsenic, and wherein a top surface of the main layer is at least 5 microns below a top surface of the substrate, and the implanted phosphorus forms a lightly-doped layer of the n-type buried layer, the lightly-doped layer extending at least 2 microns below the main layer, wherein the lightly-doped layer has an average doping density of 1×1016 cm−3 to 1×1017 cm−3, and at least 90 percent of n-type dopants in the lightly-doped layer are phosphorus.