Method of making a low-Rdson vertical power MOSFET device

A method for making a low-Rdson vertical power MOSFET device in an epitaxial layer of a first conductivity type supported on a substrate with a bottom of the epitaxial layer configured as a bottom electrode of the vertical power MOSFET device comprises the following steps:

• forming a lightly doped epitaxial layer on a lightly doped substrate;
• forming a vertical MOSFET device in the epitaxial layer;
• depositing a bottom passivation layer covering a bottom surface of the substrate;
• forming a plurality of openings in the bottom passivation layer;
• etching the substrate through the openings on the bottom passivation layer forming a plurality of grooves penetrating the substrate exposing portions of a bottom surface of the epitaxial layer;
• depositing a metal layer covering the bottom surface of the substrate, sidewalls of the grooves and the exposed portions of the bottom surface of the epitaxial layer wherein the metal layer forming a bottom metal electrode of the vertical power MOSFET,
• wherein the substrate being doped with a second conductivity type opposite to the first conductivity type of the epitaxial layer thus forming a PN junction at an interface of the substrate and the epitaxial layer therefore providing an etch stop when reversed bias to stop an electric-chemical etching process after etching the grooves through the substrate, and
• wherein the method further comprising implanting dopant of the first conductivity type from the bottom of the substrate forming a plurality of heavily doped regions at the exposed portions of the bottom of the epitaxial layer corresponding to the grooves.