P-type LDMOS device with buried layer to solve punch-through problems and process for its manufacture

摘要

P-type LDMOS devices have been difficult to integrate with N-type LDMOS devices without adding an extra mask because the former have been unable to achieve the same breakdown voltage as the latter due to early punch-through. This problem has been overcome by preceding the epitaxial deposition of N- silicon onto the P- substrate with an additional process step in which a buried N+ layer is formed at the surface of the substrate by ion implantation. This N+ buried layer significantly reduces the width of the depletion layer that extends outwards from the P- well when voltage is applied to the drain thus substantially raising the punch-through voltage.