Silcon carbide semiconductor device having schottky barrier diode and method for manufacturing the same

An SiC semiconductor device comprising:

• a substrate made of silicon carbide, having a first conductivity type, and having a principal surface and a rear surface opposite to each other;
• a drift layer made of silicon carbide, having a first conductivity type, and disposed on the principal surface of the substrate, wherein an impurity concentration of the drift layer is lower than that of the substrate;
• an insulating layer disposed on the drift layer, and including an opening, wherein a part of the substrate and a part of the drift layer disposed between the opening and the rear surface of the substrate are defined as a cell;
• an ohmic electrode disposed on the rear surface of the substrate;
• a Schottky electrode contacting with the drift layer through the opening of the insulating layer;
• a Schottky barrier diode provided by the cell, the ohmic electrode and the Schottky electrode;
• a termination structure that is disposed on an outer periphery of the cell, and that includes a resurf layer disposed in a surface part of the drift layer, wherein the resurf layer surrounds the cell;
• and
• a plurality of second conductivity type layers disposed in another surface part of the drift layer, contacting the Schottky electrode, surrounded by the resurf layer, and separated from one another, wherein:
• each second conductivity type layer substantially has a hexagonal shape;
• the plurality of second conductivity type layers is arranged so as to have a honeycomb structure on a contact region between the Schottky electrode and the drift layer;
• the plurality of second conductivity type layers is arranged so as to have a point symmetry on the contact region with respect to a center of the contact region;
• a two-dimensional plane passing through the center of the contact region and perpendicular to the principal surface of the substrate is defined as a first plane;
• a plurality of cross sections corresponding to the plurality of second conductivity type layers taken along the first plane is defined as a plurality of first cross sections;
• and
• the plurality of second conductivity type layers is configured so that an arrangement of the plurality of first cross sections on the first plane is substantially symmetric.

A method for manufacturing an SiC semiconductor device, comprising:

• forming a drift layer on a principal surface of a substrate by epitaxial growth, wherein the drift layer and the substrate are made of silicon carbide and have a first conductivity type;
• forming a first mask on the drift layer, wherein the first mask has a first ring-shaped opening;
• forming a resurf layer having a second conductivity type by implantation of impurities into the drift layer through the ring-shape opening of the first mask;
• removing the first mask;
• forming a second mask on the drift layer and the resurf layer, the second mask having a plurality of second openings;
• forming a plurality of second conductivity type layers in a surface of the drift layer by implantation of impurities into the drift layer through the plurality of second openings of the second mask, wherein
• the plurality of second conductivity type layers includes a center member and a plurality of ring members, and
• each ring member surrounds the center member and is arranged substantially in a point symmetric manner with respect to a center of a region on which the plurality of second conductivity type layers is formed;
• removing the second mask;
• forming an insulating layer on the drift layer, the resurf layer, and the plurality of second conductivity type layers;
• forming a third opening on the insulating layer through photolithography-etching;
• forming a Schottky electrode contacting with the drift layer through the third opening of the insulating layer;
• and
• forming an ohmic electrode on a rear surface of the substrate, the rear surface being opposite to the principal surface of the substrate.