Method of making silicon carbide semiconductor device having multi-layered passivation film with uneven surfaces

1. A method of making a silicon carbide semiconductor device provided as a semiconductor chip having a chip edge, the method comprising:

forming a first conductivity type silicon carbide drift layer on a front surface of a silicon carbide substrate, the drift layer having an impurity concentration less than an impurity concentration of the substrate;

forming an interlayer insulation film on the drift layer, the forming the insulation film including forming an opening in the insulation film;

forming a semiconductor element in a cell region of the drift layer;

forming a surface electrode on the drift layer in such a manner that the surface electrode is electrically coupled to the semiconductor element through the opening of the insulation film;

forming a passivation film above the drift layer around the periphery of the cell region to cover an outer edge of the surface electrode, the forming the passivation film including forming an opening to the passivation film in such a manner that the surface electrode is exposed outside through the opening of the passivation film; and

forming a back electrode on a back surface of the substrate in such a manner that the back electrode is electrically coupled to the semiconductor element, the back surface of the substrate being opposite to the front surface of the substrate, wherein

the forming the passivation film further includes forming an uneven surface in a front side of the passivation film in such a manner that the uneven surface has a shape independent of a shape of a surface underlying the passivation film, and

a length from an inner edge of the opening of the passivation film to the chip edge measured along the uneven surface of the front side of the passivation film is greater than a length from the inner edge of the opening of the passivation film to the chip edge measured along a back side of the passivation film, the back side of the passivation film being placed on the surface underlying the passivation film so that the back side has a shape dependent on the surface underlying the passivation film, wherein

the forming the passivation film further includes forming a first film layer in such a manner that the first film layer has the shape dependent of the shape of the underlying surface of the passivation film, the forming the passivation film further including forming a second film layer on the first film layer, the first and second film layers being formed from different materials, and

the forming the second film layer includes forming the uneven surface by etching the second film layer and using the first film layer as a stopper layer.

2. The method of claim 1 , wherein the forming of the uneven surface includes forming the uneven surface by etching the second film layer so that the shape of the second film layer is independent from the shape of the first film layer.

3. The method of claim 1 , wherein the forming of the uneven surface includes forming the uneven surface by etching the second film layer so that the thickness of the second film layer is non-uniform and includes multiple projections and recesses that define a comb-shaped surface.

4. The method of claim 1 , wherein the forming of the uneven surface includes forming the uneven surface by etching the second film layer so that the surface area of the second film layer is greater than the surface area of the first film layer.