Wide band gap semiconductor device and method for producing the same
A wide band gap semiconductor device is disclosed. A first trench in a gate electrode part and second trench in a source electrode part (Schottky diode) are disposed close to each other, and the second trench is deeper than the first trench. A metal electrode is formed in the second trench to form a Schottky junction on a surface of an n-type drift layer in the bottom of the second trench. Further, a p+-type region is provided in part of the built-in Schottky diode part being in contact with the surface of the n-type drift layer, preferably in the bottom of the second trench. The result is a small wide band gap semiconductor device which is low in on-resistance and loss. Electric field concentration applied on a gate insulating film is relaxed to suppress lowering of withstand voltage and increase avalanche breakdown tolerance at turning-off time.
1. A wide band gap semiconductor device comprising:
a silicon carbide semiconductor substrate;
a second conductivity type silicon carbide semiconductor layer having a high impurity concentration and disposed on one principal surface of the semiconductor substrate;
a second conductivity type silicon carbide drift layer having a low impurity concentration and disposed on the second conductivity type silicon carbide semiconductor layer;
a first conductivity type silicon carbide base layer disposed on the drift layer;
a second conductivity type silicon carbide source region selectively disposed on a principal surface of the base layer;
a first trench having a depth extending from a principal surface of the source region to reach the drift layer;
a gate insulating film lining the first trench;
a control electrode which is filled in the first trench, inside the gate insulating film, so as to be located in a position facing the source region, the base layer and the drift layer;
a second trench provided near the first trench and having a depth extending from the principal surface of the base layer to reach the drift layer so as to be deeper than the first trench;
a first main electrode which is disposed in the second trench to form a Schottky junction between the first main electrode and a surface of the drift layer located in the second trench so that the first main electrode covers the principal surface of the source region and the principal surface of the base layer in common;
third trenches each of which has a depth extending from the other principal surface of the silicon carbide semiconductor substrate to reach the second conductivity type silicon carbide semiconductor layer having the high impurity concentration; and
a second main electrode which is electrically connected to inner surfaces of the third trenches and the other principal surface of the silicon carbide semiconductor substrate.
2. A wide band gap semiconductor device according to claim 1 , further comprising a first conductivity type region being in contact with a bottom of the second trench.
3. A wide band gap semiconductor device according to claim 1 , wherein the distance between central lines of the first and second trenches is not longer than 10 μm.
4. A method of producing a wide band gap semiconductor device as defined in claim 1 , comprising the steps of:
grinding the other principal surface of the semiconductor substrate to provide the semiconductor substrate as a thin layer before forming the second main electrode;
forming the third trenches on the other principal surface of the ground semiconductor substrate; and
forming the second main electrode.