Insulated gate semiconductor device
A CSTBT includes a carrier stored layer ( 113 ) formed between a P base region ( 104 ) and a semiconductor substrate ( 103 ) and the carrier stored layer has an impurity concentration higher than that of the semiconductor substrate ( 103 ). The P base region ( 104 ) in a periphery of a gate electrode ( 110 ) functions as a channel. When it is assumed that an impurity concentration of a first carrier stored layer region ( 113 a ) just under the channel is ND 1 and an impurity concentration of a second carrier stored layer region ( 113 b ) other than just under the channel is ND 2 in the carrier stored layer ( 113 ), the relationship of the impurity concentrations is defined by ND 1 <ND 2. Thus, a gate capacity and a short-circuit current can be controlled and variation in threshold voltage can be prevented.
1. An insulated gate semiconductor device comprising:
a first conductivity type first base region;
a second conductivity type collector region formed on a lower main face of the first conductivity type first base region;
a collector electrode connected to the collector region;
a second conductivity type second base region selectively formed on an upper main face of the first conductivity type first base region;
a first conductivity type carrier stored layer formed between the second base region and the first base region and having an impurity concentration higher than that of the second base region;
a first conductivity type emitter region selectively formed in the second base region;
a trench selectively formed in the second base region and having a depth reaching inside of the first conductivity type first base region;
a gate electrode buried in the trench through an insulation film; and
an emitter electrode connected to both the second base region and the emitter region,
wherein the second base region located in the periphery of the gate electrode functions as a channel region, and when it is assumed that an impurity concentration of a first carrier stored layer region located just under the channel region is ND 1 and an impurity concentration of a second carrier stored layer region other than just under the channel region is ND 2 in the carrier stored layer, the relationship between the impurity concentrations is defined by ND 1 <ND 2 .
2. The insulated gate semiconductor device according to claim 1 , wherein the impurity concentration ND 1 of the first carrier stored layer region and the impurity concentration ND 2 of the second carrier stored layer region are defined by
ND 1 <7E16cm −3 , ND 2 <3E17cm −3 and ND 2 /ND 1 >5.
3. The insulated gate semiconductor device according to claim 1 , wherein the trench has a first trench and a second trench,
a first gate electrode is buried in the first trench through the insulation film,
a dummy second gate electrode is buried in the second trench through the insulation film, and
only the second base region located in the periphery of the first gate electrode works as the channel region and the second base region located in the periphery of the dummy second gate electrode does not work as the channel region.
4. The insulated gate semiconductor device according to claim 3 , wherein the impurity concentration ND 1 of the first carrier stored layer region and the impurity concentration ND 2 of the second carrier stored layer region is defined by
ND 1 <7E16cm −3 , ND 2 <3E17cm −3 and ND 2 /ND 1 >5.
5. The insulated gate semiconductor device according to claim 3 , wherein a plurality of the dummy second gate electrodes are regularly arranged.
6. The insulated gate semiconductor device according to claim 5 , wherein the impurity concentration ND 1 of the first carrier stored layer region and the impurity concentration ND 2 of the second carrier stored layer region is defined by
ND 1 <5E16cm −3 , ND 2 <1E17cm −3 and ND 2 /ND 1 >5.
7. The insulated gate semiconductor device according to claim 3 , wherein a potential of the dummy second gate electrode is set to the same value as that of the emitter electrode, so that the second base region in the periphery of the dummy second gate electrode does not work as the channel region.
8. The insulated gate semiconductor device according to claim 1 , wherein the carrier stored layer is selectively formed in a unit cell to obtain the relational expression of ND 1 <ND 2 .