Patent ID: 9685335
Date: 2017-06-20
CPC Classifications: H01L

Claim:
1. A power device comprising: a first field stop layer of a first conductive type; a second field stop layer formed on the first field stop layer and of the first conductive type, the second field stop layer having a region with an impurity concentration higher than the first field stop layer; a drift region formed on the second field stop layer and of the first conductive type, the drift region having an impurity concentration lower than the first field stop layer; a plurality of power device cells formed on the drift region; and a collector region formed below the first field stop layer, the second field stop layer including a first region having a first impurity concentration and a second region having a second impurity concentration higher than the first impurity concentration, the first region being laterally oriented with respect to and in contact with the second region, the first region having an impurity concentration gradient that increases along a vertical direction of the second field stop layer from an interface of the first region with the drift region to a first maximum impurity concentration and that decreases along the vertical direction from the first maximum impurity concentration to an interface of the first region with the first field stop layer, and the second region having an impurity concentration gradient that increases along the vertical direction of the second field stop layer from an interface of the second region with the drift region to a second maximum impurity concentration and that decreases along the vertical direction from the second maximum impurity concentration to an interface of the second region with the first field stop layer, wherein the first maximum impurity concentration is different than the second maximum impurity concentration.