Semiconductor device incorporating epitaxial layer field stop zone

Abstract

A semiconductor device includes a semiconductor body having a base region incorporating a field stop zone where the base region and the field stop zone are both formed using an epitaxial process. Furthermore, the epitaxial layer field stop zone is formed with an enhanced doping profile to realize improved soft-switching performance for the semiconductor device. In some embodiments, the enhanced doping profile formed in the field stop zone includes varying, non-constant doping levels. In some embodiments, the enhanced doping profile includes one of an extended graded doping profile, a multiple stepped flat doping profile, or a multiple spike doping profile. The epitaxial layer field stop zone of the present invention enables complex field stop zone doping profiles to be used to obtain the desired soft-switching characteristics in the semiconductor device.

What is claimed is: 
     
         1 . A semiconductor device, comprising:
 a heavily doped semiconductor layer;   an epitaxial layer of a first conductivity type formed on the semiconductor layer, the epitaxial layer including a first portion of the first conductivity type adjacent the semiconductor layer forming a field stop zone, and the epitaxial layer further including a second portion of the first conductivity type forming a base region, the field stop zone having a first side adjacent the semiconductor layer and a second side adjacent the base region, the base region having a first side adjacent the field stop zone and a second side opposite the first side; and   a device region formed in the second side of the base region, the device region comprising at least one PN junction,   wherein the first portion of the epitaxial layer forming the field stop zone has a doping profile of the first conductivity type including non-constant and varying doping levels within the first portion and the second portion of the epitaxial layer forming the base region has a constant doping level of the first conductivity type.   
     
     
         2 . The semiconductor device of  claim 1 , wherein the field stop zone comprises a graded doping profile of the first conductivity type having a first doping level at the first side of the field stop zone and a second doping level at the second side of the field stop zone, the doping level varying linearly between the first side and the second side of the field stop zone from the first doping level to the second doping level. 
     
     
         3 . The semiconductor device of  claim 2 , wherein the first doping level is higher than the second doping level. 
     
     
         4 . The semiconductor device of  claim 3 , wherein the second doping level is higher than or the same as the constant doping level of the base region. 
     
     
         5 . The semiconductor device of  claim 1 , wherein the field stop zone comprises a multiple stepped flat doping profile of the first conductivity type having a first doping level as a background doping level and having multiple flat top regions with step increase in doping levels from the first doping level, the multiple flat top regions being spaced apart within the field stop zone. 
     
     
         6 . The semiconductor device of  claim 5 , wherein the multiple flat top regions have the same or different doping levels. 
     
     
         7 . The semiconductor device of  claim 6 , wherein the multiple flat top regions have increasing doping levels from the first flat top region near the first side of the field stop zone to the last flat top region near the base region. 
     
     
         8 . The semiconductor device of  claim 5 , wherein each of the flat top regions has a thickness, the thickness of the multiple flat top regions being the same or different. 
     
     
         9 . The semiconductor device of  claim 8 , wherein the multiple flat top regions have increasing thicknesses from the first flat top region near the first side of the field stop zone to the last flat top region near the base region. 
     
     
         10 . The semiconductor device of  claim 5 , wherein the background doping level is higher than or the same as the constant doping level of the base region. 
     
     
         11 . The semiconductor device of  claim 1 , wherein the field stop zone comprises a multiple spike doping profile of the first conductivity type having a first doping level as a background doping level and having multiple spike doping regions with spike increase in doping levels from the first doping level, the multiple spike doping regions being spaced apart within the field stop zone. 
     
     
         12 . The semiconductor device of  claim 11 , wherein the multiple spike doping regions have the same or different doping levels. 
     
     
         13 . The semiconductor device of  claim 12 , wherein the multiple spike doping regions have increasing doping levels from the first spike doping region near the first side of the field stop zone to the last spike doping region near the base region. 
     
     
         14 . The semiconductor device of  claim 11 , wherein each of the spike doping regions has a thickness, the thickness of the multiple spike doping regions being the same or different. 
     
     
         15 . The semiconductor device of  claim 14 , wherein the multiple spike doping regions have increasing thicknesses from the first spike doping region near the first side of the field stop zone to the last spike doping region near the base region. 
     
     
         16 . The semiconductor device of  claim 11 , wherein the background doping level is higher than or the same as the constant doping level of the base region. 
     
     
         17 . The semiconductor device of  claim 1 , wherein the semiconductor device comprises a PN junction diode and the semiconductor layer comprises a semiconductor substrate of the first conductivity type, the semiconductor device further comprising a body region of a second conductivity type, opposite the first conductivity type, being formed in the second side of the base region. 
     
     
         18 . The semiconductor device of  claim 1 , wherein the semiconductor device comprises an insulated gate bipolar transistor (IGBT) and the semiconductor layer comprises a semiconductor substrate of a second conductivity type, opposite the first conductivity type, the semiconductor device further comprising a body region of the second conductivity type being formed in the second side of the base region, a source region of the first conductivity type being formed in the body region, a gate dielectric layer and a conductive gate being formed on the epitaxial layer at the second side of the base region. 
     
     
         19 . The semiconductor device of  claim 1 , wherein the semiconductor device comprises a trench gate insulated gate bipolar transistor (IGBT) and the semiconductor layer comprises a semiconductor substrate of a second conductivity type, opposite the first conductivity type, the semiconductor device further comprising a body region of the second conductivity type being formed in the second side of the base region, a source region of the first conductivity type being formed in the body region, a gate dielectric layer and a conductive gate being formed in a trench formed in the epitaxial layer at the second side of the base region. 
     
     
         20 . The semiconductor device of  claim 1 , wherein the semiconductor device comprises a reverse conducting insulated gate bipolar transistor (RC-IGBT) and the semiconductor layer comprises one or more doped regions of the first conductivity type and being heavily doped, and one or more doped regions of a second conductivity type, opposite the first conductivity type, the semiconductor device further comprising a body region of the second conductivity type being formed in the second side of the base region, a source region of the first conductivity type being formed in the body region, a gate dielectric layer and a conductive gate being formed on the epitaxial layer at the second side of the base region. 
     
     
         21 . The semiconductor device of  claim 1 , wherein the semiconductor device comprises a trench gate reverse conducting insulated gate bipolar transistor (RC-IGBT) and the semiconductor layer comprises one or more doped regions of the first conductivity type and being heavily doped, and one or more doped regions of a second conductivity type, opposite the first conductivity type, the semiconductor device further comprising a body region of the second conductivity type being formed in the second side of the base region, a source region of the first conductivity type being formed in the body region, a gate dielectric layer and a conductive gate being formed in a trench formed in the epitaxial layer at the second side of the base region. 
     
     
         22 . The semiconductor device of  claim 17 , wherein the first conductivity type comprises N-type conductivity and the second conductivity type comprises P-type conductivity.