Semiconductor device and method of manufacturing the same

Abstract

In a semiconductor device having an LDMOSFET, a source electrode is at the back surface thereof. Therefore, to reduce electric resistance between a source contact region in the top surface and the source electrode at the back surface, a poly-silicon buried plug is provided which extends from the upper surface into a P + -type substrate through a P-type epitaxial layer, and is heavily doped with boron. Dislocation occurs in a mono-crystalline silicon region around the poly-silicon buried plug to induce a leakage failure. The semiconductor device has a silicon-based plug extending through the boundary surface between first and second semiconductor layers having different impurity concentrations. At least the inside of the plug is a poly-crystalline region. Of the surface of the poly-crystalline region, the portions located on both sides of the foregoing boundary surface in adjacent relation thereto are each covered with a solid-phase epitaxial region.

1 . A method of manufacturing a semiconductor device, comprising the steps of:
 (a) preparing a semiconductor wafer, comprised of a silicon-based single crystal of a first conductivity type, having a first semiconductor layer with a first impurity concentration and a second semiconductor layer with a second impurity concentration, the second semiconductor layer abutting the first semiconductor layer;   (b) forming a hole for a buried plug extending from a first main surface of the wafer which is closer to the second semiconductor layer through the second semiconductor layer toward a second main surface of the wafer which is closer to the first semiconductor layer to reach an inside of the first semiconductor layer;   (c) removing a silicon-based oxide film from an inner surface of the hole;   (d) after the step (c), burying a poly-silicon member in the hole in a state where there is substantially no silicon-based oxide film over the inner surface of the hole; and   (e) after the step (d), performing a thermal process at a temperature of 800° C. or more with respect to the wafer.   
     
     
         2 . A method of manufacturing the semiconductor device according to  claim 1 ,
 wherein the first conductivity type is a P-type.   
     
     
         3 . A method of manufacturing the semiconductor device according to  claim 1 ,
 wherein the poly-silicon member is doped with boron.   
     
     
         4 . A method of manufacturing the semiconductor device according to  claim 1 ,
 wherein the second semiconductor layer is an epitaxial layer.   
     
     
         5 . A method of manufacturing the semiconductor device according to  claim 1 ,
 wherein the first impurity concentration is higher than the second impurity concentration.   
     
     
         6 . A method of manufacturing the semiconductor device according to  claim 1 ,
 wherein a boron concentration of the poly-silicon member is higher than the first impurity concentration.   
     
     
         7 . A method of manufacturing the semiconductor device according to  claim 1 ,
 wherein the first impurity concentration is at least 1000 times higher than the second impurity concentration.   
     
     
         8 . A method of manufacturing the semiconductor device according to  claim 1 ,
 wherein an upper end of the poly-silicon member is coupled to a P + -type contact region of an LDMOSFET.   
     
     
         9 . A method of manufacturing the semiconductor device according to  claim 1 ,
 wherein the step (c) includes the sub-step of:   (c1) cleaning the inner surface of the hole using a diluted hydrofluoric acid at a temperature of 70° C. or more and less than 90° C.   
     
     
         10 . A method of manufacturing the semiconductor device according to  claim 1 ,
 wherein the step (c) includes the sub-step of:   (c2) performing a plasma process with respect to the inner surface of the hole using a reductive gas atmosphere containing hydrogen as a main component thereof.   
     
     
         11 . A method of manufacturing the semiconductor device according to  claim 1 ,
 wherein, after the step (e), the poly-silicon member in the hole is crystal-grown into a solid-phase epitaxial state.