Field electrode termination structure for trench-based transistor devices

Abstract

A semiconductor device includes: a trench formed in a surface of a semiconductor substrate and extending lengthwise in a direction parallel to the surface; a body region adjoining the trench; a source region adjoining the trench above the body region; a drift region adjoining the trench below the body region; a field electrode in a lower part of the trench and separated from the substrate; and a gate electrode in an upper part of the trench and separated from the substrate and the field electrode. A first section of the field electrode is buried below the gate electrode in the trench. A second section of the field electrode transitions upward from the first section in a direction toward the surface. The separation between the second section and the gate electrode is greater than or equal to the separation between the first section and the gate electrode.

What is claimed is: 
     
         1 . A semiconductor device, comprising:
 a trench formed in a first main surface of a semiconductor substrate and extending lengthwise in a direction parallel to the first main surface;   a body region of a second conductivity type adjoining the trench;   a source region of a first conductivity type adjoining the trench above the body region;   a drift region of the first conductivity type adjoining the trench below the body region;   a field electrode disposed in a lower part of the trench and separated from the semiconductor substrate; and   a gate electrode disposed in an upper part of the trench and separated from the semiconductor substrate and the field electrode,   wherein a first section of the field electrode is buried below the gate electrode in the trench,   wherein a second section of the field electrode transitions upward from the first section in a direction toward the first main surface,   wherein the separation between the second section of the field electrode and the gate electrode is greater than the separation between the first section of the field electrode and the gate electrode,   wherein the second section of the field electrode transitions upward from the first section in a termination region of the semiconductor device which is outside an active area of the semiconductor device that includes the body region and the source region,   wherein the gate electrode is contacted in a different region of the semiconductor device than the second section of the field electrode.   
     
     
         2 . The semiconductor device of  claim 1 , wherein the gate electrode is contacted in the active area of the semiconductor device. 
     
     
         3 . The semiconductor device of  claim 1 , wherein a same type of dielectric material separates the first and the second sections of the field electrode from the gate electrode. 
     
     
         4 . The semiconductor device of  claim 1 , further comprising an electrically conductive layer formed above the trench and which is electrically connected to the field electrode at the second section has a lengthwise extension which is transverse to the lengthwise extension of the trench. 
     
     
         5 . A method of producing a semiconductor device, the method comprising:
 forming a trench in a first main surface of a semiconductor substrate, the trench extending lengthwise in a direction parallel to the first main surface;   forming a field electrode in a lower part of the trench and separated from the semiconductor substrate;   forming a gate electrode in an upper part of the trench and separated from the semiconductor substrate and the field electrode so that a first section of the field electrode is buried below the gate electrode in the trench, a second section of the field electrode transitions upward from the first section in a direction toward the first main surface in a termination region of the semiconductor device which is outside an active area of the semiconductor device, and the separation between the second section of the field electrode and the gate electrode is greater than or equal to the separation between the first section of the field electrode and the gate electrode;   forming a body region of a second conductivity type adjoining the trench in the active area;   forming a source region of a first conductivity type adjoining the trench above the body region in the active area;   forming a drift region of the first conductivity type adjoining the trench below the body region; and   contacting the gate electrode in a different region of the semiconductor device than the second section of the field electrode.   
     
     
         6 . The method of  claim 5 , wherein forming the field electrode comprises:
 lining a bottom and sidewalls of the trench with a first dielectric;   after lining the bottom and the sidewalls of the trench with the first dielectric, filling the trench with an electrically conductive material;   thinning part of the electrically conductive material to form the first and the second sections of the field electrode, such that the second section of the field electrode transitions upward from the first section in the termination region;   filling a space in the trench formed by thinning the electrically conductive material with a second dielectric;   thinning the second dielectric over the first section of the field electrode so that a lateral thickness of the second dielectric measured in a horizontal direction toward the second section of the field electrode is greater than or equal to a vertical thickness of the second dielectric measured in a vertical direction toward the first section of the field electrode; and   forming the gate electrode in a space formed in the trench after the second dielectric is thinned over the first section of the field electrode.   
     
     
         7 . The method of  claim 6 , wherein thinning part of the electrically conductive material to form the first and the second sections of the field electrode comprises:
 forming a first mask which protects a portion of the electrically conductive material; and   thinning the part of the electrically conductive material unprotected by the first mask.   
     
     
         8 . The method of  claim 7 , wherein etching the second dielectric comprises:
 forming a second mask which protects a part of the second dielectric adjoining the portion of the electrically conductive material which was protected by the first mask during the thinning of the electrically conductive material; and   etching a part of the second dielectric unprotected by the second mask down to the first section of the field electrode to expose the first section,   wherein an overhang between the second mask and the first mask defines the amount of separation between the second section of the field electrode and the gate electrode.   
     
     
         9 . The method of  claim 8 , further comprising:
 after exposing the first section of the field electrode and after depositing the third dielectric but before forming the gate electrode, forming a gate dielectric along an upper part of the sidewalls of the trench.   
     
     
         10 . The method of  claim 6 , wherein the third dielectric is formed by high density plasma chemical vapor deposition. 
     
     
         11 . The method of  claim 6 , wherein the third dielectric is formed as part of a gate oxidation process during which an accelerated oxidation rate of heavily phosphorus-doped polysilicon forms the third dielectric. 
     
     
         12 . The method of  claim 5 , wherein thinning part of the electrically conductive material to form the first and the second sections of the field electrode comprises:
 forming a first mask which protects a portion of the electrically conductive material; and   thinning the part of the electrically conductive material unprotected by the first mask.   
     
     
         13 . The method of  claim 12 , wherein thinning the second dielectric over the first section of the field electrode comprises:
 forming a second mask which protects a part of the second dielectric adjoining the portion of the electrically conductive material which was protected by the first mask during the thinning of the electrically conductive material; and   thinning the part of the second dielectric unprotected by the second mask,   wherein an overhang between the second mask and the first mask defines the amount of separation between the second section of the field electrode and the gate electrode.   
     
     
         14 . The method of  claim 13 , further comprising:
 after thinning the part of the second dielectric unprotected by the second mask but before forming the gate electrode, forming a gate dielectric along an upper part of the sidewalls of the trench.   
     
     
         15 . The method of  claim 5 , further comprising:
 implementing contacts for the gate electrode and contacts for the second section of the field electrode using a single lithography step.   
     
     
         16 . A method of producing a semiconductor device, the method comprising:
 forming trenches in a first main surface of a semiconductor substrate, the trenches extending lengthwise in a direction parallel to the first main surface;   forming a field electrode in a lower part of the trenches and separated from the semiconductor substrate;   forming a gate electrode in an upper part of the trenches and separated from the semiconductor substrate and the field electrode so that a first section of the field electrode is buried below the gate electrode in the trenches, a second section of the field electrode transitions upward from the first section in a direction toward the first main surface in a termination region of the semiconductor device which is outside an active area of the semiconductor device, and the separation between the second section of the field electrode and the gate electrode is greater than or equal to the separation between the first section of the field electrode and the gate electrode;   forming body regions of a second conductivity type adjoining the trenches in the active area;   forming source regions of a first conductivity type adjoining the trenches above the body regions in the active area;   forming a drift region of the first conductivity type adjoining the trenches below the body regions;   forming an electrically conductive layer above the trenches and which is electrically connected to the field electrode in the trenches at the second section and has a lengthwise extension which is transverse to the lengthwise extension of the trenches; and   contacting the gate electrodes in a different region of the semiconductor device than the second section of the field electrodes.   
     
     
         17 . The method of  claim 16 , further comprising:
 after forming the gate electrode in the upper part of the trenches but before forming the electrically conductive layer above the trenches, forming an interlayer dielectric over the semiconductor substrate; and   forming, using a common lithography process, contact openings which extend through the interlayer dielectric to the source regions, the body regions, the gate electrodes, the second section of the field electrodes and to field termination structures formed in an edge termination region of the semiconductor substrate.   
     
     
         18 . The method of  claim 16 , further comprising:
 implementing contacts for the gate electrode and contacts for the second section of the field electrode using a single lithography step.   
     
     
         19 . A semiconductor device, comprising:
 a trench formed in a first main surface of a semiconductor substrate and extending lengthwise in a direction parallel to the first main surface;   a body region of a second conductivity type adjoining the trench;   a source region of a first conductivity type adjoining the trench above the body region;   a drift region of the first conductivity type adjoining the trench below the body region;   a field electrode disposed in a lower part of the trench and separated from the semiconductor substrate; and   a gate electrode disposed in an upper part of the trench and separated from the semiconductor substrate and the field electrode,   wherein a first section of the field electrode is buried below the gate electrode in the trench,   wherein a second section of the field electrode transitions upward from the first section in a direction toward the first main surface,   wherein the separation between the second section of the field electrode and the gate electrode is greater than or equal to the separation between the first section of the field electrode and the gate electrode,   wherein the second section of the field electrode transitions upward from the first section in a termination region of the semiconductor device which is outside an active area of the semiconductor device that includes the body region and the source region,   wherein an electrically conductive layer formed above the trench and which is electrically connected to the field electrode at the second section has a lengthwise extension which is transverse to the lengthwise extension of the trench,   wherein the gate electrode is contacted in a different region of the semiconductor device than the second section of the field electrode.