Resurf semiconductor device charge balancing
Breakdown voltage BVdss is enhanced and ON-resistance reduced in RESURF devices ( 40, 60, 80, 80′, 80″ ), e.g., LDMOS transistors, by careful charge balancing, even when body ( 44, 44′, 84, 84′ ) and drift ( 50, 50′, 90, 90′ ) region charge balance is not ideal, by: (i) providing a plug or sinker ( 57 ) near the drain ( 52, 92 ) and of the same conductivity type extending through the drift region ( 50, 50′, 90, 90′ ) at least into the underlying body region ( 44, 44′ 84, 84′ ), and/or (ii) applying bias Viso to a surrounding lateral doped isolation wall ( 102 ) coupled to the device buried layer ( 42, 82 ), and/or (iii) providing a variable resistance bridge ( 104 ) between the isolation wall ( 102 ) and the drift region ( 50, 50′, 90, 90′ ). The bridge ( 104 ) may be a FET ( 110 ) whose source-drain ( 113, 114 ) couple the isolation wall ( 102 ) and drift region ( 50, 50′, 90, 90′ ) and whose gate ( 116 ) receives control voltage Vc, or a resistor ( 120 ) whose cross-section (X, Y, Z) affects its resistance and pinch-off, to set the percentage of drain voltage coupled to the buried layer ( 42, 82 ) via the isolation wall ( 102 ).
1. A method for balancing charge in regions of a RESURF device, comprising: providing a body region of a first conductivity type, having a portion extending to a horizontal first surface and to a first depth from the first surface and having a buried layer of a second opposite conductivity type underlying the body region;
providing a source region of the second opposite conductivity type in the body region proximate the first surface;
providing a drift region of the second opposite conductivity type in the body region spaced apart from the source region and having a portion extending to the first surface and to a second depth less than the first depth;
providing a drain region of the second opposite conductivity type in the drift region, spaced apart from the body region and proximate the first surface, wherein a vertical side of the drain region facing the source region defines a lateral extent of the drain region; and
providing a plug region of the second, opposite conductivity type, wherein a bottom of the plug region is lower than a bottom of the drain region and above the buried layer, the plug region vertically extends to a depth exceeding the second depth, a first portion of the plug region laterally extends toward the drift region beyond the lateral extent of the drain region, and a second portion of the plug region that is distinct from the first portion also laterally extends toward the drift region beyond the lateral extent of the drain region, thus increasing an effective drain area in a direction perpendicular to Ids current flow, wherein the plug region further includes a third portion that extends toward the drift region to a lateral extent that is not beyond the lateral extent of the drain region, wherein the third portion connects the first portion and the second portion, giving the plug region a lateral outline that has a corrugated shape.
2. The method of claim 1 , wherein the step of providing the plug region, comprises providing the plug region extending into but not through the body region.
3. The method of claim 2 , wherein the step of providing the plug region extending into but not through the body region, comprises providing the plug region extending into the body region to within about 0.1 to 2 micrometers of the buried layer.
4. The method of claim 1 , wherein the step of providing the plug region comprises, providing a plug region having a doping level intermediate between a doping level of the drift region and the drain region.
5. The method of claim 1 , wherein the step of providing the plug region comprises, providing a plug region having a graded doping density that decreases with depth from the first surface.
6. The method of claim 1 , further comprising:
forming the buried layer underlying the body region.
7. The method of claim 1 , further comprising:
forming a dielectric region within the drift region and between the source region and the drain region, wherein the plug region extends partially underneath the dielectric region.
8. The method of claim 1 , wherein the depth of the plug region is less than a depth of the buried layer, so that a portion of the body region is located between the plug region and the buried layer.
9. The method of claim 1 , wherein the first portion and the second portion define the plug region to have a lateral shape of isolated rectangles.
10. A method for balancing charge in regions of a RESURF device, comprising:
providing a body region of a first conductivity type, having a portion extending to a horizontal first surface and to a first depth from the first surface;
providing a source region of the second opposite conductivity type in the body region proximate the first surface;
providing a drift region of the second opposite conductivity type in the body region spaced apart from the source region and having a portion extending to the first surface and to a second depth less than the first depth;
providing a drain region of the second opposite conductivity type in the drift region, spaced apart from the body region and proximate the first surface, wherein a vertical side of the drain region facing the source region defines a lateral extent of the drain region; and
providing a plug region of the second, opposite conductivity type, wherein a bottom of the plug region is lower than a bottom of the drift region, the plug region vertically extends to a third depth between the first depth and the second depth, and the plug region includes a first portion that extends toward the drift region to a first lateral extent that is beyond the lateral extent of the drain region, and a second portion connected to the first portion that extends toward the drift region to a second lateral extent that is not beyond the lateral extent of the drain region, thus increasing an effective drain area in a direction perpendicular to Ids current flow, wherein the plug region further includes a third portion that extends toward the drift region to a lateral extent that is not beyond the lateral extent of the drain region, wherein the third portion connects the first portion and the second portion, giving the plug region a lateral outline that has a corrugated shape.
11. The method of claim 10 , wherein the plug region further includes a third portion that extends into the drift region to a third lateral extent that is beyond the lateral extent of the drain region, wherein the second portion connects the first portion and the third portion, giving the plug region a lateral outline that has a corrugated shape.
12. The method of claim 10 , wherein the second lateral extent is before the lateral extent of the drain region.
13. The method of claim 10 , wherein the plug region has a lateral outline with a corrugated shape.
14. The method of claim 10 , wherein the plug region has a lateral outline with a globular shape.