Power junction field effect power transistor with highly vertical channel and uniform channel opening

Abstract

A semiconductor vertical junction field effect power transistor formed by a semiconductor structure having top and bottom surfaces and including a plurality of semiconductor layers with predetermined doping concentrations and thicknesses and comprising at least a bottom layer as drain layer, a middle layer as blocking and channel layer, a top layer as source layer. A plurality of laterally spaced U-shaped trenches with highly vertical side walls defines a plurality of laterally spaced mesas. The mesas are surrounded on the four sides by U-shaped semiconductor regions having conductivity type opposite to that of the mesas forming U-shaped pn junctions and defining a plurality of laterally spaced long and vertical channels with a highly uniform channel opening dimension. A source contact is formed on the top source layer and a drain contact is formed on the bottom drain layer. A gate contact is formed on the bottom of the U-shaped trenches for the purpose of creating and interrupting the vertical channels so as to turn on and turn off the transistor.

1 . A vertical junction field-effect transistor (VJFET) having a plurality of semiconductor layers, comprising:
 a drain layer of heavily doped semiconductor of a first conductivity type and operable as a drain for said transistor;   a blocking layer of lightly doped semiconductor of the first conductivity type formed on top of said drain layer;   a channel layer formed on top of said blocking layer; the channel layer having a plurality of vertical channels of the first conductivity type spaced apart by U-shaped regions of heavily doped semiconductor of the second conductivity type; the second conductivity type having an opposite conductivity of the first conductivity type; wherein the sides of the U-shaped regions form vertical gate junctions with said vertical channels; and   a source layer of very heavily doped semiconductor of the first conductivity type on top of said vertical gate junctions and operable as a source for said transistor;   wherein said vertical gate junctions produce a vertical channel opening of a uniform width for operation of the VJFET.   
   
   
       2 . The vertical junction field-effect transistor according to  claim 1 , wherein the U-shaped regions are doped by angled ion implantation. 
   
   
       3 . The vertical junction field-effect transistor according to  claim 1 , further comprising gate ohmic contacts to very heavily doped semiconductor of the second conductivity type formed on the inside bottom of the U-shaped regions. 
   
   
       4 . The vertical junction field-effect transistor according to  claim 3 , further comprising passivation regions covering the sides of the U-shaped regions, at least part of the gate ohmic contacts, and the sides of the source layer on top of said vertical gate junctions. 
   
   
       5 . The vertical junction field-effect transistor according to  claim 4 , further comprising a dielectric fill layer filling an area between the sides of the passivation regions. 
   
   
       6 . The vertical junction field-effect transistor according to  claim 1 , further comprising a metal ohmic contact layer on top of the source layer. 
   
   
       7 . The vertical junction field-effect transistor according to  claim 1 , wherein the VJFET is a normally-off transistor. 
   
   
       8 . The vertical junction field-effect transistor according to  claim 1 , wherein the vertical gate junctions are perpendicular to said source layer to within twenty degrees) (20°). 
   
   
       9 . The vertical junction field-effect transistor according to  claim 1 , wherein an opening dimension of the vertical channel opening is uniform to within 0.3 um. 
   
   
       10 . The vertical junction field-effect transistor according to  claim 1 , wherein the vertical channel opening has a channel length (L vc ) between 0.5 um and 3.5 um. 
   
   
       11 . A vertical junction field-effect transistor (VJFET) having a plurality of semiconductor layers, comprising:
 an n + -type drain layer operable as a drain for said transistor;   an n − -type blocking layer formed on top of said drain layer;   a channel layer formed on top of said n − -type blocking layer; the channel layer having a plurality of vertical n-type channels spaced apart by U-shaped p + -type regions; wherein the sides of the U-shaped p + -type regions form vertical p + n gate junctions with said vertical n-type channels; and   an n ++ -type source layer on top of said vertical p + n gate junctions and operable as a source for said transistor;   wherein said vertical p + n gate junctions are operable as a gate for said transistor and produce a vertical channel opening of a uniform width for operation of the VJFET.   
   
   
       12 . The vertical junction field-effect transistor according to  claim 11 , wherein the U-shaped p + -type regions are doped by angled ion implantation. 
   
   
       13 . The vertical junction field-effect transistor according to  claim 11 , further comprising p ++ -type gate ohmic contacts to the inside bottom of the U-shaped p + -type regions. 
   
   
       14 . The vertical junction field-effect transistor according to  claim 13 , further comprising passivation regions covering the sides of the U-shaped p + -type regions, at least part of the p ++ -type gate ohmic contacts, and the sides of the n ++ -type source layer on top of said vertical p + n gate junctions. 
   
   
       15 . The vertical junction field-effect transistor according to  claim 14 , further comprising a dielectric fill layer filling an area between the sides of the passivation regions. 
   
   
       16 . The vertical junction field-effect transistor according to  claim 11 , further comprising a metal ohmic contact layer on top of the n ++ -type source layer. 
   
   
       17 . The vertical junction field-effect transistor according to  claim 11 , wherein the VJFET is a normally-off transistor. 
   
   
       18 . The vertical junction field-effect transistor according to  claim 11 , wherein the vertical p + n gate junctions are perpendicular to said source layer to within twenty degrees (20°). 
   
   
       19 . The vertical junction field-effect transistor according to  claim 11 , wherein an opening dimension of the vertical channel opening is uniform to within 0.3 um. 
   
   
       20 . The vertical junction field-effect transistor according to  claim 11 , wherein the vertical channel opening has a channel length (L vc ) between 0.5 um and 3.5 um.