Transverse junction field effect transistor

Abstract

A transverse JFET of SiC, employing an n + -type SiC substrate and comprising a channel region having carriers of high mobility, bringing a high yield is obtained. This transverse JFET has an n + -type SiC substrate, a p-type SiC film formed on a front face of the n + -type SiC substrate, an n-type SiC film, including a channel region, formed on the p-type SiC film, source and drain regions formed on the n-type SiC film separately on both sides of the channel region respectively, and a gate electrode provided on the SiC substrate or on the p-type SiC film.

1 . A transverse junction field effect transistor comprising: 
 an n + -type SiC substrate;    a p-type SiC film formed on a front face of said SiC substrate;    an n-type SiC film formed on said p-type SiC film;    a channel region formed in said n-type SiC film;    a source region and a drain region, respectively comprising films consisting of n-type SiC formed on said n-type SiC film respectively separately on opposite sides of said channel region; and    a gate electrode arranged in one of the following arrangements: on a back side of said SiC substrate, or on and surrounded by a flat region of said front face of said SiC substrate with said flat region extending laterally beyond said gate electrode, or on and surrounded by a flat region of said p-type SiC film with said flat region extending laterally beyond said gate electrode.    
   
   
       2 . The transverse junction field effect transistor according to  claim 1 , wherein: 
 said p-type SiC film ( 2 ) is formed on said front face of said SiC substrate;    said n-type SiC film ( 3 ), including said channel region ( 11 ), is formed on said p-type SiC film; and    said gate electrode ( 14 ) is provided in contact with said SiC substrate.    
   
   
       3 . The transverse junction field effect transistor according to  claim 2 , wherein a region of said p-type SiC film ( 2 ) corresponds to a region of said n-type SiC film ( 3 ) as viewed in plan.  
   
   
       4 . The transverse junction field effect transistor according to  claim 2 , wherein said gate electrode ( 14 ) is arranged on said front face of said SiC substrate ( 1   n ) in a vicinity of an end of said p-type SiC film ( 2 ).  
   
   
       5 . The transverse junction field effect transistor according to  claim 2 , wherein said gate electrode ( 14 ) is arranged in a back gate structure on said back side of said SiC substrate ( 1   n ) opposite said front face.  
   
   
       6 . The transverse junction field effect transistor according to  claim 2 , wherein a thickness (a) of said channel region ( 11 ) is smaller than a width of a depletion layer in said n-type SiC film resulting from a: built-in potential on a junction between said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) formed on said p-type SiC film.  
   
   
       7 . The transverse junction field effect transistor according to  claim 2 , further comprising a low-concentration n-type SiC film ( 7 ), arranged in contact between said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ), containing an n-type impurity of a lower concentration than an n-type impurity concentration of said channel region ( 11 ).  
   
   
       8 . The transverse junction field effect transistor according to  claim 2 , wherein said channel region ( 11 ) contains an n-type impurity of a higher concentration than an impurity concentration of portions of said n-type SiC film located on both sides thereof.  
   
   
       9 . The transverse junction field effect transistor according to  claim 2 , further comprising a conductor film ( 17 ) arranged in contact with a surface of said channel region ( 11 ).  
   
   
       10 . The transverse junction field effect transistor according to  claim 9 , wherein a length of said conductor film ( 17 ) along a channel length direction is smaller than a channel length (L) of said channel region in said channel length direction.  
   
   
       11 . The transverse junction field effect transistor according to  claim 9 , wherein a thickness (a) of said channel region ( 11 ) is smaller than a width of a depletion layer in said n-type SiC film resulting from a built-in potential on a junction between said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) formed on said p-type SiC film.  
   
   
       12 . The transverse junction field effect transistor according to  claim 9 , wherein said conductor film ( 17 ) is either a metal film or a semiconductor film containing a high-concentration impurity.  
   
   
       13 . The transverse junction field effect transistor according to  claim 2 , wherein said SiC substrate ( 1 ) is a 6H—SiC substrate, and both of said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) are made of 6H—SiC.  
   
   
       14 . The transverse junction field effect transistor according to  claim 2 , further comprising a buffer layer of 4H—SiC, wherein said SiC substrate is a 6H—SiC substrate, both of said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) are made of 4H—SiC, and said p-type SiC film ( 2 ) consisting of 4H—SiC is formed on said 6H—SiC substrate with said buffer layer of 4H—SiC therebetween.  
   
   
       15 . The transverse junction field effect transistor according to  claim 2 , wherein said SiC substrate ( 1 ) is a 4H—SiC substrate, and both of said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) are made of 4H—SiC.  
   
   
       16 . The transverse junction field effect transistor according to  claim 2 , further comprising a buffer layer of 6H—SiC, wherein said SiC substrate is a 4H—SiC substrate, both of said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) are made of 6H—SiC, and said p-type SiC film consisting of 6H—SiC is formed on said 4H—SiC substrate with said buffer layer of 6H—SiC therebetween.  
   
   
       17 . The transverse junction field effect transistor according to  claim 1 , wherein said channel region ( 11 ) is formed by reducing a thickness of said n-type SiC film.  
   
   
       18 . The transverse junction field effect transistor according to  claim 17 , wherein said p-type SiC film ( 2 ) has an untrenched flat face, and said gate electrode ( 14 ) comprises two gate electrode elements formed on said flat face of said p-type SiC film ( 2 ) which forms said flat region of said p-type SiC film.  
   
   
       19 . The transverse junction field effect transistor according to  claim 17 , wherein said gate electrode ( 14 ) is formed in a back gate structure provided on a flat region of said back side of said SiC substrate.  
   
   
       20 . The transverse junction field effect transistor according to  claim 17 , further comprising a low-concentration n-type SiC film ( 7 ), arranged in contact between said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ), containing an n-type impurity of a lower concentration than an n-type impurity concentration of said channel region ( 11 ).  
   
   
       21 . The transverse junction field effect transistor according to  claim 17 , wherein said channel region ( 11 ) contains an n-type impurity of a higher concentration than an impurity concentration of portions of said n-type SiC film located on both sides thereof.  
   
   
       22 . The transverse junction field effect transistor according to  claim 20 , wherein said channel region ( 11 ) contains an n-type impurity of a higher concentration than an impurity concentration of portions of said n-type SiC film located on both sides thereof.  
   
   
       23 . The transverse junction field effect transistor according to  claim 17 , wherein a thickness (a) of said channel region ( 11 ) is smaller than a width of a depletion layer in said n-type SiC film resulting from a built-in potential on a junction between said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) formed on said p-type SiC film.  
   
   
       24 . The transverse junction field effect transistor according to  claim 21 , wherein a thickness (a) of said channel region ( 11 ) is smaller than a width of a depletion layer in said n-type SiC film resulting from a built-in potential on a junction between said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) formed on said p-type SiC film.  
   
   
       25 . The transverse junction field effect transistor according to  claim 17 , further comprising a conductor film ( 17 ) arranged in contact with a surface of said channel region ( 11 ).  
   
   
       26 . The transverse junction field effect transistor according to  claim 25 , wherein a length of said conductor film ( 17 ) along a channel length direction is smaller than a channel length (L) of said channel region in said channel length direction.  
   
   
       27 . The transverse junction field effect transistor according to  claim 25 , wherein a thickness (a) of said channel region ( 11 ) is smaller than a width of a depletion layer in said n-type SiC film resulting from a built-in potential on a junction between said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) formed on said p-type SiC film.  
   
   
       28 . The transverse junction field effect transistor according to  claim 25 , wherein said conductor film ( 17 ) is either a metal film or a semiconductor film containing a high-concentration impurity.  
   
   
       29 . The transverse junction field effect transistor according to  claim 17 , wherein said source region and said drain region ( 22 ,  23 ) contain an n-type impurity of a higher concentration than an impurity concentration of portions of said n-type SiC film ( 3 ) located on both sides of said channel region ( 11 ).  
   
   
       30 . The transverse junction field effect transistor according to  claim 17 , wherein an impurity concentration of said p-type SiC film ( 2 ) exceeds 10 19  cm −3 .  
   
   
       31 . The transverse junction field effect transistor according to  claim 17 , further comprising a source electrode ( 12 ) formed on said source region ( 22 ), and a drain electrode ( 13 ) formed on said drain region ( 23 ), wherein said source electrode, said drain electrode and said gate electrode are made of metals coming into ohmic contact with SiC, containing impurities, in contact with the respective electrodes.  
   
   
       32 . The transverse junction field effect transistor according to  claim 31 , further comprising an insulating film ( 5 ) covering a surface portion excluding said source electrode ( 12 ), said drain electrode ( 13 ) and said gate electrode ( 14 ).  
   
   
       33 . The transverse junction field effect transistor according to  claim 17 , wherein said SiC substrate ( 1 ) is a 6H—SiC substrate, and both of said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) are made of 6H—SiC.  
   
   
       34 . The transverse junction field effect transistor according to  claim 17 , further comprising a buffer layer of 4H—SiC, wherein said SiC substrate is a 6H—SiC substrate, both of said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) are made of 4H—SiC, and said p-type SiC film ( 2 ) consisting of 4H—SiC is formed on said 6H—SiC substrate with said buffer layer of 4H—SiC therebetween.  
   
   
       35 . The transverse junction field effect transistor according to  claim 17 , wherein said SiC substrate ( 1 ) is a 4H—SiC substrate, and both of said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) are made of 4H—SiC.  
   
   
       36 . The transverse junction field effect transistor according to  claim 17 , further comprising a buffer layer of 6H—SiC, wherein said SiC substrate is a 4H—SiC substrate, both of said p-type SiC film ( 2 ) and said n-type SiC film ( 3 ) are made of 6H—SiC, and said p-type SiC film ( 2 ) consisting of 6H—SiC is formed on said 4H—SiC substrate with said buffer layer of 6H—SiC therebetween.