Bondable top metal contacts for gallium nitride power devices

Abstract

An embodiment of a semiconductor device includes a gallium nitride (GaN) substrate having a first surface and a second surface. The second surface is substantially opposite the first surface, at least one device layer is coupled to the first surface, and a backside metal is coupled to the second surface. A top metal stack is coupled to the at least one device layer. The top metal stack includes a contact metal coupled to a surface of the at least one device layer, a protection layer coupled to the contact metal, a diffusion barrier coupled to the protection layer, and a pad metal coupled to the diffusion barrier. The semiconductor device is configured to conduct electricity between the top metal stack and the backside metal.

What is claimed is: 
     
         1 . A semiconductor device, comprising:
 a gallium nitride (GaN) substrate having a first surface and a second surface, the second surface being substantially opposite the first surface;   at least one device layer coupled to the first surface;   a backside metal coupled to the second surface; and   a top metal stack coupled to the at least one device layer and comprising:
 a contact metal coupled to a surface of the at least one device layer; 
 a protection layer coupled to the contact metal; 
 a dielectric layer comprising a gap; 
 a diffusion barrier over the dielectric layer and contacting the protection layer in the gap of the dielectric layer; and 
 a pad metal coupled to the diffusion barrier; 
   wherein the semiconductor device is configured to conduct electricity between the top metal stack and the backside metal.   
     
     
         2 . The semiconductor device of  claim 1  wherein the contact metal forms an Ohmic contact with at least a portion of the at least one device layer. 
     
     
         3 . The semiconductor device of  claim 1  wherein the contact metal forms a Schottky contact with at least a portion of the at least one device layer. 
     
     
         4 . The semiconductor device of  claim 1  wherein the contact metal comprises at least one of:
 platinum, 
 palladium, 
 titanium, 
 titanium nitride, 
 aluminum, 
 silver, or 
 nickel. 
 
     
     
         5 . The semiconductor device of  claim 1  wherein the protection layer comprises gold. 
     
     
         6 . The semiconductor device of  claim 1  wherein the pad metal has a thickness of at least 2 microns and comprises at least one of:
 aluminum, or 
 copper. 
 
     
     
         7 . The semiconductor device of  claim 1  wherein the diffusion barrier comprises at least one of:
 nickel, 
 chromium, 
 molybdenum, 
 tungsten, or 
 titanium. 
 
     
     
         8 . The semiconductor device of  claim 1  further comprising an aluminum bond wire configured to electrically connect the pad metal to a package. 
     
     
         9 . The semiconductor device of  claim 1  wherein the backside metal comprises a solderable material. 
     
     
         10 . The semiconductor device of  claim 9  further comprising a solder mechanically and electrically connecting the backside metal to a package.