Process of forming high electron mobility transistor (hemt) and hemt formed by the same

Abstract

A process of forming a field effect transistor (FET) of a type of high electron mobility transistor (HEMT) reducing damages caused in a semiconductor layer is disclosed. The process carries out steps of: (a) depositing an insulating film on a semiconductor stack; (b) depositing a conductive film on the insulating film; (c) forming an opening in the conductive film and the insulating film by a dry-etching using ions of reactive gas to expose a surface of the semiconductor stack; and (d) forming a gate electrode to be in contact with the surface of the semiconductor stack through the opening, the gate electrode filling the opening in the conductive film and the insulating film.

1 - 19 . (canceled) 
     
     
         20 . A semiconductor device being a type of high electron mobility transistor (HEMT), comprising:
 a semiconductor layer on a substrate;   an insulating film on the semiconductor layer, the insulating film having an opening;   a gate electrode in contact with a surface of the semiconductor layer through the opening, the gate electrode filling the opening and extending in peripheries of the opening of the insulating film; and   a conductive film provided between the insulating film and a portion of the gate electrode in the peripheries of the opening,   wherein the gate electrode includes a Schottky metal in contact with the semiconductor layer and a cover metal provided on the Schottky metal, the Schottky metal having a portion around the opening that covers the conductive film thereunder, and   wherein the conductive film is made of pure tantalum (Ta) or pure tungsten (W).   
     
     
         21 . The semiconductor device according to  claim 20 ,
 wherein the conductive film has a thickness smaller than or equal to a thickness of the Schottky metal.   
     
     
         22 . The semiconductor device according to  claim 20 ,
 wherein the Schottky metal and the conductive film are made of tungsten silicide (WSi).   
     
     
         23 . The semiconductor device according to  claim 20 ,
 wherein the insulating film includes a first film made of silicon nitride (SiN) in contact with the semiconductor layer, and a second film made of silicon oxide (Si02) provided on the first film.   
     
     
         24 . The semiconductor device according to  claim 23 ,
 wherein the SiN film has a thickness of 30±5 nm, and the Si02 film has a thickness of 300±30 nm.   
     
     
         25 . A semiconductor device type of high electron mobility transistor (HEMT), comprising:
 a semiconductor layer on a substrate;   an insulating film on the semiconductor layer, the insulating film having an opening;   a gate electrode in contact with a surface of the semiconductor layer through the opening, the gate electrode filling the opening and extending in peripheries of the opening of the insulating film; and   a conductive film provided between the insulating film and a portion of the gate electrode in the peripheries of the opening,   wherein the conductive film is made of pure tantalum (Ta) or pure tungsten (W).