Method for manufacturing a field-effect transistor

Abstract

A method for manufacturing a field-effect transistor includes forming an active layer of an oxide semiconductor, forming a conducting film to cover the active layer, patterning the conducting film through an etching process using an etchant to form a source electrode and a drain electrode, and performing, at least before the patterning the conducting film, a treatment on the active layer so that an etching rate of the active layer is less than an etching rate of the conducting film.

1 - 17 . (canceled) 
     
     
         18 . A method for manufacturing a field-effect transistor, comprising:
 forming an active layer of an oxide semiconductor;   forming a conducting film to cover the active layer;   patterning the conducting film through an etching process using an etchant to form a source electrode and a drain electrode; and   performing, at least before the patterning of the conducting film, a treatment on the active layer so that an etching rate of the active layer is less than an etching rate of the conducting film, the treatment performed on the active layer comprising a heating process at a temperature in a range between 200° C. and 500° C.   
     
     
         19 . The method according to  claim 18 , wherein the temperature of the heating process is higher than a temperature of the forming of the active layer of the oxide semiconductor. 
     
     
         20 . The method according to  claim 18 , wherein the conducting film used to form the source electrode and the drain electrode comprises a conducting film containing Al or Mo. 
     
     
         21 . The method according to  claim 20 , wherein the etchant used to form the source electrode and the drain electrode contains at least one of phosphoric acid, nitric acid, and acetic acid. 
     
     
         22 . The method according to  claim 20 , wherein the conducting film used to form the source electrode and the drain electrode comprises a multilayer film in which a conducting film containing Al or Mo is formed as a lowermost layer of the multilayer film. 
     
     
         23 . The method according to  claim 20 , wherein the conducting film used to form the source electrode and the drain electrode comprises a multilayer film in which a conducting film containing Al is formed as a lowermost layer of the multilayer film, and
 a pattern of an upper layer above the lowermost layer of the multilayer film obtained by patterning of the upper layer is used as a mask when etching of the lowermost layer is performed.   
     
     
         24 . The method according to  claim 23 , wherein the etchant used for the etching of the conducting film containing Al as the lowermost layer contains at least an organic alkali solution. 
     
     
         25 . The method according to  claim 18 , wherein the conducting film used to form the source electrode and the drain electrode comprises a conducting film containing indium oxide. 
     
     
         26 . The method according to  claim 25 , wherein the etchant used for the etching of the conducting layer to form the source electrode and the drain electrode contains oxalic acid. 
     
     
         27 . The method according to  claim 25 , wherein the conducting film used to form the source electrode and the drain electrode comprises a multilayer film in which a conducting film containing indium oxide is formed as a lowermost layer of the multilayer film. 
     
     
         28 . The method according to  claim 18 , wherein the treatment performed on the active layer comprises a laser irradiation process. 
     
     
         29 . The method according to  claim 18 , wherein the oxide semiconductor contains at least one element selected from the group consisting of In, Zn, Sn, and Ti. 
     
     
         30 . The method according to  claim 29 , wherein the oxide semiconductor contains at least one element selected from the group consisting of alkaline earth elements. 
     
     
         31 . The method according to  claim 29 , wherein the oxide semiconductor contains at least one element selected from the group consisting of rare earth elements, Al, Zr, and Hf. 
     
     
         32 . The method according to  claim 18 , wherein the oxide semiconductor comprises an n-type oxide semiconductor which undergoes substitutional doping with at least one dopant selected from the group consisting of a divalent cation, a trivalent cation, a tetravalent cation, a pentavalent cation, a hexavalent cation, a heptavalent cation, and an octavalent cation, and
 wherein a valence of the dopant is more than a valence of a metal ion constituting the n-type oxide semiconductor, provided that the dopant is excluded from the metal ion.