Sputtering target, oxide semiconductor thin film, and method for producing these

Abstract

A sputtering target including an oxide that includes an indium (In) element, a tin (Sn) element, a zinc (Zn) element and an aluminum (Al) element, wherein the oxide includes a homologous structure compound represented by InAlO 3 (ZnO) n , (m is 0.1 to 10) and a bixbyite structure compound represented by In 2 O 3 .

1 . A sputtering target comprising an oxide that comprises an indium (In) element, a tin (Sn) element, a zinc (Zn) element and an aluminum (Al) element, wherein the oxide comprises a homologous structure compound represented by InAlO 3 (ZnO) m  (m is 0.1 to 10) and a bixbyite structure compound represented by In 2 O 3 . 
     
     
         2 . The sputtering target according to  claim 1 , wherein the homologous structure compound is one or more selected from homologous structure compounds represented by InAlZn 4 O 7 , InAlZn 3 O 6 , InAlZn 2 O 5  and InAlZnO 4 . 
     
     
         3 . The sputtering target according to  claim 1 , wherein the atomic ratio of In, Sn, Zn and Al satisfies the following formulas (1) to (4):
   0.10≦In/(In+Sn+Zn+Al)≦0.75  (1)
     0.01≦Sn/(In+Sn+Zn+Al)≦0.30  (2)
     0.10≦Zn/(In+Sn+Zn+Al)≦0.70  (3)
     0.01≦Al/(In+Sn+Zn+Al)≦0.40  (4)
   
       wherein in the formulas In, Sn, Zn and Al independently indicate an atomic ratio of each element in the sputtering target. 
     
     
         4 . The sputtering target according to  claim 1  that has a relative density of 98% or more. 
     
     
         5 . The sputtering target according to  claim 1  that has a bulk specific resistance of 10 mΩcm or less. 
     
     
         6 . The sputtering target according to  claim 1  that does not comprise a spinel structure compound represented by Zn 2 SnO 4 . 
     
     
         7 . An oxide semiconductor thin film formed by a sputtering method with the use of the sputtering target according to  claim 1 . 
     
     
         8 . A method for producing an oxide semiconductor thin film, wherein the film is formed by a sputtering method with the use of the sputtering target according to  claim 1  in an atmosphere of a mixed gas that comprises: one or more selected from water vapor, an oxygen gas and a nitrous oxide gas; and a rare gas. 
     
     
         9 . The method for producing an oxide semiconductor thin film according to  claim 8 , wherein the formation of the oxide semiconductor thin film is conducted in an atmosphere of a mixed gas that comprises a rare gas and at least water vapor. 
     
     
         10 . The method for producing an oxide semiconductor thin film according to  claim 9 , wherein the ratio of the water vapor contained in the mixed gas is 0.1% to 25% in terms of a partial pressure ratio. 
     
     
         11 . The method for producing the oxide semiconductor thin film according to  claim 8  comprising:
 transporting substrates in sequence to positions opposing to 3 or more of the sputtering targets arranged in parallel with a prescribed interval in a vacuum chamber; 
 applying a negative potential and a positive potential alternately from an AC power source to each of the targets; and 
 causing plasma to be generated on the target by applying at least one output from the AC power source while switching the target to which a potential is applied among two or more targets that are divergently connected to this AC power source, thereby forming a film on a substrate surface. 
 
     
     
         12 . The method for producing an oxide semiconductor thin film according to  claim 11 , wherein the AC power density of the AC power source is 3 W/cm 2  or more and 20 W/cm 2  or less. 
     
     
         13 . The method for producing an oxide semiconductor thin film according to  claim 11  or  12 , wherein the frequency of the AC power source is 10 kHz to 1 MHz. 
     
     
         14 . A thin film transistor comprising, as a channel layer, the oxide semiconductor thin film formed by the method for producing an oxide semiconductor thin film according to  claim 8 . 
     
     
         15 . The thin film transistor according to  claim 14  that has a field effect mobility of 10 cm 2 /Vs or more.