Sputtering Target of Sintered Ti-Nb Based Oxide, Thin Film of Ti-Nb Based Oxide, and Method of Producing The Thin Film

Abstract

A sputtering target of sintered Ti—Nb based oxide is provided. The sputtering target consists of titanium (Ti), niobium (Nb), and remainder being oxygen and unavoidable impurities, and the atomic ratio of Ti and Nb is 0.39≦(Nb/(Ti+Nb))≦0.79. The sputtering target of sintered Ti—Nb based oxide has a high refractive index and a low extinction coefficient. Also provided is a thin film of Ti—Nb based oxide obtained by using the foregoing target, which enables high-rate deposition. The thin film has superior transmittance, is subject to minimal reduction and variation of reflectivity, and is useful as an interference or protective film of an optical information recording medium, or as a part of a constituent layer of an optical recording medium. The thin film can also be applied to a glass substrate; that is, it can be used as a heat reflecting or antireflection film, or an interference filter.

We claim: 
     
         1 . A Ti—Nb based oxide thin film consisting of titanium (Ti), niobium (Nb), and remainder of oxide and unavoidable impurities, said thin film having an atomic ratio of Ti and Nb of 0.39≦(Nb/(Ti+Nb))≦0.79, a refractive index in a wavelength region of 400 to 410 nm exceeding 2.5, and an extinction coefficient of 0.01 or less. 
     
     
         2 . A Ti—Nb based oxide thin film according to  claim 1 , wherein the atomic ratio of Ti and Nb is 0.46≦(Nb/(Ti+Nb))≦0.79. 
     
     
         3 . A Ti—Nb based oxide thin film according to  claim 1 , wherein the atomic ratio of Ti and Nb is 0.57≦(Nb/(Ti+Nb))≦0.75. 
     
     
         4 . A Ti—Nb based oxide thin film according to  claim 3 , wherein the thin film has a refractive index variation, which is obtained from a difference in refractive index before and after storing the thin film that was sputtered-deposited on a glass substrate for 200 hours in 80° C. and 80% environment, of 0.012 or less. 
     
     
         5 . A Ti—Nb based oxide thin film according to  claim 3 , wherein the thin film has a refractive index variation, which is obtained from a difference in refractive index before and after storing the thin film that was sputtered-deposited on a glass substrate for 200 hours in 80° C. and 80% environment, of 0.01 or less, and wherein the extinction coefficient is 0.001 or less. 
     
     
         6 . A Ti—Nb based oxide thin film according to  claim 1 , wherein the thin film has a refractive index variation, which is obtained from a difference in refractive index before and after storing the thin film that was sputtered-deposited on a glass substrate for 200 hours in 80° C. and 80% environment, of 0.012 or less. 
     
     
         7 . A Ti—Nb based oxide thin film according to  claim 1 , wherein the thin film has a refractive index variation, which is obtained from a difference in refractive index before and after storing the thin film that was sputtered-deposited on a glass substrate for 200 hours in 80° C. and 80% environment, of 0.01 or less, and wherein the extinction coefficient is 0.001 or less. 
     
     
         8 . A Ti—Nb based oxide thin film according to  claim 1 , wherein the thin film is an optical interference film, a protective film, or a part of a constituent layer of an optical recording medium. 
     
     
         9 . A Ti—Nb based oxide thin film according to  claim 1  produced by a process comprising the steps of depositing the thin film on a substrate by sputtering using a mixed sputtering gas consisting of argon and 0.5% to 5% oxygen. 
     
     
         10 . A method of producing a thin film of Ti—Nb based oxide, comprising the steps of using a mixed sputtering gas of argon and 0.5% to 5% oxygen, and depositing a Ti—Nb based oxide thin film in the sputtering gas by sputtering the thin film on a substrate such that the thin film consists of titanium (Ti), niobium (Nb), and remainder of oxide and unavoidable impurities and has an atomic ratio of Ti and Nb of 0.39≦(Nb/(Ti+Nb))≦0.79, a refractive index in a wavelength region of 400 to 410 nm exceeding 2.5, and an extinction coefficient of 0.01 or less. 
     
     
         11 . A method of producing a thin film of Ti—Nb based oxide, comprising the steps of
 depositing a thin film on a substrate by sputtering a sputtering target of sintered Ti—Nb based oxide, wherein the sputtering target consists of titanium (Ti), niobium (Nb), and remainder being oxide and unavoidable impurities, TiNb 2 O 7  exists in the sputtering target as an intermediate compound between TiO 2  and Nb 2 O 5  confirmable by XRD measurement, an atomic ratio of Ti and Nb in the target is 0.39≦(Nb/(Ti+Nb))≦0.79, relative density of the target is 90% or more, and specific resistance of the target is 0.5 Ωcm or less; and 
 using, during said depositing step, a mixed sputtering gas of argon and oxygen in which 0.5% to 5% of oxygen is mixed with argon to produce a thin film of Ti—Nb based oxide in which the thin film consists of titanium (Ti), niobium (Nb), and remainder being oxide and unavoidable impurities, atomic ratio of Ti and Nb of the thin film is 0.39≦(Nb/(Ti+Nb))≦0.79, a refractive index of the thin film in a wavelength region of 400 to 410 nm exceeds 2.5, and an extinction coefficient is 0.01 or less.