Thin Film Comprising Titanium Oxide, and Method of Producing Thin Film Comprising Titanium Oxide

Abstract

A thin film is provided that primarily comprises titanium oxide and includes Ti, Ag and O. The thin film contains 29.6 at % or more and 34.0 at % or less of Ti, 0.003 at % or more and 7.4 at % or less of Ag, and oxygen as the remainder thereof and has a ratio of oxygen to metals, O/(2Ti+0.5Ag), of 0.97 or more. The thin film has a high refractive index and a low extinction coefficient. In addition, the thin film has superior transmittance, minimally deteriorates in reflectance, and is useful as an interference film or a protective film for an optical information recording medium. The film may also be applied to a glass substrate to provide a heat reflective film, an antireflective film, or an interference filter. A method of producing the thin film is also disclosed.

We claim: 
     
         1 . A method of producing a thin film mainly comprising titanium oxide, comprising the step of sputtering a sintered sputtering target that comprises components of Ti, Ag and O, contains the respective components at a composition ratio of (TiO 2-m ) 1-n Ag n , where 0≦m≦0.5 and 0.0001≦n≦0.2, and has a specific resistance of 10 Ωcm or less, wherein said sputtering step is performed under an argon gas atmosphere without oxygen or with 0.1 to 16% of oxygen to form a thin film on a substrate such that the thin film contains 29.6 atomic percent (at %) or more and 34.0 at % or less of Ti, 0.003 at % or more and 7.4 at % or less of Ag, and oxygen as the remainder thereof, and has a ratio of oxygen to metals, O/(2Ti+0.5Ag), of 0.97 or more. 
     
     
         2 . A method of producing a thin film mainly comprising titanium oxide according to  claim 1 , wherein said sputtering is DC sputtering, and wherein, when an oxygen gas ratio used in the sputtering gas atmosphere is represented as b (%), the oxygen gas ratio is adjusted during said sputtering step to be in a range of 0<b≦83.3n-0.17 when the composition ratio n of Ag in the sputtering target is 0.0001≦n≦0.01. 
     
     
         3 . A method of producing a thin film mainly comprising titanium oxide according to  claim 1 , wherein said sputtering is DC sputtering, and wherein, when an oxygen gas ratio used in the sputtering gas atmosphere is represented as b (%), the oxygen gas ratio is adjusted during said sputtering step to be in a range of 17n-0.17≦b≦83n-0.17 when the composition ratio n of Ag is 0.01≦n≦0.2. 
     
     
         4 . A method of producing a thin film mainly comprising titanium oxide according to  claim 1 , wherein said sputtering step is performed by adjusting an oxygen gas ratio (b) to b=0% when the composition ratio m is in a range of 0≦m≦0.05 and the composition ratio n of Ag is 0.0001≦n≦0.01. 
     
     
         5 . A method of producing a thin film mainly comprising titanium oxide, comprising the step of sputtering a sputtering target that has a sintered structure, contains Ti, Ag and O as its constituent elements with a composition represented as (TiO 2-m ) 1-n Ag n  where m and n are numerals satisfying 0≦m≦0.5 and 0.0001≦n≦0.2, has a specific resistance of 10 Ωcm or less, has a matrix phase of titanium oxide, and has a Ag phase dispersed as particles within the matrix phase, wherein said sputtering step is performed under an argon gas atmosphere without oxygen or with 0.1 to 16% of oxygen to form a thin film on a substrate such that the thin film contains 29.6 atomic percent (at %) or more and 34.0 at % or less of Ti, 0.003 at % or more and 7.4 at % or less of Ag, and oxygen as the remainder thereof, and has a ratio of oxygen to metals, O/(2Ti+0.5Ag), of 0.97 or more. 
     
     
         6 . The method according to  claim 5 , wherein the Ag phase particles existing in the sintered structure of the sputtering target have an average grain size of 15 μm or less. 
     
     
         7 . A thin film comprising titanium oxide produced by a process comprising the step of sputtering a sintered sputtering target that comprises components of Ti, Ag and O, contains the respective components at a composition ratio of (TiO 2-m ) 1-n Ag n , where 0≦m≦0.5 and 0.0001≦n≦0.2, and has a specific resistance of 10 Ωcm or less, wherein said sputtering step is performed under an argon gas atmosphere without oxygen or with 0.1 to 16% of oxygen to form the thin film on a substrate such that the thin film contains 29.6 atomic percent (at %) or more and 34.0 at % or less of Ti, 0.003 at % or more and 7.4 at % or less of Ag, and oxygen as the remainder thereof, and has a ratio of oxygen to metals, O/(2Ti+0.5Ag), of 0.97 or more. 
     
     
         8 . The thin film comprising titanium oxide according to  claim 7 , wherein the thin film has a refractive index in a wavelength region from 400 to 410 nm of 2.6 or more and an extinction coefficient in a wavelength region from 400 to 410 nm of 0.1 or less. 
     
     
         9 . The thin film comprising titanium oxide according to  claim 8 , wherein the thin film has a ratio of oxygen to Ti (O/Ti) of 2 or more. 
     
     
         10 . The thin film comprising titanium oxide according to  claim 9 , wherein the thin film has an extinction coefficient in a wavelength region from 400 to 410 nm of 0.03 or less. 
     
     
         11 . The thin film comprising titanium oxide according to  claim 10 , wherein the thin film is an interference film or a protective film. 
     
     
         12 . The thin film comprising titanium oxide according to  claim 11 , wherein the thin film forms part of an optical recording medium. 
     
     
         13 . The thin film comprising titanium oxide according to  claim 7 , wherein the thin film has a ratio of oxygen to Ti (O/Ti) of 2 or more. 
     
     
         14 . The thin film comprising titanium oxide according to  claim 7 , wherein the thin film has an extinction coefficient in a wavelength region from 400 to 410 nm of 0.03 or less. 
     
     
         15 . The thin film comprising titanium oxide according to  claim 7 , wherein the thin film is an interference film or a protective film. 
     
     
         16 . The thin film comprising titanium oxide according to  claim 7 , wherein the thin film forms part of an optical recording medium.