Low refractive index sio2 film and process for producing the same

Abstract

A low refractive index SiO 2 film is provided which uses a starting material for forming an SiO 2 film and has a lower refractive index than the conventional SiO 2 film. A starting material gas comprising a gas containing a fluorine atom, a gas containing a silicon atom and an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms with a part or the whole of hydrogen atoms substituted by a fluorine atom, and a gas containing an oxygen atom is subjected to plasma CVD in a vacuum chamber 1 to form an SiO 2 film on a web 2 in a plasma zone 5 . The SiO 2 film thus formed has, introduced thereinto, at least one low refractive index element selected from a fluorine atom, an alkyl group having 1 to 4 carbon atoms, and an alkyl group having 1 to 4 carbon atoms with a part or the whole of hydrogen atoms substituted by a fluorine atom, and the SiO 2 film with the low refractive index element introduced thereinto has a lower refractive index than an SiO 2 film with the low refractive index element not introduced thereinto.

1 . A low refractive index SiO 2  film comprising an SiO 2  film with a low refractive index element introduced thereinto, the low refractive index element being at least one member selected from the group consisting of a fluorine atom, an alkyl group having 1 to 4 carbon atoms, and an alkyl group having 1 to 4 carbon atoms with a part or the whole of hydrogen atoms substituted by a fluorine atom.  
     
     
         2 . The low refractive index SiO 2  film according to  claim 1 , which is adapted for use as an antireflection film.  
     
     
         3 . The low refractive index SiO 2  film according to  claim 1 , which has been prepared by CVD using at least one starting material selected from the group consisting of a gas containing a fluorine atoms, a starting material containing a silicon atom and an alkyl group having 1 to 4 carbon atoms, and a starting material containing a silicon atom and an alkyl group having 1 to 4 carbon atoms with a part or the whole of hydrogen atoms substituted by a fluorine atom.  
     
     
         4 . The low refractive index SiO 2  film/according to  claim 3 , wherein the gas containing a fluorine atom is selected from the group consisting of CF 4 , C 2 F 6 , C 3 F 6 , and SF 6 .  
     
     
         5 . The low refractive index SiO 2  film according to  claim 3 , wherein the starting material containing a silicon atom and an alkyl group having 1 to 4 carbon atoms comprises at least one compound selected from the group consisting of HMDSO, TMDSO, octamethylcyclotetrasiloxane, TEOS, MTMOS, methylsilane, dimethylsilane, trimethylsilane, diethylsilane, propylsilane, and phenylsilane.  
     
     
         6 . The low refractive index SiO 2  film according to  claim 3 , wherein the starting material containing a silicon atom and an alkyl group having 1 to 4 carbon atoms with a part or the whole of hydrogen atoms substituted by a fluorine atom comprises at least one compound selected from the group consisting of HMDSO, TMDSO, octamethylcyclotetrasiloxane, TEOS, MTMOS, methylsilane, dimethylsilane, trimethylsilane, diethylsilane, propylsilane, and phenylsilane, a part or the whole of hydrogen atoms in each of said compounds being substituted by a fluorine atom.  
     
     
         7 . A process for producing a low refractive index SiO 2  film, comprising forming a thin film on a substrate by CVD using a starting material gas comprising a gas containing a fluorine atom, a gas containing a silicon atom and an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms with a part or the whole of hydrogen atoms substituted by a fluorine atom, and a gas containing an oxygen atom.  
     
     
         8 . A process for producing a low refractive index SiO 2  film, comprising the steps of: 
 (1) introducing a mixed gas, comprising a gas containing a fluorine atom, a volatile gas of an organic compound containing a silicon atom and an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms with a part or the whole of hydrogen atoms substituted by a fluorine atom, and a gas containing an oxygen atom, into a vacuum chamber maintained in a vacuum of 10 −3  to 1 mmHg (Torr) and bringing the mixed gas to a plasma stream by glow discharge; and    (2) bringing the plasma stream into contact with the surface of a substrate disposed within the vacuum chamber to form a thin film on the substrate.