Composite substrate, surface acoustic wave device, and method for manufacturing composite substrate

Abstract

A method for manufacturing a composite substrate includes: forming a first intermediate layer including thermally synthesized silica on a surface of a support substrate; forming a second intermediate layer including an inorganic material on a surface of a piezoelectric single crystal substrate; flattening a surface of the second intermediate layer; and bonding a surface of the first intermediate layer to the flattened surface of the second intermediate layer.

1 . A method for manufacturing a composite substrate comprising:
 forming a first intermediate layer including thermally synthesized silica on a surface of a support substrate;   forming a second intermediate layer including an inorganic material on a surface of a piezoelectric single crystal substrate;   flattening a surface of the second intermediate layer; and   bonding a surface of the first intermediate layer to the flattened surface of the second intermediate layer.   
     
     
         2 . The method for manufacturing a composite substrate according to  claim 1 , further comprising flattening the surface of the first intermediate layer. 
     
     
         3 . The method for manufacturing a composite substrate according to  claim 1 , further comprising forming irregularities on the surface of the piezoelectric single crystal substrate. 
     
     
         4 . The method for manufacturing a composite substrate according to  claim 1 , wherein the first intermediate layer is a layer of thermally synthesized silica in which a silica layer deposited by chemical vapor deposition is sintered at a temperature of 800° C. or more. 
     
     
         5 . The method for manufacturing a composite substrate according to  claim 1 , wherein the first intermediate layer is a layer of thermally synthesized silica in which a silica layer deposited by physical vapor deposition is sintered at a temperature of 800° C. or more. 
     
     
         6 . The method for manufacturing a composite substrate according to  claim 1 , wherein the first intermediate layer is a layer of thermally synthesized silica in which a solution of an organic silicon compound is applied and sintered at a temperature of 800° C. or more. 
     
     
         7 . The method for manufacturing a composite substrate according to  claim 1 , wherein a material of the support substrate is selected from silicon, sapphire, silicon carbide, silicon nitride, aluminum nitride, and silica glass. 
     
     
         8 . The method for manufacturing a composite substrate according to  claim 1 , wherein a material of the support substrate is silicon, and the first intermediate layer is formed by thermal oxidation of the support substrate. 
     
     
         9 . The method for manufacturing a composite substrate according to  claim 1 , further comprising heating the second intermediate layer at a highest temperature lower than a Curie temperature of the piezoelectric single crystal. 
     
     
         10 . The method for manufacturing a composite substrate according to  claim 9 , wherein the highest temperature in the heating the second intermediate layer is a temperature of 600° C. or less. 
     
     
         11 . The method for manufacturing a composite substrate according to  claim 1 , wherein
 in addition to the surface of the support substrate, a thermally synthesized silica layer having a material the same as a material of the first intermediate layer is also formed on a back surface of the support substrate.   
     
     
         12 . The method for manufacturing a composite substrate according to  claim 1 , wherein an amorphous silicon layer is further deposited on at least one of the surface of the first intermediate layer and the surface of the second intermediate layer, and then the first intermediate layer is bonded to the second intermediate layer. 
     
     
         13 . The method for manufacturing a composite substrate according to  claim 12 , wherein a total thickness of the amorphous silicon layer is 50 nm or less. 
     
     
         14 . The method for manufacturing a composite substrate according to  claim 1 , wherein an activation process is applied to at least one surface of the first intermediate layer and the second intermediate layer, and then the surface of the first intermediate layer is bonded to the surface of the second intermediate layer. 
     
     
         15 . The method for manufacturing a composite substrate according to  claim 14 , wherein the surface activation process is any one of ozone water treatment, UV ozone treatment, ion beam treatment, and plasma treatment. 
     
     
         16 . The method for manufacturing a composite substrate according to  claim 1 , wherein the surface of the first intermediate layer and/or the surface of the second intermediate layer is flattened by chemical-mechanical polishing. 
     
     
         17 . The method for manufacturing a composite substrate according to  claim 1 , wherein a material of the second intermediate layer includes any one of SiOx, Al 2 O 3 , AlN, SiN, SiON, and Ta 2 O 5 . 
     
     
         18 . The method for manufacturing a composite substrate according to  claim 1 , wherein the second intermediate layer is formed by chemical vapor deposition. 
     
     
         19 . The method for manufacturing a composite substrate according to  claim 1 , wherein the second intermediate layer is formed by physical vapor deposition. 
     
     
         20 . The method for manufacturing a composite substrate according to  claim 1 , wherein the second intermediate layer is formed in which a solution of an organic silicon compound is applied and the applied organic silicon compound is hardened. 
     
     
         21 . The method for manufacturing a composite substrate according to  claim 1 , comprising:
 performing a process of ion implantation into the piezoelectric single crystal substrate prior to the bonding; and   performing peeling at an interface in a region in which the ion is implanted after the bonding.   
     
     
         22 . The method for manufacturing a composite substrate according to  claim 21 , wherein in the performing the ion implantation process, a hydrogen ion is implanted in an amount of 6.0×10 16  atoms/cm 2  to 2.75×10 17  atoms/cm 2 . 
     
     
         23 . The method for manufacturing a composite substrate according to  claim 21 , wherein in the performing the ion implantation process, a hydrogen molecule ion is implanted in an amount of 3.0×10 16  atoms/cm 2  to 1.37×10 17  atoms/cm 2 . 
     
     
         24 . The method for manufacturing a composite substrate according to  claim 21 , wherein in the peeling, mechanical peeling is performed along the interface of the region in which the ion is implanted. 
     
     
         25 . The method for manufacturing a composite substrate according to  claim 21 , wherein the peeling is performed using a flash lamp annealing. 
     
     
         26 . The method for manufacturing a composite substrate according to  claim 21 , comprising grinding and/or polishing the piezoelectric single crystal substrate to reduce a thickness after the bonding.