Fabrication process of semiconductor substrate

Abstract

SOI substrates are fabricated with sufficient quality and with good reproducibility. At the same time, saving of resources and reduction of cost are realized by reuse of wafer and the like. Carried out to achieve the above are a step of bonding a principal surface of a first substrate to a principal surface of a second substrate, the first substrate being an Si substrate in which at least one layer of non-porous thin film is formed through a porous Si layer, a step of exposing the porous Si layer in a side surface of a bonding substrate comprised of the first substrate and the second substrate, a step of dividing the porous Si layer by oxidizing the bonding substrate, and a step of removing porous Si and oxidized porous Si layer on the second substrate separated by the division of the porous Si layer.

What is claimed is:  
     
         1 . A fabrication process of semiconductor substrate comprising: 
 a step of bonding a principal surface of a first substrate to a principal surface of a second substrate, said first substrate being an Si substrate in which at least one layer of non-porous thin film is formed through a porous Si layer;    a step of exposing said porous Si layer in a side surface of a bonding substrate comprised of said first substrate and said second substrate;    a step of dividing said bonding substrate in said porous Si layer by oxidizing said bonding substrate; and    a step of removing a porous Si and oxidized porous Si layer on said second substrate separated by the division of said bonding substrate in said porous Si layer.    
     
     
         2 . A fabrication process of semiconductor substrate comprising: 
 a step of bonding a principal surface of a first substrate to a principal surface of a second substrate, said first substrate being an Si substrate in which at least one layer of non-porous thin film is formed through a porous Si layer and in which said porous Si layer is exposed in a side surface thereof;    a step of dividing said bonding substrate in said porous Si layer by oxidizing a bonding substrate comprised of said first substrate and said second substrate; and    a step of removing a porous Si and oxidized porous Si layer on said second substrate separated by the division of said bonding substrate in said porous Si layer.    
     
     
         3 . The fabrication process of semiconductor substrate according to    claim 1    or    claim 2   , wherein after removing the porous Si and oxidized porous Si layer on the first substrate separated by said division of the porous Si layer, the first substrate is again used as a raw material for said first substrate before bonding.  
     
     
         4 . The fabrication process of semiconductor substrate according to    claim 1    or    claim 2   , wherein after removing the porous Si and oxidized porous Si layer on the first substrate separated by said division of the porous Si layer, the first substrate is again used as a raw material for said second substrate before bonding.  
     
     
         5 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein at least one layer of non-porous thin film is formed through a porous Si layer on each of two principal surfaces of said first substrate and said second substrate is bonded to each of said two principal surfaces.  
     
     
         6 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein said nonporous thin film is a single-crystal Si layer.  
     
     
         7 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein said nonporous thin film comprises an oxidized Si layer and a single-crystal Si layer.  
     
     
         8 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein said nonporous thin film is a single-crystal compound semiconductor layer.  
     
     
         9 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein said second substrate is an Si substrate.  
     
     
         10 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein said second substrate is an Si substrate in which an oxidized Si film is formed at least on a principal surface to be bonded.  
     
     
         11 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein said second substrate is a light transparent substrate.  
     
     
         12 . The fabrication process of semiconductor substrate according to    claim 5   , wherein said second substrates respectively bonded to the two principal surfaces of said first substrate are those selected from Si substrate, Si substrate with an oxidized Si film formed at least on a principal surface to be bonded, and light transparent substrate.  
     
     
         13 . The fabrication process of semiconductor substrate according to    claim 12   , wherein the second substrate bonded to one principal surface of said first substrate and the second substrate bonded to the other principal surface thereof are made of respective materials different from each other.  
     
     
         14 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein a surface flattening process in a direction spreaded with the principal surface of the second substrate is carried out after removing said porous Si and oxidized porous Si layer.  
     
     
         15 . The fabrication process of semiconductor substrate according to    claim 14   , wherein said surface flattening process is annealing in an ambient containing hydrogen.  
     
     
         16 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein removal of said porous Si and oxidized porous Si layer is selectively carried out by soak in either one of hydrofluoric acid, a mixture solution in which at least one of alcohol and hydrogen peroxide solution is added to hydrofluoric acid, buffered hydrofluoric acid, and a mixture solution in which at least one of alcohol and hydrogen peroxide solution is added to buffered hydrofluoric acid.  
     
     
         17 . The fabrication process of semiconductor substrate according to    claim 8   , wherein removal of said porous Si and oxidized porous Si layer is carried out by selective chemical etching of porous Si with an etchant having a faster etch rate of porous Si against a compound semiconductor.  
     
     
         18 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein removal of said porous Si and oxidized porous Si layer is carried out by polishing the layer, using said non-porous thin film as a stopper.  
     
     
         19 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein bonding of said first substrate to said second substrate is making the substrates into close contact with each other.  
     
     
         20 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein bonding of said first substrate to said second substrate is carried out by a method selected from anodic bonding, pressing, annealing, and combinations thereof.  
     
     
         21 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein formation of the non-porous thin film on the porous Si layer is carried out by performing anodization of an Si substrate to form porous Si and thereafter forming a non-porous thin film on said porous Si.  
     
     
         22 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein formation of the non-porous thin film on the porous Si layer is carried out by implanting ions of at least one element of rare gases, hydrogen, and nitrogen into an Si substrate to form a porous layer in a certain depth from a surface thereof.  
     
     
         23 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein formation of the non-porous thin film on the porous Si layer is carried out by anodizing an Si substrate to form a porous Si layer, thereafter forming a non-porous thin film on said porous Si layer, and then implanting ions of at least one element of rare gases, hydrogen, and nitrogen through the non-porous thin film into said porous Si layer so as to have a projected range thereof in said porous Si layer.  
     
     
         24 . The fabrication process of semiconductor substrate according to    claim 21   , wherein said anodization is carried out in an HF solution.  
     
     
         25 . The fabrication process of semiconductor substrate according to    claim 1    or    2   , wherein prior to the oxidation of said bonding substrate, a layer of a material having a smaller coefficient of thermal expansion than Si is formed on at least one of outer surfaces of said bonding substrate.