Acceleration sensor and process for the production thereof

Abstract

The purpose of the present invention is to provide an acceleration sensor having a novel structure, by which high precision and high reliability can be realized. A singlecrystal silicon substrate ( 1 ) is bonded through an SiO 2 film ( 9 ) to a singlecrystal silicon substrate ( 8 ), and the singlecrystal silicon substrate ( 1 ) is made into a thin film. A cantilever ( 13 ) is formed on the singlecrystal silicon substrate ( 1 ), and the thickness of the cantilever ( 13 ) in a direction parallel to the surface of the singlecrystal silicon substrate ( 1 ) is made smaller, than the thickness of the cantilever in the direction of the depth of the singlecrystal silicon substrate ( 1 ), and movable in a direction parallel to the substrate surface. In addition, the surface of the cantilever ( 13 ) and the part of the singlecrystal silicon substrate ( 1 ), opposing the cantilever ( 13 ), are, respectively, coated with an SiO 2 film ( 5 ), so that an electrode short circuit is prevented in a capacity-type sensor. In addition, a signal-processing circuit ( 10 ) is formed on the singlecrystal silicon substrate ( 1 ), so that signal processing is performed as the cantilever ( 13 ) moves.

1 . An acceleration sensor, characterized in that it comprises: 
 a second singlecrystal silicon substrate, which is bonded onto a first singlecrystal silicon substrate, an insulating film being interposed between the substrates;    a movable beam, formed on at least one of said first or second singlecrystal silicon substrate, and which is movable in a direction parallel to the surface of the substrate; and    a signal-processing circuit, formed on at least one of the said first or second singlecrystal silicon substrate for effecting signal processing as said beam moves owing to an acceleration.    
     
     
         2 . An acceleration sensor as claimed in    claim 1   , wherein said beam is smaller in thickness in a direction parallel to the surface of said singlecrystal silicon substrates as compared to the thickness in a direction of the depth of said singlecrystal silicon substrates.  
     
     
         3 . An acceleration sensor as claimed in    claim 1   , wherein at least one of the surface of said beam and the surface of second singlecrystal silicon substrate opposing said beam is covered with an insulator.  
     
     
         4 . A process for producing an acceleration sensor, comprising: 
 a first step of forming, on a main surface of a first singlecrystal silicon substrate, a groove of a predetermined depth at an area surrounding a beam to be formed;    a second step of depositing, on the main surface of said first singlecrystal silicon substrate, a film of a polycrystalline silicon, amorphous silicon or mixture thereof, so as to fill said groove with said silicon film, and smoothing the surface of said silicon film;    a third step of bonding the main surface of said first singlecrystal silicon substrate to the second singlecrystal silicon substrate with an insulating film interposed therebetween;    a fourth step of polishing a surface of said first singlecrystal silicon substrate on the side opposite to the surface thereof bonded to the second singlecrystal silicon substrate to a predetermined degree, so as to make the first singlecrystal silicon substrate a thin film; and    a fifth step of exposing said film of polycrystalline silicon, amorphous silicon or a mixture thereof on said polished surface of the first singlecrystal silicon substrate at an area corresponding to the position where said groove is formed, and removing said silicon film by etching from said exposed area, so as to make the beam movable.    
     
     
         5 . A process for producing an acceleration sensor as claimed in    claim 4   , wherein, in said first step, said predetermined depth is set according to the thickness of said beam in the vertical direction thereof.  
     
     
         6 . A process for producing an acceleration sensor as claimed in    claim 4   , wherein, in said third step, said insulating film is formed on the surface of said second singlecrystal silicon substrate.  
     
     
         7 . A process for producing an acceleration sensor as claimed in    claim 4   , wherein, in said second step, there remains said flat silicon film on the main surface of said first singlecrystal silicon substrate.  
     
     
         8 . A process for producing an acceleration sensor as claimed in    claim 7   , wherein, prior the said third step, there is added a step of making said silicon film remaining on the main surface of said singlecrystal silicon substrate to be resistant to the etching in said fifth step, except for the silicon film positioned at an area surrounding said movable beam.  
     
     
         9 . A process for producing an acceleration sensor as claimed in    claim 4   , wherein said first step additionally includes a step of forming a concave portion on the main surface of said first singlecrystal silicon substrate, at the position where said beam is to be formed.  
     
     
         10 . A process for producing an acceleration sensor as claimed in    claim 4   , wherein, prior to said fifth step, there is added a step of forming a semi-conductor element on said first or second singlecrystal silicon substrate.  
     
     
         11 . A process for producing an acceleration sensor, comprising: 
 a first step of boding the main surface of a first singlecrystal silicon substrate to a second singlecrystal silicon substrate with an insulating film interposed therebetween;    a second step of polishing a surface of said first singlecrystal silicon substrate opposite to the bonded surface of the singlecrystal silicon substrate to a predetermined degree, so as to make the first singlecrystal silicon substrate a thin film;    a third step of forming a groove in the first singlecrystal substrate, the groove extending from the polished surface side of the substrate to said insulating film in an area surrounding a movable beam to be formed;    a fourth step of depositing, from the polished surface side of the said first singlecrystal silicon substrate, a film of a polycrystalline silicon, amorphous silicon, or mixture thereof, so as to fill said groove with said silicon film, and smoothing the surface of said silicon film; and    a fifth step of forming a semiconductor element on said first or second singlecrystal silicon substrate, and thereafter removing by etching said silicon film from said polished surface side of said first singlecrystal silicon substrate, so as to make the beam movable.    
     
     
         12 . A process for producing an acceleration sensor as claimed in    claim 11   , wherein, in said first step, said insulating film is formed on the surface of said second singlecrystal silicon substrate.  
     
     
         13 . A process for producing an acceleration sensor as claimed in    claim 11   , wherein said fifth step includes a step of removing said insulating film at a position corresponding to the position where said beam is formed.  
     
     
         14 . A process for producing an acceleration sensor as claimed in    claim 11   , wherein said first step includes a step of forming, prior to said bonding, a concave portion in an area of the main surface of said first singlecrystal silicon substrate, corresponding to the position where said beam is to be formed.