Method for manufacturing a semiconductor pressure sensor

Abstract

Method for manufacturing a semiconductor pressure sensor, wherein, in a silicon substrate, trenches are dug and delimit walls; a closing layer is epitaxially grown, that closes the trenches at the top and forms a suspended membrane; a heat treatment is performed so as to cause migration of the silicon of the walls and to form a closed cavity underneath the suspended membrane; and structures are formed for transducing the deflection of the suspended membrane into electrical signals.

1 . A method for manufacturing a semiconductor pressure sensor, comprising the steps of: 
 providing a wafer comprising a bulk region of semiconductor material;    forming a membrane above and at a distance from said bulk region;    forming a closed cavity between said membrane and said bulk region; and    forming structures for transducing the deflection of said membrane into electrical signals;    wherein, said step of forming a membrane comprises the steps of: 
 digging a plurality of first trenches in said bulk region, said first trenches delimiting a plurality of first walls of semiconductor material;  
 epitaxially growing, starting from said first walls, a closing layer of semiconductor material, said closing layer closing said trenches at the top and forming said membrane; and  
 carrying out a heat treatment, thereby causing migration of the semiconductor material of said first walls and forming a closed cavity.  
   
   
   
       2 . The method according to  claim 1  wherein said first walls comprise columns with polygonal cross sections.  
   
   
       3 . The method according to  claim 1  wherein said step of carrying out a heat treatment is performed in a deoxidizing environment.  
   
   
       4 . The method according to  claim 3  wherein said deoxidizing environment comprises hydrogen atoms.  
   
   
       5 . The method according to  claim 1  wherein said step of forming transducer structures comprises forming contact structures in electrical contact with said membrane and with said bulk region so as to form a pressure sensor of capacitive type.  
   
   
       6 . The method according to  claim 1 , wherein said first walls are arranged at a first distance from one another, the method further comprising the steps of: 
 digging second trenches in said bulk region adjacent to said first trenches, said second trenches delimiting second walls of semiconductor material, said second walls being arranged at a second distance from one another greater than said first distance;    closing said second trenches at the top through a portion of said closing layer;    modifying the spatial arrangement of said semiconductor material forming said second walls and forming a labyrinthine cavity delimiting pillars of semiconductor material; and    forming an insulating region in said labyrinthine cavity.    
   
   
       7 . The method according to  claim 6  wherein said step of digging second trenches is carried out simultaneously to said step of digging first trenches.  
   
   
       8 . The method according to  claim 6  wherein said step of forming an insulating region comprises the steps of: 
 oxidizing said pillars through openings formed in said portion of said closing layer; and    filling said labyrinthine cavity with insulating material.    
   
   
       9 . The method according to  claim 6  wherein said step of forming transducer structures comprises: 
 forming first contact structures, electrically connected to said membrane;    forming second contact structures, electrically connected to said portion of said closing layer; and    forming third contact structures, electrically connected to said bulk region.    
   
   
       10 . The method according to  claim 1  wherein said step of forming transducer structures comprises forming resistive elements carried by said membrane.  
   
   
       11 . The method according to  claim 10  wherein said membrane has a first conductivity type, and said step of forming resistive elements comprises introducing ionic dopant species of a second conductivity type within said membrane.  
   
   
       12 . The method according to  claim 10  wherein said step of forming transducer structures further comprises the step of electrically connecting said resistive elements in a bridge configuration.  
   
   
       13 . A semiconductor pressure sensor, comprising: 
 a bulk region of semiconductor material;    a buried cavity overlying a first part of the bulk region; and    a membrane suspended above said buried cavity, wherein, said bulk region and said membrane are formed in a monolithic substrate, and in that said monolithic substrate carries structures for transducing the deflection of said membrane into electrical signals.    
   
   
       14 . The pressure sensor according to  claim 13 , of capacitive type, wherein said bulk region and said membrane form electrodes of a capacitive sensing element, and said transducer structures comprise contact structures in electrical contact with said membrane and with said bulk region.  
   
   
       15 . The pressure sensor according to  claim 14  wherein said bulk region has a first conductivity type, and said membrane has a second conductivity type.  
   
   
       16 . The pressure sensor according to  claim 14  wherein said monolithic substrate accommodates a capacitive reference element arranged adjacent to said capacitive sensing element.  
   
   
       17 . The pressure sensor according to  claim 16  wherein said capacitive reference element comprises: 
 an insulating region overlying a second part of the bulk region, said second part of the bulk region being adjacent to said buried cavity overlying the first part of the bulk region; and    an electrode region overlying said insulating region and adjacent to said membrane.    
   
   
       18 . The pressure sensor according to  claim 17  wherein said membrane and said electrode region have a circular or polygonal shape.  
   
   
       19 . The pressure sensor according to  claim 17  wherein said contact structures comprise: 
 a first metal region, in contact with said membrane;    a second metal region, extending outside said membrane and in direct electrical contact with said bulk region; and    a third metal region, in contact with said electrode region.    
   
   
       20 . The pressure sensor according to  claim 13 , of piezoelectric type, wherein said transducer structures comprise piezoresistive elements carried by said membrane, and contact structures in electrical contact with said piezoresistive elements.  
   
   
       21 . The pressure sensor according to  claim 20  wherein the bulk region has a first conductivity type and the piezoresistive element has a second conductivity type.  
   
   
       22 . The pressure sensor according to  claim 20  the bulk region and the membrane are monocrystalline silicon, and the piezoresistive element is polysilicon.  
   
   
       23 . A semiconductor pressure sensor comprising: 
 a common substrate of a semiconductor material;    a sensing capacitor including a sensor cavity within a first part of the common substrate, a deflectable membrane overlying and closing the sensor cavity, said membrane being made of the semiconductor material, and    a reference capacitor including an insulating region within a second part of the common substrate, the insulating region being adjacent to the sensor cavity and having a plurality of cavities, and an electrode region of the semiconductor material overlying the insulating region.    
   
   
       24 . The semiconductor pressure sensor of  claim 23 , wherein the substrate is of first conductivity type, and the membrane and electrode region are of second conductivity type.  
   
   
       25 . The semiconductor pressure sensor of  claim 23  wherein the sensor cavity is filled with hydrogen gas.  
   
   
       26 . The semiconductor pressure sensor of  claim 23  wherein the plurality of cavities in the insulating region are filled with an insulating material.  
   
   
       27 . The semiconductor pressure sensor of  claim 23  further comprising: 
 a first contact region formed in said membrane,    a second contact region formed in said bulk region surrounding the membrane;    a third contact region formed in said electrode region, and    a fourth contact region formed in said bulk region surrounding the electrode region.    
   
   
       28 . The semiconductor pressure sensor of  claim 23  wherein the membrane forms a first electrode.  
   
   
       29 . The semiconductor pressure sensor of  claim 23  wherein the common substrate underlying both the sensing capacitor and the reference capacitor forms a bottom electrode for the pressure sensor.  
   
   
       30 . A semiconductor pressure sensor comprising: 
 a sensing capacitor having a first electrode and a first dielectric region underlying the first electrode;    a reference capacitor having a second electrode and a second dielectric region underlying the second electrode; and    a semiconductor substrate underlying the first and second dielectric regions and forming a bottom electrode;    wherein, the first electrode is a deflectable membrane and the first dielectric region is a cavity filled with a gas.    
   
   
       31 . The semiconductor pressure sensor of  claim 30  wherein the second dielectric region is an insulating region.  
   
   
       32 . The semiconductor pressure sensor of  claim 30  wherein the first and second electrodes are of a first conductivity type and the semiconductor substrate is of a second conductivity type.  
   
   
       33 . The semiconductor pressure sensor of  claim 30  wherein the first and second electrodes share a monocrystalline structure with the substrate.  
   
   
       34 . The semiconductor pressure sensor of  claim 30  wherein the gas is hydrogen gas.  
   
   
       35 . The semiconductor pressure sensor of  claim 30  further comprising: 
 a first contact region formed in said first electrode;    a second contact region formed in said substrate surrounding the first electrode;    a third contact region formed in said second electrode; and    a fourth contact region formed in said substrate and surrounding the second electrode.