Application of a strain-compensated heavily doped etch stop for silicon structure formation

Abstract

A method of making a silicon micromechanical structure, from a lightly doped silicon substrate having less than <5×10 19 cm −3 boron therein. A p+ layer having a boron content of greater than 7×10 19 cm −3 and a germanium content of about 1×10 21 cm −3 is placed on the substrate. A mask is formed on the second side, followed by etching to the p+ layer. An insulator is put on the p+ layer and an electronic component is fabricated thereon. Preferred micromechanical structures are pressure sensors, cantilevered accelerometers, and dual web biplane accelerometers. Preferred electronic components are dielectrically isolated piezoresistors and resonant microbeams. The method may include the step of forming a lightly doped layer on the p+ layer to form a buried p+ layer prior to etching.

1 . A method of making a silicon micromechanical structure, comprising the steps of: 
 forming a lightly doped silicon substrate having a first and second side and having less than 5×10 19  cm −3  boron therein;    placing a p+ layer on the first side of said substrate, said p+ having a boron content of greater than 7×10 19  cm −3  and a germanium content of about 1×10 21  cm −3 ;    forming a mask on the second side for etching a predetermined pattern;    etching said second side to said p+ layer; and    depositing an insulator on said p+ layer and fabricating an electronic component on said insulator.    
     
     
         2 . The method of  claim 1 , wherein said boron content is greater than 1×10 20  cm −3  and the germanium content is from about 0.5×10 21  cm −3  to about 2.0×10 21  cm −3 .  
     
     
         3 . The method of  claim 1 , wherein said micromechanical structure is a pressure sensor.  
     
     
         4 . The method of  claim 3 , wherein said electronic component is selected from the group consisting of dielectrically isolated piezoresistors and resonant microbeams.  
     
     
         5 . The method of  claim 1 , wherein said micromechanical structure is a cantilevered accelerometer.  
     
     
         6 . The method of  claim 5 , wherein said electronic component is selected from the group consisting of dielectrically isolated piezoresistors and resonant microbeams.  
     
     
         7 . The method of  claim 1 , wherein said micromechanical structure is a dual web biplane accelerometer formed by forming a said p+ layer on both sides of said substrate, forming a proof mask and flexure etching on both sides of said layer until said etching reaches said p+ layers.  
     
     
         8 . The method of  claim 7 , wherein said electronic component is selected from the group consisting of dielectrically isolated piezoresistors and resonant microbeams.  
     
     
         9 . The method of  claim 1 , wherein said micromechanical structure includes a dielectrically isolated piezoresistor formed on a top surface of a first wafer, a second wafer is bonded to said first wafer, and said second wafer forms a single crystal piezoresistor.  
     
     
         10 . A method of making a silicon micromechanical structure, comprising the steps of: 
 forming a lightly doped silicon substrate having a first and second side and having less than 5×10 19  cm −3  boron therein;    placing a p+ layer on the first side of said substrate, said p+ having a boron content of greater than 7×10 19 cm   −3  and a germanium content of about 1×10 21  cm −3 ;    forming a lightly doped layer on said p+ layer to form a buried p+ layer;    forming a mask on the second side for etching a predetermined pattern;    etching said second side to said buried p+ layer; and    depositing an insulator on said lightly doped layer and fabricating an electronic component on said insulator.    
     
     
         11 . The method of  claim 10 , wherein said boron content is greater than 1×10 20  cm −3  and the germanium content is from about 0.5×10 21  cm −3  to about 2.0×10 21  cm −3 .  
     
     
         12 . The method of  claim 10 , wherein said micromechanical structure is a pressure sensor.  
     
     
         13 . The method of  claim 12 , wherein said electronic component is selected from the group consisting of dielectrically isolated piezoresistors and resonant microbeams.  
     
     
         14 . The method of  claim 10 , wherein said micromechanical structure is a cantilevered accelerometer.  
     
     
         15 . The method of  claim 14 , wherein said electronic component is selected from the group consisting of dielectrically isolated piezoresistors and resonant microbeams.  
     
     
         16 . The method of  claim 10 , wherein said micromechanical structure is a dual web biplane accelerometer formed by forming a said p+ layer on both sides of said substrate, forming a proof mask and flexure etching on both sides of said layer until said etching reaches said p+ layers.  
     
     
         17 . The method of  claim 16 , wherein said electronic component is selected from the group consisting of dielectrically isolated piezoresistors and resonant microbeams.  
     
     
         18 . The method of  claim 10 , wherein said micromechanical structure includes a dielectrically isolated piezoresistor formed on a top surface of a first wafer, a second wafer is bonded to said first wafer, and said second wafer forms a single crystal piezoresistor.  
     
     
         19 . A device produced according to the method of  claim 1 .  
     
     
         20 . The device of  claim 19 , wherein said boron content is greater than 1×10 20  cm −3  and the germanium content is from about 0.5×10 21  cm −3  to about 2.0×10 21  cm −3 .  
     
     
         21 . The device of  claim 19 , wherein said micromechanical structure is a pressure sensor.  
     
     
         22 . The device of  claim 21 , wherein said electronic component is selected from the group consisting of dielectrically isolated piezoresistors and resonant microbeams.  
     
     
         23 . The device of  claim 19 , wherein said micromechanical structure is a cantilevered accelerometer.  
     
     
         24 . The device of  claim 23 , wherein said electronic component is selected from the group consisting of dielectrically isolated piezoresistors and resonant microbeams.  
     
     
         25 . The device of  claim 19 , wherein said micromechanical structure is a dual web biplane accelerometer formed by forming a said p+ layer on both sides of said substrate, forming a proof mask and flexure etching on both sides of said layer until said etching reaches said p+ layers.  
     
     
         26 . The device of  claim 25 , wherein said electronic component is selected from the group consisting of dielectrically isolated piezoresistors and resonant microbeams.  
     
     
         27 . The device of  claim 19 , wherein said micromechanical structure includes a dielectrically isolated piezoresistor formed on a top surface of a first wafer, a second wafer is bonded to said first wafer, and said second wafer forms a single crystal piezoresistor.  
     
     
         28 . A device produced according to the method of  claim 10 .  
     
     
         29 . The device of  claim 28 , wherein said boron content is greater than 1×10 20 cm   −3  and the germanium content is from about 0.5×10 21  cm −3  to about 2.0×10 21  cm −3 .  
     
     
         30 . The device of  claim 28 , wherein said micromechanical structure is a pressure sensor.  
     
     
         31 . The device of  claim 30 , wherein said electronic component is selected from the group consisting of dielectrically isolated piezoresistors and resonant microbeams.  
     
     
         32 . The device of  claim 23 , wherein said micromechanical structure is a cantilevered accelerometer.  
     
     
         33 . The device of  claim 32 , wherein said electronic component is selected from the group consisting of dielectrically isolated piezoresistors and resonant microbeams.  
     
     
         34 . The device of  claim 28 , wherein said micromechanical structure is a dual web biplane accelerometer formed by forming a said p+ layer or both sides of said substrate, forming a proof mask and flexure etching on both sides of said layer until said etching reaches said p+ layers.  
     
     
         35 . The device of  claim 34 , wherein said electronic component is selected from the group consisting of dielectrically isolated piezoresistors and resonant microbeams.  
     
     
         36 . The device of  claim 28 , wherein said micromechanical structure includes a dielectrically isolated piezoresistor formed on a top surface of a first wafer, a second wafer is bonded to said first wafer, and said second wafer forms a single crystal piezoresistor.