Method of fabricating an electromechanical structure including at least one mechanical reinforcing pillar

Abstract

The invention relates to a method of fabricating an electromechanical structure presenting a first substrate ( 1 ) including at least one layer ( 1 ′) of monocrystalline material covered in a sacrificial layer ( 2 ) that presents a free surface, the structure presenting at least one mechanical reinforcing pillar received in said sacrificial layer, the method being characterized in that it comprises: a) making at least one well region ( 51, 52 ) in the sacrificial layer ( 2 ) by etching, at least in the entire thickness of the sacrificial layer ( 2 ), the well region defining at least one said mechanical pillar; b) depositing a first functionalization layer ( 4, 31 ) of a first material, relative to which the sacrificial layer is suitable for being etched selectively, the functionalization layer ( 4 ) filling at least one well region ( 5 1 ) at least partially and covering the free surface of the sacrificial layer ( 2 ) at least around the well region(s); and b′) depositing a filler layer ( 6, 32 ) of a second material different from the first material for terminating the filling of the well region(s) ( 5 ′), said filler layer ( 6 ) covering the first functionalization layer ( 4 ) at least in part around the well region(s) ( 5 ′), and planarizing the filler layer ( 6, 32 ), the pillar(s) being formed by the superposition of at least the first material and the second material in the well region(s); and releasing the electromechanical structure by removing at least partially the sacrificial layer ( 2 ). The invention also relates to an electromechanical structure obtained by the method.

1 . A method of fabricating an electromechanical structure presenting a first substrate including at least one layer of monocrystalline material covered in a sacrificial layer that presents a free surface, the structure presenting at least one mechanical reinforcing pillar received in said sacrificial layer, wherein the method comprises:
 a) making at least one well region ( 51 ,  52 ) in the sacrificial layer ( 2 ) by etching, at least in the entire thickness of the sacrificial layer ( 2 ), the well region defining at least one said mechanical pillar;   b) depositing a first functionalization layer ( 4 ,  31 ) of a first material, relative to which the sacrificial layer is suitable for being etched selectively, the functionalization layer ( 4 ) filling at least one well region ( 51 ) at least partially and covering the free surface of the sacrificial layer ( 2 ) at least around the well region(s); and   b′) depositing a filler layer ( 6 ,  32 ) of a second material different from the first material for terminating the filling of the well region(s) ( 5   1 ), said filler layer ( 6 ) covering the first functionalization layer ( 4 ) at least in part around the well region(s) ( 5   1 ), and planarizing the filler layer ( 6 ,  32 ), the pillar(s) being formed by the superposition of at least the first material and the second material in the well region(s);   and releasing the electromechanical structure by removing at least partially the sacrificial layer ( 2 ).   
     
     
         2 . A method according to  claim 1 , wherein the monocrystalline material is selected from Si, Ge, quartz, or a perovskite. 
     
     
         3 . A method according to  claim 1 , wherein the filler layer is planarized until the first functionalization layer is reached. 
     
     
         4 . A method according to  claim 1 , also including:
 c) assembly with a second substrate opposite from the first substrate via an assembly surface of the first substrate.   
     
     
         5 . A method according to  claim 4 , wherein the second substrate presents an assembly surface covered in a bonding layer. 
     
     
         6 . A method according to  claim 1 , wherein prior to step c) it implements depositing a bonding layer on said assembly surface of the first substrate and/or on the second substrate, said layer forming an interface between the two substrates. 
     
     
         7 . A method according to  claim 6 , wherein the filler layer is planarized until the first functionalization layer is reached, and wherein a bonding layer of the second material is made on the first substrate prior to bonding. 
     
     
         8 . A method according to  claim 1 , wherein the first material is selected from: silicon nitride; doped or insulating polycrystalline Si; a metal; and a polymer. 
     
     
         9 . A method according to  claim 1 , wherein the second material is selected from: silicon oxide; doped or insulating polycrystalline Si; and a polymer. 
     
     
         10 . A method according to  claim 1 , including a step d) of etching the sacrificial layer through at least one through opening formed in the first substrate, in order to release the electromechanical structure. 
     
     
         11 . A method according to  claim 1 , wherein before or after step b′), it includes a step b″) of making at least one well in the first insulating layer, which well extends at least as far as the sacrificial layer, and depositing a conductive material at least in said well(s) in order to form at least one electrode. 
     
     
         12 . A method according to  claim 1 , including the first functionalization layer and a second functionalization layer, one of the functionalization layers being conducive and the other insulating, and in that between steps b) and b′), it includes a step b 0 ) of depositing the second functionalization layer, with the functionalization layer that is conductive forming a first interconnection level. 
     
     
         13 . A method according to  claim 12 , wherein the second functionalization layer is made of a third material selected from: silicon nitride; doped or insulating polysilicon Si; and a metal. 
     
     
         14 . A method according to  claim 13 , wherein the first functionalization layer covers a portion only of the well region(s), the other portion of the well regions being covered by the second functionalization layer, thereby enabling the conductive pillars and insulating pillars to be formed. 
     
     
         15 . A method according to  claim 12 , wherein the sacrificial layer is covered by both the first functionalization layer and the second functionalization layer, together. 
     
     
         16 . A method according to  claim 12 , wherein the second functionalization layer covers the entire surface of the sacrificial layer and of the third functionalization layer. 
     
     
         17 . A method according to  claim 1 , wherein the second material of the filler layer is selected to be identical to the material of the sacrificial layer. 
     
     
         18 . A method according to  claim 12 , wherein the first functionalization layer is insulating, the second functionalization layer is conductive, and in that after step b 0 ) it includes a step b′ 1 ) of depositing an insulating layer constituting a third functionalization layer. 
     
     
         19 . A method according to  claim 18 , wherein planarizing the filler layer continues until the third functionalization layer is reached. 
     
     
         20 . A method according to  claim 18 , wherein after step b′ 1 ), it includes a step b′ 2 ) of making at least one via in said third functionalization layer and of depositing a conductor at least in said via, said deposit forming a contact on the conductive second functionalization layer so as to form a second interconnection level. 
     
     
         21 . A method according to  claim 19 , including successively depositing additional functionalization layers alternatively of conductive material and of insulating material and making vias so as to form additional interconnection levels from the conductive layers. 
     
     
         22 . A method according to  claim 20 , wherein the last interconnection level covers the entire surface so as to make a ground plane. 
     
     
         23 . A method according to  claim 19 , wherein the last interconnection level is plane and includes interconnection areas to make it possible, during assembly with the second substrate, to connect elements of the second substrate to the electromechanical structure. 
     
     
         24 . An electromechanical structure presenting a first substrate presenting at least one monocrystalline layer, a sacrificial layer, and at least one mechanical reinforcing pillar received in the sacrificial layer, the structure being suitable for being fabricated by a method according to  claim 1 , and wherein at least one mechanical support region is a well region received at least in the entire thickness of the sacrificial layer, at least one said well region being covered in a first layer of a first mechanical support material and being filled with a second layer of a second mechanical support material, the pillar(s) being formed by superposing at least the first and second materials in the well region(s).