Method for making a stressed structure designed to be dissociated

Abstract

The invention concerns a method of making a complex microelectronic structure by assembling two substrates through two respective linking surfaces, the structure being designed to be dissociated at a separation zone. The invention is characterized in that is consists, prior to assembly, in producing a state difference in the tangential stresses between the two surfaces to be assembled, said difference being selected so as to obtain in the assembled structure a predetermined stress state at the time of dissociation.

1 . A method of producing a complex structure, the structure being adapted to be dissociated in a separation region, the method comprising assembling two substrates at respective connecting faces thereof, wherein prior to assembly, a tangential stress state difference is created between the connecting faces by applying mechanical forces to curve each of the two substrates wherein the tangential stress state difference is selected to produce a predetermined stress state within the complex structure at the moment of dissociation.  
   
   
       2 . The method according to  claim 1 , wherein the tangential stress state difference between the connecting faces is selected to minimize the stresses in the separation region at the moment of dissociation.  
   
   
       3 . The method according to  claim 1 , further comprising curving the two substrates curved so that the connecting faces comprise respectively concave and convex faces.  
   
   
       4 . The method according to  claim 3 , wherein curving the two substrates comprises curving so that the connecting faces comprise complementary faces.  
   
   
       5 . The method according to  claim 4 , wherein curving the two substrates comprises curving so that the connecting faces comprise respectively spherical concave and spherical convex faces.  
   
   
       6 . The method according to  claim 1  wherein applying mechanical forces comprises creating a pressure difference between the connecting faces.  
   
   
       7 . The method according to  claim 6 , wherein creating a pressure difference between the connecting faces comprises aspirating one of the two substrates onto a concave preform having a suitable profile and imparting the profile to a face of the one substrate, and wherein the one substrate rests on the concave preform at its periphery.  
   
   
       8 . The method according to  claim 6 , wherein creating the pressure difference between the connecting faces comprises aspirating one of the two substrates into a cavity, the one substrate resting locally at its periphery on a seal bordering the cavity.  
   
   
       9 . The method according to  claim 1  wherein applying mechanical forces comprises deforming one of the two substrates between complementary first and second preforms, one of which is concave and the other of which is convex, and imparting selected profiles to the connecting face.  
   
   
       10 . The method according to  claim 9 , wherein the first complementary preform comprises the other of the two wherein the substrate is curved to have a selected profile.  
   
   
       11 . The method according to  claim 9 , wherein the second preform includes aspiration channels for keeping the one substrate curved when the first preform has been removed.  
   
   
       12 . The method according to  claim 1 , wherein applying mechanical forces comprises applying mechanical forces simultaneously to the two substrates by deforming the two substrates between two preforms having selected profiles to be imparted to the connecting faces.  
   
   
       13 . The method according to  claim 1 , wherein applying mechanical forces comprises applying mechanical forces to at least one of the substrates by means of a preform comprising a mold.  
   
   
       14 . The method according to  claim 13 , wherein the preform comprises a porous mold.  
   
   
       15 . The method according to  claim 1 , wherein applying mechanical forces comprises applying mechanical forces to the two substrates using at least one deformable preform.  
   
   
       16 . The method according to  claim 1 , wherein assembling the two substrates comprises molecular bonding.  
   
   
       17 . The method according to  claim 1  further comprising treating the connecting faces to facilitate bonding.  
   
   
       18 . The method according to  claim 1 , wherein the two substrates are assembled by direct contact, wherein the face of at least one of the two substrates is adapted to prevent air from being trapped between the connecting faces.  
   
   
       19 . The method according to  claim 18  further comprising piercing at least one of the two substrates.  
   
   
       20 . The method according to  claim 19 , wherein piercing at least one of the two substrates comprises piercing the substrate at its center.  
   
   
       21 . The method according to  claim 18  further comprising forming in at least one of the two substrates at least one dead-end channel discharging at the edge of the substrate.  
   
   
       22 . The method according to  claim 1 , wherein the two substrates are assembled by means of a flow layer.  
   
   
       23 . The method according to  claim 1  wherein the two substrates are assembled at a temperature higher than room temperature.  
   
   
       24 . The method according to  claim 23  further comprising heating the two substrates by contact with heated preforms.  
   
   
       25 . A method according to  claim 24 , wherein the preforms are heated to respective different temperatures.  
   
   
       26 . A method for transferring a thin layer from a source substrate to a target substrate comprising the following steps: 
 ionically implanting the source substrate through a face thereof to create a buried weakened layer at a particular depth relative to the face of the source substrate, a thin layer thereby being delimited between the face and the buried weakened layers;    curving each of the source substrate and the target substrate by applying mechanical forces to create a tangential stress state difference between the face of the source substrate and a face of the target substrate;    assembling the face of the source substrate to the face of the target substrate to form an assembled structure; and    dissociating the thin layer from a remainder of the source substrate,    wherein the tangential stress state difference is selected to produce a predetermined stress state within the assembled structure at the moment of dissociation.    
   
   
       27 . The method according to  claim 26 , wherein creating a tangential stress state difference between the faces comprises creating a tangential stress state difference to minimize internal stresses at the moment of dissociation.