Method of making a transitor

Abstract

The invention relates to a method for manufacturing a transistor comprising the preparation of a stack of layers of the semiconductor on insulator type comprising at least one substrate on which an insulating layer and an initial semiconductor layer are successively disposed. The method includes the formation of at least one oxide pad extending from a top face of the insulating layer, the formation of an additional layer made from semiconductor material covering the oxide pad and intended to form a channel for the transistor, the formation of a gate stack above the oxide pad, and the formation of a source and drain on either side of the gate stack.

1 . A method for manufacturing a transistor on a stack of layers of the semiconductor on insulator type comprising at least one substrate on which an insulating layer and an initial semiconductor layer are successively disposed, wherein it comprises:
 the formation of at least one oxide pad extending from a top face of the insulating layer, the formation of at least one oxide pad comprising the following steps:
 the formation of at least one cavity in the initial semiconductor layer by etching; 
 the formation of a layer of oxide on the surface of said stack of layers of the semiconductor on insulator type, produced so that, in the bottom of the cavities, the film of oxide formed extends at least as far as the insulating layer; 
 a partial removal of the film of oxide so as to bare the initial semiconductor layer outside the cavity and to keep at least part of the film of oxide in the cavity in order to leave in place the oxide pad extending from the insulating layer; 
   the formation of an additional layer made from semiconductor material covering the oxide pad and intended to form a channel for the transistor;   the formation of a gate stack above the oxide pad;   the formation of a source and drain on either side of the gate stack.   
     
     
         2 . A method according to  claim 1 , wherein the formation of a source and drain is effected so as to form the source and drain at least partly in the cavity. 
     
     
         3 . A method according to  claim 1 , wherein the formation of a source and drain is effected so as to form the source and drain at least partly on either side of the oxide pad. 
     
     
         4 . A method according to  claim 1 , wherein the formation of the oxide pad is effected so that the width L of the oxide pad is greater than or equal to the width Lg of the gate stack. 
     
     
         5 . A method according to  claim 4 , wherein the gate stack is formed by lithography and wherein the formation of the oxide pad is effected so that: L≧Lg+2×Des, L being the width L of the oxide pad, Lg being the width of the gate stack and Des being the maximum imprecision of misalignment of the lithography. 
     
     
         6 . A method according to  claim 1 , comprising a step of formation of spacers on the flanks of the gate stack and wherein the formation of the oxide pad is effected so that: Lg+2×Lsp≧L, L being the width L of the oxide pad, Lg being the width of the gate stack and Lsp being the width of the spacers. 
     
     
         7 . A method according to  claim 1 , wherein the partial removal of the film of oxide effected so as to bare the initial semiconductor layer outside the cavity and to preserve at least part of the oxide film in the cavity comprises an etching step of the mechanical and chemical type with stoppage on the initial semiconductor layer. 
     
     
         8 . A method according to  claim 1 , wherein the additional layer of semiconductor material covering the oxide pad and intended to form a channel for the transistor is a layer of monocrystalline semiconductor material. 
     
     
         9 . A method according to  claim 1 , wherein the formation of the additional layer of semiconductor material covering the oxide pad and intended to form a channel for the transistor comprises the transfer of a layer of crystalline semiconductor material onto the oxide pad. 
     
     
         10 . A method according to  claim 9 , wherein the transfer of the additional layer of semiconductor material is effected by means of a method comprising a detachment of a thin film of monocrystalline semiconductor material by rupture of a thicker layer at a weakened region of a substrate of monocrystalline semiconductor material. 
     
     
         11 . A method according to  claim 1 , wherein the initial semiconductor layer is crystalline and wherein the formation of an additional layer of semiconductor material covering the oxide pad and intended to form a channel for the transistor comprises:
 the deposition of a layer of amorphous semiconductor material on the initial semiconductor material and the oxide pad,   heat treatment carried out so as to crystallise the layer of amorphous semiconductor material by solid-phase epitaxy from the initial semiconductor layer.   
     
     
         12 . A method according to  claim 1 , wherein the formation of a source and drain comprises the doping of the source and drain regions on either side of the gate stack. 
     
     
         13 . A method according to  claim 1 , wherein the formation of a source and drain comprises:
 an etching of at least the additional layer of semiconductor material so as to remove at least a portion of the thickness of the additional layer of semiconductor material that is not situated under the gate stack and so as to preserve at least part of the additional layer of semiconductor material at the channel of the transistor;   a growth of the source and drain regions by epitaxy from the semiconductor material remaining in place.   
     
     
         14 . A method according to  claim 13 , wherein the formation of a source and drain also comprises the doping of the source and drain regions during the step of growth of the source and drain regions by epitaxy. 
     
     
         15 . A method according to  claim 13 , wherein said etching of at least the additional layer of semiconductor material is an anisotropic etching wherein the favoured direction of etching is perpendicular to the plane of the substrate. 
     
     
         16 . A method according to  claim 13 , wherein said etching of at least the additional layer of semiconductor material removes, on either side of the gate stack, the entire thickness of the additional layer of semiconductor material and the entire thickness of the initial semiconductor layer. 
     
     
         17 . A method according to  claim 16 , wherein the growth of the source and drain regions by epitaxy is initiated from the semiconductor material forming the channel. 
     
     
         18 . A method according to  claim 13 , wherein said etching preserves, on either side of the gate stack, a film formed by at least a portion of the thickness of the initial semiconductor layer and optionally by a portion of the additional layer of semiconductor material. 
     
     
         19 . A method according to  claim 18 , wherein the growth of the source and drain regions by epitaxy is initiated at least by said film preserved on either side of the gate stack. 
     
     
         20 . A method according to  claim 1 , wherein the formation of at least one cavity is effected by etching of only part of the thickness of the initial semiconductor layer in the bottom of the cavities so as to preserve an uninterrupted semiconductor layer on the surface of the insulating layer. 
     
     
         21 . A method according to  claim 20 , wherein the formation of an oxide layer on the surface of said stack of layers of the semiconductor on insulator type is effected by oxidation of the initial semiconductor layer in order to form a continuous film of oxide on the uncovered surface of the initial semiconductor layer. 
     
     
         22 . A method according to  claim 1 , wherein the formation of at least one cavity is effected by etching of the whole of the thickness of the initial semiconductor layer in the bottom of the cavities. 
     
     
         23 . A method according to  claim 22 , wherein the formation of a layer of oxide on the surface of said stack of layers of the semiconductor on insulator type is effected by a deposition of oxide over the entire surface of said stack of layers. 
     
     
         24 . A method according to  claim 1 , wherein the formation of at least one cavity in the initial semiconductor layer by etching comprises, prior to the etching, a step of oxidation of the initial semiconductor layer in the regions to be etched and over a thickness corresponding to the thickness to be etched. 
     
     
         25 . A method according to  claim 1 , wherein the initial semiconductor layer is a layer of silicon, germanium, silicon-germanium or materials of the elements in columns III/V of the periodic classification of elements and wherein the additional layer of semiconductor material is a layer of silicon, germanium, silicon-germanium or materials of the elements in columns III/V of the periodic classification of elements. 
     
     
         26 . A method according to  claim 1 , wherein identical materials are provided for the initial semiconductor layer and the additional layer of semiconductor material. 
     
     
         27 . A method according to  claim 1 , wherein the insulating layer is a buried oxide layer in the stack of layers of the semiconductor on insulator type and wherein the initial semiconductor layer is the active layer in the stack of layers in the semiconductor on insulator type.