Local strain generation in an SOI substrate
Method to strain a channel zone of a transistor of the semiconductor on insulator type transistor that makes use of an SMT stress memorization technique in which regions located under the insulation layer of the substrate (FIG. 6 ) are amorphized, before the transistor gate is made.
1. A method for making a transistor with a strained channel on a semiconductor on insulator type substrate comprising a support layer, a surface semiconducting layer and an insulating layer separating the support layer and the surface semiconducting layer, the method comprising:
a) forming a stencil on the surface semiconducting layer provided with a plurality of openings, at least two openings in the stencil and at least one stencil block located between the two openings being arranged facing a first zone in the surface semiconducting layer in which a transistor channel is provided,
b) making regions in the support layer that are not protected by the stencil and are facing the openings and the first zone of the surface semiconducting layer amorphous, to keep at least one non-amorphised crystalline portion of the support layer, between two amorphous regions,
c) recrystallizing said amorphous regions to form recrystallised regions in the support layer, recrystallisation being made such that a mechanical strain is applied on the substrate during this recrystallisation through a stressor layer deposited on the substrate,
d) removing the stencil and the stressor layer,
e) forming a gate for the transistor on the first zone of the surface semiconducting layer, the gate facing the recrystallised regions.
2. The method according to claim 1 , wherein the stressor layer is deposited after the stencil has been formed and before recrystallisation.
3. The method according to claim 1 , wherein the stencil is based on a strained material, the stencil forming the stressor layer during step c).
4. The method according to claim 1 , wherein at least one opening in the stencil exposes a second zone of the surface semiconducting layer in which or on which a source or drain zone of the transistor is made or is to be made.
5. The method according to claim 1 , wherein the stencil blocks are elongated parallel blocks that extend along the direction of their length along a predetermined direction, this predetermined direction being orthogonal to a given axis passing through the first zone of the surface semiconducting layer, this axis being parallel to a direction along which a current is to be circulated in the first zone between a source zone and a drain zone of the transistor.
6. The method according to claim 5 , wherein in step a), the surface semiconducting layer is based on a strained semiconducting material, the mechanical strain applied by the stressor layer in step c) being a mechanical strain of the type opposite to the type of the mechanical strain of this material.
7. The method according to claim 6 , wherein in step a), the substrate is of the sSiGeOI ( strained Silicon Germanium On insulator ) type provided with an SiGe surface layer strained in biaxial compression, the mechanical strain applied in step c) by the stressor layer being a mechanical tension strain.
8. The method according to claim 1 , wherein the thickness of the surface semiconducting layer is less than 25 nm and the thickness of the insulating layer is less than 25 nm.
9. The method according to claim 1 , wherein the surface semiconducting layer is based on an III-V material.