Method of fabricating a device with a concentration gradient and the corresponding device

1. A method, comprising:

forming, within a semiconductive substrate, at least one continuous region of an alloy having a composition with a non-uniformity extending in a direction substantially perpendicular to the thickness of the substrate; and

wherein forming the continuous region comprises:

forming a cavity in the substrate; and

forming a plurality of zones of a semiconductive alloy within the cavity, the zones having different compositions in said direction; and

wherein forming the plurality of zones comprises forming, at least on vertical walls of the cavity, a stack of layers of the semiconductive alloy having respectively different compositions of the semiconductive alloy, each layer in the stack having a first side edge directly adjacent a bottom surface of the cavity and a second side edge directly adjacent a top surface of the cavity.

2. The method according to claim 1 , wherein the semiconductive substrate further has a horizontal bottom surface.

3. The method according to claim 1 , wherein each layer zone extends at least partially in a direction substantially parallel to side walls of the cavity.

4. The method according to claim 1 , wherein each zone is formed of the semiconductive alloy in which the semiconductive alloy comprises silicon and germanium and each zone has a different ratio of silicon to germanium.

5. A method, comprising

forming, within a semiconductive substrate, at least one continuous region of a material having a composition with a non-uniformity extending in a direction substantially perpendicular to a thickness of the substrate; and

wherein forming the continuous region comprises forming a plurality of zones of a semiconductive alloy, the zones having different compositions in said direction; and

etching of a top surface of the zones of the continuous region, the etching having different characteristics depending on the composition.

6. A semiconductive device, comprising:

a semiconductive substrate having a cavity, and

at least one continuous region of an alloy having a composition with a non-uniformity extending in a direction substantially perpendicular to the thickness of the substrate filling the cavity to form a plurality of zones of a semiconductive alloy within the cavity, the zones having different compositions in said direction,

wherein the plurality of zones comprises a stack of layers, each layer in the stack having a first side edge directly adjacent a bottom surface of the cavity and a second side edge directly adjacent a top surface of the cavity.

7. The device according to claim 6 , in which the semiconductive alloy within the cavity has a gradual variation of composition extending across the cavity.

8. The device according to claim 6 , in which each zone is formed of the semiconductive alloy having a different composition.

9. The device according to claim 6 , in which the composition with the non-uniformity extends perpendicular to the top surface.

10. The device according to claim 6 , wherein the semiconductive alloy comprises silicon and germanium and each zone has a different ratio of silicon to germanium.

11. A semiconductor device, comprising:

a semiconductive substrate including a cavity formed in a top surface,

a stack of material layers provided in the cavity, the stack having a thickness extending through the layers of the stack which is parallel to the top surface of the semiconductive substrate, the stack having a side edge defining with the top surface of the semiconductive substrate a top face;

in which the side edge portion of the top face comprises a profile that is sloping relative to the top surface of the substrate.

12. The device according to claim 11 in which the side edge comprises a convex or concave profile.

13. A method, comprising

forming, within a semiconductive substrate, at least one continuous region of a material having a non-uniform composition in a direction substantially perpendicular to the thickness of the substrate, wherein forming the continuous region comprises depositing a plurality of conformal layers in a trench, each layer formed of an alloy material, and each alloy material layer having a gradually differing material concentration so as to form the non-uniform composition; and

etching a top surface of the deposited layers which fill the trench.

14. The method according to claim 13 , wherein the etching forms a top surface having one of a convex and a concave profile.