Selectively etching for nanowires

1. A method for selectively etching layers of a first material with respect to layers of a second material in a stack, wherein layers of the first material alternate with layers of the second material, comprising:

partially etching the layers of the first material with respect to the layers of the second material;

selectively depositing a deposition layer on the stack, wherein portions of the deposition layer covering the layers of the second material are thicker than portions of the deposition layer covering the layers of the first material, the selectively depositing comprising:

providing a first reactant, wherein some of the first reactant deposits on the stack;

purging some of the first reactant, wherein some undeposited first reactant is not purged; and

providing a second reactant, wherein the undeposited first reactant combines with the second reactant, wherein the combined undeposited first reactant and second reactant selectively deposits on the layers of the second material with respect to the layers of the first material, and wherein some of the second reactant reacts with the deposited first reactant to form part of the deposition layer; and

selectively etching the layers of the first material with respect to the layers of the second material to completely remove the layers of the first material, wherein the layers of the second material are protected by the deposition layer.

2. The method, as recited in 1 , wherein the undeposited first reactant combined with the second reactant selectively deposits on the layers of the second material with respect to the layers of the first material to provide the deposition layer that is nonconformal.

3. The method, as recited in claim 1 , wherein the first material is SiGe and the second material is Si.

4. A method for selectively etching layers of a first material with respect to layers of a second material in a stack, wherein layers of the first material alternate with layers of the second material, wherein the first material is SiGe and the second material is Si, comprising:

partially etching the layers of the first material with respect to the layers of the second material;

selectively depositing a deposition layer on the stack, wherein portions of the deposition layer covering the layers of the second material are thicker than portions of the deposition layer covering the layers of the first material, the selectively depositing comprising:

providing a first reactant, wherein some of the first reactant deposits on the stack:

purging some of the first reactant, wherein some undeposited first reactant is not purged; and

providing a second reactant, wherein the undeposited first reactant combines with the second reactant, wherein the combined undeposited first reactant and second reactant selectively deposits on the layers of the second material with respect to the layers of the first material, and wherein some of the second reactant reacts with the deposited first reactant to form part of the deposition layer; and

selectively etching the layers of the first material with respect to the layers of the second material to completely remove the layers of the first material, wherein the layers of the second material are protected by the deposition layer, wherein the selectively etching the layers of the first material with respect to the layers of the second material comprises providing an atomic layer etch process.

5. The method, as recited in claim 4 , wherein the atomic layer etch process comprises a plurality of cycles, wherein each cycle comprises:

an oxidation phase, wherein the oxidation phase selectively oxidizes the layers of the second material with respect to the layers of the first material; and

an etch phase with selectively etches the layers of the first material with respect to the oxidized layers of the second material.

6. The method, as recited in claim 1 , wherein the selectively etching the layers of the first material with respect to the layers of the second material to completely remove the layers of the first material, comprises:

selectively etching the layers of the first material with respect to the layers of the second material;

selectively depositing a deposition layer on the stack, wherein portions of the deposition layer covering the layers of the second material are thicker than portions of the deposition layer covering the layers of the first material; and

selectively etching the layers of the first material with respect to the layers of the second material.

7. The method, as recited in claim 1 , wherein the selectively etching the layers of the first material with respect to the layers of the second material to completely remove the layers of the first material comprises selectively etching the layers of the first material with respect to the layers of the second material without selectively depositing a deposition layer on the stack.

8. A method for selectively etching layers of a first material with respect to layers of a second material in a stack, wherein layers of the first material alternate with layers of the second material, comprising:

partially etching the layers of the first material with respect to the layers of the second material, wherein the partially etching the layers of the first material with respect to the layers of the second material comprises:

providing an etch gas; and

transforming the etch gas into a plasma, wherein the plasma selectively etches the layers of the first material with respect to the layers of the second material to create recessed layers of the first materials;

selectively depositing a deposition layer on the stack, wherein portions of the deposition layer covering the layers of the second material are thicker than portions of the deposition layer covering the layers of the first material, the selectively depositing comprising:

providing a first reactant, wherein some of the first reactant deposits on the stack;

purging some of the first reactant, wherein some undeposited first reactant is not purged; and

providing a second reactant, wherein the undeposited first reactant combines with the second reactant, wherein the combined undeposited first reactant and second reactant selectively deposits on the layers of the second material with respect to the layers of the first material, and wherein some of the second reactant reacts with the deposited first reactant to form part of the deposition layer; and

selectively etching the layers of the first material with respect to the layers of the second material to completely remove the layers of the first material, wherein the layers of the second material are protected by the deposition layer.

9. A method for selectively etching layers of a first material with respect to layers of a second material in a stack, wherein layers of the first material alternate with layers of the second material, comprising:

partially etching the layers of the first material with respect to the layers of the second material, wherein the partially etching the layers comprises providing an atomic layer etch process;

selectively depositing a deposition layer on the stack, wherein portions of the deposition layer covering the layers of the second material are thicker than portions of the deposition layer covering the layers of the first material, the selectively depositing comprising:

providing a first reactant, wherein some of the first reactant deposits on the stack;

purging some of the first reactant, wherein some undeposited first reactant is not purged; and

providing a second reactant, wherein the undeposited first reactant combines with the second reactant, wherein the combined undeposited first reactant and second reactant selectively deposits on the layers of the second material with respect to the layers of the first material, and wherein some of the second reactant reacts with the deposited first reactant to form part of the deposition layer; and

selectively etching the layers of the first material with respect to the layers of the second material to completely remove the layers of the first material, wherein the layers of the second material are protected by the deposition layer.

10. The method, as recited in claim 9 wherein the atomic layer etch process comprises a plurality of cycles, wherein each cycle comprises:

an oxidation phase, wherein the oxidation phase selectively oxidizes the layers of the second material with respect to the layers of the first material; and

an etch phase, wherein the etch phase selectively etches the layers of the first material with respect to the oxidized layers of the second material.

11. A method for selectively etching layers of a first material with respect to layers of a second material in a stack, wherein layers of the first material alternate with layers of the second material, wherein the first material is Si and the second material is SiGe, comprising:

partially etching the layers of the first material with respect to the layers of the second material;

selectively depositing a deposition layer on the stack, wherein portions of the deposition layer covering the layers of the second material are thicker than portions of the deposition layer covering the layers of the first material, the selectively depositing comprising:

providing a first reactant, wherein some of the first reactant deposits on the stack;

purging some of the first reactant, wherein some undeposited first reactant is not purged; and

providing a second reactant, wherein the undeposited first reactant combines with the second reactant, wherein the combined undeposited first reactant and second reactant selectively deposits on the layers of the second material with respect to the layers of the first material, and wherein some of the second reactant reacts with the deposited first reactant to form part of the deposition layer; and

selectively etching the layers of the first material with respect to the layers of the second material to completely remove the layers of the first material, wherein the layers of the second material are protected by the deposition layer.

12. A method for selectively etching layers of a first material with respect to layers of a second material in a stack, wherein layers of the first material alternate with layers of the second material, comprising:

partially etching the layers of the first material with respect to the layers of the second material;

selectively depositing a deposition layer on the stack, wherein portions of the deposition layer covering the layers of the second material are thicker than portions of the deposition layer covering the layers of the first material, the selectively depositing comprising:

providing a first reactant, wherein some of the first reactant deposits on the stack;

purging some of the first reactant, wherein some undeposited first reactant is not purged; and

providing a second reactant, wherein the undeposited first reactant combines with the second reactant, wherein the combined undeposited first reactant and second reactant selectively deposits on the layers of the second material with respect to the layers of the first material, and wherein some of the second reactant reacts with the deposited first reactant to form part of the deposition layer, wherein the first reactant is a silicon containing precursor and the second reactant is an oxidizing gas, wherein the undeposited first reactant is an undeposited silicon containing precursor, wherein the undeposited silicon containing precursor reacts with the oxidizing gas to form undeposited silicon oxide, wherein the undeposited silicon oxide selectively deposits on the layers of the second material; and

selectively etching the layers of the first material with respect to the layers of the second material to completely remove the layers of the first material, wherein the layers of the second material are protected by the deposition layer.

13. A method for selectively etching silicon germanium with respect to silicon in a stack, wherein at least one layer of silicon germanium is between two layers of silicon, comprising:

partially etching the silicon germanium with respect to silicon;

coating the stack with a selective deposition process, wherein the selective deposition process deposits more on silicon than silicon germanium, the selective deposition process comprising:

providing a silicon precursor, wherein some of the silicon precursor deposits on the stack;

purging some of the silicon precursor, wherein some undeposited silicon precursor remains;

providing an oxidizing gas, wherein the undeposited silicon precursor combines with the oxidizing gas to form undeposited silicon oxide, wherein the undeposited silicon oxide nonconformally and preferentially deposits on silicon with respect to the silicon germanium, and wherein some of the oxidizing gas oxidizes the deposited silicon precursor to transform the deposited silicon precursor into silicon oxide; and

selectively etching silicon germanium with respect to the silicon oxide to completely remove the silicon germanium.

14. The method, as recited in claim 13 , wherein the partially etching the silicon germanium with respect to the silicon, comprises:

providing an etch gas; and

transforming the etch gas into a plasma, wherein the plasma selectively etches the layers of the first material with respect to the layers of the second material to create recessed layers of the first material.

15. The method, as recited in claim 13 , wherein the partially etching the silicon germanium with respect to the silicon comprises providing an atomic layer etch process, the atomic layer etch process comprising:

an oxidation phase, wherein the oxidation phase selectively oxidizes the silicon forming silicon oxide with respect to the silicon germanium; and

an etch phase, wherein the etch phase selectively etches the silicon germanium with respect to the silicon oxide.

16. A method for selectively etching silicon with respect to silicon germanium in a stack, wherein at least one layer of silicon is between two layers of silicon germanium, comprising:

partially etching the silicon with respect to the silicon germanium;

coating the stack with a selective deposition process, wherein the selective deposition process deposits more on silicon germanium than silicon, the selective deposition process comprising:

providing a silicon precursor, wherein some of the silicon precursor deposits on the stack;

purging some of the silicon precursor, wherein some undeposited silicon precursor remains;

providing an oxidizing gas, wherein the undeposited silicon precursor combines with the oxidizing gas to form undeposited silicon oxide, wherein the undeposited silicon oxide nonconformally and preferentially deposits on the silicon germanium with respect to the silicon, and wherein some of the oxidizing gas oxidizes the deposited silicon precursor to transform the deposited silicon precursor into silicon oxide; and

selectively etching the silicon with respect to the silicon oxide to completely remove the silicon.

17. The method, as recited in claim 16 , wherein the partially etching the silicon with respect to the silicon germanium comprises:

providing an etch gas comprising a fluorocarbon and hydrogen; and

transforming the etch gas into a plasma, wherein the plasma selectively etches the silicon with respect to the silicon germanium.

18. The method, as recited in claim 17 , wherein the etch gas further comprises a sulfur containing component.