Spacer structure for semiconductor device

1. A method for forming a semiconductor device, comprising:

forming a vertical structure over a substrate;

forming a gate structure over a portion of the vertical structure;

exposing sidewalls of the portion of the vertical structure;

forming a plurality of spacers over the sidewalls of the portion of the vertical structure; and

forming a void in each of the plurality of spacers by selectively etching an inner portion of each of the plurality of spacers from an outer portion of each of the plurality of spacers.

2. The method of claim 1 , wherein forming the plurality of spacers comprises:

forming a plurality of recess structures over the sidewalls of the portion of the vertical structure;

forming a spacer material stack in each of the plurality of recess structures; and

annealing the spacer material stack to form an oxide layer over each spacer material stack.

3. The method of claim 1 , wherein forming the void comprises:

selectively etching a first portion of the plurality of spacers from a second portion of the plurality of spacers;

annealing the second portion of the plurality of spacers to form an oxide layer on an outer portion of each of the second portion of the plurality of spacers; and

selectively etching an inner portion of each of the second portion of the plurality of spacers from the oxide layer.

4. The method of claim 1 , wherein exposing the sidewalls of the portion of the vertical structure comprises:

masking the portion of the vertical structure using the gate structure; and

etching an other portion of the vertical structure.

5. The method of claim 1 , further comprising epitaxially growing an epitaxial region over the void in each of the plurality of spacers.

6. The method of claim 1 , further comprising replacing the gate structure with an other gate structure.

7. The method of claim 1 , wherein forming the void comprises forming a rectangular void.

8. The method of claim 1 , wherein forming the void comprises forming a void surrounded on four sides by a dielectric material.

9. The method of claim 1 , wherein forming the void in each of the plurality of spacers comprises forming voids having substantially equal volumes.

10. A method for forming a semiconductor device, comprising:

forming a vertical structure with alternating first and second nano-sheet layers in a portion of the vertical structure and over a substrate;

forming a gate structure over the portion of the vertical structure;

forming a recess structure in each of the second nano-sheet layers in the portion of the vertical structure;

forming a spacer material stack in the recess structure by:

depositing a dielectric layer over the recess structure to form an other recess structure: and

forming a sacrificial layer by depositing a silicon germanium alloy in the other recess structure and over the vertical structure; and

forming a void in the spacer material stack.

11. The method of claim 10 , wherein forming the recess structure comprises:

etching an other portion of the vertical structure to expose sidewalls of the portion of the vertical structure; and

etching a portion of the second-nano-sheet layers from the portion of the vertical structure.

12. The method of claim 10 , wherein forming the spacer material stack comprises:

exposing the first nano-sheet layers in the portion of the vertical structure;

depositing the spacer material stack in the recess structure; and

annealing the spacer material stack to form an oxide layer on the recess structure.

13. The method of claim 10 , wherein forming the void comprises:

removing a portion of the spacer material stack adjacent to the gate structure; and

covering the recess structure with an other portion of the spacer material stack away from the gate structure to form an opening in the recess structure.

14. The method of claim 13 , wherein removing the portion of the spacer material stack comprises selectively etching the portion of the spacer material stack from the other portion of the spacer material stack using a hydrogen chloride gas.

15. The method of claim 10 , further comprising:

masking the void with the spacer material stack; and

epitaxially growing an epitaxial region over sidewalls of the portion of the vertical structure.

16. A method, comprising:

forming a stack of nano-sheets on a substrate;

patterning the stack of nano-sheets to form a vertical structure;

forming, around the vertical structure, a sacrificial gate having a sidewall spacer;

recessing portions of the sidewall spacer to expose corresponding portions of the nano-sheets; and

forming an inner spacer on the exposed portions of the nano-sheets, wherein forming the inner spacer comprises:

forming a dielectric layer in contact with the vertical structure;

forming a void structure adjacent to the dielectric layer;

forming an other dielectric layer in contact with a source/drain region; and

enclosing the void structure by the other dielectric layer on one side of the void structure and the dielectric layer on three sides of the void structure.

17. The method of claim 16 , further comprising filling the void structure with air to form an air spacer structure between the dielectric layer and the other dielectric layer.

18. The method of claim 16 , wherein the void structure has length, width, and height dimensions in a range of about 1 nm to about 8 nm.

19. The method of claim 16 , wherein forming the void structure comprises forming the inner spacer having an overall dielectric constant of less than about 3.5.

20. The method of claim 16 , wherein the source/drain region extends below the nano-sheets into a base region of the vertical structure.