Method for forming semiconductor device structure with protection layer

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

providing a substrate and a nanostructure stack, wherein the substrate has a base and a fin over the base, and the nanostructure stack is over the fin;

forming an isolation layer over the base and surrounding the fin;

forming a first protection layer over the nanostructure stack and the isolation layer;

forming a second protection layer over the first protection layer, wherein a top portion of the second protection layer is over the nanostructure stack, and the first protection layer and the second protection layer are made of different materials;

forming a mask layer over the second protection layer, wherein the top portion of the second protection layer protrudes from the mask layer;

thinning the top portion of the second protection layer, wherein the top portion becomes a thinned top portion after the top portion is thinned;

removing the mask layer;

removing the first protection layer and the second protection layer over the nanostructure stack; and

forming a gate stack wrapped around the nanostructure stack.

2 . The method for forming the semiconductor device structure as claimed in claim 1 , wherein the first protection layer is made of an oxide-containing material.

3 . The method for forming the semiconductor device structure as claimed in claim 1 , wherein the second protection layer is made of a nitride-containing material.

4 . The method for forming the semiconductor device structure as claimed in claim 1 , wherein the second protection layer has a sidewall portion over a sidewall of the nanostructure stack, and the top portion of the second protection layer is thicker than the sidewall portion before the top portion is thinned.

5 . The method for forming the semiconductor device structure as claimed in claim 1 , wherein the second protection layer is thicker than the first protection layer.

6 . The method for forming the semiconductor device structure as claimed in claim 1 , wherein the thinned top portion of the second protection layer is thicker than the first protection layer.

7 . The method for forming the semiconductor device structure as claimed in claim 1 , wherein the thinning of the top portion of the second protection layer comprises a physical etching process.

8 . The method for forming the semiconductor device structure as claimed in claim 7 , wherein the physical etching process comprises a plasma etching process.

9 . The method for forming the semiconductor device structure as claimed in claim 1 , wherein the thinned top portion of the second protection layer protrudes from the mask layer.

10 . The method for forming the semiconductor device structure as claimed in claim 1 , wherein a first bottom portion of the first protection layer and a second bottom portion of the second protection layer remain over the isolation layer after the first protection layer and the second protection layer over the nanostructure stack are removed, and the gate stack is over the first bottom portion of the first protection layer and the second bottom portion of the second protection layer.

11 . A method for forming a semiconductor device structure, comprising:

forming a protruding structure over a substrate;

forming an isolation layer surrounding a lower portion of the protruding structure;

forming a first protection layer over the protruding structure and the isolation layer;

forming a second protection layer over the first protection layer, wherein the second protection layer has a top portion and a lower portion, the top portion extends along a top of the protruding structure, and the lower portion extends along a sidewall of the protruding structure;

forming a mask layer over the second protection layer;

thinning the top portion of the second protection layer such that the top portion becomes a thinned top portion after the mask layer is formed;

removing the mask layer;

at least partially removing the first protection layer and the second protection layer to expose the top and the sidewall of the protruding structure; and

forming a gate stack over the protruding structure.

12 . The method for forming the semiconductor device structure as claimed in claim 11 , wherein the first protection layer and the second protection layer are made of different materials.

13 . The method for forming the semiconductor device structure as claimed in claim 11 , wherein the thinning of the top portion of the second protection layer is performed while the lower portion of the second protection layer is covered by the mask layer.

14 . The method for forming the semiconductor device structure as claimed in claim 11 , wherein the second protection layer has a bottom portion extending along a top of the isolation layer, and the bottom portion of the second protection layer is thicker than the lower portion of the second protection layer.

15 . The method for forming the semiconductor device structure as claimed in claim 11 , wherein the gate stack is formed to extend across an interface between the first protection layer and the second protection layer.

16 . A method for forming a semiconductor device structure, comprising:

forming a protruding structure over a substrate;

forming an isolation layer surrounding a lower portion of the protruding structure;

forming a protection layer over the protruding structure and the isolation layer, wherein a first portion of the protection layer over a top of the protruding structure is thicker than a second portion of the protection layer extending along a sidewall of the protruding structure;

thinning the first portion of the protection layer;

etching the protection layer after the first portion of the protection layer is thinned such that the top and the sidewall of the protruding structure are exposed; and

forming a gate stack over the protruding structure.

17 . The method for forming the semiconductor device structure as claimed in claim 16 , further comprising:

forming a second protection layer over the protruding structure and the isolation layer before the protection layer is formed, wherein the protection layer is thicker than the second protection layer.

18 . The method for forming the semiconductor device structure as claimed in claim 17 , wherein the protection layer contains nitrogen, and the protection layer and the second protection layer are made of different materials.

19 . The method for forming the semiconductor device structure as claimed in claim 16 , further comprising:

forming a mask layer laterally surrounding the second portion of the protection layer, where the first portion of the protection layer protrudes from a top of the mask layer; and

removing the mask layer after the thinning of the first portion of the protection layer.

20 . The method for forming the semiconductor device structure as claimed in claim 16 , wherein a remaining portion of the protection layer remains over the isolation layer after the etching of the protection layer, and the gate stack at least partially covers the remaining portion of the protection layer.