Nanowire stack GAA device and methods for producing the same
The current disclosure describes techniques for forming a gate-all-around device where semiconductor layers are released by etching out the buffer layers that are vertically stacked between semiconductor layers in an alternating manner. The buffer layers stacked at different vertical levels include different material compositions, which bring about different etch rates with respect to an etchant that is used to remove at least partially the buffer layers to release the semiconductor layers.
1. A structure, comprising:
a substrate;
a vertical stack of semiconductor strips over the substrate, the vertical stack of semiconductor strips including:
a first semiconductor strip of a first semiconductor material;
a second semiconductor strip of the first semiconductor material, the second semiconductor strip being separated from the first semiconductor strip in a vertical direction;
first residual material on a lower surface of the first semiconductor strip having a first molar ratio between a second semiconductor material and the first semiconductor material; and
second residual material on a lower surface of the second semiconductor strip having a second molar ratio between the second semiconductor material and the first semiconductor material that is different from the first molar ratio;
a gate structure adjacent to a first portion of the first semiconductor strip and a first portion of the second semiconductor strip, the gate structure including:
a gate electrode; and
a gate dielectric layer extending along lateral sidewalls of the gate electrode;
a source/drain structure contacting a second portion of the first semiconductor strip and a second portion of the second semiconductor strip;
a first spacer layer laterally between the gate structure and the source/drain structure, and including:
a first spacer portion between the first semiconductor strip and the second semiconductor strip;
a second spacer portion above the vertical stack; and
a third spacer portion extending from the first spacer portion to the second spacer portion; and
a second spacer layer laterally between the gate structure and the first spacer layer;
wherein the first semiconductor strip includes a different thickness from that of the second semiconductor strip.
2. The structure of claim 1 , wherein the second portion of the first semiconductor strip substantially aligns vertically with the second portion of the second semiconductor strip.
3. The structure of claim 1 , wherein the gate structure wraps around the first portions of both the first semiconductor strip and the second semiconductor strip, separately.
4. The structure of claim 1 , wherein the second portions of the first semiconductor strip and the second semiconductor strip are edge portions that contact the source/drain structure in a lateral direction.
5. The structure of claim 1 , wherein the source/drain structure wraps around each of the second portions of the first semiconductor strip and the second semiconductor strip.
6. A structure, comprising:
a substrate;
a vertical stack of semiconductor strips over the substrate, the vertical stack of semiconductor strips including a first semiconductor strip of a first semiconductor material and a second semiconductor strip of the first semiconductor material, the second semiconductor strip separated from the first semiconductor strip in a vertical direction, the first semiconductor strip having a different thickness from that of the second semiconductor strip;
a gate structure surrounding a first portion of the first semiconductor strip and a first portion of the second semiconductor strip, the gate structure including:
a gate electrode; and
a gate dielectric layer along lower and lateral walls of the gate electrode;
a first dielectric layer having:
a lower portion surrounding a second portion of the first semiconductor strip and a second portion of the second semiconductor strip, the lower portion including facets between the first semiconductor strip and the second semiconductor strip; and
an upper portion over the lower portion;
a source/drain structure contacting the first semiconductor strip and the second semiconductor strip, the upper portion of the first dielectric layer laterally separating the source/drain structure from the gate structure; and
a second dielectric layer between the upper portion of the first dielectric layer and the gate dielectric layer.
7. The structure of claim 6 , wherein the second dielectric layer contacts the gate structure.
8. The structure of claim 6 , wherein the source/drain structure contacts an edge portion of each of the first semiconductor strip and the second semiconductor strip.
9. The structure of claim 6 , wherein the source/drain structure wraps around each of the first semiconductor strip and the second semiconductor strip.
10. The structure of claim 1 , wherein the second semiconductor strip is between the first semiconductor strip and the substrate, and the first semiconductor strip is thicker than the second semiconductor strip.
11. The structure of claim 10 , wherein:
the vertical stack further includes a third semiconductor strip and a fourth semiconductor strip;
the third semiconductor strip is between the second semiconductor strip and the substrate;
the fourth semiconductor strip is between the third semiconductor strip and the substrate;
the second semiconductor strip is thicker than the third semiconductor strip; and
the third semiconductor strip is thicker than the fourth semiconductor strip.
12. The structure of claim 6 , wherein the second semiconductor strip is between the first semiconductor strip and the substrate, and the second semiconductor strip is thicker than the first semiconductor strip.
13. The structure of claim 12 , wherein:
the vertical stack further includes a third semiconductor strip and a fourth semiconductor strip;
the third semiconductor strip is between the second semiconductor strip and the substrate;
the fourth semiconductor strip is between the third semiconductor strip and the substrate;
the third semiconductor strip is thicker than the second semiconductor strip; and
the fourth semiconductor strip is thicker than the third semiconductor strip.
14. A structure, comprising:
a substrate;
a vertical stack of semiconductor strips over the substrate, the vertical stack including:
a first semiconductor strip of a first semiconductor material; and
a second semiconductor strip of the first semiconductor material, the
second semiconductor strip between the first semiconductor strip and the substrate;
a gate structure surrounding a first portion of the first semiconductor strip and a first portion of the second semiconductor strip, the gate structure including:
a gate electrode;
a gate dielectric layer including a high-k dielectric material, wherein the gate dielectric layer separates the gate electrode from the vertical stack and extends along lateral sidewalls of the gate electrode; and
an interfacial layer, wherein the interfacial layer separates the gate dielectric layer including a high-k dielectric material from the vertical stack;
a first dielectric layer extending along lateral sidewalls of the gate dielectric layer, and including a first low-k dielectric material;
a source/drain structure contacting the first semiconductor strip and the second semiconductor strip, the first dielectric layer separating the source/drain structure from the gate structure; and
a second dielectric layer laterally between the first dielectric layer and the source/drain structure;
wherein a thickness of each of the first and second semiconductor strips varies in a consistent manner along a vertical direction.
15. The structure of claim 14 , wherein the first dielectric layer includes:
a first spacer portion between the first semiconductor strip and the second semiconductor strip;
a second spacer portion above the vertical stack;
a third spacer portion extending from the first spacer portion to the second spacer portion; and
a fourth spacer portion extending from the first spacer portion to the second spacer portion, wherein the first semiconductor strip separates the third spacer portion from the fourth spacer portion.
16. The structure of claim 14 , wherein the second dielectric layer—includes a second low k dielectric material.
17. The structure of claim 14 , wherein the interfacial layer is an interfacial silicon oxide layer.
18. The structure of claim 14 , wherein the gate dielectric layer wraps around the first semiconductor strip and the second semiconductor strip, and the gate electrode layer is adjacent three surfaces of the vertical stack.