Semiconductor device strain relaxation buffer layer
A method for forming a semiconductor device comprises forming a first buffer layer with a first melting point on a substrate. A second buffer layer is formed on the first buffer layer. The second buffer layer has a second melting point that is greater than the first melting point. Annealing process is performed that increases a temperature of the first buffer layer such that the first buffer layer partially liquefies and causes a strain in the second buffer layer to be substantially reduced.
1. A method for forming a semiconductor device, the method comprising:
epitaxially growing a first buffer layer on a substrate, the first buffer layer having a first melting point;
epitaxially growing a second buffer layer on the first buffer layer, the second buffer layer having a second melting point, the second melting point greater than the first melting point;
removing a portion of the second buffer layer and the first buffer layer to expose a portion of the substrate and form a first portion of the second buffer layer and a second portion of the second buffer layer prior to performing an annealing process, wherein a layer of a first semiconductor material is formed on the first portion of the second buffer layer;
performing the annealing process at a temperature greater than or equal to the first melting point and less than the second melting point to partially liquefy the first buffer layer and cause a reduction in strain in the second buffer layer; and
cooling the first buffer layer below the first melting point.
2. The method of claim 1 , further comprising forming a layer of a second semiconductor material on the second portion of the second buffer layer following the forming the layer of the first semiconductor material.
3. The method of claim 1 , wherein the second buffer layer includes a first crystalline material.
4. The method of claim 1 , wherein the first buffer layer includes a second crystalline material.
5. The method of claim 1 , wherein the annealing process increases the temperature of the first buffer layer such that the temperature is at least equal to the first melting point and less than the second melting point.
6. The method of claim 1 , further comprising forming a layer of a first semiconductor material on the second buffer layer; and forming a gate stack on the first semiconductor material.
7. The method of claim 1 , wherein the second buffer layer is thicker than the first buffer layer.
8. The method of claim 1 , wherein forming the first buffer layer comprises epitaxially growing germanium on a silicon substrate, and forming the second buffer layer comprises epitaxially growing silicon-germanium on the first buffer layer.
9. A method for forming an active region of a semiconductor device, the method comprising:
epitaxially forming a first buffer layer on a substrate, the first buffer layer having a first melting point;
epitaxially forming a second buffer layer on the first buffer layer, wherein the first and second buffer layers have different lattice constants and wherein the second buffer layer is thicker than the first buffer layer;
performing an annealing process to selectively liquefy and reflow the first buffer layer relative to the second buffer layer to cause a strain reduction in the second buffer layer;
cooling the first buffer layer below the first melting point; and
forming a layer of a first semiconductor material on a first portion of the second buffer layer.
10. The method of claim 9 , further comprising forming a layer of a second semiconductor material on a second portion of the second buffer layer.
11. The method of claim 9 , wherein the second buffer layer includes a first crystalline material.
12. The method of claim 9 , wherein the first buffer layer includes a second crystalline material.
13. The method of claim 9 , further comprising forming a hardmask layer on the second buffer layer prior to performing the annealing process.
14. The method of claim 9 , wherein the first buffer layer has a melting point less than the second buffer layer, and wherein the annealing process increases a temperature of the first buffer layer such that the temperature is at least equal to the melting point of the first buffer layer and less than a melting point of the second buffer layer.
15. The method of claim 9 , wherein the first buffer layer includes germanium and the second buffer layer includes silicon germanium.
16. The method of claim 9 , further comprising removing a portion of the second buffer layer and the first buffer layer to expose a portion of the substrate prior to performing the annealing process.