Structures with doped semiconductor layers and methods and systems for forming same
Methods and systems for depositing material, such as doped semiconductor material, are disclosed. An exemplary method includes providing a substrate, forming a first doped semiconductor layer overlying the substrate, and forming a second doped semiconductor layer overlying the first doped semiconductor layer, wherein the first doped semiconductor layer comprises a first dopant and a second dopant, and wherein the second doped semiconductor layer comprises the first dopant. Structures and devices formed using the methods and systems for performing the methods are also disclosed.
1. A method of forming a structure, the method comprising the steps of:
providing a monocrystalline substrate within a reaction chamber;
using a chlorine-free precursors, epitaxially forming a first doped semiconductor layer overlying the substrate; and
epitaxially forming a second doped semiconductor layer overlying the first doped semiconductor layer,
wherein the first doped semiconductor layer comprises a first dopant and a second dopant,
wherein the second doped semiconductor layer comprises the first dopant;
wherein the first doped semiconductor layer is selectively formed on a first portion of a surface of the substrate; and,
wherein the second doped semiconductor layer is selectively formed overlying the first doped semiconductor layer
wherein a concentration of carbon is greater in the first doped semiconductor layer than in the second doped semiconductor layer.
2. The method of claim 1 , wherein the first dopant comprises a first p-type dopant.
3. The method of claim 1 , wherein the second dopant comprises a second p-type dopant.
4. The method of claim 1 , wherein the first dopant comprises boron and the second dopant comprises gallium.
5. The method according to claim 1 wherein the first doped semiconductor layer comprises p-type silicon germanium.
6. The method according to claim 1 wherein the second doped semiconductor layer comprises p-type silicon germanium.
7. The method according to claim 1 wherein the second doped semiconductor layer comprises p-type germanium.
8. The method of claim 1 , further comprising a step of epitaxially forming a cap layer overlying the second doped semiconductor layer, the cap layer comprising at least one of silicon and germanium.
9. The method of claim 5 wherein the cap layer further comprises a p-type dopant selected from boron and gallium.
10. The method according to claim 1 wherein the second doped semiconductor layer does not comprise the second dopant.
11. The method according to claim 1 wherein the first portion comprises monocrystalline silicon.
12. The method according to claim 1 wherein forming the first doped semiconductor layer comprises providing a silicon precursor, a germanium precursor, a boron precursor, and a gallium precursor to the reaction chamber.
13. The method according to claim 12 , wherein forming the second doped semiconductor layer comprises providing a germanium precursor to the reaction chamber.
14. The method according to claim 13 , wherein forming the second doped semiconductor layer further comprises providing a boron precursor to the reaction chamber.
15. The method according to claim 14 , wherein forming the second doped semiconductor layer further comprises providing a gallium precursor to the reaction chamber.
16. The method according to claim 14 , wherein forming the second doped semiconductor layer further comprises providing a silicon precursor to the reaction chamber.
17. A structure formed according to the method of claims 1 ,
wherein the first doped semiconductor layer more than 5×10 20 at/cm 3 boron;
wherein the first doped semiconductor layer comprises between about 10 at % and about 90 at % silicon;
wherein the first doped semiconductor layer comprises between about 10 at % and about 90 at % germanium;
wherein a thickness of the first doped semiconductor layer is between about 1 nm and about 50 nm;
wherein a thickness of the second doped semiconductor layer is between about 1 nm and about 50 nm;
wherein the first doped semiconductor layer comprises between at least 1×10 20 at/cm 3 gallium; and,
wherein the second doped semiconductor layer comprises at least 5×10 20 at/cm 3 boron.
18. The structure of claim 17 , wherein a concentration of the second dopant in the first doped semiconductor layer is higher near a top surface relative to bulk first doped semiconductor layer material.
19. The structure of claim 17 , further comprising an epitaxially-formed cap layer.