Crystallization annealing processes for production of CIGS and CZTS thin-films
In one embodiment, a method includes depositing a chalcogenide precursor layer onto a substrate, and annealing the precursor layer in the presence of a gaseous phase comprising volatile species, the partial pressure of each volatile species being approximately constant over substantially all of the surface of the precursor layer, the partial pressure of each species being between approximately 0.1 mTorr and 760 Torr, where the presence of the gaseous phase reduces decomposition of volatile species from the precursor layer during annealing.
1. A method comprising:
depositing a precursor layer onto a substrate, the precursor layer comprising chalcogenide material with one or more volatile species; and
annealing the precursor layer in the presence of a gaseous phase comprising one or more of the volatile species, the partial pressure of each volatile species being approximately constant over substantially all of the surface of the precursor layer,
the partial pressure of each species being between approximately 0.1 mTorr and 760 Torr, wherein the presence of the gaseous phase reduces decomposition of the volatile species from the precursor layer during annealing.
2. The method of claim 1 , wherein annealing comprises:
generating a vacuum of approximately 1 mTorr to 0.001 mTorr;
heating the precursor layer to a first temperature of approximately 350 degrees Celsius to approximately 700 degrees Celsius at a rate of approximately 50 degrees Celsius/minute;
introducing the gaseous phase in the presence of the precursor layer, the partial pressure of each species of the gaseous phase being between approximately 0.1 mTorr and 760 Torr;
holding the precursor layer at the first temperature for approximately 5 minutes to approximately 120 minutes;
cooling the precursor layer to a second temperature below approximately 200 degrees Celsius at a rate of approximately 50 degrees Celsius/minute.
3. The method of claim 1 , wherein during annealing the rate of desorption of the volatile species from the precursor layer is approximately equal to the rate of absorption of the volatile species by the precursor layer from the gaseous phase.
4. The method of claim 1 , wherein the precursor layer comprises Cu, Zn, and Sn, and one or more of S or Se; and wherein the volatile species comprise one or more of Sn, S, or Se.
5. The method of claim 4 , wherein the precursor layer comprises Cu x Zn y Sn a (S z Se 1-z ), and wherein approximately 0.5≦x≦3, y=1, 0≦z≦1, 0.5≦α≦3, and 0≦β≦5.
6. The method of claim 1 , wherein the precursor layer comprises Cu, one or more of In or Ga, and one or more of S or Se; and wherein the volatile species comprise one or more of In, S, or Se.
7. The method of claim 6 , wherein the precursor layer comprises CU x (In y Ga( 1-y) ) α (S z Se 1-z )β, and wherein approximately 0.1≦x≦0.7, 0≦y≦1, 0≦z≦1, 0.3≦α≦0.8, and β=1.
8. The method of claim 1 , wherein the annealing is performed in a constrained volume.
9. The method of claim 1 , wherein the annealing is performed in a furnace.
10. The method of claim 9 , wherein during annealing, a temperature of the furnace walls is approximately 5 degrees Celsius to approximately 50 degrees Celsius greater than a temperature of the precursor layer, and wherein the volatile species from the gaseous phase preferentially deposits onto the precursor layer compared to the furnace walls.
11. The method of claim 1 , wherein the partial pressure of each component of the gaseous phase is kept approximately constant over substantially all of the surface of the precursor layer by controlling the inlet and outlet gas flow rates.
12. The method of claim 1 , wherein the partial pressure of each component of the gaseous phase is kept approximately constant over substantially all of the surface of the precursor layer by using a uniform vapor distribution system.
13. The method of claim 12 , wherein the uniform vapor distribution system comprises a heated gas path that prevents condensation of the volatile species from the gaseous phase.
14. The method of claim 1 , wherein the partial pressure of each component of the gaseous phase is kept approximately constant over substantially all of the surface of the precursor layer by controlling a reservoir temperature of a reservoir comprising the volatile species.
15. The method of claim 14 , wherein the reservoir temperature is greater than the melting point of the volatile species.
16. The method of claim 1 , wherein the partial pressure of each component of the gaseous phase is kept approximately constant over substantially all of the surface of the precursor layer for substantially all of the duration of the annealing.
17. The method of claim 1 , wherein the gaseous phase comprises gaseous sulfur, gaseous sulfur compounds, gaseous selenium, gaseous selenium compounds, or any combination thereof.
18. The method of claim 17 , wherein the gaseous sulfur IS at a partial pressure of approximately 10 mTorr to approximately 100 Torr.
19. The method of claim 17 , wherein the gaseous sulfur comprises S 2 gas, S 8 gas, or any combination thereof.
20. The method of claim 17 , wherein the gaseous sulfur compounds comprise H2S gas.
21. The method of claim 17 , wherein the gaseous selenium compounds comprise H 2 Se gas, SnS gas, or any combination thereof.
22. The method claim 1 , wherein the gaseous phase further comprises a carrier gas.
23. The method of claim 22 , wherein the carrier gas comprises one or more of Ar or N 2 .
24. The method of claim 22 , wherein the carrier gas is at a partial pressure of approximately 0.1 mTorr to approximately 760 Torr.