Asymmetric cyclic desposition etch epitaxy
The present disclosure relates to a method of forming an epitaxial layer through asymmetric cyclic deposition etch (CDE) epitaxy. An initial layer growth rate of one or more cycles of the CDE process are designed to enhance a crystalline quality of the epitaxial layer. A growth rate of the epitaxial material may be altered by adjusting a flow rate of one or more silicon-containing precursors within a processing chamber wherein the epitaxial growth takes place. An etch rate may also be altered by adjusting a temperature or partial pressure of one or more vapor etchants, or the temperature within the processing chamber. In some embodiments, an initial layer thickness that is greater than a critical thickness of the epitaxial material for strain relaxation is achieved with a low growth rate, followed by a high growth rate for the remainder of epitaxial growth. Other methods are also disclosed.
1. A method to form an epitaxial layer on a substrate within a processing chamber, comprising:
exposing the substrate to a continuous etchant flow of one or more vapor etchants to continuously and selectively remove amorphous portions of an epitaxial material from the substrate;
while exposing the substrate to the continuous etchant flow, providing first intermittent pulses of one or more source vapors to deposit a first layer of the epitaxial material on a surface of the substrate with a first growth rate; and
after providing the first intermittent pulses of the one or more source vapors, and while exposing the substrate to the continuous etchant flow, providing second intermittent pulses of the one or more source vapors to deposit the epitaxial material with a second growth rate, which is different than the first growth rate.
2. The method of claim 1 , wherein providing the first intermittent pulses comprises:
exposing the substrate to the one or more source vapors for a first duration;
determining a first thickness of the epitaxial material after the first duration;
determining the first growth rate of the epitaxial material from the first duration and the first thickness; and
exposing the substrate to the one or more source vapors with a first frequency selected to maintain the first growth rate until the first thickness is greater than or equal to a first threshold.
3. The method of claim 2 , wherein providing the second intermittent pulses comprises:
exposing the substrate to the one or more source vapors for a second duration;
determining second thickness of the epitaxial material after the second duration;
determining the second growth rate of the epitaxial material from the second duration, the first thickness, and the second thickness; and
periodically the substrate to the one or more source vapors with a second frequency selected to maintain the second growth rate until the second thickness is greater than or equal to a second threshold.
4. The method of claim 1 , wherein the first growth rate is changed to the second growth rate by adjusting an etch rate of the one or more vapor etchants.
5. The method of claim 4 , wherein adjusting the etch rate comprises changing a partial pressure of the one or more vapor etchants within the processing chamber.
6. The method of claim 1 , wherein the first growth rate is changed to the second growth rate by adjusting a flow rate of the one or more source vapors within the processing chamber.
7. The method of claim 1 , the one or more vapor etchants comprising chlorine (Cl 2 ), hydrogen chloride (HCl), monogermane (GeH 4 ), or a combination thereof.
8. The method of claim 1 , the one or more source vapors comprising silane (SiH 4 ), di-silane (Si 2 H 6 ), or trisilane (Si 3 H 8 ), or a combination thereof.
9. The method of claim 1 ,
wherein the first intermittent pulses are provided at a first frequency; and
wherein the second intermittent pulses are provided at a second frequency, which is greater than the first frequency.
10. The method of claim 3 , wherein the second duration is less than the first duration.
11. A method to form an epitaxial layer, comprising:
providing a substrate within a processing chamber;
exposing the substrate to a continuous etchant flow of one or more vapor etchants to selectively remove amorphous portions of an epitaxial material;
while exposing the substrate to the continuous etchant flow, providing first intermittent pulses of one or more source vapors to deposit a first layer comprising crystalline portions and amorphous portions of the epitaxial material on a top surface of the substrate, wherein the first intermittent pulses comprise a first frequency to achieve a first growth rate; and
after providing the first intermittent pulses of the one or more source vapors, and while exposing the substrate to the continuous etchant flow, providing second intermittent pulses of the one or more source vapors to deposit a second layer, comprising crystalline portions and amorphous portions of the epitaxial material, on a top surface of the first layer, wherein the second intermittent pulses comprise a second frequency, which is different from the first frequency to achieve a second growth rate, which is different than the first growth rate.
12. The method of claim 11 , wherein providing the first intermittent pulses comprises:
determining a first thickness of the first layer after a first duration;
determining the first growth rate of the first layer from the first thickness and the first duration; and
exposing the substrate to the first intermittent pulses of the one or more source vapors with the first growth rate until the first thickness is greater than or equal to a threshold thickness of the epitaxial material, which achieves strain relaxation within the epitaxial material.
13. The method of claim 12 , wherein the first growth rate is further changed to the second growth rate by adjusting:
an ambient temperature within the processing chamber;
an ambient pressure within the processing chamber;
a partial pressure of the one or more vapor etchants;
a partial pressure of the one or more source vapors;
a first flow rate of the one or more vapor etchants; or
a second flow rate of the one or more source vapors.
14. A method of forming a strained channel on a substrate within a processing chamber, comprising:
exposing the substrate to a continuous etchant flow of one or more vapor etchants to continuously and selectively remove amorphous portions of an epitaxial material from the substrate;
while exposing the substrate to the continuous etchant flow, providing first intermittent pulses of one or more source vapors at a first frequency to deposit a first layer of the epitaxial material on a top surface of the substrate with a first growth rate; and
adjusting an etch rate of the one or more vapor etchants while providing the first intermittent pulses of the one or more source vapors, to deposit a second layer of the epitaxial material on a top surface of the first layer with a second growth rate, which is different than the first growth rate.
15. The method of claim 14 , wherein adjusting the etch rate of the one or more vapor etchants comprises changing an ambient temperature within the processing chamber, an ambient pressure within the processing chamber, or a partial pressure of the one or more vapor etchants.
16. The method of claim 14 , further comprising:
after providing the first intermittent pulses of the one or more source vapors, and while exposing the substrate to the continuous etchant flow, providing second intermittent pulses of the one or more source vapors at a second frequency, which is different than the first frequency, to deposit the epitaxial material.
17. The method of claim 14 , wherein the second growth rate is greater than the first growth rate.
18. The method of claim 16 , wherein the first growth rate is changed to the second growth rate by adjusting:
a partial pressure of the one or more source vapors;
a first flow rate of the one or more vapor etchants; or
a second flow rate of the one or more source vapors.
19. The method of claim 14 , the one or more vapor etchants comprising chlorine (Cl 2 ), hydrogen chloride (HCl), monogermane (GeH 4 ), or a combination thereof.
20. The method of claim 14 , the one or more source vapors comprising silane (SiH 4 ), di-silane (Si 2 H 6 ), or trisilane (Si 3 H 8 ), or a combination thereof.