Methods for forming a self-aligned contact via selective lateral etch
In some embodiments methods of processing a substrate include: providing a substrate having a contact structure formed on the substrate, wherein the contact structure comprises a feature defined by gate structures, a silicon nitride layer disposed on a upper surface of the gate structures and on sidewalls and a bottom of the feature, and an oxide layer disposed over the silicon nitride layer and filling the feature; etching an opening through the oxide layer to the silicon nitride layer disposed on the bottom of the opening, wherein a width of the opening is less than a width of the feature; expanding the opening in the oxide layer to form a tapered profile; exposing the substrate to ammonia and nitrogen trifluoride to form an ammonium fluoride gas that forms an ammonium hexafluorosilicate film on the oxide layer; and heating the substrate to a second temperature to sublimate the ammonium hexafluorosilicate film.
1. A method of processing a substrate, comprising:
(a) providing a substrate having a contact structure formed on the substrate, wherein the contact structure comprises a feature defined by gate structures, a silicon nitride layer disposed on a upper surface of the gate structures and on sidewalls and a bottom of the feature, and an oxide layer disposed over the silicon nitride layer, wherein the oxide layer fills the feature;
(b) etching an opening in the oxide layer, wherein the opening is formed through the oxide layer to the silicon nitride layer disposed on the bottom of the opening and wherein a width of the opening is less than a width of the feature;
(c) expanding the opening in the oxide layer to form a profile tapered toward a top surface of the substrate;
(d) exposing the substrate to a first process gas comprising ammonia and nitrogen trifluoride to form an ammonium fluoride (NH 4 F) gas, wherein the ammonium fluoride (NH 4 F) gas reacts with the oxide layer to form an ammonium hexafluorosilicate ((NH 4 ) 2 SiF 6 ) film on the oxide layer; and
(e) heating the substrate to a second temperature to sublimate the ammonium hexafluorosilicate ((NH 4 ) 2 SiF 6 ) film.
2. The method of claim 1 , further comprising etching the opening using a fluorine-containing process gas.
3. The method of claim 1 , wherein expanding the opening further comprises exposing the substrate to a second process gas.
4. The method of claim 3 , wherein expanding the opening further comprises applying a bias power to the substrate while exposing the substrate to the second process gas.
5. The method of claim 4 , wherein the second process gas is argon.
6. The method of claim 4 , wherein the bias power is applied at about 200 watts to about 1000 watts.
7. The method of claim 1 , wherein the opening has a top portion and a bottom portion and wherein a ratio of a diameter of the top portion to the bottom portion is about 5:1 to about 20:1.
8. The method of claim 1 , further comprising exposing the substrate to the first process gas at a temperature of less than about 50 degrees Celsius.
9. The method of claim 1 , further comprising repeating (d)-(e) for 3-5 cycles, wherein each cycle is performed for about 20 seconds.
10. The method of claim 1 , further comprising repeating (d)-(e) until the oxide layer is substantially etched from the sidewalls and bottom of the feature.
11. The method of claim 1 , wherein a ratio of ammonia and nitrogen trifluoride is about 1:1 to about 100:1.
12. The method of claim 1 , wherein the first process gas further comprises an inert gas.
13. The method of claim 12 , wherein the first process gas comprises greater than about 90% inert gas.
14. The method of claim 1 , wherein exposing the substrate to a first process gas further comprises providing radio frequency (RF) power to the first process gas to form a plasma.
15. The method of claim 1 , wherein the second temperature is greater than about 100 degrees Celsius to vaporize the ammonium hexafluorosilicate ((NH 4 ) 2 SiF 6 ) film.
16. A method of processing a substrate, comprising:
(a) providing a substrate having a contact structure formed on the substrate, wherein the contact structure comprises a feature defined by gate structures, a silicon nitride layer disposed on a upper surface of the gate structures and on sidewalls and a bottom of the feature, and an oxide layer disposed over the silicon nitride layer, wherein the oxide layer fills the feature;
(b) etching an opening in the oxide layer, wherein the opening is formed through the oxide layer to the silicon nitride layer disposed on the bottom of the opening and wherein a width of the opening is less than a width of the feature;
(c) expanding the opening in the oxide layer to form a profile tapered toward a top surface of the substrate by applying a bias power to the substrate while exposing the substrate to a second process gas;
(d) exposing the substrate to a first process gas comprising ammonia and nitrogen trifluoride to form an ammonium fluoride (NH 4 F) gas, wherein the ammonium fluoride (NH 4 F) gas reacts with the oxide layer to form an ammonium hexafluorosilicate ((NH 4 ) 2 SiF 6 ) film on the oxide layer;
(e) heating the substrate to a second temperature to sublimate the ammonium hexafluorosilicate ((NH 4 ) 2 SiF 6 ) film; and
(f) repeating (d)-(e) until the oxide layer is substantially etched from the sidewalls and bottom of the feature.
17. A computer readable medium, having instructions stored thereon which, when executed, cause a process chamber to perform a method of processing a substrate, the method comprising:
(a) providing a substrate having a contact structure formed on the substrate, wherein the contact structure comprises a feature defined by gate structures, a silicon nitride layer disposed on a upper surface of the gate structures and on sidewalls and a bottom of the feature, and an oxide layer disposed over the silicon nitride layer, wherein the oxide layer fills the feature;
(b) etching an opening in the oxide layer, wherein the opening is formed through the oxide layer to the silicon nitride layer disposed on the bottom of the opening and wherein a width of the opening is less than a width of the feature;
(c) expanding the opening in the oxide layer to form a profile tapered toward a top surface of the substrate;
(d) exposing the substrate to a first process gas comprising ammonia and nitrogen trifluoride to form an ammonium fluoride (NH 4 F) gas, wherein the ammonium fluoride (NH 4 F) gas reacts with the oxide layer to form an ammonium hexafluorosilicate ((NH 4 ) 2 SiF 6 ) film on the oxide layer; and
(e) heating the substrate to a second temperature to sublimate the ammonium hexafluorosilicate ((NH 4 ) 2 SiF 6 ) film.
18. The computer readable medium of claim 17 , wherein expanding the opening further comprises applying a bias power to the substrate while exposing the substrate to a second process gas.
19. The computer readable medium of claim 18 , wherein the second process gas is argon.
20. The computer readable medium of claim 18 , wherein the bias power is applied at about 200 watts to about 1000 watts.