System and method for selective etching of silicon nitride during substrate processing
View Patent ↗A system (FIG. 5 ) and methods for selectively etching silicon nitride in the presence of silicon oxide that provide high selectivity while stabilizing silicon oxide etch rates. The invention comprises a processing chamber ( 10 ), dispense lines ( 20, 21, 22 ), feed lines ( 30, 31, 32 ), a recirculation line ( 40 ), a process controller ( 200 ), a concentration sensor ( 50 ), a particle counter ( 55 ), and a bleed line ( 90 ). The invention dynamically controls the concentration ratio of the components of the etchant being used and/or dynamically controls the particle count within the etchant during the processing of the at least one substrate. As a result etchant bath life is increased and etching process parameters are more tightly controlled.
1. A method of etching silicon nitride from at least one substrate comprising:
providing a closed-loop circulation system having a process chamber and a recirculation line fluidly coupled to the process chamber;
supplying sulfuric acid, phosphoric acid, and water to the closed-loop circulation system in predetermined amounts so as to form a mixture having a predetermined concentration ratio and a predetermined volume, the mixture filling the process chamber and overflowing into the recirculation line;
submerging at least one substrate in the mixture within the process chamber;
circulating the mixture through the closed-loop circulation system;
continuously measuring concentration ratio of the mixture with a concentration sensor;
comparing the measured concentration ratio to the predetermined concentration value to determine whether the measured concentration value is within a predetermined range of the predetermined concentration ratio; and
upon determining that the measured concentration ratio is not within the predetermined range of the predetermined concentration ratio, automatically feeding a volume of sulfuric acid, phosphoric acid, and/or water into the closed-loop circulation system while bleeding a substantially equal volume of the mixture from the closed-loop circulation system to return the concentration ratio of the mixture back within the predetermined range, the feeding and the bleeding occurring during processing of the at least one substrate.
2. The method of claim 1 wherein the sulfuric acid, phosphoric acid, and water are initially supplied to the process chamber via dispense lines.
3. The method of claim 1 wherein the volume of sulfuric acid, phosphoric acid, and/or water added to the mixture during the feeding step are supplied via spike lines.
4. The method of claim 1 wherein the predetermined concentration ratio is approximately 2 parts sulfuric acid, 2 parts phosphoric acid, and 1 part water.
5. The method of claim 1 further comprising filtering the overflowed mixture.
6. The method of claim 1 further comprising:
continuously measuring particle counts in the mixture with a particle counter;
comparing the measured particle count to a predetermined particle count to determine whether the measured particle count is greater than the predetermined particle count; and
upon detecting the mixture having a particle count that is greater than the predetermined particle count, automatically bleeding a volume of the mixture from the closed-loop circulation system and feeding a substantially equal volume of sulfuric acid, phosphoric acid, and/or water into the closed-loop circulation system to return the particle count of the mixture back to or below the predetermined particle count, the feeding and bleeding occurring during processing of the at least one substrate.
7. The method of claim 1 wherein the mixture is circulated through the closed-loop circulation system during the feeding of sulfuric acid, phosphoric acid, and/or water into the closed-loop circulation system and during the bleeding of the mixture from the closed-loop circulation system.
8. The method of claim 1 further comprising heating the mixture prior to submerging the at least one wafer therein.
9. The method of claim 8 wherein the mixture is heated to a temperature at or near 160-180° C.
10. The method of claim 9 wherein the mixture is heated to a temperature at or near 165° C.
11. A method of etching silicon nitride from at least one substrate comprising:
(a) supplying sulfuric acid, phosphoric acid, and water to a process chamber in predetermined amounts so as to form a predetermined volume of mixture having a predetermined concentration ratio;
(b) circulating the mixture through the process chamber in a closed-loop circulation system;
(c) submerging at least one substrate in the mixture within the process chamber;
(d) bleeding a volume of mixture from the closed loop system so as to reduce the effect of etch-by-products in the circulating mixture; and
(e) feeding phosphoric acid, sulfuric acid, and/or water to replace the volume of mixture bled from the closed loop;
wherein the volume bled is selected to maintain or return the concentration ratio of the mixture to within a predetermined range of the predetermined concentration ratio; and
wherein the bleeding and feeding of steps (d) and (e) occur during processing of the at least one substrate.
12. The method of claim 11 wherein the bleeding and feeding of steps (d) and (e) are performed continuously or at set intervals.
13. The method of claim 11 further comprising:
(f) continuously measuring the concentration ratio of the mixture with a concentration sensor during processing of the at least one substrate;
(g) comparing the measured concentration ratio to the predetermined concentration value to determine whether the measured concentration value is within a predetermined range of the predetermined concentration ratio; and
(h) upon determining that the measured concentration ratio is not within the predetermined range of the predetermined concentration ratio, automatically performing steps (d) and (e).
14. The method of claim 11 wherein the mixture is circulated through the process chamber in the closed-loop circulation system during the bleeding and feeding of steps (d) and (e).
15. A method of etching silicon nitride from at least one substrate comprising:
providing a closed-loop circulation system having a process chamber and a recirculation line fluidly coupled to the process chamber;
supplying a predetermined volume of an etchant to the closed-loop circulation system, the etchant filling the process chamber and overflowing into the recirculation line;
submerging at least one substrate in the etchant within the process chamber;
circulating the etchant through the closed-loop circulation system;
continuously measuring particle count of the etchant with a particle counter;
upon detecting the etchant having a measured particle count above a predetermined particle count, automatically bleeding a volume of contaminated etchant from the closed-loop circulation system while replacing the volume by feeding fresh etchant into the closed-loop circulation system during the processing of the at least one substrate to return the particle count of the etchant within the closed-loop circulation system to or below the predetermined particle count.
16. The method of claim 15 wherein the etchant is circulated through the closed-loop circulation system during the bleeding of contaminated etchant from the closed-loop circulation system and during the feeding of fresh etchant into the closed-loop circulation system.