Megasonic cleaning using supersaturated cleaning solution
View Patent ↗A method and system for the megasonic cleaning of one or more substrates that reduces damage to the substrate(s) resulting from the megasonic energy. The substrates are supported in a process chamber and contacted with a cleaning solution comprising a cleaning liquid having carbon dioxide gas dissolved in the cleaning liquid in such amounts that the carbon dioxide gas is at a supersaturated concentration for the conditions within the process chamber. Megasonic energy is then transmitted to the substrate. The cleaning solution provides protection from damage resulting from the application of megasonic/acoustical energy. In another aspect, the invention is a system for carrying out the method. The invention is not limited to carbon dioxide but can be used in conjunction with any gas that, when so dissolved in a cleaning liquid, protects substrates from being damaged by the application of megasonic/acoustical energy.
1. A method of cleaning at least one substrate comprising:
(a) positioning a substrate in a process chamber having a gaseous environment with a first temperature and a first partial pressure for a first gas;
(b) providing a transmitter so that at least a portion of the transmitter is in close proximity to and spaced from a surface of the substrate;
(c) supplying a solution to the surface of the substrate so as to form a film of the solution on the surface of the substrate, the film being in contact with the portion of the transmitter the solution comprising a cleaning liquid and the first gas dissolved in the solution at a supersaturated concentration for the first temperature and the first partial pressure; and
(d) applying acoustical energy via the transmitter through the film of the solution and to the substrate.
2. The method of claim 1 wherein step (d) is completed before concentration of the first gas in the solution is lowered to a saturation concentration for the first temperature and the first partial pressure.
3. The method of claim 1 wherein the first gas is carbon dioxide.
4. The method of claim 3 wherein the supersaturated concentration of the carbon dioxide in the cleaning liquid is in the range of 50 to 2000 part per million.
5. The method of claim 4 wherein the supersaturated concentration of the carbon dioxide in the cleaning liquid is approximately 1000 parts per million.
6. The method of claim 1 further comprising, prior to step (c), creating the solution in a gaseous environment having a second temperature and a second partial pressure of the first gas by dissolving the first gas in the cleaning liquid in an amount such that the first gas is at or below a saturation concentration for the second temperature and the second partial pressure.
7. The method of claim 6 wherein the first gas is dissolved into the cleaning liquid through a membrane contactor.
8. The method of claim 1 wherein said substrate is a semiconductor wafer and steps (b)–(d) are performed subsequent to the wafer undergoing etching of lines or trenches of materials including poly silicon, metal or dielectric.
9. The method of 1 wherein the solution further comprises a second gas dissolved in the cleaning liquid.
10. The method of claim 9 wherein the first gas protects the substrate from damage resulting from the acoustical energy and the second gas promotes particle removal from the substrate.
11. The method of claim 9 wherein the second gas is dissolved in the cleaning liquid at a supersaturated concentration for the first temperature and a partial pressure of the gaseous environment of the process chamber for the second gas.
12. The method of claim 1 wherein the acoustical energy is megasonic energy.
13. The method of claim 1 wherein the process chamber at or near atmospheric pressure.
14. The method of claim 1 wherein the gaseous environment of the process chamber comprises air.
15. The method of claim 1 wherein the wafer is supported in the process chamber in a substantially horizontal orientation.
16. The method of claim 1 wherein step (d) is completed before the concentration of the first gas in the solution is lowered to a saturation concentration for the first temperature and first partial pressure; wherein the solution is created prior to step (c) by providing the liquid in a gaseous environment having a second temperature and a second partial pressure of the first gas and dissolving the first gas in the cleaning liquid in an amount such that the first gas is at or below a saturation concentration for the second temperature and second partial pressure; wherein the first gas is carbon dioxide; wherein the solution further comprises a second gas dissolved in the cleaning liquid that results in particle removal from the from the substrate; wherein steps (b)–(d) are performed subsequent to the substrate undergoing a metal line etch step; wherein the gaseous environment of the process chamber comprising air; and wherein pressure of the gaseous environment within the process chamber being at or near atmospheric pressure.
17. The method of claim 1 wherein the cleaning liquid is selected from a group consisting of deionized water, RCA solutions, dilute acids, dilute bases and semi-aqueous solvents.
18. The method of claim 1 wherein the transmitter comprises a linear edge, step (b) comprising providing the transmitter so that the linear edge is in close proximity to and spaced from the surface of the substrate, and step (c) comprising the film of the solution being in contact with the linear edge.
19. The method of claim of claim 18 wherein the linear edge is an elongated edge.
20. The method of claim 18 wherein step (b) comprises providing the transmitter so that the linear edge is substantially parallel to the surface of the substrate.
21. The method of claim 1 wherein the transmitter comprises an elongate forward portion, step (b) comprising providing the transmitter so that the elongate forward portion extends in close proximity to and spaced from the surface of the substrate and step (c) comprising the film of the solution being in contact with a portion of the elongate forward portion of the transmitter.
22. The method of claim 1 wherein the transmitter comprises a rod-like probe portion, step and step (c) comprising the film of the solution being in contact with a the rod-like probe portion.