Apparatus and methods for processing semiconductor substrates using supercritical fluids

• US 6,848,458 B1
• Filed: 02/05/2002
• Issued: 02/01/2005
• Est. Priority Date: 02/05/2002
• Status: Expired due to Fees

• Current Assignee: Novellus Systems Incorporated (Lam Research Corporation)
• Original Assignee: Novellus Systems Incorporated (Lam Research Corporation)
• Inventors: Reinhardt, Karen A., Shrinivasan, Krishnan, Gopinath, Sanjay, Juarez, Francisco, Banerjee, Souvik
• Primary Examiner(s): KORNAKOV, MIKHAIL
• Application Number:
  US10/067,520
• Time in Patent Office: 1,092 Days
• Field of Search: 134/103.1, 134/105, 134/107, 134/108, 134/109, 134/110, 134/184
• US Class Current: 134/108
• CPC Class Codes: B08B 7/0021 by liquid gases or supercritical fluids
• CPC Class Codes: H01L 21/67057 with the semiconductor substrates being dipped in baths or vessels
• CPC Class Codes: Y10S 134/902 Semiconductor wafer

Abstract

The present invention pertains to a system for cleaning wafers that includes specialized pressurization, process vessel, recirculation, chemical addition, depressurization, and recapture-recycle subsystems, as well as methods for implementing wafer cleaning using such a system. A solvent delivery mechanism converts a liquid-state sub-critical solution to a supercritical cleaning solution and introduces it into a process vessel that contains a wafer or wafers. The supercritical cleaning solution is recirculated through the process vessel by a recirculation system. An additive delivery system introduces chemical additives to the supercritical cleaning solution via the solvent delivery mechanism, the process vessel, or the recirculation system. Addition of chemical additives to the sub-critical solution may also be performed. The recirculation system provides efficient mixing of chemical additives, efficient cleaning, and process uniformity. A depressurization system provides dilution and removal of cleaning solutions under supercritical conditions. A recapture-recycle system introduces captured-purified solvents into the solvent delivery mechanism.

Claims

1. A system for cleaning semiconductor wafers, the system comprising:

a solvent delivery mechanism configured to provide a supercritical cleaning solution;

a process vessel in downstream fluid communication with the solvent delivery mechanism, said process vessel comprising a wafer support that includes;

a plurality of point contacts configured to support the wafer or plurality of wafers while making minimal contact with the wafer or plurality of wafers; and

a plurality of wafer guides configured to position the wafer plurality of wafers in the wafer support, wherein each of the plurality of wafer guides is inclined at an angle of between about 60 and 85 degrees to the vertical (perpendicular to the wafer support surface) and is arranged around the periphery of the wafer or each of the plurality of wafers; and

a recirculation system in fluid communication with the process vessel, said recirculation system comprising at least one flow distribution element configured to allow the supercritical cleaning solution to recirculate through the process vessel such that a flow field is established over at least one surface of a wafer or a plurality of wafers in the wafer support to thereby clean the surface or surfaces that contact the flow field.

2. The system of claim 1, wherein the solvent delivery mechanism comprises:

a source of a sub-critical cleaning solvent or a sub-critical cleaning solution in a liquid state;

an inlet configured to receive the sub-critical cleaning solvent or the sub-critical cleaning solution and deliver it to a supercritical solution generator configured to convert the sub-critical cleaning solvent or the sub-critical cleaning solution into the supercritical cleaning solution; and

an outlet configured to deliver the supercritical cleaning solution from the supercritical solution generator to the process vessel.

3. The system of claim 2, further comprising an additive delivery mechanism, said additive delivery mechanism configured to provide a chemical additive to at least one of the sub-critical cleaning solvent, the sub-critical cleaning solution, or the supercritical cleaning solution.

4. The system of claim 2, wherein the supercritical solution generator comprises:

a pump configured to pressurize the sub-critical cleaning solvent or the sub-critical cleaning solution to at least its critical point; and

a heat exchanger in fluid communication with the pump, said heat exchanger configured to heat the sub-critical cleaning solvent or the sub-critical cleaning solution to at least its critical temperature.

5. The system of claim 4, further comprising:

a pressure sensor configured to measure the pressure in the process vessel; and

a pressure controller configured to control the pressure in the process vessel in response to pressure information from the pressure sensor;

wherein control is achieved by adjustment of at least one of the pump and the heat exchanger.

6. The system of claim 4, wherein the solvent delivery mechanism further comprises a buffer vessel in downstream fluid communication with the heat exchanger, said buffer vessel capable of storing between about 5 and 25 times the volume of the supercritical cleaning solution than the volume of the process vessel.

7. The system of claim 6, further comprising:

a first pressure sensor configured to measure the pressure in the process vessel;

a flow control valve in downstream fluid communication with buffer vessel; and

a first pressure controller configured to control the pressure in the process vessel in response to pressure information from the first pressure sensor;

wherein control is achieved by adjustment of the flow control valve.

8. The system of claim 7, further comprising:

a second press sensor configured to measure the pressure in the buffer vessel; and

a second pressure controller configured to control the press in the buffer vessel in response to pressure information from the second pressure sensor;

wherein control is achieved by adjustment of at least one of the pump and the heat exchanger.

9. The system of claim 3, wherein the recirculation system comprises the additive delivery mechanism, said additive delivery mechanism configured to provide the chemical additive to the supercritical cleaning solution.

10. The system of claim 1, wherein the recirculation system comprises:

a pump configured to move the supercritical cleaning solution through the recirculation system;

an inline static mixer configured to provide a circuitous path to the supercritical cleaning solution.

11. The system of claim 10, wherein the recirculation system further comprises:

a first particulate filter in upstream fluid communication with the pump, said first particulate filter configured to remove particulates from the supercritical cleaning solution before said supercritical cleaning solution enters the pump; and

a second particulate filter in upstream fluid communication with the process vessel, said filter configured to remove particulates from the supercritical cleaning solution before said supercritical cleaning solution enters the process vessel.

12. The system of claim 11, wherein the recirculation further comprises a differential pressure transducer configured to measure the pressure in the recirculation system at a point upstream from the first particulate filter and at a point downstream from the second particulate filter.

13. The system of claim 12, wherein pressure information from the differential pressure transducer is used to control flow of the supercritical cleaning solution through the recirculation system.

14. The system of claim 1, wherein the recirculation system comprises isolation valves for stopping fluid communication of the recirculation system with the process vessel.

15. The system of claim 1, further comprising a depressurization system configured to vent the supercritical cleaning solution from the system.

16. The system of claim 15, wherein the depressurization system is configured to vent the supercritical cleaning solution from the process vessel.

17. The system of claim 15, wherein the depressurization system comprises a plurality of control valves in parallel fluid communication, said plurality of control valves comprising:

a first exhaust flow control valve configured to meter the release of the supercritical cleaning solution no faster than said supercritical cleaning solution can be introduced into the process vessel by the solvent delivery mechanism;

a second exhaust control valve having a higher flow coefficient than the first exhaust control valve; and

a dump valve having a higher flow coefficient than the second exhaust control valve.

18. The system of claim 15, further comprising a solvent recycle system in downstream fluid communication with the depressurization system, said solvent recycle system configured to capture vapor resulting from release of the supercritical cleaning solution by the depressurization system.

19. The system of claim 18, wherein the solvent recycle system is further configured to purify sub-critical media after capture to produce a recycled solvent.

20. The system of claim 19, wherein the solvent recycle system is further configured to deliver the recycled solvent to the solvent delivery mechanism for use in production of the supercritical cleaning solution.

21. The system of claim 19, wherein the solvent recycle system further comprises at least one of a filter, a distillation device, a liquid-gas separation device or a semi-permeable membrane to purify the sub-critical media.

22. The system of claim 1, wherein the process vessel comprises a first and a second plate, which when mated create a process cavity that encloses the wafer support.

23. The system of claim 22, wherein the process vessel comprises a corrosion resistant material.

24. The system of claim 23, wherein the corrosion resistant material comprises at least one of stainless steel, aluminum, titanium, hastelloy, and a nickel-iron alloy.

25. The system of claim 22, wherein the process cavity has a plurality of plenums configured to receive the supercritical cleaning solution from a process vessel inlet.

26. The system of claim 22, wherein the process vessel further comprises:

a slot configure to allow insertion of the wafer or the plurality of wafers into the process vessel; and

a door mechanism configured to seal the slot while the process vessel is charged with the supercritical solution.

27. The system of claim 26, wherein the door mechanism comprises a sealing mechanism configured to allow internal pressure in the process vessel to reinforce its sealing ability.

28. The system of claim 22, further comprising:

a primary seal configured to form a fluid-tight seal between the first and second plates when mated; and

a secondary seal configured to form a fluid-tight seal between the first and second plates when mated.

29. The system of claim 28, wherein the primary seal is a pressure-energized bore seal.

30. The system claim 28, wherein the primary seal is a spring-energized U-cup seal.

31. The system claim 28, wherein the secondary seal comprises two or more distinct sealing members.

32. The system of claim 28, wherein the secondary seal comprises at least one of a metal gasket, an elastomeric O-ring, a spring-energized U-cup, a T-seal, and a back-up seal.

33. The system of claim 28, wherein the primary and secondary seals comprise at least one of VITON™

, EPDM, silicone, KALREZ™

, CHEMREZ™

, polyurethane, fluoropolymer, aluminum, brass, copper, stainless steel, and nickel.

34. The system of claim 32, wherein the back-up seal comprises at least one of fiberglass-reinforced plastic, polyvinyl chloride, and Delrin.

35. The system of claim 25, further comprising a plurality of flow distribution manifolds each dimensioned to mate with one of the plurality of plenums, when mated, said plurality of plenums and flow distribution manifolds are configured to create the flow field.

36. The system of claim 35, wherein each of the plurality of flow distribution manifolds comprises a plurality of holes configured to direct flow of the supercritical cleaning solution from its corresponding plenum to the process cavity.

37. The system of claim 35, wherein each of the plurality of flow distribution manifolds comprises a plurality of grooves configured to direct the flow of the supercritical cleaning solution from its corresponding plenum and onto an interior surface of the process cavity before flowing onto said at least one surface of the wafer or plurality of wafer.

38. The system of claim 37, wherein each of the plurality of grooves comprises between about 8 and 72 grooves.

39. The system of claim 38, wherein the angular in between grooves is between about 5 and 45 degrees.

40. The system of claim 39, wherein the angle of tangency is between about 15 and 75 degrees.

41. The system of claim 35, wherein the plurality of flow distribution manifolds comprise at least one of stainless steel, hastalloy, aluminum, titanium, and nickel-iron alloys.

42. The system of claim 1, wherein the plurality of point contacts and wafer guides comprises at least one of quartz, ruby, sapphire, ceramic alumina, aluminum, and titanium.

43. The system of claim 1, wherein the wafer support comprises a wafer rotation mechanism, the wafer rotation mechanism configured to allow rotation of the wafer or plurality of wafers during processing.

44. The system of claim 43, wherein the wafer rotation mechanism comprises a magnetically coupled drive.

45. The system of claim 1, wherein the recirculation system is configured such that the flow field produces approximately equal fluid pressure and flow dynamics on both sides of the wafer or plurality of wafers.

46. The system of claim 1, wherein the process vessel comprises a heater configured to heat one or more walls of the process vessel.

47. The system of claim 1, wherein the recirculation system comprises a heater configured to maintain the temperature of the supercritical cleaning solution as it traverses the recirculation system.

48. The system of claim 3, wherein the process vessel comprises the additive delivery mechanism, said additive delivery mechanism configured to provide the chemical additive to the supercritical cleaning solution.

49. The system of claim 3, wherein the solvent delivery mechanism comprises the additive delivery mechanism, said additive delivery mechanism configured to provide the chemical additive to the supercritical cleaning solution.

50. The system of claim 3, wherein the recirculation system comprises the additive delivery mechanism, said additive delivery mechanism configured to provide the chemical additive to a solvent to produce the sub-critical cleaning solution.

51. The system of claim 3, wherein the additive delivery mechanism comprises a syringe pump configured to deliver a liquid to the supercritical cleaning solution without the supercritical cleaning solution losing its supercritical state.

52. The system of claim 6, wherein the buffer vessel comprises a heater configured to maintain the temperature of the supercritical cleaning solution in the buffer vessel.

53. The system of claim 1, further comprising a pulsing mechanism coupled to at least one of the recirculation system and the process vessel, said pulsing mechanism comprises to control the pressure of the supercritical cleaning solution to which the wafer or plurality of wafers are exposed in manner that provides a pulsed pressure distribution.

54. The system of claim 35, wherein the of plurality of flow distribution manifolds further comprises a plurality of contoured surfaces configured to mediate the flow field.

55. The system of claim 54, wherein the plurality of contoured surfaces comprises at least one of fins, chevrons, baffles, convexities, and concavities.

56. The system of claim 11, wherein the first and second particulate filters are self-cleaning filters.

57. The system of claim 35, wherein at least one of the plurality of flow distribution manifolds is a showerhead.

58. A system for cleaning semiconductor wafers, the system comprising:

a solvent delivery mechanism configured to provide a supercritical cleaning solution, wherein the solvent delivery mechanism comprises;

a source of a sub-critical cleaning solvent or a sub-critical cleaning solution in a liquid state;

an inlet configured to receive the sub-critical cleaning solvent or the sub-critical cleaning solution and deliver it to a supercritical solution generator configured to convert the sub-critical cleaning solvent or the sub-critical cleaning solution into the supercritical cleaning solution, wherein the supercritical solution generator comprises;

a pump configured to pressurize the sub-critical cleaning solvent or the sub-critical cleaning solution to at least its critical point; and

a heat exchanger in fluid communication with the pump, said heat exchanger configured to heat the sub-critical cleaning solvent or the sub-critical cleaning solution to at least its critical temperature;

an outlet configured to deliver the supercritical cleaning solution from the supercritical solution generator to a process vessel; and

a buffer vessel in downstream fluid communication with the heat exchanger;

the process vessel in downstream fluid communication with the solvent delivery mechanism, said process vessel comprising a wafer support; and

a recirculation fluid communication with the process vessel, said recirculation system comprising at least one flow distribution element configured to allow the supercritical cleaning solution to recirculate through the process vessel such that a flow field is established over at least one surface of a wafer or a plurality of wafers in the wafer support to thereby clean the surface or surfaces that contact the flow field;

wherein the buffer vessel is capable of storing between about 5 and 25 times the volume of supercritical solution that the process vessel can store.

59. A system for cleaning semiconductor wafers, the system comprising:

a solvent delivery mechanism configured to provide a supercritical cleaning solution;

a process vessel in downstream fluid communication with the solvent delivery mechanism, said process vessel comprising a wafer support; and

a recirculation system fluid communication with the process vessel, said recirculation system comprising;

at least one flow distribution element configured to allow the supercritical cleaning solution to recirculate through the process vessel such that a flow field is established over at least one surface of a wafer or a plurality of wafers in the wafer support to thereby clean the surface or surfaces that contact the flow field;

a pump configured to move the supercritical cleaning solution through the recirculation system;

an inline static mixer configured to provide a circuitous path to the supercritical cleaning solution

a first particulate filter in upstream fluid communication with the pump, said first particulate filter configured to remove particulates from the supercritical cleaning solution before said supercritical cleaning solution enters the pump;

a second particulate filter in upstream fluid communication with the process vessel, said filter configured to remove particulates from the supercritical cleaning solution before said supercritical cleaning solution enters the process vessel; and

a differential pressure transducer configured to measure the pressure in the recirculation system at a point upstream from the first particulate filter and at a point downstream from the second particulate filter.