Supercritical fluid cleaning process for precision surfaces

• US 20020014257A1
• Filed: 05/18/2001
• Published: 02/07/2002
• Est. Priority Date: 08/05/1999
• Status: Active Grant

• Current Assignee: SC Fluids, Inc.
• Original Assignee: SC Fluids, Inc.
• Inventors: Jafri, Ijaz H., Boyd, Jim, Moritz, Heiko D., Costantini, Michael A., Heathwaite, Rick M., Chandra, Mohan, Mount, David J.
• Granted Patent: US 6,602,349 B2
• Time in Patent Office: Days
• US Class Current: 134/19
• CPC Class Codes: B01J 3/008 Processes carried out under supercritical conditions
• CPC Class Codes: B01J 3/06 Processes using ultra-high pressure, e.g. for the formation of diamonds; Apparatus therefor, e.g. moulds or dies B01J3/04 takes precedence
• CPC Class Codes: B08B 7/0021 by liquid gases or supercritical fluids
• CPC Class Codes: H01L 21/67034 for drying
• CPC Class Codes: H01L 21/67126 Apparatus for sealing, encapsulating, glassing, decapsulating or the like processes H01L23/02, H01L23/28
• CPC Class Codes: Y02P 20/54 using solvents, e.g. supercritical solvents or ionic liquids
• CPC Class Codes: Y10S 134/902 Semiconductor wafer

Abstract

A dry process for the cleaning of precision surfaces such as of semiconductor wafers, by using process materials such as carbon dioxide and useful additives such as cosolvents and surfactants, where the process materials are applied exclusively in gaseous and supercritical states. Soak and agitation steps are applied to the wafer, including a rapid decompression of the process chamber after a soak period at higher supercritical pressure, to mechanically weaken break up the polymers and other materials sought to be removed, combined with a supercritical fluid flush to carry away the loose debris.

Claims

1. A supercritical fluid cleaning process for cleaning precision surfaces comprising the steps:

(a) selecting process materials comprising a process gas which is convertible at a critical point of temperature and pressure to a supercritical fluid for said cleaning process,

(b) selecting supercritical fluid operating parameters for said process gas including a supercritical temperature, a lower supercritical pressure, and a higher supercritical pressure, said higher supercritical pressure being preferably at least twice said lower supercritical pressure,

(c) loading, closing and sealing at least one substrate with a said precision surface in a pressure vessel, said vessel being connected to a source of said process gas and a source of said supercritical fluid and having at least one port for exhausting byproducts of said process, said vessel configured with means for heating the interior thereof and having independent means for isolating said vessel from inflow of said process materials and outflow of said byproducts,

(d) purging and pressurizing said vessel with process gas and supercritical fluid to said higher supercritical pressure while heating said interior to said supercritical temperature so as to displace all other gases with supercritical fluid without entering a liquid phase condition,

(e) soaking said wafer at said higher supercritical pressure for a predetermined soak period,

(f) agitating said substrate by rapidly decompressing said vessel to said lower supercritical pressure and flushing said vessel with said supercritical fluid for a predetermined period of time, then rapidly elevating said vessel to said higher supercritical pressure,

(g) rinsing said substrate at said higher supercritical pressure,

(h) drying said substrate with supercritical fluid and process gas by maintaining said vessel at supercritical temperature when decreasing vessel pressure to ambient, and

(i) opening said vessel and unloading said substrate.

2. A supercritical fluid cleaning process according to claim 1, said vessel being also connected to a source of supercritical fluid mixture comprising said supercritical fluid and selected additives in solution, said process further comprising additional step (d.1) filling said vessel with said supercritical fluid mixture so as to replace said supercritical fluid, and in said step (f) said flushing said vessel with said supercritical fluid comprising said supercritical fluid mixture.

3. A supercritical fluid cleaning process according to claim 2, further comprising at least one repetition of steps (e) and (f) sequentially for at least two iterations during said process.

4. A supercritical fluid cleaning process according to claim 2, further comprising at least one repetition of steps (d. 1) through (f).

5. A supercritical fluid cleaning process according to claim 1, said process materials comprising carbon dioxide.

6. A supercritical fluid cleaning process according to claim 1, said process being conducted as repetitive cycles with a processed substrate being unloaded and a new said substrate being loaded for each consecutive cycle.

7. A supercritical fluid cleaning process according to claim 1, said vessel configured as an inverted vessel with an underside vertically operated lid upon which said substrate is mounted for said processing.

8. A supercritical fluid cleaning process according to claim 2, said means for heating the interior comprising at least one heat exchanger platen in said vessel.

9. A supercritical fluid cleaning process according to claim 8, said at least one heat exchanger platen comprising upper and lower platens between which said substrate is supported during said process.

10. A supercritical fluid cleaning process according to claim 2, said step (c) comprising loading and processing said substrate with said precision surface facing downward.

11. A supercritical fluid cleaning process according to claim 2, said vessel configured for reversing the direction of flow of said process materials.

12. A supercritical fluid cleaning process according to claim 2, said vessel being also connected to a source of a process gas mixture of said process gas and selected additives.

13. A supercritical fluid cleaning process according to claim 12, said vessel being also connected to a source of process gas in liquid state.

15. A supercritical fluid cleaning process according to claim 14, further comprising at least one repetition of steps (g) and (h) sequentially for at least two iterations thereof during said process.

16. A supercritical fluid cleaning process according to claim 14, further comprising at least one repetition of steps (e) through (h).

17. A supercritical fluid cleaning process according to claim 14, said process being conducted as repetitive cycles with a processed said substrate being unloaded and an unprocessed said substrate being loaded for each consecutive cycle.

18. A supercritical fluid cleaning process according to claim 14, said vessel configured as an inverted vessel with an underside vertically operated lid upon which said substrate is mounted for said processing.

19. A supercritical fluid cleaning process according to claim 14, said step (c) comprising loading and processing said substrate with said precision surface facing downward.

20. A supercritical fluid cleaning process according to claim 14, said vessel configured for reversing the direction of flow of said process materials.

21. A supercritical fluid cleaning process according to claim 14, said vessel further comprising a divergent inflow channel and a convergent outflow channel.

22. A supercritical fluid cleaning process according to claim 14, said vessel being also connected to a source of a process gas mixture of said process case and said additives.

23. A supercritical fluid cleaning process according to claim 14, said vessel being also connected to a source of liquid carbon dioxide.

25. A supercritical fluid cleaning process according to claim 14, further comprising at least one repetition of steps (g) and (h) sequentially for at least two iterations thereof during said process.

26. A supercritical fluid cleaning process according to claim 14, further comprising at least one repetition of steps (e) through (h).

27. A supercritical fluid cleaning process according to claim 14, said process being conducted as repetitive cycles with a processed said substrate being unloaded and an unprocessed said substrate being loaded for each consecutive cycle.

14. A supercritical fluid cleaning process for cleaning precision surfaces comprising the steps:

(a) selecting process materials comprising carbon dioxide as a process gas which is convertible at a critical point of temperature and pressure to a supercritical fluid for said cleaning process, and additives soluble in said process gas,

(b) selecting supercritical fluid operating parameters for said process gas including a supercritical temperature, a lower supercritical pressure, and a higher supercritical pressure, said higher supercritical pressure being preferably at least twice said lower supercritical pressure,

(c) loading, closing and sealing at least one substrate with a said precision surface in a pressure vessel, said vessel being connected to a source of said process gas and a source of said supercritical fluid and a source of supercritical fluid mixture comprising said supercritical fluid and said additives, and having at least one port for exhausting byproducts of said process, said vessel configured with upper and lower heat exchanger platens for heating the interior thereof and having independent means for isolating said vessel from inflow of said process materials and outflow of said byproducts,

(d) purging and pressurizing said vessel with process gas and supercritical fluid to said higher supercritical pressure while heating said interior to said supercritical temperature so as to displace all other gases with supercritical fluid without entering a liquid phase condition,

(e) filling said vessel with said supercritical fluid mixture so as to replace said supercritical fluid,

(f) soaking said wafer at said higher supercritical pressure for a predetermined soak period,

(g) agitating said substrate by rapidly decompressing said vessel to said lower supercritical pressure and flushing said vessel with said supercritical fluid for a predetermined period of time, then rapidly elevating said vessel to said higher supercritical pressure,

(h) rinsing said substrate with said supercritical fluid at said higher supercritical pressure,

(i) drying said substrate with supercritical fluid and process gas by maintaining said vessel at supercritical temperature when decreasing vessel pressure to ambient without entering a liquid phase condition,

(j) opening said vessel and unloading said substrate.

24. A supercritical fluid cleaning process for cleaning precision surfaces comprising the steps:

(a) selecting process materials comprising carbon dioxide as a process gas which is convertible at a critical point of temperature and pressure to a supercritical fluid for said cleaning process, and additives soluble in said process gas,

(b) selecting supercritical fluid operating parameters for said process gas including a supercritical temperature, a lower supercritical pressure, and a higher supercritical pressure, said higher supercritical pressure being preferably at least twice said lower supercritical pressure,

(c) loading, closing and sealing at least one substrate with a said precision surface in a pressure vessel, said vessel being connected to a source of said process gas and a source of said supercritical fluid and a source of supercritical fluid mixture comprising said supercritical fluid and said additives, and having at least one port for exhausting byproducts of said process, said vessel configured as an inverted vessel with an underside vertically operated lid upon which said substrate is mounted for said processing, said vessel further comprising a divergent inflow channel and a convergent outflow channel, said vessel configured with upper and lower heat exchanger platens for heating the interior thereof and having independent means for isolating said vessel from inflow of said process materials and outflow of said byproducts,

(d) purging and pressurizing said vessel with process gas and supercritical fluid to said higher supercritical pressure while heating said interior to said supercritical temperature so as to displace all other gases with supercritical fluid without entering a liquid phase condition,

(e) filling said vessel with said supercritical fluid mixture so as to replace said supercritical fluid,

(f) soaking said wafer at said higher supercritical pressure for a predetermined soak period,

(g) agitating said substrate by rapidly decompressing said vessel to said lower supercritical pressure and flushing said vessel with said supercritical fluid for a predetermined period of time, then elevating said vessel to said higher supercritical pressure,

(h) rinsing said substrate with said supercritical fluid at said higher supercritical pressure,

(i) drying said substrate with supercritical fluid and process gas by maintaining said vessel at supercritical temperature when decreasing vessel pressure to ambient without entering a liquid phase condition,

(j) opening said vessel and unloading said substrate.