Air filtering within clean environments

• US 5,607,647 A
• Filed: 10/04/1994
• Issued: 03/04/1997
• Est. Priority Date: 12/02/1993
• Status: Expired due to Term

• Current Assignee: Entegris Incorporated
• Original Assignee: Extraction Systems, Inc. (Entegris Incorporated)
• Inventors: Kinkead, Devon A.
• Primary Examiner(s): Warden, Robert J.
• Assistant Examiner(s): Dawson, E. Leigh
• Application Number:
  US08/317,315
• Time in Patent Office: 882 Days
• Field of Search: 422/122, 422/169, 422/170, 422/171, 422/177, 454/187, 454/53, 95/285, 95/287, 96/135, 55/284, 55/315, 55/318, 55/350.1, 55/482, 55/485, 55/524, 250/492.2
• US Class Current: 422/122
• CPC Class Codes: A61L 9/046 with the help of a non-organic compound
• CPC Class Codes: B01D 46/12 in multiple arrangements
• CPC Class Codes: B01D 53/46 Removing components of defined structure
• CPC Class Codes: F24F 3/167 Clean rooms, i.e. enclosed spaces in which a uniform flow of filtered air is distributed air distribution by perforated walls F24F7/10

Abstract

An air filtering system for filtering air streams for use in a clean environment to effectively remove a process-limiting molecular contaminant therefrom comprising sequentially arranged upstream and downstream air filtering beds. The upstream air filtering bed is positioned to receive an air stream for use in the clean environment and comprises an upstream reagent selected to effectively remove the process-limiting molecular contaminant from the air stream as the air stream passes through the upstream air filtering bed, the upstream reagent releasing a characteristic volatile component into the air streams. The downstream air filtering bed is positioned to receive the air stream that has passed through the upstream air filtering bed and comprises a downstream reagent selected to remove the characteristic volatile component released by the upstream reagent into the air stream. Clean environments (e.g., a deep UV processing station) incorporating the above-mentioned air filtering system are also disclosed.

Claims

1. An air filtering system for filtering an air stream for use in a clean environment to effectively remove a process-limiting molecular contaminant therefrom comprising sequentially arranged upstream and downstream air filtering beds,

said upstream air filtering bed being constructed and arranged for filtering air for use in a clean environment, being positioned to receive an air stream from the clean environment and comprising activated carbon particles in the size range of 20×

140 mesh impregnated with an upstream chemically active reagent of sulfuric acid in a quantity selected to reduce the concentration of a process-limiting molecular contaminant in the air stream to a level below that which is detrimental to a process associated with the clean environment as said air stream passes through the upstream air filtering bed, said upstream chemically active reagent releasing a characteristic volatile component into said air stream at a concentration level that is detrimental to the associated clean environment process, and

said downstream air filtering bed being constructed and arranged to filter air for use in a clean environment, being positioned to receive the air stream that has passed through said upstream air filtering bed and comprising activated carbon particles in the size range of 20×

140 mesh impregnated with a downstream reagent selected to reduce the concentration of the characteristic volatile component released by said upstream reagent of sulfuric acid to a level below that which is detrimental to the associated clean environment process.

2. The air filtering system of claim 1 wherein said downstream reagent is a base.

3. The air filtering system of claim 1 wherein said sulfuric acid is impregnated on activated carbon particles at a doping level of 5-90%.

4. The air filtering system of claim 3 wherein said doping level is 20-50%.

5. The air filtering system of claim 1 wherein said downstream reagent is potassium hydroxide or potassium iodide.

6. The air filtering system of claim 5 wherein said downstream reagent is impregnated on activated carbon particles at a doping level of 5-15%.

7. The air filtering system of claim 1 wherein the air stream of the clean environment is subject to molecular contamination including airborne proton acceptors and said upstream reagent comprises sulfuric acid impregnated on an adsorbent media at a doping level selected to remove the airborne proton acceptors from the airstream as the air stream passes through said upstream air filtering bed.

8. The air filtering system of claim 1 wherein said upstream and downstream reagents are impregnated on activated carbon particles in the size range of 20×

50 mesh.

9. The air filtering system of claim 1 wherein said upstream and downstream air filtering beds respectively comprise a molecular chemical filter comprising an air permeable web of non-woven fibrous carrier material of pleated form, said web comprising a matrix formed of a multiplicity of synthetic fibers and characterized in that activated carbon particles are distributed throughout said web, bound in the interstices of the matrix in a manner preventing loss to the air stream particles in quantity detrimental to the clean environment.

10. The air filtering system of claim 1 wherein said upstream and downstream air filtering beds are integrated into a common pleated non-woven carrier material.

11. The air filtering system of claim 1 further comprising an intermediate air filtering bed disposed between said upstream and downstream air filtering beds and comprising an intermediate reagent selected to remove the volatile component released by said upstream reagent.

12. The air filtering system of claim 1 further comprising an intermediate air filtering bed disposed between said upstream and downstream air filtering beds and comprising an intermediate reagent selected to remove the process-limiting molecular contaminant from said air stream.

13. The filtering system of claim 1 wherein said upstream reagent releases into the air stream said characteristic volatile component at a concentration of about 600 ppt or greater.

14. An air filtering system for filtering an air stream for use in a clean environment to effectively remove a process-limiting molecular contaminant therefrom comprising sequentially arranged upstream and downstream air filtering beds,

said upstream air filtering bed being constructed and arranged for filtering air for use in a clean environment, being positioned to receive an air stream from the clean environment and comprising whetlerite to reduce the concentration of a process-limiting molecular contaminant in the air stream to a level below that which is detrimental to a process associated with the clean environment as said air stream passes through the upstream air filtering bed, said whetlerite releasing a characteristic volatile component into said air stream at a concentration level that is detrimental to the associated clean environment process, and

said downstream air filtering bed being constructed and arranged to filter air for use in a clean environment, being positioned to receive the air stream that has passed through said upstream air filtering bed and comprising activated carbon particles in the size range of 20×

140 mesh impregnated with downstream reagent selected to reduce the concentration of the characteristic volatile component released by said whetlerite to a level below that which is detrimental to the associated clean environment process.

15. The air filtering system of claim 14 wherein the downstream reagent is a metal salt.

16. The air filtering system of claim 14 wherein the downstream reagent is an acid suitable for exposure to air for use in a clean environment.

17. The filtering system of claim 14 wherein said upstream reagent releases into the air stream said characteristic volatile component at a concentration of about 600 ppt or greater.

18. An air handling system for providing a filtered air stream, substantially free of a process-limiting molecular contaminant, for use in a clean environment comprising:

a semiconductor device processing station that releases a process-limiting molecular contaminant into air within a clean environment;

a recirculating air system for recirculating and filtering an airstream from adjacent said processing station, said recirculating air system comprising

an air filtering system comprising sequentially arranged upstream and downstream air filtering beds, said upstream air filtering bed being constructed and arranged to filter air for use in a clean environment, being positioned to receive the air stream recirculated by said recirculating air system and comprising activated carbon particles in the size range of 20×

140 mesh impregnated with an upstream reagent of sulfuric acid in a quantity selected to reduce the concentration of the process-limiting molecular contaminant released by said semiconductor device processing station from the air stream as the air stream passes through said upstream air filter, said upstream reagent releasing a characteristic volatile component into the air stream at a concentration level that is detrimental to the clean environment, and said downstream air filtering bed being constructed and arranged to filter air for use in a clean environment, being positioned to receive the air stream that has passed through said upstream air filtering bed and comprising activated carbon particles in the size range of 20×

140 mesh impregnated with a downstream reagent selected to reduce the concentration of the characteristic volatile component released by said upstream reagent of sulfuric acid to level below that which is detrimental to the associated clean environment process.

19. The clean environment of claim 18 further comprising a make-up air system for drawing air from an atmosphere that is subject to molecular contamination including airborne proton acceptors, said make-up air system comprising an air filtering system comprising an upstream air filtering bed positioned to receive air streams recirculated by said recirculating air system and comprising an upstream reagent selected to effectively remove airborne proton acceptors from the air stream as the air stream passes through said upstream air filter, said upstream reagent releasing a characteristic volatile component into the air stream, and a downstream air filtering bed positioned to receive the air stream that has passed through said upstream air filtering bed and comprising a downstream reagent selected to remove the characteristic volatile component released into said air stream by said upstream reagent of the upstream air filtering bed in said make-up air system.

20. The filtering system of claim 18 wherein said upstream reagent releases into the air stream said characteristic volatile component at a concentration of about 600 ppt or greater.

21. A deep UV photolithography station comprising

a deep UV lithographic process tool;

a recirculating air system for recirculating and filtering an airstream from adjacent said lithographic processing station, said recirculating air system comprising

an air filtering system comprising an upstream air filtering bed positioned to receive the air stream recirculated by said recirculating air system and comprising activated carbon particles in the size range of 20×

140 mesh impregnated with sulfuric acid for effectively removing airborne proton acceptors from the air stream as the air stream passes through said upstream air filtering bed, and a downstream air filtering bed positioned to receive the air stream that has passed through said upstream air filtering bed and comprising activated carbon particles in the size range of 20×

140 mesh impregnated with a base selected to remove volatile sulfuric acid or sulfuric acid components released into said air stream.

22. The deep UV photolithography station of claim 21 further comprising a make-up air system for drawing air from an atmosphere that may be subject to a molecular contaminant including airborne proton acceptors, said makeup air system comprising an air filtering system comprising an upstream air filtering bed positioned to receive the air stream recirculated by said recirculating air system and comprising an upstream reagent selected to effectively remove airborne proton acceptors from the air stream as the air stream passes through said upstream air filtering bed, said upstream reagent releasing a characteristic volatile component into the air stream in sufficient quantity to be detrimental to the clean environment, and a downstream air filtering bed positioned to receive the air stream that has passed through said upstream air filtering bed and comprising a downstream reagent selected to remove the characteristic volatile component released by said upstream reagent into said air stream.

23. The air filter of claim 21 wherein said upstream reagent is impregnated on activated carbon particles at a doping level of between 5% and 90%.

24. The air filter of claim 23 wherein said doping level is between 20% and 50%.

25. An air filtering system comprising at least two chemically active air filtering beds in sequence along an air stream associated with a clean environment, said system comprising

a first chemically active air filtering bed, constructed and arranged to filter air for use inside a clean environment, comprising activated carbon particles in the size range of 20×

140 mesh impregnated with a reagent of sulfuric acid in a quantity selected to reduce the concentration of a first contaminant in an air stream associated with a clean environment to a level that is below that which is detrimental to a process associated with the clean environment, said reagent of sulfuric acid having the characteristic of releasing a contaminant into the air stream that is different from said first contaminant,

a downstream chemically active air filtering system, constructed and arranged to filter air for use in a clean environment, comprising activated carbon particles in the size range of 20×

140 mesh impregnated with a reagent having the characteristic of reducing the concentration of the contaminant released by said sulfuric acid reagent to a level that is below that which is detrimental to the associated clean environment, wherein

the chemically active air filtering beds in said system are selected and cooperatively arranged so that said air filtering system has removed from the air stream said first contaminant and any volatile contaminants detrimental to said clean environment released by said system.

26. The filtering system of claim 25 wherein said upstream reagent of sulfuric acid releases into the air stream said characteristic volatile component at a concentration of about 600 ppt or greater.

27. A method for filtering an air stream for use in a clean environment to reduce the concentration of a process-limiting molecular contaminant therein to a level below that which is detrimental to a process associated with the clean environment, said method comprising the steps of:

providing an upstream air filtering bed within an air handling system of a clean environment to receive an air stream from the clean environment, said upstream air filtering bed comprising an upstream chemically active reagent in a quantity selected to reduce the concentration of a process-limiting molecular contaminant in the air stream to a level below that which is detrimental to a process associated with the clean environment as said air stream passes through the upstream air filtering bed, said upstream chemically active reagent releasing a characteristic volatile component into said air stream at a concentration level that is detrimental to the associated clean environment process, and

providing a downstream air filtering bed within the air handling system of the clean environment to receive the air stream that has passed through said upstream air filtering bed, said downstream air filtering bed comprising a downstream reagent selected to reduce the concentration of the characteristic volatile component released by said upstream reagent to a level below that which is detrimental to the associated clean environment process.

28. The method of claim 27 wherein the upstream air filtering bed that is provided comprises activated carbon particles in the size range of 20×

140 mesh impregnated with sulfuric acid.

29. The method of claim 28 wherein the downstream air filtering bed that is provided comprises activated carbon particles in the size range of 20×

140 mesh impregnated with a base.

30. The method of claim 29 wherein the activated carbon particles of the downstream air filtering bed are impregnated with potassium hydroxide.

31. The method of claim 29 wherein the activated carbon particles of the downstream air filtering bed are impregnated with potassium iodide.

32. The method of claim 27 wherein said upstream air filtering bed that is provided releases into the air stream said characteristic volatile component at a concentration level of about 600 ppt or greater.

33. The method of claim 27 wherein said upstream reagent that is provided has a higher vapor pressure than water under normal operating conditions.

34. The method of claim 27 wherein said upstream reagent that is provided off-gases at a level that is detrimental to processes conducted within the clean environment under normal operating conditions.

35. The method of claim 27 wherein the upstream reagent that is provided is selected to reduce the concentration of amines from the air stream as the air stream passes through said upstream air filtering bed.