Vacuum assisted debris removal system

• US 5,973,764 A
• Filed: 06/19/1997
• Issued: 10/26/1999
• Est. Priority Date: 06/19/1997
• Status: Expired due to Fees

• Current Assignee: ASML Holding NV
• Original Assignee: SVG Lithography Systems Incorporated (ASML Holding NV)
• Inventors: Olson, Sean, McCullough, Andrew W.
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): Dalakis, Michael
• Application Number:
  US08/878,633
• Time in Patent Office: 859 Days
• Field of Search: 355/30, 355/73, 355/76, 250/441.11
• US Class Current: 355/30
• CPC Class Codes: G03F 7/70241 Optical aspects of refractive lens systems, i.e. comprising only refractive elements
• CPC Class Codes: G03F 7/70358 Scanning exposure, i.e. relative movement of patterned beam and workpiece during imaging
• CPC Class Codes: G03F 7/70866 of mask or workpiece
• CPC Class Codes: G03F 7/70916 Pollution mitigation, i.e. mitigating effect of contamination or debris, e.g. foil traps

Abstract

A vacuum manifold having a rectangular opening with vacuum access bores connected into the rectangular opening for an illumination field to be projected there through. A vacuum manifold is placed between a photosensitive resist covered wafer and a lens element in a photolithographic tool. The relatively high illumination energy in an illumination field used for projecting an image of a reticle onto a photosensitive resist covered wafer often results in ablated, evaporated, and effused material being coated on the lens element. The vacuum manifold placed between the lens element and the photosensitive resist covered wafer creates an airflow for removing debris or contamination preventing coating of the lens surface. This prevents image quality from degradation over time, as well as reduces downtime needed for cleaning or maintenance of the photolithographic tool.

Claims

1. A vacuum assisted debris removal system for use in photolithography comprising:

a manifold having a planar top surface and a planar bottom surface and an illumination field opening, said manifold placed between a lens element having a surface and a photosensitive resist covered substrate forming a first gap between the surface of the lens element and the planar top surface of said manifold and a second gap between the planar bottom surface of said manifold and a photosensitive resist covered substrate, said manifold having bores open and adjacent to the illumination field opening, said manifold positioned to establish a first flow pattern in the first gap across the surface of the lens element and towards the photosensitive resist covered substrate, and a second flow pattern in the second gap across the photosensitive resist covered substrate and towards the illumination field opening, and

a vacuum source coupled to said manifold,

whereby a flow pattern is obtained preventing the lens element from being coated with debris.

2. A vacuum assisted debris removal system as in claim 1, wherein:

said illumination field opening is rectangular having a pair of longitudinal sides and a pair of lateral sides.

3. A vacuum assisted debris removal system as in claim 2, wherein:

the bores are open along the pair of longitudinal sides.

4. A vacuum assisted debris removal system as in claim 3, wherein:

the bores are open along the pair of lateral sides.

5. A vacuum assisted debris removal system as in claim 1, further comprising:

a passage connecting the bores open to the illumination field together, said passage connected at one end to said vacuum source.

6. A vacuum assisted debris removal system as in claim 1, wherein:

the bores open to the illumination field opening are spaced substantially equally apart.

7. A vacuum assisted debris removal system for use in photolithography comprising:

a vacuum manifold having a top substantially planar surface and a bottom substantially planar surface, said vacuum manifold having a rectangular illumination field opening formed therein and a plurality of bores extending there through, the plurality of bores having a longitudinal axis substantially parallel to the top and bottom substantially planar surfaces, the plurality of bores having one end open to the rectangular illumination field and another end coupled to a vacuum port, said vacuum manifold mounted so as to be fixed with respect to projection optics adjacent a lens element, and forming a first gap between the top substantially planar surface and the lens element and a second gap between the bottom substantially planar surface and a substrate, so that a first flow pattern is formed in the first gap across the surface of the lens element and towards the illumination field opening and in the direction of the substrate, and a second flow pattern is formed in the second gap across the substrate and towards the illumination field opening,

whereby debris and contamination is carried away from the lens element preventing the lens element from being coated.

8. A vacuum assisted debris removal system for use in photolithography as in claim 7 wherein:

the rectangular illumination field has a pair of longitudinal edges and a pair of lateral edges, the plurality of bores being open along the pair of longitudinal edges.

9. A vacuum assisted debris removal system for use in photolithography as in claim 7 wherein:

said plurality of bores having one end open to the rectangular illumination field are spaced substantially equally apart.

10. A vacuum assisted debris removal system for use in photolithography comprising:

an illumination source having an illumination field;

a reticle placed adjacent said illumination source;

projection optics positioned to project an image of said reticle and having a lens element;

a wafer stage positioned to receive at least a portion of the image of said reticle;

a planar vacuum manifold placed between the lens element and said wafer stage forming a first gap between a top surface of said planar vacuum manifold and a surface of the lens element and a second gap between a bottom surface of said planar vacuum manifold and said wafer stage and fixed relative to said projection optics, said vacuum manifold having a plurality of bores and an illumination field opening therein sized to accommodate the illumination field, the illumination field opening having a periphery, the plurality of bores opening on the periphery of the illumination field opening; and

a vacuum system coupled to the plurality of bores of said vacuum manifold,

whereby airflow is created by said vacuum system in the first gap between the lens element and the top surface of said planar vacuum manifold and is directed downward at the illumination field opening away from the lens element preventing the lens element from becoming coated with debris, and airflow is created in the second gap between the bottom surface of said vacuum manifold and the wafer stage and is directed upward at the illumination field opening.

11. A vacuum assisted debris removal system for use in photolithography as in claim 10 wherein:

the illumination field is rectangular having a pair of longitudinal sides and a pair of lateral sides.

12. A vacuum assisted debris removal system for use in photolithography as in claim 11 wherein:

the plurality of bores are open along the pair of longitudinal sides.

13. A vacuum assisted debris removal system for use in photolithography as in claim 10 wherein:

the plurality of bores are substantially equally spaced apart along the periphery of said illumination field.

14. A vacuum assisted debris removal system for use in photolithography comprising:

a manifold having an illumination field opening placed between a lens element having a surface and a photosensitive resist covered substrate, said manifold having bores open to the illumination field opening and positioned to establish a flow pattern across the surface of the lens element and downward towards the photosensitive resist covered substrate; and

a vacuum source coupled to said manifold,

whereby a flow pattern is obtained preventing the lens element from being coated with debris.

15. A vacuum assisted debris removal system for use in photolithography comprising:

an illumination source having an illumination field;

a reticle placed adjacent said illumination source;

projection optics positioned to project an image of said reticle and having a lens element;

a wafer stage positioned to receive at least a portion of the image of said reticle;

a vacuum manifold placed between the lens element and said wafer stage forming a gap between a top surface of said vacuum manifold and a surface of the lens element and fixed relative to said projection optics, said vacuum manifold having a plurality of bores and an illumination field opening therein sized to accommodate the illumination field, the illumination field opening having a periphery, the plurality of bores opening on the periphery of the illumination field opening; and

a vacuum system coupled to the plurality of bores of said vacuum manifold,

whereby airflow is created by said vacuum system in the gap between the lens element and the top surface of said vacuum manifold and is directed downward at the illumination field opening away from the lens element preventing the lens element from becoming coated with debris.

16. A vacuum assisted debris removal system for use in photolithography comprising:

projection optics having a lens element with a surface;

a planar manifold having an illumination field opening therein and a top surface positioned adjacent said projection optics forming an upper gap between the surface of said lens element and the top surface of said planar manifold, said planar manifold having a plurality of side bores therein opening to said illumination field opening; and

a vacuum system coupled to the plurality of side bores in said planar manifold, said vacuum system forming a gas flow pattern in the upper gap between the surface of the lens element and the top surface of said planar manifold in a direction towards the illumination field opening and down away from the surface of the lens element of said projection optics.

17. A method of preventing coating of an element of projection optics used in photolithography comprising:

placing a manifold having an illumination field opening and a top surface between the element and a substrate; and

forming a gas flow between the element and the top surface of the manifold towards the illumination field opening, then down away from the element into the illumination field opening, towards the substrate and through the manifold to a vacuum source,

whereby any possible contaminants are directed away from the element of the projection optics preventing the element from becoming coated with debris.