FOCUS CONTROL FOR OPTICAL INSTRUMENTS

• US 3,648,587 A
• Filed: 10/10/1968
• Issued: 03/14/1972
• Est. Priority Date: 10/20/1967
• Status: Expired due to Term

• Current Assignee: Guy William W. Stevens
• Original Assignee: Guy William W. Stevens
• Inventors: Stevens, Guy William W.
• Primary Examiner(s): Matthews, Samuel S.
• Assistant Examiner(s): Hutchison, Kenneth C.
• Application Number:
  US04/776,300
• Time in Patent Office: 1,251 Days
• Field of Search: 331/94.5 73/37.5,37.6,37.7 95/44 350/204
• US Class Current: 355/44
• CPC Class Codes: G03B 3/02 moving lens along baseboard
• CPC Class Codes: G03F 7/70341 Details of immersion lithography aspects, e.g. exposure media or control of immersion liquid supply chemical composition of immersion liquids G03F7/2041

Abstract

A method and apparatus particularly for making minute and very accurate images such as the negatives which are printed on photoresists in the production of microelectronic circuits. The method and apparatus employ an objective lens assembly adapted to be positioned in close proximity to a photographic emulsion layer, for focusing thereon an image of an object to be copied. In combination with the objective lens assembly there is provided a source of liquid, the liquid being of approximately the same refractive index as that of the emulsion and of a type that will not cause the emulsion to swell, and a liquid supply nozzle mounted for movement with the assembly and adapted to discharge the liquid so that a liquid stream fills the space between the assembly and the emulsion layer with a continuously renewed pool of liquid. There is further provided in combination with the assembly a device for sensing the pressure of the liquid in the nozzle so that the distance between the assembly and the emulsion layer may be monitored by noting variations in the liquid pressure in the nozzle from that obtained when the emulsion is correctly spaced.

Claims

1. An optical instrument for use in producing a greatly reduced high-resolution photographic copy of an object comprising:

an objective lens assembly of the liquid immersion type that includes at least one lens having a planar lens surface, said assembly being adapted to be positioned in proximity to a photographic emulsion layer to focus thereon an image of the object to be copied;

liquid supply nozzle means mounted to move with the objective lens assembly relative to the photographic emulsion layer, and adapted to direct a stream of liquid into contact with the proximately positioned photographic emulsion layer so as to fill the space between the layer and the planar lens surface with a continuously renewed pool of the liquid; and

a connection adapted to be connected to means for sensing variations in the venting of liquid from the nozzle from that obtaining when the objective lens assembly is correctly spaced from the photographic emulsion layer.

2. An optical instrument as claimed in claim 1 wherein the nozzle surrounds the objective lens assembly coaxially and has a single outlet opening arranged to face the photographic emulsion layer during operation.

3. An optical instrument as claimed in claim 1 wherein the nozzle surrounds the objective lens assembly coaxially and has several outlet openings equally spaced about its axis and arranged to face the photographic emulsion layer during operation.

4. An optical instrument as claimed in claim 1 in combination with means for supplying liquid to the nozzle at a constant head.

5. An optical instrument as claimed in claim 1 in combination with means for sensing variations in the venting of liquid from the nozzle, the said means comprising a pressure sensing instrument in communication with the liquid in the nozzle upstream of a restricted outlet from the nozzle.

6. An optical instrument for use in producing a greatly reduced high-resolution photographic copy of an object comprising:

an objective lens assembly, said assembly including at least one lens and a transparent cover element airspaced from said lens, said assembly being adapted to be positioned in proximity to a photographic emulsion layer to focus thereon an image of the object to be copied;

liquid supply nozzle means mounted to move with the objective lens assembly relative to the photographic emulsion layer, and adapted to direct a stream of liquid into contact with the proximately positioned photographic emulsion layer so as to fill the space between the layer and the cover element with a continuously renewed pool of said liquid;

means for supplying liquid to the nozzle at a constant head; and

a connection adapted to be connected to means for sensing variations in the venting of liquid from the nozzle from that obtaining when the objective lens assembly is correctly spaced from the photographic emulsion layer.

7. An optical instrument as claimed in claim 6 wherein the nozzle surrounds the objective lens assembly coaxially and has a single outlet opening arranged to face the photographic emulsion layer during operation.

8. An optical instrument as claimed in claim 6 wherein the nozzle surrounds the objective lens assembly coaxially and has several outlet openings equally spaced about its axis and arranged to face the photographic emulsion layer during operation.

9. An optical instrument as claimed in claim 6 in combination with means for sensing variations in the venting of liquid from the nozzle, the said means comprising a pressure sensing instrument in communication with the liquid in the nozzle upstream of a restricted outlet from the nozzle.

10. An apparatus which comprises:

an objective lens assembly adapted to focus on a photographic emulsion surface spaced therefrom;

a chamber mounted for movement with said objective lens assembly relative to said photographic emulsion, said chamber being adapted to contain a liquid and having at least one restricted outlet for directing a stream of liquid to fill the space between said objective and said surface;

liquid supply means in communication with said chamber for providing a constant flow of liquid into said chamber;

means for collecting said liquid after it has been discharged from said restricted outlet;

means connecting said collecting means to said liquid supply means to recirculate said liquid; and

means for sensing pressure variations introduced in said liquid stream by variations in the spacing between said objective and said surface.

11. A method of monitoring the spacing Between a microscope objective lens assembly and a photographic emulsion surface on which said objective lens assembly is adapted to focus, said method comprising:

flowing a stream of liquid, the liquid being of approximately the same refractive index as the photographic emulsion and of a type that will not cause the emulsion to swell, between said objective lens assembly and said surface at a substantially constant flow rate to fill the space therebetween; and

sensing the pressure variations introduced into said liquid stream by variations in the spacing between said objective lens assembly and said surface.

12. In the production of a greatly reduced high-resolution photographic copy of an object using an objective lens assembly to focus an image of the object on a photographic emulsion layer, the improved method of monitoring the spacing of the objective lens assembly and the said layer and maintaining a dust-free zone therebetween which comprises directing a stream of liquid, the liquid being of approximately the same refractive index as the photographic emulsion and of a type that will not cause the emulsion to swell, into contact with the photographic emulsion layer from a liquid supply nozzle mounted to move with the objective lens assembly relative to the layer, such that the liquid fills the space between the layer and the objective lens assembly when they are proximately spaced with a continuously renewed pool of the liquid, and sensing variations in the venting of liquid from the nozzle from that obtaining when the objective lens assembly is correctly spaced from the layer.

13. The method as claimed in claim 12 wherein the liquid is delivered to the nozzle at a constant head.

14. A method as claimed in claim 12 wherein the liquid is delivered to the nozzle at a constant head, and a manometer connected to the nozzle indicates variations in venting of the liquid from the nozzle.

15. The method as claimed in claim 12 wherein the liquid issues from said nozzle at a substantially constant flow rate.