Apparatus and method for ion beam polishing and for in-situ ellipsometric deposition of ion beam films

• US 5,529,671 A
• Filed: 07/27/1994
• Issued: 06/25/1996
• Est. Priority Date: 07/27/1994
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Litton Systems Incorporated (Northrop Grumman Corporation)
• Inventors: Debley, William P., Larson, John G.
• Primary Examiner(s): NGUYEN, NAM X
• Application Number:
  US08/282,098
• Time in Patent Office: 699 Days
• Field of Search: 204/192.11, 204/192.34, 204/298.04, 204/298.36, 356/139.1, 356/152.2
• US Class Current: 204/192.34
• CPC Class Codes: C23C 14/022 by means of bombardment with energetic particles or radiation
• CPC Class Codes: C23C 14/505 for rotation of the substrates
• CPC Class Codes: G02B 1/10 Optical coatings produced by application to, or surface treatment of, optical elements G02B1/08 takes precedence
• CPC Class Codes: G02B 1/113 using inorganic layer materials only

Abstract

The invention uses an ion beam to polish a rotatable substrate from an oblique angle between the horizontal and the center line of the gun to the substrate to upgrade the quality of substrates. Alternatively, the substrates are left in the high vacuum chamber without breaking the vacuum for in-situ deposition of thin films thereby avoiding contamination, and to provide premium optics. A wobble stick arrangement is provided to align the ellipsometer reflected beam with the ellipsometer detector during operation without breaking the vacuum which, if broken, would admit contamination.

Claims

1. The method of polishing a surface of a substrate to an improved surface flatness, comprising the steps of:

establishing a vacuum equal to or exceeding 10^-8 torr in a vacuum chamber;

mounting the substrate for rotation in the chamber;

directing an ion beam from a gun at the rotating substrate surface at an oblique angle of approximately 45 to 60 degrees between the substrate and the center line of the gun to the substrate; and

,

maintaining the ion beam until 200 or more angstroms of surface have been removed from the substrate to achieve a surface smoothness of 1/2 to 3/4 angstrom.

2. The method of claim 1, wherein:

using a previously polished substrate as said substrate to be polished in the chamber to an improved surface smoothness; and

,

producing the vacuum by a contamination free cryogenic pump integral with the chamber.

3. The method of claim 2 wherein:

rotating the substrate about 36 revolutions per minute.

4. The method of claim 1, wherein,

producing the ion beam by a 3 centimeter ion beam gun;

and,

spacing the gun approximately 20 centimeters from the rotating substrate surface to be polished.

5. The method of claim 1 wherein:

said ion gun is operated at a current of 25 to 50 milliamperes at 600-950 volts DC.

6. The method of claim 1 for both polishing and depositing coatings on substrates comprising the further steps of:

depositing said coatings in-situ immediately following said polishing without breaking the vacuum.

7. The method of claim 6 wherein:

using a second ion gun integral with said chamber to effect the deposition.

8. The method of polishing and in-situ coating a substrate in a vacuum chamber comprising the steps of:

using an ion gun beam to polish the substrate to a flatness of 1/2 to 3/4 angstrom by directing the ion gun beam at the substrate from an oblique angle of 45-60 degrees relative to the substrate while the substrate is being rotated; and

using a second ion gun to deposit the coating in-situ without breaking the vacuum to achieve super reflectivity in the coating.

9. The method of claim 8 wherein:

using a previously polished substrate as said substrate in the chamber to be polished to an improved surface smoothness;

determining the oblique angle that the substrate will receive light in its subsequent commercial application; and

accomplishing said polishing at approximately the same oblique angle that the substrate will receive light in its commercial application.

10. The method of polishing and coating substrates using a vacuum gas chamber to produce anti-reflection coatings, comprising the steps of:

using a first ion gun integral with the chamber using a first gas to polish the substrates to 1/2 to 3/4 angstrom flatness by directing the ion beam at the rotating substrate from an oblique angle of 45 to 60 degrees relative to the substrates for a length of time necessary to obtain said degree of flatness determined by timing the polishing based on prior known polishing times for the same materials;

using a second ion gun having a second gas to deposit said coating to form the anti-reflection coating; and

,

using a cryogenic pump to maintain said chamber free of contaminants and at about 10^-8 torr.

11. The method of claim 10 further comprising the steps of:

using an ellipsometer to measure the thickness of each coating while the coating is being deposited.

12. The method of claim 11, further comprising the step of:

using a witness piece and an ellipsometer to measure the thickness of film deposited of a witness piece in order to estimate the thickness of similar film material deposited on substrates.

13. The method of claim 12 further comprising:

operating the first ion gun at 25-50 milliamperes at 600-950 volts D.C.;

spacing the first ion gun approximately 20 centimeters from the substrate surface;

rotating the substrate at approximately 36 revolutions per minute; and

,

directing an ellipsometer beam at the witness piece at about 70 degrees from the vertical and reflecting the beam at the same angle from the witness piece relative to the vertical to center the beam on the detector.

14. An apparatus for polishing substrate surfaces to an improved surface flatness, comprising in combination:

a vacuum chamber having an ultra high vacuum equal to or exceeding 10^-8 torr;

an ion beam gun;

means mounting a substrate having a previously polished surface in the chamber;

means for directing the ion beam from said gun at the substrate polished surface at an oblique angle of 45-60 degrees between the substrate and the centerline of the gun to the substrate;

means for rotating said substrate; and

means for maintaining the ion beam until 200 or more angstroms of surface have been removed from the substrate to achieve a surface flatness of 1/2 to 3/4 angstrom.

15. The apparatus of claim 14 further comprising:

a cryogenic pump integral with the chamber for producing the ultra high vacuum.

16. The apparatus of claim 14, further comprising:

means for spacing the gun approximately 20 cm from the substrate to be polished; and

,

said ion beam gun being a three centimeter gun.

17. The apparatus of claim 14 further comprising:

means for rotating the substrate at about 36 revolutions/minute.

18. The apparatus of claim 14 further comprising:

means for operating said gun at a current of 25-50 milliamperes at 600-900 volts dc.

19. The apparatus of claim 14 for both polishing and depositing coatings on substrates further comprising:

means for in-situ coating said substrates immediately following said polishing without breaking the vacuum.

20. The apparatus of claim 19 wherein:

said means for coating comprises a second ion gun integral with said chamber to effect the deposition.

21. Apparatus for further polishing and in-situ coating a previously polished substrate in a vacuum chamber comprising in combination:

means for mounting the previously polished substrate for rotation in the chamber;

an ion gun having a beam to polish the substrate to a flatness of 1/2 to 3/4 angstrom;

means for directing the ion gun beam at the substrate from an oblique angle of 45-60 degrees relative to the horizontal;

means for rotating the substrate while in the beam; and

,

a second ion gun to deposit the coating in-situ without breaking the vacuum to achieve improved reflectivity in the coating.

22. The apparatus of claim 21 wherein the oblique angle that the substrate will receive light in its subsequent commercial application is determined, further comprising:

means for polishing the substrate at approximately the same oblique angle that the substrate will receive light in its commercial application.

23. Apparatus for further polishing and coating previously polished substrates using a vacuum gas chamber to produce anti-reflection coatings, comprising in combination:

means for rotating the substrates in the chamber;

a first ion gun integral with the chamber in a first gas to polish the substrates to 1/2 to 3/4 angstrom flatness by directing the ion beam at the rotating substrate from an oblique angle of approximately 45 to 60 degrees relative to the substrate for an amount of time necessary to obtain said degree of flatness determined by timing the polishing based on prior known polishing times for the same materials;

a second gas and a second ion gun to deposit said coating, layer by layer, to form the anti-reflection coating; and

,

a cryogenic pump to maintain said chamber free of contaminants and at about 10^-8 torr.

24. The apparatus of claim 23 comprising in combination:

an ellipsometer to measure the thickness of each coating while the coating is being deposited.

25. The apparatus of claim 24, comprising in combination:

a witness piece and an ellipsometer to measure the thickness of film deposited on the witness piece in order to estimate the thickness of similar film material deposited on substrates.

26. The apparatus of claim 25, comprising in combination:

said ellipsometer having a source of light and a detector for reflected light;

said ellipsometer reflecting a polarized beam of light off of the witness piece onto the receiver; and

,

a wobble stick to tilt the witness piece in order to line up the ellipsometer beam reflected from the witness piece to the detector of the ellipsometer.