Method for making optical microstructures having profile heights exceeding fifteen microns

• US 6,410,213 B1
• Filed: 06/09/1998
• Issued: 06/25/2002
• Est. Priority Date: 06/09/1998
• Status: Expired due to Term

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Morris, G. Michael, Emmel, Peter M., Raguin, Daniel H.
• Primary Examiner(s): Huff, Mark F.
• Assistant Examiner(s): BARRECA, NICOLE M
• Application Number:
  US09/094,340
• Time in Patent Office: 1,477 Days
• Field of Search: 430/321, 430/323, 430/396, 430/945
• US Class Current: 430/321
• CPC Class Codes: G03F 7/001 Phase modulating patterns, e.g. refractive index patterns
• CPC Class Codes: G03F 7/70358 Scanning exposure, i.e. relative movement of patterned beam and workpiece during imaging
• CPC Class Codes: Y10S 430/136 Coating process making radiation sensitive element
• CPC Class Codes: Y10S 430/146 Laser beam

Abstract

Fabrication of arbitrary profile micro-optical structures (lenses, gratings, etc.) and, if desired, with optomechanical alignment marks simultaneously during fabrication is based upon the use of low-contrast photosensitive material that, when exposed to a spatially variable energy dosage of electromagnetic radiation, can be processed to achieve multi-level or continuous surface-relief microstructures. By varying the exposure dose spatially based upon predetermined contrast curves of the photosensitive material, arbitrary one-dimensional (1-D) or two-dimensional (2-D) surface contours, including spherical, aspherical, toroidal, hyperbolic, parabolic, and ellipsoidal, can be achieved with surface sags greater than 15 μm. Surface profiles with advanced phase correction terms (e.g., Zernike polynomials) can be added to increase the alignment tolerance and overall system performance of the fabricated structure can also be fabricated. The continuous-relief pattern can be used as is in the photosensitive material, transferred into the underlying substrate through an etch process, electroformed into a metal, or replicated into a polymer.

Claims

1. A method for fabricating an optical microstructure on a substrate comprising the steps of:

coating the substrate with a photosensitive material to produce a photosensitive material coating to a height exceeding 15 μ

m;

producing a surface-relief microstructure pattern on the photosensitive material coating by a single-step exposure of the photosensitive material coating with a scanning beam of electromagnetic radiation, wherein said scanning beam is focused onto a portion of the photosensitive material where said pattern is to be formed, and said beam is multiply translated across said portion while changing its intensity with an optical modulator to provide a scanning beam having an exposure dosage varying with said translations over the photosensitive material coating to produce an optical microstructure pattern as a result of the photosensitive material coating responding to the electromagnetic radiation, wherein a width of said focused beam is smaller than a width of said pattern, and

developing said exposed pattern in said photosensitive material to form an optical microstructure.

2. The method of claim 1 further comprising the step of:

exposing the photosensitive material coating to provide alignment marks or metrology marks or both simultaneously with the surface-relief microstructure pattern.

3. The method of claim 1 wherein the optical microstructure is a microlenses having a depth profile >

15 μ

m.

4. The method of claim 1 wherein the optical modulator includes a laser pattern generator (LPG), and the single-step exposure is performed using the laser pattern generator (LPG) such that the exposure dosage is varied by modulating either the dwell time or the radiation power of the scanning beam.

5. The method of claim 4 wherein the photosensitive material is a photoresist and the laser pattern generator (LPG) is operated to focus the scanning beam into one or more focused spots that are scanned across the photoresist by translating the substrate, moving the one or more focused spots, or a combination thereof.

6. The method of claim 1 wherein the surface-relief microstructure pattern is a specified profile selected from a group consisting of spherical, aspherical, periodial, hyperbolic, parabolic, and ellipsoidal.

7. The method of claim 1 further comprising the step of:

transferring the surface-relief microstructure pattern into the underlying substrate using a process selected from the group consisting of wet chemical etching, dry chemical etching, ion milling, reactive ion etching, reactive ion beam etching, and chemical-assisted ion beam etching.

8. The method of claim 1 wherein the optical microstructure is a plurality of microlenses and the method further comprises the steps of:

developing and etching the surface-relief microstructure pattern to create a master element having a plurality of microstructure profiles;

providing a polymer material; and

fabricating the plurality of microlenses in the polymer material using the master element by a process selected from the group consisting of cast-and-cure, embossing, compression molding, injection molding, and compression-injection molding.

9. The method of claim 1 wherein the photosensitive material is a photoresist, and the single-step exposure patterns the photoresist to a depth exceeding 15 μ

m to produce a photoresist mold for the surface-relief microstructure pattern, the surface-relief microstructure pattern being a microlens having a sag exceeding 15 μ

m.

10. The method of claim 1 wherein the single-step exposure is performed without multiple masks or thermal reflow.

11. The method of claim 1 wherein the optical microstructure is a microlens having a sag of at least 20 μ

m, and the microlens has a numerical aperture (NA) of at least 0.5.

12. A microlens fabricated in accordance with the method of claim 1.

13. The method of claim 1 wherein the photosensitive material is a photoresist.

14. The method of claim 13 wherein the step of providing the surface-relief microstructure pattern includes the step of:

developing the photoresist to provide a grayscale response so as to create a multilevel profile or a continuous-relief profile in the photoresist in a single exposure during which the beam is scanned over the substrate.