High-efficiency, multilevel, diffractive optical elements

• US 4,895,790 A
• Filed: 09/21/1987
• Issued: 01/23/1990
• Est. Priority Date: 09/21/1987
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Swanson, Gary J., Veldkamp, Wilfrid B.
• Primary Examiner(s): Dees, Jose G.
• Assistant Examiner(s): Loney, Donald J.
• Application Number:
  US07/099,307
• Time in Patent Office: 855 Days
• Field of Search: 156/643, 156/659.1, 156/654, 350/417, 350/663, 350/162.17, 350/162.19, 350/162.2, 350/409, 350/162.21, 350/417, 350/162.24, 430/22, 430/321, 430/296, 430/323, 430/394, 430/942, 430/5, 430/322, 430/323, 430/312, 430/313, 430/302, 430/360, 430/319, 430/320, 430/329, 430/4, 430/6
• US Class Current: 430/321
• CPC Class Codes: G02B 27/4222 in projection exposure systems, e.g. photolithographic systems
• CPC Class Codes: G02B 3/08 with discontinuous faces, e.g. Fresnel lens diffractive Fresnel lenses G02B5/1876
• CPC Class Codes: G02B 5/1857 using exposure or etching means, e.g. holography, photolithography, exposure to electron or ion beams
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08
• CPC Class Codes: G03F 1/00 Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
• CPC Class Codes: G03F 7/001 Phase modulating patterns, e.g. refractive index patterns
• CPC Class Codes: G03F 7/70308 Optical correction elements, filters or phase plates for manipulating imaging light, e.g. intensity, wavelength, polarisation, phase or image shift
• CPC Class Codes: Y10S 359/90 Methods

Abstract

The method utilizes high resolution lithography, mask aligning, and reactive ion etching. In particular, at least two binary amplitude masks are generated. A photoresist layer on an optical element substrate is exposed through the first mask and then etched. The process is then repeated for the second and subsequent masks to create a multistep configuration. The resulting optical element is highly efficient.

Claims

1. Method for making high efficiency multilevel, diffractive, optical elements comprising:

generating a plurality of binary amplitude masks including the multilevel information, the masks being configured to provide 2^N levels where N is the number of masks; and

utilizing the masks'"'"' information serially for serial etching of 2^N levels into the optical element, the etching depths for the masks being related by a fixed ratio.

2. The method of claim 1 wherein the masks are made by lithographic pattern generators.

3. The method of claim 1 wherein the etching is by ion beam etching.

4. The method of claim 1 wherein the etching process includes coating the optical element substrate with photoresist, exposing the photoresist through the masks, developing the photoresist, and etching the substrate.

5. The method of claim 1 including three masks and eight levels.

6. The method of claim 1 wherein the binary amplitude masks are defined by calculating equiphase boundaries utilizing the equation ##EQU5## and the algorithm

7. The method of claim 1 wherein the masks are made by electron beam pattern generators.

8. The method of claim 1 wherein the etching is by reactive ion etching.

9. The method of claim 1 wherein the optical element is a lens.

10. The method of claim 1 wherein the optical element corrects for spherical aberration.

11. The method of claim 1 wherein the optical element is corrected for chromatic aberration.

12. Method for making high-efficiency, multilevel diffractive optical elements comprising:

making a master optical element according to the method of claim 1; and

using the master optical element to emboss multiple replicated optical components.

13. The method of claim 12 wherein the master optical element is copied in metal which is used for the embossing.

14. Method for making high efficiency multilevel, diffractive, optical elements comprising:

generating a plurality of binary amplitude masks including the multilevel information by lithographic pattern generation, the masks configured to provide 2^N levels where N is the number of masks;

aligning a first one of the masks with respect to the optical element;

coating the optical element with photoresist;

exposing the photoresist through the aligned mask;

developing the photoresist;

etching the optical element;

aligning the next one of the masks with respect to the pattern etched with the first of the masks; and

repeating the coating, exposing, developing, etching, and aligning steps for each of the masks to produce 2^N levels into the optical element.