# US 10,768,349 B2 · Reflective diffraction grating and fabrication method

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- Number: US 10,768,349 B2
- Document ID: US10768349B2
- Status: Granted
- Kind: B2
- Application number: 15/638,981
- Filed: 2017-06-30
- Published: 2017-10-19
- Granted: 2020-09-08
- Earliest claimed: 2014-03-28
- Assignees: Lumentum Operations LLC
- Applicants: Lumentum Operations LLC
- Inventors: John Michael Miller; Hery Djie; Patrick Lu; Xiaowei Guo; Qinghong Du; Eddie Chiu; Chester Murley
- Web page: https://patentgrep.com/patent/US10768349B2

## CPC

- G02B 5/1861: {Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials (G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence)}
- B29D 11/00769: {Producing diffraction gratings}
- G02B 1/10: Optical coatings produced by application to, or surface treatment of, optical elements (G02B1/08 takes precedence)
- G02B 5/1814: {structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings (G02B5/189 takes precedence)}
- G02B 5/1857: {using exposure or etching means, e.g. holography, photolithography, exposure to electron or ion beams}
- G02B 5/208: {for use with infrared or ultraviolet radiation, e.g. for separating visible light from infrared and/or ultraviolet radiation}
- G03F 7/001: {Phase modulating patterns, e.g. refractive index patterns}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- B29D: PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE (making granules B29B9/00; making preforms B29B11/00)
- G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)

## Abstract

A reflective diffraction grating and a fabrication method are provided. The reflective diffraction grating includes a substrate, a UV-absorbing layer, a grating layer having a binary surface-relief pattern formed therein, and a conforming reflective layer. Advantageously, the UV-absorbing layer absorbs light at a UV recording wavelength to minimize reflection thereof by the substrate during holographic patterning at the UV recording wavelength.

## Claims

### Claim 1

An apparatus comprising:
a substrate;
an ultraviolet (UV)-absorbing layer, configured as a single layer made of a UV-absorbing dielectric material and configured to absorb light at a UV recording wavelength,
the UV-absorbing dielectric layer being disposed directly on the substrate and separate from the substrate,
the UV-absorbing dielectric layer having a thickness of at least 1.2 μm, and
the UV-absorbing dielectric material configured to have a transmission intensity of less than 25% at the UV recording wavelength; and
a reflective grating disposed directly on the UV-absorbing dielectric material;
the UV recording wavelength being between 300 nm and 450 nm, and
the UV recording wavelength being different from an operating wavelength for the reflective grating.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the UV-absorbing dielectric material that forms the UV-absorbing layer has an extinction coefficient of greater than about 0.025 at the UV recording wavelength.

### Claim 3 (depends on 1)

The apparatus of claim 1, wherein the reflective grating comprises a grating layer that is disposed over the UV-absorbing layer and a reflective layer that is disposed over the grating layer.

### Claim 4 (depends on 3)

The apparatus of claim 3, wherein the grating layer is patterned and an upper portion of the grating layer is etched to form a surface-relief pattern.

### Claim 5 (depends on 4)

The apparatus of claim 4, wherein the surface-relief pattern includes ridges separated by grooves or the surface-relief pattern is a binary surface-relief pattern.

### Claim 6 (depends on 4)

The apparatus of claim 4, wherein the reflective layer is a conforming reflective layer conforming to the surface-relief pattern.

### Claim 7 (depends on 6)

The apparatus of claim 6, further comprising:
an adhesion layer; and
a barrier layer,
wherein the adhesion layer and the barrier layer are located between the surface-relief pattern and the conforming reflective layer.

### Claim 8 (depends on 7)

The apparatus of claim 7, wherein the conforming reflective layer is formed of gold and the adhesion layer is formed of titanium.

### Claim 9 (depends on 7)

The apparatus of claim 7, wherein the barrier layer is formed of titanium nitride.

### Claim 10 (depends on 6)

The apparatus of claim 6, wherein the conforming reflective layer is formed of gold.

### Claim 11 (depends on 1)

The apparatus of claim 1, wherein the UV-absorbing layer is a continuous, unpatterned layer.

### Claim 12 (depends on 1)

The apparatus of claim 1, wherein the UV-absorbing dielectric material has an extinction coefficient configured to suppress recording of spurious gratings in the reflective grating.

### Claim 13 (depends on 1)

The apparatus of claim 1, wherein the thickness of the UV-absorbing dielectric layer is less than 2 μm.

### Claim 14

A method of fabrication, the method comprising:
providing a substrate;
depositing an ultraviolet (UV)-absorbing layer, configured as a single layer made of a UV-absorbing dielectric material and for absorbing light at a UV recording wavelength to minimize reflection thereof,
the UV-absorbing dielectric layer having a thickness of at least 1.2 μm,
the UV-absorbing dielectric material having a transmission intensity of less than 25% at the UV recording wavelength,
the UV recording wavelength being between 300 nm and 450 nm, and
the UV-absorbing dielectric material being disposed directly on the substrate and separate from the substrate; and
forming a reflective grating directly on the UV-absorbing dielectric material,
the UV recording wavelength being different from an operating wavelength for the reflective grating.

### Claim 15 (depends on 14)

The method of claim 14, wherein the UV-absorbing dielectric material that forms the UV-absorbing layer has an extinction coefficient of greater than about 0.025 at the UV recording wavelength.

### Claim 16 (depends on 14)

The method of claim 14, wherein the reflective grating comprises a grating layer that is disposed over the UV-absorbing layer and a reflective layer that is disposed over the grating layer.

### Claim 17 (depends on 16)

The method of claim 16, wherein the grating layer is patterned and an upper portion of the grating layer is etched to form a surface-relief pattern.

### Claim 18 (depends on 17)

The method of claim 17, wherein the surface-relief pattern includes ridges separated by grooves or the surface-relief pattern is a binary surface-relief pattern.

### Claim 19 (depends on 17)

The method of claim 17, wherein the reflective layer is a conforming reflective layer conforming to the surface-relief pattern.

### Claim 20 (depends on 19)

The method of claim 19, further comprising:
depositing an adhesion layer over the surface-relief pattern; and
depositing a barrier layer over the adhesion layer,
wherein the adhesion layer and the barrier layer are located between the surface-relief pattern and the conforming reflective layer.

### Claim 21 (depends on 20)

The method of claim 20, wherein the conforming reflective layer is formed of gold and the adhesion layer is formed of titanium.

### Claim 22 (depends on 20)

The method of claim 20, wherein the barrier layer is formed of titanium nitride.

### Claim 23 (depends on 19)

The method of claim 19, wherein the conforming reflective layer is formed of gold.

### Claim 24 (depends on 14)

The method of claim 14, wherein the UV-absorbing layer is a continuous, unpatterned layer.

### Claim 25 (depends on 14)

The method of claim 14, wherein the UV-absorbing dielectric material has an extinction coefficient sufficient to suppress recording of spurious gratings in the reflective grating.