# US 10,502,958 B2 · H2-assisted slanted etching of high refractive index material

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- Number: US 10,502,958 B2
- Document ID: US10502958B2
- Status: Granted
- Kind: B2
- Application number: 16/174,305
- Filed: 2018-10-30
- Published: 2019-05-02
- Granted: 2019-12-10
- Earliest claimed: 2017-10-30
- Assignees: Facebook Technologies, LLC
- Applicants: Facebook Technologies, LLC
- Inventors: Nihar Ranjan Mohanty
- Web page: https://patentgrep.com/patent/US10502958B2

## CPC

- G02B 27/0172: {characterised by optical features}
- G02B 6/122: Basic optical elements, e.g. light-guiding paths
- H01J 27/022: {Details}
- H05H 1/16: using externally-applied electric and magnetic fields
- G02B 6/34: utilising prism or grating {(G02B6/293 takes precedence)}
- G02B 2027/0109: {comprising details concerning the making of holograms}
- G02B 2027/0178: {Eyeglass type (eyeglass details G02C)}
- H05H 1/4652: {using inductive coupling means, e.g. coils}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H)
- H05H: PLASMA TECHNIQUE (apparatus or processes specially adapted for producing X-rays H05G2/00); PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS

## Abstract

Techniques for fabricating a slanted structure are disclosed. In one embodiment, a method of fabricating a slanted structure in a material layer includes injecting a first reactive gas into an reactive ion source generator, generating a plasma that includes reactive ions in the reactive ion source generator, extracting at least some of the reactive ions from the plasma to form a collimated reactive ion beam towards the material layer, and injecting a second reactive gas onto the material layer. The collimated reactive ion beam and the second reactive gas etch the material layer both physically and chemically to form the slanted surface-relief structure. In some embodiments, the first reactive gas includes a low-molecular-weight gas (e.g., H2 or He). In some embodiments, a surface layer of the internal cavity of the reactive ion source generator includes a layer of an oxide material (e.g., aluminum oxide or Y2O3).

## Claims

### Claim 1

A method of fabricating a slanted surface-relief structure in a material layer, the method comprising:
injecting a first reactive gas into an reactive ion source generator, wherein the first reactive gas comprises a low-molecular-weight gas;
generating a plasma in the reactive ion source generator, the plasma including reactive ions;
extracting at least some of the reactive ions from the plasma to form a collimated reactive ion beam towards the material layer; and
injecting a second reactive gas onto the material layer,
wherein the collimated reactive ion beam and the second reactive gas etch the material layer both physically and chemically to form the slanted surface-relief structure.

### Claim 2 (depends on 1)

The method of claim 1, further comprising:
rotating the material layer based on a desired slant angle of the slanted surface-relief structure.

### Claim 3 (depends on 1)

The method of claim 1, wherein the first reactive gas comprises at least one of CF4, CHF3, CH2F2, CH3F, C4F8, C4F6, C2F6, C2F8, NF3, CLF3, N2O, N2, O2, SF6, C12, BCl3, HBr, Hz, Ar, He, or Ne.

### Claim 4 (depends on 1)

The method of claim 1, wherein the material layer includes a semiconductor substrate, a SiO2 layer, a Si3N4 material layer, a titanium oxide layer, an alumina layer, a SiC layer, a SiOxNy layer, an amorphous silicon layer, a spin on carbon (SOC) layer, an amorphous carbon layer (ACL), a diamond like carbon (DLC) layer, a TiOx layer, an AlOx layer, a TaOx layer, or a HFOx layer.

### Claim 5 (depends on 1)

The method of claim 1, wherein extracting at least some of the reactive ions from the plasma to form the collimated reactive ion beam comprises:
applying an extraction voltage on an extraction grid adjacent to the reactive ion source generator; and
applying an acceleration voltage on an acceleration grid to extract and accelerate at least some of the reactive ions,
wherein the extraction grid and the acceleration grid are aligned; and
wherein the acceleration voltage is lower than the extraction voltage.

### Claim 6 (depends on 1)

The method of claim 1, wherein the second reactive gas comprises at least one of CF4, CHF3, N2, O2, SF6, Cl2, BCl3, or HBr.

### Claim 7 (depends on 1)

The method of claim 1, wherein:
the slanted surface-relief structure comprises a slanted surface-relief optical grating.

### Claim 8 (depends on 7)

The method of claim 7, wherein:
the slanted surface-relief optical grating comprises a plurality of ridges; and
a leading edge of each ridge is parallel to a trailing edge of the ridge.

### Claim 9 (depends on 8)

The method of claim 8, wherein:
a slant angle of the leading edge and a slant angle of the trailing edge are greater than 30 degrees with respect to a surface normal of the material layer.

### Claim 10 (depends on 8)

The method of claim 8, wherein a difference between a length of the leading edge and a length of the trailing edge is less than 10% of the length of the trailing edge.

### Claim 11 (depends on 7)

The method of claim 7, wherein:
a depth of the slanted surface-relief optical grating is greater than 100 nm.

### Claim 12 (depends on 7)

The method of claim 7, wherein:
a duty cycle of the slanted surface-relief optical grating is greater than 60%.

### Claim 13 (depends on 1)

The method of claim 1, wherein:
the first reactive gas comprises H2;
the reactive ions include H+ ions;
the material layer includes a SiOmNn layer or a Si3N4 layer; and
the H+ ions react with the SiOmNn layer or the Si3N4 layer to form a SiHxNy layer.

### Claim 14 (depends on 13)

The method of claim 13, wherein the collimated reactive ion beam and the second reactive gas react with the SiHxNy layer to generate SiF4, NH3, and HCN gases.

### Claim 15

A chemically assisted reactive ion beam etching (CARIBE) system for fabricating a slanted surface-relief structure in a material layer, the CARIBE system comprising:
an reactive ion source generator configured to generate a plasma using a first reactive gas, the plasma including reactive ions, and the first reactive gas including a low-molecular-weight gas;
one or more aligned collimator grids configured to extract and accelerate at least some of the reactive ions in the plasma to form a collimated reactive ion beam towards the material layer; and
a gas ring configured to inject a second reactive gas onto the material layer,
wherein the collimated reactive ion beam and the second reactive gas etch the material layer both physically and chemically to form the slanted surface-relief structure in the material layer.

### Claim 16 (depends on 15)

The CARIBE system of claim 15, wherein:
the reactive ion source generator includes an internal cavity configured to enclose the plasma; and
a surface layer of the internal cavity includes an oxide material.

### Claim 17 (depends on 16)

The CARIBE system of claim 16, wherein the oxide material includes Y2O3 or aluminum oxide.

### Claim 18 (depends on 15)

The CARIBE system of claim 15, further comprising:
a neutralizer configured to inject an electron beam into the collimated reactive ion beam to neutralize the collimated reactive ion beam.

### Claim 19 (depends on 15)

The CARIBE system of claim 15, wherein:
the reactive ion source generator comprises an inductively coupled plasma generator.

### Claim 20 (depends on 15)

The CARIBE system of claim 15, wherein:
the first reactive gas comprises at least one of CF4, CHF3, CH2F2, CH3F, C4F8, C4F6, C2F6, C2F8, NF3, CLF3, N2O, N2, O2, SF6, H2, Cl2, BCl3, HBr, Ar, He, or Ne; and
the second reactive gas comprises at least one of CF4, CHF3, N2, O2, SF6, Cl2, BCl3, or HBr.