# US 10,770,306 B2 · Method of etching a cavity in a stack of layers

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- Number: US 10,770,306 B2
- Document ID: US10770306B2
- Status: Granted
- Kind: B2
- Application number: 16/240,044
- Filed: 2019-01-04
- Published: 2019-07-11
- Granted: 2020-09-08
- Earliest claimed: 2018-01-05
- Assignees: STMicroelectronics (Crolles 2) SAS
- Applicants: STMicroelectronics (Crolles 2) SAS
- Inventors: Pierre Bar; Francois Leverd; Delia Ristoiu
- Web page: https://patentgrep.com/patent/US10770306B2

## CPC

- H10P 50/73: {using masks for insulating materials}
- G02B 6/3636: {the mechanical coupling means being grooves (G02B6/3652 takes precedence)}
- G02B 6/3652: {the additional structures being prepositioning mounting areas, allowing only movement in one dimension, e.g. grooves, trenches or vias in the microbench surface, i.e. self aligning supporting carriers}
- G02B 6/3692: {with surface micromachining involving etching, e.g. wet or dry etching steps (surface micromachining involving subtractive techniques B81C1/00055)}
- H10P 14/3252: {Alternating layers, e.g. superlattice}
- H10P 50/242: {of Group IV materials}
- H10P 50/283: {by chemical means}
- H10P 50/695: {characterised by the process involved to create the mask, e.g. lift-off masks or sidewalls or to modify the mask}
- G02B 6/42: Coupling light guides with opto-electronic elements
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A cavity is etched in a stack of layers which includes a first layer made of a first material and a second layer made of a second material. To etch the cavity, a first etch mask having a first opening is formed over the stack of layer. The stack of layers is then etched through the first opening to a depth located in the second layer. A second mask having a second opening, the dimensions of which are smaller, in top view, than the first opening, is formed over the stack of layer. The second opening is located, in top view, opposite the area etched through the first opening. The second layer is then etched through the second opening to reach the first layer. The etch method used is configured to etch the second material selectively over the first material.

## Claims

### Claim 1

A method, comprising:
depositing a first layer made of a first material;
depositing a second layer made of a second material on top of an upper surface of the first layer;
depositing a third layer made of the first material on top of an upper surface of the second layer;
depositing a fourth layer made of the second material on top of an upper surface of the third layer;
wherein the third layer includes a first opening and wherein material of the fourth layer is located within the first opening;
forming a first etch mask over the fourth layer, the first etch mask having a second opening aligned with the first opening;
etching the fourth layer through the first opening to form a first cavity having a depth which does not reach the second layer;
forming a second etch mask over the fourth layer and within the first cavity, the second etch mask having a third opening which is aligned with the first cavity, wherein dimensions of the third opening are, in top view, smaller than dimensions of the first opening and second opening; and
etching a remaining portion of the fourth layer and the second layer through the third opening to form a second cavity having a depth which reaches the upper surface of the first layer.

### Claim 2 (depends on 1)

The method of claim 1, further comprising etching the first layer through the second cavity.

### Claim 3 (depends on 1)

The method of claim 1, wherein the first and second materials are insulating materials.

### Claim 4 (depends on 1)

The method of claim 1, wherein the first and second materials are, respectively, silicon nitride and silicon oxide.

### Claim 5 (depends on 1)

The method of claim 1, wherein etching the fourth layer comprises performing a plasma etch by means of a plasma made up of CF4 and of nitrogen.

### Claim 6 (depends on 1)

The method of claim 1, wherein etching the remaining portion of the fourth layer and the second layer comprises performing plasma etch by means of a plasma made up of C4F8 and of dioxygen.

### Claim 7 (depends on 1)

The method of claim 1, further comprising removing the first mask before forming the second mask.

### Claim 8

A method, comprising:
a) forming a stack of layers which includes a first layer made of a first material, a second layer made of a second material, the first layer forming a lower layer of the stack, and an upper surface of the first layer being in contact with a lower surface of the second layer, a third layer made of the first material above the second layer, and a fourth layer made of the second material above the third layer, wherein the third layer includes a layer opening such that a bottom of the fourth layer extends through the layer opening and is in contact with a top of the second layer;
b) forming, on an upper surface of the stack of layers, a first etch mask having a first opening;
c) etching the stack of layers opposite the first opening to a depth located at least at the second layer and passing through the layer opening;
d) forming, on the upper surface of the stack, a second mask having a second opening, wherein dimensions of the second opening are, in top view, smaller than dimensions of the first opening, the second opening being located, in top view, opposite an area etched at step c); and
e) etching the second layer opposite the second opening by an etch method capable of etching the second material selectively over the first material, to reach the upper surface of the first layer.

### Claim 9 (depends on 8)

The method of claim 8, wherein, in top view, all the dimensions of the first opening are greater than 100 μm.

### Claim 10 (depends on 8)

The method of claim 8, wherein, in top view, all the dimensions of the second opening are smaller by from 20 to 100 μm than the dimensions of the first opening.

### Claim 11 (depends on 8)

The method of claim 8, wherein the first and second materials are insulating materials.

### Claim 12 (depends on 8)

The method of claim 8, wherein the first and second materials are, respectively, silicon nitride and silicon oxide.

### Claim 13 (depends on 8)

The method of claim 8, wherein the etch method implemented at step c) is a method of plasma etching by means of a plasma made up of CF4 and of nitrogen.

### Claim 14 (depends on 8)

The method of claim 8, wherein the etch method implemented at step e) is a method of plasma etching by means of a plasma made up of C4F8 and of dioxygen.

### Claim 15 (depends on 8)

The method of claim 8, comprising a step f), subsequent to step e), of etching completely through the first layer forming the lower layer of the stack to reach an insulating layer below the first layer.

### Claim 16 (depends on 8)

The method of claim 8, further comprising removing the first mask before forming the second mask.