# US 12,765,332 B2 · Use of tin thin film for bonding and as masking film

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- Number: US 12,765,332 B2
- Document ID: US12765332B2
- Status: Granted
- Kind: B2
- Application number: 18/572,450
- Filed: 2022-06-30
- Published: 2025-04-24
- Granted: 2026-10-13
- Earliest claimed: 2021-07-07
- Assignees: University of South-Eastern Norway
- Applicants: University of South-Eastern Norway
- Inventors: Avisek Roy; Eivind Bardalen; Per Alfred Øhlckers
- Web page: https://patentgrep.com/patent/US12765332B2

## CPC

- H10P 76/405: {characterised by their composition, e.g. multilayer masks}
- H10P 14/6319: {Formation by plasma treatments, e.g. plasma oxidation of the substrate}
- H10P 50/242: {of Group IV materials}
- H10P 76/4085: {characterised by the processes involved to create the masks}
- H10P 90/00: Preparation of wafers not covered by a single main group of this subclass, e.g. wafer reinforcement
- H10P 50/642: {Chemical etching}
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10

## Abstract

The present invention relates to a method for micromachining a silicon structure especially for SLID bonding, comprising the steps of preparing a silicon wafer with a metal pattern on said silicon, said silicon being exposed outside said pattern, the metal pattern at least having an upper surface consisting of Sn. The method comprising a step of DRIE etching of the structure for etching cavities in said exposed silicon wafer essentially without etching said Sn top layer. The method also relates to the use of Sn as an etching mask in micromachining av silicon structures.

## Claims

### Claim 1

A method for micromachining a silicon structure, comprising:
preparing a silicon wafer with a metal pattern on the silicon, the silicon being exposed outside the metal pattern, the metal pattern at least having an upper surface consisting of Sn;
Deep Reactive Ion etching (“DRIE”) of the structure for etching cavities in the exposed silicon wafer essentially without etching the Sn top layer;
wherein an under seal metal (“USM”) layer has been provided between the silicon wafer and the metal pattern; and
before the DRIE, performing a wet etching removing the USM layer outside thus exposing the silicon outside the metal pattern, metal of the USM layer being at least one of Au and TiW.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the DRIE includes reactive ion etching with CHF3 being the primary driving gas.

### Claim 3 (depends on 2)

The method according to claim 2, wherein the wet etching process is based on a 10% KOH at 80° C.

### Claim 4 (depends on 1)

The method according to claim 1, wherein the metal pattern is constituted by a Sn layer stacked on top of at least one of Cu, Au, Ag, Ni or Cu—Ni, comprising a Solid-Liquid-InterDiffusion (“SLID”) metal pattern suitable for a SLID bonding process.

### Claim 5 (depends on 1)

The method according to claim 1, wherein the metal patterns comprise a Cu layer and an Sn layer.

### Claim 6 (depends on 1)

The method according to claim 1, wherein the SLID bonding comprises bonding a corresponding Cu—Sn pattern on the metal pattern providing a Cu—Sn SLID bonding, with a resulting Cu3Sn layer between the Cu layers.

### Claim 7 (depends on 1)

The method according to claim 1, comprising using the Sn metal pattern on a silicon wafer as an etching mask during an etching process including the DRIE.

### Claim 8 (depends on 1)

The method according to claim 1, comprising using the Sn metal pattern on a silicon wafer, wherein the wafer is covered with the USM layer, the Sn metal layer being used as an etching mask during an etching process including the wet etch process, the USM metal being at least one of Au or TiW metal.