# US 2017/0283255 A1 · Stabilized transient liquid phase metal bonding material for hermetic wafer level packaging of mems devices

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- Number: US 2017/0283255 A1
- Document ID: US20170283255A1
- Status: Published application
- Kind: A1
- Application number: 15/087,120
- Filed: 2016-03-31
- Published: 2017-10-05
- Earliest claimed: 2016-03-31
- Assignees: Texas Instruments Incorporated
- Applicants: Texas Instruments Incorporated
- Inventors: John Charles EHMKE; Simon Joshua JACOBS
- Web page: https://patentgrep.com/patent/US20170283255A1

## CPC

- B23K 20/16: with interposition of special material to facilitate connection of the parts, e.g. material for absorbing or producing gas
- B23K 20/026: {with diffusion of soldering material}
- B23K 20/233: without ferrous layer
- B23K 20/24: Preliminary treatment
- B81C 1/00269: {Bonding of solid lids or wafers to the substrate}
- C25D 5/10: Electroplating with more than one layer of the same or of different metals (for bearings C25D7/10)
- C25D 5/12: at least one layer being of nickel or chromium
- C25D 5/50: by heat-treatment
- C25D 5/505: {of electroplated tin coatings, e.g. by melting}
- C25D 5/611: {Smooth layers}
- C25D 7/123: {Semiconductors first coated with a seed layer or a conductive layer}
- B23K 35/3033: {Ni as the principal constituent}
- B23K 2101/42: Printed circuits
- B81C 2203/019: characterised by the material or arrangement of seals between parts
- B81C 2203/036: Fusion bonding
- B23K: SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B81C: PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS (making microcapsules or microballoons B01J13/02; processes or apparatus specially adapted for the manufacture or treatment of piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/01)
- C25D: PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR

## Abstract

In described examples, a transient liquid phase (TLP) metal bonding material includes a first substrate and a base metal layer. The base metal layer is disposed over at least a portion of the first substrate. The base metal has a surface roughness (Ra) of between about 0.001 to 500 nm. Also, the TLP metal bonding material includes a first terminal metal layer that forms an external surface of the TLP metal bonding material. A metal fuse layer is positioned between the base metal layer and the first terminal metal layer. The TLP metal bonding material is stable at room temperature for at least a predetermined period of time.

## Claims

### Claim 1

A transient liquid phase (TLP) metal bonding material, comprising:
a first substrate;
a base metal layer disposed over at least a portion of the first substrate, wherein the base metal layer has a surface roughness (Ra) of between about 0.001 to 500 nm;
a first terminal metal layer that forms an external surface of the TLP metal bonding material; and
a metal fuse layer positioned between the base metal layer and the first terminal metal layer, wherein the metal fuse layer has a thickness of between about 200 to 400 Å, and wherein the TLP metal bonding material is stable at room temperature for at least a predetermined period of time.

### Claim 2 (depends on 1)

The material of claim 1, wherein a plurality of metal layers is positioned on at least the portion of the first substrate, and the base metal layer is positioned on at least a portion of a surface of the plurality of metal layers.

### Claim 3 (depends on 1)

The material of claim 1, wherein the first terminal metal layer has a lower melting point than both the metal fuse layer and the base metal layer.

### Claim 4 (depends on 1)

The material of claim 1, wherein the first substrate is selected from the group consisting of: a semiconductor wafer, a glass wafer, a ceramic wafer, and a stack of semiconductor, glass or ceramic wafers.

### Claim 5 (depends on 1)

The material of claim 1, wherein the metal fuse layer includes a low rate of reaction with the first terminal metal layer.

### Claim 6 (depends on 1)

The material of claim 1, wherein the base metal layer has a thickness of between about 15,000 to 45,000 Å.

### Claim 7 (depends on 1)

The material of claim 1, wherein the first terminal metal layer has a thickness of between about 5,000 to 25,000 Å.

### Claim 8 (depends on 1)

The material of claim 1, wherein the base metal layer includes a metal selected from the group consisting of gold, silver, platinum, palladium, copper, zinc, tin, lead and cadmium.

### Claim 9 (depends on 1)

The material of claim 1, wherein the base metal layer includes gold.

### Claim 10 (depends on 1)

The material of claim 1, wherein the first terminal metal layer includes a metal selected from the group consisting of indium, yin, lead alloys, tin alloys, indium alloys, bismuth alloys, and gallium alloys.

### Claim 11 (depends on 1)

The material of claim 1, wherein the first terminal metal layer includes indium.

### Claim 12 (depends on 1)

The material of claim 1, wherein the metal fuse layer is selected from the group consisting of chrome, nickel, cobalt, palladium, platinum, copper, rhodium, ruthenium and tin.

### Claim 13 (depends on 1)

The material of claim 1, wherein the metal fuse layer includes nickel.

### Claim 14

A method of making a transient liquid phase (TLP) metal bonding material, the method comprising:
electroplating a base metal over at least a portion of a first substrate to form a base metal layer having a surface roughness (Ra) of between about 0.001 to 500 nm;
electroplating a metal fuse on the base metal layer and forming a metal fuse layer of between 200 and 400 Å; and
electroplating a first terminal metal onto the metal fuse layer and forming a terminal metal layer to form the TLP metal bonding material, wherein the TLP metal bonding material is stable at room temperature for at least a predetermined period of time.

### Claim 15 (depends on 14)

The method of claim 14, wherein a plurality of metal layers is positioned on at least the portion of the first substrate, and electroplating the base metal includes: electroplating the base metal onto at least a portion of a surface of the plurality of metal layers.

### Claim 16 (depends on 14)

The method of claim 14, wherein the first substrate is selected from the group consisting of: a semiconductor wafer, a glass wafer, a ceramic wafer, and a stack of semiconductor, glass or ceramic wafers.

### Claim 17 (depends on 14)

The method of claim 14, wherein the metal fuse layer is formed at a deposition rate of less than 100 Å per second.

### Claim 18 (depends on 14)

The method of claim 14, wherein the base metal layer includes gold.

### Claim 19 (depends on 14)

The method of claim 14, wherein the first terminal metal layer includes indium.

### Claim 20 (depends on 14)

The material of claim 14, wherein the metal fuse layer includes nickel.

### Claim 21

A method of forming a hermetic bond, the method comprising:
in contact with a second material, placing a transient liquid phase (TLP) metal bonding material including a first substrate, a base metal layer, a metal fuse layer and a first terminal layer, wherein the base metal layer has a surface roughness (Ra) of between about 0.001 to 500 nm and is disposed over at least a portion of the first substrate, wherein the first terminal metal layer forms the external surface of the TLP metal bonding material and is positioned between the base metal layer and the first terminal metal layer, wherein the metal fuse layer has a thickness of between about 200 to 400 Å, and wherein the second material includes a second substrate and a second terminal metal layer;
heating the TLP metal bonding material; and
melting the first terminal metal layer to form a first molten metal that dissolves the metal fuse layer, wherein the first molten metal diffuses into the first terminal metal layer and the second terminal metal layer to form an intermetallic compound that is thermally stable for at least a predetermined period of time, and wherein the intermetallic compound includes the hermetic bond between the TLP metal bonding material and the second material;
wherein the TLP metal bonding material is stable at room temperature for at least a predetermined period of time.

### Claim 22 (depends on 21)

The method of claim 21, wherein a plurality of metal layers is positioned on at least the portion of the first substrate, and the base metal layer is positioned on at least a portion of a surface of the plurality of metal layers.

### Claim 23 (depends on 21)

The method of claim 21, wherein the second substrate is selected from the group consisting of: a semiconductor wafer, a glass wafer, a ceramic wafer, and a stack of semiconductor, glass or ceramic wafers.

### Claim 24 (depends on 21)

The method of claim 21, wherein the intermetallic compound includes the fuse metal, first terminal metal, second terminal metal, and at least part of the base metal.

### Claim 25 (depends on 21)

The method of claim 21, wherein the intermetallic compound has a melting point that is greater than a melting point of the first terminal metal layer and a melting point of the second terminal metal layer.

### Claim 26 (depends on 25)

The method of claim 25, wherein the intermetallic compound includes at least in part indium and gold.

### Claim 27 (depends on 26)

The method of claim 26, wherein the intermetallic compound includes between 20-30% indium by atomic percent.