Refractory seed metal for electroplated MEMS structures

Patent metadata

Field	Value
Publication number	US-9845235-B2
Application number	US-201514844132-A
Country	US
Kind code	B2
Filing date	Sep 3, 2015
Priority date	Sep 3, 2015
Publication date	Dec 19, 2017
Grant date	Dec 19, 2017

Abstract

A system and method for a micro-electrical-mechanical system (MEMS) device including a substrate and a free-standing and suspended electroplated metal MEMS structure formed on the substrate. The free-standing and suspended electroplated metal MEMS structure includes a metal mechanical element mechanically coupled to the substrate and a seed layer mechanically coupled to and in electrical communication with the mechanical element, the seed layer comprising at least one of a refractory metal and a refractory metal alloy, wherein a thickness of the mechanical element is substantially greater than a thickness of the seed layer such that the mechanical and electrical properties of the free-standing and suspended electroplated metal MEMS structure are defined by the material properties of the mechanical element.

First claim

What is claimed is:

1. A micro-electrical-mechanical system (MEMS) device comprising:
a substrate; and
a free-standing and suspended electroplated metal MEMS structure formed on the substrate and comprising:
a metal mechanical element mechanically coupled to the substrate;
a seed layer mechanically coupled to and in electrical communication with the mechanical element, the seed layer comprising at least one of a refractory metal and a refractory metal alloy; and
a protective layer mechanically coupled to the mechanical element, the protective layer being formed on at least one additional surface of the mechanical element not covered by the seed layer;
wherein a thickness of the mechanical element is substantially greater than a thickness of the seed layer such that the mechanical and electrical properties of the free-standing and suspended electroplated metal MEMS structure are defined by the material properties of the mechanical element, with a product of a residual stress in the metal mechanical element and the thickness of the metal mechanical element being greater than three times (3×) that of a product of a residual stress in the seed layer and the thickness of the seed layer.

2. The MEMS device of claim 1 wherein the mechanical element is composed of a nickel-tungsten alloy.

3. The MEMS device of claim 1 wherein the seed layer is left intact on an underside of the mechanical element that faces the substrate.

4. The MEMS device of claim 3 wherein the MEMS device is a switch, the switch further comprising at least one conductive contact formed on the substrate and with the mechanical element comprising a beam cantilevered over the conductive contact;
wherein the seed layer provides an ohmic contact between the beam and the at least one conductive contact when the beam is in a contacting position.

5. The MEMS device of claim 1 wherein the at least one of the refractory metal and refractory metal alloy of the seed layer has a melting voltage of greater than 0.4 V and a melting temperature of greater than 1850° C.

6. The MEMS device of claim 1 wherein the at least one of the refractory metal and refractory metal alloy comprises ruthenium, tantalum, niobium, rhodium, molybdenum, tungsten, vanadium, chromium, zirconium, hafnium, and/or alloys thereof.

7. The MEMS device of claim 1 wherein the at least one of the refractory metal and refractory metal alloy is resistant to etchants used in micro- and nanofabrications, the etchants comprising one or more of sulfuric acid, hydrofluoric acid, buffered oxide, hydrogen peroxide and alkali photoresist developer solutions.

8. The MEMS device of claim 1 wherein the MEMS device is an inertial sensor.

9. A method of creating a micro-electrical-mechanical system (MEMS) device comprising:
providing a substrate; and
forming a free-standing metal MEMS structure on the substrate, wherein forming the free-standing metal MEMS structure comprises:
applying a sacrificial release layer on a portion of the substrate;
applying a layer of seed metal over the substrate and the sacrificial release layer, wherein the seed metal comprises at least one of a refractory metal and a refractory metal alloy;
applying a photoresist layer on a portion of the layer of seed metal;
electroplating a metallic material onto the layer of seed metal not covered by the photoresist layer to form a free-standing structure;
coating at least one additional side of the free-standing structure with a protective layer, the protective layer comprising a material that is resistant to damage or etching during a fabrication processes; and
subsequent to coating at least one additional side of the free-standing structure with a protective layer, removing the photoresist layer, the sacrificial release layer, and a portion of the layer of seed metal not in contact with the free-standing structure, such that the free-standing structure is cantilevered over the substrate;
wherein a portion of the layer of seed metal in contact with the free-standing structure remains on an underside of the free-standing structure subsequent to the removing of the photoresist layer, the sacrificial release layer, and the portion of the layer of seed metal not in contact with the free-standing structure.

10. The method of claim 9 wherein a thickness of the free-standing structure is substantially greater than a thickness of the layer of seed metal such that the mechanical and electrical properties of the free-standing metal MEMS structure are defined by the electroplated metallic material of the free-standing structure.

11. The method of claim 9 wherein the one of the refractory metal and the refractory metal alloy comprises one of ruthenium, tantalum, niobium, rhodium, molybdenum, tungsten, vanadium, chromium, zirconium, hafnium, and/or alloys thereof.

12. The method of claim 9 wherein coating the at least additional side of the free-standing structure with a protective layer comprises coating every exposed side of the free-standing structure with the protective layer.

13. The method of claim 9 wherein electroplating the metallic material onto the layer of seed metal comprises electroplating a nickel-tungsten alloy.

14. The method of claim 9 wherein removing the sacrificial release layer comprises performing a wet etching via application of at least one of sulfuric acid, hydrofluoric acid, buffered oxide, and hydrogen peroxide; and
wherein the layer of seed metal is resistant to sulfuric acid, hydrofluoric acid, buffered oxide, and hydrogen peroxide and to alkali photoresist developer solutions.

15. The method of claim 9 further comprising forming a conductive layer on the substrate, the conductive layer comprising at least one MEMS contact, wherein the layer of seed material functions as an ohmic contact between the free-standing structure and the at least one MEMS contact when the free-standing structure is in a contacting position, with the layer of seed material having a melting voltage of greater than 0.4 V and a melting temperature of greater than 1850° C.

16. The method of claim 9 wherein applying the layer of seed metal and electroplating the metallic material further comprises selecting a thickness for each of the layer of seed metal and the metallic material to be applied such that a product of a residual stress in the free-standing structure and the thickness of the free-standing structure is greater than three times (3×) that of a product of a residual stress in the layer of seed metal and the thickness of the layer of seed metal.

17. A free-standing and suspended metal micro-electro-mechanical system (MEMS) structure of a MEMS device, wherein the metal MEMS structure is fabricated by:
applying a sacrificial release layer on a portion of a substrate;
applying a seed layer of refractory metal over the substrate and the sacrificial release layer;
applying a photoresist layer on a portion of the seed layer;
electroplating a metallic material onto the seed layer in an area not covered by the photoresist layer to form a free-standing structure, the free-standing structure being mechanically coupled to and electrically connected with the seed layer; and
removing the photoresist layer, the sacrificial release layer, and a portion of the seed layer such that a layer of refractory metal remains on an underside of the free-standing structure to collectively form a free-standing and suspended metal MEMS structure on the substrate;
wherein applying the seed layer and electroplating the metallic material further comprises selecting a thickness for each of the seed layer and

Assignees

• Gen Electric

Inventors

• Brewer Joleyn Eileen
• Keimel Christopher Fred
• Aimi Marco Francesco
• Minnick Andrew
• Ruffalo Renner Stephen

Classifications

• B81B2203/0127

  Diaphragms, i.e. structures separating two media that can control the passage from one medium to another; Membranes, i.e. diaphragms with filtering function · CPC title

• B81B3/0075 Primary

  For improving wear resistance · CPC title

• B81B3/0027 Primary

  Structures for transforming mechanical energy, e.g. potential energy of a spring into translation, sound into translation · CPC title

• B81C1/00134

  comprising flexible or deformable structures (manufacture of MEMS devices for specific applications, see relevant places, e.g. gyroscopes G01C19/5719, pressure sensors G01L9/0042, accelerometers G01P15/0802, acoustic transducers or diaphragms therefor H04R31/00) · CPC title

• B81B2203/053

  Translation according to an axis perpendicular to the substrate · CPC title