Method of adding mass to MEMS structures

• US 20040219340A1
• Filed: 04/29/2003
• Published: 11/04/2004
• Est. Priority Date: 04/29/2003
• Status: Active Grant

• Current Assignee: North Star Innovations Inc. (Wi-LAN Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: McNeil, Andrew C., Li, Gary, OʼBrien, Gary J.
• Granted Patent: US 7,005,193 B2
• Time in Patent Office: Days
• US Class Current: 428/209
• CPC Class Codes: B81B 2201/025 Inertial sensors not provided for in B81B2201/0235 - B81B2201/0242
• CPC Class Codes: B81B 3/0078 Constitution or structural means for improving mechanical properties not provided for in B81B3/007 - B81B3/0075
• CPC Class Codes: G01P 15/08 with conversion into electric or magnetic values
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/0888 for indicating angular acceleration
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type
• CPC Class Codes: Y10T 428/24917 including metal layer

Abstract

A proof mass (11) for a MEMS device is provided herein. The proof mass comprises a base (13) comprising a semiconductor material, and at least one appendage (15) adjoined to said base by way of a stem (21). The appendage (15) comprises a metal (17) or other such material that may be disposed on a semiconductor material (19). The metal increases the total mass of the proof mass (11) as compared to a proof mass of similar dimensions made solely from semiconductor materials, without increasing the size of the proof mass. At the same time, the attachment of the appendage (15) by way of a stem (21) prevents stresses arising from CTE differentials in the appendage from being transmitted to the base, where they could contribute to temperature errors.

Claims

1. A proof mass for a MEMS device, comprising:

a base comprising a first material; and

at least one appendage adjoined to said base by way of a stem, said appendage comprising a second material which is denser than said first material.

2. The proof mass of claim 1, wherein said appendage is adjoined laterally to said base by way of said stem.

3. The proof mass of claim 1, wherein said appendage is adjoined vertically to a major surface of said base by way of said stem.

4. The proof mass of claim 1, wherein said first material comprises polysilicon.

5. The proof mass of claim 1, wherein said stem and said appendage comprise a metal.

6. The proof mass of claim 1, wherein said second material is a metal selected from the group consisting of gold and aluminum.

7. The proof mass of claim 1, wherein said appendage comprises a semiconductor material having a layer of metal disposed thereon as the second material.

8. A method for making a proof mass, comprising the steps of:

providing a substrate;

defining a proof mass on the substrate, the proof mass comprising a base with an appendage adjoined thereto by way of a stem, the base comprising a first material; and

depositing a second material on the appendage;

wherein the first and second materials are diverse.

9. The method of claim 8, wherein the second material has a higher density than the first material.

10. The method of claim 8, wherein the first material is a semiconductor, and wherein the second material is a metal.

11. The method of claim 10, wherein the second material is selected from the group consisting of aluminum and gold.

12. The method of claim 8, wherein the appendage also comprises the first material.

13. The method of claim 12, wherein the appendage further comprises a third material, and wherein the first, second and third materials are diverse.

14. The method of claim 8, wherein the step of defining the proof mass comprises the steps of:

depositing a layer of the first material on the substrate; and

patterning the layer of the first material to define the base, appendage and stem.

15. The method of claim 14, further comprising the step of depositing a sacrificial layer on the substrate, and wherein the layer of the first material is deposited over the sacrificial layer.

16. The method of claim 15, wherein the sacrificial layer contains an opening that exposes a portion of the substrate, the opening defining an anchor for the proof mass.

17. A method for making a proof mass for a MEMS device, comprising the steps of:

providing a substrate;

defining a base on the substrate, the base comprising a first material; and

forming an appendage comprising a second material and being attached to the base by way of a stem;

wherein the second material has a higher density than the first material.

18. The method of claim 17, wherein the step of forming the appendage comprises the steps of:

depositing a sacrificial layer over the base;

depositing a layer of the second material over the sacrificial layer; and

at least partially removing the sacrificial layer while leaving the layer of the second material.

19. The method of claim 18 wherein, after the sacrificial layer is deposited over the base, a trench is formed in the sacrificial layer which divides the sacrificial layer into a first portion which is interior to the trench and a second portion which is exterior to the trench, and further comprising the step of backfilling the trench with a third material, wherein the sacrificial layer is partially removed by chemical etching and wherein the third material is resistant to the chemical etch used to partially remove the sacrificial layer.

20. The method of claim 17, wherein the stem comprises the second material.