Method of trimming micro-machined electromechanical sensors (MEMS) devices

• US 6,642,067 B2
• Filed: 09/24/2001
• Issued: 11/04/2003
• Est. Priority Date: 10/03/2000
• Status: Expired due to Term

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Dwyer, Paul W.
• Primary Examiner(s): Niebling, John F.
• Assistant Examiner(s): Simkovic, Viktor
• Application Number:
  US09/963,142
• Publication Number:
  US 20020068370A1
• Time in Patent Office: 771 Days
• Field of Search: 438/17, 438/50, 438/51, 438/52, 438/53, 438/54
• US Class Current: 438/17
• CPC Class Codes: B81C 1/00666 Treatments for controlling internal stress or strain in MEMS structures
• CPC Class Codes: B81C 2201/0167 by adding further layers of materials having complementary strains, i.e. compressive or tensile strain
• CPC Class Codes: B81C 99/0035 Testing
• CPC Class Codes: B81C 99/0065 Process control; Yield prediction

Abstract

A method for delicately adjusting an orientation of features in completed micro-machined electromechanical sensor (MEMS) devices after initial formation and installation within the device packaging to trim one or more performance parameters of interest, including modulation, bias and other dynamic behaviors of the MEMS devices.

Claims

1. A method of compensating MEMS devices, the method comprising:

manufacturing the MEMS device in a substrate having a first coefficient of thermal expansion;

forming an oxide film on one or more predetermined surface areas over respective corresponding portions of the of the MEMS device each having a first shape and being effective for control of one or more performance parameters of interest, the oxide film having a second coefficient of thermal expansion different from the first coefficient of thermal expansion; and

changing one of the first shapes to a second shape different from the first shape by removing a portion of the oxide film from the surface area of the MEMS device over the corresponding portion of the of the MEMS device effective for control of one of the performance parameters of interest.

2. The method recited in claim 1, further comprising modeling the MEMS device.

3. The method recited in claim 1, further comprising measuring the performance parameters of the MEMS device after the oxide film is formed.

4. The method recited in claim 1, further comprising measuring the performance parameters of the MEMS device after a portion of the oxide film is removed.

6. The method recited in claim 1, further comprising installing cover plates on the MEMS device after removing a portion of the oxide film.

27. The method recited in claim 1 wherein removing a portion of the oxide film from one or more of the predetermined surface areas of the MEMS device further comprises irradiating the portion of the oxide film.

5. A method of compensating MEMS devices, the method comprising:

manufacturing the MEMS device in a substrate having a first coefficient of thermal expansion;

forming an oxide film on one or more predetermined surface areas of the of the MEMS device most effective for control of one or more performance parameters of interest, the oxide film having a second coefficient of thermal expansion different from the first coefficient of thermal expansion;

removing a portion of the oxide film from one or more of the predetermined surface areas of the MEMS device;

measuring the performance parameters of the MEMS device after a portion of the oxide film is removed; and

removing an additional portion of the oxide film from one or more of the predetermined surface areas of the of the MEMS device after measuring the performance parameters after a portion of the oxide film is removed.

7. A method of compensating MEMS devices, the method comprising:

manufacturing the MEMS device in a substrate having a first coefficient of thermal expansion;

forming an oxide film on one or more predetermined surface areas of the of the MEMS device most effective for control of one or more performance parameters of interest, the oxide film having a second coefficient of thermal expansion different from the first coefficient of thermal expansion;

installing cover plates on the MEMS device; and

subsequent to installing cover plates on the MEMS device, removing a portion of the oxide film from one or more of the redetermined surface areas of the MEMS device.

8. The method recited in claim 7, further comprising forming a window in one of the cover plates in an area aligned with a portion of the oxide film.

9. A compensation method for MEMS devices, the method comprising:

manufacturing the MEMS device in a silicon substrate using conventional micro-machining techniques;

growing an oxide film layer on one or more portions of the MEMS device determined to apply a physical stress effective for control of a performance parameter of the MEMS device;

performing initial measurements of the performance parameter;

irradiating the oxide film layer to remove a predetermined portion thereof; and

performing post-irradiation measurements of the performance parameter.

10. The method recited in claim 9, further comprising modeling the performance parameter prior to manufacturing the MEMS device.

11. The method recited in claim 9, further comprising repeating the irradiating the oxide film layer to remove an additional predetermined portion thereof.

12. The method recited in claim 9, further comprising installing top and bottom cover plates on the MEMS device.

13. The method recited in claim 12 wherein the installing top and bottom cover plates on the MEMS device is performed before the performing initial measurements of the performance parameter.

14. The method recited in claim 13, further comprising etching window apertures in one of the top and bottom cover plates in an area corresponding to the oxide film layer and on a side of the substrate adjacent to the oxide film layer.

15. A method of manufacturing an acceleration sensor, the method comprising:

forming one or more frames in a substantially planar silicon substrate;

suspending a pendulous proof mass from each of the frames by one or more flexures formed in the substrate;

thermally growing a silicon dioxide film over at least a portion of each of the one or more flexures;

disposing a pair of silicon cover plates on opposite surfaces of the substrate, one or more of the cover plates having a window portion formed therein opposite the portion of each of the one or more flexures having the silicon dioxide film thermally grown thereover; and

removing at least a portion of the silicon dioxide film from at least one of the flexures.

16. The method recited in claim 15 wherein the silicon dioxide film is thermally grown over a portion of each of the one or more flexures correlated to a performance parameter of the sensor.

17. The method recited in claim 16 wherein the portion of the silicon dioxide film removed is correlated to the performance parameter of the sensor according to a finite element analysis model.

18. The method recited in claim 15 wherein the silicon dioxide film is thermally grown in an amount and at a location correlated to a performance parameter of the sensor.

19. The method recited in claim 18 wherein the amount and location of the silicon dioxide film is correlated to the performance parameter of the sensor according to a finite element analysis model.

20. A method of manufacturing MEMS devices, the method comprising:

correlating one or more performance parameters of interest in a MEMS device to a location and an amount of an oxide film having a thermal expansion coefficient different from a base material of the MEMS device and formed on a surface of the MEMS device;

micro-machining the MEMS device in a substrate of the base material;

growing the oxide film on the substrate at an elevated temperature;

protecting the MEMS device with a top and a bottom cover plate;

forming window material in one of the top and bottom cover plate;

measuring the performance parameter;

removing a portion of the oxide film correlated to the performance parameter; and

determining that a suitable portion of the oxide film has been removed.

21. The method recited in claim 20, further comprising removing an additional portion of the oxide film.

22. The method recited in claim 21, further comprising measuring the performance parameter after removing an additional portion of the oxide film.

23. The method recited in claim 20 wherein removing a portion of the oxide film correlated to the performance parameter includes selectively irradiating the oxide film with laser radiation having a frequency selected to transmit through the window material and be absorbed by the oxide film.

24. The method recited in claim 20 wherein determining that a suitable portion of the oxide film has been removed includes measuring the performance parameter.

25. The method recited in claim 20 wherein correlating one or more performance parameters of interest includes modeling the MEMS device using finite element analysis.

26. The method recited in claim 25 wherein removing a portion of the oxide film correlated to the performance parameter includes removing a portion of the oxide film correlated to the performance parameter by the modeling the MEMS device.