Method and apparatus for characterizing microelectromechanical devices on wafers

• US 20050286105A1
• Filed: 06/23/2004
• Published: 12/29/2005
• Est. Priority Date: 06/23/2004
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Feinstein, Casey, Simonian, Dmitri
• Granted Patent: US 7,345,806 B2
• Time in Patent Office: Days
• US Class Current: 359/224.1
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01N 21/956 Inspecting patterns on the surface of objects contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10

Abstract

The invention provides a method and apparatus for evaluating the quality of microelectromechanical devices having deformable and deflectable members using resonation techniques. Specifically, product quality characterized in terms of uniformity of the deformable and deflectable elements is inspected with an optical resonance mapping mechanism on a wafer-level.

Claims

1. A method of evaluating a quality of a plurality of microelectromechanical devices on a wafer, each microelectromechanical device having a reflective and deflectable plate attached to a deformable hinge that is held on the wafer;

the method comprising;

measuring a distribution of a parameter that characterizes a mechanical property of the microelectromechanical device; and

evaluating a uniformity of the microelectromechanical device on the wafer based on the measured distribution of the parameter.

2. The method of claim 1, wherein the microelectromechanical device is a micromirror array device having an array of micromirrors.

3. The method of claim 2, wherein the step of measuring the distribution of the parameter further comprises:

measuring the parameter from a number of micromirrors at a time;

repeating the parameter measurement for the micromirrors across the wafer; and

obtaining the distribution based on the measured parameter of the micromirrors across the wafer.

4. The method of claim 2, wherein the number of micromirrors is 100 or less.

5. The method of claim 2, wherein the number of micromirrors is from 500 to 5000.

6. The method of claim 2, wherein the number of micromirrors is 1000 or more.

7. The method of claim 3, wherein the mechanical property is a resonance frequency.

8. The method of claim 2, wherein each of the plurality of the mirror plates on the wafer has a dimension of 50 microns or less.

9. The method of claim 2, wherein each of the plurality of the mirror plates on the wafer has a dimension of 20 microns or less

10. The method of claim 2, wherein the plurality of the mirror plates on the wafer is organized into a set of mirror plate arrays, wherein the adjacent mirror plates within an array have a center-to-center distance of 20 microns or less.

11. The method of claim 7, wherein the step of measuring the parameter further comprises:

illuminating the number of the mirror plates with a light beam;

applying an AC voltage to the number of mirror plates such that the mirror plates oscillate in the vicinity of their equilibrium states; and

sweeping the frequency of the AC voltage, and measuring the frequency response of the reflected light beam from the illuminated mirror plates.

12. The method of claim 11, wherein the parameter is measured in the absence of a DC voltage.

13. The method of claim 11, wherein the AC voltage has an amplitude that is 10% or less of a voltage amplitude necessary for rotating the mirror plate to an ON state that corresponds to a rotation angle of 120 degrees or more.

14. The method of claim 13, wherein the amplitude of the AC voltage is 1% or less of the amplitude of the voltage necessary for rotating the mirror plate to the ON state.

15. The method of claim 11, further comprising:

measuring the uniformity with a quality-peak Q that is a function of the full-width-half-maximum (FWHM) of the frequency response, wherein the FWHM is defined as a ratio of the frequency integrated over the frequency scan range to the peak value of the frequency resonance peak.

16. The method of claim 2, wherein the step of evaluating the quality of the mirror plates further comprises:

calculating a variation of the resonance frequencies of the mirror plate across the wafer; and

evaluating the quality of the mirror plates based on the calculated variation.

17. The method of claim 16, further comprising:

marking a die on the wafer as “

good”

if the variation of the resonance frequency of the die is equal to or less than the predetermined quality criterion.

18. The method of claim 17, wherein the predetermined criterion is that the variation of the resonance frequency is 2% or less.

19. The method of claim 17, wherein the predetermined criterion is that the variation of the resonance frequency is 1% or less.

20. The method of claim 2, further comprising:

after the step of forming the mirror plates and hinges on a wafer, placing the wafer having the mirror plates and hinges into a chamber that has a pressure of lower than 1 Torr.

21. The method of claim 20, wherein the pressure inside the chamber is 200 mTorr or less.

22. The method of claim 20, wherein the pressure inside the chamber is 100 mTorr or less.

23. The method of claim 20, wherein the wafer is light transmissive.

24. The method of claim 23, wherein the light transmissive wafer is glass.

25. The method of claim 24, wherein the step of forming the mirror plates and hinges on the glass wafer further comprises:

depositing a sacrificial material on the glass wafer;

forming the mirror plates and hinges on the sacrificial material; and

removing the sacrificial material so as to free the mirror plates.

26. The method of claim 2, wherein the steps are performed in the absence of a semiconductor wafer having a plurality of electrodes and circuitry formed thereon.

27. The method of claim 11, further comprising:

detecting a light beam reflected from the mirror plates, wherein the reflected light propagates along a direction that is perpendicular to a surface of the plats of the microelectromechanical devices when the plates are at a natural resting state.

28. The method of claim 2, wherein the step of determining the uniformity further comprises:

passing the microelectromechanical device if the uniformity is within a predetermined threshold; and

failing the microelectromechanical device if the uniformity is beyond the predetermined threshold.

29. A method of evaluating a quality of a plurality of microelectromechanical devices on a wafer, each microelectromechanical device having a reflective and deflectable plate attached, the method comprising:

applying an AC voltage in the absence of a DC voltage to a plurality of the plates to cause each of the plurality of plates to resonate in the vicinity of an equilibrium state;

detecting a resonate frequency of the plate; and

determining the quality of the microelectromechanical device based upon the detected resonance frequency.

30. The method of claim 29, wherein the step of determining the quality further comprises:

passing the microelectromechanical device if the detected resonance frequency is within a predetermined threshold; and

failing the microelectromechanical device if the detected resonance frequency is beyond the predetermined threshold.

31. A method of evaluating a quality of a plurality of microelectromechanical devices on a wafer, each microelectromechanical device having a reflective and deflectable plate attached, the method comprising:

moving a plurality of plates of the microelectromechanical devices to a particular state with a DC voltage;

applying an AC voltage to the plurality of plates to cause each of the plurality of plates to resonate in the vicinity of an equilibrium position of the particular state;

detecting a resonate frequency of the plate; and

determining the quality of the microelectromechanical device based upon the detected resonance frequency;

wherein in the particular position, the plate has an angle to a substrate on which the plates are formed; and

wherein the angle is 140 degrees or more.

32. The method of claim 31, wherein the step of determining the quality further comprises:

passing the microelectromechanical device if the detected resonance frequency is within a predetermined threshold; and

failing the microelectromechanical device if the detected resonance frequency is beyond the predetermined threshold.

33. The method of claim 31, wherein the angle is 180 degrees or more.

34. The method of claim 31, wherein the angle is 200 degrees or more.

35. The method of claim 31, wherein the angle is 220 degrees or more.