Thermally-induced voltage alteration for analysis of microelectromechanical devices

• US 6,407,560 B1
• Filed: 06/19/2000
• Issued: 06/18/2002
• Est. Priority Date: 03/03/1998
• Status: Expired due to Term

• Current Assignee: US Department of Energy (Government of the United States of America), National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Walraven, Jeremy A., Cole, Edward I. Jr.
• Primary Examiner(s): Nguyen, Vinh P.
• Application Number:
  US09/596,858
• Time in Patent Office: 729 Days
• Field of Search: 324/752, 324/750, 324/158.1, 324/73.1, 324/765, 324/500, 324/537, 356/445, 356/373, 356/375, 250/231.14, 250/227.11, 382/145
• US Class Current: 324/754.23
• CPC Class Codes: G01R 31/2853 Electrical testing of internal connections or -isolation, e.g. latch-up or chip-to-lead connections G01R31/31717 takes precedence; test of chip-to-PCB or lead-to-PCB connections G01R31/66
• CPC Class Codes: G01R 31/311 of integrated circuits G01R31/31728 takes precedence

Abstract

A thermally-induced voltage alteration (TIVA) apparatus and method are disclosed for analyzing a microelectromechanical (MEM) device with or without on-board integrated circuitry. One embodiment of the TIVA apparatus uses constant-current biasing of the MEM device while scanning a focused laser beam over electrically-active members therein to produce localized heating which alters the power demand of the MEM device and thereby changes the voltage of the constant-current source. This changing voltage of the constant-current source can be measured and used in combination with the position of the focused and scanned laser beam to generate an image of any short-circuit defects in the MEM device (e.g. due to stiction or fabrication defects). In another embodiment of the TIVA apparatus, an image can be generated directly from a thermoelectric potential produced by localized laser heating at the location of any short-circuit defects in the MEM device, without any need for supplying power to the MEM device. The TIVA apparatus can be formed, in part, from a scanning optical microscope, and has applications for qualification testing or failure analysis of MEM devices.

Claims

1. An apparatus for analyzing a microelectromechanical (MEM) device formed on a substrate, comprising:

(a) a laser producing a laser beam;

(b) means for focusing and scanning the laser beam to irradiate a portion of the MEM device and thereby generate an induced voltage at the location of any short-circuit defects therein, the focusing and scanning means further providing a position signal to indicate the location of the laser beam on the irradiated portion of the MEM device; and

(c) means, comprising inputs of the induced voltage and the position signal, for indicating the location of each short-circuit defect within the irradiated portion of the MEM device.

2. The apparatus of claim 1 wherein the substrate comprises silicon.

3. The apparatus of claim 2 wherein the MEM device comprises a plurality of stacked layers of polycrystalline silicon.

4. The apparatus of claim 1 further including a stage for holding the MEM device.

5. The apparatus of claim 4 wherein the stage comprises means for heating or cooling the MEM device.

6. The apparatus of claim 1 wherein the laser beam has a wavelength in the range of 0.3 μ

m to 2.5 μ

m.

7. The apparatus of claim 6 wherein the laser comprises a neodymium:

yttrium-vanadium-oxide (Nd;

YVO₄) laser or a neodymium;

aluminum;

garnet (Nd;

YAG) laser.

8. The apparatus of claim 1 further comprising a photodetector for detecting a portion of the laser beam reflected or scattered from the MEM device.

9. The apparatus of claim 8 wherein the photodetector is a silicon or germanium photodetector.

10. The apparatus of claim 8 wherein the means for indicating the location of each short-circuit defect within the irradiated portion of the MEM device further includes an input from the photodetector to generate a reflected-light image of the irradiated portion of the MEM device.

11. The apparatus of claim 10 wherein the means for indicating the location of each short-circuit defect within the irradiated portion of the MEM device provides the reflected-light image of the irradiated portion of the MEM device superposed with an image of each short-circuit defect within the irradiated portion of the MEM device.

12. The apparatus of claim 1 further including a voltage amplifier, connected between the MEM device and the means for indicating the location of each short-circuit defect within the irradiated portion of the MEM device, for amplifying the induced voltage.

13. The apparatus of claim 12 wherein the voltage amplifier is an ac-coupled voltage amplifier.

14. The apparatus of claim 1 further including a switch matrix, connected between the MEM device and the means for indicating the location of each short-circuit defect within the irradiated portion of the MEM device, for selecting among a plurality of electrical connections to the MEM device.

15. The apparatus of claim 14 wherein the switch matrix is computer controlled.

16. The apparatus of claim 1 wherein the laser beam irradiates the MEM device from a top side of the substrate proximate to the MEM device.

17. The apparatus of claim 1 wherein the laser beam irradiates the MEM device from a bottom side of the substrate distal from the MEM device, with the laser beam being transmitted through the substrate.

18. The apparatus of claim 1 wherein the means for focusing and scanning the laser beam comprises a scanning optical microscope.

19. The apparatus of claim 1 wherein the means for indicating the location of each short-circuit defect within the irradiated portion of the MEM device further comprises an image processor.

20. An apparatus for analyzing a microelectromechanical (MEM) device formed on a substrate, comprising:

(a) a stage for holding the MEM device;

(b) a laser generating a laser beam;

(c) a scanning optical microscope for focusing and scanning the laser beam to irradiate a portion of the MEM device and thereby generate an induced voltage at the location of any short-circuit defect therein, the scanning optical microscope further providing a position signal to indicate the location of the laser beam on the irradiated portion of the MEM device; and

(d) a display for receiving inputs of the induced voltage and the position signal to indicate the location of each short-circuit defect within the irradiated portion of the MEM device.

21. The apparatus of claim 20 wherein the substrate comprises silicon, and the MEM device comprises polycrystalline silicon.

22. The apparatus of claim 20 wherein the stage comprises means for heating or cooling the MEM device.

23. The apparatus of claim 20 wherein the laser beam has a wavelength in the range of 0.3 μ

m to 2.5 μ

m.

24. The apparatus of claim 20 wherein the scanning optical microscope further includes a photodetector for detecting a portion of the laser beam reflected or scattered from the MEM device.

25. The apparatus of claim 24 wherein the display further includes an input from the photodetector to generate a reflected-light image of the irradiated portion of the MEM device.

26. The apparatus of claim 20 further including a voltage amplifier connected between the MEM device and the display for amplifying the induced voltage.

27. The apparatus of claim 20 further including a switch matrix connected between the MEM device and the display for selecting among a plurality of electrical connections to the MEM device.

28. An apparatus for analyzing a microelectromechanical (MEM) device formed on a substrate, comprising:

(a) a constant-current source connected to the MEM device to supply a constant current and a variable voltage thereto, the voltage provided by the constant-current source to the MEM device changing in response to a change in power demand by the MEM device;

(b) a laser producing a laser beam;

(c) means for focusing and scanning the laser beam to irradiate a portion of the MEM device and thereby change the power demand by the MEM device when the laser beam irradiates any short-circuit defect in the MEM device, the focusing and scanning means providing a position signal to indicate the location of the laser beam on the MEM device; and

(d) means, comprising inputs of the changing voltage and the position signal, for indicating the location of each short-circuit defect within the irradiated portion of the MEM device.

29. The apparatus of claim 28 wherein the substrate comprises a semiconductor substrate.

30. The apparatus of claim 29 wherein the laser beam has a wavelength in the range of 0.3 μ

m to 2.5 μ

m.

31. The apparatus of claim 28 further comprising a stage for holding the MEM device.

32. The apparatus of claim 31 wherein the stage comprises means for heating or cooling the MEM device.

33. The apparatus of claim 28 further comprising a photodetector for detecting a portion of the laser beam reflected or scattered from the MEM device.

34. The apparatus of claim 33 wherein the means for indicating the location of each short-circuit defect within the irradiated portion of the MEM device further includes an input from the photodetector to generate a reflected-light image of the MEM device.

35. The apparatus of claim 34 wherein the reflected-light image of the MEM device is superposed with an image of the short-circuit defect.

36. The apparatus of claim 28 further comprising a voltage amplifier, connected between the constant-current source and the means for indicating the location of each short-circuit defect within the irradiated portion of the MEM device, for amplifying the changing voltage.

37. The apparatus of claim 28 further comprising a switch matrix connected between the constant-current source and the MEM device for controlling a plurality of electrical connections to the MEM device.

38. The apparatus of claim 37 wherein the switch matrix is computer controlled.

39. The apparatus of claim 28 wherein the means for indicating the location of each short-circuit defect within the irradiated portion of the MEM device comprises an image processor.

40. The apparatus of claim 28 wherein the means for focusing and scanning the laser beam to irradiate a portion of the MEM device comprises a scanning optical microscope.

41. A method for analyzing a microelectromechanical (MEM) device, comprising steps for:

(a) irradiating a portion of the MEM device with a focused and scanned laser beam and thereby generating an induced voltage at the location of any short-circuit defect therein; and

(b) sensing the position of the focused and scanned laser beam and the induced voltage for determining the location of each short-circuit defect in the MEM device.

42. The method of claim 41 further including a step for heating or cooling the MEM device.

43. The method of claim 41 wherein the sensing step comprises forming an image showing the location of each short-circuit defect within the MEM device.

44. The method of claim 41 further including a step for generating a reflected-light image of the irradiated portion of the MEM device by detecting a reflected or scattered portion of the irradiating laser beam.

45. The method of claim 44 further including a step for amplifying the induced voltage prior to the sensing step.

46. A method for analyzing a microelectromechanical (MEM) device, comprising steps for:

(a) supplying electrical power to the MEM device from a constant-current source having a constant current and a variable voltage that changes in response to a change in a power demand by the MEM device;

(b) irradiating a portion of the MEM device with a focused and scanned laser beam and thereby changing the power demand of the MEM device; and

(c) detecting any short-circuit defects within the irradiated portion of the MEM device by sensing a position of the focused and scanned laser beam and a change in the variable voltage from the constant-current source.

47. The method of claim 46 wherein the step for detecting each short-circuit defect within the MEM device further comprises forming an image showing the location of the short-circuit defect in the MEM device.

48. The method of claim 47 further including steps for forming a reflected-light image of the MEM device and superposing the reflected light-image with the image of the short-circuit defect thereby forming a composite image for locating each short-circuit defect in the irradiated portion of the MEM device.

49. The method of claim 48 wherein the reflected-light image is generated by detecting a portion of the laser beam reflected or scattered from the MEM device using a photodetector.

50. The method of claim 46 further comprising a step for amplifying the change in the variable voltage prior to the detecting step.