SYSTEM AND METHOD FOR DETECTING LOCAL MECHANICAL STRESS IN INTEGREATED DEVICES

• US 20090219508A1
• Filed: 02/29/2008
• Published: 09/03/2009
• Est. Priority Date: 02/29/2008
• Status: Active Grant

• Current Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Original Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Inventors: Slinkman, James A., Dahayanaka, Daminda, Moszkowicz, Leon, Bumm, Lloyd, Kaszuba, Philip V.
• Granted Patent: US 7,944,550 B2
• Time in Patent Office: Days
• US Class Current: 356/32
• CPC Class Codes: G01B 21/32 for measuring the deformation in a solid
• CPC Class Codes: G01Q 60/30 Scanning potential microscopy

Abstract

A method of detecting local mechanical stress in integrated devices is provided, the method comprising: enabling the detection of a photovoltage difference between a scan probe device and a surface portion of an integrated device, the scan probe device being configured to deflect in response to the photovoltage difference; measuring the deflection of the scan probe device in response to the photovoltage difference between the scan probe device and the surface portion of the integrated device; and calculating a local stress level within the integrated device by determining a local work function of the surface portion of the integrated device based upon the deflection of the scan probe device.

Claims

1. A method of detecting mechanical stress in integrated devices, the method comprising:

enabling the detection of a photovoltage difference between a scan probe device and a surface portion of an integrated device, the scan probe device being configured to deflect in response to the photovoltage difference;

measuring the deflection of the scan probe device in response to the photovoltage difference between the scan probe device and the surface portion of the integrated device; and

calculating a local stress level within the integrated device by determining a local work function of the surface portion of the integrated device based upon the deflection of the scan probe device.

2. The method as in claim 1, wherein irradiating with a first laser signal and a second laser signal at the integrated device enables the detection of the photovoltage difference.

3. The method as in claim 2, wherein the first laser signal and the second laser signal are modulated in an alternating manner.

4. The method as in claim 2, wherein the first laser signal is positioned at a first angle of incidence with respect to the surface portion of the integrated device and the second laser signal is positioned at a second angle of incidence with respect to the surface portion of the integrated device.

5. The method as in claim 4, wherein the first angle of incidence and the second angle of incidence are the same or different from one another.

6. The method as in claim 4, wherein the first angle of incidence and the second angle of incidence is approximately at a Brewster angle with respect to the surface portion of the integrated device.

7. The method as in claim 2, wherein the first laser signal has a third angle of incidence with respect to the second laser signal.

8. The method as in claim 1, wherein the local stress level within the integrated device is measured approximately at a 100-nanometer scale.

9. A method of detecting mechanical stress in integrated devices, the method comprising:

irradiating with a first laser signal and a second laser signal at a surface portion of an integrated device enabling the detection of a photovoltage difference between a scan probe device and the surface portion of the integrated device, the scan probe device being suspended over the integrated device;

measuring the deflection of the scan probe device in response to the photovoltage difference; and

calculating a local stress level within the integrated device at the surface portion by determining a local work function of the surface portion of the integrated device based on the deflection of the scan probe device.

10. The method as in claim 9, wherein the local stress level is derived from the measurement of the deflection of the scan probe device in response to the photovoltage difference.

11. The method as in claim 9, wherein the first laser signal is positioned at a first angle of incidence with respect to the surface portion of the integrated device and the second laser signal is positioned at a second angle of incidence with respect to the surface portion of the integrated device.

12. The method as in claim 11, wherein the first angle of incidence and the second angle of incidence is approximately at a Brewster angle.

13. The method as in claim 9, wherein the first laser signal has a third angle of incidence with respect to the second laser signal.

14. The method as in claim 9, wherein the first laser signal couples locally to a first wave vector in the surface portion of the integrated device and the second laser signal couples locally to a second wave vector in the surface portion of the integrated device detecting differing work functions at the surface portion of the integrated device.

15. The method as in claim 9, wherein the photovoltage difference is detected by scanning a tip of the scan probe device, the tip of the scan probe device being applied a time varying electrical stimulus with a frequency at or proximate to the mechanical resonant frequency of the scan probe device.

16. The method as in claim 9 further comprising, applying a biasing voltage between the integrated device and the scan probe device based on the photovoltage difference to actively null the deflection of the scan probe device.

17. The method as in claim 9 further comprising:

acquiring a topographic image of the surface portion of the integrated device; and

maintaining a constant separation distance between the scan probe device and the integrated device based on the topographic image when irradiating with the first laser signal and the second laser signal at the surface portion of the integrated device.

18. An apparatus for detecting mechanical stress in integrated devices, the apparatus comprising:

an integrated device having a surface portion with a local work function;

a scan probe device suspended over the integrated device;

an optical controller configured for enabling the detection of a photovoltage difference between the integrated device and the scan probe device, the scan probe device being configured to move in response to the photovoltage difference;

a scan probe detector configured for measuring the movements of the scan probe device in response to the photovoltage difference; and

a processing unit in signal communication with the scan probe detector, the processing unit being configured for calculating a local stress level within the integrated device by determining the local work function of the surface portion of the integrated device based upon the deflection of the scan probe device.

19. The apparatus of claim 18, wherein the scan probe device includes a cantilever with a fine tip, the fine tip being configured to oscillate at a resonant frequency, the scan probe device being configured to move along a z-directional plane.

20. The apparatus of claim 18, wherein the optical controller includes a first light-emitting source and a second light-emitting source.

21. The apparatus of claim 20, wherein the first light-emitting source is positioned at a first angle of incidence with respect to the surface portion of the integrated device and the second light-emitting source is positioned at a second angle of incidence with respect to the surface portion of the integrated device.

22. The apparatus of claim 21, wherein the first angle of incidence and the second angle of incidence is approximately at a Brewster angle.

23. The apparatus of claim 20, wherein the first light-emitting source has a third angle of incidence with respect to the second light-emitting source.

24. The apparatus of claim 18, further comprising a power source configured for applying a biasing voltage between the integrated device and the scan probe device based on the photovoltage difference.

25. The apparatus of claim 18, further comprising a probe controller configured for adjusting the height of the scan probe device.