MICRO-MECHANICAL PROBES FOR CHARGE SENSING

• US 20010011887A1
• Filed: 06/12/1997
• Published: 08/09/2001
• Est. Priority Date: 06/12/1996
• Status: Active Grant

• Current Assignee: Princeton University
• Original Assignee: Princeton University
• Inventors: STURM, JAMES C., PANGAL, KIRAN, FIREBAUGH, SAMARA L.
• Granted Patent: US 6,300,756 B2
• Time in Patent Office: Days
• US Class Current: 324/109
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge

Abstract

A method and apparatus for measuring a charge on surface, such as on a semiconductor wafer, arising during plasma processing is provided. Such a charge may be measured on an insulating film applied to such a wafer. By the present invention, the charge on such an insulator exposed to plasma is measured in-situ using micro-cantilevers. The micro-cantilevers include an insulating base positioned on the substrate and a cantilevered beam extending therefrom to over the substrate. The beam is formed of a conductive material. A charge on the beam causes an opposite charge to form on the substrate. The opposite charges attract to move or deflect the beam towards the substrate. The amount of movement or deflection corresponds to the magnitude of the charge. This movement or deflection of the beam can be measured to determine the charge by bouncing a light source, such as a laser, off of the beam. In another embodiment, the cantilever includes a flexible bridge interconnected between the base and a rigid beam. In this embodiment, the surface of the beam does not bend. Rather, movement of the beam is accomplished by the bending of the flexible bridge. This allows for easier measurements of the movement of the beam because the surface of the beam remains planar.

Claims

1. An apparatus for measuring charge on a surface comprising:

insulating base means positioned on the substrate;

beam means extending from the base to over the substrate;

wherein when a charge is formed on the beam, an opposite charge is formed on the substrate causing the beam to deflect towards the substrate; and

means for measuring the deflection of the beam means.

2. The apparatus in

claim 1

wherein the base means and beam means are microscopic in dimension.

3. The apparatus of the

claim 2

wherein the beam means is comprised of polycrystalline silicon.

4. The apparatus of

claim 2

wherein the means for measuring deflection of the beam means comprises light means for reflecting off of the beam means to a light position detector means.

5. The apparatus of

claim 4

wherein the light means comprises a laser.

6. An apparatus for measuring charge on a substrate comprising:

an insulated base positioned on the substrate;

a flexible bridge extending from base;

a conductive beam interconnected with the flexible bridge, the beam having a surface charge mirroring the charge on the substrate, the bridge bending to move the beam towards the substrate based on the electrical attraction between the charge on the beam and the charge on the substrate; and

means for measuring the movement of the beam with respect to the substrate.

7. The apparatus in

claim 6

wherein the base and beam are microscopic in dimension.

8. The apparatus of the

claim 7

wherein the beam is comprised of polycrystalline silicon.

9. The apparatus of

claim 8

wherein the means for measuring the deflection comprises bouncing a light source off the beam to a light position detector.

10. The apparatus of

claim 9

wherein the light source comprises a laser.

11. A method of measuring a charge on a surface comprising the steps of:

positioning an insulated base on a substrate;

interconnecting a conductive beam with the insulating base, the beam extending over the substrate;

allowing a charge to form on the substrate in response to a charge on the beam;

allowing the beam to move towards the substrate because of an electrical attraction between the charge on the beam and the charge on substrate; and

measuring the deflection of the beam.

12. The method of

claim 11

wherein the step of measuring the deflection of the beam comprising reflecting a light source off of the beam to a light position detector.

13. The method of

claim 11

wherein the step of measuring the deflection of the beam comprises measuring the change in angle of a light source reflected off the beam.

14. The method of

claim 11

wherein the step of measuring the deflection of the beam comprises measuring defraction of a light source directed at the beam.

15. The method of

claim 11

further comprising positioning a plurality of beams to extend over the substrate.

16. The method of

claim 15

wherein the step measuring the deflection of the beams comprising inspecting the beams.

17. The method of

claim 15

further comprising utilizing beams of varying size.

18. The method of

claim 17

further comprising the step of allowing the beams to deflect to contact the substrate and stick thereto.

19. The method of

claim 18

wherein the step of measuring the deflection comprises visually inspecting the stuck beams.

20. The method of

claim 11

wherein the substrate is non-conductive and the method includes the step of applying a conductive layer over a portion of the substrate prior to positioning an insulated base on the substrate.