Method and apparatus for measurement of microscopic electrical characteristics

• US 6,208,151 B1
• Filed: 12/18/1998
• Issued: 03/27/2001
• Est. Priority Date: 12/23/1997
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Aton, Thomas John, Files, Leigh Ann
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): Nguyen, Vincent Q.
• Application Number:
  US09/216,204
• Time in Patent Office: 830 Days
• Field of Search: 324/718, 324/719, 324/716, 324/765, 324/713, 324/715, 324/724, 324/691
• US Class Current: 324/691
• CPC Class Codes: G01R 1/071 containing electro-optic elements

Abstract

The improved method for microscopic measurement of electrical characteristics comprises a standard atomic force microscope (AFM). The AFM includes a pointed, conductively coated tip attached to one end of a softly compliant cantilever arm, also capable of conducting electricity. The other end of the cantilever arm is attached to the top of a piezo-electric z-axis driver which will raise and lower the cantilever arm as the AFM tip is scanned across the surface of a sample. A piezo-electric X-Y scanstage controller may also be provided and connected to the bottom of the z-axis driver. The X-Y scanstage is preferably capable of scanning the movement of the entire system including the Z-axis driver, cantilever arm and AFM tip.

Claims

1. A method of microscopic electrical measurement comprising the steps of:

connecting a volt measurement system at two spaced apart points on a sample;

connecting a conductive probe to the sample at a point on said sample between said two spaced apart points;

injecting a measured current from a current source through the conductive probe and into the sample;

moving the conductive probe to different locations on the sample between said two spaced apart points;

recording the voltage across the two spaced apart points resulting from said injecting of a measured current as a function of the location of the probe on the sample; and

recording the current injected into the sample as a function of the location of the probe on the sample.

2. The method of claim 1 further comprising the step of attaching an ammeter to the current source and the conductive probe to measure the amount of current flowing through the conductive probe.

3. The method of claim 1 wherein a constant current source is utilized to measure and control the current injected into the sample.

4. The method of claim 1 further comprising the step of providing a conductive probe tip on an arm of the conductive probe which is capable of conducting electricity.

5. The method of claim 1 further comprising the step of providing a Z-axis driver which is capable of measuring the vertical movement of the conductive probe.

6. The method of claim 1 further comprising the step of providing an X-Y scanstage into the design of the conductive probe which is capable of monitoring and recording the location of the conductive probe tip as it is moved across the sample.

7. A method of measuring the electrical characteristics as a function of position on a semiconductor device comprising the steps of:

connecting a volt measurement system at two spaced apart points on a semiconductor device;

providing a conductive probe;

injecting a measured electric current into said conductive probe using a current source;

providing a conductive tip on said conductive probe;

contacting the conductive tip of the conductive probe with the semiconductor device at points on said semiconductor device between said two spaced apart points to allow current to flow through the semiconductor device from the current source to said two spaced apart points;

recording the voltage measured by the volt measurement system across the two spaced apart points resulting from said injecting of a measured electric current as a function of the location of the conductive tip of the conductive probe on the semiconductor device; and

recording the measured electric current as a function of the location of the conductive tip of the conductive probe on the sample.

8. The method of claim 7 further comprising the step of providing an ammeter coupled to the current source and the conductive probe to measure the current flowing through the conductive probe.

9. The method of claim 7 wherein a constant current source is provided to measure and control the current injected into the sample.

10. The method of claim 7 further comprising the step of providing a Z-axis driver into the conductive probe which is capable of measuring the vertical movement of an arm of the conductive probe.

11. The method of claim 7 further comprising the step of providing an X-Y scanstage into the design of the conductive probe which is capable of monitoring and recording the location of the conductive probe tip as it is scanned across a sample.

12. The method of claim 7 wherein the semiconductor device further comprises a P-N junction.

13. The method of claim 12 further comprising the steps of:

measuring the depth of the P-N junction by sectioning the semiconductor device through the P-N junction; and

forming a polished edge and recording the current and voltage as a function of location of the conductive tip on the polished edge.

14. A system for microscopic measurement of an electric field in a sample, said sample having a first end and a second end comprising:

a sample having a first end and a second end;

a voltmeter connected across said first end and said second end of said sample;

a conductive probe connected to a current source for injecting current from the current source through the conductive probe and into the sample between said first end and said second end;

a scanstage controller for scanning the conductive probe along the sample; and

a recorder to record current flow and location of said conductive probe and voltage across said first end and said second end on the sample resulting from said injecting current and from said current source into said sample.

15. The system of claim 14 further comprising an ammeter connected to the current source for measuring the current supplied by the current source.

16. The system of claim 14 wherein the current source further comprises a constant current source capable of controlling and measuring the current injected into the sample.

17. The system of claim 14 wherein the conductive probe further comprises:

a conductive tip;

a conductive arm;

the conductive tip attached to the conductive arm; and

the conductive tip capable of being scanned across the sample to inject current into the sample.

18. The system of claim 14 further comprising a Z-axis driver capable of measuring the vertical movement of the arm of the conductive probe.

19. The system of claim 14 further comprising an X-Y scanstage capable of scanning the conductive probe across selected portions of the sample.

20. The system of claim 14 wherein the sample further comprises a semiconductor device with at least one P-N junction.

21. The system of claim 20 further comprising:

a voltmeter connected with two electrically conductive leads extending from the semiconductor device; and

a conductive tip carried by the conductive probe to inject electrical current at selected locations on the semiconductor device.