Defect classification utilizing data from a non-vibrating contact potential difference sensor

• US 7,900,526 B2
• Filed: 11/30/2007
• Issued: 03/08/2011
• Est. Priority Date: 11/30/2007
• Status: Expired due to Fees

• Current Assignee: Qcept Investments, LLC
• Original Assignee: Qcept Technologies, Inc.
• Inventors: Hawthorne, Jeffrey Alan, Steele, M. Brandon, Yang, Yeyuan, Schulze, Mark
• Primary Examiner(s): Raevis, Robert R
• Application Number:
  US11/948,518
• Publication Number:
  US 20090139312A1
• Time in Patent Office: 1,194 Days
• Field of Search: None
• US Class Current: 73/866
• CPC Class Codes: G01N 27/002 by investigating the work function voltage
• CPC Class Codes: G01Q 60/30 Scanning potential microscopy
• CPC Class Codes: H01L 22/14 for electrical parameters, e.g. resistance, deep-levels, CV, diffusions by electrical means

Abstract

A method and system for identifying and classifying non-uniformities on the surface of a semiconductor or in a semiconductor. The method and system involves scanning the wafer surface with a non-vibrating contact potential difference sensor to detect the locations of non-uniformities, extracting features characteristic of the non-uniformities, and applying a set of rules to these features to classify the type of each non-uniformity.

Claims

1. A method of classifying a non-uniformity of a semiconductor wafer, comprising the steps of:

providing a semiconductor comprising a wafer having a wafer surface;

providing a contact potential difference sensor having a probe tip;

scanning the wafer surface laterally relative to the contact potential difference sensor;

generating sensor data representative of changes in contact potential difference between the sensor probe tip and the wafer surface as the sensor probe tip scans laterally relative to the wafer surface;

using the contact potential difference sensor data to detect wafer non-uniformities;

processing the contact potential difference sensor data at the location of a non-uniformity by performing the steps of integrating the potential difference sensor data wherein integrated sensor data is indicative of relative surface potential, testing the integrated sensor data by performing a threshold test to identify regions of the integrated sensor data which lie within at least one of (1) in a specific range, (2) above a specified value and (3) below a specified value, thereby determining polarity at the non-uniformity and detecting a direction of change to one of lower or higher surface potential of the wafer surface; and

using the direction of change to one of lower or higher of surface potential as one feature to classify the wafer non-uniformity.

2. The method as defined in claim 1 further including separating the sensor data between spatial change and chemical change on the wafer surface.

3. The method of claim 2 further including the steps of varying a bias voltage applied between the probe tip and the wafer surface, wherein the change in the sensor data resulting from varying the bias voltage applied to the probe tip or wafer surface is used to classify the non-uniformity as resulting from a change in one of wafer height and a change in chemical state of the wafer surface.

4. The method as defined in claim 1 where the non-uniformity is classified as either metal or non-metal.

5. The method as defined in claim 1 further including the step of providing independent data characteristic of the likelihood of the non-uniformity being a chemical change and being one of metal contamination and non-metal contamination and using the independent data and the direction of change of surface potential to analyze the type of non-uniformity.

6. The method as defined in claim 1 wherein the step of using the direction of change includes measurin&

an increase in surface potential which is indicative of a metal contamination and measuring a decrease of surface potential which is indicative of an organic contamination.

7. The method of claim 1, further including applying a bias voltage to the sensor probe tip or the wafer surface to minimize average differences in the potential difference sensed, thereby minimizing the signal component arising from changes in distance between the probe tip and the wafer surface.

8. The method of claim 7 wherein the bias voltage that minimizes the average contact potential difference between the probe tip and the wafer surface is calculated as the average of at least one vibrating Kelvin probe measurement made on a representative test wafer surface.

9. The method of claim 1 further including the step of applying an illumination to the wafer surface.

10. The method of claim 1 further including the step of characterizing shape of the non-uniformity from the sensor data in order to correlate to a particular type of the non-uniformity.

11. The method of claim 1 further including the step of classifying a non-uniformity by vibrating a Kelvin probe at the location of the non-uniformity and sensing an associated signal.

12. The method of claim 11 further including the step of classifying a non-uniformity by measuring charge present at least one of on the wafer surface, on a dielectric film present on the wafer surface, and in the dielectric film present on the wafer surface based on the magnitude of a measurement of vibrating the Kelvin probe.

13. The method of claim 11 wherein the at least one vibrating Kelvin probe measurement is compared to vibrating Kelvin probe measurements on known contaminants to classify the non-uniformity.

14. The method of claim 11 wherein the step of classifying a non-uniformity comprises measuring the sensor data at a location of a non-uniformity in an image that is formed by integrating the non-vibrating contact potential difference sensor data and transforming resulting integrated data into absolute contact potential difference values based on at least two vibrating Kelvin probe measurements on the wafer surface.

15. A system for classifying non-uniformity type of a semiconductor wafer comprising:

a potential difference sensor to produce a sensor signal;

a wafer fixture to hold a semiconductor wafer and a mechanism to scan the wafer relative to the potential difference sensor and to rotate a spindle coupled to the wafer fixture, thereby enabling relative motion between the wafer and the sensor; and

a source of independent data indicative of whether a non-uniformity type is a metallic contaminant or nonmetallic contaminant based on a direction of change of the sensor signal to a positive or negative change of surface potential, thereby enabling determination of the non-uniformity type on the wafer.

16. The system as defined in claim 15 further including a bias voltage source for applying a bias voltage to at least one of the wafer and the sensor, thereby enabling minimizing average differences in potential differences sensed to minimize a signal component arising from changes in distance between the sensor and a surface of the wafer.

17. The system as defined in claim 15 further including a vibrating Kelvin probe which measures a vibrating probe potential difference at selected locations of a non-uniformity.

18. The system as defined in claim 17 further including a device to deposit charge on a surface of the wafer, thereby enabling the classification of a non-uniformity by measuring a change in signal induced by the charge deposited on the surface of the wafer by use of the vibrating Kelvin probe.

19. The system as defined in claim 15 further including a source of light which can be applied to the wafer at selected angles of inclination with variable light intensity and variable wavelength, thereby enabling further probing of the wafer.

20. The system as defined in claim 19 wherein the source of light can be controlled to vary at least one of the light intensity and the wavelength for classifying the non-uniformity of the wafer of the semiconductor wafer.

21. A system for classifying non-uniformity type of a semiconductor wafer comprising:

a potential difference sensor to produce a sensor signal;

a wafer fixture to hold a semiconductor wafer and a mechanism to scan the wafer relative to the potential difference sensor and to rotate a spindle coupled to the wafer fixture, thereby enabling relative motion between the wafer and the sensor; and

a source of data indicative of whether a non-uniformity type is one of a metallic contaminant, nonmetallic contaminant and excess electronic charge based on the type of sensor signal, thereby enabling determination of the non-uniformity type on the wafer.