Optical measurement system using polarized light

• US 6,307,627 B1
• Filed: 11/16/1999
• Issued: 10/23/2001
• Est. Priority Date: 09/22/1997
• Status: Expired due to Term

• Current Assignee: HDI Instrumentation, Inc.
• Original Assignee: HDI Instrumentation, Inc.
• Inventors: Vurens, Gerard H.
• Primary Examiner(s): Pham, Hoa Q.
• Application Number:
  US09/441,253
• Time in Patent Office: 707 Days
• Field of Search: 356/369, 356/367, 356/364, 356/365, 356/360, 356/368, 356/237.1, 356/237--23, 356/630, 356/631, 250/225
• US Class Current: 356/369
• CPC Class Codes: G01J 4/04 Polarimeters using electric detection means G01J4/02 takes precedence
• CPC Class Codes: G01N 21/211 Ellipsometry optical thickness measurement G01B11/06

Abstract

An optical measurement system for evaluating the surface of a substrate or the thickness and optical characteristics of a thin film layer overlying the substrate includes a light source for generating a light beam, a static polarizing element for polarizing the light beam emanating from the light source, and a measurement system for measuring the light reflected from the substrate location. The measurement system includes a static beam splitting element for splitting the light reflected from the substrate into s-polarized light and p-polarized light. The measurement system further includes two optical sensors for separately measuring the amplitude of the s-polarized light and the intensity of the p-polarized light. A control system analyzes the measured amplitude of the s-polarized light and the p-polarized to determine changes in the topography of substrate or changes in the thickness or optical characteristics of the thin film layer.

Claims

1. An optical measurement system for evaluating a substrate area, the system comprising:

a laser source including a feedback system for generating an intensity-stabilized light beam,

a polarizing element for polarizing the light beam emanating from the laser system to provide stabilized polarized light,

an optical element for directing the stabilized polarized light to a particular location on the substrate,

a translatable assembly to enable relative motion of the polarized light beam relative to at least a portion of the substrate so that the polarized light beam impinges on multiple locations in a two dimensional field on the substrate,

a detection system for measuring the light beam after interaction with the particular location on the substrate, the detection system including

a beam splitting element for splitting the light beam after interaction with the particular location on the substrate into s-polarized light and p-polarized light,

a first sensor for measuring amplitude of the s-polarized light,

a second sensor for measuring amplitude of the p-polarized light, and

a control system for controlling said translatable assembly and measuring the location of the light beam in said field on the substrate.

2. The optical measurement system of claim 1, wherein the laser is a fiber-coupled laser diode.

3. The optical measurement system of claim 1, wherein the laser is a laser diode.

4. The optical measurement system of claim 1, wherein the polarizing element is a retarder.

5. The optical measurement system of claim 4, wherein the retarder is a quarter-wave plate.

6. The optical measurement system of claim 4, wherein the retarder is a liquid crystal variable retarder (LCVR).

7. The optical measurement system of claim 1, wherein the optical element is an objective lens.

8. The optical measurement system of claim 1, wherein the beam splitting element is a polarizing beam splitter.

9. The optical measurement system of claim 1, wherein the first sensor and the second sensor are photo-diodes.

10. The optical measurement system of claim 9, further comprising a light source feedback system for controlling and stabilizing the intensity of the light beam and wherein the light source feedback system includes a photo-diode for measuring the intensity of the light beam and generating an output signal based on the measured intensity, and

a light source controller coupled to the light source and the photo-diode, the light source controller controlling and stabilizing the light beam based on the output signal received from the photo-diode.

11. The optical measurement system of claim 10, further comprising a non-polarizing beam splitter for directing a portion of the light beam to the photo-diode.

12. The optical measurement system of claim 1, further comprising a light source feedback system for monitoring the intensity of the light beam.

13. The optical measurement system of claim 18, wherein the light source feedback system includes a photodiode for measuring the intensity of the light beam.

14. The optical measurement system of claim 1, in which the measuring system for the location of the light beam comprises a position indicating means for determining the particular location on the substrate upon which the polarized light beam impinges.

15. The optical measurement system of claim 14, wherein the position indicating means is a 512 position shaft encoder.

16. The optical measurement system of claim 15, wherein the control system is coupled to the position indicating means, the first sensor for measuring amplitude of s-polarized light, and the second sensor for measuring amplitude of p-polarized light, the control system compiling a data set correlating the measured amplitude of the s-polarized light and the p-polarized light with the particular locations on the substrate upon which the light beam impinges.

17. The optical measurement system of claim 16, wherein the control system includes memory for storing the data set.

18. The optical measurement system of claim 1, wherein the polarizing element is an electrical elliptical polarizer for elliptically polarizing the light beam.

19. The optical measurement system of claim 1, wherein the polarizing element is a linear polarizer for linearly polarizing the light beam.

20. The optical measurement system of claim 1, wherein the polarizing element is a circular polarizer for circularly polarizing the light beam.

21. The optical measurement system of claim 1 further comprising a system for collecting and measuring scattered light reflected from the substrate.

22. The optical measurement system of claim 21, wherein the system for collecting and measuring scattered light includes an integrating sphere.

23. A method of evaluating a substrate comprising the steps of generating an initial map of at least a portion of the substrate by:

generating an intensity-stabilized laser light beam by using a laser source and feedback,

polarizing the light beam to form a stabilized polarized light beam,

directing the polarized laser light beam to a measurement point on the substrate,

relatively transporting the polarized light beam to at least one new measurement point on the substrate in a two dimensional field,

separating the polarized light beam after interaction with a particular location on the substrate into a set of two orthogonally polarized light beams,

measuring the amplitude of each of the orthogonally polarized light beams,

compiling a data set by synchronizing the measured amplitude of each set of orthogonally polarized light beams with the location of each corresponding measurement point on the substrate;

thereafter following the aforesaid steps and generating a second map of said portion of the substrate; and

determining changes in the substrate by comparing the initial map with the second map.

24. The method of claim 23 wherein the step of polarizing the light beam includes the step of linearly polarizing the light beam.

25. The method of claim 23, wherein the step of polarizing the light beam includes the step of elliptically polarizing the light beam.

26. The method of claim 23, wherein the step of polarizing the light beam includes the step of circularly polarizing the light beam.

27. An optical measurement system for evaluating a substrate, the system comprising:

an intensity stabilized light source including a feedback system configured to generate an intensity stabilized light beam

a polarizing element for polarizing the light beam emanating from the light generating source to provide stabilized polarized light,

an optical element for focusing the stabilized polarized light at a particular location on the substrate,

a controllable translatable assembly to create relative movement between the focused stabilized polarized light and the substrate to move the location of the focused stabilized light over a two dimensional field on the substrate,

a detection system for measuring the light beam reflected from the particular location on the substrate, the detection system including

a beam splitting element to split the light beam reflected from the particular location on the substrate into s-polarized light and p-polarized light,

a first sensor for measuring amplitude of the s-polarized light,

a second sensor for measuring amplitude of the p-polarized light, and

a CPU for controlling said translatable assembly and for determining the location of the light beam and for analyzing the measured amplitude of the s-polarized light and the p-polarized light to determine characteristics of the substrate.

28. An optical measurement system for evaluating a substrate, the system comprising:

an intensity stabilized light source employing a feedback mechanism configured to generate an intensity stabilized light beam,

a polarizing element for polarizing the light beam emanating from the light source to provide a polarized light beam,

an optical system for directing the polarized light beam to a particular location on the substrate,

a controllable translatable assembly for moving the polarized light beam across at least a portion of the substrate in a two dimensional field such that the polarized light beam impinges upon multiple locations on the substrate,

a position indicator for determining the particular location on the substrate upon which the polarized light beam impinges,

a detection system configured to evaluate the light beam after interaction with the particular locations on the substrate upon which the polarized light beam impinges, the detection system including

a polarization analyzing element for separating the light from the particular locations on the substrate into s-polarized light and p-polarized light,

a first optical sensor measuring amplitude of the s-polarized light,

a second optical sensor measuring amplitude of the p-polarized light, and

a control system for controlling said translatable assembly and said position indicator for determining the particular location of the light beam, configured to compile a data set correlating the measured amplitude of the s-polarized light and the p-polarized light with the particular location on the substrate upon which the polarized light beam impinges.

29. The optical measurement system of claim 28, wherein a light source feedback system controls and stabilizes the intensity of the light beam.

30. The optical measurement system of claim 29, wherein the light source feedback system includes

a photo-diode for measuring the intensity of the light beam and generating an output signal based on the measured intensity, and

a light source controller coupled to the light source and the photo-diode, the light source controller controlling and stabilizing the light beam based on the output signal received from the photo-diode.

31. The optical measurement system of claim 30, further comprising a non-polarizing beam splitter for directing a portion of the light beam to the photo-diode.

32. The optical measurement system of claim 28, further comprising a system for measuring scattered light after interaction of the light beam with the substrate.

33. The optical measurement system of claim 32, wherein the system for collecting and measuring scattered light includes an integrating sphere.

34. The optical measurement system of claim 28, wherein the detection system further includes a non-polarizing beam splitter directing a portion of the light beam after interaction with the substrate to the third optical sensor.

35. The optical measurement system of claim 28, wherein the polarization analyzing element is a polarizing beam-splitter.

36. The optical measurement system of claim 28, further comprising a light source monitoring system for monitoring the intensity of the light beam.

37. A method of evaluating a substrate comprising the steps of

generating an intensity stabilized light beam;

polarizing the light beam to form a polarized light beam;

directing the polarized light beam to a particular location in a two dimensional field on the substrate;

separating the polarized light beam after interaction with the particular location on the substrate into two orthogonally polarized light beams;

controlling the directed light beam onto locations in said two dimensional field and determining the locations of the directed light beam; and

analyzing the measured amplitude of each of the two orthogonally polarized light beams and the measured phase difference between the two orthogonally polarized light beams for various locations in said two dimensional field to determine changes in the substrate.

38. The method of claim 37, further comprising the steps of monitoring the intensity of the light beam, and controlling and stabilizing the intensity of the light beam based on the monitored light intensity.

39. The method of claim 37, further comprising the steps of measuring scattered light after the light beam interacts with the substrate and wherein the step of analyzing includes analyzing the measured scattered light to determine changes in the substrate.

40. A method of evaluating a substrate area comprising the steps of:

generating an intensity-stabilized light beam using a laser source with a feedback system;

polarizing the light beam from said laser source to form a stabilized polarized light beam;

directing the stabilized polarized light beam to a point for measurement on the substrate;

relatively transporting the polarized light beam to a plurality of additional measurement points on the substrate within a two dimensional field so that the polarized light beam impinges on multiple locations on said substrate within said field

detecting the light beam after interaction with the substrate in said field including;

splitting the light beam after interaction with a location on said substrate into s-polarized light and p-polarized light and

measuring the amplitude of the s-polarized light with a first sensor, and

measuring the amplitude of the p-polarized light with a second sensor, and

controlling the transport of said polarized light beam while determining the location of the light beam on the substrate for compiling a data set for each measurement of said first and second sensors to determine characteristics of the substrate.

41. A method of evaluating a substrate comprising the steps of

generating an intensity stabilized light beam;

polarizing the light beam to form a polarized light beam;

directing the polarized light beam to particular locations in a two dimensional field on the substrate;

controlling the directed light beam onto locations in said two dimensional field and determining the impinging locations of the directed light beam; and

analyzing the measured phase difference between the two orthogonally polarized light beams for various locations in said two dimensional field to determine surface characteristics of the substrate.