Apparatus and process for performing ellipsometric measurements of surfaces

• US 4,957,368 A
• Filed: 03/16/1989
• Issued: 09/18/1990
• Est. Priority Date: 03/16/1989
• Status: Expired due to Fees

• Current Assignee: Tennyson Smith
• Original Assignee: Photoacoustic Technology Incorporated
• Inventors: Smith, Tennyson
• Primary Examiner(s): Rosenberger, Richard A.
• Assistant Examiner(s): PHAM, HOA Q
• Application Number:
  US07/324,449
• Time in Patent Office: 551 Days
• Field of Search: 356/364, 356/365, 356/369, 356/370, 356/372, 356/381, 356/445, 356/446, 356/448, 250/225, 250/578
• US Class Current: 356/369
• CPC Class Codes: G01B 11/065 using one or more discrete wavelengths
• CPC Class Codes: G01N 2021/4716 Using a ring of sensors, or a combination of diaphragm and sensors; Annular sensor
• CPC Class Codes: G01N 2021/8427 Coatings
• CPC Class Codes: G01N 21/211 Ellipsometry optical thickness measurement G01B11/06
• CPC Class Codes: G01N 21/41 Refractivity; Phase-affecting properties, e.g. optical path length G01N21/21 takes precedence
• CPC Class Codes: G01N 21/94 Investigating contamination, e.g. dust G01N21/85 takes precedence
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10

Abstract

A compact ellipsometric apparatus is constructed using as a building block a tri-beam ellipsometric sensor having a monochromatic source of polarized light with a diverging beam of sufficient divergence that three analyzers and associated light detectors may be placed into the beam side by side so that they each receive light reflected from a surface under study at the same angle of reflection. Pairs of these sensors are used together, with one of each pair having in the optical path a quarter wave plate matched to the monochromatic light wavelength and the other of the pair having no quarter wave plate, but with the light wavelength and angle of incidence being the same for each pair. A variety of measurements are made by constructing apparatus using one or more pairs of these basic sensors, the pairs of sensors varying from each other in the light wavelength of the source and the angle of incidence of the polarized beam of light to the surface. Various apparatus having from one to six pairs of sensors have been designed, with higher numbers of sensors providing greater generality in respect to the properties that can be measured.

Claims

1. Surface measurement apparatus for determining the properties of a surface, comprising:

a pair of ellipsometric sensors, each of the sensors having a structure including

a monochromatic light source disposed so as to emit a devergent light beam along an optical path toward the surface at an angle of incidence during operation of the apparatus.

a polarizer through which the beam passes before reflecting from the surface being measured,

a first polarizing light analyzer through which a first portion of the reflected beam passes and a first detector to measure the intensity of the first portion after it passes through the first light analyzer,

a second polarizing light analyzer through which a second portion of the reflected beam passes and a second detector to measure the intensity of the second portion after it passes through the second light analyzer, and

a third polarizing light analyzer through which a third portion of the reflected beam passes and a third detector to measure the intensity of the third portion after it passes through the third light analyzer, wherein the operating wavelength of the light source and the angle of incidence for the two sensors are the same, and wherein one of the sensors further includes a quarter wave plate matched to the wavelength of the monochromatic light source, in the optical path of the beam, and the other of the sensors has no quarter wave plate in the optical path of the beam.

2. The apparatus of claim 1, further including a second pair of sensors, the second pair of sensors having the same structure and operation as the first pair of sensors except that the light sources of the second pair of sensors operate at a different wavelength than the light sources of the first pair of sensors.

3. The apparatus of claim 2, further including at least one additional pair of sensors, the additional pairs of sensors having the same structure and operation as the first pair of sensors, except that the additional pairs of sensors operate at a different combination of source wavelength and angle of incidence than either the first or the second pair of sensors.

4. The apparatus of claim 1, further including a second pair of sensors, the second pair of sensors having the same structure and operation as the first pair of sensors except that the angle of incidence of the second pair of sensors is different than the angle of incidence of the first pair of sensors.

5. The apparatus of claim 3, further including at least one additional pair of sensors, the additonal pairs of sensors having the same structure and operation as the first pair of sensors, except that the additional pairs of sensors operate at a different combination of source wavelength and angle of incidence than either the first or the second pair of sensors.

6. The apparatus of claim 1, further including, between the light source and the polarizer of each of the sensors,

a lens set that focuses the beam to the point of reflection from the surface of the surface being studied.

7. The apparatus of claim 1, wherein the light source is a lamp with a filter.

8. The apparatus of claim 1, wherein the light source for each sensor is a light emitting diode.

9. The apparatus of claim 1, further including

collimating slits that limit the dimensions of the portion of the beam incident upon the light detectors and prevent light reflecting from any surface other than the measurement surface from entering the detectors.

10. The apparatus of claim 1, further including

an amplifier connected to the output signal of each of the detectors.

11. Surface measurement apparatus for determining the properties of a surface, comprising:

a first ellipsometric sensor having a structure including

a monochromatic light source disposed so as to emit a divergent light beam along an optical path toward the surface at an angle of incidence during operation of the apparatus,

a polarizer through which the beam passes before reflecting from the surface being measured,

a first polarizing light analyzer through which a first portion of the reflected beam passes and a first detector to measure the intensity of the first portion after it passes through the first light analyzer,

a second polarizing light analyzer through which a second portion of the reflected beam passes and a second detector to measure the intensity of the second portion after it passes through the second light analyzer, and

a third polarizing light analyzer through which a third portion of the reflected beam passes and a third detector to measure the intensity of the third portion after it passes through the third light analyzer; and

a second ellipsometric sensor having a structure including

a monochromatic light source disposed so as to emit a divergent light beam along an optical path toward the surface at an angle of incidence during operation of the apparatus,

a polarizer through which the beam passes before reflecting from the surface being measured,

a first polarizing light analyzer through which a first portion of the reflected beam passes and a first detector to measure the intensity of the first portion after it passes through the first light analyzer,

a second polarizing light analyzer through which a second portion of the reflected beam passes and a second detector to measure the intensity of the second portion after it passes through the second light analyzer, and

a third polarizing light analyzer through which a third portion of the reflected beam passes and a third detector to measure the intensity of the third portion after it passes through the third light analyzer, and

a quarter wave plate matched to the wavelength of the monochromatic light source, in the optical path of the beam, wherein the operating wavelength of the light source for the first sensor and the second sensor are the same, and the angle of incidence for the first sensor and the second sensor are the same.

12. Surface measurement apparatus for determining the properties of a surface, comprising:

means for measuring the properties of the surface by an ellipsometric measurement, the means including at least one pair of ellipsometric sensors, the sensors of each pair having no moving parts and operating at the same light wavelength and angle of incidence, the sensors of each pair differing in that one sensor has a quarter wave plate in the optical path and the other sensor has no quarter wave plate in the optical path.

13. The apparatus of claim 12, wherein the means for measuring includes at least two pairs of ellipsometric sensors, each of which pairs of sensors operates at a different combination of light wavelength and angle of incidence than the other pairs of sensors.

14. A process for measuring surface properties of a surface, with an apparatus having no moving parts, comprising the steps of:

furnishing at least one pair of ellipsometric sensors that each measure the ellipsometric parameters del and psi without using any moving parts, each of the pairs of sensors being characterized by its wavelength of monochromatic radiation emitted by a light source in the sensor, and angle of incidence of the monochromatic light beam of the surface being measured, one of each pair of sensors having a quarter wave plate in the optical path and the other sensor of the pair having no quarter wave plate in the optical path;

setting the different pairs of ellipsometric sensors to different combinations of wavelength of monochromatic radiation and angle of incidence;

measuring the properties of a region of the surface using the pairs of ellipsometric sensors and without changing the surface properties of the region during the period when the two measurements are made; and

calculating the surface properties of the measured region from the measured properties.

15. The process of claim 14, wherein the two sensors, supplied in the step of furnishing, utilize light sources with divergent beams.

16. The process of claim 14, including the additional step of:

moving the apparatus relative to the surface to a second surface location, and repeating the steps of setting, measuring, and calculating at the second surface location.