Optical profiler for films and substrates

• US 5,042,949 A
• Filed: 03/17/1989
• Issued: 08/27/1991
• Est. Priority Date: 03/17/1989
• Status: Expired due to Term

• Current Assignee: Veeco Metrology Inc. (Veeco Instruments Incorporated)
• Original Assignee: Sloan Technology Company Limited (Veeco Instruments Incorporated)
• Inventors: Young, James M., Cohen, Daniel A., Robinson, Jay E., Greenberg, Jeffrey S.
• Primary Examiner(s): TURNER, SAMUEL A
• Application Number:
  US07/325,378
• Time in Patent Office: 893 Days
• Field of Search: 356/345, 356/356, 356/358, 356/359, 356/360, 356/368, 356/381, 356/382, 356/445, 356/376, 356/361
• US Class Current: 356/451
• CPC Class Codes: G01B 11/0608 Height gauges
• CPC Class Codes: G01B 11/0675 using interferometry

Abstract

An optical non-contact surface profiler for determining (i) the surface profile of a transparent layer on a light-absorbing or opaque substrate, (ii) the surface profile of a light-absorbing or opaque substrate through a transparent layer, and (iii) the thickness profile of a transparent layer on a light-absorbing or opaque surface. A microscope alternatively configured in interferometric mode and in spectrophotometric mode provides phase data from an interference pattern and reflectance data from a reflectance pattern, respectively. A photo-sensing device receives the interference patterns and reflectance patterns and inputs the corresponding phase data and reflectance data to a computing device. The computing device processes the data to determine the appropriate surface or film thickness profiles.

Claims

1. An optical profiler for determining a surface profile from a transparent-film light-absorbing substrate combination in which the light-absorbing substrate is beneath the transparent film, comprising:

a bi-configurable optical assembly which may be configured for performing interferometry in a first configuration and for performing spectrophotometry in a second configuration;

the assembly comprising an adjustable wavelength light source for defining discrete wavelengths of illumination;

means for establishing the first configuration wherein a dual beam interference pattern is obtained for each of a plurality of wavelengths;

means for establishing the second configuration wherein a reflectance pattern is obtained for each of a plurality of wavelengths;

photosensing means for measuring the intensity across each interference pattern and each reflectance pattern; and

a computer for determining (i) the surface profile of the transparent film on the light-absorbing substrate, or (ii) the sub-surface profile of the light-absorbing substrate beneath the transparent film, or (iii) both said surface profiles, the surface profiles being determined from the intensity measurements across each interference pattern and each reflectance pattern.

2. The apparatus of claim 1, wherein a film thickness profile is calculated using the reflectance profiles obtained at multiple wavelengths.

3. An optical profiler for determining a surface profile from a transparent-film light-absorbing substrate combination in which the light-absorbing substrate is beneath the transparent film, comprising:

an optical assembly for creating an interference pattern at each of a plurality of discrete wavelengths;

an optical assembly for creating a reflectance pattern at each of a plurality of discrete wavelengths;

an intensity measuring means for measuring the intensity at each point of an interference pattern and for measuring the intensity at each point of a reflectance pattern;

a means for calculating phase value from the intensity measurements of the interference patterns using mutliwavelength phase-measured interferometry algorithms;

a means for calculating a film thickness profile from the intensity measurements of the reflectance patterns;

a means for calculating a phase correction factor from the film thickness profile; and

a means for calculating a surface profile of the transparent-film light-absorbing substrate combination from the phase value, the phase correction, and the film thickness profile.

4. The apparatus of claim 3, further comprising a means for calculating a sub-surface profile of the light-absorbing substrate beneath the transparent film by subtracting the film thickness from the surface profile of the transparent-film light-absorbing substrate combination.

5. An optical profiler for determining a surface profile from a transparent-film light-absorbing substrate combination in which the light-absorbing substrate is beneath the transparent film, comprising:

an optical assembly for creating an interference pattern at each of a plurality of discrete wavelengths;

an intensity measuring means for measuring the intensity at each point of the interference pattern;

a means for calculating phase value and fringe visibility from the intensity measurements; and

a means for determining (i) the surface profile of the transparent film on the light-absorbing substrate, or (ii) the sub-surface profile of the light-absorbing substrate beneath the transparent film, or (iii) both said surface profiles, the surface profiles being determined from the intensity measurements across the interference patterns.

6. A method for determining surface profiles for a light-absorbing substrate beneath a transparent film using an optical assembly, a photosensing device and a computer, the optical assembly having an adjustable wavelength light source for defining discrete wavelengths of light, the method comprising the steps of:

creating an interference pattern at the photosensing device with the optical assembly for each of a plurality of illumination wavelengths;

calculating with the computer a phase value from the interference patterns using multiwavelength phase measured interferometry algorithms;

creating a reflectance pattern at the photodetecting device with the optical assembly for each of a plurality of beam wavelengths;

calculating with the computer the film thickness from the reflectance patterns;

calculating with the computer a phase correction to compensate for an error in the phase value due to refraction of the light beam by the transparent film, wherein the phase correction is calculated from the film thickness and the illumination wavelengths of each reflectance pattern; and

calculating with the computer the surface profile of the transparent film on the light-absorbing substrate from the phase value, the film thickness, and the phase correction.

7. The method of claim 6, further comprising the step of:

calculating with the computer the surface profile of the light-absorbing substrate beneath the transparent film by subtracting the film thickness from the surface profile of the transparent film on the light-absorbing substrate.

8. A method for determining a film thickness profile of a transparent film on a light-absorbing substrate with an optical assembly, a photosensing device and a computer, wherein the optical assembly has an adjustable wavelength light source for defining discrete wavelengths of light, the method comprising the steps of:

illuminating the film with discrete illumination wavelengths, a portion of which is reflected back from the film surface and another portion of which is reflected back from the light-absorbing substrate, thereby creating a film interference pattern between the wavelengths reflected from the light-absorbing substrate;

creating an image of the film interference pattern at the photosensing device with the optical assembly for each of multiple illumination wavelengths;

inputting to the computer intensity data representative of the the image at the photosensing device; and

calculating the film thickness profile with the computer using the intensity data.

9. The method of claim 8, wherein the step of calculating the film thickness profile is by calculating reflectivity from the intensity data and calculating the film thickness profile from the reflectivity.

10. A method for determining the index of refraction of a transparent film on a light-absorbing substrate of known surface geometry using an optical assembly for producing a beam of light, a photosensing array, and a computer for measuring the surface profile of the light-absorbing substrate, the method comprising the steps of:

determining the surface profile of the light-absorbing substrate beneath the transparent film using an assumed index of refraction of the transparent film;

comparing the calculated surface profile of the light-absorbing substrate to the known surface geometry of the light-absorbing substrate; and

varying the assumed index of refraction of the transparent film and recalculating substrate until the calculated surface profile is the same as the known surface geometry;

wherein the unknown index of refraction is the determined index of refraction at which the calculated surface profile equals the known surface geometry.

11. An optical profiler using imaging spectrophotometry to determine a thickness profile of a transparent film, comprising:

an optical assembly for illuminating the film, said assembly having a light source and a plurality of interchangeable filters, each filter defining a discrete wavelength of the illumination, such that said assembly may illuminate the film with a discrete illumination wavelength creating an interference pattern at the film;

photosensing means, responsive to said optical assembly, for receiving from said assembly an image of the film interference pattern for multiple illumination wavelengths and for measuring an intensity profile representative of the image of the film interference pattern; and

a computer for receiving the intensity profile from the photosensing means and calculating the film thickness over the area of the film.