Optical profiler for films and substrates

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.

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.

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.

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.

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.

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.