Method and apparatus for optically measuring characteristics of a thin film by directing a P-polarized beam through an integrating sphere at the brewster's angle of the film

A method of optically measuring at least one characteristic of a thin film on a reflecting substrate, comprising the steps of:

• splitting a beam of collimated light from a source;
• passing one portion of the beam through a photodiode detector to generate one analog signal corresponding to the light intensity of the source;
• p-polarizing the other portion of the beam and directing it into an integrating sphere and onto the film at substantially the Brewster's angle of the film;
• reflecting all the light into the sphere, including (i) all diffusely reflected light and (ii) the light specularly reflected at a region inside the sphere where the specularly reflected light is incident;
• generating another analog signal corresponding to the sensed light intensity within the sphere;
• converting both analog signals to digital signals and dividing the digitized signals of said one and other signals to compensate for variations in light intensity from the source;
• and
• using said other digitized signal measuring a characteristic of the film.

Apparatus for optically measuring at least one characteristic of a thin film on a reflecting substrate, comprising:

• an integrating sphere;
• means for directing a p-polarized beam of collimated light of known intensity through the sphere and onto the film at substantially the Brewster's angle of the film;
• means for maintaining the film substantially in contact with the sphere so that all of the light will be reflected into the sphere, including (i) all diffusely reflected light and (ii) the light specularly reflected at a region inside the sphere where the specularly reflected light is incident;
• light-sensitive detecting means for generating an analog signal indicative of the intensity of light within the sphere;
• and
• means, including an analog-to-digital converter and processor, for measuring said at least one characteristic of the film from said analog signal.

An apparatus for optically measuring at least one characteristic of a thin film on a reflecting substrate, comprising:

• means for splitting a beam of collimated light from a source;
• detector means through which one portion of the beam is passed to generate one analog signal corresponding to the light intensity of the source;
• an integrating sphere closely adjacent the film;
• means for p-polarizing the other portion of the beam and directing it into the sphere and onto the film at substantially the Brewster's angle of the film for causing all the light to be reflected into the sphere, including (i) all diffusely reflected light and (ii) the light specularly reflected at a region inside the sphere where the specularly reflected light is incident;
• means for generating another analog signal corresponding to the sensed light intensity within the sphere;
• means for converting both analog signals to digital signals and dividing the digitized signals of said one and other signals to compensate for variations in light intensity from the source;
• and
• mean responsive to said other digitized signal for measuring a characteristic of the film.