Instrument for measuring thickness of thin film

Claim 2

An instrument for measuring the thickness of a thin film deposited on a substrate surface comprising: light source means for emitting light to be projected upon said substrate and film; projection means for projecting alternately and in succession two light beams of different wavelengths lambda 1, and lambda 2 onto the substrate and film to be measured along the same light path, said two light beams being absorbed or reflected depending upon the thickness of the film to be measured; a first splitting means for splitting light beams transmitted through or reflected from the film to be measured into two bundles of light; a first filter means comprising a first filter for transmitting only the light beam of wavelength lambda 1 and a second filter for transmitting only the ligth beam of wavelength lambda 2; means for condensing said two light beams of wavelengths lambda 1 and lambda 2 derived from said filter means; a photo-electric converter for converting light beams condensed by said condensing means into electric signals; means for detecting the minimum difference between a first signal and a second signal from said converter, said first signal depending on the light beam of wavelength lambda 1, said second signal depending on the light beam of wavelength lambda 2.

Claim 3

An instrument defined in claim 1 wherein said light beam projection means comprises a second splitting means for splitting into two light beams the light emitted from said light source means, a second filter means comprising a third filter for transmitting only the light beam of wavelength lambda 1 of the two light beams from said second splitting means and a fourth filter for transmitting only the light beam of wavelength lambda 2 of the two light beams from said second splitting means, means for alternately chopping said two light beams from said second filter means, a second condensing means for condensing said two light beams from said chopping means, and a window for transmitting said two light beams derived from said second condensing means onto the substrate and film to be measured along the same light path.

Claim 4

An instrument defined in claim 1 wherein said first splitting means comprises a dichroic mirror.

Claim 5

An instrument defined in claim 1 wherein said photoelectric converter is provided with a slit adapted to intercept only said two light beams condensed by said condensing means.

Claim 6

An instrument defined in claim 2 wherein said second splitting means comprises a dichroic mirror.

Claim 7

An instrument defined in claim 2 wherein said light beam projecting means is provided with stop means for controlling quantity of light of at least one light beam from said second splitting means.

Claim 8

An instrument defined in claim 2 wherein said chopping means is pRovided with a rotary disk having a transparent area partly formed therein.

Claim 9

An instrument defined in claim 2 further comprising an additional converter means for converting one of two light beams derived from said second splitting means into an electric signal, said electric signal being applied to said detecting means for phase detection.

Claim 10

An instrument defined in claim 2 further comprising means for supporting a plurality of substrates, and means adapted to move said substrates one by one into such a position that two light beams from said light beam projection means are projected along the same light path and to remove said substrates one by one from said specified position.

Claim 11

An instrument for measuring the thickness of a thin film deposited on a substrate surface comprising: light source means for emitting light to be projected upon said substrate and film; projection means for projecting alternately and in succession two light beams of different wavelengths lambda 1 and lambda 2 onto the substrate and film to be measured along the same light path, said two light beams being absorbed or reflected depending upon the thickness of the film to be measured; a first splitting means for splitting light beams transmitted through or reflected from the film to be measured into two bundles of light; a first filter means comprising a first filter for transmitting only the light beam of wavelength lambda 1 and a second filter for transmitting only the light beam of wavelength lambda 2; means for condensing said two light beams of wavelenths lambda 1 and lambda 2 derived from said filter means; a photoelectric converter for converting light beams consensed by said condensing means into electric signals; means for detecting the minimum difference between a first signal and a second signal from said converter, said first signal depending on the light beam of wavelength lambda 1, said second signal depending on the light beam of wavelength lambda 2said detecting means comprising an amplifier having a detector for detecting an excess input to prevent an error in measuring due to the excess input and a gain decreasing circuit responsive to the output of said excess input detector for decreasing the gain thereof.

Claim 12

An instrument for measuring the thickness of a thin film deposited on a substrate surface comprising: light source means for emitting light to be projected upon said substrate and film; projection means for projecting alternately and in succession two light beams of different wavelengths lambda 1 and lambda 2 onto the substrate and film to be measured along the same light path, said two light beams being absorbed or reflected depending upon the thickness of the film to be measured; a first splitting means for splitting light beams transmitted through or reflected from the film to be measured into two bundles of light; a first filter means comprising a first filter for transmitting only the light beam of wavelength lambda 1 and a second filter for transmitting only the light beam of wavelength lambda 2; means for condensing said two light beams of wavelenths lambda 1 and lambda 2 derived from said filter means; a photoelectric converter for converting light beams consensed by said condensing means into electric signals; means for detecting the minimum difference between a first signal and a second signal from said converter, said first signal depending on the light beam of wavelength lambda 1, said second signal depending on the light beam of wavelength lambda 2said detecting means comprising an amplifier having a detector for detecting an excess input to prevent an error in measuring due to the excess input and a gain decreasing circuit responsive to the output of said excess input detector for decreasing the gain thereof.