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Thin Film Measurement

IP.com Disclosure Number: IPCOM000087604D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 53K

Publishing Venue

IBM

Related People

Mathisen, ES: AUTHOR [+2]

Abstract

The measurement of thin films on reflective substrates can be achieved by measuring the reflectance as a function of wavelengths and integrating the reflectance, the reflectance being measured with a spectrophotometer, such as indicated schematically in the figure. As shown, light from a polychromatic light source 1 enters a fiber-optic bundle 2. Light is reflected from a substrate 3 and picked up by bundle 2 and transmitted to the monochromator 4, where it is analyzed across the spectrum of wavelengths. The output is detected by a detector 5 to provide an output signal from which the reflectance can be determined.

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Thin Film Measurement

The measurement of thin films on reflective substrates can be achieved by measuring the reflectance as a function of wavelengths and integrating the reflectance, the reflectance being measured with a spectrophotometer, such as indicated schematically in the figure. As shown, light from a polychromatic light source 1 enters a fiber-optic bundle 2. Light is reflected from a substrate 3 and picked up by bundle 2 and transmitted to the monochromator 4, where it is analyzed across the spectrum of wavelengths. The output is detected by a detector 5 to provide an output signal from which the reflectance can be determined.

Fiber-optic bundle 2 is a two-way bifurcated bundle serving as both the source and detector. Such a bundle is advantageous because it is small in size and easy to use. It also provides for a normal (0 degree) angle of incidence where most normal spectrophotometers and reflectance attachments are limited to 11 degrees or more. Additionally, if the surface of the substrate 3 tilts, only the normal incidence beams are collected by bundle 2.

The measurement of the thickness of a thin film on a reflecting substrate can be achieved by measuring the reflectance as a function of wavelength and integrating the reflectance over the wavelength range of 400 to 700 nm.

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The integrated reflectance is then a function of the thickness of the dielectric film. IR = IR(t).

The reflectance can be defined mathematically as follows: R = r/2/(1) + r/2/(2) 2r(1)r(2)COS(2 Delta - Phi) over 1 + r/2/(1) r/2/(2) + 2r(1)r(2) COS(2 Delta - Phi) r/2/(1) = (n(O) - n(1) over n(O) + n(1))/2/ r/2/(2) = (n(2) - n(1))/2/ + k/2/(2) over (n(2) + n(1))/2/ + k(2) Delta = 2 n(1)t over Lambda COS Theta Phi = tan/-1/ 2n(1)k(2) over n/2/(1) - n/2/(2) - k...