Patent ID: 6057928
Filing Date: 2000-05-02
Classification: G01N

Abstract:
A non-contact method for determining at least one of the index of refraction and dielectric constant of a thin film with a thickness on a substrate at a desired frequency having a corresponding wavelength longer than the thickness of the thin film, the method comprising:(a) simultaneously impinging upon the thin film on said substrate at an incident angle in free space an input desired-frequency pulse having a first wavelength and a first duration and an input reference pulse having a second wavelength shorter than said first wavelength and a second duration shorter than said first duration, creating a reflected output desired-frequency pulse and a reflected output reference pulse;(b) modulating the reflected output reference pulse by the reflected output desired-frequency pulse;(c) detecting the reflected output reference pulse with a photo detector; and(d) repeating steps (a)-(c) over a plurality of delay times between said input desired-frequency pulse and said input reference pulse until a complete field waveform of said reflected output desired-frequency pulse is characterized;(e) measuring a measured phase change and a measured field reflectance from said complete field waveform of said reflected output desired-frequency pulse at said incident angle with respect to a complete field waveform of said input desired-frequency pulse;(f) repeating steps (a)-(e) for a plurality of incident angles in a range of angles, said range encompassing a Brewster's angle for said thin film, thus creating a first dataset of measured phase changes and a second dataset of measured field reflectances for said plurality of incident angles; and(g) identifying the index of refraction for said thin film by iteratively calculating a calculated phase change and a calculated field reflectance for each said incident angle at one or more indices of refraction and selecting the index of refraction that provides a best mathematical curve fit for both said first and second datasets.