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Thick Film Measurement

IP.com Disclosure Number: IPCOM000088866D
Original Publication Date: 1977-Aug-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 5 page(s) / 134K

Publishing Venue

IBM

Related People

Ananthakrishnan, RB: AUTHOR [+3]

Abstract

An "Algorithm For Computing Thin-Film Thicknesses" (hereinafter referred to as "Fast Algorithm"), is described by Ananthakrishnan et al. on pp. 3618-3620 in the April 1976 issue of the IBM Technical Disclosure Bulletin. As indicated by the title, the algorithm is optimized for thin films of oxide, over silicon, due to wavelength bandwidth limitation. For measurement of film thicknesses over 40,000 angstroms and up to 75,000 angstroms, a modification of the indicated algorithm is required.

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Thick Film Measurement

An "Algorithm For Computing Thin-Film Thicknesses" (hereinafter referred to as "Fast Algorithm"), is described by Ananthakrishnan et al. on pp. 3618-3620 in the April 1976 issue of the IBM Technical Disclosure Bulletin. As indicated by the title, the algorithm is optimized for thin films of oxide, over silicon, due to wavelength bandwidth limitation. For measurement of film thicknesses over 40,000 angstroms and up to 75,000 angstroms, a modification of the indicated algorithm is required.

Figs. 1-3 show actual reflectivity vs. wavelength curves for 20,000 angstroms, 50,000 angstroms and 75,000 angstroms thick oxide films over silicon wafers. From these figures, it can be observed that as the oxide thickness increases, the useful information from which the film thickness can be extracted occurs at higher and higher wavelengths. As a result, the application of a conventional Fast Algorithm when applied across the full wavelength spectrum would not yield the required results due to the lack of utilizable data in the low end of the spectrum. Further analyses indicated that by considering only the reflectance information contained in the useful higher wavelength region and truncating or discarding the reflectance information in the low end of the spectrum, the correct thick film thicknesses can be extracted.

This Fast Algorithm modification is shown in Fig. C, which is based on the discarding of data corresponding to a lower cut-off wavelength,...