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Measurement of Photoresist Thickness in AZ PVP Oxide Nitride Silicon Film Sandwich

IP.com Disclosure Number: IPCOM000087600D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Ewalt, AB: AUTHOR

Abstract

Use of the lift-off process to define semiconductor geometries requires control of the thickness of many layers simultaneously. An optical technique for measuring the photoresist (AZ) thickness in such a composite without destroying the sample wafer has been developed. This algorithm is specific with respect to the film's composition and ordering (Fig. 1).

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Measurement of Photoresist Thickness in AZ PVP Oxide Nitride Silicon Film Sandwich

Use of the lift-off process to define semiconductor geometries requires control of the thickness of many layers simultaneously. An optical technique for measuring the photoresist (AZ) thickness in such a composite without destroying the sample wafer has been developed. This algorithm is specific with respect to the film's composition and ordering (Fig. 1).

Fig. 2 shows the measurement sequence followed. The reflectivity R (Lambda) of the sample is measured, and its Fourier Transform F (x) computed with respect to the variable x = 4 Pi n (Lambda)/Lambda [n(Lambda) = index of refraction of SiO(2)]. The value of x, x(max), at which F (x) is a maximum, is used as an initial estimate of the total film optical thickness.

Next, a correction term, A, based on the film ordering and the thicknesses of the underlying layers is computed. A = 1.523 T(p) + 1.461 T(O) + 2.03 T(N) + 3668.

The AZ thickness is now found algebraically: T(A) = (1.461 x(max) - A)/1.6513.

The unit used throughout is angstrom.

In addition to being nondestructive, the technique has the added advantage over tally-step measurements in that it is much faster and may be performed on standard film thickness analyzer hardware.

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