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Laser Interferometric Monitor of Polymer Thin Film Properties During Device Fabrication

IP.com Disclosure Number: IPCOM000062153D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Feger, C: AUTHOR [+4]

Abstract

Disclosed is an in-situ and versatile process monitor which can measure thermal properties and thickness uniformities of transparent polymer films. The technique of laser interferometry allows one to non-destructively detect small changes in thickness and index of refraction of thin transparent films over reflective substrates from variations in the intensity of laser light reflected from those films [*]. Polymer properties which are relatable to changes in film thickness and/or refractive index include thermal expansion coefficient, stress level, drying/shrinkage rates, solvent intake/swelling/dissolution and thickness uniformity. Polymer films accessible with laser interferometry can be structures ranging in complexity from a single layer on a Si substrate to modules containing multiple levels of thin film wiring.

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Laser Interferometric Monitor of Polymer Thin Film Properties During Device Fabrication

Disclosed is an in-situ and versatile process monitor which can measure thermal properties and thickness uniformities of transparent polymer films. The technique of laser interferometry allows one to non-destructively detect small changes in thickness and index of refraction of thin transparent films over reflective substrates from variations in the intensity of laser light reflected from those films [*]. Polymer properties which are relatable to changes in film thickness and/or refractive index include thermal expansion coefficient, stress level, drying/shrinkage rates, solvent intake/swelling/dissolution and thickness uniformity. Polymer films accessible with laser interferometry can be structures ranging in complexity from a single layer on a Si substrate to modules containing multiple levels of thin film wiring. Among the above polymer properties to be measured, the laser interferometry technique has been used most fully to characterize the temporal and spatial development of thickness non-uniformities in polyimide thin films during bake. In other words, the present instrument was first used to monitor the drying of wet polymer films. In these experiments, the shrinkage (solvent loss) rates at the center and edge of a polyimide film freshly spun onto a Si wafer were measured with two interferometers assembled around a hot plate in a hood. As shown in the drawing, each interferometer consists of a low power CW laser 10 (e.g., 1 mw HeNe) and a photodiode 12 coupled to a strip chart recorder 14. The laser 10 is directed to hit the surface of a transparent polymer film 16 at approximately normal incidence. The photodiode 12 monitors the intensity of the coherently interfering beams reflected from the front and back surfaces of the film 16 on a reflective substrate 18 (e.g., Si wafer). Int...