Surface acoustic wave thermogravimetric measurements of thin polymer films
ABSTRACT The increased use of thin film polymers in microelectronic applications has resulted in the need to better understand their chemical, thermal, mechanical, and electrical properties. Of particular interest are changes in mass and viscoelasticity during curing of new high temperature polymers. A highly sensitive technique that can monitor mass and viscoelastic changes in thin polymer films during curing to high temperature is needed. In this work a surface acoustic wave (SAW) based system was developed that was capable of measuring the mass loss due to water outgassing during cure of thin polymer films in a temperature range of 20 to 400/spl deg/C. It also could measure the apparent glass transition temperature of acoustically thin films, and film resonance for acoustically thick films. The principle limitations of the system are the limited accuracy of temperature compensation and the limited ability to separate mass loss effects from viscoelastic effects.
Conference Paper: Measurement of Humidity Using Surface Acoustic Waves[Show abstract] [Hide abstract]
ABSTRACT: A technique is described for measuring humidity with high sensitivity and wide dynamic range using surface acoustic waves. A delay-line-stabilized SAW oscillator is used, the delay line being coated with a thin film of a suitable hygroscopic material. Sorption of moisture produces rapid changes in the electrical and mechanical properties of the film. This results in a change in the velocity of the surface acoustic wave and hence in the frequency of the SAW oscillator. With polyimide used as the hygroscopic material, the frequency of a 75-MHz oscillator fabricated on a 128 degree Y-X LiNbO//3 substrate is found to vary by more than 150 kHz as the relative humidity is varied from near 0% RH to 100% RH. The calculated detection limit (assuming oscillator short-term stability of 1 part in 10**7 ) is less than 1. 5 ppm//v of humidity, or a corresponding dew point of -72 degree C. Simultaneous humidity and temperature sensing has been demonstrated using a dual-delay-line approach.IEEE 1985 Ultrasonics Symposium; 02/1985
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ABSTRACT: Surface acoustic wave (SAW) devices have been used in two techniques for the characterization of thin-film properties: (1) the determination of diffusivity for gases or vapors from sorption transients and (2) the determination of effective surface area in porous films from 77 K nitrogen adsorption isotherms. In the first experiment, a gas or vapor is adsorbed by a polymer film and diffused through it; the transient response of sorption vs. time indicates the diffusivity. In the second experiment, nitrogen is adsorbed by the internal and external surfaces of a porous film; the equilibrium measurement of adsorption vs. pressure indicates surface area.IEEE 1987 Ultrasonics Symposium; 02/1987
Conference Paper: Monitoring Thin-Film Etching Using Surface Acoustic Waves[Show abstract] [Hide abstract]
ABSTRACT: The use of a surface-acoustic-wave (SAW) device to monitor etching of thin films is described. The device is a delay-line-stablized SAW oscillator in which the propagation path is coated with a thin film of the material to be etched. Removal of material decreases the mass loading on the delay line and this increases the frequency of the oscillator. The technique is illustrated by applying it to monitor etching of photoresist in a plasma reactor. The frequency of a 75-MHz oscillator fabricated on 128 degree Y-X LiNbO//3 substrate is found to increase by more than 690 kHz for a 1- mu m decrease in film thickness. Using a dual oscillator arrangement, it is possible to monitor simultaneously substrate temperature and thickness of material removed.IEEE 1987 Ultrasonics Symposium; 02/1987