Hertzian contact Lamb wave sensors.

摘要

This dissertation describes the development of ultrasonic Hertzian contact Lamb wave transducer and its applications in semiconductor process monitoring and non-destructive testing. The Hertzian contact transducer excites the lowest order Lamb wave modes selectively with high signal to noise ratio. It couples energy to the sample plates through a dry, solid-to-solid contact enabling novel ultrasonic applications.;Lamb wave propagation in layered anisotropic plates is investigated using the surface impedance method. Internal field and energy distributions are discussed to form a basis for the Lamb wave excitation problem. Combining these results with the angular spectrum method and normal mode theory, a general 2 dimensional model for Lamb wave excitation by mode conversion is developed. The model is used to evaluate the mode selectivity and efficiency of Lamb wave transducers operating on multilayered plates with general anisotropy.;The normal mode theory is also used to analyze Lamb wave excitation by surface contact sources. Several Hertzian contact transducers are implemented using this analysis and it is shown that these transducers can be used to selectively excite the lowest order Lamb waves.;An ultrasonic temperature sensor (UTS) using Hertzian contact transducers is implemented and used for accurate, in-situ temperature measurement in various semiconductor processing environments. The UTS is sensitive to temperature in a wide range and it is not affected by the optical and electronic properties of the semiconductor wafers. Applications of the UTS in a rapid thermal processor, and in particular its use in a unique method for monitoring both crystallization and temperature during the manufacture of thin film transistors are discussed. A real-time wafer temperature tomography system based on the UTS is also described.;When used as point-like source and receiver pairs, Hertzian contact Lamb wave transducers provide accurate phase velocity measurements. For characterization of anisotropic plates, a wavefront correction method is derived and the results are compared with measurements on single crystal and composite plates. It is shown that it is possible to use the same technique for delamination detection in composite plates.