SBIR-STTR Award

The objective of this proposal is to develop an ultrasonic technique for the measurement of the thickness of thin films in an integrated circuit manufacturing environment. Our approach is to use ultrasound in the regime where the wavelength is comparable to that of light; that is in the frequency range of 1-10 GHz. In this range, it will be possible to measure the thickness of very thin and opaque films. Also, because the mechanical impedances of materials vary significantly more than their dielectric constants, we expect to be able to measure the individual thicknesses of layered thin films. An XY scan will be made to generate film thickness contour map of the wafer. ANTICIPATED

Benefits:
This project will demonstrate the feasibility of a technique which can be developed into a commercial thin/thick film thickness measurement system. Economical, quantitative, simple, inexpensive, and nonrestrictive measurements of the thickness of transparent and opaque, simple and multiple films, will have a great impact on the cost and quality control of thin film deposition in an integrated circuits manufacturing environment.

The principal objective of this proposal is the construction of a prototype ultrasonic system for the measurement of the thickness of all types of thin films in an integrated circuit manufacturing environment. The system will be capable of producing accurate and repeatable measurements of the individual thicknesses of very thin and opaque films in a single or multiple layer configuration. The system will be computer-controlled and fully automated so that contour maps of thickness uniformity over 20 cm (8-inch) wafers can be generated. The hardware components will include an automated mechanical scanner which moves the wafer in its plane beneath a transducer. The transducer will be mounted on a nanopositioner Z-stage equipped with a 'soft landing' mechanism, and will be pressed, with a small (about 5 N) but constant and reproducible force, against the upper surface of the wafer at selected points. At each of these points, an ultrasonic wave is excited and coupled into the wafer by means of a Hertizian contact. The signal is reflected at interfaces and the reflection coefficient of the back-scattered signal is analyzed. The data is then inverted, yielding a measurement of the film thickness. As the values of these measurements are calculated, they are displayed on a computer screen and contour thickness maps are generated. Along with the construction of the hardware, we will develop a fast, robust and reliable inversion algorithm for multiple films by expanding on the very promising results of Phase I. The electronic circuitry will consist of a base band system and a super-heterodyne system (proposed as an optional task). These systems, both designed in Phase I, are capable of operating at the microwave frequency range of 0.5-7.0 GHz. In this regime, the wavelength of sound is comparable to that os visible light so that accurate measurements of very thin films can be made. The first system benefits from an earlier development while the second system promises better signal-to-noise ratio but perhaps at a lower overall scanning speed. Anticipated

Benefits:
This project will demonstrate the viability of a novel thin film thickness measurement system with distinct advantages over currently available instruments.