A Practical Total Integrated Scatterometer

Universal acceptance of a proposed standard measurement method can depend not only upon how soundly it is based in scientific theory but on its cost and technical implementation as well. A total integrated scatterometer for the optical shop is described with emphasis on economy, rapid measurement, repeatability, and ergonomic packaging as controlling design criteria. The advent of low-cost microvolt resolution in digital multimeters allows the use of large-area silicon photovoltaic cells for detection of the scatter and specular light from the sample. The thin cell profile permits placement of the scatter detector closer to the sample port for minimal scatter obscuration. The large cell area accepts the blur circle from an inexpensive molded acrylic dome for scatter collection. A dedicated pocket computer and printer calculates, displays and prints sample RMS roughness, average, and standard de-viation for multiple measurements; it also controls laser user-access, prints a tutorial, and identifies sample, operator and date/time. The laser is a 2mW HeNe (633 nm); safety issues are addressed. The specular beam reflects off the specular detector and onto an alignment target screen, ensuring sample alignment and measurement repeatability. The inverted design provides a gravity-loading sample stage that is completely accessible; custom sample mounts are readily added. Component sources are provided. Performance and correlation to other scatterometer and roughness measurement techniques such as optical and mechanical profilers are presented.