Abstract
The ultraviolet range of wavelengths, 200 -400 rim, hold considerable promise for improved measurement and characterization of certain thin films on wafers. In this region of the spectrum, small differences in chemical composition and variation in the optical constants of materials can produce important differences in the reflectivity. These can be observed by using a high sensitivity microspectrophotometer system. It is also well known that small differences in the composition and structure of metallic and semi-metaffic surfaces will cause pronounced differences in ultraviolet light reflectance. The visible-near infrared wavelength range from 400 - 900 rim has been well exploited for many years by the use of computerized microspectrophotometer systems (See Notes 1 , 2and3)designed to measure reflection spectra and mathematically calculate thickness and other properties of films. Many thousands of these units have been installed in wafer fabrication facilities throughout the world, and they are in routine use for film thickness production control. The present paper will not dwell on the well-known capability of these systems. In recent years there has been new research into and development of improved photolithography systems which use deep ultraviolet light to expose photoresist patterns on wafers. Deep ultraviolet radiation is generated for these systems by excimer laseis which emit wavelengths near 250 nm, and in other designs by quartz mercury lamps which produce a strong emission line also near 250 nm. In order to characterize sublayer surfaces below the photoresist to achieve known and reproducible reflectance which can affect exposure time, it will be necessary to measure and control reflectance and absorption of fihns produced by chemical vapor deposition, metallization, or other means.
