The semiconductor industry is continually moving towards more complex processor designs. The new chips occupy bigger areas and surface properties of silicon wafers used in manufacturing, such as PV and RMS, become critical. One of most important characteristics of wafers is their site flatness, defined as height parameters over area occupied by the projected semiconductor chip. Smaller critical dimensions, shorter wavelength, and higher numerical aperture steppers impose more stringent requirements on PV and RMS of the site's profile. As the wafer goes through the manufacturing process, its value increases, so detecting defective sites is essential to lowering the production costs. To resolve this problem Veeco Process Metrology has designed the RTI 4100--a high performance laser Fizeau interferometer especially suited for inspection of site wafer flatness. High accuracy data taken y the instrument is analyzed by automated software package that performs evaluation of the user selectable sites and qualifies them using various user defined rejection criteria. In this paper, we present some aspects of the instruments' design and its measurement capabilities with interest to the semiconductor industry.
Demand for faster disk drives with bigger storage capacity calls for higher quality of aluminum disks used in their production. Accordingly, decreasing tolerances on disk flatness and tighter specifications on defect presence (pockets) must be met by aluminum bland suppliers. At the same time volume of production is growing requiring automated quality control at high speed. Veeco Process Metrology has developed high performance automated 95 mm aluminum blank disk tester based on Twymann-Green interferometer working a wavelength of 10.6 micrometer. It is a fully automated tool for high volume production with throughput of one disk per second. Lateral resolution of 0.6 mm in the disk plane allows flatness and shape testing as well as pocket detection. The use of long wavelength makes interferometer insensitive to environmental vibrations and dust. Vertical accuracy of instrument is 300 nm (PV) and repeatability is 130 nm (RMS). In this paper we present technical design issues and metrological capabilities of the device. The interferometer is supplied with new automated analysis software which automatically detects defects on the disk surface (pockets) as small as 0.5 micrometer in depth and performs shape categorization.
Requirements on wafer flatness, like most semiconductor specifications, are becoming increasingly tight, with greater accuracy and resolution needed for measurements. In addition to traditional peak-to-valley surface deviation and root-mean- square roughness measurements, it is desirable to measure the flatness of silicon wafers over a small area, or site flatness. This involves dividing the wafer into many sub- regions and calculating the surface statistics for these smaller regions in addition to the overall wafer statistics. Veeco Metrology has developed a high-resolution phase-shifting laser Fizeau interferometer for site flatness testing. The system is designed with 40 mm X 40 mm square field and a 1000 X 1000 pixel CCD camera. Features as small as 100 micrometer may be measured by the system with high resolution, repeatability, and accuracy. A motorized stage allows any region of the wafer to be measured by the system such that problem areas do not escape measurement. This paper discusses the overall system design and presents data from the wafer flatness tester developed by Veeco. Data on lateral resolution, vertical repeatability and accuracy are presented. In addition, the site flatness statistics of a silicon wafer measured by the instrument are given.