Performance criteria and evaluation of surface scanners

• Published in: Journal of aerosol science 1989, Vol.20 (4), p.457-469
• Main Authors: Takami, Katsumi, Yachi, Toshiaki, Hourai, Izuo, Yatsugake, Yasuo
• Format: Article
• Language: English
• Subjects: Applied sciences; Electronics; Exact sciences and technology; Microelectronic fabrication (materials and surfaces technology); Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
• ISSN: 0021-8502; 1879-1964
• DOI: 10.1016/0021-8502(89)90079-7

Performance criteria and testing methods for two types of laser surface scanners (bare wafer scanner and patterned wafer scanner) are discussed along with the experimental results. A Practically Detectable particle Size (PDS) using Polystyrene Latex (PSL) spheres is introduced on the basis of a signal to noise ratio of three. The PDS was approx. 0.16 μm diameter for the bare wafer scanner examined. The counting efficiency test near the lower detection limit is replaced by a measurement of reproducibility from scan to scan giving about 97–98% at the PDS with low particle density. The normalized full width at half maximum (FWHM) of a Pulse Height Analyzer (PHA) histogram (size resolution power) was about 100% at the PDS. To estimate the overall performance of the scanner, a figure of merit is defined by combining scan rate, PDS and normalized FWHM. For the patterned wafer scanner, it is shown that the PDS and the reproducibility should be measured individually for every specific pattern. A counting efficiency test was carried out by measuring the appearance frequency of particle signals on a map with each dot individually identified as a particle, by a photomicroscope. The counting efficiency varied from 30 to 90% for 2.02 μm PSL spheres on a specific Poly-Si patterned wafer depending on the location of particles with respect to the substrate pattern.