The traditional approach to semiconductor wafer inspection is based on the use of stand-alone metrology tools, which
while highly sensitive, are large, expensive and slow, requiring inspection to be performed off-line and on a lot sampling
basis. Due to the long cycle times and sparse sampling, the current wafer inspection approach is not suited to rapid
detection of process excursions that affect yield. The semiconductor industry is gradually moving towards deploying
integrated metrology tools for real-time "monitoring" of product wafers during the manufacturing process. Integrated
metrology aims to provide end-users with rapid feedback of problems during the manufacturing process, and the benefit
of increased yield, and reduced rework and scrap. The approach of monitoring 100% of the wafers being processed
requires some trade-off in sensitivity compared to traditional standalone metrology tools, but not by much. This paper
describes a compact, low-cost wafer defect monitor suitable for integrated metrology applications and capable of
detecting submicron defects on semiconductor wafers at an inspection rate of about 10 seconds per wafer (or 360 wafers
per hour). The wafer monitor uses a whole wafer imaging approach to detect defects on both un-patterned and patterned
wafers. Laboratory tests with a prototype system have demonstrated sensitivity down to 0.3 µm on un-patterned wafers
and down to 1 µm on patterned wafers, at inspection rates of 10 seconds per wafer. An ideal application for this
technology is preventing photolithography defects such as "hot spots" by implementing a wafer backside monitoring
step prior to exposing wafers in the lithography step.
The basic physical principles underlying three common techniques for the vicarious calibration of the post-launch performance of meteorological satellite sensor are briefly reviewed. The techniques considered are: (a) using 'radiometrically stable' desert calibration targets which yield relative degradation rates; (b) congruent path aircraft/satellite radiance measurements which yield absolute calibrations; and radiative transfer model simulation methods which yield absolute calibrations. The applications of the three techniques will be illustrated, using the visible and near-IR channels of the Advanced Very High Resolution Radiometer flown on the NOAA polar-orbiting operational environmental satellites as an example. The establishment of inter-satellite calibration linkages, and cross-satellite sensor calibration will be briefly mentioned.
Preliminary results of a sensitivity analysis of the post- launch calibration of the visible (channel 1; approximately equals 0.58 - 0.68 micrometer) and near-infrared (channel 2; approximately equals 0.72 - 1.1 micrometer) channels of the advanced very high resolution radiometer using the southeastern part of the Libyan desert (21 - 23 degrees N; 28 - 29 degrees E) as a radiometrically stable calibration target are presented. It is observed that small but finite changes in the Lambertian surface albedo, and in the contributions of gaseous and particulate scattering and absorption to the upward radiation at the top of the atmosphere lead to changes in the relative degradation rates of comparable magnitude.
The relative degradation in time of the visible(channel 1: 0.58-0.68jim) and nearinfrared(channel 2: 0.72-1.lpm) channels of the Advanced Very High Resolution Radiometer(AVHRR), onboard the NOAA polar-orbiting operational environmental satellites(POES), has been determined, usi.ng the southeastern Libyan desert(21-23°N latitude; 2829° E longitude) as a time-invariant calibration target. A statistical procedure was used on the reflectance data for the two channels from the B3 data of the International Satellite Cloud Climatology Project(ISCCP) to obtain the degradation rates for the AVHRRs on NOAA-7, -9, and -11 spacecraft. The degradation rates per year for channels 1 and 2 are respectively: 3.6% and 4.3%(NOAA-7); 5.9% and 3.5%(NOAA-9); and 1.2% and 2.0%(NOAA-11). The use of the degradation rates thus determined, in conjunction with t1absolute" calibrations obtained from congruent aircraft and satellite measurements, in the development of correction algorithms is illustrated with the AVHRR on the NOAA-9 spacecraft.
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