As the cost per finished wafer increases, in-line characterization becomes an effective way to identify and control critical process parameters prior to end-of-line. In-line characterization enables testing of important process specifications during fabrication. By using in-line characterization, process problems can be immediately discovered. Alternatively, waiting for results from parametric probe can be a costly choice. This work focuses on the application of in-line electrical measurement of critical oxide thicknesses for process control. Specifically, in-line characterization is being applied to test structures in an effort to electrically characterize tunnel oxide thickness on Non-Volatile Memory parts. Using a Keithley Semiconductor Metrology System we have been able to obtain this electrical information without the need to scrap material following the measurement. We will summarize the necessary steps for implementation of such an electrical test and we will present a methodology to control film thickness using the results of electrical measurements.
The Infrared Background Signature Survey (IBSS) Satellite was launched in 1991 aboard the Space Shuttle Discovery. At the end of this mission an on-orbit straylight experiment was performed to verify the off-axis rejection performance of the IBSS IR telescope. After this experiment the sensor was pointed into flight direction (RAM) for about 1 hour to study contamination effects. Back on earth the telescope was disassembled from the cryostat and the straylight performance was measured once again. Test results showed a surprisingly slight increase in the telescope point source transmittance (PST) compared to pre-flight measurements. This degradation mainly was caused by enhanced scattering from the scanning mirror in front of the telescope. For verification the scan mirror was removed and the bidirectional reflectance distribution function (BRDF) of the contaminated mirror surface was measured directly and compared to pre-flight measurements on the clean mirror surface. The BRDF shows a local degradation by a factor of up to 12 caused by micro-meteorite impacts. On the scan mirror surface some molecular contamination was found. Measurements show that the loss of IR reflectance in the 7 to 15 micrometers wavelength band is below 1%.
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