Enhanced contamination control methods in advanced wafer processing
Semiconductor manufacturing is a highly complex process, with a high need for process control, but equally important are effective methods for contamination control. Methods for detection of airborne and surface molecular contaminants were enhanced to meet the increasing requirements for future More Moore and More than Moore applications. Improved qualitative and quantitative contamination analysis methods of organic and inorganic compounds allow exact monitoring of contamination in front- as well as back-end processes. By the use of state-of-the-art analytical systems combined with validated analytical procedures and advanced sample preparation techniques contamination analytical results with higher reproducibility and reliability are being ensured.
Investigation of the Airborne Molecular Contamination Behavior in 300 mm Semiconductor Front - End Manufacturing
Front-end manufacturing of power semiconductor devices requires numerous different processes and materials. To control the complexity of fully automated 300 mm manufacturing lines, which typically utilize closed wafer containers, so called FOUPs (Front Opening Unified Pod), a systematic FOUP management concept is mandatory. This concept has to fulfill the quality targets in terms of organic and inorganic contaminants to assure the highest yield level of the semiconductor products. The focus of this study is to understand the behavior of airborne molecular contaminations (AMC) and to define strategies to prevent yield loss driven by AMC. The first step was to achieve a comprehensive knowledge of the AMC level within the different process steps of a selected power technology. Sampling and analysis procedures based on laser spectroscopy, measurements of electrical conductivity and mass spectrometry systems were used to understand the AMC level of the investigated components. A special automated research platform to analyze the gas phase in the FOUPs was used within the 300 mm high volume power semiconductor fab at Infineon Technologies Dresden. A pronounced dependence of the investigated component level on the different production steps was found. First offline root cause analyses due to contaminations of FOUPs with boron were performed using mass spectrometry, and the air filter systems used within the 300 mm cleanroom could be identified as a second source for boron contaminations. Other special experiments investigated the time dependency of the AMC level in the FOUP atmospheres. With this work, Infineon Dresden has established methods and strategies to prevent AMC-caused yield losses.
Neuronal uptake inhibitors, nisoxetine and fluoxetine on rat vascular contractions.
The importance of neuronal uptake processes in rat arteries and veins was compared using nisoxetine and fluoxetine, selective inhibitors for neuronal uptake of norepinephrine and serotonin, respectively. Nisoxetine (10(-7) - 10(-5) M) increased the sensitivity to exogenous norepinephrine in the portal and mesenteric veins (10-fold) and in the mesenteric artery (2.5-fold). Responses to field stimulation were also increased afternisoxetine in all three vessels. After nisoxetine, aortic responses to norepinephrine were unaltered and in all tissues, serotonin-induced contractions were reduced. Fluoxetine did not potentiate responses to norepinephrine or to field stimulation except in the mesenteric vein where sensitivity to norepinephrine was increased and the relaxation rate after field stimulation was prolonged. Although serotonin has been detected in blood vessels, fluoxetine did not increase vascular responses to serotonin. These studies suggest that rat mesenteric veins have a highly sensitive neuronal uptake mechanism of norepinephrine. Furthermore, these data provide indirect evidence against a functionally important serotonergic uptake process in rat blood vessels and suggest that neuronal uptake of serotonin does not exert a major role in terminating the vascular action of this biogenic amine.