Institute for Systems Research
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Item Real-Time Growth Rate Metrology for a Tungsten CVD Process by Acoustic Sensing(2000) Henn-Lecordier, Laurent; Kidder, John N., Jr.; Rubloff, Gary W.; Gogol, C. A.; Wajid, A.; ISRAn acoustic sensor, the Leybold Inficon ComposerTM, was implemented downstream to a production-scale tungsten chemical vapor deposition (CVD) cluster tool for in-situ process sensing. Process gases were sampled at the outlet of the reactor chamber and compressed with a turbo-molecular pump and mechanical pump from the sub-Torr process pressure regime to above 50 Torr as required for gas sound velocity measurements in the acoustic cavity. The high molecular weight gas WF6 mixed with H2 provides a substantial molecular weight contrast so that the acoustic sensing method appears especially sensitive to WF6 concentration.By monitoring the resonant frequency of exhaust process gases, the depletion of WF6 resulting from the reduction by H2 was readily observed in the 0.5 Torr process for wafer temperatures ranging from 300 to 350 C. Despite WF6 depletion rates as low as 3-5%, in-situ wafer-state metrology was achieved with an error less than 6% over 17 processed wafers.
This in-situ metrology capability combined with accurate sensor response modeling suggests an effective approach for acoustic process sensing in order to achieve run-to-run process control of the deposited tungsten film thickness.
Item Influence of Gas Composition on Wafer Temperature Control in a Tungsten Chemical Vapor Deposition Reactor(2000) Chang, Hsiao-Yung; Adomaitis, Raymond A.; Kidder, John N., Jr.; Rubloff, Gary W.; ISRExperimental measurements of wafer temperature in a single-wafer,lamp-heated CVD system were used to study the wafer temperature responseto gas composition. A physically based simulation procedure for theprocess gas and wafer temperature was developed in which a subset ofparameter values were estimated using a nonlinear, iterative parameteridentification method, producing a validated model with true predictivecapabilities.With process heating lamp power held constant, wafertemperature variations of up to 160 degrees K were observed by varying feed gasH_2/N_2 ratio. Heat transfer between the wafer and susceptor wasstudied by shifting the instrumented wafer off the susceptor axis,exposing a portion of the wafer backside to the chamber floor. Modelpredictions and experimental observations both demonstrated that the gasvelocity field had little influence on the observed wafer and predictedgas temperatures.
Item Education in Semiconductor Manufacturing Processes through Physically-Based Dynamic Simulation(1997) Lu, G. Brian; Oveissi, Mansour; Eckard, David; Rubloff, Gary W.; ISRWe have developed physically-based dynamic simulators relevant to semiconductor manufacturing processes, which realistically reflect the time-dependent behavior of equipment, process, sensor, and control systems using commercial simulation software (VixSimTm) under Windows. Following on their successful research use for engineering design, we are applying them to manufacturing education and training. Because they reflect quantitatively and visually the detailed response of the system to user-initiated actions in real time, these simulators promise a new paradigm of active learning through ﲨands-on operation of sophisticated, expensive processing equipment. The student experience is open- ended, offering not only guided exercises but also the chance to experiment freely with the virtual equipment. Simulator modules are in development for use by both experienced engineers and manufacturing operators, with enhanced graphical interfaces tailored to the student and application.Item Contamination Control for Gas Delivery from a Liquid Source in Semiconductor Manufacturing(1996) Lu, Guangquan; Rubloff, Gary W.; Durham, Jim; ISRGas delivery from a liquid source, common in semiconductor manufacturing, raises contamination control concerns not only due to impurity levels in the source. In addition, the lower vapor pressure of impurity species compared to that of the host (source) species causes impurity concentrations in delivered gas to increase as the source is used up. A physics-based dynamic simulator to describe the time-dependent variation of impurity level in such a gas delivery system has been developed and applied to important case of CHCIF2 impurities in host CHF3 liquid, as routinely used for dry etching processes. For a cylinder of CHF3 liquid with 100 ppm of CHCIF2 at 21.1o C (70o F), the concentration of CHCIF2 in the delivered gas is initially ~ 21 ppm, and rises slowly to ~ 100 ppm with ~ 25% of the initial material remaining. With further usage, the CHCIF2 level increases quickly to ~ 350 ppm when ~ 15% of the initial source material is left; at this point, the source has reached the liquid-dry point, i.e., all the remaining source material is gaseous, and the impurity concentration in delivered gas remains constant at 350 ppm until all material is gone. The time- dependence of CHCIF2 impurity concentration is also dependent on the operating temperature of the liquid source: for higher temperatures, the fast rise in impurity concentration and the liquid-dry point occur earlier, while the final impurity level after this point is lower. The dynamic simulator represents a useful tool for avoiding contamination problems with liquid delivery systems and for optimizing materials usage (for cost and environmental benefits) by structuring source usage procedures consistent with contamination-sensitivity of the process. The results also suggest benefits in materials usage if specific source temperatures (different from room temperature) were imposed. The physical basis of the dynamic simulator allows more general application to other systems.