Publications

"Using Miniature Residual Gas Analyzers in Process Control Applications" Said Boumsellek, 2001 Annual Symposium of the Rocky Mountain Chapter of the American Vacuum Society (Invited Talk)

Abstract: Residual gas analyzers (RGAs) were considered for a long time as bulky and delicate instruments to be used mainly for troubleshooting vacuum leaks. The emergence of miniature RGAs has changed that perception by exhibiting new features such as ease-of-installation and -use, ruggedness, and interchangeability. The small footprint combined with the ability to operate directly at higher pressures enables these sensor-type RGAs to be integral part of the process tool. The sensors can be strategically deployed on a cluster tool to monitor multiple chambers in a network fashion. The interchangeability of the sensors vis-à-vis the driving electronics adds a plug-and-play concept needed for easy troubleshooting, upgrade, and replacement in fabrication facilities. Using an open source, miniature RGAs extend the upper pressure limit by three orders of magnitude and therefore offer a large cost saving over differentially pumped devices. Among several applications, these RGAs are employed to monitor tool pump down following PM cycles on etchers. Examining pump down curves early helps qualifying the tool for process in real-time and hence increasing tool uptime. In sputtering tools, the sensors monitor and control the gas composition during wafer photoresist degassing and during thin film deposition. By implementing fault detection schemes, tool productivity is significantly enhanced through reducing the scrap of increasingly expensive wafers.

"Trade-offs in Miniature Quadrupole Designs" S. Boumsellek and R.J. Ferran, J American Society for Mass Spectrometry. 12, 633-640, 2001

Abstract: Pressing needs for miniature mass spectrometers became apparent during the last decade in process monitoring and control, space exploration, and environmental screening. Besides the small footprint, common requirements include low cost, low power consumption, field portability, reliability, autonomy, and ease-of-use. Design concepts and construction technologies of miniaturized quadrupole sensors were guided by cost reduction requirements without sacrifice of performance. The first miniature and complete quadrupole mass spectrometer system was introduced as the Micropole sensor. The concept featured a novel technique to assemble and operate multiple miniature quadrupoles in parallel. The short analyzer length offers a significant advantage by enabling direct mass filtering at pressures up in the 10^-2 torr range. High voltages at higher frequencies (10-20 MHz) are required for acceptable mass resolving powers. Additional trade-offs were uncovered in miniature sensors leading to designs optimized for each class of applications. Real time ray tracing of ions injected and filtered in the quadrupole field is used early in the design stage to predict the performance and reliability of the device.

"Using partial pressure analysis to monitor wet clean recovery" T.P. Schneider, C.H. Huffman, K.Morse, R.V. Meurs, and C.A. Tripp, Solid State Technology, August 2000.

Abstract: In general, when a fault in a vacuum system occurs, particularly after wet cleaning, it is usually the troubleshooting that takes the largest amount of time. Equipping the troubleshooter with a partial pressure analyzer, however, provides an effective tool for accelerating the troubleshooting process and, hence, accelerating corrective action. This tool can be an effective means for productivity enhancement of vacuum process tools.

"Using partial-pressure analysis to detect contamination in an oxygen gas supply", Thomas P. Schneider, Kelly J. Taylor, David A. Rothenbury, Mark Chavis, Timothy Hoff, and Craig H. Huffman, Micro Magazine, 35, Jan 1999

Abstract: Partial-pressure analyzers can not only be used to identify and monitor residual gases during a contamination event; they also are effective tools for full-time process monitoring.

"Miniature Quadrupole Arrays for Residual and Process Gas Analysis" S. Boumsellek and R.J. Ferran, J. Inst. Env. Sci. Tech. 42, 27, 1999.

Abstract: This paper includes computer simulations based on ray tracing to aid in the design of miniature quadrupoles. These quadrupoles are then assembled in a matrix-like pattern to operate in parallel. The tradeoffs between sensitivity and resolution for different mechanical and electrical configurations are examined using real-time trajectories of ions. The dependence of resolution versus sensitivity is computed and compared with experimental results. The pressure dependence of the sensitivity is simulated near the upper limit (mtorr range) of the operating pressure. Space charge effects at the inlet of the mass filter are evaluated to properly design electrode apertures and spacing. Using the results of ray tracing, miniature quadrupole arrays were designed and constructed. Performance parameters were derived from recorded spectra and compared with computations. Since they are able to operate at higher pressures, these sensor-type devices are used as residual gas analyzers (RGAs) and as process gas analyzers (PGAs) in many semiconductor applications. Networking multiple sensors to monitor the state of the semiconductor manufacturing tool and the wafers at different stages of the process enables real-time, wafer-to-wafer control using preset fault detection schemes.

"Mass Spectrometry Using Miniature Quadrupole Arrays" S. Boumsellek, Proceedings 47th ASMS Conference on Mass Spectrometry and Allied Topics, June 13-17, 1999, Dallas, TX

Abstract: Mass spectrometers have evolved into standard tools in a wide range of applications. Increasing demands for miniaturized versions of these instruments need to satisfy applications in such areas as planetary exploration, residual gas analysis, and environmental monitoring. Common requirements include small footprint, field portability, reliability, low power consumption, and low cost

"Miniature Sensors for Gas Analysis", S. Boumsellek, 46th International Symposium Vacuum, Thin films, Surfaces/Interfaces, and Processing (Seattle, WA), Oct 25-29 1999, Abstract p.123 (Invited Talk)

Abstract: Mass spectrometers have evolved into standard tools for quantitative and qualitative analysis of gas composition. For numerous applications in such fields as planetary exploration, environmental monitoring, hazardous gas detection, and residual gas analysis, more compact and robust versions of these instruments are needed. Common requirements include small footprint, portability, low cost, low power consumption, autonomy, and ease-of-use.

"Real-Time In Situ Residual Gas Monitoring", T.P. Schneider, P. Krocak, B. Van Eck, Future FAB International Vol 1, 1998

Abstract: In situ real-time process monitoring (RTPM) was used to investigate residual gases during ion implantation processing. The data indicates a clear difference in the partial pressure trends of H2+, H2O+, CO+/C2H4+ and CO2+ between the processing of normal wafers, wafers with insufficiently cured photoresist (PR), and wafers without PR. This work was done using two commercially available ion implantation systems (Varian 160 XP and Eaton NV20A). SEM micrographs are included to demonstrate the ability of RPTM to predict the results of the processing. This information can be used to determine the type of error encountered during processing. This affords the user the capability for fault detection and classification (FDC).

"High pressure effects in miniature arrays of quadrupole analyzers from 10-9 to 10-2 tor" R.J. Ferran and S. Boumsellek, J. Vac. Sci. Tech. A14, 1258, 1996

Abstract: The design, construction, and characterization of a miniature array of 16 rods forming nine quadrupole mass analyzers for residual gas analysis are presented. The novel design takes advantage of the reduction of the dimension and hence the mean free path to broaden the dynamic range by extending the operating pressure range up to 10 mTorr at the high end while maintaining the low-end sensitivity and mass resolution. The small size, low weight, low power consumption, and low cost of this mass analyzer enable many new applications such as in situ process control in high pressure processes. Applications which take advantage of the capability of operating the source pressure two orders of magnitude higher than conventional devices such as high-pressure contaminant monitoring and discussed. Data on high-pressure effects on the ionizer lifetime in various atmosphere and nonlinearities of the signal and presented and correlated with theoretical analysis. Ray tracing simulations and Monte Carlo statistical calculations are used to provide an understanding of the sensitivity reduction at pressures substantially higher than 10 mTorr. These calculations take into account the ion charge density in the source and dissociation, charge exchange, and energy loss by ions when colliding with residual molecules along the length of the rod.
© 1996 American Vacuum Society.

"Volatile Contamination Monitoring for Titanium and Titanium Nitride Sputter Systems" R.J. Markle, S. Uhling, G. Magsamen, J. Fidler, R.J.Ferran, and S.Boumsellek, Semiconductor FabTech. 5, 237, 1996.

Abstract: This paper describes a recently initiated project at Advanced Micro Devices, its motivation, and initial results. The project applies a Ferran Scientific Micropole Analyzer on an Anelva 1015 sputter deposition system. A system description of each is provide, along with observations of moisture and other species monitored during wafer processing, process equipment idle periods, and controlled experiments.