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Tutorials, Publications, and Technical Notes
Understanding the basics of process pressure control
Stephen P; Hinkle, Luke D; Sullivan, John J. Semiconductor International. Vol.
19, no. 11, pp. 4. 1996.
L. D. Hinkle and R. P. Jacobs, Jr., Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, January 1993, Volume 11, Issue 1, pp. 261-263.
The spinning rotor gas friction gauge (SRG) is being used increasingly for measurement and calibration of gauges in cases where a single gas type environment is not achievable. This may involve gas mixtures composed of molecules with differing mass values and surface interaction characteristics. Since the molecular momentum transfer and hence rate of rotational decay of the spinning rotor depend on molecular mass and accommodation coefficient, the calibration of the pressure indication must reflect the gas mixture ratio. The theoretical expression for the calibration factor is derived and compared with experimental data in the molecular flow regime. Agreement to within 5% is typical with inert gas mixtures. The proper application of this method allows the SRG to accurately calibrate other high vacuum gauges for use with known gas mixtures encountered in processing conditions.
Primary pressure standard for calibration in the medium vacuum range
L. D. Hinkle, J. Provost, and D. J. Surette Journal of Vacuum Science & Technology A, September 1997, Volume 15, Issue 5, pp. 2802-2806
Primary standards for gas pressure in the range from ~ 0.1 to 10 Pa (1 to 100 mTorr) have received a significant amount of attention in recent years. The interest in the calibration capability in this vacuum range is, to some degree, driven by the increasingly stringent requirements for the semiconductor processing industry. We present a new standard that is based on calculating the gas pressure required to restore a diaphragm to a null position, while the diaphragm is tilted to various, measured inclinations. With this as a basis, the calculations are relatively simple; there are no gas property dependent effects; and the system design is simple, robust, and easily automated. A formal evaluation of uncertainty for the system being developed in this facility is reviewed and compared with other primary standards. For the medium vacuum range, it is anticipated that this standard will offer numerous practical advantages relative to liquid manometers, dead weight testers, volume expansion systems, and conductance-based systems. It is intended that this technique will enable more widespread capability for the calibration, and verification of vacuum gauging in a pressure range of critical interest to many processes.
Primary and transfer standards for vacuum and mass flow in an industrial calibration facility
Hinkle L.D., Uttaro F.L., Vacuum, Volume 47, Number 6, June 1996, pp. 523-526(4)
The calibration of vacuum gauging and related gas flow instrumentation is of concern in a variety of settings, including the national standards laboratories, research laboratories, vacuum equipment manufacturing facilities and vacuum processing facilities. Here, a review is presented of the methodology and performance of standards for vacuum and mass flow suitable for a production environment. Special emphasis is placed on new techniques for primary and transfer standards which allow reasonable accuracy without requiring highly skilled operators. Such standards complement the state-of-the-art standards which are continually developed and improved at the national standards laboratories.
Toward understanding the fundamental mechanisms and properties of the thermal mass flow controller
L. D. Hinkle and C. F. Mariano, Journal of Vacuum Science & Technology A, May 1991, Volume 9, Issue 3, pp. 2043-2047
The thermal mass flow controller (MFC) is the upstream gas metering device chosen for a majority of vacuum processes. The purpose of this paper is to identify the important physical phenomena and key parameters which govern the performance of MFCs, but which have been previously unmentioned in the literature. Detailed analytical, simulation, and experimental results define the roles of the various heat transfer mechanisms which characterize the behavior of an MFC. The effect of the gas species is of particular, practical concern in view of the wide variety of gases used in processes and the need for higher levels of measurement reliability. The research shows that for some gases the present use of a gas correction factor should be replaced by a gas correction function.
Pressure-dependent damping of a particle levitated in vacuum
A novel method of levitation, using an actively controlled electric field, launches, captures, and stably suspends a microscopic (~15 µm) particle in high vacuum. While held to within one diameter in the vertical direction, the particle is allowed to oscillate nearly freely in the horizontal plane under the influence of a central restoring force. The damping of horizontal oscillations was measured over the pressure range from 10–2 to 10–8 Torr. The damping was observed to be proportional to pressure down to less than 10–6 Torr, where residual (pressure independent) damping became significant. An absolute high vacuum gauge based on the pressure-dependent damping observed with this apparatus could operate linearly throughout at least a six decade range. A prototype gauge design is suggested.
Brownian motion of a particle levitated in vacuum
A glass microbubble (diameter ~15 µm, wall 0.65 µm) was levitated in high vacuum by an actively controlled electric field. While held vertically, the particle moved freely in the horizontal plane under the influence of a central restoring force. The Brownian motion of the particle was observed and quantified by successive measurements of the oscillation amplitude in a horizontal axis. Brownian motion was exhibited throughout the pressure range from 7×10–6 to 7×10–4 Torr. The statistical behavior of the oscillation amplitude is consistent with the theoretical prediction for Brownian motion in a low pressure gas. These measurements constitute the first direct observation of Brownian motion of a levitated particle in an environment below 1 Torr. In addition to the experimental verification of low pressure Brownian motion theory, this work serves as an important step in the development of a standardizing high vacuum gauge.
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