AVS2010 Session VT-TuP: Vacuum Technology Poster Session and Student Posters

Built in the 1980’s, the insertion device beamline-17 at the X-ray storage ring of the Brookhaven Lab’s National Synchrotron Light Source (NSLS) has been using superconducting-wiggler generated hard X-rays to facilitate cutting edge research. By sharing the wiggler’s horizontal beam fan, three inline and one adjacent beamlines (17B1-B3 and 17C) have been designed to perform material stress-strain mapping, mineral phase transition under high-pressure, laser heating, and diffraction crystallography. To meet present-day high demand of hard X-rays for nano-structure probing via surface and interface scattering experiments and for large-volume high-press studies, a new beamline dubbed 17A, which also shares the wiggler’s beam fan, has been constructed at immediately downstream to the common monochromator for all the branch beamlines at 17. For the purpose of improving beam quality, user safety and system vacuum, the degraded monochromator was replaced during the 17A construction by a custom-made monolithic unit to accommodate (1) a Si-crystal for the white beam bending (7.6-deg) into the 17A line, (2) a water-cooled white-beam filter followed by a collimated aperture for beam steering, (3) a Hevi-Met alloy of tungsten for bremsstrahlung shielding, (4) an ASME-certified burst disk for high pressure release, and (5) a sputter ion pump for outgas removal and high vacuum upkeep. Flanged to the beam exit port at the SS monochromator chamber is a round SS spool piece and a copper-brazed Be-window, installed to separate the beamline-17A vacuum from its upstream beamline-17 vacuum. At 1.4-meter downstream of the Si-crystal in monochromator is a 6-way cross, set to install a phosphor screen and a CCTV for the beam image viewing and profile recording. Along the beam path of 2.6-meter from the 6-port optical enclosure, a 200 L/s sputter ion pump is hooked and sealed beneath the round beam pipe to remove desorbed gases from photon-stimulated scattering amid two Be-windows. For beam size confinement, residual gas analysis, synchrotron radiation blockage and shock wave monitoring, a tungsten slit, a tee-port, a tantalum-plated safety shutter and a Be-window are respectively installed at 0.7-, 1.5-, 1.8- and 2.5-meter off the ion pump. Prediction of pressure profile along the 17A was performed using the Monte-Carlo based Molflow code for gas conductance estimate and the finite-difference based Vaccalc code for pressure distribution calculations. Details of beamline vacuum versus pre-cleaned and pre-baked assemblies encompassing the segmented beampipe will be presented. (Work performed under auspices of the US DOE, under contract DE-AC02-98CH10886)

Historically filaments used in most scientific instruments have been constructed from pure Rhenium. Rhenium has been the preferred material due to its resistance to oxidation and good emission qualities. However, Rhenium tends to be soft and has a tendency to warp and change shape during its operation. A new Yttria/Rhenium alloy has been developed for the purpose of improving the performance of filaments used in analytical instrumentation. The Yttria/Rhenium alloy filament exhibits the same electrical properties as pure Rhenium but has the advantage of not warping or changing shape, thereby improving the performance and lifetime of filaments used in analytical instrumentation.

Yttria alloys of rhenium were formed by sintering various concentration of yttria into rhenium. The sintered yttria/rhenium alloy bars were then drawn down to wires with diameters between 0.010” and 0.003”.

Pure Rhenium filaments and Rhenium/Yttria alloy filaments of different configurations were tested to compare their properties. Testing was done using a custom filament station to measure the various filament electrical characteristics. Filaments were also tested in commercial instruments to monitor their performance. Electron microscopy studies were performed to study the grain characteristics..

Electrical studies in the filament testing station on pure rhenium filaments and various Yttria/Rhenium alloy filaments demonstrated that Yttria/Rhenium alloy filaments exhibited similar electrical properties as Rhenium. This enables these new alloy filaments to be used interchangeably with the standard rhenium filaments in analytical instrumentation.

Studies on the rhenium/yttria alloy filaments in commercial instruments demonstrated increased cycle lifetime as compared to standard rhenium filaments. The enhanced lifetime was attributed to the improved structural strength of the Yttria/Rhenium alloy filament. The Yttria/Rhenium filaments manufactured into different configurations all demonstrated less tendency to sag, warp or change shape as compared to pure Rhenium filaments.

Electron microscopy studies demonstrated that yttria oxide particles intermixed with the rhenium particles which minimized the grain growth in the alloy filament. In comparison, the pure rhenium filaments exhibited larger grain sizes. This smaller grain size in the alloy filament appears to strengthen the filament wire to provide a more stable filament that displays less sag or warping than pure rhenium filaments. The property of holding its shape has been demonstrated for multiple configurations. The Yttria/Rhenium material improves the performance of emission filaments used in analytical instrumentation.

A new two-stage flow dividing system has been developed for the calibration of ultrahigh vacuum gauges from 10^–9 Pa to 10^–5 Pa for N₂, Ar, and H₂. This system is designed based on the techniques of the calibration system in high vacuum region from 10^–7 Pa to 10^–2 Pa [1].

The system consists of four chambers: an initial chamber V₀, a flow divider V₁, a calibration chamber V₂, and an evacuation chamber V₃. Chambers between V₀ and V₁ and chambers between V₁ and V₂ are connected to each other with a capillary and a sintered filter, respectively. The chamber V₂ is evacuated by a turbo molecular pump (1100 L/s for N₂) through an orifice of 30 mm in diameter. The flow divider V₁ is evacuated by a subsidiary turbo molecular pump (220 L/s for N₂). The pressure P₀ in the initial chamber is changed in 12 steps using a pressure controller in the range from 10² Pa to 10⁵ Pa. The time interval for each step is 600 seconds. Following the change in the P_0, the pressure P₁ in the flow divider and the pressure P₂ in the calibration chamber similarly change from 10^-4 Pa to 10 Pa and from 10^-9 Pa to 10^-5 Pa, respectively. The pressure P₂ is determined from the pressure P₁ using a pressure ratio of P₂ to P₁. The ratio is pressure independent because the conductances of sintered filter C₁ and the effective pumping speed of the turbo molecular pump though the orifice C_main are pressure independent at molecular flow region.

The modifications of this system from the previous one are listed below. (1) TiN coated stainless steel vacuum chambers are used as V₂ and V₃ to decrease outgassing from the chambers [2]. (2) The conductance of the sintered filter is 1000 times smaller than that of previous system to control the pressure in the range from 10^-9 Pa to 10^-5 Pa. (3) The ratio P₂/P₁ is measured using a calibrated ionization gauge and a calibrated spinning rotor gauge. The ratio for N₂, Ar, and H₂ is obtained to be 6.41 x10^–7, 6.26 x10^–7, and 8.36 x10^–7, respectively.

The pressure P₂ is measured by an Extractor gauge (EXG) and an Axial-Symmetric Transmission gauge (ATG). The typical background pressure was (2-4)x10^-9 Pa. These gauges were calibrated from 10^–9 to 10^–5 Pa for N₂, Ar, and H₂ with an uncertainty of about 5% with the confidence level of 95% (k=2). The linearities of these gauges were within ±2%. The fluctuations of pressure indications were within ±2% for 1 hour.

[1] H. Yoshida, K. Arai, H. Akimichi, M.Hirata, J. Vac. Sci. Technol. A 26 128 (2008)

[2] H. Akimichi, M Hirata, Metrologia 42 S184 (2005)

With a quartz tuning-folk resonator vibrating at the resonant frequcny in the viscuos flowing gas, we found that the measurement of the resonator’s Δf and ΔZ enabled to derive the pressure and the viscosity of the viscous flowing gas simultaneously. The parameter of Δf is the frequency change from its vibrating frequency in high vacuum. Another parameter of ΔZ is the impedance change from the resonator impedance in high vacuum. Also the ΔZ is related to the pressure and the viscosity of the gas. We focused on the pressure dependence of Δf and of ΔZ to derive the pressure and the viscosity.

In this experiment, to achieve the precise measurements of Δf and ΔZ, we paid careful attention to the temperature control because Δf was very sensitive to the temperature. We used the constant-temperature chamber in which the resonator, the driving circuit for the resonator, mass flow controllers, and the absolute pressure gauge were installed. The temperature variation was ±0.1ºC during the experiment. In addition the driving circuit was stored in a thermostatic box which temperature was maintained at 30±0.02ºC to minimize the frequency drift. The driving circuit applied constant driving voltage(Vd) to the resonator and the driving current(Id) passing through the resonator was monitored. The impedance of the resonator (Z) was given by the ratio of Vd to Id. The resonator was a tuning-folk type quartz resonator and had a vibration frequcny of 32kHz. The measured gases were Ne, Ar, N₂, O₂, Kr. The gas was charged at 130 kPa initially, and was vacuumed at the rate of 20 Pa/sec. The pressure of the gas was measured with the capacitance manometer.

The results showed that P-ΔZ for every gas showed the same characteristics; the ΔZ has larger value for higher pressure. For the higher mass of the gas showed the larger ΔZ at atmospheric pressure except for Ne. The every P-ΔZ curve did not across each other except for Ne.

The P-Δf graph showed also the same tendency. The Δf has larger value for higher pressure, however, for the higher mass of the gas showed the larger Δf at atmospheric pressure including Ne. The every P-ΔZ curve did not intersect one another except for Ne. Then showed close but not the same characteristics.

The ΔZ-Δf plot revealed the difference between the P-ΔZ and P-Δf. The ΔZ-Δf curves did not intersect one another above 1 kPa and that the ΔZ-Δf curves were arranged in order of the viscosity of the gas. Then the pressure and the viscosity of the gas can be derived simultaneously from ΔZ-Δf curve.

This paper address technical issues in calibrating discharge coefficients of sonic nozzles used to measure the volume flow rate of low vacuum dry pumps. The first challenging issue comes from the technical limit that their calibration results available from the flow measurement standard laboratories do not fully cover the low vacuum measurement range of 10^-3 ~ 10² mbar although the use of sonic nozzles for precision measurement of gas flow has been well established in national metrology institutes. The second one is to make an ultra low flow sonic nozzle sufficient to measure the throughput range of 10^-2 mbar-l/s. Those small-sized sonic nozzles exploited in this study not only to achieve the noble stability and repeatability of gas flow but also to minimize effects of the fluctuation of down stream pressures for the measurement of the volume flow rate of vacuum pumps. These distinctive properties of sonic nozzles are exploited to measure the pumping speed of low vacuum dry pumps widely used in the vacuum-related academic and industrial sectors.

Sonic nozzles have been standard devices for measurement of steady state gas flow, as recommended in ISO 9300. This paper introduces two small-sized sonic nozzles of diameter 0.03 mm and 0.2 mm precisely machined according to ISO 9300. The constant volume flow meter (CVFM) readily set up in the Vacuum center of KRISS was used to calibrate the discharge coefficients of the machined nozzles. The calibration results were shown to determine them within the 3 % measurement uncertainty. Calibrated sonic nozzles were found to be applicable for precision measurement of steady state gas flow in the vacuum process in the ranges of 0.6 ∼ 2,050 cc/min. Those flow conditions are equivalent to the very fine gas flow with Reynolds numbers of 26 ∼ 8,500. Those encouraging results may confirm that calibrated sonic nozzles enable precision measurement of extremely low gas flow encountered very often in the low vacuum processes. Both calibrated sonic nozzles are demonstrated to provide the precision measurement of the volume flow rate of the dry vacuum pump within one percent difference in reference to CVFM. Calibrated sonic nozzles are applied to a new 'in-situ and in-field' equipment designed to measure the volume flow rate of low vacuum dry pumps in the semiconductor and flat display processes.

We present a model to capture these pattern-dependencies by tracking the spatial and temporal distribution of the ion and radical species within the DRIE chamber. The model implementation uses a time-stepped algorithm with three levels – corresponding to the three different length scales – and a coarse-grain approach where multiple features in a given region are characterized by a particular shape, size and density. The local radical species concentration distribution above the wafer is determined at each time step using current feature geometries to compute their Knudsen transport coefficient which is linked to the radical transport mechanisms within other areas in the chamber. At the end of each time step, etch rate estimates based on this radical concentration distribution and current feature geometries are used to update feature depth information for the next time interval. At the wafer scale, our modeling results achieve a success comparable to that of previously-developed wafer-level models with an etch rate RMS error percentage between 2.1% and 8.2%. The results also show that feature-level etch evolution substantially impacts the wafer-level fluorine concentration and thereby modifies the wafer and die etch rate uniformity. We expect a similar model could be incorporated into CAD software tools to evaluate masks and correct potential design issues before they are made. Our results also shed light on possible tool and process modifications to allow users the capability of altering across-wafer etch rate variability. Sandia National Laboratories is a multi program laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

A plasma enhanced atomic layer deposition reactor (PE-ALD) was built for the purpose of growing thin films on wafers up to 2.5” in diameter. Internationally, papers have been published describing characteristics of both homebuilt [1,2,3] and commercially available ALD reactors [4]. The construction of this reactor was strategically designed using these descriptions, within an allowable project time and budget. Design characteristics include an inert carrier gas, millisecond speed precursor valves, a remotely generated inductively coupled plasma, and a chamber with a high volume to surface ratio geometry. The reactor will act to complement and increase the current application repertoire versus our commercially available reactor located in the University’s thin films laboratory. In this regard, the chamber must be optimized to accommodate unique recipe applications currently unattainable with the in-house system. The functionality of this reactor will include three separate modes of operation: a thermal reaction mode (thermal ALD) for use with general recipe applications, an isolated chamber mode necessary for high aspect ratio substrates, and a plasma enhanced mode (plasma enhanced ALD) for greater process recipe versatility such as metals and nitrides. ALD allows for a precision unattainable with other deposition processes. Unlike CVD, ALD is not dependent upon precursor flux upon the substrate surface, instead relying upon step-wise A + B = P synthesis. Reactor characteristics such as laminar gas flow and plasma ion locality concentration and intensity will be modeled with COMSOL finite element simulations. ALD deposition cycle times are optimized according to ALD chemical reactions and by in-situ monitoring of sample growth rates by means of fiber optic spectroscopy. Important considerations included an optimized pumping rate and a minimization of unavoidable deposition upon all surfaces other than the process wafer. Process optimization was also pursued by means of vacuum gauge feedback and automation of precursor valve cycle sequence by means of a Lab View enabled PC. Other automated controllable growth parameters include substrate heater temperatures, reactor wall temperatures and the energies of plasma ion bombardment upon the substrate surface species. Safety concerns have also been addressed by ensuring suitable gas exhaust, pump maintenance, hard-wired safety valve shut-off programming and gas cylinder and hazardous materials safety training of individual users. The chamber design, multitude of process optimizations, and comparisons with existing designs and models allow for substantial research parameters to be explored and discussed.

Thermophotovoltaics (TPV) are devices capable of converting infrared electromagnetic radiation into electricity. Strained Layer Superlattices allow TPV devices to operate at longer wavelengths. In order to determine the performance of these devices, a unique test apparatus was designed and constructed. As the devices become sensitive to longer wavelengths (lower temperatures) in the infrared, the need to control the sample's ambient temperature becomes paramount. Here, we present a custom, cryogenic vacuum chamber specifically designed to test long wavelength TPV cells. The tester utilizes two copper heat shields cooled via conduction with two liquid nitrogen reservoirs to block outside thermal radiation. A blackbody source illuminates a temperature controlled sample at high vacuum, ~10^-6 Torr. The chamber is also connected to multiple thermocouples and a source-meter for measurement and testing purposes. This test apparatus will enable future research into low temperature TPV and other optoelectronic devices.

The measurement of TMP pumping speed is normally performed with the throughput and orifice methods dependent on the mass flow regions. However, in the UHV range of the molecular flow region, the high uncertainties of the gauges, mass flow rates, and conductance are too critical to precisely accumulate reliable data. With UHV gauges of uncertainties less than 15% and a calculated conductance of the orifice, about 35% of pumping speed uncertainties are experimentally derived in the pressure range of less than 10^-6 mbar. In order to solve the uncertainty problems of pumping speeds in the UHV range, we introduced an SRG with 1% accuracy and a constant volume flow meter (CVFM) to measure the finite mass flow rates down to 10^-3 mbar-L/s with 3% uncertainty for the throughput method. In this way we have performed the measurement of pumping speed down to less than 10^-6 mbar with an uncertainty of 6% for a 1000 L/s TMP. In this article we suggest that the CVFM has an ability to measure the conductance of the orifice experimentally with flowing the known mass through the orifice chambers, so that we may overcome the discontinuity problem encountering during introducing two measurement methods in one pumping speed evaluation sequence.

The Advanced Electron-Photon Facility (ALPHA), built at Indiana University, is a multipurpose electron accelerator to be used for DoD radiation effects testing as well as IU’s interest in a compact high-brightness x-ray source. ALPHA consists of a 50 MeV linear accelerator source and 20 m storage ring which operates at 1x10^-11 Torr. A Lambertson magnet, used to inject/extract the electron beam into and out of the ring, has been uniquely designed for optimal vacuum behavior and septum straightness while maintaining magnetic field quality. The design minimizes the ultrasonically-tested, 1018 steel pole tip exposure to UHV via a nickel plated surface and an exterior stainless steel vacuum body, welded to the pole tip. The magnet assembly yielded positive results in magnetic field and vacuum testing and is currently being commissioned in the ring.