A new energy-efficient approach to high vacuum pumping

Recent experiments have shown that an efficienty trapped mechanical rotary pump operating with completely degassed oil is capable of pressures in the 10^?7 mbar range. By greatly enlarging the zeolite trap and mounting it immediately adjacent to the work chamber it can be made to funtion simultaneously as a high speed sorption pump for vapours. Outgassed vapours from the work chamber and vapours originating from the pump oil are both pumped by the zeolite. The zeolite is operated at room temperature except during bakeout and is maintained at very low surface coverages to obtain corresponding low equilibrium pressures of water and hydrocarbons. Gases which are not sorbed by the zeolite are pumped by the mechanical pump. Vapour pumping continues for periods of months even when all power to the system is shut down. High vacuum is attainable within a few minutes after reapplying power. If desired, the zeolite can be cooled to raise the pumping speeds for all gases to approximately those for vapours, and to reduce ultimate pressures to the 10^?8 mbar range. This principle can be used as the basis for practical pumping systems which provide clean high vacua with low power consumption. Two pumping stations with speeds for vapours in the 12/s^?1 and 400ls^?1 range, respectively, are discussed.     

Vacuum System Evacuation to Base Pressure

A study has been made to compare the times taken to evacuate a turbomolecular and scroll pumped chamber to a base, high vacuum, pressure. A small test header (26.7 litre) was evacuated via two different paths: through a fore-line, switching paths once ‘cross-over’ pressure was reached, and directly through a turbomolecular pump (TMP) where the TMP was not operational until cross-over pressure was reached. When starting the TMP/switching paths at 0.1 mbar, pump-down times were significantly slower through the TMP; the time taken to reach 0.1 mbar increased by between 2 and 8 minutes dependent upon the TMP model (from a 24% increase in time with nEXT300 to a 232% increase for the nEXT240). For pressures below 8 · 10⁻⁶ mbar there was no significant difference in required pumpdown time between the two methods. The variation between methods being less than the ±30% uncertainty in pressure gauge measurement. The increase in pumpdown times to achieve pressures down to 10”⁵ mbar when evacuating through the TMP was seen for all TMP models tested, however a greater difference was seen for a TMP configured with Holweck drag stages than those containing Siegbahn drag stages. The best pumpdown time for pressures down to 10⁻⁵ mbar was achieved when pumping through the TMP whilst allowing the TMP to ‘start’ operation from atmospheric pressure.     

Hochvakuumpumpe gegen Atmosphäre

High vacuum pump working against atmosphere The OnTool^TM Booster vacuum pump consists of side channel and Holweck pump stages, achieves 10⁻⁵ mbar (10⁻³ Pa) pressure and works against atmosphere. Research, which is done on side channel pump stages, shows ways to increase the compression and pumping speed and to reduce their power consumption. The experiments show that rotors with radial blades machined on both sides at the periphery of the rotor have a better performance than rotors with radial blades machined only on one side of the rotor, rotors with semicircular blades or rotors with straight blades. It was also shown that the compression ratio of side channel pump stages depends on the number of radial blades at the periphery of the rotor. The compression ratio of side channel pump stages achieves its maximum at a specific number of radial blades in the rotor N_m = D · k_m because the momentum and energy transfer from rotor to gas in the side channel has its maximal value with this number of radial blades. Reduction of the axial gaps between the rotor and the stator increases the compression ratio of side channel pump stages as expected due to lower leakage along the gaps.     

Turbomolecular pumps designed for plasma processes industry. Turbomolekularpumpen speziell für die Plasmaindustrie

Plasma processes are a very popular method to produce high‐grade quality thin films on many different substrates. There are a large variety of different coating systems. Such systems go from small‐scale machines (i.e. Optical coating systems for ophthalmic lenses and filters), through mid‐size machines (such as systems for deposition on flexible substrates used in the food, electronics and packaging industry or systems used for producing optical and magnetic data storage media), up to large‐area systems (i.e. used for architectural glass coating or in the flat panel display industry). Even if all of these systems look very different, there are few common specific points that characterize most of these applications. The plasma is normally based on Argon, Oxygen, Nitrogen (and more recently Krypton) mixtures in the mid 10^–3 mbar range. The base pressure is generally over the mid 10^–7 mbar range. The deposition rate is very high and so the demand for gas throughput is high as well. (i.e. a glass coater can ionize more than 2000 sccm of Argon per cathode segment). There is a high probability of debris and particle generation within the process; roughing and venting cycles are fast and sometimes uncontrolled (they can be described as air‐in rushes in some cases). Uptime and reliability are not an option, but a must in industrial production environments. It is therefore difficult to believe that turbo molecular pumps originally designed to reach the 10^–10 mbar range with a high number of pumping stages and very tight clearances, are capable to work reliability in this demanding environment. We are keener to think that if we want a reliable and performing pumping solution the design of the turbomolecular pump must be specific and dedicated to the application. Ideally this development process is done side by side with the ultimate equipment users, matching at best process requirements and turbomolecular pump design know‐how. As Varian Vacuum Technologies, we have followed that process and this article is sharing the results.     

Kennfeldanalyse einer Schraubenvakuumpumpe

Operating Performance of Screw Vacuum Pumps This paper presents detailed analyses of the operating performance of a dry‐running screw vacuum pump. The characteristic parameters, suction speed and final attainable pressure ‐ which primarily define the operating performance of screw vacuum pumps ‐ are explored in experimental and theoretical investigations. Experiment and simulation in combination are used to show the correlation between the main physical and technical characteristics and the operating performance of screw vacuum pumps. This basic knowledge is essential for understanding the specific machine physics of positive displacement vacuum pumps, especially for screw vacuum pumps, and is useful in view of further design and optimization processes. The experiment covers measurements of the operating performance of the investigated isochoric screw vacuum pump working against ambient pressure. As operating parameters intake pressure (1000mbar to 10^‐3mbar) and rotor speed are varied over a wide range. The theoretical analysis of the operating performance contains simplifying models as well as simulations of the thermodynamic processing. The impact of external leakages, clearance vacuum flows and further losses on operating performance are described in detail.     

Optimized annular triode ion pump for experimental areas in the LHC

The large hadron collider will be the world next generation accelerator to be operational in 2007 at CERN. The UHV requirements force the installation of ion pumps in the experimental areas of ATLAS. Due to the unacceptable particle background that standards ion pumps may generate, a reduction in the amount of material constitutive of the pump body is required. Hence, a stainless steel 0.8 mm thick body annular triode ion pump has been designed. A pumping speed of ∼20 l/s at 10⁻⁹ mbar is provided by 15 pumping elements. Finite elements analysis and destructive tests have been performed in its design. Final vacuum tests results are shown.     

Die Membranpumpe - Entwicklung und technischer Stand

The modern diaphragm pump has become a proven device for generating coarse and fine vacuum. The article describes disigns and functions of various construction types as well as state-of-the art development and manufacturing. Physical and technical demands have resulted in diaphragm pumps with typical ultimate pressures of 70 to 0,1 mbar and a pumping speed of several m³/h. As an almost chemically resistant pump, the diaphragm pump is used in the chemical laboratory. Combining a diaphragm pump with an oil-free, not against atmosphere compressing pump, a contamination-free pump assembly for (ultra-)high vacuum is obtained which is well suited for coating technology, vacuum metallurgy and semiconductor industry due to its oilfree operation.     

Kompakt-Vakuum-Meßgeräte mit PC-Anschluß – Windows-Software zur Prozeß-Auswertung

Personal computers, which are almost omnipresent nowadays, offer an economic way for storage, analysis and documentation of measurement data. In the following paragraph a new concept of vacuum gauges together with a corresponding Windows®®-software is presented, that enables the user to analyze various pressure measurements, such as pump diagrams and other process curves. The first group of instruments contains digital vacuum transmitters with an integrated display unit (VTA). They cover pressure ranges from 1600 mbar down to 10^?5 mbar. The second group consists of digital vacuum transmitters with logging capability (VTS). These pressure loggers have appropriately sealed housings and are suitable for being directly inserted into the evacuation volume, e. g. into vacuum packs. After the evacuation process has finished, the pressure data, that have been stored internally by the gauge, can be easily read out and analyzed via PC.     

Völlig ölfreie neue Vorvakuumpumpe für saubere Anwendungen

Totally oil-free vacuum pumps have been gaining popularity for applications where clean forevacuum is needed, or clean gases are being pumped. The trend for these simple applications has been to substitute the complicated and expensive process pumps used in the production of semiconductors with simpler alternatives. In order to produce such a cost effective oil-free vacuum pump, the well known reliable and robust piston principle has been adapted as a vacuum pump. The resulting product is made up of four stages of compression arranged in series producing an ultimate pressure of 3 ? 4 × 10^?2 mbar. All compression spaces are totally dry as is the crank case. For additional cleanliness the grease lubricated bearings situated in the crank case are separately sealed. The special valve geometry, and the use of new low coefficient of friction sliding materials, combine to produce a very robust and low maintenance pump. The new pump is capable of surviving operational accidents such as the ingestion of broken wafers or liquid water. Applications for this new pump include load locks, analytical instruments, and research.     

COSY,eine neue Forschungsanlage mit Ultra-Hochvakuum-Technologie

The report shows that the development, construction and later successful operation of UHV facilities in the pressure range of ≤10^?10mbar is not possible without a highly sensitive nondestructive testing technique. The example of the large technical research facility COSY is used to demonstrate that the leakage rates (≤10^?10mbar · I · s^?1) and surface purities required can only be achieved by strict compliance with fundamental UHV production conditions and by the rigorous application of helium leak detection techniques and mass-spectrometric residual gas analysis.     

Structural and optical properties of γ-alumina thin films prepared by pulsed laser deposition

Preparation of γ-alumina thin films by pulsed laser deposition from a sintered α-alumina target is investigated. The films were deposited on (100) silicon substrates at 973 K with varying oxygen partial pressures in the range 2.0 × 10⁻⁵-3.5 × 10^− 1 mbar. X-ray diffraction results indicated that the films were polycrystalline γ-Al₂O₃ with cubic structure. The films prepared in the oxygen partial pressure range 2.0 × 10^− 5-3.5 × 10^− 2 mbar contained nanocrystals of sizes in the range 10-16 nm, and became amorphous at pressures > 3.5 × 10^− 1 mbar. Topography of the films was examined by atomic force microscopy using contact mode and it showed the formation of nanostructures. The root-mean square surface roughness of the film prepared at 2.0 × 10^− 5 mbar and 3.5 × 10^− 1 mbar were 1.4 nm and 3.5 nm, respectively. The thickness and optical properties were studied using ellipsometry in the energy range 1.5-5.5 eV for three different angles of incidence. The refractive index was found to decrease from 1.81 to 1.73 with the increase of oxygen partial pressures from 2.0 × 10^− 5 to 3.5 × 10^− 2 mbar. The variation in the refractive index has been found to be influenced by the microstructure of the films obtained as a function of oxygen partial pressure.     

A study on the interface and bulk charge density of AlN films with sputtering pressure

An attempt to correlate deposition-induced effects and the morphological properties with the electrical properties of the aluminum nitride (AlN) films have been made. The AlN film was sputter deposited on silicon while increasing the pressure in steps from 2×10⁻³ to 8×10⁻³ mbar. An X-ray diffractogram revealed that the intensity of (0 0 2) orientation increased till 6×10⁻³ mbar pressure, but it changed to (1 0 0) orientation of the AlN film at 8×10⁻³ mbar. The FTIR spectra of the absorption band of the films were observed around 682 cm⁻¹ and became prominent at 6×10⁻³ mbar. A decrease in the grain size was seen by SEM images at 8×10⁻³ mbar. The AFM measurements revealed that the surface roughness varied from 1.56 to 3.24 nm with pressure. It was found that the insulator charge density (Q_in) increased from 1.4×10¹¹ cm⁻² to 1.3×10¹² cm⁻² with increase in pressure. On the other hand, the interface state density (D_it) was found minimum (7.3×10¹¹ eV⁻¹ cm⁻²) at 6×10⁻³ mbar. It is found that presence of the Q_in and D_it are primarily governed by the sputtering pressure of the AlN film.     

Kolbenmanometer mit Kraftmesszelle zur Kalibrierung sehr kleiner Drücke

Piston gauges are very precise pressure gauges. In the conventional design, the force exerted by the pressure balances the gravitational force on a piston or cylinder. Due to the mass of piston or cylinder, the smallest measurable pressure is limited to a few kPa (a few 10 mbar). The company DH Instruments, Inc. has developed a new piston gauge in which the pressure‐ induced force on the piston is measured by a mass comparator. Thereby, the measuring range is substantially extended towards smaller pressures. The instrument offers a measuring range from 1 Pa to 15 kPa (0,01 mbar to 150 mbar) for gauge and absolute pressure. The resolution is 1 mPa (10^‐5 mbar) and the uncertainty (5 mPa + 3·10^‐5 p). The piston gauge is calibrated through the determination of mass and piston‐cylinder effective area. An automated pressure controller is included in the instrument. Integrated software allows multi‐point calibrations with another device to be run unattended. The system has been used to perform an automatic test of capacitance diaphragm gauges in a variety of ranges.     

An UHV system to study gassing and outgassing of metals under friction

An UHV dynamic expansion system to study gassing and outgassing of metals under friction in vacuum has been developed. The vacuum chamber of the system has two main parts separated by a wall with a central orifice of nominal conductance of 5.27 l s⁻¹ for N₂ at 300 K. The main part of the system is equipped with a quadrupole mass-spectrometer, ion gauge and the gas line supply. The chamber closer to the pumping systems is also equipped with an ion gauge. The pumping of the system is performed by: (I) a turbomolecular and (II) a cryogenic pump, which can operate either independently or in parallel. The ultimate pressure of chambers 1 and 2 are respectively 5.2.10⁻¹¹ mbar and 1.10⁻⁹ mbar. The friction cell allocated in chamber 2 consists of a sample holder and a linear motion feedthrough with a steel ball indent allows the friction experiments. The sample holder lets to apply a load to the sample surface with a normal force in the range of 0,02 N to 0,85 N. Heating of the sample up to 500°C is provided by electron bombardment. The temperature of the sample as well as the electrical resistance between the indent and the sample surface can be measured. The results show that pressure increase caused by the deformation of the sealing bellow of the friction cell, i.e. without friction, is 1.7×10⁻¹¹ mbar (0.6% of the base pressure). The outgassing of the sample caused by friction depends on the normal force as well as on the sweep frequency. The behavior of the total pressure is characterised by an oscillating current supported on a continuous current, which is not possible to explain at present time.     

Verbesserung des Vakuums in Isoliergefäßen aus Glas

Improving the vacuum would increase the insulation capacity of commercially available glass containers by a factor of about two. To do this, pressures of 10^?4 mbar must be attained. Different approaches were taken to meet this objective. As an alternative to today's commonly practiced sealing method, three possibilities are introduced which eliminate the necessity of pump stub narrowing which causes reduced conductance. Furthermore, depending on the sealing process used, the gases occuring during sealing are either avoided completly or they can at least be reduced by having the chance of exact temperature control resp. by a lower separation temperature. A completly different approach was taken by using Getters, of which a metal hydride on a TiVMn base proved especially suitable. It is activated by heat and can be integrated into the normal production process without any problem. Aside from a shorter pump period, the added advantage here is the containment of the gasses occuring during sealing as well as that of the longterm gasses.     

Plasma dynamics studies during deposition of thin film PbTe on a glass substrate

PbTe thin films were prepared by pulsed laser deposition using a Nd:YAG laser (532 nm) in an argon atmosphere. Dynamic processes in the gas phase induced by Nd:YAG laser ablation of PbTe are investigated by analyzing the light emitted by the plume. Pressure in the chamber varied from 1.0×10⁻⁵ to 1.0 mbar. Space and time-resolved optical spectroscopy measurements indicate the presence of both neutral, Pb(I) and Te(I) and ionized, Pb(II) and Te(II), species. The velocities of the species remain unchanged for argon pressures up to 10⁻¹ mbar, which suggests that expansion of the plume occurs without further collision with the foreign gas in this pressure range. It is found that an addition of 5×10⁻¹ mbar Ar enhances the emission line intensity and leads to a decrease in species velocity observed at large distances from the target surface. Furthermore, a region of maximum emission intensity at distance of 5-10 mm from the target is found when a gas environment is present.     

A study of structural transition in nanocrystalline titania thin films by X-ray diffraction Rietveld method

Structural and microstructural analyses of nanocrystalline titania thin films prepared by pulsed laser deposition have been carried out. At lower oxygen partial pressures (≤10⁻⁴ mbar), rutile films were formed, whereas at 1.2 × 10⁻³ mbar of oxygen partial pressure, the thin films contained both rutile and anatase phases. At 0.04 and 0.05 mbar of oxygen partial pressure, the film was purely anatase. Addition of oxygen has also shown a profound influence on the surface morphology of the as deposited titania films. Modified Rietveld method has been used to determine crystallite size, root mean square strain and fractional coordinates of oxygen of the anatase films. The influence of crystallite size and strain on the rutile to anatase phase transition is investigated.     

Experimente zur Gasreibung zwischen 10–3 und 10 mbar bei 330 K. Friction Experiments at 330 K with Gases in the Pressure Range between 10–3 und 10 mbar

Friction experiments were designed using a cylindrical friction device connected to the driving unit of a turbomolecular vacuum pump TMP 340 M and were carried out in Ar, Kr and He gas at low pressures. A carbon fiber tube rotating between 220 and 860 cps formed the inner friction surface. The outer part was an aluminium alloy tube at a distance of d = 0.4 mm as well as at d = 0.8 mm. We determined the deceleration forces on the rotating carbon fiber tube at a constant temperature of 330 K. Absolute viscosity was calculated using a simple formula derived from it's definition. We investigated in the development of absolute viscosity at pressures between 10^?3 and 10 mbar. We show the importance of pumping borders within the experimental set up. Linear connections of the resulting data were tested. Our data were indicativ of slip flow effects.     

Exciting Dilute Magnetic Semiconductor: Copper-Doped ZnO

The present study is focused on the copper-doped ZnO system. Bulk copper-doped ZnO pellets were synthesized by a solid-state reaction technique and used as target material in pulsed laser deposition. Thin films were grown for different Cu doped pellets on sapphire substrates in vacuum (5×10^?5 mbar). Thin films having (002) plane of ZnO showed different oxidation states of dopants. M–H curves exhibited weak ferromagnetic signal for 1–3 % Cu doping but for 5 % Cu doped thin film sample showed the diamagnetic behavior. For deeper information, thin films were grown for 5 % Cu doped ZnO bulk pellet in different oxygen ambient pressures and analyzed. PL measurement at low temperature showed the emission peak in thin films samples due to acceptor-related transitions. XPS results show that copper exists in Cu²⁺ and Cu⁺¹ valence states in thin films and with increasing O₂ ambient pressure the valence-band maximum in films shifts towards higher binding energy. Furthermore, in lower oxygen ambient pressure (1×10^?2 mbar) thin films showed magnetic behavior but this vanished for the film grown at higher ambient pressures of oxygen (6×10^?2 mbar), which hints towards the decrease in donor defects.     

Das Drehscheiben-Vakuummeter als primäres Totaldruckmeßgerät im Hochvakuum

An absolute vacuum gauge exploiting the phenomenon of molecular drag between coaxial discs has been developed. The device consists of a silicon disc 92 mm in diameter suspended on a calibrated torsion fibre above a rotor of matching size which rotates at speeds up to 51000 rpm. Molecules leaving the rotor communicate a torque to the suspended disc by molecular drag. The angular deflection thus produced is sensed optically and is about 2° at 10^?6 mbar. The factors relevant to absolute measurement such as geometry, edge effects and tangential momentum accommodation are discussed in this article. Experimental comparisons with a spinning rotor gauge demonstrate that the rotating disc gauge has a universal application for primary total pressure measurement in high vacuum with an associated uncertainty in measurement of ±3% in the 10^?6 mbar range.