mass_spectrometer Pfeiffer обзор (1248468), страница 8
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30:Diagram of theelectronic modulesof a QMG 422.All of the optional input and output channels remain activated and the data, including any limits and threshold values,remain available. If the optional operatingconsole CS 422 is used, there is no needfor a computer. This operating unit thenalso serves as the front panel of the QMS422.
The control units QMS 422 or QMI422 are designed as rack modules.The QuadStarTM software is the commonoperating interface for all mass spectrometers (with the exception of the PrismaTM80). This allows the exchange of measureddata and control parameters between dif-Fig. 31:Scan analog measurement of air. The massrange is freely selectable, the y axis can beswitched from linearto logarithmic.30ferent units.
At the same time, this alsofacilitates ease of operation between different systems for the user. A dynamic dataexchange with other programs is possiblevia DDE. Measured data that is alreadystored can be transferred to other evaluation programs after conversion into ASCIIformat.Fig. 33:Concentration ofnitrogen, oxygen,argon and carbondioxide displayed as afunction of the currenttime. The time andconcentration axes arefreely selectable.Fig. 34:The leaktest is usedfor simple detection ofleaks in vacuumapparatus.
Display oftime lapse of thehelium signal and theactual intensity as achart. Additionalacoustic signal ifdesired.Fig. 35:Simultaneous displayof mass spectrometerdata and analog data,e.g. of a vacuum gauge.31FundamentalsFig. 32:Scan bargraph measurement of air.Intelligent peakrecognition routinesallow major datareduction withoutsignificant loss ofinformation.1 Fundamentals of mass spectrometrymass spectrometersPrisma™F1Prisma™M2SPM 200HPA 200Prisma™M2QMG 422LANLANLANLANLANLANQMG 422LANfibre optic cableOHA 200QuadStar™Windows NT or 98Fig. 36:Linkage of differentmass spectrometersto a commonnetwork.It is possible to connect several massspectrometers via a common ArcNet network.
(Fig. 36) Each of the mass spectrometers within this network can carry outits own independent measurement tasks.The individual mass spectrometers areconnected via an optical LAN interface andfiber optic cables to the host computer in anetwork. The use of the fiber optic cablesand optical hubs allows a fast and trouble-32computer withArcNet boardfree data transfer, even over long distances (up to several hundred meters) as wellas a clear voltage isolation between themass spectrometers and PC. The massspectrometers integrated into the networkare not affected when a system is switched off or a new system is added.Quadrupole mass spectrometers requirea working pressure or total pressure lessthan 1 · 10-5 mbar (high vacuum). Sincemany processes operate at higher pressures, the mass spectrometer cannot besolely selected based on analyzer, ionsource and detector.A coordinated system consisting of amass spectrometer, gas inlet with pressure reduction, vacuum pumps/pumpingstations and total pressure measurementis required.
In addition to knowledge ofFundamentals1.3 Mass spectrometer in connection withgas inlet and pump systemsthe properties of the mass spectrometer,knowledge of the characteristics of thepumps and gas inlet systems is necessaryfor a targeted design of an optimalsystem for the particular application.The advantage here is supply from asingle source. Pfeiffer Vacuum offers individually tailored mass spectrometersystems for your application using in-house components.
The following chaptersdescribe some typical systems.Fig. 37:Monitoring of gascomposition onproduction system.331 Fundamentals of mass spectrometry1.3.1 Mass spectrometers – set upsfor inlet pressures < 10 mbarFor a classical residual gas analysis in thehigh vacuum range, the analyzer of themass spectrometer should be connecteddirectly to the vacuum chamber with thegreatest possible conductance tubing.
Thedirect insertion of the analyzer into theinterior of the vacuum chamber is the bestscenario. However, the analyzer should beprotected from intense bombardment byany particle beams that may coat or erodethe analyzer. Only so-called “open” ionsources (axial, screen, cross-beam ionsources) are used for this task. The upperpressure limit for such an arrangement isa few 10-04 mbar.However, many processes, such as sputtering, CVD, MOCVD, plasma etching andion plating, operate at higher total pressures of up to a few mbar.
In this pressurerange, differentially pumped mass spectrometers with open, gas-tight or specialion sources are used. The attachment ofthe process chamber to the analyzer unitshould be implemented with a direct,short connection with a small internal surface area and a low dead volume toensure a fast response time of the massspectrometer to changes in the partialpressure conditions in the process chamber.Fig.
37 shows three variants of a differentially pumped mass spectrometer with anopen ion source and an axial gas inlet. Inall three variants, the reduction of thepressure in the process chamber to theoperating pressure of the mass spectrometer is carried out via a fixed or variableconductance value (aperture or gas metering valve) in front of the open ion source.Therefore, the pressure in the ion sourceequals the pressure in the analysis vacuum chamber.A UHV gas metering valve (Fig. 38 a) tovary the conductance is preferable when alarge process pressure range is to becovered and continuous heating of the gasinlet up to 200 °C is recommended.
Withthe valve combinations b) and c), both aprocess gas measurement as well as aresidual gas analysis at low total pressuresis possible. For residual gas analysis bothvalves (b) and the gate valve (c) areopened resulting in the mass spectrometer(open ion source) being directly connectedto the process chamber with a high conductance path (DN 40).
The design withthe valve combination HPI 010 allows thea) 50 mbar > p > 1 · 10–4 mbarQuadStarTMUDV 040b) 10 mbar > p > 1 · 10–7 mbarFig. 38:Differentially pumpedmass spectrometerwith an open ionsourcea) with a UHV gasmetering valve toadjust the conductanceb) with a SVV doublevalve (an aperture valve and a gate valve)c) with HPI 010 valvecombination(one gate valve, 2 xaperture valve)34p < 1 · 10–5 mbarRS-232-C orfiber-optic cableRS-232-C orLAN interfaceprocess chamberPrismaTMopen ion sourceC-SEM2 x relay output,2 x analog input,4 x analog output2 x relay inputSVV double gate valvewith 1 x apertureTMU 07124 VDC90–240 V, 50/60 Hzc) 10 mbar > p > 1 · 10–7 mbarMVP 015–4HPI 010, manual,with 2 x aperturespprocess > pion source = panalyzerinfluence of the background spectrum ofthe analysis unit on the measured resultsis greater, and thus determines the attainable limits of detection and the dynamicmeasuring range.An example for a differentially pumpedmass spectrometer with a gas-tight ionsource is shown in Fig.
39.In this case, the pressure in the processchamber is reduced in 2 steps, before andafter the ion source. The pressure in theion source is thus a factor of approx. 10–50higher than the background pressure inthe analyzer vacuum chamber.In contrast to the systems with an openion source, this set-up can reduce theinfluence of the background spectrum ofthe analyzer unit and thus lower limits ofdetection can be achieved. At the sametime, however, the risk of contaminationof the ion source increases so that thisdesign should mainly be used for the analysis of non-condensable and non-corrosive gas mixtures.
A classical residual gasanalysis is only possible to a very limiteddegree with this type of design.A new ion source was specially developedfor the continual monitoring of the processand residual gas of sputtering processes(the SPM ion source), [16,17]. In thisFundamentalsoptimization of the inlet conditions for2 process steps operating in differentpressure ranges as well as residual gasanalysis.In order to attain the lowest possibledetection limit and a large dynamic measuring range, memory-free pumpingsystems with a high compression ratio arenecessary for this arrangement.
A suitablecombination consists of e.g. a turbo-dragpump TMU 071 with an oil-free 4-stagemembrane pump as the backing pump.The gas load at the process pressure liesin the range of 1–5 · 10-4 mbar · l/s, so thata pumping speed of approx. 50–200 l/s issufficient for the turbopump. This gives apumping speed for the backing pump ofapprox. 1 l/min, or approx. 10 l/min whenthe turbo-drag-pump is operated with apurge gas. Because of the simple singlestage pressure reduction and the relativelylow total pressure in the whole analyzerunit, the arrangements shown in Fig.
38are also suitable for the analysis of corrosive gas mixtures. For these applications,the turbopump is operated with an inertpurge gas and the pressure in the analyzerunit is reduced further, if necessary, withsmaller apertures. However, with thisreduction of the working pressure, theQuadStarTMp (ion source)< 1 · 10–4 mbarprocess chamberRS 232 C orfibre-optic cablep < 1 · 10–5 mbarRS-232-C orLAN interface10 mbar > p > 5 · 10–4 mbarTMPrismagas-tight ion sourceC-SEMTMU 0712 x relay output,2 x analog input,4 x analog output2 x relay input24 VDC230 V, 50 HzMVP 015–4pprocess > pion source > panalyzerFig. 39:Differentially pumpedmass spectrometerwith a gas-tight ionsource.351 Fundamentals of mass spectrometrydesign, the ion source is not a separatecomponent of the analyzer but is integrated into the analyzer vacuum chamber(Fig.
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