mass_spectrometer Pfeiffer обзор (1248468), страница 12
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If the energy of the electrons ischanged during the selected ionization50procedure (Electron Impact Ionization),excitation spectra can be used to differentiate between neutral particles in aground state and excited neutral particles (so-called radicals, see “Appearance Potential Spectroscopy”).The density and mass of the neutralparticles in the plasma (with this theunit can be calibrated easily.)You can obtain a measurement of theelectron energy and its density; to doso, the plasma monitor must be operated as a Langmuir probe.Consequently the mass spectrometricplasma diagnostic delivers the most comprehensive information about a plasma inthe most demanding procedures.1.4.4 Solution variationsHeavy-duty mass spectrometers operatewith a pressure of < 10–5 mbar.
Mostplasma processes operate at a pressureof 0.1 mbar or less.Therefore, a single-stage differentiallypumped mass spectrometer is offered as astandard version.The PPM 422 (Fig. 53) is a unit consistingof a differentially pumped mass spectrometer including a control unit and software for mass and energy resolved measurements of positive and negative ions,neutral particles and appearance potential.A Cylindrical Mirror Analyzer (CMA) isused as an energy filter in the PPM 422. Alinear beam path is achieved throughspherical converging and diverging elements on the input and output of the filter.This allows for a high immersion depth inthe process recipients.The CMA is set to a fixed kinetic energy ofthe occurring ions for energy analysis. Theentire analyzer including energy and massfilters is set to a variable electric bias.This allows a linear energy scale to begenerated; since with this counter fieldmethod the kinetic energy of the ions inthe analyzer is always the same, an energydispersion cannot occur.Likewise, to avoid an energy dispersion,we purposely dispensed with so-calledFundamentalsMaximum process pressure ≤ 10-2 mbarEnergy range ± 500 eVIonsIonsIonsEnergy resolution : 0.3 eV FWHMMass range: 512, 1024 and 2012 amuTurbomolecularPump fordifferential pumpingdrift lenses in the PPM 422.
Drift lensescould be used to increase the immersiondepth of a plasma monitor. However, youwould introduce a complex energy dispersion.In order to use this unit to measure neutralparticles with an energy resolution corresponding to the CMA, the ion source itselfmust contribute as little as possible toenergy dispersion. The PPM 422 uses a socalled field-free ion source that is expanded horizontally in the flow directionof the ions. The energy dispersion of theion source is shown in the followingexamples.The physical functionality of the PPM 422is described in detail in the unit’s operating manual and in additional documents[10].Units from the PPM 400 family are bestused when you have lesser requirementsregarding the energy resolution or if youdispense with a high energy resolution infavor of increased sensitivity.Units of the type PPM 400/EPD 400 (Fig.
54)likewise are differentially pumped massspectrometers with the most varying combinations of ion sources and energy analyzers.Different types of energy filters or ionoptics and an ion source can be combinedin a PPM 422.With all Pfeiffer Vacuum operated units ofthis type (PPM 422, PPM 400), the electrical potential of the first exposed aperturein the plasma can be selected freely.This is especially important in order tominimize disruptions to the plasma by thedetector.Fig. 53:Schematic diagramof a PPM 422Fig.
54:Schematic diagram ofthe PPM 400/ EPD 400Four configurations:• Three-lens opticspos. and neg. ions• Three lenses andcross beamion sourceneutrals and pos. and neg.ions• Two lenses andcross beamions and neutral particlesno energy analysis• Cross beamion sourceappearence spectroscopy511 Fundamentals of mass spectrometry1.4.5 Measurements with the plasmamonitorSeveral application examples are shownbelow to illustrate various measurementoptions with a plasma process monitor.The energy distribution of Ar and Cu ionsfrom the plasma of a DC planar magnetronis displayed. The maximum of the distribution determines the plasma potential.– 6.0 VDC was applied to the extractionhood of the analyzer.
Argon ions areformed to this potential through resonantcharge exchange. Application of the spectrum at – 6 eV can be used to calibrate theenergy scale.Fig. 55The chronological sequence of the iondensities with a magnetically modulatedAr-H2 plasma became calibrated energy.The ignition of a filament supplied withalternating current can be seen clearlynext to the periodicity induced by themagnetic modulation.Fig. 56The chronological sequence of the negative ions in a power-modulated silaneplasma was measured with a PPM 422 anda multi channel scaler.Fig.
5752FundamentalsThe resolution of the entire system isvery important in regards to the energymeasurement of neutrals. Not only theresolution of the energy filter (CMA) butalso the energy distribution of the ionsformed in the ion source determine theresult.In previous experiments on externallygenerated thermal ions, the energy resolution of the CMA was determined to 0.3 eV(FWHM). Measurement of the ions formedin the ion source of the PPM 422 show thattheir energy distribution lies in the sameorder of magnitude and leads to an additional epansion of the curve from 0.3 eV to0.64 eV.The PPM 422 therefore can be used tomeasure ions with an energy resolution of0.3 eV and neutrals with an energy resolution of 0.64 eV.(A closer look shows that the electricalfield of an extraction aperture reaches intothe formation chamber set at 100 VDC andthus leads to a shift of the energy scale byapproximately 2 eV.)Fig.
58The energy distribution of neutral Cuatoms was calibrated with a DC planarmagnetron. The ion source of the unit wasraised to + 100 VDC to discriminateagainst a high energetic ion. However, thestandard unit required slight modificationto reach this level of sensitivity. The aperture angle between the ion source and theextraction opening was increased.Fig. 59531 Fundamentals of mass spectrometryNegative ions were extracted from apower-modulated silane plasma. The clusters within the plasma can be detectedacross a large mass range.Fig.
60You can differentiate between neutralparticles in a ground state and excitedneutral particles from a plasma, so-calledradicals, by varying the electron energy inthe PPM 422.Additional application examples aredescribed in the selected publications[12, 13, 14, 15,16, 17, 18, 19].Fig. 611.4.6 Measurement range extension:While a broad palette of applications iscovered in the above mentioned units,new trends in processing must be takeninto account.While in the past low pressure plasmaswere applied for the most part, todaymore gas discharges, which are operatedat atmospheric pressure, are used.If possible, we try to fall back on availableinstruments and functional units toexpand the pressure range of the analysisunit so that customers owning standardunits only need to make the most necessary new investments.54For time-resolved measurements < 0.1 seconds and to increase the sensitivity, thesignal of all mass spectrometers fittedwith an ion counter can be processed further with a readily available signal processing unit.For this purpose, a signal converter, whichtransfers the counting pulse of the counterto TTL signals, is used.Screening against magnetic fields:An additional option is screening againstmagnetic fields (up to 10 m Tesla flow density) that occur during some plasma processes and that can disrupt operation.
TheMeasurements at the substrate level aredescribed in publication [11].Langmuir probes:Langmuir probes can be used in additionto a plasma monitor to determine the electron energy and the density in the plasma.However, since the electrical potential ofthe first exposed aperture of the plasmacan be selected freely with these units, itcan be operated principally as a Langmuirprobe. In this case, you are dealing onlywith a “single sample”.Fundamentalsapertures are integrated in the chamber ofthe plasma monitor.Screenings against high magnetic fieldswithin the process system can be obtainedon request.The molecular beam inlet deals with aself-centering second differential pumpstage that can be retrofitted on all PPM422 and PPM 400 units in operation. In thisdesign also, the electrical potential of thefirst exposed aperture can be selectedfreely.Fig.
62552 Mass spectrometers for residual gas analysisContentsPage2 Mass spectrometers for residual gas analysis2.1Residual Gas Analysis at HVPrismaTMPrismaTMPrisma2.2–TalkStarTM585859QMS 200 F60Residual Gas Analysis at UHV62PrismaTMQMS 200 M with C-SEM62TMQMS 200 – Connectivity64Prisma56TM8056Components for multiplex mode and Software-Update65QMG 422 with QMA 12566Stand-alone Components, QMG 4226757AppendixAnalysisof IonsIonenanalyseGasanalysisGasanalyseResidualgas analysisPartialdruckmessungFundamentals2.1 Residual Gas Analysis at HVPrisma™ 80Cheap residual gas analysis and leak detectionUser-friendly softwareSelectable partial pressuresRobust analyzerHigh reliability of operation by two filaments.Technical DataMass rangeRod system, diameter/lengthDetectorDetection limitSensitifity for ArOperating pressure, max.Contribution to neighboring mass (40/41)Peak ratio reproducibility2)Resolution, at 10% peak height1)2)1–80 amu6 mm/100 mmFaraday1 · 10-12 mbar1 · 10-3 A/mbar1 · 10-4 mbar 1)< 10 ppm± 0,5 %0,5–2,5 amuat reduced emission current of 0,2 mA: 1 · 10-3 mbarat constant conditions while 8 hours, N2 and Ar from AirOperating temperature/electronicsOperating temperature/analyzerMeasurement speed, scan analogMeasurement speed, scan BargraphMeasurement speed, MIDMeasuring channelsRS-232-C interfaceDigital outputVoltageWeight0–40 °Cmax.
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