US3842267A - Method and apparatus for measuring, by ionization, the flux of vapour emitted during vacuum vaporization - Google Patents

Method and apparatus for measuring, by ionization, the flux of vapour emitted during vacuum vaporization Download PDF

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Publication number
US3842267A
US3842267A US00330537A US33053773A US3842267A US 3842267 A US3842267 A US 3842267A US 00330537 A US00330537 A US 00330537A US 33053773 A US33053773 A US 33053773A US 3842267 A US3842267 A US 3842267A
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vapour
jet
magnetic field
ions
flux
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US00330537A
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P Genequand
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Battelle Development Corp
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Battelle Development Corp
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
    • G01F1/64—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by measuring electrical currents passing through the fluid flow; measuring electrical potential generated by the fluid flow, e.g. by electrochemical, contact or friction effects
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J41/00—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas; Discharge tubes for evacuation by diffusion of ions
    • H01J41/02—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas
    • H01J41/04—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas with ionisation by means of thermionic cathodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/26—Mass spectrometers or separator tubes
    • H01J49/28—Static spectrometers
    • H01J49/30—Static spectrometers using magnetic analysers, e.g. Dempster spectrometer

Definitions

  • the amplitude of the variable component of the electric influenge is rneasuredyvhghthe paclgage Q1 imlsexercises in the course of its r evohTtions al orTg the circular trajectory on an electrode situated externally to the trajectory, the amplitude forming the measure of the flux.
  • the present invention concerns a method for measuring, by ionization, the flux of vapour emitted by a substance subjected to vaporization in vacuum, whereby a jet is produced within the vapour and part of the particles contained in this jet are ionized.
  • vacuum vaporization consists in heating in an enclosure devoid of air (pressure below a limit of the order of torr) a crucible containing a substance the temperature of which is increased to the point where it vaporizes, and to allow the vapour thus created to condense onto one or several substrates and to coat them with a film which is usually extremely fine (thickness between a few dozen Angstrom units and a few microns).
  • the speed of condensation therefore the speed with which the thickness of the deposited film increases, and the quality of this film depend on the speed of evaporation, consequently, on that of the vapour flow emitted by the substance contained in the crucible.
  • a slim jet is isolated within the vapour by means of one or several diaphragms, and submitted to the impact of ionizing rays, most of the time an electron beam projected in or through the jet.
  • the ionic current I is proportionate to the electronic current I and to the number n of particles of vapour (molecules or atoms) contained in a unit volume (density of vapour), which in turn is equal to the ratio of the vapour flux 11) per unit of surface (that is, the quantity to be measured) to the mean speed V of these particles within the jet.
  • the evaporated substance is a dielectric, as is the case in the antireflection treatment of optic parts or in certain stages of manufacture of integrated circuits.
  • the zone of ionization (the one in which the jet of vapour and the ionizing electronic beam meet) a shape that will ensure that the ionization efficiency will be as little as possible at the mercy of incidental fluctuations of theparticles of vapour, that is, of variations in the position of the crucible with respect to the diaphragms delimitating the jet.
  • this gauge does not contain the grating with which certain common types of ionization gauges of the triode type are provided. Therefore, it is not affected by those inconveniences resulting from the uncertain shape of the diffuse cloud which forms around this grating.
  • vapour is complex, i.e., consisting of different constituents
  • the known procedures do not allow to isolate from the overall flux the flux of one of its constituents. They permit still less to carry out a spectrum analysis of the overall flux, i.e., to measure the partial flux of each of its constituents. Only the techniques of mass spectrography permit an analysis of the constituents. They are, however, not adaptable to the measurement of the vapour flux.
  • a primary object of the invention is to avoid these inconveniences.
  • the process of the invention is characterized by the fact that an essentially uniform magnetic field is produced in a volume crossed by the said jet and is directed essentially perpendicularly to the jet, so that a section of this jet is permanently immersed in the magnetic field;
  • the particles contained in a delimited volume situated within this section are ionized through being submitted to the action of at least one pulse of an ionizing radiation so that these ionized particles constitute a package of ions describing, under the influence of this field, a circular trajectory;
  • the volume arranged in the air gap of the magnet by means of the ionisation of the vapor jet at least one package of ions, a so-called ion package, is formed. Due to the effect of the magnetic field, it describes a circular trajectory in the air gap in a plane which is essentially defined by the jet of the vapor particles and the direction perpendicular to the direction of the magnetic field.
  • the electrical signal which can be measured, an alternative tension, for instance, and which is induced in the electrode by the rotating package of ions, is used to measure the vapor flux.
  • the ionization takes place periodically pulsating with the cyclotronic or rotation frequency of the ion package, whereby an amplification of the signal to be measured is accomplished.
  • a vapor flux which consists only of one type of particles, one obtains as signal to be measured an alternative tension with the cyclotronic frequency.
  • the present invention also has for an object to provide a gauge for carrying out this procedure.
  • the gauge is characterized by the fact that it comprises:
  • a magnetic circuit provided with a gap in which prevails an essentially uniform magnetic field and placed in such a way that the jet traverses this gap by forming an essentially right angle with this field;
  • a source of ionizing radiation which emits this radiation in the form of a beam of which the axis intersects the axis of the jet and of which the intensity is modulated in at least one pulse, so that this source is capable of ionizing the particles of the jet which happen to be, for the duration of the pulse, in the volume defined by the intersection of the jet and the beam, which volume is situated in the magnetic field, and capable of transforming these particles into a package of ions which cyclically describe, under the influence of the magnetic field, a circular trajectory;
  • the said supply and measuring equipment comprises:
  • a detection circuit connected to this electrode and adjusted in such a way as to measure the amplitude of the periodic component of the electric charge which the package of ions induces upon this electrode in the course of its revolutions along this circular trajectory, the value of this amplitude constituting the measure of the said flux.
  • FIG. 1 is an overall diagram showing the position of the gauge with respect to a system of vacuum evaporation.
  • FIG. 2 is a sectional view passing through the median plane (following line II-II of FIG. 4) of a first part of the gauge pictured in FIG. 1.
  • FIGS. 3 and 4 are partial sections, horizontal and transverse respectively, of this same first part, following lines III-III and lV-IV, respectively, of FIG. 2.
  • FIG. 5 shows a block diagram of a second part of the gauge represented in FIG. I, as well as the connections of this second part with the first.
  • a typical gauge according to the present invention comprises a probe which is arranged in the vacuum space, and a supply and measuring system which is situated externally to the space, the connection between these two parts being provided by electric lines.
  • FIG. 1 gives the diagram of a vacuum space delimited by a bell jar l and a plate 2, the latter being connected by a conduit 3 to a pumping set (not shown).
  • the vacuum space encloses a crucible 4 containing a substance 5 to be evaporated, such as aluminum, for instance.
  • the crucible 4 is brought up to a high temperature by means of a heating system constituted, for instance, by a spiral electric heater coil 6 which is connected by a line 7 which crosses the plate 2 through an insulator 8, to a high-frequency generator 9 situated externally.
  • a heating system constituted, for instance, by a spiral electric heater coil 6 which is connected by a line 7 which crosses the plate 2 through an insulator 8, to a high-frequency generator 9 situated externally.
  • the substance 5 gives rise to a cloud of vapour 10 which tends to expand in the whole of the vacuum space and to condense on the cold parts, particularly on the objects 11 to be metallized, such as, for instance, plates which one wants to alluminumcoat.
  • the gauge comprises a probe 12 situated in proximity to the objects 11 and connected, by a line 13 which crosses the plate 2 through an insulator 14, to a supply and measuring system 15. The gauge therefore consists of both the probe 12 and the equipment 15.
  • the probe which is pictured on a large scale in FIGS. 2 to 4, comprises the following elements:
  • a set of metallic walls 27 to 32 which delimit within the air gap 24 a volume 33 electrically screened, that is, protected from the influence of electric charges outside the enclosure 27-32, the volume 33 being centered with respect to the axis 34 of the poles 25, 26.
  • the walls 27 to 30 are mounted so as to form, between the four of them, a monolithic frame 35, and the walls 31 and 32 are assembled so as to constitute two closures which shut off the volume 33 but are electrically independent one from the other and independent from the frame 35.
  • the walls 27 and 29 of the frame 35 are pierced with openings 36 and 37, respectively, which are disposed in line with the opening 23 of the base plate 22, the axis 38 of this alignment being shifted with respect to the center of the volume 33, therefore with respect to the axis 34 of the poles, and passing through the center of the crucible 4 (see FIG. 1).
  • the walls 31 and 32 are pierced with holes 39 and 40, respectively, which are aligned along a common axis 41 that is parallel to the axis 34 of the poles 25, 26 but shifted with respect to the latter in such a way as to intersect the axis 38 of the openings 23, 36, and 37 at a point of intersection 42.
  • the frame 35 and the walls 31 and 32 are fixed to the base plate 22 by means of insulating feet 46 (for the frame 35), 47 (for the wall 31), and 48 (for the wall 32);
  • a measuring electrode consisting of a plate 43 situated inside the volume 33 and borne by a conductor pin 44 traversing the wall 28 through an insulator 45 which provides the pin 44 with electric insulation from the wall 28. Facing the pin 44 is an equilibrium electrode 55;
  • an electron gun 49 comprising a cathode 50, a Wehnelt electrode 51, a modulation electrode 52, all of which are placed to one side of and externally to the volume 33, facing the opening 39 of the wall 31, and a collecting electrode 53 situated on the other side of and externally to the volume 33, facing the opening 40 of the wall 32.
  • the electron gun 49 thus is located in such a way as to emit, along the axis 41, an electron beam 54 which goes right through the volume 33, passing through the jet 56.
  • A' circuit 67 permitting the measuring of the current carried by the electron beam 54, is connected to the collecting electrode 53, and a source 68 brings to the collecting electrode 53 the positive voltage required to enable it to play its collecting role.
  • the measuring and supply, equipment 15 also includes a set of two amplifiers 68, 69, of which the first is a preamplifier 68 having a gain G l and thus serving as an impedance transformer, whereas the second, which has a gain G greater than 1, ensures the required amplification of the signal picked up by the measuring electrode 43.
  • the output of the preamplifier 68 is connected to an inner shield 70 which encloses the wire 71 that makes the connection with the measuring electrode 43, an outer shield 72 being adjusted externally to the whole equipment and communicating with the ground.
  • the external shield 72 is connected to the frame 35 of the probe, so that this frame is also joined to the ground.
  • the internal shield 70 is interrupted shortly before the wire 71 traverses frame 35, and the external shield 72 is provided at this point with an opening enabling the equilibrium electrode 55 to exert an electrostatic influence on the wire 71. Further on we shall see the reason for this arrangement, which, however, is not indispensable, but which improves the performances of the gauge.
  • the output of the amplifier 69 is connected to a synchronous detector 73, which also receives, through the intermediary of a line 74, the signal generated by the oscillator 63.
  • the synchronous detector 73 is connected to an instrument 75 comprising an indicator or a recorder of any convenient type.
  • the walls 31 and 32 are each connected to one of the two outputs 76 and 77 of a symmetrizing circuit 78, which is excited by a pulse generator 79 providing rectangular pulses at a frequency less than that of the sinusoidal signal provided by the generator 63.
  • a continuous voltage source 80 brings the two walls 31, 32 to a positive polarization voltage with respect to the ground.
  • the gauge so constituted works in the following manner.
  • the opening 23 (FIGS. 2 and 4) provided in the base plate 22 serves the function of a diaphragm and isolates within the cloud of vapour 10 a jet 56 in which the particles of vapour move in the direction of the arrow 57 (from bottom to top) and have a mean velocity V determined by the temperature of the cloud 10.
  • the package of ions 58 Under the action of the uniform magnetic induction produced by the magnet 21 in its air gap 24, consequently in the volume 33 delimited by the frame 35, the package of ions 58 describes a circular trajectory 59, as shown in FIG. 2 respecting the package of ions 58' which moves in the direction of the arrow 59'.
  • the radius R of the circular trajectory 59 is dependant on the mass of ions (m). their speed (V), their charge (q). and the magnetic induction (B) prevailing in the air gap. which dependance is in accordance with the known formula R m v/qB.
  • the package 58 With each revolution the package 58 induces in the measuring electrode 43, due to electrical influence, a charge of which the amplitude is, in its turn, proportional to the radius R, to the number of ions contained in the package, and to the number of-revolutions performed in each unit of time.
  • the number of ions contained in the package being proportional to the intensity I of the electronic current in the beam 54 and to the numerical density n of the particles (molecules, atoms) in the vapour over the window 23, that is to say, to the quotient of the flux (b of this vapour by the speed V of the particles which make it up, it follows from this that the signal applied to the amplifier 68 has an amplitude equal to S K I d), in which expression K is a constant that is independent of the speed V.
  • the signal S is directly proportional to the flux in the jet 56, consequently to the quantity which one wishes to measure, and is independent of the average speed V, consequently of the temperature of the vapour.
  • the signal S has its origin in the fact that the particles composing the jet 56 have a speed that is aimed in a well determined direction, in this case the direction 57.
  • the particles which possess velocities distributed at random in all directions, as is the case for the molecules of the residual gas, produce individual signals which, statistically, have a null average. The result is that the gauge eliminates from the start anyperturbation due to residual gas.
  • a synchronous detector 73 it is not indispensable to use a synchronous detector 73 to detect the signal provided by the measuring electrode 43, but it does offer the advantage of improving the signal to noise ratio and of easily eliminating parasitic signals which could be caused by charges that might be sporadically carried off by the jet of vapour.
  • a similar filtering effect, though less efficient, could be obtained by effecting a selective amplification of the signal, through adjusting the amplifiers 68 and 69 to the frequency of the revolutions (cyclotron frequency) described by the package of ions 58.
  • the package of ions 58 which re-forms at each revolution, has a tendency to diffuse around the trajectory 59 and, as a result, to create a space charge which in its turn tends to perturb the movement of this package, it is advisable to empty periodically the volume 33 of all the ions it contains. This is the role which has been assigned to the walls 31 and 32, between which the pulse generator 78 periodically establishes a purging field.”
  • the frequency of the purging pulses is of the order of 50 to 100 times lower than the frequency of the *recharging" oscillator 63; in other words, the volume 33 is purged of all its ions every 50 to I revolutions.
  • This arrangement also renders it possible to impose to all the ions a well defined lifetime, less than the undetermined lifetime which they would have if one allowed solely the action of the perturbations; this is a particularity which is not devoid of importance, like recombination. diffusion. etc., for the lifetime of the ions determines the factor of sensitivity of the gauge.
  • the walls 31, 32 are maintained at a positive potential, of the order of a fraction of a volt, which confines the package of ions 58 by preventing, thanks to the electric basin thus created, the ions from drifting either one way or the other in the direction of the axis 41 of the electron beam 54 and from colliding with the walls 31, 32.
  • these walls 31, 32 act simultaneously for the ions as confining electrodes and as extracting electrodes.
  • the presence of the symmetrizing circuits 64 and 78 is explained by the fact that they eliminate any perturbation which might result from an electric influence exerted upon the measuring electrode by the voltages applied to the electrode of modulation 52 or the electrodes of extraction 31, 32. In this way, the influence exerted upon the electrode 43 by the voltage applied by the output 65 of the symmetrizer 64 to the electrode 52 is compensated by the opposite influence exerted by the equilibrium electrode to which the output 66 of this same symmetrizer 64 applies a polarity voltage opposed to the first. This is also the case with the two opposite voltages applied to the extraction electrodes 31 and 32, of which the direct influences upon the measuring electrode 43 annul each other.
  • an electronic beam as an ionizing source presents many advantages with regard to simplicity of use, so that this is the device which will mostly be reverted to, even if the beam, instead of being modulated in the periodic manner described in connection with FIG. 5, is modulated in sporadic pulses as mentioned earlier.
  • the length of time needed to move along the orbit 59 depends on the ratio g/m of the ions.
  • the frequency of the signal released by the probe is, for a given magnetic induction, specific to the evaporated substance.
  • a spectrum analysis which gives the partial fluxes of the different constituents of a complex vapor containing several evaporated substances.
  • the cyclotronic frequency of an ionized particles is with a constant magnetic field and according to the foregoing explanation proportional'to the elementary charges q on the particle and reciprocally proportional to the mass of the particle. Since the ionization of the particle in the vapor jet is mostly unifold, only, (one elementary charge is transferred per particle, only, multiple ionizations can be observed relatively seldom, only), with thefrequency analysis according to the invention of the alternative tension signal induced in the electrode one can'conclude directly to the mass of the particles included in the ionized vapor jet. Moreover also in accordance with the foregoing explanation the amplitude with the specific measuring frequency is proportional to the vapor flux.
  • the preamplifier 68 is of the differential type and has two inputs, one of which is connected to the electrode 43, the other one to the electrode'43.
  • a method for measuring the flux of vapour emitted by a substance subjected to vacuum vaporization comprising the steps of directing a portion of the vapour in the form of a jet through a selected region,
  • Apparatus for measuring the flux of vapour emitted by a substance subjected to vacuum vaporization comprising a probe situated inside a vacuum chamber and provided with a screen having an opening, the screen being so located as to intercept the vapour and to let it escape through the opening in the form of a vapour jet, and
  • a supply and measuring equipment disposed externally to the vacuum chamber and connected to the probe by electric conductors, said probe comprismg a magnet provided with a gap in which prevails an essentially uniform magnetic field and so located that the vapour jet traverses the gap by forming an essentially right angle with the magnetic field;
  • an electron gun which emits an ionizing electron beam of which the axis intersects the axis of the vapour jet and of which the intensity is modulated in at least one pulse, so that the electron beam is capable of ionizing the particles of the vapour jet which happen to be, for the duration of the pulse, in the volume defined by the intersection of the vapour jet and the electron beam, which volume is situated in the magnetic field, and capable of transforming these particles into a package of ions which cyclically describe, under the influence of the magnetic field, a circular trajectory;
  • said supply and measuring equipment comprising a detection circuit connected to the fixed electrode to measure the amplitude of the electric signal which the package of ions induces, by electric influence, upon the electrode in the course of its revolutions along the circular trajectory, the value of said amplitude constituting the measure of the flux.
  • the electron gun comprises an electrode capable of modulating the intensity of the electron beam
  • the supply and measuring equipment comprises a pulse generator which is connected to the modulating electrode
  • the detection circuit comprises a detector that is synchronized by the pulse generator.
  • a pair of confinement electrodes are disposed on opposite sides of the package of ions and substantially perpendicular to the magnetic field
  • the supply and measuring equipment comprises a continuous voltage source connected to the electrodes to produce between them an electric field of confinement to maintain the circular trajectory of the package of ions in a plane substantially perpendicular to the direction of the magnetic field and approximately midway between the confinement electrodes.
  • Apparatus as in claim 10, wherein the supply and measuring equipment comprises a pulse generator connected to the confinement electrodes to apply to them periodically symmetrical voltage pulses producing between the electrodes an electric field capable of eliminating any perturbation from the ions produced by the pulses of ionized radiation.
  • the fixed electrode comprises a plate essentially parallel to a plane defined by the axis of the vapour jet and the direction of the magnetic field, the plate having a position that is essentially symmetrical with respect to the volume of intersection of the vapour jet and the electron beam.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Analytical Chemistry (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
  • Electron Tubes For Measurement (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
  • Measurement Of Radiation (AREA)
  • Physical Vapour Deposition (AREA)
  • Length-Measuring Devices Using Wave Or Particle Radiation (AREA)
US00330537A 1972-02-09 1973-02-07 Method and apparatus for measuring, by ionization, the flux of vapour emitted during vacuum vaporization Expired - Lifetime US3842267A (en)

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CH191872A CH570610A5 (cs) 1972-02-09 1972-02-09

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US (1) US3842267A (cs)
JP (1) JPS4889794A (cs)
BE (1) BE795278A (cs)
CA (1) CA983581A (cs)
CH (1) CH570610A5 (cs)
DE (1) DE2305102A1 (cs)
FR (1) FR2171824A5 (cs)
GB (1) GB1394155A (cs)
IE (1) IE37274B1 (cs)
IT (1) IT992543B (cs)
LU (1) LU66996A1 (cs)
NL (1) NL7301762A (cs)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4010366A (en) * 1975-09-22 1977-03-01 Xerox Corporation Measurement of the mass and charge of charged particles
US4024399A (en) * 1975-01-06 1977-05-17 Jersey Nuclear-Avco Isotopes, Inc. Method and apparatus for measuring vapor flow in isotope separation
US5395886A (en) * 1991-04-01 1995-03-07 Dow Corning Corporation Modified fluorohydrocarbon polymers

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6311808A (ja) * 1986-07-02 1988-01-19 Mitsubishi Electric Corp 膜厚監視装置

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2694151A (en) * 1953-06-26 1954-11-09 Cons Eng Corp Mass spectrometry
US2958774A (en) * 1957-05-07 1960-11-01 Ca Nat Research Council Omegatron with orbit increment detection
US2967239A (en) * 1954-02-19 1961-01-03 Gen Electric Method and apparatus for analyzing constituents of a substance
US3086110A (en) * 1958-03-15 1963-04-16 Philips Corp Mass spectrometer
US3247373A (en) * 1962-12-18 1966-04-19 Gca Corp Mass spectrometer leak detector with means for controlling the ion source output

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2694151A (en) * 1953-06-26 1954-11-09 Cons Eng Corp Mass spectrometry
US2967239A (en) * 1954-02-19 1961-01-03 Gen Electric Method and apparatus for analyzing constituents of a substance
US2958774A (en) * 1957-05-07 1960-11-01 Ca Nat Research Council Omegatron with orbit increment detection
US3086110A (en) * 1958-03-15 1963-04-16 Philips Corp Mass spectrometer
US3247373A (en) * 1962-12-18 1966-04-19 Gca Corp Mass spectrometer leak detector with means for controlling the ion source output

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4024399A (en) * 1975-01-06 1977-05-17 Jersey Nuclear-Avco Isotopes, Inc. Method and apparatus for measuring vapor flow in isotope separation
US4010366A (en) * 1975-09-22 1977-03-01 Xerox Corporation Measurement of the mass and charge of charged particles
US5395886A (en) * 1991-04-01 1995-03-07 Dow Corning Corporation Modified fluorohydrocarbon polymers

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CH570610A5 (cs) 1975-12-15
FR2171824A5 (cs) 1973-09-21
GB1394155A (en) 1975-05-14
IT992543B (it) 1975-09-30
IE37274L (en) 1973-08-09
JPS4889794A (cs) 1973-11-22
BE795278A (fr) 1973-08-09
DE2305102A1 (de) 1973-08-16
IE37274B1 (en) 1977-06-22
CA983581A (en) 1976-02-10
NL7301762A (cs) 1973-08-13
LU66996A1 (cs) 1973-04-19

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