EP1959476A1 - Mass spectrometer - Google Patents

Abstract

The mass spectrometer has an ionization chamber (b) with a feed channel (a) for examining the gas, an electron gun for ionizing the gas, electrodes for accelerating the ionizing electrons. Other electrodes are provided for mass dependent separation of the ions by acceleration or deceleration. An energy filter (k) is designed as a 90[deg] sector for the ions and is fully planar. The components are arranged on a level non-conductive substrate. The energy filter is produced on the substrate and the doped semiconductor plates are placed on the cabling by a single photolithography and etching.

Description

• eine Ionisationskammer mit einem Zuführkanal für das zu untersuchende Gas,
• eine Elektronenquelle zum Ionisieren des zu untersuchenden Gases,
• Elektroden zum Beschleunigen der ionisierenden Elektronen,
• Elektroden zum masseabhängigen Separieren der Ionen durch Beschleunigung/Verzögerung derselben,
• einen Detektor für die separierten Ionen, und
• eine Verdrahtung mit metalliscehn Drähten.

The invention relates to a mass spectrometer, comprising:

• an ionization chamber with a feed channel for the gas to be examined,
• an electron source for ionizing the gas to be examined,
• Electrodes for accelerating the ionizing electrons,
• Electrodes for mass-dependent separation of the ions by acceleration / deceleration of the same,
• a detector for the separated ions, and
• a wiring with metalliscehn wires.

Mass spectrometers are widely used. While mass spectrometers were primarily used for scientific purposes, today there are more and more applications related to environmental protection, measurements of air quality for the detection of harmful gases, process monitoring and control, safety checks z. In airports, and the like. For this purpose, mass spectrometers are particularly suitable, which have small dimensions and are therefore easy to transport and use everywhere. Another requirement for large scale application is that these mass spectrometers are inexpensive to manufacture.

Small size distinguishes known mass spectrometers which have a quadrupole mass separator ( WO 2004/013890 . GB 234908 A ). The disadvantage is that in such Quadrupolmassenseparatoren very high demands are placed on the electrode geometry, so that a separator can not be produced by the usual in microsystem etching or deposition. Since the systems consist of several components that need to be precisely adjusted to each other and positioned, an expensive and complex single system processing is necessary.

In another mass spectrometer, a magnetic field separator is used ( WO 96/16430 ). However, this requires a certain minimum size, since on the one hand for the magnetic field separator very high magnetic field strengths must be present, while elsewhere the magnetic field must be shielded in order not to influence the ionization or ion optics.

A mass spectrometer of the type mentioned at the outset has been developed for use in a microsystem which can be produced by the methods customary in microsystem technology ( DE 197 20 278 A1 ). This mass spectrometer has very small dimensions. However, the production is very complex, since it requires on the one hand self-supporting insulated grids for the acceleration of the ionization of the gas to be examined and on the other hand electrically contacted, galvanically grown structures of copper or nickel must be produced. The construction of the individual components is carried out separately on a total of four substrates, which must be connected to a monolithic system with a suitable construction and connection technology.

The object of the invention is to provide a mass spectrometer of the type mentioned, which can be produced easily and inexpensively and is suitable for mass production.

• dass es einen als 90°-Sektor ausgeführten Energiefilter für die Ionen aufweist,
• es vollständig planar aufgebaut ist,
• die Komponenten auf einem ebenen nichtleitenden Substrat angeordnet sind,
• die Ionisationskammer, die Elektroden zum Beschleunigen der Elektronen und Ionen, der Detektor für die Ionen und der Energiefilter durch Photolithographie und Ätzen eines auf das Substrat und die Verdrahtung aufgebrachten dotierten Halbleiterplättchens hergestellt sind und die vorgenannten Teile durch ein zweites flaches nichtleitendes Substrat bedeckt sind.

The solution according to the invention consists in a mass spectrometer of the type mentioned in the introduction,

• that it has an energy filter designed as a 90 ° sector for the ions,
• it is completely planar,
• the components are arranged on a flat non-conductive substrate,
• the ionization chamber, the electrodes for accelerating the electrons and ions, the detector for the ions and the energy filter are produced by photolithography and etching a doped semiconductor chip applied to the substrate and the wiring and the aforementioned parts are covered by a second flat non-conductive substrate.

The function of the mass spectrometer with the mass-dependent separation of the ions by acceleration / deceleration is based on the fact that the acceleration through the fields of the electrodes different ions reach a different speed and due to these differences in speed, the separation takes place. The corresponding transmitted ion beam is not monochromatic, but also contains ions of greater or lesser mass, which had a greater or lesser start speed due to the thermal movement. In order to filter out these non-monochromatic ions, the energy filter is provided in which between two electrodes with different, in particular opposite potential, the ions are deflected by 90 ° in a channel between the electrodes. By this measure, a higher accuracy is obtained.

The particular advantage of the invention, however, is that the mass spectrometer is constructed completely planar and can be produced from wafers with the techniques of microelectronics. The components are arranged on a flat, nonconducting substrate on which the metallic connection wiring has first been applied. The ionization chamber, the electrodes for accelerating the electrons and ions, the detector for the ions and the energy filters are produced by photolithography and etching of a wafer applied to the substrate and the wiring, wherein all components are produced in a photolithographic and etching step. Subsequently, the components are then covered by a flat non-conductive substrate so as to obtain a closed unit.

In an advantageous embodiment, the electron source is a thermal emitter. In another advantageous embodiment, the electron source comprises a plasma chamber having a rare gas feed passage and a microwave line for introducing and maintaining the plasma, the plasma chamber, the feed channel and the microwave line also being formed by etching the semiconductor die together with the others Parts are made.

The electrodes for mass-dependent separation of the ions by acceleration / deceleration are at an advantageous Embodiment designed as a time-of-flight mass separator and arranged. In a first gate electrode arrangement, the ion beam is pulsed. Only short ion pulses reach the drift path, where the pulse diverges due to the different velocities of the ions. At a second gate electrode arrangement, the ion pulse is scanned. Different maturities corresponding to different masses. The energy filter then ensures that only ions with exactly one energy reach the detector and are registered there.

In the case of a traveling-field separator, a larger number of electrodes are provided in the measuring path, which are subjected to alternating electrical voltages which "migrate" from one end to the other end with the ions. Only the ions at exactly the speed corresponding to the "rate of migration" of the electric fields always pass through electrodes to which no voltage is currently applied. All other ions that are out of sync move between electrodes that are being applied with an electrical voltage so that they are deflected to the side.

The detector for the ions is advantageously designed as a Faradaydetektor. In another advantageous embodiment, which has greater sensitivity, the detector for the ions is designed as an electron multiplier.

The electrodes for accelerating the electrons may be two apertured electrodes to which different electrical potentials can be applied. These Electrodes may also be made of the semiconductor material such that the prior art grating arrangement for accelerating electrons of the prior art (US Pat. DE 197 20 278 A ), which is difficult to manufacture, is avoided.

Advantageously, the mass spectrometer has a microcontroller, by which it is controlled.

The metallic conductors of the wiring and the electrodes are advantageously electrically connected by eutectic semiconductor metal contacts. For this purpose, bumps of a suitable metal are arranged on the wires or printed conductors in the corresponding places, which form the eutectic semiconductor metal contacts during bonding with the semiconductor chip.

In a particularly advantageous embodiment, the semiconductor material is doped silicon. A particularly advantageous metal for the eutectic contacts is gold.

The non-conductive substrates are advantageously made of borosilicate glass or quartz glass.

The invention is also characterized by a method for producing the mass spectrometer. According to these methods, the metal wiring on which metal pads for connection to the semiconductor electrodes are disposed is applied to a flat non-conductive substrate. Cores are then etched into the die in order for the semiconductor resistor to contact only the metal pads but not the wiring during bonding. Subsequently, the Semiconductor platelets are then applied to the substrate and arranged on the same a mask for photolithography. The alignment of the mask with respect to the wiring and gold pads can be done optically by using light of a wavelength for which the silicon wafer is transparent. For silicon, a wavelength above 1.2 μm is suitable. After appropriate exposure and mask removal, the semiconductor die is then locally etched in one step to create the components of the mass spectrometer. Subsequently, the semiconductor wafer is covered with a second non-conductive substrate.

At the second non-conductive substrate can be applied in advance, a further wiring to z. B. electrodes of electrode pairs to each other.

Fig. 1

die prinzipielle Anordnung der wesentliche Teile einer vorteilhaften Ausführungsform des Massenspektrometers ohne Verdrahtung und nichtleitende Substrate;

Fig. 2

einen Schnitt entlang der Linie A-A von Fig. 1, wobei die nichtleitenden Substrate mit dargestellt sind.

Fig. 3

in einer ähnlichen Darstellung wie Fig. 1 eine andere Ausführungsform;

Fig. 4

in ähnlicher Darstellung wie Fig. 2 einen Schnitt entsprechend der Linie A-A von Fig. 3

Fig. 5 und Fig. 6

den Figuren 1 und 2 bzw. 3 und 4 entsprechende Darstellungen einer dritten Ausführungsform;

Fig. 7

eine Draufsicht auf die Beschleunigungselektrodenanordnung;

Fig. 8

einen Schnitt entlang der Linie A-A von Fig. 7; und

Fig. 9

das Prinzip der Herstellung des Massenspektrometers der Erfindung.

The invention will be described below with reference to advantageous embodiments with reference to the accompanying drawings. Show it:

Fig. 1

the basic arrangement of the essential parts of an advantageous embodiment of the mass spectrometer without wiring and non-conductive substrates;

Fig. 2

a section along the line AA of Fig. 1 , wherein the non-conductive substrates are shown.

Fig. 3

in a similar representation as Fig. 1 another embodiment;

Fig. 4

in a similar representation as Fig. 2 a section corresponding to the line AA of Fig. 3

Fig. 5 and Fig. 6

the Figures 1 and 2 and Figures 3 and 4 are respective views of a third embodiment;

Fig. 7

a plan view of the acceleration electrode assembly;

Fig. 8

a section along the line AA of Fig. 7 ; and

Fig. 9

the principle of manufacturing the mass spectrometer of the invention.

In Fig. 1 2, the finished semiconductor chip is shown, which in this embodiment is made of doped silicon and in which the corresponding components are produced by etching. The spectrometer has a supply channel a for the sample gas, which is passed into the ionization chamber b . The electrons required for the ionization with an energy of typically 70 eV are extracted from a plasma chamber d and accelerated between two aperture openings c lying at different potentials. The entire area between the apertures is evacuated to the sides of the system. The noble gas is supplied via the channel e of the plasma chamber d . It is excited by the microwave waveguide f with microwaves to generate the plasma and thereby release the required electrons. The pressure in the plasma chamber is controlled by the pre-pressure upstream of channel e or a connected capillary.

The ions from the ionization chamber b are extracted by an electric field between the chamber wall and ion optics g on a further aperture, accelerated with defined energy and focused. The ion beam is pulsed at the first gate electronics array h . Thus, only short ion pulses reach the drift path i , where the pulse diverges due to the different velocities of the ions. At the second money electrode arrangement j , the ion pulse is scanned. The energy filter k ensures that ions only reach the detector 1 with exactly one energy and are registered there.

3 and 4 show another embodiment, which in the area of the accelerating electrodes of the embodiment of the Fig. 1 and 2 different. An alternating voltage is applied to the electrodes m of the traveling-field separator, so that ions which pass between electrodes which are currently subjected to a voltage are deflected to the side and removed from the beam. Only the ions at exactly the right speed, passing through the electrodes when there is no voltage across them, reach the energy filter k , whose two electrodes on both sides of the quarter-circle-shaped channel are at opposite potentials, so only ions with a well-defined one Let energy through. These ions then strike the detector 1 again .

The embodiment of the FIGS. 5 and 6 is different from the one of Fig. 1 and 2 in that, instead of a noble gas plasma, a thermal emitter n is used to release the electrons required for the ionization.

In FIGS. 7 and 8 the electrode area of the mass spectrometer according to the invention is shown. The support for the system is the borosilicate glass 1, to which metallic conductor tracks 2 are applied in order to connect the electrodes electrically. The electrical contact between the metal interconnects 2 and the silicon electrodes 4 via a eutectic gold-silicon contact 5. Goldpads 3 at the contact points between conductor 2 and silicon electrode 4 alloy during bonding with the highly doped silicon and thus make an ohmic contact. The structure of the electrodes is in Fig. 8 shown in section.

In Fig. 9 the principle of manufacturing the mass spectrometer is shown. By etching in the silicon wafer recesses 8 are generated, which provide in the finished mass spectrometer for the required distance between the metallic interconnects 2 on the carrier substrate 1 and the silicon wafer 6 . This is necessary so that the substrate 1 and the silicon wafer 6 can be bonded flat. The depth of the etching pits 8 is designed so that the gold pads 3 come into contact with the bottom of the etching pit 8 when joining substrate 1 and silicon platelets 6 . The arrangement thus produced according to I is then bonded in step II . In step III , after applying a corresponding mask and exposure by etching, the desired structure is produced. The upper substrate 7 shown in I, II and III is not actually present at these steps. It also carries a conductor and is then bonded to the device at IV , electrodes being connected by the conductor disposed on the upper substrate 7 .

The production of the mass spectrometer can take place in uniform steps in wafers. The final mass spectrometer shown in the figures may have dimensions as small as 5x10 mm. Due to the small size and low demands on the pumping power of a vacuum pump are made.

Claims (17)

Mass spectrometer comprising an ionization chamber (b) with a feed channel (a) for the gas to be investigated, an electron source (d, n) for ionizing the gas to be examined, Electrodes (c) for accelerating the ionizing electrons, Electrodes (g, hj, m) for mass-dependent separation of the ions by acceleration / deceleration thereof, a detector (1) for the separated ions, and a wiring with metallic conductors, characterized, that it has an energy filter (k) for the ions, designed as a 90 ° sector, it is completely planar, the components are arranged on a flat non-conductive substrate (1), - The ionization chamber (b), the electrodes (g, hj, m) for accelerating the electrons and ions, the detector (1) for the ions and the energy filter (k) by photolithography and etching a on the substrate (1) and the Wiring (2) applied doped semiconductor chip (6) are made and the aforementioned parts are covered by a second flat non-conductive substrate (7). Mass spectrometer according to claim 1, characterized in that the electron source (s) is a thermal emitter. Mass spectrometer according to claim 1, characterized in that the electron source has a plasma chamber (d) with a supply channel (e) for a noble gas and with a microwave line (f) for introducing microwaves for generating and maintaining the plasma, the plasma chamber (d) , the feed channel (e) and the microwave line (f) are produced by etching the semiconductor chip (6). Mass spectrometer according to one of claims 1 to 3, characterized in that the electrodes (g, h, j) are designed and arranged for mass-dependent separation of the ions by acceleration / deceleration as a time-of-flight mass separator. Mass spectrometer according to one of claims 1 to 3, characterized in that the electrodes (g, m) for mass-dependent separation of the ions formed by acceleration / deceleration as Wanderfeldseparator and are arranged. Mass spectrometer according to one of claims 1 to 5, characterized in that the detector (1) for the ions is designed as a Faradaydetektor. Mass spectrometer according to one of claims 1 to 5, characterized in that the detector (1) is designed for the ions as an electron multiplier. Mass spectrometer according to one of claims 1 to 7, characterized in that the electrodes (c) for accelerating the electrons are two apertured electrodes to which different electrical potentials can be applied. Mass spectrometer according to one of claims 1 to 8, characterized in that it comprises a microcontroller. Mass spectrometer according to one of claims 1 to 9, characterized in that the metallic conductors (2) and the electrodes (4) are electrically connected by eutectic metal-semiconductor contacts. Mass spectrometer according to one of claims 1 to 9, characterized in that the metallic conductors (2) and the electrodes (4) are electrically connected by eutectic gold-semiconductor contacts. Mass spectrometer according to one of claims 1 to 9, characterized in that the semiconductor material is doped silicon. Mass spectrometer according to one of claims 1 to 12, characterized in that the non-conductive substrates (1, 7) consist of borosilicate glass or quartz glass. A method of manufacturing a mass spectrometer comprising an ionization chamber for the gas to be tested with a gas supply channel, an electron source for the gas ionizing electrons, electrodes for accelerating the electrons, electrodes for focusing and accelerating ions exiting the ionization chamber and for mass dependent separation the same by acceleration / deceleration, an ion detector, lead wiring in the form of metallic conductors for the aforementioned components, and an energy filter for the ions, designed as a 90 ° sector, characterized in that the metal wiring is applied to a flat non-conductive substrate, on the metal pads for connection to the semiconductor electrodes are arranged, are etched into the semiconductor wafer of the wiring corresponding recesses, the semiconductor wafer is applied to the substrate, a mask for photolithography opt is aligned with light of a wavelength above about 1.2 microns on the semiconductor die, which is then locally etched, and then that the semiconductor wafer is covered with a second non-conductive substrate. A method according to claim 12, characterized in that with the second non-conductive substrate further wiring is applied. A method according to claim 14 or 15, characterized in that doped silicon is used as the semiconductor material. Method according to one of claims 14 to 16, characterized in that gold is used as the metal for the metal pads.

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