JP4973441B2 - Atmosphere analyzer and atmosphere analysis method - Google Patents

Description

  The present invention relates to an atmosphere analysis apparatus and an atmosphere analysis method, and in particular, an atmosphere analysis apparatus and an atmosphere analysis method characterized by a configuration for detecting substances contained in the atmosphere with high accuracy without being affected by water vapor. It is about.

  In the field of manufacturing precision electronic devices such as semiconductor devices in recent years, organic substances contained in the manufacturing environment such as clean rooms have an impact on device performance and manufacturing yield, so pollutants in the atmosphere are detected. It is requested.

  In order to detect contaminants in such an atmosphere by a simple method, a quartz micro balance (QCM) sensor using a quartz resonator is used (for example, see Patent Documents 1 and 2). .

  This QCM sensor utilizes a phenomenon in which the oscillation frequency of the crystal resonator changes depending on the weight of the resonator. When contaminants in the atmosphere naturally adsorb on the surface of the resonator, the QCM sensor It detects the presence of pollutants by change.

For example, the change in oscillation frequency ΔF [Hz] is: F ₀ [MHz] is the fundamental frequency, N [Hz · cm] is the vibration frequency of the crystal, A [cm ² ] is the electrode area, and ρ [g · cm ^-3 ] is the density of the quartz crystal to be used, and Δm [g] is the mass of the adsorbed substance,
ΔF = −F ₀ ² · Δm / (N · ρ · A)
It is represented by

Accordingly, since the oscillation frequency changes by ΔF due to the adsorption Δm of the substance, the concentration of the pollutant can be measured by measuring this ΔF.
Incidentally, as a sensitivity, a highly sensitive QCM sensor in which the oscillation frequency changes by 1 Hz just by adsorbing 0.5 ng of substance per 1 cm ^{2 of} electrode has been announced (for example, see Non-Patent Document 1).

Since this QCM sensor is small and has the feature of being able to measure with high sensitivity in real time, it is used for environmental management in manufacturing factories and atmosphere management in various places.
As such a substance sensitive sensor, a sensor using a SAW (surface acoustic wave) element is known in addition to a QCM sensor using a crystal resonator (see, for example, Patent Document 2).
JP-T-2006-524804 JP 2002-048797 A http: // www. pr. fujitsu. com / jp / news / 2006/09/25. htm

  However, substance sensitive sensors such as QCM sensors also detect water (humidity) that is normally contained in the atmosphere, so they are more affected by changes in humidity than changes in the concentration of the material of interest. There are drawbacks.

  In addition, when using a material sensitive sensor such as a current QCM sensor for environmental management, the detection sensitivity is not always sufficient because of the natural adsorption of pollutants in the atmosphere, and there is a voice that desires a higher sensitivity. is there.

  Therefore, an object of the present invention is to measure the concentration of a substance in the atmosphere in real time and with high sensitivity without being affected by humidity.

FIG. 1 is a diagram illustrating the basic configuration of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
In addition, the code | symbol 8 in a figure is an electrode for applying a voltage to the piezoelectric body crystal 2 with the sensor electrode 3. FIG.
In order to solve the above-described problems, the present invention provides a substance sensitive sensor 1 using a piezoelectric crystal 2, a sensor electrode 3 provided on the main surface of the substance sensitive sensor 1, and a sensor in an atmosphere analyzer. At least a counter electrode 4 that is opposed to the electrode 3 with a gap is provided, a DC bias applying mechanism 6 that generates a potential difference between the sensor electrode 3 and the counter electrode 4 is provided, and the sensor electrode 3 and the counter electrode 4 is characterized in that an ultraviolet ray source 5 is provided at a position where ultraviolet rays can be irradiated to the space between the two.

  Thus, by providing the counter electrode 4 opposed to the sensor electrode 3 with a gap and applying a DC bias between the sensor electrode 3 and the counter electrode 4, not only natural adsorption but also the atmosphere Since substances that are naturally ionized therein can be accelerated and adsorbed by an electric field, the detection efficiency is increased.

  In particular, since the ultraviolet ray source 5 is provided at a position where the space between the sensor electrode 3 and the counter electrode 4 can be irradiated with ultraviolet rays, the contaminants in the atmosphere are ionized by photoexcitation. Since the substance is accelerated by the electric field between the sensor electrode 3 and the counter electrode 4 and adsorbed on the sensor electrode 3, the sensitivity is greatly improved.

At this time, the energy of the ultraviolet rays is preferably 12.6 eV or less so as not to photoionize water molecules, and moreover, it may be 12 eV or less so as not to ionize oxygen. desirable.
Note that the difference in frequency change between when the voltage is applied and when the voltage is not applied is reflected in the amount of the substance that is naturally ionized in the atmosphere, so it is used as a charged particle monitor in the atmosphere. be able to.

  Further, the DC bias applying mechanism 6 that generates a potential difference between the sensor electrode 3 and the counter electrode 4 may be provided outside the atmosphere analyzer, but is preferably housed in the main body of the atmosphere analyzer. The overall configuration of the apparatus can be reduced in size.

  The substance sensitive sensor 1 using the piezoelectric crystal 2 in this case is typically a crystal resonator, and the sensor electrode 3 is one of a pair of electrodes for applying a voltage from the oscillation circuit 7. These electrodes may be used.

  Alternatively, the material sensitive sensor 1 using the piezoelectric crystal 2 may use a surface acoustic wave element. In this case, the sensor electrode 3 is provided between the input electrode and the output electrode provided at both ends of the surface acoustic wave element. It is necessary to provide as a DC bias application electrode.

Further, as the ultraviolet ray source 5, a deuterium discharge tube having an MgF ₂ window that is small and emits only ultraviolet rays having an energy of 10.78 eV or less is desirable.
Alternatively, the ultraviolet ray source 5 may be provided outside the atmosphere analyzer, and for example, an Nd: YAG laser capable of generating a ninth harmonic that becomes an ultraviolet ray of 118 nm corresponding to 10.5 eV may be used.

  In addition, a pair of the atmosphere analyzers having the above-described configuration may be provided in the same housing, and one ultraviolet source 5 of the pair of atmosphere analyzers may be removed.

By adopting such a configuration, it is possible to measure the concentration of the contaminant from which the influence of water that is not ionized is removed by taking the difference between the detection results of the two.
In addition, charged particles such as ions are present in the atmosphere without irradiation with ultraviolet light. Therefore, when the measurement target substance is narrowed down by the ionization potential value, the ions existing in the atmosphere become obstacles. However, this effect can be eliminated by taking the difference between the detection results of the two.

  In this case, ultraviolet rays in the vicinity of 10 eV can hardly pass through the atmosphere. However, for the sake of completeness, ultraviolet shielding means for shielding ultraviolet rays from the ultraviolet source 5 may be provided between the pair of atmosphere analyzers. good.

  As an atmosphere analysis method, a sensor electrode 3 provided on the main surface of the substance sensitive sensor 1 using the piezoelectric crystal 2 and a counter electrode 4 opposed to the sensor electrode 3 with a gap are provided. With the direct current bias applied, the space between the sensor electrode 3 and the counter electrode 4 is intermittently irradiated with ultraviolet rays, and is not photoionized by the ultraviolet rays due to the frequency change of the material sensitive sensor 1 when irradiated or not irradiated. It is characterized by detecting adsorption of substances other than substances.

In this way, by intermittently irradiating the space between the sensor electrode 3 and the counter electrode 4 with ultraviolet rays, a substance that is not photoionized by the irradiated ultraviolet rays, typically water, can be obtained with only one atmosphere analyzer. It is possible to measure the concentration of pollutants that eliminates the effects of.
In order to remove the influence of water, it is necessary to irradiate ultraviolet rays having an energy of 12.6 eV or less as ultraviolet rays. Further, in order not to ionize oxygen, it is necessary to irradiate ultraviolet rays having an energy of 12 eV or less. There is.

  According to the present invention, it is possible to measure the concentration of a substance in the atmosphere in real time and with high sensitivity without being affected by humidity with a simple apparatus configuration.

Here, an embodiment of the present invention will be described with reference to FIGS.
See Figure 2
FIG. 2 is a conceptual configuration diagram of the atmosphere analyzer according to the embodiment of the present invention. The crystal resonator 11 is provided with electrodes 13 and 14 on the surface of the crystal 12 and is opposed to one electrode 13 with a gap. The counter electrode 15, the ultraviolet source 16 that irradiates the gap between the electrode 13 and the counter electrode 15, the DC high voltage source 17 that forms an accelerating electric field between the electrode 13 and the counter electrode 15, and the pair of electrodes 13 and 14 An oscillation circuit 18 that applies a voltage, a frequency counter 19 that measures an oscillation frequency from the oscillation circuit, an ultraviolet source 20 with an on / off control circuit that supplies power to the ultraviolet source 16 and controls on / off, and a frequency It consists of a central control device 21 for controlling the counter 19 and the UV source power supply 20 with an on / off control circuit, typically a personal computer (PC).

  In this case, the gap between the electrode 13 and the counter electrode 15 is 3 to 10 mm, and the voltage of the DC high voltage source 17 is such that the electric field between the electrode 13 and the counter electrode 15 is 1000 V / cm or more. Such a voltage is necessary and depends on the gap.

The ultraviolet ray source 16 generates ultraviolet rays having energy that does not photoionize water molecules, and the ionization energy of water molecules is 12.61 eV. Further, the intensity of the ultraviolet light may be 5 × 10 ⁻⁸ W / nm ² or more.
In order to avoid the influence of oxygen, it is necessary to irradiate ultraviolet rays having an energy of 12 eV or less.

As such an ultraviolet ray source 16, there is a deuterium discharge tube having an MgF ₂ window which is small and emits only ultraviolet rays having an energy of 10.78 eV or less.
Alternatively, the ultraviolet ray source 16 may be provided outside the atmosphere analyzer, and for example, an Nd: YAG laser that generates the ninth harmonic that becomes an ultraviolet ray of 118 nm corresponding to 10.5 eV may be used.
In this case, since ultraviolet rays in the vicinity of 10 eV can hardly pass through the atmosphere, it is desirable to place the MgF ₂ window as close as possible to the gap between the electrode 13 and the counter electrode 15.

See Figure 3
FIG. 3 is an explanatory diagram of the ionization potential of a typical molecule. When a deuterium discharge tube having an MgF ₂ window that emits only ultraviolet rays having an energy of 10.78 eV or less is used, in addition to water, , O ₂ , N ₂ , NO _{2 and} other molecules that do not affect the production of the product are not ionized, so that the target pollutant can be detected with high sensitivity.

See Figure 4
FIG. 4 is an example of an atmosphere analysis method using the atmosphere analyzer of the present invention. In the atmosphere to be measured, first, between A and B, for example, for about 10 minutes, the frequency is not irradiated with ultraviolet rays. Measure the change (decrease) in ΔF.

At this time, water reaches the sensor electrode by natural diffusion and adsorbs, and molecules that are naturally ionized in the atmosphere are accelerated by the electric field to reach the sensor electrode and adsorb, and the mass Δm increases. The oscillation frequency decreases by ΔF.
Therefore, the gradient in the figure is a value reflecting the amount of adsorption per unit time.

Next, the frequency change (decrease) ΔF is measured by irradiating ultraviolet rays between B and C, for example, for about 10 minutes.
At this time, although water is not ionized by ultraviolet rays, the various organic substances to be managed shown in FIG. 3 are photoionized, and therefore move along the electric field formed between the electrodes and adsorb to the sensor electrode. .

Compared with the conventional QCM that relies only on natural diffusion, the substances present in the space between the crystal resonator and the electrode are actively collected, so that the sensitivity can be improved.
In addition, since the adhesion of water is constant regardless of UV irradiation, the effect of water adsorption can be avoided by comparing ΔF when UV light is not irradiated and ΔF when UV light is irradiated. Can do.

In addition, the substance to be measured can be narrowed down by the energy of the irradiated ultraviolet rays.
At this time, there are charged particles such as ions in the atmosphere without irradiating with ultraviolet rays. Therefore, when narrowing down the measurement target substance by the ionization potential value, the ions existing in the atmosphere become obstacles. By comparing ΔF when the ultraviolet rays are not irradiated and ΔF when the ultraviolet rays are irradiated, the influence of ions originally present in the atmosphere can be avoided.

Therefore, the gradient of the difference between ΔF when the ultraviolet ray is not irradiated and ΔF when the ultraviolet ray is irradiated in this case is a value reflecting the concentration of the organic substance to be managed.
Thereafter, the atmosphere is analyzed in real time again by intermittently irradiating ultraviolet rays.

  In addition, the frequency change ΔF when no voltage is applied between the sensor electrode and the counter electrode in a state where no ultraviolet light is irradiated is compared with the frequency change ΔF when a voltage is applied between the sensor electrode and the counter electrode. By doing so, it can be used as a charged particle monitor in the atmosphere.

  In addition, a pair of atmosphere analyzers having the above-described configuration may be provided in the same housing, and an ultraviolet ray source may be provided only in one of the pair of atmosphere analyzers. In this case, the ultraviolet rays are irradiated intermittently. However, by always irradiating one atmosphere analyzer with ultraviolet rays, it is possible to always obtain ΔF in a state where ultraviolet rays are not irradiated and ΔF in a state where ultraviolet rays are irradiated in real time.

Based on the above, next, the atmosphere analyzer of Example 1 of the present invention will be described with reference to FIG.
See Figure 5
FIG. 5 is a schematic configuration diagram of the atmosphere analysis device according to the first embodiment of the present invention, which is attached to the base 41 and faces the crystal resonator 31 sandwiched between a pair of electrodes 32 and 33 and one electrode 32. Thus, for example, the counter electrode 34 provided at a distance of 5 mm, the crystal resonator 31, and the aluminum cylindrical casing 42 provided so as to surround the counter electrode 34, the inner wall of the case 42, and the crystal resonator 31 A deuterium discharge tube 35 having an MgF ₂ window 36 provided as close as possible to a gap between the counter electrode 34 and a mesh-like lid member 43 covering the upper portion of the housing 42.
The mesh-shaped lid member 43 allows the atmosphere to be measured to flow in and out freely, and protects the crystal unit 31 and the counter electrode 34 from mechanical damage.

  Further, in the base 41, a DC high voltage power supply 44 for applying a DC bias between the electrode 32 and the counter electrode 34, an oscillation circuit 45 for applying a voltage between the pair of electrodes 32 and 33, and an oscillation frequency are provided. An ultraviolet source power supply 47 with an on / off control circuit for supplying power with a frequency counter 46 to be detected and a deuterium discharge tube 35 and controlling on / off is stored.

  In this case, the crystal unit 31 uses a crystal unit having a crystal diameter of, for example, 8 mm. On the other hand, the size of the counter electrode 34 is arbitrary, and the sensitivity increases as the area increases. Same diameter of 8 mm.

With such an apparatus configuration, it is possible to realize an atmosphere analysis apparatus that is simple, small, and capable of performing an atmosphere analysis with high accuracy in real time.
Even if it is used disposable, it can be used for several months without refreshing the gas adsorption surface of the crystal resonator.

  In addition, when used disposablely, the crystal resonator and counter electrode mounting portion in the base portion and the receiving portion for the DC high voltage power source or the like may be detachably provided separately, whereby the DC high voltage power source Parts that are not affected by gas adsorption such as can be used continuously.

Next, with reference to FIG. 6, the atmosphere analyzer of Example 2 of the present invention will be described.
See FIG.
FIG. 6 is a schematic configuration diagram of an atmosphere analyzer according to the second embodiment of the present invention. The quartz crystal resonator 31 sandwiched between a pair of electrodes 32 and 33 and one electrode 32 are opposed to each other, for example, 5 mm. Two pairs of the counter electrodes 34 provided apart from each other are attached to the base 51 and surrounded by a cylindrical casing 52 made of aluminum. For example, an ultraviolet shielding wall 54 made of quartz is interposed between a pair of atmosphere analysis elements. The upper part of the housing 52 is covered with a mesh-like lid member 53.
In this case, the deuterium discharge tube 35 having the MgF ₂ window 36 is disposed only in the vicinity of the gap between the one crystal unit 31 and the counter electrode 34.

Further, in the base 51, a DC high voltage power supply 44 that applies a DC bias between the electrode 32 and the counter electrode 34, an oscillation circuit 45 that applies a voltage between the pair of electrodes 32 and 33, and an oscillation frequency are provided. An ultraviolet source power supply 47 with an on / off control circuit for supplying power with a frequency counter 46 to be detected and a deuterium discharge tube 35 and controlling on / off is stored.
In this case, the DC high voltage power supply 44 may share one DC high voltage power supply 44, and the frequency counter 46 may also share one frequency counter 46 by switching intermittently. It may be provided one by one.

  By adopting such an apparatus configuration, one atmosphere analyzer is always irradiated with ultraviolet rays without intermittently irradiating ultraviolet rays, so that ΔF in a state where ultraviolet rays are not irradiated and ΔF in a state where ultraviolet rays are irradiated are obtained. Can be acquired at any time.

Next, with reference to FIG. 7, an atmosphere analyzer according to Example 3 of the present invention will be described.
See FIG.
FIG. 7 is a schematic configuration diagram of the atmosphere analyzer according to the third embodiment of the present invention, which is attached to the base 41, provided with an input electrode 62 and an output electrode 63 at both ends, and a sensor between the two. The surface acoustic wave element 60 made of the LiTaO ₃ substrate 61 provided with the electrode, that is, the substance adsorption electrode 64, is opposed to the substance adsorption electrode 64, for example, the counter electrode 65 provided at a distance of 5 mm, the surface acoustic wave element 60, and the opposite. An aluminum cylindrical casing 42 provided so as to surround the electrode 65, and an MgF ₂ window 36 provided on the inner wall of the casing 42 and as close as possible to the gap between the substance adsorption electrode 64 and the counter electrode 65. It consists of a deuterium discharge tube 35 and a mesh-like lid member 43 that covers the top of the housing 42.

  Further, in the base 41, a direct current high voltage power supply 44 for applying a direct current bias between the substance adsorption electrode 64 and the counter electrode 65, an amplifier 48 connected between the input electrode 62 and the output electrode 63, Electric power is supplied through an oscillation circuit 49 that applies an electric signal between the input electrode 62 and the output electrode 63, a frequency counter 46 that detects a frequency change from the output of the amplifier 48, and a deuterium discharge tube 35. An ultraviolet source power supply 47 with an on / off control circuit for controlling on / off is stored.

In this case, when an electric signal of 100 MHz to 1 GHz is applied from the oscillation circuit 49 between the input electrode 62 and the output electrode 63 of the surface acoustic wave element 60, the input electrode 62 and the output are output by the piezoelectric effect of the LiTaO ₃ substrate 61. Surface waves having opposite phases to each other are excited between the electrodes 63 for use.

  In this case, when a substance in the atmosphere is adsorbed on the substance adsorbing electrode 64, the center frequency of the excited surface acoustic wave changes, so that the concentration of the pollutant in the atmosphere is measured by measuring the change in this frequency. It becomes possible.

  The embodiments and examples of the present invention have been described above, but the present invention is not limited to the configurations and conditions described in the embodiments and examples, and various modifications can be made. In each of the above-described embodiments, the substance-sensitive sensor and the counter electrode are described as being housed in one housing on the premise of the disposable type, but the housing is not essential.

  Moreover, in Example 2 described above, an ultraviolet shielding wall is provided between the pair of atmosphere analysis elements, but 118 nm ultraviolet rays are readily absorbed in the atmosphere and are not necessarily essential.

  As an example of use of the present invention, atmosphere management in a manufacturing factory for precision electronic devices such as semiconductor devices is typical, but not limited to precision electronic devices, it is applied to atmosphere management in various manufacturing factories. Furthermore, it is also applied to general environmental management such as sick house management.

It is explanatory drawing of the fundamental structure of this invention. It is a notional block diagram of the atmosphere analyzer of an embodiment of the invention. It is explanatory drawing of the ionization potential of a typical molecule | numerator. It is explanatory drawing of an example of the atmosphere analysis method using the atmosphere analyzer of this invention. It is a schematic block diagram of the atmosphere analyzer of Example 1 of this invention. It is a schematic block diagram of the atmosphere analyzer of Example 2 of this invention. It is a schematic block diagram of the atmosphere analyzer of Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Material sensitive sensor 2 Piezoelectric crystal 3 Sensor electrode 4 Counter electrode 5 Ultraviolet source 6 DC bias application mechanism 7 Oscillation circuit 8 Electrode 11 Crystal oscillator 12 Crystal 13, 14 Electrode 15 Counter electrode 16 Ultraviolet source 17 DC high voltage source 18 Oscillation Circuit 19 Frequency counter 20 Ultraviolet source power supply with on / off control circuit 21 Central controller 31 Crystal oscillator 32, 33 Electrode 34 Counter electrode 35 Deuterium discharge tube 36 MgF ₂ window 41, 51 Base 42, 52 Housing 43, 53 Mesh-shaped lid member 44 DC high-voltage power supply 45 Oscillation circuit 46 Frequency counter 47 UV source power supply with on / off control circuit 48 Amplifier 49 Oscillation circuit 54 UV shielding wall 60 Surface acoustic wave element 61 LiTaO ₃ substrate 62 Input electrode 63 For output Electrode 64 Material adsorption electrode 65 Counter electrode

Claims (7)

At least a substance sensitive sensor using a piezoelectric crystal, a sensor electrode provided on a main surface of the substance sensitive sensor, and a counter electrode opposed to the sensor electrode with a gap, the sensor electrode and the sensor electrode A direct-current bias application mechanism for generating a potential difference with the counter electrode is provided, and an ultraviolet light source is provided at a position where ultraviolet light can be irradiated to the space between the sensor electrode and the counter electrode. Atmosphere analyzer. 2. The substance sensitive sensor using a piezoelectric crystal is a crystal resonator, and the sensor electrode is one of a pair of electrodes for applying a voltage from an oscillation circuit. The atmospheric analysis apparatus described. The atmosphere analyzer according to claim 1 or 2, wherein the ultraviolet light source is a deuterium discharge tube having an MgF ₂ window. An atmosphere analyzer according to claim 1, wherein a pair of the atmosphere analyzers according to claim 1 are provided in the same housing, and one of the ultraviolet sources of the pair of atmosphere analyzers is removed. 5. The atmosphere analyzer according to claim 4, wherein an ultraviolet shielding means for shielding ultraviolet rays from the ultraviolet source is provided between the pair of atmosphere analyzers. In a state in which a DC bias is applied between a sensor electrode provided on a main surface of a substance sensitive sensor using a piezoelectric crystal and a counter electrode opposed to the sensor electrode with a gap, the sensor electrode An atmosphere analysis method characterized by detecting the adsorption of a substance other than water vapor from a frequency change of a substance sensitive sensor when ultraviolet rays are intermittently irradiated to a space between the counter electrode and irradiated and not irradiated. The atmosphere analysis method according to claim 6, wherein the ultraviolet ray is an ultraviolet ray having an energy of 12 eV or less.

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