JP4860972B2 - Vibration sensor, vacuum gauge using vibration sensor, and measurement method - Google Patents

Description

  The present invention relates to a vibration sensor, a vacuum gauge using the vibration sensor, and a measurement method, and more particularly to a vibration sensor that can measure the degree of vacuum and can measure cleaning, dirt, and the like of the vibration sensor itself. is there.

Conventionally, as a device for measuring the degree of vacuum, a vacuum gauge is known which measures the degree of vacuum by measuring a resonance frequency.
As such a vacuum gauge, for example, Patent Document 1 proposes a vacuum gauge having a structure integrally formed by etching a vibrating body and a support body as shown in FIG. 15 and a control circuit. As shown in FIG. 15, the support member 53 and the torsion bar 51 constitute a support portion that supports the vibrating body 52. The vibrating body 52 and the support portion etch a single silicon single crystal. Thus, they are integrally formed. In addition, an excitation electrode 55 and a circuit 58 are provided, and a detection electrode 56 and a circuit 59 and a control circuit 510 are provided. As described above, the torsion bar structure is vibrated, and the degree of vacuum is measured by measuring the frequency at which the vibration amplitude becomes maximum, that is, the resonance frequency.

Furthermore, it is also known that the viscosity of the atmosphere changes depending on the degree of vacuum in the molecular flow region of medium vacuum or higher.
As a vacuum gauge for measuring pressure from the viscosity of such a gas, for example, Patent Document 2 discloses a rotary viscometer as shown in FIG.
In FIG. 16, 61 is a measuring head, 62 is a rotating body of magnetic stainless steel balls, and 63 is a pipe-shaped rotating body chamber that houses the rotating body 62. Reference numerals 64a and 64b are permanent magnets for magnetically suspending the rotating body 62. Reference numerals 68a to 68d denote drive coils for generating a rotating magnetic field, and reference numeral 617 denotes a computer that receives an output from each coil and performs calculation / control. In this vacuum gauge, the rotating body 62 magnetically levitated as described above is rotated about 4000 r.m. by a rotating magnetic field by the drive coils 68a and 68b. p. After accelerating to s, the driving is stopped, and the rate at which the rotational speed is attenuated by the viscous resistance of the gas to be measured is detected. Based on this, the degree of vacuum is obtained by converting the viscosity coefficient of the gas previously input by the computer 617 into a pressure.
Japanese Patent No. 2518814 JP-A-9-292300

However, the above-described conventional vacuum gauge has problems such as a limited use range, complicated wiring, and loss of reliability due to the influence of the surrounding environment. Specifically, it has the following problems (1) to (6).
(1) Since an oscillating electric field and an oscillating magnetic field are generated, it is difficult to use near an electron beam.
In the conventional one, a voltage is applied between the electrodes for the purpose of exciting the vibrating body, and electrostatic attraction is used. For this reason, an oscillating electric field is generated around. However, in the case of a very precise vacuum apparatus using an electron beam, such as an electron microscope or an electron beam drawing apparatus, the trajectory of the electron beam is affected by this oscillating electric field. Therefore, a vacuum gauge must be installed at a location away from the electron beam, and it is difficult to measure the degree of vacuum in the vicinity of the electron beam that is really necessary.
(2) Since it is affected by an oscillating electric field and an oscillating magnetic field, it is difficult to use in the vicinity of plasma.
Conventionally, the capacitance between the electrodes is measured for the purpose of measuring the displacement of the vibrating body, or the voltage of the electrodes placed in an electrostatic field is measured. These measured values are affected by the oscillating electric field and oscillating magnetic field of the environment. For this reason, in sputter devices and ion beam processing devices that generate an oscillating electric field and magnetic field, a vacuum gauge must be installed at a location away from them, and the degree of vacuum in the vicinity of the truly necessary process phenomenon must be measured. It was difficult.
(3) A plurality of electric wirings are required, and the structure becomes complicated.
In the conventional apparatus, an electric signal for exciting the vibrating body and an electric signal wiring for measuring the displacement of the vibrating body must be taken out from a vacuum gauge installed inside the vacuum apparatus. Therefore, it is necessary to take out a large number of wires through the high-vacuum container, resulting in a complicated structure and high cost.
(4) It is difficult to increase measurement accuracy due to the influence of signal transmission noise.
In general, when an electric signal is transmitted, noise is added to the signal. This noise leads to a decrease in the resolution of the vacuum gauge. Therefore, it is difficult to increase measurement accuracy.
(5) Reliability is impaired due to the influence of dirt on the vibrator.
The force exerted on the vibrating body by the molecules of the atmosphere changes depending on the dirt of the vibrating body. In the conventional vacuum gauge, since this point is not taken into consideration, the reliability is impaired.
(6) When the vibrating body affected by the temperature change of the vibrating body is made of a material whose physical property value changes depending on the temperature, such as silicon, the measured value also changes when the environmental temperature changes. In the conventional vacuum gauge, since this point is not taken into consideration, the reliability is impaired.

In view of the above-described problems, the present invention provides a vibration sensor and a vacuum capable of measuring the degree of vacuum, the use range is not limited, the wiring is simplified, the influence of signal transmission noise can be reduced, the measurement can be performed with high reliability, and the like. The purpose is to provide a vessel.
Another object of the present invention is to provide a measurement method that can clean the sensor itself using the vibration sensor or measure the amount of components adsorbed on the sensor. .

In order to solve the above problems, the present invention provides a vibration sensor configured as follows, a vacuum gauge using the vibration sensor, and a measurement method.
That is, the vibration sensor of the present invention is
A single optical fiber, and a vibrating body provided on one end side of the optical fiber so that the direction of vibration amplitude coincides with the optical axis of the optical fiber;
Arranged on the other end of the optical fiber, other optical source for the light guided to the end portion of the one from the end emitted to the vibration member side of the optical fiber, and emission by the light source of the light A light source control device that modulates the intensity of light from the light source in order to vibrate the vibrator with pressure ,
Photodetection means for detecting the displacement of the vibrating body vibrated by the radiation pressure ,
The light detecting means is configured to be able to detect the displacement of the vibrating body by a change in the amount of reflected light that is emitted to the vibrating body side, reflected by the vibrating body, and guided through the optical fiber. It is a feature.
According to the above configuration, since only light is used for measurement, the surrounding electromagnetic field is not affected.
Therefore, if this is applied to an electron microscope, a vibration sensor that does not affect the electron beam can be realized even in the vicinity of the electron beam.
Moreover, since only light is used, it is not affected by the surrounding electromagnetic field. Therefore, the degree of vacuum near the plasma in the plasma apparatus can also be measured.
Further, since only one optical fiber is used, the wiring is simpler than that of the conventional example in which a plurality of electrical wirings need to be connected.
Further, since an optical fiber is used, the influence of signal transmission noise can be reduced.
Further, in the present invention, a light source used to vibrate the vibrating body by radiation pressure after intensity modulation by the light source control device,
The light source used for detecting the reflected light guided from one end of the optical fiber and emitted from the other end by the light detection means is configured by the same light source or different light sources. be able to.
At that time, when the same light source is used, excitation and measurement cannot be performed at the same time.
In the case of using different light sources, the light source used for the excitation and the light source used for the detection are light sources having different wavelengths,
An optical mixer that reflects light of a specific wavelength is disposed in an optical path between the light source and the other end of the optical fiber, and the light source control device modulates the intensity of the light source used for the excitation. on the other hand,
The light source used for the detection is configured to maintain a constant intensity, and light modulated by the light source control device from the light source used for the excitation is guided to the vibrating body via the optical mixer. While vibrating the vibrating body,
Light from the light source used for detection reflected by the vibrating body and emitted from the other end side of the optical fiber is guided to the light detection means via the optical mixer and detected by the light detection means. It can be constituted as follows.
According to this configuration, measurement is possible even during vibration, frequency response analysis with high accuracy is possible, and measurement with higher accuracy can be realized.
In the present invention, in the optical path leading to the other end of the optical fiber, the light from the light source is passed and guided to the vibrating body,
A light distributor that guides the light from the light source reflected by the vibrating body to the light detection unit, and the light that has been intensity-modulated by the light source control device from the light source is transmitted through the light distributor. While guiding the body to vibrate the vibrator,
The light from the light source reflected by the vibrating body may be guided to the light detection means via the light distributor and detected by the light detection means.
With this configuration, most optical components can be configured with fibers, and further miniaturization can be achieved.
The vacuum gauge according to the present invention includes any one of the vibration sensors described above, and is configured to measure the degree of vacuum based on a measurement result of displacement caused by the vibration of the vibrating body. It is said.
Further, the measurement method of the present invention is a measurement method using the vibration sensor described in any of the above,
Before measuring the displacement due to vibration of the vibrating body, the displacement is measured by cleaning the vibrating body by increasing the temperature of the vibrating body by increasing the output of a light source.
According to this, since the so-called self-cleaning that removes dirt on the diaphragm can be performed, a highly reliable vacuum gauge can be realized.
Further, the measurement method of the present invention is a measurement method using the vibration sensor described in any of the above,
Before measuring the displacement due to the vibration of the vibrating body, it has a process of measuring the physical properties of the vibrating body from the displacement of the vibrating body while keeping the output of the light source constant.
According to this, since the spring constant of the vibrating body can be measured in advance, the influence of the change in the physical property value due to the temperature change or the like can be corrected, and a highly reliable vacuum gauge can be realized.
The measuring method of the present invention is a measuring method for measuring the amount of a component adsorbed by a vibrating body using any one of the vibration sensors described above and a further vacuum gauge,
Based on the degree of vacuum measured by the vacuum gauge and the displacement of the vibrating body with respect to the vibration, the amount of the component adsorbed on the vibrating body in the environment where the vibrating body is installed is measured.
According to this, it is possible to measure the amount of dirt components such as oil contained in the environment adsorbed to the vibrating body.

According to the present invention, the range of use is not limited, wiring is simplified, the influence of signal transmission noise can be reduced, highly reliable measurement is possible, and a vibration sensor and vacuum device capable of measuring the degree of vacuum, etc. are realized. can do.
In addition, the present invention can realize a measuring method that can clean the sensor itself using the vibration sensor or measure the amount of a component adsorbed on the sensor.

Next, an embodiment of the present invention will be described.
[Embodiment 1]
In Embodiment 1 of the present invention, a configuration example of a vibration sensor to which the present invention is applied will be described.
FIG. 1 shows a schematic configuration of the vibration sensor in the present embodiment.
In FIG. 1, 1 is a vibrating body, 2 is a diaphragm, 3 is a beam-like elastic support part, and 4 is a housing.
Reference numeral 5 denotes an optical fiber exit end, 6 denotes an optical fiber core, and 7 denotes an optical fiber.
8 is a vacuum chamber, 9 is a connector, 10 is an optical fiber, and 11 is an optical fiber exit end.
Reference numeral 12 denotes a lens, 13 denotes an optical distributor (beam splitter), and 14 denotes a light source.
Reference numeral 15 denotes a driver, 16 denotes a control device, 17 denotes a display device, 18 denotes a photodetector, and 19 denotes an amplifier.
The vibrating body 1 includes a vibration plate 2 , a beam-like elastic support portion 3 that is an elastic support member that supports the vibration plate, and a housing 4. The housing 4 is fixed to the optical fiber emitting end 5. .
An optical fiber 7 having an optical fiber core 6 is fixed to the optical fiber exit end 5. These are installed inside the vacuum chamber 8, and the optical fiber 7 is connected to a connector 9 fixed to the vacuum chamber 8, and is connected to an external optical fiber 10. The other end of the optical fiber 10 (on the other end side of the optical fiber ) is connected to the optical fiber exit end 11, and an optical lens 12 for entering the optical fiber from there is provided, and an optical distributor 13 (beam) Connected to the splitter). On one side of the light branched by the light distributor 13, a light source 14 such as a semiconductor laser is provided and connected to a driver 15. A photodetector 18 is provided on the other side of the beam splitter and is connected to an amplifier 19. The amplifier 19 and the driver 15 are connected to the control device 16, and the control device 16 is connected to the display device 17.

In the above configuration, the emitted light emitted from the light source 14 is reflected by the light distributor 13, condensed at one point by the action of the lens 12, and guided into the optical fiber 10 from the optical fiber emitting end placed there. . This light is guided to the optical fiber 7 in the vacuum chamber through the connector 9 and is emitted from the end face of the optical fiber core 6 fixed to the optical fiber emitting end 5.
The output Shako is per the diaphragm 2 provided such that the direction of the vibration amplitude at one end side of the optical fiber is coincident with the optical axis of the optical fiber, since the reflector, the diaphragm of the light radiation pressure It receives a force according to the intensity of light. Accordingly, a force corresponding to the intensity change of the light source 14 acts on the diaphragm 2.

In general, when light travels in the optical surface due to refraction or reflection, the momentum of the light changes. A force according to this change in momentum acts on the optical surface. This principle is known as light radiation pressure. Since the light emitted from the optical fiber is reflected by the vibrating body, it receives the radiation pressure of this light and gives a thrust to the vibrating body. Therefore, the vibrator can be vibrated by intensity- modulating the light source of the light emitted from the optical fiber.
There is another principle that light can vibrate a vibrating body. That is the effect of heat. Light hits the vibrating body, and part of it is absorbed and changed to heat. Then, the temperature of one surface of the vibrating body rises, and the vibrating body deforms according to the linear thermal expansion coefficient. This deformation is restored when the light is extinguished and the heat diffuses again and the temperature drops. Therefore, the vibrating body can be vibrated according to the intensity of light also by the action of this heat. However, since it takes time for heat to diffuse in order to decrease the temperature, the response speed is inferior to the case where the radiation pressure of light is used.

Further, a part of the light reflected by the diaphragm again enters the optical fiber core 6, but only a small part of the light reaches the optical fiber core 6 again and can enter.
In other words, light that is emitted from the optical fiber, reflected by the vibrating body, and incident on the optical fiber again diffuses, so that only part of the light enters the optical fiber. The amount of light depends on the degree of light diffusion. The degree of diffusion increases with distance. Accordingly, the amount of light incident on the optical fiber changes depending on the size of the gap between the vibrating body and the optical fiber. If this light quantity change is caught by the light detection means, the displacement of the vibrating body can be measured.

The above situation will be described with reference to FIG.
FIG. 2 is a diagram for explaining the principle of measuring the displacement of the diaphragm in the present embodiment. In FIG. 2, 6 is an optical fiber core, and 2 is a diaphragm. These correspond to the core 6 and the diaphragm 2 of the optical fiber described in FIG.
The core 6 of the optical fiber has a small cross-sectional area with a diameter of 5 μm, for example. The light emitted from 6 reaches the diaphragm 2 while spreading and is reflected there. Even after reflection, it returns and spreads, but when it reaches the core 6 again, only a part of it can enter the core because the cross-sectional area of light is large.
Here, when the light spreading angle is α and the distance between the core 6 and the diaphragm 2 is d, the cross-sectional area is approximately proportional to αd ² . Therefore, the amount of light incident on the core changes according to the change of the displacement d of the diaphragm 2.
The light that has entered the core is transmitted to the optical fiber 7 and the connector 9 optical fiber 10, exits from the optical fiber exit end 11, is collimated by the lens 12, passes through the optical distributor 13, and is converted into an electrical signal by the photodetector 18. After being converted, the signal is formed by the amplifier 19 and connected to the control device 16.

Next, a control operation at the time of measurement by the vibration sensor in the present embodiment will be described.
FIG. 3 shows a flowchart for explaining a control operation in measurement by the vibration sensor in the present embodiment.
In FIG. 3, first, the light source is driven to vibrate the diaphragm (100).
After vibration, it is necessary to measure the displacement of the diaphragm. Since the displacement is measured by the amount of light incident on the photodetector from the optical fiber, it is affected by the intensity of the light source. In other words, it cannot be measured when vibrating. Therefore, time to vibrate the vibrating plate, separately and time for measuring the displacement of the vibration plate performs a control light Minamotosei.
FIG. 4 and FIG. 5 show examples of such control patterns. The horizontal axis represents time, and the vertical axis represents the force applied to the diaphragm and the displacement of the diaphragm.
FIG. 4 shows step-like excitation. When the diaphragm receives this force, the diaphragm starts to vibrate at the natural frequency of the diaphragm as shown in FIG. 4, but gradually attenuates. FIG. 5 shows a case where vibration is applied with a sine wave. As before, the displacement gradually attenuates when the excitation is stopped.
As described above, when the preset excitation time has passed, the displacement and vibration waveform of the diaphragm are measured (101).
Next, as in the prior art, the degree of vacuum is calculated from the vibration waveform based on the measurement result (102).
The obtained degree of vacuum, that is, the pressure inside the chamber 8 is displayed (103).

In this embodiment, only light is used. It is known that light does not affect the surrounding electromagnetic field unless it is very strong light.
Therefore, by applying the present embodiment to an electron microscope, it is possible to measure the degree of vacuum or the like that does not affect the electron beam even in the vicinity of the electron beam.
Moreover, since only light is used, it is not affected by the surrounding electromagnetic field. Therefore, the pressure near the plasma in the plasma apparatus can also be measured.
Furthermore, since only one optical fiber is used, it is not necessary to connect a plurality of electric wires as in the conventional example, and the wiring becomes simple.
In this embodiment, since an optical fiber is used, the influence of signal transmission noise can be reduced.

In the vibrating body 1 shown in FIG. 1 of the present embodiment, the elastic support portion 3 that supports the diaphragm 2 is configured by a beam-shaped elastic member, but is not limited to such a configuration. .
In addition to this, for example, as shown in FIG. 12, the elastic support portion may be constituted by a torsion spring, a so-called torsion bar.
In this way, by configuring the elastic support portion with a torsion spring, the deformation state of the elastic body can be twisted instead of bent.
In bending deformation, the bending moment increases at the base portion of the elastic body, and the stress at that portion tends to increase. That is, stress concentration occurs.
In contrast, torsional deformation is less likely to cause stress concentration. Increased stress can lead to material failure.
Therefore, by configuring the elastic support portion with a torsion spring as described above and utilizing its torsional deformation, the degree of freedom in material selection can be expanded, and the life of the elastic body can be extended. Sensor design constraints can be relaxed.

In addition to this, for example, as shown in FIG. 13, the elastic support portion may be constituted by a coil spring.
In this way, by configuring the elastic support portion with a coil spring, the length of the elastic body can be increased, so that the design range of the spring constant can be expanded. Specifically, the spring constant can be lowered.

[Embodiment 2]
In Embodiment 2 of the present invention, a configuration example in which a light source for excitation and a measurement light source having different wavelengths are used will be described.
FIG. 6 shows a configuration in which a vibration light source and a measurement light source having different wavelengths are used in the vibration sensor of the present embodiment.
In the first embodiment, the vibration and the displacement measurement of the diaphragm are performed with the same light source. However, the present embodiment is different from the first embodiment only in that separate light sources are used for them. Description of overlapping parts is omitted as appropriate.
In FIG. 6, 14 constitutes a second light source, and 15 is its driver.
Reference numeral 20 denotes an optical mixer (dichroic mirror), 21 denotes a first light source, and 22 denotes a driver.
The vibrating body 1 includes a diaphragm 2, an elastic support portion 3 that supports the diaphragm 2, and a housing 4, and the housing is fixed to the optical fiber emitting end 5. An optical fiber 7 having an optical fiber core 6 is fixed to the optical fiber exit end 5. These are installed inside the vacuum chamber 8, and the optical fiber 7 is connected to a connector 9 fixed to the vacuum chamber and connected to an external optical fiber 10.
The other end of the optical fiber 10 is connected to the optical fiber exit end 11, in the optical path between the optical fiber emission end 11 and the light source, an optical lens 12 is provided to be incident on the optical fiber, especially Teinami It is connected to an optical mixer (dichroic mirror) 20 that reflects only long light. On one side branched by the optical mixer (dichroic mirror) 20, a first light source 21 that emits light having a wavelength reflected by the optical mixer 20 is provided, and the first light source 21 is connected to the driver 22.
On the one side that has passed through the optical mixer 20, a light distributor 13 (beam splitter) is provided. On the other hand, on the other side, the second light source 14 that emits light having a wavelength that passes through the optical mixer 20 is provided. A second light source 14 is connected to the driver 15. A photodetector 18 is provided on the other side of the beam splitter, connected to the amplifier 19, the amplifier 19 and the driver 15 are connected to the control device 16, and the control device 16 is connected to the display device 17.

In the above configuration, the light emitted from the first light source 21 is reflected by the optical mixer 20, condensed at one point by the action of the lens 12, and enters the optical fiber 10 from the optical fiber emitting end placed there. Led. This light is guided to the optical fiber 7 in the vacuum chamber through the connector 9 and is emitted from the end face of the optical fiber core 6 fixed to the optical fiber emitting end 5.
Since the emitted light hits the diaphragm 2 and is reflected, the diaphragm receives a force corresponding to the intensity of the light by the action of the radiation pressure of the light. Therefore, a force corresponding to the intensity change of the light source 14 acts on the diaphragm 2.
Further, the light reflected by the diaphragm returns in the reverse direction of the original optical path, but is reflected by the optical mixer 20 and thus does not affect the photodetector described later.
The light emitted from the second light source 14 is reflected by the light distributor 13, passes through the light mixer 20, and is condensed at one point by the action of the lens 12. Then, the core of the optical fiber guided from the optical fiber exit end placed therein to the optical fiber 10, guided to the optical fiber 7 in the vacuum chamber via the connector 9, and fixed to the optical fiber exit end 5. 6 exits from the end face.
The emitted light hits the diaphragm 2, and a part of the reflected light is incident on the optical fiber core 6 again, but only a small part of the light reaches the optical fiber core 6 again and can enter.

As described in the first embodiment, the amount of light that enters the core changes according to the displacement of the diaphragm. Light entering the core is transmitted to the optical fiber 7, the connector 9, and the optical fiber 10. Then, the light exits from the optical fiber exit end 11, is collimated by the lens 12, passes through the optical mixer 20, passes through the optical distributor 13, is converted into an electrical signal by the photodetector 18, and is shaped by the amplifier 19. , Connected to the control device 16.
As described above, the first light source 21 is used for exciting the diaphragm, and the second light source 14 is used for measuring the displacement of the diaphragm. As described above, the light from the first light source does not enter the photodetector 18 due to the action of the optical mixer 20. Therefore, vibration and measurement can be performed simultaneously.

Next, a control operation at the time of measurement by the vibration sensor in the present embodiment will be described.
FIG. 7 shows a flowchart for explaining a control operation at the time of measurement by the vibration sensor in the present embodiment.
In FIG. 7, the second light source is driven at a constant light intensity for use in measuring displacement. While sweeping (scanning) the frequency for driving the first light source in the vicinity of the resonance frequency of the vibrating body, the vibration amplitude and phase of the vibrating body at that time are measured. That is, the frequency response analysis of the vibrating body is performed (200).
In the next step, as in the prior art, the degree of vacuum is calculated from this vibration waveform (201).
The obtained degree of vacuum, that is, the pressure inside the chamber 8 is displayed (202).

According to the present embodiment, the following points are advantageous compared to the first embodiment.
In the first embodiment, the vibration of the diaphragm and the displacement measurement are performed with the same light source. Therefore, when measuring the displacement, it is necessary to make the light of a certain intensity from the light source. That is, since vibration and measurement could not be performed at the same time, the behavior of the vibrating body was measured by measuring the residual vibration after the excitation force was stopped.
On the other hand, in this embodiment, measurement can be performed even during excitation by using a light source for excitation and a light source for measurement having a different wavelength. Therefore, a frequency analysis method for measuring the amplitude and phase of the vibrating body while changing the frequency of the sinusoidal excitation signal can be used. In this method, since the input signal intensity for each frequency can be made much stronger than in the case of measuring the residual vibration, a high SN ratio (signal / noise ratio) can be expected. Therefore, it is possible to realize a vacuum gauge with higher accuracy.

[Embodiment 3]
In Embodiment 3 of the present invention, a configuration example having a sequence for increasing the output of the light source and increasing the temperature of the vibrating body before measuring the degree of vacuum will be described. Since the vibration sensor here is the same as that in the first or second embodiment, the description of the same parts as those in the first or second embodiment is omitted.
In this embodiment, first, before measuring the degree of vacuum, the output of the light source for exciting the vibrating body is increased for a certain period of time. Then, the diaphragm of the vibrating body is exposed to strong light for a certain period of time, but part of it is absorbed and changed to heat. This heat raises the temperature of the vibrator. For example, when the temperature rises to 300 ° C., the organic substance having a small molecular weight evaporates and the surface of the vibrator is cleaned.

In general, there are various molecules that cause dirt in the atmosphere. For example, organic substances such as oil. When this molecule touches the diaphragm, a part is adsorbed and the surface of the diaphragm becomes dirty.
When the molecules constituting the atmosphere gas are reflected by the diaphragm, the force exerted by the molecules in the atmosphere on the vibrating body varies depending on the contamination of the vibrating body. Therefore, the measured value of the degree of vacuum also changes depending on the contamination of the diaphragm.
If the dirt gets worse over time, the measured value will drift with it, and the reliability of the vacuum gauge will be significantly reduced.
This contamination can be solved by increasing the temperature of the vibrating body as described above. This is because dirty molecules evaporate with increasing temperature.
In order to increase the temperature, it is only necessary to apply strong light to the diaphragm for a certain period of time. A part is absorbed by the diaphragm, and the temperature of the diaphragm can be raised.
As described above, according to the present embodiment, such dirt can be cleaned by the self-cleaning function for keeping the sensor clean by the sensor itself. Thereby, measurement reliability can be improved by always keeping the surface of the vibrating body clean.

[Embodiment 4]
In Embodiment 4 of the present invention, a configuration example of the following measuring method will be described as a measuring method having a process of measuring the physical properties of the vibrating body from the displacement of the vibrating body.
That is, a configuration example having a sequence for calculating the spring constant of the vibrating body from the displacement of the vibrating body at that time while keeping the output of the light source constant before measuring the degree of vacuum will be described. Since the vibration sensor of the second embodiment is used here, the description of the parts overlapping with those of the second embodiment is omitted.

The vibration type vacuum gauge is based on the measurement principle that the behavior of the vibrating body, that is, the resonance frequency and the attenuation factor change depending on the degree of vacuum. If the spring constant changes due to the influence of temperature or the like, the resonance frequency shifts. Since it is not possible to distinguish whether the resonance frequency shift is due to a change in the spring constant or a change in the degree of vacuum, the measurement value of the vacuum gauge is ultimately affected.
Therefore, it is possible to predict the resonance frequency by measuring in advance the spring constant that changes due to the influence of temperature, etc. before the measurement. The influence of can be corrected.
In this embodiment, the spring constant can be measured by applying a constant output of the light source, that is, applying a constant force to the vibrating body, and measuring the displacement of the vibrating body at that time. As a result, it is possible to configure a vacuum gauge that is not affected by the change in the physical property value of the vibrator that changes due to the influence of the environmental temperature or the like.
Further, since the spring constant changes with temperature, the spring constant measured here can be said to be a function of the temperature of the environment. Therefore, according to the present embodiment, it is possible to simultaneously measure the environmental temperature and the degree of vacuum, and it is possible to realize a vibration sensor having a function that has not existed in the past.

FIG. 8 is a flowchart for explaining a control operation at the time of measurement by the vibration sensor in the present embodiment.
In FIG. 8, since the second light source is used for measuring displacement, it is driven with a constant light intensity, and first the physical properties of the vibrating body are measured (300).
This will be described with reference to the time chart of FIG.
The first light source is turned on, the diaphragm is pushed with a constant light intensity and a constant force f, and the displacement h of the vibrating body at this time is measured by the light detection means.
As shown in the figure, the measurement is performed by turning on / off the force, and the displacement of the vibrating body vibrates slightly, but waits for a time when the vibration is sufficiently suppressed.
The spring constant of the vibrating body can be calculated by h / f. If the mass of the vibrating body is m, the natural vibration frequency of this vibrating body can be calculated by the following equation.

Next, the vibration amplitude and phase of the vibrating body at that time are measured while sweeping (scanning) the frequency at which the first light source is driven around the resonance frequency of the vibrating body of the above formula. That is, the frequency response analysis of the vibrating body is performed (301).
The resonance frequency of the above vibrating body is subtracted from the horizontal axis of this frequency response. As a result, even if the spring constant changes due to temperature or the like and the frequency of the vibrating body changes, the influence can be canceled.
In the next step, as in the prior art, the degree of vacuum is calculated from this vibration waveform (302).
The obtained degree of vacuum, that is, the pressure inside the chamber 8 is displayed (303).
According to this embodiment, even if the spring constant of the vibrating body changes due to environmental changes, the influence can be canceled, so that highly reliable vacuum measurement can be performed.

[Embodiment 5]
In Embodiment 5 of the present invention, a configuration example in which another vacuum gauge is installed in the vacuum chamber will be described.
When an organic substance such as oil is present in the environmental atmosphere, it is adsorbed to the vibration body, and the behavior of the vibration body, that is, the resonance frequency and the attenuation factor change according to the amount of adsorption. The same effect can be achieved by changing the degree of vacuum, but by measuring the degree of vacuum with a vacuum gauge provided separately, it is possible to correct the change in degree of vacuum and know the amount of components adsorbed on the vibrator. it can.

FIG. 10 shows the configuration of the vibration sensor of this embodiment. A description of the same parts as those in the first embodiment will be omitted.
In FIG. 10, reference numeral 23 denotes another vacuum gauge installed in the vacuum chamber. The vacuum gauge may be a vacuum gauge based on the vibration sensor of the first embodiment or the like, or may be another system such as a Pirani vacuum gauge or an ionization vacuum gauge.
This vacuum gauge is connected to the control device 16.

FIG. 11 shows a flowchart for explaining a control operation at the time of measurement by the vibration sensor in the present embodiment.
In FIG. 11, first, intense light is applied to the vibrating body for a certain period of time, and the temperature of the vibrating body is raised to evaporate the dirt component (400). This is the same as the third embodiment described above.
Next, a vacuum degree is measured with the vacuum gauge 23 (401).
Next, the vibration behavior of the vibrating body is measured (402).
The vibrating body has a natural frequency expressed by the following equation.

Here, k is a spring constant, which mainly represents the spring constant of the diaphragm 2, and m is a mass of the vibrating body, particularly a mass of the diaphragm that is moved by vibration.
This equation means that the natural frequency varies with the mass change of the diaphragm.
Therefore, if the natural frequency is measured, the mass of the component adsorbed on the diaphragm can be measured.
However, the natural frequency and the attenuation rate are actually changed depending on the degree of vacuum of the environment as described in the prior art.
Therefore, the diaphragm is estimated by predicting the change of the natural frequency and the attenuation rate based on the degree of vacuum of the vacuum gauge 23 provided separately, and taking the difference between the predicted value and the actual measured value. The mass of the component adsorbed on the surface, that is, m is measured (403).
Then, the mass of the component adsorbed on the obtained diaphragm is displayed (404).

As a component adsorbed on the diaphragm, a vacuum component such as an oil component can be considered. Measuring and monitoring the contamination of such a vacuum environment is important for exerting the performance of vacuum equipment such as sputtering and electron microscopes.
In this embodiment, the measurement of the degree of vacuum is mainly used. However, it is possible to measure the contamination of the vacuum environment by using the same action and the same configuration and measuring the amount of adsorption to the diaphragm.

[Embodiment 6]
In the sixth embodiment of the present invention, a configuration example in which the optical system of the first embodiment is changed will be described.
FIG. 14 shows a configuration of the vibration sensor of the present embodiment.
In the present embodiment, the only difference is that the optical system is changed from that of the first embodiment.
Reference numeral 1 denotes a vibrating body. The vibrating body includes a diaphragm 2, an elastic support portion 3 that supports the diaphragm 2, and a housing 4. The housing is fixed to the optical fiber emitting end 5. An optical fiber 7 having an optical fiber core 6 is fixed to the optical fiber output end 5. These are installed inside the vacuum chamber 8, and the optical fiber 7 is connected to a connector 9 fixed to the vacuum chamber and connected to an external optical fiber 10.
The other end of the optical fiber 10 is connected to an optical distributor 24, in this case an optical fiber coupler. This optical fiber coupler has the function of a half mirror, and can mix two lights into one, or conversely branch one light into two.
One end of the optical distributor 24 is provided with an optical fiber emitting end 25 and an optical lens 26 for entering the optical fiber, and a light source 14 such as a semiconductor laser is provided. The light source 14 is connected to the driver 15.
At the other end of the optical distributor 24, an optical fiber output end 11 and a detector 18 are provided and connected to an amplifier 19. The amplifier 19 and the driver 15 are connected to the control device 16, and the control device 16 is connected to the display device 17.

In the above configuration, the light emitted from the light source 14 is condensed at one point by the action of the lens 26 and guided to the optical fiber from the optical fiber emitting end 25 placed there. This light passes through the optical distributor 24, is guided to the optical fiber 7 in the vacuum chamber through the connector 9, and is emitted from the end face of the optical fiber core 6 fixed to the optical fiber emitting end 5. Since the emitted light hits the diaphragm 2 and is reflected, the diaphragm receives a force corresponding to the intensity of the light by the action of the radiation pressure of the light.
A part of the light reflected by the diaphragm is incident again on the core 6 of the optical fiber. The light incident on the core is transmitted to the optical fiber 7, the connector 9, and the optical fiber 10, passes through the optical distributor 22, exits from the optical fiber exit end 11, and is converted into an electrical signal by the photodetector 18. .
The subsequent operation is the same as that of the first embodiment described with reference to FIG.
According to the present embodiment, most of the optical components can be made of fibers, so that further miniaturization can be achieved.
Further, if a fiber laser is used as the light source, the lens 26 is not necessary and the size can be further reduced. The fiber laser is a laser having a core portion of the fiber as a light emitting layer, and is widely known.

It is a figure which shows the structure of the vibration sensor in Embodiment 1 of this invention. It is a figure explaining the principle which measures the displacement of the diaphragm in Embodiment 1 of this invention. 3 is a flowchart for explaining a control operation in measurement by the vibration sensor according to the first embodiment of the present invention. In Embodiment 1 of this invention, it is a figure which shows the example of a control pattern which vibrates in a step shape at the time of dividing the time which vibrates a diaphragm, and the time which measures the displacement of a diaphragm into a light source. . In Embodiment 1 of this invention, it is a figure which shows the example of a control pattern which vibrated with the sine wave at the time of dividing the time which vibrates a diaphragm, and the time which measures the displacement of a diaphragm, and performing light source control. . It is a figure which shows the structure of the vibration sensor in Embodiment 2 of this invention. 7 is a flowchart for explaining a control operation in measurement by a vibration sensor in Embodiment 2 of the present invention. 6 is a flowchart for explaining a control operation in measurement by a vibration sensor according to Embodiment 4 of the present invention. It is a figure which shows the time chart at the time of measuring the physical property of the vibrating body in Embodiment 4 of this invention. It is a figure which shows the structure of the vibration sensor in Embodiment 5 of this invention. 7 is a flowchart for explaining a control operation in measurement by a vibration sensor according to Embodiment 5 of the present invention. It is a figure explaining the example which comprised the elastic support part in Embodiment 1 of this invention with the torsion spring. It is a figure explaining the example which comprised the elastic support part in Embodiment 1 of this invention with the coil spring. It is a figure which shows the structural example which changed the optical system in Embodiment 6 of this invention. It is a figure explaining the structure of the vacuum gauge of patent document 1 which is a prior art example. It is a figure explaining the structure of the vacuum gauge disclosed by patent document 2 which is a prior art example.

Explanation of symbols

1: Vibrator 2: Diaphragm 3: Elastic support part 4: Housing 5: Optical fiber exit end 6: Optical fiber core 7: Optical fiber 8: Vacuum chamber 9: Connector 10: Optical fiber 11: Optical fiber exit end 12 : Lens 13: Optical distributor (beam splitter)
14: Light source 15: Driver 16: Control device 17: Display device 18: Photo detector 19: Amplifier

Claims (10)

A vibration sensor,
A single optical fiber;
A vibrating body provided on one end side of the optical fiber so that the direction of vibration amplitude coincides with the optical axis of the optical fiber;
Arranged on the other end side of the optical fiber,
Light source for the other light guided to the end portion of the one from the end emitted to the vibration member side of the optical fiber, and by radiation pressure by light of the light source from the light source to vibrate the vibrating body A light source control device for modulating the intensity of light;
Photodetection means for detecting the displacement of the vibrating body vibrated by the radiation pressure ,
The light detecting means is configured to be able to detect the displacement of the vibrating body by a change in the amount of reflected light that is emitted to the vibrating body side, reflected by the vibrating body, and guided through the optical fiber. A characteristic vibration sensor. A light source used to vibrate the vibrator by radiation pressure after intensity modulation by the light source control device;
The reflected light emitted from one derived from the end portion the other end of the optical fiber, and a light source used for detection by said light detecting means,
The vibration sensor according to claim 1, wherein the light sources are the same. A light source used to vibrate the vibrator by radiation pressure after intensity modulation by the light source control device;
The reflected light emitted from one derived from the end portion the other end of the optical fiber, and a light source used for detection by said light detecting means,
The vibration sensor according to claim 1, wherein the vibration sensors are different light sources. The light source used for the excitation and the light source used for the detection are light sources having different wavelengths, and light that reflects light of a specific wavelength in an optical path between the light source and the other end side of the optical fiber. Having a mixer,
The light source control device is configured to modulate the intensity of the light source used for the excitation while keeping the intensity of the light source used for the detection constant,
The light that has been intensity-modulated by the light source control device from the light source used for the excitation is guided to the vibrating body via the optical mixer to vibrate the vibrating body, and is reflected by the vibrating body and the light. The light from the light source used for the detection emitted from the other end side of the fiber is guided to the light detection means via the optical mixer and detected by the light detection means. The vibration sensor described in 1. The light from the light source that is reflected by the vibrating body is guided to the vibrating body while passing the light from the light source in the optical path to the other end of the optical fiber. Having a light distributor leading to
Light from the light source that has been intensity-modulated by the light source control device is guided to the vibrating body via the light distributor to vibrate the vibrating body, and light from the light source reflected by the vibrating body The vibration sensor according to claim 1, wherein the vibration sensor is guided to the light detection means via the light distributor and detected by the light detection means.   The said vibrating body is provided with the diaphragm supported by the elastic support member, and this elastic support member is comprised by the torsion spring or the coil spring, The any one of Claims 1-5 characterized by the above-mentioned. Vibration sensor.   A vacuum gauge comprising the vibration sensor according to any one of claims 1 to 6 and configured to measure a degree of vacuum based on a measurement result of displacement caused by vibration of the vibrating body. .   It is a measuring method using the vibration sensor of any one of Claims 1-6, Comprising: Before measuring the displacement by the vibration of the said vibrating body, the output of a light source is enlarged and the temperature of the said vibrating body is increased. Measuring the displacement by cleaning the vibrating body by raising the height.   It is a measuring method using the vibration sensor of any one of Claims 1-6, Comprising: Before measuring the displacement by the vibration of the said vibrating body, keeping the output of a light source constant, the vibration in that case A measuring method comprising a step of measuring physical properties of the vibrating body from a displacement of the body. A measurement method for measuring the amount of a component adsorbed by a vibrating body using the vibration sensor according to any one of claims 1 to 6 and another vacuum gauge,
A measuring method, comprising: measuring an amount of a component adsorbed on a vibrating body in an environment where the vibrating body is installed based on a degree of vacuum measured by the vacuum gauge and a displacement of the vibrating body with respect to vibration.

Images