JPS6098327A - Acoustic vibration type vacuum gauge - Google Patents

Abstract

PURPOSE:To quicken response speed and to measure precisely a vacuum degree by detecting an acoustic impedance of a gas seen from a mechanical vibration part varying with the vacuum degree. CONSTITUTION:AC signal generated from an oscillator 21 is impressed to a transmitting transducer 11 existing in a space 1. Acoustic wave generated from the transducer 11 is attained to a receiving transducer 12. An output signal of the transducer 12 is amplified and detected by a synchronous amplifying detector 31 by an output of the oscillator 21 given through a phase controller 23. The detected output is given to an indicating meter 32, and the vacuum degree of the space 1 is read.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention utilizes acoustic vibration phenomena to
The present invention relates to a vacuum gauge that measures a degree of vacuum of approximately 0 Torr with high precision and high efficiency.

<Prior art> Schulz gauges and Villany gauges have traditionally been used to measure relatively low vacuums from 1□ q''orr to 10 Torr.The Schulz gauge is used to measure the vacuum level in the space where the degree of vacuum is to be measured, as shown in Figure 1. In 1, an anode 3 and a collector electrode 4 are arranged near the filament 2, and electrons e- emitted from the filament 2 are attracted and accelerated by the potential vI of the anode 3, and the moving electrons e- are transferred to molecules existing in the space 1. Ions generated upon collision are collected by a collector 4 to which -Vc is applied, and are read by an ammeter 6.

In order to be able to operate even in low nitrogen conditions, there are eight short lines between the filament 2, anode 3, and collector 4. The problem with this vacuum gauge is that it has a short life because it has a filament 2, and when it is used in plasma, it is affected by plasma ions, which makes it difficult to use it inside a sputter equipment. .

As shown in Fig. 2, the Villany gauge is connected to the heater 5 with a resistance of 111χ1 at +Ij'+Koshiba 1, and l to -.
i>,? The heater 5 is kept in a heat generating state by flowing heat. The gas molecules in the space 1 that collide with the heater 5 remove heat from the heater 5, causing the temperature T of the heater 5 to decrease. bring. Heater 5'
By reading the m pressure V with the 111 pressure gauge 7, subtracting R from the equation V = RI, and knowing the temperature T from this, you can know the number of molecules in the space 1, and therefore, you can measure the degree of vacuum. .

The problems with this vacuum gauge are that it is easily affected by the ambient temperature, making precise measurement difficult, and because it uses temperature changes, the response speed is not very fast.

Since the heater 5 generates heat, it is easily attacked by active gas in the plasma etching apparatus.

On the other hand, in the field of pressure gauges, for example, there are pressure gauges that utilize the fact that the acoustic transmission characteristics of gas change with pressure changes.
Publication No. 4-12834, Japanese Patent Publication No. 56-6500,
It is known from Japanese Patent Publication No. 56-41928. This method involves arranging one or two electro-acoustic or acousto-electric transducers as a unit in a small volume gas chamber, and adjusting the input and output of the transducers according to changes in the stiffness of the gas in the gas chamber due to atmospheric pressure. The first use is that the phase between signals changes. In practice, a method is used in which an electrical self-oscillation circuit including a self-exciting device is used to detect changes in atmospheric pressure as changes in oscillation frequency.

According to this method, the above-mentioned drawbacks of conventional vacuum gauges are largely solved. However, this method also has the disadvantages of requiring a small volume chamber connected to the outside world through a narrow and preciously large acoustic resistance, and of having a complicated air circuit.

<Installation of the invention> This invention is aimed at 10 to 1 O-4 Torr.
By actively utilizing the fact that the acoustic transmission characteristics of gas significantly change in the vacuum range of The present invention provides a precise υ-type vacuum gauge that is free from the effects of 1st pressure and has a fast response speed.

In other words, the key point of this invention is that the acoustic impedance of the gas (depending on the degree of gas, etc.) as seen from the mechanical vibration part of the transducer changes as the degree of vacuum changes, and the transducer changes. The point is that it takes advantage of the fact that the force of the sound waves emitted from the deuser into the gas changes.

<Example> The present invention will be described in detail below with reference to Examples.

FIG. 3 shows a first embodiment of the invention, in which an alternating current of frequency f from an oscillator 21 is applied to a transmitting transducer 11 located in space I. In FIG. .

As a result, the transmitting transducer 11 generates a sound wave, which propagates through the low-density space 1 with a reduced amount of noise and reaches the receiving transducer 12. The reception transducer 12 generates an AC output signal with a magnitude proportional to this, and the output signal is sent to the synchronous amplification detector 31 by the output of the oscillator 21 given through the phase adjuster 23.
The signal is amplified and detected. This detection output is read by the indicator 32. In other words, the acoustic impedance of the gas viewed from the mechanical vibration parts of the transmitting transducer 11 and the receiving transducer 12 changes as the vacuum degree of the space 1 changes, and from the transmitting transducer 11 to the space 1
The effort of the sound waves emitted to the receiving transducer 12 changes, the output of the sound waves received by the receiving transducer 12 also changes, and the propagation attenuation in the space 1 also changes depending on the degree of vacuum.
2 allows you to read the degree of vacuum in space 1.

The smaller the number of molecules in the space 1, the more difficult it is for sound waves to propagate, so the output of the reception transducer 12 decreases as the degree of vacuum increases. Therefore, the receiving transducer 12
The degree of vacuum in the space 1 can be measured by reading the magnitude of the output.

FIG. 4 shows an embodiment in which the above embodiment is operated by a pulse signal. A gate signal having a frequency fl from the oscillator 21 is pulse-modulated with a pulse having a frequency f2 from the oscillator 22 using a gate circuit 25, and the modulated output is applied to the transducer 11. The sound waves generated thereby propagate through the space 1 while being attenuated as the number of gas molecules decreases, and are reflected by the reflection plate 13 and reach the transducer 11, where they are converted into a passive signal and amplified and detected. This becomes the input to the device 31. The amplification/detection panel 31 amplifies and detects the output signal r of the transducer 11 in synchronization with the reference signal f2 whose phase is adjusted by a phase adjuster 23, and this output is read by an indicator 32. Transducer 11
, a connection point 14 between the gate circuit 25 and the synchronous amplification detector 31
The 0 signal includes both the input and output signals of the transducer 11 and has a waveform as shown in FIG. 5A. The input (transmission) signal 16 and the output (reception) signal 17 occur alternately, and the JNM of the valley train is T=]/l'2. On the other hand, the phase of the synchronizing signal of the width detector 31 is adjusted by using the phase adjuster 23, and the phase of the synchronizing signal of the width detector 31 is adjusted.
At the connection point 15 of No. 2, only the output signal has a selected waveform as shown in FIG. 5B. In this case as well, the degree of vacuum is measured based on the change in the acoustic impedance and the change in propagation attenuation in response to the vacuum opening of the transducer 11.

Next, FIG. 6 shows another embodiment. This embodiment focuses on the fact that the higher the degree of vacuum, the less sound waves are emitted from the surface of the transducer into the air, and therefore the reflection increases when focusing on the electrical terminals of the transducer. The degree of vacuum is measured by resisting the increase.

An input short signal of alternating current of frequency f is applied from the oscillator 21 to the transducer 11, whereby the electrical signal is converted into a sound wave by the transducer 11 and emitted into the container 8 defining the space 1. . When the pressure inside the container 8 is close to atmospheric pressure, the volumetric impedance of the sound emitting part of the transducer 11 and the air are kept close to matching conditions. ', the electrical signal sent to the terminal is converted into an efficient J:<note change A h and emitted into the air, and as a result, there is little reflection at the electrical terminal. However, as the degree of J in the container 8 increases, the sound signal emitted from the transducer 11 into the container 8 decreases, and as a result, 1 g of air flows into the electrical terminal. A large portion will be reflected at this terminal.

A case in which a piezoelectric kenmata device is used as the transducer 11 will now be explained in more detail, taking as an example. FIG. 7 shows details of the transducer 11 in FIG. 6. H poles 19 and 20 are formed on both sides of the piezoelectric transducer main body 18, and the portion where the electrodes 20 are not formed is used as a wave transmitting/receiving surface. When an electric signal with a frequency f is applied to the transducer 11, an elastic wave a is generated in the transducer body 18 due to the thickness amplitude, for example, and this becomes a sound wave and is emitted into the circulation. However, as the sky level rises, the mismatch in acoustic impedance at the interface between the transducer 11 and the air rush increases, so a part of the elastic wave a becomes a reflected wave C and appears on the electrode again. be exposed.

The operating principle of the circuit shown in FIG. 6 will be explained. The electrical signal of frequency f is supplied to the transducer 11, and the reflected wave from the transducer 11 is input to the summation circuit 26. On the other hand, the electrical signal of frequency f from the oscillator 21 is applied to the summation circuit 26 through the phase adjuster 23, and among the signals from the transducer 11, the input electrical signal is canceled and only the reflected signal is sent from the summation circuit 26. The output is This output is detected by a synchronous amplification detector 31 using a reference signal obtained by adjusting the phase of the output of the oscillator 21 by a second phase adjuster 24, and this detection output is read by an indicator 32.

FIG. 8 shows another embodiment of the above principle. The electrical impedance Zf seen from the electrical terminal of the transducer 11 can be expressed as the sum of the stopping impedance Z1 when the transducer 11 does not emit sound waves and the dynamic impedance Zm as a reaction due to the sound wave being emitted. .

ZO: Mechanical impedance of the transducer IJ, Z1, and mechanical impedance of the transducer IJ.

In the vicinity of the resonant frequency of the transducer 11, r, m, and S are
The natural motion loss, effective mass and effective stiffness of

The frequency characteristic of the absolute value of the manufactured impedance Zm is the 9th
As shown in the figure, the curve changes from curve 33 to curve 34 as the atmospheric pressure decreases. Therefore, according to the vertical arrow 35 in the figure,! As is clear, the acoustic impedance ZO of the air in the container 8 can be found by reading the peak impedance Zm at a certain frequency fO. Since the acoustic impedance zO of air indicates a change in the degree of vacuum, it is possible to determine the degree of vacuum opening.

In this method, control accuracy can be obtained by using a loss r at the resonant frequency that is close to the acoustic impedance Zo of air, and by measuring at the resonant frequency.

Effects> As detailed above, this invention actively utilizes the vibration phenomenon to create a highly accurate and highly stable vacuum gauge within the vacuum degree range of 10 to IQ'l'orr. It's something to do,
Compared to conventional vacuum gauges, it does not have heat generating parts such as heaters or filaments, so it has an extremely long hold time even in active plasma, operates without being affected by ion shadows, and uses an all-electronic operating mechanism. , it is possible to obtain a precise vacuum gauge with faster response speed than those using thermal operation.

In addition, compared to the conventional barometer using a v@hook, it does not require a small gas chamber connected to the outside world by a small or loud receptacle, and it still uses the amplitude of a short-frequency alternating current signal. True η
What is the vacuum level of plasma equipment that can reduce the surface area of t1 and uses a relatively low atmosphere, such as sputter oil refining and plasma etching equipment? Ideal for Mi+ feet.

[Brief explanation of drawings]

Figure 1A is a diagram showing the conventional Schulz gauge, Figure 1B is an enlarged view of its 'acid part', Figure 2 is a diagram showing the conventional Villaney gauge, $31n] The illusion of this invention. Figure 4 shows the second embodiment of the invention without showing the first embodiment, Figure 5 shows the operation of the embodiment of Figure 4. 6 is a block diagram of the third embodiment of the present invention, FIG. 7 is a partially enlarged view of the transducer 11 in FIG. 6, and FIG. Figure 19 is a diagram showing the dynamic impedance of the transducer and the wave number characteristic diagram. The space in which the vacuum should be measured, 2: filament, 3 near node, 4: collector, 5: heater, 6: circle 1. flowmeter,
7: % pressure gauge, 11 and 12: electric sound 144 scale sound ring' drowsiness transducer (transducer), 13: reflector, 21 and 22: oscillator, 23 and 24: phase adjuster,
25: Gate, 26: Sum circuit, 31: Synchronous amplification detector,
32: Output indicating instrument. Patent Applicant Agent of Nippon Telegraph and Telephone Public Corporation Hasty Bei 71'71 Figure A 9 Yoshi 3 Figure 1j Jl 31 I 7 Suf 9 Figure

Claims (5)

[Claims] (1) The electric sound 4 that was raised to the sky-1 that should be measured! Viewed from the mechanical vibration center of the main transport means, the electric sound transmission means that applies an alternating current electric signal to the electric sound transmission means, and the electric sound that changes depending on the degree of vacuum of the space. and a detector stage for detecting the sound impedance of the gas as an AC No. 100 fd signal having the same frequency as the AC electric signal from the above-mentioned electric current changing means. (2) The electric sound changing means is a device that is activated by an alternating current air signal, and during that time, the electric sound is changed to (
The sound proboscis 4 ('Q) emitted from the φ Pig detector consists of a 1 Q transducer, and the detector stage 1 is iiJ.
91: To the Kiaisho Transformer 91: It is to be determined by means of calculating the difference in amplitude between the output of the sound energy transformer and the output of the sound energy transformer. 1] Acoustic swing ω-type vacuum system as described in the first body of the range of the ΔII tree. (3) The above-mentioned ``Hina Ki Aichi Aiki Kyogyu Stage B, the reversible line to which the above-mentioned Father Bji Electric No. 18 is supplied, the Ki Ai Weather Iron Exchanger, and the -
The iJ raft is installed facing λ/j from the transducer, and the sonic wave radiated from the transducer and arrived is transmitted to the transducer.
The detecting means consists of a high-frequency reflector that reflects to Awe・417. Father b offered to L vessel
11. - It is a means for detecting the difference in amplitude and width between the air signal and the output reflected from the sound wave reflector and received by the sound transducer. ``On-an-kyoku-gata-sho-ri-zo-no-go'' as set forth in claim 1(1). (4) The electric sound converting means has the former 6 self-direction θ11, and the first 6-power conversion means. The reversible electric pressure device to which air (No. 6 is supplied, ii + I, 4, and the means for discharging it is mentioned above) Tun Qishogo and its reversible "(・, between the wall surface of Qi Qian Chang Qiann and the space" f-1
The reflection Bi'L that sea 1 construction, screw 1. . '1Ll-偲+1. :i It is a means to use the 1st spirit of the 11th shi of the shi j! 1
9 similar conventions) ir・) ((の1!・("1 bill 1st sand・1jlI hj,,,'s 魇p(-ge vibration form orashi meter. (5) The electric sound;
e exchange Df ′iJ, l, Kigoshika・supplied 2 i
'ij:, child] ト:J Ebisu's electric 8-piece bamboo converter, and the detection means is a means for detecting the electrical impedance of the electric sound converter based on the amplitude of the alternating current electric signal. An acoustic warning vibration type vacuum gauge according to claim 1, characterized in that: