JP2771061B2 - Method for measuring film thickness of airtight high-frequency window - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a microwave tube such as a traveling wave tube or a klystron, or a device for utilizing microwave power of such a microwave tube, between a vacuum portion and an external waveguide. The thickness of the high frequency airtight window for measuring the thickness of the thin film on the surface of the dielectric disk provided inside the high frequency airtight window having airtightness provided in
It is related to the setting method .

[0002]

2. Description of the Related Art FIG.
FIG. 1 is a side cross-sectional view showing a conventional hermetic high-frequency window described in Japanese Patent Laid-Open Publication No. H10-207, in which 1 is a rectangular waveguide, 2 is a circular waveguide disposed between rectangular waveguides 1, and 3 is a circular waveguide. The dielectric disk 4 airtightly brazed inside the waveguide 2 is made of titanium nitride, titanium oxide, chromium oxide, or the like provided on both surfaces of the dielectric disk 3 for suppressing high-frequency discharge. It is a thin film.

Next, the operation will be described. The rectangular waveguide of side microwave is input and output from the rectangular waveguide 1 on the other side through the induction conductor disc 3.

An airtight high-frequency window having this structure is generally
It has features that the allowable microwave power is considerably large, the microwave reflection is small, and the reliability is high. However, when microwaves of higher power are passed through the hermetic high-frequency window, small holes may be formed in the surface of the dielectric disk 3 and the hermeticity may be insufficient. This small hole is considered to be caused by collision of electrons accelerated by a high-frequency electric field (high-frequency discharge). The occurrence of this high-frequency discharge is determined by the intensity and direction of the high-frequency electric field and the proportion of secondary electron emission from the surface of the dielectric disk 3 due to electron collision.

[0005] Therefore, in order to reduce secondary electron emission from the surface of the dielectric disk 3, the entire surface of the dielectric disk 3 is coated with a thin film 4 of titanium nitride, titanium oxide, chromium oxide or the like. High frequency discharge is suppressed. In order to reduce secondary electron emission from the surface of the dielectric disk 3, it is desirable that the thickness of the coating film is sufficiently large. However, if the thickness of the thin film 4 is too large, the microwave is reflected by the coating film, and the characteristics as a microwave window deteriorate.

Therefore, in order to prevent microwave reflection and to suppress secondary electron emission, it is necessary to form a thin film 4 having a thickness of about several nanometers on the entire surface of the dielectric disk 3. is there. As a conventional representative film thickness measuring method, there is a film thickness monitor during coating (quartz film thickness meter)
There is a method of measuring the film thickness by using a method, a method of estimating the film thickness by measuring the surface resistance, and a method of measuring the film thickness by an Auger electron analyzer.

[0007]

In a conventional hermetic high-frequency window, the film thickness is measured by a film thickness monitor (a quartz film thickness meter) when coating the thin film 4 on the surface of the dielectric disk 3, and the coating process is performed. The film thickness is regulated by management. However, since the thickness of the dielectric disk 3 is not very flat, the measurement of the film thickness is very difficult, and the change in film thickness and film quality after film formation cannot be confirmed. was there.

In the method using the surface resistance, there is a problem that the measurement of this very thin film is insufficient in accuracy and difficult to measure after assembling the window. Further, the film thickness measuring method using the Auger electron analyzer is a destructive measuring method, and thus has a problem that it cannot be measured after the airtight high-frequency window is assembled.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is intended to confirm the presence or absence of a very thin film of an airtight high-frequency window and to measure the film thickness. Film thickness measurement of airtight high-frequency window
The purpose is to obtain a fixed method .

[0010]

According to a first aspect of the present invention, there is provided a method for measuring the film thickness of an airtight high-frequency window, which measures a decrease in the Q value at a ghost mode resonance frequency of the airtight high-frequency window and uses the measured value as a film thickness. Is converted to.

[0011]

[0012]

According to the first aspect of the present invention, the method for measuring the film thickness of the hermetic high-frequency window utilizes the ghost mode resonance of the hermetic high-frequency window, and the Q value of the ghost mode resonance is reduced by increasing the loss due to the thin film. Therefore, what appears in the decrease can be converted into a film thickness.

[0013]

[0014]

[Embodiment 1] An embodiment of the first aspect of the present invention will be described below with reference to the drawings. In FIG. 1, portions corresponding to those in FIG. 6 are denoted by the same reference numerals, and description thereof is omitted. In FIG. 1, reference numeral 5 denotes a network analyzer which outputs a high-frequency signal and analyzes the frequency of an input signal. Reference numeral 6a denotes an excitation device which is inserted through an opening of the rectangular waveguide 1 on one side and to which an output signal of the network analyzer 5 is applied. Probe, 6b
Is a detection probe which is inserted through the opening of the rectangular waveguide 1 on the other side and detects a resonance state.

Next, the operation will be described. In an airtight high-frequency window, generally, the frequency f and VSW as shown in FIG.
The relationship with R is seen. In FIG. 2, the hermetic high-frequency window is designed so that the VSWR becomes small near the operating frequency 7, but a sharp change in the VSWR is observed at a frequency outside the window. This rapidly changing frequency is called a ghost mode frequency 8, and at this frequency, the specific mode (TE311, TE1) is set inside the hermetic high frequency window.
21, TE111, TE011, etc.) are in a resonance state. The microwave resonance state of this specific mode is
Since it mainly occurs due to the dielectric disk 3, the presence of the thin film 4 on its surface greatly affects. That is, since the thin film 4 is located where the electromagnetic field generated by resonance is strong, a large loss occurs. Therefore, the energy stored by the resonance decreases, and the Q value decreases.

In particular, if the resonance of TE111 or TE011, which is a ghost mode having a frequency equal to or lower than the cutoff frequency of the rectangular waveguide 1, is used, microwaves are not transmitted to the rectangular waveguide 1, so that the Q value increases. The measurement of the loss due to the thin film 4 can be performed with high accuracy. As shown in FIG. 1, resonance is measured at the ghost mode frequency 8 using two probes 6a and 6b for excitation and detection, and a Q value is obtained from the measured value.

FIG. 3 shows an example of measuring ghost mode resonance. The horizontal axis is the frequency f, and the vertical axis is the quantity S indicating the intensity of resonance.
₂₁ . The Q value of the resonance curve 9 without the thin film 4 is a value obtained by dividing the resonance frequency 8 by the half width 10. The half width 12 of the resonance curve 11 when the thin film 4 is coated is
The Q value is much smaller than the half width 10 when the thin film 4 is not provided. By utilizing this fact, if the measurement of the decrease of the Q value near the ghost mode frequency is performed in advance by using several types of hermetic high-frequency windows whose film thickness is known,
From the measured value of the decrease in the Q value at the ghost mode resonance frequency 8, the thickness of the thin film 4 of the hermetic high-frequency window having the same configuration can be converted.

Embodiment 2 FIG. In the first embodiment, two probes 6a and 6b are used. However, after the airtight high-frequency window is attached to the device, one probe 6a or 6b is used.
The ghost mode is excited and detected, and the Q value can be obtained from the measurement of the resonance at the ghost mode frequency 8 in the same manner as described above. Compared to the method using two probes 6a and 6b, the accuracy of measurement is lower with one probe, but there is an advantage that measurement can be performed regardless of what device is connected to the hermetic high-frequency window.

Embodiment 3 FIG. FIG. 4 shows an embodiment of the first aspect of the present invention, in which a small window 13 is provided in the rectangular waveguide 1 of an airtight high-frequency window. In this embodiment, a small probe window 13 is provided. For example, a small hole is made in the probe window 13 at a position not far from the connection portion with the circular waveguide 2 on the side surface of the rectangular waveguide 1 and a dielectric such as ceramics is fitted into the hole to form a vacuum airtight. With a structure that keeps

Attach two probes 6a and 6b for excitation and detection to the probe window 13 to excite the inside of the hermetic high-frequency window, and measure the decrease of the Q value at the ghost mode resonance frequency 8 in the same manner as described above. By doing so, the thickness of the thin film 4 of the hermetic high-frequency window can be converted. This inspection method has an advantage that the measurement can be performed without removing the waveguide even after the hermetic high-frequency window is installed in the device and regardless of what is connected to the hermetic high-frequency window.

Embodiment 4 FIG. Figure 5 is a billing shows another embodiment of the first aspect of the invention, provided with a probe window 13 on the side surface of the circular waveguide 2 hermetic high-frequency window. The probe window 13 may be provided on the side surface 2a of the circular waveguide 2 connected to the rectangular waveguide 1 as shown in FIG. 5, or may be provided on the other side surface of the circular waveguide 2. Good. Even when the probe window 13 is used, the third embodiment can be used.
It has exactly the same functions and advantages as.

[0022]

As described above, according to the first aspect of the present invention, the inside of the hermetic high-frequency window is excited at the ghost mode frequency, the Q value in the resonance state is measured, and the film thickness is converted from the measured value. As a result, the measurement can be performed at any time even after the airtight high-frequency window is assembled. Therefore, it is possible to measure the change in film thickness and film quality after film formation. Can be

[0023]

[Brief description of the drawings]

FIG. 1 is a sectional view showing a method for measuring a film thickness of an airtight high-frequency window according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing an example of a VSWR measurement with respect to a frequency of an airtight high-frequency window.

FIG. 3 is a characteristic diagram showing an example of measurement of a Q value for converting a film thickness of a thin film of an airtight high-frequency window.

4 is a cross-sectional view illustrating a film thickness measurement method using a gas-tight high-frequency window according to an embodiment of the invention of claim 1.

FIG. 5 is a cross-sectional configuration diagram showing a film thickness measuring method using an airtight high-frequency window according to another embodiment.

FIG. 6 is a side sectional view of a conventional hermetic high-frequency window.

Claims (1)

(57) [Claims] 1. A circular waveguide is arranged between rectangular waveguides,
A dielectric disk is hermetically sealed inside the circular waveguide, and a thin film for suppressing high-frequency discharge is provided on the surface of the dielectric disk. A hermetic high-frequency window in which the vicinity of the disk is excited by a high frequency of a predetermined ghost mode frequency to form a resonance state, a Q value in the resonance state is measured, and the measured value is converted into a film thickness of the thin film. Thickness measurement method.