JP7453718B1 - Surface potential measuring device - Google Patents

Abstract

[Problem] To provide a surface potential measuring device capable of accurate measurement even in a vacuum where static elimination using plasma is necessary. [Solution] The surface potential measuring device comprises a grounded metal case 1 with a detection window 2 open, a detection electrode 5 disposed within the case 1 and provided at a position corresponding to the detection window 2, a detection circuit to which the detection electrode 5 is connected, and an electrically insulating substrate 6 supporting the detection electrode and detection circuit, in which the case 1 is equipped with permanent magnets M1, M2, and magnetic field lines B pass over the detection window 2. [Selected Figure] Figure 2

Description

The present invention relates to a surface potential measuring device.

Surface potential measuring devices that measure the surface potential of an object in a non-contact manner are known.
For example, as shown in FIG. 6, this type of measuring device includes a metal case 1 having a detection window 2, a vibrator 4 provided with a piezoelectric element 3, a detection electrode 5, a signal detection circuit, and a vibrator. An electrically insulating substrate 6 having a drive circuit 4 and the like is provided.
The vibrator 4 is located between the detection window 2 and the detection electrode 5, and opens and closes the detection window 2 facing the detection electrode 5 by its vibration. Then, the vibrator 4 chops the lines of electric force from the surface of the charged object W, which is the charged object to be measured, directly facing the detection window 2 toward the detection electrode, and converts the lines of electric force into an alternating current voltage for the detection circuit. is detected. The surface potential of the object to be measured is detected from this AC voltage (see Patent Documents 1 and 2).

Japanese Patent Application Publication No. 2007-212209 Japanese Patent Application Publication No. 2003-021656 JP2018-056115A

Such a measuring device is sometimes used to check the static elimination effect when a charged object is neutralized, and a surface potential measuring device is sometimes provided near the static eliminating process.
On the other hand, plasma may be used to remove static electricity from a charged object in a vacuum. This is because a static eliminator that uses corona discharge or the like cannot be used in a vacuum.
In the above-mentioned plasma-based static eliminator, the plasma supplied into the vacuum chamber functions as a conductor connecting the surface of the charged object and a grounded object such as the wall of the vacuum chamber, and transfers the surface charge of the charged object to the ground. Static electricity can be removed by flowing the electricity (see Patent Document 3).

In order to perform static elimination and surface potential measurement under vacuum as described above, the case 1 of the charged potential measuring device is placed in a vacuum chamber in advance.
Note that the above-mentioned vacuum condition is, for example, about 1×10 ⁻³ [Pa].
When plasma is supplied to eliminate static electricity under such a vacuum, the plasma diffuses in a short time. In particular, electrons in plasma spread easily. Therefore, electrons in the plasma supplied near the charged object W tend to enter the case 1 through the detection window 2.

Inside the case 1, the electrically insulating substrate 6 is provided as described above. As shown in FIG. 6, if electrons e enter the case 1 through the detection window 2, the substrate 6 will be charged by the electrons e that have entered.
When the substrate 6 is charged in the case 1, the detection electrode 5 detects the surface potential of the substrate 6 as well as the surface potential of the charged object W to be measured. In particular, since the substrate 6 is closer to the detection electrode 5 than the charged object W to be measured, the influence of the surface potential of the substrate 6 is large. In other words, it was not possible to accurately measure the surface potential in an environment that required plasma static elimination.

An object of the present invention is to provide a surface potential measuring device that can perform accurate measurements even under a vacuum that requires static elimination using plasma.

The first invention includes a metal case that is installed in a vacuum where plasma exists, has a detection window facing the measurement target opened, and is grounded, and a metal case that is placed in the case and corresponds to the detection window. A surface potential measuring device comprising a detection electrode provided at a position, a detection circuit to which the detection electrode is connected, and an electrically insulating substrate supporting the detection electrode and the detection circuit, wherein the case is permanent. A magnet is provided, and the magnetic field lines are configured to pass over the detection window, and the electrons in the plasma near the detection window are rotated around the magnetic field lines by the magnetic field lines, collide with the case, and pass through the case. The configuration is such that it flows to ground .

In a second aspect of the present invention, the case is made of a non-magnetic metal, and includes the permanent magnet sandwiching the detection window on its outer surface.

In a third invention, the case is made of magnetic metal.

According to the first invention, electrons in the plasma that approach the detection window rotate around the magnetic lines of force due to the magnetic force of the permanent magnet and collide with the case, so that they do not enter the case. Further, even if electrons enter the case, the electrons rotate around the magnetic lines of force within the case and collide with the inner wall of the case. Therefore, the board inside the case will not be charged by electrons that enter through the detection window. Furthermore, since the metal case is grounded, electrons that collide with the case flow to the ground and do not charge the case.
Therefore, the detection electrode can accurately measure the surface potential of the measurement target.

According to the second invention, since the direction of the magnetic lines of force is not easily influenced by the shape of the case, a magnetic field that prevents electrons from entering through the detection window can be set only by the position of the permanent magnet.

According to the third invention, the case made of magnetic metal can suppress the spread of the magnetic field outside the case and concentrate the lines of magnetic force near the detection window. Furthermore, the influence of the magnetic field on external electronic equipment can be reduced.

FIG. 1 is an external perspective view of the first embodiment. FIG. 2 is a cross-sectional view of the first embodiment. FIG. 3 is a diagram showing the magnetic field near the detection window of the first embodiment. FIG. 4 is a graph showing the surface potential measurement results of the conventional device and the first embodiment. FIG. 5 is a cross-sectional view of the second embodiment. FIG. 6 is a cross-sectional view of a conventional surface potential measuring device.

[First embodiment]
The first embodiment will be described using FIGS. 1 to 3.
FIG. 1 is an external perspective view of the first embodiment, FIG. 2 is a sectional view of FIG. 1, and FIG. 3 is a diagram showing a magnetic field. This is a surface potential measuring device in which permanent magnets M1 and M2 are attached to a pair of opposing outer surfaces (outer surfaces) of a case 1 made of non-magnetic metal and having a square prism outer shape.
Except for the permanent magnets M1 and M2, the conventional measuring device shown in FIG. 6 is the same as the conventional measuring device shown in FIG.
Further, the case 1 is grounded.

Permanent magnets M1 and M2 have a substantially flat plate shape. The permanent magnets M1 and M2 are attached to the inner surface of a cover 7 made of a non-magnetic metal plate bent into a U-shape, and are attached to the case 1 via the cover 7. Thereby, the permanent magnets M1 and M2 are arranged so as to be located on the same plane with the detection window 2 in between. The cover 7 has an opening 7a that exposes the detection window 2.
As shown in FIGS. 2 and 3, the pair of permanent magnets M1 and M2 are arranged such that the S pole of one permanent magnet M1 and the N pole of the other permanent magnet M2 face each other with the detection window 2 in between. ing. Therefore, the permanent magnets M1 and M2 are configured in the surface potential measuring device so that the line of magnetic force B shown by the thin arrow crosses the opening surface of the detection window 2, that is, the line of magnetic force B passes over the detection window 2. .

[Action/effect, etc.]
A case will be described in which a charged object to be measured, which is placed opposite to the detection window 2, is neutralized by plasma while the surface potential measuring device as described above is installed in a vacuum chamber. Note that the wall surface of the vacuum chamber is grounded.
The plasma supplied for static elimination spreads within the vacuum chamber, functions as a conductor that connects the surface of the charged object W with the grounded wall of the vacuum chamber, and the case 1, and removes the charge on the surface of the charged object W. Static electricity can be removed.

In this way, most of the electrons and ions in the plasma that contributed to static elimination immediately come into contact with a grounding object such as the wall of the vacuum chamber (not shown) and flow to the ground. There is also an electron e heading towards (see Figure 6).
If such electrons e enter the case 1 through the detection window 2 of the case 1, the substrate 6 will be charged.

However, in the first embodiment, there are lines of magnetic force B near the detection window 2 that cross the opening of the detection window 2. Therefore, the electrons approaching the detection window 2 move around the lines of magnetic force B while turning as indicated by the bold line arrows in FIG. During this swirling process, the electrons e collide with the case 1 and flow to the ground, so they do not intersect the magnetic lines of force B and enter the case 1. Therefore, the electrons e do not charge the substrate 6 within the case 1.

Therefore, when measuring the surface potential of the charged object W after the charged object W is subjected to static elimination processing, the charged potential of the substrate 6 does not affect the measurement of the surface potential of the charged object W. In other words, accurate measurement results can be obtained.

[Confirmation experiment]
An experiment was conducted to compare the surface potential measuring device of the first embodiment with a conventional surface potential measuring device.
The conventional surface potential measuring device has the same configuration as the surface potential measuring device of the first embodiment except that it does not include permanent magnets M1 and M2.
Using each of these surface potential measuring devices, the surface potential was set to zero in advance in a vacuum chamber, and the surface potential of a grounded metal plate was measured. Note that during the measurement, plasma for static elimination was supplied into the vacuum chamber.

The measurement results are shown in FIG. 4.
In the figure, the broken line graph (1) is the measurement result with the conventional surface potential measuring device, and the solid line graph (2) is the result of the measurement with the surface potential measuring device of the first embodiment.
As shown in FIG. 4, the conventional surface potential measuring device measures a negative potential whose absolute value increases as plasma is supplied.
Since the metal plate is grounded, the potential detected by the detection electrode 5 is influenced by the potential of the substrate 6, which is charged by electrons that have entered the case 1.

On the other hand, the measurement result with the surface potential measuring device of the first embodiment maintains zero potential.
From this, it was confirmed that permanent magnets M1 and M2 can prevent electrons from entering the case 1.

[Second embodiment]
FIG. 5 is a sectional view of the case 11 of the second embodiment. The case 11 is made of magnetic metal and includes a detection window 12.
The case 11 has the same configuration as the case 1 of the first embodiment except for the material, and the same reference numerals as in FIG. 1 are used for the same components as in the first embodiment.

Further, in the second embodiment, the permanent magnet M3 is fixed to the bottom surface 11a of the case 11 on the side opposite to the surface on which the detection window 12 is formed. The permanent magnet M3 has an N pole and an S pole at both ends located on side surfaces 11b and 11c that stand up from the edge of the bottom surface 11a, respectively.
The lines of magnetic force B of the permanent magnet M3 arranged in this manner pass through the case 11 and above the detection window 12 as shown by the arrow.

[Action/effect, etc.]
Also in this second embodiment, electrons approaching the detection window 12 rotate around the magnetic lines of force B, collide with the case 11, and flow to the ground. Therefore, for example, even if plasma for static elimination is supplied, electrons will not enter the case 11 and charge the substrate 6. Therefore, accurate surface potential measurement can be performed.
In the second embodiment, since the case 11 confines the lines of magnetic force, the influence of the magnetic field on the outside can be reduced.

In the above embodiments, the outer shapes of the cases 1 and 11 are square prisms, but the outer shapes of the cases may be of any shape.
Further, the arrangement of the permanent magnets M1, M2, and M3 is not limited to the above arrangement as long as magnetic lines of force can pass over the detection windows 2 and 12 to prevent electrons from entering the case.

Note that when the case is made of a magnetic material, the lines of magnetic force are confined and the influence of the magnetic field on the outside can be suppressed, but the direction of the lines of magnetic force may be affected by the shape of the case.
On the other hand, when the case is made of a non-magnetic material, there is an advantage that the direction of the magnetic lines of force and the strength of the magnetic field can be controlled only by the arrangement of the permanent magnets. The material of the case, the shape and arrangement of the permanent magnets, the strength of magnetic force, etc. may be appropriately set in consideration of the installation location, the object to be measured, etc.

It is useful for measuring surface potential in environments that require plasma supply.

1, 11 Case 2, 12 Detection window 5 Detection electrode 6 Substrate M1, M2, M3 Permanent magnet B Lines of magnetic force

Claims (3)

It is installed in a vacuum where plasma exists,
A detection window facing the measurement target is opened, and a grounded metal case is installed.
Placed inside the above case,
a detection electrode provided at a position corresponding to the detection window;
a detection circuit to which the detection electrode is connected;
A surface potential measuring device comprising the above detection electrode and an electrically insulating substrate supporting the detection circuit,
The above case is
It is equipped with a permanent magnet and is configured so that lines of magnetic force pass over the detection window,
A surface potential measuring device configured such that electrons in the plasma near the detection window rotate around the magnetic lines of force, collide with the case, and flow to earth via the case. The above case is
Made of non-magnetic metal,
The surface potential measuring device according to claim 1, further comprising: the permanent magnet sandwiching the detection window on its outer surface. The surface potential measuring device according to claim 1, wherein the case is made of magnetic metal.

Images