Surface potential measurement device

Abstract

To provide a surface potential measurement device capable of performing correct measurement even under vacuum requiring static elimination by using plasma.SOLUTION: A surface potential measurement device includes: a grounding metal case 1 having an opening detection window 2; a detection electrode 5 arranged inside the case 1 and positioned to correspond to the detection window 2; a detection circuit to which the detection electrode 5 is connected; and an electrically insulating substrate 6 for supporting the detection electrode and the detection circuit. The case 1 includes permanent magnets M1, M2, and a magnetic field line B passes over the detection window 2.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a surface potential measuring device. [Background technology]

[0002] 2. Description of the Related Art Surface potential measuring devices that measure the surface potential of an object in a non-contact manner are known. As shown in FIG. 6, for example, this type of measuring device has an electrically insulating substrate 6 provided with a vibrator 4 having a piezoelectric element 3 attached thereto, a detection electrode 5, a signal detection circuit, a drive circuit for the vibrator 4, etc., within a metal case 1 having a detection window 2. The oscillator 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. The oscillator 4 chops the electric field lines that run from the surface of the charged object W, which is the charged measurement target and is placed facing the detection window 2, to the detection electrode, and the detection circuit detects the electric field lines as an AC voltage. The surface potential of the measurement target is detected from this AC voltage (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-212209 A [Patent Document 2] JP 2003-021656 A [Patent Document 3] JP 2018-056115 A Summary of the Invention [Problem to be solved by the invention]

[0004] Such a measuring device is sometimes used to confirm the effect of neutralizing a charged object when the object is neutralized, and the surface potential measuring device is sometimes provided near the neutralization process. On the other hand, plasma is sometimes used to remove static electricity from a charged object in a vacuum, because a static eliminator that uses corona discharge or the like cannot be used in a vacuum. In the above-mentioned static elimination device using plasma, the plasma supplied into the vacuum chamber functions as a conductor connecting the surface of the charged object to a grounded body such as the vacuum chamber wall, and can discharge the surface charge of the charged object by flowing it to the ground (see Patent Document 3).

[0005] In order to perform static elimination and surface potential measurement under the above-mentioned vacuum, the case 1 of the charge potential measuring device is placed in a vacuum chamber beforehand. The above vacuum condition is, for example, 1×10 -3 It is about [Pa]. When plasma is supplied to remove static electricity under such a vacuum, the plasma diffuses in a short time. In particular, electrons in the plasma tend to diffuse. Therefore, electrons in the plasma supplied near the charged object W tend to enter the case 1 through the detection window 2.

[0006] As described above, the electrically insulating substrate 6 is provided inside the case 1. 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 becomes 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 perform accurate surface potential measurement in an environment that requires plasma de-electrification.

[0007] An object of the present invention is to provide a surface potential measuring device capable of performing accurate measurement even under a vacuum where static elimination using plasma is required. [Means for solving the problem]

[0008] The first invention is a surface potential measuring device comprising a metal case having an opening for a detection window and being grounded, a detection electrode disposed within the case and provided at a position corresponding to the detection window, 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 equipped with a permanent magnet and magnetic field lines pass over the detection window.

[0009] In a second aspect of the present invention, the case is made of a non-magnetic metal and is provided with the permanent magnet on its outer surface, sandwiching the detection window therebetween.

[0010] In a third aspect of the present invention, the case is made of a magnetic metal. Effect of the Invention

[0011] According to the first invention, electrons in the plasma approaching the detection window revolve around the magnetic field lines due to the magnetic force of the permanent magnet and collide with the case, and therefore do not enter the case. Even if electrons do enter the case, they revolve around the magnetic field lines inside the case and collide with the inner wall of the case. Therefore, the substrate inside the case is not 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.

[0012] According to the second aspect of the present invention, the direction of the magnetic field lines is not easily affected by the shape of the case, so that a magnetic field into which electrons have difficulty entering through the detection window can be set simply by the position of the permanent magnet.

[0013] According to the third aspect of the present invention, the magnetic metal case can suppress the spread of the magnetic field outside the case and concentrate the magnetic field lines in the vicinity of the detection window. Also, the effect of the magnetic field on external electronic devices can be reduced. [Brief description of the drawings]

[0014] [Figure 1]FIG. 1 is an external perspective view of the first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the first embodiment. [Diagram 3] FIG. 3 is a diagram showing the magnetic field near the detection window in the first embodiment. [Figure 4] FIG. 4 is a graph showing the results of measuring the surface potential of the conventional device and the first embodiment. [Diagram 5] FIG. 5 is a cross-sectional view of the second embodiment. [Figure 6] FIG. 6 is a cross-sectional view of a conventional surface potential measuring device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [First embodiment] The first embodiment will be described with reference to FIGS. Fig. 1 is an external perspective view of the first embodiment, Fig. 2 is a cross-sectional view of Fig. 1, and Fig. 3 is a diagram showing the magnetic field. This surface potential measuring device has permanent magnets M1 and M2 attached to a pair of opposing outer side surfaces (outer surfaces) of a case 1 made of a non-magnetic metal and having an external shape of a rectangular prism. Other than the permanent magnets M1 and M2, the measuring device is the same as the conventional measuring device shown in FIG. Also, case 1 is grounded.

[0016] The permanent magnets M1 and M2 are generally flat. The permanent magnets M1 and M2 are attached to the inner surface of the cover 7, which is made by bending a non-magnetic metal plate into a U-shape, and are attached to the case 1 via the cover 7. As a result, the permanent magnets M1 and M2 are arranged so as to be positioned on the same plane with the detection window 2 in between. The cover 7 is formed with an opening 7a that exposes the detection window 2. 2 and 3, the pair of permanent magnets M1, M2 are arranged so that the S pole of one permanent magnet M1 and the N pole of the other permanent magnet M2 face each other across the detection window 2. Therefore, the permanent magnets M1, M2 are configured in the surface potential measuring device so that the magnetic field lines B indicated by the thin arrows cross the opening surface of the detection window 2, i.e., the magnetic field lines B pass over the detection window 2.

[0017] [Actions and Effects] A case will be described in which, with the above-mentioned surface potential measuring device installed in a vacuum chamber, a charged object to be measured, which is placed opposite the detection window 2, is neutralized by plasma. The wall surface of the vacuum chamber is grounded. The plasma supplied for static elimination spreads within the vacuum chamber and functions as a conductor connecting the surface of the charged object W with the grounded wall of the vacuum chamber and with the case 1, thereby eliminating the charge on the surface of the charged object W.

[0018] In this way, most of the electrons and ions in the plasma that contributed to the neutralization immediately come into contact with a grounded body such as the wall of the vacuum chamber (not shown) and flow to the earth, but some electrons e move toward the detection window 2 (see Figure 6). If such electrons e enter the case 1 through the detection window 2 of the case 1, the substrate 6 will become charged.

[0019] However, in this first embodiment, there are magnetic field lines B that cross the opening of the detection window 2 near the detection window 2. Therefore, electrons approaching the detection window 2 move while circling around the magnetic field lines B as shown by the thick arrows in FIG. 3. In the process of circling, the electrons e collide with the case 1 and flow to the earth, so they do not intersect with the magnetic field lines B and enter the case 1. Therefore, the electrons e do not charge the substrate 6 inside the case 1.

[0020] Therefore, when measuring the surface potential of the charged object W after the charge removal process, the charge 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.

[0021] [Confirmatory experiment] An experiment was carried out 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 the permanent magnets M1 and M2. Using each of these surface potential measuring devices, the surface potential of a grounded metal plate was measured in a vacuum chamber after the surface potential was set to zero in advance. Note that during the measurement, a plasma for static elimination was supplied into the vacuum chamber.

[0022] The measurement results are shown in FIG. In the figure, the dashed line graph (1) shows the measurement results using a conventional surface potential measuring device, and the solid line graph (2) shows the results using the surface potential measuring device of the first embodiment. As shown in FIG. 4, in the conventional surface potential measuring device, a negative potential whose absolute value increases with the supply of plasma is measured. 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 .

[0023] On the other hand, the measurement result obtained by the surface potential measuring device of the first embodiment shows that the potential is maintained at zero. From this, it was confirmed that the permanent magnets M1 and M2 can prevent electrons from entering the case 1.

[0024] [Second embodiment] 5 is a cross-sectional view of the case 11 of the second embodiment. The case 11 is made of a magnetic metal and has a detection window 12. Case 11 has the same structure as case 1 of the first embodiment except for the material, and the same components as in the first embodiment are designated by the same reference numerals as in FIG.

[0025] 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 its N pole and S pole at both ends positioned on the sides 11b and 11c rising from the edge of the bottom surface 11a, respectively. Magnetic field lines B of the permanent magnet M3 thus arranged pass through the inside of the case 11 and above the detection window 12 as shown by the arrow.

[0026] [Actions and Effects] In the second embodiment, too, electrons approaching the detection window 12 revolve around the magnetic field lines B, collide with the case 11, and flow to the earth. Therefore, even if a static electricity removing plasma is supplied, the electrons will not enter the case 11 and charge the substrate 6. This allows accurate surface potential measurement. In the second embodiment, the case 11 confines the magnetic field lines, so that the influence of the magnetic field on the outside can be reduced.

[0027] In the above embodiment, the outer shape of the cases 1 and 11 is a rectangular prism, but the outer shape of the case may be any shape. Furthermore, as long as the magnetic field lines pass over the detection windows 2 and 12 and can prevent electrons from entering the case, the arrangement of the permanent magnets M1, M2, and M3 is not limited to the above.

[0028] If the case is made of a magnetic material, the magnetic field lines are contained, reducing the effect of the magnetic field on the outside. However, the direction of the magnetic field lines may be affected by the shape of the case. On the other hand, if the case is non-magnetic, there is the advantage that the direction of the magnetic field lines and the strength of the magnetic field can be controlled simply by the arrangement of the permanent magnets. The material of the case, the shape and arrangement of the permanent magnets, and the strength of the magnetic field can be set appropriately taking into account the installation location and the object to be measured. [Industrial Applicability]

[0029] This is useful for measuring surface potential in an environment that requires the supply of plasma. [Explanation of symbols]

[0030] 1,11 cases 2,12 Detection window 5. Detection electrode 6 Substrate M1,M2,M3 Permanent magnet B magnetic field lines

Claims

1. a grounded metal case having an open detection window; Located in the case, a detection electrode provided at a position corresponding to the detection window; a detection circuit to which the detection electrodes are connected; an electrically insulating substrate supporting the detection electrodes and the detection circuit; A surface potential measuring device comprising: The above case is The detector is provided with a permanent magnet and configured so that magnetic field lines pass over the detection window. Surface potential measuring device.

2. The above case is It is made of non-magnetic metal, The outer surface of the device is provided with the permanent magnets that sandwich the detection window. The surface potential measuring device according to claim 1 .

3. The case is made of magnetic metal. The surface potential measuring device according to claim 1 .

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