JP4383264B2 - Surface potential distribution measuring method and measuring apparatus - Google Patents

Description

  The present invention relates to a surface potential distribution measuring method and measuring apparatus.

  Patent Documents 1 and 2 are known as methods for measuring surface charge distribution or surface potential distribution in a dielectric such as a photoconductive photoreceptor with high resolution on the order of microns. In the measurement methods described in these patent documents, the surface of the measurement sample is scanned with a charged particle beam, and secondary electrons generated on the measurement sample surface are detected. In the case of this method, the electric field distribution on the surface of the measurement sample is directly measured, and the surface potential distribution is calculated arithmetically based on this electric field distribution.

  The inventor first scans a charged particle beam with respect to a sample having a surface potential distribution, and under the condition that there exists a “state in which the velocity vector in the sample vertical direction of incident charged particles is reversed”. A method for measuring the surface potential distribution was proposed (Patent Document 3).

  In this method, it is possible to measure the surface potential distribution of the measurement sample, but in the velocity region where the velocity vector of the charged particle is inverted, the velocity of the charged particle is “not so large”, so the influence of the pull-in voltage of the detection means The trajectory of the incident charged particles may be bent, and the scanning position may be deviated from the “target position”, or the charged particle speed may change due to the influence of the detector.

JP 2003-295696 A JP 2003-305881 A Japanese Patent Application No. 2003-406002

  The present invention has been made in view of the circumstances described above, and “a measurement sample having a surface potential distribution is scanned with a charged particle beam by a charged particle optical system, and among the charged particles incident on the sample surface, In `` Surface potential distribution measurement method that captures and detects charged particles whose normal direction component on the sample surface of the incident velocity vector is inverted by a detector and obtains a detection signal '', the measurement error due to the influence of the pull-in voltage of the detection means The problem is to prevent or reduce.

The surface potential distribution measuring method according to the present invention is described as follows: “A measurement sample having a surface potential distribution is scanned with a charged particle beam by a charged particle optical system, and of charged particles incident on the sample surface, the sample surface of the incident velocity vector thereof. Is a surface potential distribution measuring method for obtaining a detection signal by capturing and detecting charged particles whose components in the normal line direction are reversed by a detecting means (claim 1).
That is, the measurement sample is a photoconductive sample.
A photoconductive sample as a measurement sample is held by holding means.
The holding means has a three-layer structure in which a dielectric layer is sandwiched between conductive layers, and a photoconductive sample as a measurement sample is held in a plane on one conductive layer of the holding means.
The photoconductive sample held in the holding means is irradiated with a charged particle beam scanned two-dimensionally by a charged particle optical system to uniformly charge the measurement sample to a desired potential. Then, a uniformly charged measurement sample is irradiated with a light image and exposed to form an “electrostatic latent image that is a surface potential distribution as a measurement target”.

By interposing a two-dimensional shield member that allows charged particles to pass between the optical axis of the charged particle optical system and the capturing unit of the detection means, and applying a bias voltage to the conductive layer of the holding means, The formed surface potential distribution is changed in a bias manner.
Then, the charged particle optical system scans the charged particle beam for measurement, and detects “charged particles whose normal velocity components on the measurement sample surface of the incident velocity vector are reversed among the charged particles incident on the measurement sample surface”. A detection signal is obtained by detection by means.

  Supplementing a little, the “surface potential distribution” as a measurement object is a distribution of potentials on a substantial surface of the sample, that is, “a region of the sample surface and its immediate vicinity (about several μm from the surface)”. The cause of the surface potential distribution is the charge existing on the sample surface (ions, etc.), the charge existing locally on the surface layer of the sample to some extent (the ions captured by being shot and captured on the sample surface, The shot electrons are captured in the electron orbits of the material molecules and remain in the surface layer portion in a state of negative ionization of the material molecules), or the sample surface portion is conductive and this portion In some cases, a voltage is applied from the outside to generate a potential distribution on the sample surface. Therefore, the “surface charge” refers to a state in which the charge distribution state is “a state in which the in-plane distribution range of the measurement sample is larger than that in the measurement sample internal direction”.

  “Charged particles” are “charged fine particles” such as electrons and ions, and can be scanned by the action of an electric field or a magnetic field. As the charged particle beam for scanning the measurement sample, an “electron beam or ion beam” can be preferably used.

  The “charged particle optical system” is a charged particle beam scanning unit that scans a charged particle beam and irradiates the charged particle toward a desired portion of the measurement sample. Having a gun and having an electromagnetic lens or the like that scans and focuses the electron beam generated by the electron gun ”or“ having a liquid metal ion gun as the source of the charged particle beam and the ion beam generated by the ion gun What has an electromagnetic lens etc. for scanning and focusing can be mentioned as a suitable example.

The scanning for measuring the measurement sample using the charged particle beam can be performed two-dimensionally or one-dimensionally. If the two-dimensional scanning is performed, the surface potential distribution of the two-dimensional region on the surface of the measurement sample can be measured, and if the one-dimensional scanning is performed, the linear region on the surface of the measurement sample (a straight line or a curve may be used. Or the elliptical linear region can be considered).

The “two-dimensional” in the “two-dimensional shield member ” means that the shield member has an area region that can shield the electric field due to the pull-in voltage of the detection means, and the actual shape is not limited to a planar shape. , Which can be described later, “a three-dimensional shape such as a cylindrical shape or a hemispherical shape”.

By interposing a “two-dimensional shield member that allows charged particles to pass through at substantially the same potential as the ground potential” between the optical axis of the charged particle optical system and the capture unit of the detection means, The electric field is “effectively shielded or mitigated against the spatial region where the charged particles are secondarily scanned”.
The surface potential distribution measuring apparatus according to the present invention is an “apparatus for carrying out the surface potential distribution measuring method according to claim 1”, and is a sample holding means, a charging means, an exposure means, a voltage applying means, It has a particle optical system, a detection means, a measurement means, and a shield member .

The “sample holding means” has a three-layer structure in which a dielectric layer is sandwiched between conductive layers. On one conductive layer, a photoconductive sample as a measurement sample is covered with a surface on which the surface potential distribution is formed. It is held in a plane as a scanning plane.
The “charging unit” uniformly charges the measurement sample held by the sample holding unit.
The “exposure unit” exposes the measurement sample uniformly charged by the charging unit by irradiation with a light image, and forms an electrostatic latent image as a surface potential distribution on the measurement sample.
The “voltage applying unit” applies a bias voltage to one conductive layer of the sample holding unit, and changes the surface potential distribution formed on the measurement sample in a bias manner.
"Charged particle optical system" is a means for scanning the scan surface of the measuring sample held by the sample holding means for measuring a charged particle beam, also serves as the charging means. Therefore, the charge for charging the measurement sample surface and the charged particles of the charged particle beam scanned for measurement have the same polarity.

The “detecting means” captures and detects “charged particles whose components in the normal direction of the incident velocity vector on the sample surface are reversed” among the charged particle beams scanned for measurement .
The “measuring unit” is a unit that calculates the surface potential of the measurement sample based on the detection result by the detecting unit, and can be specifically configured by a microcomputer or the like.

The “two-dimensional shield member ” is disposed between the optical axis of the charged particle optical system and the capturing unit of the detection means, and allows the charged particles to pass therethrough at substantially the same potential as the ground potential.

As the two-dimensional shield member, a “grid mesh (mesh-like structure made of a conductor)” can be preferably used (Claim 3), and the grid mesh has an opening efficiency (ratio of opening area per unit area). Is preferably 25% or more. Among the “charged particles in which the component in the normal direction of the sample surface of the incident velocity vector is inverted (hereinafter referred to as“ inverted charged particles ”)” when the aperture efficiency is 25% or less, what is absorbed by the grid mesh The detection accuracy by the detector decreases. On the other hand, if the aperture efficiency is too large, the electric field caused by the detector pull-in voltage cannot be effectively shielded against charged particles. The upper limit of the opening efficiency is preferably about 90% .

"2-dimensional shielding member" in the surface potential distribution measuring apparatus according to claim 2 or 3, wherein, this was cylindrical, can be provided so as to surround the optical axis of the charged particle optical system (claim 4) . Further, the two-dimensional shield member may be formed in a substantially hemispherical shape so as to cover the measurement sample (claim 5). Of course, the two-dimensional shield member may be a “planar shape” and may be arranged like a “screen” between the optical axis of the charged particle optical system and the detector.

The surface potential distribution measuring apparatus according to any one of claims 2 to 5, wherein the two-dimensional shield member can be “held by a lens barrel of a charged particle optical system” ( claim 6 ).
The surface potential distribution measuring apparatus according to any one of claims 2 to 6 , as described above, "measures the surface potential distribution by an electrostatic latent image formed on a photoconductive photosensitive member as a measurement object". It is possible to provide a charging means for uniformly charging a photoconductive sample as a measurement sample, and an exposure means for performing exposure by irradiating a light image to the uniformly charged photoconductive sample.

  As described above, in the present invention, since a two-dimensional shield member is interposed between the optical axis of the charged particle optical system and the capturing unit of the detecting unit, the detecting unit for the charged particle to be scanned (applied to the capturing unit). The effect of the electric field due to the pull-in voltage is effectively shielded or reduced. For this reason, it is possible to effectively prevent or reduce the trajectory of the incident charged particles from being bent and deviating from the “scanning position from the target position” or the speed of the charged particles changing due to the influence of the detector.

Embodiments of the invention will be described below.
The form shown in FIG. 1 is an “apparatus using an electron beam as a charged particle beam”.
This surface potential distribution measuring device is a device for measuring the surface potential distribution of the measurement sample 0. Each part of the apparatus is housed in a hermetic casing 27, and the inside of the hermetic casing 27 can be decompressed to a “substantial vacuum state” by a suction means 29. In FIG. 1A, it is assumed that a surface potential distribution is formed in the measurement sample 0 and the inside of the sealed casing 27 is depressurized.

The electron beam that scans the measurement sample 0 is emitted from the electron gun 10, passes through the beam monitor 13, passes through the aperture 17 and the beam blanker 18 while being focused by the condenser lens 15, and is two-dimensionally scanned by the scanning lens 19 using a deflection coil. To be biased. The deflected electron beam is focused toward the surface of the measurement sample 0 by the objective lens 21.

  The beam monitor 13 is for monitoring the intensity of the electron beam emitted from the electron gun 10, and the aperture 17 is used to determine the “current density (number of irradiated particles per unit time) of the electron beam irradiated to the measurement sample 0. The beam blanker 18 is for “turning the electron beam on and off”. Each unit arranged in the electron beam irradiation path from the electron gun 10 to the measurement sample 0 is connected to a driving power source (not shown), and these are controlled by a control means such as a computer (not shown).

  The electron gun 10, beam monitor 13, condenser lens 15, aperture 17, beam blanker 18, scanning lens 19, objective lens 21 and driving power source (not shown) constitute a “charged particle optical system”.

As described above, the electron beam deflected two-dimensionally by the scanning lens 19 scans the surface of the measurement sample 0 two-dimensionally.
When an ion beam is used as the charged particle beam, a “liquid metal ion gun” or the like may be used instead of the electron gun 10.

Although details will be described later, the measurement sample 0 having a surface potential distribution “has a negative charge on the surface or in the vicinity of the surface (a shallow internal region in the vicinity of the surface)” and has a surface potential distribution corresponding to the charged state. The measurement sample 0 is planarly supported by the support portion 23 as shown in the figure. The support portion 23 is grounded by a “conductive plate-like member”. The surface potential distribution of the measurement sample 0 forms an electric field that causes a Coulomb repulsive force to act on each electron of the electron beam in the space on the sample surface side. The support part 23 is a sample holding means for “holding the surface having the surface potential of the measurement sample 0 having the surface potential distribution as the surface to be scanned”.

Here, the principle of the surface potential distribution will be described.
As shown in FIG. 1B, the z-direction is defined as “the direction of the normal line standing on the surface of the measurement sample 0”, and the x-axis and y-axis are taken in parallel to the sample surface and the (x, y) coordinates are set to The surface is set (the y direction is a direction orthogonal to the drawing).
At this time, when “two-dimensionally scanned region: S” is represented by S (x, y) using two-dimensional coordinates, for example, 0 mm ≦ x ≦ 1 mm and 0 mm ≦ y ≦ 1 mm. . The surface potential distribution formed in this region: S (x, y) is Vp (x, y) (<0).
Assuming that the time from the start to the end of the two-dimensional scanning of the measurement sample 0 by the electron beam is T ₀ ≦ T ≦ _TF , the time when scanning is performed: T is the scanning region: S (x , Y) corresponds to each scanning position in 1: 1.

  FIG. 1B illustrates the vicinity of the measurement sample 0 in an explanatory manner. The “scanned area: S” in the measurement sample 0 can be “changed in size” by setting the magnification of the scanning lens 19, for example, from a low magnification of about 5 mm × 5 mm to a high magnification of about 1 μm × 1 μm. Can be observed at various magnifications.

  The velocity of the electron beam emitted from the electron gun 10 is “v”, and the components in the x, y, and z directions are “vx, vy, vz”. Strictly speaking, the velocity components of each electron in the electron beam: vx, vy, and vz change with the scanning of the electron beam, but for the sake of simplicity of explanation, vx = vy = 0 and vz = v.

  The “acceleration voltage” of the electron beam in the electron gun 10 is Vb, and the surface potential of the measurement sample is Vp (<0) as described above. The electrons in the electron beam initially move toward the measurement sample 0 at a speed corresponding to the acceleration voltage: Vb. However, as the sample surface approaches, the electron beam is repelled and decelerated by the Coulomb force due to the negatively charged state of the measurement sample. The

  FIG. 2B illustrates the case where the electron acceleration voltage Vb is “Vb> −Vp with respect to −Vp”. In this case, although the electrons are gradually decelerated, they reach the measurement sample 0. FIG. 2A illustrates the case where the acceleration voltage of electrons: Vb is “Vb <−Vp with respect to −Vp”. In this case, the velocity of electrons in the electron beam gradually decreases due to the repulsive Coulomb force of the measurement sample, and the velocity: v becomes 0 before reaching the measurement sample 0, and then the velocity: v (on the sample surface) due to the action of the repulsive Coulomb force. The direction of the component in the normal direction: vz) is reversed. Thus, the electron whose speed: v is reversed is the above-mentioned “inverted charged particle”.

  Such inverted charged particles are captured by the detecting means 25 shown in FIG. As shown in FIG. 1B, a “drawing voltage” having a polarity (positive polarity) opposite to that of electrons is applied to the detection means 25 (capture unit) from a power source EA. (Electronic) "is captured. The number of captured electrons is amplified and converted into a detection signal corresponding to the intensity (number of electrons captured per unit time).

  Since the electrons captured by the detection means 25 are repelled by the surface potential distribution of the measurement sample 0: Vp (x, y), the intensity of the electrons captured at time: T: F (T) is Time: Surface potential distribution with T as a parameter: Corresponding to Vp {x (T), y (T)}. In the case described above, the inverted charged particles captured by the detection means 25 are electrons satisfying Vb <−Vp (x, y). Therefore, the measurement result is “surface potential distribution of measurement sample 0: Vp ( x, y) is obtained by dividing the acceleration voltage in the electron gun 10 by a region of 2 minutes using Vb as a measurement threshold value.

  That is, in the scanning region: S (x, y), the “region where the inverted charged particles are captured” is a region of the surface potential distribution: −Vp (x, y)> Vb, and the inverted charged particles are not captured. The region is a region of surface potential distribution: −Vp (x, y) <Vb.

  Therefore, by sampling the detection signal obtained from the detection means 25 at an appropriate interval, it is possible to specify for each “small area corresponding to sampling” whether −Vp (x, y) is larger or smaller than the measurement threshold value Vb. . Such an operation is executed by “measuring means realized by a CPU or a microcomputer”.

  In the above, the case of the “electron beam” as the charged particle beam has been described. However, in the above example, if the “liquid metal ion gun” is used instead of the electron gun 10, the measurement using the ion beam as the charged particle beam is performed. It can be carried out. When the surface potential distribution of the measurement sample 0: Vp (x, y)> 0, “plus ions such as gallium” or protons may be used as the charged particles of the charged particle beam.

In general, when the maximum value of the absolute value of the surface potential distribution: Vp (x, y) in the measurement sample 0 is Max | V (x, y) |, the acceleration voltage: Vb is
Vb <Max | V (x, y) |
By scanning the charged particle beam under the following conditions, it is possible to specify the “surface magnitude: Vp (x, y)“ measurement threshold: magnitude relationship with respect to Vb ”.

  The surface potential distribution shown in FIG. 3: Vp (x, y) (<0, the surface potential distribution when the surface on the support portion 23 supporting the measurement sample 0 is in the grounded state) is the center portion (x = 0). The potential increases in the minus direction as the distance from the center increases, and is approximately −830 V in the peripheral region at a distance of 0.1 mm or more from the center.

  With respect to such a surface potential distribution: Vp (x, y), an area where −Vp (x, y)> 600 V is measured when the acceleration voltage: Vb is 600 V and 740 V: S600, and −Vp Region (x, y)> 750V: S750 is shown. Outside these regions S600 and S750, most of the electrons of the charged particle beam (electron beam) reach the measurement sample, and the number of inverted charged particles is small, so the number of electrons detected by the detection means is very small.

  If measurement is performed by switching the acceleration voltage: Vb to a plurality of stages, the surface potential distribution: Vp (x, y) can be obtained as “acceleration voltage for each measurement (that is, threshold for measurement): a region that is rounded for each Vb”. Therefore, by using these, the “surface potential distribution: the overall state of Vp (x, y)” can be specified by calculation. Of course, the finer the step of switching the acceleration voltage: Vb and the greater the number of measurements, the more accurate measurement becomes possible. It is possible to easily obtain the “surface potential distribution profile” and the like by calculation by the measuring means.

  When the acceleration voltage: -Vb is not necessarily equal to the threshold value due to the influence of the surrounding electric field environment, the electrostatic field environment can be calculated in advance and corrected based on it.

  The detection means 25 generates “scintillation light” by trapped electrons by a scintillator, and amplifies the scintillation light with an electron multiplier or the like to obtain a detection signal.

As shown in FIG. 1, a two-dimensional shield member 26 is disposed between the optical axis of the charged particle optical system and the capture unit of the detection means 25. In this embodiment, the shield member 26 is a planar “grid mesh” as shown in FIG. 4, and is arranged in a “partition” shape between the capture portion of the detection means 25 and the optical axis of the charged particle optical system. To ground potential.

  As shown in FIG. 4, the grid mesh 26 is composed of an outer frame 26A made of a conductor and conductive thin wire portions 26B stretched in a lattice shape on the inside thereof, and the outer frame 26A is grounded to ground the conductive thin wire portions 26B. The stretched surface becomes a two-dimensional substantially equipotential surface substantially equal to the ground potential.

  The grid mesh 26 at a substantially ground potential is interposed between the optical axis of the charged particle optical system and the capture unit of the detection unit 25, so that the influence of the electric field due to the drawing voltage applied to the capture unit of the detection unit 25 is achieved. Are shielded against the “charged particle beam incident on the measurement sample 0”, so that the charged particle beam is incident on the “target position” of the measurement sample with high accuracy without being deviated from its trajectory.

  On the other hand, the inverted charged particles are attracted to the ground potential of the grid mesh 26 and travel toward the grid mesh 26 and pass through the opening (between the conductive thin wire portions). Head.

As described above, the aperture ratio of the grid mesh 26 is preferably 25% or more and about 90% or less. However, when the pitch of the conductive thin wire portions 26B is 1 mm, the width of the conductive thin wires is 0.5 mm or less. Opening ratio: 25% or more can be realized. If the width of the thin conductive wire is 0.1 mm at a pitch of 1 mm, an aperture ratio of about 80% can be realized .

  As the material constituting the grid mesh 26, a conductive material can be used as appropriate. However, by using a nonmagnetic material such as aluminum or copper, or a weak magnetic material such as SUS, the influence of the magnetic field is suppressed as much as possible. I can do it.

The surface potential distribution measuring apparatus described above includes a sample holding means 23 that holds a surface having a surface potential of a measurement sample 0 having a surface potential distribution as a scanned surface, and a measurement sample 0 held by the sample holding means. A charged particle optical system 10 to 21 that scans a surface to be scanned with a charged particle beam, and the charged particle beam that captures charged particles whose components in the normal direction of the sample surface of the incident velocity vector are inverted, Detection means 25 for detecting the intensity corresponding to the position on the sample surface, measurement means (not shown) for calculating the surface potential of the measurement sample based on the detection result by the detection means, and light from the charged particle optical system A two-dimensional shield member 26 is disposed between the shaft and the capturing part of the detection means and allows charged particles to pass therethrough at substantially the same potential as the ground potential .

With this apparatus, a charged particle beam is scanned by a charged particle optical system on a measurement sample 0 having a surface potential distribution, and among charged particles incident on the sample surface, the normal line on the sample surface of the incident velocity vector. In the surface potential distribution measurement method for obtaining a detection signal by capturing and detecting charged particles whose direction components are reversed by the detection means 25, the ground potential is approximately equipotential between the optical axis of the charged particle optical system and the detector. Then, a surface potential distribution measuring method is performed in which a two-dimensional shield member 26 that allows charged particles to pass through is interposed.

FIG. 5 shows only the main part of the embodiment .
In this embodiment, the sample holding means 230 for supporting the measurement sample 0 in a plane has a three-layer structure in which the dielectric layer 232 is sandwiched between the conductive layers 231 and 233, and the conductive layer 233 is grounded and conductive. A bias voltage is applied to the layer 231 from the variable DC power supply EB.

  When a bias voltage is applied to the conductive layer 231, the potential distribution on the surface side of the sample 0 is obtained by superimposing a “uniform bias potential” on the surface potential distribution of the measurement sample 0. In the case of using an electron beam as the charged particle beam, the electron beam acceleration voltage: Vb is sufficiently increased in advance, and the polarity of the bias voltage applied to the conductive layer 231 is set to have a negative polarity so as to be incident as an electron beam. A bias potential that repels electrons is formed.

When the bias voltage: Vg is applied, the surface potential distribution on the measurement sample surface: Vp (x, y) is
Vp (x, y) = Vs (x, y) + Vg
It becomes.

As in the case of FIG. 1, if the sample holding means 23 supporting the back side of the measurement sample 0 is grounded, Vg = 0 and Vp (x, y) = Vs (x, y) It is.
As shown in FIG. 5, when a bias voltage: Vg is applied, for example, when Vg = −1000 V is applied, the surface potential at the center (x = 0) is approximately −1520 V in the example of the potential distribution shown in FIG. (= −520V−1000V), and in a portion away from the center by 0.1 mm, it becomes approximately −1830V, and the surface potential is lowered by 1000V as a whole.

The condition for “the normal component of the incident velocity vector on the sample surface to be reversed” of the charged particle beam incident on the measurement sample is determined by acceleration voltage: Vb and bias potential: Vg.
Vth =-(Vb + Vg)
In this case, Vb = 1.6 kV and Vg = −1000 V can be obtained in order to obtain the same detection signal as in the region of S600 in FIG. 3, and Vb = 1.6V in order to obtain the same detection signal as in the region of S750. It may be 1.75 kV and Vg = −1000 V, or Vb = 1.6 kV and Vg = −850 V.

  In this way, by having voltage application means (sample holding means 230 and variable DC power supply EB) that changes the surface potential distribution of the measurement sample 0 in a bias manner, the above-mentioned Vth can be changed even when the acceleration voltage Vb is fixed. It is possible to measure the surface potential distribution. When changing the voltage applied by the voltage applying means, the inversion threshold value Vth can be set “more finely” by finely setting the change step of the applied potential. Further, measurement is possible even when the surface potential distribution is “a distribution that changes from plus to minus”.

When the surface potential distribution in the measurement sample is “potential distribution by the conductor pattern”, a method of applying a potential bias to the voltage itself applied to the conductor may be used in addition to the method of applying a voltage to the back surface. When the charged particle beam is positively charged, the inversion threshold: Vth is
Vth = Vb-Vg
It becomes.

FIG. 6 shows only one part of one form of the surface potential distribution measuring apparatus . Those which are not likely to be confused are given the same reference numerals as in FIG.

In this embodiment , the two-dimensional shield member is cylindrical and is provided so as to surround the optical axis of the charged particle optical system. That is, the two-dimensional shield member is a cylindrical grid mesh 26A (formed so as to be wound in a cylindrical shape as shown in FIG. 4) 26A, and is shown near the sample around the optical axis of the charged particle optical system. It is arranged as follows. The electric field exerted by the pull-in voltage of the detection means 25 affects not only the area where the sample area to be scanned and the capture part of the detection means are connected, but also the periphery thereof, and therefore surrounds the entire optical axis of the charged particle optical system. When covered with the cylindrical grid mesh 26A as described above, the action of the electric field due to the pull-in voltage can be effectively shielded in the enclosed region.

  By using the cylindrical grid mesh 26A in this way, it has been experimentally confirmed that the “shift of the locus of incident charged particles (electrons)” when this is not used can be reduced to 1/5 or less. .

FIG. 7 shows the main part of one form of the surface potential distribution measuring apparatus , and those which are not likely to be confused are given the same reference numerals when placed in FIG.

In this embodiment, the two-dimensional shield member 26B1 is a substantially hemispherical grid mesh, and is disposed so as to cover the sample surface of the measurement sample 0. In the case of this embodiment, the influence of the pull-in voltage of the detection means 25 on the charged particles (electrons) incident on the surface of the measurement sample is reduced, and the reverse charged particles that have gone out of the grid mesh 26B1 are collected by the detection means 25. The efficiency is higher than the embodiment of FIG.

  In this embodiment, in addition to the grid mesh 26B1, a second grid mesh 26B2 slightly larger than the grid mesh 26B1 is provided outside the grid mesh 26B1 so that an appropriate voltage can be applied from the DC voltage power supply EC. Yes. For example, when the grid mesh 26B1 is grounded and −100V is applied to the outer grid mesh 26B2 by the DC voltage power supply EC, the inverted charged particles easily reach the detection means 25, and the voltage applied to the grid mesh 26B2 is increased. When the voltage is applied, the inverted charged particles are difficult to reach the detection means 26, and thus the outer grid mesh 26B2 can have the function of “energy filter”.

FIG. 8 shows a main part of one form of the surface potential distribution measuring apparatus , and those which are not likely to be confused are given the same reference numerals when placed in FIG.

In this embodiment, a two-dimensional shield member 26C is held by a lens barrel 21C of a charged particle optical system. The two-dimensional shield member 26 </ b > C is a “cylinder made of a conductive material”, is provided so as to surround a space region through which a charged particle beam to be scanned passes, and is grounded.

When such a shield member 26C is used, the distance between the objective lens 21 of the charged particle optical system and the measurement sample 0 is as large as about 10 mm or more, and the particle trajectory region subjected to the effect of the electric field due to the pull-in voltage is large. In addition, the influence of the voltage (particle orbital variation and velocity variation) can be effectively reduced. In this embodiment, a grid mesh 26 is also provided in addition to the two-dimensional shield member 26C . Thus, a plurality of two-dimensional shield members can be used. It goes without saying that the grid mesh 26 can also be held in the lens barrel 21C.

That is, in the surface potential distribution measuring apparatus, what is held in the lens barrel of the charged particle optical system can be the shield surface member itself according to claims 3 to 5 , or a shield separate from these members. It can also be a surface member.

FIG. 9 shows a main part of one embodiment of the surface potential distribution measuring apparatus according to claim 2 . Those that are not likely to be confused are given the same reference numerals as in FIG.
The surface potential distribution measuring apparatus in FIG. 9 performs measurement using “surface potential distribution by an electrostatic latent image formed on a photoconductive photoreceptor” as a measurement target, and measurement sample 0 is “photoconductive sample”. is there.
Further, the holding means 230 for holding the measurement sample is the “three-layer structure” described with reference to FIGS.

  This surface potential distribution measuring apparatus includes a “charging unit” that uniformly charges a measurement sample 0 that is a photoconductive sample, and an “exposure unit” that performs exposure by irradiating a light image onto the uniformly charged photoconductive sample. It has.

  In this embodiment, a charged particle optical system is used as a charging means for uniformly charging the measurement sample 0. The “charged particle optical system” will be described by taking “an electron beam using system” as an example.

  The measurement sample 0 is two-dimensionally scanned with the electron beam to charge the measurement sample 0 uniformly. At this time, the acceleration voltage Vb of the electron beam is set to an acceleration voltage higher than “secondary electron emission ratio: acceleration voltage at which δ becomes 1”. In this case, since the amount of incident electrons is “exceeding the amount of secondary electrons emitted”, electrons are accumulated in the measurement sample, and the measurement sample is uniformly charged negatively.

  By appropriately adjusting the acceleration voltage: Vb and the irradiation time, the measurement sample can be charged to a desired surface potential. As charging means, apart from the above, contact charging, injection charging, ion irradiation charging, etc. can be used.

  The “exposure means” includes a semiconductor laser 90 as a light source, a collimating lens 91, an aperture 92, an image pattern 93, mirrors M 1 and M 2, and an imaging lens 94. When the semiconductor laser 90 is turned on, the emitted laser light is converted into a parallel light beam by the collimator lens 91 and irradiates a translucent image pattern 93 through the aperture 92.

  The light that has passed through the image pattern 93 is reflected by the mirror M 1, passes through the imaging lens 94, is reflected by the mirror M 2, and irradiates the measurement sample 0, and forms an optical image of the image pattern 92 on the surface of the measurement sample 0. To do. The measurement sample 0 is exposed by this optical image, and an electrostatic latent image corresponding to the image pattern 92 is formed on the measurement sample 0. This electrostatic latent image is a surface potential distribution as a measurement target, and is measured as described above.

FIG. 10 shows another embodiment of the surface potential distribution measuring apparatus , which is considered not to be confused with the same reference numerals as those in FIG.
Since the electrostatic latent image formed on the photoconductive photoconductor has a “measurable time” of several tens of seconds due to dark decay, the measurement sample 0 is a photoconductive photoconductor (photoconductive sample). ), The “electrostatic latent image forming means” is disposed in the sealed casing.

  10, the electron gun 10, beam monitor 13, condenser lens 15, aperture 17, beam blanker 18, scanning lens 19, objective lens 21, and support portion 23 are the same as those in the embodiment shown in FIG. Therefore, the description relating to FIG. 1 is incorporated.

  The electron gun 10, the beam monitor 13, the condenser lens 15, the aperture 17, the beam blanker 18, the scanning lens 19, and the objective lens 21 constitute a charged particle scanning system 11A, and each component of the charged particle scanning system 11A includes: The charged particle beam control unit 31 is controlled, and the charged particle scanning system 11A and the charged particle beam control unit 31 constitute a “charged particle optical system”. The measurement sample 0 is a “photoconductive photoreceptor”, and is supported in a planar manner on the upper surface of the grounded conductive support portion 23.

  Reference numeral 34 denotes a semiconductor laser as a light source, reference numeral 35 denotes a collimating lens, reference numeral 36 denotes an aperture, reference numeral 37 denotes a mask, and reference numerals 38, 39, and 40 denote lenses constituting an “imaging lens”. These constitute a “light image irradiating unit” and constitute an “exposure unit” together with the semiconductor laser control unit 33 and a light image irradiation control unit (not shown).

  A light image irradiation control unit (not shown) can perform focusing and magnification conversion by adjusting the positional relationship between the imaging lenses 38, 39, and 40 and the mask 37.

  Reference numeral 25 denotes a detection means, reference numeral 260 denotes a signal processing unit, reference numeral 260A denotes a monitor, and reference numeral 280 denotes an output device such as a printer. The signal processor 260, the monitor 260A, and the output device 280 constitute “measurement means”. Reference numeral 290 denotes a light-emitting element for static elimination.

  Each of the above parts is disposed in the casing 30 as shown in the figure, and the inside of the casing can be highly decompressed by the suction means 32. That is, the casing 30 has a function as a “vacuum chamber”. The entire apparatus is controlled by a host computer 50 (control means, which controls each part of the apparatus comprehensively). The charged particle beam control unit 31 and the signal processing unit 260 described above can be set as “part of the function” in the host computer 50.

  In the state shown in FIG. 10, the measurement sample 0 whose surface is uniformly charged is placed on the support portion 23, and the inside of the casing 30 is highly decompressed. In this state, the semiconductor laser 34 is turned on and an optical image of the mask 37 is formed on the uniformly charged surface of the measurement sample 0. By this exposure, a pattern of an electrostatic latent image corresponding to the irradiated light image is formed on the measurement sample 0.

  The surface on which the pattern of the electrostatic latent image is formed is scanned two-dimensionally with an electron beam, and as described above, the inverted charged particles (electrons) repelled by the surface potential of the measurement sample 0 are grounded. It is captured by the detection means 25 through the grid mesh 26, and its intensity is detected and converted into an electrical signal.

  As in the embodiment described above, the acceleration voltage: Vb is switched, and the measurement is repeated each time the switching is performed, and the “surface potential distribution profile” of the electrostatic latent image is controlled by the host computer 50. The signal processing unit 260 can calculate and output to the output device 280.

  In order to form a pattern of an electrostatic latent image on the measurement sample 0, which is a photoconductive sample, it is necessary to uniformly charge the surface prior to exposure with the light image. Similarly to the embodiment described above, the two-dimensional scanning of the electron beam is used.

  FIG. 11 shows another embodiment of a surface potential distribution measuring apparatus that measures an electrostatic latent image formed on a photoconductive photoreceptor. In order to avoid confusion, the same reference numerals as those in FIGS. 1 and 10 are assigned to those which are not likely to be confused.

  The electron gun 10, the aperture 13, the condenser lens 15, the aperture 17, the beam blanker 18, the scanning lens 19, and the objective lens 21 constituting the charged particle scanning system 11A have the same configuration as that shown in FIGS. The grid 26, the detection means 25, the signal processing unit (not shown), and the like are the same as those described above with reference to FIG. Reference numeral 300 denotes a casing.

  A measurement sample 01, which is a photoconductive photoconductor, is formed in a drum shape, which is a general form of a photoconductive photoconductor, and is rotated at a constant speed in the direction of the arrow (counterclockwise) by a driving unit (not shown). After the measurement sample 01 is set in the casing 300, the inside of the casing 300 is highly decompressed by suction means (not shown).

  The charging portion denoted by reference numeral 42 is, for example, a contact-type charging means such as a charging brush or a charging roller, and uniformly charges the measurement sample 01 in the casing under reduced pressure. At this time, the measurement sample 01 is rotated at a constant speed in the direction of the arrow (counterclockwise). Of course, as in the example described with reference to FIG. 10, the measurement sample 01 can be charged by charging using an electron beam.

  The “exposure section” denoted by reference numeral 41 performs exposure by irradiating the uniformly charged sample 01 with a light image. As the exposure unit 41, for example, an “optical scanning device” that is widely known in connection with an optical printer or the like can be used, and “optical image irradiation” can be performed by optical writing. When “irradiation of an optical image” is performed by optical writing in this way, the pattern form of the electrostatic latent image formed by writing can be arbitrarily changed, and a desired pattern (area pattern or line) of the electrostatic latent image can be changed. Pattern) can be easily formed.

  When an optical scanning device is used as the exposure unit 41, if the optical scanning device is large and difficult to install in the casing 300, the optical scanning device is provided outside the casing 300, and the casing 300 is A transparent window part may be provided, and the photoconductive sample 01 may be irradiated with a light image from the outside through this window part.

  The scanning of the electron beam by the charged particle scanning system 11A may be performed by deflecting the electron beam two-dimensionally as in the embodiment of FIGS. 1 and 10, but the measurement sample 01 is at a constant speed in the direction of the arrow. Since scanning is performed while rotating, the electron beam can be deflected one-dimensionally in a direction orthogonal to the drawing, and two-dimensional scanning can be realized by combining this deflection and rotation of the measurement sample 01.

  The photoconductive sample as a measurement sample can be a known appropriate one, and has a structure in which a single photoconductive layer is provided on a conductive substrate, or a charge generation layer on a conductive support. And a “function-separated type photoreceptor” in which a charge transport layer is formed.

  To add a little, a scanning electron microscope or the like has a “measurement method for detecting reflected electrons”, and this reflected electron is generally defined as “electron beam to be scanned and the interaction between the sample material” and incident electrons. The electrons are scattered behind the sample and jump out of the surface of the sample. The energy of the reflected electrons is comparable to the energy of the incident electrons, and the intensity of the reflected electrons is said to increase as the atomic number of the sample increases. This is a measurement method for inspecting the difference in the composition of the sample and unevenness.

  As described above, the “inverted charged particle” in the present invention is a “charged particle that is inverted before reaching the sample surface” under the influence of the potential distribution on the surface of the measurement sample. The measurement method according to the present invention for measuring the surface potential distribution by detecting the difference is completely different from the measurement method for detecting the reflected electrons.

It is a figure for demonstrating one form of a surface potential distribution measuring apparatus . It is a figure for demonstrating inversion of the charged particle by surface potential distribution. It is a figure for demonstrating the example of the measured surface potential distribution. It is a figure for demonstrating the grid mesh as an example of a two-dimensional shield member . It is a figure which shows the principal part of another form of a surface potential distribution measuring apparatus . It is a figure which shows the principal part of the other form of a surface potential distribution measuring apparatus . It is a figure which shows the principal part of the other form of a surface potential distribution measuring apparatus . It is a figure which shows the principal part of the other form of a surface potential distribution measuring apparatus . It is a figure for demonstrating embodiment which measures the surface potential distribution of the electrostatic ray image of a photoconductive sample. It is a figure for demonstrating another form of implementation which measures the surface potential distribution of the electrostatic ray image of a photoconductive sample. It is a figure for demonstrating the form which measures the surface potential distribution of the electrostatic ray image of a photoconductive sample.

Explanation of symbols

0 Measurement sample
10 electron gun 21 objective lens 25 detection means

Claims (6)

A charged particle beam is scanned by a charged particle optical system on a measurement sample having a surface potential distribution, and among the charged particles incident on the sample surface, the component in the normal direction of the sample surface of the incident velocity vector is inverted. A method for measuring a surface potential distribution of a photoconductive sample as a measurement sample by a surface potential distribution measurement method for obtaining a detection signal by capturing and detecting charged particles by a detection means,
A holding means having a three-layer structure in which a dielectric layer is sandwiched between conductive layers, a photoconductive sample as a measurement sample is held flat on one conductive layer,
The photoconductive sample held by the holding means is irradiated with a charged particle beam scanned two-dimensionally by a charged particle optical system, so that the measurement sample is uniformly charged to a desired potential and then uniformly charged. The measured sample is exposed to a light image and exposed to form an electrostatic latent image that is a surface potential distribution as a measurement target.
Between the optical axis of the charged particle optical system and the capturing part of the detection means, a two-dimensional shield member that allows charged particles to pass through is interposed,
By applying a bias voltage to the conductive layer of the holding means, the surface potential distribution formed on the measurement sample is changed in a bias manner,
The charged particle optical system scans a charged particle beam for measurement, and detects charged particles whose normal velocity component on the measurement sample surface of the measurement sample surface is reversed among the charged particles incident on the measurement sample surface. A surface potential distribution measuring method, characterized in that a detection signal is obtained by capture detection by means. An apparatus for carrying out the surface potential distribution measuring method according to claim 1,
It has a three-layer structure in which a dielectric layer is sandwiched between conductive layers, and a photoconductive sample as a measurement sample is held on one conductive layer in a plane with the surface forming the surface potential distribution as the surface to be scanned. Sample holding means,
Charging means for uniformly charging the measurement sample held by the sample holding means;
Exposure means for performing exposure by irradiation of a light image on a measurement sample uniformly charged by the charging means, and forming an electrostatic latent image as a surface potential distribution on the measurement sample;
A voltage applying means for applying a bias voltage to one of the conductive layers of the sample holding means to change the surface potential distribution formed on the measurement sample in a bias manner;
A charged particle optical system also serving as the charging unit, which scans the surface to be scanned of the measurement sample on which the electrostatic latent image is formed by the exposure unit with a charged particle beam; and
Detecting means for capturing charged particles in which the normal component of the incident velocity vector on the surface of the measurement sample is inverted among the charged particle beams to be scanned;
Measurement means for calculating the surface potential of the measurement sample based on the detection result by the detection means;
A surface potential distribution measuring apparatus comprising: a two-dimensional shield member that is disposed between an optical axis of the charged particle optical system and a capturing unit of the detecting means and allows the charged particles to pass therethrough. In the surface potential distribution measuring apparatus according to claim 2,
A surface potential distribution measuring apparatus, wherein the two-dimensional shield member is a grid mesh. In the surface potential distribution measuring apparatus according to claim 2 or 3,
  A surface potential distribution measuring apparatus, wherein the two-dimensional shield member is cylindrical and is provided so as to surround the optical axis of the charged particle optical system. In the surface potential distribution measuring apparatus according to claim 2 or 3,
A surface potential distribution measuring apparatus, wherein the two-dimensional shield member has a hemispherical shape and is arranged so as to cover a measurement sample .   In the surface potential distribution measuring apparatus according to any one of claims 2 to 5,
  A surface potential distribution measuring apparatus, wherein a two-dimensional shield member is held by a lens barrel of a charged particle optical system.

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