JP5089865B2 - Surface potential distribution measuring method and surface potential distribution measuring apparatus - Google Patents

Description

  The present invention relates to a surface potential distribution measuring method and a surface potential distribution measuring apparatus, and more particularly to a surface potential distribution measuring method using a charged particle beam and a surface potential distribution measuring apparatus suitable for carrying out the measuring method.

  In an electrophotographic image forming apparatus such as a laser printer or a digital copying machine, light from a light source modulated in accordance with image information is condensed on a photoconductor via a scanning optical system, and a predetermined direction ( In the main scanning direction, an electrostatic latent image is formed on the photosensitive member. Then, toner is attached to the electrostatic latent image, and the toner is transferred onto paper or the like to form an output image.

  The electrostatic latent image formed on the photoconductor greatly affects the quality of the output image. Therefore, various methods and apparatuses for evaluating the electrostatic latent image formed on the photoreceptor have been proposed. The evaluation result is fed back to the design of the image forming apparatus to improve the quality of the output image. For example, Patent Literature 1 and Patent Literature 2 propose a method of scanning a sample surface with an electron beam and observing an electrostatic latent image using secondary electrons emitted by the scanning.

  By the way, in recent years, digitization of image information has progressed rapidly, and the demand for further quality improvement of the output image of the image forming apparatus is increasing year by year. However, in the methods disclosed in Patent Document 1 and Patent Document 2, it is difficult to obtain an evaluation result of accuracy necessary to meet the request.

JP-A-3-29867 Japanese Patent Laid-Open No. 3-49143

  The present invention has been made under such circumstances, and a first object of the present invention is to provide a surface potential distribution measuring method capable of accurately measuring the surface potential distribution of an object.

  A second object of the present invention is to provide a surface potential distribution measuring apparatus capable of measuring the surface potential distribution of an object with high accuracy.

According to a first aspect of the present invention, there is provided a surface potential distribution measuring method in which a surface of an object on which a latent image is formed is scanned with a charged particle beam, and the distribution state of the surface potential of the object is measured. Detecting repulsive electrons repelled in the vicinity of the object surface before the charged particles reach the surface of the object while changing at least one of an acceleration voltage of a particle beam and an applied voltage applied to the object; Obtaining a plurality of contrast images based on detection results in the detecting step; measuring a diameter of the latent image for each of the plurality of contrast images based on a detection amount of the repelling electrons; wherein the step of based on the measurement result in the step of measuring determining the distribution of the surface potential of the object; only contains the accelerating voltage Vacc, the surface potential of the object relative to the incident electron Using the temporal Vp, the acceleration voltage is set so that both the | Vacc |> | Vp | region and the | Vacc | <| Vp | region exist simultaneously in the plurality of contrast images, and the latent image And measuring the diameter of the latent image from a boundary between the | Vacc |> | Vp | region and the | Vacc | <| Vp | region in the contrast image. This is a potential distribution measurement method.

According to this, it becomes possible to accurately measure the surface potential distribution of the object body.

According to a second aspect of the present invention, there is provided a surface potential distribution measuring apparatus for scanning a surface of a sample on which a latent image is formed with a charged particle beam and measuring a distribution state of the surface potential of the sample. A housing set at a predetermined position in the housing; a beam generator disposed in the housing and generating the charged particle beam; and disposed between the beam generator and the sample in the housing. An optical system including a scanning lens for deflecting a charged particle beam from the beam generating device and an objective lens for focusing the charged particle beam from the scanning lens on the surface of the sample; A detector for detecting repelled electrons repelled in the vicinity of the sample surface before reaching the sample surface; and changing the acceleration voltage of the charged particle beam through the beam generator A child beam is focused on the sample surface, a plurality of contrast images are acquired based on a plurality of detection results of the detection device at different acceleration voltages, and the plurality of contrast images are determined based on the detection amount of the repulsive electrons. A processing device that measures the diameter of each of the latent images and obtains a distribution state of the surface potential of the sample based on the measured diameters of the plurality of latent images. The processing device includes the acceleration voltage Vacc. The surface potential potential Vp of the object with respect to incident electrons is used so that both the | Vacc |> | Vp | region and | Vacc | <| Vp | region exist simultaneously in the plurality of contrast images. An acceleration voltage is set, and the diameter of the latent image is measured from the boundary between the | Vacc |> | Vp | region and the | Vacc | <| Vp | region in the contrast image. A surface potential distribution measuring apparatus according to claim.

According to this, it becomes possible to accurately measure the surface potential distribution of the specimen.

In this case, pre-Symbol processor, when changing the acceleration voltage, it is possible to further correct the shifting of the focal position of the charged particle beam to an optical axis direction.

In this case, pre-Symbol processor controls the voltage applied to the objective lens, can be to correct the deviation of the focusing position.

In the above SL each surface potential distribution measuring apparatus, pre-Symbol processor, when changing the acceleration voltage, it is possible to further compensate for variations in the scanning range of the charged particle beam at the sample surface.

In this case, pre-Symbol processor controls the voltage applied to the scanning lens can be to correct for variations in the scanning range.

In the above SL each surface potential distribution measuring apparatus, pre-Symbol processor may be a further based on the distribution state of the surface potential of the sample to calculate the profile of the surface potential distribution.

In the above SL each surface potential distribution measuring apparatus, it is possible to further comprises a power supply circuit for applying a bias voltage prior Symbol sample.

In the above SL each surface potential distribution measuring apparatus, prior Symbol sample can be assumed that a photoreceptor.

In the above SL each surface potential distribution measuring apparatus, before the sample and the beam generator in Kikatami body is disposed between a predetermined position to be set, the housing inner dividable gate valve into two areas Can be further provided.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a surface potential distribution measuring apparatus 100 according to an embodiment of the present invention.

  A surface potential distribution measuring apparatus 100 shown in FIG. 1 includes an electron gun 10, a housing 30, a condenser lens (electrostatic lens) 35, a beam blanking electrode 37, a gate valve 40, an aperture 51, a stigmeter 53, a scanning lens ( A deflection electrode) 55, an objective lens 57, a beam emission opening 61, a sample stage 81, a detector 91, a control system 3, a discharge system 83, a driving power source (not shown), and the like.

  The electron gun 10 emits an electron beam as a charged particle beam. Here, as shown in FIG. 2 as an example, the electron gun 10 is a field emission electron gun from which electrons are emitted from the emitter 11, and includes an extraction electrode 31 and an acceleration electrode 33.

  The extraction electrode 31 is disposed on the −Z side of the emitter 11, and a voltage (extraction voltage Vext) for generating a strong electric field in the emitter 11 is applied as shown in FIG. 2. Thereby, an electron beam is emitted from the tip of the emitter 11. In the present embodiment, it is assumed that an electron beam is emitted in the −Z direction.

  The acceleration electrode 33 is disposed on the −Z side of the extraction electrode 31 and is applied with a voltage (acceleration voltage Vacc) for applying desired energy to the electron beam emitted from the emitter 11.

  Returning to FIG. 1, the condenser lens 35 is disposed on the −Z side of the acceleration electrode 33 and narrows the electron beam.

  The beam blanking electrode 37 is disposed on the −Z side of the condenser lens 35 and turns on / off the electron beam.

  The gate valve 40 is disposed on the −Z side of the beam blanking electrode 37, and is a valve for dividing the inside of the housing 30 into a region including the electron gun 10 and a region including the sample table 81. The gate valve 40 can be opened only when necessary, such as during measurement. Hereinafter, for convenience, an area including the electron gun 10 is referred to as an “electron gun chamber”, and an area including the sample stage 81 is referred to as a “sample chamber”.

  The aperture 51 is arranged on the −Z side of the gate valve 40 and defines the beam diameter of the electron beam that has passed through the opening of the gate valve 40 when the gate valve 40 is in the open state.

  The stigmator 53 is disposed on the −Z side of the aperture 51 and corrects astigmatism.

  The scanning lens 55 is disposed on the −Z side of the stigmator 53 and deflects the electron beam from the stigmator 53.

  The objective lens 57 is disposed on the −Z side of the scanning lens 55 and focuses the electron beam from the scanning lens 55 on the surface of the sample 71 through the beam emission opening 61.

  Hereinafter, an optical system including the condenser lens 35, the beam blanking electrode 37, the aperture 51, the stigmator 53, the scanning lens 55, and the objective lens 57 is also referred to as an electron beam optical system 5.

  The sample table 81 has a sample 71 mounted thereon, and can move two-dimensionally in the XY plane by a drive mechanism (not shown). The sample stage 81 has conductivity and is grounded.

  The detector 91 is arranged in the vicinity of the sample 71 and detects electrons repelled in the vicinity of the surface of the sample 71 (hereinafter also referred to as “primary repulsive electrons”) before reaching the surface of the sample 71. As the detector 91, a scintillator, a photomultiplier tube, or the like is used. Further, a positive voltage (for example, 10 kV) is applied to the detector 91 in order to increase the detection sensitivity of primary repulsive electrons.

  The electron gun 10, the electron beam optical system 5, the sample table 81, and the detector 91 are accommodated in the housing 30.

  The exhaust system 83 is composed of a plurality of exhaust devices and places the inside of the housing 30 in a high vacuum state. Here, air is exhausted from below the housing 30 (−Z side), but is not limited thereto. Moreover, you may exhaust from several places.

  The control system 3 includes a computer, an input device, a display device, a printer device, and the like. The computer controls the electron gun 10, the electron beam optical system 5, the sample stage 81, and the exhaust system 83 according to a program installed in advance according to an instruction from the operator, and outputs the detector 91. A surface potential distribution of the sample 71 is obtained based on the signal. In the present embodiment, as an example, the surface potential of the sample 71 is assumed to be negative.

  Here, the relationship between the acceleration voltage of electrons irradiated on the sample 71 (hereinafter also referred to as “incident electrons”) and the surface potential of the sample 71 will be described with reference to FIGS. 3A and 3B. . 3A and 3B are simplified for the sake of clarity. Here, the surface potential potential at the position irradiated with the incident electrons on the surface of the sample 71 is Vp (<0). Therefore, it can be considered that the voltage Vp is applied between the point B and the surface of the sample 71. In FIGS. 3A and 3B, the potential is illustrated as electrical potential energy of the unit charge.

  The incident electrons are not affected by the surface potential potential Vp in a section where the potential potential is 0 (V) (between AB), and are directed toward the surface of the sample 71 at a speed corresponding to the acceleration voltage Vacc (−Z direction). Move to. After the point B, the incident electrons are affected by the surface potential potential Vp.

The influence of the surface potential potential Vp on the incident electrons is greatly different depending on the magnitude relationship between the acceleration voltage Vacc and the surface potential potential Vp.
(1) In the case of | Vacc |> | Vp | In this case, as shown in FIG. 3A, although the speed of the incident electrons is gradually reduced after passing the point B, most of the incident electrons are incident. The electrons reach the surface of the sample 71.
(2) In the case of | Vacc | <| Vp | In this case, as shown in FIG. 3 (B), the incident electrons are gradually decelerated after passing the point B, 0 before reaching. Then, starting from that point, the process proceeds in the direction away from the surface of the sample 71 (+ Z direction). That is, the velocity vector of the incident electrons in the Z-axis direction is reversed before reaching the surface of the sample 71, and the incident electrons return without reaching the surface of the sample 71. A part of the incident electrons that have not reached the surface of the sample 71 is set to be detected by the detector 91 as primary repulsive electrons.

  For example, “reflected electrons” used in a scanning electron microscope (SEM) is “scattered at the outermost surface of the sample or slightly inside, and some of the electrons escaped into space” (Japan) “Surface analysis dictionary” p235 edited by Surface Science Society, Kyoritsu Publishing Co., Ltd., published in 1986), “primary repulsion electron” in this specification is completely different.

  Therefore, the surface potential of the sample 71 can be measured by detecting the primary repulsive electrons with the detector 91 while changing the acceleration voltage of the incident electrons. That is, the surface potential distribution of the sample 71 can be measured by scanning the surface of the sample 71 with an electron beam and detecting primary repulsive electrons while changing the acceleration voltage Vacc during measurement.

  At this time, as shown in FIG. 4 (A) as an example, the acceleration voltage | Vacc | may be gradually increased from 0, and as shown in FIG. 4 (B) as an example, the acceleration voltage | Vacc | May be gradually increased from | V0 | to | V1 |. For example, as shown in FIG. 4C, the acceleration voltage | Vacc | is gradually decreased from | V1 | to | V0 |. May be. In FIGS. 4A to 4C, the acceleration voltage is shown to change continuously for convenience. However, since data processing takes time during actual measurement, the acceleration voltage is It changes in steps.

  For example, if the surface potential distribution of the sample 71 in the X-axis direction is Vp (x), V0 is a value set based on the minimum absolute value (Min | Vp (x) |) of the predicted absolute value of the surface potential. V1 is a value set based on the maximum absolute value (Max | Vp (x) |) of the predicted surface potential. Thus, as shown in FIG. 5 as an example, when Vacc = V0, many primary repulsive electrons are detected by the detector 91, but are hardly detected when Vacc = V1. If Min | Vp (x) | and Max | Vp (x) | cannot be predicted before measurement, they may be measured over a wide range.

  Normally, when the acceleration voltage Vacc changes, as shown in FIG. 6A to FIG. 6C as an example, when other parameters of the electron beam optical system 5 are constant, the optical axis direction (here, The focusing position of the electron beam with respect to (Z-axis direction) changes. When | Vacc | increases, the focusing position shifts in the −Z direction, and when | Vacc | decreases, the focusing position shifts in the + Z direction. Thereby, if the position of the sample surface is constant in the Z-axis direction, the resolution changes according to the acceleration voltage.

  By the way, the distance between the principal point of the objective lens 57 and the focusing position in the Z-axis direction, that is, the so-called working distance (referred to as WD) is shown in FIGS. 7A to 7C as an example. It changes in accordance with the applied voltage 57 (referred to as Vol). A substantially inversely proportional relationship is established between Vol and WD. Therefore, by changing the applied voltage Vol to the objective lens 57 in conjunction with the change of the acceleration voltage | Vacc |, the focusing position can be made substantially constant in the Z-axis direction. For example, when the acceleration voltage | Vacc | is gradually increased, the applied voltage Vol to the objective lens 57 may be gradually increased. Thereby, the focusing position is corrected, and a good detection result can be obtained even for an arbitrary acceleration voltage.

  As an example, as shown in FIGS. 8 and 9, when the acceleration voltage Vacc changes, the size of the scanning region on the sample surface changes. For example, when the magnification is constant, the size of the scanning region is substantially proportional to the reciprocal of the absolute value of the acceleration voltage. The vertical axis in FIGS. 8 and 9 is the length of the scanning region in the longitudinal direction.

  By the way, when the voltage applied to the scanning lens 55 (Vscan) changes, the deflection angle (θ) of the electron beam changes. This deflection angle θ has a relationship represented by the following equation (1) with the applied voltage Vscan and the acceleration voltage | Vacc |. Here, α is a coefficient.

  θ ≒ α × Vscan / | Vacc | (1)

  Therefore, by changing the applied voltage Vscan to the scanning lens 55 in conjunction with the change in the acceleration voltage | Vacc |, the variation in the size of the scanning region can be suppressed. For example, when the acceleration voltage | Vacc | is gradually increased, the applied voltage Vscan to the scanning lens 55 may be gradually increased.

  Next, a method for measuring the surface potential distribution of the sample 71 using the surface potential distribution measuring apparatus 100 configured as described above will be described with reference to FIGS. The flowchart in FIG. 10 is a process performed by an operator, and the flowchart in FIG. 11 is a process performed by a computer constituting the control system 3. Note that the gate valve 40 is in a closed state, the electron gun chamber is in a high vacuum state, and the sample chamber is in an atmospheric pressure state. Here, it is assumed that the surface of the sample 71 is scanned two-dimensionally.

  In the first step 401, the sample 71 on which a latent image is formed is placed on the sample table 81.

  In the next step 403, the exhaust system 83 is operated to bring the sample chamber into a high vacuum state.

  In the next step 405, the gate valve 40 is opened.

  In the next step 407, the computer constituting the control system 3 is instructed to measure the surface potential distribution. Then, the process performed by the operator ends.

  When the computer constituting the control system 3 receives an instruction to measure the surface potential distribution, in the first step 501, the computer sets an initial value 1 to a counter i in which the number of repetitions is stored.

  In the next step 503, the acceleration voltage Vacc is set to a preset initial value.

  In the next step 505, the applied voltage to the objective lens 57 is adjusted according to the acceleration voltage Vacc so that the working distance WD does not change.

  In the next step 507, the applied voltage to the scanning lens 55 is adjusted according to the acceleration voltage Vacc so that the size of the scanning region does not change.

  In the next step 509, a contrast image is captured (see FIGS. 12A and 12B). The white area in the contrast image is an area where the detection amount by the detector 91 is large, and the black area is an area where the detection amount by the detector 91 is small. The boundary between the white area and the black area is where the output signal of the detector 91 changes greatly. In the case of Vacc = −750V (see FIG. 12B), since the velocity of incident electrons is faster than in the case of Vacc = −600V (see FIG. 12A), the region where the incident electrons are inverted is reduced. And the black area is increasing.

  In the next step 511, binarization processing is performed on the contrast image to obtain binarized data. For example, when measuring the distribution state of the surface potential in the X-axis direction and the Y-axis direction, binarized data is acquired in the X-axis direction and the Y-axis direction.

  In the next step 513, the diameter of the latent image is calculated based on the binarized data. For example, when measuring the distribution state of the surface potential in the X-axis direction and the Y-axis direction, the diameter of the latent image is calculated in the X-axis direction and the Y-axis direction. The diameter of the latent image calculated here is stored in a memory (not shown) in association with the acceleration voltage Vacc.

  In the next step 515, it is determined whether or not the value of the counter i is equal to a preset value N (an integer of 2 or more). If the value of the counter i is not equal to N, the determination here is denied and the routine proceeds to step 517.

  In this step 517, 1 is added to the value of the counter i.

  In the next step 519, a preset increment (Δv) is added to the current acceleration voltage Vacc. Then, the process returns to step 505.

  Thereafter, the processes in steps 505 to 519 are repeated until the determination in step 515 is affirmed.

  When the value of the counter i becomes equal to N, the determination at step 515 is affirmed, and the routine proceeds to step 521.

  In this step 521, as shown in FIG. 12C as an example, based on the data indicating the surface potential distribution stored in the memory (the diameter of the latent image for each acceleration voltage Vacc), the surface potential distribution profile. Is calculated.

  In the next step 523, the calculation result is displayed on the display device. And the acquisition process of surface potential distribution is complete | finished. Note that FIG. 12C shows a potential distribution profile in the X-axis direction. In this case, the potential of the center (x = 0) of the latent image is about −520V, and the potential increases in the negative direction toward the outside. In the peripheral portion where | x | = 0.1 mm or more, about −830V. It turns out that it is about. Here, the operator can instruct the direction of the potential distribution profile displayed on the display device. It is also possible to display the potential distribution profile three-dimensionally. Furthermore, the calculation result can be printed by a printer.

  Further, the surface charge distribution of the sample 71 may be further obtained based on the measurement result according to the request of the operator.

  Here, an example of a method for forming an electrostatic latent image on the surface of the photoconductor when a photoconductor as a sample is used will be described. The photoreceptor is composed of a charge generation layer (referred to as CGL) and a charge transport layer (referred to as CTL) laminated on a conductive support. When the photoconductor is exposed with its surface charged, light is absorbed by a CGL charge generating material (referred to as CGM), and positive and negative charge carriers are generated. One of these carriers is injected into the CTL and the other into the conductive support by an electric field. Carriers injected into the CTL move to the surface of the CTL by an electric field in the CTL, and are erased by combining with the charge on the surface of the photoreceptor. Thereby, a charge distribution, that is, an electrostatic latent image is formed on the surface of the photoreceptor.

  As is clear from the above description, in the surface potential distribution measuring apparatus 100 according to the present embodiment, a processing apparatus is realized by a computer constituting the control system 3 and a program executed by the computer. It should be noted that at least a part of the processing device realized by processing according to a program by a computer may be configured by hardware, or all may be configured by hardware.

  In this embodiment, the electron gun 10 constitutes a beam generator, the electron beam optical system 5 constitutes an optical system, the detector 91 constitutes a detector, and the gate valve 40 constitutes a gate valve. Yes.

  And in the process performed by the computer which comprises the said control system 3, the surface potential distribution measuring method which concerns on this invention is implemented.

  As described above, according to the surface potential distribution measuring apparatus 100 according to the present embodiment, the electron beam is changed while changing the acceleration voltage of the electron beam (charged particle beam) emitted from the electron gun 10 (beam generating apparatus). Focusing on the surface of the sample 71, the primary repulsive electrons repelled in the vicinity of the surface of the sample 71 before reaching the surface of the sample 71 are detected by the detector 91 (detection device). Then, the distribution state of the surface potential of the sample 71 is obtained based on a plurality of detection results of the detector 91 at different acceleration voltages. In this case, since the primary repulsive electrons to be detected do not reach the sample surface, there is no possibility of being affected by the material and surface shape of the sample. Therefore, the surface potential distribution of the sample can be measured with high accuracy.

  Further, according to the present embodiment, since the gate valve 40 is provided, for example, even when gas is easily released from the sample or when the sample is frequently exchanged, the electron gun chamber is always kept at a high vacuum. And deterioration of the electron gun 10 can be suppressed.

  Further, according to the present embodiment, when changing the acceleration voltage, the applied voltage Vol to the objective lens 57 is simultaneously adjusted according to the acceleration voltage. Thereby, it can suppress that a converging position shifts | deviates regarding an optical axis direction. Therefore, the measurement accuracy of the surface potential distribution of the sample can be further improved.

  Further, according to the present embodiment, when changing the acceleration voltage, the applied voltage Vscan to the scanning lens 55 is simultaneously adjusted according to the acceleration voltage. Thereby, it can suppress that the magnitude | size of a scanning area | region changes. Therefore, the measurement accuracy of the surface potential distribution of the sample can be further improved.

  In the above embodiment, for example, when the expected absolute value of the surface potential is small, the acceleration voltage at the time of measuring the surface potential distribution becomes small, and the electron beam is correctly guided by the influence of disturbance such as an external magnetic field. It may be difficult to scan. In this case, as shown in FIG. 13 as an example, an electrode 85 may be formed on the sample table 81, and a power source 86 for applying a negative voltage (Vsub) to the electrode 85 may be further provided. As a result, the bias voltage Vsub is applied to the sample 71. For example, when the surface potential is 0 to −500 V, if Vsub = −500 V, the acceleration voltage when measuring the surface potential distribution is −500 V to −1000 V, and if Vsub = −2000 V, the surface potential is The acceleration voltage when measuring the distribution is −2000 V to −2500 V, and the influence of disturbance can be reduced. That is, the control of the electron beam is facilitated, the measurement accuracy is further improved, and the allowable range of the processing accuracy of each component constituting the electron beam optical system 5 can be widened.

  In addition, when the bias voltage Vsub is applied, the ratio between the minimum value and the maximum value of the acceleration voltage when measuring the surface potential distribution can be made smaller than when the bias voltage Vsub is not applied. As a result, the influence of the variation in the size of the scanning area and the variation in the focusing position of the electron beam due to the change in the acceleration voltage is relatively small with respect to the measurement result of the surface potential distribution. It is also possible to omit at least one of the correction of the scanning area.

  In the above embodiment, the case where the sample on which the latent image is formed is set in the surface potential distribution measuring apparatus has been described. However, the latent image may be formed on the sample in the surface potential distribution measuring apparatus. In this case, the surface potential distribution measuring device has a function of forming a latent image. Thereby, surface potential distribution measurement in real time becomes possible.

  As an example, FIG. 14 shows a surface potential distribution measuring apparatus 200 having a function of forming a latent image. In this surface potential distribution measuring apparatus 200, a pattern forming apparatus 220 that scans the surface of a sample with light to form a latent image pattern is added to the surface potential distribution measuring apparatus 100 in the above embodiment. In FIG. 14, the control system is omitted.

  The pattern forming apparatus 220 in FIG. 14 includes a semiconductor laser 201, a collimating lens 203, an aperture 205, and an imaging lens composed of three lenses (207, 209, 211). Further, in the vicinity of the sample 71, an LED 213 for discharging the surface of the sample is disposed. The pattern forming device 220 and the LED 213 are controlled by a control system (not shown).

A method for forming a latent image in the surface potential distribution measuring apparatus 200 will be briefly described.
(1) The LED 213 is turned on, and the sample surface is neutralized.
(2) The sample surface is uniformly charged using an electron beam emitted from the electron gun 10. Here, by setting the acceleration voltage to a voltage higher than the voltage at which the secondary electron emission ratio becomes 1, the amount of incident electrons exceeds the amount of emitted electrons, so that electrons are accumulated in the sample and charge up occurs. As a result, the sample is negatively charged. In addition, it can be charged to a desired potential by controlling the acceleration voltage and the irradiation time.
(3) The semiconductor laser 201 is caused to emit light. Laser light from the semiconductor laser 201 becomes substantially parallel light by the collimator lens 203, is made a prescribed beam diameter by the aperture 205, and is then condensed on the sample surface by the imaging lens. As a result, a latent image pattern is formed on the sample surface.

  Therefore, in the surface potential distribution measuring apparatus 200, the electron gun 10, the electron beam optical system 5, the pattern forming apparatus 220, and the LED 213 constitute a latent image forming apparatus.

  Moreover, although the said embodiment demonstrated the case where a sample was plate shape, this invention is not limited to this, For example, a sample may be cylindrical. In this case, as an example, a latent image forming device may be provided like a surface potential distribution measuring device 250 shown in FIG. The surface potential distribution measuring apparatus 250 is obtained by adding a latent image forming apparatus to the surface potential distribution measuring apparatus 100 in the above embodiment. The forming apparatus includes a charging unit 75, an exposure unit 76, and a charge removal unit 77. Here, the surface of the sample 71 is charged by the charging unit 75, and a latent image pattern is formed by the exposure unit 76. After the surface potential distribution is measured, the surface of the sample 71 is neutralized by the neutralization unit 77. In this case, if the sample is a photosensitive drum used in an electrophotographic image forming apparatus such as a laser printer or a digital copying machine, image formation is performed by feeding back the measurement result of the surface potential distribution to the design of the image forming apparatus. The process quality of each process is improved, and high image quality, high durability, high stability, and energy saving can be realized.

  In this case, as shown in FIG. 16 as an example, the exposure unit 76 includes a semiconductor laser 110, a collimating lens 111, an aperture 112, a cylinder lens 113, two folding mirrors (114, 118), a polygon mirror 115, And two scanning lenses (116, 117) may be provided.

  The semiconductor laser 110 emits laser light for exposure. The collimating lens 111 makes the laser light emitted from the semiconductor laser 110 substantially parallel light. The aperture 112 defines the beam diameter of the light that has passed through the collimating lens 111. Here, it is possible to generate an arbitrary beam diameter in the range of 20 μm to 200 μm by changing the size of the aperture 112. The cylinder lens 113 shapes the light transmitted through the aperture 112. The folding mirror 114 bends the optical path of the light from the cylinder lens 113 in the direction of the polygon mirror 115.

  The polygon mirror 115 has a plurality of deflection surfaces, and deflects light from the folding mirror 114 at a constant angular velocity within a predetermined angle range. The two scanning lenses (116, 117) convert the light deflected by the polygon mirror 115 into constant speed light. The folding mirror 118 bends the optical path of the light from the scanning lens 117 in the direction of the sample 71.

  The operation of the exposure unit 76 will be briefly described. The light emitted from the semiconductor laser 110 is once imaged near the deflection surface of the polygon mirror 115 via the collimating lens 111, the aperture 112, the cylinder lens 113, and the folding mirror 114. The polygon mirror 115 is rotated at a constant speed in the direction of the arrow in FIG. 16 by a polygon motor (not shown), and the light imaged in the vicinity of the deflection surface is deflected at a constant angular velocity with the rotation. The deflected light further passes through the two scanning lenses (116, 117), and is converted into light that scans the longitudinal direction of the folding mirror 118 at a constant angular range within a predetermined angular range. Then, this light is reflected by the folding mirror 118 and scans the surface of the sample 71. That is, the light spot moves in the generatrix direction of the sample 71. Thereby, an arbitrary latent image pattern including a line pattern can be formed in the bus line direction of the sample 71.

  Moreover, although the case where an electron beam was used as a charged particle beam was demonstrated in the said embodiment, not only this but an ion beam may be used. In this case, an ion gun is used instead of the electron gun. For example, when a gallium (Ga) liquid metal ion gun is used as the ion gun, the acceleration voltage is a positive voltage, and a bias voltage is applied to the sample 71 so that the surface potential is positive.

  In the above embodiment, the case where the surface potential of the sample is negative has been described. However, the surface potential of the sample may be positive. That is, the surface charge may be a positive charge. In this case, the sample may be irradiated with a positive ion beam such as gallium.

  Moreover, although the said embodiment demonstrated the case where the gate valve 40 was arrange | positioned at the -Z side of the beam blanking electrode 37, it is not limited to this. In short, the gate valve 40 only needs to be disposed between the electron gun 10 and the sample stage 81.

  In the above embodiment, the field emission type electron gun is used as the electron gun. However, the present invention is not limited to this, and a thermionic emission electron gun may be used. As shown in FIG. A Schottky emission (SE) type electron gun may be used. This Schottky emission type electron gun has an emitter 11, a suppressor electrode 12, a lead electrode 31, an acceleration electrode 33, and the like. If is a filament current, Ie is an emission current, and Vs is a suppressor voltage. The SE type electron gun is also called a hot cathode field emission electron gun.

  In the above embodiment, for example, in the case of preliminary measurement, when changing the acceleration voltage, at least one of the applied voltage Vol to the objective lens 57 and the applied voltage Vscan to the scanning lens 55 is not adjusted. Also good.

  As described above, the surface potential distribution measuring method of the present invention is suitable for measuring the surface potential distribution of an object with high accuracy. The surface potential distribution measuring apparatus of the present invention is suitable for measuring the surface potential distribution of a sample with high accuracy.

It is a figure for demonstrating the surface potential distribution measuring apparatus which concerns on one Embodiment of this invention. It is a figure for demonstrating the electron gun in FIG. 3A and 3B are diagrams for explaining the relationship between the acceleration voltage and the potential of the sample surface, respectively. FIG. 4A to FIG. 4C are diagrams for explaining a method of changing the acceleration voltage. It is a figure for demonstrating the relationship between an acceleration voltage and a primary repulsion electron. FIGS. 6A to 6C are diagrams for explaining the relationship between the acceleration voltage and the focusing position, respectively. FIGS. 7A to 7C are diagrams for explaining the relationship between the voltage applied to the objective lens and the working distance, respectively. It is a figure for demonstrating the relationship between the magnitude | size of the scanning area | region for every acceleration voltage, and a magnification. It is a figure for demonstrating the relationship between the magnitude | size of a scanning area | region, and the reciprocal number of the absolute value of an acceleration voltage. It is a flowchart (the 1) for demonstrating the measuring method of surface potential distribution. It is a flowchart (the 2) for demonstrating the measuring method of surface potential distribution. FIGS. 12A to 12C are diagrams for explaining the measurement results. It is a figure for demonstrating the bias voltage applied to a sample. It is a figure for demonstrating the modification 1 of the surface potential distribution measuring apparatus of FIG. It is a figure for demonstrating the modification 2 of the surface potential distribution measuring apparatus of FIG. It is a figure for demonstrating the exposure part in FIG. It is a figure for demonstrating the electron gun different from the electron gun of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Control system (processing apparatus), 5 ... Electron beam optical system (optical system), 10 ... Electron gun (beam generation apparatus), 30 ... Housing | casing, 40 ... Gate valve (gate valve), 55 ... Scan lens, 57 ... objective lens, 71 ... sample (object), 75 ... charging part (part of latent image forming apparatus), 76 ... exposure part (part of latent image forming apparatus), 77 ... neutralizing part (one of latent image forming apparatus) Part), 82 ... power supply (power supply circuit), 91 ... detector (detection device), 100 ... surface potential distribution measurement device, 200 ... surface potential distribution measurement device, 220 ... pattern formation device (part of latent image formation device) 250: Surface potential distribution measuring device.

Claims (14)

A surface potential distribution measuring method of scanning a surface of an object on which a latent image is formed with a charged particle beam and measuring a distribution state of the surface potential of the object,
Detecting repulsive electrons repelled in the vicinity of the object surface before the charged particles reach the surface of the object while changing at least one of an acceleration voltage of the charged particle beam and an applied voltage applied to the object When;
Obtaining a plurality of contrast images based on the detection results in the detecting step;
Measuring the diameter of the latent image for each of the plurality of contrast images based on the detection amount of the repelled electrons;
Look including a; on the basis of the measurement result in the step of measuring a step of determining the distribution of the surface potential of the object
Using the acceleration voltage Vacc and the surface potential potential Vp of the object with respect to incident electrons,
The acceleration voltage is set so that both the | Vacc |> | Vp | region and the | Vacc | <| Vp | region simultaneously exist in the plurality of contrast images,
In the step of measuring the diameter of the latent image, the diameter of the latent image is measured from a boundary between the | Vacc |> | Vp | region and the | Vacc | <| Vp | region in the contrast image. A surface potential distribution measuring method.   2. The surface potential distribution measuring method according to claim 1, wherein, in the measuring step, the amount of detection of the repelled electrons is binarized, and the diameter of the latent image is measured from a boundary between the two values.   3. The surface potential distribution measuring method according to claim 1, further comprising a step of obtaining a surface charge distribution state of the object based on a measurement result in the measuring step.   The surface potential distribution measuring method according to claim 1, wherein the object is a photoconductor. A surface potential distribution measuring device that scans a surface of a sample on which a latent image is formed with a charged particle beam and measures a distribution state of the surface potential of the sample,
A housing in which the sample is set at a predetermined position therein;
A beam generator disposed in the housing for generating the charged particle beam;
A scanning lens disposed between the beam generating device and the sample in the housing and deflecting the charged particle beam from the beam generating device, and an objective for focusing the charged particle beam from the scanning lens on the sample surface An optical system including a lens;
A detection device that is disposed in the vicinity of the sample in the housing and detects repulsive electrons repelled in the vicinity of the sample surface before reaching the sample surface;
The charged particle beam is focused on the sample surface while changing the acceleration voltage of the charged particle beam via the beam generator, and a plurality of contrast images are obtained based on a plurality of detection results of the detection device at different acceleration voltages. For each of the plurality of contrast images, the diameter of the latent image is measured based on the detected amount of the repulsive electrons, and the surface potential of the sample is measured based on the measured diameter of the plurality of latent images. a processing device for determining the distribution state; equipped with,
The processing apparatus uses the acceleration voltage Vacc and the surface potential potential Vp of the object with respect to incident electrons, and the regions of | Vacc |> | Vp | and | Vacc | <| Vp | The acceleration voltage is set so that both exist simultaneously, and the diameter of the latent image is measured from the boundary between the | Vacc |> | Vp | region and the | Vacc | <| Vp | region in the contrast image. A surface potential distribution measuring device.   The surface potential distribution measuring apparatus according to claim 5, wherein the processing device binarizes a detection amount of the repulsive electrons and measures a diameter of the latent image from a boundary between the two values.   7. The surface potential distribution measuring apparatus according to claim 5, wherein the processing apparatus further corrects a deviation in a focusing position of the charged particle beam with respect to an optical axis direction when the acceleration voltage is changed. 8.   8. The surface potential distribution measuring apparatus according to claim 7, wherein the processing device corrects the deviation of the focusing position by controlling a voltage applied to the objective lens.   9. The surface according to claim 5, wherein the processing apparatus further corrects a variation in a scanning range of the charged particle beam on the sample surface when the acceleration voltage is changed. 10. Potential distribution measuring device.   The surface potential distribution measuring apparatus according to claim 9, wherein the processing device corrects a variation in the scanning range by controlling a voltage applied to the scanning lens.   The surface potential distribution measuring apparatus according to any one of claims 5 to 10, wherein the processing apparatus further calculates a surface potential distribution profile based on a surface potential distribution state of the sample.   The surface potential distribution measuring apparatus according to claim 5, further comprising a power supply circuit that applies a bias voltage to the sample.   The surface potential distribution measuring apparatus according to claim 5, wherein the sample is a photoconductor.   6. A gate valve disposed between the beam generating device and a predetermined position where the sample is set in the housing, and further comprising a partition valve capable of dividing the interior of the housing into two regions. The surface potential distribution measuring apparatus according to any one of ˜13.