JP5673866B2 - Evaluation method of electrostatic latent image - Google Patents

Description

  The present invention relates to an electrostatic latent image evaluation method, an electrostatic latent image evaluation apparatus, and an image forming apparatus, and in particular, to evaluate the electrostatic latent image forming ability of a photoreceptor sample in a short time with high resolution. It is made to be able to.

As a method for measuring the surface potential of a photoreceptor used in an electrophotographic image forming apparatus such as a copying machine or a laser printer, an electrostatic attraction or induction caused as an interaction at that time is brought close to a sample having a potential distribution. There is a method of measuring current and converting it into a potential distribution. In the surface potential measurement method using this method, the resolution is theoretically as low as several millimeters, and a high resolution of 1 μm cannot be obtained.
As an evaluation of LSI chips, a method of measuring an electric potential on the order of 1 μm using an electron beam is known. However, this evaluation is an evaluation of the conductive portion of the LSI. The potential is as low as about +5 V and the potential is limited, and the negative charge of several hundreds to thousands of V in the photoconductor sample targeted by the present invention. Can not cope with.

  As an observation method of an electrostatic latent image using an electron beam, there is an invention described in Patent Document 1. Samples to be evaluated are limited to samples that can store and hold LSI chips and electrostatic latent images, and ordinary photoconductors that cause dark decay cannot be measured. Since a normal dielectric can hold a charge semipermanently, even if measurement is performed over time after forming a charge distribution, the measurement result is not affected. However, in the case of a photoconductor, since the resistance value is not infinite, the electric charge cannot be held for a long time, and the surface potential decreases with time due to dark decay. The time that the photoconductor can hold the charge is at most 10 to 60 seconds even in the dark room. Therefore, even if an attempt is made to observe in an electron microscope (SEM) after charging and exposure, the electrostatic latent image disappears at the preparation stage. After the latent image is formed, it must be measured within 3 seconds at the latest.

Further, in the X-ray microscope described in Patent Document 2, the operating wavelength is completely different, and the charging potential in the electrophotographic process cannot be set to −500 to −1000 V, and the electrophotographic image forming apparatus It is not possible to reproduce and measure the environment equivalent to the actual machine.
In view of this, the present inventors have invented a method capable of measuring an electrostatic latent image even for a photoconductor sample having dark attenuation, and applied for a patent (for example, Patent Document 3, Patent Document 4, Patent Document 5). And Patent Document 6).

By the way, as shown in FIG. 5, a general photoreceptor includes a substrate (Sub) 21, an undercoat layer (UL) 22, a charge generation layer (CGL) 23, and a charge transport layer (CTL) 24. . The UL 22 is provided for the purpose of preventing charge injection leakage from the substrate side.
Among the photoconductors having this configuration, the organic photoconductor (OPC) has a problem that the photoconductor is fatigued as the number of output images increases, and image distortion occurs.

It is important to evaluate the influence of the fatigue of the photoreceptor on the electrostatic latent image in order to improve the image quality of the electrostatic latent image and improve the durability of the photoreceptor.
As a method for evaluating the influence on the electrostatic latent image due to the fatigue of the photoreceptor, a surface potential due to the residual charge is measured by a vibration capacity method using a fatigue tester such as the OPC drum test apparatus described in Patent Document 7. It has been known.

However, in the surface potential measurement by the conventional vibration capacity method, the spatial resolution is only a few millimeters and only macro evaluation can be performed. If the residual charge can only be grasped macroscopically, it is difficult to optimize the design for high image quality, so it is necessary to measure the microscopic state on the micron scale.
In such a case, evaluation on the micron scale is possible by using the output image. However, the transfer and fixing processes must be performed and it takes time to evaluate, and the characteristics of the photoconductor alone should be evaluated. I can't.

  In addition, in the conventional evaluation method, when an attempt is made to observe in a vacuum apparatus after conducting a fatigue test of the photoconductor in the atmosphere, a predetermined time is required for moving the photoconductor. May be unable to make a valid assessment.

  The present invention has been made in view of the above problems, and is an electrostatic latent image evaluation method capable of evaluating the electrostatic latent image forming ability of a photoreceptor sample in a short time with high resolution. An object is to provide an evaluation apparatus and an image forming apparatus.

The present invention is a method for measuring and evaluating an electrostatic latent image of a photoconductor sample based on a detection signal obtained by irradiating a photoconductor sample having a surface charge distribution with a charged particle beam. wherein a charging step of the photosensitive member sample is charged by irradiation with an electron beam, a charge eliminating step for neutralizing performs light irradiation to the photoreceptor sample was charged, provided with, the measurement region of the photosensitive member sample Repeating the charging step of irradiating the electron beam and the neutralizing step of irradiating the light without irradiating the measurement region of the photosensitive member sample with the photosensitive member sample. after fatigue, the charging step and charged to the photoreceptor sample at a position and has been performed the neutralization step to form an electrostatic latent image pattern by exposing, charging area in order to perform one evaluation Change multiple times The difference in the detection signal caused by the difference in the area of the charging region is captured as a plurality of images, a plurality of electrostatic latent images are extracted from the obtained plurality of images, and the plurality of extracted electrostatic latent images are extracted. The most important feature is that the electrostatic latent image is evaluated by comparing the sizes of the electrostatic latent images.

By using the method for evaluating an electrostatic latent image according to the present invention, it is possible to perform photoconductor fatigue equivalent to a real machine in a short time and to immediately measure the electrostatic latent image on the photoconductor.
By irradiating light while irradiating an electron beam, the photoconductor is subjected to light fatigue. Since it is generated in a vacuum, it is not significantly affected by exposure to NOx gas as in a fatigue experiment in the atmosphere. Simultaneous irradiation of electron beam irradiation and light irradiation is possible, and fatigue can be carried out efficiently.

  Also, in the method of rotating the photosensitive drum as in the prior art, the charging means and the exposure means are arranged separately, so that charging by electron beam irradiation and exposure by light irradiation can be performed simultaneously. It was not easy. In the method for evaluating an electrostatic latent image according to the present invention, it is possible to efficiently perform light fatigue in a short time by enabling charging and exposure to be performed simultaneously.

Conventionally, in corona charging and scorotron charging, since discharge in the air is used, it is difficult to control the amount of electrons irradiated to the photoreceptor sample even though the passing current flowing through the substrate can be controlled. It was.
In the method for evaluating an electrostatic latent image according to the present invention, it can be charged by irradiating an electron beam in a vacuum apparatus, and one of the features is that an electron irradiation current density that directly affects light fatigue can be controlled, Thereby, light fatigue can be given efficiently.

Although not particularly limited in the present invention, it is preferable that a beam blanker is provided, and in the static elimination step, the beam blanker is turned on so that the electron beam is not irradiated onto the measurement region of the photoconductor sample.
By superimposing the light irradiation signal on the beam blanker signal, it is possible to synchronize the ON / OFF switching of the electron beam irradiation and the light irradiation.
Further, although not particularly limited in the present invention, the irradiation time of the electron beam for charging is preferably longer than the time until the surface potential of the photoconductor sample reaches the saturated charging potential by the irradiation of the electron beam. .
By setting the light irradiation extinction time longer than the time until the saturation potential is reached, the saturation potential can be reliably reached and fatigue conditions equivalent to the actual machine can be ensured.

In the present invention, although not particularly limited, the light irradiation time for static elimination is preferably longer than the time until the surface potential of the photoreceptor sample reaches the residual potential by light irradiation.
By setting the light irradiation lighting time longer than the time until the residual potential is reached, the charge can be sufficiently discharged.

Further, although not particularly limited in the present invention, a plurality of images obtained by changing a charging region a plurality of times to perform one evaluation, capturing differences in detection signals caused by different areas of the charging region as a plurality of images, and It is preferable to evaluate the formed electrostatic latent image by extracting a plurality of electrostatic latent images from the images and comparing the sizes of the extracted plurality of electrostatic latent images.
Comparing the size of multiple electrostatic latent images with the means to measure by changing the charged area multiple times when evaluating, the means to measure the size of the latent image from the electrostatic latent image obtained by the measurement By evaluating the electrostatic latent image formed using these, the latent image sharpness of the electrostatic latent image formed on the electrophotographic photosensitive member, which has not been conventionally possible, can be quantitatively determined. It becomes possible to evaluate.

Although not particularly limited in the present invention, electrostatic latent images having different charged area areas are measured, and a latent image area ratio between a latent image area in a wide charged area and a latent image area in a narrow charged area is determined. It is preferable to calculate and use the calculated latent image area ratio as an evaluation index of the latent image forming ability.
The latent image area ratio (S2 / S1) value when the area of the latent image in the wider charged area is S1 and the latent image area in the smaller charged area is S2 is used as an evaluation index of the latent image forming ability. Thus, it becomes possible to evaluate the latent image forming ability under various photoconductors and writing conditions.
In addition, by evaluating the electrostatic latent image, it can be fed back to the design and the process quality of each process is improved, so that an image having excellent quality, durability and stability can be obtained, and energy saving can be achieved. It is possible to provide an electrophotographic photosensitive member (latent image carrier) that can be converted into a photoconductor.

It is a schematic diagram which shows the Example of the evaluation apparatus of the electrostatic latent image which concerns on this invention. 2A and 2B show examples of an optical scanning device applicable to the electrostatic latent image evaluation apparatus according to the present invention, FIG. 3A is a perspective view, FIG. 2B is a perspective view showing an example of a light source unit, and FIG. It is a perspective view which shows another example. It is sectional drawing which shows the specific example of the vacuum chamber and exposure apparatus part in the said Example. It is a schematic diagram which shows another Example of the evaluation apparatus of the electrostatic latent image which concerns on this invention. It is sectional drawing which expands and shows the structure of the photoreceptor which is a measuring object of this invention. It is a graph which shows the relationship between the acceleration voltage of an electron beam with respect to a photoreceptor sample, and a charging potential. It is sectional drawing which shows the illumination optical system used for the evaluation apparatus of the electrostatic latent image which concerns on this invention. (A) is an optical arrangement | positioning figure which shows the layout of the illumination optical system of FIG. 7, (b) is one form of an opening mask, (c) is a front view which shows the other form of an opening mask. It is a graph which shows the relationship between LD drive current and the optical output of the evaluation apparatus of the electrostatic latent image which concerns on this invention. It is a timing chart which shows the example of the photoreceptor fatigue | fatigue operation | movement in the evaluation apparatus of the electrostatic latent image which concerns on this invention. It is a schematic diagram which shows the various examples of the latent image formation pattern by the scanning optical system applicable to the evaluation apparatus of the electrostatic latent image which concerns on this invention. It is a schematic diagram showing the principle of charge distribution and potential distribution detection by secondary electrons obtained by irradiating an electron beam to a latent image formed on a photoreceptor. It is sectional drawing which shows the structure of the beam blanking apparatus used in the evaluation apparatus of the electrostatic latent image which concerns on this invention. It is a timing chart which shows the example of the beam blanking electrode signal and the deflection | deviation electrode signal in the evaluation apparatus of the electrostatic latent image based on this invention. It is a flowchart which shows an example of the evaluation method of the electrostatic latent image which concerns on this invention. It is a graph which shows the relationship between the electric field strength to a photoreceptor sample, and the quantum efficiency of the carrier production amount which generate | occur | produces when light is irradiated to CGL. It is a graph which shows the experimental result which performed the light fatigue experiment with the phthalocyanine type photoreceptor (film thickness of 30 micrometers). It is a schematic diagram which shows the principle of the electrostatic latent image evaluation by this invention. It is a graph and a conceptual diagram which show the electric field strength distribution of the perpendicular direction of a photoreceptor sample in the electromagnetic field simulation by the electric charge distribution from which only a peripheral charge differs. It is a flowchart which shows another example of the evaluation method of the electrostatic latent image which concerns on this invention. It is a conceptual diagram which shows the latent image profile in the state where the sharpness of a latent image is high and low. It is a conceptual diagram which shows the example of the sharpness evaluation of an electrostatic latent image applicable to the evaluation method of the electrostatic latent image which concerns on this invention. It is a schematic diagram which shows the relationship between a latent image area and a circle equivalent diameter. It is a figure which shows an example of the measurement result of an electrostatic latent image. It is a schematic diagram which shows another example of the evaluation apparatus of the electrostatic latent image which concerns on this invention. It is a figure which shows the relationship between the incident electron to a photoreceptor sample, and a sample. It is a figure which shows an example of the latent image depth measurement result by the evaluation apparatus of the electrostatic latent image which concerns on this invention. 1 is a schematic diagram illustrating an embodiment of an image forming apparatus according to the present invention.

  Embodiments of an electrostatic latent image evaluation method, an electrostatic latent image evaluation apparatus, and an image forming apparatus according to the present invention will be described below with reference to the drawings.

<Evaluation device for electrostatic latent image>
FIG. 1 shows an embodiment of an electrostatic latent image evaluation apparatus for executing the electrostatic latent image evaluation method according to the present invention. In FIG. 1, the electrostatic latent image evaluation apparatus is roughly divided into a charged particle beam irradiation apparatus 4, an exposure apparatus 6, a sample mounting table 7, and a detector 8 such as primary inversion charged particles and secondary electrons. And a signal detector 9 and an image processing means 10. On the sample mounting table 7, a photoconductor sample 20 to be evaluated is mounted. The charged particle beam irradiation device 4, the sample mounting table 7, and the detector 8 are arranged in a vacuum chamber 40.

  The charged particle beam irradiation apparatus 4 is configured by incorporating components into the vacuum chamber 40 as follows. An electron gun 41 that irradiates a charged particle beam is attached near the upper end of the vacuum chamber 40, and below that, a suppressor electrode 42, an extractor or extraction electrode 43, an acceleration electrode 44, a condenser lens 45, a beam blanking electrode 46, A gate valve 47, a movable diaphragm 48, a stigmator or correction electrode 49, a deflection electrode (corresponding to a scanning lens) 50, an electrostatic objective lens 51, and a beam emission opening 52 are arranged in this order. The suppressor electrode 42 and the extraction electrode 43 control the electron beam, the acceleration electrode 44 controls the energy of the electron beam, and the condenser lens 45 focuses the electron beam generated from the electron gun. The beam blanking electrode 46 turns on / off the electron beam, and the gate valve 47 and the movable diaphragm 48 function as an aperture for controlling the irradiation current of the electron beam. The deflection electrode 50 functions as a scanning lens for scanning the electron beam that has passed through the beam blanker, and the electron beam that has passed through the deflection electrode 50 is again converged on the surface of the photoreceptor sample 20 by the objective lens 51. A driving power source (not shown) is connected to each lens.

  As used herein, charged particles refer to particles that are affected by an electric or magnetic field, such as an electron beam or an ion beam. In the case of an ion beam, a liquid metal ion gun or the like is used instead of an electron gun.

  The exposure apparatus 6 is a so-called known laser scanner, and its details are shown in FIG. The exposure apparatus 6 includes a light source 61 such as an LD (laser diode) that emits light having a wavelength with sensitivity with respect to the photoconductor sample 20, a collimator lens 62, an aperture 63, a condenser lens 64, a galvano mirror, a polygon mirror, and the like. A deflector 65, a scanning imaging lens 66, a mirror 67, and the like are provided. The exposure apparatus 6 can generate a desired beam diameter and beam profile on the photoconductor sample 20, and can scan the surface of the photoconductor sample 20 with the beam. The LD control means can irradiate the photoconductor sample 20 with a light beam with an appropriate exposure time and exposure energy.

A line pattern can be formed on the photosensitive member sample 20 by providing a scanning mechanism including the optical deflector 65, the scanning imaging lens 66, and the like. However, the scanning mechanism is omitted, and a dot pattern is formed on the photosensitive member sample 20. May be formed. Further, a multi-beam scanning optical system may be configured by using a VCSEL or the like as shown in FIGS. 2B and 2C as a light source.
In addition, when a scanning mechanism with a scanning mechanism is used as the main scanning direction, a mechanism for scanning in the sub-scanning direction in addition to the main scanning direction is provided to form a two-dimensional exposure pattern. You may make it do.

  In the embodiment shown in FIG. 1, the exposure apparatus 6 composed of a scanning optical system includes a vacuum chamber 40 so that the vibration of the optical deflector 65 composed of a polygon motor or the like and the influence of the electromagnetic field do not affect the trajectory of the electron beam. Arranged outside. The exposure apparatus 6 can be moved away from the electron beam trajectory position, and the charged particle beam irradiation apparatus 4 can be suppressed from being affected by disturbance. The scanning optical system is configured to enter the vacuum chamber 40 through an optically transparent entrance window 68.

  FIG. 3 shows specific structures of the vacuum chamber 40 and the exposure apparatus 6 of the above embodiment. As shown in FIG. 3, an incident window 68 through which light can be incident from the outside is disposed inside the vacuum chamber 40 at an angle of 45 ° with respect to the vertical axis of the vacuum chamber 40. An exposure apparatus 6 that causes the scanning beam 77 to enter the chamber 40 is disposed outside the vacuum chamber 40. As described above, the exposure apparatus 6 includes a scanning optical system, and includes a light source unit, a scanning lens, synchronization detecting means, an optical deflector 65 including a polygon mirror, a mirror 72 for bending an optical path, and the like. The main part of the exposure device 6 is disposed on the optical housing 69, and the upper part is covered with a cover 71 to be shielded from light. The optical housing 69 is mounted on a horizontal translation table 83, and the translation table 83 is mounted on the vibration isolation table 81 via a plurality of columnar structures 82. The path of the scanning beam 77 bent obliquely downward at an angle of approximately 45 ° by the mirror 72 is shielded by an external light shielding cylinder 73, an internal light shielding cylinder 75, and a labyrinth portion 74 interposed between the inside and outside light shielding cylinders. Has been.

  A vacuum chamber 40 is fixed on the vibration isolation table 81. A sample stage 78 serving as the sample mounting table is attached in the vacuum chamber 40 so as to be movable in two orthogonal directions within a horizontal plane. A photoconductor sample 20 can be placed on the sample stage 78, and the charged particle beam irradiation device 4 that irradiates the photoconductor sample 20 with a charged particle beam from directly above is attached to the vacuum chamber 40. The inside of the charged particle beam irradiation apparatus 4 is also communicated with the vacuum chamber 40 and kept in a vacuum. In the vacuum chamber 40, after the electrostatic latent image is formed on the photoconductor sample 20, the detection end of the detector 8 that detects the electron beam emitted by irradiating the photoconductor sample 20 with the charged particle beam is photosensitive. It extends toward the body sample 20.

  The scanning lens 66 shown in FIGS. 1 to 3 has an fθ characteristic, and when the optical polarizer 65 rotates at a constant angular velocity, the light beam travels on the image plane, that is, the surface of the photoreceptor sample 20 at a substantially constant velocity. It is configured to move in. Further, the beam spot diameter on the surface of the photoconductor sample 20 is also maintained at a substantially constant diameter so that scanning is possible.

  Since the exposure apparatus 6 including the scanning optical system is disposed away from the vacuum chamber 40, vibration generated by driving the optical deflector 65 such as a polygon scanner is directly transmitted to the vacuum chamber 40. There is little influence of the vibration. Although not shown in FIG. 3, if a damper is inserted between the structure 82 and the vibration isolation table 81, the vibration isolation effect can be further enhanced.

  As described above, an apparatus for exposing the photoreceptor sample 20 is an exposure apparatus using a scanning mechanism, so that an arbitrary latent image pattern including a line pattern can be formed in the generatrix direction of the photoreceptor sample 20. it can. In order to form a latent image pattern at a predetermined position on the photoconductor sample 20, it is more preferable to have a synchronization detecting means for detecting a scanning beam from the optical deflector 65.

  FIG. 4 shows an embodiment of the electrostatic latent image evaluation apparatus in the case where the photosensitive member sample has a cylindrical shape. Since it is basically the same as the embodiment shown in FIG. 1, the same components or the same functional parts are denoted by the same reference numerals. The cylindrical photoconductor sample 20 is driven to rotate about its central axis. The light scanning direction by the exposure device 6 is a direction parallel to the central axis of the photoconductor sample 20 on the surface of the photoconductor sample 20, and this is called a main scanning direction. As the photoconductor sample 20 rotates, the surface of the photoconductor sample 20 moves in a direction orthogonal to the main scanning direction. This moving direction is called the sub-scanning direction. An electrostatic latent image of an arbitrary pattern can be formed on the surface of the photoconductor sample 20 by main scanning by the exposure device 6 and sub-scanning by rotation of the photoconductor sample 20. The example shown in FIG. 4 is different from the embodiment of FIG. 1 only in the above points, and the other configurations and functions are the same as those of the embodiment of FIG.

Here, the configuration of the above-described photoreceptor sample 20 will be described. As shown in FIG. 5, a general photosensitive member is provided with an undercoat layer (UL) 22, a charge generation layer (CGL) 23, and a charge transport layer (CTL) 24 in this order on a conductive support 21. Configured.
When the surface of the photoconductor is exposed in a charged state, light is absorbed by the charge generation material (CGM) of the charge generation layer 23, and positive and negative charge carriers are generated. Of the positive carriers, those injected into the CTL 24 are moved to the surface of the CTL 24 by the electric field, and are combined with the negative charges on the surface of the photoreceptor to disappear. On the other hand, the negative carrier reaches the conductive support 21.
As described above, normally, positive and negative carriers can move in the photoconductor, but if the light irradiation is performed in a large amount or for a long time, the photoconductor is fatigued and the movement of the carrier is prevented. As a result, each carrier is trapped by the photoconductor and becomes a residual charge.

  FIG. 16 shows the relationship between the electric field strength on the photoconductor sample and the quantum efficiency of the amount of carrier generated when CGL is irradiated with light. Electric field strength E on the photosensitive member sample = charge potential / photosensitive member film thickness.

  Next, the principle of the electrostatic latent image evaluation method using the electrostatic latent image evaluation apparatus described so far will be described.

<Charging>
First, the photosensitive member sample 20 is irradiated with an electron beam. As shown in FIG. 6A, when the acceleration voltage | Vacc | is set to an acceleration voltage higher than the acceleration voltage at which the secondary electron emission ratio is 1, the amount of incident electrons exceeds the amount of emitted electrons. It accumulates on the photoreceptor sample 20 and causes charge up. As a result, the photoreceptor sample 20 can be uniformly charged negatively. The relationship between the acceleration voltage of the electron beam and the charged potential of the photoconductor sample 20 is as shown in FIG. 6B. By appropriately performing the acceleration voltage of the electron beam and the irradiation time, an image using an electrophotographic process is used. The same charging potential as that of the actual apparatus of the forming apparatus can be formed. When the irradiation current is larger, the target charging potential can be reached in a shorter time, and therefore irradiation is performed with several nA. Thereafter, the amount of incident electrons is reduced to 1/100 to 1/1000 in order to enable observation of an electrostatic latent image described later.

<Static elimination>
Next, the photoconductor sample 20 is irradiated with light to give light fatigue. A light emitting diode (LED) or a semiconductor laser having a wavelength of 400 to 800 nm is used as a light source for illumination that gives light fatigue. As the simplest configuration of the illumination optical system for performing light irradiation, there is a method of irradiating the entire sample with divergent light without using a lens. In this case, it is possible to appropriately adjust the exposure amount by adjusting the amount of current supplied to the LED. In this embodiment, as shown in FIGS. 7 and 8A, an illumination optical system having a configuration different from the above-described configuration while using an LED as a light source is used.

  In FIG. 7 and FIG. 8A, the light beam emitted from the light source 17 is converted into a parallel light beam by the collimating lens 18, and the diameter of the light beam is regulated by the aperture 19 toward the aperture mask 200. The light beam that has passed through the aperture mask 200 forms an image corresponding to the shape of the aperture of the aperture mask 200 on the image plane by the action of the imaging lens 210. Here, the image plane is a uniformly charged surface of the photoconductor sample mounted on the sample mounting table 28. The shape of the opening of the opening mask 200 may be a rectangle as shown in FIG. 8B, a circle as shown in FIG. 8C, or a more complicated shape.

  As shown in FIG. 8A, when the distance between the imaging lens 210 and the aperture mask 200 is L1, and the distance from the imaging lens 210 to the image plane is L2, it is perpendicular to the optical axis of the imaging lens 210. In this direction, the image forming magnification β = L2 / L1, and a mask pattern image corresponding to this magnification is formed.

  The imaging lens 210 is disposed so that the aperture mask 200 and the surface of the photoreceptor sample are conjugate. Since the imaging magnification β and the size of the mask pattern are known in advance, the illumination area imaged on the surface of the photoreceptor sample can be calculated. The exposure optical path in the exposure means that can form a desired pattern on the photoreceptor sample is provided avoiding the region through which the charged particle beam that scans the photoreceptor sample two-dimensionally passes. Therefore, the imaging lens 210 is installed such that the optical axis is inclined with respect to the normal line set on the uniformly charged surface of the photoconductor sample.

Further, as shown in FIG. 8A, the aperture mask 200 is also tilted with respect to the optical axis so that the image of the mask pattern by the light beam that has passed through the imaging lens 210 matches the surface of the photosensitive member sample. Has been. Assuming that the inclination of the aperture mask 200 with respect to the optical axis is α and the inclination θ with respect to the optical axis of the surface of the photoreceptor sample, α = θ = 45 ° in this embodiment. Thereby, the imaging magnification becomes equal (L1 = L2). In addition, the mask pattern image formed on the surface of the photosensitive member sample is √2 times the direction orthogonal to the drawing of FIG. 8A within a plane parallel to FIG. The mask pattern is designed in consideration of the above. In a general case where the imaging magnification is other than equal magnification, L1 · tanθ = L2 · tanθ between L1, L2, α, and θ.
The relationship holds.

Further, if the region irradiated by the irradiation optical system is S (mm ² ) and the light output on the image plane is Pi (mW), the light irradiation density is Pi / S (mW / mm ² ). Can be represented. By using such an optical system, it is possible to irradiate a predetermined region of the photoreceptor sample.
FIG. 9 shows the relationship between the LED drive current IF and the light output Pon. LED light emission is caused by raising the drive current IF to a threshold current or higher. Therefore, the light output Pon can be controlled and the amount of light on the image plane can be adjusted by changing the amount of current under conditions equal to or higher than the threshold current, and an appropriate light irradiation light amount density can be set.
The present invention is characterized in that light fatigue is given to the photoreceptor sample. The light irradiation optical system for giving light fatigue and the optical system for erasing the charged charges may be made common.

FIG. 10 shows a timing chart for light fatigue the photoconductor.
At time T0, the photosensitive member is irradiated with an electron beam. The surface potential of the photoreceptor rises and reaches a saturated charging potential at time T1. Thereafter, the saturated charging potential is maintained until time T2.
At time T2, the light irradiation output signal is turned ON, and the photosensitive member is irradiated with light. By irradiating light, hole carriers generated in CGL reach the surface, the surface charge is neutralized and attenuated, and the charge is eliminated at time T3. In addition, since the residual potential remains even after the charge is eliminated, the potential does not become 0 but changes at a constant value.
At time T4, the light output signal is turned off, and the surface potential of the photosensitive member rises again due to the irradiated electron beam.

The above steps T0 to T4 are repeated, and the photoconductor is fatigued by repeating charging and discharging of the photoconductor. At this time, since there is a time difference between the time when the electron beam is irradiated and the time until the charged potential is saturated, the charging potential is set to the minimum time from the time when the electron beam is irradiated. It is desirable to set it longer than the time until saturation. That is, it is desirable to set so that T2-T0> T1-T0. Specifically, when a sample area of 1 mm ^{2 is} irradiated with an electron beam irradiation current of ² nA, it is desirable that the turn-off time is 2 seconds or longer.

In addition, since there is a time difference between the time when the light output signal is turned on and the light irradiation is started and the time until the light is removed, the light irradiation time is at least the time until the charged potential is discharged. It is desirable to set longer. That is, it is desirable to set T4 so that T4-T2> T3-T2. Specifically, when a sample area of 1 mm ² is irradiated with a light irradiation amount of 100 μW, the light irradiation time is desirably 1 second or longer.
By comprising in this way, the fatigue of both the electrostatic fatigue at the time of charging and the light fatigue by light irradiation can be given.

  When the fatigue process is completed, a latent image is formed and the electrostatic latent image is measured. The charging can be realized by using the same method as described above.

<Exposure>
Next, the photosensitive sample 20 is exposed by the exposure device 6 to form an electrostatic latent image. The optical system of the exposure apparatus 6 is adjusted so as to form a desired beam diameter and beam profile. The required exposure energy is a factor determined by the characteristics of the photoreceptor sample, but is usually about ² to 10 mJ / m ² . For photoreceptors with low sensitivity, ten or more mJ / m ² may be required. The charging potential and the required exposure energy are preferably set in accordance with the photoreceptor characteristics and process conditions.

In this way, exposure conditions matched to the actual machine of the electrophotographic apparatus, for example, an exposure energy density of 0.5 to 10 mJ / m ² and a beam spot diameter of 30 to 100 μm are set, and further, duty, image frequency, writing density, It is preferable to set conditions such as an image pattern. As an image pattern, in addition to 1-dot isolation, a 1-dot lattice as shown in FIG. 11A, 2by2 as shown in FIG. 11B, 2-dot isolation as shown in FIG. Various patterns such as a 2-dot line as shown in (d) can be formed. In this manner, an arbitrary electrostatic latent image can be formed on the photoreceptor sample 20.

<Observation>
Next, the photoconductor sample 20 is scanned with an electron beam, and the emitted secondary electrons are detected by a detector (scintillator) 8 and converted into an electric signal to observe a contrast image. In this way, the charged portion remaining without being exposed has a large amount of detected secondary electrons, and the exposed portion has a light and dark contrast image with a small amount of detected secondary electrons. The dark part can be regarded as a latent image part by exposure.

  When a latent image is formed on the surface of the photoreceptor sample 20 and there is a charge distribution, an electric field distribution corresponding to the surface charge distribution is formed in the space. For this reason, the secondary electrons generated when the electrons are incident on the surface of the photoconductor sample 20 are pushed back by the electric field, and the amount reaching the detector 8 is reduced. Accordingly, the charge leaks in the exposed portion to be black, and the non-exposed portion becomes white in which the charge does not leak, and a contrast image corresponding to the surface charge distribution can be obtained and measured.

FIG. 12A illustrates the potential distribution in the space between the charged particle trap 24 and the photoconductor sample in an explanatory manner using contour lines. The surface of the sample is in a state of being uniformly charged to the negative polarity except for the portion where the potential is attenuated by light attenuation. Since the charged particle trap 24 is given a positive potential, the potential increases as it approaches the charged particle trap 24 from the surface of the sample, as shown by the solid potential contour line group.
Accordingly, the secondary electrons el1 and el2 generated at the points Q1 and Q2 in the figure, which are parts of the sample that are uniformly charged to the negative polarity, are attracted to the positive potential of the charged particle trap 24, and the arrows G1 and G2 And is captured by the charged particle trap 24.

  On the other hand, in FIG. 12A, in the vicinity of the point Q3 in the central portion of the portion where the negative potential is attenuated by light irradiation, the arrangement of the potential contour lines is a semi-elliptical shape centered on the point Q3 as shown by the broken line. Thus, in this partial potential distribution, the closer to Q3 point, the higher the potential. Therefore, the secondary electron el3 generated in the vicinity of the point Q3 is subjected to an electric force restrained on the sample side, as indicated by an arrow G3. For this reason, the secondary electron el3 is captured in the “potential hole” indicated by the broken potential contour lines and does not move toward the charged particle trap 24. FIG. 12B schematically shows the “potential hole”.

  In other words, the secondary electrons detected by the charged particle trap 24 have a portion where the intensity (number of secondary electrons) is large, that is, the “ground portion of the electrostatic latent image”, that is, a portion that is uniformly negatively charged. Corresponding to (part represented by points Q1 and Q2 in FIG. 12 (a)), the part with low intensity is the “image part of the electrostatic latent image”, that is, the part irradiated with light (point in FIG. 12 (a)). This corresponds to the portion represented by Q3).

  Therefore, if the electric signal obtained by the secondary electron detector 8 shown in FIG. 1 is sampled by the signal detector 9 at an appropriate sampling time, the surface potential distribution: V (X, Y) using the sampling time: T as a parameter. ) Can be specified for each “micro area corresponding to sampling”, and the surface potential distribution (potential contrast image): V (X, Y) can be configured as two-dimensional image data by the signal processing means 10. If this is output by an output device, the pattern of the electrostatic latent image can be obtained as a visible image.

  For example, if the intensity of secondary electrons to be captured is expressed as “brightness or weakness”, the image portion of the electrostatic latent image is dark, the ground portion is bright and contrasted, and a bright and dark image corresponding to the surface charge distribution is obtained. It can be expressed (output). Of course, if the surface potential distribution can be known, the surface charge distribution can also be known.

  By using such a method, it is possible to always measure the same region. Generally, even if the photoconductors are produced in the same lot, the sensitivity is locally different on a micron order scale. For this reason, once the photoconductor is taken out, its location cannot be specified accurately and accurate evaluation cannot be performed.

  In the present invention, photo fatigue of a photoconductor and measurement of an electrostatic latent image on a micron order scale can be performed at the same location in the same apparatus. Can be done accurately.

Here, a specific example of the above-described photoreceptor fatigue experiment will be described. The experimental conditions are as follows.
Photoconductor: Azo pigment type photoconductor (film thickness 30 μm)
Acceleration voltage: 1.6 kV
Charging potential: -650V
Charging area: Wide area: Narrow area = 3.75: 1
Writing density: 600 dpi
Pattern: 1 dot isolated, 2 dots isolated Duty: 50%
Light source: wavelength 655 nm
Beam spot diameter: Main 60 × Sub 80 μm

When the measurement was repeated 10 times under the condition that the size of the latent image was 100 μm, the variation was 0.5% in the initial stage and 1.1% after 1 hour of fatigue.
When the measurement was repeated 10 times under the condition that the size of the latent image was 150 μm, the variation was 1.0% in the initial stage and 2.1% after 1 hour fatigue.

  In the above embodiment, the electron beam is continuously irradiated. However, as another embodiment, the electron beam irradiation may be turned off in accordance with the light irradiation.

  That is, when the electron beam irradiation is ON, the light irradiation is turned OFF, and when the electron beam irradiation is OFF, the light irradiation is turned ON. Thereby, static elimination time (T3-T2) can be advanced. Even in this case, the charging process and the charge eliminating process can be repeated, and an environment equivalent to that of the actual machine can be provided.

Here, as a method for turning off the electron beam irradiation, a mechanical shielding member may be used for the electron beam trajectory. In this case, a shielding member capable of high-speed response is required. Therefore, as another method, a configuration may be adopted in which the electron beam is directed in a direction that does not electrically hit the sample.
Specifically, as shown in FIG. 13, a beam blanking electrode 46 is provided between the electron gun 41 and the photoconductor sample 20, and the beam blanker signal is turned ON in accordance with the light irradiation signal. When the beam blanker signal is ON, the electron beam is bent by applying a voltage, and does not pass through the subsequent partition valve 47, and the electron beam does not reach the sample. As a result, it is possible to prevent the electron beam from hitting the sample.

  The beam blanker signal is preferably used once for each line scan so that it does not become an abnormal signal when the scanning signal is suddenly switched. In a normal beam blanker, a blanker signal is provided in accordance with the horizontal synchronizing signal for each line scan. In this case, the beam blanker signal may be turned ON during the light irradiation period. That is, when the light irradiation is ON, the beam blanker may be always turned ON. By doing in this way, it is possible to turn on / off the electron beam irradiation on the sample without using a new light shielding member, while synchronizing with the light irradiation output at high speed.

  By using such means, fatigue of both electrostatic fatigue during charging and light fatigue due to light irradiation can be given, and the photoreceptor can be fatigued under conditions closer to the actual electrophotographic process. it can.

<Operation>
FIG. 15 shows a flow of latent image evaluation of a fatigue photoconductor. Repeated charging by electron beam irradiation and static elimination by light irradiation. When the number of repetitions reaches a predetermined number, an electrostatic latent image pattern is formed by electron beam irradiation, a signal is detected by scanning an electron beam, and the electrostatic latent image is measured.
In the conventional method of rotating the photosensitive drum, since the charging unit and the exposure unit are arranged at different locations, it is impossible to irradiate both at the same time. On the other hand, in the apparatus for evaluating an electrostatic latent image according to the present invention described below, since it is possible to perform electron beam irradiation and light irradiation simultaneously, light fatigue can be efficiently applied in a short time.

In this embodiment, a fatigue experiment is performed using a timing chart at the time of photoreceptor fatigue by electron beam irradiation and light irradiation shown in FIG. Irradiating an electron beam with an irradiation current density EB1 (C / mm ² ) gives an electric field strength, and irradiating with an amount of light PO (W / mm ² ) generates a large number of carriers and gives light fatigue. Can do.
After the end of fatigue, the electron beam irradiation current density is temporarily turned off. Even if it is not turned off, if it is a weak irradiation current density of about 1/100 or less, since it is hardly charged, the same effect can be obtained.

FIG. 17 shows the results of an experiment in which the above light fatigue experiment was performed with a phthalocyanine photoconductor (film thickness 30 μm).
In order to observe photoreceptor fatigue, scanning with a weak electron beam irradiation current of about 1 to 20 pA is preferable.
By using the above-described electrostatic latent image evaluation method according to the present invention, it is possible to improve the quality of the evaluation result and directly evaluate the characteristic value.
Note that there may be a state in which one of the electron beam and the light is not temporarily irradiated.

  FIG. 18 shows the principle of electrostatic latent image evaluation according to the present invention. In FIG. 18, reference numeral 1 denotes an uncharged area of the photoconductor sample, 2 denotes a charged area, and 3 denotes an electrostatic latent image distribution. First, as shown in FIG. 18A, for example, the charging area 2 is set to a narrow area and charged in this area, and a latent image 3 is formed in a predetermined pattern in the charging area. Charging is performed by irradiating the photosensitive sample with a charged particle beam, and the latent image 3 is formed by exposing the latent image 3 to a predetermined pattern using, for example, an optical scanning device. Next, as shown in FIG. 18B, a latent image with narrow band charging is measured. This measurement can be performed by irradiating a charged particle beam and detecting electrons emitted from the sample with a detector. By processing this detection signal, an electrostatic latent image as shown in FIG. 18C is extracted.

Next, as shown in FIG. 18 (d), the charging area 2 is set to a wide area and charged in this area, and a latent image 3 is formed in a predetermined pattern in the charging area. Charging and latent image formation are performed by the same method as before. Next, as shown in FIG. 18 (e), a latent image with broadband charging is measured. This measurement is also performed in the same manner as before, and an electrostatic latent image as shown in FIG. 18F is extracted by subjecting the obtained detection signal to image processing. This measurement and image processing are performed in the same manner as before.
The electrostatic latent image extracted by the narrow area charging thus obtained and the electrostatic latent image extracted by the wide area charging are superimposed as shown in FIG. To evaluate the electrostatic latent image. In other words, a latent image profile is created from the two electrostatic latent images, and the latent image profile is evaluated.

(Operation of evaluation apparatus and evaluation method)
Figure 19 is a charge amount in the vicinity of the center are the same, only the peripheral charges, wide-area charge 4.3 mm ^2, in the narrow-range charging and so 0.27 mm ^2, in electromagnetic field simulation by charge distribution differs more than 10 times The electric field strength distribution in the vertical direction of the photoreceptor sample is shown. In the latent image visualization by secondary electron measurement, it is possible to detect a latent image with the electric field intensity Ez = 0 in the vertical direction of the sample as a threshold level. As a result, it has been found that when the charged region is narrowed, the electric field strength changes in the vertical direction from the sample surface due to the influence of the edge effect due to the peripheral charge. When the charged region becomes narrow, the offset level of the electric field strength generated on the sample surface is shifted as a whole.
Therefore, it was found that the offset level of the electric field strength generated on the sample surface can be changed by narrowing the charging region.

  Therefore, at least twice, changing the charged area, capturing the electrostatic latent image as an image, measuring the size of the latent image from the obtained electrostatic latent image, and comparing the size of each electrostatic latent image By doing so, it is preferable to quantitatively evaluate the performance of the formed electrostatic latent image.

  Specifically, a latent image is formed by irradiating a laser beam after being charged by irradiating an electron beam. At this time, it is desirable to set the charging area C1 larger than the measurement area for detecting secondary electrons. For this reason, the observation magnification is enlarged and the observation area is changed to CS0. Next, an electron beam is scanned to detect electrons emitted from the sample, thereby acquiring an image based on a latent image. By processing the acquired image, the latent image and the latent image area S1 are measured.

  Thereafter, the charging area is changed to C2. Changing the charging region can be realized by changing the value of the deflection electrode voltage of the electron beam optical system, for example. Then, the observation magnification is enlarged, the observation region is changed to CSO, the electron beam is scanned, and the electrons emitted from the sample are detected, thereby acquiring an image by a latent image. By processing the acquired image, the latent image diameter and the latent image area S2 are measured.

  Although the electrostatic latent image can be evaluated by extracting the latent image at least twice, the same measurement may be performed with different charged regions. At the nth time, the charged area is changed to Cn and charged, a latent image is formed by exposure, the observation magnification is enlarged, and the observation area is changed to C0. By scanning the electron beam and detecting the obtained signal, an image based on the latent image is acquired. By processing the acquired image, the latent image and the latent image area Sn are measured. Further, the contour of the latent image can be extracted by performing image processing, and the latent image diameter and latent image area in the horizontal and vertical directions can be calculated.

  By combining the ring slice data, a latent image profile as shown in FIG. 21 can be obtained. FIG. 21A shows an example where the sharpness of the latent image is low, and the difference between the latent image areas S1, S2, and S3 is large. FIG. 21B shows an example in which the sharpness of the latent image is high, and the difference between the latent image areas S1, S2, and S3 is small.

As an analysis method, latent image data may be taken at least twice, and two pieces of slice information may be combined to form a latent image profile. In addition, the evaluation value may be calculated from two data.
The latent image profile can be converted into the electric field intensity profile by grasping the charging area and the electric field intensity bias level by simulation in advance.

  As shown in FIG. 21, when attention is paid to the latent image areas S1, S2, and S3 in the charged regions C1, C2, and C3, a good electrostatic latent image, that is, a state in which the latent image sharpness is high (FIG. 21B). Then, the latent image profile becomes sharp. In this case, the change in the size of the latent image areas S1, S2, and S3 is small. Conversely, when the latent image sharpness is low (FIG. 21A), the latent image area decreases in the order of the latent image areas S1, S2, and S3, and the difference between the areas is large. That is, it is possible to determine whether the formed latent image is good or bad by paying attention to the size of the latent image or the change in the latent image area.

  As another method, the exposure may be performed with fixed illumination, and a mask may be applied to a region where charges are to be left so that exposure is not possible, and the rest other than the light-shielded portion may be erased. As a result, desired peripheral charges can be erased without blocking the trajectory of the charged particle beam.

The light-shielding member may be a fixed light-shielding member in which a non-exposed portion is formed by vapor deposition or the like on a transparent object such as glass, or a liquid crystal or the like that changes the transmittance freely.
In this way, the uniformly charged photoreceptor sample 20 is exposed, and an electrostatic latent image pattern corresponding to the light shielding pattern of the light shielding member 93 is formed.

  Another method is to evaluate the electrostatic latent image by changing the charged region at least twice, and after the electrostatic exposure, the electrostatic latent image is once erased and then exposed again. A method of forming an image and extracting feature values of the latent image may be used.

  Specifically, after charging by irradiating with an electron beam, a latent image is formed by scanning a laser beam and condensing a light spot. Then, by scanning the electron beam and detecting the signal, an image based on the latent image is acquired. Thereafter, the electrostatic latent image is erased, and when charging again, the charging area is changed to the first charging. Similarly, by forming a latent image by laser light irradiation and scanning the electron beam to detect a signal, an image by the latent image can be acquired.

  Here, when the evaluation is performed by paying attention to specific two times among the plurality of charged region measurements, the area of the latent image in the wider charged region is S1, and the latent image area in the smaller charged region is When S2 is set, the latent image area ratio (S2 / S1) may be measured, and the value may be used as an evaluation index of the latent image forming ability. By measuring the latent image area ratio, the sharpness of the latent image can be measured.

The measurement flow is shown in FIG.
The number of charged areas set for one evaluation is assumed to be two. First, the charging area C1 is set and charged to form an electrostatic latent image having a predetermined pattern. A predetermined observation area C0 is set, an electron beam is irradiated, emitted electrons are detected, and electrostatic latent image data is captured. If the number of operations i so far has not reached 2, after setting “i = i + 1”, the process returns to the step of erasing the electrostatic latent image by the above-described method and newly setting the charged area. Then, charging, electrostatic latent image pattern formation, and observation area C0 are set again to capture electrostatic latent image data. When the number of operations i reaches 2, a latent image pattern is extracted by image processing, latent image areas S1 and S2 are calculated, S2 / S1 is measured, and a latent image area ratio is calculated.

The higher the latent image forming capability, the steeper or sharpness of the profile of the electric field intensity distribution of the latent image, so that the latent image cross-sectional area ratio increases and approaches the maximum value of 1.
Thus, by measuring the latent image cross-sectional area ratio, it is possible to easily measure the relative sharpness of the electrostatic latent image distribution.

FIG. 22 shows an example of the sharpness evaluation of the electrostatic latent image by the above method. In FIG.
The latent image area ratio (S2 / S1) under the latent image forming condition A is set to A (S2 / S1).
The latent image area ratio (S2 / S1) under the latent image forming condition B is set to B (S2 / S1).
When
A (S2 / S1) <B (S2 / S1)
When the above relationship is established, it can be evaluated that the latent image forming condition B has higher latent image sharpness and higher latent image forming ability. It is desirable to set the latent image area serving as a reference when performing this evaluation to the same level as much as possible.

The equivalent circle diameter when the latent image area is S is as shown in FIG.
Equivalent circle diameter D = 2 × (S / π) ^ 0.5 (2)
Can be expressed as

  Here, a specific example of the photoreceptor fatigue experiment based on the above-described latent image area ratio will be described below. The experimental conditions are as follows.

Experimental conditions Photoconductor: Phthalocyanine photoconductor (thickness 30 μm)
Acceleration voltage: 1.4 kV
Charging potential: -500V
Charging area: Wide area: Narrow area = 3.75: 1
Writing density: 600 dpi
Pattern: 2 dots isolated Duty: 100%
Light source: wavelength 655 nm
Beam spot diameter: main 45 × sub 50μm
Exposure energy density: 3 mJ / m ^ 2
An example of the measurement result of the latent image area ratio under the above conditions is shown in FIG.
It was found that the latent image area ratio initially 0.71 was 0.69 after 30 minutes fatigue, 0.64 after 2 hours fatigue, and attenuated with increasing fatigue time. In other words, the latent image sharpness of the photoconductor sample decreases with fatigue.

Such an evaluation method is suitable because the latent image sharpness changes due to electrostatic fatigue or light fatigue of the photoreceptor, and the original electrostatic latent image profile becomes dull. By using a photoconductor that is found through this evaluation method and has little change in latent image sharpness between the initial stage and after fatigue, a high-quality image can be output continuously.
It was also confirmed that the rank of the latent image area ratio has a correlation with the output image quality. As described above, it was found that it is effective to evaluate the latent image sharpness in the photoconductor sample.

  In a multi-beam scanning optical system using a VCSEL or the like as a light source, a plurality of four or more light sources are used to form a single latent image pattern under complicated exposure conditions while many beams overlap. Become. In such a case, it is difficult to understand the degree of influence of each parameter. The evaluation method of the present invention is particularly effective under such latent image forming conditions.

FIG. 25 is a diagram showing another embodiment of the electrostatic latent image evaluation apparatus of the present invention. A voltage application unit that can apply a voltage ± Vsub is connected to the sample mounting table 7 below the sample. In addition, a grid mesh 12 is arranged above the photoconductor sample 20 in order to suppress the incident electron beam from being affected by the sample charge.
By using such a measuring apparatus, it is possible to measure the surface charge distribution and the surface potential distribution profile with higher accuracy.

  FIG. 26 is a diagram showing the relationship between incident electrons and a sample. FIG. 4A shows the case where the acceleration voltage is larger than the surface potential potential, and FIG. 4B shows the case where the acceleration voltage is smaller than the surface potential potential.

The primary incident charged particles are detected under a potential potential and an acceleration voltage condition in which a region where the velocity vector of the charged particles incident on the photoconductor sample is inverted before reaching the photoconductor sample exists. . Specifically, an electrostatic latent image is measured by applying a voltage to the back surface of the photoreceptor sample in order to change the potential potential on the surface of the photoreceptor sample.
The acceleration voltage is generally expressed as positive, but the applied voltage Vacc of the acceleration voltage
Is negative, and in order to have a physical meaning as a potential potential, it is easier to explain it by expressing it negatively. Therefore, here, the acceleration voltage is expressed as negative (Vacc <0), and the potential potential of the sample is Vp (<0).

Here, the potential is the electrical potential energy of the unit charge. Therefore, the incident electrons move at a speed corresponding to the acceleration voltage Vacc at the potential 0 (V). That is, assuming that the charge amount of electrons is e and the mass of electrons is m, the initial velocity of electrons v0 is
^{mv0 2/2 = e × |} Vacc |
It is represented by In addition, the energy conservation law is almost completely established in a vacuum, so that it moves at a constant speed in the region where the acceleration voltage does not work, and as it approaches the sample surface, the potential increases and is affected by the Coulomb repulsion of the sample charge. Slows down.

Therefore, the following phenomenon generally occurs.
In FIG. 6A, since | Vacc | ≧ | Vp |, the electron reaches the sample although the speed is reduced.
In FIG. 5B, since | Vacc | <| Vp |, the velocity of the incident electrons is gradually decelerated under the influence of the potential potential of the sample, and the velocity becomes zero before reaching the sample. Go in the opposite direction.

  Therefore, the surface potential can be measured by measuring a condition in which the energy on the sample surface, that is, the landing energy when the energy of the incident electrons is changed, is almost zero. Here, among primary inversion charged particles, the case of electrons in particular will be referred to as primary inversion electrons. Since the amount of secondary electrons generated when reaching the sample and the primary inverted charged particles differ greatly in the amount reaching the detector, the secondary electrons and the primary inverted charged particles are discriminated based on the boundary of contrast between light and dark. be able to. Primary inversion electrons are electrons that are affected by the potential distribution on the sample surface and reverse before reaching the sample surface.

  A scanning electron microscope or the like is provided with a backscattered electron detector. In this case, the backscattered electrons are generally reflected (scattered) from the back surface due to the interaction with the sample material. It refers to electrons that jump out of the surface of the sample. The energy of the reflected electrons is comparable to the energy of the incident electrons. In general, the intensity of reflected electrons increases as the atomic number of the sample increases. The method of detecting reflected electrons by a scanning electron microscope is for detecting a difference in composition of the sample and unevenness.

  FIG. 27 is a diagram showing an example of a latent image depth measurement result. At each scanning position (x, y), the difference between the acceleration voltage Vacc and the sample lower applied voltage Vsub is Vth (= Vacc−Vsub), and Vth (x, y) when the landing energy is almost zero is measured. Thus, the potential distribution V (x, y) can be measured. Vth (x, y) has a unique correspondence with the potential distribution V (x, y). If Vth (x, y) is a gentle charge distribution, the potential distribution V (x , Y).

  The upper curve in FIG. 27 shows an example of the surface potential distribution generated by the charge distribution on the sample surface. The acceleration voltage of the electron gun that performs two-dimensional scanning was set to −1800V. The potential at the center (horizontal axis coordinate = 0) is about -600V, the potential increases in the negative direction as it goes from the center to the outside, and the potential in the peripheral region whose radius exceeds 75 μm from the center is about -850V. ing.

  The oval in the middle of the figure is an image of the detector output when the back surface of the sample is set to Vsub = −1150V. At this time, Vth = Vacc−Vsub = −650V.

  The oval in the lower part of the figure is an image of the detector output obtained under the same conditions as above except that Vsub = −1100V. At this time, Vth is -700V.

Therefore, the surface potential information of the sample can be measured by scanning the sample surface with electrons while changing the acceleration voltage Vacc or the applied voltage Vsub and measuring the Vth distribution.
By using this method, it is possible to visualize the latent image profile on the micron order, which has been difficult in the past.

  In the method of measuring the latent image profile with primary inversion electrons, the energy of incident electrons changes drastically, resulting in a shift in the trajectory of incident electrons, resulting in a change in scanning magnification and distortion. Sometimes. In that case, the electrostatic field environment and the electron trajectory can be calculated in advance, and correction can be performed based on the calculation, thereby making it possible to measure with higher accuracy.

(Image forming device)
A photoconductor using the above evaluation may be mounted on the image forming apparatus. Hereinafter, an embodiment of the image forming apparatus of the present invention will be described.
FIG. 28 schematically shows the laser printer according to the first embodiment. The laser printer 100 has a “cylindrical photoconductive photosensitive member” as the image carrier 111. Around the image carrier 111, a charging roller 112 as a charging unit, a developing device 113, a transfer roller 114, and a cleaning device 115 are provided. In this embodiment, a contact-type charging roller 112 that generates less ozone is used as the “charging means”, but a corona charger that uses corona discharge can also be used as the charging means. Further, an optical scanning device 117 is provided to perform “exposure by optical scanning of the laser beam LB” between the charging roller 112 and the developing device 113.

  In FIG. 28, reference numeral 116 denotes a fixing device, reference numeral 118 denotes a cassette, reference numeral 119 denotes a registration roller pair, reference numeral 120 denotes a paper feed roller, reference numeral 121 denotes a conveyance path, reference numeral 122 denotes a discharge roller pair, and reference numeral 123 denotes a tray. Yes. When forming an image, the image carrier 111, which is a photoconductive photosensitive member, is rotated at a constant speed in the clockwise direction, and the surface thereof is uniformly charged by the charging roller 112. An electrostatic latent image is formed by the exposure by engraving. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed. This electrostatic latent image is reversely developed by the developing device 113, and a toner image is formed on the image carrier 111. The cassette 118 storing the transfer paper is detachable from the main body of the image forming apparatus 100, and the uppermost sheet of the stored transfer paper is fed by the paper feeding roller 120 in the state of being mounted as shown in the figure. The transferred transfer paper is fed to the registration roller pair 119 at the leading end. The registration roller pair 119 feeds the transfer paper to the transfer unit at the same timing as the toner image on the image carrier 111 moves to the transfer position. The transferred transfer paper is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 114. The transfer paper on which the toner image is transferred is fixed on the toner image by the fixing device 116, passes through the conveyance path 21, and is discharged onto the tray 123 by the discharge roller pair 122. After the toner image is transferred, the surface of the image carrier 111 is cleaned by the cleaning device 115 to remove residual toner, paper dust, and the like.

The image carrier 111 uses a photosensitive member evaluated by the electrostatic latent image evaluation method according to the present invention using the electrostatic latent image evaluation device according to the present invention. By doing so, it is possible to provide an image forming apparatus that can use a very desirable tourist object, has excellent resolving power, and has high definition, high durability, and high reliability.
It is particularly suitable for an image forming apparatus equipped with a multi-beam scanning optical system such as a VCSEL.

DESCRIPTION OF SYMBOLS 4 Charged particle beam irradiation apparatus 40 Vacuum chamber 41 Electron gun 46 Beam blanking electrode 6 Exposure apparatus 61 Light source 7 Sample mounting base 8 Detector 9 Signal detection part 10 Image processing means 11 Conductive plate 12 Grid mesh 17 Light source 20 Photoconductor sample 77 Scanning beam 78 Sample stage 100 Laser printer 111 Image carrier 113 Developing device 115 Cleaning device 116 Fixing device

Japanese Patent Laid-Open No. 03-049143 Japanese Patent Laid-Open No. 03-200100 JP 2003-295696 A JP 2003-305881 A JP 2005-166542 A JP 2006-084434 A Japanese Patent Laid-Open No. 03-053178

Claims (5)

A method for measuring and evaluating an electrostatic latent image of a photoreceptor sample by a detection signal obtained by irradiating a charged particle beam to a photoreceptor sample having a surface charge distribution,
Comprising a charging step of charging by irradiating an electron beam on the photosensitive member samples in a vacuum, a neutralization step of neutralizing performs light irradiation to the photoreceptor sample was charged, and
The charging step of irradiating the measurement region of the photoconductor sample with the electron beam; and the neutralizing step of irradiating the measurement region of the photoconductor sample without irradiating the electron beam. After the photoconductor sample is fatigued by repeating the process, an electrostatic latent image pattern is formed by charging and exposing the photoconductor sample at a position where the charging step and the static elimination step are performed. ,
Change the charged area multiple times to make one evaluation,
The difference in detection signal that occurs due to the difference in the area of the charged region is captured as multiple images,
Extracting a plurality of electrostatic latent images from the plurality of obtained images,
An electrostatic latent image evaluation method for evaluating an electrostatic latent image by comparing sizes of the plurality of extracted electrostatic latent images.   2. The method for evaluating an electrostatic latent image according to claim 1, further comprising: a beam blanker, wherein, in the static elimination step, the electron beam is not irradiated to a measurement region of the photoconductor sample by turning on the beam blanker.   3. The method for evaluating an electrostatic latent image according to claim 1, wherein an irradiation time of the electron beam for charging is longer than a time until the surface potential of the photosensitive member sample reaches a saturated charging potential by irradiation of the electron beam. .   4. The method for evaluating an electrostatic latent image according to claim 1, wherein a light irradiation time for static elimination is longer than a time until the surface potential of the photoconductor sample reaches a residual potential by light irradiation. Measure electrostatic latent images with different charged areas,
Calculate the latent image area ratio between the latent image area in the wide charged area and the latent image area in the narrow charged area,
Evaluation of an electrostatic latent image according to claim 1, wherein the calculated latent image area ratio as an evaluation index of the latent image forming capability.

Images