JP2009063764A - Measuring device for photoreceptor electrostatic latent image, image forming apparatus, and measuring method for photoreceptor electrostatic latent image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the distribution of charges or potential generated on the surface of a dielectric, at high resolution in micron order. <P>SOLUTION: A measuring device for a photoreceptor electrostatic latent image includes a means for generating electrostatic charges on a sample by emitting an electron beam; an exposure optical system means for forming an electrostatic latent image. The device scans the surface of a sample with an electron beam and measures the distribution of an electrostatic latent image on the surface of the sample based on the detection signal obtained by scanning. The device also includes a radiation light shield means for reducing an electrostatic latent image change caused by radiation light emission from an emitter to an observation area of the sample. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for measuring an electrostatic latent image on a photoreceptor.

  The sample of the electrostatic latent image by the electron beam is limited to an LSI chip or a sample that can store and hold the electrostatic latent image. That is, a normal photoconductor that causes 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 charge cannot be held for a long time, dark decay occurs, and the surface potential decreases with time. The time that the photoconductor can hold the charge is at most several tens of 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 in the preparation stage.

Therefore, there is a method of measuring an electrostatic latent image even for a photoconductor sample having dark attenuation (see Patent Documents 1, 2, and 3). If there is a charge distribution on the sample surface, an electric field distribution corresponding to the surface charge distribution is formed in the space. For this reason, the secondary electrons generated by the incident electrons are pushed back by this electric field, and the amount reaching the detector is reduced. Therefore, a portion where the electric field intensity is strong is dark and a weak portion is bright and contrasted, and a contrast image corresponding to the surface charge distribution can be detected. Therefore, when exposed, the exposed portion is black and the non-exposed portion is white, and the electrostatic latent image formed thereby can be measured.
JP 2003-295696 A JP 2003-305881 A JP 2005-166542 A

  By the way, when an electron beam source that heats a filament, such as thermionic emission or thermal field emission, is used as an electron beam, the tip of the chip emits orange or yellow light, irradiated with radiated light, and part of it reaches the sample ( FIG. 12). The amount thereof is a very weak light amount of 1 uW or less, and for example, there is no problem with a normal scanning electron microscope (SEM) or electron microscope (TEM).

  However, in the case of latent image measurement, the integral light quantity is important in the case of a photoconductor having sensitivity to a light source of 800 nm or less when exposed for a long time even if it is weak light emission. The state changes. For example, in the case of a photoconductor having a required exposure energy of 4 mJ / m 2, the required exposure energy is reached if a weak light of 1 nW / mm 2 is irradiated for 4 s. For this reason, it is necessary to suppress the influence of the light emitted from the filament reaching the sample. In addition, light emission here refers to the light emitted from the electron gun itself with the thermal excitation of the filament. It is not photon emission or fluorescence generated when electrons collide with a solid or other material.

The present invention has been made in view of such a situation, and an object of the present invention is to provide an apparatus for measuring the charge distribution or potential distribution generated on the surface of the dielectric with high resolution on the order of microns. In particular, an object is to provide an apparatus for measuring an electrostatic latent image on a photoreceptor.
It is well known that the surface charges described here are strictly scattered in the sample. For this reason, the surface charge refers to a state in which the charge distribution state is largely distributed in the in-plane direction compared to the thickness direction. Further, the charge includes not only electrons but also ions.
Further, there may be a state in which there is a conductive portion on the surface and a voltage is applied to the conductive portion, thereby causing a potential distribution on the surface of the sample or in the vicinity thereof.

  The invention according to claim 1 is characterized in that the observation region of the sample has radiation light shielding means for reducing fluctuations in the electrostatic latent image due to irradiation of radiation emitted from the emitter.

  The invention according to claim 2 is characterized in that the light-shielding means includes means for decentering the central axis of the electron beam and scanning the sample.

  The invention according to claim 3 is characterized in that a multipole lens is used as means for shifting the central axis of the electron beam.

  The invention according to claim 4 is characterized in that the conductive antireflection means is used in the region irradiated with the radiation emitted from the emitter.

  The invention according to claim 5 is characterized in that the anti-reflection means is a sub-wavelength structure having a periodic structure of 8 hundred nanometers or less.

  The invention according to claim 6 is characterized in that an electron lens for allowing electrons to pass through the pinhole is used on the electron gun side of the pinhole.

  The invention of claim 7 is an electron gun using a means for heating a filament and a means for applying an electric field as an electron source.

  The invention according to claim 8 is characterized in that it has means for measuring under the condition that the velocity vector in the sample vertical direction of the incident charged particle exists so as to be reversed.

  In the invention of claim 9, the wavelength of the writing light source is 780 nm or less, the beam spot diameter on the surface of the photoconductor is 60 μm or less, the beam spot diameter on the surface of the photoconductor is A, and the formed latent image diameter is An image forming apparatus satisfying 1.0 <B / A <2.0 when B is satisfied is provided.

  The invention according to claim 10 is a method for measuring an electrostatic latent image, wherein the radiated light is shielded from the observation region of the sample in order to reduce fluctuations in the electrostatic latent image caused by irradiation with the radiated light emitted from the emitter. It is characterized by.

  According to the present invention, the charge distribution or potential distribution generated on the surface of the dielectric can be measured with a high resolution on the order of microns. In particular, an electrostatic latent image on the photoreceptor can be measured.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 (a) shows an embodiment of the present invention.
It consists of a charged particle beam irradiation unit that irradiates a charged particle beam, an exposure unit, a sample placement unit, a detection unit such as primary inversion charged particles and secondary electrons. 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.

Hereinafter, an embodiment in which an electron beam is irradiated will be described.
The electron beam irradiation unit is generated from an electron gun for generating an electron beam, a suppressor electrode and an extraction electrode for controlling the electron beam, an acceleration voltage for controlling the energy of the electron beam, and the electron gun. Condensing the condenser lens for focusing the electron beam, the pinhole, the eccentric lens for changing the traveling direction of the electron beam, the scanning lens for scanning the electron beam passing through the eccentric lens, and the scanning lens again Objective lens. A driving power source (not shown) is connected to each lens.

There are a first pinhole and a second pinhole before and after the decentered lens.
A scintillator, a photomultiplier tube, or the like is used as a means for detecting secondary electrons, primary inversion electrons, or the like. Usually, the scintillator is configured to capture charged particles by applying a high voltage of about 8 to 10 kV.
In order to guide the detected charged particles to the detector, an emitted particle generating member that generates emitted particles at the time of charged particle collision is disposed.

The exposure unit consists of a light source such as an LD (laser diode) having a wavelength with sensitivity, a collimate lens, an aperture, a condenser lens, etc., and can generate a desired beam diameter and beam profile on the sample. It is possible. In addition, an appropriate exposure time and exposure energy can be irradiated by the LD control means.
In order to form a line pattern, a scanning mechanism using a galvanometer mirror or a polygon mirror may be attached to the optical system (see FIG. 10).
Further, in order to form a latent image pattern at a predetermined position, a synchronization detection unit that detects a scanning beam from the light deflection unit may be provided.
The shape of the sample may be a flat surface or a curved surface.

  The scanning optical system is preferably arranged outside the vacuum chamber so that the influence of the vibration of the deflector such as a polygon motor or the influence of the electromagnetic field does not affect the trajectory of the electron beam. By moving away from the position of the electron beam orbit, the influence of disturbance can be suppressed. The scanning optical system is preferably incident from an optically transparent entrance window.

FIG. 2 is a cross-sectional view of the present embodiment. As shown in FIG. 2, an incident window through which the light source can enter from the outside is disposed inside the vacuum chamber at a position of 45 ° with respect to the vertical axis of the vacuum chamber, and a scanning optical system is disposed outside the vacuum chamber. It has a configuration. In FIG. 2, the scanning optical system includes a light source unit, a scanning lens, synchronization detection means, an optical deflector, and the like.
The scanning lens has fθ characteristics, and the light beam moves at a substantially constant speed with respect to the image plane when the optical polarizer rotates at a constant speed. Further, the beam spot diameter can be scanned substantially uniformly.

  Since the scanning optical system is arranged away from the vacuum chamber, the vibration generated when driving an optical deflector such as a polygon scanner is less affected by being directly propagated to the vacuum chamber. Further, although not shown in FIG. 2, if a damper is inserted between the structure and the vibration isolation table, a more effective vibration isolation effect can be obtained.

  There are electrons and ions as emitted particles, and it is common to detect and measure electrons. However, it is also possible to detect positive ions by applying a negative pull-in voltage to the detector and observe the contrast image. is there.

  If there is a charge distribution on the sample surface, an electric field distribution corresponding to the surface charge distribution is formed in the space. For this reason, the secondary electrons generated by the incident electrons are pushed back by this electric field, and the amount reaching the detector is reduced. Accordingly, at the charge leak portion, the exposed portion is black and the non-exposed portion is white, and a contrast image corresponding to the surface charge distribution can be measured.

FIG. 3A illustrates the potential distribution in the space between the charged particle trap 24 and the sample SP in the form of contour lines. Since the surface of the sample SP is uniformly charged to a negative polarity except for the portion where the potential is attenuated due to light attenuation, and the charged particle trap 24 is given a positive potential, In the “potential contour line group”, the “potential becomes higher” as it approaches the charged particle trap 24 from the surface of the sample SP.
Therefore, the secondary electrons el1 and el2 generated at the points Q1 and Q2 in the figure, which are “negatively uniformly charged portions” in the sample SP, are attracted to the positive potential of the charged particle trap 24, and the arrow G1. And is displaced as indicated by the arrow G2 and is captured by the charged particle trap 24.

On the other hand, in FIG. 3A, the point Q3 is “a portion where the negative potential is attenuated by light irradiation”, and the arrangement of potential contour lines is “as shown by the broken line” in the vicinity of the point Q3. “The closer to Q3 point, the higher the potential”. In other words, the secondary electron el3 generated in the vicinity of the point Q3 is subjected to an electric force restrained on the sample SP side as indicated by an arrow G3. For this reason, the secondary electron el3 is captured in the “potential hole” indicated by the broken line potential contour and does not move toward the charged particle trap 24. FIG. 3B schematically shows the “potential hole”.
That is, the intensity of the secondary electrons (number of secondary electrons) detected by the charged particle trap 24 is such that the portion with the high intensity is “the ground portion of the electrostatic latent image (the portion that is uniformly negatively charged FIG. 3 ( The portion having a low intensity corresponds to “the image portion of the electrostatic latent image (the portion irradiated with light” and the portion represented by the point Q3 in FIG. 3A). ) ”.

Therefore, if the electrical signal obtained by the secondary electron detection unit 25 is sampled at an appropriate sampling time by the signal processing unit, the surface potential distribution: V (X, Y) using the sampling time: T as a parameter as described above. Can be specified for each “small area corresponding to sampling”, and the signal processing unit 25 configures the surface potential distribution (potential contrast image): V (X, Y) as two-dimensional image data, which is output. If output by the apparatus, an electrostatic latent image is 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 is known, the surface charge distribution can also be known.

  Here, the center axis of the electron beam is a line connecting the center of the emitter and the center of the first pinhole from the emitter side. As shown in FIG. 12A, when the central axis is aligned to the sample, it is ideally ideal for SEM and has small aberration. However, since the radiated light reaches the sample, even if it is weak, if it is considered by the integrated light quantity, it will affect the electrostatic latent image. FIG. 12B is a diagram showing the relationship between the central axis of the electron beam, the emitted light, the electron beam, and the sample.

  Therefore, in the present invention, as a solution, it is preferable to arrange a multipole lens as shown in FIG. 1A and intentionally shift the second pinhole position. FIG. 1B shows the relationship between the central axis of the electron beam and the radiation, electron beam, and sample.

  The multipole lens is a lens having a structure in which a plurality of electrodes or magnetic poles are arranged in a plane (XY) perpendicular to the electron beam optical axis (Z axis). There are dipoles, quadrupoles, hexapoles and octupoles. These can induce stronger lens action and deflection action than ordinary rotationally symmetric lenses. This is used to decenter the electron beam. FIG. 1B shows a configuration using decentering lenses 1 and 2 having two steps of quadrupole lenses, and the decentering lens 2 is shifted in parallel with respect to the central axis. As shown in FIG. 1B, when the electron beam is shifted in parallel from the central axis, and the position of the second pinhole is also shifted from the center, the electron beam passes through the second pinhole, and the emitted light passes through the pinhole. I can't do it. Therefore, it is possible to shield the radiation from reaching the sample by this method.

The electron beam is affected by the electromagnetic field and the incident electron trajectory is bent, but the emitted light travels straight without being affected by the electromagnetic field, so it is possible to reach the sample by forming a pinhole at the offset position. Can be suppressed.
If the axis is shifted, the aberration increases and the resolution decreases. However, it is an effective means for the problem of suppressing the electrostatic latent image fluctuation of the photoconductor.

Another method is shown in FIG. The second-stage decentered lens itself has a symmetric configuration with respect to the central axis. Even in this method, it is possible to decenter the electron beam, and there is a light shielding effect.
The distance from the emitter center to the first pinhole is L1, and the pinhole diameter is φ1
The distance from the emitter center to the second pinhole is L2, and the pinhole diameter is φ2.
Then, the diameter of the emitted light in the second pinhole is φ3 = φ1 × L2 / L1 in the geometric calculation,
The amount of eccentricity may be shifted by 0.5 × (φ3 + φ2). It is possible to completely block the emitted light.
In the case of L1 = 50 mm, L2 = 100 mm, and φ1 = φ2 = 0.05 mm, the emitted light can be shielded by decentering by 0.075 mm or more. In the case of 0.075 mm or less, the light cannot be completely shielded, but can be greatly reduced by shifting.

Yet another method is shown in FIG. In this method, the second pinhole is on the central axis, and the deflecting lens is used to make the electron beam obliquely incident on the second pinhole. Although it reaches the sample surface without being scattered by the holes, it is separated from the scanning electron beam region, and the scanning region, that is, the measurement region is not irradiated with the emitted light.
Therefore, the electrostatic latent image fluctuation | variation by a radiated light can be suppressed by removing the radiated light which arrives at a sample from the observation area | region of a sample.

(Embodiment of claim 5)
As another method for reducing the radiated light emitted from the emitter, there is a method of applying an antireflection coating in the lens barrel irradiated with the radiated light.
As an antireflection part, a place where the radiated light in the lens barrel is more likely to hit and leak easily is appropriate. It is even better if it is in the vicinity of a pinhole or in a narrow space where radiated light directly hits.

When the electron beam hits the member without passing through the pinhole, secondary electrons are emitted. When this collides with the dielectric material, charges are accumulated, the electric field environment changes, and the electron beam stabilization is hindered. FIG. 8A shows a configuration in which a conductive cap is attached to the top of the pinhole to prevent this. An antireflection film may be attached to the inner surface.
As an antireflection film, there is a dielectric multilayer film. In the case of a dielectric multilayer film, charges are accumulated. On the other hand, a conductive antireflection film is better. By using Sn / In 2 O 3 ultrafine particles or noble metal ultrafine particles as the film structure, the conductivity can be increased. If it is about 10 ^ 9 Ω / sq or less, it is possible to prevent the electric field environment from changing due to the charge being accumulated in the field.

  Another method is to use a nanometer order periodic structure. When a periodic structure having a wavelength shorter than the wavelength of light is formed on the glass surface, a structure in which the refractive index is smoothly changed from the refractive index 1 of air to the refractive index of the structure can be formed. This structure eliminates a sudden change in refractive index and can prevent reflection significantly. FIG. 8B shows an antireflection means by the sub-wavelength structure of the V groove.

If the period Λ <= 800 nm and the aspect ratio h / Λ> = 2, near infrared light can be cut from visible light, which is the sensitivity range of the photoreceptor. This subwavelength structure is characterized by being independent of a specific wavelength and having little angle dependency. Moreover, it is only a surface structure and has the advantage that a new part and process are not required.
In a narrow space as shown in FIG. 8B, since the radiated light is easily scattered, it is effective to have a sub-wavelength structure on the inner side surface.

(Example of Claim 6)
FIG. 6 shows an embodiment in which an electron lens is disposed between the nth and n + 1st pinholes. In order to clarify the function, a necessary configuration is shown in a simplified manner. The synchrotron radiation that has passed through the nth has a spread. The figure exaggerates the spread. The electron beam that has passed through the n-th can pass through the (n + 1) -th pinhole by the electron lens. The electron lens may be an electrostatic lens or a magnetic lens. A plurality of electron lenses may be arranged or a relay lens may be configured. In this method, the emitted light from the emitter cannot be completely blocked, but the current amount of the electron beam and the ratio of the amount of emitted light can be significantly reduced.
The distance from the center of the emitter to the nth pinhole is L_n, and the pinhole diameter is φ_n
The distance from the emitter center to the (n + 1) th pinhole is L_n + 1, and the pinhole diameter is φ_n + 1
Then, the diameter of the emitted light at the nth pinhole is φ_n × L_n + 1 / L_n in the geometric calculation.
As the amount of radiation,
[φ_n × L_n + 1 / (φ_n + 1 × L_n)] ^ 2
Can only be suppressed.

FIG. 7 shows another embodiment in which an electron lens is arranged between the emitter and the first one. The opening angle of the emitter Zr O / W is effective because it is as wide as ± 100 mrad in the range of the central flat portion. For example, at a position 15 mm away from the emitter, it is about φ3 mm. If a pin hole of φ0.05 is arranged here, it becomes 1/3600, and the S / N ratio is improved.
With this method, the amount of light can be significantly suppressed.

(Example of Claim 7)
As the electron gun, a thermal field emission electron gun is preferable. The thermal field emission electron gun here refers to an electron gun that emits electrons by heating a cathode to a high temperature and applying an electric field. A Schottky electron gun is also included. The configuration of the Schottky electron gun is shown in FIG. If the heating temperature of the cathode is about 1000K or less and about 700K, it is a thermal field emission phenomenon, and if the heating temperature of the cathode is 1000K or more and a high temperature of 1800K, Schottky emission occurs. Usually a ZrO / W emitter is used. Brightness is high and electron source is small compared to thermionic gun. Compared with a field emission electron gun, the cathode is heated to a high temperature of 1800K, so that the current stability is high, a large probe current can be obtained, and the operating pressure may be slightly high. have.
There is a demerit that light is emitted when the filament is heated, but this can be suppressed by the above-described method.

(Embodiment of claim 8)
By measuring the profile of the surface charge distribution and the surface potential distribution, it is possible to measure with higher accuracy.

FIG. 12 is a view showing another embodiment of the surface potential distribution measuring apparatus of the present invention.
A voltage application unit that can apply a voltage Vsub is connected to the sample installation unit below the sample. Further, the upper portion of the sample has a configuration in which a grid is arranged in order to suppress the incident electron beam from being affected by the sample charge.

FIG. 13 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.
There is a region where a state where the velocity vector of the incident charged particles in the sample vertical direction is reversed before reaching the sample, and the primary incident charged particles are detected.

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 more preferable to express it as negative. Here, the acceleration voltage is expressed as negative (Vacc <0).
The acceleration potential of the electron beam is Vacc (<0), and the potential potential of the sample is Vp (<0).
A potential is an electrical potential energy possessed by a 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 represented by mv02 / 2 = e × | Vacc |. In vacuum, due to the law of conservation of energy, 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 the velocity decreases due to the influence of Coulomb repulsion of the sample charge.

Therefore, the following phenomenon generally occurs.
In FIG. 9A, since | Vacc | ≧ | Vp |, the electrons reach the sample although the speed is reduced.
In FIG. 4B, in the case of | Vacc | <| Vp |, the velocity of the incident electrons is gradually decelerated due to the influence of the potential potential of the sample, and the velocity becomes zero before reaching the sample. Go in the opposite direction.

In a vacuum with no air resistance, the energy conservation law is almost completely established.
Therefore, the surface potential can be measured by measuring a condition in which the energy on the sample surface, that is, the landing energy, is substantially zero when the energy of the incident electrons is changed. Here, primary inversion charged particles, particularly electrons, are referred to as primary inversion electrons. The secondary electrons generated when the sample reaches the sample and the primary inversion charged particles differ greatly in the amount reaching the detector, so that they can be identified from the boundary of contrast between light and dark.

A scanning electron microscope or the like has a backscattered electron detector. In this case, the backscattered electrons are generally reflected (scattered) on the rear back surface due to the interaction with the material of the sample, and the sample. It refers to the electrons that jump out of the surface. The energy of the reflected electrons is comparable to the energy of the incident electrons. It is said that the intensity of the reflected electrons increases as the atomic number of the sample increases, and this is a detection method for understanding the difference in composition of the sample and unevenness.
In contrast, primary inversion electrons are electrons that are inverted before reaching the sample surface under the influence of the potential distribution on the sample surface, and are completely different phenomena.

FIG. 14 is a diagram illustrating an example of a latent image depth measurement result.
If the difference between the acceleration voltage Vacc and the sample lower applied voltage Vsub is Vth (= Vacc−Vsub) at each scanning position (x, y), Vth (x, y) when the landing energy becomes almost zero. Can be measured to measure the potential distribution V (x, y). 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. 14 shows an example of the surface potential distribution generated by the charge distribution on the sample surface. The acceleration voltage of the electron gun for 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 a latent image profile with primary inverted electrons, the energy of incident electrons changes drastically, and the trajectory of incident electrons may shift, resulting in a change in scanning magnification or distortion. Will be.
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.

(Embodiment of claim 9)
The process of forming a latent image can be quantitatively analyzed in detail by evaluating the photosensitive member by the electrostatic latent image measuring method performed by the electrostatic latent image measuring apparatus of the present embodiment, so that the exposure amount is optimized. The charging and exposure conditions that do not impose a burden on the photoreceptor can be known, and energy saving and high durability can be realized.

Furthermore, in order to improve the output image quality, attempts have been made to reduce the beam spot diameter to 60 μm or less by optimizing the optical system and shortening the light source wavelength to 780 nm or less. Photoconductors have low sensitivity to short-wavelength light, and small-diameter beams are strongly affected by light scattering and charge diffusion within the photoconductor, increasing the latent image diameter and shallowing the latent image depth. Therefore, the final output image has a problem in that the stability of gradation and sharpness cannot be obtained.
The beam spot diameter here is defined as a diameter in a range where the beam spot light quantity distribution is equal to or larger than the maximum light quantity e-2. The latent image diameter is defined as a diameter in a range where the latent image charge density distribution is equal to or larger than e−2 of the charge density difference of the portion where the charge density difference is the largest with reference to the charge density of the portion where the light is not irradiated.

It is known that the composition and thickness of the charge transport layer affect the light scattering and charge diffusion degree, and the charge generation layer composition affects the sensitivity, but no clear correlation is known. Therefore, a photoconductor is produced by changing the composition and thickness of the charge transport layer and the composition of the charge generation layer, and used in the image forming apparatus in the electrostatic latent image measurement method performed by the electrostatic latent image measurement apparatus of this embodiment. For example, exposure is performed under the same conditions as in the above, for example, a charging potential of 800 V, an exposure energy of 4 mJ / m 2, a light source wavelength of 780 nm or less, and a beam spot diameter of 60 μm or less, and latent images are measured. As shown, when the beam spot diameter on the photoreceptor surface is A and the latent image diameter to be formed is B,
1.0 <B / A <2.0
If a photoconductor that satisfies the above conditions is selected, gradation and sharpness stability can be realized in the final output image.

  Here, the lower limit of 1.0 is a theoretical limit that light scattering and charge diffusion always occur in any photoconductor and cannot be less than this, and the upper limit of 2.0 is a step in the final output image. This is the limit necessary to ensure the stability of tonality and sharpness.

  Hereinafter, an embodiment of the image forming apparatus of the present invention will be described. FIG. 15 schematically shows a 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. 111, 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.

  By using the highly desirable latent image carrier according to the present invention, it is possible to manufacture an image forming apparatus that has excellent resolution, high definition, high durability, and high reliability.

The actions or effects of each claim are described below.
(1) Effect on Claim 1 It is possible to suppress fluctuations in the electrostatic latent image by having means for shielding the sample from being irradiated with the radiated light emitted from the emitter against the observation region of the sample. Thus, the electrostatic latent image on the photoconductor can be measured with a resolution of micron order with high accuracy.

(2) Effect of Claim 2 By decentering with respect to the central axis of the electron beam, the electron beam and the emitted light can be separated, and the emitted light can be shielded.
As a result, it is possible to measure an electrostatic ray image with a high resolution on the order of microns.

(3) Effect of claim 3 By using a multipole lens, the electron beam can be easily deflected, the electron beam and the emitted light can be separated, and the emitted light can be shielded. it can.
As a result, it is possible to measure an electrostatic ray image with a high resolution on the order of microns.

(4) Effect on Claim 4 By using the antireflection means, the amount of light applied to the sample can be suppressed by the reflected light being reflected and scattered by the member. In addition, electric charges are not accumulated in the lens barrel by the conductive antireflection means, not the dielectric, and the electric field environment is not disturbed.

(5) Effect on Claim 5 By using a subwavelength structure having a periodic structure of 8 hundred nanometers or less as the conductive antireflection means, antireflection is realized without any new treatment such as coating. be able to. Further, since it does not depend on a specific wavelength and has little angle dependency, it is effective for preventing scattering of radiated light having a wide band.

(6) Effect on Claim 6 By using an electron lens for allowing electrons to pass through the pinhole on the electron gun side of the pinhole, the amount of radiated light reaching the sample can be reduced to a level with no problem.

(7) Effect on Claim 7 By using an electron gun having means for heating a filament and means for applying an electric field, the current stability is high, and a large probe current required for charging can be obtained.

(8) Effect on Claim 8 Quantitative measurement of potential depth is possible by having means to measure under conditions where the velocity vector in the sample vertical direction of incident charged particles is reversed. Thus, the potential distribution can be measured with high accuracy.

(9) Effect on Claim 9 By evaluating the electrostatic latent image using any one of the measurement method and the measurement device according to claims 1 to 8, it is possible to feed back to the design, and the process quality of each process is In order to improve, it is possible to provide a latent image carrier and a scanning optical system excellent in high image quality, high durability, high stability, and energy saving. By developing and visualizing, high density, high image quality, and high durability are achieved. An image forming apparatus can be provided.

(10) Effect on Claim 10 In order to reduce the electrostatic latent image fluctuation due to the irradiation of the emitted light emitted from the emitter with respect to the observation region of the sample, the electrostatic latent image fluctuation is prevented by shielding the emitted light. Therefore, it is possible to measure the electrostatic latent image on the photosensitive member with a resolution of micron order with high accuracy.

  Each of the above-described embodiments is a preferred embodiment of the present invention, and various modifications can be made without departing from the scope of the present invention. The present invention can be applied to a surface charge distribution measuring device, a surface potential distribution measuring device, an electrostatic latent image measuring device in an electrophotographic process, and a high-quality image forming apparatus.

It is a block diagram of embodiment of this invention. It is a block diagram of embodiment of this invention. It is a principle model diagram of charge distribution / potential distribution detection by secondary electrons. It is a block diagram of other embodiment of this invention. It is a block diagram of other embodiment of this invention. It is a block diagram of other embodiment of this invention. It is a block diagram of other embodiment of this invention. It is a figure of the antireflection means by the subwavelength structure of V groove. It is a block diagram of other embodiment of this invention. It is a block diagram of an exposure optical system. It is a block diagram of other embodiment of this invention. It is a figure of the example of a measurement by grid mesh arrangement | positioning. It is a figure which shows the relationship between an incident electron and a sample. It is a figure which shows an example of a latent image depth measurement result. It is a block diagram of the apparatus of this invention. It is a figure regarding the conventional structure.

Claims (10)

By irradiating the sample with an electron beam, a means for generating a charged charge on the sample, an exposure optical system means for forming an electrostatic latent image, and the surface of the sample are scanned with the electron beam. In the measurement device for the electrostatic latent image of the photosensitive member that measures the distribution of the electrostatic latent image on the sample surface by the detection signal obtained by
An apparatus for measuring a photosensitive member electrostatic latent image, comprising: a radiant light shielding unit for reducing fluctuation of an electrostatic latent image due to irradiation of radiant light emitted from an emitter with respect to an observation region of a sample.   2. The apparatus for measuring an electrostatic latent image on a photosensitive member according to claim 1, further comprising means for decentering with respect to the central axis of the electron beam as the radiation light shielding means.   3. The apparatus for measuring an electrostatic latent image on a photosensitive member according to claim 2, further comprising means for using a multipole lens as means for decentering with respect to the central axis of the electron beam.   2. The apparatus for measuring an electrostatic latent image on a photosensitive member according to claim 1, wherein conductive antireflection means is used in a region irradiated with radiation emitted from the emitter.   5. The apparatus for measuring a latent electrostatic image on a photosensitive member according to claim 4, wherein the electroconductive reflection preventing means is a sub-wavelength structure having a periodic structure of 8 hundred nanometers or less.   2. The apparatus for measuring an electrostatic latent image on a photosensitive member according to claim 1, wherein an electron lens for allowing electrons to pass through the pinhole is used on the electron gun side of the pinhole.   2. The apparatus according to claim 1, further comprising means for heating the filament and means for applying an electric field as the electron source.   2. The apparatus for measuring a latent image on a photosensitive member according to claim 1, further comprising means for measuring the velocity vector of the incident charged particles in the vertical direction of the sample in a condition where there is an inversion region. A latent image is formed by performing optical scanning on the photosensitive surface of the latent image carrier measured using the measuring device according to claim 1, developed, and visualized. An image forming apparatus,
When the wavelength of the writing light source is 780 nm or less, the beam spot diameter on the surface of the photosensitive member is 60 μm or less, the beam spot diameter on the surface of the photosensitive member is A, and the formed latent image diameter is B. An image forming apparatus satisfying 0 <B / A <2.0. By irradiating a sample with charged particles, a charged charge is generated on the sample, an electrostatic latent image is formed using a laser optical system, and the sample surface is scanned with an electron beam, and obtained by the scanning. In the method for measuring a photosensitive member electrostatic latent image, the electrostatic latent image distribution on the sample surface is measured by a detection signal.
A method for measuring an electrostatic latent image of a photosensitive member, wherein radiation light is shielded to reduce an electrostatic latent image variation caused by irradiation of radiation emitted from an emitter with respect to an observation region of a sample.

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