JP5091081B2 - Method and apparatus for measuring surface charge distribution - Google Patents

Description

  The present invention relates to a surface charge distribution measuring method and a measuring apparatus for carrying out this measuring method.

  In an electrophotographic image forming apparatus such as a copying machine or a laser printer, the following image forming process is usually performed when an image is output.

a. Charging process for uniformly charging photoconductive photoconductors
b. An exposure process in which an electrostatic latent image is formed by photoconductivity by irradiating light to a photoreceptor.
c. Development process for forming a visible image on a photoreceptor using charged toner particles
d. Transfer process to transfer the developed visible image to a transfer material such as a piece of paper
e. Fixing process that fuses and fixes the transferred image onto the transfer material
f. A cleaning step of cleaning residual toner on the photoreceptor after transfer of the visible image; g. A neutralization process for neutralizing residual charges on the photoreceptor.

  The process factor and process quality in each of these processes greatly affect the quality of the final output image. In recent years, in addition to high image quality, there has been an increasing demand for environmentally friendly imaging processes such as high durability, high stability, and energy saving, and there is a strong demand for improving the process quality of each process. Yes.

  In the image forming process, the electrostatic latent image formed on the photoconductor by charging / exposure is a “factor that directly affects the behavior of the toner particles”, and it is important to evaluate the quality of the electrostatic latent image on the photoconductor. Become. By observing the electrostatic latent image on the photoconductor and feeding back the results to the design, it is possible to improve the process quality of the charging and exposure processes, resulting in improved image quality, durability, stability, and savings. Further improvement in energy can be expected.

  However, it is extremely difficult to measure an electrostatic latent image formed on a photoconductive photoreceptor by charging and exposure.

  As a method for measuring the potential distribution, the conventional method is to “close a sensor head such as a cantilever to a sample with a potential distribution, and measure the electrostatic attraction and induced current generated as an interaction at that time and convert it to a potential distribution. The electrostatic attraction type observation device is commercially available as an SPM (scanning probe microscope), and the induced current type is disclosed in Patent Documents 1 and 2 and the like.

  In these methods, the sensor head needs to be close to the sample. For example, in order to obtain a spatial resolution of 10 μm, the distance between the sensor and the sample needs to be 10 μm or less.

Measurement under these conditions is
・ Absolute distance measurement is required.

  ・ Measurement takes time, and the latent image changes during that time.

  -Discharge and adsorption occur between the sensor head and the sample.

・ The sensor itself disturbs the electric field.
In practice, it is extremely difficult to appropriately measure the electrostatic latent image.

  A method of developing the electrostatic latent image to form a toner image, transferring the resulting toner image to paper or tape, and measuring the state (quality) of the electrostatic latent image with this toner image is considered. In the method, the state of the electrostatic latent image is indirectly observed through the development / transfer process, and the electrostatic latent image itself is not measured.

  As a method for measuring an electrostatic latent image, Patent Document 3 discloses a method of measuring a charging characteristic, a photosensitive characteristic, and a dark attenuation characteristic with a surface potential meter or the like. However, in the measurement method described in Patent Document 3, the spatial resolution obtained is only on the order of centimeters or millimeters, and the original image quality of 600 dpi (1 dot: 42 μm), 1200 dpi (1 dot: 21 μm) is required. Compared to the micron-order spatial resolution, it is many orders of magnitude worse and is not necessarily sufficient for evaluating the electrostatic latent image itself.

  Patent Documents 4 and 5 describe the measurement of an electrostatic latent image by irradiating an electrostatic latent image or surface charge distribution with an electron beam. However, in the measurement technique described in Patent Document 5, what holds the charge distribution to be measured is a conductor sample such as an LSI chip, and the measurement technique described in Patent Document 4 stably holds charges. It can only be applied to a dielectric sample capable of being applied, and cannot be applied to a sample whose charge distribution attenuates with time due to dark decay, such as a photoconductive sample.

  That is, a normal dielectric can hold a charge semi-permanently, and thus the charge distribution can be measured over time. However, since a photoconductive sample has a finite resistance value, the surface charge can be measured. Cannot be maintained for a long time, and the surface potential decreases with time due to dark decay. The time for which the photoconductive sample can hold the surface charge is at most several tens of seconds even in a dark room. For this reason, 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.

  Further, when the surface charge distribution is measured by an electron beam, the surface charge distribution itself may be lost by the electron beam irradiation.

  Furthermore, if the intensity of the electric field (electric field vector in which the incident side of the electron beam is positive in the direction perpendicular to the measurement sample surface) formed by the surface charge distribution on the measurement sample surface increases, a binary value which will be described later in the measurement result. Phenomenon occurs. When the surface charge distribution is an electrostatic latent image, in an actual electrophotographic process, there is an electric field strength (Eth) necessary for adhering toner particles. Is not done.

  If the electric field strength distribution in the electrostatic latent image can be approximated by a smooth curve such as a Gaussian distribution, the latent image diameter in Eth can be calculated on a computer, but in reality, an error factor is added. In general, it is desirable to capture directly as a contrast image in Eth.

Japanese Patent No. 3009179 Japanese Patent Laid-Open No. 11-184188 JP 2002-82572 A Japanese Patent Laid-Open No. 3-49143 JP-A-3-29867

This invention makes it a subject to implement | achieve the method and apparatus which measure the surface charge distribution by the electrostatic latent image of the sample surface accurately .

That is, it is an object of the present invention to realize a method and apparatus for measuring the surface charge distribution by the electrostatic latent image on the sample surface appropriately and accurately at a desired electric field strength level.

Hereinafter, means for solving the problem will be described. Prior to the description of the invention of claim 1 and below, reference techniques 1 to 17 and terms are preliminarily described.
The method for measuring the surface charge distribution of the present invention is as follows: “A sample having a charge on the surface is irradiated with a charged particle beam and scanned one-dimensionally or two-dimensionally. Is a method of measuring.

A “charged particle beam” is a so-called charged particle beam that is affected by an electric field or magnetic field, such as an electron beam or an ion beam.
The measurement method of Reference Technique 1 has the following characteristics.
That is, scanning is performed with the charged particle beam irradiation current set to “a magnitude that does not cause the surface charge distribution of the sample to disappear”.

The “irradiation current” of the charged particle beam in the surface charge distribution measurement method of Reference Technology 1 can be 1E-10A (10 ⁻¹⁰ A or less, the same applies hereinafter) ( Reference Technology 2). The irradiation current in the measurement method described in Reference Technique 1 or 2 is preferably “1E-12A or more” ( Reference Technique 3).

In the surface charge distribution measurement method of Reference Techniques 1 to 3 , when the sample is a “precharged sample” such as a photoconductive sample, the acceleration voltage of the charged particle beam to be irradiated with respect to the charged potential: V : V1 is the condition:
V1> | V |
Is preferably satisfied ( Reference Technique 4).

In the method for measuring the surface charge distribution of Reference Techniques 1 to 4 described above, “an electron beam can be used as a charged particle beam to be irradiated” ( Reference Technique 5).
In the surface charge distribution measurement methods of Reference Techniques 1 to 5 , “intensity of secondary electrons generated by scanning of charged particle beam” can be detected as a detection signal ( Reference Technique 6).

  In this specification, “secondary electrons” refer to electrons generated in a sample “caused” by a charged particle beam to be scanned, and are literally “electrons generated secondarily by an impact by an electron beam”. Does not mean. That is, the secondary electrons include cases where the secondary electrons are actually higher-order electrons such as tertiary electrons.

In the surface charge distribution measurement method of Reference Techniques 1 to 6, it is possible to “irradiate the sample with an electron beam to form a charge distribution on the sample surface” ( Reference Technique 7). The so-called charge distribution can be “with a desired pattern” or “uniform distribution”.

The measurement method of the surface charge distribution of Reference Techniques 1 to 7 is that “ the surface charge distribution to be measured is an electrostatic latent image formed by charging and exposure on a photoconductive photoreceptor as a sample”. ( Reference technique 8). In this case, an electrostatic latent image can be formed by performing exposure after irradiating a photoconductive photoconductor as a sample with an electron beam to form a uniform charge distribution on the sample surface ( Reference Technique 9). ).

The “exposure” in the measurement method of the surface charge distribution of the reference technique 9 can be performed by irradiation with a desired light beam ( reference technique 10) or can be performed by “light scanning” ( reference technique 11).

The surface charge distribution measuring apparatus of the reference technique 12 is “an apparatus for carrying out the surface charge distribution measuring method according to claim 1”, and includes a holding unit, a charged particle beam scanning unit, and a measuring unit.

  The “holding means” holds a sample having a charge distribution as a measurement target in a measurement state.

  The “charged particle beam scanning means” is means for irradiating the sample held by the holding means with a charged particle beam to scan one-dimensionally or two-dimensionally.

"Measuring means" means for measuring the charge distribution by capturing charged particles that are electrically affected by the charge distribution as a measurement target, detecting the intensity as a detection signal corresponding to the position on the sample surface It is.
The “charged particle beam irradiation current in the charged particle beam scanning means” can be set to a magnitude that does not cause the surface charge distribution of the sample to disappear.

  “Charged particles that are electrically affected by the charge distribution” are charged particles that constitute the scanned charged particle beam (for example, the surface charge of the sample and the charged particles of the charged particle beam have the same polarity). In some cases, the scanned charged particles are repelled and captured by the surface charge of the sample), and the charged particles generated in the photoconductive sample by the impact of the charged particle beam (the aforementioned “secondary electrons” are It is an example).

In the surface charge distribution measuring apparatus of Reference Technique 12 , the charged particle beam scanning unit is an electron beam scanning unit, and the measuring unit detects “the intensity of secondary electrons generated in the sample accompanying the scanning of the electron beam as a detection signal”. ( Reference technique 13).

The surface charge distribution to be measured in the surface charge distribution measuring apparatus of Reference Technique 12 or 13 can be “an electrostatic latent image formed by charging and exposure on a photoconductive photosensitive member as a sample” In this case, it can have “charging means” for uniformly charging the sample and “exposure means” for exposing the uniformly charged sample ( reference technique 14).

In the surface charge distribution measuring apparatus of the reference technique 14 , the charged particle beam scanning means can be an electron beam scanning means, and the electron beam scanning means can also serve as the charging means ( reference technique 15).

The “exposure means” of the surface charge distribution measuring apparatus of the reference technique 14 or 15 may be configured to perform exposure by irradiation with a desired light beam ( reference technique 16), or may be configured to perform exposure by optical scanning. ( Reference technique 17).

The method for measuring the surface charge distribution according to claim 1 has the following characteristics.

Then, the step of binarizing the potential contrast image obtained by the measurement and calculating the diameter of the latent image obtained at the binarized boundary portion is equivalent to “a bias component of the electric field strength generated on the sample surface corresponding to the measurement region”. This is repeated a plurality of times by shifting to a plurality of stages in the area area.
Further, “a potential profile of an electrostatic latent image is obtained from a plurality of obtained latent image diameters”.

A surface charge distribution measuring apparatus according to claim 2 is an apparatus for carrying out the surface charge distribution measuring method according to claim 1 , wherein the holding means, the charged particle beam scanning means, the measuring means, and the electric field strength. It has variable means and means for obtaining a potential profile .

“Holding means” is means for holding a sample having a surface charge distribution by an electrostatic latent image as a measurement target in a measurement state.
The “charged particle beam scanning means” is means for irradiating the sample held by the holding means with a charged particle beam to scan one-dimensionally or two-dimensionally.

The “measuring means” is means for capturing the charged particles that are electrically affected by the charge distribution, detecting the intensity as a detection signal in correspondence with the position on the sample surface, and measuring the charge distribution. .

The “field strength varying means” is a means for shifting and changing the bias component of the field strength generated on the sample surface in a plurality of stages in the area corresponding to the measurement region .
The “ means for obtaining a potential profile” is a method of binarizing the potential contrast image obtained by the measurement by the measuring means, calculating a latent image diameter obtained at the binarized boundary, and obtaining a plurality of latent images obtained. This is means for obtaining a potential profile of the electrostatic latent image based on the image diameter.

3. The measuring apparatus according to claim 2, wherein the holding means holds the sample in the “measurement state”, and the “measurement state” here means a state in which measurement is possible. In a state where the charge distribution in the sample can be measured, generally, a space in which a charged particle beam is scanned over the sample and charged particles that are electrically affected by the charge distribution are captured is in a “highly decompressed state”. . Therefore, the holding means is a means that can realize not only the sample but also the reduced pressure state.

The “electric field strength varying means” in the surface charge distribution measuring apparatus according to claim 2 can be a conductive member for applying a voltage ( claim 3 ). In this case, using the grid mesh or hole plate or perforated grid mesh as the conductive member, it can be made to form a bias component in the vicinity of the sample surface (claim 4).

Further, as the “electric field intensity varying means” in the surface charge distribution measuring apparatus according to claim 2, 3 or 4 , the pull-in voltage of the detector that captures charged particles that are electrically influenced by the charge distribution in the measuring means is varied. Means may be included ( claim 5 ). The means using the conductive member, which is the electric field strength varying means, and the means for varying the detector pull-in voltage may be used in combination.

The surface charge distribution measuring apparatus according to any one of claims 2 to 5, the charged particle beam scanning unit to the electron beam scanning means, measuring means is not accompanied with the scanning of the "electron beam, secondary generated in the sample it can be configured to detect as the electron intensity "a detection signal (claim 6).

The surface charge distribution measuring apparatus according to any one of claims 2 to 6 , for forming an "electrostatic latent image as a measurement object formed by charging and exposure on a photoconductive photosensitive member as a sample ". to a "charging unit" uniformly charging the sample, performs exposure with respect to uniformly charged the sample may have a "exposure means" (claim 7), in this case, the charged particle beam scanning means was an electron beam scanning means can "serve also as the charging means to the electron beam scanning means" (claim 8).

The "exposure means" of the surface charge distribution measuring apparatus according to claim 7 or 8 may be configured to perform exposure by irradiation with a desired light beam ( claim 9 ), or may be configured to perform exposure by light scanning. ( Claim 10 ).

Also in the measuring method according to claim 1 and the measuring apparatus according to claims 2 to 10 which implement this, the irradiation current of the charged particle beam is preferably set to “a magnitude that does not cause the surface charge distribution of the sample to disappear”.
Specifically, 1E-10A or less, preferably 1E-12A or more.

Further, when the sample is a “precharged sample” such as a photoconductive sample, the charged voltage: V1 of the charged particle beam to be irradiated is the condition:
V1> | V |
Is preferably satisfied.

As in the measurement method according to claim 1 , the measurement is repeated by shifting the “electric field intensity generated on the sample surface” in a plurality of stages in order to change the detection signal amount, and when the profile of the surface charge distribution is calculated, the measurement is repeated. Each time, a new surface charge distribution (electrostatic latent image) may be formed under the same conditions. However, as described above, the irradiation current of the charged particle beam is set to “a size that does not cause the surface charge distribution of the sample to disappear”. By setting, multiple measurements can be performed on the surface charge distribution formed on the sample surface.

Further, exposure for forming an electrostatic latent image to be measured can be performed by “irradiation of a mask pattern”.

In the measurement method and apparatus of the present invention, the target of measurement is “surface charge distribution by electrostatic latent image ”. However, if the surface charge distribution is known, the surface potential and the electric field distribution in the vicinity of the surface can be reliably known. Therefore, it can be said that the measurement object is a surface potential distribution or an electric field distribution near the surface.

As described above, according to the present invention, a novel surface charge distribution measuring method and apparatus can be realized. According to the method and apparatus of the first to tenth aspects, the surface charge distribution by the electrostatic latent image can be binarized and measured at a desired electric field strength level.
By measuring the electrostatic latent image with the method and apparatus of the present invention and feeding back the result to the design, it is possible to improve the process quality of the charging process and the exposure process of the image formation by the electrophotographic process, As a result, further improvement in image quality, durability, stability and energy saving can be expected.

Hereinafter, embodiments will be described.
FIG. 1 is a diagram showing a case where the surface charge distribution measuring apparatus is implemented for “electrostatic latent image measurement” .
Reference numeral 11 is a charged particle gun, reference numerals 12 and 12A are apertures, reference numeral 13 is a condenser lens for charged particles, reference numeral 14 is a beam blanker, reference numeral 15 is a scanning lens for charged particle beams, reference numeral 16 is an objective lens for charged particle beams, Each is shown.

  The charged particle gun 11, the apertures 12 and 12 A, the condenser lens 13, the beam blanker 14, the scanning lens 15, and the objective lens 16 constitute a “charged particle beam irradiation unit”, and each component is controlled by a charged particle beam control unit 31. It has come to be. Each of the condenser lens 13, the scanning lens 15, and the objective lens 16 is connected to a “drive power source (controlled by the charged particle beam control unit 31)” (not shown).

  The “charged particle beam irradiation unit” and the charged particle beam control unit 31 constitute “charged particle beam scanning means”.

  Reference numeral 17 denotes a semiconductor laser as a light source, reference numeral 18 denotes a collimating lens, reference numeral 19 denotes an aperture, and reference numerals 21, 22, and 23 denote lenses constituting an “imaging lens”. These constitute the “light image irradiating unit” and constitute the “exposure means” together with the semiconductor laser control unit 32.

  The semiconductor laser control unit 32 controls blinking of light emission of the semiconductor laser 17 and adjustment / setting of the light emission intensity. In addition, the positional relationship between the imaging lenses 21, 22, and 23 is adjusted by a lens control unit (not shown) so that focusing and defocusing can be performed.

  Reference numeral 24 denotes a charged particle trap, reference numeral 25 denotes a secondary electron detector, reference numeral 26 denotes a signal processor, and reference numeral 27 denotes an output device such as a printer for “outputting measurement results”. The charged particle trap 24, the secondary electron detector 25, the signal processor 26, and the output device 27 constitute “observation means”.

  Reference numeral 28 denotes a sample mounting table, reference numeral SP denotes a sample, and reference numeral 29 denotes a “light emitting element for charge removal”. Sample SP is a “photoconductive photoreceptor”. In this embodiment, the light emitting element 29 is an LED that emits light in a wavelength region in which the sample SP has sensitivity, and blinking is controlled by the LED control unit 35. Of course, the semiconductor laser 17 emits laser light in a wavelength region in which the sample SP has sensitivity.

  The sample mounting table 28 is a grounded metal plate. The sample mounting table 28 is driven by the sample table driving unit 34 to place the sample SP at an “appropriate measurement position”.

  Each of the above parts is arranged in a casing 30 as shown in the figure, and the inside of the casing can be highly decompressed by an intake part 33. That is, the casing 30 has a function as a “vacuum chamber”.

  The sample SP is held on the sample mounting table 28, is positioned at an appropriate measurement position by the sample table driving unit 34, and the inside of the casing 30 is highly decompressed by the intake unit 33 to be in a “measurement state”. Therefore, the sample mounting table 28, the mounting table driving unit 34, the casing 30, and the intake unit 33 constitute “holding means” that holds a sample having a charge distribution as a measurement target in a measurement state.

  Further, as shown in the figure, the entire apparatus is controlled by a computer 40 as “control means”. In the figure, the charged particle beam control unit 31, the signal processing unit 26, the semiconductor laser control unit 32, the LED control unit 35, and the like can be set as a part of the function of the computer 40.

In the state shown in FIG. 1, the sample SP whose surface is uniformly charged is placed on the sample placing table 28, and the inside of the casing 30 is highly decompressed.
When the semiconductor laser 17 is turned on in this state, the emitted laser beams are collimated by the collimating lens 17, the beam diameter is regulated by the aperture 19, and the “uniformly charged sample” of the sample SP is formed by the imaging lenses 21, 22, and 23. Focused as a light spot "on the surface".

  The semiconductor laser control unit 32 controls the emission intensity and emission time of the semiconductor laser 17 and controls the focus / defocus state by the imaging lenses 21 to 23 to generate a desired spot diameter and beam profile on the sample SP. It is possible to irradiate with appropriate exposure time and exposure energy. That is, the “desired light beam” can be irradiated to the sample SP.

  It is also possible to add a “scanning mechanism using a galvanometer mirror or a polygon mirror” to the optical system of such an exposure means, so that a line pattern is exposed by optical scanning to form a line-shaped electrostatic latent image. .

  As described above, the sample SP is exposed to a light spot having a “desired spot diameter and beam profile”, and an electrostatic latent image, that is, a surface charge distribution corresponding to the light intensity distribution of the light spot is formed. The

  The sample surface on which the electrostatic latent image is thus formed is scanned two-dimensionally with a charged particle beam. That is, when a charged particle beam is emitted from the charged particle gun 11, the emitted charged particle beam passes through the aperture 12 and the beam diameter is regulated, and then is converged by the condenser lens 13 while being focused by the aperture 12 A and the beam blanker 14. Pass through.

  The charged particle beam focused by the condenser lens 13 is focused on the surface (sample surface) of the sample SP by the objective lens 16. At this time, by deflecting the direction of the charged particle beam by the scanning lens 15, the position where the charged particle beam is focused is displaced two-dimensionally on the sample SP surface (for example, the horizontal direction in the drawing and the direction orthogonal to the drawing). Can be made.

  In this way, the “sample surface on which the electrostatic latent image is formed” of the sample SP is two-dimensionally scanned by the charged particle beam. The area to be scanned can be changed in size by changing the magnification of the scanning lens. For example, the scanning area can be scanned at various magnifications such as a low magnification of about 5 mm × 5 mm and a high magnification of about 1 μm × 1 μm. can do.

  When the above scanning is performed, a trapping voltage having a predetermined polarity is applied to the charged particle trap 24. Then, by the action of the trapping voltage, “charged particles that are electrically affected by the electrostatic latent image pattern” are captured by the charged particle trap 24, and the intensity (number of trapped particles per unit time) is detected. Is converted to

  The “region to be scanned two-dimensionally by the charged particle beam: S” of the sample SP is represented by S (X, Y) using two-dimensional coordinates, for example, 0 mm ≦ X ≦ 1 mm, 0 mm ≦ Y ≦ 1 mm. It is. The electrostatic latent image pattern formed in this region: S (X, Y) is defined as its surface potential distribution: V (X, Y).

Since the two-dimensional scanning of the region by the charged particle beam is performed under a predetermined condition, the scanning is performed when the time from the start to the end of the two-dimensional scanning is T ₀ ≦ T ≦ _TF . Time: T corresponds to 1: 1 with each scanning position in the scanning area: S (X, Y).

  Since the charged particles captured by the charged particle trap 24 are electrically influenced by the surface potential distribution of the electrostatic latent image pattern: V (X, Y), the intensity of the charged particles captured at time: T: F (T) has a correspondence relationship with surface potential distribution: V {X (T), Y (T)} with time: T as a parameter.

This correspondence can be known by observing the intensity of the charged particles influenced by the reference potential: V _N, and calibrating the intensity of the charged particles: F based on the known correspondence. Thus, the potential: V corresponding to the intensity: F can be known.

  Therefore, by sampling the detection signal obtained from the charged particle trap 24 at an appropriate interval, the surface potential distribution: V (X, Y) can be specified for each “micro area corresponding to sampling”.

  As described above, the charged particle beam is a particle beam that is affected by an electric field or a magnetic field such as an electron beam or an ion beam. An “electron gun” is used, and if an ion beam is used, a “liquid metal ion gun” or the like is used.

  In the embodiment shown in FIG. 1, the charged particle gun 11 is an “electron gun”, and therefore, the case where an electron beam is used as a charged particle beam will be specifically described below. At this time, the “sample surface on which the electrostatic latent image is formed” of the sample SP is two-dimensionally scanned by the electron beam.

  In order to form an electrostatic latent image on the sample SP, it is necessary to uniformly charge the surface of the sample SP prior to exposure with a light image. Regarding the uniform charging of the sample SP, charging may be performed outside the observation apparatus, and the uniformly charged sample SP may be mounted on the sample mounting table 28. However, as described above, the inside of the casing 30 is highly advanced. If the pressure inside the casing 30 is reduced from the set of the sample SP, the charged potential disappears due to dark decay until scanning by the electron beam becomes possible unless the suction by the suction portion 33 is performed very strongly. In some cases, the electrostatic latent image cannot be observed.

  From this point of view, it is preferable that the uniform charging of the sample SP is performed in the casing 30 “after realizing a high degree of decompression”. When charging is performed under a high pressure reduction, charging by corona discharge, which is often performed in an electrophotographic apparatus, is difficult to implement, but charging by a so-called contact type charging means is possible.

In the embodiment of FIG. 1 , charging by an electron beam is performed using a charged particle beam scanning unit.

  When the sample SP is irradiated with the electron beam, “secondary electrons (including higher-order emitted electrons such as tertiary electrons as described above)” are generated from the sample SP due to the impact of the irradiated electrons. In the balance between the amount of electrons irradiated to the sample SP as an electron beam and the amount of secondary electrons generated, the amount of secondary electrons emitted: the amount of irradiated electrons with respect to R2: the ratio of R1: If R1 / R2 is 1 or more The amount of electrons irradiated by subtraction exceeds the amount of secondary electrons, and the difference between the two accumulates in the sample SP to charge the photoconductive material SP.

  Therefore, the amount of electrons emitted from the electron gun 11 and the acceleration voltage thereof are adjusted, and the “ratio: the condition that R1 / R2 is greater than 1” is set, and the electron beam is scanned two-dimensionally. SP can be uniformly charged. Such adjustment of the amount of emitted electrons and the acceleration voltage is performed by the charged particle beam control unit 31. Further, the charged particle beam control unit 31 controls the beam blanker 14 to turn on / off the electron beam accompanying the scanning of the electron beam.

  FIG. 2 schematically shows a state in which the surface of the sample SP is charged by the electron beam as described above. The sample SP shown in FIG. 2 is a so-called “function-separated type photoconductor”, in which a charge generation layer 2 is provided on a conductive layer 1 and a charge transport layer 3 is formed thereon.

  Electrons irradiated by the electron gun are shot into the surface of the charge transport layer 3, captured in the electron orbits of the charge transport layer material molecules on the surface of the charge transport layer 3, and the charge transport layer in a state in which the molecules are negatively ionized. 3 remains on the surface. This state is a “state in which the sample SP is charged”.

  When the light LT is irradiated to the sample SP in such a charged state, the irradiated light LT passes through the charge transport layer 3 and reaches the charge generation layer 2. Generate negative charge carriers. Of the generated positive and negative charge carriers, the negative carriers move to the conductive layer 1 (at ground potential) due to the repulsive force of the negative charge on the surface of the charge transport layer 3, and the positive carriers are transferred to the charge transport layer 3. Are offset by the negative charges (captured electrons) on the surface portion of the same layer 3.

  In this manner, the charged charge is attenuated in the portion irradiated with the light LT in the sample SP, and a surface charge distribution according to the intensity distribution of the light LT is formed. This surface charge distribution is nothing but an electrostatic latent image.

  The sample SP uniformly charged as described above is exposed by a light beam to form an electrostatic latent image. This exposure is performed by the aforementioned “exposure means”. That is, the semiconductor laser 17 is turned on, and the collimated light beam is condensed on the surface of the sample SP by the action of the imaging lenses 21, 22, and 23.

  Of course, a semiconductor laser 17 having a light emission wavelength in a wavelength region in which the sample SP is sensitive is used. Further, since the exposure energy is “time integration of optical power” on the surface of the sample SP, the sample SP can be exposed with the desired exposure energy by controlling the lighting time of the semiconductor laser 17.

  Returning to FIG. 1, in the state where the electrostatic latent image is formed on the sample SP as described above, the scanning region of the sample SP is two-dimensionally scanned by the electron beam. Secondary electrons generated by this scanning are detected by the charged particle trap 24. Since the target of detection is secondary electrons and negative polarity, the charged particle trap 24 applies a positive voltage (attraction voltage) for capturing secondary electrons, and positively generates secondary electrons generated by scanning of the electron beam. Capture by aspiration with voltage. The captured electrons are converted into scintillation luminance in the secondary electron detector 25 and further converted into an electric signal (detection signal).

  In the space between the surface of the sample SP and the charged particle trap 24, the charge on the surface of the sample SP (negative charge that forms an electrostatic latent image) and the positive trapping voltage applied to the charged particle trap 24. Thus, a “potential gradient” is formed.

  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 detector 25 is sampled by the signal processor 26 at an appropriate sampling time, as described above, the surface potential distribution: V (X, Y) using the sampling time T as a parameter. ) 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 the image is output by the image processing device 27, 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.

  Although the electrostatic latent image actually projected onto the sample SP is very small, the image output from the output device 27 can be appropriately enlarged to “a size suitable for observation”.

  In addition, when the surface of the sample SP set in the casing 30 is initially charged unevenly for some reason, such a charged state becomes a measurement noise, so that the charging process in the measurement is performed. Prior to this, it is preferable to cause the light emitting element 29 for charge removal to emit light by the LD control unit 35 to perform light charge removal of the sample SP.

  As described above, secondary electrons generated by the electron beam applied to the image portion (light-irradiated portion) of the electrostatic latent image formed on the sample SP are not captured by the charged particle trap 4. Therefore, in the image portion of the electrostatic latent image, the “equivalent amount of incident electrons” of the irradiated electron beam is accumulated as an external charge. Therefore, if the amount of incident electrons of the electron beam is large, the charge distribution on the surface of the sample SP disappears due to scanning of the electron beam.

In order to avoid this, the “irradiation current” which is the irradiation amount of the electron beam may be made smaller than the charged charge density Q ₀ in the surface charge distribution . The irradiation current of the electron beam can be adjusted by changing the diameters of the apertures 12 and 12A shown in FIG.

Assuming that the dielectric film thickness in the sample SP is d (substantially the film thickness of the charge transport layer), the relative dielectric constant is ε, and the vacuum dielectric constant is ε ₀ (= 8.85E-12 F / m). Electric capacity: C
C = ε · ε ₀ / d
Given in. As these general values, when the film thickness of the sample SP is d = 30 μm, the dielectric constant is ε = 3, and the charging potential is V = −800 V, the charged charge density per 1 μm ² is Q ₀ :
Q ₀ = C · V = 7.08E-16
It becomes.

Charge density per unit area by electron beam irradiation: Q (C / μm ² ) is: electron beam irradiation current irradiating sample SP: i (A), irradiation time: t (seconds), irradiation area: S (μm) ² )
Q = i × t / S
Can be expressed as
Q ≦ Q ₀
Therefore, the irradiation current i can be determined as follows.

i ≦ Q ₀ × S / t
The measurement area is preferably as wide as possible in order to form a desired electrostatic latent image. In order to obtain a spatial resolution of 2 μm or more, measurement is performed in the case of a video signal having a width of about 1 mm and an aspect ratio of 4: 3. An area of about S = 1000 × 750 μm ² is appropriate. Measurement time (irradiation time): t is preferably at least 5 seconds or more.

Then, the irradiation current i satisfying such a condition:
i ≦ Q ₀ × S / t = 7.08E−16 × 7.5 × E + 5/5
= 1.06 × E-10≈1E-10 (A)
It becomes. Therefore, the irradiation current i is preferably “1E-10 (A) or less” .

In order for the secondary electron detector 25 to detect secondary electrons with high sensitivity, the irradiation current: i is preferably 1E-12 (A) or more . When the irradiation current i is smaller than this, the detection signal obtained by the secondary electron detection unit 25 becomes small, and it is difficult to ensure a sufficient S / N ratio.

  As a method of controlling the irradiation current: i, the relationship between the irradiation current: i and the aperture diameter of the apertures 12 and 12A is measured in advance using a Faraday cup or the like, and the apertures 12 and 12A are based on the result. And a method of controlling the irradiation current i by changing the opening diameter of.

  In addition, the “irradiation current: i” in the above description is the so-called current that reaches the sample surface of the sample SP, and the “charged charge density” of the sample surface of the sample SP is the uniform charge when forming the electrostatic latent image. The so-called charging charge density due to. In the case of general surface charge distribution measurement, this charged charge density may be considered as “average charge density in the measurement region”, and can be calculated by measuring the potential with a vibration capacitance type surface potential meter or the like.

In the form being described, the sample surface of the sample SP is charged to a negative polarity by irradiation with an electron beam. Therefore, when scanning with an electron beam to measure an electrostatic latent image, the “incident electrons” of the scanned electron beam are decelerated due to the influence of the repulsive electric field on the sample surface, and the acceleration voltage of the electron beam is small. There is a risk of rebound without reaching the sample surface.

In order to avoid this, the acceleration voltage of the irradiation electron beam: V1 (V) is set to the charged potential: V (V) of the sample surface of the sample SP.
V1> | V |
Should be set . For example, the charging voltage: V = −2 KV and the acceleration voltage: V1 may be 2 KV or more.

  The sample SP, which is a photoconductive photosensitive member on which an electrostatic latent image is formed, is scanned with an electron beam, and the emitted secondary electrons are detected by a secondary electron detection unit 25 including a scintillator, a photomultiplier tube, and the like. Then, the potential contrast image is observed by converting it into an electrical signal (detection signal). For the conversion from the potential contrast image to the potential, a conversion table representing the correlation between the potential and the signal intensity is prepared in advance. The potential may be obtained by referring to the conversion table from the signal intensity, or may be calculated according to a conversion calculation expression that changes to the conversion table.

  Alternatively, a known reference potential may be arranged in the electron beam scanning region, and a method of calculating a potential distribution by comparing the signal intensity of secondary electron detection with the reference potential may be used. In general, a portion having a lower potential than a portion having a high potential becomes brighter because the amount of secondary electrons emitted increases. As a contrast image, a relatively low potential portion is displayed in white and a high potential portion is displayed in black.

  In the above description, the case where the electron beam is scanned two-dimensionally to measure the electrostatic latent image formed in a spot shape by the light spot has been described. However, the electrostatic latent image is formed in a line shape. If the state of charge distribution in the direction perpendicular to the line is to be examined, the scanning with the electron beam may be one-dimensional scanning (scanning in the direction perpendicular to the line).

FIG. 4 shows another example of the surface charge distribution measuring apparatus . In FIG. 4, the same reference numerals as those in FIG. 1 are given to those that are not likely to be confused in order to avoid complication. Moreover, illustration was simplified and only the inside of casing 30A was shown.

  The charged particle gun 11, the apertures 12 and 12A, the condenser lens 13, the beam blanker 14, the scanning lens 15 and the objective lens 16 constituting the “charged particle beam irradiation unit” have the same configuration as that of FIG. Is an electron gun. The charged particle trap 24 and the secondary electron detector and signal processor (not shown) are the same as those described above with reference to FIG.

  The sample SP1 is formed in a drum shape, which is a general form of a photoconductive photoconductor, and is rotated at a constant speed in the direction of the arrow (counterclockwise) by a driving unit (not shown). After the sample SP is set in the casing 30A, the inside of the casing 30A is highly decompressed by the suction means 32.

  The charging portion denoted by reference numeral 41 is, for example, a contact-type charging unit such as a charging brush or a charging roller, and uniformly charges the sample SP1 in a casing under reduced pressure. At this time, the sample SP1 is rotated at a constant speed in the direction of the arrow. Of course, as in the example described with reference to FIG. 1, the sample SP1 can be charged by charging using an electron beam.

  The “exposure section” denoted by reference numeral 42 performs exposure by irradiating a sample SP1 whose sample surface is uniformly charged with a light image. As the exposure unit 42, for example, an “optical scanning device” widely known in connection with an optical printer or the like can be used, and “irradiation of an optical image” can be performed by optical writing. As described above, when “irradiation of an optical image” is performed by optical writing, the pattern of the electrostatic latent image formed by writing can be arbitrarily changed, and an electrostatic latent image having a desired pattern can be easily formed. Note that the charge removal unit indicated by reference numeral 29A performs light charge removal on the sample SP1 prior to forming the electrostatic latent image. Further, the exposure unit 42 may be of the “method for irradiating a desired light beam” shown in FIG.

  When an optical scanning device is used as the exposure unit 42, if the optical scanning device is large and difficult to install in the casing 30A, the optical scanning device is provided outside the casing 31A and is transparent to the casing 30A. A window part may be provided, and the light image may be irradiated to the sample SP1 from the outside through this window part.

  The scanning of the electron beam by the charged particle beam irradiation unit may be performed by deflecting the electron beam two-dimensionally, as in the embodiment of FIG. 1, but the sample SP1 is scanned while rotating at a constant speed in the direction of the arrow. Therefore, the two-dimensional scanning can be realized by deflecting the electron beam one-dimensionally in a direction orthogonal to the drawing and combining this deflection with the rotation of the sample SP1.

  FIG. 5 shows an example of the optical scanning device mentioned above as an example of the exposure unit 42.

  A laser beam from a semiconductor laser 51 as a light source is converted into a parallel beam by a collimator lens 52, converged in a sub-scanning direction by a cylindrical lens 53, and formed as a “line image long in the main scanning direction” at the deflection reflection surface position of the polygon mirror 55. Let me image.

  The reflected light beam is deflected at a constant angular velocity by rotating the polygon mirror 55 at a constant speed, and this deflected light beam is guided to the drum-shaped sample SP1 by the fθ lens 56 and the folding mirror 54, and on the sample surface by the action of the fθ lens 56. A light spot is imaged, and the sample surface is optically scanned to irradiate a light image.

The surface charge distribution measuring apparatus shown in FIG. 1 (FIG. 4) includes holding means 28, 30 (30A), 33, 34 for holding a sample SP having a charge distribution as a measurement object in a measurement state, and the holding means. Charged particle beam scanning means 11-16, 31 for irradiating the held sample SP (SP1) with a charged particle beam to scan one-dimensionally or two-dimensionally, and charged particles that are electrically affected by the charge distribution And measuring means 24 to 27 for measuring the charge distribution by detecting the detected intensity as a detection signal corresponding to the position on the sample surface, and the irradiation current of the charged particle beam in the charged particle beam scanning means I can be set to such a size that the surface charge distribution of the sample is not lost.

Further, the charged particle beam scanning unit is "electron beam scanning means", measuring means for detecting the intensity of the "secondary electrons generated in the wake sample without the scanning of the electron beam" as a detection signal. Charging means 11-16, 31 (41) for uniformly charging the sample SP (SP1) with an electrostatic latent image formed by charging and exposure on the photoconductive photoconductor as the sample SP (SP1) as a measurement object. ) and performs exposure with respect to uniformly charged sample having exposure means 17～23,32 (42).

Further, the charged particle beam scanning means also serves as a charging means in an electron beam scanning means, in the embodiment of FIG. 1, the exposure means performs the exposure by the "irradiation of the desired light beam". Further, in the surface charge distribution measuring apparatus of FIG. 5, the exposure means 41 performs exposure by “optical scanning”.

In these surface charge distribution measuring apparatuses, a sample SP (SP1) having a surface charge is irradiated with a charged particle beam to scan one-dimensionally or two-dimensionally, and the sample SP (SP1) is detected by a detection signal obtained by this scanning. ) a method of measuring the surface charge distribution of the emission current of the charged particle beam, the measuring method of performing scanning is performed by setting a size that does not eliminate the surface charge distribution of the sample.

The emission current of the charged particle beam is 1E-10A or less, is a 1E-12A above, the charge potential of the sample SP to be pre-charged (SP1): V to an acceleration voltage of the charged particle beam to be irradiated: V1 is the condition:
V1> | V |
To satisfy.

Electron beam is used as a charged particle beam to be irradiated, the intensity of the secondary electrons produced by scanning the charged particle beam is detected as a detection signal. Further, the sample SP is irradiated with an electron beam to form a charge distribution on the sample surface, and the surface charge distribution to be measured is formed on the photoconductive photoconductor as the sample SP by charging and exposure. A uniform electric charge distribution is formed on the surface of the sample by irradiation of the electron beam on the photoconductive photosensitive member that is the electrostatic latent image , and the exposure is performed thereafter.

Exposure, the apparatus of FIG. 1 more in the "irradiation of the desired light beam", in the apparatus of FIG. 4 is performed respectively by "optical scanning".

Embodiments relating to the invention described in claim 1 and below will be described below .

  As described above, the electric field formed in the external space of the sample surface of the sample having the surface charge distribution (electrostatic latent image) to be measured (in the direction perpendicular to the sample surface, the electron beam incident side is positive. When the intensity of (the electric field vector) increases, a binarization phenomenon occurs in the measurement result.

This “binarization phenomenon” will be described with reference to FIG.
FIG. 6A shows the distribution of “electric field strength” on the sample surface. The horizontal axis represents the position of the sample surface (cross-sectional position including the center of the electrostatic latent image formed by the light spot), and the vertical axis represents the electric field strength (on the electron beam incident side in the direction perpendicular to the sample surface ( The magnitude of the electric field vector (positive in the upper part of the figure) is shown.

  The number of secondary electrons captured by the charged particle trap is inversely proportional to the electric field intensity. When the detection signal is viewed as the above-described potential contrast image due to light and dark, the electric field intensity is zero or less in the region of electric field intensity distribution. On the other hand, it is “bright”, and it becomes “dark” in the region where the electric field intensity is 0 or more, and the resulting contrast image by light and dark is as shown in FIG. FIG. 6C shows a “line profile” of the luminance signal (detection signal detected by the secondary electron detector) in the cross section indicated by the broken line in FIG.

  As described above, in the actual electrophotographic process, there is an electric field strength (Eth) necessary for the toner particles to adhere to the electrostatic latent image, and the toner particles do not adhere to the electrostatic latent image at an electric field strength of less than Eth. Development is not performed.

  Therefore, in the case of “measuring the surface charge distribution (or surface potential distribution) of the electrostatic latent image in relation to the development characteristics”, it is preferable to directly capture as a contrast image of an area having an electric field strength equal to or higher than Eth.

To do this, it is only necessary to change the electric field strength generated on the sample surface in order to change the amount of detection signal, and repeat the measurement by changing the electric field strength generated on the sample surface in multiple stages. For example, the profile of the surface potential distribution can be calculated.

FIG. 7 shows an embodiment of the surface charge distribution measuring apparatus according to claim 2 . In order to avoid complications, the same reference numerals as those in FIG.
That is, in FIG. 7, what has the same code | symbol as FIG. 1 is the same as that of what is shown in FIG. 1, The description regarding FIG. 1 is used for the description about these.

That is, the apparatus shown in FIG. 7 is an apparatus for carrying out the surface charge distribution measurement method as in FIG. 1 and measures a sample SP having “charge distribution by electrostatic latent image” as a measurement object. Holding means 28, 30, 33, 34 for holding in a state, and charged particle beam scanning means 11 for irradiating the sample SP held by the holding means with a charged particle beam for one-dimensional or two-dimensional scanning. 16, 31 and measuring means for capturing the charged particles that are electrically affected by the charge distribution in the sample SP, detecting the intensity as a detection signal corresponding to the position on the sample surface, and measuring the charge distribution 24 to 27.

The charged particle beam scanning means is an electron beam scanning means, and the measurement means detects the intensity of secondary electrons generated in the sample as the electron beam scans as a detection signal, and the photoconductive property of the sample SP. Charging means 11-16, 31 for uniformly charging the sample SP, and an exposure means for exposing the uniformly charged sample, with an electrostatic latent image formed on the photoconductor by charging and exposure as a measurement object and a 17～23,32, charged particle beam scanning means also serves as a charging means in an electron beam scanning means, exposure means performs exposure by irradiation of desired light beam.

To "change detection signal amount" in the embodiment of FIG. 7, having a field strength varying means 44 and 45 for changing the electric field intensity generated in the sample surface.

Among the electric field intensity varying means 44 and 45, indicate by reference numeral 45 is the "conductive member for applying a voltage", so that a voltage can be applied from the voltage applying unit 44.

More specifically, the conductive member 45 for applying a voltage is a “grid mesh” as shown in FIG .

  As shown in FIG. 7, the grid mesh 45 is arranged above the sample surface of the sample SP, and a voltage is applied by the voltage applying means 44. The power supply application means 44 is a power supply capable of generating a high voltage up to several tens of KVs, and can arbitrarily set a voltage value applied to the grid mesh 45.

  FIG. 9 schematically shows the state in the vicinity of the sample SP. The grid mesh 45 is formed in a mesh shape with a conductive material (Au, Cu, Ni, etc. are preferable) (see FIG. 8A), and the electron is applied depending on the applied voltage value applied from the voltage applying means 44. The electric field distribution in the vicinity of the sample surface is “uniformly bias-level shifted” without blocking the irradiation of the beam to the sample SP. The pitch and shape of the grid mesh 45 can be appropriately set depending on the measurement area and measurement magnification of the sample.

  When a voltage is applied to the grid mesh 45, the uniform electric field formed by the grid mesh 45 is superimposed on the electric field formed by the charge distribution on the sample surface, and becomes a bias component of the electric field strength on the sample surface. The electric field strength distribution is shifted.

For example, in order to “shift as a bias component” the electric field strength of 2 × 10 ⁶ V / m, a voltage of 2000 V may be applied 1 mm above the sample surface.

  FIG. 10A shows a state in which a voltage is applied to the grid mesh 45 and the bias component of the electric field strength on the sample surface is shifted by −Eb. By this shift, the level of electric field strength: 0 is shifted upward from the state of FIG. That is, since the electric field strength E: Eb in the original state becomes E = 0 due to the bias shift, a substantially binary image with the electric field strength Eb as a threshold value is obtained.

  Due to the bias shift of the electric field intensity, the bright portion of the potential contrast image increases, and the electric field intensity before the shift: Eb can be brightened and darkened as shown in FIG. 10B. By processing this result, the latent image diameter can be calculated.

  If the amount of shift of the bias component: -Eb is changed, the level of the electric field strength: 0 changes, so various cut points obtained by binarizing the electric field strength distribution shown in FIG. 10A at various strength levels. Potential contrast images can be obtained. Of course, by adjusting the applied voltage value Eb to the grid mesh 45, it is possible to obtain a potential contrast image with the development start voltage Eth as a starting point.

  As another example of the electric field strength varying means, there is one that changes the pull-in voltage of the charged particle trap.

  As described above, secondary electron detection is performed using a combination of a scintillator (phosphor), which is a charged particle trap, and a photomultiplier tube. Since secondary electrons generated from the sample SP have low energy, the surface of the scintillator is used. It is accelerated by the influence of an electric field of a high voltage (drawing voltage) for trapping applied to the light and converted into light by a scintillator. This light passes through the light pipe and is amplified as a current by a photomultiplier tube (PMT) and extracted as a current signal.

Usually, since the drawing voltage to the scintillator (charged particle trap) is about 10 KV, the electric field in the vicinity of the sample surface is only about 10 ⁴ to 10 ⁵ V / m. Accordingly, when the “electric field generated by the charge distribution of the sample” is dominant over the electric field formed by the pull-in voltage, the secondary electrons are easily affected by the electric field due to the charge distribution on the sample surface.

  In such a case, the bias voltage component of the electric field strength can be reduced by increasing the voltage applied by the pull-in voltage power supply 24A shown in FIG. 9 and “increasing the pull-in voltage” or by bringing the charged particle trap 24 close to the sample. Can be changed.

  By combining the application of the electric field by the grid mesh 45 and the change of the pull-in voltage, a more effective bias shift of the electric field strength can be realized.

  Further, as the charged particle trap, a microchannel plate (MCP) may be used instead of the scintillator. The secondary electrons input to the MCP are collected by the pull-in voltage applied to the input surface of the MCP, and can be amplified to increase several thousand times, greatly increasing the signal component of the secondary electrons. As a result, the S / N ratio of the detection signal can be effectively improved.

  In addition, it is possible to measure the profile of the potential distribution of the electrostatic latent image by changing the bias component of the electric field intensity above the sample surface: Eb in multiple stages and repeating the measurement to capture the data and processing it on the computer. is there.

  FIG. 11 shows a flow chart in the case of measuring the potential distribution profile of the electrostatic latent image by changing the value of the bias component: Eb n times.

The process parameter: i is started as 1, and the electric field bias: Eb is set to the initial value, the potential contrast image is taken and binarized, and the latent image diameter is calculated at the binarized boundary. The calculated latent image diameter is taken into the memory, the process parameter: i is changed to i + 1, and the above process is repeated. By repeating this process N times, n latent image diameters having n types of electric field biases Eb as threshold values can be obtained, whereby the potential profile of the electrostatic latent image can be known.
The computer 40 performs processing necessary to calculate the potential profile.

  Of course, in this process, since the sample scanning with the electron beam is repeated n times, the irradiation current of the electron beam is sufficiently large so that the electrostatic latent image is not lost by the incident electrons during the measurement of n times. Set smaller.

  As the “conductive member for applying a voltage” in the electric field strength varying means, in addition to the grid mesh 45, a “grid mesh with a hole (a hole is formed in the center of the mesh) shown in FIG. And “Hole plate (a hole is formed in the central portion of the conductive plate)” shown in FIG. 8C can be used. The size of the holes formed in the grid mesh with holes or the hole plate is preferably “equivalent to the measurement region”.

12, to the embodiment shown in FIG. 4, an example of adding a voltage applying means (not shown) similar to the grid mesh 45 and the uses in the embodiment of FIG. In this apparatus, the measurement method according to the first aspect can be performed on the sample SP1 formed on the drum.

It is a figure which shows one form of a surface charge distribution measuring apparatus . It is a figure for demonstrating one example of the photoconductive photoreceptor which is an example of a sample. It is a figure for demonstrating a measurement principle. It is a figure which shows another form of a surface charge distribution measuring apparatus . It is a figure for demonstrating the optical scanning device which is an example of an exposure means. It is a figure for demonstrating the electric field strength distribution by an electrostatic latent image, and the binarized potential contrast image. It is a figure which shows one Embodiment of a surface charge distribution measuring apparatus. It is a figure which shows a grid mesh, a grid mesh with a hole, and a hole plate as an electroconductive member for applying the voltage in an electric field strength variable means. It is a figure which shows typically the mode of the sample vicinity in embodiment of FIG. It is a figure for demonstrating the effect | action of the electric field strength change by an electric field strength variable means. It is a flowchart for demonstrating an example of the measuring method of Claim 1. It is a figure which shows the other form of implementation of a surface charge distribution measuring apparatus.

Explanation of symbols

10 Electrostatic latent image observation device 11 Charged particle gun (electron gun)
17 Semiconductor laser 21, 22, 23 Imaging lens SP Sample 24 Charged particle trap

Claims (10)

A sample having a surface charge distribution due to an electrostatic latent image on the surface is irradiated with a charged particle beam to scan one-dimensionally or two-dimensionally, and the surface charge distribution is measured by a detection signal obtained by the scanning , The process of binarizing the potential contrast image obtained by the measurement and calculating the latent image diameter obtained at the binarized boundary portion is performed in the area region corresponding to the measurement region with the bias component of the electric field strength generated on the sample surface. A method for measuring a surface charge distribution, wherein the potential profile of the electrostatic latent image is obtained from a plurality of latent image diameters obtained by shifting to a plurality of stages and repeating a plurality of times . An apparatus for carrying out the surface charge distribution measuring method according to claim 1,
Holding means for holding a sample having a surface charge distribution by an electrostatic latent image as a measurement object in a measurement state;
Charged particle beam scanning means for irradiating a charged particle beam to the sample held by the holding means to scan one-dimensionally or two-dimensionally; and
Measuring means for capturing charged particles that are electrically affected by the charge distribution, detecting the detected intensity as a detection signal corresponding to the position on the sample surface, and measuring the charge distribution;
Electric field strength variable means for changing the bias component of the electric field strength generated on the sample surface by shifting it in a plurality of stages in the area corresponding to the measurement region ,
The potential contrast image obtained by the measurement by the measuring means is binarized to calculate the latent image diameter obtained at the binarized boundary, and the electrostatic latent image is obtained from the plurality of latent image diameters obtained. A surface charge distribution measuring apparatus having means for obtaining a potential profile . The surface charge distribution measuring apparatus according to claim 2,
A surface charge distribution measuring apparatus using a conductive member for applying a voltage as the electric field strength varying means . In the surface charge distribution measuring apparatus according to claim 3,
A surface charge distribution measuring apparatus, wherein a bias component is formed in the vicinity of a sample surface using a grid mesh, a hole plate, or a grid mesh with holes as a conductive member for applying a voltage . In the surface charge distribution measuring apparatus according to claim 2, 3 or 4,
An apparatus for measuring a surface charge distribution, comprising means for varying a pull-in voltage of a detector that captures charged particles that are electrically influenced by the charge distribution in the measurement means as the electric field strength varying means . In the surface charge distribution measuring apparatus according to any one of claims 2 to 5,
An apparatus for measuring surface charge distribution, wherein the charged particle beam scanning means is an electron beam scanning means, and the measurement means detects the intensity of secondary electrons generated in the sample accompanying the scanning of the electron beam as a detection signal . In the surface charge distribution measuring apparatus according to any one of claims 2 to 6,
A surface charge distribution measuring apparatus comprising: charging means for uniformly charging a sample; and exposure means for exposing a uniformly charged sample . In the surface charge distribution measuring apparatus according to claim 7,
An apparatus for measuring surface charge distribution, wherein the charged particle beam scanning means is an electron beam scanning means, and the electron beam scanning means also serves as the charging means . In the surface charge distribution measuring apparatus according to claim 7 or 8,
An apparatus for measuring a surface charge distribution, wherein the exposure means performs exposure by irradiation with a desired light beam . In the surface charge distribution measuring apparatus according to claim 7 or 8,
An apparatus for measuring surface charge distribution, wherein the exposure means performs exposure by optical scanning .

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