JP2012018112A - Device for measuring electrostatic latent image, method for measuring electrostatic latent image, and program for measuring electrostatic latent image - Google Patents

Abstract

The present invention relates to an electrostatic latent image measuring apparatus and electrostatic latent image measurement capable of preventing density unevenness and banding caused by image formation by measuring or evaluating a latent image area in units of dots at the time of manufacture. It aims to provide a method.
[Solution]
Charged particle irradiation means for generating charged charges on the sample 23 by irradiating charged particles, exposure means having a light source, electrostatic latent image measurement means for measuring an electrostatic latent image formed on the sample 23 by the exposure means, The exposure means emits laser light of different wavelengths, and the laser light of different wavelengths from the exposure means is doted onto the sample 23 using a common imaging optical system 22. A unit for forming an electrostatic latent image for each unit and a light amount variable unit for varying the exposure amount of the light source are provided, and the electrostatic latent image measuring unit calculates the latent image area of the electrostatic latent image for each dot formed on the sample. measure.
[Selection] Figure 1

Description

  The present invention relates to an electrostatic latent image measuring device, an electrostatic latent image measuring method, and an electrostatic latent image measuring program, and more specifically, an electrostatic latent image measuring device and an electrostatic latent image that perform electrostatic latent image evaluation in units of dots. The present invention relates to a measurement method and an electrostatic latent image measurement program.

  In recent years, multi-color image forming apparatuses have been increasing in speed year by year and are being used for simple printing as an on-demand printing system, and higher-definition image quality is required. Along with this, a technique for recording an image on a photoconductor at high speed by simultaneously scanning a beam from a plurality of light sources using a multi-beam optical system and simultaneously writing a plurality of lines has been considered and is already known. Yes.

  However, in an image recording apparatus using a multi-beam optical system, the wavelength varies depending on the oscillation wavelength variation among multiple light sources in the multi-beam optical system and the difference in wavelength transition of the multiple light sources due to the temperature rise in the apparatus. Differences occur in the spectral sensitivity characteristics and image formation state of the photoreceptor due to the difference. Along with this, a difference occurs in the area of the latent image recorded on the photosensitive member by each light source, which causes a problem of density unevenness and banding in image formation. Such image formation problems are more likely to occur in image patterns that require image formation in dot units, such as halftone dots, as compared to a solid portion. In this case, it is necessary to perform image evaluation in dot units.

  To solve this problem, multi-beam optics can be used so that the image dot area is uniform even when there is a wavelength difference, such as setting the exposure to compensate for the difference in latent image area due to the wavelength difference. It is necessary to design the system. However, in the case of using a common imaging optical system that forms an image of laser light on a sample, the conventional potential measuring device cannot only evaluate the latent image area due to the difference in the wavelength of the laser light. There is a problem that the latent image area cannot be evaluated in dot units.

  For example, Patent Document 1 discloses that a common imaging optical system uses laser light from light sources having different wavelengths as a common imaging optical system in order to provide a potential measuring device that can measure the potential characteristics of photosensitive drums having different maximum spectral sensitivities. A configuration is disclosed in which a photoconductor is exposed to light and potential characteristics at each wavelength are measured. Patent Documents 2 to 5 disclose that a charge distribution on a sample is generated by scanning the surface of the sample with a charged particle beam, charging the sample, and exposing the charged sample through an optical system. Has been.

  However, the inventions described in the above patent documents cannot evaluate the electrostatic latent image in dot units described above. Furthermore, it has not been possible to derive a condition for compensating for the change in the latent image area due to the wavelength in order to solve the above-mentioned problems. Accordingly, no consideration is given to measures against image formation problems such as density unevenness and banding caused by variations in oscillation wavelength between light sources when a multi-beam optical system is used. In addition, when a multi-beam optical system is used, multiple light sources are evaluated using a common imaging optical system, so that high-precision optical path adjustment is required when repeating the measurement by replacing the light source. There is a problem that requires adjustment work. At that time, there is a possibility that the optical characteristics may be changed, and it is necessary to efficiently measure or evaluate the change in the latent image area in dot units according to the actual machine.

  The present invention measures or evaluates the latent image area in units of dots at the time of manufacturing, thereby preventing the possibility of density unevenness and banding caused by image formation. Measures or evaluates the change in latent image area in dot units according to the actual machine efficiently, preventing the possibility of changes in optical characteristics during high-precision adjustment work required for replacement It is an object of the present invention to provide an electrostatic latent image measuring apparatus and an electrostatic latent image measuring method capable of performing the same.

  An electrostatic latent image measuring apparatus according to the present invention includes a charged particle irradiation unit that generates charged charges on a sample by irradiating charged particles, an exposure unit including a light source, and an electrostatic latent image formed on the sample by the exposure unit. An electrostatic latent image measuring device comprising: an electrostatic latent image measuring device configured to measure a laser beam having a different wavelength, and exposing the laser beam having a different wavelength from the exposure unit to a common connection. The image optical system is used to form an electrostatic latent image in dot units on the sample and includes a light amount varying means for varying the exposure amount of the light source. The electrostatic latent image measuring means is a static unit in dot units formed on the sample. The most important feature is to measure the latent image area of the electrostatic latent image.

  Further, the electrostatic latent image measuring method according to the present invention includes a charged particle irradiation process for generating a charged charge on a sample, an exposure process for emitting a laser beam having a different wavelength to form an electrostatic latent image on the sample, An electrostatic latent image measurement method including an electrostatic latent image measurement step of measuring an electrostatic latent image by detecting secondary electrons when scanning charged particles, and forming a common image of laser beams having different wavelengths Forming an electrostatic latent image in dot units on a sample using an optical system, measuring the latent image area of the electrostatic latent image for each different laser beam, and electrostatic latent images for each laser beam having a different wavelength; The step of measuring the amount of change by comparing the latent image areas of the image, and the amount of exposure to be exposed to the sample by the light source is varied by the light amount varying means, and the latent image area of the electrostatic latent image for each laser beam of a different wavelength The most important feature is that it has a process of deriving the condition that .

  According to the electrostatic latent image measuring device of the present invention, it is possible to evaluate a change in the latent image area in units of dots using a common imaging optical system for light sources having different wavelengths, and measure independently by changing the light source. Adjustments such as high-accuracy optical path adjustment that are required when repeating the process can be omitted, and changes in optical characteristics that may occur at that time can be prevented. The latent image area can be evaluated. In addition, since it is possible to derive conditions for compensating for the change based on the change in the latent image area in dot units depending on the measured wavelength, the possibility of density unevenness and banding caused by image formation is prevented. be able to.

  Further, according to the electrostatic latent image measuring method according to the present invention, similarly to the above, it is possible to evaluate the change in the latent image area in dot units using a common imaging optical system for light sources having different wavelengths. Adjustment work such as high-accuracy optical path adjustment, which is necessary when repeating the measurement with a different light source, etc. can be omitted, and changes in optical properties that may occur at that time can be prevented, making it efficient. In addition, the latent image area can be evaluated in dot units according to the actual machine. In addition, since it is possible to derive conditions for compensating for the change based on the change in the latent image area in dot units depending on the measured wavelength, the possibility of density unevenness and banding caused by image formation is prevented. be able to.

It is a schematic diagram which shows the Example of the electrostatic latent image evaluation apparatus which concerns on this invention. It is a schematic diagram which shows the example of the imaging optical system of the electrostatic latent image evaluation apparatus which concerns on this invention. It is a flowchart which shows an example of the procedure of the latent image area change calculation applicable to this invention. It is a model figure which shows the principle of the charge distribution and potential distribution detection by a secondary electron. It is a figure which shows the latent image area change by a wavelength, and its compensation example. It is a graph which shows the relationship between a latent image area and exposure energy density. It is a schematic diagram which shows the example of formation of the opening part of the aperture which comprises the said imaging optical system. It is a schematic diagram which shows the aspect of another Example of the said imaging optical system. It is a schematic diagram which shows the structure of ND filter. It is the top view (a) which shows typically the temperature control mechanism of the light source applicable to this invention, and a front view (b). It is a graph which shows the relationship between light source temperature and an oscillation wavelength. It is a block diagram which shows the whole structure of the electrostatic latent image evaluation apparatus which concerns on this invention. It is a flowchart which shows the detail of the measuring method of the latent image area shown in FIG.

  Embodiments of an electrostatic latent image measuring device, an electrostatic latent image measuring method, and an electrostatic latent image measuring program according to the present invention will be described below with reference to the drawings. The present invention has the following characteristics when evaluating a latent image of a multi-beam optical system. That is, in the present invention, a single or a plurality of laser beams having different wavelengths are exposed to a sample using one common optical system to form an electrostatic latent image in dot units, and the electrostatic latent image is used, for example, by using an electron beam. It is possible to measure changes in the latent image area depending on the wavelength of the electrostatic latent image in dot units by measuring using the measured electrostatic latent image measuring device, and further, a condition for compensating for the difference in the latent image area It is characterized by having a light quantity variable means for guiding the light.

  The features of the present invention described above will be described in detail with reference to the following drawings. First, the configuration of an electrostatic latent image measuring apparatus that measures an electrostatic latent image on a photoreceptor will be described with reference to FIG. The electrostatic latent image measurement apparatus according to the present embodiment includes a charged particle irradiation unit 10 that is a charged particle irradiation unit that irradiates a charged particle beam, an imaging optical system 22, a sample 23 that is a photoconductor to be measured, A sample placement unit 26 made of a conductor and a detection unit 24 that is an electrostatic latent image measurement unit that detects primary inversion charged particles, secondary electrons, and the like. Here, the charged particles refer to particles that are affected by an electric field or a magnetic field such as an electron beam or an ion beam. In the following examples, the case of irradiating an electron beam will be described as an example. Moreover, the sample installation part 26 can be designed based on a suitable prior art.

  The charged particle irradiation unit 10 mainly includes an electron gun 11 for generating an electron beam, an extraction electrode 12 (extractor) for controlling the electron beam, an acceleration electrode 13 for controlling the energy of the electron beam, and an electron. Electrostatic lens 14 (condenser lens) for focusing the electron beam generated from the gun, movable diaphragm 17 for controlling the irradiation current of the electron beam, beam blanking electrode (beam) for turning the electron beam on / off Blanker) 15, partition plate 16, astigmatism correction (sting meter) 18 for correcting astigmatism, scanning lens (deflection electrode) 19 for scanning the electron beam that has passed through the beam blanker 15, and scanning lens 19. It comprises an objective lens 20 for condensing the emitted electron beam again and a beam exit opening 21. With these configurations, the charged particle irradiation means is formed. A driving power source (not shown) is connected to each lens. In the case of an ion beam, a liquid metal ion gun or the like is used instead of an electron gun.

  The electron beam emitted from the electron gun 11 passes through an extraction electrode (extractor) 12 and an acceleration electrode 13. Then, the light passes through the condenser lens 14 while converging at the positions of the partition plate 16 and the movable diaphragm 17, and is two-dimensionally deflected by the astigmatism correction (sting meter) 18 and the scanning lens 19. Then, the objective lens 20 focuses the electron beam again, passes through the beam exit opening 21, and charges the sample 23.

  As shown in FIG. 2, the imaging optical system 22 includes a plurality of light sources 100, 101, and 102 as exposure means, and the imaging optical system 22 includes the dichroic prism 103 and the dichroic prism 103 in the X-axis direction (paper surface). The collimator lens 104, the aperture 105, the half mirror 106, the first imaging lens 107, which are sequentially arranged in the horizontal direction), and the second, which are sequentially arranged in the direction opposite to the Y-axis direction (downward on the paper surface) of the half mirror 106. The imaging lens 108 and the photodiode 109 are provided. The imaging optical system 22 generates a desired beam diameter and beam profile on the sample 23.

  The light sources 100, 101, and 102 are laser light sources having different oscillation wavelengths. For example, when a semiconductor laser that oscillates at 405 nm, 655 nm, and 780 nm, which is generally required as an electrophotographic image forming apparatus, is used, a common imaging optical system is used for a plurality of light sources 100, 101, and 102. 22 can be used to measure the spectral sensitivity of the photoconductor at different wavelengths. Furthermore, by evaluating the electrostatic latent image as an evaluation index using the electrostatic latent image measuring device, it is possible to measure the latent image area in units of dots with high accuracy. In addition, if a semiconductor laser that oscillates at 650 nm, 655 nm, or 660 nm is used in consideration of wavelength variation of the multi-beam light source, the relationship between the wavelength difference and the latent image area change can be evaluated, and density unevenness, banding, etc. caused by wavelength variation Can take measures against this problem. The wavelengths described above are not limited to those in the above embodiments, and can be selected as appropriate. Also, the number of light sources can be selected as appropriate, and may be one as will be described later.

  The light sources 100, 101, and 102 can irradiate a light beam with an aperture 105 set to an appropriate exposure time and exposure energy, and an appropriate size described later, under the control of the light quantity control unit 40. That is, in other words, the light amount control unit 40 is a light amount variable unit that varies the amount of exposure, and the amount of exposure can be varied by the power of the light source, the light emission time of the light source, the aperture size varying unit described later, and the like. it can. In this way, by recognizing the relationship between the change of each parameter by the light quantity varying means and the change amount of the latent image area, the numerical value can be used to compensate for the variation of the latent image area.

  The collimator lens 104 is a lens having a refractive index of about 1.5, and shapes light beams emitted from the plurality of light sources 100, 101, and 102 into substantially parallel light. The aperture 105 has, for example, a rectangular opening whose width in the Y-axis direction (main scanning direction) is 5.5 mm and whose width in the Z-axis direction (sub-scanning direction) is 1.18 mm, and the center of the opening is a coupling lens. It is arranged so as to be located at or near the focal position 104. The beam spot size from the light sources 100, 101, 102 can be controlled by the size of the opening of the aperture 105. By setting the size of the opening of the aperture 105 corresponding to the beam spot size to be measured in advance, it is possible to perform measurement with a plurality of beam spot sizes without changing the configuration of other optical systems. At this time, the beam diameter on the sample 23 is desirably 200 μm or less.

  The half mirror 106 splits the light beam that has passed through the aperture 105, makes one incident on the first imaging lens 107, and makes one incident on the photodiode 109 via the second imaging lens 108. The photodiode 109 serves as a light amount detection unit, and transmits the detected light amount to the light amount control unit 40 described above. The imaging lens 107 condenses the light beam on the sample 23. When the imaging optical system 22 is incorporated into the electrostatic latent image measurement device as in the configuration of FIG. 1, the first imaging lens 107 is a sample installed in the sample installation unit 26 via a reflection mirror. A light beam is condensed on the light source 23. Further, in order to form a line pattern as an exposure pattern, the imaging optical system 22 may be provided with a scanning mechanism using a galvano mirror or a polygon mirror.

  A method for measuring a change in the latent image area depending on the light source wavelength based on the operations of the electrostatic latent image measuring apparatus and the imaging optical system of the present embodiment will be described with reference to the flowchart of FIG. In this figure, N is the number of light sources having different wavelengths to be measured.

(Step 1: hereinafter referred to as “S1”)
In S <b> 1, the sample 23 is charged by irradiating the sample 23 with an electron beam from the electron gun 11. By setting the acceleration voltage | Vacc | to be higher than the acceleration voltage at which the secondary electron emission ratio is 1, the amount of incident electrons exceeds the amount of emitted electrons, so that electrons are accumulated in the sample 23. Then, the sample 23 is charged up. As a result, the surface of the sample 23 is uniformly negatively charged. A desired charging potential can be formed on the sample 23 by appropriately adjusting the acceleration voltage and the irradiation time. That is, in other words, the charged particle irradiation means generates a charged charge on the sample 23 by irradiating the electron beam.

(Step 2: hereinafter referred to as “S2”)
In S2, the sample 23 is exposed using the imaging optical system 22 described above.
At this time, light sources other than the exposure light source to be measured among the light sources 100, 101, and 102 are not caused to emit light. In the present embodiment, measurement is performed by forming an electrostatic latent image in dot units from the imaging optical system 22 and the exposure unit. However, if the exposure energy density at that time is too small, a latent image is not formed. The density is desirably 1 mJ / m ² or more. In order to easily measure the change in the latent image area due to the wavelength using the latent image area as an evaluation index, the exposure amount between the light sources 100, 101, and 102 must be kept constant. This amount of exposure is monitored by the laser beam divided by the half mirror 106 with the photodiode 109, and the light amount control unit 40 controls the power of the light source through the amount of current flowing through the light sources 100, 101, 102, thereby obtaining a desired amount of light. It is possible to emit light with an exposure amount.

(Step 3: hereinafter referred to as “S3”. Further, FIG. 13 shows a detailed flowchart of Step 3.)
After the above exposure, when the electron gun 11 scans the sample 23 with an electron beam, secondary electrons are emitted (S3-1). The secondary electrons are detected by the electron detector 24-1 in FIG. 12, which includes a scintillator, a photomultiplier tube, etc. (S3-2), converted into an electrical signal by the signal processor 24-2 in FIG. Based on the signal, it is output as a potential contrast image in the measurement result output unit 24-3. (S3-3) At this time, the detection unit 24 can associate each scanning position with the detected amount of secondary electrons at that position by synchronizing with the scanning signal from the scanning lens 19.

  In this way, the charged portion on the sample 23 is measured with a large amount of detected secondary electrons, and the exposed portion is measured with a small amount of detected secondary electrons. The contrast image can be obtained. That is, since the dark part can be regarded as an electrostatic latent image by exposure, the area of the latent image can be measured based on the light / dark boundary when the light beam is exposed without being scanned.

  If there is a charge distribution on the surface of the sample 23, an electric field distribution corresponding to the surface charge distribution is formed in the space. For this reason, the secondary electrons generated in the exposure unit 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. 4A illustrates the potential distribution in the space between the detector 24 and the sample 23 in an explanatory manner with contour display. Since the surface of the sample 23 is uniformly charged to a negative polarity except for a portion where the potential is attenuated due to light attenuation, and a positive potential is applied to the detector 24, “shown by a solid line” In the “potential contour line group”, the “potential increases” as it approaches the detector 24 from the surface of the sample 23.

  Therefore, the secondary electrons el1 and el2 generated at the points Q1 and Q2 in the figure, which are “negatively charged portions” in the sample 23, are drawn to the positive potential of the detector 24, and the arrows G1 and It is displaced as indicated by G2, and is captured by the detector 24.

  On the other hand, in FIG. 4A, 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 acted on by the electric force restrained on the sample 23 side as indicated by the arrow G3. Therefore, the secondary electron el3 is captured in the “potential hole” indicated by the broken line potential contour and does not move toward the detector 24.

  FIG. 4B schematically shows the “potential hole”. That is, the intensity of secondary electrons (number of secondary electrons) detected by the detector 24 is such that the portion where the intensity is high is “the ground portion of the electrostatic latent image (partly uniformly charged negatively FIG. 4A). "Part represented by points Q1 and Q2 in FIG. 4)" and the part having a low intensity is "an image portion of the electrostatic latent image (part irradiated by light and represented by point Q3 in FIG. 4A)" It will correspond to.

  Therefore, when the electrical signal obtained by the detection unit 24 is received from the scanning lens 19 and sampled at an appropriate sampling time by the signal processing unit, the surface potential distribution is set using the sampling time T as a parameter as described above. V (X, Y) can be specified for each “small area corresponding to sampling”, and the surface potential distribution (potential contrast image) V (X, Y) is configured as two-dimensional image data by the signal processing unit. If the measurement result output unit images this, an electrostatic latent image is obtained as a visible image. Note that image output can also be performed by a host computer 1001 shown in FIG.

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.

  Further, the latent image area can be calculated by performing image processing on the latent image. For example, the latent image area can be calculated by performing binarization processing on the latent image (S3-4), extracting the outline of the latent image pattern, and counting the number of pixels occupying the inside of the outline. (S3-5). According to the above configuration, the charged particle beam is irradiated to the sample 23 having the surface charge distribution or the surface potential distribution, and the charge distribution or potential distribution state of the sample 23 is measured by the detection signal obtained by the irradiation. In this method, the electrostatic characteristics of the sample 23 can be grasped by measuring the latent image state when the exposure conditions are changed.

  That is, the processing unit of S3 according to the present invention forms an electrostatic latent image in dot units on the sample 23 using the common imaging optical system 22 with laser beams of different wavelengths from the exposure unit, and the sample 23 The latent image areas of the electrostatic latent images in dot units formed in the above are compared, and a change amount of each latent image area depending on different wavelengths is measured.

(Step 4: S4)
Returning to FIG. In S4, the sample 23 is neutralized using the LED 25. The charged charge generated on the sample 23 can be eliminated by irradiating the light beam. Here, the LED 25 emits light for charge removal and prepares for the next measurement. By performing the above process, latent image measurement can be performed.

(Steps 5 and 6: S5 and S6)
In S5, it is determined whether or not the measurement is performed with a different light source wavelength. When the measurement is performed, a new light source is selected in S6.

(Step 7: S7)
In S7, the exposure amount of the imaging optical system 22 is adjusted in order to keep the same exposure amount for each light source wavelength. In order to measure the change in the latent image area depending on the wavelength, it is not preferable that there is a difference in exposure amount between the light sources. Therefore, the exposure amount can be maintained by adjusting the drive current amount based on the exposure amount measured by the photodiode 109 and controlling to output the same exposure amount as the light source used first.

  Based on the above process, by evaluating the latent image area using the imaging optical system 22 common to the light sources 100, 101, and 102 having different wavelengths, the change in the latent image area in units of dots can be evaluated. . As a result, adjustment work such as high-accuracy optical path adjustment that is required when repeating the measurement by changing the light source can be omitted, and changes in optical characteristics that may occur at that time can be prevented. Thus, the latent image area can be evaluated in dot units according to the actual machine efficiently. In addition, since it is possible to derive conditions for compensating for the change based on the change in the latent image area in dot units depending on the measured wavelength, the possibility of density unevenness and banding caused by image formation is prevented. be able to.

  Next, a method for improving conventional problems such as density unevenness and banding based on the change in the latent image area due to the wavelength measured by the above method will be described.

  If differences in latent image areas due to wavelengths (650 nm, 655 nm, and 660 nm) as shown in FIG. 5A appear, this difference causes density unevenness and banding on the image. To solve this problem, the latent image areas can be made uniform as shown in FIG. 5B by controlling the power, light emission time, beam size on the photosensitive member, and the like for each light source.

The relationship between the exposure energy density and the latent image area is shown in FIG. Here, characteristic diagrams of light sources that oscillate at different wavelengths λ1 and λ2 are shown. Note that this characteristic diagram is obtained by, for example, mounting an imaging optical system 22 as shown in FIG. 2 on the electrostatic latent image device, changing the light source output at that time, and measuring the area of each latent image. Can do. When the imaging optical system 22 of FIG. 2 is used, the beam size is determined by the size of the aperture 105, and the beam size is maintained even if the light source output is changed. The beam size at this time can be obtained by evaluating the optical system alone and measuring the beam diameter on the sample 23. The exposure energy can be obtained from the amount of exposure transmitted through the aperture 105, and can be measured in the same manner by evaluating the optical system alone. As described above, since the exposure energy reaching the sample 23 and the beam size at a certain light source output are obtained, the exposure energy density can be calculated. Further, by measuring the latent image area at that time, the characteristics of the exposure energy density and the latent image area shown in FIG. 6 can be obtained. By performing the above procedure even at different wavelengths, it is possible to obtain characteristics of exposure energy density and latent image area at a plurality of wavelengths.

  In FIG. 6, for example, when exposure is performed at a certain exposure energy density P1, the latent image area of the latent image formed is λ1 and λ2, respectively, due to factors such as a difference in photoreceptor sensitivity and a difference in imaging state. S1 and S2. At this time, if the exposure energy density of the light source oscillating at λ2 is set to P2 using the relationship between the latent image area and the exposure energy density at the wavelength in this characteristic diagram, the change in the latent image area between the two wavelengths is compensated. As shown in FIG. 5B, the latent image areas can be made uniform even if the wavelength changes. Also, by using this characteristic diagram as a function and processing it electronically, the computer automatically evaluates the dot area of the latent image area and automatically calculates each parameter for compensating the latent image area. Is possible.

  The exposure energy density varies depending on the power of the light source, the light emission time of the light source, and the beam size on the photoconductor. By controlling these parameters, it is possible to compensate for the change in the latent image area due to the wavelength difference. The power of the light source can be changed by controlling the amount of current flowing through the light source, and the exposure time of the light source can be changed by controlling the time during which the drive current flows. These can be arbitrarily set by controlling using the light quantity control unit 40 via the computer 1001. The beam size on the photoconductor is determined by the light source wavelength and the beam spot size, and changes with the size of the opening of the aperture 105.

  That is, the electrostatic latent image measuring device according to the present invention has means for deriving a condition that the latent image areas at different wavelengths are the same by varying the light amount or beam spot size with which the sample 23 is exposed by the light source by the light amount variable means. have. Further, the electrostatic latent image measuring method according to the present invention uses the electrostatic latent image in units of dots on the sample 23 by using laser light having different wavelengths from the above-described exposure means and a common imaging optical system, A step of comparing the latent image areas of the latent images in dot units formed on 23, a step of measuring changes in the latent image areas depending on different wavelengths, and an amount of light that exposes the sample 23 by the light sources 100, 101, and 102. Alternatively, the method includes a step of varying the beam spot size by the light amount varying means and deriving a condition that the latent image areas at different wavelengths are the same.

  From this, using this embodiment, by clarifying the relationship between the change in the latent image area caused by the wavelength and the parameter that can change the latent image area, wavelength variation between light sources occurs in the multi-beam optical system. The latent image area can be kept constant.

[Second Embodiment]
In the first embodiment, in order to perform measurement with different beam spot sizes, the aperture 105 is created in advance and attached for each measurement. However, the size of the aperture 105 is controlled by a stepping motor, a piezoelectric element, or the like. Also good.

  The aperture 105 shown in FIG. 7 has an adjustment slit orthogonal to the optical axis, and is formed in a square shape by overlapping them. FIG. 7A shows the slit 105a that can be adjusted in the horizontal direction, and FIG. 7B shows the slit 105b that can be adjusted in the vertical direction. By arranging these two adjustment slits so as to overlap each other, the square aperture 105 shown in FIG. 7C is configured. Each adjustment slit can be independently moved by a movable means (not shown), and an opening having a desired size can be formed according to an input electric signal. The moving amount resolution of the adjusting mechanism is preferably 0.5 μm or less.

  By using this configuration, the size of the opening of the aperture 105 for each light source can be easily controlled, and adjustment work associated with the creation and replacement of the aperture 105 for each measurement can be omitted. No change in optical properties. Further, since the size of the opening of the arbitrary aperture 105 can be easily controlled, the beam spot size can be efficiently derived so as to compensate for the difference in the latent image area depending on the wavelength.

[Third embodiment]
In the first embodiment, the amount of current flowing through the light source is controlled in order to keep the exposure amount between the light sources 100, 101, 102 constant. However, the amount of current is constant, and an ND filter is added to the imaging optical system 23. The exposure amount may be made constant by inserting 30. This configuration is shown in FIG.

  In the imaging optical system shown in FIG. 8, the ND filter 30 is inserted behind the optical path of the first imaging lens 107 in the same imaging optical system 22 shown in FIG. An ND filter 30 is prepared for each of the light sources 100, 101, and 102 so that a desired exposure amount is exposed to the sample 23, and the ND filter 30 corresponding to the measurement light source is attached for each measurement to change the light source wavelength. Also, the exposure amount can be kept constant.

  By using this configuration, it is possible to align the exposure amounts of the light sources 100, 101, and 102 without being affected by the change in exposure amount caused by passing through the half mirror or the imaging lens. In addition, since the amount of current flowing through the light sources 100, 101, and 102 can be made constant, it is possible to perform an evaluation in accordance with an actual machine without being affected by a change in rising characteristics of the optical output waveform due to the amount of current.

[Fourth Embodiment]
In the third embodiment, the ND filter 30 corresponding to each light source is attached for each measurement in order to keep the exposure amount between the light sources 100, 101, and 102 constant. A filter may be used. A variable ND filter is shown in FIG.

  A variable ND filter 30a shown in FIG. 9A is a circular ND filter whose optical density is continuously changed in the circumferential direction, and the amount of transmitted light is continuously changed by rotating the variable ND filter 30a. Can do. A variable ND filter 30b shown in FIG. 9B is a rectangular ND filter in which the optical density is continuously changed in the linear direction. The amount of transmitted light can be continuously changed by moving the variable ND filter 30b in the linear direction.

  By using the above-described ND filter 30 and electrically controlling the laser light transmission position with a stepping motor (not shown) or the like, the exposure amount at that time is determined from the relationship between the laser light transmission position on the ND filter 30 and the transmittance at that position. Can be requested. Further, this control can be performed by the light amount control unit 40 which is a light amount varying means, and an instruction can be issued by the host computer 1001 described later. By using this configuration, it is possible to easily control the exposure amount for each light source, and it is possible to omit troublesome work associated with selection and replacement of the ND filter 30 for each measurement. In addition, since the arbitrary filter transmittance can be easily controlled, it is possible to efficiently derive the exposure amount so as to compensate for the difference in the latent image area depending on the wavelength.

[Fifth Embodiment]
In the first embodiment, a plurality of light sources having different oscillation wavelengths are used as the light source. However, one of the light sources may be used, and the oscillation wavelength may be changed by adjusting the temperature using a Peltier element or the like. . At this time, it is desirable that the temperature adjustment resolution is 0.1 ° C. or less. The temperature adjustment mechanism of the light source is shown in FIG.

  FIG. 10A is a plan view of the temperature adjustment mechanism of the light source, and FIG. 10B is a front view. The temperature adjustment mechanism includes a light source 51, a copper plate 52, a Peltier element 53, a heat sink 54, and a temperature sensor 55. The light source 51 is fixed to the copper plate 52, and its temperature changes due to heat radiation and heat absorption from the Peltier element 53.

  The Peltier element 53 is a plate-like semiconductor element that utilizes the Peltier effect in which heat is transferred from one metal to the other when a current is applied to a joint between two kinds of metals. One side absorbs heat and the other side generates heat. The temperature change by the Peltier element 53 is read by the temperature sensor 55, the deviation from the temperature to be set is measured, and the temperature control unit 50 controls the amount of current flowing through the Peltier element 53, thereby adjusting the light source temperature to a desired temperature. It becomes possible to do. Note that a heat sink 54 is attached to one surface of the Peltier element 53 in order to stably perform heat dissipation and heat absorption by the Peltier element 53. Further, this control can be performed by giving an instruction to the temperature control unit 50 from the light amount control unit 40 which is a light amount variable means, and the temperature can be set and monitored by the host computer 1001 which will be described later. is there.

  In the semiconductor laser, the oscillation wavelength linearly changes as shown in FIG. 11 when heat is applied. Therefore, if the relationship between the light source temperature and the oscillation wavelength is measured in advance, oscillation at an arbitrary wavelength can be performed through temperature adjustment. At this time, when the light source temperature rises, the oscillation efficiency of the light source decreases and the output also changes. However, by using any of the methods described in the first, third, and fourth embodiments, the exposure amount between each oscillation wavelength Can be kept constant. Further, by using the configuration of the aperture 105 described in the first and second embodiments, it is possible to perform measurement at the size of the opening of the arbitrary aperture 105. By using these configurations, the relationship between a plurality of wavelengths and the latent image area can be easily evaluated even when one light source is used.

  The block diagram of FIG. 12 shows an example in which the entire electrostatic latent image measurement device is controlled by the host computer 1001. The configuration of the apparatus is the same as that of the embodiment shown in FIG. In FIG. 12, the electrostatic latent image measuring apparatus according to the present invention includes a light amount control unit 40, a sample stage control unit 1003, an LED control unit 1004, and a charged particle control unit 1002. The entire measuring apparatus can be controlled, instructed and monitored by the host computer 1001. In addition, the detection result of the detection means 24 that is an electrostatic latent image measurement means can be monitored from the terminal of the host computer 1001, and the host computer 1001 changes the appropriate setting related to the measurement by the detector 24. You can also. The detector 24 includes an electron detection unit 24-1 that detects secondary electrons, a signal processing unit 24-2 that converts a secondary electron signal into a processing signal and calculates an electron trajectory of the secondary electrons, and a measurement result thereof. A measurement result output unit 24-3 for imaging the image and an image processing unit 24-4 for binarizing the image. The signal processing unit 24-2, the measurement result output unit 24-3, and the image processing unit 24-4 may be included in the detector 24 or on the host computer 1001 side.

  The light quantity control unit 40 is configured to control the exposure amounts of a plurality of light sources that are exposure means, and to set the exposure amounts from the host computer 1001 as described above. The sample stage control unit 1003 controls the movement of the sample 23 on the sample setting unit 26, and the moving amount and moving direction can be set from the host computer 1001. The LED control unit 1004 controls the above-described residual charge removal, and this residual charge removal can be set from the host computer 1001. The charged particle control unit 1002 controls each of the acceleration voltage control unit 1002-1, the scanning lens control unit 1002-2, and the objective lens control unit 1002-3. The acceleration voltage control unit 1002-1 controls the energy of the electron beam. The scanning lens control unit 1002-2 controls the scanning position of the electron beam, and the objective lens control unit 1002-3 controls the focal position of the electron beam.

  With the configuration described above, the operation of the entire electrostatic latent image measurement device can be controlled from the host computer 1001, and the latent image area in each of the above-described embodiments can be measured. In the host computer 1001, the electrostatic latent image program according to the present invention is running, and by controlling each means in the host computer 1001, the method shown in the flowcharts of FIGS. 3 and 13 is realized. Yes.

  In this way, in the development process of the photoreceptor in the image forming apparatus, the electrostatic latent image measurement method in each of the above embodiments can be automatically performed even in an unattended state, and the image development apparatus can be efficiently developed. At the same time, image quality can be improved.

DESCRIPTION OF SYMBOLS 10 Charged particle irradiation part 11 Electron gun 12 Extraction electrode 13 Acceleration electrode 14 Electrostatic lens 15 Beam blanking electrode 16 Partition plate 17 Movable diaphragm 18 Astigmatism correction 19 Scanning lens 20 Objective lens 21 Beam emission opening part 22 Imaging optical system 23 Sample 24 Detector 25 LED
26 Sample setting part

JP 2009-163175 A JP 11-296026 A JP 2003-295696 A JP 2006-84434 A JP 2009-300535 A

Claims (18)

Charged particle irradiation means for generating a charged charge on a sample by irradiating charged particles; and
Exposure means comprising a light source;
An electrostatic latent image measuring device comprising: an electrostatic latent image measuring unit that measures an electrostatic latent image formed on the sample by the exposure unit;
The exposure means emits laser light of different wavelengths,
An electrostatic latent image in units of dots is formed on the sample using laser light having different wavelengths from the exposure means using a common imaging optical system,
A light amount varying means for varying the exposure amount of the light source,
The electrostatic latent image measuring device, wherein the electrostatic latent image measuring means measures the latent image area of the electrostatic latent image of the dot unit formed on the sample. Means for comparing the latent image area of the electrostatic latent image for each laser beam of a different wavelength from the exposure means to measure the amount of change;
The electrostatic latent image measuring device according to claim 1, further comprising: means for varying an exposure amount to be exposed to the sample by the light source by a light amount varying unit, and deriving a condition that the latent image areas at the different wavelengths are the same. .   The electrostatic latent image measuring device according to claim 1, wherein the light quantity varying unit varies the power of the light source.   The electrostatic latent image measuring device according to claim 1, wherein the light quantity varying unit varies a light emission time of the light source. The imaging optical system includes an aperture size varying unit that varies the size of the aperture opening.
The electrostatic latent image measuring device according to claim 1, wherein the light quantity varying unit controls the operation of the aperture size varying unit.   The aperture size varying means has a plurality of adjustment slits in a direction orthogonal to the optical axis direction of the laser beam from the exposure means, and the plurality of adjustment slits are stacked so as to form a square shape. The electrostatic latent image measuring device according to claim 5, wherein the size of the electrostatic latent image is variable. The electrostatic latent image measuring device according to claim 1, wherein the imaging optical system includes a light amount detection unit that detects a change in an exposure amount of the light source.
  8. The electrostatic latent image measuring device according to claim 1, wherein the imaging optical system includes an ND filter for varying the exposure amount according to a wavelength from the light source.   9. The electrostatic latent image measuring device according to claim 8, wherein the light amount varying means varies the exposure amount according to a position where the laser light from the light source passes through the ND filter.   The electrostatic latent image measuring device according to claim 1, wherein the imaging optical system includes temperature control means for varying a temperature of the light source for oscillating the laser beams having different wavelengths.   An electrostatic latent image evaluation program for causing a computer to function as the electrostatic latent image measuring device according to any one of claims 1 to 10. A charged particle irradiation process for generating a charged charge on the sample;
An exposure step of emitting laser beams of different wavelengths to form an electrostatic latent image on the sample;
An electrostatic latent image measurement method including an electrostatic latent image measurement step of measuring the electrostatic latent image by detecting secondary electrons when scanning charged particles,
The step of forming an electrostatic latent image in units of dots on a sample using laser light having different wavelengths using a common imaging optical system, and measuring the latent image area of the electrostatic latent image for each different laser light When,
Comparing the latent image area of the electrostatic latent image for each laser beam of a different wavelength to measure the amount of change;
And a step of deriving a condition that the latent image area of the electrostatic latent image is the same for each laser beam having a different wavelength by varying an exposure amount to be exposed to the sample by the light source by a light amount varying unit. An electrostatic latent image measuring method.   The electrostatic latent image measuring method according to claim 12, wherein the power of the light source is changed in order to derive an exposure amount at which the latent image areas for the laser beams having different wavelengths are the same.   13. The electrostatic latent image measuring method according to claim 12, wherein the light emission time of the light source is changed in order to derive an exposure amount at which the latent image areas for the laser beams having different wavelengths are the same.   13. The electrostatic latent image measuring method according to claim 12, wherein the beam spot size of the light source is changed in order to derive an exposure amount at which the latent image areas for the laser beams having different wavelengths are the same.   The electrostatic latent image measurement method according to claim 13, wherein the power of the light source is changed so that the exposure amount when the light sources that oscillate the different wavelengths are used is the same.   16. The electrostatic latent image measuring method according to claim 13, wherein the transmittance of the ND filter is changed so that the exposure amount when using the light sources that oscillate the different wavelengths is uniform. 18. The electrostatic latent image measuring method according to claim 12, wherein the temperature of the light source is varied in order to oscillate the laser beams having different wavelengths.

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