JP4801613B2 - Electrostatic latent image evaluation method / electrostatic latent image evaluation apparatus - Google Patents

Description

  The present invention relates to an electrostatic latent image evaluation method and apparatus.

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 step for uniformly charging the photoconductive photoconductor (b) Exposure step for irradiating the photoconductor with light to form an electrostatic latent image by photoconductivity (c) Using charged toner particles A developing step for forming a visible image on the photoreceptor (d) a transferring step for transferring the developed visible image to a transfer material such as a piece of paper (e) a fixing step for fusing and fixing the transferred image on the transfer material (F) Cleaning step for cleaning residual toner on photoconductor after transfer of visible image (g) Static elimination step for eliminating residual charge on photoconductor

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 a growing 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. .
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 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 result to the design, it is possible to improve the process quality of the charging and exposure processes, resulting in image quality, durability, stability and savings. Further improvement in energy can be expected.

Patent Documents 1 and 2 are known as methods for measuring surface charge distribution or surface potential distribution in a dielectric such as a photoconductive photoreceptor with high resolution on the order of microns.
In the measurement methods described in these patent documents, the surface of the measurement sample is scanned with a charged particle beam, and secondary electrons generated on the measurement sample surface are detected. In the case of this method, the electric field distribution on the surface of the measurement sample is directly measured, and the surface potential distribution is calculated arithmetically based on this electric field distribution.
Further, a method described in Patent Document 3 is known as a method for evaluating a photoconductive photoconductor using the surface potential distribution measuring method.
In the one described in Patent Document 3, an electrostatic latent image pattern is formed by projecting a light image of a mask pattern for resolution inspection, and a pitch of any of a plurality of basic pattern pairs having different pitches included in the pattern is determined. A method for evaluating the resolving power of a photoconductive photosensitive member or the like by observing whether even a basic pattern pair can be identified is shown.

JP 2003-295696 A JP 2003-305881 A Japanese Patent Application Laid-Open No. 2004-233261

In the evaluation method described in Patent Document 3, whether or not a basic pattern pair can be identified is judged by a person visually observing an image and the resolution is evaluated. However, a human qualitative judgment process is involved. Thus, the judgment results vary.
Also, depending on the image, it is often difficult to determine whether or not identification is possible, and even if the result of the determination differs for each person performing the judgment, or even if the person performing the judgment is the same, the physical and mental state of the person performing the judgment (fatigue) There is a problem that the judgment result varies depending on the degree.
Further, since the determination is based on the binary value of “whether or not the pattern can be resolved”, information on the resolution level of the latent image pattern (that is, intermediate information such as “degree of crushing” and “degree of fading”). Cannot be reflected in the judgment results.
This makes it difficult to extract the difference when, for example, comparison is made with respect to photoreceptors having slightly different resolutions.

  In view of the above problems, the present invention provides a quantitative evaluation method and an evaluation apparatus based on a numerical index capable of calculating a resolving power even in a latent image that is difficult to judge visually. Objective.

In order to achieve the above object, according to the first aspect of the present invention, the surface on which the electrostatic latent image pattern is formed of the photoconductive sample on which the electrostatic latent image pattern is formed by charging and exposure of a light image, The charged particle beam is scanned two-dimensionally, the charged particles affected by the electrostatic latent image pattern are captured, the intensity signal is detected in correspondence with the position on the surface, and the electrostatic An electrostatic latent image evaluation method for evaluating an electrostatic latent image by observing a charge distribution state in a latent image pattern, wherein a light amount distribution in any cross section included in the optical image is a periodic light amount A cross-sectional light amount distribution having a fluctuation in value, a cross-sectional profile including an electrostatic latent image pattern is extracted from the detected intensity signal, and a feature amount is obtained from the intensity signal of the exposed part and the non-exposed part of the cross-sectional profile. Extract the latent of the photoconductive sample It is intended to calculate the resolution, the feature amount, the exposed portions of the cross-section profile, a contrast which is calculated from the average value of the intensity signals of the non-exposed portion to form a plurality of electrostatic latent image patterns having different spatial frequencies The latent image in the spatial frequency band of the photoconductive sample is calculated by calculating the response function of the latent image by calculating the contrast at each spatial frequency and obtaining the average value of the contrast calculated at each spatial frequency. The resolving power is calculated .

According to a second aspect of the present invention, in the electrostatic latent image evaluation method according to the first aspect, a plurality of electrostatic latent image patterns having different exposure energies are formed, and the contrast at each exposure energy is calculated and compared. It is characterized in that the exposure energy that maximizes the value is obtained.
According to a third aspect of the present invention, there is provided the electrostatic latent image pattern of a charging means and an optical image exposure means for forming an electrostatic latent image pattern, and a photoconductive sample on which the electrostatic latent image pattern is formed. Charged particle beam scanning means for two-dimensionally scanning the formed surface with a charged particle beam, and capturing charged particles that are electrically affected by the electrostatic latent image pattern, and outputting the intensity signal on the surface An electrostatic latent image evaluation apparatus comprising: an evaluation unit that detects a charge distribution state in the electrostatic latent image pattern, and detects the charge distribution state in the electrostatic latent image pattern. The light image exposure means having a light amount distribution having a cross-sectional light amount distribution having a periodic light amount value variation, and a cross-sectional profile including the electrostatic latent image pattern is extracted from the detected intensity signal, and the cross-sectional profile exposure unit , Non-exposed area intensity And the evaluation means for extracting the feature amount from the evaluation means, wherein the feature amount extracted by the evaluation means is a contrast calculated from an average value of intensity signals of the exposed portion and the non-exposed portion of the cross-sectional profile, The optical image exposure means for forming a plurality of electrostatic latent image patterns having different frequencies, and the evaluation means for calculating a response function of the latent image by calculating contrast at each spatial frequency, each spatial frequency The evaluation means is provided for calculating an average value of the contrast calculated in step 1 and calculating a latent image resolving power in the spatial frequency band of the photoconductive sample .

According to a fourth aspect of the invention, in the electrostatic latent image evaluation apparatus according to the third aspect, the exposure energy control means for forming a plurality of electrostatic latent image patterns having different exposure energies is calculated and compared with the contrast at each exposure energy. And the above-mentioned optical image exposure means for obtaining the exposure energy that maximizes the contrast .

According to the present invention, by extracting the feature quantity of the intensity signal from the cross-sectional profile of the latent image pattern, a quantitative electrostatic latent image evaluation method based on a numerical index that does not depend on human visual evaluation, and An evaluation device can be provided.
Evaluation method and apparatus capable of quantitatively evaluating electrostatic latent image resolving power based on numerical index by calculating contrast of intensity signal from cross-sectional profile of latent image pattern in electrostatic latent image evaluation method and apparatus An apparatus can be provided.
In the electrostatic latent image evaluation method and apparatus, by calculating the contrast of the intensity signal from the cross-sectional profile of the latent image pattern in a wide spatial frequency band, the quantitative electrostatic latent image resolving power based on the numerical index is wide spatial frequency. It is possible to provide an evaluation method and an evaluation apparatus capable of evaluating over a band.

In the method and apparatus for evaluating an electrostatic latent image, a contrast of an intensity signal is calculated from a cross-sectional profile of a latent image pattern in a wide spatial frequency band, and a representative value in the spatial frequency band is calculated. It is possible to provide an evaluation method and an evaluation apparatus capable of clearly comparing and evaluating the superiority or inferiority of each electrostatic latent image resolving power by using the representative value in the property sample.
In the electrostatic latent image evaluation method and apparatus, by calculating and comparing the contrast of the intensity signal from the cross-sectional profile of the latent image pattern under a plurality of different light image exposure energy conditions, the light image exposure energy condition that maximizes the resolving power is obtained. An evaluation method and an evaluation apparatus that can be specified can be provided.

Embodiments of the present invention will be described below with reference to the drawings.
An outline of the electrostatic latent image evaluation apparatus and an evaluation process based on the evaluation method will be described with reference to the apparatus diagram of FIG. FIG. 1 is a diagram showing an embodiment of an electrostatic latent image observation apparatus (electrostatic latent image evaluation apparatus).
In FIG. 1, reference numeral 11 is a charged particle gun, 12 is an aperture, 13 is a condenser lens for charged particles, 14 is a beam blanker, 15 is a scanning lens for charged particle beams, and 16 is an objective lens for charged particle beams.
The charged particle gun 11, the aperture 12, the condenser lens 13, the beam blanker 14, the scanning lens 15, and the objective lens 16 constitute a charged particle beam irradiation unit 10b, and each component of the charged particle beam irradiation unit 10b is a charged particle. It is controlled by the beam controller 10a.
The charged particle beam irradiation unit 10b and the charged particle beam control unit 10a constitute a “charged particle beam scanning unit” and also have a function as a charging unit for forming an electrostatic latent image pattern.

In FIG. 1, reference numeral 17b denotes a semiconductor laser (LD) as a light source, 17a denotes an LD control unit for driving the light source, 18 denotes a collimating lens, 19 denotes an aperture, 20 denotes a mask pattern, and 21, 22 and 23 denote "imaging lenses". The lens which comprises "is shown. These constitute “optical image exposure means”.
The optical image exposure means not only controls blinking of the light emitted from the semiconductor laser 17b and adjustment / setting of the light emission intensity, but also performs focusing and magnification conversion by adjusting the positional relationship between the imaging lenses 21, 22, 23 and the mask pattern 20. To get.

In FIG. 1, reference numeral 24 denotes a charged particle detector, 25a denotes a signal processing unit, 25b denotes a resolving power calculation unit, 26 denotes a monitor (display unit), and 27 denotes an output device (output unit) such as a printer. The charged particle detector 24, the signal processing unit 25a, the resolving power calculation unit 25b, the monitor 26, and the output device 27 constitute “evaluation means”.
In FIG. 1, reference numeral 28 denotes a sample mounting table, 00 denotes a photoconductive sample, and 29 denotes a light-emitting element for charge removal. The sample mounting table 28 is a grounded metal plate.
Each of the above parts is disposed in a casing 30 as shown in the figure, and the inside of the casing can be highly decompressed by a vacuum control unit 31. That is, the casing 30 has a function as a “vacuum chamber”.
The entire apparatus is controlled by the host PC 32. The charged particle beam control unit 10a, the signal processing unit 25a, and the like described above can be set as “part of the function” in the host PC 32.

In the state shown in FIG. 1, the photoconductive sample 00 whose surface is uniformly charged is placed on the sample placing table 28, and the inside of the casing 30 is highly decompressed.
In this state, the semiconductor laser 17b is turned on to form an optical image of the mask pattern 20 on the uniformly charged surface of the photoconductive sample 00.
By this exposure, an electrostatic latent image pattern corresponding to the irradiated light image is formed on the photoconductive sample 00. The surface on which the electrostatic latent image pattern 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, the beam diameter is regulated, and then passes through the beam blanker 14 while being focused by the condenser lens 13. .

The charged particle beam focused by the condenser lens 13 is focused on the surface of the photoconductive sample 00 by the objective lens 16. At this time, the direction of the charged particle beam is deflected by the scanning lens 15 so that the position where the charged particle beam is focused is two-dimensionally on the surface of the photoconductive sample 00 (for example, the horizontal direction of the drawing is orthogonal to the drawing). Direction).
In this way, the surface of the photoconductive sample 00 on which the electrostatic latent image pattern is formed is two-dimensionally scanned with the charged particle beam. The size of the scanned region can be changed by setting the magnification of the scanning lens. For example, various magnifications such as a low magnification of about 5 mm × 5 mm and a high magnification of about 1 μm × 1 μm can be used. Can be observed.
At this time, a capture voltage having a predetermined polarity is applied to the charged particle detector 24. By this action of the trapping voltage, “charged particles that are electrically affected by the electrostatic latent image pattern” are captured by the charged particle detector 24, and the intensity (number of trapped particles per unit time) is detected. Converted to a signal.

The “region to be scanned two-dimensionally by a charged particle beam: S” of the photoconductive sample 00 is represented by S (X, Y) using two-dimensional coordinates, for example, 0 mm ≦ X ≦ 1 mm, 0 mm ≦ Y ≦ 1 mm. 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, if the time from the start to the end of the two-dimensional scanning is T0 ≦ T ≦ TF, the scanning is performed. Time: T corresponds to each scanning position in the scanning area: S (X, Y) 1: 1.
Since the charged particles captured by the charged particle detector 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 affected by the reference potential: VN, and by calibrating the intensity of the charged particles: F based on the known correspondence. The electric potential: V corresponding to the intensity: F can be known.
Therefore, by sampling the detection signal obtained from the charged particle detector 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, an “ion gun” or the like is used.
Hereinafter, the case where an electron beam is used as the charged particle beam will be specifically described. At this time, the charged particle gun 11 is an “electron gun”, and the “surface on which the electrostatic latent image pattern is formed” of the photoconductive sample 00 is two-dimensionally scanned with an electron beam.

In order to form an electrostatic latent image pattern on the photoconductive sample 00, it is necessary to uniformly charge its surface prior to exposure with a light image. For uniform charging of the photoconductive sample 00, charging may be performed outside the observation apparatus, and the uniformly charged photoconductive sample 00 may be mounted on the sample mounting table 28. As described above, The inside of the casing 30 needs to be highly decompressed. If the inside of the casing 30 is decompressed after setting the photoconductive sample 00, the charged potential is attenuated due to dark decay before scanning with the electron beam becomes possible. In some cases, the electrostatic latent image pattern cannot be observed.
From this point of view, it is preferable that the uniform charging of the photoconductive sample 00 is performed in the casing 30 “after high pressure reduction is realized”.
In the embodiment shown in FIG. 1, the charged particle beam scanning unit is used to perform charging with an electron beam.

When the photoconductive sample 00 is irradiated with an electron beam, “secondary electrons” are generated from the photoconductive sample 00 by the impact of the irradiated electrons. In the balance between the amount of electrons irradiated to the photoconductive sample 00 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: R1 / R2 is 1 or more If so, the amount of electrons irradiated by subtraction exceeds the amount of secondary electrons, and the difference between the two accumulates in the photoconductive sample 00 to charge the photoconductive sample 00.
Therefore, by adjusting the amount of electrons emitted from the electron gun 11 and the acceleration voltage thereof, and setting the “ratio: the condition that R1 / R2 is greater than 1” and scanning the electron beam two-dimensionally, The conductive sample 00 can be charged uniformly.
Such adjustment of the amount of emitted electrons and the acceleration voltage is performed by the charged particle beam control unit 10a. Further, the on / off of the electron beam accompanying the scanning of the electron beam is performed by controlling the beam blanker 14 by the charged particle beam control unit 10a.

FIG. 2 schematically shows a state in which the surface of the photoconductive sample 00 is charged with an electron beam as described above. The photoconductive sample 00 shown in FIG. 2 is a so-called “function-separated type photoreceptor” in which a charge generation layer 42 is provided on a conductive layer 41 and a charge transport layer 43 is formed thereon. It is.
Electrons irradiated by the electron gun 11 are shot into the surface of the charge transport layer 43, trapped in the electron orbits of charge transport layer material molecules on the surface of the charge transport layer 43, and charge transported in a state in which the molecules are negatively ionized. It remains on the surface of layer 43. This state is a state in which the photoconductive sample 00 is charged.
When the photoconductive sample 00 in such a charged state is irradiated with the light LT, the irradiated light LT passes through the charge transport layer 43 and reaches the charge generation layer 42, and the energy in the charge generation layer 42 is generated. To generate positive and negative charge carriers.

Of the generated positive and negative charge carriers, the negative carriers move to the conductive layer 41 due to the repulsive force of the negative charge on the surface of the charge transport layer 43, and the positive carriers are transported through the charge transport layer 43 and the same layer. It counteracts with the negative charge (captured electrons) on the surface of 43.
In this manner, the charged charge is attenuated in the portion irradiated with the light LT in the photoconductive sample 00, and a charge distribution according to the intensity distribution of the light LT is formed. This charge distribution pattern is nothing but an electrostatic latent image pattern.
The photoconductive sample 00 uniformly charged as described above is exposed to a light image to form an electrostatic latent image pattern. This exposure is performed by the aforementioned “optical image exposure means”. That is, the semiconductor laser 17b is turned on, and an image of the mask pattern 20 is formed on the surface of the photoconductive sample 00 by the action of the imaging lenses 21, 22, and 23.
In order to obtain good imaging characteristics, the mask pattern 20 and the imaging lenses 21, 22, and 23 included in the optical image exposure unit are arranged at appropriate positions based on a known imaging optical technique. Further, when the optical axis 33 of the optical image exposure means is not perpendicular to the photoconductive sample 00 as shown in FIG. 1, the mask pattern 20 is arranged with an appropriate inclination with respect to the optical axis 33.

Of course, the semiconductor laser 17b having a light emission wavelength in a wavelength region in which the photoconductive sample 00 has sensitivity is used. Further, since the exposure energy is a time integration of the light intensity on the surface of the photoconductive sample 00, the light exposure time of the semiconductor laser 17b is controlled by the LD control unit 17a so that the photoconductive sample 00 has a desired exposure. Exposure by energy can be performed.
The LD control unit 17a and the semiconductor laser 17b constitute an “exposure energy control unit”.
The mask pattern in the mask pattern 20 is “a mask pattern for resolving power inspection”. In the embodiment being described, the mask pattern is also a negative pattern so that a negative latent image can be formed on the photoconductive sample, and the portion corresponding to the portion irradiated with light when forming the electrostatic latent image is light transmissive. The other part is light-shielding.

FIG. 3 shows an example of the mask pattern. This mask pattern is a pattern in which a resolution inspection pattern is formed as a transmission part in a light-shielding part (hatched part). As shown in the figure, the resolution inspection pattern is a “basic pattern in which three rectangular shapes are periodically arranged in parallel at a predetermined pitch” and a plurality of sets of basic pattern pairs P1 in which the sizes and pitches of the rectangles are changed stepwise. ~ P6 are arranged as shown in the figure.
The spatial frequency of each basic pattern pair is distributed in the range of 10 to 100 LinePair / mm. As an example, the above-described spatial frequency band has been described. Of course, as long as the projection resolution of the optical image exposure unit described below is allowed, the spatial frequency band is not limited to the above-described spatial frequency band, and is higher or lower than an arbitrary spatial frequency band. Basic pattern pairs can be used.
Here, a mask pattern having three parallel patterns as basic patterns is used. However, the basic pattern may be any pattern that includes a periodic transmittance change, that is, two or more parallel patterns. Further, the transmission part of the mask pattern is not limited to one in which the transmittance changes in a binary manner, and may include a gray part including, for example, a sine wave.

In a state where the electrostatic latent image pattern is formed on the photoconductive sample 00 as described above, the scanning region of the photoconductive sample 00 is two-dimensionally scanned with an electron beam. Secondary electrons generated by this scanning are detected by the charged particle detector 24.
Since the detection target is a secondary electron and a negative charge, the charged particle detector 24 applies a positive voltage (capture voltage) for capturing secondary electrons, and positively generates secondary electrons generated by scanning the electron beam. Capture by aspiration with voltage. The captured electrons are converted into scintillation luminance by a scintillator, which is further converted into an electric signal.
In the space between the surface of the photoconductive sample 00 and the charged particle detector 24, the charge on the surface of the photoconductive sample 00 (negative charge forming an electrostatic latent image) and the charged particle detector 24 are applied. A “potential gradient” is formed by the positive trapping voltage.
Based on the known principle in Patent Document 3 described above, an intensity signal corresponding to the distribution of the electrostatic latent image pattern is obtained by the potential gradient. The intensity here is the detection intensity (number of secondary electrons) of secondary electrons, and the signal is low in the area where the electrostatic latent image pattern is formed and high in the area where it is not formed. It becomes.

If the intensity signal obtained by the charged particle detector 24 is sampled by the signal processing unit 25a at an appropriate sampling time, the surface potential distribution: V (X, Y) is obtained using the sampling time: T as a parameter as described above. It can be specified for each “small area corresponding to sampling”, and the surface charge distribution (potential contrast image): V (X, Y) is converted into two-dimensional intensity image data as shown in FIG. 4 by the signal processing unit 25a. Can be configured.
The intensity image data obtained as described above includes the electrostatic latent image pattern pairs L1 to L6 formed by the mask pattern 20 including the basic pattern pairs P1 to P6 shown in FIG. In FIG. 4, each electrostatic latent image pattern pair L1 to L6 has a dark central portion.

The resolution calculation process is shown below. The resolving power here is defined as a general term for an index (contrast and response function described later) representing the spatial resolution of the electrostatic latent image.
In the resolving power calculation unit 25b, the contrast is calculated from the cross-sectional profile including the electrostatic latent image pattern obtained from the intensity image data of FIG. FIG. 5a shows a cross-sectional profile of the straight line CS1 shown in FIG. 4, that is, the electrostatic latent image pattern pair L1. The intensity Imin of the exposed part and the intensity Imax of the non-exposed part are extracted from FIG. 5a, and the contrast C is calculated by the equation shown in FIG. 5b.
FIG. 5b shows an example in which the intensities of the plurality of exposed portions and the non-exposed portions are constant. However, when the intensities are not constant as in FIG. 5c, the intensities Imax (n) and Imin (n) (however, (n = 1, 2, 3,...) can be extracted and averaged using the equation shown in FIG.
From this contrast C, the resolution level of the electrostatic latent image pattern pair can be known.

In FIG. 5a showing the cross-sectional profile of the straight line CS1 shown in FIG. 4 as an example, the contrast is high because of the large difference between the exposed part and the non-exposed part, but shown in FIG. In the cross-sectional profile of the straight line CS2 (on the latent image pattern pair L6), the electrostatic latent image pattern pair is thick and spread (the pattern is crushed), and the intensity of the non-exposed portion cannot be extracted, that is, Imax = Imin, and contrast C is output as 0.
It should also be noted that the contrast of the electrostatic latent image pattern pair varies depending on the exposure energy of the semiconductor laser 17b.
FIG. 6 shows an outline of changes in the cross-sectional profile of the exposure energy level and the electrostatic latent image pattern pair at that time. When the exposure energy is high, the width of the pattern is widened as shown by a broken line, and when the exposure energy is low, the width of the pattern is narrowed as shown by a dotted line and the intensity of Imin is increased (the latent image becomes shallow and the pattern is faint). State).

Corresponding to this change, the contrast C of the electrostatic latent image pattern pair accompanying the change in exposure energy changes as a curve having a peak as shown in FIG.
By utilizing this fact and calculating the contrast C when the exposure energy is changed with a certain width, it is possible to find the exposure energy E1 having the peak value Cmax of C in FIG.
As described above, the exposure energy can be easily controlled by changing the lighting time by the LD controller 17a.
For example, when comparing the contrast of a plurality of photoconductive samples, taking into consideration the dependence on exposure energy as shown in FIG. 7, the contrast when exposed in advance with the optimum exposure energy (exposure energy E1 in FIG. 7). A method of performing comparison using the value of Cmax may be used. By this method, it is possible to output a comparison result in which the exposure energy dependency of each photoconductive sample is canceled.

As described above, the contrast C is an index including the “pattern collapse degree” and the “pattern blurring degree” in the electrostatic latent image pattern pair, and the resolution of the electrostatic latent image pattern pair is determined based on this value. You can see the level.
Further, the contrast C is calculated in the electrostatic latent image pattern pairs L1 to L6 in FIG. 4 and plotted for each spatial frequency of the basic pattern pairs P1 to P6 of the mask pattern 20 corresponding to L1 to L6. A response function (spatial frequency characteristic of resolving power) as shown in FIG. 8 can be obtained.
With this value, the resolution level in a wide spatial frequency band can be known, and can be used as an effective evaluation index when comparing the resolution characteristics of a plurality of photoconductive samples, for example.
In this case, the comparison of the exposure energy dependence of each photoconductive sample canceled by plotting the response function using the value of the contrast Cmax when the exposure is performed with the optimum exposure energy (exposure energy E1 in FIG. 7) in advance. The result can also be output.

Furthermore, by taking the average of the contrast C of each plot constituting the response function, the representative value of the resolution level in the spatial frequency band of the basic pattern pairs P1 to P6 can be grasped, and by using this value, When comparing the resolution characteristics of a plurality of photoconductive samples, superiority or inferiority can be determined more clearly.
The evaluation results described above are displayed on the display unit 26 or output by the output unit 27, whereby a quantitative evaluation result based on a numerical index can be obtained visually or as data.
If the surface of the photoconductive sample 00 set in the casing 30 is initially charged unevenly for some reason, such a charged state becomes an observation noise. Prior to the charging step, the photoconductive sample 00 is preferably subjected to light discharge by irradiating light with light from the light emitting element 29 (semiconductor laser or light emitting diode) for discharging.
In addition, the light neutralization by the light emitting element 29 is performed prior to each observation when the same photoconductive sample 00 is observed a plurality of times by changing the formation conditions of the electrostatic latent image pattern. The light-emitting element 29 for light neutralization may be omitted depending on circumstances.

  Evaluation reflecting the resolution level information of the latent image pattern (that is, intermediate information such as “crushing degree” and “blurring degree”) by the quantitative evaluation method and evaluation apparatus based on the numerical index described above. A result can be obtained, which makes it easy to extract a slight difference when, for example, comparison is made with respect to photoconductive samples having different resolving powers.

It is a schematic block diagram of the electrostatic latent image evaluation apparatus which concerns on one Embodiment of this invention. It is a schematic diagram of the surface of the photoconductive sample charged with an electron beam. It is a figure which shows an example of a mask pattern. It is a figure which shows intensity | strength image data when an electrostatic latent image pattern is formed in the surface of a photoconductive sample with a mask pattern. FIG. 5 is a diagram showing a cross-sectional profile of an electrostatic latent image pattern pair L1 on a straight line CS1 in FIG. It is a figure which shows the cross-sectional profile change in the level of exposure energy, and an electrostatic latent image pattern pair. It is a figure which shows the change of the contrast of an electrostatic latent image pattern pair accompanying the change of exposure energy. It is a figure which shows the relationship between the spatial frequency of a basic pattern pair, and contrast.

Explanation of symbols

00 Photoconductive sample 10a, 10b Charged particle beam scanning means 17a, 17b, 18, 19, 20, 21, 22, 23 Optical image exposure means 17a, 17b Exposure energy control means 24, 25a, 25b, 26, 28 Evaluation means

Claims (4)

A surface of the photoconductive sample on which the electrostatic latent image pattern has been formed by charging and exposure of the light image is two-dimensionally scanned with a charged particle beam to form the electrostatic latent image. By capturing charged particles that are electrically affected by the image pattern, detecting the intensity signal corresponding to the position on the surface, and observing the charge distribution state in the electrostatic latent image pattern. An electrostatic latent image evaluation method for evaluating a latent image,
The light quantity distribution of any cross-section included in the optical image is a cross-sectional light quantity distribution having a periodic light quantity value variation,
And, a cross-sectional profile including the electrostatic latent image pattern is extracted from the detected intensity signal,
And, the feature amount is extracted from the intensity signal of the exposed portion and the non-exposed portion of the cross-sectional profile, and the latent image resolving power of the photoconductive sample is calculated .
The feature amount is a contrast calculated from an average value of intensity signals of the exposed and non-exposed portions of the cross-sectional profile,
By forming a plurality of electrostatic latent image patterns with different spatial frequencies and calculating the contrast at each spatial frequency, the response function of the latent image is calculated,
An electrostatic latent image evaluation method, comprising: calculating a latent image resolving power in the spatial frequency band of the photoconductive sample by obtaining an average value of contrasts calculated at each spatial frequency . The electrostatic latent image evaluation method according to claim 1,
A method for evaluating an electrostatic latent image , comprising: forming a plurality of electrostatic latent image patterns having different exposure energies; and calculating and comparing a contrast at each exposure energy to obtain an exposure energy that maximizes the contrast . Charging means and optical image exposure means for forming an electrostatic latent image pattern;
Charged particle beam scanning means for two-dimensionally scanning the surface on which the electrostatic latent image pattern is formed of the photoconductive sample on which the electrostatic latent image pattern is formed with a charged particle beam;
Evaluation of capturing charged particles that are electrically affected by the electrostatic latent image pattern, detecting the intensity signal corresponding to the position on the surface, and observing the charge distribution state in the electrostatic latent image pattern An electrostatic latent image evaluation apparatus comprising:
The light image exposure means in which the light quantity distribution of any cross-section included in the light image is a cross-sectional light quantity distribution having a periodic light quantity value variation;
The evaluation means for extracting a cross-sectional profile including the electrostatic latent image pattern from the detected intensity signal, and extracting a feature amount from the intensity signal of the exposed portion and the non-exposed portion of the cross-sectional profile, and
The feature amount extracted by the evaluation means is a contrast calculated from an average value of intensity signals of the exposed portion and the non-exposed portion of the cross-sectional profile,
The optical image exposure means for forming a plurality of electrostatic latent image patterns having different spatial frequencies;
The evaluation means for calculating the response function of the latent image by calculating the contrast at each spatial frequency, and
An electrostatic latent image evaluation apparatus comprising the evaluation means for calculating an average value of contrasts calculated at each spatial frequency and calculating a latent image resolution of the photoconductive sample in the spatial frequency band . In the electrostatic latent image evaluation apparatus according to claim 3,
Exposure energy control means for forming a plurality of electrostatic latent image patterns having different exposure energies;
An electrostatic latent image evaluation apparatus comprising: the optical image exposure means for obtaining an exposure energy that maximizes contrast by calculating and comparing contrast at each exposure energy .

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