JP6398961B2 - Electron beam irradiation apparatus and electron beam irradiation method - Google Patents

Description

  The present invention relates to an electron beam irradiation apparatus and an electron beam irradiation method for irradiating an irradiated surface while scanning a focused electron beam.

  Electron beam irradiation is applied as a high-density energy source to material processing such as fine cutting and welding, and processing such as surface modification by heating. Other high density energy sources include laser irradiation and plasma irradiation. However, although the electron beam irradiation has a demerit that requires a high vacuum atmosphere, the irradiation area is small and the electron beam can be made to penetrate deeply in the thickness direction of the object to be processed. Therefore, there are many advantages such as easy scanning and swinging of the electron beam, high speed, and high thermal efficiency.

  In general, an electron beam irradiation apparatus for performing electron beam irradiation includes an electron gun having a filament for emitting electrons, a grid for controlling electrons emitted from the filament, and an anode for accelerating the electrons emitted from the filament. And an electromagnetic lens (focusing coil) and a deflection coil. In this electron beam irradiation apparatus, an electron beam emitted from an electron gun is focused on an irradiated surface by an electromagnetic lens and scanned in a predetermined direction by changing the traveling direction of the electron beam by a deflection coil.

  In such an electron beam irradiation apparatus, when the control current value applied to the electromagnetic lens is constant, the distance from the electron gun to the irradiation position of the electron beam changes according to the deflection direction. The electron beam intensity (energy density) cannot be made uniform. For example, when the focal length of the electron beam is adjusted so that the electron beam is focused at the position of the irradiated surface directly under the electron gun, the electron beam intensity increases at the center in the scanning direction, and increases in the scanning direction. It becomes weak at both ends.

  Against this background, Patent Document 1 discloses that the electron across the plate width direction of the steel sheet while appropriately adjusting the focal length of the electron beam so that the electron beam intensity is always the same even if the irradiation position of the electron beam changes. A technique for performing beam irradiation (dynamic focusing technique) is described. Further, as an improvement of the technique described in Patent Document 1, Patent Document 2 describes that an electron beam is corrected while the focal length is corrected by individual control from both sides of the electron beam irradiation area of the substrate immediately below the electron gun. Techniques for scanning are described.

  On the other hand, in Patent Document 3, it is essential that the focal length and alignment (optical axis) of the electron beam are normal in the initial state before the electron beam is scanned over a predetermined region of the irradiated surface. As a device for adjusting the focal length and optical axis of the electron beam on the surface, a camera for photographing the beam spot on the irradiated surface, an image processing device for processing the image of the photographed beam spot, and data from the image processing device Accordingly, an apparatus for controlling the focal length and initial deflection amount of the electron beam is described.

  In Patent Document 4, light is emitted from an electron beam irradiation unit by excitation by electron beam irradiation, light emission from the electron beam irradiation unit is optically detected, and the electron beam irradiation position and electron beam focus are detected. A technique is described in which one or more pieces of information of distance, electron beam irradiation spot diameter, and electron beam irradiation energy are acquired and the irradiation state of the electron beam is controlled based on the acquired information.

  In this way, improvements are made with respect to the electron beam irradiation method and the adjustment of the initial state, and the uniformity of the electron beam intensity is improved over the entire scanning region of the electron beam.

Japanese Patent Laid-Open No. 2-118022 Japanese Patent Laid-Open No. 4-39852 JP-A-6-203777 JP 2002-222748 A

  In general, the response delay of the electromagnetic lens and the deflection coil cannot be ignored as the scanning range of the electron beam is increased to increase the scanning speed in order to improve productivity. In other words, in the above-described dynamic focusing technique, the actual focal length and scanning position are delayed with respect to the focal length and scanning position assumed by the control current applied to the electromagnetic lens and the deflection coil.

  At this time, even if the control current pattern of the electromagnetic lens in the scanning direction is a symmetric pattern centered on the position directly under the electron gun as in the technique described in Patent Document 1, the electron lens actually does not respond to the response delay of the electromagnetic lens. It does not have a symmetric pattern centered directly under the gun. Also, even if the control current pattern is set separately on both sides of the base point from the position directly under the electron gun as in the technique described in Patent Document 2, the nonuniformity of the electron beam intensity is corrected due to the response delay. Can not. Further, as in the technique described in Patent Document 3, even if the initial state of the electron beam is controlled, response delays of the electromagnetic lens and the deflection coil cannot be dealt with.

  Therefore, in order to make the electron beam intensity uniform in the entire scanning region of the electron beam, it is necessary to set a control current pattern of the electromagnetic lens in consideration of the response delay of the electromagnetic lens and the deflection coil.

  The difficulty in setting the control current pattern of the electromagnetic lens is that the irradiation state of the electron beam is invisible. That is, the irradiation state of the electron beam must be indirectly observed and confirmed by some means. As a means for observing the irradiation state of an electron beam, there is known a method (beam profiler technology) in which a slit or a metal wire is installed at an irradiation position of an electron beam and a current waveform passing through the slit or hitting the metal wire is measured. ing.

  Since the slit or the metal wire is installed in a direction orthogonal to the scanning direction of the electron beam, the measurement result is a result integrated with the direction of the slit or the metal wire. Therefore, in order to know the irradiation diameter of the electron beam, it is necessary to estimate the current distribution of the electron beam from the measured current waveform. Furthermore, when the electron beam has an elliptical shape, it is necessary to measure by changing the direction of the slit or the metal wire (and changing the scanning direction of the electron beam). Further, in order to confirm the uniformity of electron beam irradiation, it is necessary to measure by installing or moving slits or metal wires at a plurality of points in the scanning range.

  A method of confirming the uniformity of the focal length and intensity of the electron beam from the processing state of the processing object is also conceivable. However, in this case, it is necessary to collect a sample of the processing object for each adjustment, which is inefficient. On the other hand, as in the technique described in Patent Document 4, a method for obtaining information on the irradiation state of the electron beam from light emission by excitation of the irradiation unit can be easily confirmed and is considered to be efficient. However, the specific example of the knife edge method described in Patent Document 4 cannot be applied to the evaluation of the deviation of the focal position of the electron beam.

  That is, the knife edge method described in Patent Document 4 is based on the premise that the optical system is adjusted to be focused on the most focused position of the electron beam, and the deviation from the focal position of the electron beam due to the position variation of the irradiation unit. This is considered to be a method of indirectly detecting the deviation from the focal position of the optical system. On the other hand, the inventors of the present invention are concerned with the change in the focal position (height) of the electron beam itself adjusted by the electromagnetic lens, and the focus of the electron beam due to the position variation of the irradiation part. It is not a change of position.

  Further, although Patent Document 4 mentions a configuration using a two-dimensional CCD element or the like as a light detection unit, how to obtain information on the electron beam irradiation state except for the knife edge method, No examples are given.

  The present invention has been made in view of the above problems, and an object of the present invention is to irradiate an electron beam with uniform intensity over the entire scanning region by efficiently evaluating and controlling the deviation of the focal position of the electron beam. An object is to provide an electron beam irradiation apparatus and an electron beam irradiation method.

  An electron beam irradiation apparatus according to the present invention is an electron beam irradiation apparatus that irradiates a surface to be irradiated while scanning a focused electron beam, a focusing unit that adjusts a focal position of the electron beam, and an electron beam irradiation apparatus. Deflection means for scanning the electron beam by deflecting, and a focus position of the electron beam according to a control pattern of the focusing means set in advance according to a deflection angle or scanning position of the electron beam deflected by the deflection means. Dynamic focus control means for controlling, imaging means for taking an image of fluorescence or phosphorescence generated when the electron beam is scanned on the irradiated surface in synchronization with scanning of the electron beam, and the imaging means Luminance distribution extraction means for extracting fluorescence or phosphorescence emission luminance distribution at each scanning position of the electron beam from a photographed fluorescence or phosphorescence image Defocus evaluation means for evaluating the defocus of the electron beam based on the emission luminance distribution of the fluorescence or phosphorescence extracted by the emission luminance distribution extraction means, and the defocus evaluation means Alternatively, a light emission width calculating unit that calculates a plurality of emission widths of the fluorescence or phosphorescence corresponding to a plurality of light emission luminance levels from a phosphorescence emission luminance distribution, and the plurality of the fluorescence or phosphorescence calculated by the light emission width calculation unit. Index calculation means for calculating an index based on the emission width, and evaluating the deviation of the focal position of the electron beam by comparing the index with a preset reference value, and the dynamic focus control means The control pattern is corrected based on the evaluation result of the defocus evaluation means.

  The electron beam irradiation apparatus according to the present invention is characterized in that, in the above invention, the plurality of light emission luminance levels in the light emission width calculating means are set in proportion to a peak level of the light emission luminance distribution of the fluorescence or phosphorescence. .

In the electron beam irradiation apparatus according to the present invention, in the above invention, the emission width calculation unit is configured to calculate the fluorescence or phosphorescence as R ₁ % (0 <R ₁ <100) of the peak level of the emission luminance distribution of the fluorescence or phosphorescence. The emission width W ₁ is calculated from the emission luminance distribution, and the emission of the fluorescence or phosphorescence is calculated as R ₂ % (0 <R ₂ <100 and R ₂ <R ₁ ) of the peak level of the emission luminance distribution of the fluorescence or phosphorescence. calculating the emission width W ₂ from the luminance distribution, the index calculating means, and calculates the index value P according to equation (1) below.

  The electron beam irradiation apparatus according to the present invention is characterized in that, in the above invention, the emission width calculating means calculates the emission width of fluorescence or phosphorescence in a direction orthogonal to the scanning direction of the electron beam.

  The electron beam irradiation apparatus according to the present invention is characterized in that, in the above invention, a plurality of the reference values are set for each irradiation position of the electron beam.

  The electron beam irradiation apparatus according to the present invention is characterized in that, in the above invention, the irradiated surface is a surface of a steel plate having a forsterite film directly under a surface layer or a transparent film.

  An electron beam irradiation method according to the present invention is an electron beam irradiation method for irradiating an irradiated surface while scanning a focused electron beam, and a focusing step for adjusting a focal position of the electron beam using a focusing means. And a deflection step of scanning the electron beam by deflecting the electron beam using a deflecting means, and the preset deflection angle or scanning position of the electron beam deflected in the deflection step. A dynamic focus control step for controlling the focal position of the electron beam in accordance with a control pattern of the focusing means, and a fluorescent or phosphorescent image generated when the electron beam is scanned on the irradiated surface is synchronized with the scanning of the electron beam. A photographing step for photographing and a fluorescent or phosphorescent image photographed in the photographing step at each scanning position of the electron beam. A light emission luminance distribution extracting step for extracting a light emission luminance distribution of fluorescence or phosphorescence, and a focus for evaluating a deviation of a focal position of the electron beam based on the light emission luminance distribution extracted in the light emission luminance distribution extraction step. A defocus evaluation step, and the defocus evaluation step includes a light emission width calculation step of calculating a plurality of light emission widths of the fluorescence or phosphorescence corresponding to a plurality of light emission luminance levels from the light emission luminance distribution of the fluorescence or phosphorescence, and An index calculation step of calculating an index based on the emission widths of the plurality of the fluorescence or phosphorescence calculated in the emission width calculation step, and comparing the index with a preset reference value The deviation of the focal position of the beam is evaluated, and the dynamic focus control step is based on the evaluation result in the defocus evaluation step. There characterized in that it comprises a step of modifying the control pattern.

  According to the electron beam irradiation apparatus and the electron beam irradiation method of the present invention, it is possible to irradiate an electron beam with uniform intensity over the entire scanning region by efficiently evaluating and controlling the shift of the focal position of the electron beam.

FIG. 1 is a schematic diagram showing a configuration of an electron beam irradiation apparatus according to first to third embodiments of the present invention. FIG. 2 is a flowchart showing the flow of focus adjustment processing according to the first embodiment of the present invention. FIG. 3 is a diagram showing an example of a fluorescent image obtained when an electron beam is irradiated with the surface of a steel plate having a forsterite coating directly under the surface layer or transparent coating as an irradiated surface. Figure 4 is a diagram illustrating the calculated emission luminance distribution L (Y) for the section X ₆ shown in FIG. FIG. 5 is a diagram illustrating a result of calculating the light emission width W (X _i ) for the sections X _{1 to} X ₁₁ illustrated in FIG. FIG. 6 is a diagram illustrating an example of a fluorescence image obtained after correcting the control pattern. FIG. 7 is a diagram showing the results of calculating the emission width W (X _i ) for the fluorescent image shown in FIG. FIG. 8 is a diagram illustrating an example of a fluorescence image obtained when the irradiation interval of the dot-shaped electron beam is set to be sufficiently large. FIG. 9 is a diagram for explaining the contents of the processing of step S2 and step S3 in the second embodiment of the present invention. FIG. 10 shows the result of calculating the average values of the emission widths W _x and W _y and the aspect ratio W _y / W _x for 25 examples of fluorescent images taken by performing electron beam irradiation under the same conditions including the fluorescent image shown in FIG. FIG. FIG. 11 is a diagram illustrating an example of a fluorescence image obtained after correcting the control pattern. FIG. 12 shows the result of calculating the average values of the emission widths W _x and W _y and the aspect ratio W _y / W _x for 25 examples of fluorescent images taken by performing electron beam irradiation under the same conditions including the fluorescent image shown in FIG. FIG. FIG. 13 is a schematic diagram illustrating a configuration of an electron beam irradiation apparatus including a stigmator. FIG. 14 is a flowchart showing the flow of focus adjustment processing according to the third embodiment of the present invention. Figure 15 is a diagram illustrating the calculated emission luminance distribution L (Y) for the section X ₆ shown in FIG. FIG. 16 is a diagram showing a relationship between the light emission width W ₁ and the light emission width W ₂ when the control current of the electromagnetic lens is changed so that the focal position of the electron beam moves back and forth on the irradiated surface. FIG. 17 shows iron when the directional electromagnetic steel sheet is irradiated with an electron beam in the setting of the index P (X _i ) calculated by the light emission width W ₁ and the light emission width W ₂ shown in FIG. 16 and the control current of each electromagnetic lens. It is a figure which shows a loss.

  Hereinafter, the configuration and operation of an electron beam irradiation apparatus according to first to third embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
First, the configuration and operation of the electron beam irradiation apparatus according to the first embodiment of the present invention will be described with reference to FIGS.

〔Constitution〕
FIG. 1 is a schematic diagram showing a configuration of an electron beam irradiation apparatus according to the first embodiment of the present invention. As shown in FIG. 1, an electron beam irradiation apparatus 1 according to the first embodiment of the present invention emits electrons from a filament 2a that emits electrons, a grid 2b that controls electrons emitted from the filament 2a, and a filament 2a. An electron gun 2 having an anode 2c for accelerating the electrons, an electromagnetic lens (focusing coil) 3, a deflection coil 4, a beam control device 5, an imaging device 6, an image processing device 7, and a display device 8. And.

  The electromagnetic lens 3 functions as a focusing unit according to the present invention, the deflection coil 4 functions as a deflecting unit according to the present invention, the beam control device 5 functions as a dynamic focus control unit according to the present invention, and the imaging device 6 The image processing apparatus 7 functions as the light emission luminance distribution extracting unit and the defocus evaluation unit according to the present invention.

  In this electron beam irradiation apparatus 1, the focal length and the deflection angle of the electron beam emitted from the electron gun 2 are controlled by the action of the electromagnetic lens 3 and the deflection coil 4 that are current-controlled by the beam control apparatus 5. A predetermined range on S is scanned. During the electron beam irradiation, the inside of the electron beam irradiation apparatus 1 is kept in a vacuum atmosphere.

  The beam control device 5 holds a pattern of control current output to the electromagnetic lens 3 and the deflection coil 4. This control current pattern is obtained by determining the control current of the electromagnetic lens 3 and the deflection coil 4 in accordance with the deflection angle or scanning position of the electron beam, and finally in which irradiation direction (irradiation position) during scanning of the electron beam. ), The control currents of the electromagnetic lens 3 and the deflection coil 4 are adjusted so that the focal position of the electron beam always matches the irradiated surface S.

  The imaging device 6 is provided outside the electron beam irradiation device 1 through the observation window or inside the electron beam irradiation device 1 in a form having a vacuum resistant structure, and the entire scanning range of the electron beam on the irradiated surface S ( (Or a part of them) is placed in the imaging field of view. The imaging device 6 acquires from the beam control device 5 a synchronization signal indicating one scanning of the electron beam (a pulse signal that is turned on during scanning or a pulse signal that indicates the scanning start timing, etc.), and Exposure is performed during each scanning and during scanning, and an image of fluorescence or phosphorescence emitted from the irradiated surface S by irradiation with an electron beam is taken.

  The irradiated surface S is formed of a material that emits fluorescence or phosphorescence when irradiated with an electron beam. When the surface to be irradiated S is a substance that does not emit fluorescence or phosphorescence, a flat plate or the like coated with a fluorescent material or phosphorescent material as an adjustment target is disposed instead at the electron beam irradiation position. In addition, the imaging device 6 may include a bandpass filter that selectively transmits fluorescence or phosphorescence as necessary.

  The image processing device 7 acquires a fluorescent or phosphorescent image photographed by the imaging device 6, and the fluorescence or phosphorescent light at each irradiation position (or each electron beam deflection direction) on the irradiated surface S from the acquired image. A light emission luminance distribution is extracted, and a shift (focus shift) of the focal position of the electron beam from the irradiated surface S is evaluated at each irradiation position from the extracted light emission luminance distribution.

  The display device 8 displays various types of information such as a fluorescent or phosphorescent image captured by the imaging device 6 and a defocus evaluation result by the image processing device 7. The operator repeats the beam irradiation test while correcting the control current pattern of the electromagnetic lens 3 on the basis of the defocus evaluation result displayed on the display device 8, so that there is no defocus over the entire irradiation range and the intensity. Approaches to uniform electron beam irradiation.

[Focus adjustment method]
Next, an electron beam focus adjustment method will be described with reference to FIGS. In the following description, the imaging device 6 captures a fluorescent image. However, a similar process may be performed by capturing a phosphorescent image.

  FIG. 2 is a flowchart showing the flow of focus adjustment processing according to the first embodiment of the present invention. The flowchart shown in FIG. 2 starts at the timing when the electron beam irradiation is started, and the focus adjustment process proceeds to the process of step S1.

  In the process of step S1, the beam control device 5 controls the electromagnetic lens 3 and the deflection coil 4 according to the initial control current pattern of the electromagnetic lens 3 and the deflection coil 4 (hereinafter abbreviated as a control pattern), thereby irradiating the surface to be irradiated. The electron beam is irradiated onto S, and the imaging device 6 captures the electron beam irradiation part to acquire the fluorescence image I (X, Y). Here, the X coordinate of the fluorescent image is the electron beam scanning direction, and the Y coordinate is the direction orthogonal to the electron beam scanning direction. FIG. 3 is a diagram showing an example of a fluorescence image obtained when an electron beam is irradiated with the surface of a steel plate having a forsterite coating immediately below the surface layer or transparent coating as the irradiated surface S.

  In the example shown in FIG. 3, the luminance of the B (blue) channel is extracted in accordance with the fluorescence color using an RGB color camera as the imaging device 6. Further, as a control pattern, a control current is applied to the deflection coil 4 so that the electron beam is scanned while being irradiated in the form of dots with a close interval of the beam diameter, and the control current of the electromagnetic lens 3 is set in the irradiation direction. A constant control pattern was used. Thereby, the process of step S1 is completed, and the focus adjustment process proceeds to the process of step S2.

In the process of step S2, the image processing apparatus 7 uses the following mathematical expression (2) to calculate the fluorescence image I (X, Y) at each irradiation position from the fluorescence image I (X, Y) acquired in the process of step S1. ) Of the emission luminance distribution L (Y). Here, in Equation (2), the section X _i is a section indicating irradiation positions set at appropriate intervals in the X direction, that is, the electron beam scanning direction, and N (X _i ) is an X coordinate point in the section X _i. Is the number of That is, light emission luminance distribution L (Y) represents an average intensity profile in the Y direction in the section _{X i} of the fluorescence image I (X, Y). 4, of the section indicated by _X 1 _{to X 11} in FIG. 3 is a diagram illustrating the results of calculating the light emission intensity distribution L of the section _{X 6} (Y). Thereby, the process of step S2 is completed, and the focus adjustment process proceeds to the process of step S3.

In the process of step S3, the image processing apparatus 7 calculates the emission width W (X _i ) of the fluorescent image at each irradiation position from the emission luminance distribution L (Y) extracted in the process of step S2. In the present embodiment, the light emission width W (X _i ) is defined as the half width in the light emission luminance distribution L (Y). That is, the image processing device 7 calculates the maximum value L _max of the light emission luminance distribution L (Y) and the base luminance L _base when there is no light emission, and averages them L _thr = (L _max + L _base ) / 2. On the other hand, a width in the Y direction where L (Y) ≧ L _thr is set as a light emission width W (X _i ) (see FIG. 4). The base luminance L _base is used to calculate an average luminance value in a section where there is no light emission away from the light emitting part of the light emission luminance distribution L (Y), or to obtain an average luminance level in a fluorescent image when no electron beam irradiation is performed in advance. It is calculated by keeping it. FIG. 5 is a diagram illustrating a result of calculating the light emission width W (X _i ) for the sections X _{1 to} X ₁₁ illustrated in FIG. Thereby, the process of step S3 is completed, and the focus adjustment process proceeds to the process of step S4.

In the process of step S4, the image processing apparatus 7 determines whether or not the absolute value of the difference between the light emission width W (X _i ) calculated in the process of step S3 and the reference value W _ref is within an allowable range. The reference value W _ref is a value set in advance. The reference value W _ref is an irradiation width at which the beam diameter is minimized (that is, in focus) by measurement with an electron beam irradiation setting or an electron beam irradiation setting that can obtain an optimum processing effect of the irradiated surface S. The light emission width in the setting is set by obtaining it by an irradiation experiment. If the absolute value of the difference is within the allowable range at all irradiation positions as a result of the determination (step S4: Yes), the image processing device 7 ends the series of focus adjustment processes. On the other hand, when there is an irradiation position where the absolute value of the difference does not fall within the allowable range (step S4: No), the image processing apparatus 7 determines that the defocus of the electron beam has occurred and performs the focus adjustment process. The process proceeds to S5.

In the process of step S5, the beam control device 5 corrects the control current pattern of the electromagnetic lens 3 by changing the control current of the electromagnetic lens 3 so that the focal position of the electron beam is located on the irradiated surface S. . In the example shown in FIGS. 3 and 5, the reference value _{W ref} is set to 11.5 (pixels), if you set the tolerance ± 0.5 and (pixels), the defocus in a section _{X 5} other sections Yes, it is determined that the control pattern needs to be corrected. 6 is a fluorescence image obtained after correcting the control pattern, and FIG. 7 is a diagram showing a result of calculating the emission width W (X _i ) for the fluorescence image shown in FIG. As shown in FIG. 7, it can be seen that the light emission width W (X _i ) is substantially equal to the reference value W _ref and is constant, and the defocus is eliminated. Thereby, the process of step S5 is completed, and the focus adjustment process returns to the process of step S1.

[Second Embodiment]
Next, the structure of the electron beam irradiation apparatus which is the 2nd Embodiment of this invention and its focus adjustment method are demonstrated. The configuration of the electron beam irradiation apparatus according to the present embodiment is the same as that of the electron beam irradiation apparatus according to the first embodiment shown in FIG. Only explained.

[Focus adjustment method]
In the case of irradiating a dot-shaped electron beam with a close interval as shown in the first embodiment or when performing continuous electron beam scanning, the fluorescence image I (X, Y) is shown in FIG. As shown in FIG. 6, thin band-like light emission is observed. For this reason, in the first embodiment, only the light emission width in the Y direction (direction orthogonal to the scanning direction of the electron beam) can be evaluated. On the other hand, when the stay and movement of the irradiation position of the electron beam are repeated and the irradiation interval of the dot-shaped electron beam is set sufficiently large, a fluorescent image in which each dot is separated as shown in FIG. can get. Therefore, in this embodiment, using such a beam irradiation method, the emission width in the X direction (scanning direction of the electron beam) is calculated in addition to the emission width in the Y direction, and the defocus of the electron beam is evaluated.

  Specifically, in the present embodiment, the processes in steps S2 to S4 are different from the processes in steps S2 to S4 in the first embodiment. Therefore, hereinafter, only the processes in steps S2 to S4 in the present embodiment will be described with reference to FIGS.

FIG. 9 is a diagram for explaining the contents of the processing in step S2 and step S3 in the present embodiment. In the process of step S2 in the present embodiment, the image processing apparatus 7 first divides the fluorescent image I (X, Y) in the X direction for each dot-like light emission (dot number) (or each dot-like light emission occurs). Cut out from the fluorescence image I (X, Y) so that it is included one by one). In the following, each divided fluorescent image is _denoted as I _n (X, Y) (n is a dot number). Next, the image processing device 7 searches for the position (X _max , Y _max ) where the luminance is maximum for each dot number n, and the light emission luminance distribution L _x (X) = I _n (X, Y) in the X direction. _max ) and the emission luminance distribution L _y (Y) = I _n (X _max , Y) in the Y direction are extracted.

In the process of step S <b _{> 3} , the image processing device 7 calculates the maximum luminance L _max (= I _n (X _max , Y _max )). Further, the image processing device 7 calculates an average value of luminance in a region sufficiently away from the dot-like light emission from each fluorescent image I _n (X, Y) as the base luminance L _base (or when there is no light emission in advance). The average luminance is calculated from the fluorescence image of the above and used as the base luminance L _base ). Then, the image processing device 7 calculates a threshold value L _thr (= (L _max + L _base ) / 2) for luminance, and the half value width W _x , L of the luminance distribution in the X direction that satisfies L _x (X) ≧ L _thr. A half-value width W _y of the luminance distribution in the Y direction that satisfies _y (Y) ≧ L _thr is calculated.

In the process of step S4, the image processing device 7 performs, for each dot number n, the reference value W _xref for the half value width W _x of the luminance distribution in the X direction and the half value width W _y of the luminance distribution in the Y direction. respectively compared with the reference value _{W aref} for the reference value _{W yref,} further the aspect ratio _W y / _{W x.} Then, the image processing device 7 determines whether or not the half widths W _x and W _y and the aspect ratio W _y / W _x are all within the allowable range for all the dot numbers n. As a result of the determination, if all are within the allowable range, the image processing apparatus 7 ends the series of focus adjustment processes. On the other hand, if there is a full width at half maximum or an aspect ratio that does not fall within the allowable range, the image processing apparatus 7 determines that a defocus of the electron beam has occurred, and advances the focus adjustment process to the process of step S5.

In the present embodiment, whether or not defocusing has occurred is determined by determining whether or not the half widths W _x and W _y and the aspect ratio W _y / W _x are all within the allowable range. Whether or not defocusing has occurred may be evaluated by determining whether or not two of the half-value widths W _x and W _y and the aspect ratio W _y / W _x are within an allowable range.

FIG. 10 shows the result of calculating the average values of the emission widths W _x and W _y and the aspect ratio W _y / W _x for 25 examples of fluorescent images taken by performing electron beam irradiation under the same conditions including the fluorescent image shown in FIG. FIG. As shown in FIG. 10, the reference value W _xref = 10.5 (pixel), the reference value W _yref = 12.0 (pixel), the reference value W _aref = 1.1, and the allowable range is ± Assuming that 0.5 and the aspect ratio are ± 0.05, the emission widths W _x and W _y and the aspect ratio W _y / W _x are outside the allowable ranges except for a part. That is, it is determined that there is a defocus of the electron beam and the control pattern needs to be corrected.

FIG. 11 is a diagram illustrating an example of a fluorescence image obtained after correcting the control pattern. FIG. 12 shows the result of calculating the average values of the emission widths W _x and W _y and the aspect ratio W _y / W _x for 25 examples of fluorescent images taken by performing electron beam irradiation under the same conditions including the fluorescent image shown in FIG. FIG. As shown in FIG. 12, as a result of correcting the control current pattern of the electromagnetic lens 3 by changing the control current of the electromagnetic lens 3 so that the focal position of the electron beam is positioned on the irradiated surface S, the reference value On the other hand, it can be seen that the emission widths W _x and W _y and the aspect ratio W _y / W _x are all within the allowable range. Thereby, it can be determined that the control pattern has been corrected to an appropriate control pattern.

  Note that according to the present embodiment, not only a simple defocusing of the electron beam but also a state where the shape of the electron beam is distorted into an elliptical shape (that is, astigmatism occurs) can be evaluated. FIG. 13 is a schematic diagram illustrating a configuration of an electron beam irradiation apparatus including a stigmator.

  As shown in FIG. 13, the stigmeter 9 is current-controlled by the beam control device 5 similarly to the electromagnetic lens 3 and the deflection coil 4, and corrects the shape of the electron beam by the magnetic field generated inside. According to the configuration of the electron beam irradiation apparatus as shown in FIG. 13, by adjusting the pattern of the control current of the stigmator 9 in the process of step S5, the shape of the electron beam is changed into a circular shape along with the adjustment of the focal position of the electron beam. Or it can adjust to the elliptical shape of a desired aspect ratio.

In this embodiment, the light emission width is calculated to evaluate the defocus, but the light emission area may be calculated to evaluate the defocus. That is, for each fluorescent image I _n (X, Y), a comparison is made with the threshold value L _thr (= (L _max + L _base ) / 2) of the luminance, and pixels of I _n (X, Y) ≧ L _thr and calculating the area Q _n, may be evaluated defocus by performing a comparison between the reference value and the area Q _n predetermined.

[Third Embodiment]
Next, a configuration of an electron beam irradiation apparatus according to the third embodiment of the present invention and a focus adjustment method thereof will be described. As in the third embodiment, the configuration of the electron beam irradiation apparatus according to the present embodiment is the same as the configuration of the electron beam irradiation apparatus according to the first embodiment shown in FIG. Only the focus adjustment method will be described with reference to FIGS.

[Focus adjustment method]
FIG. 14 is a flowchart showing the flow of focus adjustment processing according to the third embodiment of the present invention. In the present embodiment, the processing in steps S3 to S5 in the first embodiment is changed to the processing in steps S13 to S15 shown in FIG. 14 described below. Since the processes of steps S11 and S12 shown in FIG. 14 are the same as the processes of steps S1 and S2 in the first embodiment, the description thereof is omitted below.

In the process of step S13, the image processing device 7 uses the emission luminance distribution L (Y) extracted in the process of step S12 to emit the emission width W ₁ (X _i ) and emission width W ₂ (X) of the fluorescent image at each irradiation position. _i ) is calculated. Here, the light emission width W ₁ (X _i ) is defined as a width corresponding to R ₁ % (0 <R ₁ <100) of the peak level of the light emission luminance distribution L (Y). That is, the image processing apparatus 7, the maximum luminance _{L max (= I n (X} max, Y max)) was calculated and the base luminance _{L base,} L ₁ = a _{(L max -L base) × R} 1/100 + L base On the other hand, the width in the Y direction where L (Y) ≧ L ₁ is calculated as the light emission width W ₁ (X _i ). Similarly, the light emission width W ₂ (X _i ) is defined as a width corresponding to R ₂ % (0 <R ₂ <100 and R ₂ <R ₁ ) of the peak level of the light emission luminance distribution L (Y). . That is, the image processing apparatus _7, L ₂ = as _{(L max -L base) × R} 2/100 + L base relative to _L (Y) ≧ L ₂ become Y direction width emission width _W 2 _{(X i)} calculate. FIG. 15 shows a light emission width W ₁ (X _i ) and a light emission width W ₂ (X _i ) when R ₁ = 50% and R ₂ = 25% for the same light emission luminance distribution L (X ₆ ) as FIG. FIG. Thereby, the process of step S13 is completed, and the focus adjustment process proceeds to the process of step S14.

In the process of step S14, the image processing apparatus 7 uses the index P (X _i ) for evaluating the defocus based on the light emission width W ₁ (X _i ) and the light emission width W ₂ (X _i ) calculated in the process of step S13. ) To determine whether the difference between the calculated index P (X _i ) and the preset reference value P _ref is within an allowable range. The index P (X _i ) is calculated using the following formula (3). A method for determining the constant K in Equation (3) will be described later. The reference value P _ref is the value of the index P (X _i ) in the electron beam irradiation setting for obtaining the optimum processing effect of the irradiated surface S, or the beam diameter is minimized by measurement with a beam profiler or the like (ie, The value of the index P (X _i ) in the irradiation setting (in focus) is set by obtaining the value by an irradiation experiment. As a result of the determination, if the difference is within the allowable range at all irradiation positions (step S14: Yes), the image processing device 7 ends the series of focus adjustment processes. On the other hand, when there is an irradiation position where the difference does not fall within the allowable range (step S14: No), the image processing apparatus 7 determines that the defocus of the electron beam has occurred, and performs the focus adjustment process in step S15. Proceed to the process.

In the process of step S15, the beam control device 5 modifies the control current pattern of the electromagnetic lens 3 by changing the control current of the electromagnetic lens 3 so that the focal position of the electron beam is located on the irradiated surface S. . Specifically, when the difference (P (X _i ) −P _ref ) is greater than 0, the beam control device 5 has a short focal length of the electron beam and the focal position is closer to the electron gun 2 than the irradiated surface S. And the control current of the electromagnetic lens 3 is adjusted in the direction of increasing the focal length. On the other hand, when the difference is smaller than 0, the beam control device 5 determines that the focal length of the electron beam is long and the focal position is on the opposite side of the irradiated surface S from the electron gun 2, and shortens the focal length. The control current of the electromagnetic lens 3 is adjusted in the direction. Thereby, the process of step S15 is completed, and the focus adjustment process returns to the process of step S11.

Next, a method for determining the constant K in the above equation (3) will be described. FIG. 16 is a diagram showing the relationship between the light emission width W ₁ and the light emission width W ₂ when the control current of the electromagnetic lens 3 is changed so that the focal position of the electron beam moves back and forth the irradiated surface S. In FIG. 16, a range of values that can be taken by the inclination of the straight line when a straight line that is divided into a short focal length side and a long focal length side with a point A at which the light emission width W ₁ is minimized is obtained. . This range of values is a range of values that the constant K can take. In particular, among the values of the constant K within this range, a value is selected such that the index P (X _i ) changes monotonously with respect to the change in focal length. Thereby, the length of the focal length can be determined in the process of step S15.

FIG. 17 shows iron when the directional electromagnetic steel sheet is irradiated with an electron beam in the setting of the index P (X _i ) calculated by the light emission width W ₁ and the light emission width W ₂ shown in FIG. 16 and the control current of each electromagnetic lens. It is a figure which shows a loss. In the example shown in FIG. 17, the index P (X _i ) is calculated with the value of the constant K being 1.1. In this example, since the iron loss is minimum in the vicinity where the value of the index P (X _i ) is 0.4, the control current of the electromagnetic lens 3 is adjusted by setting the reference value P _ref to about 0.4. Then, the focus position can be optimized. According to the study by the present inventors, the value of the constant K is preferably in the range of 1.0 to 1.2.

  Normally, the imaging angle of the imaging device 6 is inclined with respect to the optical axis of the electron beam in order to avoid interference with the electron beam. For this reason, the fluorescent image or the phosphorescent image is distorted, and the correspondence between the length on the captured image and the actual length on the irradiated surface S varies depending on the location. Accordingly, when the reference value for the emission width is set in units of pixels in the first to third embodiments, the imaging device 6 is calibrated to correspond to the length on the captured image and the length on the irradiated surface S. The reference value may be different depending on the location on the image so that the value does not change depending on the location on the image. Alternatively, the light emission width may be measured by converting to the actual length on the irradiated surface S instead of the pixel unit, and a reference value set with the actual length may be used.

  In addition, as described above, when an object to be processed by electron beam irradiation itself exhibits fluorescence or phosphorescence, such as iron loss improvement processing of a steel sheet having a forsterite film directly under the surface layer or transparent film, the defocus of the electron beam is caused. At the detected stage, a warning is given by display or voice, and the defocus evaluation result is recorded, so that the electron beam irradiation device can be used as a processing state monitoring device. Furthermore, the electron beam irradiation device can also be used as a processing state control device by feeding back the defocus evaluation result to the beam control device 5 and automatically changing the control pattern during processing to suppress defocusing of the electron beam. it can. Even if the object to be processed does not exhibit fluorescence or phosphorescence, if there is thermal radiation accompanying heating by the electron beam and it can be detected by the imaging device 6, the light emission can be used.

  As is apparent from the above description, in the electron beam irradiation apparatus 1 according to the first to third embodiments of the present invention, the image processing apparatus 7 scans each electron beam from the fluorescence image captured by the imaging apparatus 6. The fluorescence emission luminance distribution at the position is extracted, the deviation of the focal position of the electron beam is evaluated based on the extracted emission luminance distribution of the fluorescence, and the beam control device 5 gives the evaluation result of the deviation of the focal position of the electron beam. Since the pattern of the control current of the electromagnetic lens 3 is corrected based on this, it is possible to irradiate the electron beam with uniform intensity over the entire scanning region by efficiently evaluating and controlling the defocus of the electron beam.

  The embodiment to which the invention made by the present inventors is applied has been described above, but the present invention is not limited by the description and the drawings that constitute a part of the disclosure of the present invention. That is, other embodiments, examples, operational techniques, and the like made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Electron beam irradiation apparatus 2 Electron gun 2a Filament 2b Grid 2c Anode 3 Electromagnetic lens (focusing coil)
4 Deflection coil 5 Beam control device 6 Imaging device 7 Image processing device 8 Display device S Irradiated surface

Claims (8)

An electron beam irradiation apparatus that irradiates an irradiated surface while scanning a focused electron beam,
Focusing means for adjusting the focal position of the electron beam;
Deflecting means for scanning the electron beam by deflecting the electron beam;
Dynamic focus control means for controlling the focus position of the electron beam in accordance with a control pattern of the focusing means set in advance according to the deflection angle or scanning position of the electron beam deflected by the deflection means;
Imaging means for capturing a fluorescent or phosphorescent image generated when the electron beam is scanned on the irradiated surface in synchronization with the scanning of the electron beam;
A light emission luminance distribution extracting means for extracting a light emission luminance distribution of the fluorescence or phosphorescence at each scanning position of the electron beam from a fluorescent or phosphorescent image photographed by the imaging means;
A defocus evaluation unit that evaluates a shift of the focal position of the electron beam based on the emission luminance distribution of the fluorescence or phosphorescence extracted by the emission luminance distribution extraction unit, and
The defocus evaluation means is calculated by a light emission width calculating means for calculating a plurality of light emission widths of the fluorescence or phosphorescence corresponding to a plurality of light emission luminance levels from the light emission luminance distribution of the fluorescence or phosphorescence, and calculated by the light emission width calculation means. And an index calculation means for calculating an index based on the emission widths of the plurality of fluorescence or phosphorescences, and the deviation of the focal position of the electron beam is evaluated by comparing the index with a preset reference value. And
The dynamic focus control means corrects the control pattern based on the evaluation result of the defocus evaluation means ,
The plurality of light emission luminance levels in the light emission width calculating means are set as a ratio to the peak level of the light emission luminance distribution of the fluorescence or phosphorescence,
The emission width calculating means calculates the emission width W ₁ from the emission luminance distribution of the fluorescence or phosphorescence as R ₁ % (0 <R ₁ <100) of the peak level of the emission luminance distribution of the fluorescence or phosphorescence, and the fluorescence Or the emission width W ₂ is calculated from the emission luminance distribution of the fluorescence or phosphorescence as R ₂ % (0 <R ₂ <100 and R ₂ <R ₁ ) of the peak level of the emission luminance distribution of phosphorescence , and the index calculation The means is an electron beam irradiation apparatus characterized in that the value P is calculated as an index according to the following formula (1) .

An electron beam irradiation apparatus that irradiates an irradiated surface while scanning a focused electron beam,
Focusing means for adjusting the focal position of the electron beam;
Deflecting means for scanning the electron beam by deflecting the electron beam;
Dynamic focus control means for controlling the focus position of the electron beam in accordance with a control pattern of the focusing means set in advance according to the deflection angle or scanning position of the electron beam deflected by the deflection means;
Imaging means for capturing a fluorescent or phosphorescent image generated when the electron beam is scanned on the irradiated surface in synchronization with the scanning of the electron beam;
A light emission luminance distribution extracting means for extracting a light emission luminance distribution of the fluorescence or phosphorescence at each scanning position of the electron beam from a fluorescent or phosphorescent image photographed by the imaging means;
A defocus evaluation unit that evaluates a shift of the focal position of the electron beam based on the emission luminance distribution of the fluorescence or phosphorescence extracted by the emission luminance distribution extraction unit, and
The defocus evaluation means is calculated by a light emission width calculating means for calculating a plurality of light emission widths of the fluorescence or phosphorescence corresponding to a plurality of light emission luminance levels from the light emission luminance distribution of the fluorescence or phosphorescence, and calculated by the light emission width calculation means. And an index calculation means for calculating an index based on the emission widths of the plurality of fluorescence or phosphorescences, and the deviation of the focal position of the electron beam is evaluated by comparing the index with a preset reference value. And
The dynamic focus control means corrects the control pattern based on the evaluation result of the defocus evaluation means ,
2. The electron beam irradiation apparatus according to claim 1, wherein a plurality of reference values are set for each irradiation position of the electron beam. 3. The electron beam irradiation apparatus according to claim 2 , wherein the plurality of light emission luminance levels in the light emission width calculating unit are set at a ratio to a peak level of a light emission luminance distribution of the fluorescence or phosphorescence. The emission width calculating means calculates the emission width W ₁ from the emission luminance distribution of the fluorescence or phosphorescence as R ₁ % (0 <R ₁ <100) of the peak level of the emission luminance distribution of the fluorescence or phosphorescence, and the fluorescence Or the emission width W ₂ is calculated from the emission luminance distribution of the fluorescence or phosphorescence as R ₂ % (0 <R ₂ <100 and R ₂ <R ₁ ) of the peak level of the emission luminance distribution of phosphorescence, and the index calculation 4. The electron beam irradiation apparatus according to claim 3 , wherein the means calculates the value P as an index according to the following formula (1).

The emission width calculation means of claims 1-4, characterized in that to calculate the emission width direction of the fluorescent or phosphorescent perpendicular to the scanning direction of the electron beam, the electron beam irradiation according to any one apparatus.   The electron beam irradiation apparatus according to any one of claims 1 to 5, wherein the irradiated surface is a surface of a steel plate having a forsterite film directly under a surface layer or a transparent film. An electron beam irradiation method for irradiating an irradiated surface while scanning a focused electron beam,
A focusing step of adjusting the focal position of the electron beam using a focusing means;
A deflection step of scanning the electron beam by deflecting the electron beam using deflection means;
A dynamic focus control step for controlling a focus position of the electron beam according to a control pattern of the focusing means set in advance according to a deflection angle or a scanning position of the electron beam deflected in the deflection step;
A photographing step of photographing an image of fluorescence or phosphorescence generated when the electron beam is scanned on the irradiated surface in synchronization with the scanning of the electron beam;
A light emission luminance distribution extracting step of extracting a light emission luminance distribution of the fluorescence or phosphorescence at each scanning position of the electron beam from the fluorescent or phosphorescent image photographed in the photographing step;
A defocus evaluation step for evaluating a shift of the focal position of the electron beam based on the emission luminance distribution of the fluorescence or phosphorescence extracted in the emission luminance distribution extraction step, and
The defocus evaluation step is calculated in a light emission width calculation step for calculating a plurality of light emission widths of the fluorescence or phosphorescence corresponding to a plurality of light emission luminance levels from the light emission luminance distribution of the fluorescence or phosphorescence, and in the light emission width calculation step. An index calculation step for calculating an index based on the emission widths of the plurality of fluorescence or phosphorescences, and evaluating the deviation of the focal position of the electron beam by comparing the index with a preset reference value And
It said dynamic focus control step, see contains the step of modifying the control pattern based on the evaluation result of the defocus evaluation step,
The plurality of light emission luminance levels in the light emission width calculating step are set as a ratio to the peak level of the light emission luminance distribution of the fluorescence or phosphorescence,
In the emission width calculating step, the emission width W ₁ is calculated from the emission luminance distribution of the fluorescence or phosphorescence as R ₁ % (0 <R ₁ <100) of the peak level of the emission luminance distribution of the fluorescence or phosphorescence, and the fluorescence Or calculating the emission width W ₂ from the emission luminance distribution of the fluorescence or phosphorescence as R ₂ % (0 <R ₂ <100 and R ₂ <R ₁ ) of the peak level of the emission luminance distribution of phosphorescence , The index calculation step includes a step of calculating a value P as an index according to the following formula (1) .

An electron beam irradiation method for irradiating an irradiated surface while scanning a focused electron beam,
A focusing step of adjusting the focal position of the electron beam using a focusing means;
A deflection step of scanning the electron beam by deflecting the electron beam using deflection means;
A dynamic focus control step for controlling a focus position of the electron beam according to a control pattern of the focusing means set in advance according to a deflection angle or a scanning position of the electron beam deflected in the deflection step;
A photographing step of photographing an image of fluorescence or phosphorescence generated when the electron beam is scanned on the irradiated surface in synchronization with the scanning of the electron beam;
A light emission luminance distribution extracting step of extracting a light emission luminance distribution of the fluorescence or phosphorescence at each scanning position of the electron beam from the fluorescent or phosphorescent image photographed in the photographing step;
A defocus evaluation step for evaluating a shift of the focal position of the electron beam based on the emission luminance distribution of the fluorescence or phosphorescence extracted in the emission luminance distribution extraction step, and
The defocus evaluation step is calculated in a light emission width calculation step for calculating a plurality of light emission widths of the fluorescence or phosphorescence corresponding to a plurality of light emission luminance levels from the light emission luminance distribution of the fluorescence or phosphorescence, and in the light emission width calculation step. An index calculation step for calculating an index based on the emission widths of the plurality of fluorescence or phosphorescences, and evaluating the deviation of the focal position of the electron beam by comparing the index with a preset reference value And
It said dynamic focus control step, see contains the step of modifying the control pattern based on the evaluation result of the defocus evaluation step,
2. The electron beam irradiation method according to claim 1, wherein a plurality of the reference values are set for each electron beam irradiation position .

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