Charge-over prevention method and charge-over prevention device

Abstract

PURPOSE: To provide a charge-up prevention method and a charge-up prevention device that prevent charge-up of an EUV mask in a device that irradiates an EUV mask with an electron beam, detects the electrons generated, and acquires an image.CONSTITUTION: A charge-up prevention method includes an electron gun, an objective lens, a deflection system, a stage, detection means for detecting secondary electrons or reflected electrons to generate an image, providing a band-shaped groove around an area where a pattern is formed on the surface of an EUV mask to electrically isolate it, electrically connecting the internal pattern of a black border that reduces the effects of flare from an EUV light source to the surrounding area, and providing a claw electrode that externally controls the potential of the internal pattern or a conductive connecting portion provided on the substrate of the EUV mask that externally controls the potential of the internal pattern, and the claw electrode or the conductive connecting portion prevents charge-up caused by the black border in the area where the pattern is formed on the surface of the EUV mask.SELECTED DRAWING: Figure 3

Description

【Technical Field】 【0001】 The present invention relates to a charge-up prevention method and a charge-up prevention device. 【Background Art】 【0002】 Semiconductor devices have been shrinking annually according to Moore's law, and in the most advanced devices, the minimum feature size has become 20 nm or less. In order to achieve a small feature size, an exposure technique capable of forming a smaller pattern is required. 【0003】 Conventionally, a laser beam with a wavelength of 193 nm has been used for exposure. However, since the optical resolution has already been greatly exceeded, in recent years, an exposure technique using EUV light with a wavelength of 13.5 nm has been vigorously promoted. As a result, in the logic 7-nanometer generation, TSMC and others have successfully achieved practical application for the first time in the world. 【0004】 The evolution of exposure technology means the reduction of the feature size of the photomask pattern and the increase in the number of patterns. To perform semiconductor exposure, a patterned insulator quartz plate called a photomask is used. A fine pattern based on circuit design data is drawn on this quartz plate. A master plate called a template for nanoimprint is also made of quartz. 【0005】 In order to examine whether the patterns formed on these masks are of correct dimensions, electron microscope technology is essential because optical technology has insufficient resolution. In order to obtain a high-definition electron beam image, it is necessary to irradiate electrons with a small beam spot size on the sample surface and detect signal electrons. At that time, it is essential that the sample surface is not charged and does not adversely affect the irradiated electron beam and signal electrons. 【Disclosure of the Invention】 【Problems to be Solved by the Invention】 【0006】 Conventionally, retarding has been used to inexpensively reduce aberrations in electron beam optics. This method involves first accelerating the energy of the electron beam emitted from the electron gun to a high energy of several tens of kilovolts, then focusing the electron beam using an electron optics system, and finally reducing the electron energy to below 1 kilovolt by applying a reverse bias voltage to the sample before irradiating the sample. A key feature of this method is that it can maintain high resolution despite the low energy of the sample irradiation. 【0007】 The higher the energy of the electron beam, the shorter the wavelength, allowing for a smaller beam size and improved image resolution. However, it has been found that directly scanning semiconductor devices with high-energy electron beams to obtain images and observe them can cause damage to the semiconductor device due to the semi-permanent effects of the high-energy electrons. To prevent this, semiconductor CDSEMs employ retarding techniques to reduce the electron beam energy while simultaneously narrowing the beam size. 【0008】 In retarding methods, it is necessary that the measurement point potential on the sample surface is at the desired potential. However, with photomasks or nanoimprint templates made of silica, a dielectric material, unlike semiconductor wafers which are normally conductive, the voltage applied to the electrodes located below the sample used to apply the voltage differs from the potential at the surface of the photomask. Therefore, it is extremely difficult to always adjust to the target surface potential. Furthermore, when the sample moves due to XY stage movement, the capacitance constituting the measurement system changes, which causes a change in the retarding voltage effectively applied to the sample surface. 【0009】 Furthermore, in devices that form images by accelerating secondary electrons generated on the sample surface to a predetermined energy, such as multi-beam inspection systems, there was a problem in that the retarding voltage became unpredictable, causing problems in image formation. [Means for solving the problem] 【0010】 The present invention has the characteristic of being able to stably apply a desired retarding voltage to the surface of a sample in which a pattern is formed on an insulating substrate such as a photomask, as described above, and to acquire a high-resolution and stable image. 【0011】 To solve the aforementioned problems, the present invention provides an electron beam inspection apparatus that applies a retarding voltage to a sample to slow down a high-speed electron beam and irradiate it, thereby generating a high-resolution image, comprising: an electron gun that generates an electron beam of a predetermined high acceleration voltage; an objective lens that narrows the electron beam of the predetermined high acceleration voltage generated by the electron gun and irradiates the sample with it; a deflection system that scans the electron beam narrowed by the objective lens in two dimensions across the surface of the sample; a retarding voltage application device that applies a predetermined retarding voltage to the sample; a detection device provided at the tip of the objective lens, facing the sample, for detecting the potential or capacitance of the sample surface; and a correction device that corrects the first retarding voltage to correct the potential of the sample surface to a constant value based on the potential or capacitance of the sample surface detected by the detection device. 【0012】 In this system, a sample surface potential control device is provided to control the second potential of the sample surface by applying an external voltage. Based on the potential or capacitance detected by the detector, the sample surface potential control device is instructed to control the second potential, or the correction means is instructed to control the first retarding voltage, or both are controlled. 【0013】 Furthermore, the system divides the measurement point coordinate system or the sample surface vertically and horizontally, associating each intersection point with a sub-region. Based on the potential or capacitance measured in real time, it corrects the first retarding voltage, the second potential, or both in accordance with the sample's movement. 【0014】 Furthermore, the sample surface is divided vertically and horizontally, and a table is created in which the pre-measured potential or capacitance is registered, corresponding to a sub-region at each intersection. Based on this table, the first retarding voltage, the second potential, or both are corrected according to the movement of the sample. 【0015】 Furthermore, a groove is provided in a band-like shape around the area where the pattern is formed on the surface of the sample to electrically separate it. A claw electrode is provided to electrically connect the pattern inside the black border to the pattern outside the border, allowing the potential of the pattern to be controlled from the outside. 【0016】 Furthermore, instead of claw electrodes, conductive connecting parts are formed on the substrate. 【0017】 Furthermore, the sample is designed to form a pattern on an insulating substrate. [Effects of the Invention] 【0018】 The present invention enables the stable application of a desired retarding voltage to the surface of a sample in which a pattern is formed on an insulating substrate such as a photomask, thereby acquiring a high-resolution and stable image. 【0019】 Furthermore, by measuring the potential or capacitance of the sample surface in real time and controlling the retarding voltage or the potential of the sample surface, stable and high-resolution images can always be obtained even when the sample moves. 【0020】 Furthermore, by pre-registering the potential or capacitance of the sample surface in a table, with the sample divided vertically and horizontally, the retarding voltage and the potential of the sample surface are automatically corrected as the sample moves, enabling the acquisition of stable and high-resolution images at all times. [Example 1] 【0021】 Figure 1 shows a diagram illustrating one embodiment of the present invention. 【0022】 In FIG. 1, the electron gun 1 is a known device for generating electrons, which generates electrons from TFE or LaB6, or a field emitter or a photoelectron gun. After being adjusted through a focusing lens and an aperture (not shown) so as to have an acceleration voltage of about several hundred to several tens of kV and a current of, for example, about several pA to several hundred nA, it is narrowed down from the nm order to the order of several hundred nm by the objective lens 5 described later, and then irradiated onto the surface of the sample 9. A bias voltage (retarding voltage 8) is applied to the substrate (mask) of the sample 9 to optimize the irradiation energy or the energy of the electrons generated on the surface of the sample 9 (about several hundred V to 1 kV). 【0023】 The blanking device 2 turns on and off the electrons generated by the electron gun 1 at high speed. 【0024】 The blanking aperture 3 is a diaphragm that blocks the electrons deflected by the blanking device 2. 【0025】 The objective aperture 4 restricts the electrons incident on the objective lens 5. 【0026】 The objective lens 5 is for narrowing down the electron beam and irradiating the sample 9. 【0027】 The deflection device 6 deflects the electron beam and two-dimensionally scans the narrowed electron beam onto the sample 9, and is a two-stage deflection system (electrostatic, electromagnetic). 【0028】 The surface potential and capacitance detection device 7 is a disk-shaped plate with a hole in the center installed at the tip of the objective lens 5, and is an electrode for measuring the potential on the surface of the sample 9 or measuring the capacitance (electrostatic capacitance) (measuring the potential or capacitance with a device not shown). The shape of the electrode does not have to be circular, and it does not have to be at the center or have a hole. The electrode for capacitance measurement can also use the metal itself that constitutes the objective lens. 【0029】 The potential / capacitance detection signal 71 is a signal (surface potential signal or capacitance detection signal) detected by the surface potential / capacitance detection device 7, and is used to detect the potential or capacitance of the surface of the sample 9 in real time using a personal computer (not shown) based on this signal. In the case of a surface potential signal, it is a signal for measuring the potential of the surface of the sample 9 (or the retarding upper electrode 81), and is a known method that generates a minute potential corresponding to the potential of the surface of the sample 9 (retarding upper electrode 81), amplifies it, and measures (detects) that potential. In the case of a capacitance detection signal, it is a known method for supplying a minute high-frequency voltage and detecting the current that flows at that time to calculate the capacitance. Other surface potential and capacitance measurement means known in the world can also be used. 【0030】 The retarding voltage 8 is a retarding voltage applied to the sample 9, which is a reduction voltage used to reduce a predetermined high-voltage electron beam emitted from the electron gun 1, for example, from 5KV to 35KV, to about 500V to 1KV (in this example, a reduction voltage that is 500V to 1KV lower than 5KV to 35KV). 【0031】 The retarding upper electrode 81 is an electrode used to draw the potential from the upper surface of the sample 9 to the outside. 【0032】 The retarding lower electrode 82 is an electrode that draws the potential from the underside of the sample 9 to the outside. A retarding voltage 8 is usually applied to this retarding lower electrode 82. 【0033】 The insulator 10 electrically insulates the retarding lower electrode 82. 【0034】 Sample 9 is a sample such as a mask, which is fixed on an insulator 10 and a retarding voltage 8 is applied. The electron beam, slowed down by the retarding voltage 8, is irradiated onto the sample 9. After being focused into a small spot with high voltage in the objective lens 5, it is slowed down by the retarding voltage 8, and the sample 9 is irradiated with a low-energy electron beam, which reduces damage and contamination and generates a high-resolution image. 【0035】 The XYZ stage 11 is a stage that fixes the sample 9 and automatically moves it to arbitrary coordinates (X, Y) and (Z). The movement can be precisely measured in real time in the X, Y, and Z directions as needed using a laser interferometer (not shown). More specifically, there is an insulator on the stage, and above that is a photomask holding mechanism made of a conductor called a mask palette, which can also serve as the lower electrode. On the other hand, a separate claw electrode is placed on the palette, from which a voltage can be applied to the top of the photomask. 【0036】 The vacuum chamber 12 is a container that houses the XYZ stage 11, on which the sample 9 is fixed, and other components in a vacuum. 【0037】 The vacuum pump 13 is an oil-less vacuum exhaust system that evacuates the vacuum chamber 12, such as a dry pump or TMP, into a vacuum. 【0038】 The vibration isolation device 14 is designed to isolate vibrations from the outside, such as from the vacuum chamber 12. 【0039】 The electron detection device 21 is a known detector that detects secondary electrons emitted when the sample 9 is irradiated with an electron beam and scanned in two dimensions. 【0040】 Next, we will briefly explain the operation of the configuration shown in Figure 1. (1) Sample 9 (mask fixed in holder), such as a mask, is automatically transported and fixed to the XYZ stage 11 by a robot. (2) The XYZ stage 11 is moved to the indicated position while measuring the position of the photomask in real time using a laser interferometer according to the design data of the pattern provided on the photomask, so that a predetermined position of the sample 9 is irradiated with an electron beam. At the same time, the surface potential / capacitance detection device 7 measures the potential (or capacitance) of the surface of the sample 9 (or the retarding upper electrode 81) in real time and corrects it to a reference value (or the value of the reference point) (correcting either the retarding voltage 8, the potential of the retarding upper electrode 81, or both), so that the potential of the surface of the sample 9 remains constant even when the sample 9 is moved. As a result, even when the sample 9 is moved, the surface of the sample 9 always has the same potential, and it becomes possible to scan the sample 9 while irradiating it with a low-acceleration electron beam decelerated by the retarding voltage 8, and to always acquire stable and high-resolution secondary electron images, etc. The following will be explained in detail in order. 【0041】 Figure 2 shows an example of a sample (mask) of the present invention. Figure 2 shows a cross-sectional structure of a typical photomask. Figure 2(a) shows an example of the structure of an EUV mask, and Figure 2(b) shows an example of the structure of a DUV mask. 【0042】 In Figure 2(a), EUV masks generally have a conductive reflective film 32 made of MoSi or the like on an insulating substrate 31 of ultra-low thermal expansion silica, and a Ta-based absorption layer with a pattern 33 formed on top of that. Therefore, the region where the pattern is formed is electrically conductive throughout. 【0043】 In Figure 2(b), in the case of the illustrated DUV mask, there may be no conductive film beneath the pattern 34 layer, so pattern 34 often becomes an island-like floating state that is not electrically connected to anything. When such a mask is irradiated with an electron beam, the surface potential changes due to charging, making it impossible to acquire a stable and high-resolution secondary electron image. 【0044】 Figure 3 shows an example of the black border of the present invention. Figure 3(a) shows a side view, and Figure 3(b) shows a top view. 【0045】 In Figure 3, photomask 35 is an example of sample 9. 【0046】 The bias electrode 36 is an electrode for applying a potential to the back surface of the photomask 35. 【0047】 The black border 37 is provided to reduce the effects of flare generated by the EUV lithography system, and as a result, it has a structure that electrically isolates the enclosed area from its surroundings. 【0048】 The claw electrode 38 is an electrically connected electrode for applying the bias voltage 1 to the surface of the photomask 35. The shape of the electrode is arbitrary, but it can also be a needle-shaped electrode to penetrate the insulator on the surface. 【0049】 The bias voltage 1 is the voltage applied to the claw electrode 38 (on the surface of the photomask 35). 【0050】 Bias voltage 2 is the voltage applied to the back surface of the photomask 35. 【0051】 Next, I will explain the structure. (1) In Figure 3, the EUV mask in Figure 2(a) is constructed by first applying approximately 50 layers of reflective film material such as MoSi to a quartz substrate, and then forming an absorption layer for creating the pattern 33. In this state, applying a voltage to the peripheral area from the outside will bring the entire surface of the photomask to the desired potential. (2) However, EUV lithography equipment uses a short wavelength of 13.5 nm and employs multiple mirrors, and the light source is not necessarily high-performance. As a result, a malfunction phenomenon called flare occurs, where light scatters in directions other than the intended one, degrading the quality of the light source. Consequently, EUV light reaches adjacent areas that should not be exposed, causing malfunctions. To prevent this, an electrically insulating boundary region called a black border 37 is provided around the area where the main pattern of the photomask is written, as shown in the figure. 【0052】 The boundary, known as Black Border 37, is formed by engraving MoSi conductors that form the reflective layer into the quartz glass substrate. As a result, the region enclosed by Black Border 37 is electrically isolated from the surrounding region and becomes an insulator. 【0053】 If an insulating state is achieved, even if a voltage is applied from the periphery of the mask surface, the region surrounded by the insulator will not reach the desired potential. Furthermore, when observing by irradiating with an electron beam such as a SEM, charge gradually accumulates at the observation site, altering the image. To avoid this, the present invention provides a special claw electrode 38 for conducting electricity to the region surrounded by the black border 37, as shown in Figure 3. This allows conductivity between the periphery and the interior of the mask, releasing the charge and bringing them to the same surface potential. The claw electrode 38 used in this case should be as thin and flat as possible, and its surface should be coated with an insulator with high dielectric strength, such as Teflon®, to prevent discharge between it and the opposing objective lens 5 (the distance between the objective lens 5 and the photomask is about a few millimeters (e.g., 3 mm)). Multiple claw electrodes 38 may be provided around the periphery of the photomask, not just one. Also, since there may be multiple insulating regions separated by the black border, the voltage applied to each of the multiple claw electrodes 38 may be controlled independently. Furthermore, it is desirable to be able to apply independent voltages inside and outside the black border. 【0054】 Figure 4 shows an example of the black border of the present invention. 【0055】 In Figure 4, the black border 41 is formed by etching the MoSi conductor that forms the reflective layer into the quartz glass substrate, as described above. 【0056】 The peripheral region 42 is a peripheral region electrically separated by the black border 41. 【0057】 The measurement target area 43 is the area to be measured, separated by the black border 41. 【0058】 The connecting portion 44 is a conductive portion formed to electrically connect the measurement target area 43 and the peripheral area 42 electrically separated by the black border 41. 【0059】 Next, we will explain Figure 4 in detail. (1) In Figure 4, the black border itself is very large compared to the actual pattern size that is formed. Therefore, a pattern (connecting portion 44) is formed in which the peripheral and inner regions are connected somewhere, leaving a portion of the border so as not to limit the performance of the black border 41. In this way, electrical conductivity occurs between the peripheral and interior regions of the mask separated by the black border 41, making it possible to make the potential of the two regions the same. In addition, it becomes possible to dissipate the charge generated by electron beam irradiation, and the image is not distorted by the charge-up phenomenon. Applying voltage with the claw electrode to the outer peripheral region of the mask is sufficient. (2) On the other hand, it is not always possible to form the above pattern (connecting portion 44). In that case, wiring can be formed on the black border 41 using conductive materials such as Ta or W, which have the property of absorbing EUV light, using a FIB or electron beam mask correction device used for mask correction, to establish conductivity. Multiple points of conductivity can be established. Since the mask correction device can also form wiring in three dimensions, it is easy to wire across the black border 41. As a result, the area partitioned by the black border 41 is connected to the outer periphery, and conductivity can be established on the outer periphery by contacting electrodes from the outside, so that the mask surface is at the desired potential everywhere and the EUV mask does not charge up. 【0060】 Figure 5 shows a schematic diagram illustrating the surface potential of the present invention. 【0061】 In Figure 5, C1 represents the capacitance between the lower surface of the objective lens 5 and the surface of the mask (retarding upper electrode 81). 【0062】 C2 represents the capacitance between the mask surface (retarding upper electrode 81) and the bias electrode (retarding lower electrode 82). 【0063】 E represents a retarding voltage of 8. 【0064】 Next, I will explain how it works. (1) Figure 5 schematically illustrates the principle by which the potential generated in the internal region separated by a black border in an insulated state within the electron beam inspection apparatus, or on the floating surface of the DUV photomask, is determined. Since the photomask does not necessarily have a conductive reflective layer like an EUV mask, the entire surface is not necessarily conductive. In this case, the surface potential when an external voltage is applied to the floating region from the lower electrode of the substrate is determined capacitively. Opposite the photomask surface (surface of sample 9) is a metal objective lens 5 inside the electron beam inspection apparatus chamber. Because the photomask surface and the objective lens 5 are close together, it is equivalent to having two metal electrodes, forming a large capacitance C1. On the other hand, a dielectric such as quartz exists between the photomask surface and the back surface, forming a large capacitance C2 between the pattern on the photomask surface and the lower electrode 82 of the photomask. 【0065】 Therefore, the potential of the photomask surface in between is roughly determined by the ratio of the magnitudes of the two capacitances. (2) When the photomask moves by the XYZ stage 11 during measurement, the distance to the objective lens 5 and the distance from the surrounding material change, which changes the capacitance C1 of the measurement system. As this change occurs, the bias voltage (retarding voltage 8) applied to the substrate is distributed, so when the same voltage is applied, the surface potential changes with the movement of the XYZ stage 11. In other words, if a measurement is performed while applying a constant retarding voltage, the bias potential generated on the substrate surface will differ depending on the location, resulting in completely different measurements. In the case of a measurement device that is sensitive to surface potential, in the worst case, an image may not be formed, or the position where the image is formed may fluctuate, making the measurement unstable. (3) Therefore, by correcting the potential of the bias electrode (retarding voltage 8) or the potential of the mask surface (first potential) so that the potential of the mask surface (potential distributed by capacitance C1 and capacitance C2) remains constant even when the XYZ stage 11 moves, and by automatically controlling the system so that the potential of the mask surface remains constant, the potential of the mask surface will remain constant even when the XYZ stage is moved, making it possible to acquire stable and high-resolution secondary electron images. 【0066】 Figure 6 shows an example of a capacitance-potential map table for the mask of the present invention. 【0067】 Figure 6(a) shows an example of a capacitance map table, and Figure 6(b) shows an example of a surface potential map table. 【0068】 Figure 6(a) shows the XYZ stage 11 (or mask) divided into i sections in the X direction and j sections in the Y direction, with the capacitance C1(i,j) at the intersection point (i,j) measured and registered. 【0069】 Figure 6(b) shows the XYZ stage 11 (or mask) divided into i sections in the X direction and j sections in the Y direction, with the potential V(i,j) at the intersection point (i,j) measured and registered. 【0070】 Here, capacitance C1 and potential V are measured as follows. (1) Sample surface potential V: There are various methods for determining the sample surface potential V. The surface potential can be determined using commercially available surface potential meters of various principles and types. The surface potential meter can be placed at the tip of the objective lens 5 to measure the potential at the measurement point on the mask. The voltage applied to the substrate (retarding voltage 8 in Figure 1 or the potential of the retarding upper electrode 81) is automatically adjusted while the XYZ stage 11 is moving or stopped so that the measured potential becomes a constant value. (2) Similar results can be obtained by measuring the capacitance generated between the objective lens and the sample surface. The capacitance is measured at a specific coordinate on the XY coordinate system. The sample 9 is moved by the XYZ stage 11 and the capacitance is measured. Since the capacitance difference represents a change in surface potential, the voltage applied to the sample 9 (retarding voltage 8 in Figure 1 or the potential of the retarding upper electrode 81) is changed by the amount of the capacitance change, and adjusted so that the surface potential becomes substantially the desired value. (3) The surface potential V can also be determined by examining the energy of secondary electrons generated by actually irradiating the substrate with an electron beam. Specifically, by providing a mesh grid on the surface of the secondary electron detection device and applying a predetermined voltage, the energy of the secondary electrons can be determined by examining the amount of secondary electrons detected after passing through the mesh. By changing the grid voltage, the energy distribution can be determined, and as a result, the change in the sample surface potential V, which is the basis of the energy shift of secondary electrons, can be detected. The surface potential can be maintained at a desired value by automatically adjusting the bias voltage applied to the substrate (retarding voltage 8 in Figure 1 or the potential of the retarding upper electrode 81) so that there is no change in the measured value. (4) The surface potential change or capacitance change associated with the movement of the XYZ stage 11, as determined above, is a quantity unique to a particular device and remains constant unless the internal workings of the device are changed. 【0071】 Therefore, once data on the change in surface potential V or capacitance associated with XYZ stage movement is acquired and registered, the correction amount can be estimated thereafter by inputting the position coordinates. Thus, the data on the change in surface potential or capacitance corresponding to the measurement point coordinates XY is stored in a memory device as a map table, as shown in Figures 6(b) and (a). During actual measurement, the voltage applied to the mask (sample 9) is automatically adjusted based on this map table, thereby keeping the surface potential constant at the desired value. 【0072】 Figure 7 shows the mask surface potential setting flowchart of the present invention. 【0073】 In Figure 7, S1 moves the XY stage. Here, the coordinates of the moved position are (Xi, Yj). 【0074】 S2 measures the surface potential or capacitance. This involves measuring the potential Vij of the surface of the mask facing the objective lens 5, or measuring the capacitance Cij between the objective lens 5 and the surface of the mask facing it, with the XY stage moved to coordinate (i,j). 【0075】 S3 calculates a correction value. This is calculated based on the surface potential Vij or capacitance Cij measured in S2, so that it matches either a reference value, the potential (capacitance) at a specific location, or an arbitrary specified value. 【0076】 S4 sets the applied voltage. This sets the potential of the retarding lower electrode 82 or retarding upper electrode 81 in Figure 1 to a predetermined value and corrects it so that the surface potential or capacitance is always constant. 【0077】 S5 determines if the measurement is complete. If YES, the process ends. If NO, repeat steps S1 onwards. 【0078】 As described above, by measuring the surface potential or capacitance each time the XYZ stage 11 is moved and correcting it to remain constant (correcting the potential of the retarding lower electrode 82 or retarding upper electrode 81 in Figure 1), the surface potential of the mask (sample 9) can be kept constant, making it possible to acquire a stable and high-resolution secondary electron image. For real-time correction, the surface potential or capacitance can be measured at any measurement point and the applied retarding voltage value can be corrected. 【0079】 Figure 8 shows the mask surface potential setting flowchart (part 2) of the present invention. In Figure 8, instead of measuring the surface potential and capacitance in real time as in Figure 7, the surface potential and capacitance at the mask coordinates are read from the surface potential map table (b) or capacitance map table (a) in Figure 6, which have been measured and registered in advance, and then corrected. 【0080】 In Figure 8, S11 moves the XY stage. Here, the position of movement is given by coordinates (Xi, Yj). 【0081】 S12 reads the correction value. As described above, this reads the surface potential or capacitance at the mask coordinates from the pre-registered surface potential map table (b) in Figure 6 or the capacitance map table (a) in Figure 6. If there are no matching coordinates in the table, the values ​​(potential or capacitance) of several nearby coordinates are read. 【0082】 S13 calculates a correction value. This is done by calculating a correction value based on the surface potential Vij or capacitance Cij read in S12, so that it matches either a reference value, the potential (capacitance) at a specific location, or an arbitrary specified value. 【0083】 S14 sets the applied voltage. This sets the potential of the retarding lower electrode 82 or retarding upper electrode 81 in Figure 1 to a predetermined value and corrects it so that the surface potential or capacitance is always constant. 【0084】 S15 determines if the measurement is complete. If YES, the process ends. If NO, repeat steps S11 onwards. 【0085】 As described above, by reading the surface potential or capacitance from a pre-registered table each time the XYZ stage 11 is moved and correcting it to always remain constant (correcting the potential of the retarding lower electrode 82 or retarding upper electrode 81 in Figure 1), the surface potential of the mask (sample 9) can be kept constant, making it possible to acquire a stable and high-resolution secondary electron image. Note that since the Z-axis height affects the capacitance value, it is desirable to automatically control the height to a desired constant height (distance between the sample surface and the objective lens). 【0086】 Figure 9 shows a configuration diagram of another embodiment of the present invention. Figure 9 shows an external view of a multi-electron beam inspection apparatus. The multi-electron beam inspection apparatus is a device that can acquire two-dimensional images at ultra-high speed by irradiating a sample 9 in a planar manner with multiple electron beams at once, and then re-accelerating the secondary electrons generated in the sample 9 to form an image. In this apparatus, it is very important to uniformly accelerate the secondary electrons generated on the surface of the sample 9, and if the surface potential varies, it will cause problems in the operation of the beam splitter 541 and prevent the image from being formed at the desired position, so controlling the surface potential is extremely important. 【0087】 Generally, inspection devices measure large volumes of data at high speed, so they may move step-by-step like conventional SEMs or review devices, or the XYZ stage 11 may move continuously. The present invention can be used even in such cases. Specifically, it is as follows. (1) In the case of step-by-step processing, correction values ​​can be stored as a map (see Figure 6) for each step. On the other hand, if stage 11 moves continuously, the following procedure is followed. For example, as shown in Figure 6, the area of ​​the photomask is divided into approximately 100 equal parts, and the surface potential or capacitance of sample 9 at the center coordinates of each area is measured. This is stored as a map (see Figure 6). Since the surface potential or capacitance value changes smoothly as the photomask moves, correction values ​​at coordinates that cannot be measured directly can be estimated by interpolation. (2) For example, using the measurement point coordinates and map data output from the laser interferometer, interpolation calculations such as least squares, spline, Lagrangian interpolation, or two-dimensional weighting calculations such as Gaussian filtering can be performed to estimate the surface potential or capacitance at the measurement point coordinates for intermediate coordinates not included in the table in Figure 6. Correction values ​​at any coordinate can be estimated from these values. The XYZ coordinates of the measurement points are captured and corrections are performed in real time as the stage moves continuously. (3) On the other hand, the global substantially applied retarding potential of the measurement target area is determined by the principle described above. However, if local capacitance changes are to be considered, the surface potential can be estimated by calculating the area of ​​the pattern that contributes to capacitance formation directly below the objective lens 55 using pattern design data (CAD data such as GDI) drawn on the photomask, and then calculating the capacitance. By calculating and controlling a correction amount from the capacitance thus estimated (controlling the potential of the retarding upper electrode 81 or retarding lower electrode 82), the potential of the measurement point on the surface of the sample 9 can be set to a desired value. [Brief explanation of the drawing] 【0088】 [Figure 1] This is a diagram illustrating one embodiment of the present invention. [Figure 2] This is an example of a sample (mask) of the present invention. [Figure 3] This is an example of the black border of the present invention. [Figure 4] This is an example of the black border of the present invention. [Figure 5] This is a schematic diagram illustrating the mask surface potential of the present invention. [Figure 6] This is an example of a map table of capacitance and potential for the mask of the present invention. [Figure 7] This is a flowchart for setting the mask surface potential of the present invention. [Figure 8] This is the mask surface potential setting flowchart (part 2) of the present invention. [Figure 9] This is a diagram illustrating another embodiment of the present invention. [Explanation of symbols] 【0089】 1: Electronic gun 2: Blanking device 3: Blanking Aperture 4: Objective Aperture 5: Objective lens 6: Deflection device 7: Surface potential / capacitance detection device 71: Potential / Capacitance Detection Signal 8: Retarding voltage 81: Retarding upper electrode 82: Retarding lower electrode 83: First potential 9: Sample 10: Insulator 11: XYZ Stage 12: Vacuum Chamber 13: Vacuum pump 14: Vibration isolator 21: Electronically transmitted 31: Insulating substrate 32: Conductive reflective layer 33: Absorption layer (pattern) 34: Pattern 35: Photomask 36: Bias electrode 37: Black Border 38: Claw electrode 41: Black Border 42: Peripheral area 43: Measurement target area 44:Connection part

Claims

[Claim 1] In a device that detects electrons generated by irradiating an EUV mask with an electron beam to acquire an image, a method for preventing charge-up of the EUV mask, An electron gun that generates an electron beam, An objective lens that narrows the electron beam generated by the electron gun and irradiates it onto an EUV mask, A deflection system that scans the electron beam, which has been narrowed by the objective lens, in two dimensions across the surface of the EUV mask, A stage for mounting the aforementioned EUV mask and moving it to a predetermined position, A detection means that irradiates the surface of the EUV mask with a narrowly focused electron beam, detects the emitted secondary electrons or backscattered electrons, and generates an image. The surface of the EUV mask is provided with grooves in a band shape around the area where a pattern is formed to electrically isolate it, electrically connects the pattern inside the black border that reduces the effect of flare from the EUV light source to the surrounding area, and includes a claw electrode that controls the potential of the internal pattern from the outside, or a conductive connecting part provided on the substrate of the EUV mask that controls the potential of the internal pattern from the outside. A method for preventing charge-up, characterized in that, with respect to the region where the claw electrode or the conductive connecting portion forms a pattern on the surface of the EUV mask, the potential of the region inside the black border is set independently of other regions of the EUV mask, and the surface potential during electron beam irradiation is controlled by controlling this potential. [Claim 2] The charge-up prevention method according to claim 1, characterized in that the claw electrode or the conductive connecting portion connects the inner region and the periphery while leaving the black border intact to the extent that the performance of the black border is not limited. [Claim 3] The charge-up prevention method according to claim 1 or 2, characterized in that the conductive connecting portion is formed of a conductive material of Ta,W having the property of absorbing EUV light. [Claim 4] The charge-up prevention method according to any one of claims 1 to 3, characterized in that the claw electrode or the conductive connecting portion connects the inner region and the periphery across the black border. [Claim 5] In a device for detecting electrons generated by irradiating an EUV mask with an electron beam and acquiring an image, in a device for preventing charge-up of the EUV mask, An electron gun that generates an electron beam, An objective lens that narrows the electron beam generated by the electron gun and irradiates it onto an EUV mask, A deflection system that scans the electron beam, which has been narrowed by the objective lens, in two dimensions across the surface of the EUV mask, A stage for mounting the aforementioned EUV mask and moving it to a predetermined position, A detection means that irradiates the surface of the EUV mask with a narrowly focused electron beam, detects the emitted secondary electrons or backscattered electrons, and generates an image. The EUV mask comprises a groove in the shape of a band around the area where a pattern is formed on the surface of the EUV mask to electrically isolate it, a claw electrode that electrically connects the pattern inside the black border to the surrounding area to reduce the effect of flare from the EUV light source, or a conductive connecting portion provided on the substrate of the EUV mask that externally controls the potential of the internal pattern, A charge-up prevention device characterized by controlling the surface potential during electron beam irradiation by setting and controlling the potential of the region inside the black border in the region where the claw electrode or the conductive connecting portion forms a pattern on the surface of the EUV mask, independently of other regions of the EUV mask.

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