Electron detection equipment and electron beam inspection equipment

Abstract

PURPOSE: To provide an electron detection device that detects electrons emitted from a sample with high sensitivity and low noise.CONSTITUTION: An electron detection device includes a hole through which a first primary electron beam generated by an electron gun passes, a shielded tube which applies a potential to repel secondary electrons placed in the hole, electron detection means arranged around the shielded tube, and means for blocking electrons generated by irradiation with the first electron beam from entering an adjacent electron detection means. The electron detection device is configured such that the sample is irradiated with primary electrons, and the generated secondary electrons are pulled straight up and directly detected.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an electron detection device for detecting electrons emitted from a sample. [Background technology]

[0002] Semiconductor devices are shrinking every year according to Moore's Law, and cutting-edge devices are approaching the mass production stage. Even the latest devices have minimum feature sizes of less than 20 nm. In order to achieve this character size, exposure techniques capable of forming smaller patterns are required.

[0003] Conventionally, a laser beam with a wavelength of 193 nm has been used for exposure, but Since the dimensional limits have already been exceeded by a large margin, in recent years, lithography technology that utilizes EUV light with a wavelength of 13.5 nm has been actively pursued.

[0004] This technology is said to have originated in Japan, but companies such as ASML (registered trademark) have been researching and developing it for practical use for over 10 years. The optical system of the exposure tool itself is almost complete, but until a few years ago, EUV exposure tools were skipped for use in 20nm generation exposure because they were unable to obtain the light source power of 100W to 200W required for economical mass production.

[0005] Instead, so-called double or triple exposure techniques have been developed that can achieve even smaller feature sizes by repeating the exposure process multiple times using the existing 193 nm wavelength.

[0006] In principle, immersion lithography using a laser beam with a wavelength of 193 nm is repeated multiple times. This makes it possible to create patterns as small as possible. However, it is known that the repeated exposure process is limited by the need for alignment accuracy on the order of nm, which is one order of magnitude higher than conventional methods, and by the large roughness that comes from the large molecular structure of the chemically amplified resist optimized for 193 nm exposure. Currently, double patterning, which repeats the exposure process twice, which is said to be the economic limit, is in practical use, and is used to realize lines and spaces of 20 nm to 16 nm in memory devices with relatively simple structures.

[0007] Not only memory devices with simple structures, but also CPUs and logic devices are being upgraded and their functions are being expanded. It is necessary to reduce the pattern size in order to reduce power consumption. To utilize complex patterns without defects, logic devices can be exposed by double or triple exposure. To create this, a fairly complex pattern is required. It is very difficult to split the patterns on the two photomasks so that they can be used for multiple exposures. Complex calculations are required for the required results. Depending on the pattern, the division calculations may diverge. may not be obtained.

[0008] To avoid these complications, a method called complementary lithography is used. Lithography facilitation technology proposed by Intel is going to be used for 2016. This exposure method is characterized by using a pattern that reduces complex logic circuits to a simple L&S pattern like memory circuits. In this way, the complex logic device pattern is limited to only the L&S pattern that is easiest to expose and the process of cutting the lines, so there is no need for complex pattern division calculations, and the process is simple, and it is calculated to be possible up to about 8 nm.

[0009] As mentioned above, when complex exposure methods such as double patterning and triple patterning are used, the number of photomasks required increases with each divided exposure, and more mask inspections and precise measurements are required than ever before. For example, in double patterning, two photomasks are used in sequence, so the absolute position accuracy and alignment accuracy of the lines formed on the mask between the two masks are more important than ever before. Optical correction to expose finer patterns also becomes more complex and precise. Masks using inverse lithography use high-order diffracted light, so the pattern size used for correction is even smaller. In mask production, defects of a size that could be ignored in the past now affect device yields, so it is necessary to reduce the defect density more than ever before, and fine particles are also subject to observation.

[0010] These trends will not be limited to conventional 193 nm exposure; when EUV becomes practical, similar multi-patterning techniques will be used at even smaller sizes in the future, and the inspection requirements will tend to increase exponentially.

[0011] Due to these demands, photomasks are constantly required to be inspected for defects at higher resolution and at higher speeds. One promising method to meet these demands is ultra-fast electron beam inspection equipment. DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0012] Conventional electron beam inspection devices have sufficient resolution, but have a problem in that the inspection speed is far slower than required.

[0013] The main reason for this is that the electron detection devices that can be used with conventional electron beam inspection equipment have a narrow dynamic range and problems with saturation characteristics that degrade linearity, response speed, and lifespan. Increasing the speed also degrades the image SNR, making it difficult to achieve both high resolution and high inspection speed.

[0014] To overcome this, the inventors have previously proposed an ultrafast electron detection device that detects electrons by directly irradiating an APD with electrons (see JP 2015-210998 A).

[0015] However, when attempting to detect large amounts of current with high sensitivity using a single APD, although performance is far better than before, new issues arise in that counting losses occur due to the APD's dead time, the input-output relationship is not constant, and the SNR and linearity of the acquired image deteriorate. [Means for solving the problem]

[0016] The present invention relates to an ultra-high speed electron detection device that enables high speed inspection using an electron beam and It is an object of the present invention to provide a scanning electron beam inspection apparatus incorporating a detection device.

[0017] The present invention is an ultrafast electron detector that detects an electron beam emitted from or reflected by a sample at ultrafast speeds. Secondary electrons emitted from the sample or electrons reflected by the sample are first converted into light by hitting an ultrafast scintillator plate with a response time of the order of ps to ns and having the magnitude required for signal electron detection. The light generated by the scintillator is then reduced directly or by a light guide or optical lens and irradiated onto a small-area photodetector element.

[0018] Therefore, the present invention provides an ultrafast electron detector that detects an electron beam emitted from a sample, an electron beam reflected by a sample, or both of these electron beams at ultrafast speeds, and is provided with an energy stabilizing means that converts the electron beam emitted from the sample and accelerated, or the electron beam reflected by the sample, or both of these electron beams into an electron beam of constant energy, a first detector that converts the electron beam whose energy has been stabilized by the energy stabilizing means into light, and a second detector that inputs the light converted by the first detector, amplifies it, and outputs an electrical signal.

[0019] In this case, the energy stabilization means applies a predetermined voltage between the sample or a mesh provided near the surface of the sample and the first detector or a mesh provided near the surface of the first detector, thereby making the energy of the electron beam constant.

[0020] The first detector is a scintillator that converts the electron beam into light at high speed.

[0021] The second detector is an MPPC element in which a plurality of avalanche diodes are arranged in parallel.

[0022] The second detector is a ring-shaped disk having a hole in the center through which the primary electron beam passes, and is provided with a plurality of independent detectors formed by dividing the ring-shaped disk into a plurality of parts in the circumferential direction.

[0023] Furthermore, the voltage applied to the energy stabilizing means is adjusted so that only electrons emitted from the sample or electrons reflected by the sample are detected and amplified by the first and second detectors.

[0024] Also, a scanning electron beam inspection device incorporating an ultra-high speed electron detector is provided. Effect of the Invention

[0025] In the present invention, the second detector is made up of an MPPC element consisting of a circuit in which a large number of APDs are arranged electrically in parallel, which provides a fast response speed and makes it possible to make the dead time of the APD negligible, thereby making it possible to avoid the counting loss phenomenon that occurs when a large number of electrons are irradiated, which was a problem in the conventional technology.

[0026] In addition, because the electrons emitted or reflected from the sample are converted into light once, they do not interact with the electron beam, and can be freely transported to another location without loss. This allows multiple scintillator sources to be detected independently and efficiently.

[0027] It is also possible to obtain an electron detector with a wide input / output dynamic range. When a large amount of electrons or photons are incident, many APDs operating independently detect the electrons or photons, so that electrons or photons can be detected with virtually no dead time. Electrons can be detected with good linearity from small to large amounts.

[0028] In addition, the light emitted by the scintillator can be reduced in size and irradiated onto an MPPC with a smaller area for detection, which makes it possible to reduce dark noise caused by thermal noise, which is proportional to the MPPC area.

[0029] In addition, by compressing or shrinking the electron group that is generated on the sample surface and drifts while spreading, and accelerating it and irradiating it on a small scintillator, the photons can be detected with a small scintillator and a small photon detection device, which reduces the thermal noise generated by the photon detection device. Because the scintillator can be made smaller, costs can be reduced and it becomes easier to place multiple scintillators in a column.

[0030] In addition, a scintillator with the size or dimensions required for detecting electrons can be used. Alternatively, the signal electrons that spread in all directions can be collected by an electron lens and irradiated onto the scintillator, so that the signal electrons generated on the sample surface can be detected almost completely. In addition, the electric field used for accelerating the secondary electrons can be localized by using a conductive mesh with a large opening ratio and a shield tube provided on the scintillator, so that it does not adversely affect the beam trajectory or aberration of the primary electrons.

[0031] In addition, since the life of the scintillator is very long, the life of the entire electron detection device is also very long, making it virtually maintenance-free.

[0032] In addition, a scanning electron beam inspection device incorporating the ultra-high speed electron detector of the present invention can detect the electron beam emitted or reflected from a sample (e.g., a mask or semiconductor wafer) at ultra-high speed, perform dimensional measurement, defect detection, etc. in a short time, and greatly improve throughput. Since there is almost no maintenance required, the operating rate of the device can be increased. Example 1

[0033] Fig. 1 shows a configuration diagram of one embodiment of the present invention. In Fig. 1, a primary electron beam 31 is irradiated onto a sample 13 while being planarly scanned, and the generated secondary electrons and reflected backscattered electrons are converted into light at ultra-high speed by a scintillator 9, which is a first detector, and this converted light is amplified by an MPPC 4, which is a second detector, to output a signal, making it possible to detect signal electrons (secondary electrons, backscattered electrons, etc.) at ultra-high speed.

[0034] In FIG. 1, an electron gun 1 is a known type that generates a primary electron beam 31, such as a hot cathode type, a TFE, a field emitter, or a photoexcitation type.

[0035] The electron gun control device 2 is a known device that supplies a high voltage, a bias voltage, and, in the case of a hot cathode electron gun, a filament heating power supply, etc., so that the electron gun 1 generates a primary electron beam 31 .

[0036] The deflection electrode 3 is a known type that is composed of two stages of deflection electrodes, namely, a deflection electrode (upper) 3-1 and a deflection electrode (lower) 3-2, and applies a predetermined deflection voltage to the electrodes in pairs in the X and Y directions to deflect the primary electron beam 31 in two stages and scan the sample 13 in the X and Y directions.

[0037] The electron beam scan control device 322 applies a predetermined scanning voltage to the deflection electrodes 3, and narrows the primary electron beam 31 onto the sample 13 to scan it in the X and Y directions.

[0038] The shield tube 41 is for applying a negative voltage to the secondary electrons emitted from the sample 13 to prevent them from traveling upward on the axis and to direct them towards the scintillator 9 .

[0039] The blocking bias 5 is a negative blocking bias voltage applied to the shield tube 42 to prevent secondary electrons emitted from the sample 13 from passing upward on the axis.

[0040] The bias circuit 61 applies a bias voltage to the MPPC 4 (described later with reference to FIG. 6 etc.).

[0041] MPPC4 is an abbreviation for Multi-Pixel Photon Counter, and is a photon counting device in which a Geiger mode APD (Avalanche Diode) is made into a multi-pixel device (described in detail using FIG. 6, etc.).

[0042] The amplifier 6 amplifies the signal amplified by the MPPC 4 .

[0043] The PC 7 is a personal computer that performs various processes and controls according to programs.

[0044] The display device 8 is a display that displays images and the like.

[0045] The scintillator 9 converts and amplifies electrons (secondary electrons, reflected electrons, etc.) into light at an extremely high speed (to be described later).

[0046] The mesh 10 applies an acceleration voltage to attract secondary electrons and the like emitted from the sample 13 .

[0047] The umbrella 11 forms an electric field such that secondary electrons emitted from the sample 13 are accelerated by the voltage applied to the mesh 10 and collide efficiently with the scintillator 9. The umbrella 11 is made of a non-magnetic, conductive metal or the like.

[0048] The objective lens 12 narrows the primary electron beam 31 and irradiates it onto the sample 13 .

[0049] The sample 13 is a specimen (photomask, wafer, etc.) to be observed, inspected, and measured, and a bias voltage is applied to it by a sample bias circuit 14 as necessary.

[0050] The sample bias circuit 14 applies a bias voltage to the sample 13 .

[0051] Next, with reference to Figures 2 to 5, a detailed description will be given of a configuration for detecting and amplifying electrons (secondary electrons, reflected electrons, etc.) emitted and reflected from the sample 13 with high sensitivity and at ultra-high speed using the scintillator 9 and MPPC 4 in Figure 1.

[0052] Fig. 2 shows an explanatory diagram (part 1) of the main part of the present invention. Fig. 2(a) shows an example in which the mesh 10 is arranged on the entire front surface (the reflected electron detection section 331 and the secondary electron detection section 321) of the detector (first detector + second detector), and Fig. 2(b) shows an example in which the mesh 10 is arranged on the secondary electron detection section 321 on the front surface of the detector (first detector + second detector). The rest of the configuration is the same.

[0053] In (a) of Fig. 2, the detector (first detector + second detector) 34 has a structure in which the scintillator 9, which is the first detector in Fig. 1, and the MPPC 4, which is the second detector, are stacked (see Figs. 6 to 10 and their explanations), and has a backscattered electron detection unit 331 on the inside and a secondary electron detection unit 321 on the outside. Since backscattered electrons with high energy gather at the center and secondary electrons with low energy gather at the periphery, the backscattered electron detection unit 331 is provided in the center and the secondary electron detection unit 321 is provided outside it, so that the backscattered electrons and secondary electrons can be separated and detected separately.

[0054] The mesh 10 is applied with a positive voltage to accelerate low-energy secondary electrons emitted from the sample 13, and an example is shown here in which it is disposed in front of both the backscattered electron detection unit 331 and the secondary electron detection unit 321 of the detector 34. In this case, the high-energy backscattered electrons reflected from the sample 13 have a Gaussian distribution in the upward direction of the axis, and many of them are detected by the illustrated backscattered electron detection unit 331, which is closer to the axis. On the other hand, the low-energy secondary electrons emitted from the sample 13 are accelerated in the direction of the mesh 10 to which a high voltage is applied, and collide with the illustrated secondary electron detection unit 321, and to a lesser extent with the backscattered electron detection unit 331 on the inside, where they are amplified and detected. However, overall, the secondary electron component in the secondary electron detection unit 321 is greater, and as a result, it can be considered that secondary electrons are detected.

[0055] In addition, in FIG. 2(b), the mesh 10 is disposed only in front of the secondary electron detection unit 321 and not in front of the reflected electron detection unit 331, so that all secondary electrons accelerated and attracted to the secondary electron detection unit 321 can be amplified and detected.

[0056] As described above, by placing the mesh 10 in front of the detectors (first detector + second detector) 34 and applying a positive voltage, low-energy secondary electrons emitted from the sample 13 are accelerated and attracted and amplified and detected by the outer secondary electron detection section 321, while high-energy reflected electrons reflected by the sample 13 are detected and amplified by the inner reflected electron detection section 331.

[0057] At this time, the energy of the secondary electrons emitted when the primary electron beam 31 is narrowed by the objective lens 12 and irradiated onto the sample 13 is 0.1 eV to several eV, and this is accelerated by 10 KV applied to the mesh 10, so the fluctuation rate of the secondary electrons when they collide with the scintillator 9, which is the first detector constituting the detector 34, is (0.1 eV to several eV) / 10,000, which is about ±0.01%. That is, the secondary electrons emitted from the sample 13 are accelerated by 10 KV applied to the mesh 10, and the fluctuation of the energy of the secondary electrons when they collide with the scintillator 9 is adjusted to be a constant energy of about ±0.01% or less. As a result, the energy of the secondary electrons emitted from the sample 13 is made constant (here, constant at 10 KV ±0.01%) and input to the scintillator 9, and it becomes possible to convert it into the amount (number) of light that accurately corresponds to the number of secondary electrons. After being converted into light, the secondary electrons are amplified by a second detector, for example, an MPPC4, making it possible to detect a signal corresponding to the number of the secondary electrons.

[0058] Furthermore, the electrons reflected by sample 13 have almost the same energy as the primary electrons, for example 10 KV, so that when they enter scintillator 9, which is the first detector, the fluctuation is about 0.01% or less, similar to the case of the secondary electrons described above, and it becomes possible to output a signal corresponding to the number of electrons reflected from sample 13 from detector 34. The details will be described below in sequence.

[0059] Fig. 3 shows an explanatory diagram (part 2) of the main part of the present invention. In Fig. 3, an energy filter 101 is placed between a sample 13 and a detector (first detector + second detector) 34, and high-energy backscattered electrons 33 and low-energy secondary electrons 32 are separated and amplified and detected by a backscattered electron detector 331 and a secondary electron detector 321.

[0060] In Fig. 3, EXB101 is an energy filter that applies both an electric field and a magnetic field to separate the electrons (reflected electrons, secondary electrons) by changing the deflection angle as shown in the figure depending on the difference in their energies, and detects each independently. By providing EXB101, it becomes possible to amplify and detect low-energy electrons (secondary electrons, etc.) in the outer secondary electron detection unit 321, and to amplify and detect high-energy electrons (reflected electrons, etc.) in the inner reflected electron detection unit 331.

[0061] As described above, by disposing the energy filter 101 between the sample 13 and the detectors (first detector + second detector) 34, it becomes possible to amplify and detect low-energy electrons (secondary electrons, etc.) in the outer secondary electron detection section 321, and to amplify and detect high-energy electrons (reflected electrons, etc.) in the inner reflected electron detection section 331.

[0062] Fig. 4 shows an explanatory diagram (part 3) of the main part of the present invention. In Fig. 4, the secondary electron detection unit 321 in Fig. 2(b) is lowered downward to be as close as possible to the sample 13, and the secondary electrons emitted from the sample 13 can be efficiently collected by making the opening larger when viewed from the sample 13, and providing a mesh 10 on the front to apply a high voltage (for example, 10 KV) to accelerate and attract the secondary electrons emitted from the sample 13, enabling efficient amplification and detection.

[0063] As described above, the secondary electron detection unit 321 is brought closer to the sample 13 to enlarge the opening, and the secondary electrons emitted from the sample 13 are efficiently accelerated and collected by applying a high voltage (e.g., 10 KV) to the mesh 10 arranged in front of the secondary electron detection unit 321, making it possible to amplify and detect the secondary electrons.

[0064] Fig. 5 is an explanatory diagram (part 4) of the main part of the present invention. In Fig. 5, the potential of the mesh 10 is controlled to detect the difference.

[0065] 5A shows an example of no bias (normal state in which a positive 10 KV is applied to the mesh 10). In the case of FIG. 5A, as shown in the figure, the detector 34 can detect both reflected electrons and secondary electrons.

[0066] Fig. 5(b) shows a state with a bias. In the case of Fig. 5(b), for example, a voltage (a negative voltage of several volts to several tens of volts) is applied to the mesh 10 such that the secondary electrons are reflected and cannot be detected, so that the secondary electrons cannot be detected and the high-energy reflected electrons can be amplified and detected.

[0067] As described above, when an arbitrary voltage is applied to the mesh 10, only electrons with energy equal to or greater than the applied voltage collide with the detector 34 and are amplified and detected. By taking the difference between the two, the number or amount of electrons in either one can be accurately detected.

[0068] Fig. 6 shows an example of a detector of the present invention. Fig. 6 shows a schematic configuration of an MPPC4, which is a second detector constituting the detector 34, with Fig. 6(a) showing an MPPC photograph (perspective view), Fig. 6(b) showing a schematic diagram, and Fig. 6(c) showing an example of an equivalent circuit of the MPPC.

[0069] 6(a), the primary electron passing hole is a hole through which the primary electron beam passes. The primary electron beam that passes through the hole is narrowed by the objective lens 12 and is planarly scanned while irradiating the sample 13, emitting secondary electrons and reflecting reflected electrons.

[0070] 6(b) is a schematic diagram (with the scintillator 9 omitted) of the MPPC 4 and the mesh 10 placed in front of it, viewed from below. There is a primary electron passage hole in the center, and the mesh 10 is placed in front of the MPPC 4. A positive high voltage (for example, 10 KV) is applied to the mesh 10, and secondary electrons emitted from the sample 13 are accelerated to a certain energy, and then collide with a scintillator 9 (not shown) placed between the MPPC 4 and the mesh 13 to be converted into light, which is then incident on the MPPC 4 shown in the figure for amplification and output as a signal.

[0071] FIG. 6(c) shows an example of an equivalent circuit of an MPPC. The MPPC4 is configured by arranging multiple D1 (avalanche diodes) in parallel as shown in the figure, and further connecting R1 (quenching resistor) in series to each of them in parallel. When light is input to one D1 (avalanche diode), the D1 in Geiger mode discharges and current flows. When the current flows, the current is limited by R1 (quenching resistor) and falls below the discharge voltage, the discharge stops, and one pulse is output. When two photons are input simultaneously, they are in parallel and a pulse with approximately twice the peak is output. Similarly, when n photons are input simultaneously, n times the pulse is output.

[0072] A bias power supply 43 is a power supply that applies a bias voltage to D1 to maintain it in the Geiger mode.

[0073] The current detector 44 detects the pulse current generated by D1 and converts it into a voltage signal.

[0074] By using the MPPC 4 having the above-mentioned configuration, secondary electrons emitted from the sample 13 and reflected electrons are converted to light by the scintillator 9 at a constant energy, and then amplified and detected at ultra-high speed and with high precision by the MPPC 4. Next, the features of the MPPC in FIG. 6 will be described.

[0075] The MPPC4 is a device with an overall size of several mm square, consisting of tens to tens of thousands of small APDs (D1) with a square of several microns as shown in Figure 6, arranged in parallel. This MPPC4 can be purchased from Hamamatsu Photonics (registered trademark) and other companies. It is also possible to fabricate and use devices smaller than this. It has a volume that is less than one ten-thousandth of that of a conventional PMT (photomultiplier tube). It is a plate-shaped solid element made of silicon, and is very robust as it does not have glass or vacuum-sealed parts like a PMT. The weight of the device alone is very light, on the order of grams.

[0076] As shown in FIG. 6(c), each APD (D1) constituting the MPPC4 is electrically connected in parallel via a resistor for controlling avalanche amplification, called a quenching resistor R1. One end of the parallel circuit is connected to a bias power supply 43 for controlling the avalanche phenomenon of about 50V to 100V, and the other end is connected to a current detection device 44 with a virtual earth input. Since there is slight variation in the characteristics of each APD (D1) constituting the MPPC4 array, the bias voltage applied to the entire array is experimentally determined so that all APD (D1) elements constituting the array are in Geiger mode. When a single photon is input to each APD in Geiger mode, avalanche amplification occurs with an amplification factor of up to 1 million times. Of course, it may be set to a voltage with a different amplification factor.

[0077] A quenching resistor R1 with a fixed value for current limiting is connected to each APD, and since a constant voltage is applied to the terminals, when avalanche amplification occurs, the electrical resistance of the APD becomes negligibly small and acts just like a switch, causing a constant current to flow through the quenching resistor R1. Since each APD is connected in parallel, the sum of the avalanche currents generated in each APD is output to the current detector 44 connected to the output terminal.

[0078] Since MPPC4 has a large number of APDs arranged spatially, the probability that an incident photon will be incident on the same APD is extremely small. Therefore, for example, if one photon is input to MPPD4, one unit of current is generated, and if N photons are input at the same time, N units of current are generated. From this property, it is possible to know how many photons or electrons were simultaneously incident on MPPC4 from the output current. Since the output signal is an analog signal proportional to the number of incident photons, it is converted to a digital signal using an AD converter and imported into a PC for imaging. The current output by each APD element depends on the value of the quenching resistor R1 and is not strictly constant, so a standardization process can be performed on the computer to make it strictly constant.

[0079] It is also possible to use a digital MPPC that uses a signal summing method in which whether or not each APD is in an avalanche state is converted into a digital signal of 0 or 1 inside the silicon chip, and then a digital product-sum operation is performed to calculate the number of AAPDs in the avalanche state, which is the total output of the entire MPPC4. In this case, since the output is converted into a digital signal beforehand, there is no need to convert it into a digital signal using an AD conversion device. Furthermore, the signal summation results are very accurate. With such an integrated IC, image processing can also be performed inside the chip.

[0080] Fig. 7 shows an example (part 2) of the detector of the present invention. Fig. 7 shows a schematic configuration in which the first detector constituting the detector 34, the scintillator 9 as the second detector, and the MPPC 4 are incorporated into the device of Fig. 1.

[0081] FIG. 7(a-1) shows a top view of the detector 34, and FIG. 7(a-2) shows a cross-sectional view thereof, which show a configuration example in which the mesh 10 is not provided.

[0082] In FIG. 7(a-1), the MPPC 4 has a hole in the center for the primary electron beam, and the primary electron beam passes through this hole from top to bottom and is narrowed by the objective lens 12 in FIG. 1 to irradiate and planarly scan the sample 13.

[0083] (a-2) of Fig. 7 shows a cross-sectional view. Secondary electrons emitted from the sample 13 are accelerated and attracted by the positive voltage (for example, 5 KV here) applied to the scintillator 9, collide with the scintillator 9, and convert the secondary electrons into light. The converted light enters the MPPC 4, where it is amplified and outputs a signal. At this time, a negative voltage is applied to the shield tube 41 to prevent the secondary electrons from traveling upward on the axis, and they travel in the direction of the positive voltage applied to the scintillator 9, improving the light collection efficiency of the secondary electrons.

[0084] In addition, in Figures 7(b-1) and (b-2), a mesh 10 is provided between the sample 13 and the scintillator 9 shown in the figure, a positive acceleration voltage (5 KV in the figure) is applied between the mesh 10 and the scintillator 9 (in Figures 7(a-1) and (a-2) a positive voltage is applied between the sample 13 and the scintillator 9), and a positive voltage (for example, several volts to several tens of volts) is also applied between the sample 13 and the mesh 10, so that secondary electrons emitted from the sample 13 are efficiently collected. The rest is the same as in Figures 7(a-1) and (a-2), so a description will be omitted.

[0085] Here, the configuration of FIG. 7 will be described in detail.

[0086] In Fig. 7, a primary electron beam 31 generated and accelerated by the electron gun 1 in Fig. 1 is reduced to a desired beam spot size by an objective lens 12 placed directly above the sample 13, and then scanned over the surface of the sample 13, and signal electrons such as secondary electrons and reflected electrons generated on the surface of the sample 13 are detected by a detector consisting of a scintillator 9 and an MPPC 4. The signal electrons rise while spreading out in a cone shape in the vertical direction from the point on the surface of the sample 13 irradiated with the primary electron beam 31, so that the signal electrons tend to be distributed symmetrically with respect to the axis of the primary electron beam. In order to efficiently detect the signal electrons, it is necessary to provide a hole (a hole for the primary electron beam) for the primary electrons to pass through at the center of the detector and to position it near the axis of the primary electron beam.

[0087] For this reason, as shown in (a-1) and (b-1) of FIG. 7, the scintillator 9 is provided directly on the light receiving surface of the MPPC 4, and the surface of the scintillator 9 is covered with a thin conductive aluminum film. The main purpose of the aluminum film is to prevent the surface of the scintillator 9 from being charged by incident electrons, but it also functions as an anti-reflection film to prevent the light generated by the scintillator 9 from leaking out of the MPPC 4. The scintillator 9 on the MPPC 4 may be attached with an adhesive that takes into account the refractive index, or the scintillator 9 may be directly deposited by evaporation, CVD, sputtering, or the like. As the scintillator 9, inorganic scintillators, direct transition type semiconductor scintillators, ceramic materials, plastic scintillators containing heavy atoms, halide scintillators using inner shell transition emission, or liquids, etc. may be used.

[0088] There is also a hole (primary electron beam hole) through which the primary electron beam passes, and a shield tube 41 is provided to prevent the electric and magnetic fields in the surrounding areas from affecting the primary electron beam. The primary electron beam passes through the shield tube 41. The shield tube 41 is made of a non-magnetic material, with a diameter of a few mm and a thickness of 1 mm or less. A gap will inevitably form between the detector and the shield tube 41. If electrons hit the gap, they will not be detected, so a conductive umbrella-shaped component is used to extend the electric field outward, repelling the electrons so that they do not enter the gap and head towards the detector.

[0089] When accelerating electrons to make the scintillator 9 glow in front of the detector, as shown in Figures 7(b-1) and (b-2), a conductive mesh 10 with a high aperture ratio (preferably 90% or more) is placed a few mm away from the scintillator 9, and a voltage of about 1 to 10 kV is applied between the mesh 10 and the conductive thin film provided on the surface of the scintillator. It is desirable to apply a slight positive potential of about 10 V to the sample 13 so that the signal electrons generated on the surface of the sample 13 can reach the sample itself. It is desirable to keep this space in a vacuum state of more than 10-3 Pascals to prevent discharge.

[0090] Figure 8 shows an example (part 3) of the detector of the present invention. It shows a schematic configuration in which the primary electron beam is made ring-shaped and focused to a single fine point by the objective lens 12 to irradiate the sample 13 while scanning the plane. The rest is the same as in Figure 7, so the explanation is omitted.

[0091] FIG. 8(a-1) shows a top view of the detector 34, and FIG. 8(a-2) shows a cross-sectional view thereof, which show a configuration example in which the mesh 10 is not provided.

[0092] In FIG. 8(a-1), the MPPC 4 has a ring-shaped hole for the primary electron beam, and the ring-shaped primary electrons pass through this hole from top to bottom and are narrowed by the objective lens 12 to become a point, which irradiates the sample 13 while performing planar scanning.

[0093] FIG. 8 (a-2) shows a cross-sectional view. Secondary electrons emitted from the sample 13 are accelerated and attracted by a positive voltage (e.g., 5 KV) applied to the scintillator 9, collide with the scintillator 9, and convert the secondary electrons into light. The converted light enters the MPPC 4, where it is amplified and outputs a signal. At this time, a negative voltage is applied to the ring-shaped shield tube 41 to prevent the secondary electrons from traveling upward on the axis, and they travel in the direction of the positive voltage applied to the scintillator 9, improving the light collection efficiency of the secondary electrons. At this time, it becomes possible to detect secondary electrons and reflected electrons in the center of the detector composed of the scintillator 9 and the MPPC 4, and the detection efficiency can be improved.

[0094] In addition, in (b-1) and (b-2) of FIG. 8, a mesh 10 is provided between the sample 13 and the scintillator 9 shown in the figure, a positive acceleration voltage (5 KV in the figure) is applied between the mesh 10 and the scintillator 9 (in (a-1) and (a-2) of FIG. 8, a positive voltage is applied between the sample 13 and the scintillator 9), and a positive voltage (for example, several volts to several tens of volts) is also applied between the sample 13 and the mesh 10, so that secondary electrons emitted from the sample 13 are efficiently collected. The rest is the same as in (a-1) and (a-2) of FIG. 8, so a description thereof will be omitted. In this case, it becomes possible to detect secondary electrons and reflected electrons in the central part of the detector composed of the scintillator 9 and the MPPC 4, and the detection efficiency can be improved.

[0095] Here, FIG. 8 is characterized by the use of a hollow electron beam (hollow beam) as the primary electron beam. A hollow electron beam is a ring-shaped beam, and is sometimes used to prevent electrons from repelling each other when using a high-current electron beam. Like a normal beam, it can be focused to a single point on the surface of the sample 13 by the objective lens 12. As shown in (a-1) and (b-1) of Figure 8, a scintillator 9 is also placed in the center, and a ring-shaped shielded tube 41 through which primary electrons pass is provided around it. If necessary, a scintillator 9 can also be placed outside the ring-shaped shielded tube 41. This has the advantage that even if electrons (secondary electrons, reflected electrons, etc.) generated on the surface of the sample 13 rise completely vertically, they can be properly detected by the scintillator 9 located directly above. Signal electrons that fly to the periphery of the primary electron beam axis are detected by the scintillator 9 placed outside the ring-shaped shielded tube 41.

[0096] Fig. 9 shows a fourth example of a detector according to the present invention. Fig. 9 shows a schematic configuration in which the first detector, the scintillator 9 as the second detector, and the MPPC 4 constituting the detector 34 are divided into, for example, four in the circumferential direction and incorporated into the device of Fig. 1.

[0097] FIG. 9(a-1) shows a top view of the detector 34, and FIG. 9(a-2) shows a cross-sectional view thereof, which show a configuration example in which the mesh 10 is not provided.

[0098] In FIG. 9(a-1), MPPC 4 has a hole in the center for the primary electron beam, and the surrounding area is divided into four parts in the circumferential direction, and each part is blocked by a partition 431 to prevent electrons and light from entering the adjacent part. The primary electron beam passes through the central hole from top to bottom and is narrowed by objective lens 12 of FIG. 1 to irradiate and scan the surface of sample 13.

[0099] (a-2) of Fig. 7 shows a cross-sectional view. Secondary electrons emitted from the sample 13 are accelerated and attracted by a positive voltage (e.g., 5 KV) applied to the scintillator 9 divided into four, collide with the scintillator 9, and convert the secondary electrons into light. The converted light enters the MPPC 4 divided into four, where it is amplified and outputs a signal. At this time, a negative voltage is applied to the shield tube 41 to prevent the secondary electrons from traveling upward on the axis, and they travel in the direction of the positive voltage applied to the scintillator 9 divided into four, improving the light collection efficiency of the secondary electrons.

[0100] 9(b-1) and (b-2) show a configuration in which a mesh 10 is provided between the sample 13 and the scintillator 9 shown in the figure, a positive acceleration voltage (5 KV in the figure) is applied between the sample 13 and the four-part scintillator 9, and a positive voltage (e.g., 50 V) is also applied between the four-part scintillator 9 and the mesh 10, so as to efficiently collect secondary electrons emitted from the sample 13. The rest is the same as in FIG. 7(a-1) and (a-2), so a description thereof will be omitted.

[0101] Here, the configuration shown in Figure 9 will be explained in detail. Figure 9 shows the case where a 4CH (4-division) detector is used. The 4CH detector is used to obtain information about the direction in which electrons generated on the surface of the sample 13 are emitted. By adding or subtracting the detected signals of each CH, it is possible to extract the necessary components and determine the direction in which the electrons are emitting. 3D information can be obtained. Since the sensitivity output by each detector is not necessarily uniform, the detectors are used after being calibrated so that the output sensitivity of each channel is the same by multiplying them by an appropriate coefficient. By using this information, it is possible to emphasize the edge information of the surface structure of the sample 13 and obtain 3D information.

[0102] 9, a shield tube 41 is provided where the primary electron beam passes, and electrically independent detectors are arranged so as to be symmetrical with respect to the axis of the primary electron beam. The heights are also made the same. The detectors may be arranged not only in a plane, but also three-dimensionally in the height direction along the axis of the primary electron beam.

[0103] In addition, by extending partition-like electrodes in all four directions from the shield tube 41 through which the primary electron beam passes, it is possible to surround the scintillator 9 and separate the detection range of the signal electrons that fly to the detector. A bias voltage that generates a repulsive force against the signal electrons is applied to the shield tube 41 and the partitions 431. Due to this repulsive force, the electrons coming from the sample 13 are bent and fly towards the scintillator 9. The signal electrons are detected by each detector, and an electric signal is sent to the amplifier.

[0104] Fig. 10 shows a fifth example of a detector according to the present invention. Fig. 10 shows a schematic configuration in which the first detector constituting the detector 34, the scintillator 9 as the second detector, and the MPPC 4 are divided into, for example, four in the circumferential direction, and a smaller MPPC 4 is used by focusing light with a light guide 45 (Fig. 10(a-1) and (a-2)) and a lens 46 (Fig. 10(b-1) and (b-2)), and this is incorporated into the device of Fig. 1.

[0105] FIG. 10(a-1) shows a top view of the detector 34, and FIG. 10(a-2) shows a cross-sectional view thereof, which show a configuration example in which the mesh 48 is not provided.

[0106] In FIG. 10(a-1), MPPC 4 has a hole in the center for the primary electron beam, and the surrounding area is divided into four parts in the circumferential direction, and each part is blocked by partitions 47 to prevent electrons and light from entering the adjacent parts. The primary electron beam passes through the central hole from top to bottom and is narrowed by objective lens 12 of FIG. 1 to irradiate and scan the surface of sample 13.

[0107] (a-2) of Fig. 10 shows a cross-sectional view. Secondary electrons emitted from the sample 13 are accelerated and attracted by a positive voltage (e.g., 5 KV) applied to the four-divided scintillator 9, collide with the scintillator 9, and convert the secondary electrons into light. The converted light enters the four-divided MPPC 4, where it is amplified and outputs a signal. At this time, a negative voltage is applied to the shield tube 41 to prevent the secondary electrons from traveling upward on the axis, and they travel in the direction of the positive voltage applied to the four-divided scintillator 9, improving the collection efficiency of the secondary electrons.

[0108] 10(b-1) and (b-2) show a configuration in which a mesh 48 is provided between the sample 13 and the scintillator 9 shown in the figure, a positive acceleration voltage (50 V in the figure) is applied between the sample 13 and the four-part scintillator 9, and a positive voltage (for example, 5 KV) is also applied between the four-part scintillator 9 and the mesh 10, so that secondary electrons emitted from the sample 13 are efficiently collected. Also, in FIG. 10(b-2), instead of the light guide 45 in FIG. 10(a-2), a lens 46 is used to guide the light generated by the scintillator 9 to a small MPPC 4. The rest is the same as in FIG. 10(a-1) and (a-2), so a description thereof will be omitted.

[0109] Here, the configuration of FIG. 10 will be described in detail. FIG. 10 shows an example in which light generated in the scintillator 9 by electron beam irradiation is reduced and irradiated to the MPPC4. Unlike a single APD, the MPPC4 has an excellent feature that the electron detection speed does not deteriorate even if the total area of ​​the MPPC4 is increased, since the electric capacity of each APD does not increase. However, as the area of ​​the MPPC4 increases, noise caused by thermal noise, called dark noise, increases in proportion to the area. This noise is proportional to the absolute temperature, so it can be reduced by cooling. However, if a cooling device is provided inside the vacuum device, the device becomes extremely complicated, the volume increases, and the cost and maintenance become difficult, so that the good points of the MPPC4 may disappear. On the other hand, if the area of ​​the MPPC4 is reduced, the electron detection efficiency decreases, and the image SNR deteriorates.

[0110] In the present invention, attention has been paid to this point, and the area of ​​the MPPC 4 has been successfully made as small as possible while maintaining a high electron detection efficiency. First, the area of ​​the scintillator 9, which converts the electrons generated on the surface of the sample 13 into light, is made as large as possible and necessary. Specifically, the location where the signal electrons will arrive is found by experiment or electron trajectory simulation, and a scintillator 9 of a necessary and sufficient size is placed at that location.

[0111] This improves the detection efficiency of signal electrons generated on the surface of the sample 13. Meanwhile, the light generated by the scintillator 9 is converged or its cross-sectional area is reduced using an optical element (after being reduced by the light guide 45 in (a-2) of FIG. 10 or the lens 46 in (b-2) of FIG. 10) before being irradiated onto the MPPC 4. In this way, high electron detection efficiency is ensured by the large scintillator 9, and small dark noise is achieved by using as small an MPPC 4 as possible.

[0112] Here, it is desirable that the size of each APD constituting the APD array in the MPPC 4 used is as small as possible (several microns or less), the number of elements is tens of thousands or more, and the area of ​​the MPPC 4 is 1 square mm or less. In order to reduce the light generated by the scintillator 9, there are a method using a light guide 45 as shown in FIG. 10(a-2) and a method using an optical lens 46 as shown in FIG. 10(b-2). Furthermore, it is possible to obtain the effect of shortening the vertical dimension by using a reflecting mirror, a Fresnel lens, a holographic lens, or a diffraction element. When a light guide or the like is used in contact with the photon detection device, it is desirable to match the refractive index of the contacting members and insert a new anti-reflection film so as to prevent unnecessary reflection from occurring and causing signal loss. Furthermore, a wavelength selection optical filter may be inserted between the MPPC 4 and the light guide 45 to select the wavelength component incident on the MPPC 4.

[0113] Fig. 11 shows a configuration diagram (part 1) of another embodiment of the present invention. Fig. 11 shows an example in which the light emitted by the scintillator 9, which is generated by accelerating electrons emitted from the sample 13, is reduced in area by a light guide 91 and enters an MPPC 4 that is smaller in area than the scintillator 9. Other configurations are similar to those in Fig. 1, so explanations will be omitted.

[0114] In FIG. 11, a light guide 91 is made of a single material such as glass or acrylic, or a bundle of glass fibers.

[0115] MPPC4 is a device that has a large number of APDs, each measuring a few microns on a side, arranged in an array. When a bias voltage is applied to an APD, the gain at first is the same as that of a normal photodiode. However, when the threshold voltage of about 50V is exceeded, the gain increases dramatically, and finally it reaches an operation mode called Geiger mode, in which a single electron (or photon) is amplified by nearly one million times when it is incident. In Geiger mode, the sensitivity is such that a single electron incident from outside the MPPC4 can be detected, but the same amplification occurs when a single electron is generated due to thermal fluctuations inside the device, so it is not possible to distinguish between a single incident electron (photon) and an electron generated by heat. Therefore, these become a source of noise. The generation of thermal electrons is proportional to the area of ​​the APD. In other words, the larger the area of ​​the APD, the more frequently thermal electrons are generated, and the more noise there is.

[0116] On the other hand, since the signal electrons emitted from the sample 13 are scattered over a wide range, in order to detect the signal electrons efficiently, it is advantageous for the detector to have as large an area as possible.

[0117] As described above, the two requirements are in conflict with each other. In order to resolve this conflict in the present invention, a method has been found to achieve both high detection efficiency and low noise by making the area of ​​the scintillator 9 for detecting electrons as large as possible and reducing the light generated by the scintillator 9 so that it can be input to the MPPC 4, which has the smallest possible area. Figure 11 shows an example in which a light guide 91 with different area ratios on the entrance side and exit side is used, and the larger area is connected to the scintillator 9 and the smaller area is connected to the MPPC 4, which is a photon detection device.

[0118] The light generated by the large-area scintillator 9 is reduced in size by the light guide 91 and guided to the MPPC 4, a small-area photon detector, where it is converted into an electric current. In this way, both highly efficient detection and low dark noise can be achieved.

[0119] Fig. 12 shows a configuration diagram (part 2) of another embodiment of the present invention. Fig. 12 shows an example in which the light emitted by the scintillator 9 due to the acceleration of electrons emitted from the sample 13 is reduced in area by a lens 51 and enters an MPPC 4 that is smaller in area than the scintillator 9. The other configuration is the same as in Fig. 1, so a description thereof will be omitted.

[0120] In FIG. 12, lens 51 is a lens that reduces light. Although the figure shows a single lens configuration, multiple lenses may be used. For example, a lens system may be used in which a reduced parallel beam is emitted when a parallel beam is incident. Signal electrons generated by irradiating sample 13 with a primary electron beam are accelerated and attracted by a positive voltage (e.g., 10 KV) applied to mesh 10 and the like, and collide with scintillator 9. The colliding electrons emit a large amount of light. The emitted light is focused by lens 51 so that the cross-sectional area is reduced to one-tenth or less, and the area is reduced, and the light is incident on MPPC4, a photon detection device. MPPC4 receives the incident light, amplifies it, and outputs a detection current.

[0121] By adopting the above-described configuration, the area of ​​the MPPC 4 is less than one-tenth of the area of ​​the scintillator 9, making it possible to reduce the dark noise to one-tenth or less compared to the case where an MPPC 4 with the same area as the scintillator 9 is used.

[0122] Fig. 13 shows another embodiment of the present invention (part 3). Fig. 13 shows a configuration example in which signal electrons (secondary electrons, reflected electrons, etc.) are reduced in size using an electron lens 53 and input to a detector (scintillator 9 + MPPC 4). The rest of the configuration is the same as Fig. 11 and Fig. 12, so a description thereof will be omitted.

[0123] 13, electron lens 53 is an electrostatic lens or a magnetic lens that reduces signal electrons (secondary electrons emitted from sample 13, reflected electrons, etc.) from sample 13 to an area smaller than the aperture of electron lens 531. Here, the configuration is characterized in that, before being incident on scintillator 9, signal electrons (secondary electrons, etc.) generated and floating on the surface of sample 13 are accelerated by reducing their cross-sectional area using electron lens 531 such as an electrostatic lens or a magnetic lens having a first aperture, and then irradiated onto scintillator 9 having an area smaller than the first aperture or a part thereof. The signal electrons are detected by MPPC 4, which is a photon detection device smaller in size than the first aperture.

[0124] With the above-mentioned configuration, both the scintillator 9 and the MPPC 4 can be made small. Therefore, not only can the dark noise be reduced, but the cost of the scintillator 9 can be reduced because a small scintillator 9 is sufficient. In addition, since the size of the MPPC 4 can be made small, there is more freedom in the arrangement inside the microscope tube. Since no lenses or light guides are used, signal loss can be reduced, contributing to the formation of high-quality images. Since the detector can be made very small in this way, it is possible to arrange many detectors in one electron beam device and simultaneously measure groups of signal electrons that are generated when many electron beams are irradiated simultaneously onto the surface of the sample 13.

[0125] Fig. 14 shows an explanatory diagram (part 1) of another detector of the present invention. Fig. 14(a) shows an overall configuration diagram, and Fig. 14(b) shows an example of an electron beam aperture.

[0126] In FIG. 14(a), a projection lens 51 serves to collimate the primary electron beam generated by the electron gun 1.

[0127] The electron beam aperture 52 is for extracting a plurality of predetermined narrow portions from the parallel primary electron beam to form a plurality of primary electron beams, and is provided with a plurality of circular diaphragms, for example, as shown in Fig. 14(b). Such an aperture may be a blanking type aperture that can be opened and closed electrically.

[0128] The support portion 53 holds a detector including an MPPC 54 and a scintillator 53 .

[0129] The first reduction lens 56 is the first lens that reduces the size of the multiple primary electron beams that have passed through the electron beam aperture 52 .

[0130] The second reduction lens 57 is used to further reduce and narrow the multiple primary electron beams reduced by the first reduction lens 56, and to irradiate the multiple primary electron beams onto the sample 13 while performing planar scanning.

[0131] Next, the operation of the configuration in FIG. 14 will be described in detail.

[0132] (1) In Fig. 14, primary electron beam 31 generated by electron gun 1 is converted into a parallel beam by illumination lens 51, and then passed through primary electron beam aperture 52 to be shaped into multiple primary electron beams. The number of primary electron beams simultaneously irradiated onto the surface of sample 13 increases in proportion to the number of primary electron beams. If the primary electron beam passes through the center of electron beam aperture 52, it becomes difficult to position a secondary electron detection device so that the trajectories of the primary electrons and secondary electrons are separate, so it is desirable to provide multiple holes on the periphery.

[0133] (2) The multiple shaped primary electron beams pass through a support part 53 having holes to allow the primary electron beams to pass through, and then pass through a first reduction lens 56 and a second reduction lens 57 to compress the beam diameter, after which they are irradiated almost perpendicularly onto the surface of the sample 13.

[0134] (3) The irradiated electrons generate secondary electrons on the surface of sample 13. The generated secondary electrons are accelerated by a bias voltage (e.g., 10 KV) applied between sample 13 and a conductive film provided on the surface of scintillator 55, pass through the second reduction lens and the first reduction lens, and are then incident on scintillator 55. The bias voltage is adjusted so that the height of the scintillator becomes the focal position of the secondary electrons. In other words, it is adjusted so that an image of the primary electron spot is formed on the surface of the scintillator.

[0135] (4) The detector consisting of the scintillator 55 and MPPC 54 calculates the trajectory of the secondary electrons and is installed at the location where the secondary electrons return. The detectors may be arranged in a large number in an array in advance, and addresses or the like may be assigned to each element so that they can be electrically selected and used by a computer or the like as necessary. This function makes it possible to respond to changes in the trajectory of the secondary electrons that occur when the bias voltage is changed.

[0136] In this manner, the secondary electrons generated by irradiating the sample 13 with multiple split primary electron beams are detected simultaneously and in parallel by the respective detectors (scintillator 55, MPPC 54), making it possible to acquire images at high speed.

[0137] Fig. 15 shows an explanatory diagram (part 2) of another detector of the present invention. While Fig. 14 is composed of a support part 53, an MPPC 54, and a scintillator 55, Fig. 15 is composed of an MPPC 54, a transparent support part 531, and a scintillator 55. The other components are the same as those in Fig. 14, so the explanation will be omitted.

[0138] In Fig. 15, transparent support part 531 is characterized in that scintillator 55, which performs detection, is supported by a transparent member. The transparent member used for transparent support part 532 uses various optical elements such as lenses and holograms. By using these optical elements, it becomes possible to reduce, enlarge, or move the position of the light generated by scintillator 55. In other words, it becomes possible to place the electron detector anywhere.

[0139] Fig. 16 shows an explanatory diagram (part 3) of another detector of the present invention. Fig. 16 is characterized in that a mesh 58 is provided on the sample 13 of Fig. 15, and secondary electrons generated on the surface of the sample 13 are accelerated to a desired acceleration energy before being incident on the second reduction lens 57, thereby improving the detection efficiency of the secondary electrons.

[0140] 16, mesh 58 is a mesh provided on sample 13, and accelerates (for example, 5 KV) secondary electrons emitted from sample 13. This mesh 56 is provided on sample 13, and an acceleration voltage (for example, 5 KV) is applied to it to accelerate the secondary electrons, and the accelerated secondary electrons pass through second reduction lens 57 and first reduction lens 56, and are further accelerated to finally collide with scintillator 55. By accelerating the secondary electrons immediately after their generation, it is possible to prevent the generated secondary electrons from dispersing and scattering, and the detection efficiency can be improved.

[0141] Fig. 17 shows an explanatory diagram (part 4) of another detector of the present invention. In Fig. 17, in addition to Fig. 16, a mesh 59 is provided on the scintillator 55 so that the energy of the secondary electrons passing through the second reduction lens 57 and the first reduction lens 56 is kept constant and they proceed along the designed trajectory (they proceed along the designed trajectory without being affected by the mechanical shapes of the second reduction lens 57 and the first reduction lens 56).

[0142] In FIG. 17, mesh 59 is provided in front of scintillator 55 .

[0143] Mesh 58 is a mesh provided in front of sample 13. Here, meshes 59 and 58 are held at the same potential so that the secondary electrons passing through second reduction lens 57 and first reduction lens 56 are not affected by the surrounding geometric structure and follow a trajectory as designed. Here, for example, 5 KV (voltage for accelerating secondary electrons) is applied to mesh 58 as shown in the figure, and 10 KV (voltage for accelerating secondary electrons that have passed through mesh 59) is applied to mesh 58.

[0144] With the above-mentioned configuration, when a plurality of primary electron beams are irradiated onto sample 13 and scanned in parallel on a plane, secondary electrons and reflected electrons corresponding to the plurality of primary electron beams are emitted and reflected from sample 13, respectively. These emitted and reflected secondary electrons and reflected electrons are accelerated in parallel upward by mesh 58, pass through second contraction lens 57 and first reduction lens 56 with a constant energy, pass through mesh 59, and are accelerated in parallel by a positive voltage (e.g., 10 KV) applied between mesh 59 and scintillator 55, and are converted into light in parallel by scintillator 55. These converted lights are amplified and detected in parallel by MPPC 54, making it possible to output signals in parallel.

[0145] At this time, electrons accelerated to high energy (such as reflected electrons) take an inward orbit, while electrons accelerated to low energy (such as secondary electrons) take an outward orbit, and are detected and output in parallel by multiple divided detectors (scintillator 55, MPPC 54).

[0146] Fig. 18 shows an explanatory diagram (part 5) of the detector of the present invention. Fig. 18 is characterized in that it realizes a resolution higher than the size of the irradiated primary electron beam and can improve throughput. It will be explained in detail below.

[0147] (1) In Fig. 18, primary electrons are emitted from the electron gun 1, and then accelerated to a desired energy to generate a hollow electron beam (see Fig. 18(b)), which is then focused to one point by the objective lens 121 and irradiated onto the sample 13. An acceleration voltage of about 1 KV to 50 KV is used.

[0148] (2) A hollow electron beam (hollow beam) can be generated by uniformly irradiating a parallel electron beam onto an electron beam aperture 52 hollowed out in a concentric shape using an irradiation lens 51. The concentric holes may be formed by using many small holes to form a concentric shape, or may be rectangular or double-encircled. These apertures may be of the blanking aperture type that allows a large number of aperture arrays to be electrically opened and closed. A concentric aperture may be formed by selectively opening and closing a portion of the array. Furthermore, a grating lens or a thin-film lens that functions as a concave lens may be used to reduce aberration.

[0149] The electron beam aperture 52 is preferably made of a non-magnetic material such as titanium, MO, or W, and is preferably heated to 100° C. or higher to prevent contamination. It is also preferably conductive to prevent charging.

[0150] (3) The generated hollow electron beam is focused to a single point by the objective lens 121. The focused primary electron beam scans the XY plane by the deflection electrode 122. The deflection electrode 122 can be placed anywhere necessary, such as above or below the objective lens 121 (in FIG. 18, the electrostatic electrode 122 is placed below the objective lens 121).

[0151] (4) The focused primary electron beam is irradiated onto the sample 13, generating secondary electrons. The generated secondary electrons have very low energy and are emitted in all directions, so that they cannot form a point image with the objective lens 121 as is. In this embodiment, a positive acceleration voltage is applied to the mesh 58 directly above the sample 13, and almost all of the generated secondary electrons are accelerated to the desired energy. This acceleration voltage relatively reduces the energy variation of the secondary electron group, resulting in a secondary electron beam with one uniform energy. Therefore, the higher the energy, the better the energy uniformity.

[0152] (5) The secondary electrons accelerated to the desired energy pass through the objective lens 121 and finally collide with the scintillator 55, where they are accelerated or decelerated by the mesh 59 so as to optimize the light emission, and then collide with the scintillator and emit light. The emitted light is detected by each of the multiple divided parts of the MPPC 4, either directly or via a reflecting mirror (a highly sensitive CCD or CMOS device may also be used). (6) As shown in FIG. 18, the detected light point is an enlarged image of secondary electrons generated by the primary electron beam focused to a desired size by the objective lens 121. This point image is dynamically scanned in the XY direction in response to the deflection of the primary electron beam. The enlarged image of the light point contains information on the distribution of the amount of secondary electrons generated at the irradiation point of the primary electron beam. By performing image analysis using the scanning period of the primary electron beam to extract a detailed luminance distribution of the light point from the image, it is possible to extract changes in the sample surface in an area smaller than the spot size. In other words, the resolution of the primary electron beam optical system can be increased. This is just like drawing a picture with ten pencil leads bound together, and by measuring the luminance distribution and separating it into ten leads, an image with the resolution of each pencil drawing can be obtained.

[0153] (7) For example, if secondary electrons generated from a 10 nm primary electron beam spot size are magnified 10,000 times using an electron optical system and an optical system, they will become dots of about 100 microns. Since the minimum pixel size of current two-dimensional light detection devices is about 1 micron, the brightness distribution of these dots can be sufficiently separated and detected by a two-dimensional light detection device. If this point image is continuously extracted by a computer and divided into the brightness of each part corresponding to each pixel, and image processing such as rotation correction and brightness correction is performed at high speed to form an appropriate image, and the pixels are rearranged in the correct order so that a single image can be reconstructed, an image with a resolution smaller than the beam size can be obtained. These processes do not necessarily need to be performed in real time, so the necessary processes can be performed by an image processing computer after the image is acquired.

[0154] (8) For example, if the light spot is divided into four and each pixel is assigned to a different part, the same resolution as irradiating a beam size of 2.5 nm can be obtained, and the throughput can be four times higher. Normally, increasing the resolution results in a decrease in throughput, but this method has the advantage of being able to increase both the resolution and the throughput.

[0155] (9) In order to obtain higher resolution, it is very important that the scintillator components are uniform and fine. When using a particulate scintillator, high resolution can be obtained by making the particle size on the order of nanometers. Plastic scintillators, for example, are uniform at the nano level. Since a fluorescence microscope can achieve nano-order resolution, if separation is possible to that extent, one point can be separated into multiple beam components.

[0156] (10) The above method has the same effect as concentrating multiple beams in a multi-beam format in close proximity. On the other hand, contrary to the commonly known multi-beam method, only the axial center of the lens is used, so lens distortion is small and aberration correction is not required, making it easy to realize a multi-beam inspection device. This effect can be obtained whether the beam spot size is large or small, making it possible to realize an inspection device with high resolution and ultra-high speed, or low resolution and ultra-high speed. Conversely, if the beam size is made small from the beginning and the resolution of the photodetector is increased, it is possible to achieve a resolution of less than 1 nm and high throughput that was previously impossible to achieve. In particular, when achieving high resolution, it is easy to narrow the electron beam because the electron beam is less likely to spread due to electrostatic repulsion in a hollow beam.

[0157] Unlike conventional multi-beam inspection devices, the detected secondary electrons are pulled up vertically and detected directly without using a beam separator, resulting in less aberration and higher resolution and efficiency.

[0158] Furthermore, because the above method separates the beams using image analysis, the alignment direction of the beams, which is an issue with multi-beam inspection devices, is not an issue, and the method can be easily deployed in an inspection device that performs high-speed inspection by continuously moving the XY stage at a constant speed. [Brief description of the drawings]

[0159] [Figure 1] FIG. 1 is a configuration diagram of one embodiment of the present invention. [Diagram 2] FIG. 1 is an explanatory diagram (part 1) of a main part of the present invention. [Diagram 3] FIG. 2 is an explanatory diagram (part 2) of the main part of the present invention. [Figure 4] FIG. 3 is an explanatory diagram (part 3) of the main part of the present invention. [Diagram 5] FIG. 4 is an explanatory diagram of the main part of the present invention (part 4). [Figure 6] 1 is an example (part 1) of a detector according to the present invention. [Figure 7] 2 is a second example of a detector according to the present invention. [Figure 8] 13 is a third example of a detector according to the present invention. [Figure 9] 13 is a fourth example of a detector according to the present invention. [Figure 10] 5 is a fifth example of a detector according to the present invention. [Figure 11] FIG. 1 is a configuration diagram (part 1) of another embodiment of the present invention. [Figure 12] FIG. 2 is a configuration diagram (part 2) of another embodiment of the present invention. [Figure 13] FIG. 11 is a configuration diagram (part 3) of another embodiment of the present invention. [Figure 14] FIG. 2 is an explanatory diagram (part 1) of another detector according to the present invention. [Figure 15] FIG. 2 is an explanatory diagram (part 2) of another detector according to the present invention. [Figure 16] FIG. 4 is an explanatory diagram (part 3) of another detector according to the present invention. [Figure 17] FIG. 4 is an explanatory diagram (part 4) of another detector according to the present invention. [Figure 18] FIG. 5 is an explanatory diagram (part 5) of another detector according to the present invention. [Explanation of symbols]

[0160] 1: Electron gun 2: Electron gun control device 3: Deflection electrode 3-1: Deflection electrode (top) 3-2: Deflection electrode (bottom) 31: Primary electron beam 32: Secondary electron 321: Secondary electron detector 322: Electron beam scanning control device 33: Backscattered electron 331: Backscattered electron detector 34: Detector (first detector + second detector) 4, 54: MPPC 41: Shielded tube 411: Quenching resistor 42: Avalanche photodiode 421: Support glass 43: Bias power supply 431, 47: Folding screen 44: Current detection device 441: Support part 45, 91: Light guide 46: Lens 5: Bias for blocking 51: Irradiation lens 52: Electron beam aperture 521: Hollow beam 522:Reflector 523: Optical magnifying lens 524: Optical 2D detector 53: Support part 531:Electron lens 532: Transparent support part 56: 1st reduction lens 57: Second reduction lens 6: Amplifier 61: Bias circuit 7: PC 8:Display device 9,55: Scintillator 10, 48, 93, 58, 59: Mesh 101:Energy Filter (EXB) 11: Umbrella 12, 121: Objective lens 122: Deflection electrode 13: Sample 131: Lens control circuit 14: Sample bias circuit

Claims

1. In an electron detection device for detecting electrons emitted from a sample, a hole directly above the sample through which a first primary electron beam generated by the electron gun passes; a shield tube that applies a potential to the hole to repel the signal electrons and the secondary electrons; an electron detection means disposed around the shield tube and in contact with both sides of a partition made of a plurality of electrodes to which a bias voltage is applied so that signal electrons and secondary electrons are repelled; the plurality of partitions serve to block the signal electrons and the secondary electrons generated by irradiation of the first primary electron beam from simultaneously entering the electron detection means adjacent to both sides of the partitions, a blocking means for dividing a detection range of the signal electrons and the secondary electrons so that the signal electrons and the secondary electrons come into the detection range, an electron detection device which irradiates a sample with the primary electron beam, generates signal electrons and secondary electrons, and raises the signal electrons and secondary electrons directly above the sample, thereby directly detecting the signal electrons and secondary electrons;

2. 2. The electron detection device according to claim 1, wherein said electron detection means is divided into four parts so as to be able to detect electrons independently.

3. 3. The electron detection device according to claim 1, wherein the electron detection means are arranged in an array.

4. 4. The electron detection device according to claim 1, wherein the electron detection means is a scintillator.

5. 5. An electron detection apparatus, wherein the device for detecting light from the scintillator of claim 4 is a two-dimensional light detection device.

6. 6. An electron beam inspection system comprising a multi-electron beam inspection system incorporating any one of claims 1 to 5.

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