Electron detection device and electron beam inspection device

Abstract

PURPOSE: To detect electrons emitted from a sample with high sensitivity and low noise in an electron detection device and an electron beam inspection device.CONSTITUTION: An electron detection device includes: an electronic gun that emits an electron beam: an objective lens that reduces the emitted electron beam and irradiates a sample with it; an electron beam scanning device that performs planar scanning of the electron beam with which the sample is irradiated; a scintillator that converts electrons emitted from the sample by the electron beam irradiated by the electron beam scanning device into light; an MPPC that receives light from the scintillator and converts it into an electrical signal; and a passage hole for a primary electron beam formed at the center of the MPPC. The electron detection device is configured to detect light converted by the scintillator as an electric signal to detect electrons with high sensitivity and low noise.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Semiconductor devices are shrinking every year in accordance with Moore's Law, and cutting-edge devices are reaching the mass production stage. Even the latest devices have minimum feature sizes of less than 20 nm. To achieve this character size, exposure technology capable of forming smaller patterns is required.

[0003] Conventionally, a laser beam with a wavelength of 193 nm has been used for exposure, but it can be optically resolved. As the dimensional limits have already been exceeded, in recent years, lithography technology that uses 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 not able to obtain the 100W to 200W light source power required for economical mass production, and so were skipped for use in 20nm generation exposure.

[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, an order of magnitude higher than conventional methods, and by the large roughness that results from the large molecular structure of the chemically amplified resist optimized for 193 nm exposure. Currently, double patterning, in which the exposure process is repeated twice, which is said to be the economic limit, is in practical use, and is used to achieve 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 enhanced and are becoming more and more popular. It is necessary to reduce the pattern size to reduce power consumption. To utilize complex patterns without defects, logic devices can be exposed by double or triple exposure. To create such a pattern, a fairly complex pattern is required. It is very difficult to separate the patterns on the two photomasks so that they can be used for multiple exposures. Complex calculations are required for the required results. may not be obtained.

[0008] To avoid these complications, a method called complementary lithography is used. The lithography facilitation technology proposed by Intel (registered trademark) is about to be used in 2018. This exposure method is characterized by using patterns that reduce complex logic circuits to simple L&S patterns like memory circuits. By doing so, the complex logic device patterns are limited to the L&S patterns that are easiest to expose and the process of cutting those lines, so complex pattern division calculations are not required, the process is simple, and calculations suggest that it can be used 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 separate exposure, resulting in the need for more frequent mask inspections and more precise measurements than ever before. For example, in double patterning, two photomasks are used in sequentially stacked fashion, making the absolute positional accuracy and alignment precision of the lines formed on the masks between the two masks more important than ever before. Optical corrections for exposing finer patterns also become more complex and precise. Masks using inverse lithography, for example, use higher-order diffracted light, making the pattern size used for correction even smaller. In mask production, defects of a size that were previously negligible now affect device yield, so defect densities must be reduced more than ever before, and even small particles must be observed.

[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, which will tend to increase the amount of inspection required exponentially.

[0011] Due to these requirements, photomasks are constantly being required to have higher resolution and faster defect inspection. An effective method to meet these demands is the use of ultra-high speed electron beam inspection equipment. DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0012] Conventional electron beam inspection devices have sufficient resolution, but have had the problem 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 impossible to achieve both high resolution and high inspection speed.

[0014] To overcome this problem, 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 with conventional methods, new issues arise in that counting errors 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 the The object is to provide a scanning electron beam inspection device 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 on the order of ps to ns, which is large enough to detect signal electrons, and then the light generated by the scintillator is 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 the 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 stabilizing 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 stabilizing the energy of the electron beam.

[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 with a hole in the center to allow the primary electron beam to pass through, and is provided with a plurality of independent detectors formed by dividing the ring-shaped disk into a plurality of sections 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] In addition, the scanning electron beam inspection device incorporates an ultra-high speed electron detector. [Effects 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. This provides a fast response speed and makes it possible to minimize the dead time of the APDs so that it can be ignored, thereby making it possible to avoid the counting loss phenomenon that occurs when a large number of electrons are irradiated, a problem that has been encountered in the past.

[0026] In addition, because the electrons emitted or reflected from the sample are converted into light, they do not interact with the electron beam and can be transported freely to another location without loss. This allows for efficient independent detection even when there are multiple scintillator light sources.

[0027] Furthermore, an electron detector with a wide input / output dynamic range can be obtained. When a large amount of electrons or photons is incident, many APDs operating independently detect the electrons or photons, so 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 and irradiated onto an MPPC with a smaller area for detection, which reduces dark noise due to thermal noise that is proportional to the MPPC area.

[0029] Furthermore, by compressing or shrinking the electron groups that are generated on the sample surface and drifting as they spread, and then accelerating and irradiating them onto a small scintillator, the photons can be detected using 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 secondary electrons can be localized by using a conductive mesh with a large opening ratio and a shielding tube on the scintillator, which prevents adverse effects on the beam trajectory and aberration of the primary electrons.

[0031] Furthermore, 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] Furthermore, a scanning electron beam inspection device incorporating the ultra-high speed electron detector of the present invention can detect electron beams emitted or reflected from a sample (e.g., a mask or semiconductor wafer) at ultra-high speed, allowing for dimensional measurement, defect detection, etc. to be performed in a short time, greatly improving throughput. Since there is almost no maintenance required, the availability of the device can be increased. Example 1

[0033] Fig. 1 shows the configuration of one embodiment of the present invention. In Fig. 1, a primary electron beam 31 is irradiated onto a sample 13 while being scanned in a plane, 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, and a signal is output, making it possible to detect signal electrons (secondary electrons, backscattered electrons, etc.) at ultra-high speed.

[0034] In FIG. 1, the 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 photoexcited type.

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

[0036] The deflection electrode 3 is a well-known two-stage deflection electrode consisting of a deflection electrode (upper) 3-1 and a deflection electrode (lower) 3-2, which are applied in pairs in the X and Y directions with predetermined deflection voltages to deflect the primary electron beam 31 in two stages and scan it over the sample 13 in the X and Y directions.

[0037] The electron beam scanning 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 used to apply 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 toward 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 (details will be described 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, backscattered electrons, etc.) into light at an ultra-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 the sample 13 by a sample bias circuit 14 as required.

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

[0051] Next, referring 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 ultra-high speed using the scintillator 9 and MPPC 4 of Figure 1.

[0052] Figure 2 shows an explanatory diagram (part 1) of the main parts of the present invention. Figure 2(a) shows an example in which the mesh 10 is arranged over the entire front surface (backscattered electron detection section 331 and secondary electron detection section 321) of the detector (first detector + second detector), and Figure 2(b) shows an example in which the mesh 10 is arranged over 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] 2(a), the detector (first detector+second detector) 34 is a detector having 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 descriptions), and has a backscattered electron detection unit 331 on the inside and a secondary electron detection unit 321 on the outside. Since high-energy backscattered electrons gather at the center and low-energy secondary electrons 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, making it possible to separate the backscattered electrons and secondary electrons and detect them separately.

[0054] The mesh 10 is applied with a positive voltage to accelerate low-energy secondary electrons emitted from the sample 13. Here, an example is shown 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, high-energy backscattered electrons reflected from the sample 13 form a Gaussian distribution upward on the axis, and many are detected by the backscattered electron detection unit 331 shown in the figure, which is closer to the axis. On the other hand, low-energy secondary electrons emitted from the sample 13 are accelerated toward the mesh 10 to which a high voltage is applied, and collide with the secondary electron detection unit 321 shown in the figure, and some further collide with the backscattered electron detection unit 331 further 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 being detected.

[0055] In addition, in FIG. 2(b), the mesh 10 is arranged only in front of the secondary electron detection unit 321 and not in front of the backscattered 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 detector (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 unit 321, while high-energy backscattered electrons reflected by the sample 13 are detected and amplified by the inner backscattered electron detection unit 331.

[0057] In this case, when the primary electron beam 31 is narrowed by the objective lens 12 and irradiated onto the sample 13, the energy of the emitted secondary electrons is 0.1 eV to several eV. These electrons are accelerated by the 10 kV applied to the mesh 10, so that 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, or approximately ±0.01%. In other words, the secondary electrons emitted from the sample 13 are accelerated by the 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 a constant energy of approximately ±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, where it can be converted 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, such as an MPPC 4, and a signal corresponding to the number of secondary electrons can be detected.

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

[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 the sample 13 and the detectors (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, respectively.

[0060] 3, EXB101 is an energy filter that applies both an electric field and a magnetic field to separate electrons (backscattered electrons, secondary electrons) by varying the deflection angle as shown in the figure depending on the difference in their energies, and detects each electron 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 (backscattered electrons, etc.) in the inner backscattered electron detection unit 331.

[0061] As described above, by placing 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 unit 321, and to amplify and detect high-energy electrons (backscattered electrons, etc.) in the inner backscattered electron detection unit 331.

[0062] Fig. 4 shows an explanatory diagram (part 3) of the main part of the present invention. In Fig. 4, the secondary electron detector 321 of 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 are efficiently collected by making the opening larger when viewed from the sample 13, and providing a mesh 10 on the front surface 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 (for example, 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 which the potential of the mesh 10 is controlled to detect the difference.

[0065] 5(a) 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. 5(a), as shown in the figure, the detector 34 can detect both reflected electrons and secondary electrons.

[0066] Figure 5(b) shows a state with a bias. In this case, for example, a voltage (a negative voltage of several volts to several tens of volts) is applied to the mesh 10 so that secondary electrons are reflected and cannot be detected, so secondary electrons cannot be detected and 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 can collide with the detector 34 and be 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 MPPC 4, which is a second detector constituting the detector 34, with Fig. 6(a) showing a photograph (perspective view) of the MPPC, 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 scanned across the surface of the sample 13 while irradiating it, emitting secondary electrons and reflecting backscattered electrons.

[0070] 6(b) is a schematic diagram (scintillator 9 is omitted) of the MPPC 4 viewed from below and the mesh 10 placed in front of it. 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, converting them into light. This light is then incident on the MPPC 4 shown in the figure, amplified, and a signal is output.

[0071] Figure 6(c) shows an example of an MPPC equivalent circuit. The MPPC4 is configured by arranging multiple D1 (avalanche diodes) in parallel as shown, and then connecting R1 (quenching resistors) in series with each other, and then connecting these in parallel. When light is input to one D1 (avalanche diode), that D1 in Geiger mode discharges and current flows. As the current flows, R1 (quenching resistor) limits the current, causing it to fall below the discharge voltage, stopping the discharge and outputting a single pulse. When two photons are input simultaneously, they are parallelized, and a pulse with approximately twice the peak is output. Similarly, when n photons are input simultaneously, n times the pulse is output.

[0072] The bias power supply 43 is a power supply that applies a bias voltage to D1 to maintain the Geiger mode state.

[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-described configuration, secondary electrons emitted from the sample 13 and reflected electrons can be converted into light by the scintillator 9 at a constant energy level, and then the light can be 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 explained.

[0075] An MPPC4 is a device with an overall size of a few mm square, consisting of a large number of small APDs (D1) with a square of a few microns, as shown in Figure 6, arranged in parallel, ranging from tens to tens of thousands of them. This MPPC4 can be purchased from Hamamatsu Photonics (registered trademark), etc. Smaller devices can also be fabricated and used. It has a volume less than one ten-thousandth of that of a conventional PMT (photomultiplier tube). It is a plate-shaped solid-state element made of silicon, and is extremely robust because it does not have glass or vacuum-sealed parts like a PMT. The device itself is very light, weighing in the order of grams.

[0076] As shown in Figure 6(c), each APD (D1) that makes up the MPPC4 is electrically connected in parallel via a quenching resistor R1, which is used to control avalanche amplification. One end of the parallel circuit is connected to a bias power supply 43 of approximately 50 to 100 V to control the avalanche phenomenon, 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) that makes up the MPPC4 array, the bias voltage applied to the entire array is determined experimentally so that all APD (D1) elements that make up the array are in Geiger mode. When each APD in Geiger mode receives a single photon, avalanche amplification occurs with an amplification factor of up to one million times. Of course, a voltage with a different amplification factor may also be set.

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

[0078] Because the MPPC4 contains a large number of APDs spatially distributed, the probability that an incident photon will strike the same APD is extremely small. Therefore, for example, if one photon is input to the MPPC4, one unit of current is generated, and if N photons are input simultaneously, N units of current are generated. This property makes it possible to determine from the output current how many photons or electrons simultaneously entered the MPPC4. The output signal is an analog signal proportional to the number of incident photons, so it is converted to a digital signal using an AD converter and input into a PC for use in imaging. The current output by each APD element depends on the value of the quenching resistor R1 and is not strictly constant, so normalization processing 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 each APD is in an avalanche state or not 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 an avalanche state, which is used as the total output of the entire MPPC4. In this case, since the output is converted into a digital signal in advance, there is no need to convert it into a digital signal using an AD converter. 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 a second example of a detector according to the present invention, 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 shown in Fig. 1.

[0081] 7(a-1) shows a top view of the detector 34, and FIG. 7(a-2) shows a cross-sectional view thereof, which show an example of a configuration without the mesh 10. In FIG.

[0082] In (a-1) of Figure 7, 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, is narrowed by the objective lens 12 of Figure 1, and scans the sample 13 in a plane while irradiating it.

[0083] (a-2) in Figure 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 in this case) applied to the scintillator 9, collide with the scintillator 9, and are converted 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 instead travel in the direction of the positive voltage applied to the scintillator 9, improving the collection efficiency of the secondary electrons.

[0084] 7(b-1) and (b-2) show a configuration in which a mesh 10 is provided between the sample 13 shown in the figure and the scintillator 9, a positive acceleration voltage (5 kV in the figure) is applied between the mesh 10 and the scintillator 9 (a positive voltage is applied between the sample 13 and the scintillator 9 in FIGS. 7(a-1) and (a-2)), 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 FIGS. 7(a-1) and (a-2), so a description thereof will be omitted.

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

[0086] In Figure 7, a primary electron beam 31 generated and accelerated by the electron gun 1 in Figure 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 backscattered 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 the signal electrons tend to be distributed symmetrically with respect to the axis of the primary electron beam. To efficiently detect the signal electrons, a hole (primary electron beam hole) through which the primary electrons pass must be provided in the center of the detector and positioned near the axis of the primary electron beam.

[0087] For this reason, as shown in Figure 7(a-1) and (b-1), a scintillator 9 is mounted directly on the light-receiving surface of the MPPC 4, and the surface of the scintillator 9 is coated with a thin conductive aluminum film. The primary purpose of the aluminum film is to prevent incident electrons from charging the surface of the scintillator 9, but it also functions as an anti-reflection coating to prevent 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 it may be deposited directly by evaporation, CVD, or sputtering. The scintillator 9 may be an inorganic scintillator, a direct transition semiconductor scintillator, a ceramic material or a plastic scintillator containing heavy atoms, a halide scintillator that uses inner shell transition emission, or a liquid.

[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 area 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 and is a few millimeters in diameter and less than 1 mm thick. A gap inevitably forms between the detector and the shield tube 41. If electrons hit the gap, they will not be detected, so a conductive umbrella-shaped member is used to extend the electric field outward, repelling the electrons and preventing them from entering the gap and heading towards the detector.

[0089] When electrons are accelerated in front of the detector to make the scintillator 9 glow, a conductive mesh 10 with a high aperture ratio (preferably 90% or more) is placed a few mm away from the scintillator 9, as shown in Figures 7(b-1) and (b-2), 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 it. It is desirable to maintain this space in a vacuum state of more than 10-3 Pascals to prevent discharge.

[0090] Figure 8 shows a third example of a detector according to the present invention. It shows a schematic configuration in which the primary electron beam is ring-shaped and focused to a single fine point by an objective lens 12, which irradiates a sample 13 while scanning the sample across a plane. The rest of the configuration is the same as in Figure 7, so a description will be 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 an example of a configuration in which the mesh 10 is not provided.

[0092] In (a-1) of Figure 8, 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, are narrowed by the objective lens 12 to form a fine spot, and scan the sample 13 while irradiating it.

[0093] (a-2) in Figure 8 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 are converted into light. The converted light enters the MPPC 4, where it is amplified and output as 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 instead travel in the direction of the positive voltage applied to the scintillator 9, improving the collection efficiency of the secondary electrons. At this time, secondary electrons and backscattered electrons can be detected in the center of the detector composed of the scintillator 9 and the MPPC 4, thereby improving detection efficiency.

[0094] 8(b-1) and (b-2) show a configuration in which a mesh 10 is provided between the sample 13 shown in the figure and the scintillator 9, a positive acceleration voltage (5 kV in the figure) is applied between the mesh 10 and the scintillator 9 (a positive voltage is applied between the sample 13 and the scintillator 9 in FIGS. 8(a-1) and (a-2)), 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 FIGS. 8(a-1) and (a-2), so a description thereof will be omitted. In this case, secondary electrons and backscattered electrons can be detected in the center of the detector consisting of the scintillator 9 and MPPC 4, thereby improving the detection efficiency.

[0095] Here, Figure 8 is characterized by the use of a hollow electron beam (holo 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 onto 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 shield tube 41 through which primary electrons pass is provided around it. If necessary, scintillators 9 can also be placed outside the ring-shaped shield tube 41. This has the advantage that even if electrons (secondary electrons, backscattered 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 shield 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 that make up the detector 34 are divided into, for example, four parts in the circumferential direction and incorporated into the device of Fig. 1.

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

[0098] In (a-1) of Figure 9, 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, and the primary electron beam passes through the hole in the center from top to bottom, is narrowed by objective lens 12 of Figure 1, and scans the surface of sample 13 while irradiating it.

[0099] (a-2) in Figure 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 four-divided scintillator 9, collide with the scintillator 9, and are converted 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 instead travel in the direction of the positive voltage applied to the four-divided scintillator 9, 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-divided scintillator 9, and a positive voltage (for example, 50 V) is also applied between the four-divided scintillator 9 and the mesh 10, thereby efficiently collecting 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 4-channel (4-division) detector is used. The 4-channel 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 from each channel, 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 calibrated by multiplying them by an appropriate coefficient so that the output sensitivity of each channel is the same. Using this information makes it 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 symmetrically about 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 primary electron beam axis.

[0103] In addition, partition-like electrodes can be extended in all directions from the shield tube 41 through which the primary electron beam passes, surrounding the scintillator 9 and separating 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 partition 431. This repulsive force causes the electrons coming from the sample 13 to bend and fly towards the scintillator 9. The signal electrons are detected by each detector, and an electrical signal is sent to an amplifier.

[0104] Fig. 10 shows a fifth example of a detector of the present invention. Fig. 10 shows a schematic configuration in which the first detector, the scintillator 9 as the second detector, and the MPPC 4 that make up the detector 34 are divided into, for example, four parts in the circumferential direction, and a smaller MPPC 4 is used by focusing light using a light guide 45 ((a-1) and (a-2) in Fig. 10) and a lens 46 ((b-1) and (b-2) in Fig. 10), 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 an example of a configuration without the mesh 48.

[0106] In FIG. 10(a-1), the 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 47 to prevent electrons and light from entering the adjacent part. The primary electron beam passes through the hole in the center from top to bottom, is narrowed by the objective lens 12 in FIG. 1, and scans the surface of the sample 13 while irradiating it.

[0107] (a-2) in Figure 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 are converted 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 instead 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 illustrated sample 13 and the scintillator 9, a positive acceleration voltage (50 V in the illustration) is applied between the sample 13 and the four-divided scintillator 9, and a positive voltage (for example, 5 KV) is also applied between the four-divided scintillator 9 and the mesh 10, thereby efficiently collecting secondary electrons emitted from the sample 13. 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 FIGS. 10(a-1) and (a-2), so a description thereof will be omitted.

[0109] The configuration shown in Figure 10 will now be described in detail. Figure 10 shows an example in which light generated by the scintillator 9 upon electron beam irradiation is reduced and then irradiated onto the MPPC4. Unlike a single APD, the MPPC4 has the excellent advantage that increasing the overall area of ​​the MPPC4 does not increase the electrical capacitance of each APD, resulting in no degradation in electron detection speed. However, as the area of ​​the MPPC4 increases, the noise caused by thermal noise, known as dark noise, increases in proportion to the area. This noise is proportional to the absolute temperature and can be reduced by cooling. However, incorporating a cooling device inside the vacuum chamber would make the device extremely complex, increase its volume, increase costs, and make maintenance more difficult, potentially negating the advantages of the MPPC4. On the other hand, reducing the area of ​​the MPPC4 reduces the electron detection efficiency and degrades the image SNR.

[0110] In the present invention, we have focused on this point and succeeded in minimizing the area of ​​the MPPC 4 while maintaining high electron detection efficiency. First, the area of ​​the scintillator 9, which converts 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 determined using experiments or electron trajectory simulation, and a scintillator 9 of a necessary and sufficient size is placed at that location.

[0111] This increases 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 Figure 10 or the lens 46 in (b-2) of Figure 10) before being irradiated onto the MPPC 4. In this way, high electron detection efficiency is ensured by the large scintillator 9, and low dark noise is achieved by using an MPPC 4 that is as small as possible.

[0112] Here, it is desirable that the dimensions of each APD constituting the APD array in the MPPC 4 be as small as possible (a few microns or less), that the number of elements be tens of thousands or more, and that the area of ​​the MPPC 4 be 1 square millimeter or less. To reduce the light generated by the scintillator 9, methods such as using a light guide 45 as shown in Figure 10(a-2) or an optical lens 46 as shown in Figure 10(b-2) can be used. Furthermore, the vertical dimension can be shortened by using a reflecting mirror, a Fresnel lens, a holographic lens, or a diffractive element. When using a light guide or the like in contact with the photon detection device, it is desirable to match the refractive index of the contacting components and insert an anti-reflection film to prevent unwanted reflections and signal loss. Furthermore, a wavelength-selective optical filter may be inserted between the MPPC 4 and the light guide to select the wavelength components 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 electrons emitted from a sample 13 are accelerated to cause a scintillator 9 to emit light, and the light is reduced in area by a light guide 91 and incident on 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.

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

[0115] The MPPC4 is a device consisting of 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 initially exhibits the same amplification as a normal photodiode. However, once the threshold voltage of about 50V is exceeded, the gain increases dramatically, eventually reaching an operating mode known as Geiger mode, in which a single incident electron (or photon) is amplified nearly one million times. In Geiger mode, the MPPC4 is sensitive enough to detect a single electron incident from outside the device. However, the same amplification occurs when a single electron is generated due to internal thermal fluctuations. Therefore, it is impossible to distinguish between a single incident electron (photon) and an electron generated by heat. This results in noise. The generation of thermal electrons is proportional to the area of ​​the APD. In other words, the larger the APD's area, the more frequently thermal electrons are generated, resulting in increased noise.

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

[0117] As described above, the two requirements contradict each other. In order to resolve this contradiction, the present invention has found a method for achieving 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 as small an area as possible. Figure 11 shows an example in which a light guide 91 with different area ratios on the entrance and exit sides is used, with the larger area connected to the scintillator 9 and the smaller area 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. This makes it possible to achieve both highly efficient detection and low dark noise.

[0119] Fig. 12 shows a configuration diagram (part 2) of another embodiment of the present invention. Fig. 12 shows an example in which electrons emitted from a sample 13 are accelerated to cause a scintillator 9 to emit light, and the light is reduced in area by a lens 51 and incident on 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 Figure 12, lens 51 is a lens that reduces the size of 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 or 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 its cross-sectional area is reduced to one-tenth or less, and then incident on MPPC4, a photon detection device. Upon receiving the incident light, MPPC4 amplifies it and outputs a detection current.

[0121] By adopting the above 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 less than one-tenth of that when an MPPC 4 with the same area as the scintillator 9 is used.

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

[0123] 13, electron lens 53 is an electrostatic or magnetic lens that reduces signal electrons from sample 13 (secondary electrons emitted from sample 13, reflected electrons, etc.) 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 or magnetic lens, having a first aperture, and then irradiated onto scintillator 9 or a portion thereof, which has an area smaller than the first aperture. The signal electrons are detected by MPPC 4, a photon detector smaller in size than the first aperture.

[0124] By configuring it as described above, both the scintillator 9 and the MPPC 4 can be made small. This not only reduces dark noise, but also reduces the cost of the scintillator 9, since a smaller scintillator 9 is sufficient. Furthermore, the MPPC 4 can be made smaller, allowing for greater flexibility in its placement within the electron tube. Since no lenses or light guides are required, signal loss can be reduced, contributing to the formation of high-quality images. Because the detector can be made very small in this way, it is possible to place many of them in a single electron beam device and simultaneously measure the signal electron groups generated when many electron beams are irradiated simultaneously onto the surface of the sample 13.

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

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

[0127] The electron beam aperture 52 is used to extract 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 consisting of 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 and planarly scan the sample 13 with the multiple primary electron beams.

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

[0132] (1) In Figure 14, a primary electron beam 31 generated by an electron gun 1 is converted into a parallel beam by an illumination lens 51, and then passes through a 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 a sample 13 increases in proportion to the number of primary electron beams. If the primary electron beam passes through the center of the 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 formed multiple 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 the sample 13. The generated secondary electrons are accelerated by a bias voltage (e.g., 10 kV) applied between the sample 13 and a conductive film provided on the surface of the scintillator 55, and after passing through the second reduction lens and the first reduction lens, are incident on the 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. A large number of detectors may be arranged in an array in advance, and an address may be assigned to each element so that they can be electrically selected and used by a computer or the like as needed. This function makes it possible to respond to changes in the trajectory of the secondary electrons due to changes in the bias voltage.

[0136] In this way, the secondary electrons generated by irradiating the sample 13 with the 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 Fig. 14, so their explanation will be omitted.

[0138] In Figure 15, the transparent support part 531 is characterized in that the scintillator 55 that performs detection is supported by a transparent member. The transparent member used for the 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 the scintillator 55. In other words, the electron detector can be placed 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 entering the second reduction lens 57, thereby improving the detection efficiency of the secondary electrons.

[0140] 16, mesh 58 is a mesh provided above sample 13, and accelerates (for example, 5 KV) secondary electrons emitted from sample 13. Mesh 56 is provided above sample 13, and an acceleration voltage (for example, 5 KV) is applied 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 until they finally collide with scintillator 55. By accelerating the secondary electrons immediately after they are generated, it is possible to prevent the generated secondary electrons from dispersing and scattering, and the detection efficiency can be improved.

[0141] Figure 17 shows an explanatory diagram (part 4) of another detector of the present invention. In Figure 17, in addition to Figure 16, a mesh 59 is provided on top of 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 travel along the designed trajectory (they travel 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 the designed trajectory. Here, as shown in the figure, for example, 5 KV (voltage for accelerating secondary electrons) is applied to mesh 58, and 10 KV (voltage for accelerating secondary electrons that have passed through mesh 59) is applied to mesh 59.

[0144] With the above configuration, when multiple primary electron beams are irradiated onto sample 13 and scanned in parallel over a plane, secondary electrons and backscattered electrons corresponding to the multiple primary electron beams are emitted and reflected from sample 13, respectively. These emitted and reflected secondary electrons and backscattered electrons are accelerated in parallel upward by mesh 58, pass through second contraction lens 57 and first contraction lens 56 at a constant energy, and pass through mesh 59. A positive voltage (e.g., 10 KV) is applied between mesh 59 and scintillator 55, and the multiple secondary electrons and backscattered electrons are accelerated in parallel by scintillator 55, and are converted into light in parallel by scintillator 55. These converted light beams 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 backscattered electrons) take an inward orbit, while electrons accelerated to low energy (such as secondary electrons) take an outward orbit, so they are detected in parallel by multiple divided detectors (scintillator 55, MPPC 54) and output.

[0146] Figure 18 shows an explanatory diagram (part 5) of the detector of the present invention. Figure 18 is characterized by realizing a resolution higher than the size of the irradiated primary electron beam and improving throughput. This 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 a single 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 a concentrically cut electron beam aperture 52 using an irradiation lens 51. The concentric holes may be formed by using many small holes to form a concentric circle, or may be rectangular or double-surrounded. These apertures may be blanking apertures that electrically open and close a large number of aperture arrays. A concentric aperture may be formed by selectively opening and closing part of the array. Furthermore, a grating lens or thin-film lens that functions as a concave lens may be used to reduce aberrations.

[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 is scanned across the XY plane by the deflection electrode 122. The deflection electrode 122 can be placed where 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 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 in the secondary electron group, resulting in a secondary electron beam with a single 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. After being accelerated and decelerated by the mesh 59 to optimize light emission, the electrons 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 reflecting mirrors (high-sensitivity CCD or CMOS devices may also be used). (6) As shown in Figure 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 about the distribution of secondary electrons generated at the point of irradiation by the primary electron beam. By performing image analysis using the scanning cycle of the primary electron beam to extract the detailed brightness distribution of the light point from the image, it is possible to extract changes on 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 like drawing a picture using a bundle of ten pencil leads. If you measure the brightness distribution and separate the ten leads, you can obtain images with the resolution of each pencil.

[0153] (7) For example, if secondary electrons generated from a 10-nm primary electron beam spot are magnified 10,000 times using an electron-optical system and optical system, they will result in dots of approximately 100 microns. Since the minimum pixel size of current two-dimensional photodetection devices is approximately 1 micron, the brightness distribution of these dots can be easily separated and detected by a two-dimensional photodetection device. This point image is continuously extracted by a computer, 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. Then, the pixels are rearranged in the correct order so that a single image can be reconstructed. This processing does not necessarily have to be performed in real time; the necessary processing 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 parts and each part corresponds to a pixel, the same resolution as when irradiating with a 2.5 nm beam size can be obtained, and the throughput can be four times higher. Normally, increasing the resolution results in a decrease in throughput, but this method is characterized by its ability to increase both the resolution and the throughput.

[0155] (9) To achieve higher resolution, it is very important that the scintillator components are uniform and fine. When using a particulate scintillator, high resolution can be achieved by making the particle size nanometer-order. Plastic scintillators, for example, are uniform at the nanometer level. Fluorescence microscopes can achieve nanometer-order resolution, so if separation is possible to that extent, a single point can be separated into multiple beam components.

[0156] (10) The above method has the same effect as focusing multiple beams in close proximity in a multi-beam format. Conversely to commonly known multi-beam methods, this method utilizes only the axial center of the lens, resulting in minimal lens distortion and eliminating the need for aberration correction, making it easy to realize a multi-beam inspection system. This effect can be achieved regardless of whether the beam spot size is large or small, making it possible to realize high-resolution, ultra-high-speed inspection systems or low-resolution, ultra-ultra-high-speed inspection systems. Conversely, by reducing the beam size from the start and increasing the resolution of the photodetector, it is possible to achieve resolutions below 1 nm and high throughput, which were previously unachievable. In particular, when achieving high resolution, hollow beams make it easier to narrow the electron beam because they are less likely to spread due to electrostatic repulsion.

[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 so it can be easily deployed in inspection devices that perform high-speed inspections by continuously moving the XY stage at a constant speed. [Brief explanation of the drawings]

[0159] [Figure 1] FIG. 1 is a configuration diagram of an embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram (part 1) of the main part of the present invention. [Figure 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. [Figure 5] FIG. 4 is an explanatory diagram (part 4) of the main part of the present invention. [Figure 6] 1 is an example (part 1) of a detector according to the present invention. [Figure 7] 1 is a second example of a detector according to the present invention. [Figure 8] 10 is a third example of a detector according to the present invention. [Figure 9] 10 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. 10 is a configuration diagram (part 2) of another embodiment of the present invention. [Figure 13] FIG. 10 is a configuration diagram (part 3) of another embodiment of the present invention. [Figure 14] FIG. 1 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. 10 is an explanatory diagram (part 3) of another detector according to the present invention. [Figure 17] FIG. 10 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 of 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 (1st detector + 2nd detector) 4, 54:MPPC 41: Shielded pipe 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: Pass-through blocking bias 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: First 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, an electron gun that emits an electron beam; an objective lens that reduces the emitted electron beam and irradiates it onto a sample; an electron beam scanning device that scans the electron beam irradiated onto the sample in a plane; a scintillator that converts electrons emitted from a sample by the electron beam irradiated by the electron beam scanning device into light; an MPPC that receives light from the scintillator and converts it into an electrical signal; a passage hole for a primary electron beam formed at the center of the MPPC; The light converted by the scintillator is detected as an electrical signal by the MPPC, thereby detecting electrons with high sensitivity and low noise.

2. 2. The electron detection device according to claim 1, wherein the means for accelerating the energy of the electrons emitted from the sample is a bias voltage applied to the sample.

3. 3. The electron detection device according to claim 1, wherein the means for accelerating the energy of the electrons is a bias voltage applied to a mesh provided between the sample and the scintillator.

4. 4. The electron detection device according to claim 1, further comprising an energy filter for separating the accelerated electrons.

5. 5. The electron detection device according to claim 4, wherein the energy filter is a mesh.

6. 5. The electron detection device according to claim 4, wherein the energy filter is an EXB.

7. 7. An electron beam inspection device incorporating any one of claims 1 to 6.

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