JP2024086882A - Electron detection device and electron beam inspection device - Google Patents

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

The present invention relates to an electron detection device that detects electrons emitted from a sample.

Semiconductor devices are shrinking every year in accordance with Moore's Law, and the minimum feature size of cutting-edge devices, even in mass-produced devices, is now less than 20 nm. In order to achieve smaller feature sizes, exposure technology capable of forming smaller patterns is required.

Conventionally, laser light with a wavelength of 193 nm has been used for exposure, but because this has already far exceeded the limit of dimensions that can be optically resolved, in recent years, exposure technology that utilizes EUV light with a wavelength of 13.5 nm has been actively pursued.

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 20 nm generation exposure because they were unable to obtain the 100W to 200W light source power required for economical mass production.

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.

In principle, it is possible to create any number of small patterns by repeating immersion lithography using a laser beam with a wavelength of 193 nm several times. 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 caused by 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.

Not only memory devices with a simple structure, but also CPUs and logic devices require pattern reduction to expand their functions and reduce power consumption. Logic devices use complex patterns that do not repeat, so to create logic devices with double or triple exposure, a fairly complex pattern is required. In order to divide a pattern that can be realized with a single exposure into patterns on two photomasks so that it can be used with multiple exposures, extremely complex calculations are required. Depending on the pattern, the division calculation may diverge and the required result may not be obtained.

In order to avoid these complexities, a lithography facilitation technology called complementary lithography, which is mainly proposed by Intel (registered trademark), is being used. This exposure method is characterized by using a pattern in which a complex logic circuit is reduced to a simple L&S pattern like a memory circuit. 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.

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 a sequentially stacked manner, 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 for exposing 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. When producing masks, it is necessary to reduce the defect density more than ever before, as defects of a size that could be ignored in the past now affect device yields, and fine particles are also subject to observation.

These trends will not be limited to conventional 193 nm exposure, but will tend to increase exponentially in the future when EUV becomes practical, as similar multi-patterning techniques will be used at even smaller sizes in the future.

Due to the above requirements, photomasks are constantly being required to have higher resolution and faster defect inspections, and an effective method for meeting these requirements is the use of ultra-high speed electron beam inspection equipment.

Conventional electron beam inspection equipment provides sufficient resolution, but the inspection speed is slow and far from what is required.

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 life span. Increasing the speed also degrades the image SNR, making it difficult to achieve both high resolution and high inspection speed.

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

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 dead time of the APD, the input/output relationship is not constant, and the SNR and linearity of the acquired image deteriorate.

An object of the present invention is to provide an ultra-high speed electron detection device that enables high speed inspection using an electron beam, and a scanning electron beam inspection device incorporating said detection device.

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, 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.

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 stabilization 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 stabilization means into light, and a second detector that inputs the light converted by the first detector, amplifies it, and outputs an electrical signal.

At this time, 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 stabilizing the energy of the electron beam.

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

The second detector is an MPPC element in which multiple avalanche diodes are arranged in parallel.

The second detector is a ring-shaped disk with a hole in the center through which the primary electron beam passes, and is provided with multiple independent detectors that are divided into multiple parts in the circumferential direction.

In addition, the voltage applied to the energy stabilization means is adjusted so that only electrons emitted from the sample or reflected by the sample are detected and amplified by the first and second detectors.

It is also designed to be a scanning electron beam inspection device incorporating an ultra-high speed electron detector.

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, so that the response speed is fast and the dead time of the APD can be made small enough to be negligible, making it possible to avoid the counting loss phenomenon that occurred when a large number of electrons were irradiated, which was a problem in the past.

In addition, because the electrons emitted or reflected from the sample are first converted into light, they do not interact with the electron beam and can be transported freely to another location without loss. This means that even if there are multiple scintillator light sources, each can be detected independently and efficiently.

In addition, it is possible to obtain an electron detection device with a large input/output dynamic range. When a large amount of electrons or photons are incident, a large number of APDs operating independently each detect electrons or photons, so that electrons or photons can be detected with virtually no dead time. It is possible to detect small to large amounts of electrons with good linearity.

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 reduces dark noise caused by thermal noise that is proportional to the MPPC area.

In addition, by compressing or shrinking the electron group that is generated on the sample surface and drifts as it spreads, accelerating it and irradiating it on a small scintillator, the photons can be detected using a small scintillator and a small photon detection device, reducing 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.

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 is possible to prevent any adverse effects on the beam trajectory and aberration of the primary electrons.

In addition, because the scintillator has a very long lifespan, the entire electron detection device also has a very long lifespan, making it virtually maintenance-free.

In addition, a scanning electron beam inspection device incorporating the ultrafast 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 ultrafast speeds, allowing dimensional measurements and defect detection to be performed in a short time, greatly improving throughput. Since almost no maintenance is required, the operating rate of the device can be increased.

Figure 1 shows a configuration diagram of one embodiment of the present invention. In Figure 1, a primary electron beam 31 is irradiated onto a sample 13 while being planarly scanned, and the generated secondary electrons and reflected 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. This configuration makes it possible to detect signal electrons (secondary electrons, reflected electrons, etc.) at ultra-high speeds.

In FIG. 1, the electron gun 1 is a known type such as a hot cathode type, TFE, field emitter, or optically excited type that generates a primary electron beam 31.

The electron gun control device 2 is a well-known device that supplies high voltage, 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 the primary electron beam 31.

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

The electron beam scanning control device 322 applies a predetermined scanning voltage to the deflection electrode 3, narrowing the primary electron beam 31 onto the sample 13 and scanning it in the X and Y directions.

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 along the axis and to direct them toward the scintillator 9.

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.

The bias circuit 61 applies a bias voltage to the MPPC 4 (described later using Figure 6, etc.).

MPPC4 is an abbreviation for Multi-Pixel Photon Counter, and is a photon counting device that converts a Geiger mode APD (avalanche diode) into a multi-pixel device (described in detail using Figure 6, etc.).

The amplifier 6 amplifies the signal amplified by the MPPC 4.

PC7 is a personal computer that performs various processes and controls according to programs.

The display device 8 is a display that displays images, etc.

The scintillator 9 converts electrons (secondary electrons, reflected electrons, etc.) into light at ultra-high speed and amplifies it (described later).

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

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

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

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

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

Next, referring to Figures 2 to 5, we will explain in detail the 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.

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 placed on the entire front surface (reflected 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 placed 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.

In FIG. 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 FIG. 6 to FIG. 10 and their explanations), and has a backscattered electron detector 331 on the inside and a secondary electron detector 321 on the outside. Since high-energy backscattered electrons gather in the center and low-energy secondary electrons gather in the periphery, the backscattered electron detector 331 is provided in the center and the secondary electron detector 321 is provided outside it, so that the backscattered electrons and secondary electrons can be separated and detected separately.

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 placed 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 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, the inner backscattered electron detection unit 331, 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.

In addition, in FIG. 2B, the mesh 10 is placed only on the front side of the secondary electron detection unit 321, and not on the front side 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.

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 unit 321, while high-energy backscattered electrons reflected by the sample 13 can be detected and amplified by the inner backscattered electron detection unit 331.

In this case, 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 the 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%. 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 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, making it possible to convert it into the amount (number) of light that accurately corresponds to the number of secondary electrons. After being converted to light, the secondary electrons are amplified by a second detector, such as an MPPC4, making it possible to detect a signal corresponding to the number of secondary electrons.

In addition, 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 first detector, the scintillator 9, 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.

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

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 depending on the difference in their energy, and detect 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 amplify and detect high-energy electrons (reflected electrons, etc.) in the inner reflected electron detection unit 331.

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 section 321, and to amplify and detect high-energy electrons (reflected electrons, etc.) in the inner reflected electron detection section 331.

Figure 4 shows an explanatory diagram (part 3) of the main part of the present invention. In Figure 4, the secondary electron detector 321 in Figure 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. In other words, the opening is made large when viewed from the sample 13, and a mesh 10 is provided on the front to apply a high voltage (e.g., 10 KV), accelerating and drawing in the secondary electrons emitted from the sample 13, enabling efficient amplification and detection.

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 them.

Figure 5 shows an explanatory diagram of the main part of the present invention (part 4). In Figure 5, the electric potential of the mesh 10 is controlled to detect the difference.

Figure 5 (a) shows an example without bias (normal state with positive 10 kV applied to mesh 10). In the case of Figure 5 (a), as shown, both reflected electrons and secondary electrons can be detected by detector 34.

Figure 5(b) shows the state with bias. In the case of Figure 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 the secondary electrons cannot be detected and the high-energy reflected electrons can be amplified and detected.

As described above, if an arbitrary voltage is applied to the mesh 10, only electrons with energy equal to or greater than the applied voltage will 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.

Figure 6 shows an example of a detector of the present invention. Figure 6 shows the schematic configuration of MPPC4, which is the second detector that constitutes detector 34, with (a) in Figure 6 showing a photograph of the MPPC (perspective view), (b) in Figure 6 showing a schematic diagram, and (c) in Figure 6 showing an example of an equivalent circuit of the MPPC.

In FIG. 6A, the primary electron passage 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 backscattered electrons.

Figure 6(b) is a schematic diagram of the MPPC4 and the mesh 10 placed in front of it viewed from below (scintillator 9 is omitted). There is a primary electron passage hole in the center, and the mesh 10 is placed in front of the MPPC4. A positive high voltage (e.g., 10 KV) is applied to the mesh 10, and secondary electrons emitted from the sample 13 are accelerated to a certain energy, then collide with the scintillator 9 (not shown) placed between the MPPC4 and the mesh 13 and converted into light, which is then incident on the MPPC4 shown in the figure for amplification and output as a signal.

Figure 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 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 become parallel and a pulse with approximately twice the peak is output. Similarly, when n photons are input simultaneously, n times the pulse is output.

The bias power supply 43 is a power supply that applies a bias voltage to D1 to maintain it in the Geiger mode.

The current detection device 44 detects the pulse current generated by D1 and converts it into a voltage signal.

By using an MPPC4 having the above-described 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 MPPC4.
Next, the features of the MPPC in FIG. 6 will be described.

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.

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 array of the MPPC4, 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 rate of up to 1 million times. Of course, a voltage with a different amplification rate may be set.

A quenching resistor R1 with a fixed value for current limiting is connected to each APD, and a constant voltage is applied to the terminals, so 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 detection device 44 connected to the output terminal.

Since MPPC4 has a large number of APDs arranged spatially, the probability that incident photons will be incident on the same APD is extremely small. Therefore, for example, when one photon is input to MPPD4, one unit of current is generated, and when N photons are input simultaneously, N units of current are generated. Due to this property, it is possible to know from the output current how many photons or electrons are simultaneously incident on MPPC4. 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 use in imaging. The current output by each APD element depends on the value of quenching resistor R1 and is not strictly constant, so a standardization process can be performed on a computer to make it strictly constant.

As a signal summing method, a digital MPPC can be used in which whether or not each APD is in an avalanche state is first 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 APDs in an avalanche state, which is used as the total output of the entire MPPC4. In this case, since the output has already been converted into a digital signal, 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.

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

Figure 7 (a-1) shows a top view of the detector 34, and Figure 7 (a-2) shows a cross-sectional view, showing an example of the configuration when the mesh 10 is not present.

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 while irradiating it.

(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 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 collection efficiency of the secondary electrons.

In addition, in (b-1) and (b-2) of FIG. 7, 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. 7, 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. 7, so a description is omitted.

Here, we explain the configuration in Figure 7 in detail.

In FIG. 7, the primary electron beam 31 generated and accelerated by the electron gun 1 in FIG. 1 is reduced to the desired beam spot size by the 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 the signal electrons tend to be distributed symmetrically with respect to the primary electron beam axis. In order to efficiently detect the signal electrons, it is necessary to provide a hole (primary electron beam hole) for the primary electrons to pass through in the center of the detector and place it near the primary electron beam axis.

For this reason, as shown in (a-1) and (b-1) of FIG. 7, a scintillator 9 is provided 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 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. The scintillator 9 may be an inorganic scintillator, a direct transition type semiconductor scintillator, a ceramic material or a plastic scintillator containing heavy atoms, a halide scintillator that uses inner shell transition light emission, or a liquid, etc.

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 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 so that they do not enter the gap and head towards the detector.

When accelerating electrons to make the scintillator 9 glow in front of the detector, as shown in Figures 7(b-1) and 7(b-2), a conductive mesh 10 with a high aperture ratio (preferably 90% or more) is placed several mm away from the scintillator 9, and a voltage of about 1 to 10 kV is applied between the mesh 10 and a 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 maintain this space in a vacuum state of more than 10-3 Pascals to prevent discharge.

Figure 8 shows an example (part 3) of a 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.

Figure 8 (a-1) shows a top view of the detector 34, and Figure 8 (a-2) shows a cross-sectional view, showing an example of the configuration when the mesh 10 is not present.

In (a-1) of FIG. 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 become a point, and are irradiated onto the sample 13 while performing planar scanning.

(a-2) in FIG. 8 shows a cross-sectional view. Secondary electrons emitted from the sample 13 are accelerated and attracted by the 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 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, making it possible to improve the detection efficiency.

In addition, in (b-1) and (b-2) of FIG. 8, the mesh 10 is provided between the sample 13 and the scintillator 9 shown in the figure, and 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 V to several tens of V) 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 the explanation is omitted. In this case, it becomes possible to detect secondary electrons and reflected electrons in the center part of the detector composed of the scintillator 9 and the MPPC 4, and it becomes possible to improve the detection efficiency.

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 a high-current electron beam is used. 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 shield tube 41 through which primary electrons pass is provided around it. If necessary, a scintillator 9 can also be placed outside the ring-shaped shield tube 41. By doing so, 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 shield tube 41.

Figure 9 shows an example (part 4) of a detector of the present invention. Figure 9 shows a schematic configuration in which the first detector, the scintillator 9, and the MPPC 4, which are the second detectors constituting the detector 34, are divided into, for example, four in the circumferential direction and incorporated into the device of Figure 1.

Figure 9 (a-1) shows a top view of the detector 34, and Figure 9 (a-2) shows a cross-sectional view, showing an example of the configuration when the mesh 10 is not present.

In (a-1) of Figure 9, 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 431 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 the objective lens 12 of Figure 1 to irradiate the sample 13 and perform a planar scan.

(a-2) in 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 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.

In addition, in (b-1) and (b-2) of FIG. 9, 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 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. 7, so a description is omitted.

Here, the configuration 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 and 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.

As shown in FIG. 9, a shield tube 41 is provided where the primary electron beam passes, and electrically independent detectors are arranged so as to be axially symmetrical with respect to the axis of the primary electron beam. They are also arranged at the same height. The detectors may be arranged not only in a planar manner, but also three-dimensionally in the height direction along the axis of the primary electron beam.

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 electrical signal is sent to the amplifier.

Figure 10 shows an example (part 5) of a detector of the present invention. Figure 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 parts in the circumferential direction, and a smaller MPPC 4 is used by focusing light with a light guide 45 ((a-1) and (a-2) in Figure 10) and a lens 46 ((b-1) and (b-2) in Figure 10), and this is incorporated into the device of Figure 1.

Figure 10 (a-1) shows a top view of the detector 34, and Figure 10 (a-2) shows a cross-sectional view, showing an example of the configuration when the mesh 48 is not present.

In (a-1) of Figure 10, 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 parts. The primary electron beam passes through the central hole from top to bottom, and is narrowed by the objective lens 12 of Figure 1 to irradiate the sample 13 and perform a planar scan.

Figure 10 (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 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.

In addition, in (b-1) and (b-2) of FIG. 10, 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. In addition, in (b-2) of FIG. 10, instead of the light guide 45 in (a-2) of FIG. 10, 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 (a-1) and (a-2) of FIG. 10, so a description is omitted.

Here, the configuration of FIG. 10 will be described in detail. FIG. 10 shows an example in which light generated by the scintillator 9 due to electron beam irradiation is reduced and irradiated to the MPPC4. Unlike a single APD, the MPPC4 has the excellent feature that even if the total area of the MPPC4 is increased, the electrical capacity of each APD does not increase, so there is no deterioration in the electron detection speed. 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, but if a cooling device is provided inside the vacuum device, the device becomes extremely complex, 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.

In this invention, we have focused on this point and succeeded in making the area of the MPPC 4 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 determined using experiments or electron trajectory simulation, and a scintillator 9 of a necessary and sufficient size is placed at that location.

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 focused or its cross-sectional area is reduced using optical elements (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 as small an MPPC 4 as possible.

Here, it is desirable that the dimensions of each APD constituting the APD array in the MPPC4 used are as small as possible (several microns or less), the number of elements is tens of thousands or more, and the area of the MPPC4 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 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 members and insert a new anti-reflection film to prevent unnecessary reflection from occurring and signal loss. Furthermore, a wavelength selection optical filter may be inserted in between to select the wavelength component incident on the MPPC4.

Figure 11 shows a diagram of another embodiment of the present invention (part 1). This figure 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. The rest of the configuration is the same as in Figure 1, so a description is omitted.

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

The MPPC4 is a device in which a large number of APDs, each measuring several microns on a side, are arranged in an array. When a bias voltage is applied to an APD, the gain is initially the same as that of a normal photodiode. However, once the threshold voltage of about 50V is exceeded, the gain increases dramatically, and finally it reaches an operating 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 is performed when a single electron is generated due to internal thermal fluctuations, so it is not possible to distinguish between a single incident electron (photon) and an electron generated by heat. These therefore 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 greater the noise.

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.

As described above, these two requirements are in conflict with each other. In order to resolve this conflict, the present invention has found a way 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 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.

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 detection device, where it is converted into electric current. In this way, it is possible to achieve both highly efficient detection and low dark noise.

Figure 12 shows a diagram of another embodiment of the present invention (part 2). This figure 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 rest of the configuration is the same as in Figure 1, so a description will be omitted.

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, etc., 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.

By adopting the above configuration, the area of the MPPC4 is less than one-tenth the area of the scintillator 9, making it possible to reduce dark noise to one-tenth or less compared to when an MPPC4 with the same area as the scintillator 9 is used.

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

In FIG. 13, the electron lens 53 is an electrostatic lens or a magnetic lens that reduces the signal electrons (secondary electrons emitted from the sample 13, reflected electrons, etc.) from the sample 13 to an area smaller than the aperture of the electron lens 531. Here, the signal electrons (secondary electrons, etc.) generated and floating on the surface of the sample 13 are accelerated by reducing their cross-sectional area using an electron lens 531 such as an electrostatic lens or a magnetic lens with a first aperture before being incident on the scintillator 9, and then irradiated onto the scintillator 9 or a part thereof having an area smaller than the first aperture. The signal electrons are detected by the MPPC4, a photon detection device smaller in size than the first aperture.

By configuring as described above, both the scintillator 9 and the MPPC4 can be made small. This not only reduces dark noise, but also reduces the cost of the scintillator 9, as a small scintillator 9 is sufficient. Furthermore, since the size of the MPPC4 can be made small, there is more freedom in its placement within the telescope tube. As no lenses or light guides are used, signal loss can be reduced, contributing to the formation of high-quality images. As 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 that are generated when many electron beams are irradiated simultaneously onto the surface of the sample 13.

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

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

The electron beam aperture 52 is used to extract multiple narrow portions from the parallel primary electron beam to form multiple primary electron beams, and is provided with multiple circular apertures, for example as shown in FIG. 14(b). Such an aperture may be a blanking type aperture that can be opened and closed electrically.

The support portion 53 holds the detector consisting of the MPPC 54 and the scintillator 53.

The first reduction lens 56 is the first lens that reduces the multiple primary electron beams that pass through the electron beam aperture 52.

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.

Next, the operation of the configuration in Figure 14 will be described in detail.

(1) In FIG. 14, the primary electron beam 31 generated by the electron gun 1 is converted into a parallel beam by the illumination lens 51, and then passed through the 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 the 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 the 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.

(2) The multiple molded primary electron beams pass through a support part 53 having holes through which the primary electron beams can pass, 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.

(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, pass through the second reduction lens and the first reduction lens, and are then 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.

(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 needed. This function makes it possible to respond to changes in the trajectory of the secondary electrons that occur when the bias voltage is changed.

In this way, 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.

Figure 15 shows an explanatory diagram (part 2) of another detector of the present invention. While Figure 14 is composed of a support part 53, an MPPC 54, and a scintillator 55, Figure 15 is composed of an MPPC 54, a transparent support part 531, and a scintillator 55. The rest of the configuration is the same as Figure 14, so the explanation is omitted.

In FIG. 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 is possible to reduce, enlarge, or move the position of the light generated by the scintillator 55. In other words, it becomes possible to place the electron detector anywhere.

Figure 16 shows an explanatory diagram (part 3) of another detector of the present invention. The feature of Figure 16 is that a mesh 58 is provided on the sample 13 of Figure 15, and the 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, improving the detection efficiency of the secondary electrons.

In FIG. 16, mesh 58 is a mesh provided on sample 13, and accelerates (e.g., 5 KV) the secondary electrons emitted from sample 13. Mesh 56 is provided on sample 13, and an acceleration voltage (e.g., 5 KV) is applied to it to accelerate the secondary electrons, which then 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 their generation, it is possible to prevent the generated secondary electrons from dispersing and scattering, and detection efficiency can be improved.

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 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).

In FIG. 17, mesh 59 is provided on the front surface of scintillator 55.

Mesh 58 is a mesh provided on the front surface of sample 13. Here, meshes 59 and 58 are held at the same potential, and 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 (a voltage that accelerates secondary electrons) is applied to mesh 58 as shown in the figure, and 10 KV (a voltage that accelerates secondary electrons that have passed through mesh 59) is applied to mesh 59.

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

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 split detectors (scintillator 55, MPPC 54).

Figure 18 shows an explanatory diagram (part 5) of the detector of the present invention. The detector shown in Figure 18 is characterized by achieving a resolution higher than the size of the irradiated primary electron beam and improving throughput. A detailed explanation is provided below.

(1) In FIG. 18, primary electrons are emitted from the electron gun 1, accelerated to the desired energy, and a hollow electron beam (see FIG. 18(b)) is generated, 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.

(2) A hollow electron beam (hollow beam) can be generated by uniformly irradiating a parallel electron beam onto an electron beam aperture 52 that has been 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 lattice lens or thin-film lens that acts as a concave lens may be used to reduce aberration.

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 static electricity.

(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 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).

(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.

(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. 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 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 has secondary electron generation amount distribution information 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 bundled together, and by measuring the luminance distribution and separating it into ten leads, it is possible to obtain a resolution image drawn by each pencil.

(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 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. This point image is continuously extracted by a computer, and the brightness of each part is divided so that it corresponds to each pixel. 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.

(8) For example, if the light spot is divided into four and each pixel is assigned to a different part, the resolution can be obtained as if a beam size of 2.5 nm were used, and the throughput can be increased four-fold. 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.

(9) 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 nanometer level. Fluorescence microscopes can achieve nano-order resolution, so if separation to that extent is possible, one point can be separated into multiple beam components.

(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 unnecessary, 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, with a hollow beam, it is easy to narrow the electron beam because it is less likely to spread due to electrostatic repulsion.

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.

In addition, 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, so this method can be easily deployed in an inspection device that performs high-speed inspection by continuously moving the XY stage at a constant speed.

FIG. 1 is a configuration diagram of an embodiment of the present invention. FIG. 1 is an explanatory diagram (part 1) of a main portion of the present invention. FIG. 2 is an explanatory diagram (part 2) of the main part of the present invention. FIG. 3 is an explanatory diagram of a main part of the present invention (part 3). FIG. 4 is an explanatory diagram of a main part of the present invention. 1 is a diagram showing an example (part 1) of a detector according to the present invention. 2 is a second example of a detector according to the present invention. 13 is a third example of a detector according to the present invention. 13 is a fourth example of a detector according to the present invention. 5 is a fifth example of a detector according to the present invention. FIG. 1 is a configuration diagram (part 1) of another embodiment of the present invention. FIG. 2 is a configuration diagram (part 2) of another embodiment of the present invention. FIG. 11 is a configuration diagram (part 3) of another embodiment of the present invention. FIG. 13 is an explanatory diagram (part 1) of another detector according to the present invention. FIG. 2 is an explanatory diagram (part 2) of another detector according to the present invention. FIG. 4 is an explanatory diagram (part 3) of another detector according to the present invention. FIG. 4 is an explanatory diagram (part 4) of another detector according to the present invention. FIG. 5 is an explanatory diagram (part 5) of another detector according to the present invention.

1: Electron gun 2: Electron gun control device 3: Deflection electrode 3-1: Deflection electrode (upper)
3-2: Deflection electrode (bottom)
31: Primary electron beam 32: Secondary electrons 321: Secondary electron detector 322: Electron beam scanning control device 33: Reflected electrons 331: Reflected electron detector 34: Detector (first detector + second detector)
4, 54: MPPC
41: Shield tube 411: Quenching resistor 42: Avalanche photodiode 421: Support glass 43: Bias power supply 431, 47: Partition 44: Current detection device 441: Support 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 two-dimensional detector 53: Support 531: Electron lens 532: Transparent support 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 (4)

In an electron detection device for detecting electrons emitted from a sample, the device comprises: an aperture through which a first primary electron beam generated by an electron gun passes;
a shield tube disposed in the hole for applying a potential to repel secondary electrons;
an electron detection means disposed around the shield tube;
a blocking means for blocking electrons generated by irradiation of the first electron beam from entering the adjacent electron detection means,
An electron detection device characterized in that secondary electrons generated by irradiating a sample with the primary electrons are pulled up directly upward and the secondary electrons are directly detected. The electron detection device according to claim 1, characterized in that the electron detection means is divided into four parts so that electrons can be detected independently. The electron detection device according to any one of claims 1 to 2, characterized in that the electron detection means are arranged in an array. An electron beam inspection device incorporating any one of claims 1 to 3 into a multi-electron beam inspection device.

Images