JP2023112187A - Electron detection device - Google Patents

Abstract

PURPOSE: To provide an electron detection device capable of detecting an electron emitted from a sample with high sensitivity and low noise.CONSTITUTION: An electron detection device comprises: an electron optical system which enlarges a secondary electron or reflected electron emitted or reflected by a sample irradiated with a primary electron reduced to a smaller size, a first element which converts the enlarged image of the electron enlarged by the electron optical system into an enlarged image of light, a second element which detects the enlarged image of light converted by the first element with a plurality of divided parts respectively, and means which generates electron generation amount distribution information at the irradiation point of the sample based upon an image of pixels corresponding to the plurality of divided parts of the second element and a scanning signal of the primary electron beam, reduced to the smaller size, with which the sample is irradiated, and the electron detection device is configured to generate the electron generation amount distribution information at the point where the sample is irradiated with the primary electron.SELECTED DRAWING: Figure 18

Description

The present invention relates to an electron detector for detecting electrons emitted from a sample.

Semiconductor devices are shrinking every year according to Moore's law, and the minimum feature size of state-of-the-art devices is less than 20 nm even in mass-produced devices. Achieving small feature sizes requires exposure techniques that can form smaller patterns.

Conventionally, a laser beam with a wavelength of 193 nm has been used for exposure, but since it has already greatly exceeded the size limit that can be optically resolved, exposure technology using EUV light with a wavelength of 13.5 nm has been actively promoted in recent years. It is

This technology is said to originate in Japan, and has been researched and developed for practical use by companies such as ASML (registered trademark) for more than 10 years. The optical system of the main body of the exposure equipment is almost complete, but until a few years ago EUV exposure equipment could not obtain the light source power of 100W to 200W required for economical mass production, so it will be used for 20nm generation exposure that was skipped.

Instead, a so-called double or triple exposure technique has been developed, in which an even smaller feature size can be realized by repeating an existing exposure process using a wavelength of 193 nm multiple times.

In principle, any number of small patterns can be produced by repeating immersion lithography using a laser beam with a wavelength of 193 nm. 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 before, and the large roughness resulting from the large molecular structure of the chemically amplified resist optimized for 193 nm exposure. ing. At present, double patterning, which is said to be economically limited, and repeats the exposure process twice, is put into practical use, and is used to realize lines and spaces of 20 nm to 16 nm in memory devices with relatively simple structures. It is

Not only memory devices with simple structures, but also CPUs and logic devices need pattern reduction in order to expand functions and reduce power consumption. Since the logic device uses complex patterns without repetition, a fairly complex pattern is required to fabricate the logic device by double or triple exposure. A very complicated calculation is required in order to divide a pattern that can be realized by a single exposure into patterns on two photomasks so that it can be used by a plurality of exposures. Depending on the pattern, the required result may not be obtained due to divergence of division calculation.

In order to avoid these complications, a lithography facilitation technique 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 complicated logic circuit is reduced to a simple L&S pattern like a memory circuit. In this way, complicated logic device patterns are limited to the L&S patterns that are the easiest to expose and the process of cutting the lines, so there is no need for complicated pattern division calculations, and the process is simple and easy to calculate. It is said to go up to about 8 nm.

As described above, when complex exposure methods such as double patterning and triple patterning are used, the number of photomasks required increases with each divisional exposure, requiring more mask inspections and more precise measurements than ever before. become. For example, in double patterning, since two photomasks are sequentially stacked, the absolute position accuracy and alignment accuracy of lines formed on the mask between the two masks are more important than ever. Optical corrections for exposing finer patterns also become more complex and precise. A mask using inverse lithography uses up to high-order diffracted light, so the pattern size used for correction is even smaller. In the production of masks, it is necessary to lower the defect density more than before, for example, defects of a size that could be ignored in the past have an effect on device yield, and fine particles are also subject to observation.

These trends are not limited to conventional 193 nm exposure, and in the future, when EUV is put into practical use, the same multi-patterning technology will be used at even smaller sizes in the future, so the inspection requirements will increase exponentially. tend to go.

Due to the above requirements, photomasks continue to be required to be inspected for defects at higher resolution and at higher speed. An ultra-high-speed electron beam inspection system is one of the leading methods to meet these demands.

Although conventional electron beam inspection systems are adequate in terms of resolution, they suffer from inspection speeds that are far from what is required.

The main reason for this is that the electron detectors that can be used in conventional electron beam inspection systems have problems in terms of saturation characteristics, response speed, and lifespan, where the dynamic range is narrow and linearity is degraded. Therefore, there is a problem that resolution and inspection speed cannot be achieved at the same time.

In order to overcome this problem, the inventor previously proposed an ultrafast electron detection device that detects electrons by directly irradiating the APD with electrons (see Japanese Patent Application Laid-Open No. 2015-210998).

However, when trying to detect a large amount of current with high sensitivity using a single APD, the performance is much better than the conventional one, but due to the dead time of the APD, count loss occurs and the input/output relationship is not constant. , a new problem arises in that the SNR of the acquired image is degraded and the linearity is degraded.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ultrahigh-speed electron detector that enables high-speed inspection using an electron beam, and a scanning electron beam inspection apparatus incorporating the detector.

The present invention provides an ultrafast electron detector for detecting an electron beam emitted from or reflected by a sample at an ultrahigh speed, in which secondary electrons emitted from the sample or electrons reflected by the sample are once detected as signal electrons. After converting into light by applying it to an ultrafast scintillator plate having a response time of ps to ns order having a required size, the light generated by the scintillator is reduced directly or by a light guide or an optical lens, and light detection with a small area Irradiate the element.

Therefore, the present invention provides an ultrafast electron detector for detecting an electron beam emitted from a sample, an electron beam reflected by the sample, or both electron beams at an ultrahigh speed. energy constant means for converting the electron beam reflected by the sample or both electron beams into an electron beam of constant energy; and a first detector for converting the electron beam whose energy is constant by the energy constant means into light. , and a second detector that receives the light converted by the first detector, amplifies it, and outputs an electric signal.

At this time, the energy constant means applies a predetermined voltage between the sample or the mesh provided near the surface of the sample and the first detector or the mesh provided near the surface of the first detector. is applied to keep the energy of the electron beam constant.

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

Also, the second detector is an MPPC element in which a plurality of avalanche diodes are arranged in parallel.

The second detector is a ring-shaped disc having a hole in the center for passing the primary electron beam, and is provided with a plurality of independent detectors obtained by dividing the ring-shaped disc in the circumferential direction. I'm trying

Also, the voltage applied to the energy constant 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.

Also, a scanning electron beam inspection apparatus incorporating an ultra-high-speed electron detector is provided.

In the present invention, the second detector consists of an MPPC element consisting of a circuit in which a large number of APDs are arranged and electrically connected in parallel, so that the response speed is fast and the dead time of the APDs can be made small enough to be ignored. , it is possible to avoid the counting loss phenomenon that occurs when a large amount of electrons are irradiated, which has been a problem in the past.

In addition, since the electrons emitted or reflected from the sample are first converted into light, they do not interact with the electron beam, so they can be freely transported to another location without loss. As a result, even if there are a plurality of scintillator light emission sources, each can be efficiently detected independently.

Also, it is possible to obtain an electron detector having a large input/output dynamic range. Since a large number of APDs operating independently detect electrons and photons when a large amount of electrons or photons are incident, electrons or photons can be detected substantially without dead time. It can detect from a small amount of electrons to a large amount of electrons with good linearity.

In addition, since the light emitted by the scintillator can be reduced and irradiated to an MPPC having a smaller area for detection, dark noise due to thermal noise proportional to the MPPC area can be reduced.

In addition, by compressing or shrinking and accelerating a group of electrons that are generated on the sample surface and drift while spreading, and irradiating a small scintillator, the photons are detected by a small scintillator and a small photon detector, and the heat generated by the photon detection device noise can be reduced. Since the scintillator can be made smaller, the cost can be reduced, and a plurality of scintillators can be easily arranged in the column.

Also, a scintillator having a size or dimensions necessary for detecting electrons can be used. Alternatively, the electron lens collects the signal electrons spread in all directions and irradiates them onto the scintillator, so almost all the signal electrons generated on the sample surface can be detected.
In addition, since the electric field used for accelerating the secondary electrons can be localized by using the conductive mesh with a large aperture ratio and the shield tube provided on the scintillator, the beam trajectory and aberration of the primary electrons can be prevented from being adversely affected. .

Also, since the life of the scintillator is very long, the life of the entire electron detection device is also very long and can be almost maintenance free.

Further, in a scanning electron beam inspection apparatus incorporating the ultrafast electron detector of the present invention, an electron beam emitted or reflected from a sample (for example, a mask or a semiconductor wafer) is detected at an ultrahigh speed to measure dimensions and detect defects. and so on in a short time, and the throughput can be greatly improved. Since there is almost no maintenance, the operating rate of the equipment can be increased.

FIG. 1 shows a block diagram of one embodiment of the present invention. In FIG. 1, a sample 13 is irradiated with a primary electron beam 31 while being planarly scanned, and the generated secondary electrons and the reflected backscattered electrons are converted into light by a scintillator 9 as a first detector at an ultra-high speed. The MPPC 4, which is the second detector, amplifies the emitted light and outputs a signal. This makes it possible to detect signal electrons (secondary electrons, reflected electrons, etc.) at an ultra-high speed.

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

The electron gun controller 2 is a known device for supplying a high voltage, a bias voltage, a filament heating power supply in the case of a hot cathode electron gun, etc., so that the electron gun 1 generates a primary electron beam 31 .

The deflection electrode 3 is composed of a deflection electrode (upper) 3-1 and a deflection electrode (lower) 3-2, which are two-stage deflection electrodes, and is paired in the X and Y directions to apply a predetermined deflection voltage. , the primary electron beam 31 is deflected in two stages and scanned over the sample 13 in the X and Y directions.

The electron beam scanning controller 322 applies a predetermined voltage for scanning to the deflection electrodes 3, narrows the primary electron beam 31 on the sample 13, and scans the sample 13 in the X and Y directions.

The shield tube 41 prevents the secondary electrons emitted from the sample 13 from traveling upward on the axis and applies a negative voltage to direct them toward the scintillator 9 .

The pass-blocking bias 5 is a pass-blocking negative bias voltage for the shield tube 42 to prevent the secondary electrons emitted from the sample 13 from passing upward on the axis.

A bias circuit 61 applies a bias voltage to the MPPC 4 (described later with reference to FIG. 6 and the like).

MPPC4 is an abbreviation for Multi-Pixel Photon Counter, and is a photon counting device in which a Geiger mode APD (avalanche diode) is converted into multi-pixels (described in detail with reference to FIG. 6, etc.).

The amplifier 6 amplifies the signal amplified by MPPC4.

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

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

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

The mesh 10 applies an acceleration voltage for attracting secondary electrons emitted from the sample 13 .

The umbrella 11 forms an electric field such that the secondary electrons emitted from the sample 13 are accelerated by the voltage applied to the mesh 10 and efficiently collide with the scintillator 9 . The umbrella 11 is made of nonmagnetic and 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 sample (photomask, wafer, etc.) to be observed, inspected, or measured, and a bias voltage is applied by the sample bias circuit 14 as necessary.

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

Next, according to FIGS. 2 to 5, electrons (secondary electrons, reflected electrons, etc.) emitted and reflected from the sample 13 are detected and amplified with high sensitivity and at ultra high speed using the scintillator 9 and MPPC 4 shown in FIG. The configuration will be explained in detail.

FIG. 2 shows an explanatory diagram (part 1) of the main part of the present invention. FIG. 2(a) shows an example in which the mesh 10 is arranged over the entire front surface of the detector (first detector+second detector) (backscattered electron detector 331 and +secondary electron detector 321). (b) shows an example in which the mesh 10 is arranged in the secondary electron detection section 321 in front of the detector (first detector+second detector). Other than that, they have the same configuration.

In (a) of FIG. 2, the detector (first detector + second detector) 34 is the scintillator 9 that is the first detector in FIG. 1 and the MPPC 4 that is the second detector. It is a detector having a structure (see FIGS. 6 to 10 and their description), and has a backscattered electron detection section 331 on the inside and a secondary electron detection section 321 on the outside. High-energy backscattered electrons are concentrated in the center, and low-energy secondary electrons are concentrated in the periphery. The secondary electrons are separated from each other and made detectable.

The mesh 10 applies a positive voltage to accelerate low-energy secondary electrons emitted from the sample 13. Here, the backscattered electron detector 331 and the secondary electron detector 321 of the detector 34 shows an example of arranging in front of the entire surface of both. In this case, high-energy backscattered electrons reflected from the sample 13 have a Gaussian distribution in the upward direction of the axis, and most of them are detected by the illustrated backscattered electron detector 331 closer to the axis. On the other hand, the secondary electrons with low energy emitted from the sample 13 are accelerated in the direction of the mesh 10 to which the high voltage is applied, and collide with the secondary electron detection section 321 shown in the figure, and further a little with the backscattered electron detection section 331 inside. amplified and detected. However, as a whole, the secondary electron component in the secondary electron detector 321 is greater, and as a result, it can be considered that secondary electrons are being detected.

In FIG. 2B, the mesh 10 is arranged only in front of the secondary electron detector 321 and not in front of the backscattered electron detector 331, so that all secondary electrons are detected. All of the secondary electrons accelerated and attracted to the portion 321 can be amplified and detected.

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, etc. are accelerated and sucked and amplified and detected by the secondary electron detector 321 on the outside, while high-energy backscattered electrons reflected by the sample 13 can be detected and amplified by the backscattered electron detector 331 on the inner side. Become.

At this time, when the primary electron beam 31 is narrowed by the objective lens 12 and irradiated onto the sample 13, the energy of the secondary electrons emitted is 0.1 eV to 1.0 eV. is several eV, and is accelerated by 10 KV applied to the mesh 10, the variation rate of the secondary electrons when colliding with the scintillator 9, which is the first detector constituting the detector 34, is (0.1 eV ~1.several eV)/10,000, which is about ±0.01%. That is, the secondary electrons emitted from the sample 13 are accelerated by 10 KV applied to the mesh 10, and the variation in the energy of the secondary electrons when colliding with the scintillator 9 is constant at about ±0.01% or less. It will be adjusted to become energy. As a result, the energy of the secondary electrons emitted from the sample 13 is kept constant (here, it is constant at 10 KV±0.01%) and is input to the scintillator 9, and the amount of light ( number). After being converted into light, it is possible to amplify by a second detector such as MPPC 4 and detect a signal corresponding to the number of secondary electrons.

In addition, since the reflected electrons reflected by the sample 13 have approximately the same energy as the primary electrons, for example, 10 kV, when they are input to the scintillator 9 which is the first detector, the energy of the reflected electrons is the same as in the case of the secondary electrons described above. The fluctuation is about 0.01% or less, and it becomes possible to output a signal from the detector 34 corresponding to the number of reflected electrons from the sample 13 . Details will be described in sequence below.

FIG. 3 shows an explanatory diagram (part 2) of the main part of the present invention. In FIG. 3, the energy filter 101 is placed between the sample 13 and the detector (first detector+second detector) 34 to separate high-energy backscattered electrons 33 and low-energy secondary electrons 32. Then, the backscattered electron detector 331 and the secondary electron detector 321 separate, amplify and detect each.

In FIG. 3, the EXB 101 is an energy filter that applies both an electric field and a magnetic field to separate the electrons (backscattered electrons, secondary electrons) by varying the deflection angle as shown in the figure due to the difference in energy of the electrons. is for independent detection of The EXB 101 is provided to amplify and detect low-energy electrons (secondary electrons, etc.) in the outer secondary electron detector 321, and to detect high-energy electrons (reflected electrons, etc.) in the inner reflected electron detector 331. can be amplified and detected with

As described above, the energy filter 101 is arranged between the sample 13 and the detector (first detector + second detector) 34, and low-energy electrons (secondary electrons, etc.) are detected from the outer secondary electrons. The part 321 amplifies and detects, and high-energy electrons (backscattered electrons, etc.) can be amplified and detected by the backscattered electron detection part 331 inside.

FIG. 4 shows an explanatory diagram (part 3) of the main part of the present invention. In FIG. 4, the secondary electron detector 321 in FIG. 2(b) is lowered downward to bring it as close to the sample 13 as possible so that the secondary electrons emitted from the sample 13 can be efficiently collected. In other words, the opening viewed from the sample 13 is enlarged, and a mesh 10 is provided on the front surface to apply a high voltage (eg, 10 KV) to accelerate and attract the secondary electrons emitted from the sample 13, resulting in good efficiency. This makes it possible to amplify and detect

As described above, the secondary electron detector 321 is brought closer to the sample 13 to increase the opening, and the secondary electrons emitted from the sample 13 are directed to the mesh 10 arranged in front of the secondary electron detector 321. It is possible to apply a voltage (for example, 10 KV), accelerate efficiently, collect, amplify and detect.

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

FIG. 5(a) shows an example without bias (a normal state in which a positive 10 KV is applied to the mesh 10). In the case of FIG. 5(a), the detector 34 can detect both reflected electrons and secondary electrons, as shown.

FIG. 5(b) shows a state with bias. In the case of FIG. 5B, for example, a voltage (negative voltage of several volts to several tens of volts) is applied to the mesh 10 to such an extent that the secondary electrons are reflected and cannot be detected, so the secondary electrons are detected. can amplify and detect backscattered electrons with high energy.

As described above, when an arbitrary voltage is applied to the mesh 10, only electrons having energy equal to or higher than the applied voltage collide with the detector 34 and can be amplified and detected. If the difference between the two is obtained, the number of electrons or the amount of electrons in either one can be accurately detected.

FIG. 6 shows an example detector of the present invention. FIG. 6 shows a schematic configuration of the MPPC 4, which is the second detector that constitutes the detector 34. FIG. 6(a) shows an MPPC photograph (perspective view), and FIG. A schematic diagram is shown, and (c) of FIG. 6 shows an example of an equivalent circuit of the MPPC.

In (a) of FIG. 6, the primary electron passage hole is a hole through which the primary electron beam passes. The primary electron beam that has passed through the hole is narrowed by the objective lens 12 and is planarly scanned while illuminating the sample 13, emitting secondary electrons and reflecting backscattered electrons.

(b) of FIG. 6 is a schematic view of the MPPC 4 and the mesh 10 arranged in front thereof from below (the scintillator 9 is omitted). A primary electron passage hole is provided in the center, and a mesh 10 is arranged in front of the MPPC 4. A positive high voltage (for example, 10 KV) is applied to the mesh 10, and the secondary electrons emitted from the sample 13 are kept at a constant energy. After being accelerated, it collides with a scintillator 9 (not shown) arranged between the MPPC 4 and the mesh 13 to be converted into light, and this light enters the MPPC 4 shown in the figure for amplification and outputs a signal.

(c) of FIG. 6 shows an example of an equivalent circuit of the MPPC. The MPPC 4 is configured by arranging a plurality of D1 (avalanche diodes) in parallel as shown in the figure, and further connecting in parallel a plurality of R1 (quenching resistors) connected in series to each of them. When light is input to one D1 (avalanche diode), the D1 in Geiger mode discharges and current flows, and when the current flows, the current is limited by R1 (quenching resistor) and becomes less than the discharge voltage, and the discharge stops. and one pulse is output. When two photons are input at the same time, they are arranged in parallel, and a pulse having about twice the peak is output. Similarly, when n photons are input simultaneously, n times as many pulses are output.

A bias power supply 43 is a power supply that applies a bias voltage to D1 to maintain the Geiger mode state.

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

By using the MPPC 4 having the configuration described above, the secondary electrons emitted from the sample 13 and the reflected backscattered electrons are converted to light by the scintillator 9 at a constant energy, and then the MPPC 4 converts them into light at ultra-high speed and high accuracy. It becomes possible to amplify and detect it.
Next, the characteristics of the MPPC of FIG. 6 will be described.

The MPPC4 is a device of several mm square as a whole, in which several tens to tens of thousands of small APDs (D1) of several microns square are arranged in parallel as shown in FIG. This MPPC 4 can be purchased from Hamamatsu Photonics (registered trademark) or the like. Devices smaller than this may be fabricated and used. The volume is less than 1/10,000th 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 a vacuum-sealed part like PMT. The weight of the device itself is very light, on the order of grams.

Each APD (D1) constituting the MPPC 4 is electrically connected in parallel via a resistor for controlling avalanche amplification called a quenching resistor R1, as shown in FIG. 6(c). One end of the parallel circuit is connected to a bias power supply 43 for controlling an avalanche phenomenon of about 50V to 100V, and the other end is connected to a current detection device 44 of virtual earth input. Since each APD (D1) forming the array of MPPCs 4 has slight variations in characteristics, the bias voltage applied to the entire array is experimentally set so that all the APD (D1) elements forming the array are in the Geiger mode. decide. When one photon is input to the APD in each Geiger mode, avalanche amplification occurs, with the amplification factor reaching 1,000,000 times. Of course, it may be set to a voltage having another amplification factor.

Each APD is connected to a quenching resistor R1 having a fixed value for current limiting, and a constant voltage is applied to the terminals. A constant current flows through the quenching resistor R1 because it works just like a switch. Since the APDs are connected in parallel, the sum of the avalanche currents generated in each APD is output to the current detector 44 connected to the output terminal.

Since a large number of APDs are spatially arranged in the MPPC 4, the probability that incident photons are incident on the same APD is extremely small. Therefore, for example, if one photon is input to the MPPD 4, a current of 1 unit is generated, and if N photons are input at the same time, a current of N units is generated. From this property, it is possible to know from the output current how many photons or electrons have entered the MPPC 4 at the same time. Since the output signal is an analog signal proportional to the number of incident photons, it is converted into a digital signal using an AD conversion device, and is taken into a PC and used for imaging. Since the current output from each APD element depends on the value of the quenching resistor R1 and is not strictly constant, a normalization process may be performed on a computer so that the current is strictly constant.

In addition, as a signal addition method, whether or not each APD is in an avalanche state is once converted into a digital signal of 0 and 1 inside the silicon chip, and then a digital sum-of-products operation is performed to calculate the number of AAPDs in the avalanche state. However, it is also possible to use a digital MPPC that uses the total output of the MPPC 4 as a whole. 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 with an AD converter. Also, the signal summation result is very accurate. In such an integrated IC, image processing can also be performed inside the chip.

FIG. 7 shows an example of a detector device (part 2) of the present invention. FIG. 7 shows a schematic configuration when the scintillator 9 and MPPC 4, which are the first detector and the second detector that constitute the detector 34, are incorporated in the apparatus of FIG.

(a-1) of FIG. 7 shows a top view of the detector 34, and (a-2) of FIG.

In (a-1) of FIG. 7, the MPPC 4 has a hole for the primary electron beam in the center, and the primary electron beam passes through this hole from top to bottom and is narrowed by the objective lens 12 in FIG. Planar scanning is performed while irradiating the top of the sample 13 which is narrowed down.

(a-2) of FIG. 7 shows a cross-sectional view. Secondary electrons emitted from the sample 13 are accelerated and attracted by a positive voltage (eg, 5 KV here) applied to the scintillator 9, collide with the scintillator 9, and convert the secondary electrons into light. The converted light enters the MPPC 4, 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 the secondary electrons travel in the direction of the positive voltage applied to the scintillator 9. Improve light collection efficiency.

In (b-1) and (b-2) of FIG. 7, the mesh 10 is provided between the illustrated sample 13 and the scintillator 9, and a positive acceleration voltage ( 5 KV) is applied (a positive voltage is applied between the sample 13 and the scintillator 9 in (a-1) and (a-2) of FIG. 7), and a positive voltage is also applied between the sample 13 and the mesh 10. A voltage (for example, several volts to several tens of volts) is applied to efficiently collect the secondary electrons emitted from the sample 13 . Others are the same as (a-1) and (a-2) in FIG. 7, so the description is omitted.

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

In FIG. 7, a primary electron beam 31 generated and accelerated by the electron gun 1 of FIG. Signal electrons such as secondary electrons and reflected electrons generated on the surface of the sample 13 are detected by a scintillator 9 and a detector composed of the MPPC 4 . Since the signal electrons rise from a point on the surface of the sample 13 irradiated with the primary electron beam 31 while spreading conically in the vertical direction, the signal electrons tend to be distributed axially symmetrically with respect to the primary electron beam axis. . In order to detect the signal electrons efficiently, it is necessary to provide a hole through which the primary electrons pass (primary electron beam hole) in the center of the detector and to locate it in the vicinity of the primary electron beam axis.

Therefore, 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 thin film is to prevent the surface of the scintillator 9 from being charged by incident electrons. Function. The scintillator 9 on the MPPC 4 may be attached with an adhesive considering the refractive index, or the scintillator 9 may be deposited by direct vapor deposition, CVD, sputtering, or the like. As the scintillator 9, an inorganic scintillator, a direct transition semiconductor scintillator, a ceramic material, a heavy atom-containing plastic scintillator, a halide scintillator using inner-shell transition light emission, a liquid, or the like can be used.

Further, there is a hole through which the primary electron beam passes (primary electron beam hole), and a shield tube 41 is provided so that the primary electron beam is not affected by the electric field or magnetic field in the periphery. The primary electron beam passes through shield tube 41 . The shield tube 41 is made of a non-magnetic material and has a width of several mm in diameter and a thickness of 1 mm or less. A gap is inevitably formed between the detector and the shield tube 41 . Electrons that hit the gap are not detected, so a conductive umbrella-shaped member is used to extend the electric field to the outside, repel the electrons, and prevent the electrons from entering the gap and heading toward the detector. .

Further, when electron acceleration is performed to illuminate the scintillator 9 in front of the detector, as shown in FIGS. A highly conductive mesh 10 (preferably 90% or more) is arranged, 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. mesh 10
It is desirable to apply a slightly positive potential of about 10 V to the sample 13 so that the signal electrons generated on the surface of the sample 13 also reach the sample 13 itself. It is desirable to keep this space at a vacuum of greater than 10 minus 3 pascals so that it does not discharge.

FIG. 8 shows a detector example (No. 3) of the present invention. A schematic configuration is shown in the case where the primary electron beam is formed into a ring shape, focused on one fine point by the objective lens 12, and planarly scanned while irradiating the sample 13. FIG. Since other parts are the same as those in FIG. 7, description thereof is omitted.

(a-1) of FIG. 8 shows a top view of the detector 34, and (a-2) of FIG.

In FIG. 8(a-1), the MPPC 4 has a ring-shaped hole for the primary electron beam. is narrowed down to form a point, and the surface of the sample 13 is scanned while being irradiated.

(a-2) of FIG. 8 shows a cross-sectional view. Secondary electrons emitted from the sample 13 are accelerated and attracted by a positive voltage (eg, 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, 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 the secondary electrons travel in the direction of the positive voltage applied to the scintillator 9. To improve the efficiency of collection of next electrons. At this time, secondary electrons and reflected electrons can be detected at the central portion of the detector composed of the scintillator 9 and MPPC 4, and the detection efficiency can be improved.

In (b-1) and (b-2) of FIG. 8, the mesh 10 is provided between the illustrated sample 13 and the scintillator 9, and a positive acceleration voltage ( 5 KV) is applied (a positive voltage is applied between the sample 13 and the scintillator 9 in (a-1) and (a-2) of FIG. 8), and a positive voltage is also applied between the sample 13 and the mesh 10. A voltage (for example, several volts to several tens of volts) is applied to efficiently collect the secondary electrons emitted from the sample 13 . Others are the same as (a-1) and (a-2) in FIG. 8, so the description is omitted. At this time, secondary electrons and reflected electrons can be detected at the central portion of the detector composed of the scintillator 9 and MPPC 4, and the detection efficiency can be improved.

Here, FIG. 8 is characterized by using 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 repulsion between electrons when using a high-current electron beam. It can be focused to one point on the surface of the sample 13 by the objective lens 12 in the same way as a normal beam.
As shown in (a-1) and (b-1) of FIG. 8, a scintillator 9 is also arranged in the central part, and a ring-shaped shield tube 41 through which primary electrons pass is provided in the peripheral part. If necessary, the scintillator 9 can also be arranged outside the ring-shaped shield tube 41 . By doing so, even if the electrons (secondary electrons, reflected electrons, etc.) generated on the surface of the sample 13 rise completely in the vertical direction, they can be properly detected by the scintillator 9 located directly above. The signal electrons flying around the primary electron beam axis are detected by the scintillator 9 arranged outside the ring-shaped shield tube 41 .

FIG. 9 shows a detector example (No. 4) of the present invention. FIG. 9 shows a schematic configuration in which the first detector, the scintillator 9, and the MPPC 4, which are the second detector, which constitute the detector 34, are divided into, for example, four parts in the circumferential direction and incorporated into the apparatus shown in FIG. be.

(a-1) of FIG. 9 shows a top view of the detector 34, and (a-2) of FIG.

In (a-1) of FIG. 9, the MPPC 4 has a hole for the primary electron beam in the center, and the surrounding portion is divided into four parts in the circumferential direction. The primary electron beam passes through the hole in the center from top to bottom, is narrowed down by the objective lens 12 in FIG.

(a-2) of FIG. 7 shows a cross-sectional view. Secondary electrons emitted from the sample 13 are accelerated and attracted by a positive voltage (eg, 5 KV) applied to the scintillator 9 divided into four parts, collide with the scintillator 9, and convert the secondary electrons into light. The converted light is incident on the four-divided MPPC 4, amplified and output as 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 the secondary electrons travel in the direction of the positive voltage applied to the four-divided scintillator 9, To improve the efficiency of collection of secondary electrons.

In (b-1) and (b-2) of FIG. 9, the mesh 10 is provided between the illustrated sample 13 and the scintillator 9, and positive acceleration is applied between the sample 13 and the scintillator 9 divided into four parts. A voltage (5 KV in the figure) is applied, and a positive voltage (eg, 50 V) is also applied between the scintillator 9 divided into four parts and the mesh 10, so that the secondary electrons emitted from the sample 13 are efficiently compensated. It is designed to be collected. Others are the same as (a-1) and (a-2) in FIG. 7, so the description is omitted.

Here, the configuration of FIG. 9 will be described in detail. FIG. 9 shows a case where a 4CH (four-division) detector is used. A 4CH detector is used to obtain information about the direction in which electrons generated on the surface of the sample 13 are emitted. By adding or subtracting the detected signals of each CH, it is possible to extract a necessary component and know the direction from which electrons are emitted. 3D information can be obtained. Since the sensitivity output from each detector is not necessarily uniform, it is calibrated and used so that the output sensitivity of each channel is the same by multiplying by an appropriate coefficient. Using these pieces of information makes it possible to enhance the edge information of the surface structure of the sample 13 and acquire 3D information.

Further, as shown in FIG. 9, a shield tube 41 is provided at a place through which 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. Make sure the height is the same. The detectors may not only be arranged in a plane, but may also be arranged three-dimensionally in the height direction along the primary electron beam axis.

Screen-shaped electrodes can be extended in all directions from the shield tube 41 through which the primary electron beam passes to surround the scintillator 9 and separate the detection range of the signal electrons flying to the detector. A bias voltage is applied to the shield tube 41 and the screen 431 to generate a repulsive force against the signal electrons. Electrons coming from the sample 13 bend and fly toward the scintillator 9 due to this repulsive force. Signal electrons are detected by respective detectors and an electrical signal is sent to an amplifier.

FIG. 10 shows a detector example (No. 5) of the present invention. 10, the first detector, the scintillator 9 as the second detector, and the MPPC 4, which constitute the detector 34, are divided, for example, into four in the circumferential direction, and the light guide 45 (FIG. 10 (a-1), (a -2)), light is focused by the lens 46 ((b-1), (b-2) in FIG. 10), a smaller MPPC 4 is used, and a schematic configuration is shown when this is incorporated in the apparatus of FIG. It is.

FIG. 10(a-1) shows a top view of the detector 34, and FIG. 10(a-2) shows a cross-sectional view, which show an example configuration without the mesh 48. FIG.

In (a-1) of FIG. 10, the MPPC 4 has a hole for the primary electron beam in the center, and the surrounding portion is divided into four parts in the circumferential direction, each part being separated by a partition 47 where electrons and light are adjacent to each other. The primary electron beam passes through the hole in the center from top to bottom, is narrowed down by the objective lens 12 in FIG.

(a-2) of FIG. 10 shows a cross-sectional view. Secondary electrons emitted from the sample 13 are accelerated and attracted by a positive voltage (eg, 5 KV) applied to the scintillator 9 divided into four parts, collide with the scintillator 9, and convert the secondary electrons into light. The converted light is incident on the four-divided MPPC 4, amplified and output as 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 the secondary electrons travel in the direction of the positive voltage applied to the four-divided scintillator 9, To improve the collection efficiency of secondary electrons.

In (b-1) and (b-2) of FIG. 10, a mesh 48 is provided between the illustrated sample 13 and the scintillator 9, and positive acceleration is applied between the sample 13 and the scintillator 9 divided into quarters. A voltage (50 V in the figure) is applied, and a positive voltage (eg, 5 KV) is also applied between the four-divided scintillator 9 and the mesh 10 to efficiently compensate for the secondary electrons emitted from the sample 13. It is designed to be collected. 10(b-2), instead of the light guide 45 of FIG. 10(a-2), a lens 46 is used to guide the light generated by the scintillator 9 to the small MPPC 4. FIG. Others are the same as (a-1) and (a-2) in FIG. 10, so the description is omitted.

Here, the configuration of FIG. 10 will be described in detail. FIG. 10 shows an example in which the light generated in the scintillator 9 by electron beam irradiation is reduced and irradiated to the MPPC 4 . Unlike a single APD, the MPPC 4 has an excellent feature that even if the total area of the MPPC 4 is increased, the electric capacity of each APD does not increase, so that the electron detection speed does not deteriorate. However, when the area of the MPPC 4 increases, noise due to thermal noise called dark noise increases in proportion to the area. Since this noise is proportional to the absolute temperature, it can be reduced by cooling. The good points of MPPC4 may disappear. On the other hand, when the area of the MPPC 4 is reduced, the electron detection efficiency is lowered and the image SNR is degraded.

Focusing on this point, the present invention succeeded in minimizing the area of the MPPC 4 while maintaining high electron detection efficiency. First, the area of the scintillator 9 for converting electrons generated on the surface of the sample 13 into light is made as large as possible. Specifically, an experiment or an electron trajectory simulation is used to determine the location where the signal electrons fly, and a scintillator 9 having a necessary and sufficient size is arranged at that location.

This increases the detection efficiency of signal electrons generated on the surface of the sample 13 . On the other hand, the light generated by the scintillator 9 is converged using an optical element or reduced in its cross-sectional area (light guide 45 in FIG. 10(a-2), lens 46 in FIG. 10(b-2), etc.). After reduction), the MPPC 4 is irradiated. In this way, high electron detection efficiency is ensured by the large scintillator 9, and low dark noise is achieved by using the MPPC 4 that is as small as possible.

Here, it is desirable that the MPPC 4 to be used is as small as possible (several microns or less), the number of elements is tens of thousands or more, and the area of the MPPC 4 is 1 square mm or less. In order to reduce the light generated by the scintillator 9, a method using a light guide 45 as shown in FIG. 10(a-2), a method using an optical lens 46 shown in FIG. 10(b-2), or the like is used. There is Furthermore, by using a reflecting mirror, a Fresnel lens, a holographic lens, or a diffraction element, it is possible to obtain the effect of shortening the vertical dimension. When using a light guide or the like in contact with a photon detection device, it is necessary to match the refractive index of the contacting member and insert a new antireflection film so as not to cause signal loss due to unnecessary reflection. desirable. Furthermore, an optical filter for wavelength selection may be inserted in order to select wavelength components incident on the MPPC 4 .

FIG. 11 shows a block diagram (part 1) of another embodiment of the present invention. FIG. 11 shows an example in which the electrons emitted from the sample 13 are accelerated and the light emitted by the scintillator 9 is reduced in area by a light guide 91 and is incident on the MPPC 4 whose area is smaller than that of the scintillator 9 . Since other configurations are the same as those in FIG. 1, description thereof 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 or the like.

The MPPC4 is a device in which a large number of APDs each having a side of several microns are arranged in an array. When the APD is applied with a bias voltage, it initially has an amplification factor that a normal photodiode exhibits. However, when the threshold voltage of about 50 V is exceeded, the amplification factor suddenly increases, and finally reaches an operation mode called Geiger mode, in which an incident electron (or photon) is amplified nearly 1,000,000 times. The Geiger mode has the sensitivity to detect a single electron incident from the outside of the MPPC 4, but if a single electron is generated due to internal thermal fluctuations, the same amplification is performed, so only one incident electron (photon) is used. and heat-generated electrons cannot be distinguished. Therefore, they become a source of noise. Thermionic generation is proportional to the area of the APD. In other words, the larger the area of the APD, the more frequently thermal electrons are generated, and the more noise there is.

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 efficiently detect the signal electrons. be.

As mentioned above, the two requirements contradict each other. In the present invention, in order to solve this contradiction, the area of the scintillator 9 for detecting electrons is made as large as possible, and the light generated by the scintillator 9 is reduced to be input to the MPPC 4 having the smallest possible area. We found a method that achieves both high detection efficiency and low noise. FIG. 11 shows an example in which light guides 91 with different area ratios between the incident side and the emitting side are used, the larger area is connected to the scintillator 9, and the smaller area is connected to the MPPC 4, which is a photon detector.

The light generated by the scintillator 9 having a large area is reduced by the light guide 91, guided to the MPPC 4, which is a photon detector having a small area, and converted into a current. By doing so, it is possible to achieve both high efficiency detection and low dark noise.

FIG. 12 shows a block diagram (part 2) of another embodiment of the present invention. FIG. 12 shows an example in which the electrons emitted from the sample 13 are accelerated and the scintillator 9 emits light. Since other configurations are the same as those in FIG. 1, description thereof is omitted.

In FIG. 12, a lens 51 is a lens that reduces light. Although the figure shows a single lens configuration, a plurality of lenses may be used. For example, a lens system that emits a reduced parallel beam when a parallel beam is incident may be used. Signal electrons generated by irradiating the sample 13 with the primary electron beam are accelerated and attracted by a positive voltage (for example, 10 kV) applied to the mesh 10 or the like and collide with the scintillator 9 . The colliding electrons emit a large amount of light. The emitted light is condensed by the lens 51 so that the cross-sectional area is reduced to 1/10 or less, and is incident on the MPPC 4, which is a photon detection device. The MPPC 4 receives the incident light and amplifies it to output a detection current.

By adopting the above configuration, the area of the MPPC 4 becomes 1/10 or less of the area of the scintillator 9, so dark noise can be reduced by 10% compared to the case where the MPPC 4 having the same area as the scintillator 9 is used. It can be set to 1 or less.

FIG. 13 shows a block diagram (part 3) of another embodiment of the present invention. FIG. 13 shows a configuration example in which signal electrons (secondary electrons, reflected electrons, etc.) are reduced using the electron lens 53 and input to the detector (scintillator 9+MPPC 4). Since other configurations are the same as those in FIGS. 11 and 12, description thereof is omitted.

In FIG. 13, the electron lens 53 is an electron lens that reduces signal electrons from the sample 13 (secondary electrons emitted from the sample 13, reflected electrons, etc.) to an area smaller than the aperture of the electron lens 531. There are electrostatic lenses and magnetic lenses. Here, before entering the scintillator 9, signal electrons (secondary electrons, etc.) generated on the surface of the sample 13 are detected by an electron lens 531 such as an electrostatic lens or a magnetic lens having a first aperture. It is characterized in that the scintillator 9 having an area smaller than that of the first opening or a part thereof is irradiated after the energy is accelerated by reducing the cross-sectional area using the first opening. The signal electrons are detected by MPPC4, which is a photon detector smaller in size than the first aperture.

By configuring as described above, both the scintillator 9 and the MPPC 4 can be made smaller. Therefore, it is possible to reduce the cost of the scintillator 9 because the size of the scintillator 9 can be small as well as the dark noise can be reduced. In addition, since the size of the MPPC 4 can be reduced, the degree of freedom in its arrangement within the lens barrel is created. Since no lens or light guide is used, signal loss can be reduced, contributing to high-quality image formation. Since the detector can be made very small in this way, a large number of detectors can be arranged in one electron beam device so that the signal electron groups generated when the surface of the sample 13 is irradiated with many electron beams at the same time can be measured simultaneously. Become.

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

In FIG. 14(a), the irradiation lens 51 makes the primary electron beam generated by the electron gun 1 parallel.

The electron beam aperture 52 is for extracting a plurality of predetermined narrow portions from the parallel primary electron beam to form a plurality of primary electron beams, for example, as shown in FIG. , a plurality of circular diaphragms are provided. A blanking type aperture that can be electrically opened and closed may be used as such an aperture.

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

The first reduction lens 56 is the first lens that reduces the plurality of primary electron beams that have passed through the electron beam aperture 52 .

The second reduction lens 57 irradiates the sample 13 with the plurality of primary electron beams reduced by the first reduction lens 56 and further reduced and narrowed down, and scans the surface of the sample 13 . It is for

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

(1) In FIG. 14, the primary electron beam 31 generated by the electron gun 1 is once converted into parallel beams by the illumination lens 51, and then passed through the primary electron beam aperture 52 to form a plurality of primary electron beams. to mold. 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 were to pass through the center of the electron beam aperture 52, it would be difficult to arrange the secondary electron detector so that the trajectories of the primary electrons and the secondary electrons would be different. It is desirable to provide it in the peripheral part.

(2) A plurality of shaped primary electron beams pass through a supporting portion 53 having holes so that the primary electron beams can pass through, pass through a first reduction lens 56 and a second reduction lens 57, and become beam diameters. is compressed, the surface of the sample 13 is irradiated substantially perpendicularly.

(3) The irradiated electrons generate secondary electrons on the surface of the sample 13 . The generated secondary electrons are accelerated by a bias voltage (for example, 10 kV) applied between the sample 13 and the conductive film provided on the surface of the scintillator 55, pass through the second reduction lens and the first reduction lens, and then enter the scintillator. 55. The bias voltage is adjusted so that the height of the scintillator is the focal position of the secondary electrons. That is, the scintillator surface is adjusted so that an image of the primary electron spot can be formed.

(4) A detector composed of the scintillator 55 and MPPC 54 calculates the trajectory of secondary electrons and is installed at a place where the secondary electrons return. A large number of detectors may be arranged in advance in an array, and an address or the like may be provided for each element so that it can be electrically selected and used by a computer or the like as required. With this function, it is possible to cope with the trajectory change of the secondary electrons due to the bias voltage change.

As described above, the secondary electrons generated by irradiating the sample 13 with a plurality of divided primary electron beams are simultaneously detected by the respective detectors (scintillator 55, MPPC 54). It is possible to acquire an image at

FIG. 15 shows another detector explanatory diagram (part 2) of the present invention. 14 is composed of the supporting portion 53, the MPPC 54 and the scintillator 55, the FIG. 15 is composed of the MPPC 54, the transparent supporting portion 531 and the scintillator 55. FIG. Since other configurations are the same as those in FIG. 14, description thereof is omitted.

In FIG. 15, the transparent supporting portion 531 is characterized by supporting the scintillator 55 for detection with a transparent member. Various optical elements such as lenses and holograms are used as the transparent member used for the transparent support portion 532 . The use of these optical elements makes it possible to reduce or expand the light generated by the scintillator 55 or to move the position of the light. This means that the electron detector can be placed anywhere.

FIG. 16 shows another detector explanatory diagram (No. 3) of the present invention. In FIG. 16, a mesh 58 is provided on the sample 13 of FIG. It is characterized by improving the detection efficiency of

In FIG. 16, a mesh 58 is a mesh provided on the sample 13 and accelerates (for example, 5 KV) secondary electrons emitted from the sample 13 . The mesh 56 is provided on the sample 13, and an acceleration voltage (for example, 5 KV) is applied to it to accelerate the secondary electrons. It passes through, is further accelerated, and finally collides with the scintillator 55 . By accelerating the secondary electrons immediately after they are generated, it is possible to prevent the generated secondary electrons from dispersing and to improve the detection efficiency.

FIG. 17 shows another detector explanatory diagram (No. 4) of the present invention. In FIG. 17, a mesh 59 is further provided on the scintillator 55 in contrast to FIG. (It follows a 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 a mesh provided on the front surface of scintillator 55 .

A mesh 58 is a mesh provided on the front surface of the sample 13 . Here, the meshes 59 and 58 are held at the same potential so that the secondary electrons passing through the second reduction lens 57 and the first reduction lens 56 are not affected by the surrounding geometrical structure and pass through the trajectory as designed. It is the one that was made. Here, for example, 5 KV (voltage for accelerating secondary electrons) is applied to the mesh 58 and 10 KV (voltage for accelerating secondary electrons passing through the mesh 59) is applied to the mesh 59, as shown.

With the configuration as described above, when a plurality of primary electron beams are irradiated onto the sample 13 and the surface is scanned in parallel, secondary electrons and reflected electrons corresponding to the plurality of primary electron beams are emitted from the sample 13, respectively. A plurality of emitted and reflected secondary electrons and reflected electrons are accelerated upward in parallel by the mesh 58, and pass through the second contraction lens 57 and the first contraction lens 56 with constant energy, Passing through the mesh 59, a positive voltage (e.g., 10 kV) is applied between the mesh 59 and the scintillator 55 to accelerate a plurality of secondary electrons and reflected electrons in parallel, and the scintillator 55 converts them into light in parallel. A plurality of these converted lights are amplified and detected in parallel by the MPPC 54, respectively, and the signals can be output in parallel.

At this time, electrons accelerated to high energy (reflected electrons, etc.) take inner orbits, and electrons accelerated to low energy (secondary electrons, etc.) take outer orbits. , MPPC 54) and output in parallel.

FIG. 18 shows an explanatory diagram (No. 5) of the detector of the present invention. FIG. 18 is characterized in that a resolution higher than the size of the irradiated primary electron beam can be achieved and the throughput can be improved. A detailed description will be given below.

(1) In FIG. 18, after primary electrons are emitted from the electron gun 1, they are accelerated to a desired energy to generate a hollow electron beam (see FIG. 18(b)). The sample 13 is irradiated with convergence to a point. An acceleration voltage of about 1 KV to 50 KV is used.

(2) A hollow electron beam (holo beam) can be generated by uniformly irradiating parallel electron beams through an irradiation lens 51 to an electron beam aperture 52 hollowed concentrically. The concentric holes may be formed concentrically by using many small holes, or may be formed by using squares, or may be surrounded by doubly. These apertures may be of the blanking aperture type such that a large array of apertures can be electrically opened and closed. Portions of the array may be selectively opened and closed to form concentric circular apertures. In order to further reduce aberration, a grating lens or a thin film lens that serves as a concave lens may be used.

The electron beam aperture 52 is preferably made of a non-magnetic material such as titanium, MO, or W, and heated to 100° C. or higher to prevent contamination. It is desirable to have conductivity for antistatic purposes.

(3) The generated hollow electron beam is focused to one point by the objective lens 121 . The focused primary electron beam scans the XY plane by the deflection electrodes 122 . The deflection electrode 122 can be placed at a required location 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 applied to the sample 13 to generate secondary electrons. Since the generated secondary electrons have very low energy and are emitted in all directions, they cannot form a point image with the objective lens 121 as they are. In this embodiment, a positive acceleration voltage is applied to the mesh 58 just above the sample 13, and almost all the generated secondary electrons are accelerated to a desired energy. Due to this acceleration voltage, the energy variation of the secondary electron group is relatively reduced, resulting in a single secondary electron beam with uniform energy. Therefore, the higher this energy is, the more uniform the energy is.

(5) The secondary electrons accelerated to the desired energy pass through the objective lens 121, finally collide with the scintillator 55, and after being accelerated and decelerated by the mesh 59 so as to optimize light emission, collide with the scintillator. and emit light. The emitted light is detected by each segmented portion of the MPPC 4, either directly or via a reflector (which may be a highly sensitive CCD or CMOS device).
(6) As shown in FIG. 18, the detected light spot is an enlarged image of secondary electrons generated by the primary electron beam narrowed to a desired size by the objective lens 121 . Also, this point image is dynamically XY-scanned in accordance with the deflection of the primary electron beam. The enlarged image of the light spot 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 and extracting the detailed brightness distribution of the light points from the image, it is possible to extract changes on the sample surface in an area smaller than the spot size. That is, the resolution of the primary electron beam optical system can be increased. This is just like drawing a picture by bundling the cores of ten pencils, and it is the same as obtaining a resolution image drawn by each pencil by measuring the brightness distribution and separating them into ten. .

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

(8) For example, if a light spot is divided into four and each corresponding to a pixel, it is possible to obtain substantially the same resolution as irradiation with a beam size of 2.5 nm, and four times the throughput. Normally, increasing the resolution causes a decrease in throughput, but this method is characterized by being able to increase both the resolution and the throughput.

(9) To obtain higher resolution, it is very important that the scintillator structure is uniform and fine. When using a particulate scintillator, it is possible to obtain high resolution by making the particle size on the order of nanometers. Plastic scintillators and the like are uniform at the nano level. Since fluorescence microscopes can achieve nano-order resolution, one point can be separated into a plurality of beam components if it can be separated to that extent.

(10) The above method has the same effect as converging a plurality of beams in a multi-beam format very close to each other. On the other hand, in contrast to the generally known multi-beam system, only the central part of the lens axis is used, so lens distortion is small and aberration correction is not required, making it possible to easily implement a multi-beam inspection system. Since this effect can be obtained regardless of whether the beam spot size is large or small, it is possible to realize a high-resolution and ultra-high-speed inspection apparatus or a low-resolution and ultra-high-speed inspection apparatus. Conversely, by reducing the beam size from the beginning and increasing the resolution of the photodetector, it is possible to achieve a resolution of less than 1 nm and a high throughput, which cannot be achieved conventionally. In particular, when high resolution is to be achieved, it is easy to narrow the electron beam because the electron beam is less likely to spread due to electrostatic repulsion in the hollow beam.

Unlike the conventional multi-beam inspection system, the detected secondary electrons are lifted vertically and the electrons are directly detected without using a beam separator, so that aberrations are small and higher resolution and efficiency can be realized.

Furthermore, in the above method, since the beams are separated by image analysis, the direction in which the beams are arranged, which is a problem in the multi-beam inspection system, does not matter. It can be easily expanded to any type of inspection equipment.

1 is a configuration diagram of an embodiment of the present invention; FIG. FIG. 1 is an explanatory diagram (part 1) of a main part of the present invention; FIG. 2 is an explanatory diagram (part 2) of a main part of the present invention; FIG. 3 is an explanatory diagram (part 3) of a main part of the present invention; FIG. 4 is an explanatory diagram (part 4) of a main part of the present invention; It is an example of the detector of the present invention (No. 1). It is a detector example (2) of the present invention. It is an example of the detector of the present invention (No. 3). It is an example of the detector of the present invention (No. 4). It is an example of the detector of the present invention (No. 5). FIG. 10 is a block diagram (part 1) of another embodiment of the present invention; FIG. 2 is a block diagram (part 2) of another embodiment of the present invention; FIG. 11 is a block diagram (part 3) of another embodiment of the present invention; It is another detector explanatory drawing (1) of this invention. It is another detector explanatory drawing (part 2) of this invention. It is another detector explanatory drawing (3) of this invention. It is another detector explanatory drawing (part 4) of this invention. It is another detector explanatory drawing (5) of this invention.

1: electron gun 2: electron gun controller 3: deflection electrode 3-1: deflection electrode (upper)
3-2: Deflection electrode (bottom)
31: Primary electron beam 32: Secondary electron 321: Secondary electron detector 322: Electron beam scanning controller 33: Reflected electron 331: Reflected electron detector 34: Detector (first detector + second detector)
4, 54: MPPC
41: Shield tube 411: Quenching resistor 42: Avalanche photodiode 421: Supporting glass 43: Bias power source 431, 47: Screen 44: Current detector 441: Supporting part 45, 91: Light guide 46: Lens 5: Pass blocking bias 51: Irradiation lens 52: Electron beam aperture 521: Hollow beam 522: Reflector 523: Optical magnifying lens 524: Optical two-dimensional detector 53: Supporting part 531: Electronic lens 532: Transparent supporting part 56: First reducing 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 (6)

an electron optical system for narrowly narrowing primary electrons in an electron detector for detecting electrons emitted from a sample and magnifying secondary electrons or reflected electrons emitted or reflected from the irradiated sample;
a first element that converts the magnified image of electrons magnified by the electron optical system into a magnified image of light;
a second element that detects an enlarged image of the light converted by the first element in each of the plurality of divided parts;
The amount of electrons generated at the irradiation point of the sample based on the image of pixels corresponding to each of the plurality of divided portions of the second element and the scanning signal of the narrowly focused primary electron beam irradiated on the sample. means for generating distribution information;
1. An electron detector, characterized by generating electron generation amount distribution information at a sample irradiation point of primary electrons. 2. A means for generating an image corresponding to each pixel by dividing the signal of each portion detected by the second element into luminance of pixels corresponding to each portion. The electronic detection device according to . 3. An electron detector according to claim 1, wherein said electron optical system is an objective lens. 4. An electron detector according to claim 1, wherein said first element is a scintillator. 5. An electron detector according to any one of claims 1 to 4, wherein said second element is MPPC. The primary electrons pass through a partially closed ring-shaped aperture, or a plurality of small circles or rectangles arranged at ring-shaped positions, and the primary electrons pass through the sample. 6. An electron detecting device according to claim 1, wherein the light is narrowly focused on the beam.

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