JP2024099014A - Multiple beam inspection device and multiple beam inspection method - Google Patents

Abstract

PURPOSE: To provide a multiple beam inspection device where an axis of a primary electron irradiation system and an axis of a secondary electron detection system are configured to be symmetrical, aberration caused by deflection is cancelled, and aberration generated to a primary electron and a secondary electron is reduced in the multiple beam inspection device and a multiple beam inspection method.

CONSTITUTION: A multiple beam inspection device includes a primary electron irradiation system generating and accelerating primary electron with a multiple beam electron gun, a first deflector, a second deflector, an imaging system composed of an objective lens, a third deflector, and a secondary electron detection system. Around the axis of the imaging system, an axis of the primary electron irradiation system and an axis of the secondary electron detection system are configured symmetrically, and aberration generated to the primary electron and secondary electron is reduced by cancelling aberration caused by deflection.

SELECTED DRAWING: Figure 2

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a multi-beam inspection device and a multi-beam inspection method that detects secondary electrons emitted from a sample and generates a secondary electron image of the sample.

The semiconductor industry is supported by the improved device performance and cost benefits brought about by advances in microfabrication technology, famously known as Moore's Law. However, the limits of microfabrication of semiconductor devices are determined by exposure technology. Exposure technology consists of an original plate called a photomask for creating patterns, an exposure device, and a resist that forms the pattern. Currently, exposure devices use a 4:1 reduction exposure technology, so structures formed on the photomask are four times larger than the structures on the silicon wafers on which semiconductor devices are actually made.

The biggest challenge in exposure technology is how accurately the pattern created on the photomask can be transferred to the resist film on the wafer surface. If there is an abnormality in the photomask, it will be transferred to the wafer surface by the exposure device, causing defects on the wafer.

To prevent exposure defects, it is necessary to at least inspect the photomask and correct it to make it perfect. The wavelength of the light used for exposure is becoming shorter and shorter with the times.

Since the end of the 20th century, 193 nm light sources have been used as exposure light sources, and for a long time, patterns on photomasks have been inspected using optical mask pattern inspection equipment that uses laser light such as 193 nm as illumination light.

However, since 2019, exposure technology using EUV light with a short wavelength of 13.5 nm has been fully introduced, which has made the limit of microfabrication that can be exposed smaller, and the patterns on photomasks have also become smaller from the previous minimum pattern size of around 100 nm to 60 nm or less, making it no longer possible to perform adequate inspections with the conventional 193 nm light.

On the other hand, so-called actinic inspection equipment using a wavelength of 13.5 nm is also under development. However, because the wavelength is as short as 13.5 nm, it is absorbed by air, which makes the equipment very complicated, as it is necessary to evacuate it. Also, because there are no optical lenses that can transmit 13.5 nm light, the optical system is all reflective, which is also complicated and inefficient.

The resolution of an optical device is proportional to the numerical aperture NA. For example, in the case of an optical system using 193 nm, a large numerical aperture of over 1 can be achieved by using liquid immersion or oil immersion, making it possible to resolve patterns of about 40 nm despite the long wavelength of 193 nm. On the other hand, when EUV light is used, only a small numerical aperture of 0.3 or the like can be achieved because a reflective optical system is used, and a resolution of only about 27 nm can be obtained despite the wavelength being one-tenth as short, meaning that the improvement in performance is small given the shorter wavelength.

For example, when the detection target is a particle, the reflected light weakens in proportion to the sixth power of the particle size, and the reflected light strengthens in proportion to the square of the wavelength. In other words, as the particle size becomes smaller, the signal strength weakens rapidly, and the detection sensitivity drops dramatically. As such, photomask inspection technology using optical technology is reaching its technical limits. Furthermore, conventional devices using optical principles operated in the atmosphere, making them easy to manufacture and operate, but as the wavelength becomes shorter, they are absorbed by the air, requiring a vacuum chamber, which eliminates the advantage of ease of use over electron beams.

On the other hand, electron microscopes are a technology that can achieve a resolution of less than the nm order. Electron beam inspection technology using electron beams has been developed for over 30 years. Although they have been commercialized, they have not yet been put to practical use as primary inspection equipment.

Unlike laser light, there is no electron beam source with a small energy dispersion and high brightness like a laser. Furthermore, because electrons have a negative charge, they electrostatically repel each other when narrowed down. Therefore, when the large current required for high-speed inspection is applied, the minimum beam spot size becomes larger than the optical limit, and the resolution deteriorates. In other words, when a single electron beam is used, there is a very severe trade-off between resolution and inspection speed, so it is not easy to increase the inspection speed.

For example, the maximum speed that can be achieved using a single beam known at present is at most several hundred megapixels per second. Since a photomask has a pattern written in an area of approximately 10 cm square, it is necessary to inspect the entire area. For example, in order to inspect the current patterns on photomasks at a resolution of 10 nm, which is sufficient to resolve the patterns on the photomask, it is necessary to acquire 10^14 pixels. For example, acquiring pixels at 100 megapixels per second requires 10^6 seconds, which is 277 hours, or more than 10 days. Conventional photomask inspection equipment can inspect one photomask in approximately two hours, so this is too slow to be of practical use.

Recently, research has been conducted into a method of performing high-speed inspection by simultaneously irradiating a sample with multiple electron beams, known as a multi-beam inspection device.

In this method, more than 100 small electron beams are irradiated simultaneously for scanning, making it possible to reduce the amount of current flowing through each beam, and it is said that inspection speeds can be made faster than when using a single conventional electron beam while maintaining high resolution.

However, although a lot of resources have been invested into the development of various types of inspection equipment, and although they are considered very promising, they have not yet been commercialized as semiconductor inspection equipment, as they have not been able to achieve the speed and resolution initially expected.

The equipment used in the semiconductor industry is industrial measurement equipment, a type of mission-critical equipment that must operate without malfunction 24 hours a day, 365 days a year, so robustness is essential in principle.

Scientific equipment is not practical if it is only used occasionally by university professors and students to write papers. It is necessary that performance be maintained stably over a variety of measurement conditions, measurement targets, and environmental changes, as well as over the long term.

In the multi-beam inspection device described above, the single-beam CDSEM itself already achieves the stability required for industrial measurement equipment, so the stability of the normal electron beam optical system itself is fairly well guaranteed. However, one of the reasons for the loss of robustness is the implementation of a beam splitter that does not exist in normal single-beam electron beam optical systems. Beam splitters are ultra-precision engineering devices that require high levels of processing and assembly accuracy on the order of microns.

A beam splitter is a device that separates the primary electron beam from the secondary electron beam, which are signal electrons from the sample. When using a mapping optical system, it is necessary to have both an optical system that focuses the primary electrons and an optical system that focuses the secondary electrons. In principle and in practice, it is extremely difficult to apply different electron optical systems to electrons on the same trajectory and optimize both simultaneously.

Therefore, conventionally, optimization has been attempted by separating the trajectories of the primary electron beam and the secondary electron beam and using separate optical systems. To achieve this, a beam splitter is required.

Beam splitters have traditionally been made up of Wien filters known as EXBs, or magnetic prism arrays that use only electromagnetic fields. As the name suggests, conventional beam splitters deflect the electron beam components of various energies contained in the beam, spectrally decomposing them into individual energy beams and passing them through a narrow slit to extract a portion with a consistent energy. This is a forced repurposing of this.

To separate the primary and secondary electron beams, it is necessary to deflect the primary and secondary electrons in the opposite direction to their direction of travel. To achieve this, a magnetic deflection device known as Fleming's law is used to deflect the primary and secondary electrons in the opposite directions, taking advantage of the fact that they travel in opposite directions.

EXB is a mechanism that adjusts either the primary or secondary electrons by adding a large electric field equivalent to the energy of the electrons so that they are not deflected by the magnetic field. The purpose of this is to minimize the occurrence of lens aberration by making the desired electron beam go in a straight line. The deflection amount is only about 10 degrees, which is not very large, so if left as is, the column for the primary electron beam and the column for the secondary electrons will come into contact. Therefore, to increase the separation, an electric or magnetic field is further applied to the separated electron beams to bend them in the same direction.

On the other hand, with an electromagnetic prism array, a large magnetic field can be easily applied since the electron beam is bent simply by applying a magnetic field. By using an array of two or more magnetic deflectors so that several electromagnetic deflectors bend in the same direction, a deflection of nearly 90 degrees can be achieved.

If the energy of the primary electron beam is exactly constant, like a laser, no deflection aberration occurs, so the trajectory of the electron beam can be changed ideally and freely using the above deflector.

However, because the actual primary electron beam has an energy distribution of about 1 electron volt that depends on the electron beam generation principle, as it passes through the magnetic deflection device and is deflected, the amount of deflection differs for each electron energy, causing the beam to spread out like a rainbow. In other words, the primary electron beam is spatially dispersed, and the minimum diameter of the beam spot when narrowed by the objective lens becomes larger, causing the achievable resolution to decrease.

On the other hand, secondary electron beams have an energy distribution of up to 0 to 100 electron volts, which is 100 times larger than that of primary electron beams. Therefore, when they pass through a magnetic deflection device, the electron beam spreads out more than 100 times more than the primary electron beam, making it very difficult to obtain high spatial resolution on the secondary electron detection element surface. This is a natural conclusion that comes from the fact that Wien filters such as EXB are tools for separating the energy of electron beams.

In the past, to reduce these problems, measures were taken to reduce the effects of deflection aberration by using a high acceleration voltage of 15 KV or more on the primary electron beam to reduce the proportion of apparent energy dispersion. Similarly, the effects of deflection aberration were reduced by applying an acceleration voltage of about 15 KV to the secondary electron beam to accelerate it, but this required the equipment to withstand high voltages, making it large-scale. Furthermore, to prevent the effects of aberration, electrons with a specific energy were extracted and used by passing them through a thin slit of a few microns, which reduced the amount of available signal electrons, causing the image to become darker and the SNR to deteriorate.

Furthermore, another problem was that the deflection device showed an amount of deflection that depended on the energy of the electrons, so when the sample surface became charged and the energy of the secondary electrons changed from a few volts to several hundred volts, the amount of deflection changed by 100 times, making it impossible to obtain a correct secondary electron image. Measurements were only possible when the sample potential could be fixed at 0 V or a constant potential, making it virtually impossible to measure general samples or insulators.

Therefore, the present invention aims to prevent the electron beam trajectory from dispersing due to differences in energy as much as possible, which is the complete opposite of conventional technical ideas. We propose canceling or reducing the deflection aberration caused by energy dispersion generated in the deflection device, narrowing the primary electron beam into a smaller beam, detecting secondary electrons generated on the sample surface with high spatial resolution, and applying a retarding voltage to enable high-resolution detection despite the low-energy electron beam, and further enabling high-resolution detection even in a low vacuum.

The present invention is a scanning electron microscope that irradiates a sample with primary electrons and detects secondary electrons emitted from the sample to generate a secondary electron image of the sample. The microscope is provided with a primary electron irradiation system that generates and accelerates primary electrons, a first deflection device that deflects the primary electrons generated by the primary electron irradiation system, a second deflection device composed of a magnetic field and an electric field that deflects the primary electrons deflected by the first deflection device in the opposite direction to cancel aberration, aligns the primary electrons with the axis of the imaging system to irradiate the sample, and deflects the secondary electrons emitted from the sample in the opposite direction to the primary electrons to separate them, an imaging system composed of an objective lens that narrows the primary electrons after they have been deflected by the second deflection device and aligned with the axis of the imaging system to irradiate the sample, and causes the secondary electrons emitted from the sample to enter the second deflection device, and a secondary electron detection system that detects the secondary electrons after they have been deflected by the second deflection device.

In this case, a third deflection device is provided that deflects the secondary electrons deflected and separated by the second deflection device in a direction opposite to the deflection direction of the second deflection device to cancel aberration, and a secondary electron detection system is provided that detects the secondary electrons after they have been deflected by the third deflection device and the aberration has been canceled.

The first deflection device and the third deflection device are also configured to be deflection devices having four or more poles of a magnetic field, an electric field, or a magnetic field and an electric field.

The second deflection device also has two poles in the magnetic field or four or more poles each in the magnetic field and electric field, and is designed to separate secondary electrons traveling in the opposite direction to the direction of travel of the primary electrons.

In addition, a retarding voltage is applied between the sample and the tip of the objective lens, so that the sample is irradiated with primary electrons at a low acceleration voltage.

In addition, a diaphragm is provided on the objective lens, so that the sample side is kept at a low vacuum and the opposite side at a high vacuum.

The present invention reduces the deflection aberrations generated by the first deflection device, the second deflection device, and the third deflection device by canceling each other out, thereby narrowing the primary electron beam into a smaller beam and enabling detection of secondary electrons generated on the sample surface with high spatial resolution.

It is also possible to realize a high-resolution electron beam inspection device in a low vacuum.

The present invention achieves the following: The deflection aberrations generated by the first, second, and third deflection devices are mutually cancelled out and reduced, narrowing the primary electron beam into a smaller beam, detecting secondary electrons generated on the sample surface with high spatial resolution, and applying a retarding voltage to enable detection with high resolution even in a low vacuum with a low energy electron beam.

Figure 1 shows the principle configuration of the present invention.

In Figure 1, primary electron 1 is a primary electron generated in the irradiation system.

Secondary electrons 2 are secondary electrons emitted when a finely focused primary electron is irradiated onto a sample 8.

The beam splitter 3 irradiates the sample 8 with the primary electrons 1 and separates the secondary electrons 2 emitted from the sample 8 from the primary electrons 1, and is composed of a first deflection device 4, a second deflection device 5, and a third deflection device 6.

The first deflection device 4 deflects the primary electrons 1 and is a four-pole or greater deflection device that is composed of a magnetic field, an electric field, or a magnetic field and an electric field.

The second deflection device 5 separates the primary electrons 1 from the secondary electrons 2 that travel in the opposite direction, and is a deflection device that is composed of at least a magnetic field or both a magnetic field and an electric field, with four or more poles each.

The third deflection device 6 is similar to the first deflection device and deflects secondary electrons. It is a four-pole or more deflection device that is composed of a magnetic field, an electric field, or a magnetic field and an electric field.

The objective lens 7 constitutes an imaging system, narrowing the primary electrons 1 to irradiate the sample 8, and directing the emitted secondary electrons into the second deflection device 5.

The sample 8 is an object to be irradiated with finely focused primary electrons 1, causing secondary electrons 2 to be emitted, and generating a high-resolution secondary electron image, such as a mask or a pattern on a wafer.

Next, we will explain the operation of the configuration in Figure 1.

(1) Primary electrons 1 are incident on the first deflection device 1 that constitutes the beam splitter 3, and are deflected to the left in the direction of travel as shown in the figure by the action of a magnetic field, an electric field, or a combination of a magnetic field and an electric field.

(2) The primary electrons 1 deflected in (1) and entering the second deflection device 5 are deflected to the right in the direction of travel by the second deflection device 5 due to the action of a magnetic field or both a magnetic field and an electric field. As a result, the deflection direction of the first deflection device and the deflection direction of the second deflection device are opposite to each other, and after canceling the deflection aberration, the primary electrons 1 are brought onto the axis of the objective lens 7.

(3) The primary electrons 1 deflected onto the axis of the objective lens 7 in (2) are narrowed by the objective lens 7 to irradiate the sample 8, and are scanned in the X and Y directions by a two-stage deflection system (not shown). Secondary electrons 2 are then emitted from the sample 8.

(4) The secondary electrons 2 emitted in (3) travel upward along the axis of the objective lens 7 and enter the second deflection device 5, where they are deflected by the action of the magnetic field and electric field in the travel direction shown in the figure, opposite to that of the primary electrons 1.

(5) The secondary electrons deflected to the right in the direction of travel in (4) enter the third deflection device 6 and are deflected to the left in the direction of travel as shown in the figure. As a result, the deflection directions of the second and third deflection devices are opposite to each other, and after canceling the deflection aberration, the electrons travel upward on the axis of the secondary electron detection system.

As described above, the deflection aberration of the primary electrons 1 is cancelled by the first deflection device 4 and the second deflection device 5, and the deflection aberration of the secondary electrons is cancelled by the second deflection device 5 and the third deflection device 6. This reduces the deflection aberration and irradiates the sample 8 with more finely focused primary electrons, thereby generating a high-resolution secondary electron image. Furthermore, the deflection aberration of the emitted secondary electrons is also cancelled by the second deflection device 5 and the third deflection device 6, so it is possible to reduce the deflection aberration and separate the secondary electrons from the primary electrons, and detect the secondary electrons with high sensitivity and high resolution. The following will explain in detail.

Next, we will explain the operation of the configuration in Figure 1.

(1) The primary electrons 1 that pass through the first deflection device 4 are deflected inward. Since the primary electrons 1 have an electron energy dispersion of about 1 electron volt, the amount of deflection is energy-dependent, and the primary electron beam disperses like a rainbow and expands spatially.

(2) The second deflection device 5 deflects the primary electrons 1 in the opposite direction by exactly the same amount as the first deflection device. Because the electrons are deflected in the opposite direction by exactly the same amount, the primary electron orbits that are dispersed like a rainbow converge back into a single orbit.

As described above, since it is necessary to deflect the electrons in completely opposite directions, the best results are obtained by using deflection devices with exactly the same characteristics (magnetic field, electric field, magnetic field and electric field) to deflect the electrons in opposite directions. The primary electrons dispersed by the first deflection device 4 pass through the second deflection device 5 and return to the original undispersed primary electron beam state due to the reverse dispersion effect. At this time, the primary electrons are shifted inward a specified distance from the initial axis due to the action of the first deflection device 4 and the second deflection device 5. In this state, they enter the objective lens 7, are focused by the objective lens 7, and are irradiated onto the surface of the sample 8. This reduces the dispersion of the primary electrons 1 and reduces the aberration in the objective lens 7, making it possible to focus the primary electrons into a small spot.

A deflection device can be thought of as a type of arithmetic device. The principle is that various aberrations that occur with electron beam deflection are cancelled out by performing an operation F-1(x) that is the exact opposite of the operation (F(x)) applied the first time. However, this operation has a strange property; when an inverse operation is performed, the electron beam does not return to its original trajectory, but a horizontal shift in the coordinate system occurs, making it possible to change the path of the electron beam. This is done by performing the inverse operation after a period of time has passed since the first operation. Based on this principle, it is desirable for the first deflection device and the second or third deflection device to have exactly the same characteristics but opposite actions.

(3) On the surface of the sample 8, secondary electrons 2 are generated in response to stimulation from the irradiated primary electrons 1, and are accelerated by a voltage (retarding voltage) not shown that is applied between the sample 8 and the objective lens 7, becoming secondary electrons 2 and traveling toward the objective lens 7. The secondary electrons that pass through the objective lens 7 are deflected in the opposite direction to the primary electrons 1 by the second deflection device 6.

(4) The deflected secondary electrons 2 are deflected in a manner that depends on their energy, causing dispersion, but when they are deflected in the opposite direction by the third deflection device 6, reverse dispersion occurs, and they return to their original undispersed secondary electrons 2.

As described above, by using the beam splitter 3 consisting of the first deflection device 4, the second deflection device 5, and the third deflection device 6 of the present invention, it is possible to separate the primary electrons and the secondary electrons without adding any additional chromatic aberration during deflection, even if there is energy dispersion in the primary electrons 1 or the secondary electrons 2. This significantly improves the image resolution of the mapped secondary electrons.

As a result, in this invention, the electromagnetic deflection can be deflected by more than 90 degrees, so secondary electrons can be sent back in a direction almost the same as the direction opposite to the direction from which the primary electrons came. This means that instead of having to make a large device with columns for primary and secondary electrons that open to the left and right as in conventional devices, they can be installed facing in the same direction, making it possible to make the entire electron beam device compact. In this way, because the present invention uses parallel columns and is compact, the two columns can also be implemented as one column.

Figure 2 shows a diagram of an embodiment of the present invention. This is a schematic diagram of the principle configuration of Figure 1 incorporated into an actual device. Here, primary electrons 1, secondary electrons 2, first deflection device 4, second deflection device 5, third deflection device 6, objective lens 7, and sample 8 are the same as those in Figure 1, so their explanations are omitted.

In FIG. 2, the aperture 9 is shown as a schematic diagram showing an opening that passes the primary electrons 1 deflected by the first deflection device 4 and an opening that passes the secondary electrons 2 deflected by the second deflection device 5.

Spacer 5-1 is a spacer that fixes the second deflection device 5 to the objective lens 7.

Coil 7-1 is a coil that passes a current to excite the objective lens 7.

V1 and V2 are voltages applied between the sample 8 and the sample 8. They are retarding voltages that lower the potential of the primary electrons 1 to irradiate the sample 8 with primary electrons at a low acceleration voltage, and accelerate the secondary electrons 2 emitted from the sample 8 to travel upward.

Next, we will explain the operation of the configuration in Figure 2.

(1) Primary electrons 1 generated by the electron gun are deflected inward by the first deflection device 4. They are then bent in the opposite direction by the second deflection device 5 and adjusted so that they are parallel to the trajectory of the primary electrons emitted from the electron gun. In this state, they are adjusted to enter the center (axis) of the objective lens 7 using an alignment lens or mechanical alignment mechanism (not shown). The objective lens 7 is made of a pole piece made of a high magnetic permeability material such as pure iron, permalloy, or bermundur, which is molded into an appropriate shape to generate the desired leakage magnetic field, and a copper wire coated with polyurethane or the like is wound around the pole piece to form a coil. The cut at the tip of the pole piece where the leakage magnetic field is generated is the place where the maximum magnetic field density is shown and functions as an electromagnetic lens. Of course, the objective lens 7 may be made of a permanent magnet as necessary for miniaturization and energy saving. In the case of an electromagnetic lens, heat is generated, so the temperature is kept constant by running cooling water through it. In the case of an electromagnetic type deflection device, heat is also generated, so it is desirable to cool it and manage it at a constant temperature near room temperature in order to keep the deflection amount constant. An electromagnetic deflection device consisting of an electromagnetic coil 7-1 is provided above the objective lens 7, but it is desirable to provide a gap between the devices to provide a shielding effect so that the magnetic field of the deflection device does not leak to the objective lens 7.

(2) An alignment coil or electrode is present between the electromagnetic deflection device and the objective lens 7 so that the electromagnetically deflected primary electrons can pass through the center (axis) of the objective lens 7. Of course, a control device is also present. The primary electrons that pass through the objective lens 7 are converged by the magnetic field of the objective lens 7 and form a nanometer-order spot on the surface of the sample 8.

(3) Secondary electrons 2 generated in sample 8 by the stimulation of irradiation with primary electrons 1 rise vertically due to the force of the accelerating electric field (retarding voltages V1, V2) applied between sample 8 and objective lens 7, are once focused by objective lens 7, and then diverge while being deflected in the opposite direction to primary electrons 1 by second deflection device 5.

(4) The deflected secondary electrons 2 are then deflected in the opposite direction by the third deflection device 6 and rise vertically, resulting in a shift in the direction of the secondary electrons to the right. The secondary electrons 2 form an image on the surface of the detector, and a secondary electron image of the surface of the sample 8 is obtained. Note that, although the example shows a case where the deflection amount is such that the primary and secondary electrons are parallel, the amount of beam shift is arbitrary and can be optimized depending on the configuration method of the device.

Figure 3 shows a detailed diagram of the present invention (electron source).

Figure 3(a) shows an example of a normal TFE.

In FIG. 3(a), the emitter 31 emits electrons. Examples of the emitter 31 include thermal emitters using low work function materials such as tungsten, molybdenum, and LaB6, metal oxides, etc., thermoelectric field emitters (TFEs) in which the work function is lowered by diffusing ZrO into a W tip, cold field emitters that obtain an electron beam by sharpening the emitter tip at around room temperature and applying a high electric field, or more recently, cold field emitters using MEMS (semiconductor microfabrication technology), or photocathodes that excite electrons with light such as an array, coherent, or pulsed laser.

The extractor 32 applies a voltage between the emitter 31 and the extractor 32, and extracts the electron beam using the strong electric field generated by the applied voltage.

The acceleration electrode 33 applies a voltage to the primary electrons extracted by the extractor 32 to the desired acceleration voltage.

The lens 34 focuses the primary electrons accelerated by the acceleration electrode 33.

The objective aperture 35 allows only the primary electrons that pass through the objective lens aperture 35 to enter the objective lens 8 (not shown), which then narrows the beam and irradiates it onto the sample 8.

Next, we will explain the configuration in Figure 3(a).

(1) In FIG. 3(a), a single primary electron beam is emitted from an emitter 31, and the single primary electron beam is focused by an objective lens 7 (not shown) through an objective aperture 35 with a single hole, and irradiated onto a sample 8.

Figure 3(b) shows an example of a multi-beam. The emitter 31, extractor 32, acceleration electrode 33, and lens 34 in Figure 3(b) are the same as those in Figure 3(a), so their explanation is omitted.

In FIG. 3B, the objective aperture 35 is an objective aperture having multiple holes, which form multiple primary electron beams corresponding to the holes. The diameter of the holes is on the order of several microns to several tens of microns.

Next, we will explain the configuration in Figure 3(b).

(1) In FIG. 3(b), an emitter 31 emits one primary electron beam, and an objective aperture 35 with multiple holes forms multiple primary electron beams, which are then narrowed by an objective lens 7 (not shown) and each beam is irradiated onto a sample 8.

Figure 3(c) shows an example of a multi-emitter.

In FIG. 3(c), emitter 31-1 has multiple emitters.

Extractor 32-1 has a number of extractors corresponding to the number of emitters 31-1.

The acceleration electrode 33-3 has a number of acceleration electrodes corresponding to the number of emitters 31-1.

Lens 34-1 has a number of lenses (converging lenses) corresponding to the number of emitters 31-1.

The objective aperture 35-1 has a number of holes corresponding to the number of emitters 31-1.

Next, we will explain the configuration in Figure 3(c).

(1) In FIG. 3(c), multiple emitters 31-1 emit multiple primary electron beams, which are formed by an objective aperture 35 with multiple holes, and then narrowed by an objective lens 7 (not shown) to irradiate each of the primary electron beams onto the sample 8. As a result, the multiple primary electron beams emitted from the multiple emitters are narrowed and each is irradiated onto the sample 8.

(2) For this reason, in FIG. 3(c), an array of emitters for a small multi-beam electron gun made using semiconductor microfabrication technology (MEMS technology) is used. A cold field emitter uses the high electric field generated between the emitter and extractor to create a tunnel effect and emit electrons at room temperature. When using a cold field emitter, it is desirable to use an ultra-high vacuum or extremely high vacuum to stabilize the emitter current. The size of the emitter array can be freely changed. It can be freely made from a few square millimeters or less to several square meters or more depending on the application. It can also be made on curved surfaces such as silicon or plastic. Therefore, the total current amount that determines the inspection speed can be freely made from microamperes to ampere orders.

(3) Using MEMS technology, it is possible to easily create emitter arrays with a tip curvature radius of several tens of nanometers. Emitters can be made of currently known materials such as silicon, W, Mo, CNT, and diamond.

By making the distance between the emitter tip and the extractor on the order of microns, it is possible to apply a very low voltage of only about 10 volts and still emit an electron beam at room temperature. In principle, it is the same as a conventional cold field emitter, so the energy width of the emitted electron beam is narrow at 0.3 electron volts, which is convenient for narrowing the beam. Because it is made using semiconductor technology, the characteristics of each emitter are very consistent. The width of the beam can vary over a fairly wide range, from a few microns to a few mm, depending on the area emitted.

(4) Furthermore, when operated with a low emission current of 1 microampere or less per beam, a lifespan of more than one year can easily be achieved. Since each electron beam functions as an independent point light source, multiple beams with extremely uniform current values can be obtained without interfering with each other. The current value is significantly different from that obtained by dividing a single electron source, and can easily exceed 1 nanoampere per beam, and the total current amount can be increased without limit by increasing the number of beams. For example, if 10,000 beams are used, the total current can reach 10 μA, making it possible to create extremely high-speed electron beam inspection equipment that was previously unthinkable.

(5) The extractor, anode, and lenses for collimating the electron beam can be fabricated inside the electron gun using MEMS technology, such as electrostatic lenses.

Figure 4 shows a detailed diagram of the present invention (secondary electron detection device).

Figure 4 (a) shows the case of one secondary electron detector. This Figure 4 (a) shows an example in which secondary electrons generated on the surface of the sample 8 are accelerated to form a beam with a constant energy, then focused at one point using a lens, and an electron detector is placed at that location.

Next, we will explain the features.

(1) In Figure 4(a), a detector with a much smaller cross-sectional area than the original electron beam can be used, so the detector's electrical capacitance can be kept small, enabling ultra-fast detection. Since the detection efficiency changes depending on the incident energy, to avoid this change, it is best to accelerate the secondary electrons sufficiently when they are generated so that the secondary electron energy distribution does not affect the sensitivity.

(2) In addition, by taking advantage of the fact that the focal position changes depending on the energy of the secondary electrons, it is possible to separate and detect the energies by placing multiple electron detection devices at positions different from the focal position. This corresponds to the use of secondary electrons for elemental analysis, etc. If colors are displayed according to energy, the element distribution on the surface of the sample 8 can be obtained as color changes in a color image. In this case, the secondary electrons to be detected are accelerated just before the detector to increase the sensitivity of the electron detector. Photodiodes, avalanche diodes, MCPs, photomultipliers, etc. can be used as electron detection devices.

Figure 4(b) shows a secondary electron detection device having multiple secondary electron detection elements. This Figure 4(b) corresponds to multi-electron beam detection.

(1) By irradiating the sample 8 with multiple electron beams, a group of secondary electrons is generated simultaneously in two dimensions from the surface of the sample 8. The group is accelerated by the voltage applied between the sample 8 and the objective lens 7, and then converged by the lens to form a two-dimensional secondary electron image as shown in the figure. This is the same principle as a bright-field optical microscope. Therefore, the fundamental resolution is roughly determined by the wavelength of the secondary electron beam being used and the numerical aperture NA.

(2) A two-dimensional secondary electron image of the surface of the sample 8 is reproduced in an enlarged form on the focal plane, and the brightness or contrast information of this image is detected by a plurality of secondary electron detectors arranged on a plane. As the secondary electron detector, a photodiode or avalanche diode, in which the protective film on the semiconductor surface has been removed so that secondary electrons can be directly incident, MCP, MPPC, photomultiplier, ultra-high-speed CCD, CMOS, TDI image element, etc. can be used. When a two-dimensional image element is used, the image acquisition speed can be made higher than G pixels per second per device. The most advanced device can achieve 10 G pixels per second. The acquired signal is immediately converted into a digital signal and sent to a computer for image processing. As a communication means, metal wires and optical fiber cables for high-speed communication can be used. The electrical signal generated by the electron detector is converted from an analog signal to a digital signal by an AD converter, and stored in a memory such as a DRAM, SRAM, flash memory, or HDD. Image processing such as filtering is performed by high-speed computing devices such as CPUs, ASICs, FPGAs, and GPUs, and information on the sample surface is reproduced on the display. The obtained images are synthesized as necessary to create an image of the required size and resolution. High-speed inspection can be performed by comparing the obtained image with CAD design data or a nearby image of the same shape as a reference image and detecting differences.

(3) As with a normal CDSEM, CD measurements can be performed by measuring the length of each point in the obtained image. Since it is possible to quickly capture large, high-definition images, it is also possible to extract the contours of the captured images and use them in optical simulations of photomasks.

Figure 4(c) shows a secondary electron detection device made of a two-dimensional imaging element. This Figure 4(c) is compatible with multi-electron beam detection, etc.

(1) Figure 4 (c) shows a device that can use a general high-speed photodetector. A secondary electron beam is converged and accelerated by a lens, and then collided with the surface of a scintillator to convert the electrons into light. The secondary electron image converted into light is detected using a photodiode, avalanche diode, MCP, MPPC, photomultiplier, CCD, CMOS, TDI imaging element, etc. For the scintillator, it is preferable to use a GaN-based semiconductor scintillator with a response speed of the order of nanoseconds, inorganic material, organic material, or plastic material. Note that the scintillator becomes charged when irradiated with a large amount of electron beam, so to prevent charging, a metal film such as aluminum on the order of nanometers is evaporated onto the surface and used while being earthed. It is recommended to match the emission wavelength of the scintillator with the wavelength at which the photodetector has maximum sensitivity.

(2) When performing image accumulation and electron detection, as in a two-dimensional imaging element, a scintillator with a slightly slower response speed of around 100 ns may be easier to use.

Figure 5 shows an example of the device of the present invention. This figure shows the appearance of an electron beam inspection device that uses a beam splitter.

In FIG. 5, the electron gun 41 emits primary electrons.

The blanking device 42 quickly blocks the primary electrons emitted from the electron gun 41.

The blanking aperture 43 is an aperture that blocks the primary electrons deflected by the blanking device 42.

The objective aperture 44 is an aperture that allows the central portion of the primary electrons to pass through and is narrowed by the objective lens 48 to irradiate the sample.

The first deflection device 45 is the first deflection device 4 already described.

The second deflection device 46 is the second deflection device 5 already described.

The third deflection device 47 is the third deflection device 6 already described.

The objective lens 48 narrows the primary electrons and irradiates them onto the sample.

Mirror 49 is a mirror that reflects the laser beam and is used to precisely measure the position of the XYZ stage 51.

The deflection device 50 scans a finely focused beam of primary electrons over a plane on the sample.

The XYZ stage 51 holds a sample (mask, wafer, etc.) and moves it precisely in the X, Y, and Z directions.

The vacuum chamber 52 is a container that stores the XYZ stage 51 and other components in a vacuum.

The vacuum pump 53 is a pump that evacuates the inside of the vacuum chamber 52 to a vacuum.

The electron detection device 54 is a device that detects secondary electrons.

Next, we will explain the configuration.

(1) The vacuum chamber 52 is maintained at a high vacuum, usually around minus 4 to 5 pascals, using a dry pump or TMP. The electron gun 41 is maintained at an ultra-high or extremely high vacuum. The primary electrons generated by the electron gun 41 are accelerated to the required energy and shaped into a parallel beam by a lens. The shaped electron beam passes through the blanking device 42 and blanking aperture 43. The blanking device 42 and blanking aperture 43 have the function of rapidly turning the primary electron beam on and off, and determine whether or not to irradiate the sample with the primary electron beam.

(2) When the primary electron beam source is a multi-electron beam, the blanking aperture 43 array can be equipped with the function of turning individual beams on and off. A separate blanking aperture 43 can also be provided to turn the entire primary electron beam on and off. The primary electron beam that passes through the blanking aperture 43 is irradiated onto the objective aperture 44, which determines the size and shape of the irradiated electron beam. The objective aperture 44 is a thin metal film, mainly tens of microns thick, with hole sizes and spacing ranging from several microns to several hundred microns. Aperture materials are made of high-melting point metals such as molybdenum and tungsten. Electromagnetic or mechanical beam alignment means are attached to these apertures to allow the primary electron beam to pass accurately.

(3) The primary electron beam that has passed through the objective aperture 44 is beam-shifted by the beam splitter (first deflection device, second deflection device, third deflection device) of the present invention, and then enters the objective lens 48. It is desirable to have an electromagnetic or mechanical alignment mechanism in order to accurately enter the center of the objective lens 48. It is desirable that the electron beam that enters the beam splitter is converged so that the cross section of the electron beam is small so as not to generate unnecessary aberration. It is desirable to enter the objective lens 48 vertically in order to reduce aberration. Before or after passing through the objective lens 48, the primary electron beam is deflected by a deflection device 50 for scanning the primary electron beam. In order to reduce aberration through the center of the objective lens 48, two-stage deflection or deflection is performed directly below the objective lens 48. This primary electron beam deflection is performed to scan the primary electron beam two-dimensionally on the surface of the sample. In general, the scanning width is about several microns to several hundreds of microns on the sample.

(4) As is known in general SEMs or electron beam inspection equipment, primary electron beam scanning is performed based on a stepped voltage waveform sent from a DA converter in synchronization with an image formation signal such as a pixel clock under instructions from a computer. For example, if a scanning signal is created using a 16-bit DA converter, scanning along the X-axis or Y-axis of approximately 64K pixels can be performed. Scanning in any direction is also possible by appropriately combining the X-axis and Y-axis scanning signals output to the DA converter.

(5) In order to reduce the aberration of the objective lens 48, it is desirable to perform beam scanning of the primary electrons by deflecting the beam axis of the primary electrons in two stages just before they enter the objective lens 48 so that they pass through the axial center of the objective lens 48. If the primary electron beam is scanned widely, the linearity deteriorates and scanning distortion is likely to occur. Distortion can be reduced by placing a scanning deflection electrode under the objective lens 48. However, scanning widely enough to affect the focal depth will result in a blurred image, so in that case the blur is corrected by changing the focus of the objective lens 48 in synchronization with the scanning signal (dynamic focus).

(6) Signal electrons such as secondary electrons generated on the sample surface during scanning are accelerated by the bias voltage (retarding voltage 9) applied between the sample and the objective lens 48, ascend vertically, and enter the objective lens 48. In order to reduce the aberration generated by the objective lens 48, it is desirable to accelerate as much as possible, about 15 KV. Generally, for safety reasons, the objective lens 48 is often set to ground potential and the sample potential is made negative. For example, when the irradiation energy to the sample is set to 1 KV, the sample potential is set to minus 14 KV.

(7) The secondary electron beam that passes through the objective lens 48 travels in the opposite direction to the primary electrons, so it is bent in the opposite direction to the primary electron beam by the action of the magnetic field of the beam splitter (second deflection device 46), and the secondary electron beam is separated from the trajectory of the primary electrons.

(8) The separated secondary electron beam is affected by the scanning of the primary electrons to form an image, so the secondary electron signal is also scanned. If this continues, the focal position on the electron detection element will move up, down, left, and right, making stable image detection impossible. Therefore, the secondary electron beam is scanned again in the reverse direction in synchronization with the primary electron beam scanning so that the focal position can stop at a fixed position on the electron detection element coordinates, and controlled so that the secondary electron image formed on the electron detection device does not move at all. If the size of the detection element is larger than the range of secondary electron landing points that fluctuates due to beam scanning, correct image detection can be performed without reverse scanning of the secondary electron beam.

Figure 6 shows an example of the device of the present invention (part 2). In addition to Figure 5, Figure 6 is characterized by the provision of an electron-transmitting thin film 55 on the side closer to the sample than the center of the objective lens. This thin film 55 is made of a thin silicon or its compound, metal film, or carbon film of several atomic layers such as graphene film, which is on the order of several nm to several tens of nm. Electron beams accelerated to several hundred electron volts or more can pass through these films with almost no scattering. On the other hand, these thin films have the role of mechanically separating a low vacuum region of about 10 Pascals from a high vacuum region of 10 to the power of minus 3 or more. At the same time, these thin films are conductive and a bias voltage can be applied.

The primary electron beam generated by the electron gun 41 has an energy of, for example, about 15 KV. After the beam position of the primary electrons is shifted by a deflector, it is incident on the objective lens 48. The primary electron beam incident on the objective lens 48 is narrowed down to a thin primary electron beam by the converging action of the objective lens 48, which passes through the thin film 55 and is irradiated onto the sample surface. Secondary electrons are generated on the sample surface by the irradiated primary electron beam.

The secondary electrons generated have low energy and cannot pass through the thin film (diaphragm) 55 as is. Therefore, a bias voltage is applied between the sample and the thin film 55 to accelerate the secondary electron beam and pass it through the diaphragm 55. The vacuum chamber 52 is in a low vacuum state of about 10 Pascals, so if a high bias is applied, a discharge will occur. Therefore, a voltage of several hundred volts is applied so that the electrons are given enough energy to pass through the thin film 55 without causing a discharge. In this way, the secondary electrons have enough energy to pass through the thin film 55 and enter the high vacuum region. Since there is no risk of discharge, the secondary electrons that have entered the high vacuum region are further accelerated between the thin film 55 and the objective lens 48, enter the objective lens 48, and are defocused to form an image of the sample surface on the surface of the electron detection device 54.

By adopting the above configuration, it is possible to hold the sample in a low vacuum state while using a high-energy primary electron beam, thereby preventing charging. Preventing charging makes it possible to reduce the energy distribution of the secondary electrons generated. At the same time, the secondary electron beam can be detected by passing it through the objective lens 48 so that the chromatic aberration of the beam is not large.

Figure 7 shows an example of the device of the present invention (part 3). This figure shows an example in which an aberration correction device 58 is provided. In general, this device can correct spherical aberration and chromatic aberration of the objective lens 48, etc., using a multi-stage multipole element. It has long been said that axially symmetric electromagnetic lenses can only produce positive aberrations, and therefore it is impossible to correct aberrations. However, at the end of the 20th century, Rose and Heider et al. developed a device that can create negative aberrations by combining a multipole lens such as a hexapole or octapole with a transfer lens to create an asymmetric field, and can reduce the aberration to zero when combined with the original positive aberration. By further increasing the number of poles and stages, it becomes possible to correct even higher-order aberrations. If spherical aberration and chromatic aberration can be reduced to zero, there will be no need to increase the energy of the primary electron beam to 10 KV or more, which was previously done to reduce the effect of the aberration of the objective lens.

The example in Figure 7 is characterized by the fact that an aberration correction device 58 is implemented in each of the columns on the primary electron side and the secondary electron side. The aberration correction device 58 is an element that can correct spherical aberration and chromatic aberration by combining multipoles. The advantage of this device 58 is that it makes it possible to correct the aberration of the objective lens 48 and the converging lens and focus the primary electrons to a small spot size without having to increase the energy of the primary electrons to something like 15 KV.

In FIG. 6, the energy of the primary electron beam is increased so that the effect of the energy dispersion of the primary electrons is reduced to the level of error, thereby avoiding the occurrence of chromatic aberration. However, if the energy of the primary electron beam is increased, not only does the electron beam column require a high withstand voltage, making the device larger, but unnecessary or harmful electromagnetic waves such as X-rays are emitted from the aperture where the primary electron beam is irradiated, which is not good as it can expose the sample or have a negative effect on the human body. Furthermore, in order to reduce the aberration of the secondary electrons, it is necessary to apply a bias to the substrate to accelerate them, and it is necessary to apply a high voltage to the narrow, highly discharge-prone area between the sample and the objective lens 48. If the distance between the objective lens 48 and the sample is increased to obtain a high withstand voltage, the NA becomes smaller, the resolution decreases, and the beam spot becomes larger.

The vacuum pressure resistance design is said to be several kilovolts per 1 mm interval, so to obtain a pressure resistance of 15 KV, the sample surface and the tip of the objective lens 48 must be separated by 5 mm or more, which would make degradation of resolution unavoidable. Furthermore, low vacuum technology used to prevent charging of non-conductive sample surfaces cannot be adopted because it easily discharges when a bias voltage of several hundred volts is applied.

As shown in Figure 7 of this embodiment, by using an aberration correction device 58, the aberration caused by the objective lens 48 on the primary electron beam and the aberration of the objective lens 48 on the secondary electron beam are corrected to zero, making it possible to create a system with very small aberrations even when using low energy of 5 KV or less. As a result, a primary electron beam spot as small as that when high energy is used can be created on the sample surface. Similarly, high resolution can be maintained for secondary electrons as they are input to the electron detection device 54.

Since a large sample bias (retarding voltage) exceeding several hundred volts, which causes discharge, is not applied to the primary electron beam or the secondary electron beam, low vacuum mode measurement, which is effective in preventing charging, can be performed. The vacuum chamber during high vacuum mode measurement is usually maintained at minus 4 to 5 pascals, but when performing low vacuum measurement, clean oxygen, nitrogen, air, or inert gas can be introduced from outside the chamber using a mass flow controller or the like to maintain a vacuum of about 1 to 100 pascals. In this way, when in a low vacuum state, the charge on the sample surface is neutralized by the action of positive and negative ions generated by the irradiation of the primary electron beam, and normal measurement conditions can be maintained. This effect makes it possible to perform high-speed single beam or ultra-high-speed multi-beam inspection while keeping the potential of the sample surface very stable regardless of the pattern.

Figure 8 shows an example of a beam splitter of the present invention. This Figure 8 shows examples of the first deflection device 4, second deflection device 5, and third deflection device 6 that constitute the beam splitter 3 of Figures 1 and 2 described above.

Figure 8 (a) shows an example of a parallel plate. The parallel plate type consists of two electrodes for generating an electric field and a pole piece for generating a magnetic field perpendicular to the electric field.

The electrodes used to generate the electric field in beam splitters are usually made of metal, but if a material with a relative permeability close to 1 is used, such as transparent electrodes ITO, aluminum, copper, or silver, interference with the simultaneously applied magnetic field is reduced, and it is possible to create a wide area in which the electric and magnetic fields spread uniformly across each other at right angles. This makes it possible to apply a uniform magnetic or electric field even when using a thick beam over 100 microns, as in a projection type inspection device, and to obtain good deflection characteristics. The pole pieces for applying the magnetic field are made of metals such as permalloy, which have a high magnetic permeability.

In FIG. 8(a), the pole piece 61 is shown as both a pole piece for applying a magnetic field and an electrode for applying an electric field. However, if a pole piece (2 poles) for applying a magnetic field is provided so as to be perpendicular to the electric field in addition to the electrode (2 poles) for applying an electric field using the electrode material described above, a uniform perpendicular electric field and magnetic field can be obtained over a wide range. Since the magnetic field can act by passing through an electrode made of a material with a magnetic permeability of 1, the pole piece for generating a magnetic field can also be placed behind the electrode for generating an electric field. The electrode/pole piece 61 shown in the figure usually has 4 poles arranged symmetrically about the axis. It may also be multi-pole, with 6 poles, 8 poles, 10 poles, 12 poles, 16 poles, etc.

The coils 62 pass current through them to generate a magnetic field, which is then applied to each pole piece (magnetic pole). In the case of a four-pole rotor, one coil 62 is provided for each pole piece (magnetic pole).

Yoke 63 is a yoke that shorts the magnetic field generated by coil 62 to prevent it from leaking to the outside.

By forming an axially symmetrical 4-pole, 6-pole, 8-pole, 12-pole or other multipole deflection device having the above configuration, it is possible to generate an electric field, a magnetic field, or both an electric field and a magnetic field on the axis and deflect primary or secondary electrons. The first deflection device 4 and the third deflection device 6 may deflect with only an electric field or a magnetic field, or with both an electric field and a magnetic field. The second deflection device 5 deflects with at least a magnetic field, or with an electric field and a magnetic field, and when the secondary electrons travel in the opposite direction to the travel direction of the primary electrons, it is necessary to adjust the degree of deflection by the magnetic field and electric field so as to separate the two.

Figure 8(b) shows an example of a pattern yoke type. This pattern yoke type in Figure 8(b) shows only the part that corresponds to the electrode/pole piece 61 in Figure 6(a).

In FIG. 6(b), the cut 71 is a cut made in a cylinder to form a cylindrical pole blank 74 as shown.

Tap 72 is a tap for fixing the rotating field deflector.

Tap 73 is a tap for attaching the jig.

The cylindrical pole material 74 is a cylindrical pole material (corresponding to the electrode/pole piece 61 in FIG. 6(a)) in which the cylinder is separated by the notches 71 shown in the figure.

As described above, a cylindrical pole material 74 is created by cutting a notch 71 into the cylinder to match the direction of rotation of the primary electrons (or secondary electrons), and by using this as the electrode/pole piece 61 in Figure 6(a), it becomes possible to rotate the electrode and magnetic pole in accordance with the degree to which the primary electrons (or secondary electrons) rotate as they travel, making it possible to reduce aberration.

Figure 8 (c) shows an example of a Wien filter. This well-known Wien filter (8 poles) in Figure 8 (c) consists of poles n = 1, 2, 3, 4, 5, 6, 7, 8 as shown, with poles (8 poles) that serve as both electrodes and magnetic poles arranged axially symmetrically on the inside, and eight sets of coils that generate a magnetic field are provided on the outside. The outermost part is a cylindrical yoke that short-circuits the magnetic field.

With the above configuration, by applying an electric field, a magnetic field, or both an electric field and a magnetic field to the octapoles, it is possible to deflect primary and secondary electrons, or to deflect the primary and secondary electrons in opposite directions to separate them.

Figure 9 shows an example of a beam splitter (pattern yoke type) of the present invention. This figure shows an example in which the cylindrical pole material 74 of Figure 8 (b) described above is used as the pole piece/electrode 65 of Figure 9, and shows a top view of the pattern yoke.

In FIG. 9, the pole piece/electrode 65 corresponds to the cylindrical pole material 74 in FIG. 8(b) described above, and functions as both a magnetic pole and an electrode.

The coil 66 applies a magnetic field to the pole piece/electrode 65.

The magnetic shield 67 is a cylindrical magnetic shield that short-circuits the magnetic field that is generated by passing a current through the coil 61 and directed outward (outside).

By configuring it as described above, it is possible to reduce the deflection aberration of the primary electrons or secondary electrons by configuring electrodes and magnetic poles that rotate in the axial direction of the previously described Figure 8 (b) and corresponding this to the angle of rotation in the direction of travel of the primary electrons or secondary electrons.

Figure 10 shows an explanatory diagram of the device operation of the present invention.

Figure 10(a) shows the behavior of primary electrons, and Figure 10(b) shows the behavior of secondary electrons emitted from the sample.

In FIG. 10(a), S1 is an electron gun that emits a beam of primary electrons.

S2 converts the beam into a parallel beam. This is done by converting the primary electron beam emitted from the electron gun in S1 into a parallel beam using the condenser lens shown in the figure.

S3 is deflected by the first deflector. This is deflected as shown by the first deflection device 4 in Figures 1 and 2 described above.

S4 is deflected by the second knitting device. This is deflected as shown by the second deflection device 5 in Figures 1 and 2 described above.

S5 is converged by the objective lens. This is because the objective lens 7 in Figures 1 and 2 narrows the primary electron beam.

S6 slows down the primary electrons. This applies the retarding voltage V1 or V2 in FIG. 2 described above, and slows down the primary electrons (decelerates the acceleration voltage).

S7 irradiates the sample. This scans the sample 8 with a finely focused beam of primary electrons that has been decelerated by the retarding voltage of S6. When the sample 8 is irradiated with the primary electrons, secondary electrons are generated.

As a result of the above, the primary electrons generated by the electron gun in the configuration of Figures 1 and 2 described above are deflected in two stages by the first deflector and the second deflector, resulting in a shift in the traveling direction of the primary electron beam, which can be narrowed down and irradiated onto the sample 8 while scanning it in a plane, thereby emitting secondary electrons.

Next, the operation of secondary electrons will be explained in the order shown in Figure 10 (b).

In FIG. 10(b), S11 generates secondary electrons. This corresponds to S7 in FIG. 10(a) where the sample 8 is irradiated with primary electrons while being scanned across the plane. Secondary electrons are emitted (generated).

S12 accelerates the secondary electrons. The secondary electrons generated in S11 are accelerated by the retarding voltage V1 or V2 in Figure 2 as described above.

S13 passes through the objective lens. This is because the secondary electrons accelerated in S12 travel upwards while drawing a spiral due to the action of the axially symmetric strong magnetic field of the objective lens 7 in FIG. 2 described above, and pass through the objective lens 7.

S14 is deflected by the second deflector. This is deflected as shown by the second deflection device 5 in Figures 1 and 2 described above, and the primary electrons and the secondary electrons are separated.

S15 deflects the secondary electrons using the third deflector. This deflects the secondary electrons separated by S14 in the opposite direction to cancel deflection aberrations, etc.

S16 forms an image with a projection lens. This is done by forming (imaging) an image of the secondary electrons on the surface of the electron microscope using a projection lens for the secondary electrons deflected by the third deflector of S15.

S17 detects with an electron detector. The secondary electrons imaged in S16 are detected with a secondary electron detector.

S18 is a signal amplifier. It amplifies the signal of the secondary electrons detected by S17.

S19 processes the images on a PC.

As a result of the above, the secondary electrons emitted from the sample 8 in the configurations already described in Figures 1 and 2 are separated from the primary electrons by the second and third deflectors, and are deflected in two stages, which results in a shift in the traveling direction of the secondary electron beam, and the secondary electron beam is imaged with high resolution, making it possible to detect a high-resolution secondary electron image of the surface of the sample 8.

Figure 11 shows the device adjustment flowchart of the present invention.

Figure 11(a) shows the adjustment flowchart.

In FIG. 11(a), S21 applies an initial electric field and magnetic field. This is done by initially setting the optimal voltage, current, and voltage and current values found through experiments for the first deflection device 4, second deflection device 5, and third deflection device 6 in FIG. 1 and FIG. 2.

S22 changes the electric field and magnetic field. If the first deflection device 4, second deflection device 5, and third deflection device 6 in Figures 1 and 2 do not operate adequately with the electric field and magnetic field initially set in S21, the electric field (voltage) and magnetic field (current) are finely adjusted to optimally deflect and maximize the amount of secondary electrons.

In S23, it is determined whether the amount of secondary electrons is maximum. If YES, the amount of secondary electrons detected by the detectors in FIG. 1 and FIG. 2 is maximum, and the electric field (voltage), magnetic field (current), and electric field and current of the first deflection device 4, the second deflection device 5, and the third deflection device 6 have been adjusted to the optimal deflection degree, so the process ends. If NO, S22 is repeated.

As described above, for the configurations of Figures 1 and 2, the electric field, magnetic field, and electric field and magnetic field of the first deflection device 4, second deflection device 5, and third deflection device 6 are initially set to initial values determined through experiments, and the electric field, magnetic field, and electric field and magnetic field are then adjusted so that the amount of secondary electrons is maximized, making it possible to adjust the first deflection device 4, second deflection device 5, and third deflection device 6.

Figure 11(b) shows the axis adjustment flowchart (deflection aberration).

In FIG. 11(b), S31 applies an initial electric field and magnetic field. This is done by initially setting the voltage, current, and voltage and current values that minimize the deflection aberration determined by experiment for the first deflection device 4, second deflection device 5, and third deflection device 6 in FIG. 1 and FIG. 2.

In S32, the alignment parameters are changed. If the deflection aberration of the first deflection device 4, second deflection device 5, and third deflection device 6 in Figures 1 and 2 is large and a sufficient amount of secondary electrons cannot be detected with the electric field and magnetic field initially set in S31, fine adjustments are made to the electric field and magnetic field of the opposing poles, and the central axes of the electric field and magnetic field are adjusted so that the amount of secondary electrons is maximized.

In S33, it is determined whether the amount of secondary electrons is maximum. If YES, the amount of secondary electrons detected by the detectors in FIG. 1 and FIG. 2 is maximum, and the axial centers of the electric field and magnetic field of the first deflection device 4, the second deflection device 5, and the third deflection device 6 have been optimally adjusted, so the process ends. If NO, S32 is repeated.

As described above, with the configurations of Figures 1 and 2, the deflection aberration of the first deflection device 4, the second deflection device 5, and the third deflection device 6 is initially set to the initial value determined through experiments that minimizes it, and then the deflection aberration can be adjusted to a minimum by adjusting the axial center and adjusting the strength of the opposing poles of the electric field and magnetic field so that the amount of secondary electrons is maximized.

Figure 11 (c) shows the axis adjustment flowchart (rotation direction).

In FIG. 11(b), S41 applies an initial electric field and magnetic field. This is done by initially setting the voltage, current, and voltage and current values that will result in the optimal rotation direction determined by experiment for the first deflection device 4, second deflection device 5, and third deflection device 6 in FIG. 1 and FIG. 2.

In S42, the alignment parameters are changed. If the direction of rotation caused by the first deflection device 4, second deflection device 5, and third deflection device 6 in Figures 1 and 2 is shifted and a sufficient amount of secondary electrons cannot be detected if the electric field and magnetic field initially set in S41 are left unchanged, the electric field and magnetic field of the opposing poles are finely adjusted to adjust the direction of rotation caused by the electric field and magnetic field, and the amount of secondary electrons is adjusted to be maximized.

In S43, it is determined whether the amount of secondary electrons is maximum. If the answer is YES, the amount of secondary electrons detected by the detectors in FIG. 1 and FIG. 2 is maximum, and the direction of rotation by the electric field and magnetic field of the first deflection device 4, the second deflection device 5, and the third deflection device 6 has been optimally adjusted, so the process ends. If the answer is NO, S42 is repeated.

In this way, with the configuration of Figures 1 and 2, the direction of rotation caused by the electric field and magnetic field of the first deflection device 4, second deflection device 5, and third deflection device 6 is initially set to the initial value determined by experiment, and then the direction of rotation is adjusted by adjusting the strength of the opposing poles of the electric field and magnetic field so that the amount of secondary electrons detected after passing through the deflectors is maximized. This makes it possible to optimally adjust the direction of rotation caused by the voltage and magnetic field of the first deflection device 4, second deflection device 5, and third deflection device 6. In principle, aberration can be minimized by arranging the deflection devices symmetrically with respect to the original electron beam trajectory and adjusting them so that the passing electron beams are as similar as possible and opposite to each other.

FIG. 1 is a diagram illustrating the principle of the present invention. FIG. 1 is a configuration diagram of an embodiment of the present invention. FIG. 2 is a detailed explanatory diagram (electron source) of the present invention. FIG. 2 is a detailed explanatory diagram (secondary electron detection device) of the present invention. 1 is an example of an apparatus according to the present invention. 2 is a second example of an apparatus according to the present invention. 3 is an example (part 3) of the device of the present invention. 1 is an example of a beam splitter according to the present invention. 1 shows an example of a beam splitter (pattern yoke type) of the present invention. FIG. 2 is an explanatory diagram of an operation block of the device of the present invention. 2 is a flow chart of the measures adjustment of the present invention.

1: Primary electrons 2: Secondary electrons 3: Beam splitter
4: First deflection device 5: Second deflection device 5-1: Spacer 6: Third deflection device 7: Objective lens 7-1: Coil 8: Sample 9: Aperture 31, 31-1: Emitter 32, 32-1: Extractor 33, 33-1: Acceleration electrode 34, 34-1: Lens 35, 35-1: Objective aperture 41: Electron gun 42: Blanking device 43: Blanking aperture 44: Objective aperture 45: First deflection device 46: Second deflection device 47: Third deflection device 48: Objective lens 49: Mirror 50: Deflection device 51: XYZ stage 52: Vacuum chamber 53: Vacuum pump 54: Electron detection device 55: Diaphragm (thin film)
56: Mass flow control device 57: Gas 58: Aberration correction device 61: Electrode/pole piece 62: Coil 63: Yoke 65: Pole piece/electrode 66: Coil 67: Magnetic shield 71: Notch 72:, 73: Tap 74: Cylindrical pole material V1, V2: Retarding voltage

Claims (5)

A multi-beam inspection device which irradiates a sample with primary electrons generated by a multi-beam electron gun, detects secondary electrons emitted from the sample, and generates a secondary electron image of the sample,
A primary electron irradiation system that generates and accelerates primary electrons using a multi-beam electron gun;
a first deflection device that deflects the primary electrons generated by the primary electron irradiation system;
a second deflection device, which is formed of at least a magnetic field, for deflecting the primary electrons deflected by the first deflection device in a reverse direction to cancel aberration, irradiating the sample with the primary electrons in agreement with an axis of an imaging system, and for deflecting secondary electrons emitted from the sample in a reverse direction to the primary electrons to separate them;
an imaging system including an objective lens for narrowing the primary electrons, which have been deflected by the second deflection device and aligned with an axis of the imaging system, to irradiate a sample, and for allowing secondary electrons emitted from the sample to enter the second deflection device;
a third deflection device that deflects the secondary electrons deflected and separated by the second deflection device in a direction opposite to a deflection direction of the second deflection device to cancel aberration;
a secondary electron detection system that detects the secondary electrons after being deflected by the third deflection device and canceling the aberration,
A multi-beam inspection device characterized in that the axis of the primary electron irradiation system and the axis of the secondary electron detection system are configured symmetrically around the axis of the imaging system, and the aberrations caused by the deflection are canceled out, thereby reducing the aberrations generated in the primary electrons and the secondary electrons. The multi-beam inspection device according to claim 1, characterized in that the multi-beam electron gun is composed of a cold cathode array. The multi-beam inspection device according to any one of claims 1 to 2, characterized in that a retarding bias voltage is applied between the sample and the objective lens. A multi-beam inspection device according to any one of claims 1 to 3, characterized in that a diaphragm is provided in the objective lens portion, and the sample side is maintained at a low vacuum and the opposite side at a high vacuum, with the diaphragm as a boundary. 1. A multi-beam inspection method for irradiating a sample with primary electrons generated by a multi-beam electron gun and detecting secondary electrons emitted from the sample to generate a secondary electron image of the sample, comprising:
A primary electron irradiation system that generates and accelerates primary electrons using a multi-beam electron gun;
a first deflection device that deflects the primary electrons generated by the primary electron irradiation system;
a second deflection device, which is formed of at least a magnetic field, for deflecting the primary electrons deflected by the first deflection device in a reverse direction to cancel aberration, irradiating the sample with the primary electrons in agreement with an axis of an imaging system, and for deflecting secondary electrons emitted from the sample in a reverse direction to the primary electrons to separate them;
an imaging system including an objective lens for narrowing the primary electrons, which have been deflected by the second deflection device and aligned with an axis of the imaging system, to irradiate a sample, and for allowing secondary electrons emitted from the sample to enter the second deflection device;
a third deflection device that deflects the secondary electrons deflected and separated by the second deflection device in a direction opposite to a deflection direction of the second deflection device to cancel aberration;
a secondary electron detection system for detecting the secondary electrons after the aberration is cancelled by the deflection by the third deflection device,
A multi-beam inspection method, characterized in that an axis of the primary electron irradiation system and an axis of the secondary electron detection system are configured symmetrically around the axis of the imaging system, and aberrations caused by the deflection are canceled out, thereby reducing the aberrations generated in the primary electrons and the secondary electrons.

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