JP2021048114A - Scanning electron microscope and secondary electron detection method for scanning electron microscope - Google Patents

Abstract

To provide a scanning electron microscope and a secondary electron detection method for a scanning electron microscope that cancel and reduce deflection aberrations generated at a first deflector, a second deflector, and a third deflector to detect secondary electrons generated on a sample's surface with high spatial resolution.SOLUTION: A scanning electron microscope comprises: a first deflector 4 for deflecting primary electrons generated at a primary electron irradiation system; a second deflector 5 that deflects primary electrons deflected by the first deflector in the reverse direction to cancel aberrations, makes a direction of the primary electrons agree with an axis of an imaging system to make the primary electrons be radiated to a sample, and deflects secondary electrons discharged from the sample in a direction reverse to that of the primary electrons to separate the secondary electrons, the second deflector constituted by a magnetic field and an electric field; the imaging system that thinly narrows a beam of the primary electrons deflected by the second deflector and directed to the direction made to agree with the axis of the imaging system before radiating the narrowed beam to the sample and makes the secondary electrons discharged from the sample be incident on the second deflector 5, the imaging system constituted by an objective lens; and a secondary electron detection system for detecting the secondary electrons after being deflected by the second deflector 5.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for detecting secondary electrons of a scanning electron microscope and a scanning electron microscope that detect secondary electrons emitted from a sample and generate a secondary electron image of the sample.

The semiconductor industry is supported by the improved device performance and cost benefits brought about by the advancement of microfabrication technology, which is famous for Moore's Law. However, the microfabrication limit of semiconductor devices is determined by exposure technology. The exposure technique consists of an original plate called a photomask for creating a pattern, an exposure apparatus, and a resist for forming the pattern. Since the current exposure apparatus uses a 4: 1 reduction exposure technique, a structure four times as large as the structure on the silicon wafer on which the semiconductor device is actually manufactured is formed on the photomask.

The biggest issue 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 apparatus and a defect will occur on the wafer.

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

Since a light source of 193 nm has been used as an exposure light source since the end of the 20th century, patterns on photomasks have been inspected for a long time using an optical mask pattern inspection device that uses a laser beam of 193 nm or the like as illumination light.

However, since the exposure technology using EUV light with a short wavelength of 13.5 nm was introduced in earnest in 2019, the fine processing limit that can be exposed becomes smaller, and the pattern on the photomask is as large as the conventional minimum pattern size of about 100 nm. As a result, it became as small as 60 nm or less, and sufficient inspection could not be performed with the conventional light of 193 nm.

On the other hand, a so-called actinic inspection device using a wavelength of 13.5 nm is also under development. However, when the wavelength is as short as 13.5 nm, it is absorbed by air, so that it becomes necessary to evacuate the device, which is very complicated. Further, since there is no optical lens capable of transmitting light of 13.5 nm, all the optical systems are reflective optical systems, which are also complicated and inefficient.

The resolution of the optical device has a property of being proportional to the aperture ratio NA. For example, in the case of an optical system using 193 nm, a large aperture ratio exceeding 1 can be realized by using immersion or oil immersion, so that a pattern of about 40 nm can be resolved even though the wavelength is as long as 193 nm. Can be done. On the other hand, when EUV light is used, the aperture ratio is as small as 0.3 because the reflected optical system is used, and even though the wavelength is as short as 1/10, only a resolution of about 27 nm can be obtained. However, the performance improvement is small for the shorter wavelength.

Further, for example, when the detection target is particles, the reflected light weakens in proportion to the sixth power of the particle size, and the reflected light becomes stronger at the square of the wavelength. That is, as the particle size becomes smaller, the signal strength sharply weakens, so that the detection sensitivity drops sharply. As described above, the photomask inspection technology using the optical technology has reached the technical limit. In addition, since the device using the conventional optical principle operated in the atmosphere, it was easy to manufacture and operate the device, but when the wavelength is shortened, it is absorbed by the air, so a vacuum chamber is required and it is superior to the electron beam in terms of usability. Is gone.

On the other hand, there is an electron microscope as a technique for realizing a high resolution on the order of nm or less. An electron beam type inspection technology using an electron beam has been developed for more than 30 years. Although it has been commercialized, it has not been put into practical use as a main inspection device.

Unlike a laser beam, an electron beam does not have an electron beam source with a small energy dispersion and high brightness like a laser. Furthermore, since electrons have a negative charge, when they are narrowed down, the electrons repel each other electrostatically. Therefore, when a large current required for high-speed inspection is passed, the minimum beam spot size becomes larger than the optical limit, and the resolution deteriorates. That is, when one electron beam is used, the resolution and the inspection speed have a very tight trade-off relationship, so that the inspection speed cannot be easily increased.

For example, the maximum speed that can be achieved with one currently known beam is at most hundreds of megapixels per second. Since the pattern is written on the photomask in an area of about 10 cm square, it is necessary to inspect the entire area. For example, in order to inspect the pattern on the current photomask with a resolution of 10 nm that can sufficiently resolve it, it is necessary to acquire 10 14 pixel pixels. For example, if a pixel is acquired at 100 Mpixels per second, 10 6 seconds is required, which takes 277 hours, that is, 10 days or more. Since the conventional photomask inspection device can inspect one photomask in about 2 hours, this is too slow to be practically used.

On the other hand, recently, a method called a multi-beam inspection device, in which a plurality of electron beams are simultaneously irradiated to a sample to perform high-speed inspection, has been studied.

In this method, since scanning is performed by simultaneously irradiating 100 or more small electron beams, it is possible to keep the amount of current flowing through one beam small, and the inspection speed can be increased to a conventional single electron while maintaining high resolution. It is said that the speed can be increased compared to the case where a beam is used.

However, many resources have been invested in the past and various types of inspection equipment have been developed, and although they are very promising, they have not been able to achieve the high speed and high resolution that were initially expected, and they are still in use. It has not been commercialized as an inspection device for semiconductors.

The equipment used in the semiconductor industry is an industrial measuring equipment, which is a kind of mission-critical equipment and needs to continue to operate 24 hours a day, 365 days a year without causing any trouble. Therefore, robustness is indispensable in principle.

It cannot be practically used to the extent that university professors and students can write a treatise by chance, as in the case of science and science equipment. It is necessary that the performance is kept stable for various measurement conditions, measurement targets, environmental changes, and for a long period of time.

In the above-mentioned multi-beam inspection apparatus, since the single-beam type CDSEM itself has already realized the stability as an industrial measuring apparatus, the stability of the ordinary electron beam optical system itself is considerably guaranteed. However, one cause of loss of robustness is the implementation of a beam splitter that does not exist in ordinary single-beam electron beam optics. Beam splitters are ultra-precision engineering equipment and require a high degree of machining accuracy and assembly accuracy on the order of microns.

A beam splitter is a device for separating a primary electron beam and a secondary electron beam which is a signal electron from a sample. When a mapping optical system is used, it is necessary to have an optical system for converging primary electrons and an optical system for converging secondary electrons at the same time. It is very difficult in principle and practically to apply different electron optics to electrons in the same orbit and to optimize them at the same time.

Therefore, conventionally, the trajectory of the primary electron beam and the trajectory of the secondary electron beam have been separated and optimized by using separate optical systems. A beam splitter is needed to do that.

Conventionally, the beam splitter has been composed of a Wien filter called EXB or a magnetic field prism array using only an electromagnetic field. Originally, as is clear from the name, the conventional beam splitter deflects the electron beam components of various energies contained in the beam to split the spectrum into individual energy beams and pass them through a narrow slit to align the energies. It is to take out a part of the energy, which is forcibly diverted.

In order to separate the primary electron beam and the secondary electron beam, it is necessary to deflect the primary electrons and the secondary electrons in the directions opposite to the traveling direction. For this purpose, a magnetic deflector known as Fleming's law is used to separate the primary and secondary electrons by deflecting them in opposite directions by using the fact that they travel in opposite directions. There is.

EXB is a mechanism that adjusts by applying a large electric field comparable to the energy of electrons so that either primary electrons or secondary electrons do not deflect the magnetic field. This is to suppress the occurrence of lens aberration by making the target electron beam travel straight. Since the amount of deflection cannot be as large as about 10 degrees, the column for the primary electron beam and the column for the secondary electrons come into contact with each other as they are. Therefore, an electric field or a magnetic field is further applied to the separated electron beam so that the separation becomes large, and the electron beam is bent in the same direction.

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

If the energy of the primary electron beam is exactly constant like a laser, deflection aberration does not occur, so that the trajectory of the electron beam can be ideally and freely changed by using the deflector.

However, since the actual primary electron beam has an energy distribution of about 1 electron volt depending on the electron beam generation principle, the amount of deflection differs for each electron energy as it is deflected when passing through a magnetic deflector. The beam spreads like this. That is, the primary electron beam is spatially dispersed, the minimum diameter of the beam spot when the beam is focused by the objective lens becomes large, and the reaching resolution becomes low.

On the other hand, since the secondary electron beam has an energy distribution of up to 0 to 100 electron volts, which is 100 times larger than the primary electron beam, the electron beam passes through the magnetic deflector and is 100 times more than the primary electron beam. It was very difficult to obtain high spatial resolution on the surface of the secondary electron detection element. 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.

Conventionally, in order to reduce these problems, measures have been taken to reduce the influence of deflection aberration by using a high acceleration voltage of 15 KV or more for the primary electron beam to reduce the apparent energy dispersion ratio. Similarly, since the influence of the deflection aberration has been reduced by applying an acceleration voltage of about 15 KV to the secondary electron beam to accelerate it, a withstand voltage is required for the device, which is a large scale. Furthermore, in order to prevent the influence of aberration, only electrons with a specific energy are extracted and passed through a thin slit of several microns to be used, so that the amount of signal electrons that can be used decreases, the image becomes dark, and the SNR deteriorates. Etc. have occurred.

Furthermore, as another cause, since the deflector shows the amount of deflection depending on the energy of electrons, the amount of deflection changes 100 times when the sample surface is charged and the energy of secondary electrons changes from several volts to several hundred volts. Therefore, there is a problem that a correct secondary electronic image cannot be obtained. It can be measured only when the sample potential can be fixed at 0 V or a constant potential, and it is virtually impossible to measure a general sample or insulator.

Therefore, the object of the present invention is to prevent the electron beam orbitals from being dispersed due to the difference in energy as much as possible, contrary to the conventional technical idea. The deflection aberration caused by the energy dispersion generated by the deflector is canceled or reduced to narrow the primary electron beam to a smaller beam, and the secondary electrons generated on the sample surface are detected with high spatial resolution and retarding. We propose to apply a voltage so that it can be detected with high resolution in spite of the low energy electron beam, and further, it can be detected with high resolution even in a low vacuum.

The present invention generates and accelerates primary electrons in a scanning electron microscope that irradiates a sample with primary electrons, detects the secondary electrons emitted from the sample, and generates a secondary electron image of the sample. The primary electron irradiation system, the first deflection device that deflects the primary electrons generated by the primary electron irradiation system, and the primary electrons deflected by the first deflection device are deflected in the opposite directions to cancel the aberration. , A second deflector composed of a magnetic field and an electric field that irradiates the sample in line with the axis of the imaging system and deflects the secondary electrons emitted from the sample in the opposite direction to the primary electrons to separate them. , An objective in which the primary electrons after being deflected by the second deflector and aligned with the axis of the imaging system are finely squeezed to irradiate the sample, and the secondary electrons emitted from the sample are incident on the second deflector. An imaging system composed of a lens and a secondary electron detection system for detecting secondary electrons after being deflected by the second deflection device are provided.

At this time, a third deflector is provided which cancels the aberration by deflecting the secondary electrons deflected and separated by the second deflector in the direction opposite to the deflection direction of the second deflector, and deflects by the third deflector. A secondary electron detection system for detecting secondary electrons after canceling the aberration is provided.

Further, the first deflection device and the third deflection device are set to be a deflection device having four or more poles of a magnetic field or an electric field or a magnetic field and an electric field.

Further, the second deflector has two poles of a magnetic field or four or more poles of a magnetic field and an electric field, and separates secondary electrons in a direction opposite to the traveling direction of the primary electrons.

Further, a retarding voltage is applied between the sample and the tip portion of the objective lens so that the sample is irradiated with primary electrons having a low acceleration voltage.

Further, a diaphragm is provided on the objective lens portion so that the sample side is held in a low vacuum and the opposite side is held in a high vacuum with the diaphragm as a boundary.

The present invention narrows the primary electron beam to a smaller beam and generates it on the sample surface by canceling and reducing the deflection aberrations generated by the first deflector, the second deflector, and the third deflector. Secondary electrons can be detected with high spatial resolution.

In addition, a high-resolution electron beam inspection device in a low vacuum can be realized.

The present invention cancels and reduces the deflection aberrations generated by the first, second, and third deflectors to narrow the primary electron beam to a smaller beam, and raises the secondary electrons generated on the sample surface. In addition to detecting with spatial resolution, it is possible to detect with a low energy electron beam and high resolution by applying a retarding voltage, and further, it is possible to detect with high resolution even in a low vacuum.

FIG. 1 shows a structural diagram of the principle of the present invention.

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

The secondary electrons 2 are secondary electrons emitted by finely squeezing the primary electrons and irradiating the sample 8.

The beam splitter 3 irradiates the sample 8 with the primary electron 1 and separates the tsecondary electron 2 emitted from the sample 8 from the primary electron 1. It is composed of a third deflection device 6.

The first deflection device 4 deflects the primary electron 1 and is a deflection device having four or more poles 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 and the secondary electrons 2 having opposite traveling directions, and is composed of at least a magnetic field or both a magnetic field and an electric field, and is a deflection device having four or more poles each. Is.

The third deflector 6 is the same as the first deflector, which deflects secondary electrons, and is a magnetic field, an electric field, or a deflector having four or more poles composed of a magnetic field and an electric field.

The objective lens 7 constitutes an imaging system, in which the primary electrons 1 are finely focused and irradiated to the sample 8, and the emitted secondary electrons are incident on the second deflection device 5.

Sample 8 is a sample to be irradiated with finely squeezed primary electrons 1 and emitted secondary electrons 2 to generate a high-resolution secondary electron image, for example, with a mask, a pattern on a wafer, or the like. is there.

Next, the operation of the configuration of FIG. 1 will be described.

(1) The primary electron 1 is incident on the first deflector 1 constituting the beam splitter 3 and deflected to the left in the traveling direction by a magnetic field, an electric field, or the action of a magnetic field and an electric field as shown in the figure. ..

(2) The primary electron 1 deflected in (1) and incident on the second deflecting device 5 is moved to the right by the second deflecting device 5 in the traveling direction due to the action of a magnetic field or both a magnetic field and an electric field. It is deflected, and as a result, the deflection direction of the first deflector and the deflection direction of the second deflector are opposite to each other, and after canceling the deflection aberration, the objective lens 7 is brought on the axis.

(3) The primary electrons 1 deflected on the axis of the objective lens 7 in (2) are finely focused by the objective lens 7 to irradiate the sample 8 and X, Y in a two-stage deflection system (not shown). Scanned in the direction. Then, the secondary electrons 2 are emitted from the sample 8.

(4) The secondary electrons 2 emitted in (3) travel upward on the axis of the objective lens 7, enter the second deflection device 5, and become the primary electrons 1 due to the action of the magnetic field and the electric field. It is deflected in the opposite direction of travel shown.

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

As described above, the primary electrons 1 are canceled by the first deflection device 4 and the second deflection device 5, and the secondary electrons are canceled by the second deflection device 5 and the third deflection device 6, respectively. By irradiating the sample 8 with primary electrons that have been reduced and narrowed down, it is possible to generate a high-resolution secondary electron image, and the emitted secondary electrons are also the second deflector 5 and the third. Since the deflection aberration is canceled by the deflection device 6, it is possible to reduce the deflection aberration, separate the secondary electrons from the primary electrons, and detect the secondary electrons with high sensitivity and high resolution. The details will be described below in order.

Next, the operation of the configuration of FIG. 1 will be described.

(1) The primary electron 1 that has passed through the first deflection device 4 is deflected inward. Since the primary electron 1 has an electron energy dispersion of about 1 electron volt, the amount of deflection is energy-dependent, and the beam of the primary electron is dispersed like a rainbow and swells spatially.

(2) The second deflection device 5 deflects the primary electron 1 in the opposite direction by exactly the same amount as that of the first deflection device. Since it is deflected in the opposite direction by exactly the same amount, the primary electron orbitals dispersed like a rainbow converge to one orbital again.

Since it is necessary to deflect in completely opposite directions as described above, the best results can be obtained by deflecting in opposite directions using a deflecting device (magnetic field, electric field, magnetic field and electric field) having exactly the same characteristics. The primary electrons dispersed in the first deflector 4 pass through the second deflector 5 and return to the original beam state of the primary electrons without dispersion due to the dedispersion action. At this time, due to the action of the first deflection device 4 and the second deflection device 5, the primary electrons are shifted inward by a predetermined distance from the first axis. In this state, it enters the objective lens 7, is focused by the objective lens 7, and irradiates the surface of the sample 8. As a result, the dispersion of the primary electrons 1 is reduced and the aberration in the objective lens 7 can be reduced, so that the primary electrons can be narrowed down to a small spot.

The deflection device can be thought of as a kind of arithmetic unit. This is the principle of canceling various aberrations caused by electron beam deflection by performing the operation F-1 (x), which is completely opposite to the operation (F (x)) applied the first time. However, this calculation has a mysterious property, and when the inverse calculation is performed, the electron beam does not return to the original orbit and a horizontal shift of the coordinate system occurs, so that the traveling of the electron beam can be changed. This is because the inverse operation is performed after a lapse of time from the first operation. From this principle, it is desirable that the characteristics of the first deflector and the second or third deflector are exactly the same and the operations are opposite.

(3) On the surface of the sample 8, secondary electrons 2 are generated by being stimulated by the irradiated primary electrons 1, and are accelerated by a voltage (returning voltage) (not shown) applied between the sample 8 and the objective lens 7. It becomes secondary electrons 2 and travels toward the objective lens 7. The secondary electrons that have passed through the objective lens 7 are deflected in the direction opposite to that of the primary electrons 1 by the second deflector 6.

(4) The deflected secondary electrons 2 are deflected depending on energy to cause dispersion, but the backscattering occurs by deflecting in the opposite direction by the third deflector 6, and the original secondary without dispersion is present. Return to electron 2.

As described above, when the beam splitter 3 including the first deflection device 4, the second deflection device 5, and the third deflection device 6 of the present invention is used, even if the primary electrons 1 or the secondary electrons 2 have energy dispersion. It is possible to separate the primary electrons and the secondary electrons without adding new chromatic aberration at the time of deflection. As a result, the image resolution of the secondary electrons in the mapping is significantly improved.

As a result, in the present invention, since the electromagnetic deflection can be deflected to 90 degrees or more, the secondary electrons can be sent back in the direction substantially the same as the direction in which the primary electrons come, so that the primary electrons can be sent back as in a conventional device. The column for secondary electrons and the column for secondary electrons can be installed so as to face the same direction without making a large device that opens to the left and right, and the entire electron beam device can be made compact. As described above, since the present invention is parallel columns and compact, it is possible to implement two columns as if they were one column.

FIG. 2 shows a configuration diagram of an embodiment of the present invention. This shows a schematic diagram in which the principle configuration of FIG. 1 is incorporated into an actual device. Here, the primary electrons 1, the secondary electrons 2, the first deflector 4, the second deflector 5, the third deflector 6, the objective lens 7, and the sample 8 have the same numbers as those in FIG. Omitted.

In FIG. 2, the diaphragm 9 schematically shows an opening through which the primary electrons 1 deflected by the first deflection device 4 pass and an opening through which the secondary electrons 2 deflected by the second deflection device 5 pass. It is a thing.

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

The coil 7-1 is a coil through which a current that excites the objective lens 7 is passed.

V1 and V2 are voltages applied between the sample 8 and the sample 8, and are retarding voltages. The potential of the primary electrons 1 is lowered to irradiate the sample 8 with primary electrons having a low acceleration voltage, and the sample 8 is irradiated with the primary electrons. The secondary electrons 2 emitted from 8 are accelerated and traveled upward.

Next, the operation of the configuration of FIG. 2 will be described.

(1) The primary electron 1 generated by the electron gun is deflected inward by the first deflector 4. Then, it is bent in the opposite direction by the second deflection device 5 and adjusted so as to be parallel to the orbit of the primary electron emitted from the electron gun. In this state, an alignment lens (not shown) or a mechanical alignment mechanism is used to adjust the lens 7 so that it is incident on the center (axis) of the objective lens 7. The objective lens 7 is made of a pole piece made of a high magnetic permeability material such as pure iron, permalloy, vermenzur, etc., and a copper wire or the like coated with polyurethane or the like on a member formed into an appropriate shape so as to generate a desired leakage magnetic field. It is wound to form a coil. The location of the cut at the tip of the pole piece where the leakage magnetic field is generated is the location where the maximum magnetic field density is exhibited, and functions as an electromagnetic lens. Of course, the objective lens 7 may be made of a permanent magnet as needed for miniaturization and energy saving. In the case of an electromagnetic lens, heat is generated, so keep the temperature constant by running cooling water. If the deflector is also an electromagnetic type, it generates heat, so it is desirable to cool it and control it to a constant temperature near room temperature in order to keep the amount of deflection constant. An electromagnetic deflection device composed of an electromagnetic coil 7-1 is provided above the objective lens 7, but it is desirable to provide a gap between the devices in order to have 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 exists between the electromagnetic deflector and the objective lens 7 so that the primary electrons subjected to the electromagnetic deflection can pass through the center (axis) of the objective lens 7. Of course, the control device also exists. The primary electrons that have passed through the objective lens 7 are converged by the magnetic field of the objective lens 7 to form a spot on the order of nm on the surface of the sample 8.

(3) The secondary electrons 2 generated in the sample 8 by the stimulation of the irradiation of the primary electrons 1 receive the force of the accelerating electric field (retarding voltage V1 and V2) applied between the sample 8 and the objective lens 7. It rises in the vertical direction, is once converged by the objective lens 7, and then diverges while being deflected in the direction opposite to that of the primary electrons 1 by the second deflector 5.

(4) The deflected secondary electrons 2 are then deflected in the opposite direction by the third deflector 6 and rise in the vertical direction, and as a result, the direction of the secondary electrons is shifted to the right. The secondary electrons 2 are imaged on the surface of the detector to obtain a secondary electron image on the surface of the sample 8. In the embodiment, the case where the primary electrons and the secondary electrons are parallel to each other is shown, but the shift amount of the beam is arbitrary and can be optimized by the configuration method of the apparatus.

FIG. 3 shows a detailed explanatory view (electron source) of the present invention.

FIG. 3A shows an example of normal TFE.

In FIG. 3A, the emitter 31 emits an electron. Examples of the emitter 31 include a thermal emitter using a material having a low work function such as tungsten, molybdenum, and LaB6, a metal oxide, and a thermoelectric field type emitter (TFE) in which the work function is lowered by using ZrO diffusion on a W chip. A cold field emitter that obtains an electron beam by sharpening the tip of the emitter near room temperature and applying a high electric field, or recently a cold field emitter or array using MEMS (semiconductor micromachining technology), coherent or pulsed laser, etc. There are photocathodes that excite.

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

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

The lens 34 converges the primary electrons accelerated by the accelerating electrode 33.

The objective aperture 35 is for injecting only the primary electrons that have passed through the objective lens aperture 35 into the objective lens 8 (not shown), narrowing it down finely, and irradiating it on the sample 8.

Next, the configuration of FIG. 3A will be described.

(1) In FIG. 3A, a beam of one primary electron is emitted from an emitter 31, and an objective aperture 35 having one hole narrows the beam of one primary electron with an objective lens 7 (not shown). It is squeezed and irradiated on the sample 8.

FIG. 3B shows an example of multi-beam. The emitter 31, extractor 32, acceleration electrode 33, and lens 34 in FIG. 3B are the same as those in FIG. 3A, and thus the description thereof will be omitted.

In FIG. 3B, the objective aperture 35 is an objective aperture having a plurality of holes, and forms a beam of a plurality of primary electrons corresponding to the holes. The diameter of the hole is on the order of a few microns to a few tens of microns.

Next, the configuration of FIG. 3B will be described.

(1) In FIG. 3B, the emitter 31 radiates a beam of one primary electron, and an objective aperture 35 having a plurality of holes forms a beam of a plurality of primary electrons, and an objective lens 7 (not shown) is shown. Squeeze it finely with and irradiate the sample 8 with each other.

FIG. 3C shows an example of a multi-emitter.

In FIG. 3C, the emitter 31-1 has a plurality of emitters.

The extractor 32-1 has a number of extractors corresponding to the emitter 31-1.

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

The lens 34-1 has a number of lenses (condensing lenses) corresponding to the emitter 31-1.

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

Next, the configuration of FIG. 3C will be described.

(1) In FIG. 3C, a plurality of emitters 31-1 radiate a beam of a plurality of primary electrons, and an objective aperture 35 having a plurality of holes forms a beam of a plurality of primary electrons, which is not shown. It is finely squeezed with the objective lens 7 of No. As a result, the beams of the plurality of primary electrons emitted from the plurality of emitters are finely focused and irradiated onto the sample 8.

(2) Therefore, in FIG. 3C, an array of emitters for a small multi-beam electron gun made by using semiconductor micromanufacturing technology (MEMS technology) is used. A cold-field emitter uses a high electric field generated between an emitter and an 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 an ultra-high vacuum to stabilize the emitter current. The size of the emitter array can be changed freely. It can be freely made from a few square meters or less to a few square meters or more depending on the application. It can also be made on a curved surface such as silicon or plastic. Therefore, the total amount of current that determines the inspection speed can be freely set from micro ampere to ampere order.

(3) If the MEMS technique is used, an emitter ray having a tip radius of curvature of several tens of nm can be easily produced. Currently known materials such as silicon, W, Mo, CNT, and diamond can be used as the emitter.

By setting the distance between the tip of the emitter and the extractor to the order of microns, a very low voltage of about 10 volts can be applied, and an electron beam can be emitted 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 as narrow as 0.3 electron volt, which is convenient for narrowing the beam. Since it is made by semiconductor technology, the characteristics of each emitter are very well aligned. The width of the beam can range from a few microns to a few millimeters, depending on the area of emission.

(4) Further, when operated with a low emission current of 1 microamper or less per beam, a life of more than 1 year can be easily obtained. Since each electron beam functions as an independent point light source, a multi-beam having a very uniform current value can be obtained without interfering with each other. The current value is significantly different from the case where one electron source is divided and can easily exceed 1 nanometer per beam, and the total current amount can be increased endlessly by increasing the number of beams. For example, if 10,000 beams are used, the total current will be as high as 10 μA, and it is possible to make an extremely high-speed electron beam inspection device that was unthinkable in the past.

(5) As for the lens for parallelizing the extractor, anode, and electron beam, an electrostatic lens or the like can be built in the electron gun by MEMS technology.

FIG. 4 shows a detailed explanatory view (secondary electron detection device) of the present invention.

FIG. 4A shows the case of one secondary electron detection device. In FIG. 4A, secondary electrons generated on the surface of sample 8 are accelerated to form a beam having a constant energy, then concentrated at one point using a lens, and an electron detection device is placed at that location. An example of this is shown.

Next, the features will be described.

(1) In FIG. 4A, since a detector having an area much smaller than the cross-sectional area of the original electron beam can be used, the electric capacity of the detector can be kept small and ultra-high-speed detection can be performed. Can be done. Since the detection efficiency changes depending on the incident energy, when avoiding the change, it is preferable to accelerate sufficiently when the secondary electrons are generated so that the secondary electron energy distribution does not affect the sensitivity.

(2) Further, the energy can be separated and detected by placing a plurality of electron detection devices at positions different from the focal position by utilizing the fact that the focal position changes due to the difference in the energy of the secondary electrons. This corresponds to the case where secondary electrons are used for elemental analysis and the like. If the color is displayed according to the energy, the element distribution on the surface of the sample 8 can be obtained as a change in the color of the color image. In this case, the secondary electrons to be detected are accelerated immediately before the detector to increase the sensitivity of the electron detector. As the electron detection device, a photodiode, an avalanche diode, an MCP, a photomultiplier tube, or the like can be used.

FIG. 4B shows a case of a secondary electron detection device having a plurality of secondary electron detection elements. FIG. 4B (b) corresponds to multi-electron beam detection.

(1) By irradiating the sample 8 with a multi-electron beam, the secondary electron group generated two-dimensionally simultaneously from the surface of the sample 8 is accelerated by the voltage applied between the sample 8 and the objective lens 7, and then the lens is used. It is converged 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 principle resolution is roughly determined by the wavelength of the beam of secondary electrons used and the aperture ratio NA.

(2) Since the two-dimensional secondary electron image of the surface of the sample 8 is enlarged and reproduced on the focal plane, the brightness or contrast information of this image is detected by a plurality of secondary electron detection devices arranged on a plane. Will be done. Secondary electron detectors include photodiodes, avalanche diodes, MCPs, MPPCs, photomultiplier tubes, ultra-high-speed CCDs, CMOS, and TDI image sensors that have been processed by removing the protective film on the semiconductor surface so that secondary electrons can be directly incident. Etc. can be used. When a two-dimensional image sensor is used, the image acquisition speed can be made higher than G pixels per second per device. A state-of-the-art device can achieve 10 Gpixels per second. The acquired signal is immediately converted into a digital signal and sent to a computer for image processing. As the communication means, an optical fiber cable for high-speed communication such as a metal wire can be used. The electric signal generated by the electronic detector by the AD conversion device is converted from an analog signal to a digital signal and stored in a memory such as a DRAM, SRAM, flash memory or HDD. Image processing such as a filter is performed by a high-speed arithmetic unit such as a CPU, ASIC, FPGA, and GPU, and information on the sample surface is reproduced on the display. The obtained image is combined as necessary to obtain an image of the required size and resolution. High-speed inspection can be performed by comparing the obtained image with CAD design data or images that are said to have the same shape in close proximity as a reference image and detecting the difference.

(3) CD measurement can be performed by measuring the length of each part of the obtained image in the same manner as a normal CDSEM. Since a large-screen high-definition image can be captured at high speed, the outline of the captured image can be extracted and used for optical simulation of a photomask.

FIG. 4C shows the case of a secondary electron detection device including a two-dimensional image sensor. FIG. 4C of FIG. 4 corresponds to multi-electron beam detection and the like.

(1) FIG. 4 (c) of FIG. 4 enables a general high-speed photodetector to be used. The beam of secondary electrons is converged by a lens, accelerated, and collided with the surface of a scintillator to convert electrons into light. To do. The secondary electron image converted into light is detected by using a photodiode, an avalanche diode, MCP, MPPC, photomultiplier tube, CCD, C, S, TDI image sensor, or the like. As the scintillator, it is preferable to use a GaN-based scintillator, which is a semiconductor scintillator having a high response speed on the order of ns, an inorganic material, an organic material, or a plastic-based scintillator. When the scintillator is irradiated with a large amount of electron beams, it becomes charged. Therefore, in order to prevent static electricity, a metal film such as aluminum on the order of nm is vapor-deposited on the surface and grounded. It is advisable to match the emission wavelength of the scintillator with the wavelength at which the photodetector has the maximum sensitivity.

(2) When performing electron detection by accumulating images like a two-dimensional image sensor, a scintillator having a slightly slow response speed of about 100 ns may be easy to use.

FIG. 5 shows an example of the device of the present invention. FIG. 5 shows the appearance of an electron beam type inspection device using a beam splitter.

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

The blanking device 42 blocks the primary electrons emitted from the electron gun 41 at high speed.

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 for passing the central portion of the primary electron, narrowing it down by the objective lens 48, and irradiating the sample.

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

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

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

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

The mirror 49 is a mirror that reflects a laser beam, and is for precisely measuring the position of the XYZ stage 51.

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

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

The vacuum chamber 52 is a container for storing the XYZ stage 51 and the like in a vacuum.

The vacuum pump 53 is a pump that exhausts the inside of the vacuum chamber 52 into a vacuum.

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

Next, the configuration will be described.

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

(2) When the beam source of the primary electrons is a multi-electron beam, the array of the blanking aperture 43 can have a function of turning on / off individual beams. It is also possible to separately have a blanking aperture 43 that turns on / off the entire beam of primary electrons. The beam of primary electrons that has passed through the blanking aperture 43 is applied to the objective aperture 44 that determines the size and shape of the irradiated electron beam. The objective aperture 44 is a metal thin film having a hole size and spacing of several microns to several hundreds of microns, mainly having a thickness of several tens of microns. A refractory metal such as molybdenum or tungsten is used as the aperture material. Electromagnetic or mechanical beam alignment means are attached to these apertures to allow the beam of primary electrons to pass accurately.

(3) The beam of primary electrons that has passed through the objective aperture 44 is beam-shifted by the beam splitter (first deflector, second deflector, third deflector) of the present invention, and then incident on the objective lens 48. To. 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 incident on 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 that the objective lens 48 is vertically incident in order to reduce aberrations. The beam of primary electrons is deflected by the deflector 50 for scanning the beam of primary electrons before or after passing through the objective lens 48. Two-stage deflection or deflection directly below the objective lens 48 is performed in order to reduce aberrations through the center of the objective lens 48. This beam deflection of the primary electrons is performed to two-dimensionally scan the beam of the primary electrons on the surface of the sample. Generally, 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 devices, the beam scanning of primary electrons is a stepped shape sent from a DA converter in synchronization with an image formation signal such as a pixel clock according to a command from a computer. It is based on the voltage waveform. For example, when a scanning signal is created using a 16-bit DA converter, scanning can be performed along the X-axis or Y-axis of about 64 Kpixels. It is also possible to scan in any direction by appropriately synthesizing 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, the beam axis of the primary electron is deflected by two steps immediately before the incident of the objective lens 48 so as to pass through the axis center of the objective lens 48, and the beam scan of the primary electron is performed. Is desirable. When the beam of primary electrons is scanned large, the linearity deteriorates and scanning distortion is likely to occur. Distortion can be reduced by placing a deflection electrode for scanning under the objective lens 48 and scanning. However, if the image is scanned so large that it affects the depth of focus, the image will be blurred. 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 (returning voltage 9) applied between the sample and the objective lens 48 and climb vertically to the objective. It is incident on the lens 48. In order to reduce the aberration generated in the objective lens 48, it is desirable to perform as large an acceleration as possible of about 15 KV. Generally, for safety, the objective lens 48 is often set to the ground potential to make the potential of the sample negative. For example, when the irradiation energy of the sample is set to 1 KV, the potential of the sample is set to -14 KV.

(7) Since the beam of secondary electrons passing through the objective lens 48 travels in the direction opposite to that of the primary electrons, it is bent in the direction opposite to the beam of primary electrons due to the action of the magnetic field of the beam splitter (second deflector 46). The beam of secondary electrons is separated from the orbit of the primary electrons.

(8) Since the separated beam of secondary electrons is affected by scanning the primary electrons for image formation, the secondary electron signal is also scanned. If it is left as it is, the focal position will move up, down, left and right on the electron detection element, and stable image detection will not be possible. Therefore, the secondary electron beam is scanned again in the opposite direction in synchronization with the primary electron beam scanning so that the focal position can be stopped at a fixed position on the electron detection element coordinates, and is always formed on the electron detection device. Control so that the secondary electron image does not move. When the size of the detection element is larger than the secondary electron landing point range that fluctuates due to the scanning of the beam, correct image detection can be performed without reverse scanning of the secondary electron beam.

FIG. 6 shows an example of the device of the present invention (No. 2). FIG. 6 is characterized in that, in addition to FIG. 5, a thin film 55 capable of transmitting electrons is provided on the side closer to the sample than the center of the objective lens. The thin film 55 is made of a carbon film having several atomic layers such as thin silicon or a compound thereof, a metal film or a graphene film on the order of several nm to several tens of nm. Electron beams accelerated to hundreds of electron volts or more can pass through these films with little scattering. On the other hand, these thin films have a role of mechanically separating a low vacuum region of about 10 pascals and a high vacuum region of 10 minus 3 or more. At the same time, these thin films are conductive and can apply a bias voltage.

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

Since the generated secondary electrons have low energy, they cannot pass through the thin film (septum) 55 as they are. Therefore, a bias voltage is applied between the sample and the thin film 55 to accelerate the beam of secondary electrons and allow them to pass through the diaphragm 55. Since the vacuum chamber 52 is in a low vacuum state of about 10 pascals, an electric discharge occurs when an excessively high bias is applied. Therefore, a voltage of several hundred volts is applied so that the electrons can be given enough energy to pass through the thin film 55 without causing discharge. In this way, the secondary electrons have sufficient energy and pass through the thin film 55 to enter the high vacuum region. Since there is no concern about discharge of the secondary electrons that have entered the high vacuum region, they are further accelerated between the thin film 55 and the objective lens 48, enter the objective lens 48, and are inversely converged. To form.

By adopting the above configuration, it is possible to hold the sample in a low vacuum state while using a beam of high-energy primary electrons, and antistatic can be realized. If antistatic is possible, the energy distribution of secondary electrons generated can be reduced. It becomes possible to detect by passing through the objective lens 48 so that the chromatic aberration of the beam of secondary electrons generated at the same time does not become large.

FIG. 7 shows an example of the device of the present invention (No. 3). FIG. 7 shows an example in which the aberration correction device 58 is provided. Generally, it is a device capable of correcting spherical aberration, chromatic aberration, etc. of the objective lens 48 or the like by using a multi-stage multipole element. Since there is a long-standing theorem that an axisymmetric electromagnetic lens can only produce positive aberrations, it has been said that it is impossible to correct the aberrations. However, at the end of the 20th century, Rose and Heider et al. Created a negative aberration by combining a multipole lens such as a quadrupole or an octapole with a transfer lens to create an asymmetric field, which is an aberration in the synthesis with the original positive aberration. We have developed a device that can reduce the value to 0. Higher-order aberrations can be corrected by further increasing the number of quadrupoles and the number of stages. If the spherical aberration and the chromatic aberration can be reduced to zero, it is not necessary to raise the energy of the primary electron beam to 10 KV or more, which has been conventionally performed to reduce the influence of the aberration of the objective lens.

The example of FIG. 7 is characterized in that the aberration correction device 58 is mounted on the column on the primary electron side and the column on the secondary electron side, respectively. The aberration correction device 58 is an element capable of correcting spherical aberration and chromatic aberration by combining multipole elements. The advantage of this device 58 is that the aberration correction device 58 is used to correct the aberrations of the objective lens 48 and the condensing lens and narrow down the primary electrons to a small spot size without increasing the energy of the primary electrons as high as 15 KV. To be able to do it.

In FIG. 6, by increasing the energy of the beam of the primary electrons, the influence of the energy dispersion of the primary electrons is reduced to an error level, and the occurrence of chromatic aberration has been avoided. However, when the primary electron beam is made high in energy, a high withstand voltage is required for the electron beam column, which not only makes the device large, but also does not require X-rays or the like from a place such as an aperture irradiated with the primary electron beam. Harmful electromagnetic waves are emitted and the sample is exposed to light or adversely affects the human body, which is not good. Furthermore, in order to reduce the aberration of secondary electrons, it is necessary to apply a bias to the substrate to accelerate it, and it is necessary to apply a high voltage to a narrow and very easy-to-discharge place between the sample and the objective lens 48. .. If the distance between the objective lens 48 and the sample is increased in order to obtain a high withstand voltage, the NA becomes small, the resolution is lowered, and the beam spot becomes large.

Since the vacuum withstand voltage design is said to be several kilovolts per 1 mm interval, it is necessary to separate the sample surface from the tip of the objective lens 48 by 5 mm or more in order to obtain a withstand voltage of 15 KV, and deterioration of resolution is unavoidable. Furthermore, the low vacuum technology used to prevent the surface of non-conductive samples from being charged cannot be easily incorporated by applying a bias voltage of several hundred volts.

As shown in FIG. 7 of this embodiment, when the aberration correction device 58 is used, the aberration caused by the objective lens 48 with respect to the beam of the primary electrons and the aberration of the objective lens 48 with respect to the beam of the secondary electrons are corrected to 0. It is possible to make a system with very small aberration while using low energy of 5KV or less. As a result, a beam spot of primary electrons as small as when high energy is used can be created on the sample surface. Similarly, secondary electrons can be input to the electron detection device 54 while maintaining high resolution.

Since a large sample bias (retarding voltage) exceeding several hundred volts, which causes discharge, is not applied to the beam of primary electrons or the beam of secondary electrons, low vacuum mode measurement that is effective in preventing static electricity should be performed. Can be done. 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 is used from outside the chamber using a mass flow controller or the like. The degree of vacuum can be maintained at about 1 to 100 pascals by introducing an active gas. In this low vacuum state, the charge on the sample surface is neutralized by the action of positive and negative ions generated by the beam irradiation of the primary electrons, and the normal measurement state can be maintained. Due to this effect, high-speed single-beam or ultra-high-speed multi-beam inspection can be performed while keeping the potential of the sample surface very stable regardless of the pattern.

FIG. 8 shows an example of the beam splitter of the present invention. FIG. 8 shows examples of the first deflector 4, the second deflector 5, and the third deflector 6 that constitute the beam splitter 3 shown in FIGS. 1 and 2, respectively.

FIG. 8A shows an example of a parallel flat plate. The parallel plate type consists of an electrode consisting of two poles for generating an electric field and a pole piece for generating a magnetic field orthogonal to the electric field.

The electrode for generating an electric field used in a beam splitter is usually made of metal, but if a material having a relative magnetic permeability close to 1, for example, a transparent electrode ITO, aluminum, copper, or silver, is used, the interference with the magnetic field applied at the same time becomes small. , It becomes possible to realize a region in which the electric field and the magnetic field spread uniformly at right angles to each other in a wide range. As a result, even when a thick beam exceeding 100 microns is used as in a mapping type inspection device, a magnetic field or an electric field can be uniformly applied, and good deflection characteristics can be obtained. The pole piece for applying a magnetic field is made of a metal such as permalloy, which has a large magnetic permeability.

In FIG. 8A, the pole piece 61 is shown as both a pole piece for applying a magnetic field and an electrode for applying an electric field. If a pole piece (2 poles) for applying a magnetic field is provided separately from the 2 poles) so as to be orthogonal to the electric field, a uniform orthogonal electric field magnetic field can be obtained in a wide range. Since the magnetic field can act by passing through the electrode of the material made of magnetic permeability 1, a pole piece for generating the magnetic field can be arranged behind the electrode for generating the electric field. In the illustrated electrode / pole piece 61, four poles are usually arranged axially symmetrically. Further, a multipole element such as 6 poles, 8 poles, 10 poles, 12 poles, 16 poles, etc. may be used.

The coil 62 causes a magnetic field to be generated by passing an electric current and applies it to each pole piece (magnetic pole). If there are four poles, one coil 62 is provided for each pole piece (magnetic pole).

The yoke 63 is a yoke for short-circuiting the magnetic field generated by the coil 62 so as not to leak to the outside.

An axisymmetric 4-pole, 6-pole, 8-pole, 12-pole or other multipole deflector having the above configuration is formed, and an electric field, a magnetic field, or both an electric field and a magnetic field are generated on the axis, and primary electrons or primary electrons or It is possible to deflect secondary electrons. The first deflector 4 and the third deflector 6 may be deflected only by an electric field or a magnetic field, or may be deflected by both an electric field and a magnetic field. The second deflector 5 deflects at least by a magnetic field or an electric field and a magnetic field, deflects in the opposite direction to the traveling direction of the secondary electrons with respect to the traveling direction of the primary electrons, and separates the two from the magnetic field. It is necessary to adjust the degree of deflection due to the electric field.

FIG. 8B shows an example of a pattern yoke type. The pattern yoke type of FIG. 8 (b) shows only the portion corresponding to the electrode / pole piece 61 of FIG. 6 (a).

In FIG. 6B, the notch 71 is a notch made in a cylinder and is for forming a cylindrical electrode material 74 as shown in the drawing.

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

The tap 73 is a tap for attaching a jig.

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

As described above, the cylindrical electrode material 74 created by making a notch 71 in accordance with the rotation direction of the primary electron (or secondary electron) of the cylinder is prepared, and this is used as the electrode and pole of FIG. 6 (a). By using the piece 61, the electrodes and magnetic poles can be rotated according to the degree of rotation as the primary electrons (or secondary electrons) travel, and the aberration can be reduced.

FIG. 8C shows an example of a Vienna filter. As shown in the figure, the known win filter (8 poles) of FIG. 8 (c) is composed of n = 1,2,3,4,5,6,7,8 poles, and has electrodes and magnetic poles inside. The poles (8 poles) that also serve as the above are arranged axisymmetrically, and eight sets of coils that generate a magnetic field are provided on the outside thereof. The outermost is a cylindrical yoke that shorts the magnetic field.

Under the above configuration, by applying an electric field, a magnetic field, or both an electric field and a magnetic field to the eight poles, the primary and secondary electrons are deflected, and the primary and secondary electrons are reversed in the opposite directions. It is possible to separate the two by biasing to.

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

In FIG. 9, the pole piece / electrode 65 corresponds to the cylindrical pole material 74 of FIG. 8 (b) described above, and operates 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 an outward (outside) magnetic field generated by passing an electric current through the coil 61.

With the above configuration, the electrodes and magnetic poles that rotate in the axial direction of FIG. 8B described above are configured, and these are made to correspond to the angles of rotation of the primary electrons or secondary electrons in the traveling direction. This makes it possible to reduce the aberration of deflection with respect to primary electrons or secondary electrons.

FIG. 10 shows an explanatory diagram of an apparatus operation block of the present invention.

FIG. 10A shows the operation of primary electrons, and FIG. 10B shows the operation of secondary electrons emitted from the sample.

In FIG. 10A, in S1, the electron gun emits a beam of primary electrons.

S2 is a parallel beam. This makes the beam of the primary electrons emitted from the electron gun in S1 a parallel beam by the condenser lens shown in the figure.

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

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

S5 converges on the objective lens. This is because the objective lens 7 of FIGS. 1 and 2 described above narrows the beam of the primary electron.

S6 decelerates the primary electron. This applies the retarding voltage of V1 or V2 of FIG. 2 described above to decelerate the primary electrons (decelerate the acceleration voltage).

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

As described above, the primary electrons generated by the electron gun under the configurations of FIGS. 1 and 2 described above are deflected in two stages by the first deflector and the second deflector, and as a result, the beam of the primary electrons is generated. It is possible to shift the traveling direction, squeeze it finely, perform plane scanning while irradiating the sample 8, and emit secondary electrons.

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

In FIG. 10B, S11 generates secondary electrons. This corresponds to the plane scanning while irradiating the sample 8 with the primary electron in S7 of FIG. 10 (a). Secondary electrons are emitted (generated).

S12 accelerates secondary electrons. This is because the secondary electrons generated in S11 are accelerated by the retarding voltage of V1 or V2 of FIG. 2 described above.

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

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

S15 is deflected by the third deflector. This cancels the deflection aberration and the like by deflecting the secondary electrons separated in S14 in the opposite direction.

The image of S16 is formed by a mapping lens. In this method, for the secondary electrons after being deflected by the third deflector of S15, an image of the secondary electrons is formed (imaged) on the surface of the electron presenter by the mapping lens.

S17 is detected by an electronic detector. The secondary electrons imaged in S16 are detected by the secondary electron detector.

S18 amplifies the signal. This amplifies the signal of the secondary electrons detected in S17.

Image processing in S19 is performed by a PC.

As described above, the secondary electrons emitted from the sample 8 under the configurations of FIGS. 1 and 2 described above are separated from the primary electrons by the second deflector and the third deflector, and the secondary electrons are separated from the primary electrons. As a result of two-step deflection, the traveling direction of the beam of secondary electrons can be shifted, and the beam of secondary electrons can be imaged with high resolution to detect a high-resolution secondary electron image on the surface of sample 8. Will be.

FIG. 11 shows an apparatus adjustment flowchart of the present invention.

FIG. 11A shows an adjustment flowchart.

In FIG. 11A, S21 applies an initial electric field and a magnetic field. This is initially set to the optimum voltage, current, voltage and current values obtained in the experiment for the first deflection device 4, the second deflection device 5, and the third deflection device 6 of FIGS. 1 and 2 described above. To do.

S22 changes the electric field and magnetic field. This is because the electric field (voltage), when the first deflector 4, the second deflector 5, and the third deflector 6 of FIGS. 1 and 2 do not operate sufficiently with the electric field and magnetic field initially set in S21. The magnetic field (current) is finely adjusted so that it is optimally deflected and the amount of secondary electrons is maximized.

In S23, the maximum amount of secondary electrons is determined. When YES, the amount of secondary electrons detected by the detectors of FIGS. 1 and 2 is the maximum, and the first deflection device 4, the second deflection device 5, and the third deflection device 6 have the optimum degree of deflection. Since the electric field (voltage), magnetic field (current), electric field and current have been adjusted, the process ends. If NO, repeat S22.

As described above, in the configuration of FIGS. 1 and 2, the electric field, magnetic field, electric field and magnetic field of the first deflection device 4, the second deflection device 5, and the third deflection device 6 are initially set to the initial values obtained by the experiment. By adjusting the electric field, the magnetic field, the electric field and the magnetic field so that the amount of secondary electrons is maximized, it is possible to adjust the first deflection device 4, the second deflection device 5, and the third deflection device 6. It becomes.

FIG. 11B shows an axis adjustment flowchart (deflection aberration).

In FIG. 11B, S31 applies an initial electric field and a magnetic field. This is the voltage, current, voltage and current that minimize the deflection aberration obtained in the experiment for the first deflection device 4, the second deflection device 5, and the third deflection device 6 of FIGS. 1 and 2, respectively. Initialize to a value.

S32 changes the alignment parameter. This is because, with the electric and magnetic fields initially set in S31, the deflection aberrations of the first deflector 4, the second deflector 5, and the third deflector 6 of FIGS. 1 and 2 are large, and a sufficient amount of secondary is used. If the amount of electrons cannot be detected, the electric and magnetic fields of the opposite poles are finely adjusted, and the central axes of the electric and magnetic fields are adjusted so that the amount of secondary electrons is maximized.

In S33, the maximum amount of secondary electrons is determined. When YES, the amount of secondary electrons detected by the detectors of FIGS. 1 and 2 is the maximum, and the axes of the electric and magnetic fields of the first deflector 4, the second deflector 5, and the third deflector 6 are the maximum. Now that the center has been optimally adjusted, we are finished. If NO, repeat S32.

As described above, under the configurations of FIGS. 1 and 2, the initial values obtained in the experiment in which the deflection aberrations of the first deflection device 4, the second deflection device 5, and the third deflection device 6 are minimized are initially set. From this, it is possible to adjust the deflection aberration to the minimum by adjusting the axis center by adjusting the strength of the opposite poles of the electric field and the magnetic field so that the amount of secondary electrons is maximized.

FIG. 11C shows an axis adjustment flowchart (rotational direction).

In FIG. 11B, S41 applies an initial electric field and a magnetic field. This is the voltage, current, voltage and current that are the optimum rotation directions obtained in the experiments for the first deflection device 4, the second deflection device 5, and the third deflection device 6 of FIGS. 1 and 2, respectively. Initialize to a value.

S42 changes the alignment parameter. With the electric and magnetic fields initially set in S41, the rotation directions of the first deflector 4, the second deflector 5, and the third deflector 6 of FIGS. 1 and 2 are deviated, and a sufficient amount of secondary is secondary. When the amount of electrons cannot be detected, the electric and magnetic fields of the opposite poles are finely adjusted to adjust the rotation direction due to the electric and magnetic fields, and the secondary electron amount is adjusted to the maximum.

In S43, the maximum amount of secondary electrons is determined. When YES, the amount of secondary electrons detected by the detectors of FIGS. 1 and 2 is the maximum, and the rotation of the first deflector 4, the second deflector 5, and the third deflector 6 due to the electric and magnetic fields. Now that the orientation has been optimally adjusted, we are finished. If NO, repeat S42.

Based on the above, under the configurations of FIGS. 1 and 2, the rotation directions of the first deflector 4, the second deflector 5, and the third deflector 6 due to the electric field and the magnetic field are initially set to the initial values obtained by the experiment. The first deflection device 4 is adjusted by adjusting the strength of the opposite poles of the electric field and the magnetic field so that the amount of secondary electrons detected through the deflector is maximized. , The voltage of the second deflection device 5 and the third deflection device 6 and the rotation direction due to the magnetic field can be optimally adjusted. In principle, the aberration can be minimized by arranging the deflectors symmetrically with respect to the original electron beam orbit and adjusting so that the passing electron beams are as similar as possible and opposite to each other. You can.

It is a principle block diagram of this invention. It is a block diagram of 1 Example of this invention. It is a detailed explanatory drawing (electron source) of this invention. It is a detailed explanatory view (secondary electron detection device) of this invention. This is an example of the device of the present invention. This is an example of the device of the present invention (No. 2). This is an example of an apparatus of the present invention (No. 3). An example of a beam splitter of the present invention. This is an example of a peep splitter (pattern yoke type) of the present invention. It is explanatory drawing of the apparatus operation block of this invention. It is a measure adjustment flowchart of this invention.

1: 1 primary electron 2: secondary electron 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 : Extractors 33, 33-1: Acceleration electrodes 34, 34-1: Lens 35, 35-1: Objective aperture 41: Electronic 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 and pole piece 62: Coil 63: Yoke 65: Pole piece and electrode 66: Coil 67: Magnetic shield 71: Notch 72 :, 73: Tap 74: Cylinder Electrode material V1, V2: retarding voltage

Claims (8)

In a scanning electron microscope in which a sample is irradiated with primary electrons, secondary electrons emitted from the sample are detected, and a secondary electron image of the sample is generated.
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, and
The primary electrons deflected by the first deflector are deflected in the opposite direction to cancel the aberration, and the sample is irradiated with the primary electrons aligned with the axis of the imaging system, and the secondary electrons emitted from the sample are emitted from the sample. A second deflector composed of at least a magnetic field that deflects and separates the primary electrons in the opposite direction.
After being deflected by the second deflector and aligned with the axis of the imaging system, the primary electrons are finely squeezed to irradiate the sample, and the secondary electrons emitted from the sample are incident on the second deflector. An imaging system consisting of an objective lens to be used
A scanning electron microscope comprising a secondary electron detection system for detecting secondary electrons after being deflected by the second deflection device. A third deflection device is provided to cancel the aberration by deflecting the secondary electrons deflected and separated by the second deflection device in the direction opposite to the deflection direction of the second deflection device.
The scanning electron microscope according to claim 1, further comprising a secondary electron detection system that detects secondary electrons after deflecting with the third deflection device to cancel the aberration. The scanning type according to any one of claims 1 to 2, wherein the first deflection device and the third deflection device are a magnetic field, an electric field, or a deflection device having four or more poles of a magnetic field and an electric field. electronic microscope. The second deflector has four or more poles each of a magnetic field and an electric field, and separates the secondary electrons in a direction opposite to the traveling direction of the primary electrons, according to claims 1 to 3. The scanning electron microscope according to any one. The invention according to any one of claims 1 to 4, wherein a retarding voltage is applied between the sample and the tip end portion of the objective lens, and the sample is irradiated with primary electrons having a low acceleration voltage. Scanning electron microscope. The scanning type according to any one of claims 1 to 5, wherein a diaphragm is provided in a portion of the objective lens, and the sample side is held in a low vacuum and the opposite side is held in a high vacuum with the diaphragm as a boundary. electronic microscope. In a method for detecting secondary electrons in a scanning electron microscope, which irradiates a sample with primary electrons, 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,
A first deflection device that deflects the primary electrons generated by the primary electron irradiation system, and
The primary electrons deflected by the first deflector are deflected in the opposite direction to cancel the aberration, and the sample is irradiated with the primary electrons aligned with the axis of the imaging system, and the secondary electrons emitted from the sample are emitted from the sample. A second deflector composed of at least a magnetic field that deflects and separates the primary electrons in the opposite direction.
After being deflected by the second deflector and aligned with the axis of the imaging system, the primary electrons are finely squeezed to irradiate the sample, and the secondary electrons emitted from the sample are incident on the second deflector. An imaging system consisting of an objective lens to be used
A secondary electron detection system for detecting secondary electrons after being deflected by the second deflection device is provided.
A method for detecting secondary electrons in a scanning electron microscope, which comprises canceling and reducing the deflection aberration between the first deflection device and the second deflection device and improving the resolution of a secondary electron image. The secondary of the scanning electron microscope according to claim 7, wherein the deflection aberration between the second deflector and the third deflector is further canceled and reduced, and the resolution of the secondary electron image is improved. Electron detection method.

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