JP6742015B2 - Electronic detection device and electronic detection method - Google Patents

Description

The present invention relates to an electron detection device and an electron detection method for irradiating a sample with an electron to detect and amplify the electron emitted or reflected from the sample.

A scanning electron microscope detects and amplifies signal electrons such as secondary electrons or backscattered electrons generated by irradiating a sample with a narrowed electron beam and forms an image of the sample. Is a technique for observing or measuring.

In order to obtain a high quality image, it is very important to detect and amplify signal electrons with a high SNR. An electron is one of the so-called elementary particles, and the charge amount of the electron is as small as 1.6×10 Coulomb minus 16th power. Therefore, in order to detect each electron, it is necessary to perform very large amplification without noise. There is.

An MCP (multi-channel plate) is widely used as an electric element having an extremely low noise and a very high amplification factor for detecting and amplifying electrons. The MCP is a thin plate with a thickness of about 1 mm made of high-resistance lead glass having a shape like a lotus root slice, and innumerable holes of several microns called channels are lined up. When a voltage of several KV is applied to both ends of the MCP in vacuum, the electrons incident from one surface of the MCP are multiplied by the avalanche phenomenon occurring inside the channel and are emitted from the other surface. Amplification is realized by collecting the emitted electrons at the anode and converting them into a current. It is possible to amplify the MCP by 1000 times or more per sheet, and it is possible to realize a multiplication of 10 7 or more in a multi-stage configuration using a plurality of MCPs.

However, since the glass wall forming the channel of the MCP is thick, the total area of the MCP end face is the sum of the area of the hole and the area of the wall. In other words, the part of the MCP that has electrons collides with the wall and is not detected. The ratio of holes to the total MCP area is the aperture ratio. The MCP has an aperture ratio of approximately 60%.

It is said that about 50% of the electrons incident on the MCP channel substantially contribute to the amplification, so that the maximum detection efficiency of the final signal electrons is 30% or less at present.

The signal amplified by the MCP is amplified by the current amplifier. Since the current amplifier has a large current noise, it is necessary to input a signal sufficiently larger than the noise in order to prevent the SNR from being deteriorated by the amplifier. On the other hand, since the original SNR of an image is determined by the square root of the number of electrons that make up one pixel, the SNR deteriorates as the number of detected electrons decreases.

When the number of incident electrons is sufficiently large as 1000 or more, the image SNR after current amplifier amplification can be maintained at 10 or more even if the detection rate of MCP is as low as 30%, and sufficiently high image quality can be obtained in practical use.

However, in applications such as scanning electron microscopes that detect and amplify electrons generated while scanning (for example, digital scanning) an electron beam that is narrowed down to the nm order, the number of electrons generated per pixel is 100 or less. Therefore, if the detection efficiency is low, the SNR of the original signal forming an image becomes extremely lower than 10, and there is a problem that it cannot be practically used as it is.

The image quality can be improved by increasing the irradiation electron amount per pixel, but for that purpose, it is necessary to irradiate an electron beam having a higher electron density. The objective lens that narrows the electron beam finely has aberrations, and the electron beams have negative charges and repel each other.Therefore, it is impossible to increase the current density silently at the low acceleration voltage required for stable observation. Technically difficult. Further, the large amount of electron beam irradiation has a limit in increasing the irradiation amount because it reacts with a measurement target and is damaged by a large potential difference generated by alteration and charging.

As a method of increasing the SNR without increasing the current of the electron beam with which the sample is irradiated, there is also a method of scanning the same place many times to accumulate an image, but the throughput decreases in proportion to the number of accumulations. It cannot be used when high speed is required (for example, when measuring the length of a mask pattern or inspecting a defect).

For the above reasons, it is desired to improve the detection efficiency of signal electrons (secondary electrons, backscattered electrons, etc.) so that a desired image can be formed at a high speed with a small electron beam amount.

Moreover, when the irradiation electron beam energy is changed by the retarding method, the energy of the generated secondary electrons changes and the detection efficiency changes. Therefore, even if the irradiation electron beam energy changes, the detection efficiency of the secondary electrons also changes. It is desirable not to.

The present invention is characterized by reducing the influence of the detection loss due to the aperture ratio of the electronic detection/amplification element of the MCP and further improving the detection/amplification rate.

Therefore, according to the present invention, the number of signal electrons entering the MCP or the like is increased by multiplying the secondary electrons or the like generated by electron irradiation with the secondary electron generating plate before entering the MCP or the like, and the aperture ratio of the MCP or the like is increased. An object of the present invention is to sufficiently compensate the signal electron detection loss due to the limitation so that the signal electron loss is not substantially caused and to improve the amplification factor.

At the same time, as an application of the electron multiplier, the secondary electrons and the reflected electrons are separated at the same time by utilizing the fact that the orbit changes depending on the energy difference of the secondary electrons and the reflected electrons generated in the sample. The purpose is to realize the detection.

Therefore, the present invention is an electron detection apparatus that irradiates a sample with electrons and detects and amplifies the electrons emitted or reflected from the sample, and a primary electron beam having an energy of a predetermined acceleration voltage is narrowed down to a sample. A magnetic field type objective lens for irradiating, a deflecting device for deflecting the primary electron beam so that the primary electron beam narrowed down and scanned on the sample, and a hole for passing the primary electron beam in the direction of the sample are provided. In addition, a positive first accelerating voltage that accelerates the first secondary electrons emitted when the sample is irradiated with the narrowly focused primary electron beam and scanned is applied, and at the same time, the first accelerating voltage is applied. A secondary electron generating plate that generates a second secondary electron that has been multiplied when the accelerated first secondary electron collides, and a hole that allows the primary electron beam to pass in the direction of the sample, and A positive second accelerating voltage is applied which has a hole for allowing the secondary electron of No. 1 to pass in the direction of the secondary generation plate and accelerates the second secondary electron multiplied by the secondary electron generation plate. In addition, an MCP for further multiplying the multiplied secondary electrons accelerated by the second acceleration voltage, and an anode for detecting the secondary electrons multiplied by the MCP are provided.

At this time, in the hole portion of the secondary electron generating plate through which the primary electron beam passes, the first secondary electron emitted from the sample is prevented from traveling in the opposite direction of the traveling path of the primary electron beam. A repeller electrode having a hole through which the primary electron beam passes, to which the voltage of (1) is applied, is provided.

In addition, the surface of the secondary electron generating plate on which the first secondary electrons collide to generate the second secondary electrons is convex in the traveling direction of the primary electron beam, and the second secondary electrons are generated. To increase the multiplication efficiency of.

Further, a strip-shaped, needle-circular, or particle-shaped secondary electron emitting material is formed on the surface of the secondary electron generating plate.

Further, the MCP is divided into a plurality of parts in one or more of the circumferential direction and the radial direction so that division detection/amplification is possible.

Further, the MCP is tilted toward the secondary electron generating plate.

Also, the MCP is replaced with the APD.

Further, two sets of the secondary electron generating plate and the MCP are provided coaxially with the orbit of the primary electron beam, one set of the inner side detects and multiplies backscattered electrons emitted from the sample, and one set of the outer side The first secondary electron emitted from the sample is detected and multiplied by.

The present invention increases the number of signal electrons incident on the MCP or the like by colliding the secondary electrons generated by electron irradiation with the secondary electron generating plate and multiplying them before entering the MCP or the like, thereby increasing the aperture ratio of the MCP or the like. It is possible to sufficiently compensate the secondary electron detection loss due to the limitation so that the loss of signal electrons does not substantially occur, and it is possible to improve the amplification factor.

Since the energy incident on the secondary electron generation plate can be determined independently of the landing energy of the primary electrons, it is possible to keep the secondary electron detection efficiency constant independent of the landing energy even if the retarding method is used. Becomes

At the same time, it is possible to realize simultaneous detection by separating the secondary electrons and the reflected electrons by utilizing the fact that the trajectories change depending on the energy difference between the secondary electrons emitted and reflected from the sample and the reflected electrons. It will be possible.

FIG. 1 shows a block diagram of an embodiment of the present invention.

In FIG. 1, the primary electron beam 1 is generated by a lens barrel including an electron gun such as a TFE emitter (not shown), a focusing lens, a deflecting device, and an objective lens 2 (not shown). While irradiating the surface, planar scanning (scanning in the X and Y directions) is performed to generate secondary electrons and reflected electrons. The generated secondary electrons and backscattered electrons are multiplied by the secondary electron generation plate 6 and further detected/amplified by the MCP 7 arranged to face the secondary electron generation plate 6, and an image (2 Next electronic image, reflected electronic image, etc.) is displayed.

The objective lens 2 is for focusing the primary electron beam 1 focused by a focusing lens (not shown) on the order of several hundreds of micron on the surface of the sample 3 to a fine order of nm order. It is a lens. Since the magnetic field type objective lens 2 is used, secondary electrons and the like emitted when the surface of the sample 3 is flatly scanned by the primary electron beam narrowed down are shown in FIG. 9 described later due to the strong magnetic field of the objective lens 2. While traveling in the axial direction as described above, it travels upward (in the direction opposite to the irradiation direction of the primary electron beam 1), and the negative voltage applied to the repeller electrode 5 blocks its upward travel, causing it to move outward. Then, it travels toward the secondary electron generating plate 6 to which a positive voltage is applied and collides with each other to generate second secondary electrons.

The sample 3 is a sample to be observed and measured.

The first secondary electrons 4 are secondary electrons emitted from the sample 3 (potential V2) that has been scanned in a plane with the primary electron beam 1.

The second secondary electrons 41 are secondary electrons emitted from the secondary electron generating plate 6.

The repeller electrode 5 applies a negative voltage to prevent the first secondary electrons 4 and the like from traveling upward on the axis.

The secondary electron generating plate 6 is for causing the first secondary electrons 4 and the like to collide with each other to generate the second secondary electrons 41 and multiply the electrons.

The MCP 7 detects and amplifies the second secondary electron 41.

V1, V2, V3 and V4 are voltages of the primary electron beam 1, the sample 3, the secondary electron generating plate 6 and the MCP 7 or applied voltages (see FIGS. 1 and 4 etc.). Here, V3-V2 corresponds to the first acceleration voltage, and V4-V3 corresponds to the second acceleration voltage.

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

(1) The primary electron beam 1 is accelerated by an electron beam emitted from an electron gun such as a TFE emitter, and then deflected by a deflecting device to two-dimensionally scan the surface of the sample 3 and the secondary electron generating plate 6 After passing through the space of the MCP 7, the objective lens 2 finally narrows the beam spot size to a required beam spot size and irradiates the surface of the sample 3.

(2) Secondary electrons and backscattered electrons generated by the primary electron beam 1 irradiating the sample 3 are bias voltage of several hundred volts (first accelerating voltage=) applied between the sample 3 and the electron multiplying plate 6. V3-V2) accelerates and moves above the column. Since this voltage bias can be controlled independently of the landing voltage of the primary electron beam 1, the energy of the electrons incident on the secondary electron generating plate 6 is always kept at an optimum value with high secondary electron emission efficiency.

(3) Since the hole for allowing the primary electron beam 1 to pass through is opened in the center of the MCP 7, components such as secondary electrons rising vertically to the sample 3 cannot be detected. Therefore, in order to detect components such as secondary electrons generated in the vertical direction in the sample 3, a repeller electrode 5 is provided, and a voltage of several hundreds of volts is applied to the tip of the repeller electrode 5, thereby creating a potential barrier of several hundreds of volts. Prevent electrons with the following energies from penetrating through the holes (holes on the axis) of MCP7 and going upward. Secondary electrons or the like having energy smaller than the voltage applied to the repeller electrode 5 are prevented from passing through the hole and are directed toward the MCP 7, so that they can be detected. By increasing the voltage of the repeller electrode 5, secondary electrons or the like having higher energy can be detected, but if the energy is made large enough to be comparable to the energy of the primary electron beam 1, the trajectory of the primary electron beam 1 Since there is a possibility that the primary electron beam 1 may change and the primary electron beam 1 may not be irradiated correctly, the voltage that can be applied to the repeller electrode 5 is sufficiently small compared to the energy of the primary electron beam 1. The hole and the shape of the repeller electrode 5 need to be accurately axisymmetric so as not to affect the primary electron beam 1, and the primary electron beam 1 needs to be designed so as to pass through the center of the hole. is there. Further, since the primary electron beam 1 is largely deflected and then passes through the inside of the repeller electrode 5, the primary electron beam 1 does not collide with the inside of the repeller electrode 5 when the primary electron beam 1 is deflected to the maximum. Is necessary.

(4) Secondary electrons that have moved upward in the lens barrel (column) collide with the electron multiplier plate 6. Secondary electrons and the like (first secondary electrons 41) that collide with the electron multiplier plate 6 generate more secondary secondary electrons than the original number. The generated second secondary electrons 41 are incident on the MCP7 by the bias voltage (second acceleration voltage=V4-V3) applied between the electron multiplier plate 6 and the MCP7, and the desired amplification is performed as a current signal. Take out from the anode (not shown). The signal taken out is supplied to a current amplifier and taken into the computer as a digital signal through the A/D converter. After performing various kinds of image processing, it is displayed on the display as an image having a desired size and depth, or stored in a storage device as image information.

(5) The electron multiplying plate 6 is a conductive plate whose surface is coated with a material having a high secondary electron generation efficiency (about 2 to 20). A conductive plate is preferably a low resistance metal, but since it is used to multiply very small currents of nA or less, in order to achieve the purpose of the present invention, a meg. It can be used even if the resistance value is high. As a material having a high secondary electron generation efficiency, BaO, MgF5Cu-BeO, Cu-BeO6, 2Ag-MgO-CS9, 2Cs-Sb, 10GaP-Cs 20 to 40 and the like can be used as well as MgO. For example, when a MgO thin film or the like is used, a multiplication factor of about 7 times can be obtained.

The secondary electron emitting material having a large secondary electron emitting efficiency is generally an insulator. Therefore, if a thick film is provided on the surface of the electron multiplying plate, the electric resistance value becomes very large, and a large signal cannot be extracted. Therefore, the film provided on the surface of the electron multiplying plate 6 has a large secondary electron emission ratio and preferably has a thickness of several tens nm or less so that electrons are supplied to the surface of the insulating film from the anode by the tunnel effect. It is more preferable if the secondary electron emitting material has conductivity. A composite material mixed with a conductive material can be used.

(6) It is desirable that the electron multiplication plate 6 is installed so as not to be perpendicular to the direction of secondary electrons as shown in the figure, and electron emission is further increased as compared with the case where it is arranged vertically. The amount can be increased.

Since the energy of the secondary electrons emitted from the electron multiplying plate is as low as a few eV, it is returned to the electron multiplying plate 6 again and absorbed, so that the multiplication effect does not occur. Therefore, a potential difference of a few hundred volts (second acceleration voltage=V4−V3) is applied between the electron multiplying plate 6 and the input end of the MCP 7 so that the generated secondary electrons can be efficiently incident on the MCP 7. Since there is incident energy that maximizes the detection efficiency of the MCP 7, it is desirable to adjust to that value.

The electrons input to MCP7 undergo electron multiplication due to the bias voltage applied across MCP7, and a signal current is output from the anode of MCP7.

(7) The following advantages occur when the present invention is used.

For example, as an extreme example that actually occurs during ultra-high-speed inspection, it is assumed that one or zero electrons are generated per pixel due to electron beam scanning on a sample. In a normal MCP, only 30% or less of the electrons incident on the MCP can be detected as a signal, so about 1 or 0 electrons are not detected and the image signal becomes 0. Therefore, only the noise of the amplifier or the like appears in the image.

On the other hand, when the electron multiplying plate 6 of the present invention is used, the number of electrons is increased about 7 times, so that the number of electrons provided to the MCP 7 is 7 or 0 per pixel, of which 30% is 2 Alternatively, since 0 is detected, an image can be formed.

As described above, by using the present invention, it becomes possible to form an image even under an electron beam irradiation condition where it is not possible to form an image in the related art. it is possible to _obtain.

FIG. 2 is a configuration diagram (2) of one embodiment of the present invention. FIG. 2 shows an embodiment in which the MCP 7 of FIG. 1 is divided in the circumferential direction and the radial direction and is inclined obliquely to improve the secondary electron detection efficiency. The other structure is the same as that of FIG.

In FIG. 2, the MCP 7 is an opening of a hole (having a hole perpendicular to the surface) of the channel of the MCP 7 in the direction of the second secondary electron 41 emitted from the secondary electron generating plate 6 as shown in the figure. It is inclined in the direction that maximizes the number. Further, the MCP 7 is divided into a plurality of pieces in the radial direction and the circumferential direction, for example, a total of 8 pieces of 2×4, and has a structure capable of independently detecting and amplifying the secondary secondary electrons. ing. This makes it possible to detect a stereoscopic signal.

The MCP 7 is usually composed of one sheet, but the mechanically divided elements of each individual MCP 7 may be fixed to a holder.

As described above, by inclining the MCP 7, it becomes possible to detect and amplify the second secondary electrons 41 pre-multiplied by the secondary electron generating plate 6 at the maximum aperture ratio.

FIG. 3 shows an explanatory diagram of the present invention.

FIG. 3A shows efficiency ∝ secondary electron emission efficiency of material×incident angle (Cosθ)... (Equation 1).

This “efficiency” of (Equation 1) is obtained when the primary electron beam 1 irradiates the sample 3, or the first secondary electron 4 is emitted to the secondary electron generating plate 6 and the second secondary electron 41 is emitted to the MCP 7. It represents the secondary electron generation efficiency emitted upon collision, and is obtained by the product of the "secondary electron emission efficiency of material" and the "incident angle (Cos[theta])".

“The secondary electron emission efficiency of the material” is the secondary electron generation efficiency when the electron beam 1 is vertically incident on the surface of the secondary electron generation plate 6, and is, for example, as shown in FIG. It has characteristics. That is, the secondary electron generation efficiency gradually increases when the incident energy eV is from 0 V to approximately 300 V, has a maximum value at approximately 300 V, and gradually decreases when the incident energy eV is higher than that. This is because when the voltage is higher than about 300 V, secondary electrons penetrating deeply from the surface are not emitted from the surface.

The “incident angle (Cos θ)” is the angle at which the electron beam impinges (incides) on the secondary electron generating plate 6. The smaller the incident angle, the larger the value (the higher the generation efficiency).

Therefore, in order to improve the secondary electron generation efficiency, for example, the smaller the angle at which the first secondary electrons 4 emitted from the sample 3 collide with the secondary electron generation plate 6, the better. Therefore, in consideration of both of them, θ is set to about 45 degrees in FIGS. 1 and 2 (actually, the angle θ of maximum efficiency is obtained and set in an experiment).

FIG. 4 shows an explanatory view (No. 2) of the present invention. This is the potential relationship among V1 (potential of the primary electron beam 1), V2 (potential of the sample 3), V3 (potential of the secondary electron generating plate 6) and V4 (potential of MCP7) in FIGS. It is shown schematically. Here, V2=0V.

In FIG.
V1=1.5 KV: The potential V1 of the primary electron beam 1 represents 1.5 KV.

Near V2=0: electron V2 of sample 3 represents 0V.

V3=0.3KV: The potential V3 of the secondary electron generating plate 6 represents 0.3KV.

V4=0.4KV: The potential V4 of MCP7 represents 0.4KV.

From the above relationship, the first accelerating voltage of V3-V2=0.3 KV between the sample 3 and the secondary electron generating plate 6, and V4-V3= between the secondary electron generating plate 6 and the MCP7. This means that the second acceleration voltage of 0.4 KV-0.3 KV=0.1 KV is applied. For example, as in the retarding method, if the sample potential V2 changes, V3 is automatically changed to keep the energy of the secondary electrons M incident on the secondary electron generating plate 6 constant.

From the above relationship, the first secondary electrons 4 emitted from the sample 3 are accelerated toward the secondary electron generating plate 6 by the first acceleration voltage and the second secondary electrons 4 generated in the secondary electron generating plate 6 are accelerated. The secondary electrons 41 will be accelerated toward the MCP 7 with the second acceleration voltage.

FIG. 5 is a configuration diagram (3) of the first embodiment of the present invention. FIG. 5 shows a configuration example in which an APD (avalanche photodiode) 8 is used instead of the MCP 7 in FIG. Others are the same as those in FIG.

In FIG. 5, the APD 8 detects and multiplies the second secondary electrons 41. The APD8 has a structure different from that of the MCP7 of FIG. 1 and has no channel, so in principle, the aperture ratio can be 100%, but the APD8 has a terminal for communicating with an external circuit and a peripheral portion which does not operate as the APD8. Therefore, there is a case in which all the effective electrons of the APD 8 cannot be irradiated with the signal electrons. Therefore, the first secondary electrons 4 (or reflected electrons) are made to collide with the secondary electron generating plate 6 to multiply the number of electrons, and then incident on the APD 8 to compensate for the aperture loss and improve the detection efficiency. It becomes possible.

When the APD 8 is used, it is desirable that the potential difference applied between the secondary electron generating plate 6 and the APD 8 is about 2 kV or more so that the electrons incident on the APD 8 are easily multiplied.

As described above, by using the APD 8 instead of the MCP 7 of FIGS. 1 to 5, it is possible to reduce the signal loss due to the low channel aperture ratio of the MCP 7 and efficiently detect and multiply secondary electrons. It will be possible.

FIG. 6 is a configuration diagram (4) of the first embodiment of the present invention. FIG. 6 shows a first secondary electron 4 having a low energy among the signal electrons generated when the sample 3 is irradiated with the primary electron beam 1 and a reflected electron 42 having substantially the same energy as the one electron beam 1. An example in which multiplication detection is performed by distinguishing between and will be described.

The detection/multiplication of the first secondary electron 4 having low energy is performed by the secondary electron generation plate 61 and the MCP 71 as shown in the figure, and the detection/multiplication of the reflected electron 42 having high energy is performed as shown in the figure. The next electron generating plate 62 and the MCP 72 are used.

(1) Secondary electrons of low energy (first secondary electrons) 4 are secondary electrons having low energy of about 0 to 100 eV, and are generated in all directions on the surface of the sample 3. The generated secondary electrons (first secondary electrons) 4 are accelerated and rise due to the potential difference (V3-V2=first accelerating voltage) toward the upper side of the lens barrel (column). Since it has a lateral velocity component, it spreads in a conical shape as it rises. Among the secondary electrons 4, those having large lateral energy gather at the outer peripheral portion of the cone, and those having low lateral energy gather at the central portion.

(2) On the other hand, the electron with high energy in the axial direction (reflected electron 42) is the electron whose primary electron beam 1 is reflected on the surface of the sample 3 so that the light is reflected by the mirror, and the energy is the primary electron beam 1. As high as. Actually, since the reflected electrons are generated where the primary electron beam 1 is slightly submerged in the sample 3, the scattering direction and the energy are slightly changed, and while slightly spreading, the primary electron beam 1 climbs the column substantially vertically. Of course, the reflected electrons generated from the tilted sample are scattered in the direction depending on the tilted surface, but here, the reflected electrons returning straight are dealt with.

By utilizing the above properties, it becomes possible to detect the lateral energy of the secondary electrons (first secondary electrons) 4 or to detect and multiply the secondary electrons and the reflected electrons 42 separately.

(3) Next, in order to detect the secondary electrons, the secondary electron generating plates 62 and 61 for detecting and multiplying the secondary electrons are placed at a position slightly away from the axis of the primary electron beam 1 as shown in the figure. Arrange in an annular shape. The first secondary electrons 4 generated on the surface of the sample 3 are accelerated by a potential difference (first accelerating voltage) of about 300 V given between the sample 3 and the secondary electron multiplying plate 61 to form an annular shape. It collides with the arranged secondary electron multiplying plate 61 to generate a large amount of secondary electrons (secondary secondary electrons) 41. The generated second secondary electrons 41 are accelerated by the potential difference (V4-V3=second accelerating voltage) given between the secondary electron multiplying plate 61 and the MCP 71, enter the MCP 71, and are multiplied. Become a signal.

(4) On the other hand, since the backscattered electrons 42 reflected by the sample 3 pass through a place close to the axis of the primary electron beam 1, the secondary electron multiplier 62 is shown as close to the axis of the primary electron beam 1 as possible. Place it like. The generated backscattered electrons 42 rise with the energy of the primary electron beam 1, but the secondary electrons are generated at the optimum energy for generating secondary electrons by controlling the potential of the secondary electron generation plate 62. It collides with the plate 62 and generates a large amount of second secondary electrons 43. The generated second secondary electrons 43 are attracted by the potential difference (V6-V5) given between the secondary electron generating plate 62 and the MCP 72, enter the MCP 72, are multiplied by the MCP 72, and are converted into an electric signal. To be done.

As described above, the low-energy first secondary electrons 4 and the high-energy reflected electrons 42 generated when the sample 3 is irradiated with the primary electron beam 1 and scanned in the plane are independently multiplied and detected. It becomes possible to do. In order to detect the reflected electrons more reliably, the incident angle of the primary electron beam 1 may be slightly inclined so that the reflected electrons can hit the reflector plate firmly. Alternatively, the secondary electron generating plate 62 for backscattered electrons may be extended to the inside of the repeller electrode 5.

FIG. 7 is an explanatory diagram (3) of the present invention. FIG. 7 schematically shows an example of the acceleration voltage when multiplying the first secondary electrons 4 and the backscattered electrons 42 of FIG. These are V1 (potential of primary electron beam 1), V2 (potential of sample 3), V3 (potential of secondary electron generating plate 61), V4 (potential of MCP 71), V5 (secondary electron generation) in FIG. The potential relationship between the potential of the plate 62) and V6 (potential of the MCP 72) is schematically shown. Here, V2=0V.

In FIG.
V1=1.5 KV: The potential V1 of the primary electron beam 1 represents 1.5 KV.

Near V2=0: electron V2 of sample 3 represents 0V.

V3=0.3 KV: The potential V3 of the secondary electron generating plate 61 represents 0.3 KV.

V4=0.4KV: The potential V4 of the MCP 71 represents 0.4KV.

V5=1.5KV: The potential V5 of the secondary electron generating plate 62 represents 1.5KV. Here, since the reflected electrons 42 (which are almost the same as the electrons of the primary electron beam 1) collide with each other, the potential is set to be substantially the same (slightly lower) as the potential of the primary electron beam 1. It should be noted that V5 may be any potential within the range of 0 to 1.5 KV since it is sufficient that the reflected electrons 42 (potential of the primary electron beam 1 is 1.5 KV) collide to generate secondary electrons. It is desirable that the secondary electron generation efficiency is the best at about 300 V (see FIG. 3).

V6=2.0KV: The potential V4 of MCP71 represents 2.0KV.

From the above relationship, the first accelerating voltage of V3−V2=0.3 KV between the sample 3 and the secondary electron generating plate 61, and V4−V3= between the secondary electron generating plate 61 and the MCP 71. A second accelerating voltage of 0.4 KV-0.3 KV=0.1 KV is applied to accelerate each.

Similarly, a first accelerating voltage of V5-V2=1.5 KV (preferably about 300 V (see FIG. 3) that maximizes the secondary electron generation efficiency) between the sample 3 and the secondary electron generation plate 62. An accelerating voltage of V6-V5=0.5 KV is applied between the secondary electron generating plate 62 and the MCP 72 so that the MCP 72 is accelerated.

FIG. 8 shows a configuration diagram (5) of an embodiment of the present invention. FIG. 8 shows an embodiment called a repeller electrode 5 provided at the center of the MCP 7, in which the electrode is elongated and the tip is budded small.

As shown in FIG. 8, a deflection system (electron beam deflection device) 9 for performing electron beam scanning is provided, and the primary electron beam 1 is deflected to scan the surface of the sample 3 two-dimensionally (scan in the X and Y directions). ) Do. The thickness of the primary electron beam 1 is at most on the order of about 100 microns, but the center of the objective lens 2 is placed at the center of the objective lens 2 in order to reduce the aberration generated in the objective lens 2 when the electron beam is scanned. Is deflected in two steps so that When the two-stage deflection is performed, as shown in the figure, the primary electron beam 1 passing through the MCP 7 is in a state of being largely shaken with a maximum of several mm, so that a relatively large hole is formed so as not to collide with the inner wall of the MCP 7. Is open.

Since the oscillated primary electron beam 1 is finally narrowed down to a size of several nm, the trajectory range of the primary electron beam 1 becomes conical toward the sample 3. In other words, a large aperture is required so as not to affect the scanning of the primary electron beam 1 at a place near the MCP 7, but the locus range required for scanning the primary electron beam 1 becomes narrower as it approaches the objective lens 2. Even with a small opening, the scanning of the primary electron beam 1 can be prevented.

In the present embodiment, the repeller electrode 5 is elongated and extends from the MCP 7 in the direction of the objective lens 2 (axial direction), and the tip is small. A negative voltage of several hundred volts is applied to the repeller electrode 5, and the secondary electrons (first secondary electrons) 4 generated on the surface of the sample 3 pass through the center of the hole (the hole on the shaft). It prevents you from going. The generated first secondary electrons 4 are accelerated as they go above the lens barrel (column), so that the energy becomes higher. Immediately after the secondary electrons 4 are generated, the acceleration is not sufficient, so that it is possible to prevent the electrons from passing through the hole with a small energy.

In this embodiment, the repeller electrode 5 is arranged at a position near the secondary electron generation point, and the size of the hole can be reduced to several hundreds of microns. Therefore, the secondary electron 4 generated in the sample 3 goes out of the hole. Can be reliably prevented.

FIG. 9 shows an explanatory view (No. 4) of the present invention. FIG. 9 schematically shows the behavior of the secondary electrons (first secondary electrons) 4 at the tip portion of the repeller electrode 5 of FIG.

In FIG. 9, when the surface of the sample 3 is irradiated with a primary electron beam (for example, 1.5 KV) 1 and plane-scanned, secondary electrons (first secondary electrons) 4 are emitted and the objective lens 2 The magnetic field is attracted toward the secondary electron generating plate 6 to which the first accelerating voltage (not shown) is applied in the upward direction while rotating spirally on the axis as shown in the figure. At this time, a cylindrical repeller electrode 5 with a slightly tapered tip is attached to a portion of the secondary electron (first secondary electron) 4 emitted from the sample 3 which is as close as possible and has not been accelerated yet. By arranging and applying a negative voltage (eg, −100 V), the first secondary electrons 4 are efficiently pushed from the axis to the outside of the repeller electrode 5 and the trajectory as shown in the drawing is obtained. It becomes possible to accelerate toward the secondary electron generating plate 6 (not shown) arranged in the upper direction and collide with each other to generate secondary electrons (secondary secondary electrons 41).

FIG. 10 is an explanatory diagram (5) of the present invention. FIG. 10 schematically shows a structural example of the surface of the secondary electron generating plate 6.

In FIG. 10, on the secondary electron generating plate 6, electrons (first secondary electrons 4, backscattered electrons 41, etc.) deeply dive and scatter when a substance is irradiated. Of the scattered electrons, the electrons at a distance of about 10 nm from the surface of the substance are extracted as secondary electrons outside the substance. Therefore, more secondary electrons are emitted when the sample 3 is obliquely irradiated than when the sample 3 is vertically irradiated with the electron beam. FIG. 10 shows an example of a method for emitting a lot of secondary electrons from the secondary electron generating plate 6 by utilizing this property.

FIG. 10A shows an example in which a strip-shaped material is provided on the surface of the secondary electron generating plate 6 and an electron multiplication film is formed thereon. In this example, an example (formation, coating, etc.) in which an electron multiplying material is formed on a material such as a carbon nanotube having a strip-shaped (columnar) structure is shown. As the name implies, carbon nanotubes are columnar substances having a hole diameter of several nm to several tens of nm. At present, it is possible to easily make a sheet of carbon nanotubes oriented in a specific direction. A large amount of secondary electrons can be emitted by coating the carbon nanotube itself or its surface with an electron emitting material.

FIG. 10B shows an example in which a needle circumferential material is provided on the surface of the secondary electron generating plate 6 and an electron multiplying film is formed thereon. Since the needle-shaped material shown in the drawing is provided on the surface and the electron multiplication film is formed on the surface, the distance from the electron incident on the substance to the surface is shortened, so that many secondary electrons internally scattered are emitted to the outside. It becomes possible.

FIG. 10C shows an example in which a nano-order particulate material is provided on the surface of the secondary electron generating plate 6 and the electron multiplying film is formed thereon. Since the particle-shaped material shown in the figure is provided on the surface and the electron multiplication film is formed on this, the distance from the electron incident on the substance to the surface is shortened, and a large amount of internally scattered secondary electrons are emitted to the outside. It becomes possible. The nanoparticles themselves may be formed from the electron multiplying material.

When the structure of the secondary electron generating plate 6 as described above is adopted, the electron multiplication efficiency can be improved even if the secondary electron generating plate 6 is not inclined with respect to the incident secondary electron 4 and reflected electron 42. It is possible to raise it.

FIG. 11 is an explanatory diagram (6) of the present invention. FIG. 11 is an enlarged view of a part of the surface of the secondary electron generating plate 6 in FIG. 10 and schematically shows how secondary electrons are generated and emitted. When the accelerated first secondary electrons 4 (or the reflected electrons 42) irradiate (collide) with the material of any shape in FIG. 9 on the surface of the secondary electron generating plate 6, secondary electrons are emitted. As for the generation of secondary electrons, only those generated in the vicinity of the surface of the material are emitted to the outside. Therefore, oblique electrons are efficiently emitted (proportional to Cos θ) rather than being incident vertically on the material. As shown in FIG. 11, when the first secondary electrons 4 accelerated into a protrusion (a strip shape, a needle shape, a particle shape, etc.) are incident, the secondary electrons are emitted with a Gaussian distribution around the reflection direction. Therefore, it is desirable that the oblique direction of the material is incident as much as possible to increase the secondary electron generation efficiency.

It is a block diagram of 1 Example of this invention. It is a 1 block diagram (2) of 1 Example of this invention. It is explanatory drawing of this invention. It is explanatory drawing (the 2) of this invention. FIG. 3 is a configuration diagram (3) of an embodiment of the present invention. FIG. 4 is a configuration diagram (4) of the first embodiment of the present invention. It is explanatory drawing (the 3) of this invention. FIG. 5 is a configuration diagram (5) of one embodiment of the present invention. It is explanatory drawing (the 4) of this invention. It is explanatory drawing (the 5) of this invention. It is explanatory drawing (the 6) of this invention.

1: primary electron beam 2: objective lens 3: sample 4: first secondary electron 41, 43: second secondary electron 42: reflected electron
5: Repeller electrode 6, 61, 62: Secondary electron generating plate 7, 71.72: MCP
8: APD
9: Deflection system 10: Secondary electron emission material

Claims (9)

In an electron detection device that irradiates an electron with a sample and detects and amplifies the electron emitted or reflected from the sample,
A magnetic field type objective lens that squeezes a primary electron beam having a predetermined acceleration voltage energy and irradiates the sample with the beam.
A deflection device for deflecting the primary electron beam so that the primary electron beam narrowed down is scanned on a sample;
The sample has a hole for passing the primary electron beam in the direction of the sample, and accelerates the first secondary electron emitted when the sample is irradiated with the narrowed primary electron beam and scanned. A first positive acceleration voltage is applied , and the first secondary electrons emitted from the sample by the action of the magnetic field of the magnetic field type objective lens are spirally rotated on the axis while the first acceleration is performed. Accelerating in the direction in which the voltage is applied and generating second secondary electrons multiplied when the first secondary electrons accelerated by the first accelerating voltage collide . Secondary electron generating plate that accelerates and attracts the secondary electrons of
The secondary electron generating plate has a hole for passing the primary electron beam in the direction of the sample and a hole for passing the first secondary electron in the direction of the secondary electron generating plate. further multiply the secondary electrons multiplied are accelerated by an acceleration voltage of the second applies a positive second acceleration voltage for accelerating the second secondary electrons multiplied, the second MCP that accelerates and attracts secondary electrons of
And an anode that detects secondary electrons multiplied by the MCP. In the hole portion of the secondary electron generating plate through which the primary electron beam passes, the first secondary electrons emitted from the sample are prevented from traveling in the opposite direction of the traveling path of the primary electron beam. The electron detector according to claim 1, wherein a repeller electrode having a hole through which the primary electron beam passes, to which a negative voltage is applied, is provided in the center. A surface for generating the second secondary electron said first secondary electrons to the secondary electron generating plate collides, and a convex shape with respect to the traveling direction of the primary electron beam, the second 3. The electron detection device according to claim 1, wherein the multiplication efficiency of secondary electrons is increased. The electron detection device according to claim 1, wherein a strip-shaped, needle-circular, or particle-shaped secondary electron emitting material is formed on the surface of the secondary electron generating plate. .. The electronic detection device according to any one of claims 1 to 4, wherein the MCP is divided into a plurality of portions in at least one of a circumferential direction and a radial direction to enable division detection and amplification. The electron detection device according to claim 1, wherein the MCP is tilted toward the secondary electron generation plate. 7. The electron detection device according to claim 1, wherein the MCP is replaced with APD. Two sets of the secondary electron generating plate and the MCP are provided coaxially with the trajectory of the primary electron beam, one set of the inner side detects and multiplies backscattered electrons emitted from the sample, and one set of the outer side. The electron detection device according to claim 1, wherein the first secondary electrons emitted from the sample are detected and multiplied as a set. In an electron detection method for irradiating a sample with an electron and detecting and amplifying the electron emitted or reflected from the sample,
A magnetic field type objective lens which squeezes a primary electron beam having a predetermined acceleration voltage energy and irradiates the sample with the beam;
A deflection device for deflecting the primary electron beam so that the narrowed primary electron beam is scanned on the sample,
The secondary electron generating plate is for accelerating and attracting the first secondary electrons to collide with them, and has a hole for passing the primary electron beam in the direction of the sample, and is narrowed down. By applying a positive first acceleration voltage for accelerating the first secondary electrons emitted when the sample is irradiated with the primary electron beam and scanned, and by the action of the magnetic field of the magnetic field type objective lens. The first secondary electrons emitted from the sample are accelerated in the direction in which the first acceleration voltage is applied while spirally rotating on the axis, and the first secondary electrons are accelerated by the first acceleration voltage. When the secondary electrons of collide with each other, they generate a second secondary electron that is multiplied,
The MCP is for accelerating and attracting the second secondary electrons to cause them to collide, and has a hole for passing the primary electron beam in the direction of the sample, and the first secondary electrons for the MCP. The secondary electron generating plate has a hole to pass therethrough, and a positive second accelerating voltage for accelerating the multiplied second secondary electron by the secondary electron generating plate is applied to the second electron generating plate. The secondary electrons accelerated and multiplied by the acceleration voltage of
An electron detection method, wherein the anode detects secondary electrons multiplied by the MCP.

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