JP2017135048A - Electron detecting device and electron detecting method - Google Patents

Abstract

PURPOSE: To reduce the influence of detection loss depending on electron detection by an MCP and an aperture ratio of an amplifying element, and other factors and further increase detection and amplification rates in an electron detecting device and an electron detecting method.CONSTITUTION: An electron detecting device comprises: an objective lens of a magnetic field type; an electron beam deflecting device; a secondary electron generating plate having a hole allowing a primary electron beam to pass therethrough toward a sample, applying a positive first acceleration voltage for accelerating first secondary electrons emitted when applying thinly narrowed primary electron beam to the sample and scanning it, and generating second secondary electrons multiplied as a result of collision of the first secondary electrons accelerated by the first acceleration voltage; an MCP having a hole allowing the primary electron beam to pass therethrough toward the sample, and a hole allowing the first secondary electrons to pass therethrough toward the secondary electron generating plate, applying a positive second acceleration voltage for accelerating the second secondary electrons multiplied by the secondary electron generating plate, and further multiplying the multiplied secondary electrons accelerated by the second acceleration voltage; and an anode.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electron detection apparatus and an electron detection method for detecting and amplifying electrons emitted or reflected from a sample by irradiating the sample with electrons.

  Scanning electron microscopes detect and amplify signal electrons such as secondary electrons and reflected electrons generated by irradiating a sample with a narrowly focused electron beam, and form an image of the sample. This 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. Electrons are one of so-called elementary particles, and the charge amount of electrons is as small as 1.6 x 10 minus 16 coulombs. Therefore, in order to detect individual electrons, it is necessary to perform very large amplification without noise. There is.

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

  However, since the glass wall forming the MCP channel is thick, the total area of the MCP end face is the sum of the hole area and the wall area. That is, the part with the electron which went to MCP collides with a wall, and is not detected. The ratio of holes in the total MCP area is the aperture ratio. MCP has an aperture ratio of approximately 60%.

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

  The signal amplified by the MCP is amplified by a 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 intrinsic SNR of an image is determined by the square root of the number of electrons constituting one pixel, the SNR deteriorates as the number of detected electrons decreases.

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

  However, the number of electrons generated per pixel is 100 or less in an application for detecting and amplifying electrons generated while scanning (for example, digital scanning) an electron beam narrowed down to the nm order as in a scanning electron microscope. Therefore, if the detection efficiency is low, the SNR of the original signal forming the image is extremely lower than 10, and there is a problem that it cannot be put into practical use as it is.

  Increasing the amount of irradiated electrons per pixel can improve image quality, but for that purpose, it is necessary to irradiate an electron beam with a higher electron density. The objective lens that narrows down the electron beam has aberrations, and the electron beams have negative charges and repel each other. Therefore, it is not possible to increase the current density without darkness at the low acceleration voltage required for stable observation. Technically difficult. Furthermore, large-scale irradiation of an electron beam causes a reaction with a measurement object, and a large potential difference generated by alteration or charging causes damage. Therefore, there is a limit to increase of the irradiation amount.

  As a method of increasing the SNR without increasing the current of the electron beam irradiated to the sample, there is a method of performing image accumulation by scanning the same place many times, but the throughput decreases in proportion to the number of accumulations. It cannot be used when high speed is required (for example, in the case of mask pattern length measurement, defect inspection, etc.).

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

  In addition, when the irradiation electron beam energy is changed by the retarding method, the detection efficiency changes because the energy of the generated secondary electrons changes, so the detection efficiency of the secondary electrons changes even if the irradiation electron beam energy changes. It is desirable not to.

  The present invention is characterized in that the influence of detection loss due to the aperture ratio or the like of the above-described MCP electron detection / amplification element is reduced and the detection / amplification rate is further improved.

  Therefore, the present invention increases the number of signal electrons incident on the MCP etc. by multiplying the secondary electrons generated by the electron irradiation with the secondary electron generating plate before entering the MCP etc., and the aperture ratio of the MCP etc. An object of the present invention is to sufficiently compensate for the signal electron detection loss due to the limitation so that the signal electron is not substantially lost, 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 simultaneously by utilizing the fact that the orbit changes due to the energy difference between the secondary electrons and the reflected electrons generated in the sample. The purpose is to realize detection.

  For this purpose, the present invention provides an electron detection apparatus that detects and amplifies electrons emitted or reflected from a sample by irradiating the sample with electrons, and finely squeezes a primary electron beam having energy of a predetermined acceleration voltage to the sample. A magnetic field type objective lens to be irradiated, a deflecting device for deflecting the primary electron beam so as to scan the narrowly focused primary electron beam on the sample, and a hole for allowing the primary electron beam to pass in the direction of the sample are provided. And applying a positive first acceleration voltage for accelerating the first secondary electrons emitted when the sample is irradiated with a finely focused primary electron beam and scanned, and at the first acceleration voltage. A secondary electron generating plate for generating a second secondary electron multiplied when the accelerated first secondary electron collides, a hole for allowing the primary electron beam to pass in the direction of the sample, and the first 1 secondary electron to secondary generator plate And applying a positive second acceleration voltage for accelerating the second secondary electrons multiplied by the secondary electron generating plate and accelerating by the second acceleration voltage. An MCP that further multiplies the secondary electrons and an anode that detects the secondary electrons multiplied by the MCP.

  At this time, the first secondary electrons emitted from the sample are negatively prevented from traveling in the reverse direction of the traveling path of the primary electron beam in the hole portion of the secondary electron generating plate through which the primary electron beam passes. A repeller electrode having a hole through which a primary electron beam passes at the center is provided.

  Further, the surface where the first secondary electrons collide with the secondary electron generating plate to generate the second secondary electrons is made convex with respect to the traveling direction of the primary electron beam, and the second secondary electrons are formed. Increase the multiplication efficiency.

  Further, a strip-like, needle-circular or particulate secondary electron emission material is formed on the surface of the secondary electron generating plate.

  In addition, the MCP is divided into a plurality of one or more in either the circumferential direction or the radial direction to enable division detection / amplification.

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

  Also, the MCP is replaced with APD.

  In addition, two sets of the secondary electron generating plate and the MCP are provided coaxially with the orbit of the primary electron beam, and the reflected electrons emitted from the sample are detected and multiplied by the inner set, and the outer set is set. Thus, the first secondary electrons emitted from the sample are detected and multiplied.

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

  Since the energy incident on the secondary electron generator plate can be determined independently of the primary electron landing energy, the secondary electron detection efficiency can be kept constant independently of the landing energy even if the retarding method is used. It 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 orbit changes due to the energy difference between the secondary electrons reflected and reflected from the sample and the reflected electrons. It becomes possible.

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

  In FIG. 1, a 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, an objective lens 2 (not shown), and the like. Planar scanning (scanning in the X direction and Y direction) is performed while irradiating the surface to generate secondary electrons and reflected electrons. The generated secondary electrons and reflected electrons are multiplied by the secondary electron generating plate 6, and further detected and amplified by the MCP 7 disposed opposite to the secondary electron generating plate 6, and an image (2) is displayed on a display (not shown). Next electron image, reflected electron image, etc.) are displayed.

  The objective lens 2 is for narrowing the primary electron beam 1 focused to about several hundred microns by a focusing lens (not shown) to the order of nm on the surface of the sample 3. Here, the objective lens 2 is a magnetic field type objective. It is a lens. Since the magnetic field type objective lens 2 is used, secondary electrons and the like emitted when the surface is scanned with the primary electron beam narrowly focused on the surface of the sample 3 are shown in FIG. In this way, it travels upward (in the direction opposite to the irradiation direction of the primary electron beam 1) while spirally moving on the axis, and the negative voltage applied to the repeller electrode 5 prevents the upward travel and causes it to move outward. Then, it travels toward the secondary electron generating plate 6 to which a positive voltage is applied, and collides to generate second secondary electrons.

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

  The first secondary electrons 4 are secondary electrons emitted from the sample 3 (potential V2) obtained by plane scanning 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 generating electrons by multiplying the first secondary electrons 4 and the like to generate second secondary electrons 41.

  The MCP 7 detects and amplifies the second secondary electrons 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). 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 in order to scan the surface of the sample 3 two-dimensionally. After passing through the space of the MCP 7, the object lens 2 is finally focused on the required beam spot size and irradiated onto the surface of the sample 3.

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

  (3) Since a hole through which the primary electron beam 1 passes is opened at the center of the MCP 7, components such as secondary electrons that have risen perpendicular to the sample 3 cannot be detected. Therefore, in order to detect components such as secondary electrons generated in the vertical direction on the sample 3, a repeller electrode 5 is provided, and a voltage barrier of several hundred volts is created by applying a voltage of several hundred volts to the tip thereof. Electrons having the following energy are prevented from penetrating through the holes (holes on the axis) of the MCP 7. Secondary electrons having an energy smaller than the voltage applied to the repeller electrode 5 are blocked from passing through the hole and are directed toward the MCP 7 so that they can be detected. Increasing the voltage of the repeller electrode 5 makes it possible to detect secondary electrons and the like having higher energy. However, if the voltage is increased to be comparable to the energy of the primary electron beam 1, the trajectory of the primary electron beam 1 is increased. The voltage that can be applied to the repeller electrode 5 is sufficiently smaller than the energy of the primary electron beam 1 because there is a risk that the irradiation of the correct primary electron beam 1 may not be possible. The hole and shape of the repeller electrode 5 must be made precisely axisymmetric so as not to affect the primary electron beam 1 and must be designed so that the primary electron beam 1 passes through the center of the hole. is there. Further, since the primary electron beam 1 passes through the inside of the repeller electrode 5 after being largely deflected, 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 or the like that have moved up the column (column) collide with the electron multiplier plate 6. Secondary electrons or the like (first secondary electrons 41) colliding 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 MCP 7 by a bias voltage (second acceleration voltage = V4−V3) applied between the electron multiplier 6 and the MCP 7, and are amplified as desired to obtain a current signal. It is taken out from an anode not shown. The extracted signal is supplied to a current amplifier, and is acquired as a digital signal by a computer via an A / D converter. After performing various kinds of image processing, the image having a desired size and depth is displayed on a display or stored as image information in a storage device.

  (5) The electron multiplier plate 6 is obtained by coating the surface of a conductive plate with a material having high secondary electron generation efficiency (about 2 to 20). The conductive plate is preferably a low resistance metal, but is used to multiply very small currents below nA, so in order to achieve the purpose of the present invention, it must be of mega ohms unless it is a perfect insulator. Thus, it can be used even when the resistance value is high. Examples of materials having high secondary electron generation efficiency include MgO, BaO, MgF5Cu-BeO, Cu-BeO6, 2Ag-MgO-CS9, 2Cs-Sb, 10GaP-Cs20-40. For example, when an MgO thin film is used, a multiplication factor of about 7 times can be obtained.

  A secondary electron emission material having a large secondary electron emission efficiency generally has many insulators. Therefore, if a thick film is provided on the surface of the electron multiplier plate, the electric resistance value becomes very large and a large signal cannot be taken out. Therefore, it is desirable that the film provided on the surface of the electron multiplier plate 6 has a large secondary electron emission ratio and has a thickness of several tens of nm or less so that electrons are supplied from the anode to the insulating film surface by the tunnel effect. It is even better if the secondary electron emission material is conductive. A composite material mixed with a conductive material can be used.

  (6) It should be noted that the electron multiplier plate 6 is preferably installed so as to be inclined so as not to be perpendicular to the direction of the secondary electrons as shown in the figure, and more electron emission than the case where it is arranged vertically. The amount can be increased.

  Since the energy of the secondary electrons emitted from the electron multiplier plate is as low as several eV, as it is, it returns to the electron multiplier plate 6 and is absorbed again, and no multiplication action occurs. Therefore, a potential difference of several hundred volts (second acceleration voltage = V4−V3) is applied between the electron multiplier 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 it to that value.

  Electrons input to the MCP 7 are multiplied by a bias voltage applied to both ends of the MCP 7, and a signal current is output from the anode of the MCP 7.

  (7) Use of the present invention produces the following advantages.

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

  On the other hand, when the electron multiplier plate 6 of the present invention is used, the number of electrons increases by 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, image formation can be performed.

As described above, when the present invention is used, it is possible to form an image even under an electron beam irradiation condition in which an image cannot be formed conventionally, and a high-quality image can be obtained even when an ultrafast electron beam scanning is performed. Can be obtained _.

  FIG. 2 shows a block diagram (part 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 inclined to improve the secondary electron detection efficiency. Other configurations are the same as those in FIG.

  In FIG. 2, the MCP 7 has an opening of a channel hole (a hole perpendicular to the surface) 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 where the number is maximum. 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 second secondary electrons. ing. Thereby, a three-dimensional signal can be detected.

  Note that the MCP 7 is usually constituted by one sheet, but each element of the individual MCP 7 that is mechanically divided may be fixed to the holder.

  As described above, since the MCP 7 is inclined, the second secondary electrons 41 pre-multiplied by the secondary electron generating plate 6 can be detected and amplified with the maximum aperture ratio.

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

  (A) of FIG. 3 shows the secondary electron emission efficiency × incidence angle (Cos θ) of the efficiency soot material (Equation 1).

  The “efficiency” of this (Equation 1) is that when the primary electron beam 1 irradiates the sample 3 or the first secondary electrons 4 are applied to the secondary electron generating plate 6 and the second secondary electrons 41 are applied to the MCP 7. It represents the generation efficiency of secondary electrons emitted when colliding, and is obtained by the product of “secondary electron emission efficiency of material” and “incident angle (Cos θ)”.

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

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

  Accordingly, in order to increase 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, in FIG. 1 and FIG. 2, θ = about 45 degrees (actually, the angle θ of maximum efficiency is obtained and set by experiment).

  FIG. 4 shows an explanatory diagram (part 2) of the present invention. This corresponds to the potential relationship of 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.

    -V2 = 0 vicinity: The electron V2 of the sample 3 represents 0V.

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

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

  From the above relationship, the first acceleration voltage of V3−V2 = 0.3 KV is provided between the sample 3 and the secondary electron generating plate 6, and V4−V3 = between the secondary electron generating plate 6 and the MCP7. The second acceleration voltage of 0.4 KV−0.3 KV = 0.1 KV is applied. For example, when the sample potential V2 changes as in the retarding method, the energy of the secondary electrons M incident on the secondary electron generating plate 6 is kept constant by automatically changing V3.

  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 2 generated by the secondary electron generating plate 6 is used. The secondary electrons 41 are accelerated toward the MCP 7 with the second acceleration voltage.

  FIG. 5 shows a configuration diagram (part 3) of one 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 in FIG.

  In FIG. 5, the APD 8 detects and multiplies the second secondary electrons 41. The APD 8 has a structure different from that of the MCP 7 in FIG. 1 and has no channel. Therefore, in principle, the aperture ratio can be 100%. However, the APD 8 has a terminal for exchanging with an external circuit and a peripheral portion that does not operate as the APD 8. For this reason, there is a case where all the effective electrons of the APD 8 cannot be irradiated with the signal electrons. Therefore, the first secondary electrons 4 (or reflected electrons) collide with the secondary electron generating plate 6 to increase the number of electrons, and then enter the APD 8 to compensate the aperture loss and increase the detection efficiency. It becomes possible.

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

  As described above, by using APD 8 instead of MCP 7 in FIGS. 1 to 5, signal loss due to low channel aperture ratio of MCP 7 can be reduced, and secondary electrons can be detected and multiplied efficiently. It becomes possible.

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

  The detection and multiplication of the first secondary electrons 4 having low energy are performed by the secondary electron generating plate 61 and the MCP 71 as shown in the figure, and the detection and multiplication of the reflected electrons 42 having high energy are performed by 2 as shown in the figure. This is performed by the secondary electron generating plate 62 and the MCP 72.

  (1) Low energy secondary electrons (first secondary electrons) 4 are secondary electrons having a low energy of about 0 to 100 eV, and are generated on the surface of the sample 3 in all directions. The generated secondary electrons (first secondary electrons) 4 are accelerated by the potential difference (V3−V2 = first acceleration voltage) toward the upper side of the column (column) and rise. Since it has a velocity component in the lateral direction, it spreads in a conical shape as it rises. Among the secondary electrons 4, those having a large transverse energy gather at the outer periphery of the cone, and those having a low transverse energy gather at the center.

  (2) On the other hand, electrons with high energy in the axial direction (reflected electrons 42) are those in which the primary electron beam 1 is reflected from the surface of the sample 3 so that light is reflected by a mirror. As high as Actually, the reflected electrons are generated when the primary electron beam 1 is slightly submerged in the sample 3, so that the scattering direction and energy are slightly changed and slightly expanded while climbing up the column (column) almost vertically. Of course, the reflected electrons generated from the inclined sample are scattered in a direction depending on the inclined surface, but here, the reflected electrons returning straight are handled.

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

  (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 located a little 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 acceleration voltage) of about 300 V applied between the sample 3 and the secondary electron multiplier plate 61 to form an annular shape. It collides with the arranged secondary electron multiplier 61 and generates a large amount of secondary electrons (secondary secondary electrons) 41. The generated second secondary electrons 41 are accelerated by a potential difference (V4−V3 = second acceleration voltage) applied between the secondary electron multiplier 61 and the MCP 71, enter the MCP 71, and are multiplied to be electrically charged. Signal.

  (4) On the other hand, since the reflected 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 plate 62 is shown as close to the axis of the primary electron beam 1 as possible. Arrange like this. The generated reflected electrons 42 rise with almost the energy of the primary electron beam 1, but secondary electrons are generated with the optimum energy to generate secondary electrons by controlling the potential of the secondary electron generating plate 62. A large amount of second secondary electrons 43 are generated by colliding with the plate 62. The generated second secondary electrons 43 are attracted by the potential difference (V6-V5) applied 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 electric signals. Is 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 plane are independently multiplied and detected. It becomes possible to do. In order to make the detection of the reflected electrons more reliable, the incident angle of the primary electron beam 1 may be slightly inclined so that the reflected electrons firmly hit the reflecting plate. Alternatively, the secondary electron generation plate 62 for reflected electrons may be extended to the inside of the repeller electrode 5.

  FIG. 7 shows an explanatory diagram (part 3) of the present invention. FIG. 7 schematically shows an example of the acceleration voltage when multiplying the first secondary electrons 4 and the reflected electrons 42 of FIG. This corresponds to V1 (potential of the primary electron beam 1), V2 (potential of the sample 3), V3 (potential of the secondary electron generating plate 61), V4 (potential of the MCP 71), V5 (secondary electron generation) in FIG. The potential relationship between the potential of the plate 62) and V6 (the 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.

    -V2 = 0 vicinity: The electron V2 of the sample 3 represents 0V.

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

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

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

    V6 = 2.0 KV: The potential V4 of the MCP 71 represents 2.0 KV.

  From the above relationship, the first acceleration voltage of V3-V2 = 0.3 KV is provided 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 acceleration voltage of 0.4 KV−0.3 KV = 0.1 KV is applied and accelerated.

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

  FIG. 8 is a block diagram of the first embodiment of the present invention (No. 5). FIG. 8 shows an embodiment called a repeller electrode 5 provided at the center of the MCP 7, in which the electrode extends long and the tip is stiffened.

  As shown in FIG. 8, a deflection system (electron beam deflecting device) 9 that performs electron beam scanning is provided, and the primary electron beam 1 is deflected to scan the surface of the sample 3 two-dimensionally (scanning in the X and Y directions). ) Although the thickness of the primary electron beam 1 is on the order of about 100 microns at all, in order to reduce the aberration generated in the objective lens 2 when the electron beam is scanned, the center of the objective lens 2 is centered on the primary electron beam 1. Is deflected in two stages so that the When 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 greatly shaken by several mm at the maximum, so that a relatively large hole is provided so as not to collide with the inner wall of the MCP 7. Is open.

  Since the swung primary electron beam 1 is finally narrowed to a size of several nanometers, the trajectory range of the primary electron beam 1 decreases toward the sample 3 in a conical shape. That is, a large opening is necessary near the MCP 7 so as not to affect the scanning of the primary electron beam 1, but the locus range necessary for the scanning of the primary electron beam 1 becomes narrower as the objective lens 2 is approached. Even if the aperture is small, scanning of the primary electron beam 1 can be prevented.

  In this embodiment, the repeller electrode 5 is elongated 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 secondary electrons (first secondary electrons) 4 generated on the surface of the sample 3 pass through the center portion (hole on the shaft) of the hole. It prevents you from going. The generated first secondary electrons 4 are accelerated toward the upper side of the column (column), so that the energy becomes higher. Immediately after the secondary electrons 4 are generated, acceleration is not sufficient, so that it can be prevented that the energy passes through the hole with a small energy.

  In the present embodiment, the repeller electrode 5 is disposed at a position close to the secondary electron generation point, and the size of the hole can be reduced to several hundred microns, so that the secondary electrons 4 generated in the sample 3 pass through the hole. Can be surely prevented.

  FIG. 9 shows an explanatory diagram (part 4) of the present invention. FIG. 9 schematically shows the behavior of secondary electrons (first secondary electrons) 4 at the tip of the repeller electrode 5 of FIG.

  In FIG. 9, when the surface of the sample 3 is subjected to plane scanning while irradiating the surface with a primary electron beam (for example, 1.5 KV) 1, 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 acceleration voltage (not shown) in the upward direction is applied while rotating on the axis in a spiral manner as shown in the figure. At this time, a cylindrical repeller electrode 5 having a slightly narrowed tip is formed in a portion of the secondary electrons (first secondary electrons) 4 emitted from the sample 3 as close as possible to the unaccelerated portion. By arranging and applying a negative voltage (for example, −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 FIG. It is possible to accelerate toward the secondary electron generating plate 6 (not shown) arranged in the upward direction, and collide to generate secondary electrons (second secondary electrons 41).

  FIG. 10 is an explanatory view (No. 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, reflected electrons 41, etc.) deeply sneak into the material and cause scattering. Among the scattered electrons, 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 irradiated from an oblique direction than when the electron beam is irradiated vertically. FIG. 10 shows an example of a method for emitting a large number of secondary electrons from the secondary electron generating plate 6 using 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 multiplier film is formed thereon. In this example, an example (formation, application, etc.) in which an electron multiplying material is formed on, for example, a carbon nanotube material having a strip (columnar) structure. The carbon nanotube is a columnar substance having a hole diameter of several nanometers to several tens of nanometers as the name indicates. At present, it is possible to easily make a sheet of carbon nanotubes oriented in a specific direction. By covering the carbon nanotube itself or its surface with an electron emission material, it becomes possible to emit a large number of secondary electrons.

  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 multiplier film is formed thereon. Since the electron multiplier film is formed on the surface by providing the illustrated needle-like material, the distance from the electron incident on the substance to the surface is shortened, so that many internally scattered secondary electrons 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 an electron multiplier film is formed thereon. Since the electron-multiplier film is formed on the surface by providing the particulate material shown in the figure, the distance from the electron incident on the substance to the surface is shortened, so that many internally scattered secondary electrons are emitted to the outside. It becomes possible. The nanoparticles themselves may be formed from an electron multiplier material.

  By adopting the structure of the secondary electron generating plate 6 as described above, the electron multiplication efficiency can be improved without tilting with respect to the first secondary electrons 4 and the reflected electrons 42 incident on the secondary electron generating plate 6. It becomes possible to raise.

  FIG. 11 is an explanatory view (No. 6) of the present invention. FIG. 11 is an enlarged view of a portion of the surface of the secondary electron generating plate 6 shown in FIG. 10 and schematically shows how secondary electrons are generated and emitted. When the accelerated first secondary electrons 4 (or reflected electrons 42) irradiate (collision) the material of any shape in FIG. 9 on the surface of the secondary electron generating plate 6, secondary electrons are emitted. Since only secondary electrons generated near the surface of the material are emitted to the outside, secondary electrons are emitted more efficiently when incident obliquely than when incident perpendicularly to the material (proportional to Cos θ). As shown in FIG. 11, when the first secondary electrons 4 accelerated to the protrusions (strips, needles, particles, etc.) are incident, secondary electrons are emitted in a Gaussian distribution centering on the reflection direction. Therefore, it is desirable to increase the secondary electron generation efficiency by making the oblique direction of the material as incident as possible.

1 is a configuration diagram of one embodiment of the present invention. FIG. 3 is a configuration diagram (Part 2) of an embodiment of the present invention. It is explanatory drawing of this invention. It is explanatory drawing (the 2) of this invention. FIG. 3 is a configuration diagram of an embodiment of the present invention (No. 3). FIG. 4 is a configuration diagram of an embodiment of the present invention (No. 4). It is explanatory drawing (the 3) of this invention. It is 1 Example block diagram (the 5) of this 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: 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 detects and amplifies electrons emitted or reflected from the sample by irradiating the sample with electrons,
A magnetic field type objective lens for narrowing a primary electron beam having energy of a predetermined acceleration voltage and irradiating the sample;
A deflecting device for deflecting the primary electron beam so as to scan the narrowed primary electron beam on a sample;
Accelerates the first secondary electrons emitted when the specimen is irradiated with the finely focused primary electron beam and scanned, having a hole through which the primary electron beam passes in the direction of the specimen. Generating a secondary electron that is multiplied when a first secondary electron accelerated by the first acceleration voltage collides with the first secondary electron that has been applied. The board,
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 generation plate; An MCP for applying a positive second acceleration voltage for accelerating the multiplied second secondary electrons and further multiplying the multiplied secondary electrons accelerated by the second acceleration voltage;
An electron detection apparatus comprising: an anode for detecting secondary electrons multiplied by the MCP.   The first secondary electrons emitted from the sample are prevented from traveling in the reverse direction of the traveling path of the primary electron beam in the hole portion through which the primary electron beam passes through the secondary electron generating plate. The electron detection device according to claim 1, wherein a repeller electrode having a hole through which the primary electron beam passes is provided at a center to which a negative voltage is applied.   A surface on which the first secondary electrons collide with the secondary electron generating plate to generate the second secondary electrons is convex with respect to the traveling direction of the primary electron beam, and the second 2 3. The electron detection device according to claim 1, wherein the multiplication efficiency of secondary electrons is increased.   4. The electron detection device according to claim 1, wherein a secondary electron emission material having a strip shape, a needle circumference shape, or a particle shape is formed on a surface of the secondary electron generation plate. 5. .   5. The electron detection device according to claim 1, wherein the MCP is divided into a plurality in one or more 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 inclined toward the secondary electron generating plate.   The electron detection apparatus according to claim 1, wherein the MCP is replaced with an APD.   Two sets of the secondary electron generating plate and the MCP are provided coaxially with the orbit of the primary electron beam, and the reflected electrons emitted from the sample are detected and multiplied by the inner set, and the outer 1 8. The electron detection apparatus according to claim 1, wherein the first secondary electrons emitted from the sample in pairs are detected and multiplied. In an electron detection method for detecting and amplifying electrons emitted or reflected from a sample by irradiating the sample with electrons,
A magnetic field type objective lens for narrowing a primary electron beam having energy of a predetermined acceleration voltage and irradiating the sample;
A deflector for deflecting the primary electron beam so as to scan the narrowed primary electron beam on the sample;
The secondary electron generating plate has a hole through which the primary electron beam passes in the direction of the sample, and the first electron beam emitted when the sample is irradiated with the narrowed primary electron beam and scanned. And applying a positive first acceleration voltage for accelerating the secondary electrons of the second secondary electrons, and multiplying the second secondary electrons multiplied when the first secondary electrons accelerated by the first acceleration voltage collide with each other. Generate
The MCP has a hole through which the primary electron beam passes in the direction of the sample and a hole through which the first secondary electron passes in the direction of the secondary generation plate. Applying a positive second acceleration voltage for accelerating the multiplied second secondary electrons and further multiplying the multiplied secondary electrons accelerated by the second acceleration voltage;
An electron detection method, wherein the anode detects secondary electrons multiplied by the MCP.

Images