JP2012248304A - Electron detection device and electron detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron detection device and an electron detection method, by which an electron from a sample is almost completely detected and an output current in proportion up to a large input current by reducing influence by multiplied saturation by a channel is detected.SOLUTION: The electron detection device includes: first electron multiplication means for making electrons collide with each other to emit a secondary electron for multiplication; first voltage applying means for applying voltage for accelerating, converging and colliding electrons to the first electron multiplication means; second electron multiplication means for making secondary electrons multiplied and emitted by the first electron multiplication means collide with each other to emit a secondary electrons for multiplication; second voltage applying means for applying voltage for accelerating, converging and colliding electrons emitted from the first electron multiplication means to the second electron multiplication means; an anode for colliding the secondary electrons multiplied and emitted by the second electron multiplication means to detect current; and third voltage applying means for applying voltage for accelerating and colliding the electrons emitted from the second electron multiplication means to the anode.

Description

  The present invention relates to an electron detection device and an electron detection method that detect and multiply electrons from a sample.

  Conventionally, various electron detectors are used in a scanning microscope to detect secondary electrons and the like. Among them, an annular multichannel plate (MCP) is used because of the advantage that the image cannot be shaded.

  The MCP has a honeycomb-like structure when magnified, and is provided with a large number of circular openings of about 4 to 10 microns, in which channels for multiplying electrons are formed. The surface of the channel is coated with a high efficiency electron emission material. Electrons entering the channel from the opening are accelerated by an accelerating electric field (acceleration voltage) inside the channel, and generate a large amount of secondary electrons while colliding with the surface of each channel. The number of electrons increases.

  A voltage of about 1 kV at the maximum is applied to one MCP. This voltage is set to such a level that the glass constituting the MCP does not melt. Secondary electron emission is repeatedly performed with this applied voltage, and by using one MCP, the number of electrons can be increased up to about 1000 times. Further multiplication can be performed by passing the multiplied electrons through another MCP. For example, if two sheets are used, in principle, multiplication of about 1000000 can be performed. That is, one electron on the surface of the sample can be multiplied to one million. Electron multiplication by MCP is performed by the generation of secondary electrons and essentially no noise is generated, so that a signal with an extremely high electrical SN ratio can be obtained.

  Further, since the MCP is very thin at 1 mm or less, the distance traveled in the process of multiplying electrons is short, and has a frequency response exceeding GHz. The multiplied electrons collide with the anode electrode, are converted into a current proportional to the number of electrons, and are output.

  Although the MCP has various advantages as described above, there are side walls for separating the channels between the channels, so that a part of the electrons coming to the opening hits the wall and enters the channel (opening). Absent. The wall of the channel is usually made of a low resistance metal such as Ni and serves as an electrode for applying a voltage to the MCP. Therefore, the electrons that hit there are absorbed and grounded, and the signal is lost. Therefore, the conventional MCP has a problem that it is difficult to detect electrons with an efficiency of 100% in principle.

  In addition, an image (secondary electron image) formed by the electron microscope is obtained by detecting the intensity of the secondary electrons emitted by performing planar scanning while irradiating the finely focused primary electrons on the sample surface. The secondary electrons generated on the sample surface by irradiating the primary electron beam each have secondary electron generation probability information at a specific position on the sample. By using 100% of these, the sample surface state can be reproduced. In order to use all the information of the generated secondary electrons, it is necessary to detect 100% of the electrons generated on the sample surface. However, since the actual MCP has an aperture ratio of about 60%, the unique information of about half of the electrons is not available. In order to completely reproduce the sample surface information, it is necessary to generate extra secondary electrons from the surface by irradiating the sample with a primary electron beam more than twice that when electrons can be detected with 100% efficiency. This means that the primary electron beam device needs to irradiate more than twice the amount of the primary electron beam, and the sample surface state has more than twice the number of electrons (primary electrons, secondary electrons, etc.). There is a problem that various problems such as charge-up occur due to accumulation.

  Further, when the MCP is applied to an actual electron microscope, the secondary electron trajectory generated on the sample surface has a property of being collected at one point, and therefore, only a part of the MCP is irradiated with the secondary electrons. When a very small current is input, the number of secondary electrons that can be input can be increased to a desired number of electrons, except for the problem of loss of the aperture. However, when the incident current increases, the probability of secondary electrons entering multiple channels at the same time increases, and even if multiplication is possible in one channel, multiplication is insufficient in other channels (multiplication due to saturation). There is a problem that a multiplication deficiency or counting off phenomenon occurs.

  This phenomenon is a saturation phenomenon that occurs because the maximum amount of current that can be multiplied in the entire channels constituting the MCP is determined, and there is a problem that even if a large current is input, an output current proportional to that amount is not generated.

  In addition, since electrons are concentrated and incident on one point, only a part of the MCP is overused, and there is a problem that the lifetime is shortened.

  In order to solve the above problems, the present invention detects electrons from a sample (electrons emitted from the sample, reflected by the sample, and inverted by the surface of the sample) almost completely, and also affects the influence of multiplication saturation caused by a certain channel. The purpose is to realize output current detection that is reduced and proportional to a large input current.

  To this end, the present invention provides an electron detection apparatus that multiplies and detects electrons from a sample, and emits secondary electrons to collide with electrons from the sample, thereby multiplying the first electron multiplication means. First voltage applying means for applying a voltage for accelerating, focusing and colliding electrons from the sample to the first electron multiplying means, and secondary electrons emitted after being multiplied by the first electron multiplying means A second electron multiplying means that emits secondary electrons by making them collide with each other, and the electrons emitted from the first electron multiplying means are accelerated and focused on the second electron multiplying means for collision. A second voltage applying means for applying a voltage to be applied; an anode for detecting a current by colliding with secondary electrons emitted after being multiplied by the second electron multiplying means; and a second electron multiplication on the anode. A third voltage for applying a voltage for accelerating and colliding electrons emitted from the means And a pressurizing means.

  At this time, a positive voltage is applied by the first voltage applying means by spiraling the axis by the axial magnetic field of the magnetic field type objective lens that irradiates the sample with the primary electrons finely focused on the sample. It is made to travel toward the first electron multiplying means, and it is made to collide with the first electron multiplying means to emit secondary electrons for multiplication.

  Further, the first electron multiplying means forms or coats a substance that emits one or more secondary electrons when the electrons collide.

  The first electron multiplying means is formed in a concave shape or a convex shape in the direction of travel of accelerated electrons from the sample, and multiplies the electrons by colliding with the concave inner surface or the convex outer surface. I am doing so.

  In addition, the first electron multiplying means, the second electron multiplying means, and the anode are provided with a hole through which a primary electron that is squeezed and irradiated on the sample finely passes in the center portion.

  Further, the second electron multiplying means is provided with a large number of minute holes, and after multiplying the electrons incident on the holes repeatedly hitting the inner wall of the hole, the second electron multiplying means travels toward the anode. Yes.

  The first electron multiplying means and the second electron multiplying means are formed so that the electric field is gradually increased from the electron incident portion to the light emission portion so that the emitted secondary electrons repeatedly collide. Like to do.

  The present invention can detect electrons from a sample almost completely, and can detect an output current proportional to a large input current by reducing the influence of multiplication saturation caused by a certain channel.

  The present invention realizes detection of an output current proportional to a large input current by detecting the electrons from the sample almost completely and reducing the influence of multiplication saturation caused by a certain channel.

  FIG. 1 shows a structural diagram of one embodiment of the present invention.

  1A is a structural diagram, and FIG. 1B is an incident part, an emission part, and an anode of an opening 4 constituting the first electron multiplier 2 and the second electron multiplier 3. 5 and voltages V1, V2, V3, V4, and V5 applied to the repeller electrode 7, respectively.

  Here, FIG. 1A shows a case where a hole is provided in the center portion (on the optical axis), a cylindrical repeller electrode 7 is disposed in the hole, and a primary electron beam is formed by a magnetic field type objective lens not shown. Is passed through from left to right and narrowed down to scan the sample 1 (see FIG. 2) on the left while irradiating it, and the secondary electrons emitted at that time are accelerated from left to right. The first electron multiplier 2 provided in the periphery is irradiated by applying an appropriate voltage to the repeller electrode 7 and traveling while accelerating while spiraling on the axis by the magnetic field of the magnetic field type objective lens. An example of a structure configured to multiply secondary electrons by (collision) is shown.

  More specifically, in the scanning microscope, the primary electron beam is irradiated perpendicularly to the sample 1 and the electrons (secondary electrons, reflected electrons, and inverted electrons) generated in the sample 1 are highly efficient. In order to recover, a detector having a hole in the center (on the axis) is used. The primary electron beam passes through the central hole in FIG. 1 and travels from left to right and irradiates the sample 1 (not shown) (see FIG. 2). Electrons (secondary electrons, reflected electrons, and inverted electrons) generated on the surface of the sample 1 gather in this hole portion and do not pass through the hole. Since it is not guided to the electron multiplier 2), a repeller electrode 7 is provided in the center so that an appropriate positive or negative voltage is applied so that electrons generated on the surface of the sample 1 do not go through the hole. The secondary electrons are multiplied by being repelled or attracted to collide with the first electron multiplier 2 disposed in a ring shape around the hole.

  In FIG. 1A, secondary electrons from the sample 1 are examples of electrons (emitted, reflected, and inverted electrons) from the sample 1 (see FIG. 2) (not shown). This is accelerated by the voltage applied to the doubler 2 (positive voltage V1, see FIG. 1B).

  The first electron multiplier 2 applies a positive voltage V1 for accelerating and colliding electrons from the sample 1, and emits one or more secondary electrons when the electrons collide. It is for doubling.

  Here, when the first electron multiplier 2 comes into contact with the repeller electrode 7, it becomes the same potential, so that the electrons do not reach the first electron multiplier 2 and no effect is exhibited. In order to avoid electrical contact with the repeller electrode 7, it is electrically insulated and arranged in the periphery. It is desirable that the electrodes of the first electron multiplier 2 are arranged at a place where electrons are most collected by analyzing the trajectory of the electrons. For example, it is desirable to arrange in a ring shape.

  The second electron multiplying device 3 further multiplies the secondary electrons multiplied by the first electron multiplying device 2, and is arranged between the input section and the output section (( The voltage V2 and the voltage V3 described in b) are applied, and secondary electrons are repeatedly collided and emitted to be multiplied, and then emitted from the right side toward the anode 5. The second electron multiplying device 3 is a secondary electron multiplying device constituted by a large number of fine holes (channels) called a so-called multichannel plate (MCP).

  The opening 4 is an opening (channel) provided in the second electron multiplier 3, and an opening adjacent to the opening 4 is multiplied by secondary electrons incident on the opening 4. The secondary electrons colliding with the part between the parts 4 are absorbed and are not targeted for multiplication. Usually, the ratio with respect to the whole opening 4 is about 60%.

  The anode 5 collides the secondary electrons multiplied by the second electron multiplier 3 and detects it as a current, and applies the voltage V4 of FIG. A voltage corresponding to the current detected by the anode 5 is sent to the outside as an output (output signal).

  The center hole 6 is a hole on the shaft, and is a portion where the repeller electrode 7 is disposed here.

  The repeller electrode 7 has an appropriate voltage V5 (positive or negative) so that the electrons (secondary electrons, reflected electrons, and inverted electrons) from the sample 1 do not pass through to the right side and collide with the first electron multiplier 2. (Negative voltage) is applied.

  The anode may be divided electrically or mechanically as necessary. The first electron multiplier 2 and the second electron multiplier 3 may also be divided electrically or mechanically, and are an assembly of a plurality of electron multipliers that operate independently of each other. It doesn't matter.

Referring to FIG. 1 in more detail,
(1) When the surface of the sample 1 is irradiated with the primary electron beam, secondary electrons and the like are generated on the surface of the sample 1. The secondary electrons and the like include all image formation information in the scanning microscope. Secondary electrons generated on the surface of the sample 1 are attracted to the first electron multiplier 2 by an electric field. In order for the first electron multiplier 2 to work effectively, it is necessary that the electrons have energy of several tens of eV or more. For this reason, in order to set the energy of incident electrons to an appropriate value, a voltage V1 of several tens of volts or more is applied to the first electron multiplier 2, and the electrons attracted by the voltage V1 are increased. It collides with the double device 2 and is multiplied by about twice or more.

  (2) As the first electron multiplier 2, a thin film of a high secondary electron emission material such as BaO or MgF is used as is well known. A thin film with a thickness of several to several tens of nanometers is desirable so that secondary electrons are likely to be emitted, and a conductive thin film is behind the thin film, and it is desirable that electrons can be supplied. When these materials are irradiated with electrons with energy higher than a threshold, secondary electrons that are twice to five times the number of incident electrons are generated, and the original number of electrons is doubled to five times. . For example, it is desirable to create a potential gradient so as to have an energy of about 100 eV and to cause electrons to collide with the thin film.

  (3) The speed at which electrons are generated is smaller than picoseconds, and a state in which only the number of electrons is accurately multiplied with respect to the time axis is realized. Since each electron is a copy of the original electron, it has the information at the same position.

  (4) After the number of electrons has been multiplied by two or more, it passes through the opening 4 constituting the second electron multiplier 3. Since the aperture ratio is 100% or less, a part of the multiplied electrons passes. Probabilistically, the number of secondary electrons generated on the surface of the sample 1 is more than doubled by the first electron multiplier 2, so that it was generated on the surface of the sample 100% even after passing through the opening 4. It is thought to hold electronic information. The electrons that have passed through the opening 4 are multiplied from 1000 times to 1000000 times by the second electron number multiplying device 3. The multiplied electrons eventually collide with the anode 5, losing kinetic energy and generating a current. By detecting the generated current with an electric circuit such as a current-voltage conversion circuit (not shown) or a pulse detection circuit, the amount or number of secondary electrons generated on the surface of the sample 1 can be detected.

(5) In addition to the BaO and MgF described above, the first electron multiplier 2 further includes 5Cu-BeO, Cu-BeO6, 2Ag-MgO-CS9, 2Cs-Sb, 10GaP-Cs20-40, etc. It is made of a member (metal, ceramic, plastic, etc.) whose surface is coated with a high secondary electron emission material, and is connected to a voltage applying means so that a voltage can be applied if necessary. The multiplied electrons pass through the opening 4 constituting the second electron multiplier 3. A part of the electrons cannot pass through the edge of the opening 4, but the number of electrons is increased by the first electron multiplier 2 beyond the loss by the edge of the opening 4. Even after passing through, it is possible to input 100% of the electrons inheriting the information of the electrons generated on the surface of the sample 1 to the second electron multiplier 3, and the information generated by the electrons generated on the surface of the sample 1 is lost. It becomes possible to detect without doing. Capacitors, resistors, or amplifiers necessary for current detection at the anode 5 are placed in a vacuum so that current can be detected without being affected by external noise _.

  FIG. 1B shows an incident part, an emission part, an anode 5 and a repeller of the opening 4 constituting the first electron multiplier 2 and the second electron multiplier 3 of FIG. Examples of voltages V1, V2, V3, V4, and V5 applied to the electrode 7 are schematically shown.

  FIG. 2 shows a structural diagram of another embodiment of the present invention. The first electron multiplier 2 in FIG. 1A has a structure in which the secondary electrons collide with a ring-shaped inner surface that is convex (constricted) with respect to the traveling direction of the secondary electrons to multiply the secondary electrons. On the other hand, FIG. 2 shows another structural example of the embodiment in which multiplication is performed by colliding the secondary electrons against the concave (protruding) ring-shaped outer surface. Here, the sample 1, the second electron multiplier 3, the opening 4, the anode 5, and the repeller electrode 7 are the same as the corresponding ones in FIG.

  In FIG. 2, the first electron multiplier 2 has a concave (protruding) ring-shaped structure, and multiplies the ring-shaped outer surface by irradiating electrons from the sample 1. These are arranged in a so-called insensitive area generated on the outer periphery of the center hole 6.

  The reason for this arrangement is that, as shown in FIG. 2, a groove exists between the hole of the second electron multiplier 3 (for example, multi-channel plate) and the cylindrical repeller electrode 7, and there is a dead area. Further, the electrons generated on the surface of the sample 1 are collected in an annular shape while being spiraled by the magnetic field of the magnetic field type objective lens. Therefore, if the annular electrons are incident on the insensitive region, the number of electrons increases. It is not doubled and cannot be detected. In order to prevent this, the first electron multiplier 2 is provided so as to cover the groove in the periphery of the center hole as shown in FIG. In the case of the center hole type, an annular shape is desirable. When there is no center hole, it is desirable to be a point object figure or a circle. Further, the bias shown in FIG. 3 is provided around the opening 4 so that the electrons multiplied by the first electron multiplier 2 are uniformly distributed and incident on the opening 4 of the second electron multiplier 3. An electrode 41 is provided. Usually, an electrode for applying a voltage to the glass channel is provided on the surface of the MCP which is the second electron multiplier 3 by vapor deposition or the like. In this other embodiment, an insulating film is further provided thereon to insulate from the electrode for applying a voltage to the channel, and an electrode (bias electrode 41 in FIG. 3) is provided thereon. It is desirable to have an independent voltage supply means so that a voltage V6 (see FIG. 3) different from the voltage V5 applied to the repeller electrode 7 provided in the center hole is applied. When the same voltage is applied, the electric field is narrowed from both sides, so that the distribution of incident secondary electrons is pushed into a narrow region. On the contrary, when such an electric field is used, the position where the electrons are concentrated can be moved by changing the electric field strength, thereby extending the life of the second electron multiplier 3 (for example, MCP). .

  The electrons that have converged in an annular shape are multiplied by two or more times by the first electron multiplier 2. Thereafter, the electrons are dispersedly irradiated toward the opening 4 constituting the second electron multiplier 3. Since the number of electrons generated on the surface of the sample 1 is multiplied by two or more, the information on the electrons generated on the surface of the sample 1 is lost probabilistically when the aperture ratio of the opening 4 is 60%. Without being transmitted to the second electron multiplier 3.

  FIG. 3 shows a structural diagram (FIG. 2) of the main part of the present invention.

  3A shows a side view, and FIG. 3B shows a top view. Here, the first electron multiplier 2, the second electron multiplier 3, and the repeller electrode 7 are the same as the corresponding ones in FIG.

  3A and 3B, as described above, the bias electrode 41 is configured such that the electrons multiplied by the first electron multiplier 2 are uniformly distributed in the opening 4 of the second electron multiplier 3. A bias electrode for applying a bias voltage V6 provided around the opening 4 so as to be incident on the multi-channel plate, which is normally the second electron multiplier 3, is provided on the surface of the multichannel plate. Since an electrode for applying a voltage to the electrode is provided by vapor deposition or the like, an insulating film is further provided thereon to insulate the electrode for applying a voltage to the channel, and an electrode (bias electrode 41) is provided thereon. It is provided. The bias electrode 41 has an independent voltage supply means so that a voltage V6 (see FIG. 3) different from the voltage V5 applied to the repeller electrode 7 provided in the center hole is applied. Here, when the same voltage is applied, the electric field is narrowed from both sides, so that the distribution of incident secondary electrons is pushed into a narrow region. On the contrary, when such an electric field is used, the position where the electrons are concentrated can be moved by changing the electric field strength, thereby extending the life of the second electron multiplier 3 (for example, MCP). .

  FIG. 4 shows a structural diagram of another embodiment of the present invention. FIG. 4 shows another embodiment using a mesh electrode as the first electron multiplier 2. The aperture ratio is increased as much as possible to 90% or more. A mesh electrode having a surface coated with a high secondary electron emission material is disposed in front of the opening 4 of the second electron multiplier 3. It is important that the electrons that have been multiplied by colliding with the side surface or the surface of the opening of the mesh electrode are well guided to the opening 4 constituting the second electron multiplier 3. Necessary by applying a bias voltage to the mesh electrode so that all the electrons generated by the mesh electrode (first electron multiplier 2) are guided to the opening 4 constituting the second electron multiplier. It is desirable to obtain a simple potential gradient. Moreover, it is desirable to arrange the opening 4 of the second electron multiplier 3 at the place where the electrons jumping out from the mesh electrode are most collected.

  Here, when the center hole is provided as shown in FIG. 4, an appropriate voltage is applied to the repeller electrode 7 arranged on the shaft so that the generated secondary electrons do not pass. Due to the potential gradient or the magnetic field of the magnetic field type objective lens, the secondary electrons from the sample 1 collide with the surface or side surface of the mesh electrode, and in the case of collision, the number of electrons is multiplied. If it passes, it is not multiplied.

  FIG. 5 shows a structural diagram of another embodiment of the present invention. FIG. 5 shows an example in which the first electron multiplier 2 is configured by coating the non-opening portion of the second electron multiplier 3 with a highly efficient electron emission material. In this example, electrons generated on the surface of the sample 1 are collected in the second electron multiplier 3 by an electric field. Part of the collected electrons is incident on the opening 4 of the second electron multiplier 3 and multiplied.

  On the other hand, since the non-opening portion of the second electron multiplier 3 is coated with a high-efficiency electron emission material, the electrons colliding therewith are multiplied to two or more electrons. Since the multiplied electrons are scattered, some of them enter the opening 4. Thereby, information of electrons generated on the surface of the sample 1 is transmitted to the second electron multiplier 3 and multiplied. The electron thus multiplied finally collides with the anode 5 and is converted into a current, and then detected by an electric circuit.

  Here, it is desirable that the first electron multiplying device 2 and the second electron multiplying device 3 can independently apply a voltage.

  When there is a center hole in the center of the second electron multiplier 3, the center hole is a place where a primary electron beam for irradiating the sample 1 passes, There is a repeller electrode 7, and an electric field (voltage) is applied so that electrons generated on the surface of the sample 1 do not go through the hole. Electrons generated on the surface of the sample 1 are attracted to the surface of the second electron multiplier 3. A certain electron enters the opening 4 and is multiplied by the second electron multiplier 3. On the other hand, the electrons colliding with the surface on which the first electron multiplier 2 is constructed are multiplied into a plurality of electrons by the high-efficiency electron emission material provided on the surface. The multiplied electrons enter the opening 4 and are multiplied by the second electron multiplier 3. The multiplied electrons collide with the anode 5, are converted into currents, and are detected by an electric circuit.

  FIG. 6 is a structural diagram of another embodiment of the present invention. The example of FIG. 6 is characterized in that a large number of inclined thin plate members are arranged by providing films having a secondary electron multiplication effect on both surfaces. The colliding electrons collide with the front or back of the member and generate many electrons. This member is inclined at an appropriate angle at which electrons are likely to be generated, and the electrons generated by the collision are efficiently incident on the opening 4 of the second electron multiplier 3 to be multiplied and detected. It is.

  Since this member is thin, it is possible to stack a plurality of members. By making each member electrically independent, an appropriate voltage (bias voltage) can be applied to each member. By applying an appropriate voltage to each, it is finally possible to efficiently lead to the opening 4 of the second electron multiplier 3.

  FIG. 7 shows a structural diagram of the main part of the present invention. FIG. 7 shows a method of aligning a plurality of second electron multipliers 2, for example, multi-channel plates (MCP).

  In FIG. 7, the MCP has holes called channels having a size of several microns to several tens of microns. These holes are very regularly arranged. Since it is manufactured using an optical fiber, when a lot is the same, a plurality of MCPs have holes at exactly the same positions. A higher multiplication factor can be obtained by using multiple MCPs. However, if the positions of the channel holes of each MCP are shifted, the first MCP increases as shown in FIG. Only a part of the doubled signal can be used, resulting in signal loss. In this embodiment, as shown in FIG. 7B, signal loss can be prevented by correctly aligning the holes of a plurality of overlapping MCPs.

  Each MCP is provided with an alignment mark so that precise alignment is possible. For example, a plurality of notches are precisely provided on the side surface of the MCP to form an alignment mark, or light passes through the channel portion of the MCP. Therefore, an alignment mark is provided in a part of the MCP to accurately determine the relative position of the plurality of MCPs. It is possible to match. The alignment can be maintained if temporarily fixed after alignment with a microscope or the like.

  If the alignment of the plurality of MCPs is accurately adjusted, the electrons multiplied by the first MCP are almost 100% incident on the opening 4 of the second MCP, so that no signal loss occurs.

  Further, the size of the channel hole of the first MCP can be changed from the size of the hole of the second MCP. For example, if the hole of the second MCP is enlarged, all the electron groups multiplied by the first MCP can be successfully input to the channel (opening 4) of the second MCP. Conversely, as a very small channel, all electrons can be stochastically input to the second MCP.

  The MCP has a maximum output current. The current is determined by the electric resistance value of the MCP. The MCP having a small resistance value can extract a larger output current. However, when the electrical resistance value of the entire MCP is lowered, there is a problem that heat generation increases and the MCP is melted, so that the resistance value cannot be lowered suddenly. Since the electrical resistance of the first MCP and the electrical resistance of the second MCP can be changed independently, for example, the resistance value of the MCP on which electrons are first incident is increased, and a high voltage is applied thereto. Thereby, a high multiplication factor of 1000 times or more can be obtained in the first stage. On the other hand, the electrical resistance value of the second MCP is lowered. Also lower the applied voltage. As a result, multiplication from several tens to several hundreds is performed. In this way, the maximum amount of current that can be output can be increased without melting the MCP glass.

  FIG. 8 shows a structural diagram of another embodiment of the present invention (an example of multiplication inside an umbrella). FIG. 8 corresponds to FIG. 1 and generates an electric field as shown by the dotted line in the figure along the inner part of the umbrella of the first electron multiplier 2 (inlet part and outlet part). As shown by the dotted line in the figure, an electric field is generated at the portion), and electrons are collided and emitted, and the multiplication is repeated. The electric field is generated between the sample 1 and the entrance of the first electron multiplier 2 with the voltage V11, between the entrance and the outlet with the voltage V12, and between the outlet and the second electron multiplier 3 with the voltage V11. A voltage V13 is applied to generate an electric field indicated by a dotted line in the figure.

  As described above, the first electron multiplier 2 can perform electron multiplication of several to several hundred times.

  FIG. 9 shows a structural diagram of another embodiment of the present invention (an example of multiplication outside the umbrella). FIG. 9 corresponds to FIG. 2 and generates an electric field as indicated by the dotted line in the figure along the outer part of the umbrella of the first electron multiplier 2 (inlet part and outlet part). As shown by the dotted line in the figure, an electric field is generated at the portion), and electrons are collided and emitted, and the multiplication is repeated. The electric field is generated between the sample 1 and the entrance of the first electron multiplier 2 with the voltage V11, between the entrance and the outlet with the voltage V12, and between the outlet and the second electron multiplier 3 with the voltage V11. A voltage V13 is applied to generate an electric field indicated by a dotted line in the figure.

  As described above, the first electron multiplier 2 can perform electron multiplication of several to several hundred times.

  FIG. 10 shows a structural diagram of another embodiment of the present invention (an example of multiplication with two umbrellas). FIG. 10 is a combination of the two of FIG. 8 and FIG. 9. The first electron multiplier 2 disposed on the inner side of the umbrella and the first electron disposed on the outer side. An electric field is generated along the inner part of the umbrella of the multiplier 2 as shown by the dotted line in the figure (an electric field is generated as shown by the dotted line in the inlet part and the outlet part), and the electrons The structure is such that it is multiplied by repeating the collision and release. The electric field is generated between the sample 1 and the entrance of the first electron multiplier 2 with the voltage V11, between the entrance and the outlet with the voltage V12, and between the outlet and the second electron multiplier 3 with the voltage V11. A voltage V13 is applied to generate an electric field indicated by a dotted line in the figure.

  As described above, it is possible to perform multiplication when the first electron multiplier 2 provided on the inner side and the outer side has a spread of an electron emission angle of several to several hundred times.

  FIG. 11 shows an application example of the present invention. FIG. 11 shows an application example using the electron detection device having the first electron multiplication device 2 and the second electron multiplication device 3 of FIGS. 1 to 10, and here, a scanning electron microscope is measured. An application example when used as a device will be described.

  FIG. 11A shows the entire structure, FIG. 11B shows a state where the mask 26 is scanned with the primary electron beam, and FIG. 11C shows the state shown in FIG. Further details are shown.

  In FIG. 11A, the electron gun 21 generates a primary electron beam.

  The objective lens 22 is a magnetic field type objective lens and irradiates the mask 26 which is the sample 1 by narrowing the primary electron beam.

  The sample chamber 23 is a vacuum container that houses the XY stage 25, the mask 26, and the like.

  The precision position measuring device 24 measures the position of the XY stage 25 precisely, and is a laser interferometer, for example.

  The XY stage 25 is mounted with a mask 26 and is moved in the X direction and the Y direction.

  The mask 26 is an example of a sample, and is a sample to be subjected to length measurement by acquiring a secondary electron image.

  The secondary electron detector 27 is a detector that performs planar scanning while irradiating the mask 26 with a primary electron beam, and detects secondary electrons, reflected backscattered electrons, and the like emitted at that time. The first electron multiplier 2 and the second electron multiplier 3 described above with reference to FIG.

  FIG. 11B schematically shows a state in which the primary electron beam is planarly scanned on the mask 26 of FIG. Here, a state in which scanning is performed in the horizontal direction by the XY stage 25 and scanning in the vertical direction by a beam scanning device (not shown) is schematically shown. Scanning by the XY stage in the horizontal direction repeats scanning in the horizontal direction (reverse direction) by the XY stage 25 after moving in the vertical direction by the XY stage 25 when reaching the end.

  In FIG. 11C, scanning is performed so as to slightly overlap the previous scanning when the XY stage 25 scans in the horizontal direction in FIG. 11B.

  The secondary electrons emitted from the mask 26 when scanning while irradiating the mask 26 mounted on the XY stage 25 with a narrowed primary electron beam are the first described in FIGS. Detects with high sensitivity (higher sensitivity than twice that of MCP, which is the conventional secondary electron multiplier 3) with an electron detector such as the electron multiplier 2 and the second electron multiplier 3 By acquiring an enlarged image (secondary electron image) at a high speed and measuring the pattern in the image, the length can be measured in a shorter time than in the past.

1 is a structural diagram of an embodiment of the present invention. It is other Example structure FIG. (1) of this invention. It is principal part structure figure (FIG. 2) of this invention. It is other Example structure FIG. (2) of this invention. It is other Example structure FIG. (3) of this invention. It is other Example structure FIG. (4) of this invention. It is a principal part structure figure of this invention. It is another Example structural drawing (example which multiplies inside an umbrella) of this invention. It is another Example structure figure (example which multiplies outside the umbrella) of the present invention. It is another example structure figure of the present invention (example which multiplies with two umbrellas). It is an application example of the present invention.

1: Sample 2: First electron multiplier 3: Second electron multiplier 4: Opening 41: Bias electrode 5: Anode 6: Center hole 7: Repeller electrode

Claims (9)

In an electron detection device that multiplies and detects electrons from a sample,
First electron multiplying means for causing electrons from the sample to collide to emit secondary electrons to be multiplied;
A first voltage applying means for applying a voltage for accelerating, focusing and colliding electrons from the sample to the first electron multiplying means;
Second electron multiplying means for causing secondary electrons emitted from the first electron multiplying means to collide with each other to emit secondary electrons to be multiplied,
A second voltage applying means for applying a voltage for accelerating, converging and colliding electrons emitted from the first electron multiplying means to the second electron multiplying means;
An anode for detecting a current by colliding with secondary electrons emitted after being multiplied by the second electron multiplying means;
3. An electron detection apparatus comprising: a third voltage applying unit that applies a voltage that accelerates and collides electrons emitted from the second electron multiplying unit to the anode.   A positive voltage is applied by the first voltage applying means by spiraling on the axis by an on-axis magnetic field of a magnetic field type objective lens for irradiating the sample with electrons by narrowing down the primary electrons to the sample. 2. The electron detecting device according to claim 1, wherein the electron detecting device is caused to travel toward the first electron multiplying means and to collide with the first electron multiplying means to emit secondary electrons and to multiply. .   3. The electron according to claim 1, wherein the first electron multiplying unit is formed or coated with a substance that emits one or more secondary electrons when the electrons collide with each other. Detection device.   The first electron multiplying means is formed in a concave shape or a convex shape toward the traveling direction of the accelerated electrons from the sample, and collides the electrons with the inner surface of the concave shape or the outer surface of the convex shape. 4. The electron detection device according to claim 1, wherein multiplication is performed.   The first electron multiplying means, the second electron multiplying means, and the anode are provided with a hole through which a primary electron that irradiates and squeezes the sample thinly passes in a central portion. The electron detection device according to claim 1.   The second electron multiplying means is provided with a large number of minute holes, and after multiplying the electrons incident on the holes repeatedly hitting the inner wall of the holes, the second electron multiplying means travels toward the anode. The electron detection device according to claim 1, wherein:   The first electron multiplying means and the second electron multiplying means are formed so that the electric field is gradually increased from the electron incident part to the light emission part so that the emitted secondary electrons repeatedly collide. The electron detection device according to claim 1, wherein the electron detection device is a device.   The electron detection apparatus according to claim 1, wherein the second electron multiplier is an MCP. In an electron detection method for detecting by multiplying electrons from a sample,
Accelerating and focusing electrons from the sample, causing the first voltage applying means to collide with the first electron multiplying means to which a predetermined voltage is applied to emit secondary electrons and multiplying;
The secondary electrons multiplied and emitted from the first electron multiplying means are accelerated and focused, and collided with the second electron multiplying means to which a predetermined voltage is applied by the second voltage applying means. Multiplying by multiplying secondary electrons;
A method of detecting an electric current by colliding the secondary electrons multiplied and emitted by the second electron multiplier and colliding with the anode.

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