JP2008004329A - Charged particle beam equipment - Google Patents

Abstract

A charged particle beam apparatus capable of stably acquiring good image information without depending on a sample state and imaging conditions is realized.
A reference electrostatic electrode 4 having substantially the same potential as that of a sample 1 and a pair of cylindrical filter electrodes 5 and 5 'sandwiching the reference electrostatic electrode 4 are provided between an electron gun 30 and an acceleration field electrode 14. By applying a positive potential to the cylindrical filter electrodes 5 and 5 ′ and further adjusting this potential by the control unit 9, the magnitude of energy in the generation of secondary electrons generated in the sample 1 is 2 Since the secondary electrons 51 are separated and detected, secondary electrons in the low energy band can be removed. As a result, components that brighten the entire image included in the SEM image are removed, and stable and good image information is obtained. Make it possible to obtain.
[Selection] Figure 1

Description

  The present invention relates to a charged particle beam apparatus that irradiates a sample with a charged particle beam and detects secondary electrons generated from the sample.

  In recent years, circuit patterns have been further miniaturized in semiconductor integrated circuits. In order to inspect these circuit patterns, a scanning electron microscope (abbreviated as SEM), which is a charged particle beam device with high magnification and high resolution, is used. Further, in a semiconductor integrated circuit, since a low dielectric constant film is provided on the surface or a quartz glass wafer is used, a material having high electrical insulation is frequently used.

  When these highly insulating materials are irradiated with an electron beam of a scanning electron microscope, a phenomenon of charge (charge up) in which charges are accumulated on the surface occurs. This charging phenomenon affects the image information acquired by the SEM. For example, a change in the trajectory of the primary electron beam constituting the irradiated electron beam, or a change in the trajectory of the secondary electron beam generated from the irradiated sample occurs, and as a result, the resolution decreases.

  As a technique for minimizing the deterioration of image information due to this charging phenomenon, a deceleration field forming technique (hereinafter referred to as a retarding technique) is disclosed (for example, see Patent Document 1). According to the retarding technique, in addition to the acceleration field electrode that accelerates the electron beam, a deceleration field electrode that decelerates the electron beam is provided in the vicinity of the sample. Then, while maintaining the size of the acceleration field, that is, while controlling the focal point under the condition that the influence of chromatic aberration is reduced, the energy of the electron beam incident on the sample is reduced by the deceleration field, and the resolution is maintained. Keep the charge of the sample small.

  FIG. 15 is a schematic cross-sectional view showing an example of a scanning electron microscope 100 equipped with a retarding technique. The scanning electron microscope 100 includes a sample 1, an electron detector 24, a signal detector 17, a scanning coil 13, an acceleration field electrode 14, a magnetic lens 15, a deceleration field electrode 16, variable power supplies 18 to 20, a display unit 21, and scanning control. Part 22 and the like. The sample 1, the electron detector 24, the signal detector 17, the scanning coil 13, the acceleration field electrode 14, the magnetic field lens 15, and the deceleration field electrode 16 are disposed in a high vacuum column (not shown).

  The sample 1 is a silicon wafer or the like on which a semiconductor integrated circuit is formed, the scanning coil 13 forms a deflection field for scanning the primary electron beam 11 on the sample 1, and the acceleration field electrode 14 is a primary electron beam. The magnetic field lens 15 forms a magnetic field that focuses the primary electron beam 11 on the sample 1, and the deceleration field electrode 16 forms the primary electron beam 11 on the sample. An electrostatic field that decelerates in the direction of 1 is formed, and the electron detector 24 converts it into an electrical signal corresponding to the detected secondary electron signal. The scanning control unit 22 controls the scanning coil 13 so as to scan the primary electron beam 11 on the sample 1, and the display unit 21 receives the scanning signal from the scanning control unit 22 and the electric signal from the signal detector 17. Based on the signal, image information of the scanning region of the sample 1 is formed and displayed.

  Here, the variable power sources 18 to 20 are power sources that determine the potential of the acceleration field electrode 14, the deceleration field electrode 16, and the sample 1. For example, the variable power source 18 is used for an electron gun that generates the primary electron beam 11. The positive high voltage is set, and the variable power supplies 19 and 20 are set to the ground potential.

  On the other hand, secondary electrons traveling in a direction opposite to the primary electrons are generated by the primary electrons irradiated on the sample. The secondary electrons are accelerated and sucked into the lens barrel due to the presence of the deceleration field of the primary electrons, and are detected by the electron detector 24 and the signal detector 17 arranged in the lens barrel.

FIG. 15 shows the secondary electrons 12 indicating the flight trajectory of the secondary electrons in the lens barrel. The secondary electrons 12 radiated from the sample 1 are spread at a radiation angle, are affected by a magnetic field and an electric field formed for the primary electron beam 11, and repeatedly converge and diverge in a direction perpendicular to the traveling direction. The electron detection unit 24 is reached.
International Publication No. WO99 / 46798 pamphlet, (pages 5-11, FIG. 1)

  However, according to the above background art, the acquired image information changes depending on the state of the sample 1 and the imaging conditions. That is, the magnetic field and electric field in the lens barrel formed for controlling the primary electron beam 11 vary depending on the observation conditions, and the state of the sample 1 and the secondary electrons 12 affected by the magnetic field and electric field also vary. The image information changes.

  For example, when the surface of the sample 1 is widely covered with a material having high electrical insulation, the image information includes a component that brightens the entire image. When the acceleration voltage, that is, the acceleration voltage of the primary electron beam 11 is a voltage at which the secondary electron generation efficiency from the sample 1 is smaller than 1, the surface of the sample 1 is negatively charged, and the surface potential of the sample 1 is Compared with other positions, it is about several tens of volts (volts) lower. Thereby, the low energy component of 1 to 3 eV contained in the secondary electrons is released as a part of the secondary electrons 12 without being pulled back to the sample 1, and this component is considered to be a factor that brightens the entire image. Yes.

  Further, as an example when the observation condition of the sample 1 changes, the electromagnetic field formed by the objective lens including the acceleration field electrode 14, the magnetic field lens 15, and the deceleration field electrode 16, such as a change in the sample surface height, changes. There are cases. In this case, when the electromagnetic field formed by the objective lens changes, the flight trajectory of the secondary electrons 12 may change like the secondary electrons 12 ′ indicated by broken lines in FIG. Thereby, the detection efficiency of the secondary electrons 12 ′ included in the electron detection unit 24 is reduced, and the signal intensity of the acquired image information is reduced.

  As another example, there is a case where the surface to be observed of the sample 1 is largely inclined with respect to the incident primary electron beam 11. In this case, an electric field that leaks from the deceleration field electrode 16 toward the sample 1 causes electric field distortion on the surface of the sample 1. Due to this electric field distortion, the secondary electrons emitted from the sample 1 are bent in the flight trajectory and do not reach the opening existing on the sample 1 side of the deceleration field electrode 16, and the signal intensity of the acquired image information is reduced. To do.

For these reasons, it is important how to realize a charged particle beam apparatus that can stably acquire good image information without depending on the state of the sample 1 and observation conditions.
The present invention has been made to solve the above-described problems caused by the background art, and is a charged particle beam apparatus capable of stably acquiring good image information without depending on the state of the sample 1 and the observation conditions. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, a charged particle beam apparatus according to the invention described in claim 1 is characterized in that the charged particle beam device is charged with reference to the sample irradiated with the charged particle beam and the sample potential of the sample. A charged particle beam apparatus comprising: an electrostatic field forming unit that forms an electrostatic field for accelerating and decelerating the particle beam; and a signal detection unit that detects secondary electrons generated in the irradiation direction of the charged particle beam from the sample. The electrostatic field forming means has a disk-shaped reference electrostatic electrode having a hole through which the charged particle beam passes and a cavity through which the charged particle beam passes at the center. A pair of cylindrical filter electrodes disposed at a position sandwiching the electric electrode from the front-rear direction of the passage and a variable power source for changing the potential of the cylindrical filter electrode, and the signal detection unit includes a reference electrostatic Of upward and downward, characterized in that it is arranged in at least one direction.

  In the first aspect of the present invention, the electrostatic field forming means has a disk-shaped reference electrostatic electrode having a hole through which a charged particle beam passes in the center, and a cavity through which the charged particle beam passes. A pair of cylindrical filter electrodes disposed at positions sandwiching the reference electrostatic electrode from the front-rear direction through which the charged particle beam passes, and a variable power source that changes the potential of the cylindrical filter electrode, and the signal detection unit includes the charged particle It arrange | positions in the surface surrounding a cylindrical filter electrode orthogonal to the direction which passes the beam.

  A charged particle beam device according to a second aspect of the present invention is the charged particle beam device according to the first aspect, wherein the cylindrical filter electrode is formed of a metal mesh having a cylindrical side surface. And

According to the second aspect of the present invention, the electron beam easily passes through the side surface of the cylindrical filter electrode.
According to a third aspect of the present invention, in the charged particle beam device according to the first or second aspect, the cylindrical filter electrode is set to a potential higher than the sample potential. Features.

According to the third aspect of the present invention, the traveling direction of the secondary electrons is directed to the side surface of the cylindrical filter electrode.
According to a fourth aspect of the present invention, there is provided the charged particle beam apparatus according to any one of the first to third aspects, wherein the electrostatic field forming means is configured to provide a potential of the reference electrostatic electrode. It is characterized by comprising a variable power source for changing the power.

In the invention according to the fourth aspect, the secondary electrons are selected based on the energy of the electrons.
A charged particle beam device according to a fifth aspect of the present invention is the charged particle beam device according to any one of the first to fourth aspects, wherein the signal detection unit has a plurality of different directions in the plane. It is arranged in that.

According to the fifth aspect of the present invention, secondary electrons transmitted through side surfaces in different directions of the cylindrical filter electrode are detected.
A charged particle beam device according to a sixth aspect of the present invention is the charged particle beam device according to any one of the first to fifth aspects, wherein the electrostatic field forming means applies a charged particle beam to the sample. When generating a deceleration field electric field on the exit side, a deflection electrode having a non-rotationally symmetric shape with respect to an axis oriented in the direction of passing is provided between the deceleration field electrode and the sample. To do.

In the invention described in claim 6, the flight trajectory of secondary electrons generated from the surface of the sample is corrected.
A charged particle beam device according to a seventh aspect of the present invention is the charged particle beam device according to the sixth aspect, wherein the deflection electrode has a fan-shaped curved shape, and the charged particle beams are directed in different directions. It comprises three deflection electrode plates surrounded by

According to the seventh aspect of the invention, the in-plane position of the secondary electrons generated from the surface of the sample is substantially orthogonal to the irradiation direction of the charged particle beam.
The charged particle beam apparatus according to an eighth aspect of the present invention is the charged particle beam apparatus according to the seventh aspect, wherein the charged electrode is centered on the charged particle beam by the deflection electrode plate. It occupies at least three-quarters of the 360-degree direction that is orthogonal to the beam traveling direction.

According to the eighth aspect of the present invention, a large correction is performed in the direction in which the deflection electrode plate does not exist in the flight trajectory of the secondary electrons.
The charged particle beam device according to claim 9 is the charged particle beam device according to claim 7 or 8, wherein the charged particle beam device is connected to three deflection electrode plates, and the deflection is performed. Three third variable power sources for changing the potential for each electrode plate are provided.

According to the ninth aspect of the invention, a large correction is made in the direction in which the deflection electrode plate does not exist.
The charged particle beam device according to claim 10 is the charged particle beam device according to claim 9, wherein the variable power source supplies the potential of the deflection electrode plate and the flight trajectory of the secondary electrons. The charged particle beam is changed in a direction approaching a flight trajectory.

According to the tenth aspect of the present invention, the secondary electrons reduce the influence of the spherical aberration received from the lens system that focuses the charged particle beam.
The charged particle beam device according to claim 11 is the charged particle beam device according to any one of claims 1 to 10, wherein the charged particle beam includes the reference electrostatic electrode and an acceleration lens. It is characterized by being focused between.

According to the eleventh aspect of the present invention, the influence of the electrostatic field formed by the reference electrostatic electrode on the charged particle beam is small.
A charged particle beam device according to a twelfth aspect of the present invention is the charged particle beam device according to the eleventh aspect, in which the charged particle beam device passes the charged particle beam of the reference electrostatic electrode. And an accelerating lens disposed on the surface.

In the twelfth aspect of the present invention, the charged particle beam is incident on the magnetic field lens forming the objective lens at the optimum opening angle by the acceleration lens.
A charged particle beam device according to a thirteenth aspect of the present invention is the charged particle beam device according to any one of the first to twelfth aspects, wherein the charged particle beam device focuses the charged particle beam. A rotationally symmetric lens for focusing the secondary electrons at a position is provided.

In the thirteenth aspect of the invention, the secondary electrons reduce the influence of spherical aberration received from the lens system that focuses the charged particle beam.
The charged particle beam device according to claim 14 is the charged particle beam device according to claim 13, wherein the rotationally symmetric lens includes a magnetic field coil that forms a magnetic field at the position. And

In the invention described in claim 14, the flight trajectory of the secondary electrons is changed by the magnetic field.
The charged particle beam device according to claim 15 is the charged particle beam device according to claim 13, wherein the rotationally symmetric lens includes an electrostatic electrode plate that forms an electric field at the position. The electrostatic electrode plate has an intermediate potential between the reference electrostatic electrode and the acceleration lens.

In the fifteenth aspect of the invention, the flight trajectory of the secondary electrons is changed by the magnetic field.
The charged particle beam device according to claim 16 is the charged particle beam device according to any one of claims 13 to 15, wherein the rotationally symmetric lens has the position of the reference electrostatic electrode. When it is a hole, the secondary electrons are focused in the vicinity of the hole.

In this invention, the secondary electrons are focused in the vicinity of the holes.
The charged particle beam device according to claim 17 is the charged particle beam device according to any one of claims 1 to 16, wherein the reference electrostatic electrode is divided into at least four electrodes. A voltage is applied to each of the divided electrodes to adjust the flight direction of secondary electrons emitted from the sample.

In this invention, the flight direction of the secondary electrons is adjusted by making the reference electrostatic electrode a multipolar structure.
A charged particle beam device according to an invention described in claim 18 is the charged particle beam device according to any one of claims 1 to 17, wherein only charged information is included in secondary electrons emitted from the sample. A signal detection unit for detecting low energy secondary electrons is provided below the acceleration lens.

In the invention of claim 18, low energy electrons can be detected.
The charged particle beam apparatus according to claim 19 is characterized in that in the charged particle beam apparatus, the charged particles of the charged particle beam are electrons.

  In the invention described in claim 19, an electron beam is used as the charged particle beam.

  According to the present invention, a reference electrostatic electrode having substantially the same potential as the sample and a pair of cylindrical filter electrodes sandwiching the reference electrostatic electrode are disposed along the flight trajectory of the primary electron beam that is a charged particle beam. Since the secondary electrons generated from the sample are selected and detected based on the energy at the time of generation, when a material having high electrical insulation is used for the sample, electrons of a desired energy from the secondary electrons are used. Thus, it is possible to stably acquire good image information without depending on the state of the sample 1 and the photographing conditions.

The best mode for carrying out a charged particle beam apparatus according to the present invention will be described below with reference to the accompanying drawings. Note that the present invention is not limited thereby.
(Embodiment 1)
First, the overall configuration of the scanning electron microscope 10 that is the charged particle beam apparatus according to the first embodiment will be described. FIG. 1 is a configuration diagram including a cross section of a lens barrel portion of a scanning electron microscope 10 and other control portions. The scanning electron microscope 10 includes a sample 1, an electron gun 30, a limiting aperture 2, an opening angle control lens 3, reference electrostatic electrodes 4 and 4 ', cylindrical filter electrodes 5 and 5', an acceleration lens 6, a scanning coil 13, Acceleration field electrode 14, magnetic field lens 15, deceleration field electrode 16, electron gun control unit 8, signal detection units 40 and 40 ′, scanning control unit 22, magnetic field lens control unit 7, control unit 9, display unit 21, variable power supply 18 -20, 32, 33 and power supply 34.

  Here, the sample 1, the scanning coil 13, the acceleration field electrode 14, the magnetic lens 15, the deceleration field electrode 16, the variable power sources 18 to 20, the display unit 21, and the scanning control unit 22 are exactly the same as those described in the background art section. Since it is the same, description is abbreviate | omitted. Further, the opening angle control lens 3, the reference electrostatic electrodes 4 and 4 ', the cylindrical filter electrodes 5 and 5', the acceleration lens 6, the acceleration field electrode 14, the deceleration field electrode 16, variable power supplies 18 to 20, 32 to 34 and The power source 34 forms an electrostatic field forming unit.

  The electron gun 30 generates a primary electron beam 31 that is a charged particle beam toward a vertically downward direction that is the direction of the sample 1. This generation is controlled by the electron gun control unit 8 connected to the electron gun 30.

  The limiting aperture 2 is a diaphragm that is disposed vertically below the electron gun 30 and limits the total amount of the primary electron beam 31 to a predetermined amount of electrons. The opening angle control lens 3 is disposed vertically below the limiting diaphragm 2 and controls the opening angle so that the primary electron beam 31 is incident on the subsequent lens and electrode at an appropriate opening angle in the vertical direction. It is a lens to do.

  The reference electrostatic electrodes 4 ′ and 4 are disc-shaped electrodes that are disposed vertically below the opening angle control lens 3 and have a circular hole in the center. The primary electron beam 31 passes through the circular hole portion of the electrode plate toward the sample 1. The potentials of the reference electrostatic electrodes 4 ′ and 4 are set to the same potential as that of the sample 1 by a variable power source (not shown).

  The cylindrical filter electrodes 5 and 5 'are cylindrical electrodes whose side surfaces are made of an electric conductor having a mesh shape, and the primary electron beam 31 passes through a hollow portion located at the center of the cylinder. The cylindrical filter electrode 5 is disposed vertically below the reference electrostatic electrode 4 ′, and the cylindrical filter electrode 5 ′ is disposed vertically below the cylindrical filter electrode 5 with the reference electrostatic electrode 4 interposed therebetween. . Here, variable power sources 32 and 33 are connected to the cylindrical filter electrodes 5 and 5 ', and the potentials of the cylindrical filter electrodes 5 and 5' can be changed.

  The signal detectors 40 and 40 'are disposed in the horizontal direction of the cylindrical filter electrodes 5 and 5', pass through the side walls of the cylindrical cylindrical filter electrodes 5 and 5 'having a cylindrical shape, and from inside the cavity. The emitted electrons are detected and converted into voltage signals. Here, the signal detectors 40 and 40 'detect, for example, a cylinder surrounding the cylindrical filter electrodes 5 and 5' (not shown) so as to detect the total amount of electrons emitted from the side walls of the cylindrical filter electrodes 5 and 5 '. A shape scintillator, a light guide, and the like can also be included.

  The acceleration lens 6 is an electrode plate having a lens action, which is disposed vertically below the cylindrical filter electrode 5 ′. The acceleration lens 6 is connected to a power source 34 and is set to a positive potential. As a result, the acceleration lens 6 forms an electric field distribution that focuses the primary electron beam 31 that has passed through the cylindrical filter electrode 5 ′ with the acceleration field electrode 14.

  The scanning coil 13, the acceleration field electrode 14, and the deceleration field electrode 16 have the same structure as that described in the background art section. The scanning coil 13 forms a magnetic field for scanning the primary electron beam 31, and accelerates it. The field electrode 14 is applied with a positive voltage of about 4 kV to 16 kV by the variable power source 18, and forms an electric field lens that focuses the primary electron beam 31 between the acceleration field electrode 14 and the deceleration field electrode 16.

The magnetic lens control unit 7 controls the current flowing through the magnetic lens 15 to form a magnetic field that forms an image of the primary electron beam 31 that is a charged particle beam on the surface of the sample 1.
The control unit 9 controls the electron gun control unit 8, the scan control unit 22, the magnetic lens control unit 7, and the variable power supplies 18 to 20, 32, and 33 to perform irradiation and scanning of the sample 1 with the primary electron beam 31. Further, secondary electrons generated from the sample 1 are detected by the signal detectors 40 and 40 ', and image information of the sample 1 is acquired. This image information is displayed on the display unit 21.

  Here, the generation direction of the primary electron beam 31 generated by the electron gun 30 spreads radially around the vertical downward direction. The primary electron beam 31 repeats focusing and divergence in the horizontal direction orthogonal to the traveling direction due to the influence of a diaphragm, a lens, and an electrode, which will be described later. A primary electron beam 31 'indicated by a broken line in FIG. 1 indicates a vertical position where the focusing and divergence are performed. In particular, a crossover point 41 where the primary electron beam 31 ′ is focused on one point exists between the reference electrostatic electrode 4 and the acceleration lens 6 and close to the acceleration lens 6. Further, the primary electron beam 31 ′ is refocused between the acceleration field electrode 14 and the deceleration field electrode 16 by the effect of the electromagnetic field lens. The horizontal position of the broken line indicating the primary electron beam 31 'schematically shows the vertical position of focusing and divergence in an easy-to-understand manner, and does not represent the actual flight trajectory of the primary electron beam 31. Absent.

  Next, the operation of secondary electrons generated by the scanning electron microscope 10 according to the first embodiment will be described. In this operation, the case where the potential of the sample 1 is set to the ground potential will be described. However, the potential of the sample 1 is the ground potential as long as the relative potential with respect to the acceleration field electrode 14, the acceleration lens 6, the cylindrical filter electrodes 5 and 5 ', the reference electrostatic electrodes 4 and 4', and the like is maintained. However, the potential is not limited to, and can be any potential.

  2 and 3 are explanatory views showing secondary electrons generated by the primary electron beam 31 of the scanning electron microscope 10 shown in FIG. 2 and 3, only the electrodes and lenses that determine the flight trajectory of the secondary electrons 50 are shown, and the other control portions are not shown.

  FIG. 2 is an explanatory diagram showing the flight trajectory of the secondary electrons 50 when the potentials of the cylindrical filter electrodes 5 and 5 ′ are made equal to the potential of the reference electrostatic electrode 4 by the control unit 9. The sample 1 generates secondary electrons 50 by irradiation of a primary electron beam 31 that is a charged particle beam. The secondary electrons 50 are accelerated and sucked into the acceleration field electrode 14 by the leakage electric field from the deceleration field electrode 16. The secondary electrons 50 sucked into the accelerating field electrode 14 are affected by the electromagnetic field formed by the accelerating field electrode 14, the magnetic lens 15, and the deceleration field electrode 16, and are focused and diverged while being focused and diverged. Proceeding in the direction of the acceleration lens 6 and the cylindrical filter electrode 5 'existing vertically above.

When the secondary electrons 50 reach the position of the acceleration lens 6, they are decelerated and receive a strong focusing action. The secondary electrons 50 travel in the direction of the reference electrostatic electrode 4 while focusing and diverging.
Here, since the potential of the cylindrical filter electrode 5 ′ is the same as the potential of the reference electrostatic electrode 4, the secondary electrons 50 pass through the acceleration lens 6 and enter the cylindrical filter electrode 5 ′. At that time, it is decelerated strongly and reverses the direction of travel. The secondary electrons 50 whose traveling direction has been reversed collide with the acceleration lens 6 in some cases when having a velocity component in the horizontal direction. Under the influence of the accelerating electric field formed by the electrode 14, it goes in the direction of the accelerating field electrode 14. This prevents the secondary electrons 50 from reaching the signal detectors 40 and 40 ′.

  FIG. 3 is an explanatory diagram showing the flight trajectory of the secondary electrons 51 when the potential of the cylindrical filter electrodes 5 and 5 ′ is set to a positive potential with respect to the potential of the reference electrostatic electrode 4 by the control unit 9. It is. Just like the case of FIG. 2 described above, the secondary electrons 51 are generated by the primary electron beam 31 irradiated on the sample 1 and reach the position of the acceleration lens 6.

  The secondary electrons 51 are decelerated when they reach the position of the acceleration lens 6. However, since the potential of the cylindrical filter electrode 5 ′ is maintained at a higher potential than in the case of FIG. 2, the deceleration effect received by the secondary electrons 51 is small.

  Here, the secondary electrons 51 have an electron energy distribution as shown in FIG. Here, the vertical axis represents the number of secondary electrons, and the horizontal axis represents the electron energy. The secondary electrons are generally composed of secondary electrons in a low energy band of 3 to 4 eV or less and those in an energy band exceeding 3 to 4 eV. The secondary electrons in the low energy band are part of the secondary electrons 51 when using the scanning electron microscope 10 having the deceleration field electrode 16 shown in FIGS. Is sucked into the lens barrel.

  The control unit 9 sets the positive potential applied to the cylindrical filter electrode 5 ′ to about 3 to 4 V where the electron energy of secondary electrons in the low energy band becomes zero. Thereby, the secondary electrons in the low energy band that have reached the vertical position of the cylindrical filter electrode 5 ′ are combined with the focusing effect due to the electric field formed between the cylindrical filter electrode 5 ′ and the acceleration field electrode 14. Secondary electrons 51a directed to the cylindrical filter electrode 5 'are formed. The secondary electrons 51a are transmitted through the side surface of the mesh-shaped cylindrical filter electrode 5 ', detected by the signal detection unit 40', and converted into an electrical signal.

  On the other hand, secondary electrons having an energy band exceeding 3 to 4 eV pass through the cylindrical filter electrode 5 'and the reference electrostatic electrode 4 vertically upward, and the cylindrical filter has a focusing effect similar to that of the secondary electrons 51a. Secondary electrons 51b directed to the electrode 5 are formed. The secondary electrons 51b pass through the side surface of the mesh-shaped cylindrical filter electrode 5, are detected by the signal detection unit 40, and are converted into electrical signals.

  Thereafter, the control unit 9 displays the electrical signals detected by the signal detection units 40 ′ and 40 on the display unit 21 in synchronization with the synchronization signal formed by the scanning control unit 22. At this time, the control unit 9 selects the electrical signals output from the signal detection units 40 ′ and 40 and displays only one of them on the display unit 21 as an SEM image. The control unit 9 can also display an SEM image obtained by combining these two electrical signals using an image processing method.

  As described above, in the first embodiment, the cylindrical filter electrodes 5 and 5 ′ and the reference electrostatic electrodes 4 and 4 ′ are provided between the electron gun 30 and the acceleration field electrode 14, and the cylindrical filter By applying a positive potential to the electrodes 5 and 5 ′ and further adjusting the potential by the control unit 9, the secondary electrons 51 are adjusted depending on the magnitude of energy when the secondary electrons generated in the sample 1 are generated. Therefore, secondary electrons in the low energy band can be removed, and as a result, a component that brightens the entire image included in the SEM image can be removed.

  Further, in the first embodiment, the case where the secondary electrons in the low energy band included in the secondary electrons 51 are removed is exemplified, but by adjusting the potentials of the acceleration lens 6 and the opening angle control lens 3 at the same time, The flight trajectory of the primary electron beam 31 can be optimized to improve the resolution.

  In the first embodiment, the secondary electrons 51 are minimized in the vicinity of the reference electrostatic electrode 4 so that the energy of the secondary electrons is minimized and the speed of the secondary electrons is minimized. Can be selected based on the energy of the electrons contained in the secondary electrons 51 under the condition that the potential applied to the cylindrical filter electrodes 5 and 5 'is small. be able to.

  In the first embodiment, the reference electrostatic electrodes 4 and 4 ′ are set to the same potential as the sample 1 by a variable power source (not shown), but the reference electrostatic electrodes 4 and 4 ′ with respect to the sample 1 are used. By changing the potential, sorting based on the energy of electrons contained in the secondary electrons 51 can be made more appropriate and highly accurate.

  In the first embodiment, the signal detectors 40 and 40 ′ are arranged one by one on the side surfaces of the cylindrical filter electrodes 5 and 5 ′, but surround the cylindrical filter electrodes 5 and 5 ′. A plurality of signal detectors may be provided to separately detect secondary electrons that are transmitted in different directions.

  In the first embodiment, when the focusing condition of the primary electron beam 31, for example, the voltage of the variable power sources 18 to 20 is changed, the electric field changes, so that the secondary electrons 53 generated from the sample 1 are horizontal. The spread of direction also changes. This change also changes the function of separating and detecting the secondary electrons 53 by the cylindrical filter electrodes 5 and 5 '.

  FIG. 5 is an explanatory diagram showing changes in the flight trajectory of the secondary electrons 53a that occur when the focusing condition of the primary electron beam 31 is changed. When the focusing condition of the primary electron beam 31 is changed, the secondary electrons 53a are horizontally aligned in the vicinity of the vertical position where the acceleration field electrode 14 exists like the secondary electrons 53a depending on the emission angle from the sample 1. Deviation occurs in the direction. Since the influence of spherical aberration of the accelerating lens 6 varies depending on the position in the horizontal direction, even when the secondary electrons 53a have the same electron energy, as shown in FIG. This causes a change in the flight trajectory toward. This also reduces the energy resolution when separating and detecting the secondary electrons 53a.

  Here, the control unit 9 changes the voltage of the variable power source 19 applied to the deceleration field electrode 16 to narrow the opening angle in the emission direction of the secondary electrons 53 generated from the sample 1, and consequently the secondary electrons 53. By reducing the horizontal displacement in the vicinity of the vertical position where the acceleration field electrode 14 exists, it is possible to prevent a reduction in energy resolution.

  FIG. 6 shows the secondary electrons 53b when the voltage of the variable power source 19 is further optimized as compared with the case of FIG. 5 under the condition for focusing the primary electron beam 31 similar to FIG. It is explanatory drawing of a flight orbit. Since a more optimized potential is applied between the deceleration field electrode 16 and the sample 1 as compared with the case of FIG. 5, the secondary electrons 53 generated in the sample 1 have a small emission angle spread. It will be a thing. As a result, the secondary electrons 53b have a small horizontal displacement near the vertical position where the acceleration field electrode 14 is present, and the influence of spherical aberration is also small. Become.

  Further, in order to reduce the influence of the spherical aberration of the accelerating lens 6 on the secondary electrons 53a spreading in the horizontal direction, the rotational symmetry of the horizontal position in the vicinity of the crossover point 41 where the primary electron beam 31 'converges. A magnetic field coil 71 which is a mold lens can also be provided.

  FIG. 7 is a configuration diagram in which a magnetic field coil 71 and a magnetic field coil control unit 44, which are rotationally symmetric lenses, are provided beside the acceleration lens 6 that forms the crossover point 41 in the primary electron beam 31 ′. The magnetic field coil control unit 44 is electrically connected to the control unit 9. The magnetic field coil 71 forms a magnetic field in the vertical direction at the crossover point 41 of the primary electron beam 31 '. At the crossover point 41, the primary electron beam 31 'is converged and the traveling direction and the magnetic field direction substantially coincide with each other. Therefore, the influence of the magnetic field of the magnetic field coil 71 on the primary electron beam 31' is small.

  On the other hand, the secondary electrons 53a are focused in the direction of the central axis by the magnetic field of the magnetic field coil 71, and the spread in the horizontal direction is small. And the influence of the spherical aberration which the acceleration lens 6 has when it has the expansion of a horizontal direction becomes a limited thing, and the dispersion | variation in the converging position of the secondary electron 53a can be reduced by extension.

  FIG. 7 shows an example in which the magnetic field coil 71 is used as a rotationally symmetric lens. However, instead of the magnetic field coil 71, an electrostatic electrode plate having a rotationally symmetric structure is provided, and this electrostatic electrode plate is formed. Secondary electrons can be focused in the central axis direction by an electrostatic field. At this time, the potential of the electrostatic electrode plate is set to an intermediate potential between the potentials of the reference electrostatic electrode 4 and the acceleration lens 6 so that the influence on the primary electron beam 31 'is small.

  FIG. 8 is a diagram illustrating a configuration example of the reference electrostatic electrode. FIG. 8 shows the reference electrostatic electrode viewed from the Z direction. Here, the case where the reference electrode 4 is divided into the deflection electrodes 4a to 4d is shown. Although the figure is divided into four parts, it is not limited to four parts and can be divided into any number of deflection electrodes. Reference numeral 90 is a reference electrode power source, and 91a to 91d are power sources for applying voltages to the respective deflection electrodes. These power supplies 90 and 91a to 91d can change their voltages. The reference electrode power supply 90 and the power supplies 91a to 91d are connected, and the voltage of the reference electrode power supply 90 is applied as an offset to each of the power supplies 91a to 91d, and the voltage is applied to each of the deflection electrodes 91a to 91d. An example is shown. By dividing the reference electrode into two or more poles, the dispersion direction when the secondary electrons are dispersed can be controlled.

  FIG. 9 is a block diagram showing an embodiment of the present invention. 1 and 2 are designated by the same reference numerals. In the figure, reference numeral 4 denotes a reference electrostatic electrode shown in FIG. Reference numeral 95 is a reference electrode power source for applying a voltage to the reference electrostatic electrode 4, and includes the power sources 90 and 91a to 91d of FIG. A magnetic lens control unit 97 controls the magnetic lens 15. Other configurations are the same as those shown in FIGS.

As shown in FIG. 8, by controlling the voltage applied to the divided electrodes, the effect of the secondary electron filter can be changed for each flight direction of the secondary electrons 50 (axial rotation direction).
In the above-described embodiment, the case where a total of two signal detection units are provided on the upper and lower sides of the reference electrostatic electrode 4 has been shown. However, the signal detection unit is directed upward or downward in the reference electrostatic electrode 4. One may be provided.
(Embodiment 2)
By the way, in the first embodiment, the case where the surface of the sample 1 is orthogonal to the irradiation direction of the primary electron beam 31 is shown, but with respect to the irradiation direction of the primary electron beam 31 that is a charged particle beam, There is a case in which the surface of the sample 1 is observed by tilting the sample 1 in an oblique direction greatly inclined from the orthogonal direction. FIG. 16 illustrates the flight trajectory of the secondary electrons 110 generated from the sample 1 tilted with respect to the horizontal direction when it has the same configuration as the scanning microscope 100 of FIG. The secondary electrons 110 are distorted so that the flight trajectory thereof deviates from the central axis where the primary electron beam 31 exists in accordance with the inclination of the sample 1. This is because the distribution of the leakage electric field 111 formed on the sample 1 side of the deceleration field electrode 16 shown by the broken line in FIG. 16 is non-axisymmetric with respect to the central axis of the primary electron beam 11 due to the tilted sample 1. By becoming a distribution.

  FIG. 12 is an explanatory diagram illustrating the flight trajectory of the secondary electrons 120 generated from the sample 1 tilted with respect to the horizontal direction when it has the same configuration as the scanning microscope 10 of FIG. . In FIG. 12, the secondary electrons 120 collide with the acceleration lens 6, or those that should pass through the cylindrical filter electrode 5 ′ pass through the cylindrical filter electrode 5.

  Therefore, in the second embodiment, the distribution of the leakage electric field 111 formed between the deceleration field electrode 16 and the sample 1 is shaped so that the secondary electrons 120 draw a flight trajectory along the central axis. I will show you.

  Here, the scanning electron microscope 60 according to the second embodiment (FIG. 11) includes deflection electrode plates 81 to 83 and variable power sources 86 to 88 that constitute deflection electrodes provided on the sample 1 side of the deceleration field electrode 16. Since the configuration is completely the same as that of the scanning electron microscope 10, a description of the same parts is omitted, and only the deflection electrode plates 81 to 83 and the variable power sources 86 to 88 are described.

  FIG. 10 is a diagram showing the deflection electrode plates 81 to 83 disposed on the sample 1 side of the deceleration field electrode 16 and variable power sources 86 to 88 for determining the potentials of the deflection electrode plates 81 to 83. FIG. 10A is a view of the deflection electrode plates 81 to 83 disposed on the deceleration field electrode 16 as viewed from the central axis direction of the primary electron beam 31 that is a charged particle beam from the sample 1 side. The three deflection electrode plates 81 to 83 having a fan-shaped curved shape are arranged on the side surface of the cone-shaped deceleration field electrode 16 so that the side on which the sample 1 is disposed is in an empty state of the deflection electrode plate. The

  In addition, variable power sources 86 to 88 are connected to the deflection electrode plates 81 to 83 so as to have a negative potential with respect to the potential applied to the deceleration field electrode 16. FIG. 10B is a cross-sectional view showing the AA ′ cross section of the deceleration field electrode 16 and the deflection electrode plate 81 shown in FIG. The sample 1 has an inclination such that it approaches the deceleration field electrode 16 on the side surface of the empty deceleration field electrode 16 in which the deflection electrode plates 81 to 83 do not exist. The shape of the leakage electric field 112 formed between the sample 1 having this inclination and the deceleration field electrode 16 and the deflection electrode plates 81 to 83 is schematically shown in FIG. It is indicated by a broken line.

  The deflection electrode plate 81 is set to a potential lower than the potential of the deceleration field electrode 16 by the variable power source 86. As a result, the leakage electric field 112 approximates an axisymmetric shape with respect to the central axis that forms the flight trajectory of the primary electron beam 31 and the distortion is reduced as compared with the leakage electric field 111 shown in FIG. 16 or FIG.

  FIG. 11 is a diagram showing a flight trajectory drawn by the secondary electrons 54 of the scanning electron microscope 60 having the deflection electrode plates 81 to 83 and the variable power sources 86 to 88. The leakage electric field 112 approximates to an axially symmetric shape with respect to the central axis due to the presence of the deflection electrode plates 81 to 83, and is less distorted. Therefore, the leakage electric field applied to the primary electron beam 31 and the secondary electrons 54 The effect of is small.

  As a result, the secondary electrons 54 draw a flight trajectory along the central axis, and the flight similar to the secondary electrons 51 generated when the surface of the sample 1 is horizontally arranged as shown in FIG. Draw a trajectory. Then, the secondary electrons 54 decelerated by the accelerating lens 6 and the reference electrostatic electrode 4 are transmitted through the cylindrical filter electrode 5 or 5 ', as in the case of the first embodiment, and the signal detector 40 or 40'. Is detected.

  As described above, in the second embodiment, when the surface of the sample 1 has an inclination with respect to the horizontal direction orthogonal to the traveling direction of the primary electron beam 31, on the sample 1 side of the deceleration field electrode 16, The deflecting electrode plates 81 to 83 are disposed so as to be asymmetric in the tilt direction, the potential of the deflecting electrode plates 81 to 83 with respect to the deceleration field electrode 16 is controlled, and the leakage electric field 112 has an axisymmetric shape with respect to the central axis. Since the approximation is made, the flight trajectory of the secondary electrons 54 is assumed to be along the central axis, and the energy of the secondary electrons 54 using the acceleration lens 6, the reference electrostatic electrode 4, and the cylindrical filter electrodes 5 and 5 'is used. Therefore, the image information of the sample 1 to be acquired can be stably acquired regardless of the inclination of the sample 1.

In the second embodiment, the variable power sources 86 to 88 that determine the potentials of the deflection electrode plates 81 to 83 are controlled in the same manner. However, the variable power sources 86 to 88 are individually controlled, and It is also possible to correct the distortion of the leakage electric field in a direction orthogonal to the surface tilt direction. This distortion is an error caused by the processing accuracy of the deceleration field electrode 16 having a rotationally symmetric structure with respect to the central axis, or an error in the relative position between the deceleration field electrode 16 having the deflection electrode plates 81 to 83 and the sample 1. And is particularly large when a high voltage is applied to the deceleration field electrode 16.
(Embodiment 3)
FIG. 13 is a block diagram showing a third embodiment of the present invention. 1 and 2 are designated by the same reference numerals. In the figure, 31 is a primary electron beam, 2 is a limiting aperture, 3 is an opening angle control lens, 4 'is a second reference electrostatic electrode, and 4 is a first reference electrostatic electrode. Reference numeral 5 denotes a first cylindrical filter electrode, and 5 'denotes a second cylindrical filter electrode. The reference electrostatic electrode 4 is provided between the cylindrical filter electrodes 5 and 5 '. Reference numeral 32 denotes a variable power source that applies a voltage to be applied to the cylindrical filter 5, and 33 denotes a variable power source that applies a voltage to be applied to the cylindrical filter 5 ′. Reference numeral 50 denotes secondary electrons emitted from the sample 1.

  Reference numeral 40 denotes a first secondary electron signal detector disposed above the reference electrostatic electrode 4, and 40 ′ denotes a second secondary electron signal detector provided between the reference electrostatic electrode 4 and the acceleration lens 6. , 40 ″ are third secondary electron signal detectors added to the acceleration field electrode 14. Reference numeral 13 denotes a scanning coil, and reference numeral 22 denotes a scanning control unit that gives a scanning control signal to the scanning coil 13. Reference numeral 21 denotes a display unit that displays signals detected by the signal detection units as images.

  Reference numeral 14 denotes an accelerating field electrode, 18 denotes a variable power source for applying a voltage to the accelerating field electrode 14, 15 denotes a magnetic lens, and 7 denotes a magnetic lens control unit that controls a current applied to the magnetic lens 15. Reference numeral 1 denotes a sample, 20 denotes a variable power source that applies a potential to the sample 1, 41 denotes a deceleration lens disposed between the magnetic lens 15 and the sample 1, and 19 denotes a variable power source that applies a potential to the deceleration lens 41. The operation of the apparatus configured as described above will be described as follows.

  In this embodiment, the total amount of secondary electrons having low energy is detected by the signal detection unit 40 ″. As shown in FIG. 4, secondary electrons in the 1 to 3 eV region having low energy have charging information on the surface of the sample 1. These secondary electrons are accelerated by the accelerating field electrode 14 when they are not selected by the cylindrical filter electrode 5 ′ because of their low electron energy. And only the signal which has charging information is detectable by detecting with the signal detection part 40 ''.

  In FIG. 13, secondary electrons emitted from the sample 1 are detected by dividing them into energy bands. Therefore, the first signal detection unit 40, the second signal detection unit 40 ′, and the third signal detection unit 40 ″ detect each of them. That is, the secondary electron having the highest energy is the first signal detection unit 40, the secondary electron having the next energy is the second signal detection unit 40 ', and the secondary electron having the lowest energy is the third signal. The signal detector 40 ″ detects the signal.

  However, if only charged electrons and secondary electrons are separated, the cylindrical filter electrode 5 'and the signal detection unit 40' may be omitted. FIG. 14 is a diagram illustrating another configuration example of the third embodiment. The same components as those in FIG. 13 are denoted by the same reference numerals. As can be seen from comparison with FIG. 13, the embodiment shown in FIG. 14 has a configuration without the cylindrical filter electrode 5 ′ and the signal detection unit 40 ′. Other configurations are the same as those shown in FIG.

It is a block diagram which shows the whole structure of the scanning electron microscope which is a charged particle beam apparatus. FIG. 3 is an explanatory diagram illustrating a flight trajectory of secondary electrons of the scanning electron microscope according to the first embodiment (part 1); FIG. 6 is an explanatory diagram of a flight trajectory of secondary electrons of the scanning electron microscope according to the first embodiment (No. 2). It is explanatory drawing which shows energy distribution of the secondary electron generate | occur | produced from a sample. FIG. 3 is an explanatory diagram showing a flight trajectory of secondary electrons of the scanning electron microscope according to the first embodiment (part 3); FIG. 6 is an explanatory diagram of a flight trajectory of secondary electrons of the scanning electron microscope according to the first embodiment (No. 4). FIG. 6 is an explanatory diagram of a flight trajectory of secondary electrons of the scanning electron microscope according to the first embodiment (No. 5). It is a figure which shows the structural example of a reference | standard electrostatic electrode. It is a block diagram which shows one embodiment of this invention. FIG. 6 is a configuration diagram illustrating a detailed configuration of a deflection electrode disposed in a scanning electron microscope according to a second embodiment. In the scanning electron microscope concerning Embodiment 2, it is explanatory drawing which shows the flight trajectory of the secondary electron generated when the sample 1 is inclined. In the scanning electron microscope according to the first embodiment, it is an explanatory diagram showing a flight trajectory of secondary electrons generated when the sample 1 is tilted. It is a block diagram which shows the 3rd Embodiment of this invention. It is a figure which shows the other structural example of Embodiment 3 of this invention. It is explanatory drawing which shows the structure of the conventional scanning electron microscope, and the flight trajectory of a secondary electron. It is explanatory drawing which shows the flight trajectory of the secondary electron generated when the sample 1 is inclined in the structure of the conventional scanning electron microscope.

Explanation of symbols

1 Sample 3 Opening angle control lens 4, 4 ′ Reference electrostatic electrode 5, 5 ′ Cylindrical filter electrode 6 Acceleration lens 7 Magnetic lens control unit 8 Electron gun control unit 9 Control unit 10, 60, 100 Scanning electron microscope 11, 31, 31 'Primary electron beam 12 Secondary electron 13 Scanning coil 14 Acceleration field electrode 15, 71 Magnetic field lens 16 Deceleration field electrode 17 Signal detector 18-20 Variable power source 21 Display unit 22 Scan control unit 24 Electron detection unit 30 Electron Guns 32 to 34 Variable power sources 40, 40 ', 40''Signal detector 41 Crossover point 44 Magnetic lens control units 50, 51, 53, 54 Secondary electrons 81-83 Deflection electrode plates 86-88 Variable power sources 110, 120 Secondary electrons 111, 112 Leakage electric field

Claims (19)

A sample irradiated with a charged particle beam;
An electrostatic field forming means for accelerating / decelerating the charged particle beam with reference to the sample potential of the sample;
A signal detection unit for detecting secondary electrons generated in the irradiation direction of the charged particle beam from the sample;
A charged particle beam device comprising:
The electrostatic field forming means has a disk-shaped reference electrostatic electrode having a hole that allows the charged particle beam to pass through in the center, and a cavity that allows the charged particle beam to pass through in the center. A pair of cylindrical filter electrodes disposed at positions sandwiched from the front-rear direction of passage and a variable power source for changing the potential of the cylindrical filter electrodes;
The charged particle beam device according to claim 1, wherein the signal detection unit is disposed in at least one of an upward direction and a downward direction of the reference electrostatic electrode.   2. The charged particle beam apparatus according to claim 1, wherein the cylindrical filter electrode is formed of a metal net having a cylindrical side surface.   The charged particle beam apparatus according to claim 1, wherein the cylindrical filter electrode is set to a potential higher than the sample potential.   The charged particle beam apparatus according to claim 1, wherein the electrostatic field forming unit includes a variable power source that changes a potential of the reference electrostatic electrode.   5. The charged particle beam apparatus according to claim 1, wherein the signal detection unit is arranged in a plurality of different directions in the plane.   The electrostatic field forming means is configured to generate a deceleration field electric field on the side where the charged particle beam is emitted to the sample, with respect to an axis that faces the direction in which the passage is performed between the deceleration field electrode and the sample. 6. The charged particle beam apparatus according to claim 1, further comprising a deflection electrode having a rotationally symmetric shape.   The charged particle beam apparatus according to claim 6, wherein the deflection electrode has a fan-shaped curved shape and includes three deflection electrodes that surround the charged particle beam from different directions.   The deflection electrode occupies a three-quarter region in a 360-degree direction around the charged particle beam and perpendicular to the traveling direction of the charged particle beam by the deflection electrode plate. Item 8. A charged particle beam device according to Item 7.   The charged particle beam apparatus according to claim 7 or 8, further comprising three variable power supplies connected to the three deflection electrodes and changing a potential for each of the deflection electrode plates.   10. The charged particle beam apparatus according to claim 9, wherein the variable power source changes the potential of the deflection electrode plate in a direction in which the flight trajectory of the secondary electrons approaches the flight trajectory of the charged particle beam.   The charged particle beam apparatus according to claim 1, wherein the charged particle beam is focused between the reference electrostatic electrode and an acceleration lens.   The charged particle beam apparatus according to claim 11, further comprising an acceleration lens disposed in a direction in which the charged particle beam of the reference electrostatic electrode passes.   13. The charged particle beam apparatus according to claim 1, further comprising a rotationally symmetric lens that focuses the secondary electrons at a position where the charged particle beam is focused. .   The charged particle beam device according to claim 13, wherein the rotationally symmetric lens includes a magnetic field coil that forms a magnetic field at the position.   The rotationally symmetric lens includes an electrostatic electrode plate that forms an electric field at the position, and the electrostatic electrode plate has an intermediate potential between the potentials of the reference electrostatic electrode and the acceleration lens. The charged particle beam apparatus according to claim 13.   16. The rotationally symmetric lens focuses the secondary electrons in the vicinity of the hole when the position is a hole of the reference electrostatic electrode. Charged particle beam device.   The reference electrostatic electrode is divided into at least four electrodes in a rotationally symmetric direction, and a voltage is applied to each of the divided electrodes to adjust the flight direction of secondary electrons emitted from the sample. The charged particle beam apparatus according to claim 1.   18. The signal detection unit for detecting low-energy secondary electrons having only charging information among secondary electrons emitted from the sample is disposed below the acceleration lens. A charged particle beam device according to claim 1.   The charged particle beam apparatus according to claim 1, wherein the charged particles of the charged particle beam are electrons.

Images