JP2006156134A - Reflection imaging electron microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the contrast of a mirror electron microscope. <P>SOLUTION: A separator 4 for separating an irradiated electron beam 101 and a reflected electron beam 102 of the mirror electron microscope is positioned between an objective lens 5 and an intermediate lens 8, and a restriction diaphragm 14 is positioned in a position 43 where the intermediate lens 8 projects an electron beam diffraction image of the reflected electron beam 102 formed in a focus position 41 of the objective lens 5. The restriction of the reflected electron beam using the restriction diaphragm 14 improves the contrast of a mirror electron microscope image. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a reflection imaging electron microscope such as a mirror electron microscope for observing a surface state of a sample.

  As an apparatus for observing a sample using an electron beam, a transmission electron microscope that forms an image of an electron beam transmitted through the sample, a secondary electron generated from the sample by scanning the electron beam focused on the sample, etc. There are scanning electron microscopes that image intensity. In the configuration of the conventional transmission electron microscope shown in FIG. 7, a so-called dark field image in which only the electron beam scattered by the interaction with the sample 7 is passed by disposing the limiting aperture 14 on the back focal plane 41 of the objective lens 5. By imaging under conditions, it has become possible to form an image that emphasizes the scattered electron beam. However, these electron microscopes may damage the sample by irradiating the sample with an electron beam, and it is difficult to observe a sample that is easily damaged.

  In contrast to these conventional methods, the sample is set to substantially the same potential as the electron source potential, and the direction is reflected with the direction and intensity reflecting the sample information immediately before the electron beam is incident on the sample. Japanese Patent Application Laid-Open No. 2003-202217 describes a technique for imaging mirror electrons. FIG. 5 shows the trajectory of the mirror electrons that is inverted at the equipotential surface A immediately above the sample with respect to the sample having an uneven surface. On the equipotential surface A immediately above the sample, a potential distortion reflecting the unevenness of the sample is generated, and mirror electrons are scattered in the lateral direction due to the potential distortion. Information about potential distortion can be obtained by imaging the mirror electrons including the electrons scattered in the lateral direction.

JP 2003-202217 A

  In conventional mirror electron microscopes, the irradiated electron beam irradiates the sample with a certain energy spread, so with an irradiated electron beam with a large energy width, the irradiated electron with a small energy does not reach just before the sample and is far from the sample. Inversion at the equipotential surface. FIG. 7 shows a trajectory of mirror electrons that is inverted at an equipotential surface B away from the sample shown in FIG. On the equipotential surface B, the potential distortion is small and the mirror electrons above the irregular surface are not scattered in the lateral direction. Under such conditions, there is a problem that the electron beam scattered in the lateral direction cannot be distinguished from most non-scattered mirror electron beams, and the contrast of the mirror electron image is reduced. As shown in FIG. 8, the separator 51 that separates the irradiated electron beam 101 and the reflected electron beam 102 is located on the electron source side with respect to the objective lens 5, so that irradiation is performed in the section between the separator 51 including the objective lens 5 and the sample 7. The electron beam 101 and the reflected electron beam 102 move in almost the same space.

  Here, since the electron beam diffraction image of the reflected electron beam 102 is formed on the focal plane 41 of the objective lens 5, the limiting aperture 14 is disposed on the focal plane 41 of the objective lens 5 to reflect in a specific scattering direction. By selecting the electron beam 102 and passing through the limiting aperture 14, a bright field image for selectively forming a reflected electron beam with little scattering and a dark field image for selectively forming a scattered reflected electron beam are obtained. be able to. However, since the limiting aperture 14 is disposed at a position that also acts as a limiting aperture that limits the irradiation angle of the sample with respect to the irradiation electron beam 101, when the limiting aperture is adjusted in accordance with the scattering direction of the reflected electron beam, There was a problem that the irradiated electron beam 101 collided with the restriction aperture and the sample could not be irradiated.

  The present invention has been made paying attention to the above points, and realizes an apparatus configuration capable of forming a reflected electron beam image in a specific scattering direction with a mirror electron microscope without affecting the irradiated electron beam 101. With the goal.

The object of the present invention can be achieved by the following method.
In the present invention, the limiting aperture 14 for limiting the sample emission angle of the reflected electron beam 102 is not the vicinity of the focal plane 41 of the objective lens on which the electron beam diffraction image is formed, but the separator 51 and the irradiated electron beam 101 and the reflected electron beam 102. A dark field image can be formed by disposing a limiting aperture 14 in the vicinity of a projection image plane formed by a latter stage lens of an electron beam diffraction image formed after separation. The principle of the present invention will be described in detail with reference to FIGS.
Here, as the separator 51, the ExB deflector 4 that operates by crossing an electric field and a magnetic field is used. The ExB deflector is a deflector that operates by superimposing an electric field and a magnetic field in an orthogonal manner. This operation will be described with reference to FIG. The electron beam of the acceleration voltage V ₀ is deflected by a uniform magnetic deflector having a deflection angle θ _E and a length of 2 l deflected by a parallel plate electrode type electrostatic deflector having a length of 2 l and a distance d shown in FIG. The angle θ _M is given by the following equation.

Conditions in which deflection by electric field and deflection by magnetic field cancel each other

Is referred to as the Wien condition, and the electron beam incident from above on the E × B deflector set to the Wien condition in FIG. 11 goes straight, and the electron beam incident from below undergoes deflection of θ _E + θ _M = 2θ _E It has the characteristics.

The trajectory of the irradiation electron beam 101 is shown in FIG. The optical axis 103 of the irradiation electron beam 101 and the optical axis 104 of the reflected electron beam 102 intersect at an angle of θ _IN . The ExB deflector 4 operates such that the deflection electron beam 101 has a deflection angle θ _IN = θ _E + θ _M , and the reflected electron beam 102 has a Wien condition θ _E = θ _{M, and} moves straight. To do. That is, electron beam irradiation 101 after being angle theta _IN deflected optical axis perpendicular 104 direction from the optical axis 103 to a sample containing an electron source by ExB deflector 4, by focusing near the objective lens focal plane 41, the sample 7 can be irradiated in parallel. FIG. 10 shows the trajectory of the reflected electron beam 102 where the irradiated electron beam 101 is mirror-reflected from the sample 7, and the objective lens focal plane 41 corresponds to the position of the electron diffraction image of the transmission electron microscope and is scattered from the sample 7 in the same direction. Since the emitted electron beam is focused on the focal plane 41, the scattering direction of the reflected electron beam 102 can be limited by disposing the limiting aperture 14 at the position of the objective lens focal plane (electron beam diffraction image). However, if the limiting aperture 14 is separated from the optical axis 104 of the imaging system in order to obtain a dark field image, all of the irradiation electron beam 101 is limited, and the sample 7 cannot be irradiated with the irradiation electron beam 101. .

In order to solve this problem, after the reflected electron beam 102 passes through the separator, the limiting aperture 14 is disposed on the imaging plane 43 of the electron beam diffraction image projected by the intermediate lens 8, and the imaging plane 43 is moved over the imaging plane 43. It was made movable. In the figure, the trajectories of the electron beams scattered in three directions from the sample 7 are described, but the circular aperture-shaped restricting aperture 14 is shifted to the right side from the optical axis 104 in the figure, and the upper left direction in the figure from the sample. By allowing only the reflected electron beam scattered by the beam to pass through, it is possible to observe a projection image of only the electron beam scattered in the upper left direction. Further, if the shape of the limiting diaphragm is an annular shape as shown in FIG. 12, a projected image by mirror electrons in the scattering angle range defined by the inner diameter R ₁ and the outer diameter R ₂ of the annular ring can be formed. it can.

Here, in the above description, in order to obtain a dark field image, the circular aperture-shaped limiting diaphragm was used under the condition that it was separated from the optical axis. Then, by obtaining a reflected electron beam reflected in the optical axis direction of the imaging system, a projection image with a small off-axis aberration of the reflected electron beam can be obtained. This principle will be described with reference to FIGS. After the irradiation electron beam 101 is deflected by the ExB deflector 4 from the optical axis 103 including the electron source in the direction of the optical axis 103 perpendicular to the sample by an angle θ _IN , the sample 7 is focused on the objective lens focal plane 41. Parallel irradiation can be performed from a direction perpendicular to the direction. The trajectory of the irradiation electron beam 101 is shown in FIG. 13. Under the mirror electron microscope conditions, the energy of the irradiation electron beam 101 and that of the reflected electron beam 102 are equal, so that the reflected electron beam projection image of the sample 5 is formed by the objective lens. The position of the E × B deflector 4 arranged in the vicinity of the surface position 42 corresponds to the object surface position of the irradiation electron beam for the irradiation electron beam 101 to cross the sample 5. Therefore, when the irradiation electron beam 101 is deflected, for example, by the angle θ _D by the E × B deflector 4, it enters the circular hole electrode 6 at a deflection angle of the angle θ _AP and is applied to the sample by the parallel irradiation electron beam inclined from the optical axis. The same position is irradiated. Therefore, in order to irradiate the same position of the sample by irradiating the irradiation electron beam to the circular hole electrode 6 with the deflection angle of the angle θ _AP , the X deflector and the Y deflector of the E × B deflector 4 have the angle θ _D. a deflection signal corresponding to the deflection angle may be supplied by superimposing a deflection signal corresponding to a deflection angle theta _iN. Note that the relationship between θ _AP and θ _IN is uniquely determined if the lens arrangement and the operating conditions are determined.

  The reflected electron beam 102 shown in FIG. 14 forms an electron beam diffraction pattern corresponding to the sample exit direction on the focal plane 41 of the objective lens. When the limiting aperture 14 is arranged at this focal plane position, the irradiation electron beam 101 is limited. Therefore, after the reflected electron beam 102 passes through the E × B deflector 4, the limiting aperture 14 is inserted at a position 43 where the electron beam diffraction image is projected by the intermediate lens 8. When the reflected electron beam 102 is deflected by the E × B deflector 4, the position of the electron beam diffraction image changes, but the E × B deflector 4 is different from the reflected electron beam 102 in the E × B deflector. If the operation is performed so that the so-called Wien condition in which the magnetic field and the electric field of 4 act at the same magnitude in the opposite direction is satisfied, the reflected electron beam is projected without being deflected by the E × B deflector 4. Can do.

Alternatively, a so-called hollow cone irradiating means for continuously irradiating the same place on the sample 7 with a constant irradiation angle and changing the irradiation direction is provided, and among the scattered reflected electron beams, the reflected electrons scattered in the optical axis direction are provided. By arranging the limiting aperture 14 for selecting a line on the projection plane 43 on which the focal plane of the objective lens 5 is projected by the intermediate lens, only a reflected electron beam having a specific scattering angle can be selected. This principle will be described with reference to FIGS. The trajectory of the irradiation electron beam 101 is shown in FIG. The electrode supply voltage for deflecting the irradiation electron beam 101 in the X direction by the angle θ _E by the deflection electrode of the E × B deflector 4 is V _X, and the supply for deflecting the angle θ _D / 2 for the hollow cone irradiation. Assuming that the voltage is V _D , as shown in FIG. 17, a deflection signal of V _X + V _D cos (t) is supplied to the X deflector and V _D sin (t) is supplied to the Y deflector. Furthermore, also in the magnetic field generation, a sine for deflecting the angle θ _D / 2 in the deflection coil for generating the magnetic field so that the E × B deflector 4 always has the Wien condition for the reflected electron beam. When the wave and cosine wave signals are supplied, the irradiated electron beam can be irradiated without changing the irradiation position of the sample while precessing. The reflected electron beam 102 shown in FIG. 16 forms an electron diffraction pattern on the focal plane 41 of the objective lens. After the reflected electron beam 102 passes through the E × B deflector 4 without being deflected, this electron beam is transmitted by the intermediate lens 8. A dark field image of the mirror electron microscope can be obtained by inserting the limiting aperture 14 at the position 43 where the diffraction image is projected.

  According to the present invention, it is possible to perform high-contrast image observation with less off-axis aberrations by acquiring a projection image that can selectively limit the scattering direction of the reflected electron beam.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a configuration for explaining the operation of the first embodiment. The E × B deflector 4 is disposed in the vicinity of the imaging surface 42 of the reflected electron beam 102 as a separator. The optical axis 103 and optical axis 104 of the imaging system perpendicular to the wafer 7 of the illumination system comprising an electron source, which intersect at an angle of theta _IN together. An E × B deflector 4 is disposed between the condenser lens 3 and the objective lens 5, and the irradiation electron beam 101 emitted from the electron source 1 is placed on the optical axis perpendicular to the wafer 7 by the E × B deflector 4. Deflected. The irradiation electron beam 101 deflected by the E × B deflector 4 is focused by the condenser lens 3 in the vicinity of the focal plane of the objective lens, and the upper surface 7 of the sample can be irradiated with the substantially parallel irradiation electron beam.

A negative potential that is substantially equal to or slightly higher than the acceleration voltage V ₀ applied to the electron source 1 is supplied to the sample 7 from a sample application power source 27 through a stage that holds the sample 7. A positive voltage in the range of several kV to several tens of kV with respect to the sample 7 is supplied from the circular hole electrode application power supply 26 to the circular hole electrode 6 facing the sample. Due to the deceleration electric field between the circular hole electrode 6 and the sample 7, most of the planar irradiation electron beam 101 is pulled back immediately before it collides with the sample 7 to become mirror electrons, and the shape, potential, magnetic field, etc. of the sample 7. It enters the objective lens 5 again with a direction and intensity reflecting the above.

  The reflected electron beam 102 by the mirror electrons is magnified by the objective lens 5 and forms a mirror projection image in the vicinity of the E × B deflector 4. The E × B deflector 4 acts on the reflected electron beam under Wien conditions. That is, the E × B deflector 4 does not have a deflecting action with respect to the reflected electron beam 102, and the mirror image is formed and projected in the vicinity of the E × B deflector 4, so that the deflection by the E × B deflector 4 is performed. Little aberration occurs. The mirror image by the objective lens 5 is projected by the intermediate lens 8 and the projection lens 9, and an enlarged mirror electronic image is formed on the scintillator 10. The mirror electronic image is converted into an optical image by the scintillator 10, projected onto the CCD camera 12 by the optical lens or optical fiber bundle 11, and the mirror electronic image converted into an electric signal by the CCD camera 12 is displayed on the monitor 13.

A cross section of the E × B deflector 4 viewed from the direction perpendicular to the optical axis has an octupole electromagnetic structure shown in FIG. 18, and each electromagnetic pole 51 is made of a magnetic material such as permalloy. Each electromagnetic pole operates as an electrode when a potential is applied, and operates as a magnetic pole by passing an exciting current through a coil 53 wound N times around each electromagnetic pole. When the voltage V _X is applied to each electromagnetic pole with the voltage distribution shown in FIG. 18, the electrons are deflected in the x direction. Also, when current I _{Y is} passed through each coil with current distribution as shown in FIG. 19, electrons moving from the back side to the front side of FIG. 19 are positive in the x direction, and electrons moving from the front side to the back side of the paper are It is deflected in the negative x direction. The voltage and current distribution of each electrode is optimized so that a uniform electromagnetic field is generated by an electromagnetic field calculation in which a potential or magnetic potential is applied to the actual electromagnetic pole shape. For example, α = 0.414 in the figure. Is set.

FIG. 20 is a cross-sectional view including the optical axis of the E × B deflector 4. When the E × B deflector is used as a beam separator, the crossing angle θ _IN between the irradiation system and the imaging system needs to be about 30 degrees in consideration of the arrangement relationship in which the two optical systems do not interfere with each other. In order to prevent the irradiated electron beam 101 from hitting the electromagnetic pole even if it is deflected by 30 °, the diameter of the opening must be made larger than the length of the electromagnetic pole, but if the opening is widened, the deflection voltage must be increased. Therefore, the shape of the electromagnetic pole 51 is a conical shape that spreads substantially along the electron trajectory. In addition, shield electromagnetic poles 54 are provided above and below the electromagnetic poles to suppress the bleeding of the electromagnetic field, and the electric field and the magnetic field act in the same space so that the Wien condition is always satisfied in the space. It was made to operate as a B deflector.

Next, a procedure for adjusting the irradiation electron beam 101 using the E × B deflector 4 will be described. The acceleration voltage V ₀ is constant conditions, since the ratio of the electromagnetic poles applied voltage V _X and the electromagnetic poles supply current I _Y satisfying the Wien condition is constant, V ₀ and the intensity ratio using techniques such as computer simulation Is obtained in advance and stored in the control computer 31. When the acceleration voltage V ₀ is input to the control computer 31, the control computer 31 applies V ₀ from the electron source application power source 21 to the electron source 1 and also applies the voltage V applied from the E × B deflector voltage power source 23 to the electromagnetic pole. Control is performed to make the intensity ratio of the current I _Y supplied to the electromagnetic pole from the current source 24 for _X and the E × B deflector constant. While keeping the intensity ratio of V _X and I _Y constant, V _X and I _Y are increased manually or automatically, the sample 7 is grounded, an ammeter is connected, and the irradiation electron beam with the acceleration voltage V ₀ the by measuring the current absorbed by irradiating the sample 7, the conditions electron beam irradiation reaches the sample 7, i.e. it is possible to determine the deflection angle theta _iN by E × B deflector 4 of electron beam irradiation.

Next, the control computer 31 sets the voltage applied to the sample 7 from the sample application power supply 27 through the stage holding the sample to a negative voltage that is substantially equal to or slightly higher than the acceleration voltage V ₀ of the electron beam. The irradiation electron beam is in a condition to change its direction immediately above the sample 7 to become a mirror electron beam. If the E × B deflector 4 has perfect Wien conditions for the reflected electron beam by the mirror electrons, the reflected electron beam travels straight through the E × B deflector 4 and the CCD camera 12 or the imaging system. Although it is detected by a detecting means such as a Faraday cup placed on the optical path, if no reflected electron beam is detected, the control computer 31 gives the intensity of V _X and I _{Y to} the E × B deflector 4. Fine adjustment with the ratio kept constant or control to change the ratio between the voltage V _X and the current I _Y while keeping θ _IN constant. The voltage increment ΔV and current increment ΔI when changing the ratio are

Control so that ε is approximately 1. By this adjustment, the irradiation electron beam enters the sample perpendicularly, and the conditions under which the reflected electron beam passes through the E × B deflector 4 and reaches the CCD camera 17 are determined.

Next, a method for forming the contrast of the reflected electron beam 102 using mirror electrons will be described. The reflected electron beam 102 forms a projection image of the sample 5 on the image plane 42 of the objective lens 5 and forms an electron diffraction image on the focal plane 41 of the objective lens. Since the reflected electron beam emitted in the same direction of the sample is focused on this electron diffraction image plane, the reflected electrons that do not have a potential distortion immediately above the sample and are not subjected to deflection in the lateral direction are focused near the optical axis. Therefore, if a limiting aperture is disposed at the focal plane position (electron beam diffraction image position) 41 of the objective lens and the aperture is shifted from the optical axis, electrons that are not subjected to deflection can be cut. Since it is almost cut, it is difficult to place the restriction aperture at this position. Here, since the reflected electron beam 102 is separated from the irradiation electron beam 101 by the E × B deflector 4, the limiting aperture 14 is disposed after the separation from the irradiation electron beam 101. That is, if the limiting aperture 14 is disposed at the position 43 where the electron beam diffraction image formed on the objective lens focal plane 41 of the reflected electron beam 102 is projected by the intermediate lens 8, a dark field that improves the contrast of the reflected electron beam image. Images and bright field images can be acquired. The shape of limiting aperture 14 is in the form shown in FIG. 12, are disposed a disk of a diameter 2r ₁ coaxially circular hole of diameter 2r _2. This disk is supported by a narrow bridge so that an electron beam in the range of radius r ₁ to radius r ₂ can pass as much as possible. The radius r ₁ of the disc of the limiting aperture 14 is selected so as to limit the mirror electron beam having a size that normally limits the mirror electrons reflected without being scattered, that is, the scattering electron beam having a scattering angle substantially equal to the irradiation angle for irradiating the sample. That's fine. Alternatively, a configuration in which only the scattered electron beam in a specific direction is allowed to pass through the limiting aperture 14 having a normal circular shape may be used.

As the imaging mode, the user can select a normal observation mode and a dark field mode. In the normal observation mode, the limiting aperture 14 is set outside the reflected electron beam path. However, when the user selects the dark field mode, the limiting aperture drive unit 15 sets the limiting aperture 14 on the reflected electron beam path. The The restriction aperture drive unit 15 is configured by a fine adjustment mechanism and an ancestor adjustment mechanism. The ancestor adjustment mechanism is a mechanism that moves the limiting aperture between the outside of the electron beam passage and on the passage. When the user selects switching of the observation mode, the control computer 31 instructs the ancestor adjustment mechanism to drive. The fine adjustment mechanism is a mechanism for finely adjusting the position of the stop when the user observes an image. The fine adjustment mechanism may be a mechanism that can be manually adjusted by a user. For example, as a configuration driven by a servo motor with a rotary encoder, the position address of the restriction aperture for each observation mode is stored in the control computer 31, thereby switching the observation mode. The aperture may be automatically set to the stored position address.
By acquiring a projection image that can selectively limit the scattering direction of the mirror electron beam with the apparatus configuration as described above, it is possible to perform mirror image observation with high contrast.

FIG. 2 shows a configuration for explaining the operation of the second embodiment. In this embodiment, the irradiation electron beam 101 is irradiated to the sample 7 with the irradiation angle inclined without changing the irradiation position, and the reflected electron beam reflected in the optical axis direction of the imaging system is obtained. A projection image with small off-axis aberration of the reflected electron beam is obtained. The irradiated electron beam 101 is deflected by the ExB deflector 4 from the optical axis 103 including the electron source in the direction of the optical axis 103 perpendicular to the sample at a deflection angle θ _IN , and then converges in the vicinity of the focal plane 41 of the objective lens to focus the sample 7. Parallel irradiation. The E × B deflector 4 as a separator is disposed in the vicinity of the imaging plane 42 of the reflected electron beam 102, and when the irradiation electron beam 101 is deflected by the angle θ _D by the E × B deflector 4, The light is incident at a deflection angle of angle _AP , refracted by the circular hole electrode 6 and decelerated by a deceleration electric field between the circular hole electrode 6 and the sample, and then irradiated to the same position on the sample. The relationship between θ _AP and θ _D is uniquely determined when the lens arrangement and operating conditions are determined, and are stored in the control computer 31. Further, under the condition where the acceleration voltage V ₀ is constant, the ratio of the electromagnetic pole applied voltage V _X and the electromagnetic pole supply current I _Y that satisfies the Wien condition is constant, so that V ₀ can be calculated using a method such as computer simulation. The relationship between the intensity ratios is obtained in advance and stored in the control computer 31.

When the acceleration voltage V ₀ is input to the control computer 31, the control computer 31 applies V ₀ from the electron source application power source 21 to the electron source 1 and also applies the voltage V applied from the E × B deflector voltage power source 23 to the electromagnetic pole. Control is performed to make the intensity ratio of the current I _Y supplied to the electromagnetic pole from the current source 24 for _X and the E × B deflector constant. The condition that the deflection angle of θ _IN is obtained by supplying the electromagnetic pole applied voltage V _X and the electromagnetic pole supply current I _Y to the X deflector and Y deflector of the E × B deflector 4, and the sample is irradiated vertically. It becomes. Here, when the sample is tilted and incident on the circular hole electrode 6 at a deflection angle of θ _AP , the control computer 31 causes the deflection angle θ _{D of the} E × B deflector 4 corresponding to the deflection angle of θ _AP. And an electromagnetic pole applied voltage V _X1 and an electromagnetic pole supply current I _Y1 that correspond to the deflection angle of the deflection angle angle θ _D and preserve the Wien condition, and supply them by superimposing on each electrode and coil. .

The reflected electron beam 102 forms an electron diffraction pattern corresponding to the sample exit direction on the focal plane 41 of the objective lens. However, if the limiting aperture 14 is disposed at this focal plane position, the irradiation electron beam 101 is limited. After the reflected electron beam 102 passes through the E × B deflector 4, the limiting aperture 14 is inserted at a position 43 where an electron beam diffraction image is projected by the intermediate lens 8. When the reflected electron beam 102 is deflected by the E × B deflector 4, the position of the electron beam diffraction image changes, but the E × B deflector 4 is different from the reflected electron beam 102 in the E × B deflector. Therefore, the reflected electron beam is not deflected by the E × B deflector 4 and is not deflected by the E × B deflector 4. A diffraction image can be projected.
By acquiring a projection image that can selectively limit the scattering direction of the mirror electron beam with the apparatus configuration described above, it is possible to perform image observation with low off-axis aberration and high contrast.

FIG. 3 shows a configuration for explaining the operation of the third embodiment. In the present embodiment, so-called hollow cone irradiation is performed in which the irradiation position of the irradiation electron beam 101 with respect to the sample 7 is not changed and the irradiation angle to the sample 7 is fixed.
The electrode supply voltage for deflecting the irradiation electron beam 101 in the X direction by the angle θ _D / 2 at the deflection electrode of the E × B deflector 4 is set to V _X, and the circular hole electrode 6 is deflected by the angle θ _AP for hollow cone irradiation. Assuming that the supply voltage for incidence at an angle is V _D , a deflection signal of V _X + V _D cos (t) and V _X sin (t) is applied to the Y deflector as shown in the X deflector as shown in FIG. Supply. Furthermore, also in the magnetic field generation, a sine wave for deflecting the angle θ _D / 2 in the deflection coil for generating the magnetic field so that the E × B deflector 4 always has a Wien condition with respect to the reflected electron beam. When the cosine wave signal is supplied, the irradiation electron beam can be irradiated while precessing on the sample 7 without changing the irradiation position. The reflected electron beam 102 forms an electron diffraction pattern on the objective lens focal plane 41. After the reflected electron beam 102 passes through the E × B deflector 4 without being deflected, a limiting aperture 14 is inserted at a position 43 where the electron beam diffraction image is projected by the intermediate lens 8, thereby dark field of the mirror electron microscope. An image can be obtained.
By acquiring a projection image that can selectively limit the scattering angle range of the mirror electron beam with the above-described apparatus configuration, it is possible to perform image observation with high off-axis aberration and high contrast.

The present embodiment shown in FIG. 4 has a configuration in which a mirror electron microscope is applied to high-speed wafer inspection.
The irradiation electron beam 101 emitted from the electron source 1 is converged by the condenser lens 3 and irradiated on the sample substantially in parallel. As the electron source 1, a Zr / O / W type Schottky electron source having a tip radius of about 1 μm was used. By using this electron source, a uniform planar electron beam having a large current beam (for example, 1.5 μA) and an energy width of 0.5 eV or less can be stably formed.

  As a separator, the E × B deflector 4 is disposed in the vicinity of the imaging surface of the reflected electron beam 102. The irradiation electron beam 101 is deflected to an optical axis perpendicular to the wafer 7 by the E × B deflector 4. The E × B deflector 4 has a deflecting action only on the electron beam from above. The electron beam deflected by the E × B deflector 4 is formed into a planar electron beam in a direction perpendicular to the sample (wafer) surface by the objective lens 5.

  Mirror electrons are used to detect defects. When the user sets the mirror electron microscope mode, a negative potential that is substantially equal to or slightly higher than the acceleration voltage of the electron beam is applied to the sample (wafer) 7 by the sample application power source 27, and the surface of the wafer 7 is applied to the surface. An electric field reflecting the shape of the formed semiconductor pattern and the charged state is formed. By this electric field, most of the planar electron beam is pulled back immediately before it collides with the wafer 7 and rises as mirror electrons with a direction and intensity reflecting the pattern information of the wafer 7.

  The mirror electrons change their trajectories due to distortion of the equipotential surface formed immediately above the sample. However, most of these mirror electrons can be used for image formation by adjusting the focus condition of the imaging lens. That is, if mirror electrons are used, an image with a high S / N ratio can be obtained, and shortening of the inspection time can be expected. However, in such image formation with the focus shifted, it is difficult to obtain information corresponding to the exact shape and position of the sample because it is very different from a general electron microscope image. Therefore, by providing the dark field mode of the mirror electron microscope, it is possible to form an image near the normal focal point, and information corresponding to the accurate shape and position of the sample can be obtained. When the dark field mode is set, the limiting diaphragm 14 is set on the imaging system optical path by the limiting diaphragm driving unit 15, and mirror electrons that are inverted without being laterally deflected on the equipotential surface immediately above the sample are converted by the limiting diaphragm 14. By absorbing it, it becomes possible to form an image only with the mirror electrons scattered from the defect portion, and a high-contrast defect detection image can be obtained. This image is converted into an electrical signal and sent to the image processing unit 61.

  The image processing unit 61 includes image signal storage units 62 and 63, a calculation unit 64, and a defect determination unit 65. The image storage units 62 and 63 store images of adjacent portions of the same pattern, and both the images are calculated by the calculation unit 64 to detect different locations of both images. The result is determined as a defect by the defect determination unit 65 and the coordinates are stored in the control computer 31. The captured image signal is displayed on the monitor 66 as an image.

  In the case of performing a pattern inspection between adjacent chips A and B having the same design pattern formed on the surface of the semiconductor wafer 7, first, an electron beam image signal for a region to be inspected in the chip A is captured. And stored in the storage unit 62. Next, an image signal for the inspection region corresponding to the above in the adjacent chip B is captured and stored in the storage unit 63, and at the same time, compared with the stored image signal in the storage unit 62. Further, an image signal for the corresponding inspected area in the next chip C is acquired and stored in the storage unit 62 by overwriting, and at the same time, the storage for the inspected area in the chip B in the storage unit 63 is stored. Compare with image signal. Such an operation is repeated, and comparison is performed while sequentially storing image signals for corresponding inspection regions in all inspection chips.

  In addition to the above method, it is also possible to adopt a method in which the electron beam image signal of a desired inspection region for a standard non-defective product (having no defect) is stored in the storage unit 62 in advance. In that case, the inspection area and the inspection conditions for the good product sample are input in advance to the control computer 31, the inspection for the good product sample is executed based on these input data, and the acquired image for the desired inspection region is obtained. The signal is stored in the storage unit 62. Next, the wafer 7 to be inspected is loaded on the stage, and the inspection is executed in the same procedure as before.

  The acquired image signal for the inspection region corresponding to the above is taken into the storage unit 63, and at the same time, the image signal for the sample to be inspected and the image signal for the good sample previously stored in the storage unit 62, Compare Thereby, the presence / absence of a pattern defect in the desired inspection region of the inspection object sample is detected. The standard (non-defective) sample may be a wafer that is known to be free of pattern defects in advance, different from the sample to be inspected, or may have no pattern defects in advance on the surface of the sample to be inspected. A known area (chip) may be used. For example, when a pattern is formed on the surface of a semiconductor sample (wafer), misalignment failure between the lower layer pattern and the upper layer pattern may occur over the entire wafer surface. In such a case, if the comparison object is a pattern in the same wafer or the same chip, the defect (defect) generated over the entire wafer surface is overlooked.

  However, according to this embodiment, the image signal of the area that is known to be non-defective (no defect) is stored in advance, and the stored image signal is compared with the image signal of the inspection target area. Such a defect that has occurred over the entire wafer surface can be detected with high accuracy.

Both image signals stored in the storage units 62 and 63 are taken into the calculation unit 64, where various statistics (specifically, average values of image density) are calculated based on the already determined defect determination conditions. , Statistics such as variance), difference values between neighboring pixels, and the like are calculated. Both image signals subjected to these processes are transferred into the defect determination unit 65, where they are compared and a difference signal between the two image signals is extracted. These difference signals are compared with the defect determination conditions that have already been obtained and stored, and defect determination is performed. The image signal of the pattern area determined to be a defect and the image signal of other areas are separated. The address of the defective portion is stored in the control computer 31.

With the apparatus configuration as described above, it is possible to acquire a defect image with a high contrast of the mirror electron beam projection image, and it is possible to realize high-speed wafer inspection with high defect detection sensitivity.
In the first to fourth embodiments, imaging of mirror electrons reflected without colliding with the sample as a reflected electron beam has been described. However, backscattered electrons scattered by colliding with the sample and electron beams with the sample are scattered. A dark field image can be acquired with substantially the same configuration even when secondary electrons generated secondary from the sample are imaged.

The figure which shows the structure of the mirror electron microscope which becomes the 1st Example of this invention. The figure explaining the structure of the 2nd Example of this invention. The figure explaining the structure of the 3rd Example of this invention. The figure explaining the structure of the 4th Example of this invention. The figure explaining the orbit of mirror electrons. The figure explaining the orbit of mirror electrons. The figure explaining the structure of a transmission electron microscope. The figure explaining the structure of a mirror electron microscope. The figure explaining the irradiation system of the principle of this invention. 1 is a diagram illustrating an imaging system according to the principle of the present invention. The figure explaining operation | movement of an E * B deflector. The figure explaining the structure of a restriction aperture. The figure explaining the irradiation system of the principle of this invention. 1 is a diagram illustrating an imaging system according to the principle of the present invention. The figure explaining the irradiation system of the principle of this invention. 1 is a diagram illustrating an imaging system according to the principle of the present invention. The figure explaining the voltage signal supplied to an ExB deflector. The figure explaining the voltage distribution of an 8-pole type ExB deflector. The figure explaining the current distribution of an 8-pole type ExB deflector. Sectional drawing of an 8-pole type ExB deflector.

Explanation of symbols

  1: electron source, 2: electron gun lens, 3: condenser lens, 4: E × B deflector, 5: objective lens, 6: circular hole electrode, 7: sample (wafer), 8: intermediate lens, 9: projection Lens: 10: Scintillator, 11: Optical fiber bundle, 12: CCD camera, 13: Monitor, 14: Restriction diaphragm, 15: Restriction diaphragm drive unit, 21: Electron source application power supply, 23: Voltage power supply for E × B deflector, 24 : Current supply for E × B deflector, 25: Objective lens power supply, 26: Circular electrode application power supply, 27: Sample application power supply, 28: Intermediate lens power supply, 29: Projection lens power supply, 30 :, 31: Control computer, 41 : Objective lens focal plane, 42: objective lens imaging plane, 43: electron diffraction image projection plane, 51: electromagnetic pole, 52: bobbin, 53: coil, 54: shield, 61: image processing unit, 62: image storage Section, 63: image storage section 64: operation unit, 65: defect determining section, 66: monitor, 101: electron beam irradiation, 102: reflected electron beam, 103: illumination system optical axis, 104: imaging system optical axis.

Claims (9)

An electron source applying means for applying an acceleration voltage to the electron source;
A sample voltage applying means for applying a sample voltage to a stage holding the sample;
Irradiation lens means for irradiating a sample with an electron beam emitted from the electron source as a planar irradiation electron beam having a two-dimensional spread;
Means for projecting and enlarging a sample image on a detector by projecting and enlarging a reflected electron beam emitted from the sample by irradiating the sample with the irradiation electron beam;
In a reflection imaging electron microscope provided with means for separating the irradiated electron beam and the reflected electron beam by a beam separator,
A reflection imaging electron microscope comprising a means for limiting an angle of the reflected electron beam when the sample is emitted between a beam separator for separating the irradiated electron beam and the reflected electron beam and the detector. An electron source,
A projection lens;
An intermediate lens,
An objective lens;
A sample stage for holding the sample;
Means for applying, to the sample stage or the sample, a voltage that reflects and reverses the direction of the electron beam emitted from the electron source without being incident on the sample;
Means for separating, by a beam separator, an electron beam radiated from the electron source to the sample and a reflected electron beam whose direction has been reversed without being incident on the sample;
A detector for detecting the reflected electrons,
A reflection imaging electron microscope comprising a stop for limiting an electron diffraction image of the reflected electron beam between the projection lens and the intermediate lens. An electron source,
A projection lens;
An intermediate lens,
An objective lens;
A sample stage for holding the sample;
Means for applying, to the sample stage or the sample, a voltage that reflects and reverses the direction of the electron beam emitted from the electron source without being incident on the sample;
Means for separating, by a beam separator, an electron beam radiated from the electron source to the sample and a reflected electron beam whose direction has been reversed without being incident on the sample;
A detector for detecting the reflected electrons,
A diaphragm for limiting an electron diffraction image of the reflected electron beam between the projection lens and the intermediate lens;
A limiting aperture driving unit for controlling the aperture to be movable;
A control computer for controlling the restriction aperture drive unit;
The reflection imaging electron microscope according to claim 1, wherein the limiting aperture driving unit includes means for switching an observation mode. The reflection imaging electron microscope according to any one of claims 1 to 3,
A reflection imaging electron microscope, wherein the beam separator is an E × B deflector in which an electric field and a magnetic field intersect. In the reflective imaging microscope according to any one of claims 1 to 3,
A reflection imaging electron microscope comprising: an image processing unit that performs image processing on a reflected electron beam image detected by the detector. In the reflection imaging electron microscope according to claim,
The image processing unit
A storage unit for storing a first reflected electron beam image in a first region of the sample detected by the detector and a second reflected electron beam image in a second region of the sample;
A computing unit for comparing the first reflected electron beam image and the second reflected electron beam image;
A reflection imaging electron microscope comprising a defect determination unit that determines a defect of the sample from the comparison result. 8. A reflection electron imaging electron microscope according to claim 1, further comprising a display unit for displaying the detected reflection electron beam image. The reflection imaging electron microscope according to claim 2, further comprising a limiting aperture driving unit that controls the aperture to be movable.
A reflection imaging electron microscope comprising a control computer for controlling the limiting aperture driving unit.   The exit angle when the reflected electron beam, including the mirror electron that has been reversed without being collided with the sample, is emitted from the sample after being separated from the irradiated electron beam by decelerating the electron beam emitted from the electron source and accelerated immediately before the sample. A method for observing a reflection imaging electron microscope, characterized in that sorting is performed based on the above.

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