JP5493029B2 - Charged particle beam application equipment - Google Patents

Description

  The present invention relates to a charged particle beam application apparatus using a charged particle beam, such as a charged particle beam inspection apparatus, a measurement apparatus, and a drawing apparatus.

  In a semiconductor or magnetic disk manufacturing process, a charged particle beam (hereinafter referred to as a primary beam) such as an electron beam or an ion beam is irradiated on a sample, and secondary charged particles such as secondary electrons generated (hereinafter referred to as a secondary beam). A charged particle beam length measuring device that acquires a signal of a beam) and measures the shape and dimensions of a pattern formed on a sample, a charged particle beam inspection device that checks the presence or absence of defects, and the like are used. As such a charged particle beam application apparatus, conventionally, a so-called SEM type apparatus that scans a sample with a primary beam focused in a dot shape is used. However, the SEM method has a problem that it takes a long time to acquire an image because the image is obtained by two-dimensionally scanning the primary beam. In order to improve the processing speed of the sample, that is, the inspection speed, there is another problem. This method is being studied.

  First, as a first approach, a multi-beam type charged particle beam application apparatus having a plurality of beams has been proposed. For example, in Patent Document 1, a plurality of beams formed by dividing an electron beam emitted from a single electron gun into a plurality of beams and converging them individually by lenses arranged in an array form a single optical A multi-beam type electron beam inspection apparatus that irradiates and scans a sample using an element is disclosed.

  FIG. 1 is a diagram schematically showing an electron optical system of a multi-beam type charged particle beam application apparatus. An electron source 101, a multi-beam forming unit 102, an objective lens 103, a scanning deflector 104, a sample 105, two Secondary electron detectors 106a to 106c and the like are arranged. The primary beam 107 emitted from the electron source 101 passes through the multi-beam forming unit 102 to become a plurality of (three in FIG. 1) primary beams, is individually focused, and a plurality of electron source images 108a, 108b, and 108c are formed. It is formed. A plurality of primary beams 107 pass through the objective lens 103, and project a plurality of electron source images 108a, 108b, 108c onto the sample 105 in a reduced scale. The scanning deflector 104 scans the sample 105 by deflecting a plurality of primary beams 107 that have become multi-beams by passing through the multi-beam forming unit 102 in substantially the same direction and at substantially the same angle. A plurality of primary beams 107 that have reached the surface of the sample 105 interact with substances near the sample surface, and secondary electrons such as reflected electrons, secondary electrons, and Auger electrons are generated from the sample, and a plurality of primary beams 107 are generated. The secondary beam 109 is detected by the secondary electron detectors 106a to 106c. In this way, the multi-beam type charged particle beam application device can obtain information on the sample several times faster than SEM by using multiple beams, and the inspection increases as the number of multi-beams increases. Speed can be improved.

  Here, since the multi-beam type apparatus uses a single optical element such as the objective lens 103, the central axis of the electron optical system among the primary beams 107 increases as the number of multi-beams increases. The number of beams passing through the orbit away from the (optical axis), that is, the off-axis orbit, increases, and the influence of off-axis aberration cannot be ignored. An off-axis trajectory is a trajectory that starts at a position away from the optical axis on the object plane of the electron optical system and reaches a position away from the optical axis on the image plane. It is an aberration generated by passing through an off-axis trajectory. Aberration means that the charged particle beam does not pass through the ideal position on the image plane, and the amount of the deviation, so if there is an influence of off-axis aberration, the charged particle beam will not be squeezed into a point shape on the sample and spread. Lead to degradation of resolution. Since the influence of off-axis aberrations increases as the off-axis distance from the optical axis increases, it is necessary to correct off-axis aberrations in order to achieve both inspection speed and resolution.

  Another approach is to propose a mapping-type charged particle beam application device that irradiates a primary beam over a wide area without focusing on the sample and projects the secondary beam signal onto a detector using an electron lens. Has been. Since the mapping type inspection apparatus can acquire images all at once without scanning the primary beam, it can inspect at high speed. For example, Patent Document 2 discloses a mapping type inspection apparatus that forms an image of reflected electrons and secondary electrons with an electron lens, and Patent Document 3 pulls back before colliding with a sample by a reverse electric field directly above the wafer. A mapping type inspection apparatus for detecting electrons, that is, mirror electrons, is disclosed. In order to improve the inspection speed in the mapping type apparatus, it is necessary to widen the area irradiated onto the sample at one time. Since the beam passing through the off-axis trajectory increases as the area increases, off-axis aberration becomes a problem even in the mapping type apparatus. As described above, in both multi-beam type charged particle beam application equipment and mapping type charged particle beam application equipment, in order to achieve the required inspection speed, it passes through an off-axis trajectory away from the center of the electron optical system. Therefore, it is necessary to correct off-axis aberrations in order to achieve both inspection speed and resolution.

  In the field of transmission and scanning electron microscopes, aberration correctors have been put into practical use, and it is becoming possible to observe images with higher resolution by correcting axial chromatic aberration and spherical aberration. For example, Patent Literature 4 and Patent Literature 5 disclose aberration correction means that utilize the negative chromatic aberration and aperture aberration of an electrostatic mirror.

  An aberration corrector that corrects not only axial aberrations such as aperture aberration and axial chromatic aberration but also off-axis aberrations has been proposed. For example, Patent Document 6 discloses an off-axis aberration correction unit that superimposes an octupole component while maintaining symmetry in an electron optical system including two seven-piece quadrupole subsystems. Further, Patent Document 7 proposes a charged particle beam application apparatus provided with an off-axis aberration correcting means as proposed in Patent Document 6.

JP 2007-317467 A JP 07-249393 A Japanese Patent Laid-Open No. 11-108864 Japanese Patent Laid-Open No. 05-205687 Special table 2004-519084 Japanese Patent Laid-Open No. 2003-187731 JP 2007-109531 A

  As described above, in both the multi-beam type charged particle beam application apparatus and the mapping type charged particle beam application apparatus, correction of off-axis aberration is indispensable in order to realize both inspection speed and resolution. However, as shown in Patent Document 6, the off-axis aberration correction means proposed so far needs to form a large number of multipole elements. For example, in the case of a twelve-pole, twelve power sources having very high voltage or current accuracy and stability are required per one electro-optic element, and this must be prepared by the number of multipoles. In addition, since misalignment correction cannot be realized unless the misalignment and design error of the multipole element are suppressed and the symmetry of the multipole field is sufficiently maintained, it is extremely difficult to adjust the voltage or current of each power supply, making it practical. There is a problem of lacking.

  In order to solve the above problems, for example, in the first embodiment of the present invention, in a multi-beam type charged particle beam application apparatus, an electrostatic mirror is arranged in an electron optical system, so that a multipole element that has been conventionally required An aberration correction means is provided in which the number of lens elements is reduced to about half. Furthermore, according to this means, it is possible to automatically create a multipole field maintaining symmetry, and therefore there is an advantage that adjustment becomes easy.

  Here, a representative charged particle beam application apparatus of the present invention will be described as follows.

  The present invention includes a charged particle source, a stage on which a sample is placed, an electrostatic mirror disposed in a path to a stage of a charged particle beam emitted from the charged particle source, and a charged particle source and an electrostatic mirror. The present invention relates to a charged particle beam application apparatus comprising: a path for the charged particle beam between the two and a path for the charged particle beam between the electrostatic mirror and a stage.

  Another aspect of the present invention provides a charged particle source, a stage on which a sample is placed, a charged particle optical system that irradiates the sample with a charged particle beam emitted from the charged particle source as a surface beam, A detector for detecting a secondary charged particle beam generated by collision of a surface beam, or a mirror charged particle beam pulled back without collision of the surface beam with the sample, and the secondary charged particle beam, or An electrostatic mirror disposed in a path to the mirror charged particle beam detector, a path of the secondary charged particle beam or the mirror charged particle beam between the stage and the electrostatic mirror, and an electrostatic mirror; The present invention relates to a charged particle beam application apparatus comprising: an aberration corrector that is common to both paths disposed in a path of the secondary charged particle beam or the mirror charged particle beam between a detector and a detector.

  In another aspect of the present invention, a charged particle source, a stage on which the sample is placed, a charged particle optical system that irradiates the sample with a charged particle beam emitted from the charged particle source, and the charged particle source emit the charged particle beam. An electrostatic mirror including a plurality of concentrically divided reflective electrodes arranged in a path to the stage of charged particle beam, and the charged particle beam is static in the path from the charged particle source to the stage. The present invention relates to a charged particle beam application apparatus reflected by an electric mirror.

  According to the present invention, it is possible to realize a charged particle beam application apparatus that can achieve both high defect detection sensitivity and high inspection speed. Further, according to the present invention, a charged particle beam application apparatus that can be easily adjusted can be realized.

The schematic diagram of a multi-beam type charged particle beam application apparatus. 1 is a schematic configuration diagram of a multi-beam type electron beam inspection apparatus according to a first embodiment. Schematic diagram of quadrupole field and octupole field intensity and reference trajectory for off-axis aberration correction. FIG. 3 is a schematic diagram of an electrostatic mirror, a multipole field strength, and a reference trajectory according to the first embodiment. 1 is a configuration diagram of an aberration corrector according to a first embodiment. FIG. FIG. 5 is a schematic configuration diagram of a multi-beam type electron beam inspection apparatus according to a second embodiment. The schematic diagram of the electrostatic mirror which concerns on a 2nd Example, multipole field intensity | strength, and a reference | standard trajectory. The figure regarding the structure and method of superimposing the electrostatic mirror field and multipole field which concern on a 2nd Example. FIG. 6 is a configuration diagram of an aberration corrector according to a second embodiment. The figure regarding the structure and method of superimposing the electrostatic mirror field and multipole field which concern on a 3rd Example. FIG. 6 is a schematic configuration diagram of a mapping type electron beam inspection apparatus according to a fourth embodiment. FIG. 9 is a schematic configuration diagram of a mapping type electron beam inspection apparatus according to a fifth embodiment. FIG. 10 is a schematic view of an electrode shape for forming a reflection potential of an electrostatic mirror according to a sixth embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, the same symbols are attached to the same elements, and the repeated explanation thereof is omitted. Hereinafter, although the Example in the inspection apparatus using an electron beam is shown, the effect of this invention is not lost also in the case of using an ion beam, and the case of a measuring device and a general electron microscope. In the embodiment, an example using an electron beam is shown. However, the present invention can be applied not only to electrons but also to charged particles. In this case, for each component name, electrons can be replaced with charged particles. That's fine.

  FIG. 2 is a diagram showing a schematic configuration of a multi-beam type electron beam inspection apparatus according to the first embodiment of the present invention.

  First, the apparatus configuration will be described. The electron gun 201 includes a cathode 202 made of a material having a low work function, an anode 205 having a high potential with respect to the cathode 202, and an electromagnetic lens 204 for superimposing a magnetic field on an acceleration electric field formed between the cathode and the anode. In this embodiment, a Schottky cathode that can easily obtain a large current and has stable electron emission is used. In the downstream direction in which the primary electron beam 203 is extracted from the electron gun 201, a multi-beam forming unit 102 and a beam separator 211 are arranged. In this embodiment, the multi-beam forming unit 102 includes a collimator lens 207, an aperture array 208 in which a plurality of openings are arranged on the same substrate, and a lens array 209 having a plurality of openings. In FIG. 2, the aberration corrector 212 and the electrostatic mirror 213 are arranged on the left side of the beam separator 211, the objective lens 214, the scanning deflecting deflector 215, and the stage 218 are arranged on the lower side of the beam separator 211, and two on the right side of the beam separator 211. The secondary electron detectors 223a to 223c are arranged. Further, a current limiting diaphragm, a primary beam center axis (optical axis) adjusting aligner, and the like are added to the electron optical system (not shown). The stage 218 moves with the wafer 217 placed thereon.

  A negative potential (hereinafter referred to as a retarding potential) is applied to the wafer 217 as will be described later. Although not shown, a wafer holder is interposed between the wafer 217 and the stage 218 in a conductive state, and a retarding power source 219a is connected to the wafer holder to apply a desired voltage to the wafer holder and the wafer 217. It is configured to do.

  A surface electric field control electrode 216 is provided on the electron gun direction side from the wafer 217. A scanning signal generator 237 is connected to the scanning deflector 215, and a surface electric field control power source 219b is connected to the surface electric field control electrode 216. Each part of the electron gun 201, collimator lens 207, lens array 209, beam separator 211, aberration corrector 212, electrostatic mirror 213, objective lens 214, retarding power supply 219a, and surface electric field control power supply 219b has an optical system control. The unit 239 is connected, and the system controller 235 is connected to the optical system controller 239. A stage controller 238 is connected to the stage 218, and secondary electron detectors 223a to 223c and a scanning deflection deflector 215 are also connected to the system controller 235 in the same manner. In the system control unit 235, a storage device 232, a calculation unit 233, and a defect determination unit 234 are arranged, and an image display device 236 is connected. Although not shown, it goes without saying that components other than the control system and the circuit system are disposed in the vacuum vessel and are evacuated to operate. Needless to say, a wafer transfer system for placing the wafer on the stage from outside the vacuum is provided.

  Next, wafer pattern inspection using this electron beam inspection apparatus will be described.

  The primary beam 203 emitted from the electron source 202 is accelerated in the direction of the anode 205 while receiving a focusing action by the electromagnetic lens 204 to form a first electron source image 206 (a point at which the beam diameter is minimized). Although not shown, a diaphragm is arranged in the electron gun 201 as often seen in a general electron gun so that an electron beam in a desired current range passes through the diaphragm. By changing the current, voltage, and the like applied to the anode 205 and the electromagnetic lens 204, it is possible to adjust the current amount of the primary beam passing through the stop to a desired current amount. Although not shown, an aligner for correcting the optical axis of the primary electron beam is disposed between the electron gun 202 and the collimator lens 207, and the center axis of the electron beam is shifted from the diaphragm or the electron optical system. The configuration can be corrected. Using the first electron source image 206 as a light source, the collimator lens 207 arranges the primary beam substantially in parallel. In the present embodiment, the collimator lens 207 is an electromagnetic lens. The aperture array 208 has a plurality of apertures, and the primary beam is divided into the number of beams that have passed through the apertures of the aperture array 208. In FIG. 2, three of them are shown. The divided primary beams are individually focused by the lens array 209 to form a plurality of second electron source images 210a, 210b, and 210c. The lens array 209 is composed of three electrodes each having a plurality of apertures, and acts as an Einzel lens on the primary beam passing through the apertures by applying a voltage to the central electrode among them. . In addition, the present applicant has previously proposed, for example, Japanese Patent Application Laid-Open Publication No. 2007-317467 “Charged Particle Beam Application Device” as a multi-beam type charged particle beam application device having a plurality of beams. The known lens array may be used.

  The primary beams 203 individually focused by the lens array 209 enter the beam separator 211. In this embodiment, the beam separator 211 is composed of a magnetic prism and has a function of deflecting and separating the incident beam and the outgoing beam trajectory by 90 degrees in the opposite directions, but in the case where the deflection direction and angle are different. However, the effect of the present invention is not lost. The effect of the present invention is not lost even when using a beam separator other than the magnetic prism, for example, a Wien filter that generates a magnetic field and an electric field orthogonal to each other in a plane perpendicular to the incident direction of the primary beam. .

  A plurality of second electron source images 210a, 210b, and 210c are formed on the incident surface of the beam separator 211 in order to avoid the occurrence of aberration due to the magnetic field prism. A primary beam 203 radiated from the upper side of FIG. 2 to the beam separator 211 is emitted to the left side of the page of FIG. 2, and a plurality of third electron source images corresponding to the plurality of second electron source images 210a, 210b, 210c. 220a, 220b, and 220c are formed on the exit surface of the beam separator 211. If the magnetic field prism reported in Adv. Imaging and Electron Physics (Ed. Hawkes), Vol. 120, 41, (2001) is used for the beam separator 211, not only the incident surface and the exit surface of the prism but also the path. An image is also formed at exactly half the position, and the trajectory is antisymmetric on the surface, so that aberration due to the prism separator can be avoided.

  After exiting the beam separator 211 and forming a plurality of third electron source images 220a, 220b, and 220c, the primary beam 203 enters the aberration corrector 212 and is applied to the electrostatic mirror 213. The primary beam 203 is reflected by the electrostatic mirror 213, passes through the aberration corrector 212 again, and enters the beam separator 211. For this reason, the primary beam 203 passes through the second recovery difference corrector 212 before and after reflection by the electrostatic mirror 213. Although details will be described later, the primary beam trajectory forms an equal-magnification electron optical system before and after passing through the aberration corrector 212, so that the fourth surface is located at the same position as the incident surface of the beam separator 211, that is, the third electron source image. The electron source images 220a, 220b, and 220c are formed.

  The primary beam 203 incident on the beam separator 211 again from the left side of FIG. 2 is emitted to the lower side of the sheet, and forms fifth electron source images 221a, 221b, and 221c on the emission surface. The objective lens 214 is an electromagnetic lens and projects the fifth electron source images 221a, 221b, and 221c in a reduced scale. The aberration generated in each element of the electron optical system is corrected by the effect of the aberration corrector 212, and the spread of the plurality of primary beams 203 reaching the sample wafer 217 is sufficiently large to satisfy the resolution required for inspection. It is squeezed small.

  The deflector 215 for scanning deflection is constructed and installed in an electrostatic octupole type in the objective lens. When a signal is input to the deflector 215 by the scanning signal generator 237, a plurality of primary beams 203 passing therethrough are deflected in substantially the same direction and at substantially the same angle, and raster scan the wafer 217.

  A negative potential is applied to the wafer 217 by the retarding power source 219a, and an electric field for decelerating the primary beam is formed. The retarding power source 219a and the surface electric field control power source 219b are other optical elements, that is, an electron gun 201, a collimator lens 207, a lens array 209, a beam separator 211, an aberration corrector 212, an electrostatic mirror 213, and an objective lens 214. Similarly, the system control unit 235 performs unified control via the optical system control unit 239. Stage 218 is controlled by stage controller 238. The system controller 235 controls the scanning signal generator 237 and the stage controller 238 in a unified manner to inspect a predetermined area on the wafer 217 for each stripe arranged in the stage traveling direction, and performs calibration in advance. . In the inspection apparatus according to the present embodiment, the stage is continuously moved when the inspection is executed, and the primary beam is controlled to sequentially scan the band-like region by a combination of deflection by scanning and stage movement. This band-like area is obtained by dividing a predetermined inspection area, and the entire predetermined inspection area is scanned by scanning a plurality of band-like areas.

  The plurality of primary beams 203 that have reached the surface of the wafer 217 interact with substances near the sample surface. As a result, secondary electrons such as reflected electrons, secondary electrons, Auger electrons, and the like are generated from the sample and become a secondary beam 222.

  The surface electric field control electrode 216 is an electrode for adjusting the electric field intensity near the surface of the wafer 217 and controlling the trajectory of the secondary beam 222. It is installed facing the wafer 217, and a positive potential, a negative potential, or the same potential is applied to the wafer 217 by the surface electric field control power source 219b. The voltage applied to the surface electric field control electrode 216 by the surface electric field control power source 219b is adjusted to a value suitable for the type of the wafer 217 and the observation target. For example, when it is desired to positively return the generated secondary beam 222 to the surface of the wafer 217, a negative voltage is applied to the surface electric field control power source 219b. Conversely, a positive voltage can be applied to the surface electric field control power source 219b so that the secondary beam 222 does not return to the surface of the wafer 217.

  After passing through the surface electric field control electrode 216, the secondary beam 222 is subjected to the focusing action of the objective lens 214, further deflected to the right side of FIG. 2 by the beam separator 211, and reaches the detectors 223a, 223b, and 223c. The secondary electron detection system 240 includes detectors 223a to 223c, an A / D converter 231, a storage device 232, a calculation unit 233, and a defect determination unit 234. In the defect determination unit 234, the detected signal is amplified by the amplification circuits 230a, 230b, and 230c, digitized by the A / D converter 231, and temporarily stored as image data in the storage device 232 in the system control unit 235. . Thereafter, the calculation unit 233 calculates various statistics of the image, and finally determines the presence / absence of a defect based on the defect determination condition previously determined by the defect determination unit 234. The determination result is displayed on the image display device 236. With the above procedure, the area to be inspected in the wafer 217 can be inspected in order from the end.

  In addition, this embodiment can be applied as a drawing apparatus by adding some changes. The main changes are the multi-beam forming unit 102 and the secondary electron detection system 240. In the case of application as a drawing apparatus, the multi-beam forming unit 102 requires a blanker array for individually turning on / off the electron beam downstream of the lens array 209. Further, the secondary electron detection system 240 can be applied to beam calibration and the like, but is not an essential mechanism.

  Next, details of the aberration corrector 212 and the electrostatic mirror 213 in FIG. 2 will be described with reference to FIGS.

First, a method for correcting off-axis aberration when there is no reflection by the electrostatic mirror will be described. FIG. 3 schematically shows quadrupole and octupole field strengths for correcting off-axis aberrations, and a reference trajectory in the aberration corrector. The reference trajectory expresses the space in a Cartesian coordinate system with three axes x, y, and z, the electron optical system optical axis is the z axis, and the off-axis distance from the optical axis is r (= sqrt (x ² + y ² )), the electron beam trajectory (on-axis reference trajectory) is emitted under the condition that the object surface is r = 0 and the trajectory slope dr / dz = 1 with respect to the optical axis, the object surface is r = 1, and the light This is the electron beam trajectory (off-axis reference trajectory) emitted under the condition of being parallel to the axis (dr / dz = 0). The electron beam trajectory is approximately represented by a second-order differential equation, the on-axis reference trajectory and the off-axis reference trajectory are two independent solutions of the equation, and all ideal trajectories are on-axis reference trajectories and It can be expressed by an off-axis reference trajectory.

  The aberration corrector is configured by disposing an electrostatic quadrupole, electrostatic octupole, and magnetic field quadrupole between two collimator lenses 301a and 301b. The strength of each electrostatic quadrupole field corresponds to 302a to n, and 14 electrostatic quadrupoles are used in FIG. Similarly, the strength of each electrostatic octupole field and the strength of each magnetic quadrupole field correspond to 303a to o (15 pieces) and 304a, b (2 pieces), respectively. When the quadrupole is arranged in the electron optical system, the trajectory of the electron beam is not rotationally symmetric, so it is necessary to consider two types of reference trajectories in the xy plane. Therefore, in the on-axis reference track 305 and the off-axis reference track 306, a is referred to as the x direction and b is referred to as the y direction, respectively.

  In order to correct aberrations, a concave lens is required. Since a rotationally symmetric electron lens cannot form a concave lens field, a multipole is used. Aberrations (geometric aberrations) that occur when each electron beam passes through different trajectories can be corrected by superimposing the quadrupole and octupole fields. Aberrations (chromatic aberration) caused by variations in the energy of the electron beam can be corrected by configuring the quadrupole field by both electrostatic and magnetic fields and changing the balance.

  Here, as described above, the reference trajectory needs to be considered in the x direction and the y direction. Since the electron optical system basically passes through a rotationally symmetric field outside the aberration corrector, the trajectory in the aberration corrector must pass through the same trajectory in the x and y directions. Therefore, the symmetry of the electrostatic quadrupole field strengths 302a to n, the electrostatic octupole field strengths 303a to o, and the magnetic field quadrupole field strengths 304a and 304b are important. In FIG. 3, each multipole field forms a symmetric or antisymmetric field with respect to the symmetry planes 307a to 307c. For example, in the region A indicated by the arrow, the electrostatic quadrupole field strength is 302a = 302g, 302b = 302f, 302c = 302e with the symmetry plane 307a as the boundary, and the electrostatic octupole field strength is also 303a = 303g. , 303b = 303f, 303c = 303e, forming a symmetric field. The same applies to the region B. Comparing regions A and B, the quadrupole field forms an antisymmetric field with respect to the plane of symmetry 307b for both electrostatic and magnetic fields. For example, the magnetic field quadrupole field strength has the opposite sign such that 304a = −304b. As for the electrostatic octupole field, a symmetric field is formed with respect to the symmetry plane 307b. By forming such a field in consideration of symmetry, the reference trajectory 305a on the x-direction axis and the reference trajectory 305b on the y-direction axis take a trajectory obtained by exchanging the trajectories with respect to the symmetry plane 307b. The same applies to the x-direction off-axis reference track 306a and the y-direction off-axis reference track 306b. Therefore, the configuration of the aberration corrector is basically the same-magnification electron optical system configuration.

  Next, the case where the aberration corrector and the electrostatic mirror in this embodiment are combined will be described. As described above, the off-axis aberration corrector has a plane of symmetry. If the electrostatic mirror is arranged at the position of the symmetry plane 307b in FIG. 3, the trajectory is reflected by the electrostatic mirror, traces the previous trajectory in the reverse direction, and passes through the symmetric field by the symmetric trajectory. Therefore, if the electrostatic mirror 213 is arranged after the area A in FIG. 3, the multipole field shown in FIG. 3 can be reduced to about half. Fig. 4 is a diagram schematically showing the multipole field intensity and the reference trajectory when the electrostatic mirror and the multipole field for correcting aberrations are combined. (B) shows after being reflected by the electrostatic mirror. In FIG. 4 (b), the same reference numerals as those in FIG. 4 (a) are used, and the reference numerals indicating the multipole field strength are indicated by “′”.

  The multipole field 410 in FIG. 4 (a) is a field that forms the aberration corrector 212 in FIG. 2, and is composed of a combination of a magnetic quadrupole field and an electrostatic octupole field. The electrostatic octupole field is the same as that arranged in the region A in FIG. 3 (electrostatic octupole field strength 303a to g). The magnetic quadrupole field strengths 404a to 404g are substantially the same as the electrostatic quadrupole field strengths 302a to 302g arranged in the region A in FIG. 3, and the magnetic quadrupole field strengths 404d are static in FIG. This is the intensity obtained by adding the electric quadrupole field intensity 302d to the magnetic quadrupole field intensity 304a. That is, the quadrupole field is formed by a magnetic field, and the octupole field is formed by static electricity. This is because the octupole field is symmetric and the quadrupole field is antisymmetric with respect to the symmetry plane 307b in FIG. Comparing the multipole fields in Figs. 4 (a) and (b), for example, the octupole field is 303a = 303a ', 303b = 303b', while the quadrupole field is 404a = -404a ', 404b = -404b ', the octupole fields are the same, and all quadrupole fields need to be reversed. Since the direction of the force applied to the charged particles by the magnetic field varies depending on the traveling direction of the charged particles, the intensity of the multipole field formed by the magnetic field is reversed between positive and negative with the reversal of the traveling direction of the electron beam. When the quadrupole field is composed of a magnetic field, the sign of the quadrupole field is reversed before and after reflection by the electrostatic mirror, that is, with the reversal of the traveling direction of the electron beam. This is the reason why the multipole field is composed of the electrostatic octupole field and the magnetic quadrupole field. As a result, as shown in FIGS. 4 (a) and 4 (b), the axial reference trajectories are the same trajectories for 405a and 405b ', and 405b and 405a'. Are the same orbit. The same applies to the off-axis reference trajectory.

  FIG. 5 shows the configuration of the aberration corrector 212 in this embodiment together with a schematic diagram of the electrostatic mirror 213. 5 is aligned with FIG. 2, the left and right sides of FIG. 4 are reversed. In FIG. 4, there are five cases where the positions of the magnetic quadrupole field and the electrostatic octupole field coincide with each other (for example, the magnetic quadrupole intensity 404a and the electrostatic octupole intensity 303a). There are two pole strengths and two electrostatic octupole strengths. In response, FIG. 5 includes five electrostatic octupole / magnetic quadrupoles 501a to 501e, two magnetic quadrupoles 502a and 502b, and two electrostatic octupoles 503a and 503b. The configuration of the electrostatic octupole / magnetic field quadrupoles 501a to 501e is such that the number of poles is 12, and the current and voltage may be adjusted so that the magnetic and electrostatic fields are quadrupole and octupole, respectively. , Electrically or magnetically insulated parts may be combined so that there are eight electrodes electrically and four magnetic poles magnetically.

  As described above, the geometric aberration is corrected by superimposing the octupole field on the quadrupole field, and the chromatic aberration is corrected by configuring the quadrupole field by both electrostatic and magnetic fields and changing the balance. In the configuration of FIG. 4, since the quadrupole field is configured only by a magnetic field, chromatic aberration cannot be corrected. In FIG. 4, it is necessary to arrange the octupole field intensity 303h in FIG. 3 at the position of the electrostatic mirror, which is difficult to arrange. The octupole field strength 303h in FIG. 3 is used to correct aperture aberration. Here, as a configuration of the electrostatic mirror, for example, the configuration shown in Adv. Imaging and Electron Physics (Ed. Hawkes), Vol. 120, 41, (2001). Is possible. If the configuration is such that chromatic aberration and aperture aberration are corrected by the electrostatic mirror 213 and other aberrations are corrected by the aberration corrector 212, almost all aberrations can be corrected. When correction of chromatic aberration and aperture aberration is not required, the configuration of the electrostatic mirror is a simpler configuration, for example, a configuration in which a voltage equivalent to the acceleration voltage of the electron beam is applied to one flat plate electrode. Even if it is the structure of an electrostatic mirror other than that, the effect of this invention is not lost.

  In the first embodiment, in the off-axis aberration corrector shown in FIG. 3, the electrostatic mirror is arranged at the position of the symmetry plane 307b. In contrast, in this embodiment, electrostatic mirrors are arranged at the positions of the symmetry planes 307a and c of the off-axis aberration corrector shown in FIG. 3, and the combination of the aberration corrector and the electrostatic mirror is arranged at two locations. Take the configuration.

  FIG. 6 is a schematic view of a multi-beam type electron beam inspection apparatus according to the second embodiment of the present invention. The arrangement of the electron gun 201, cathode 202, anode 205, electromagnetic lens, collimator lens 207, aperture array 208, and lens array 209 is rotated 90 degrees clockwise relative to the arrangement shown in FIG. In contrast, it is placed on the right side of the page in FIG. The configuration and function are the same as in FIG. In FIG. 6, the aberration corrector 601a and the electrostatic mirror 602a are located above the beam separator 211, the aberration corrector 601b and the electrostatic mirror 602b are located on the left side of the beam separator 211, the beam separator 603 and the objective are located below the beam separator 211. A lens 214, a scanning deflector 215, and a stage 218 are arranged. Further, secondary electron detectors 223a to 223c and the like are arranged on the right side of the beam separator 603.

  The aberration correctors 601a and 601b, the electrostatic mirrors 602a and 602b, and the beam separator 603 are connected to the optical system controller 239 in the same manner as other components. Since other configurations and their connections are the same as those in FIG. 2, their description is omitted here. The electron optical system is also provided with a current limiting diaphragm, an aligner for adjusting the central axis (optical axis) of the primary beam, and the like (not shown). Although not shown, it goes without saying that components other than the control system and the circuit system are disposed in the vacuum vessel and are evacuated to operate. Needless to say, a wafer transfer system for placing the wafer on the stage from outside the vacuum is provided.

  Since the wafer pattern inspection method using this electron beam inspection apparatus is substantially the same as that of the first embodiment, the differences from the first embodiment will be mainly described here. The primary beam 605 emitted from the electron gun 201 passes through the collimator lens 207, the aperture array 208, and the lens array 209 and is individually focused to form a plurality of second electron source images 604a, 604b, and 604c. Incident on the separator 211. Similar to the first embodiment, in this embodiment, the beam separator 211 is also composed of a magnetic prism and has a function of deflecting and separating the incident beam and the outgoing beam trajectory by 90 degrees in opposite directions. As described in the first embodiment, the effect of the present invention is not lost even when a magnetic prism having a different deflection direction or angle is used as the beam separator, or when a Wien filter or the like other than the magnetic prism is used. . A plurality of second electron source images 604a, 604b, and 604c are formed on the incident surface of the beam separator 211 in order to avoid the occurrence of aberration due to the magnetic field prism. In addition, although explanation with reference numerals is omitted, as extended in Example 1, each of the plurality of electron source images 604a, 604b, 604c formed on the incident surface of the beam separator 211 passes through the incident surface of the beam separator 211. And projection on the exit surface to avoid the occurrence of aberration by the beam separator 211.

  The primary beam 605 that is incident on the beam separator 211 from the right side of FIG. 6 is emitted to the upper side of the sheet, is incident on the aberration corrector 601a, and is irradiated on the electrostatic mirror 602a. The light is reflected by the electrostatic mirror 602a, passes through the aberration corrector 601a again, and enters the beam separator 211. The primary beam 605 that has entered the beam separator 211 again from the upper side of the paper is now emitted to the left side of the paper, similarly enters the aberration corrector 601b, is irradiated and reflected on the electrostatic mirror 602b, and passes again through the aberration corrector 601b. Then, the light enters the beam separator 211 and exits to the lower side of the drawing. Therefore, the primary beam 605 passes through the aberration correctors 601a and b twice each before and after reflection by the electrostatic mirrors 602a and b.

  The primary beam 605 emitted from the beam separator 211 is incident on the beam separator 603. The beam separator 603 is used for the purpose of separating the primary beam 605 and the secondary beam 606, and in this embodiment, generates a magnetic field and an electric field orthogonal to each other in a plane substantially perpendicular to the incident direction of the primary beam. The Wien filter is used to give the deflection angle corresponding to the energy of the passing electrons. In this embodiment, the strength of the magnetic field and electric field is set so that the primary beam goes straight, and the strength of the electromagnetic field is deflected to a desired angle with respect to the secondary electron beam incident from the opposite direction. Adjust and control. When considering the influence of the aberration generated by the Wien filter, the primary beam imaging plane, that is, the projection plane of the plurality of electron source images 604a, 604b, and 604c, should be arranged according to the height of the beam separator 603. preferable. For this purpose, one or more electromagnetic lenses or electrostatic lenses may be added between the beam separator 603 and the beam separator 211.

  In the present embodiment, when the generation of the secondary beam by the primary beam on the wafer 217 is included, there are three places where the direction of the electron beam is reversed. Since only one of the magnetic field prisms (beam separator 211) with a deflection angle of 90 degrees does not have enough space, a combination with the Wien filter (beam separator 603) is adopted, but other types are used. Even in this case, the effect of the present invention is not lost. For example, if a magnetic field prism having a deflection angle of 108 degrees is used, it is possible to take three electron beam reversal points with only one beam separator.

  As shown in Embodiment 1, after passing through the beam separator 603, the primary beam 605 is irradiated on the surface of the wafer 217, which is a sample, under the focusing action by the objective lens 214. The system controller 235 controls the scanning signal generator 237 and the stage controller 238 in a unified manner to inspect a predetermined area on the wafer 217 for each stripe arranged in the stage traveling direction, and performs calibration in advance. . In the inspection apparatus according to the present embodiment, the stage is continuously moved when the inspection is executed, and the primary beam is controlled to sequentially scan the band-like region by a combination of deflection by scanning and stage movement. This band-like area is obtained by dividing a predetermined inspection area, and the entire predetermined inspection area is scanned by scanning a plurality of band-like areas.

  The aberration generated in each element of the electron optical system is corrected by the effect of the aberration corrector 601a, b, and the spread of the plurality of primary beams 605 reaching the sample wafer 217 satisfies the resolution required for inspection. Squeezed sufficiently small.

  The secondary beam 606 generated from the wafer 217 is focused by the objective lens 214, and further deflected to the right side of FIG. 6 by the beam separator 603 and reaches the detectors 223a, 223b, and 223c. The electric field intensity adjustment by the surface electric field control electrode 216 and the processing of the detector signal are the same as in the first embodiment.

  In addition, this embodiment can be applied as a drawing apparatus by adding some changes. The main changes are the multi-beam forming unit 102 and the secondary electron detection system 240. In the case of application as a drawing apparatus, the multi-beam forming unit 102 requires a blanker array for individually turning on / off the electron beam downstream of the lens array 209. Further, the secondary electron detection system 240 can be applied to beam calibration and the like, but is not an essential mechanism.

  Next, details of the aberration correctors 601a and b and the electrostatic mirrors 602a and b in FIG. 6 will be described with reference to FIG. 3 and FIGS.

  As already described, in this embodiment, electrostatic mirrors are arranged at positions 307a and 307c on the symmetry plane of the aberration corrector in FIG. If an electrostatic mirror is placed at the position of the symmetry plane 307a in Fig. 3, the trajectory of the electron beam is reflected by the electrostatic mirror, traverses the previous trajectory in the reverse direction, and passes through the symmetric field with a symmetric trajectory. In addition, the number of multipole fields in the region A can be reduced to about half. In addition, when the electrostatic mirror is arranged at the position of the symmetry plane 307c, considering the trajectory of the electron beam emitted from the region A, the symmetrical field passes through the symmetrical trajectory, and the number of multipole fields in the region B is halved. Can be reduced to a certain extent. That is, the configuration for realizing the multipole field strength and the reference trajectory in the region A is the aberration corrector 601a and the electrostatic mirror 602a in FIG. 6, and the configuration for realizing the multipole field strength and the reference trajectory in the region B. These are the aberration corrector 601b and the electrostatic mirror 602b in FIG. Since the region A and the region B in FIG. 3 are symmetric or antisymmetric fields and orbits with the symmetry plane 307b as a boundary, it is sufficient to describe one of them. Therefore, hereinafter, only the region A, that is, the aberration corrector 601a and the electrostatic mirror 602a in FIG. 6 will be referred to.

  FIG. 7 is a diagram schematically showing the multipole field intensity and the reference trajectory when the electrostatic mirror and the multipole field for aberration correction are combined in the present embodiment. As described in the first embodiment, the multipole field may be formed by the electrostatic field when the multipole field is symmetric with respect to the symmetry plane, and by the magnetic field when the object is anti-object. In the symmetry plane 307a in FIG. 3, all the multipole fields and electron beam trajectories are symmetrical, so both the quadrupole field and the octupole field are electrostatic. That is, FIG. 7 shows that the multipole field constituting the aberration corrector has electrostatic quadrupole field strengths 302a to c and 703, electrostatic octupole field strengths 303a to d, and electrostatic mirror 602a and collimator lens 301a. An aberration corrector can be realized by combining the above. At this time, the electrostatic quadrupole field strength 703 is the strength obtained by adding the magnetic quadrupole field strength 304a to the electrostatic quadrupole field strength 302d in FIG.

  Here, the multipole for forming the electrostatic quadrupole strength 703 and the electrostatic octupole strength 303d needs to be arranged at the position of the electrostatic mirror 602a, but the quadrupole field is indispensable for the formation of the reference trajectory. Yes, the electrostatic quadrupole strength 703 cannot be omitted. Therefore, in this embodiment, the shape of the electrode that forms the reflected potential of the electrostatic mirror is divided into 12 poles, and the electrostatic mirror field and the multipole field are superimposed. FIG. 8 is a diagram relating to a configuration and method for superimposing an electrostatic mirror field and a multipole field. FIG. 8 (a) shows the shape of the electrode that forms the reflected potential of the electrostatic mirror 602a together with the x-axis and the y-axis. Normally, when a plurality of electrodes are arranged along the optical axis direction, different voltages are applied to the electrodes constituting the electrostatic mirror, but only one electrode is arranged at the same position on the optical axis. The voltage applied is one type. That is, it is general that the electrode for forming the reflected potential is also formed by one piece, and the applied voltage is only the reflected potential voltage. On the other hand, in the present embodiment, as shown in FIG. 8, the electrode that forms the reflected potential of the electrostatic mirror 602a is divided into 12 electrodes 801 to 812 and takes the shape of a dodecapole. Here, FIGS. 8 (b) to (d) show the voltages applied to the electrodes 801 to 812 broken down for each component, and (b) the reflected potential component and (c) the electrostatic quadrupole, respectively. Field component, (d) represents an electrostatic octupole field component. In order to have the effect of an electrostatic mirror, a reflection potential Vm is applied to all electrodes as shown in FIG. 8 (b). In order to form an electrostatic quadrupole field, an electrostatic quadrupole potential Vq is applied as shown in FIG. 8 (c). In order to form an electrostatic octupole field, an electrostatic octupole voltage Vo is applied as shown in FIG. 8 (d). If a voltage obtained by adding the components shown in FIGS. 8B to 8D is applied to each electrode, three fields can be superimposed. This is shown in FIG. 8 (e), and if the voltage shown here is applied to the electrodes 801 to 812 in FIG. 8 (a), it is possible to superimpose the electrostatic mirror field and the multipole field. Become.

  FIG. 9 shows the configuration of the aberration corrector 601a in this embodiment together with a schematic diagram of the electrostatic mirror 602a. Since the configuration of FIG. 9 is aligned with FIG. 6, the configuration is rotated 90 degrees counterclockwise compared to FIG. The aberration corrector 601a includes two electrostatic octupoles and electrostatic quadrupoles 901a and 901b, one electrostatic quadrupole 902, and one electrostatic octupole 903. The configuration of the electrostatic octupole / electrostatic quadrupole uses the field superposition method described in FIG. 8 to set the number of poles to 12 and adjust the voltage so that each field is quadrupole or octupole. This is possible.

  Here, as shown in FIG. 3, geometric aberration is corrected by superimposing an octupole field on the quadrupole field, and chromatic aberration is corrected by changing the balance of the quadrupole field that is composed of both electrostatic and magnetic fields. To do. In the configuration of FIG. 7, since the quadrupole field is configured only by static electricity, chromatic aberration cannot be corrected. Further, in FIG. 7, the octupole field intensity 303h for use in correcting the aperture aberration in FIG. 3 needs to be arranged at the position of the beam separator 211, which is difficult to arrange. Therefore, in the present embodiment as well as the first embodiment, if the configuration shown in, for example, Adv. Imaging and Electron Physics (Ed. Hawkes), Vol. 120, 41, (2001). It is possible to correct aberrations. If the chromatic aberration and the aperture aberration are corrected by the electrostatic mirrors 602a and 602b, and other aberrations are corrected by the aberration correctors 601a and b, it is possible to correct almost all aberrations. In the case where correction of chromatic aberration and aperture aberration is not necessary, the configuration of the electrostatic mirror may be a simpler configuration, and the effect of the present invention is not limited to other configurations of the electrostatic mirror. I will not lose.

  In the first embodiment, since the position of the electrostatic octupole field strength 303h in the off-axis aberration corrector in FIG. 3 coincides with the position of the electrostatic mirror 213, the electrostatic octupole field strength 303h corresponds to the electrostatic octupole field strength 303h. I did not place an octupole. In contrast, in the second embodiment, the positions of the electrostatic quadrupole field intensity 302d and the electrostatic octupole field intensity 303d in the off-axis aberration corrector in FIG. 3 coincide with the position of the electrostatic mirror 601a. The method of realizing the superposition of the multipole field and the electrostatic mirror field by devising the configuration of the electrostatic mirror 601a was shown. Therefore, in this embodiment, a method of superimposing the electrostatic octupole field intensity 303h on the electrostatic mirror 213 in the apparatus configuration of the first embodiment will be described. Since the present embodiment is the same as the first embodiment except for the configuration of the electrostatic mirror 213, only the configuration of the electrostatic mirror 213 and the field superposition method will be described. See Example 1 for other items.

  FIG. 10 is a diagram relating to a configuration and a method for superposing the electrostatic mirror field and the multipole field in the present embodiment. FIG. 10 (a) shows the shape of the electrode that forms the reflected potential of the electrostatic mirror 312 together with the x-axis and the y-axis. As described in the second embodiment, it is general that the electrode for forming the reflection potential of the electrostatic mirror is formed by one sheet, and the applied voltage is only the reflection potential voltage. On the other hand, in the present embodiment, as shown in FIG. 10, the electrode forming the reflected potential of the electrostatic mirror 312 is divided into eight electrodes 1001 to 1008 and takes the shape of an octupole. Here, FIGS. 10 (b) and 10 (c) show the voltages applied to the electrodes 1001 to 1008 in an exploded manner for each component, and (b) reflected potential component and (c) electrostatic octupole field, respectively. Represents an ingredient. In order to have the effect of an electrostatic mirror, a reflection potential Vm is applied to all electrodes as shown in FIG. 10 (b). In order to form an electrostatic octupole field, an electrostatic octupole voltage Vo is applied as shown in FIG. 10 (c). If a voltage obtained by adding the components shown in FIGS. 10B and 10C is applied to each electrode, two fields can be superimposed. This is shown in FIG. 10 (d), and if the voltage shown here is applied to the electrodes 1001 to 1008 in FIG. 10 (a), the electrostatic mirror field and the multipole field can be superimposed. Become.

  In this embodiment, the aberration corrector shown in the first or third embodiment is applied to a mapping type inspection apparatus.

  FIG. 11 is a diagram showing a schematic configuration of a mapping type electron beam inspection apparatus according to the fourth embodiment of the present invention.

  The electron gun 1101 includes a cathode 1102 made of a material having a low work function, an anode 1105 having a high potential with respect to the cathode 1102, and an electromagnetic lens 1104 for superimposing a magnetic field on an accelerating electric field formed between the cathode and the anode. In this embodiment, a Schottky cathode that can easily obtain a large current and has stable electron emission is used. A beam separator 211 is disposed in the downstream direction in which the primary electron beam 1103 is extracted from the electron gun 1101. In FIG. 11, the objective lens 1106 and the stage 1107 are disposed below the beam separator 211, the aberration corrector 212 and the electrostatic mirror 213 are disposed on the right side of the beam separator 211, and the projection lens 1108 and the detector 1109 are disposed above the beam separator 211. Is arranged and configured. Further, the electron optical system is also provided with a current limiting diaphragm, an aligner for adjusting the central axis (optical axis) of the primary beam, an aligner for adjusting the central axis (optical axis) of the secondary beam (not shown). . The stage 1107 moves with the wafer 217 placed thereon.

  A negative potential (hereinafter referred to as a retarding potential) is applied to the wafer 217 as will be described later. Although not shown, a wafer holder is interposed between the wafer 217 and the stage 1107 in a conductive state with the wafer, and a retarding power source 1110 is connected to the wafer holder to apply a desired voltage to the wafer holder and the wafer 217. It is configured to do.

  An optical system control unit 1130 is connected to each part of the electron gun 1101, beam separator 211, objective lens 1106, aberration corrector 212, electrostatic mirror 213, projection lens 1108, and retarding power supply 1110. Further, the optical system control unit 1130 Is connected to a system control unit 1131. A stage controller 1137 is connected to the stage 1107, and the detector 1109 is connected to the system controller 1131 through the detection signal processing circuit 1132. The system control unit 1131 is provided with a storage device 1133, a calculation unit 1134, and a defect determination unit 1135, and an image display device 1136 is connected thereto. Although not shown, it goes without saying that components other than the control system and the circuit system are disposed in the vacuum vessel and are evacuated to operate. Needless to say, a wafer transfer system for placing the wafer on the stage from outside the vacuum is provided.

  Next, wafer pattern inspection using this electron beam inspection apparatus will be described.

  The primary beam 1103 emitted from the electron source 1102 is accelerated in the direction of the anode 1105 while being focused by the electromagnetic lens 1104, and enters the beam separator 211. Although not shown, a diaphragm is arranged in the electron gun 1101 as often seen in a general electron gun, and an electron beam in a desired current range is configured to pass through the diaphragm. If the current, voltage, etc. applied to the anode 1105 and the electromagnetic lens 1104 are changed, the current amount of the primary beam passing through the aperture can be adjusted to a desired current amount. Although not shown, an aligner for correcting the optical axis of the primary electron beam is arranged between the electron gun 1102 and the beam separator 211, and the correction is made when the central axis of the electron beam is deviated from the diaphragm or the electron optical system. It can be configured.

  As in Examples 1 to 3, in this embodiment, the beam separator 211 is configured by a magnetic prism and has a function of deflecting and separating the incident beam and the outgoing beam trajectory by 90 degrees in the opposite directions. Even when the direction and angle are different, the effect of the present invention is not lost. Even when a beam separator other than the magnetic field prism, for example, a Wien filter that generates a magnetic field and an electric field orthogonal to each other in a plane perpendicular to the incident direction of the primary beam, the effect of the present invention is not lost.

  The primary beam 1103 incident on the beam separator from the left side of FIG. 11 is emitted to the lower side of the page, and an electron source image 1111 is formed on the front focal plane of the objective lens 1106. As a result, the primary beam 1103 is arranged substantially in parallel, and a wide area of the wafer 217 as a sample can be irradiated at a time.

  A negative potential is applied to the wafer 217 by the retarding power source 1110, and an electric field for decelerating the primary beam is formed. The retarding power supply 1110 is unified by the system control unit 1131 through the optical system control unit 1130 in the same manner as other optical elements, that is, the electron gun 1101, the beam separator 212, the objective lens 1106, the electrostatic mirror 213, and the projection lens 1108. Controlled. The stage 1107 is controlled by a stage control device 1137, and the system control unit 1131 controls the stage control device 1137 to inspect a predetermined area on the wafer 217 by one stripe arranged in the stage traveling direction. In addition, calibration is performed in advance.

  When the primary beam 1103 collides with the sample surface, it interacts with substances near the sample surface, secondary electrons such as reflected electrons, secondary electrons, Auger electrons are generated from the sample, and the secondary beam 1120 Become. Alternatively, the deceleration effect by the retarding potential can be strengthened, the primary beam 1103 can be pulled back without colliding with the sample surface, and the primary beam 1103 that has become mirror electrons can be used as the secondary beam 1120.

  The secondary beam 1120 is incident on the objective lens under the acceleration effect by the retarding power source 1110. By the lens action of the objective lens, a wafer projection surface 1121 is formed at the objective lens image plane position when the wafer is an object surface. In the mapping type inspection apparatus, inspection is performed by enlarging and projecting a wafer projection surface onto a detector.

  The secondary beam again enters the beam separator 211 after passing through the objective lens. The wafer projection surface 1121 is formed on the incident surface of the beam separator 211 in order to avoid the occurrence of aberration due to the magnetic field prism. A secondary beam 1120 radiated to the beam separator 211 from the lower side of the paper surface of FIG. 11 is emitted to the right side of the paper surface, and a wafer projection surface 1122 corresponding to the wafer projection surface 1121 is formed on the emission surface of the beam separator 211. If the magnetic field prism reported in Adv. Imaging and Electron Physics (Ed. Hawkes), Vol. 120, 41, (2001) is used for the beam separator 211, not only the incident surface and the exit surface of the prism but also the path. An image is also formed at exactly half the position, and the trajectory is antisymmetric on the surface, so that the aberration due to the prism separator can be canceled out.

  After exiting the beam separator 211 and forming the wafer projection surface 1122, the secondary beam 1120 enters the aberration corrector 212 and is irradiated onto the electrostatic mirror 213. The secondary beam 1120 is reflected by the electrostatic mirror 213, passes through the aberration corrector 212 again, and enters the beam separator 211. The secondary beam 1120 passes through the second recovery difference corrector 212 before and after reflection by the electrostatic mirror 213. An equal-magnification electron optical system is formed before and after passing through the aberration corrector 212, and a wafer projection surface is formed again on the incident surface of the beam separator 211. The secondary beam incident from the right side of FIG. 11 is emitted to the upper side of the paper surface, and forms a wafer projection surface 1123 on the emission surface. The wafer projection surface 1123 is enlarged and projected onto the detector 1109 by the projection lens 1108, and an enlarged projection image of the wafer is obtained. Note that the projection lens 1108 shown in FIG. 11 is assumed to be one electromagnetic lens, but for the purpose of increasing magnification or correcting image distortion, a plurality of electromagnetic lenses, one or a plurality of electrostatic lenses, or In some cases, it may be composed of such combinations.

  Due to the effect of the aberration corrector 212, the aberration generated in each element of the electron optical system is canceled, and a magnified projection image of the wafer that is clear enough to satisfy the resolution required for inspection can be acquired.

  The detector 1109 is configured by spatially distributing a plurality of detection devices corresponding to the number of pixels, such as a CCD camera and a TDI sensor. The enlarged projection image of the wafer is signal-detected by detection devices arranged at corresponding positions, and the signal is transmitted to the detection signal processing circuit 1132. After being temporarily stored as image data in the storage device 1133 in the system control unit 1131, the calculation unit 1134 calculates various statistics, and finally, based on the defect determination conditions previously determined by the defect determination unit 1135. Determine if there is a defect. The determination result is displayed on the image display device 1136. With the above procedure, the area to be inspected in the wafer 217 can be inspected in order from the end.

  As described above, the configurations and functions of the aberration corrector 212 and the electrostatic mirror 213 are the same as those in the first or third embodiment, and thus the description thereof is omitted here. See FIGS. 3, 4, 5, 9, and 10.

  In this embodiment, the aberration corrector shown in Embodiment 2 is applied to a mapping type inspection apparatus.

  FIG. 12 is a diagram showing a schematic configuration of a mapping type electron beam inspection apparatus according to the fifth embodiment of the present invention. The configuration and function of the electron gun 1101 are the same as those in FIG. A beam separator 1202 is disposed downstream of the electron gun 1101, and an object lens 1106 and a stage 1107 are disposed below the beam separator 1202. An intermediate lens 1201 is disposed above the beam separator 1202, and a beam separator 211 is disposed thereon. An aberration corrector 601a and electrostatic mirror 602a are arranged on the right side of the beam separator 211, an aberration corrector 601b and electrostatic mirror 602b are arranged on the upper side of the beam separator 211, and a projection lens 1108 and a detector 1109 are arranged on the upper side of the beam separator 211. Is configured.

  The aberration correctors 601a and b, electrostatic mirrors 602a and b, the intermediate lens 1201, and the beam separator 1202 are connected to the optical system controller 1130 in the same manner as other components. Since other configurations and their connections are the same as those in FIG. 11, description thereof is omitted here. The electron optical system is also provided with a current limiting diaphragm, an aligner for adjusting the central axis (optical axis) of the primary beam, and the like (not shown). Although not shown, it goes without saying that components other than the control system and the circuit system are disposed in the vacuum vessel and are evacuated to operate. Needless to say, a wafer transfer system for placing the wafer on the stage from outside the vacuum is provided.

  Since the wafer pattern inspection method using this electron beam inspection apparatus is substantially the same as that of the fourth embodiment, the differences from the fourth embodiment will be mainly described here. The primary beam 1203 emitted from the electron gun 201 is incident on the beam separator 1202. The beam separator 1202 is used for the purpose of separating the primary beam 1203 and the secondary beam 1204, and in this embodiment, generates a magnetic field and an electric field orthogonal to each other in a plane substantially perpendicular to the incident direction of the secondary beam. The Wien filter is used to give the deflection angle corresponding to the energy of the passing electrons. In this embodiment, the strength of the magnetic field and electric field is set so that the secondary beam travels straight, and the strength of the electromagnetic field is deflected to a desired angle with respect to the primary electron beam incident from the opposite direction. Adjust and control. In order to consider the influence of the aberration generated by the Wien filter, it is preferable to arrange the wafer projection surface 1121 of the secondary beam according to the height of the beam separator 1202. Details will be described later.

  The primary beam 1203 that has passed through the beam separator 1202 forms an electron source image 1111 on the front focal plane of the objective lens 1106 as in the fourth embodiment, and irradiates a wide area of the wafer 217 at a time. The stage 1107 is controlled by a stage control device 1137, and the system control unit 1131 controls the stage control device 1137 to inspect a predetermined area on the wafer 217 by one stripe arranged in the stage traveling direction. In addition, calibration is performed in advance.

  A secondary beam 1204 is generated and incident on the objective lens under the acceleration effect of the retarding potential. By the lens action of the objective lens, a wafer projection surface 1121 is formed at the objective lens image plane position when the wafer is an object surface. As described above, in order to avoid the influence of the aberration of the beam separator 1202, the wafer projection surface 1121 of the secondary beam is arranged according to the height of the beam separator 1202. As described in the fourth embodiment, the wafer projection surface is formed on the incident surface of the beam separator 211 in order to avoid the occurrence of aberration due to the magnetic prism. The intermediate lens 1201 adjusts the lens intensity to project the wafer projection surface 1121 onto the incident surface of the beam separator 211. In the present embodiment, the intermediate lens 1201 is assumed to be an electromagnetic lens, but the effect of the present invention is not lost even when an electrostatic lens is used.

  The secondary beam 1204 passes through the objective lens, the beam separator 1202, and the intermediate lens and enters the beam separator 211. The intermediate lens 1201 projects the wafer projection surface 1121, and the wafer projection surface 1205 is projected onto the incident surface of the beam separator 211. Form. Similar to the fourth embodiment, in this embodiment, the beam separator 211 is also composed of a magnetic prism and has a function of deflecting and separating the incident beam and the outgoing beam orbit by 90 degrees in opposite directions. As described in Example 4, the effect of the present invention is not lost even when a magnetic prism having a different deflection direction or angle is used as the beam separator, or when a Wien filter or the like other than the magnetic prism is used. . Although explanation with reference numerals is omitted, as extended in Example 4, the wafer projection surface 1205 formed on the incident surface of the beam separator 211 is projected onto the incident surface and the exit surface every time it passes through the beam separator 211. The generation of aberration due to the beam separator 211 is avoided. In the present embodiment, when the generation of the secondary beam by the primary beam on the wafer 217 is included, there are three places where the direction of the electron beam is reversed. Since only one of the magnetic prisms (beam separator 211) with a deflection angle of 90 degrees has insufficient space, a combination with the Wien filter (beam separator 1202) is adopted, but other types are used. Even in this case, the effect of the present invention is not lost. For example, if a magnetic field prism having a deflection angle of 108 degrees is used, it is possible to take three electron beam reversal points with only one beam separator.

  The secondary beam 1204 radiated to the beam separator 211 from the lower side of FIG. 12 is emitted to the right side of the paper, enters the aberration corrector 601a, and is irradiated to the electrostatic mirror 602a. The light is reflected by the electrostatic mirror 602a, passes through the aberration corrector 601a again, and enters the beam separator 211. The primary beam 605 that has entered the beam separator 211 again from the right side of the paper is now emitted upward on the paper surface, and similarly enters the aberration corrector 601b, is irradiated and reflected on the electrostatic mirror 602b, and passes again through the aberration corrector 601b. The light then enters the beam separator 211 and exits to the left side of the page. Accordingly, the secondary beam 1204 passes through the aberration correctors 601a and 601b twice before and after the reflection by the electrostatic mirrors 602a and 602b.

  The secondary beam 1204 emitted from the beam separator 211 passes through the projection lens 1108 and reaches the detector. At this time, the wafer projection surface 1123 is enlarged and projected onto the detector 1109 by the projection lens 1108 to obtain an enlarged projection image of the wafer. As in FIG. 11, the projection lens 1108 is assumed to be one electromagnetic lens, but may be constituted by a plurality of electromagnetic lenses, one or a plurality of electrostatic lenses, or a combination thereof.

  Due to the effects of the aberration correctors 601a and 601b, the aberration generated in each element of the electron optical system is canceled, and a magnified projection image of the wafer that is clear enough to satisfy the resolution required for inspection can be acquired. As in the fourth embodiment, the signal of the enlarged projection image of the wafer is transmitted from the detector 1109 to the detection signal processing circuit 1132, and the defect determination condition is passed through the storage device 1133, the calculation unit 1134, and the defect determination unit 1135 in the system control unit 1131. The presence or absence of defects is determined based on The determination result is displayed on the image display device 1136.

  As described above, the configurations and functions of the aberration correctors 601a and b and the electrostatic mirrors 602a and b are the same as those in the second embodiment, and thus the description thereof is omitted here. See FIGS. 3, 6, 7, and 8.

  In Example 1, since a general electrostatic mirror is applicable, details regarding the configuration of the electrostatic mirror are not described. In Examples 2 to 5, as shown in FIGS. 8 and 10, reflection of the electrostatic mirror is performed. The structure in which the electrode forming the potential is divided and the electrostatic mirror field and the multipole field are superimposed is described. In the present embodiment, a description will be given of a configuration in which electrodes that form the reflected potential of the electrostatic mirror are concentrically divided and arranged as a plurality of electrodes.

  FIG. 13 shows a schematic diagram of the electrode shape for forming the reflection potential of the electrostatic mirror. FIG. 13 (a) is a schematic diagram of a conventional configuration. When an electrostatic mirror is used as an aberration corrector, an electrode 1301 that forms a reflected potential, a power supply for reflected voltage 1310 that is applied to the electrode 1301, and an electrode 1301 A state of the equipotential surface 1302 formed in the vicinity is shown by a zx plan view (or a zy plan view). In order for the electrostatic mirror to function as an aberration corrector, the reflecting surface of the electrostatic mirror needs to act as a concave mirror. For this reason, the equipotential surface 1302 needs to be concave with a potential repelling charged particles.As shown in FIG.13 (a), the electrode 1301 has a concave shape, and the reflected voltage power source 1310 is negative. Apply voltage. For example, Adv. Imaging and Electron Physics (Ed. Hawkes), Vol. 120, 41, (2001) describes that the surface shape of the electrode forming the reflected potential is concave.

  On the other hand, the electrode shape for forming the reflection potential of the electrostatic mirror in the present embodiment is configured such that a plurality of concentric electrodes are arranged on a plane. FIG. 13 (b) shows a schematic diagram in the xy plane, and FIG. 13 (c) shows a schematic diagram in the z-x or zy plane. FIG. 13 (c) also shows an equipotential surface 1302 '. In this embodiment, the electrodes (reflecting electrodes) for forming the reflection potential of the electrostatic mirror are three electrodes 1303 to 1305, and in order to individually apply a voltage to each electrode, the reflection voltage power supplies 1311 to 1313 are provided. Connecting. In order to make the equipotential surface concave, the outer side becomes higher negative voltage than the center, so that the intermediate electrode 1304 and the external electrode 1305 proceed to the outside rather than the voltage applied to the center electrode 1303. The output voltage of the reflected voltage power supplies 1311 to 1313 is set so that the applied voltage becomes higher as the applied voltage increases. Accordingly, the equipotential surface 1302 'can have the same shape as the equipotential surface 1302 in FIG. Further, in the single electrode 1301 having the physical concave shape described above, the correction amount of the aberration is determined by the curvature of the concave surface and a single potential, whereas in the electrostatic mirror of the present invention, the concentric circle is formed. Since the effective concave curvature can be arbitrarily set by the plurality of divided electrodes 1303 to 1305, the correction amount of aberration can be controlled. Furthermore, if the concentric electrodes shown in FIGS. 13 (b) and 13 (c) are produced by masking and exposure, for example, an electrode with a high degree of coaxiality can be easily produced, and the adjustment of the electrostatic mirror is simplified.

  Next, the configuration of the charged particle beam application apparatus using the electrostatic mirror according to the present invention will be described. In Examples 2 to 5 described so far, aberration correction that enables correction of off-axis aberrations has been described, but for the present invention, on-axis aberrations different from off-axis aberrations, that is, spherical aberration and on-axis chromatic aberration An apparatus that makes it possible to correct the above will be described. Here, the multi-beam type electron beam inspection apparatus in FIG. 2 will be described as an example. The electron beam inspection apparatus using the electrostatic mirror according to the present invention is not only a multi-beam type electron beam inspection apparatus as shown in FIG. The present invention can also be applied to an electron beam apparatus using a primary electron beam. Hereinafter, differences from FIG. 2 will be described.

  In FIG. 2, the multi-beam forming unit 102 is arranged. In this electrostatic mirror, the multi-beam forming unit 102 is not required, and the electron beam is incident on the beam separator 211 without being divided into a plurality of parts. And In this case, a focusing lens for focusing the primary electron beam may be provided instead of the multi-beam forming unit 102. In this case, since the primary electron beam emitted from the beam separator 211 is a primary electron beam that does not substantially include an off-axis trajectory, the aberration corrector 212 is not necessary. As the electrostatic mirror 213, the electrostatic mirror having the above-described configuration is used. The center electrode 1303, the intermediate electrode 1304, and the external electrode 1305 are connected to the optical system control unit 239, and each electrode is controlled by the optical system control unit 239. Since the electrostatic mirror has a function of correcting axial aberration, that is, spherical aberration and axial chromatic aberration, the primary electron beam is reflected by the electrostatic mirror to correct spherical aberration and axial chromatic aberration. be able to. The reflected primary electron beam re-enters the beam separator 211 and irradiates the wafer. In addition, although it demonstrated by the structure which passes the beam separator 211 twice, it is not limited to this embodiment, You may use two beam separators so that it may inject into each one another beam separator, The configuration may be such that one beam separator is used and passes only once before entering the electrostatic mirror or before reflection. In other words, the beam separator is used for the primary electron beam to reach the wafer from the electron source via the electrostatic mirror, and if this path is followed, how the beam separator is arranged. It doesn't matter. Further, there may be a plurality of secondary electron detectors 223a to 223c of the secondary electron detection system 240, but at least one secondary electron detector is sufficient.

  In this embodiment, an example applied to an electron beam apparatus using a general single primary electron beam has been described. However, the electrostatic mirrors in Examples 1 to 5 (the electrostatic mirror 213 and the electrostatic mirrors 602a and 602b) are described. By applying the electrostatic mirror according to the present embodiment as either or both of them, it is possible to correct axial aberrations, that is, spherical aberration and chromatic aberration.

  In the present embodiment, the number of concentric electrodes is three, but the effect of the invention is not lost even when the number of electrodes varies. That is, it is sufficient if the number of electrodes is two or more. FIG. 13 (b) shows the configuration of the part that mainly contributes to the reflection of the primary electron beam of the electrostatic mirror, and the configuration of FIG. If included, the electrostatic mirror may have a configuration not shown.

  In the various embodiments described in detail above, examples related to the inspection using an electron beam have been shown. However, in the case of using an ion beam, the present invention is applicable to a general electron microscope such as a measuring device or a drawing device. The effect of is not lost. In the embodiments described above, the wafer is taken as an example of the sample to be observed. However, in the case where the wafer is a part of the wafer or a structure other than a semiconductor such as a magnetic disk or a biological sample. However, the effect of the present invention is not lost.

DESCRIPTION OF SYMBOLS 101 ... Electron source, 102 ... Multi-beam formation part, 103 ... Objective lens, 104 ... Scanning deflector, 105 ... Sample, 106a-c ... Secondary electron detector, 107 ... Primary beam, 108a-c ... Electron source image 109 ... multiple secondary beams, 201 ... electron gun, 202 ... cathode, 203 ... primary electron beam, 204 ... electromagnetic lens, 205 ... anode, 206 ... first electron source image, 207 ... collimator lens, 208 ... Aperture array, 209 ... lens array, 210a-c ... second electron source image, 211 ... beam separator, 212 ... aberration corrector, 213 ... electrostatic mirror, 214 ... objective lens, 215 ... deflector for scanning deflection, 216 ... surface electric field control electrode, 217 ... wafer, 218 ... stage, 219a ... retarding power supply, 219b ... surface electric field control power supply, 220a-c ... third / fourth electron source image, 221a-c ... fifth electron source Image, 222 ... secondary beam, 223a-c ... secondary electron detector, 230a-c ... amplification circuit, 231 ... A / D converter, 232 ... storage device, 233 ... arithmetic unit, 234 Defect determination unit, 235 ... system control unit, 236 ... image display device, 237 ... scanning signal generator, 238 ... stage control device, 239 ... optical system control unit, 240 ... secondary electron detection system, 301a-b ... collimator Lens, 302a-n: Electrostatic quadrupole field strength, 303a-o: Electrostatic octupole field strength, 304a, b: Magnetic quadrupole field strength, 305a ... x-axis on-axis reference trajectory, 305b ... y-axis on-axis reference Orbit, 306a ... x-axis off-axis reference orbit, 306b ... y-direction off-axis reference orbit, 307a-c ... symmetric plane, 404a-g ... magnetic quadrupole field strength, 405a ... x-axis on-axis reference orbit, 405b ... y-direction On-axis reference trajectory, 406a ... x-axis off-axis reference trajectory, 406b ... y-direction off-axis reference trajectory, 410 ... multipole field, 501a-e ... electrostatic octupole / magnetic quadrupole, 502a, b ... magnetic quadrupole, 503a, b ... electrostatic octupole, 601a, b ... aberration corrector, 602a, b ... electrostatic mirror, 603 ... beam separator, 604a-c ... second electron source image, 605 ... primary beam, 606 ... secondary Beam, 703 ... Electrostatic quadrupole field 801 to 812 ... Electrode, 901a, b ... Electrostatic octupole and electrostatic quadrupole, 902 ... Electrostatic quadrupole, 903 ... Electrostatic octupole, 1001 to 1008 ... Electrode 1101 ... Electron gun, 1102 ... Cathode, 1103 ... Primary electron beam, 1104 ... Electromagnetic lens, 1105 ... Anode, 1106 ... Objective lens, 1107 ... Stage, 1108 ... Projection lens, 1109 ... Detector, 1110 ... Retarding power source, 1111 ... Electron source image, 1120 ... Secondary Beam, 1121 ... Wafer projection surface, 1122 ... Wafer projection surface, 1123 ... Wafer projection surface, 1130 ... Optical system control unit, 1131 ... System control unit, 1132 ... Detection signal processing circuit, 1133 ... Storage device, 1134 ... Calculation unit, DESCRIPTION OF SYMBOLS 1135 ... Defect determination part, 1136 ... Image display apparatus, 1137 ... Stage control apparatus, 1201 ... Intermediate lens, 1202 ... Beam separator, 1203 ... Primary beam, 1204 ... Secondary beam, 1205 ... Wafer projection surface, 1301 ... Electrode, 1302 ... equipotential surface, 1303 ... center electrode, 1304 ... intermediate electrode, 1305 ... external electrode, 1310 ... power supply for reflected voltage, 1311-1313 ... Power supply for reflected voltage, 303a '... Electrostatic octupole field strength, 303b' ... Electrostatic octupole field strength, 404a '... Magnetic quadrupole field strength, 404b' ... Magnetic quadrupole field strength, 405a '... x-axis on-axis reference track, 405b '... y-direction on-axis reference track, 406a' ... x-direction off-axis reference track, 406b '... y-direction off-axis reference track, 1302' ... equipotential surface.

Claims (2)

A charged particle source;
A stage on which a sample is placed;
A charged particle optical system for irradiating the sample with a charged particle beam emitted from the charged particle source;
An electrostatic mirror including a plurality of concentrically divided reflective electrodes disposed in a path to the stage of the charged particle beam emitted from the charged particle source,
The charged particle beam application apparatus, wherein the charged particle beam is reflected by the electrostatic mirror along a path from the charged particle source to the stage. The charged particle beam application apparatus according to claim 1,
Furthermore, an optical system control unit that controls a voltage applied to the plurality of electrodes is provided, and the optical system control unit draws a high negative voltage from the central electrode toward the outer electrode among the plurality of electrodes. A charged particle beam application apparatus characterized in that the voltage of each electrode is controlled to be applied.

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