JP5372445B2 - Scanning electron microscope apparatus and focusing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that in order to realize an electron optical system in which a surface electric field control electrode is installed and a primary electron beam diameter is reduced, the surface electric field control electrode needs to be adjacent to a wafer, and for that reason, it becomes impossible to carry out height detection for focusing. <P>SOLUTION: A height measurement position is shifted from a primary electron irradiation position, and a height correction mechanism is installed to correct height shift due to differences of horizontal position of the height measurement position, the primary electron irradiation position, and time. Moreover, in order to minimize amount of shift, a shield plate having the same potential as that of the wafer is placed at the surrounding of the surface electric field control electrode, and height measurement is carried out by installing a light path at the plate. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a scanning electron microscope (hereinafter referred to as SEM) that irradiates an industrial product, particularly a semiconductor that is being manufactured in a semiconductor pre-process, by irradiating a focused electron beam and detecting electrons emitted from the irradiation position. Scanning Electron Microscope) equipment, especially SEM semiconductor wafer inspection equipment and SEM semiconductor pattern measuring equipment that need to take high-magnification images, observe defects detected in semiconductor wafers in more detail, and The present invention relates to a semiconductor inspection / review apparatus and a measuring apparatus for performing a more detailed inspection based on defects output from the inspection apparatus.

  With the miniaturization of semiconductors, it becomes increasingly difficult to control the semiconductor pre-process manufacturing process. When the semiconductor exposure process becomes a node of 45 nm or less, defects of 25 nm or less cause electrical defects. Therefore, it is necessary to take an image of the surface of the semiconductor wafer with very high precision and detect the appearance defect or measure the pattern width. For this purpose, SEM (Scanning Electron Microscope) inspection, review, and pattern length measurement are important in place of the conventional optical appearance inspection and length measurement. In devices equipped with these SEMs, the inspection object is irradiated with an electron beam, secondary electrons or reflected electrons emitted from the inspection object are collected and imaged, and a high resolution image compared with an optical system. Can be obtained. In addition, since the secondary electrons to be detected increase and decrease under the influence of the potential of the inspection target, the electrical characteristics of the imaging target can be visualized.

  Since the work distance of the SEM and the object to be imaged is not constant due to the warpage of the semiconductor wafer itself on the wafer surface, primary electrons cannot be obtained on the object to be imaged as it is. Therefore, Patent Document 1 describes that the surface height of a wafer is obtained with a height measuring instrument, and the focus of the SEM is set in accordance with the height position.

  The S / N of the captured image largely depends on the product of the number of primary electrons irradiated to the object and the secondary electron yield of the imaged object. Therefore, in order to obtain a high S / N image in a short time, the primary electron is used. It is necessary to increase the number of electrons to be given, that is, to increase the probe current. However, if this is done, a large number of secondary electrons are emitted from the object to be imaged in a short time, so that the sample surface is positively charged and the trajectory of the secondary electrons emitted from the sample surface is bent, or the image is captured. The electrical characteristics of the target cannot be visualized.

  For the purpose of preventing this, Patent Document 2 describes that a lower lens pole piece capable of changing a voltage relative to the wafer is installed at a location closest to the SEM wafer. By controlling this lower lens pole piece, only the secondary electrons having energy exceeding the potential generated by the electric field formed by the electrode and the wafer among the secondary electrons generated on the wafer surface are detected by the SEM detector. The charged potential of the wafer can be controlled by guiding other electrons back to the wafer.

  By combining the above two conventional techniques, it is possible to configure a practical SEM type inspection / measurement apparatus capable of focusing the SEM without being affected by the warp of the wafer and controlling the charging.

  In addition, in order to capture an SEM image with higher speed and higher resolution, a publicly known example is shown in which a plurality of electron beams are irradiated simultaneously and each of these beam spots is detected independently (Patent Document 3). In this conventional example, a hole for transmitting light for height measurement is made in the surface electric field control electrode provided for the same purpose as the lower lens pole piece of Patent Document 1 at the location closest to the electron optical system wafer. It was.

Japanese Patent Laid-Open No. 11-149895 Japanese Patent No. 3730263 JP 2007-317467 A

  In recent years, miniaturization of inspection and measurement objects has demanded SEM for higher resolution imaging. For this purpose, the SEM needs to make the beam diameter, which is the converged diameter of the primary electrons on the wafer surface, as small as possible.

  However, the lower lens pole piece having the configuration described in Patent Document 1 or the surface electric field control electrode described in Patent Document 3 (because they have almost the same effect, the surface electric field control electrode is unified below), the wafer If the potential is set to the same level as or lower than that of the wafer so that the positive charging of the laser beam does not progress, there arises a problem that the beam diameter increases.

  For example, the spread of electrons due to the Coulomb force repelling the beam on the orbit, which is a problem when the SEM aberration of diffractive aberration or chromatic aberration, or the current of the primary electron beam is large, closely affects the velocity of the electron in the electron orbit. Therefore, it is necessary to irradiate the imaging target with electrons as fast as possible.

  However, if the lower electrode piece is set to a potential equal to or lower than that of the wafer, the electron flight speed is rapidly lost, and the beam diameter increases.

  Furthermore, in the example described in Patent Document 3, if the surface electric field control electrode is set to substantially the same potential as the wafer potential or a negative potential, primary electrons irradiated to a plurality of locations cannot be separated and detected. .

  In order to minimize the increase in beam diameter, it is necessary to place the surface electric field control electrode as close as possible to the wafer and minimize the section where electrons fly at a low speed. Actually, in the known example of Patent Document 3, the distance between the surface electric field control electrode and the wafer is as close as 300 μm. However, with such a configuration, the diameter of the electron beam increases.

  In general, in order to reduce the beam diameter, it is advantageous to use a semi-in-lens type electron lens that forms a strong magnetic field up to the wafer surface, but this lens takes the form of leaking a strong magnetic field to the lower part of the objective lens. Therefore, the magnetic path for passing the magnetic field cannot be designed compactly. For this reason, even if a hole is made in the surface electric field control electrode and an optical path for height detection is provided, if the hole is opened at a location close to the wafer in the magnetic path, the aberration of the objective lens increases. You can't do this.

  In addition, when an optical path is set near the beam optical axis of the surface electric field control electrode, there is a problem that the uniformity of the electric field is lost and aberration is increased. In particular, this problem becomes a big problem when the slit light is irradiated for the height detector.

  This is because a large opening is required to irradiate the slit light, and the uniformity of the electric field is greatly destroyed. For example, when the slit height of the wafer height variation is ± 40 μm and the slit light having a length of 1 mm has an incident angle of 80 degrees with respect to the normal line of the wafer, two apertures exceeding 1 mm × 500 μm at the minimum are close to the optical axis. The surface electric field cannot be controlled.

  On the other hand, when the height is detected with one spot light, the error is 1/2 of the beam diameter at worst due to the influence of the reflectance of the target at the spot irradiation position. For this reason, height measurement with one beam spot is impossible with highly accurate and stable inspection and measurement, and it is necessary to use slit light, and preferably a plurality of slit lights. The large aperture required for this and high-resolution SEM imaging are not compatible.

In order to solve the above problems, in the present invention, a surface electric field control electrode or a shield electrode whose height from the wafer provided around the surface electric field control electrode is the same as that of the surface electric field control, or between the two electrodes. In addition, an optical path for height measurement is provided asymmetrically with respect to the optical axis at a position more than a certain distance from the optical axis of the electron optical system, and height measuring means for measuring the wafer height using this optical path is provided. It was.
Further, a memory means for holding the wafer height output from the height measuring means and a wafer position measuring means for measuring the position of the wafer are provided, and the focus position of the SEM is determined based on the wafer surface height on the electron beam optical axis measured in advance. Added control. In addition, based on the wafer surface height measured in advance and the surface height measured in real time, a mechanism to control the focus position by correcting the amount of deviation from the pre-measured result was provided.

By using the present invention, it is possible to detect the wafer height with the surface electric field control electrode close to the wafer and perform focusing, so that a high-quality SEM image can be obtained. Can realize inspection and measurement of semiconductor wafers of 45 nm or more.
The optical path for height measurement that is asymmetrical with respect to the optical axis at a position more than a certain distance from the optical axis of the electron optical system does not affect the electric field of the optical axis of the electron optical system, and controls the surface electric field The electrode was made close to the wafer. In addition, the mechanism that controls the focus position by correcting the amount of deviation from the pre-measured wafer height stored in memory and the pre-measured height based on the height measured in real time is a long-term inspection. Or, stable SEM image capture was realized with respect to fluctuations in the focus position due to changes in the time of the vacuum chamber in which the SEM was attached.

Examples of the present invention will be described below.

FIG. 1 is an overall configuration diagram of an SEM type inspection apparatus.

  The entire inspection apparatus is composed of an electron optical system 10, a table system 20, a detection system 30, an image processing system 40, a height detection system 50, a control system 60, a secondary storage device 121 and a computer 123, and is connected to a network 138. ing.

  The electron optical system 10 includes an electron gun 101, condenser lenses 102 and 103, deflectors 105 and 106, an objective lens 107, a surface electric field control plate 132, and a shield electrode 133.

  The table system 20 includes stage position measuring means 104 such as a wafer holder 134, an XY stage 117, and a laser length measuring device.

  The detection system 30 includes an ExB 110, an electron detector 111, and an A / D converter 112.

  The image processing system 40 includes a distribution unit 113, a storage unit 114 having a storage unit (1) 115 and a storage unit (2) 116, an alignment unit 119, a difference calculation unit 120, and a large difference area extraction unit 122.

  The height detection system 50 includes a light pattern projection unit 124, a light pattern imaging unit 125, a pattern storage unit 126, a height calculation unit 127, a height calculation result storage buffer 128, an in-plane height calculation unit 129, a storage unit 130, A height data correction amount calculator 131 is provided.

  The control system 60 includes a deflection control unit 118, a sequence control unit 135, a stage control unit 136, an electron optical system control unit 137, and a focusing unit 139.

The operation of each part in the above configuration will be described below.
After the electron beam emitted from the electron gun 101 passes through two condenser lenses 102 and 103, the X deflector 105 is deflected by the Y deflector 106, and then the semiconductor lens (hereinafter referred to as wafer) by the objective lens 107. The electron beam irradiation region 109 of 108 is irradiated with an electron beam. Secondary electrons and reflected electrons are generated from the irradiated electron beam irradiation region 109 irradiated with the electron beam, deflected by the ExB 110 through the objective lens 107, and then detected by the electron detector 111.

  The surface electric field control plate 132 can set the potential to be positive or negative with respect to the wafer 108. The shield electrode 133 is set to the same potential as the wafer 108. The semiconductor wafer 108 is held by a wafer holder 134 that attracts the wafer using electrostatic capacity. The A / D converter 112 converts the analog electrical signal output from the electron detector 111 into a digital signal.

  The distribution unit 113 distributes and stores the digital signal output from the A / D converter 112 to either the storage unit (1) 115 or the storage unit (2) 116 of the storage unit 114. In this embodiment, a signal detected by at least two dies to be compared is stored as a reference image in the storage unit (1) 115, and a signal detected by at least two dies to be compared is stored in the storage unit (2) 116. A case of storing as an inspection image will be described.

  The XY stage 117 includes stage position measuring means 104 such as a laser length measuring device. Position information of the XY stage 117 measured by the stage position measuring means 117 is input to the deflection control means 118, and the wafer 108 is continuously moved in one direction by controlling the X deflector 105 and the Y deflector 106. The two-dimensional image is stored in the storage unit 114 by scanning the electron beam so as to be orthogonal to the moving direction of the XY stage 117 when imaging.

  The deflection controller 118 finely adjusts the X deflector 105 and the Y deflector 106 so that an image having the same pixel size can be acquired even when the stage moving speed fluctuates while the XY stage 117 is moving. In the different modes, a two-dimensional image can be acquired by scanning the X deflector 105 and the Y deflector 106 two-dimensionally with respect to the visual field while the XY stage 117 is stationary. The alignment unit 119 uses the reference image based on a known alignment technique such as the peak of the normalized correlation of the output image, the minimum value of the sum of squares of the difference between the two images, or the absolute value of the difference. Align with the inspection image. The difference calculation means 120 compares the same patterns based on the alignment result and calculates the difference.

  Secondary storage device 121, inspection parameters are stored. The large difference area extraction unit 122 outputs, as a defect, a portion where the magnitude of the difference output from the difference calculation unit 120 with respect to the inspection parameter stored in the secondary storage device 121 is large. When an image feature is input from the difference calculation unit 120, the image feature input from the difference calculation unit 120 may be used for determination. Further, the secondary storage device 121 is set so as to be able to input and store an image stored in any area of the storage unit (1) 115 or the storage unit (2) 116 of the storage unit 114. , The coordinates of the defect extracted by the large difference area extraction unit 122 and the image feature output by the difference calculation unit 120 can be stored. Reference numeral 123 denotes a computer having a GUI terminal, which displays candidates for locations that are greatly affected by the extracted process variation on the wafer map. The computer 123 is connected to an external LAN 138, and can input inspection parameters and output acquired images and inspection results to an external device.

  The light pattern projection unit 124 illuminates the light pattern on the surface of the wafer 108 through an optical path provided in the shield electrode 133. Note that one or a plurality of line patterns, or one or a plurality of point patterns are used as the light pattern. Alternatively, a combination of lines and patterns may be used. The light pattern is illuminated on the surface of the wafer 108 while being shifted (separated) from the optical axis 1010 of the electron optical system. In this embodiment, illumination is performed with a displacement of 15 mm in the scanning direction of the stage with respect to the optical axis of the electron optical system. The vertical irradiation angle was set to 80 ° from the wafer normal.

  The light pattern imaging unit 125 images the light pattern illuminated on the surface of the wafer 108 by the light pattern projection unit 124. The pattern storage unit 126 stores an image of the light pattern illuminated on the surface of the wafer 108 imaged by the light pattern imaging unit 125. The height calculation means 127 performs processing on the image stored in the pattern storage means 126 to obtain the position of the line or point pattern irradiated on the wafer 108, and the height based on the obtained position. The calculation is performed using the principle of triangulation. The height calculation result storage buffer 128 stores the wafer height calculated by the height calculation means 127 based on the output value of the stage position measurement means 104 and the wafer position 150 where the height is measured in association with each other. To do. A combination of the light pattern projection unit 124 and the light pattern imaging unit 125 is hereinafter referred to as a height sensor.

  When the height of the wafer 108 changes, the position of the light pattern illuminated on the surface of the wafer 108 by the light pattern projection means 124 (wafer position 150 where the height is measured) changes, and the light pattern imaging means 125 Since the irradiation position of the light pattern on the wafer 108 to be imaged changes in the horizontal direction, the change is calculated and the position where the height is measured is determined.

  The in-plane height calculation means 129 calculates the height of the entire wafer or a partial area thereof from a plurality of height calculation results stored in the height calculation result storage buffer 128. The storage means 130 for storing the in-plane height data obtained by the in-plane height calculation means 129 can take the correspondence between the stored wafer height and its measurement position based on the output of the stage position measurement means 104. The stored wafer height data corresponding to the electron optical system optical axis 1010 (on the electron optical system optical axis 1010) is output based on the output of the stage position measuring means 104. is there.

  The height data correction amount calculator 131 compares the height data stored in advance in the storage means 130 with the height data acquired at the same position thereafter, and calculates each data obtained at different timings. The height data calculated in advance based on the comparison is corrected. The focusing means 139 incorporates a mechanism for controlling the excitation current of the SEM objective lens. Further, the height calculation result storage buffer 128 is also directly connected to the focusing means 139, and already stores corresponding to the optical axis 1010 of the electro-optic system based on the output data of the stage position measuring means 104, similar to the storage means 130. The wafer height data is output. The sequence control unit 135 controls the operation of the entire apparatus, and the stage control unit 136 controls the movement of the XY stage 117 based on the sequence of the sequence control unit 135. Further, the electron optical system control means 137 controls the beam current of the electron optical system 10 and the excitation current of the electron lens (objective lens 107).

  FIGS. 2A and 2B show the structure of the surface electric field control plate 132. 2A is a perspective view of the surface electric field control plate 132, and FIG. 2B is a plan view. The surface electric field control plate 132 reduces the aberration of the electron beam irradiating the wafer 108 by being close to the wafer 108 in the vicinity of the optical axis 1010 of the electron optical system, while reducing the illumination light for height measurement and the wafer 108. In order to prevent the reflected light from hitting this, the basic shape is a conical shape 201 so that the distance from the wafer is large in the peripheral portion, and a hole 202 through which primary electrons and secondary electrons pass is provided in the central portion. For the purpose of making the surface electric field uniform, the portion close to the electron optical system optical axis 1010 has a plane parallel to or nearly parallel to the wafer 108. At a position away from the optical axis 1010 of the electron optical system, there is little influence on primary electrons or secondary electrons. Therefore, there is no restriction on the shape as long as it is rotationally symmetric. Other shapes that prevent it, for example, a dome shape convex downward, may be used.

  3A to 3C show a light pattern in which the light pattern projection unit 124 illuminates the wafer 108. FIG. 3A shows a case in which the light pattern is a point beam, 302 in FIG. 3B shows a case in which the light pattern is slit light, and 303 in FIG. 3C shows a case in which a plurality of point beams are used. In the case where the light pattern is a point beam 301 as shown in FIG. 3A, if substances having different reflectivities exist at the electron beam irradiation position 109 on the wafer 108, a change in brightness occurs at the light pattern irradiation position. Therefore, the position of the pattern detected by the light pattern imaging means 125 is shifted. For example, when the illumination NA is 0.05 and the illumination light illuminated by the light pattern projection means 124 is a laser beam of 532 nm, the beam diameter is about 6.3 μm, and the illumination incident angle is the normal to the wafer. When the angle is 80 °, the height error is about 3.2 μm. This specification cannot be applied because it greatly exceeds the depth of focus (1 μm or less) of high-resolution SEM imaging targeted by the present invention.

  Since the pattern of the semiconductor device formed on the wafer 108 often has a boundary having a different reflectance in the horizontal direction or the vertical direction due to the difference in pattern density depending on the region, the pattern 302 in FIG. As shown, it is suitable for obtaining high accuracy in detecting the height of the wafer 108 that the slit-like light pattern is projected obliquely with respect to the pattern of the semiconductor device formed on the wafer 108. ing. This is because the ratio of the slit-shaped light pattern projected obliquely from the boundary of the pattern having different reflectivity is significantly reduced compared to the case of FIG. 3A, and the height measurement error is greatly increased. This is to reduce the size. Further, when a plurality of beams are illuminated as indicated by 303 in FIG. 3 (c), by using the reflected light from the illuminated light beams other than the boundary surfaces of the regions having different reflectivities among the plurality of illuminated beams. This error can be eliminated. In order to maximize this effect, illumination is performed so that a plurality of beams are not orthogonal to the semiconductor pattern.

  Hereinafter, a method of using the slit light 302 of FIG. 3B as a light pattern for illuminating the wafer 108 will be described. The width of the slit light 302 in the slit longitudinal direction was 1 mm. Assuming that the range of the height variation of the wafer 108 is 80 μm, the change in the optical path of the reflected light of the slit light 302 due to the height variation is 150 μm. The slit direction was set to be inclined 60 degrees with respect to the scanning direction of the stage.

  FIG. 4 shows the incident angle of the slit light 302 in the horizontal direction. 400 is an SEM column, 401 is a case where the horizontal incident angle is inclined 60 degrees with respect to the stage scanning direction, and 402 is a case where it is inclined 75 degrees. When the XY stage 117 is moved in the X direction, it is necessary to set the height measurement position 150 so that SEM imaging is performed after the height measurement, but the incident angle of the slit light 302 in the horizontal direction is set. Is smaller than 90 degrees, the position closest to the optical axis 1010 of the electron optical system is different from the position where the pattern is illuminated. When the horizontal incident angle is 401, the horizontal incident angle is 403. In the case of 402, the position is 404. Therefore, in the height measurement, interference with the magnetic path of the electrode and the objective lens at the positions 403 and 404 becomes a problem.

When the distance between the optical axis 1010 of the electron optical system and the slit light irradiation position is ΔX and the incident angle in the horizontal direction is φ, the distance D from the optical axis 1010 at the closest position is expressed by the following equation. The
D = Δx sin φ (Equation 1)
For this reason, in order to reduce interference with the electrode and the objective lens, it is necessary to make φ as close to 90 degrees as possible. However, when the slit light 302 is close to 90 ° incidence, the probability that the wafer 108 will be in the same direction as the boundary having different reflectivity (the boundary of the pattern area) becomes very high, and a height detection error is likely to occur. Therefore, in the present invention, the slit light 302 is rotated and incident.

As shown in FIG. 5, when the slit light 302 is rotated by ψ and the vertical incident angle of the slit light 302 is θ, the rotation angle ψ of the slit on the wafer is expressed by the following equation.
Ψ = atan (tan ψ / sin θ) (Equation 2)
Therefore, even if the incident angle φ in the horizontal direction is increased, the angle formed by the slit light 302 and the stage scanning direction can be reduced. In the present invention, ψ is set to 2 degrees so that the slit light 302 on the wafer 108 has an inclination of −14 degrees with respect to the incident angle in the horizontal direction. As a result, even when the horizontal incident angle of the slit light 302 is set to 74 degrees, the slit angle can be set to 60 degrees.

  In order to detect the slit light 302 so as to be horizontal, the light pattern projection means 124 is mounted with an angle of −2 degrees. Thus, in this embodiment, the position of the optical path closest to the optical axis of the electron optical system is 13.4 mm including the slit size, and the vertical distance from the wafer 108 at this position is the height of the wafer 108. When the maximum fluctuation is 80 μm in the range, it is about 900 μm. Therefore, in this embodiment, the surface electric field control plate 132 is designed to be separated from the wafer 108 by 1 mm or more at a position 13.4 mm from the optical axis 1010 of the electron optical system.

  The structure of the shield electrode 133 is shown in FIG. The shield electrode 133 is provided to suppress disturbance of the electric field due to a variation in the edge height of the edge of the wafer 108 when an SEM image of the edge of the wafer 108 is taken, and is set to the same potential as the wafer 108. Since the surface electric field control plate 132 is sometimes set to a voltage several KV higher than the wafer 108, there is a possibility of causing discharge when approaching, so the approach is limited, but the shield electrode 133 Is set at the same potential as that of the wafer 108, so that it can be brought closer to the wafer 108, and disturbance of the electric field due to the optical path can be suppressed by bringing it closer to the wafer 108.

  Each of the square hole 601 and the square hole 602 shown in FIG. 6B is an optical path for allowing the illumination light of the shield electrode 133 to pass therethrough. In setting the optical path of the square hole 601, it is necessary to consider the illumination of the slit light 302 and the NA of the detection system. Here, in consideration of the processing accuracy, the size is 1.3 mm × 400 μm, The gap was 0.5 mm.

  In this embodiment, the optical path is provided in the shield electrode 133. However, it is also possible to increase the size of the surface electric field control plate 132 and provide the optical path therewith. However, when a hole is provided in the surface electric field control plate 132, the voltage applied to the surface electric field control plate 132 may be significantly different from the wafer potential, and the electric field disturbance becomes large. Therefore, the illumination position 109 of the slit light 302 needs to be further away from the optical axis 1010 of the electron optical system so that the disturbance of the electric field does not affect the irradiation area of the electron beam.

  As another method, there is a method in which an optical path is not provided in the shield electrode 133, a space is provided between the surface electric field control plate 132 and the shield electrode 133, and a slit pattern is projected and detected using this space as the optical path. However, if this is done, the distance of the shield electrode 133 from the optical axis 1010 of the electron optical system becomes too large, and there is a drawback that the stability when inspecting the outer periphery of the wafer 108 is lacking.

  FIG. 7 shows the inspection area. In general, when the area 701 of the wafer 108 is inspected, the area where the SEM image is picked up is only the area 701. However, in the present invention, the height measurement and the image pickup area of the SEM image are different. It is necessary to perform stage scanning in a region 702 including a region 703 that is a region of 15 mm corresponding to the distance between the SEM and the optical axis 1010 of the SEM electron optical system. In FIG. 7, when the XY stage 117 is scanned from left to right as indicated by an arrow 711, SEM imaging can be performed after height measurement, but the XY stage is indicated from right to left as indicated by an arrow 712. When the scanning 117 is performed, the height measurement is performed after the SEM imaging, and thus focus control cannot be performed.

  First, when the inspection is performed by moving the XY stage 117 from the left to the right in the region 702, the focus control may be performed with a time delay until the SEM imaging of the place where the height measurement is performed. Here, it should be noted that the moving speed of the XY stage 117 is not necessarily constant.

In the height measurement described in the present invention, in particular, when SEM imaging is performed with a small pixel, for example, with a pixel of 50 nm or less, when SEM imaging is used with an image sensor that can operate at 1 × 10 ⁵ pixels / second, for example, 5 mm / While the stage movement speed is about s, the height measurement is possible with a pixel size of about 500 nm and a stable height measurement even at a stage movement speed of about 50 mm / s. In a region where only height measurement is performed or an area where there is no inspection pattern such as a chip boundary, it is advantageous in terms of throughput to increase the stage speed. By adopting this method, the moving time of the XY stage 117 that increases for height measurement can be suppressed to about one second. However, when this control is performed, the movement speed of the XY stage 117 changes in a complicated manner, so that the height data corresponds to the SEM imaging position 109 and the height measurement position based on the output of the stage position measurement means 104. I made it. The focus control at this time is performed by the height measurement data stored in the height calculation result storage buffer 128.

  As a method for measuring height data corresponding to a distance of 15 mm between the electron optical system optical axis 1010 and the height measurement position, the present embodiment further uses a spline function or the like based on the height data measured in advance. Insert and focus using this data. That is, in the present embodiment, the height of an arbitrary position is calculated by the inner surface height calculation means 129 using the interpolation function based on the height data measured at a plurality of positions shifted in both the X and Y directions. . By using the interpolation function, it is possible to shorten the height measurement acquisition time. The calculated height data is stored in the storage means 130.

  When this embodiment is applied to the area 702 shown in FIG. 7, when the XY stage 117 is scanned from left to right as indicated by an arrow 711, the XY stage 117 scans the area 703 in advance. Only the area 701 is scanned. Thus, when the SEM imaging position 109 is in a region 704 that is a part of the region 701, focus control is performed using height data stored in the storage unit 130 that is data calculated in advance by an interpolation function. When the SEM imaging position 109 is in the area 705 which is the remaining part of the area 701, focus control is performed using the height measurement data stored in the height calculation result storage buffer 128.

  The data stored in the height calculation result storage buffer 128 is calculated by the inner surface height calculating means 129 and the height data of the neighboring area together with the height data acquired before that, and stored in the storage means 130. Store.

  On the other hand, when the XY stage 117 is moved from the right to the left in the area 702 as indicated by the arrow 712, the focus data is already measured in the adjacent inspection area using the data stored in the storage unit 130. Take control. While the field of view of the SEM in this embodiment is 600 μm or less, the slit length of the height measuring instrument is 1 mm. Therefore, when the inspection areas are adjacent, the height data obtained next is used. There is no problem even if the focus control is performed by using it.

  Even when the XY stage 117 stage is moved from the right to the left as indicated by the arrow 712 in the area 702, the height data is measured, the height data is stored in the height calculation result storage buffer 128, and before that, Along with the acquired height data, it is used for the interpolation operation, and the data stored in the storage means 130 is updated. When the length of the inspection area such as the area 703 is less than 15 mm, the height measurement area and the SEM imaging area 109 do not overlap, but in this case as well, the memory is stored based on the height data measured in advance. Focus control is performed based on the height data stored in the means 130.

  A problem in performing focus control based on height data stored in advance is height fluctuation due to a difference in height data measurement time. The main factor is the deformation of the vacuum chamber and the deformation of the wafer itself due to fluctuations in atmospheric pressure and outside air temperature. As a result of experiments, it was found that the deformation could be about several micrometers in about one hour. Since the focusing accuracy required by the present invention is 1 μm or less, this height fluctuation is fatal.

  Therefore, if there is prior data, the previous height measurement data and the height measurement data obtained at the time of SEM image acquisition are compared to determine the amount of change, and the amount of change is used as correction data to obtain height data. The correction amount in the correction amount calculator 131 is determined. This will be described with reference to FIG. The height measurement data obtained by scanning in the X direction for a certain time and the measurement data obtained in advance are set to h (x, y, t), respectively, and the height data h (x, y, t0) measured in advance for that point Is known in advance.

  In the configuration of the present invention, h (x + Δx, y, t), which is Δx away from the desired electron optical system optical axis 1010, can be measured in real time. y, t)-h (x + Δx, y, t). Here, h (x, y, t0) −h (x + Δx, y, t0) is already an existing value. Note that h (x, y, t0) and h (x + Δx, y, t0) cannot be measured at the same time. Almost the same time is represented by the same t0.

Find the point where the height measurement has already been performed closest to (x, y, t), for example, the height of the x-coordinate before one stage scanning is almost the same position, h (xn, yn, tn) . Note that the proximity scale _DL is calculated as follows, for example, with wx and wy as weighting factors and f () as a suitably set function.
D _L = Wx (xn-x) ² + wy (yn-y) ² + f (t-tn) (Equation 3)
At this time, h (x, y, t) is determined as follows, for example.
h (x, y, t) = h (x + Δx, y, t) + h (x, y, t0) -h (x + Δx, y, t0) + h (xn, yn, tn)
-(h (xn + Δx, yn, tn) + h (xn, yn, t0) -h (xn + Δx, yn, t0)) (Equation 4)
This equation can be thought of as the height data measured in advance as a correction by the difference between the estimated height data and the measured height data in the already measured time and spatial neighborhood height data. Is performed by the height data correction amount calculator 131.

  In order to perform this calculation, the storage means 130 stores height data obtained at a plurality of timings for the same horizontal direction position, or one height data and its difference. Note that if the fitting function obtained from the height data obtained instead of the height data of each point is stored, the amount of memory can be reduced, so it may be stored in this format.

When the height sensor h (x + Δx, y, t) has come out of the edge of the wafer 108 at the edge of the wafer 108, the equation for calculating h (x, y, t) is as follows: Can be rewritten as
h (x, y, t) = h (x, y, t0) + h (xn, yn, tn) -h (xn, yn, t0) (Equation 5)
(Equation 5) is based on the variation in wafer height in the vicinity (xn, yn) of (x, y) to be obtained. If the time difference between the two is large, the accuracy deteriorating factor increases. For this reason, it is necessary to measure h (xn, yn, tn) immediately before SEM imaging, and time is required for prior measurement. Therefore, even if it is the same stage scan, use (Equation 5) only when real-time measurement is not possible, and after entering the area where height measurement can be performed in real time, control the focus using (Equation 4). Was set as follows.

  With the control described above, not only the wafer height data obtained at the time t0 in advance, but also the height data obtained in real time and the height data closest to the desired height position are used. Since estimation can be performed, highly accurate focusing can be realized.

In order to focus with higher accuracy, height data such as h (xn, yn, tn) and h (x, y, t0) is used as the average value of multiple data obtained in the vicinity. Can also be carried out without loss of generality. Also, for example, measuring the height at a small number of points on the wafer, and using this for spline interpolation or quadratic function interpolation, the wafer height data obtained at the time t0 in advance is the pre-inspection data. This is desirable to reduce the overhead. In order to execute the calculation described above, it is necessary to store heights at different times at the same point. For this reason, a height calculation result storage which is a height data storage means is stored. The data stored in the buffer 128 and the storage means 130 is stored as wafer height information at different timings at the same point when combined.
[Modification of the first embodiment]
In the embodiment described above, the method of obtaining the SEM image while scanning the XY stage 117 has been described. Next, as a modification, for example, a review SEM for sequentially observing a plurality of defects detected by inspecting the wafer 108 with another inspection apparatus, or the dimensions of the pattern formed on the wafer 108 at a plurality of locations. As described in the first embodiment, when the XY stage 117 is moved intermittently, that is, step-and-repeat is moved to sequentially image a desired area on the wafer 108 as in the case of a side-length SEM that sequentially measures. A case where focusing is performed in the same manner as described above will be described.

  In this modification, since wafer height data is not acquired at the previous t0, it is necessary to measure the height immediately before SEM imaging and to adjust the height at this position. The configurations of the electron optical system 10, the table system 20, the detection system 30, and the height detection system 50 of the SEM apparatus used for SEM imaging are the same as those described with reference to FIG. 1, but the image processing system 40, the control system 60, and the like. The configuration is slightly different. The configuration of the image processing system 41 and the control system 61 in this modification is shown in FIG.

  The image processing system 41 includes a storage unit 411 and an image processing unit 412, and in the case of a review SEM, the image processing unit 412 extracts a defect image from the SEM image of the inspection target area. On the other hand, in the case of the side length SEM, the image processing unit 412 calculates the dimension of the measurement target pattern from the SEM image of the inspection target region.

  On the other hand, the control system 61 is the same as that of the first embodiment in that it includes a deflection control means 6118, a sequence control means 6135, a stage control means 6136, an electron optical system control means 6137, and a focusing means 6139. However, the sequence control unit 6135 and the stage control unit 6136 perform control in accordance with the review SEM or the side length SEM, respectively, and move the XY stage 117 in a step-and-repeat manner to sequentially capture desired regions on the wafer 108.

  The sequence at this time will be described with reference to FIGS. 15 (a) and 15 (b). FIG. 15A and FIG. 15B show the corresponding processing flow, FIG. 15A is a diagram, and FIG. 15B is a flowchart. When the number of points to be imaged is small, the height sensor (a combination of the light pattern projection unit 124 and the light pattern imaging unit 125) can first measure the height of the SEM imaging position 109 for each SEM imaging. The position of the XY stage 117 is moved (S1501), and then the height is measured (S1502). Thereafter, the XY stage 117 is moved again so that the SEM imaging position 109 is within a range that can be imaged by the SEM (S1503), and SEM imaging is performed at that position (S1504). In order to obtain the best throughput, it is desirable to measure the height while moving the XY stage 117 without stopping the XY stage 117 in 1502.

  In another embodiment, the XY stage 117 is moved so that the observation spot or measurement spot on the wafer 108 is within the imaging field of view of the SEM in the review SEM or the side length SEM, and measurement is performed in real time at a position separated by Δx. It is also possible to focus using height data. In particular, in length measurement SEM and defect review SEM, this problem is solved by performing SEM AF, which is autofocus based on the SEM image, and eliminating the need for an accuracy of less than 1 μm. be able to. In the present embodiment shown in FIG. 1, since the wafer 108 is held by a wafer holder 134 having a capacitance type adsorption mechanism, even if ΔX is about 15 mm away, its height change amount is 1 μm. It can be suppressed to a degree or less, and there is no problem in determining the initial value when performing SEM AF.

  As an example of acquiring a SEM image by performing a step-and-repeat stage movement based on a small number of prior height measurement results, a sequence when applied to a length measurement SEM is shown in FIG.

  First, in order to obtain the height distribution of the entire wafer 108, XY is obtained so that height data can be acquired at a plurality of points set uniformly on the wafer 108, for example, positions of about 13 points indicated by black dots 1401 in FIG. The stage 117 is moved (1301), and height data is acquired (1302). If the XY stage 117 is moved intermittently, the measurement time increases with respect to the measurement point. Therefore, as shown by a plurality of lines 1402 in FIG. The height may be measured.

  Next, the stage is moved so that the height of a plurality of predetermined alignment marks (about 3 points) can be measured (1303), the height is measured (1304), and then the stage is moved so that the alignment mark can be imaged by SEM. (1305), the SEM AF range is determined from the height measurement result obtained in 1304, and SEM AF is performed (1306). In SEM AF, SEM imaging is performed by shifting the focal position from each other, a high-frequency component of the image is obtained by edge detection, this degree is used as a focus measure, and this peak is used as a focus position.

  SEM imaging of the alignment mark is performed with the focus at the in-focus position (1307), and wafer alignment is performed based on the deviation amount of the alignment mark position obtained from the predetermined alignment position and the captured SEM image (1308). Next, using the height data obtained in the height data acquisition step 1302 and the height measurement step 1304, the distribution of the height data of the entire wafer 108 is calculated by quadratic function fitting, and initial data h (x, y, t0) is calculated (1309). Further, SEM AF at the alignment mark position and then the length measurement point are imaged.

  First, the XY stage 117 is moved so that the SEM AF point provided in the vicinity of each length measurement point and the optical axis 1010 of the electron optical system of the SEM coincide with each other (1310), and the height is measured (1311). Next, the data closest to the already measured data is searched using the equation (1) (1312), and the height of the wafer 108 at the SEM optical axis position 1010 is estimated using the equation (2) (1313). Based on the wafer height, the SEM AF range is set and SEM AF is performed (1314). Next, an SEM image of an alignment point for fine alignment is taken (1315), which is preferably a unique pattern set within the deflection range of the primary beam from the position where SEM AF was performed (1315). The displacement correction is performed in comparison with the alignment position.

  Next, the image is picked up by moving the field of view to the position of the pattern for measuring the pattern width (1316), and the pattern width is measured from the obtained image. Since 1316 is within the primary beam change range, it is not necessary to move the stage for visual field movement. In 1317, based on the SEM image of the length measurement point, the pattern width at a predetermined position, the distance between patterns, and the like are measured.

  In this example, the measurement SEM is taken as an example, and an example of application in a device that moves the stage of step-and-repeat is shown. However, in the case of a defect review SEM, for example, the defect coordinates that the inspection device outputs the measurement points. If it is replaced, ADR (Automatic Defect Review) that automatically captures a high-magnification image of a defect in the same sequence can be configured.

  A second embodiment of the present invention will be described with reference to FIGS. First, FIG. 9 shows a configuration of an SEM apparatus according to the second embodiment. Reference numeral 901 denotes an electron source, which arranges electron beams in parallel using two electromagnetic lenses 902 and 903. Reference numeral 904 denotes a first aperture array in which apertures are two-dimensionally arranged, and divides the primary beam into a plurality of pieces. In this embodiment, the numerical aperture is 4, and the primary beam is divided into four. Reference numeral 911 denotes a lens array that converges the primary beam. Reference numeral 912 denotes a second aperture array, which has an effect of blocking electrons that have not converged at the position of the second aperture array 912. Reference numeral 913 denotes an electromagnetic lens. Reference numeral 914 denotes an X deflector, and 915 denotes a Y deflector, which deflects an electron beam and controls the scanning of primary electrons on the upper surface of the wafer 908. 916 is ExB, which does not deflect the primary electrons but deflects the secondary electrons in the direction of the detector. An electromagnetic lens 917 forms an image of the second aperture array 912 on the upper surface of the wafer 908 with a reduction optical system. Reference numeral 918 denotes an electromagnetic lens, and reference numeral 919 denotes an aperture. By combining the electromagnetic lens 918 and the aperture 919, the secondary electron emission direction that is significantly deviated from the wafer normal is blocked.

  Reference numerals 920, 921, 922 and 923 denote detectors. The outputs of the detectors 920 to 923 are converted into digital signals by the A / D converters 924 to 927, respectively, and then the image generation means 928 uses the output of all of the A / D converters 924 to 927 to form one image. Is generated. The image generated by the image generation unit 928 is transferred to the distribution unit 9113 and stored in either the storage unit (1) 9115 or the storage unit (2) 9116 of the storage unit 9114. In this embodiment, a signal detected by at least two dies to be compared is stored as a reference image in the storage unit (1) 9115, and a signal detected by at least two dies to be compared is stored in the storage unit (2) 9116. A case of storing as an inspection image will be described.

  Reference numeral 9117 denotes an XY stage, which includes stage position measuring means 9104 such as a laser length measuring device. Reference numeral 9118 denotes deflection control means, which receives position information of the XY stage 9117 measured by the stage position measurement means 9104, and controls the X deflector 914 and Y deflector 915 to continuously move the wafer 908 in one direction. By scanning the electron beam so as to be orthogonal to the moving direction of the XY stage 9117 when imaging while moving, a two-dimensional image is stored in the storage unit 9114. The deflection control unit 9118 finely adjusts the X deflector 914 and the Y deflector 915 so that an image having the same pixel size can be acquired even when the stage moving speed fluctuates while the XY stage 9117 is moving. In a different mode, a two-dimensional image can be acquired by scanning the X deflector 914 and the Y deflector 915 two-dimensionally with respect to the visual field while the XY stage 9117 is stationary. Reference numeral 9119 denotes alignment means, which aligns the reference image and the inspection image in the same manner as in the first embodiment. Reference numeral 9120 denotes difference calculation means, which calculates the difference by comparing the same patterns based on the alignment result.

  Reference numeral 9121 denotes a secondary storage device that stores inspection parameters. Reference numeral 9122 denotes a large difference area extraction unit, which outputs, as a defect, a portion having a large difference output from the difference calculation unit 9120 with respect to the inspection parameter stored in the secondary storage device 9121. When an image feature is input from the difference calculating unit 9120, the image feature input from the difference calculating unit 9120 may be used together for determination. Further, the secondary storage device 9121 is set so as to be able to input and store an image stored in any area of the storage unit (1) 9115 or the storage unit (2) 9116 of the storage unit 9114. , The coordinates of the defect extracted by the large difference area extraction unit 9122 and the image feature output by the difference calculation unit 9120 can be stored. Reference numeral 9123 denotes a computer having a GUI terminal, which displays candidates of locations that are greatly affected by the extracted process variation on the wafer map. The computer 9123 is connected to the external LAN 9138, and can input inspection parameters, output acquired images, and output inspection results to an external device.

  Reference numeral 9124 denotes a light pattern projection unit that illuminates the light pattern on the surface of the wafer 908 via an optical path provided in the shield electrode 9133 as in the first embodiment. As the light pattern, one or a plurality of line patterns, or one or a plurality of point patterns are used as in the first embodiment. Alternatively, a combination of lines and patterns may be used. The optical pattern is illuminated on the surface of the wafer 908 with a deviation from the optical axis 9010 of the electron optical system. In this embodiment, illumination is performed with a displacement of 15 mm in the scanning direction of the stage with respect to the optical axis 9010 of the electron optical system. The vertical irradiation angle was set to 80 ° from the wafer normal.

  Reference numeral 9125 denotes an optical pattern imaging unit that images an optical pattern illuminated on the surface of the wafer 908 by the optical pattern projection unit 9124. Reference numeral 9126 of the height detection system 950 is a pattern storage unit that stores the pattern imaged by the light pattern imaging unit 9125. Reference numeral 9127 denotes height calculation means for calculating the height of the wafer 908 irradiated with the optical pattern image, as in the first embodiment. Reference numeral 9128 denotes a height calculation result storage buffer, which associates the wafer height calculated by the height calculation means 9127 based on the output value of the stage position measurement means 9104 with the wafer position 9150 where the height is measured. Store. When the height of the wafer 9108 varies, the position of the light pattern illuminated on the surface of the wafer 908 by the light pattern projection unit 9124 (the wafer position 9150 at which the height is measured) changes, and the light pattern imaging unit 9125 Since the irradiation position of the light pattern on the wafer 908 to be imaged changes in the horizontal direction, this change is calculated and the position where the height is measured is determined.

  Reference numeral 9129 denotes in-plane height calculation means, which calculates the height of the entire wafer or its partial area from a plurality of height calculation results stored in the height calculation result storage buffer 9128. Reference numeral 9130 denotes storage means for storing in-plane height data obtained by the in-plane height calculation means 9129 as in the case of the first embodiment. Reference numeral 9131 denotes a height data correction amount calculator that corrects height data calculated in advance as in the case of the first embodiment.

  Reference numeral 9132 of the control system 960 is a focusing means and incorporates a mechanism for controlling the excitation current of the objective lens 917 of the SEM. Further, the height calculation result storage buffer 9128 is also directly connected to the focusing means 9132, and based on the output data of the stage position measuring means 9104, already stored corresponding to the electron optical system optical axis 9010, similar to the storage means 9130. The wafer height data is output. Reference numeral 9135 denotes sequence control means for controlling the operation of the entire apparatus. Reference numeral 9136 denotes stage control means for controlling the movement of the stage based on the sequence of the sequence control means 9135. Reference numeral 9137 denotes an electron optical system control means for controlling the beam current of the electron optical system and the excitation current of the electron lenses (objective lenses 917 and 918).

  FIG. 10 shows an image acquired in this embodiment. Reference numerals 1001 to 1004 denote positions corresponding to SEM images acquired by the respective detectors when the electron beam is scanned in a direction orthogonal to the scanning direction of the stage while scanning the stage, and the positions are respectively in the X and Y directions. It's off. Therefore, a single image is generated by the image generating means 928 in consideration of each positional shift. Processing other than this is in accordance with the processing described in the configuration of FIG.

  FIG. 11 shows an embodiment in which a plurality of height measuring means are further provided in the configuration of FIG. The configuration shown in FIG. 1 is different from that shown in FIG. 1 in that a light pattern projection unit 1101 and a light pattern imaging unit 1102 are further provided. In addition to the optical paths 601 and 602 for the 125 light pattern projection means and the 126 light pattern imaging means as shown in FIG. An optical path for passing reflected light is newly opened (not shown). FIG. 12 shows the arrangement of the light pattern projection means and the light pattern imaging means as seen from above. The projection position of the light pattern can illuminate the right and left sides of the electron optical system optical axis in the X direction, and the height of the SEM imaging position is set in advance regardless of the direction of movement of the stage. It can be measured. Both the output of 1102 and the output of 127 are input to the 128 height calculation result storage buffer. The 128 height calculation result storage buffer stores both the output of 1102 and the output of 127, and the center position of the height measurement positions of 1102 and 127, that is, the position of the optical axis of the electron optical system. As the acquired data, two modes of storing the average values of 1102 and 127 are provided. When only one of the two height measurements is outside the wafer, the average value is not stored, but only the height calculation result calculated in the wafer is stored.

  In the first, second, and third embodiments, the configuration in which the optical height detecting means is installed with being shifted from the beam optical axis has been described. However, the optical height detecting means is changed to other height detecting means. Even so, the same function can be realized. For example, even if the height measurement by the combination of 125 and 126 in FIG. 1 or FIG. 9 is changed to a capacitance sensor, the functions of 127, 128, 129, 130, and 131 in FIG. Focus control can be performed. Alternatively, in FIG. 11, in addition to the height measurement by the combination of 125 and 126, by changing another set of height detection means 1101 and 1102 to a capacitance sensor, two sets of height detection means are used. Focus control can be performed.

It is a block diagram which shows the structure of the outline of the SEM type | mold inspection apparatus in a 1st Example. It is an example of the surface electric field control electrode in a 1st Example. It is an example of the light pattern illuminated on the wafer in a 1st Example. It is explanatory drawing of the optical path of the height detector in a 1st Example. It is the illumination method of the slit in a height detector. It is one Example of the shield electrode in a 1st Example. It is explanatory drawing of an inspection area and a focusing method. It is a figure explaining the height estimation method. It is a block diagram which shows the structure of the outline of the SEM apparatus in a 2nd Example. It is explanatory drawing of an image pick-up area. It is a block diagram which shows the structure of the outline of the SEM apparatus in a 3rd Example. It is explanatory drawing of the optical path of a height detector. It is a sequence diagram of a length measurement SEM. It is a figure which shows the example of the initial stage height measurement position on a wafer. It is a figure explaining the imaging sequence in the case of imaging a sample, moving a stage by step and repeat. It is a block diagram of the SEM system which shows the modification of a 1st Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Electron source 102, 103 ... Condenser lens 104 ... Stage one measurement means 105 ... X deflector 106 ... Y deflector 107 ... Objective lens 108 ... Semiconductor wafer 111- ..Electron detector 113 ... Distributing means 114 ... Storage means 117 ... XY stage 118 ... Deflection control system 120 ... Difference calculation means 122 ... Difference large area extraction means 124 ... Light pattern projection means 125 ... Light pattern imaging means 126 ... Pattern storage means 127 ... Height calculation means 128 ... Height calculation result storage buffer 129 ... In-plane height calculation means 130 ...・ Storage means 131... Height data correction amount calculator 132... Surface electric field control plate 133. Electrode 135 ... Sequence control means 136 ... Stage control means 137 ... Electro-optical system control means 139 ... Focusing means

Claims (14)

Table means on which a sample can be placed and moved in a plane;
An electron gun that emits a primary electron beam, an electron lens unit that converges the primary electron beam emitted from the electron gun, and a primary electron beam focused by the electron lens unit is deflected and placed on the table means A beam deflector that scans and irradiates the surface of the sample, and an objective lens that irradiates the irradiation region of the sample with the primary electron beam deflected by the beam deflector, and
Secondary electron detection means for detecting secondary electrons and / or reflected electrons generated from the sample irradiated by scanning with a primary electron beam by the electron optical system means;
A / D conversion means for digitizing a signal obtained by detecting secondary electrons and / or reflected electrons generated from the sample by the secondary electron detection means;
Image storage means for inputting a signal digitized by the A / D conversion means and storing it as a digital image;
Image processing means for processing a digital image stored in the image storage means;
A scanning electron microscope apparatus comprising height detection / control means for detecting the height of the surface of the sample placed on the table means and controlling the focus position of the electron lens of the electron optical system means,
The height detection / control means is:
A height detector for detecting the height of the surface of the sample placed on the table means away from the electron beam optical axis of the electron optical system means;
The height of the surface of the sample in the portion on the electron beam optical axis of the electron optical system means is determined using the height information of the position of the surface of the sample separated from the electron beam optical axis detected by the height detector. A sample height estimation unit for estimating the thickness;
The primary electron beam is controlled by controlling the electron lens portion of the electron optical system means based on the height information of the sample in the portion on the electron beam optical axis of the electron optical system means estimated by the sample height estimating portion. A focus position adjustment unit for adjusting the focus position of
A surface electric field control electrode means disposed between the electron lens portion of the electron optical system means and the table means and capable of changing an electric field between the table means and the surface electric field control electrode means; The surface electric field control electrode means has a small distance from the surface of the table means on which the sample is placed in the vicinity of the opening, In a portion away from the central portion, the distance between the table means and the surface on which the sample is placed is large, and has a rotationally symmetric shape,
Shield electrode means that can be set to the same potential as the sample placed on the table means is provided outside the electron beam optical axis of the surface electric field control electrode means, and non-axis target with respect to the electron beam optical axis,
The surface electric field control electrode means is disposed between the objective lens of the electron optical system means and the table means, and the surface electric field control electrode means is disposed below the objective lens of the electron optical system means. A scanning electron microscope apparatus characterized by the above. The scanning electron microscope apparatus according to claim 1,
The height detecting unit of the height detecting / controlling unit projects an optical pattern onto a surface of the sample placed on the table unit at a position away from the electron beam optical axis of the electron optical system unit. An illumination unit, a light pattern imaging unit that images a light pattern projected on the surface of the sample from a direction different from the direction in which the light pattern is projected, and the surface of the sample obtained by imaging with the light pattern imaging unit A scanning electron microscope apparatus comprising: a height calculation unit that calculates the height of a portion of the surface of the sample on which the light pattern is projected using information on an image of the light pattern projected onto the surface. The scanning electron microscope apparatus according to claim 2,
The sample height estimation unit of the height detection / control unit includes a height information storage unit that stores height information of a portion on which a light pattern on the surface of the sample detected by the height detection unit is projected, Based on the height data of the location where the light pattern on the surface of the sample is output from the height detector and the height data stored in the height information storage unit, the electron optical system means A scanning electron microscope apparatus comprising: a sample height calculation unit that calculates the height of the sample in a portion on the electron beam optical axis. The scanning electron microscope apparatus according to claim 1,
The table means includes a position detection unit for detecting the position of the sample placed above, and the height information storage unit of the sample height estimation unit of the height detection / control unit is detected by the height detection unit. A scanning electron microscope apparatus characterized in that height information of a portion on which a light pattern on a surface of a sample is projected is stored in association with position information of the sample detected by the position detection unit. 5. The scanning electron microscope apparatus according to claim 4 , wherein the electronic height information storage unit is a height of a portion on which a light pattern on the surface of the sample obtained at different timing for the same position on the sample is projected. A scanning electron microscope apparatus characterized by storing information. 2. The scanning electron microscope apparatus according to claim 1, wherein the table means includes a rotatable rotary table and a rotation angle control unit for controlling a rotation angle of the rotary table, and the light pattern illumination means is an optical pattern. The slit light is projected to a position on the surface of the sample away from the electron beam optical axis of the electron optical system means, and the rotation angle control unit forms the slit light projected on the sample on the sample. A scanning electron microscope apparatus, wherein the rotation angle of the sample is controlled so as to intersect with the pattern. The scanning electron microscope apparatus according to claim 1, wherein the height detection / control unit includes a plurality of sets of the light pattern illumination unit and the light pattern imaging unit, the plurality of light pattern illumination units, A scanning electron microscope apparatus characterized in that each pair with an optical pattern imaging unit measures the height of the surface of the sample away from the electron beam optical axis of the electron optical system means. A sample placed on a table movable in a plane is scanned by irradiating an electron beam focused through an electron lens unit of an electron optical system of a scanning electron microscope apparatus,
Detecting secondary electrons and / or reflected electrons generated from the sample scanned by irradiation with the focused electron beam;
The signal obtained by the detection is A / D converted to obtain a digital image of the sample,
A method of acquiring an image of a sample using a scanning electron microscope apparatus for processing the obtained digital image,
In the step of obtaining a digital image of the sample,
Detecting the height of the position of the surface of the sample placed on the table away from the electron beam optical axis of the electron optical system;
Estimating the height of the surface of the sample in a portion on the electron beam optical axis using information on the height of the detected surface of the sample away from the electron beam optical axis,
Adjusting the focus position of the electron beam irradiated on the sample by controlling the electron lens unit of the electron optical system based on the estimated height information of the sample in the portion on the electron beam optical axis,
A digital image of the sample is obtained from a signal obtained by detecting secondary electrons and / or reflected electrons generated from the sample by irradiating the electron beam with the focus position adjusted and scanning the sample,
The apparatus further comprises surface electric field control electrode means arranged between the electron lens part of the electron optical system and the table and capable of changing an electric field between the table and the surface electric field control electrode means at the center. The surface electric field control electrode means has a small distance from the surface of the table on which the sample is placed in the vicinity of the opening and is separated from the center. In the part, the distance between the table and the surface on which the sample is placed is large and has a rotationally symmetric shape,
Shield electrode means that can be set to the same potential as the sample placed on the table is provided outside the electron beam optical axis of the surface electric field control electrode means, and non-axis-targeted with respect to the electron beam optical axis,
The surface electric field control electrode means is disposed between an objective lens provided in the electron optical system means and the table, and the surface electric field control electrode means is disposed below the objective lens of the electron optical system means. A method for imaging a sample using a scanning electron microscope apparatus characterized by the above.   The sample imaging method using the scanning electron microscope apparatus according to claim 8, wherein in the step of obtaining a digital image of the sample, the height of a position away from the electron beam optical axis of the electron optical system is detected. , Projecting a light pattern on the surface of the sample away from the electron beam optical axis of the electron optical system, and projecting the light pattern on the surface of the sample in a direction different from the direction in which the light pattern was projected And calculating the height of the portion of the surface of the sample on which the light pattern is projected using information on the image of the light pattern projected on the surface of the sample obtained by imaging. A sample imaging method using a scanning electron microscope apparatus. The sample imaging method using the scanning electron microscope apparatus according to claim 9, wherein the light pattern projected to a position away from the electron beam optical axis of the electron optical system is slit light. A sample imaging method using a scanning electron microscope apparatus. 9. A sample imaging method using the scanning electron microscope apparatus according to claim 8, wherein in the step of obtaining a digital image of the sample, the height of the surface of the sample in a portion on the electron beam optical axis is estimated. The height information of the location where the detected light pattern of the surface of the sample is projected is stored, and the height data of the location where the detected light pattern of the surface of the sample is projected and the storage are stored. A sample imaging method using a scanning electron microscope device, wherein the height of the sample in a portion on the electron beam optical axis is calculated based on the height data. The sample imaging method using the scanning electron microscope apparatus according to claim 10, wherein height information of a portion on which the detected light pattern of the surface of the sample is projected is obtained from the sample placed on the table. A method for imaging a sample using a scanning electron microscope device, wherein the sample is stored in association with position information. A sample imaging method using the scanning electron microscope apparatus according to claim 10, wherein height information of a location where a light pattern of the detected surface of the sample is projected is stored on the sample. A method for imaging a sample using a scanning electron microscope device, comprising storing height information of a portion onto which a light pattern on the surface of the sample is acquired at different timings for the same position. The sample imaging method using the scanning electron microscope apparatus according to claim 9, wherein slit light is used as the optical pattern at a position away from the electron beam optical axis of the electron optical system on the surface of the sample. A sample imaging method using a scanning electron microscope apparatus, wherein the projection is performed so as to intersect with a pattern formed thereon.

Images