JP6277037B2 - Charged particle beam equipment - Google Patents

Description

  The present invention relates to a charged particle beam apparatus, and more particularly to a charged particle beam apparatus capable of suppressing the influence of a magnetic field generated from a linear motor or the like.

  A charged particle beam apparatus typified by a scanning electron microscope is an apparatus that irradiates a sample by narrowing a beam emitted from a charged particle source (such as an electron source). On the other hand, a scanning electron microscope for measuring a large sample such as a semiconductor wafer is provided with a sample stage for moving the sample at least in the XY direction so as to enable beam scanning to an arbitrary position. . Patent Document 1 discloses a scanning electron microscope provided with a sample stage. Patent Document 1 discloses an in-lens unit including a plate-shaped magnetic pole disposed on a sample stage and an objective lens installed on the sample.

JP-A-5-174766

  On the other hand, with the recent demand for chip cost reduction, there is a demand for larger semiconductor wafers and higher pattern integration. When the size of the semiconductor wafer increases, a load is applied to the sample stage built in the scanning electron microscope for measuring the semiconductor wafer, and it becomes difficult to achieve relatively high stop position accuracy and stage speed. . Furthermore, the high integration of patterns tends to increase the number of measurement points for proper process management, and the load on the sample stage increases accordingly. According to the scanning electron microscope provided with the in-lens type objective lens disclosed in Patent Document 1, it is possible to perform sample observation with high resolution as compared with the out-lens type objective lens. Since the magnetic body is installed on the movable part of the sample stage, the weight increases accordingly, and it is difficult to reduce the load on the sample stage.

  The following proposes a charged particle beam apparatus that aims to perform highly accurate measurement and inspection while reducing the load on the stage. Furthermore, a charged particle beam apparatus is proposed that aims to perform high-speed sample movement while suppressing fluctuations in the magnetic field accompanying movement of the sample stage.

  As an aspect for achieving the above object, a charged particle beam including an objective lens for focusing a charged particle beam emitted from a charged particle source and a table on which a sample irradiated with the charged particle beam is placed is described below. An apparatus comprising: a guide for guiding the table in one direction; and a plurality of plate-like magnetic bodies disposed between the guide and the objective lens, the guide being made of a magnetic body, The present invention proposes a charged particle beam apparatus disposed so as to be positioned in a gap between the plurality of plate-like magnetic bodies as viewed from the irradiation direction of the charged particle beam.

  Further, as another aspect for achieving the above object, an objective lens for focusing a charged particle beam emitted from a charged particle source and a table for placing a sample irradiated with the charged particle beam are provided below. A charged particle beam device, a moving coil type linear motor that generates a driving force for moving the table in one direction, and a plate-like magnetic body disposed between the moving coil and the objective lens; We propose a charged particle beam device equipped with

  According to the above aspect, it is possible to realize both the speeding up of the measurement and inspection based on the weight reduction of the stage and the speeding up of the focus adjustment of the charged particle beam. In addition, according to the other aspect, even when a moving coil linear motor is employed, it is possible to suppress the influence of the magnetic field on the charged particle beam.

The figure which shows the outline of a scanning electron microscope. The figure which shows the outline | summary of the stage apparatus of a scanning electron microscope. The figure which shows the outline | summary of the top table of a stage apparatus. The figure which shows the outline | summary of the top table which incorporates the divided | segmented electrode. Schematic of a moving coil type linear motor. The figure which shows the structural example of a movable stage. The figure which shows the positional relationship of the objective lens and the component of a stage when a sample moves to the paper surface right side (when a beam is irradiated to the left end part vicinity of a sample). The figure which shows the positional relationship of the objective lens and the component of a stage when a sample is located in the paper surface center (when a beam is irradiated to the center of a sample). The figure which shows the positional relationship of the objective lens and the component of a stage when a sample moves to the paper surface left side (when a beam is irradiated to the right end part vicinity of a sample). The figure which shows an example of the charged particle beam apparatus which installed the plate-shaped magnetic body under the sample (The figure which shows the state which irradiates the beam to the left end part vicinity of a sample). The figure which shows an example of the charged particle beam apparatus which installed the plate-shaped magnetic body under the sample (the figure which shows the state which irradiates a beam to the center of a sample). The figure which shows an example of the charged particle beam apparatus which installed the plate-shaped magnetic body under the sample (The figure which shows the state which irradiates the beam to the right end part vicinity of a sample). The graph which shows the relationship between a movable stage position and magnetic field intensity. The graph which shows the relationship between the width | variety of a plate-shaped magnetic body, and a magnetic field intensity.

An electron microscope is an apparatus that moves an imaging target using a movable stage and images various positions of the imaging target. For high-speed movement and high-precision positioning of the movable stage, it is desirable to use a linear motor as the driving force for the movable stage. However, in an electron microscope, it is necessary to avoid magnetic field fluctuations on the electron orbit. Therefore, magnetic field fluctuations that occur with the movement of the movable stage must be avoided.
The linear motor includes a coil through which a control current is passed and a permanent magnet, and generates a driving force by an electromagnetic force. In the embodiment described below, a moving coil linear motor will be described. A moving coil type linear motor includes a field element having permanent magnet arrays arranged in a rail shape and a mover having a coil for supplying a control current. The length of the field element in the moving direction of the mover substantially corresponds to the moving stroke of the mover.

  When a linear motor is used for the movable stage of the electron microscope, a configuration in which the above-described field element is fixed and magnetic field fluctuation is suppressed is also possible. However, in order to obtain a movable stage with a smaller number of parts, it is desirable that the field element move. On the other hand, if the field element moves, the source of the magnetic field moves, which may affect the beam.

  The embodiment described below relates to a scanning electron microscope provided with a mechanism for suppressing the influence on a beam based on the movement of a magnetic body constituting a linear motor. In the following embodiments, a scanning electron microscope will be described as an example. However, as in the case of the scanning electron microscope, other charged particle beam devices such as a focused ion beam device in which a beam may be deflected by a magnetic field are described. Application is also possible.

  In an embodiment described below, in an electron microscope mainly including a magnetic lens and a movable stage, the movable stage has a plate-like magnetic body, and the thickness direction of the plate-like magnetic body is the same as that of the magnetic lens. A description will be given of an electron microscope that is parallel to the optical axis and has a structure in which the length of the plate-like magnetic body in the movable direction of the movable stage is larger than the length of the sample so that the sample does not protrude from the plate-like magnetic body. Further, an example in which the plate-like magnetic body is constituted by a plurality of plate-like magnetic bodies and a guide for guiding a sample stage made of the magnetic body is arranged in a gap between the plurality of plate-like magnetic bodies is also combined. I will explain. According to such a configuration, it is possible to suppress the influence on the beam due to the movement of the field element. Further, by using a guide made of a magnetic material, a linear motor, and a plurality of plate-like magnetic materials, the moving magnetic material is brought close to an infinite flat plate having no relative magnetic permeability and thickness distribution, and a table (sample is removed). The table weight can be suppressed and the load on the stage can be reduced as compared with the case where the plate-like magnetic body is arranged over the entire surface of the top table).

  Hereinafter, the electron microscope provided with the sample stage which has a plate-shaped magnetic body is demonstrated using drawing. FIG. 1 is a diagram showing an outline of a scanning electron microscope. The control device 113 controls the electron optical system, the stage 109, and the like based on the acceleration voltage of electrons input from the user interface by the operator, information on the wafer 110, observation position information, and the like. The wafer 110 passes through the sample exchange chamber via a wafer transfer device (not shown), and is then fixed on the sample stage 109 in the sample chamber 108. The control device 113 includes an applied voltage to the extraction electrode and the acceleration electrode, a retarding voltage applied to the wafer 110, an applied voltage to the electrostatic chuck built in the sample stage 109, the first condenser lens 104 and the second condenser lens. 105 and the excitation current to the objective lens 107 are controlled.

  The electron beam 103 extracted from the electron source 101 by the extraction electrode 102 is converged by the first condenser lens 104, the second condenser lens 105, and the objective lens 107 and irradiated onto the wafer 110. The intermediate electron beam 103 is scanned two-dimensionally on the wafer 110 by the scanning deflector 106.

  The secondary electrons 111 emitted from the wafer 110 due to the irradiation of the electron beam 103 onto the wafer 110 are captured by the secondary electron detector 112, and the secondary electron image is transmitted through a secondary electron signal amplifier (not shown). Used as a luminance signal of the display device 114. Further, since the deflection signal of the secondary electron image display device 114 and the deflection signal of the scanning deflector 106 are synchronized, the pattern shape on the wafer 110 is faithfully reproduced on the secondary electron image display device 114. .

  In order to measure or inspect the pattern on the wafer 110 at a high speed, the sample stage 109 needs to position the wafer 110 at a desired observation point at a high speed and stop it quickly. Further, it is necessary to quickly adjust the focus after positioning the visual field at a desired observation point. FIG. 2 illustrates a stage that enables such high-speed measurement and high-speed inspection.

  FIG. 2 is a sketch of the appearance of the stage apparatus. The stage mechanism includes an X table 203 that is movable only in the X direction (X direction of the coordinate axes shown in FIG. 2) with respect to the base 201 and the Y guide 110 with respect to the base 101 (see FIG. 1). There is a Y table 204 that is movable only in the Y direction of the coordinate axes shown. In this embodiment, the X direction is described as a first direction and the Y direction is described as a second direction.

  An X motor movable element 205, which is a first drive mechanism, is fixed to both ends of the X table 203, and an X motor stator 206 (magnet) fixed to the base 201 by flowing a current through the coil of the X motor movable element 205. ) Generates thrust by electromagnetic force. Similarly, a Y motor movable element 208 as a first drive mechanism is fixed to both ends of the Y table 207, and a current is passed through the coil of the Y motor movable element 208, whereby a Y motor stator 209 ( Thrust due to electromagnetic force is generated between the magnet and the magnet.

  On the Y table 207, a sub table 211 is movably coupled in the X direction on the Y table 207 by an X sub guide 210. A top table 213 guided by a Y sub guide 212 is coupled to the X table 203 via a connecting member 214. The top table 213 incorporates a sample support mechanism (electrostatic chuck or the like) for supporting the wafer 110. Further, the top table 213 incorporates a plate-like magnetic body to be described later.

  FIG. 3 is a diagram showing an outline of a top table in which a plate-like magnetic body is incorporated. The upper diagram of FIG. 3 is a diagram when the top table 213 incorporating the three plate-like magnetic bodies 301, 302, and 303 is viewed from the y direction, and the lower diagram of FIG. 3 is a diagram viewed from the z direction. The plate-like magnetic bodies 301, 302, and 303 function as a shield for suppressing the influence of the magnetic field on the beam irradiation point from the motor movable element that is a magnetic field generation source and leak from the lens gap 115 of the objective lens 107. It functions as a magnetic path for suppressing fluctuations in the magnetic field. The objective lens with the lens gap 115 opened toward the sample side is called a lower magnetic pole open lens or semi-in lens, and the sample is placed in the leakage magnetic field of the objective lens 107. According to such a lens configuration, since the sample is placed in the focused magnetic field, the distance between the objective lens main surface and the sample (working distance) can be shortened, and high resolution of the electron microscope can be realized. It becomes possible to do. On the other hand, if the magnitude of the magnetic field changes directly below the objective lens, it may affect the focusing magnetic field, and as a result, it may take time for focus adjustment. This embodiment reduces the focus adjustment time and speeds up the stage movement time by reducing the weight of the table by reducing the weight of the movable member of the stage while suppressing the influence of the magnetic field other than the focusing magnetic field of the objective lens. This is to realize high throughput of measurement and inspection by realizing both.

  In order to reduce the weight of the table, a gap is provided between the plate-like magnetic bodies 301, 302, and 303. This gap is provided in order to reduce the weight of the entire top table 213 compared to the case where the entire XY direction of the top table 213 is covered with a plate-like magnetic body. Further, in the stage structure illustrated in FIG. 3, Y sub guides 212a and 212b are arranged immediately below the gap between the plate-like magnetic bodies. The top table 213 is supported by the connecting member 214a and the connecting member 214b, and is guided by the Y sub guides 212a and 212b. The Y sub guides 212a and 212b are also formed of a magnetic material in the same manner as the plate-like magnetic body.

  Thus, a plate shape is seen from the guide direction (Y direction) of the guide for guiding the table and the direction (Z direction or electron beam irradiation direction) perpendicular to the other movement direction (X direction) of the table. Each component is arranged so that the Y sub-guides 212a and 212b made of a magnetic material are positioned in the gap between the magnetic bodies. By configuring in this way, it is possible to suppress the fluctuation of the magnetic field caused by the mover and the guide that are magnetic bodies moving to the region where the sample of the top table 213 is located, and to reduce the weight of the top table. Become. By configuring the guide or the plate-like magnetic body to be disposed under the area of the top table where the sample (wafer) is disposed, the above-described effect can be realized. Details of this effect will be described later.

  As mentioned above, when a linear motor equipped with a mover (moving coil) that generates a magnetic field is used as a sample stage (top table) drive source for a charged particle beam apparatus, pay attention to the leakage magnetic field from the linear motor. There must be. This is because the magnetic field fluctuation on the electron trajectory bends the electron beam and causes a trajectory shift in the xy direction and a trajectory shift in the z direction. Hereinafter, they are referred to as a position shift and a focus shift, respectively. FIG. 5 shows a schematic diagram of a moving coil linear motor. The Y direction linear motor 9 includes a Y direction linear motor movable element 9-1 and a Y direction linear motor field element 9-2. The Y-direction linear motor field element 9-2 is composed of a permanent magnet array arranged in a straight line so that S poles and N poles are alternately arranged, and a box-shaped yoke arranged outside the permanent magnet array and having an open surface. Become. The Y-direction linear motor mover 9-1 includes a coil and is disposed in the gap between the permanent magnet rows.

  The X-direction linear motor 10 includes an X-direction linear motor movable element 10-1 and an X-direction linear motor field element 10-2. The X-direction linear motor mover 10-1 and the field element 10-2 have the same structure as the Y-direction linear motor mover 9-1 and the field element 9-2, respectively. The mover is moved and positioned by the interaction between the magnetic field created by the permanent magnet array and the magnetic field created by the coil in the mover.

  The permanent magnet is preferably made of a material having a high residual magnetic flux density and a large coercive force, such as a neodymium magnet. As described above, the arrangement of the permanent magnets needs to be arranged linearly so that the south pole and the north pole are alternately arranged. In order to reduce the leakage magnetic flux, for example, a Halbach array is more preferable. The yoke is preferably made of a material having a magnetic permeability of several hundred to several thousand, such as pure iron, Fe-Si, and permalloy.

  FIG. 6 shows a configuration example of the movable stage. In this example, the movable stage includes a sample stage 6, a Y direction linear motor 9, and an X direction linear motor 10. The driving force of the XY stage requires at least one linear motor that is responsible for each movement in the X direction and the Y direction. The X-direction linear motor field element 10-2 is fixed to a sample chamber container (not shown) and does not move. On the other hand, the Y direction linear motor field element 9-2 is connected to the X direction linear motor movable element 10-1, and can move in the X direction. Furthermore, the sample stage 6 is connected to the Y-direction linear motor movable element 9-1 and can move in the XY directions.

  In this embodiment, both the Y-direction linear motor 9 and the X-direction linear motor 10 have the yoke open surface in the positive z-axis direction. However, the yoke open surface is set to the xy plane, that is, the linear motor is placed horizontally. It doesn't matter.

  The movable stage has a magnetic material, and the magnetic field distribution inside the objective lens 2 changes as the movable stage moves. Although it is possible to suppress this magnetic field fluctuation by moving the movable stage away from the objective lens 2, it is necessary to enlarge the sample chamber container 5 accordingly. Therefore, it is necessary to take measures to suppress magnetic field fluctuations due to magnetic material movement. The relationship between the movable stage position and the magnetic field strength will be described below.

  FIG. 7 illustrates the positional relationship between the objective lens and the components constituting the stage when the left end of the sample is irradiated with the beam. In the state illustrated in FIG. 7, the guide 11 is disposed immediately below the objective lens 2 when observing the left end of the sample. Therefore, the magnetic field strength inside the objective lens 2 is increased by the magnetization of the guide 11. The arrow in the figure represents the distance from the optical axis 8 to the Y-direction linear motor 9.

  FIG. 8 illustrates the positional relationship between the objective lens and the components constituting the stage when the beam is irradiated onto the center of the sample. In the state illustrated in FIG. 8, the magnetic body is not disposed immediately below the objective lens 2 when observing the center of the sample. Accordingly, the magnetic field strength inside the objective lens 2 is increased.

  FIG. 9 illustrates the positional relationship between the objective lens and the components constituting the stage when the right end of the sample is irradiated with the beam. In the state illustrated in FIG. 9, the guide 11 is disposed directly below the objective lens 2 when observing the right end of the sample. Therefore, the magnetic field strength inside the objective lens 2 is increased by the magnetization of the guide 11.

  FIGS. 10 to 12 illustrate the positional relationship of each component constituting the charged particle beam apparatus when a plate-like magnetic body is disposed in the sample stage (top table). In the state illustrated in FIGS. 10 to 12, the plate-like magnetic body 12 is disposed directly below the objective lens 2 regardless of the position of the movable stage. Therefore, the magnetic field strength inside the objective lens 2 is increased by the magnetization of the plate-like magnetic body 12 regardless of the position of the movable stage. The magnetic field strength in the objective lens can be obtained by CAE (Computer Aided Engineering) analysis.

  FIG. 13 shows the relationship between the movable stage position and the magnetic field strength. The horizontal axis is the distance from the optical axis to the Y-direction linear motor, and the vertical axis is the magnetic field strength in the objective lens. In a structure without a plate-like magnetic body, the magnetic field strength is strong in the order of the sample left end, sample right end, and sample center. When observing the left end of the sample, the Y-direction linear motor 9 approaches the optical axis, so the magnetic field strength is stronger than when observing the right end of the sample. When observing the center of the sample, since the magnetic material is not disposed directly below the objective lens 2, the magnetic field strength is the weakest. On the other hand, in the structure in which the plate-like magnetic body is embedded in the movable stage, the plate-like magnetic body 12 is disposed immediately below the objective lens 2 when observing the center of the sample. The magnetic field strength can be kept constant.

  FIG. 14 is a graph showing the relationship between the width of the plate-like magnetic body and the magnetic field strength. The larger the width of the plate-like magnetic body, the smaller the fluctuation of the magnetic field due to the movement of the magnetic body. For example, if the moving distance of the movable stage is 300 mm, the width of the plate-like magnetic body may be made larger than 300 mm. By making the magnetic body an infinite flat plate, the magnetic field fluctuation can be reduced, but since the size that can be mounted is limited, the width of the plate-like magnetic body is preferably larger than the sample diameter.

  Based on the above assumptions, a specific structure of the plate-like magnetic body will be described. FIG. 4 is a diagram showing an outline of the movable stage which is divided and provided with a gap between the respective plate-like magnetic bodies. The plate-like magnetic body 12 is divided into a plurality of parts, and either the guide 11 or the plate-like magnetic body 12 is arranged in the lower region of the sample. According to the configuration illustrated in FIG. 4, the movable stage can be configured with a minimum number of magnetic bodies as compared with the case where a plate-like magnetic body is simply disposed. By minimizing the number of parts to be added, high-speed positioning is possible without increasing the weight of the movable stage.

  Further, it is desirable that the guide 11 and the plate-like magnetic body 12 are made of a material having a substantially equal relative permeability. The guide 11 is preferably made of a material having high rigidity in order to prevent deformation due to external force, for example, an iron-based material. By aligning the relative magnetic permeability of the plate-like magnetic body 12 with that of the guide 11, even if the movable stage is moved, the change of the relative magnetic permeability directly below the objective lens 2 is small, and the magnetic field strength can be kept constant. Another advantage of this structure is that the magnetic field fluctuation caused by the difference in relative permeability between the plate-like magnetic body 12 and the guide 11 is reduced.

  More preferably, in the fourth embodiment, the guide 11 and the plate-like magnetic body 12 are made of the same material. By aligning the material of the plate-like magnetic body 12 with the guide 11, even if the movable stage is moved, the relative magnetic permeability just below the objective lens 2 does not change, and the magnetic field strength can be kept constant. Another advantage of this structure is that magnetic field fluctuations caused by the difference in relative permeability between the plate-like magnetic body 12 and the guide 11 are eliminated.

  If a linear motor as described above is used, magnetic field fluctuations due to the movable stage can be reduced. Therefore, it is possible to provide a movable stage that can suppress the deviation of the electron trajectory due to the movement of the movable stage and can move at high speed. In addition, an electron microscope with high resolution and high throughput can be provided. In particular, since it is possible to reduce the weight of the stage and increase the speed of focus adjustment, it is possible to increase the speed of measurement and inspection using a charged particle beam.

DESCRIPTION OF SYMBOLS 1 Electron gun 2 Electron lens 3 Column 4 Secondary electron detection part 5 Sample chamber container 6 Sample stage 7 Sample 8 Optical axis 9 Y direction linear motor 9-1 Y direction linear motor movable element 9-2 Y direction linear motor field element 10 X direction linear motor 10-1 X direction linear motor mover 10-2 X direction linear motor field element 11 Guide 12 Plate-like magnetic body

Claims (3)

In a charged particle beam apparatus comprising an objective lens for focusing a charged particle beam emitted from a charged particle source and a table for placing a sample irradiated with the charged particle beam,
A guide for guiding the table in one direction; and a plurality of plate-like magnetic bodies arranged between the guide and the objective lens. The guide is made of a magnetic body and is irradiated with the charged particle beam. A charged particle beam device, wherein the charged particle beam device is disposed so as to be positioned in a gap between the plurality of plate-like magnetic bodies when viewed from a direction. In claim 1,
The charged particle beam device, wherein the plate-like magnetic body and the guide are made of a material having substantially the same relative magnetic permeability. In claim 2,
The charged particle beam apparatus, wherein the plate-like magnetic body and the guide are made of the same material.