Charged particle beam device

Abstract

The present invention provides a platform device capable of accurately and quickly positioning a top stage relative to a lens barrel, and a charged particle beam device having the platform device. The charged particle beam device according to the present invention includes a first movable stage and a second movable stage disposed above the first movable stage. The device measures a first relative position between a sample chamber and the first movable stage, a second relative position between the sample chamber and the second movable stage, and a third relative position between the lens barrel and the sample. The relative position between the first movable stage and the second movable stage is corrected based on the first relative position and the second relative position.

Description

Technical Field

[0001] The present invention relates to a charged particle beam device. Background Art

[0002] As semiconductor devices become increasingly miniaturized, higher precision is required not only for manufacturing equipment but also for inspection and evaluation equipment. Scanning electron microscopes (SEMs) are typically used to evaluate patterns formed on semiconductor wafers and detect defects within the wafers. Length-measuring SEMs are particularly useful for evaluating the shape and dimensions of patterns.

[0003] The length measurement SEM is a device that irradiates an electron beam on a wafer, performs image processing on the obtained secondary electron signal, determines the edge of the pattern based on the change in light and dark, and measures the size of the pattern formed on the wafer. In the length measurement SEM, an XY platform is provided to observe and inspect the entire area of ​​the wafer, and the desired part on the wafer can be positioned at the beam irradiation position. The XY platform is driven by, for example, a rotary motor and a ball screw, or a linear motor. In addition, not only the XY plane, but sometimes a platform with a Z axis or a rotational motion around the Z axis is also used. In recent years, in particular, in order to achieve ultra-precision positioning, a non-contact suspension platform is often used, such as a pressure or electromagnetic force such as air.

[0004] There are several different types of suspended platforms. For example, in conventional stacked (two-stage overlapping) XY platforms, the upper axis is sometimes designed as a suspended platform for ease of control, manufacturability, and maintainability. With this configuration, the lower axis is movable in only one direction, while the upper axis is movable in multiple directions (typically six degrees of freedom). Furthermore, this is not limited to suspended platforms; configurations can also employ guide mechanisms or elastic hinges to allow the top stage, which supports wafers, to move in multiple directions (e.g., X and Z) relative to the lower axis's movable platform.

[0005] In this type of platform device, a drive unit (motor) is configured to enable movement in each degree of freedom. Position detection units (sensors) corresponding to each degree of freedom are provided, and their measurement results are constantly fed back to the drive unit, thereby controlling the control variable corresponding to each degree of freedom. This position detection unit is typically a linear scale, laser interferometer, or the like.

[0006] For example, when multiple linear scales are used to detect the position of the top table relative to the lower shaft table in multiple directions, there is a technical problem that it is difficult to improve the absolute accuracy of the top table. The main reason for this is that since the position of the top table is controlled relative to the lower shaft table, the position of the top table is affected by the deformation and posture changes of the lower shaft table. In addition, since the top table is controlled using the sensor value of the linear scale, it is greatly affected by the accuracy of the linear scale itself and the installation accuracy of the linear scale (angle deviation, etc.). As a result, even if accurate positioning can be achieved based on the sensor value, deviations will occur in the position based on the lens barrel that irradiates the electron beam, resulting in a problem of deterioration in the position accuracy of the SEM image.

[0007] On the other hand, it is also known to use a laser interferometer and a reflector as a method for directly detecting the position of the top stage relative to the lens barrel or sample chamber. The laser interferometer can illuminate the reflector with a laser and detect the stage position with a resolution of tens of picometers by interfering with the reflected wave. In addition, since the measurement can be performed at the same height as the wafer, the Abbe error is minimized, and it is widely used for position measurement of many precision stages, including length measurement SEMs. However, even when using a laser interferometer, since the relative position of the lower and upper stages cannot be measured, the position of the top and lower stages cannot be controlled with high precision using only a laser interferometer.

[0008] Similarly, in the height direction, due to the influence of the lower shaft stage and the influence of sensor accuracy, it is not easy to align the top stage height with the lens barrel as the reference. To achieve high-speed and high-precision focusing in SEMs, a height sensor (hereinafter referred to as a Z sensor) is usually installed with the lens barrel as the reference. However, its responsiveness is low, making feedback control based on the Z sensor value unrealistic.

[0009] To address such a problem, Patent Document 1 discloses a technique for adjusting the height between a sample surface and an objective lens based on a focus current determined by converging a charged particle beam using an objective lens.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: US2009 / 0113470 (US10345250) Summary of the Invention

[0013] Technical problem to be solved by the invention

[0014] The technology disclosed in Patent Document 1 allows the wafer to be aligned to the desired height by controlling the position of the top stage to align the height of the sample surface. However, since the focus current is calculated using the objective lens, the time required for height alignment increases, reducing the throughput of measurement inspections. Furthermore, it fails to improve positional accuracy in directions other than height, such as the XY directions.

[0015] In view of the above problems, the present invention aims to provide a stage device capable of accurately and quickly positioning the position of a top stage relative to a column, and a charged particle beam device having the stage device.

[0016] Technical means for solving technical problems

[0017] The charged particle beam device involved in the present invention includes a first movable stage and a second movable stage arranged above the first movable stage, measures a first relative position between a sample chamber and the first movable stage, a second relative position between the sample chamber and the second movable stage, and a third relative position between the lens barrel and the sample, and corrects the relative position between the first movable stage and the second movable stage based on the first relative position and the second relative position.

[0018] Effects of the Invention

[0019] According to the charged particle beam device involved in the present invention, even if the first movable stage (lower axis stage) is deformed, the posture changes, or there is an error in the sensor assembly, the position of the second movable stage relative to the barrel can be accurately and quickly positioned by correcting the relative position between the first movable stage and the second movable stage (top stage). BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a side sectional view of the charged particle beam device 100 .

[0021] Figure 2 1 is a top view of the charged particle beam device 100 .

[0022] Figure 3 1 is a top view of the charged particle beam device 100 .

[0023] Figure 4 FIG. 4 is a diagram showing the arrangement of the adjustment samples 7 on the top table 4 .

[0024] Figure 5 is a conceptual diagram showing platform coordinates and correction points.

[0025] Figure 6 is a flowchart showing the correction map generation process.

[0026] Figure 7 : is a flowchart showing the flow of wafer inspection processing. DETAILED DESCRIPTION

[0027] Figure 1 FIG is a side sectional view of a charged particle beam device 100 according to an embodiment of the present invention. Figure 1 In the present invention, a Y-stage 5 is disposed on the bottom surface of the inner side of the sample chamber 1, capable of free movement in the Y direction (inward from the paper) via two Y linear guides 10a and 10b. A Y linear motor 12 (12a and 12b in the accompanying drawings) is positioned between the sample chamber 1 and the Y-stage 5 to generate relative thrust in the Y direction. Within the sample chamber 1, a Y linear scale 11a is positioned in the Y direction, and a Y linear scale detector 11b is positioned on the bottom surface of the Y-stage 5, facing the Y linear scale 11a. The Y linear scale 11a measures the relative displacement in the Y direction between the Y-stage 5 and the sample chamber 1.

[0028] The top table 4 is positioned above the Y-stage 5. On the Y-stage 5, an X-linear motor 14 (stator 14a and mover 14b in the figure) is positioned between the Y-stage 5 and the top table 4 to generate thrust in the X direction. Furthermore, an X-linear scale 13a is positioned on the Y-stage 5, and an X-linear scale detector 13b is positioned on the bottom surface of the top table 4, facing the X-linear scale 13a. The X-linear scale 13a measures the relative displacement between the top table 4 and the Y-stage 5 in the X direction.

[0029] Furthermore, five motors (not shown) and five linear scales (not shown) are provided between the Y stage 5 and the top stage 4 to constrain the five degrees of freedom (Y, Z, θx, θy, θz) other than the X direction through feedback control. The five motors can be constructed using direct-drive motors such as linear motors or voice coil motors. In this case, for example, by combining two Y-direction motors and three Z-direction motors, thrust and torque for the five degrees of freedom can be generated. Furthermore, rotary motors can be used as the plurality of motors, or a redundant system can be constructed using five or more motors. Similarly, for the five linear scales, by combining two Y-direction linear scales and three Z-direction linear scales, displacement and posture changes for the five degrees of freedom can be detected. Furthermore, various position sensors other than linear scales, such as optical sensors and position sensors using electrostatic capacitance, can be used to similarly construct the platform. The control device 6 uses the obtained linear scale values ​​for the five axes to perform feedback control operations to appropriately control the thrust of the motors for the five axes. This achieves pseudo constraint other than in the X direction (as if moving only in the X direction). As a result, the top table 4 can be positioned in the X direction using the X linear scale 13 a and the X linear motor 14 .

[0030] As described above, a sample stage can be constructed in which the Y stage 5 can be positioned relative to the sample chamber 1 in the Y direction, and the top stage 4 can be positioned relative to the Y stage 5 in multiple directions including the X direction.

[0031] The wafer 2 is placed on the top table 4. The wafer 2 is placed using a wafer holding mechanism having a holding force such as a mechanical restraining force or an electrostatic force.

[0032] The sample chamber 1 is equipped with a top plate 8 and a lens barrel 3. The lens barrel 3 includes an electron optical system for imaging secondary electrons using an electron beam. The lens barrel 3 also includes a Z sensor 17 (optical sensor) that detects the relative height between the lens barrel 3 and the wafer 2. The Z sensor 17 consists of a light-emitting portion 17a and a light-receiving portion 17b, and can optically detect changes in the height of the wafer 2 surface.

[0033] An X-mirror 15x is arranged on the top stage 4. An X-laser interferometer 16x is arranged on the side of the sample chamber 1. The X-laser interferometer 16x irradiates the X-mirror 15x with laser light and uses the reflected light to measure the relative displacement in the X direction between the sample chamber 1 and the top stage 4 (hereinafter referred to as the X-laser value). The X-mirror 15x has a mirror surface on the YZ plane and has a long strip shape in the Y direction. It can also reflect laser light when the Y stage 5 moves in the Y direction. Similarly, for the Y direction, the Y laser interferometer 16y ( Figure 2 shown) and Y mirror 15y ( Figure 2 (as shown) can measure the relative displacement in the Y direction between the sample chamber 1 and the top stage 4 (hereinafter referred to as the Y laser value). Each XY laser interferometer (16x, 16y) can only measure valid values ​​within the movable range of the top stage 4, where the corresponding XY strip mirrors (15x, 15y) are illuminated by the laser. Furthermore, if the X stage moves to a position where it no longer reflects laser light, the subsequent offset in the laser value becomes unstable, making it impossible for the laser interferometer to measure absolute position.

[0034] The control device 6 includes a processing unit, a motor drive amplifier, and other components. In addition to the aforementioned five-axis control of the stage, the control device 6 uses the laser values ​​and scale values ​​in the X and Y directions as inputs to control the drive current of the linear motors, thereby driving the stage in the X and Y directions and positioning it to the desired position. PID control, for example, can be used as a control method for the linear motors.

[0035] Through the above structure, when the chip 2 moves roughly on the XY plane relative to the sample chamber 1, the relative height (Z direction) or posture (θx, θy, θz directions) between the top stage 4 and the Y stage 5 will change slightly, and a secondary electron image (SEM image) based on the lens barrel 3 can be obtained at any coordinate on the chip 2.

[0036] Furthermore, a calibration sample 7 is placed on the top stage 4. The calibration sample 7 is primarily used to adjust the electron optical system that irradiates the electron beam. It is placed on the top stage 4 so that the SEM image required for calibration can be obtained even when the wafer 2 is not being held. The calibration sample 7 is set at the same height as the wafer 2. This allows the calibration sample 7 to be observed even when the electron optical system is set up for observing the wafer 2. Typically, multiple calibration samples 7 are placed on the top stage 4.

[0037] Figure 2 1 is a top view of the charged particle beam device 100 . Figure 2 The platform position configuration is in a state where the chip 2 can be observed. Figure 1 The same reference numerals are omitted for explanation.

[0038] Lasers from laser interferometers 16x and 16y are irradiated onto mirrors 15x and 15y, and the XY coordinates of the platform can be measured together with the scale value and the laser value.

[0039] Position P1 in the figure is the intersection of the laser beams emitted from laser interferometers 16x and 16y, and barrel 3 is configured so that its center (the position at which the electron beam is irradiated for acquiring a secondary electron image) coincides with P1. This allows the position information of the measurement point (electron beam irradiation position) to be measured from the laser values ​​without Abby error relative to the wafer's posture changes (yaw) around the Z axis. Furthermore, Z sensor 17 (not shown) is also configured to detect the height of wafer 2 at position P1, thereby enabling the relative height between wafer 2 and barrel 3 at the electron beam irradiation position to be detected.

[0040] The control device 6 controls the positions of the Y stage 5 and the top stage 4 based on the measurement position information of the wafer 2 so that the desired observation position coincides with the position P1, thereby performing SEM observation.

[0041] Three adjustment samples 7 are placed on the top stage 4. These are positioned around the wafer 2 and inside the four sides of the top stage 4. They are spaced apart from each other within the effective range of the X-mirror 15x and Y-mirror 15y (the position at which the laser interferometer 16 can irradiate the surface). This arrangement of the adjustment samples 7 improves the accuracy of the reference point calibration process, described later.

[0042] Figure 3 1 is a top view of the charged particle beam device 100 . Figure 3 The platform position is configured to observe the state of the adjustment sample 7a. Figure 1 and Figure 2 The same reference numerals are omitted for explanation.

[0043] The adjustment sample 7a is positioned at the electron beam irradiation position P1, and an SEM image of the adjustment sample 7a can be acquired. At this time, the lasers of the laser interferometers 16x and 16y are irradiated to the mirrors 15x and 15y, and the XY coordinates of the stage can be measured together with the scale value and the laser value.

[0044] Thus, the adjustment sample 7 can be observed even when the wafer 2 is not held on the stage, and is therefore used for adjustment and calibration of the electron optical system. The height of the adjustment sample 7 is detected by the Z sensor.

[0045] Figure 4 FIG. 4 is a diagram showing the arrangement of the adjustment sample 7 on the top table 4 in this embodiment. Figure 4 As shown, several examples can be considered for adjusting the configuration position and reference points of the sample 7.

[0046] Figure 4 (1) is an example of setting 3 adjustment samples and 3 reference points. Figure 4 In (1), three adjustment samples 7a, 7b and 7c are respectively set at the upper left, lower left and upper right positions of the top table 4. In each adjustment sample, reference points Pa, Pb, and Pc are set for measuring the reference information of the platform position correction map. In the correction process described later, after the platform is moved to the position of these reference points, the XY laser value, Z sensor value and scale value are obtained. Therefore, each adjustment sample needs to be inside the top table 4 and within the effective range of the X mirror 15x and the Y mirror 15y (the position where the laser of the laser interferometer 16 can be irradiated). At this time, by setting the three reference points at positions far away from each other, for example, the detection sensitivity of the posture angles θx and θy converted from the Z sensor value can be improved.

[0047] Figure 4 (2) is an example of setting four adjustment samples and four reference points. The number of adjustment samples and reference points is preferably three or more, but is not limited to three. Four or more may also be set. In this case, compared to the above case with three, the accuracy may be improved due to the averaging effect.

[0048] Figure 4 (3) is an example of setting 2 adjustment samples and 3 reference points. Figure 4 In (3), two reference points Pa1 and Pa2 are set in adjustment sample 7a. Together with reference point Pc set in adjustment sample 7c, three reference points are used. In this case, from the perspective of posture detection sensitivity, even for reference points set in the same adjustment sample, it is preferable to set them so that they are spaced apart from each other.

[0049] Furthermore, from the perspective of electron optical system adjustment, it is desirable that the height of adjustment sample 7 at the reference point be set to be approximately the same height as wafer 2. However, in this embodiment, the height of adjustment sample 7 does not necessarily have to be the same as wafer 2. In other words, as long as the height of each adjustment sample is known, there is no problem even if the heights of the adjustment samples differ.

[0050] Figure 5 : is a conceptual diagram showing the platform coordinates and calibration points in this embodiment. Figure 5 In the figure, the horizontal axis represents the X coordinate of the platform, and the vertical axis represents the Y coordinate of the platform. Coordinates Ra, Rb, and Rc are respectively obtained by SEM observation. Figure 4 The platform coordinates of the reference points Pa, Pb, and Pc in (1). For example, Figure 4 In (1), when observing the reference point Pa on the upper left side of the top table 4 with SEM, the platform needs to be moved to the lower right side (X axis + side, Y axis - side), and Figure 4 The opposite side of the physical configuration in (1) becomes the platform coordinate. Ex1 is the effective X coordinate range of the Y laser interferometer 16y, that is, the length area of ​​the Y mirror 15y. Similarly, Ey1 is the effective Y coordinate range of the X laser interferometer 16x, that is, the length area of ​​the X mirror 15x. The area surrounded by Ex1 and Ey1 is the effective range of the laser interferometer, which is the area where SEM photography can be performed. The calibration points Rm1 and Rm2 are points distributed in a grid pattern at a certain interval within the effective range of the laser interferometer. The calibration points are points for obtaining data for the top stage position calibration described later (that is, points for obtaining the actual position measurement value).

[0051] Calibration point Rm1 (indicated by the white circle in the figure) is within the range of wafer 2, so both the laser interferometer value and the Z sensor value can be obtained. On the other hand, wafer 2 at calibration point Rm2 (indicated by the black dots in the figure) located near the four corners of the laser's effective range is not in the beam irradiation position, so the Z sensor value cannot be obtained. Therefore, at calibration point Rm1, the linear scale value, laser value, and Z sensor value are obtained as calibration information. At calibration point Rm2, since the Z sensor value cannot be obtained, the linear scale value and laser value are obtained as calibration information. Furthermore, since the adjustment sample 7, adjusted to the same height as wafer 2, is observed at reference points Ra, Rb, and Rc, all linear scale values, laser values, and Z sensor values ​​can be obtained.

[0052] Figure 6 This is a flowchart showing the calibration map generation process in this embodiment. This flowchart starts processing with the wafer 2 placed on the top stage 4. This flowchart is executed by the control device 6.

[0053] At S601, the stage moves to a pre-set reference point position. At S602, at the reference point position, the control device 6 acquires and stores the laser value, linear scale value, and Z sensor value. The sensor information is preferably acquired as average data, such as over a period of one second. At S603, the control device 6 determines whether the acquisition of sensor values ​​for all set reference points has been completed. If all reference point measurements have not been completed, the processes of S601 and S602 are repeated, and if completed, the process moves to S604. In this embodiment, the number of reference points is three, resulting in the execution of S601 and S602 three times, respectively.

[0054] In S604, the control device 6 uses the sensor value measured in S602 to calculate the deviation (offset) of the reference point at the current moment from the initial value. Specifically, the difference between the coordinates (X, Y, Z) and posture angles (θx, θy, θz) of the preset reference point and the current platform position is calculated, and the difference is saved in the memory 605 (set in the control device 6) as the reference point deviation in the current state. More specifically, for example, by using the Z sensor values ​​at the three reference points respectively, the deviation relative to the height in the Z direction and the posture angles in the θx and θy directions can be calculated. Similarly, for the XY direction and the θz direction, the deviation can also be calculated by using the laser value. The offset may change with environmental changes such as temperature or air pressure, so by saving the platform state when generating the correction map in this step, the changes between the actual operation described later and the implementation of this flowchart can be corrected.

[0055] At S606, the platform moves to a pre-set calibration point position. At S607, at the calibration point position, the control device 6 acquires and stores the laser value, linear scale value, and Z sensor value. The sensor information is preferably acquired as average data in the same manner as in S602. At S608, the control device 6 determines whether the acquisition of the sensor values ​​of all the set calibration points is completed. If the measurement of all the calibration points is not completed, the processing of S606 and S607 is repeated, and when it is completed, it is transferred to S609. The number of calibration points can be determined arbitrarily. If the number of calibration points is set to be larger, more accurate calibration can be expected, but there are also disadvantages in that the memory capacity to be saved increases and the time required to generate the correction map is time-consuming. In this embodiment, Figure 5 There are about ten correction points as shown, so the processes of S606 and S607 are performed about ten times each.

[0056] When the sensor values ​​of all calibration points are acquired, the control device 6 calculates the calibration formula in S609. The calibration formula is a function for calculating the control target position (the suspension amount and the posture angle in the suspension system) in each stage coordinate, which is used to position the wafer 2 at the desired position relative to the barrel 3. The control target position is the target value of the relative position and posture angle between the Y stage 5 and the top stage 4 in each stage coordinate. As the form of the calibration formula, Figure 5 The correction mapping type is effective in which the sensor values ​​of the measurement points in the image are used to calculate the control target position on arbitrary coordinates by methods such as linear interpolation or spline interpolation. In this case, the various coefficients of each coordinate used for interpolation are stored in the memory 605. In addition, as another method, it can also be implemented by using the sensor values ​​obtained at the correction points to calculate the control target position as a function of the XY coordinates by methods such as the least squares method. In this case, the coefficients of the mathematical formula used for correction are stored in the memory 605. In addition, the order related to the XY coordinates when using the formula can be arbitrarily set, whether it is a linear form as a first-order form or the coordinates as a zero-order form, or a fixed value can be used. These low-order correction formulas are particularly effective when the number of correction points is small.

[0057] As described above, the control target position for the relative position and attitude angle between the Y stage 5 and the top stage 4 in any XY coordinates can be calculated using the correction formula stored in the memory 605. By controlling the top stage 4 using this control target position, the wafer 2 can be positioned at a desired position relative to the barrel 3 in all stage coordinates.

[0058] Figure 6 The correction map generation process described above can also be performed during adjustment after platform assembly or during regular maintenance, etc. This allows for adaptation to temporal changes and maintenance of appropriate positioning accuracy.

[0059] In S604 or S609, the reference point offset and calibration formula information stored in memory 605 represents the mechanical state of the platform mechanism. Specifically, the change in the information stored in memory 605 can be considered as a long-term temporal change in the platform mechanism, enabling prediction of maintenance periods, including replacement of platform mechanism parts, and pre-failure diagnosis.

[0060] Figure 7 This is a flowchart showing the flow of wafer inspection processing in this embodiment. This flowchart starts processing in a pre-inspection state where no wafer 2 is placed on the top stage 4. This flowchart is executed by the control device 6.

[0061] At S701 , the wafer 2 is first placed on the top stage 4 . At S702 , the control device 6 performs an alignment process using an optical microscope or SEM to detect the placement position of the wafer 2 on the top stage 4 .

[0062] In S703, the platform moves to the pre-set reference point position. In S704, at the reference point position, the control device 6 obtains and stores the laser value, linear scale value, and Z sensor value. The sensor information is preferably obtained as average data such as 1 second. In S705, the control device 6 determines whether the sensor value acquisition of all the set reference points is completed. If all the reference point measurements are not completed, the processing of S703 and S704 is repeated, and if completed, it is transferred to S706. The processing of S703 to S705 is the same as that of Figure 6 The processing of S601 to S603 in is the same.

[0063] In S706, the control device 6 calculates the current offset value using the sensor value measured in S704. The calculation process in S706 is the same as that in S604. The obtained offset is stored in the memory 605. As a result, the reference point offset calculated in S604 when generating the calibration map and the current reference point offset calculated in S706 are stored in the memory 605.

[0064] In S708, the control device 6 calculates the correction amount (control target position) at the next measurement point of the platform's moving target using the information in the memory 605. Specifically, the control target position of the moving target in platform coordinates is first calculated using the correction formula stored in the memory 605 (substituting the coordinate values ​​into an interpolation operation or mathematical formula). The control target position (levitation amount and posture angle) at the next measurement point is calculated by adding the offset calculated in S706 to the control target position calculated using the correction formula.

[0065] The offset can be in any form, as long as the difference between the current and initial positions of the reference point can be calculated. For example, the offset calculated in S604 can be pre-incorporated into the calibration equation. In S706, the difference between the current reference point offset (S706) and the reference point offset (S604) when the calibration map was generated can be obtained and added to the calibration equation.

[0066] In S709, the control device 6 moves the stage to the next measurement point. At this point, the position of the top stage 4 is corrected using the control target position (levitation amount and attitude angle) calculated in S708, ensuring that it is always accurately positioned relative to the lens barrel 3. In S710, the control device 6 captures an SEM image at the measurement point and inspects or measures the pattern on the wafer 2 based on the acquired image.

[0067] In S711, the control device 6 determines whether the inspection of all the set measurement points is completed. If all the measurement points are completed, the wafer 2 is unloaded in S713, and the series of wafer processing is completed. If there are still measurement points that have not been completed in S711, it is determined in S712 whether recalibration is required. This recalibration refers to re-implementing the offset calculation process of the reference point (S703 to S706). This is effective when the same wafer is inspected for a long time or when the platform structure is deformed due to changes in the platform itself or the surrounding environment (temperature, air pressure, etc.). By recalculating the current reference point offset, it is expected to improve the accuracy of position correction.

[0068] As the conditions for recalibration in S712, the following conditions are considered:

[0069] (a) When the SEM is photographed in S710, autofocus processing is usually performed. Therefore, based on the focus value after the photograph (equivalent to the height from the barrel 3 to the wafer 2), the height deviation of the top table 4 relative to the time when the correction table was prepared is calculated (estimated). When the deviation exceeds the threshold, re-calibration is performed. If the deviation can be estimated for measurement results other than height, the estimated result can be compared with the threshold to determine whether re-calibration is required. As measurement results other than height, for example, the tilt of the barrel can be considered;

[0070] (b) When a certain time has passed since the last calculated reference point shift, or when the measured value of a sensor measuring the physical state of the charged particle beam device 100 (e.g., the platform temperature or the temperature of its surroundings detected by a temperature sensor) has changed by a certain degree or more, and when the conditions that indicate that the physical state of the platform or the charged particle beam device 100 itself has changed are met, recalibration is performed;

[0071] (c) Detecting the deviation of the measurement point pattern from the image center (field of view deviation) in the SEM image captured by the SEM. The SEM device is configured to position the pattern to be observed at the center of the field of view when the pattern is specified. If the pattern to be observed is not positioned at the center of the field of view, field of view deviation occurs. If the field of view deviation exceeds a threshold, recalibration is performed.

[0072] thus, Figure 7 In the actual wafer inspection process shown, by using the current reference point offset, information on previously measured calibration points, and the reference point offset at that time, high-precision calibration can be achieved without reducing inspection throughput.

[0073] <Summary of the Invention>

[0074] As described above, the charged particle beam apparatus 100 according to this embodiment can accurately and quickly position the top stage 4 relative to the column 3 by correcting the relative position between the Y-stage 5 and the top stage 4, even in situations where the lower axis stage is deformed, the posture changes, or there are errors in sensor assembly. Specifically, a correction table is pre-generated using the accurate coordinates of the reference points. When the stage position is specified, this correction table is used to derive a control target position, thereby controlling the relative position between the Y-stage 5 and the top stage 4 and accurately positioning the stage.

[0075] <Regarding Modifications of the Invention>

[0076] In the above embodiment, a linear guide is used as the guide mechanism for the lower axis, and a magnetic bearing is used as the guide mechanism for the upper axis. However, any combination of other guide mechanisms (e.g., fluid bearings, elastic support structures, etc.) may be used. Furthermore, the top table 4 is movable with six degrees of freedom relative to the Y-stage 5, including the X-direction. However, it is entirely possible to restrain a portion of the top table 4 using an elastic support structure or the like.

[0077] In the above embodiment, the position of the top stage 4 relative to the sample chamber 1 is measured by the laser interferometer 16, but other measuring devices may be used, such as an optical sensor.

[0078] In the above embodiment, the correction point is as follows Figure 5 The illustrated configuration is in the form of grid points, but points other than the grid points may be set as correction points.

[0079] In the above embodiment, when it is determined in S712 that recalibration is necessary, recalibration is automatically performed, but a method of displaying an alarm to remind the user to recalibrate is also effective instead of or at the same time.

[0080] In the above embodiment, the control device 6 may be configured by using hardware such as a circuit device that realizes the function, or may be configured by a computing device such as a CPU (Central Processing Unit) executing software that realizes the function.

[0081] Label Description

[0082] 1 sample room

[0083] 2 chips

[0084] 3-lens barrel

[0085] 4 top platforms

[0086] 5Y station

[0087] 6 Control device

[0088] 7 Adjust the sample

[0089] 8 top plate

[0090] 10Y linear guide

[0091] 11Y linear scale

[0092] 12Y linear motor

[0093] 13X linear scale

[0094] 14X linear motor

[0095] 15 strip mirrors

[0096] 16 Laser interferometer

[0097] 17Z sensor

[0098] 100 charged particle beam device.

Claims

1. A charged particle beam device for irradiating a sample with a charged particle beam, characterized in that: include: Sample room; a first movable stage movable in a first direction relative to the sample chamber; a second mobile station movable in a plurality of directions relative to the first mobile station; a column disposed above the second moving stage and irradiating the sample with the charged particle beam; a position detection unit for measuring a first relative position between the sample chamber and the first moving stage, a second relative position between the sample chamber and the second moving stage, and a third relative position between the lens barrel and the sample; as well as a control unit for driving the first mobile station and the second mobile station, The control unit corrects the relative position between the first mobile station and the second mobile station based on the first relative position and the second relative position. The control unit acquires a first set of the first relative position at a reference point on the second mobile station, the second relative position at the reference point, and the third relative position at the reference point, The control unit calculates an offset between the known coordinates of the reference point and the measured value of the coordinates of the reference point using the first set, The control unit corrects a position deviation of the second mobile stage relative to a target position of the second mobile stage using the offset.

2. The charged particle beam device according to claim 1, wherein The position detection unit measures the first relative position using a linear scale, The position detection unit measures the second relative position using a laser interferometer or an optical sensor. The position detection unit measures the third relative position using an optical sensor.

3. The charged particle beam device according to claim 1, wherein The control unit acquires at least one of a second set of the first relative position at a correction point on the second mobile station and the second relative position at the correction point, and a third set of the first relative position at the correction point, the second relative position at the correction point, and the third relative position at the correction point, The control unit determines a correction formula, the correction formula using at least one of the second set or the third set to calculate a control target position, the control target position being used to move the second mobile station to a specified position with the correction point as a reference, The control unit positions the second mobile stage at the designated position using the correction formula.

4. The charged particle beam device according to claim 3, wherein The control unit determines the correction equation as a function of the relative position between the first mobile stage and the second mobile stage and the relative posture between the first mobile stage and the second mobile stage.

5. The charged particle beam device according to claim 3, wherein The correction formula is configured to calculate the control target position on coordinates between the plurality of correction points by interpolating measurement results obtained by the position detection unit at the plurality of correction points.

6. The charged particle beam device according to claim 1, wherein The reference point is arranged at a position on the adjustment sample provided on the second moving stage, The reference point is arranged within a range in which the position detection unit can measure the second relative position.

7. The charged particle beam device according to claim 6, wherein The reference points are arranged at three or more points on the second moving stage.

8. The charged particle beam device according to claim 3, wherein The position detection unit measures the first relative position and the second relative position for the calibration point that is not on the sample, and does not measure the third relative position. The position detection unit measures the first relative position, the second relative position, and the third relative position of the calibration point on the sample. The control unit acquires the second set for the calibration points that are not on the sample, The control unit obtains the third set of calibration points on the sample.

9. The charged particle beam device according to claim 1, wherein The control unit estimates whether the current value of the first set has changed by more than a threshold value since the time when the offset is calculated. When the control unit estimates that the current value of the first set has changed by more than the threshold value, the position detection unit measures the first set again. The control unit recalculates the offset using the first set acquired through the re-measurement.

10. The charged particle beam device according to claim 1, wherein The control unit estimates whether the current value of the first set has changed by more than a threshold value since the time when the offset is calculated. When the control unit estimates that the current value of the first set has changed by more than the threshold value, the control unit outputs a message prompting the position detection unit to measure the first set again.

11. The charged particle beam device according to claim 1, wherein The control unit estimates whether the current value of the first set has changed by more than a threshold value since the time when the offset is calculated. When the control unit estimates that the current value of the first set has changed by more than the threshold, the position detection unit remeasures the first set or outputs a message prompting the remeasurement. The control unit performs the estimation using at least one of an elapsed time since the first set was acquired or an amount of change in the physical state of the charged particle beam device since the time when the first set was acquired.

12. The charged particle beam device according to claim 1, wherein The control unit generates an observation image of the sample using a detection result of secondary particles generated by irradiating the sample with the charged particle beam. The control unit estimates whether the current value of the first set has changed by more than a threshold value since the time when the offset is calculated. When the control unit estimates that the current value of the first set has changed by more than the threshold, the position detection unit remeasures the first set or outputs a message prompting the remeasurement. The control unit performs the estimation based on whether the amount of deviation of the visual field center of the observation image exceeds a threshold value.

13. A charged particle beam device for irradiating a sample with a charged particle beam, characterized in that: include: Sample room; a first movable stage movable in a first direction relative to the sample chamber; a second mobile station movable in a plurality of directions relative to the first mobile station; a column disposed above the second moving stage and irradiating the sample with the charged particle beam; a position detection unit for measuring a first relative position between the sample chamber and the first moving stage, a second relative position between the sample chamber and the second moving stage, and a third relative position between the lens barrel and the sample; as well as a control unit for driving the first mobile station and the second mobile station, The control unit corrects the relative position between the first mobile station and the second mobile station based on the first relative position and the second relative position. The control unit acquires a first set of the first relative position at a reference point on the second mobile station, the second relative position at the reference point, and the third relative position at the reference point, The control unit calculates an offset between the known coordinates of the reference point and the measured value of the coordinates of the reference point using the first set, The control unit acquires at least one of a second set of the first relative position at a correction point on the second mobile station and the second relative position at the correction point, and a third set of the first relative position at the correction point, the second relative position at the correction point, and the third relative position at the correction point, The control unit determines a correction formula for calculating a control target position using at least one of the second set or the third set, the control target position being used to move the second mobile stage to a specified position with the correction point as a reference. The control unit calculates the control target position using the correction formula, and adds the offset to the control target position, thereby positioning the second mobile stage at the designated position.

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