Sample stage device

A sample stage device (10) is so configured as to calculate ideal position information xtg(i), tg(i) per predetermined period that is unaffected by drive conditions relating to gaps (25, 26), etc., and to determine, per predetermined cycle and in real time, deviations dx(i), dy(i) between real-time measured positions x(i), y(i) by position detectors comprising laser interferometers (33, 34), etc., and ideal position information xtg(i), tg(i). In addition, it calculates, based on deviations dx(i), dy(i) thus determined, such speed command values vx(i), vy(i) for motors (27, 28) that measured values x(i), y(i) would follow ideal position information xtg(i), tg(i), and performs stable and high-speed positioning control for a sample table (11) through feedback control that controls speed in real time. Thus, with respect to a sample stage device, it is possible to provide a stable and high-speed positioning control method for a sample table, which is capable of suppressing noise caused by thermal drift and vibration, without being affected by drive conditions, such as the initial states of gaps, etc.

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2011/064359, filed on Jun. 23, 2011, which in turn claims the benefit of Japanese Application No. 2010-145353, filed on Jun. 25, 2010, the disclosures of which Applications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a sample stage device that holds a sample and that is provided on an electron microscope device used for semiconductor inspection and evaluation, as well as to a positioning control method for a sample table that moves with a sample mounted thereon.

BACKGROUND ART

Ordinarily, in semiconductor device and integrated circuit fabrication processes, the shapes and dimensions of various patterns formed on wafers need to be inspected and evaluated with high precision. Accordingly, not only fabrication devices, but also inspection and evaluation devices are demanded high precision to accommodate the reduced sizes of such semiconductor devices and integrated circuits. As such, for the inspection of the shapes and dimensions of various patterns formed on wafers, scanning electron microscopes (also referred to herein as SEM) with a metrology function are used.

In wafer inspection by such SEMs with a metrology function, or so-called CD-SEMs, a secondary electron image is obtained by image processing secondary electron signals obtained by scanning a wafer with an electron beam, and the shape of the pattern is determined based on changes in the brightness thereof, thereby deriving the dimensions of the pattern under inspection. SEMs comprise a sample stage device for holding a sample. Sample stage devices are configured to position a sample table, which is capable of two-dimensional movement and on which a wafer is mounted, in accordance with the site on the wafer that is to be observed.

SEM inspection of various patterns formed on wafers is required to accommodate, for example, 35 nm node design rules, and obtaining a secondary electron image for an observation site on a wafer with little noise at a high observation magnification of ×300,000 or greater is an important issue. Further, improvements in the contrast of observed images by overlaying numerous secondary electron images on top of one another are also demanded. In order to meet such issues and demands, sample stage devices needed to suppress device vibration and drift (a phenomenon where the resting position of the sample table shifts over time) on a nm scale.

A wafer size currently often inspected is 300 mm. In line therewith, sample tables of sample stage devices for mounting wafers have also become quite large compared to before. At the same time, in order to improve throughput, sample stage devices must also move and position these large sample tables at high speed. With high-power drive mechanisms for moving such large sample tables, increases in temperature occur due to heat generated by motors and drive shafts.

Accordingly, in sample stage devices, as a means for preventing sample stage device drift caused by thermal expansion/contraction due to a rise in temperature resulting from such heat generation, there is a technique in which a 20 to 100 μm gap is provided between the sample table and its drive shaft, and the drive shaft is severed from the sample table when at rest (e.g., Patent Literature 1).

Further, there is a technique in which, during fine movement of the sample table, which is a weakness thereof due to the dead zone created by such a gap, the deviation of a measurement value, which is measured by a position detector that measures the current position of the sample table, from a pre-set target value is monitored, and, when the deviation from the target position falls to or below a certain value, the fine movement drive of the sample table is stopped (e.g., Patent Literature 2).

Through such techniques, sample stage devices provided on conventional electron microscope devices are able to perform positioning control of a sample table by an open loop using a pulse motor.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, with the technique disclosed in Patent Literature 2, if the sample table is moved to a tentative target position at high speed prior to a low-speed movement of the sample table while the deviation between the current position and the target position is greater than the gap provided at the joint between the drive unit and the sample table, the actual resting position will vary due to this gap. Such variability in the resting position is due to various drive conditions of the sample table, such as the initial state of the gap (the initial gap state when moving to the tentative target position at high speed), vibration caused by changes in the acceleration of the sample table, the sample table's inertia, etc. Due to the variability of the actual resting position when the sample table is moved to a tentative target position at high speed, it will sometimes be necessary, during the subsequent low-speed movement to the actual target position, to continue moving the sample table at low speed by an extra amount corresponding to the discrepancy between the tentative target position and the actual resting position. Thus, with the technique disclosed in Patent Literature 2, there was a problem in that it took longer to move the sample table to the actual target position.

In addition, X-Y tables, which are provided on sample stage devices as sample tables capable of two-dimensional movement, comprise separate drive mechanisms for the X-axis direction and the Y-axis directions. As a result, due to the difference between the movement distances by the respective drive mechanisms, such problems as the stopping precision in the axial direction for which movement was completed first affecting and offsetting movement and stopping in the axial direction for which movement is subsequently completed may arise.

Further, because the movement to the actual target position is divided into several rounds of movements and stops by the sample table comprising high-speed movements and stops and low-speed movements and stops by the sample table, there was also a problem in that the control overhead becomes large.

Due to the above, conventional sample stage devices give rise to such problems as throughput variability, stopping precision variability due to changes in mechanical properties (properties of mechanical components), and so forth.

The present invention is made in view of the problems discussed above, and an object thereof is to provide, with respect to sample stage devices provided on electron microscope devices, a stable and high-speed sample table positioning control method capable of suppressing noise caused by thermal drift and vibration without being affected by such drive conditions as the initial gap state, etc.

Solution to Problem

In order to solve the problems mentioned above, a sample stage device of the present invention is configured to calculate, in real time, ideal position information that unaffected by drive conditions caused by gaps, etc., and to also determine, in real time, the deviation of a measured value measured by a position detector from the ideal position information. In addition, it is configured to calculate, based on the thus determined deviation, a motor speed command value so that the measured value follows the ideal position information, and to perform stable and high-speed sample stage positioning control through feedback control that controls speed in real time.

The present specification incorporates the contents of the specification and/or drawings of JP patent application no. 2010-145353 from which the present application claims priority.

Advantageous Effects of Invention

According to the present invention, a logical pattern for ideal position information that is unaffected by drive conditions is generated within a given control period in accordance with a control parameter specified through an operation screen, and a deviation from a laser metrology value is calculated. A speed command value that drives the motor in such a manner as to eliminate this positional deviation is calculated, and speed is controlled in real time. Thus, high-speed positioning control becomes possible without being affected by drive conditions resulting from the gap before driving the table, and so forth.

In addition, moving to a tentative target position becomes unnecessary, and it becomes possible to move directly to the actual target position. Control switching, such as between high-speed drive for moving to the tentative target position and low-speed drive for moving to the actual target position, etc., also becomes unnecessary, thereby making high-speed positioning control possible.

Further, it is possible to provide a stable and high-speed sample stage positioning control method capable of suppressing noise caused by thermal drift and vibration by severing the drive unit and the sample stage after driving the table.

DESCRIPTION OF EMBODIMENTS

An embodiment of a sample stage device according to the present invention is described below based on the drawings

FIG. 1is a diagram showing a schematic configuration of a sample stage device according to the present embodiment.

The embodiment inFIG. 1employs a sample stage device10in a sample chamber2of a scanning electron microscope. In this case, the sample chamber2of the scanning electron microscope is a vacuum chamber that can be evacuated with an unillustrated vacuum pump, and a sample table11is provided as a movable part of the sample stage device10.

In the scanning electron microscope, a column, which is omitted in the diagram, is integrally connected to a sample chamber housing3that defines the sample chamber2. The column houses an electron optical system for directing a primary electron beam onto a sample4. The electron optical system comprises: an electron gun that generates a primary electron beam; a deflector that scans the incident position of the primary electron beam on the sample in accordance with the desired observation area; an objective lens that focuses the primary electron beam at an observation site in the observation area on the sample; etc. In addition, the sample chamber2or column of the scanning electron microscope comprises a secondary electron detector that detects secondary electrons emitted from the sample4as it is hit by the primary electron beam. With the scanning electron microscope, a detection signal, which is outputted from the secondary electron detector as a brightness signal, is inputted to an image processing unit after being amplified and A/D converted. The image processing unit forms a detection system of the scanning electron microscope together with the secondary electron detector, and generates an observed scan image of the observation area. The observed scan image generated by the image processing unit is supplied to an information device70comprising a computer device for controlling sample observation by the scanning electron microscope, and is displayed on a screen of a display71thereof.

The sample table11of the sample stage device10is so provided as to be able to move two-dimensionally inside the sample chamber2. In the illustrated example, it is configured as an X-Y table comprising a base12, a center table13, and a top table14.

The center table13is provided on the base12as an X-axis direction moving table15of the X-Y table in such a manner as to be able to move in the X-axis direction in a two-dimensional plane (X-Y plane) in the sample chamber2. The X-axis direction moving table15is pushed and pulled in the X-axis direction by an X-axis rod19which is moved and displaced along its axis in accordance with the rotation of an X-axis ball screw17that extends in the X-axis direction. An engagement part21is formed on the X-axis rod19, and this engagement part21engages with a groove-shaped guide part23so formed in the X-axis direction moving table15as to extend in the Y-axis direction. The X-axis direction groove width of the guide part23in the X-axis direction moving table15is greater than the X-axis direction width of the engagement part21of the X-axis rod19by a predetermined amount (e.g., 50 μm), thereby creating gap parts25between the engagement part21of the X-axis rod19and the groove side walls of the guide part23.

By means of the gap parts25, the engagement part21is able to place itself in a non-contact state where it is spaced apart from the groove side walls of the guide part23on both sides in the X-axis direction. In addition, the X-axis direction moving table15is able to move in the Y-axis direction along the length of the guide part23without being restrained by the engagement part21of the X-axis rod19. Further, as the engagement part21of the X-axis rod19, by moving in the X-axis direction, comes into contact with either groove side wall of the guide part23in the X-axis direction moving table15, it begins to restrain the movement of the X-axis direction moving table15in the X-axis direction, and, through further movement, pushes and pulls the X-axis direction moving table15along the X-axis direction.

The X-axis ball screw17is linked with an X-axis pulse motor27comprising a stepping motor. Through forward/reverse rotation thereof, it displaces the X-axis rod19to advance/retreat along the X-axis direction, and ultimately moves the X-axis direction moving table15to advance/retreat along the X-axis direction.

The top table14is provided, as a Y-axis direction moving table16of the X-Y table, on the above-discussed X-axis direction moving table15as the center table13in such a manner as to be able to move in the Y-axis direction in a two-dimensional plane (X-Y plane) in the sample chamber2. It is noted that inFIG. 1, with respect to the X-axis direction moving table15and the Y-axis direction moving table16, for ease of comprehension and for purposes of convenience, connecting structures between the two have been omitted, and they have been represented as a schematic where they are placed side by side with the same directionality in the drawing. The Y-axis direction moving table16is pushed and pulled in the Y-axis direction by a Y-axis rod20which is moved and displaced along its axis in accordance with the rotation of a Y-axis ball screw18that extends in the Y-axis direction. An engagement part22is formed on the Y-axis rod20, and this engagement part22engages with a groove-shaped guide part24so formed in the Y-axis direction moving table16as to extend in the X-axis direction. The Y-axis direction groove width of the guide part24in the Y-axis direction moving table16is greater than the Y-axis direction width of the engagement part22of the Y-axis rod20by a predetermined amount (e.g., 50 μm), thereby creating gap parts26between the engagement part22of the Y-axis rod20and the groove side walls of the guide part24.

By means of the gap parts26, the engagement part22is able to place itself in a non-contact state where it is spaced apart from the groove side walls of the guide part24on both sides in the X-axis direction. In addition, the Y-axis direction moving table16is able to move in the X-axis direction along the length of the guide part24without being restrained by the engagement part22of the Y-axis rod20. Further, as the engagement part22of the Y-axis rod20, by moving in the Y-axis direction, comes into contact with either groove side wall of the guide part24in the Y-axis direction moving table16, it begins to restrain the movement of the Y-axis direction moving table16in the Y-axis direction, and, through further movement, pushes and pulls the Y-axis direction moving table16along the Y-axis direction.

The Y-axis ball screw18is linked with a Y-axis pulse motor28comprising a stepping motor. Through forward/reverse rotation thereof, it displaces the Y-axis rod20to advance/retreat along the Y-axis direction, and ultimately moves the Y-axis direction moving table16to advance/retreat along the Y-axis direction.

Further, the wafer4as a sample is positioned and mounted on the table of the Y-axis direction moving table16as the top table14. A sample holder29that positions and holds the wafer4is affixed onto the sample table11.

X-axis direction and Y-axis direction movement positions x and y of the X-axis direction moving table15and Y-axis direction moving table16, respectively, are measured by means of bar mirrors31and32attached to the X-axis direction moving table15and Y-axis direction moving table16, respectively, using laser interferometers33and34respectively corresponding thereto. The X-axis direction laser interferometer33and the Y-axis direction laser interferometer34receive from the corresponding bar mirrors31and32the reflected light of the respective emitted laser light, and measure, in real time, the X-axis direction and Y-axis direction movement positions x and y of the X-axis direction moving table15and Y-axis direction moving table16, respectively, based on the reflected light thus received.

InFIG. 1, the center table13comprises the X-axis direction moving table15, and the top table14comprises the Y-axis direction moving table16. However, the center table13may instead comprise the Y-axis direction moving table16, and the top table14the X-axis direction moving table15.

With the thus configured sample stage device10of the present embodiment, the X-axis direction moving table15and the Y-axis direction moving table16are actuated and controlled by a control device40connected to the information device70that controls sample observation by the scanning electron microscope.

The information device70controls sample observation by the scanning electron microscope, such as by configuring observation conditions for sample observation by the scanning electron microscope, actuating and controlling the electron optical system based on the thus configured observation conditions, outputting onto the screen of the display71an observed age obtained by the detection system, and so forth. Further, in the present embodiment, the information device70also serves as an input/output device for the control device40of the sample stage device10, such as by setting control parameters for driving the sample stage device10through an OSD (on-screen display) screen displayed on the screen of the display71, displaying/outputting an operation log of the sample stage device10that is controlled and actuated by the control device40based on these control parameters, and so forth.

With respect to the movement of the sample table11comprising the X-axis direction moving table15and the Y-axis direction moving table16, the information device70allows, by way of example, initial speed, maximum speed, maximum acceleration, target position, jerk time, severing distance, stopping threshold, etc., to be set as control parameters. It is noted that “initial speed” in this case does not indicate the speed at which the sample table11begins to move from rest, but instead the movement speed at which the sample table11moves to the target position as set by the operator. “Maximum speed” and “maximum acceleration” respectively indicate the “upper limit for speed” and “upper limit for acceleration” in moving the sample table11. In addition, “target position” indicates the positional coordinates of the destination of the sample table11, “jerk time” the duration of the change in the acceleration of the sample table11when beginning to move or stopping or of the change in acceleration based on inertia, “severing distance” the distance by which the engagement parts21and22of the rods19and20are to be separated from the groove side walls of the guide parts23and24in the sample table11upon completion of the movement to the target position by the sample table11, and “stopping threshold” the margin of error for the movement completion position relative to the target position.

The control device40comprises a logical pattern generation unit41, a feedback control unit42, and an operation log collection unit43. Further, the feedback control unit42comprises an X-direction feedback control unit44, which controls the movement of the X-axis direction moving table15along the X-axis direction, and a Y-direction feedback control unit45, which controls the movement of the Y-axis direction moving table16along the Y-axis direction.

Based on the control parameters that have been set at the information device70, the logical pattern generation unit41generates logical movement position information for moving the sample table11from drive start positions x(0), y(0) to target positions xtg, ytg that have been set as control parameters. This logical movement position information is generated as target position command values xtg(i), ytg(i) by breaking it up into finer intermediate target movement positions x(i), y(i) between drive start positions x(0), y(0) and target positions xtg, ytg based on control period tc of the feedback control unit42without being affected by drive conditions, such as the initial states of the gap parts25and26at drive start positions x(0), y(0), and so forth.

Based on the logical movement position information comprising a set of target position command values xtg(i), ytg(i) from drive start positions x(0), y(0) to target positions xtg, ytg thus generated by the logical pattern generation unit41, the feedback control unit42controls the driving of the sample table11per predetermined control period tc. It is noted that this control period tc, partly in connection with the fact that the actuators of the sample table11to be controlled are the pulse motors (stepping motors)27and28, is preset based on a likelihood related to their resolution and to the processing capability of the feedback control unit42itself (the proportion of the time such processing takes relative to one control period), and is, specifically, a value between 1 KHz (a period of 1 ms) and 10 KHz (a period of 100 μs).

The feedback control unit42, in terms of its function, may be divided into the X-direction feedback control unit44, which controls the movement of the X-axis direction moving table15, and the Y-direction feedback control unit45, which controls the movement of the Y-axis direction moving table16. Further, the feedback control units44and45each comprise a laser metrology value reception unit46, a speed command value generation unit47, and a pulse generation unit48. The configuration of each of the units46to48is described below taking the X-direction feedback control unit44as an example.

The laser metrology value reception unit46receives a laser metrology signal outputted from the X-axis direction laser interferometer33, calculates a laser metrology value indicating current X-axis direction movement position x(i) of the X-axis direction moving table15, and supplies it to the speed command value generation unit47and the operation log collection unit43.

For each control period tc mentioned above, based on current X-axis direction movement position x(i) of the X-axis direction moving table15, which is supplied from the laser metrology value reception unit46, and on target position command value xtg(i) corresponding to the logical movement position information generated by the logical pattern generation unit41, the speed command value generation unit47calculates deviation dx(i) between the two. Based on deviation dx(i) thus calculated, etc., the speed command value generation unit47generates speed command value vx(i) corresponding to iteration i as of that point in time in control period tc, and supplies it to the pulse generation unit48and the operation log collection unit43.

The pulse generation unit48generates motor drive pulse Px(i) for moving the X-axis direction moving table15at a speed corresponding to speed command value vx(i) supplied from the speed command value generation unit47, and supplies it to the X-axis pulse motor27and the operation log collection unit43.

Thus, for each control period tc of the speed command value generation unit47, the X-axis pulse motor27is driven by a rotation amount corresponding to motor drive pulse Px(i) supplied from the pulse generation unit48, and the engagement part21of the X-axis rod19attached to the X-axis ball screw17advances/retreats along the X-axis direction at a speed corresponding to speed command value vx(i).

In addition, for each control period tc, the operation log collection unit43collects laser metrology value (the X-axis direction movement position of the X-axis direction moving table15) x(i), target position command value xtg(i), speed command value vx(i), and motor drive pulse Px(i). Thus, log information regarding the X-axis direction moving table15from when movement of the sample table11begins up to when it ends (ceasing movement) is collected/accumulated in the operation log collection unit43.

Further, the Y-direction feedback control unit45likewise comprises units46to48similar to those of the X-direction feedback control unit44described above. Thus, in conjunction with the driving of the X-axis direction moving table15to target position xtg by the X-direction feedback control unit44, the Y-direction feedback control unit45drives the Y-axis direction moving table16to target position ytg in the same control period tc.

Thus, with respect to the movement of the sample table11to target positions xtg, ytg that have been set as the current control parameters, and as log information thereof, laser metrology values x(i), y(i), target position command values xtg(i), tg(i), speed command values vx(i), vy(i), and motor drive pulses Px(i), Py(i) for each iteration i of control period tc with respect to the speed command value generation unit47are accumulated in the operation log collection unit43as the sample table11moves. The log information regarding the movement of the sample table11to target positions xtg, ytg thus accumulated in the operation log collection unit43is read by the information device70through a predetermined operation on the OSD screen of the display71of the information device70and outputted and displayed.

Next, operations of the sample stage device10according to the present embodiment are described based onFIG. 2toFIG. 4.

FIG. 2is a flowchart of a sample table positioning control method by a sample stage device according to the present embodiment.

First, in observing the sample with the scanning electron microscope, the operator, in step S201, enters control parameters for driving the sample stage device10, e.g., initial speed, maximum speed, maximum acceleration, target position, jerk time, severing distance, stopping threshold, etc., through a predetermined OSD screen displayed on the display71of the information device70. It is noted that the arrangement may be such that, of these control parameters, the target position, for example, is set separately from the other parameters and in conjunction with the setting of one or a plurality of observation areas on the sample (wafer)4when configuring the observation conditions of the scanning electron microscope. The maximum speed and maximum acceleration may be preset by default in accordance with the limitations of the ball screws17and18and the pulse motors27and28.

With respect to the sample stage device10, as control parameters are supplied from the information device70in connection with the sample movement for sample observation, the logical pattern generation unit41of the control device40calculates, in steps S202and S203, the X-axis direction drive time and the Y-axis direction drive time for moving the sample table11to target positions xtg, ytg based on the initial speed, target position, and jerk time thereof and within the range of conditions determined by the maximum speed and maximum acceleration that have likewise been set. In this case, the X-axis direction drive time of the sample table11corresponds to drive time txtg of the X-axis direction moving table15, and the Y-axis direction drive time to drive time tytg of the Y-axis direction moving table16. For this calculation, by way of example, if it is the first movement by the sample table11since the wafer4was loaded into the sample chamber2, the positional coordinates for the initial position of the sample table11may be used for movement start positions x(0), y(0), whereas if it is not the first movement by the sample table11, the laser metrology values accumulated in the operation log collection unit43from when movement was last terminated may be used. Alternatively, regardless of whether or not it is the first movement by the sample table11, current laser metrology values x, y as calculated by the laser metrology value reception units46based on the laser metrology signals from the laser interferometers33and34may be used for movement start positions x(0), y(0).

Once drive time txtg of the X-axis direction moving table15and drive time tytg of the Y-axis direction moving table16are calculated, the logical pattern generation unit41compares the two in step S204, and determines which of the X-axis direction and Y-axis direction drive times (operation times) is longer. If one of the X-axis direction and Y-axis direction drive times is longer than the other, the logical pattern generation unit41adjusts the movement speed for the shorter drive time in the manner shown inFIG. 3.

FIG. 3is a chart illustrating a method of adjusting the drive times and movement speeds of the X-axis direction moving table and the Y-axis direction moving table.

As shown inFIG. 3, if drive time tytg in the Y-axis direction is longer than drive time txtg in the X-axis direction, the logical pattern generation unit41, in step S205, recalculates the maximum speed (the gradient of the linear portion of graph301inFIG. 3) in the X-axis direction with respect to the movement to target position (target position coordinate) xtg in the X-axis direction over drive time txtg to make it equal to drive time tytg in the Y-axis direction, and lowers the maximum speed for the movement in the X-axis direction.

Conversely, if drive time txtg in the X-axis direction is longer than drive time tytg in the Y-axis direction, it recalculates, in step S206, the maximum speed in the Y-axis direction with respect to the movement to target position ytg in the Y-axis direction over drive time tytg to make it equal to drive time txtg in the X-axis direction, and lowers the maximum speed in the Y-axis direction.

With respect to this movement speed adjustment, if the sample table11were to be moved to target positions xtg, ytg simply at the initial speed entered as a control parameter in step S201, a significant difference between times txtg, tytg at which the movements to target positions xtg, ytg are completed would arise between the X-direction movement and the Y-direction movement due to the difference between the respective movement distances as indicated by the relationship between graphs301and302inFIG. 3. InFIG. 3, even after the driving of the Y-axis direction moving table16has been completed, the X-axis direction moving table15is still being driven. Under such conditions, the Y-axis direction moving table16, whose driving has been completed earlier (corresponding to graph301), is affected, after it has stopped, by the remaining operation of the X-axis direction moving table15(the drive over the t(x)−t(y) portion of graph302), giving rise to situations where the resting position in the Y-axis direction at completion of movement, that is, target position ytg, is offset.

In order to solve such problems of positional offset after stopping, by having operation times t(x), t(y) for the X-direction and the Y-direction, respectively, for moving the sample table11to target positions xtg, ytg be equal regardless of the difference between their respective movement distances (t(x)=t(y)=tm) as indicated by graphs302and303inFIG. 3, variability in stopping precision due to differences in movement time between the directions (t(x)−t(y)) is reduced. It is noted that in step S204, if the difference between X-axis direction drive time bag and Y-axis direction drive time tytg falls within a pre-defined tolerable range, the logical pattern generation unit41does not adjust movement time, that is, movement maximum speed.

Next, in step S207, the logical pattern generation unit41calculates, per uniform control period tc that is shorter than operation time tm taken to reach target positions xtg, ytg as indicated by graphs302and303inFIG. 3, target position command values xtg(i), ytg(i) at which the X-axis direction moving table15and the Y-axis direction moving table16, respectively, are to be located. The logical pattern generation unit41thus obtains, along with the control parameters, target position command values xtg(i), ytg(i) for each iteration i (i=0, 1, 2 . . . , m) of the control period by the speed command value generation unit47based on a logical pattern that is unaffected by drive conditions, e.g., the initial state of the gap, vibration, noise, etc.

Then, based on such control parameters and target position command values xtg(i), ytg(i), the X-direction feedback control unit44and Y-direction feedback control unit45of the feedback control unit42of the control device40repeat, with every control period tc, the processes of steps S209to S218at step S208until the X-axis direction moving table15and the Y-axis direction moving table16reach target position xtg, ytg, and adjust speed command values vx(i), vy(i) in accordance with target position command values xtg(i), ytg(i).

First, in step S209, the respective speed command value generation units47of the X-direction feedback control unit44and the Y-direction feedback control unit45obtain from the laser metrology value reception units46laser metrology values, that is, current X-axis direction movement position x(i) of the X-axis direction moving table15and current Y-axis direction movement position y(i) of the Y-axis direction moving table16.

In step S210, the respective speed command value generation units47determine whether or not current X-axis direction movement position x(i) and Y-axis direction movement position y(i) thus obtained have reached target positions xtg, ytg by comparing the two using the stopping threshold of the previously-mentioned control parameters. If the results indicate that the differences between target positions xtg, ytg and current X-axis direction movement position x(i), Y-axis direction movement position y(i) fall within a stopping threshold range of the control parameters, the repeated processes of from steps S209to S218are terminated, and the later-discussed drive mechanism severing process of step S220is performed.

By contrast, if the differences between target positions xtg, ytg and current X-axis direction movement position x(i), Y-axis direction movement position y(i) do not fall within the stopping threshold range, the respective speed command value generation units47obtain target position command values xtg(i), ytg(i) generated by the logical pattern generation unit41and corresponding to relevant iteration i (i=one of 0, 1, 2 . . . , m) of control period tc.

In step S211, the respective speed command value generation units47obtain target position command values xtg(i), ytg(i) corresponding to relevant iteration i (i=one of 0, 1, 2 . . . , m) of control period tc based on a logical pattern comprising target position command values xtg(0) to xtg(m), ytg(0) to ytg(m) determined by the logical pattern generation unit41in step S207and which are unaffected by drive conditions, e.g., the initial state of the gap, vibration, noise, etc.

In step S212, based on target position command values xtg(i), ytg(i) obtained in step S211, as well as on current X-axis direction movement position x(i) and Y-axis direction movement position y(i) obtained in step S209, the respective speed command value generation units47calculate deviations dx(i), dy(i) between the two with respect to relevant iteration i of control period tc.

Then, in step S213, based on deviations dx(i), dy(i) thus calculated, the respective speed command value generation units47calculate speed command values vx(i), vy(i) that would bring these deviations dx(i), dy(i) closer to 0 in that control period tc. A method of calculating these speed command values vx(i), vy(i) will now be described based onFIG. 4.

FIG. 4is a comparative chart between a logical pattern-based case and an actual case, and relates to the movement of the X-axis direction moving table or the Y-axis direction moving table.

In the chart, graph401represents the movement of the X-axis direction moving table15or Y-axis direction moving table16to target position xtg, ytg, which is based on a logical pattern that is unaffected by drive conditions, e.g., the initial states of the gap parts25and26, vibration, noise, etc.

In addition, graph402represents the movement of the X-axis direction moving table15or Y-axis direction moving table16to target position xtg, ytg, where, in this case, it is affected by drive conditions, e.g., the initial states of the gap parts25and26, vibration, noise, etc.

In this calculation of speed command values vx(i), vy(i) for relevant control period tc, the X-axis direction moving table15or Y-axis direction moving table16is ideally driven according to graph401, which represents the displacement of the X-axis direction moving table15or Y-axis direction moving table16based on target position command values xtg(i), ytg(i) of a logical pattern that is unaffected by drive conditions.

However, in reality, due to, among other things, the gap parts25and26between the guide parts23and24in the X-axis direction moving table15and Y-axis direction moving table16and the engagement parts21and22of the rods19and20as drive mechanisms, it is impossible to drive the X-axis direction moving table15or the Y-axis direction moving table16according to graph401, which indicates the displacement of position x, y of the X-axis direction moving table15or the Y-axis direction moving table16based on target position command values xtg(i), ytg(i) of a logical pattern unaffected by drive conditions.

In reality, as indicated by graph402, which plots the positional displacement of laser metrology values x(i), y(i), it takes several control periods' worth of time for the change in position x, y to become apparent due to influences of the gap parts25and26in addition to jerk.

As a result, if, for every subsequent iteration i of control period tc, the driving of the X-axis direction moving table15and the Y-axis direction moving table16were to be controlled simply with, for example, speed command values vx(i), vy(i) for the speed indicated by the gradient of the linear portion of graph401inFIG. 4corresponding to target position command values xtg(i), ytg(i) of a logical pattern unaffected by drive conditions, this several control periods' worth of delay time would translate directly into a drop in throughput.

As such, in step S213, if, for example, at the beginning of the ith control period tc, indicated as t(i) inFIG. 4, deviations dx(i), dy(i) indicated as403in the chart are present, the respective speed command value generation units47first calculate, at the beginning of the subsequent i+1th control period tc indicated as t(i+1), such speed command values vx(i), vy(i) for the relevant ith control period tc that would make these deviations dx(i), dy(i) be 0. It is noted that, in this calculation of speed command values vx(i), vy(i) for this control period tc, by way of example, as in the case of the i+2th control period tc indicated as t(i+2) inFIG. 4, at the beginning of this control period tc, if deviations dx(i), dy(i) calculated in step S212are 0, the respective speed command value generation units47, in this embodiment, are configured to calculate the same speed command values vx(i), vy(i) as those calculated and determined in the previous i+1th control period tc.

Then, having thus calculated speed command values vx(i), vy(i) in step S213, the respective speed command value generation units47perform the checking process indicated by step S214prior to supplying speed command values vx(i), vy(i) thus calculated to the pulse generation units48.

Depending on the result of this checking process for speed command values vx(i), vy(i) indicated by step S214, if speed command values vx(i), vy(i) calculated in step S213exceed the limit of the drive mechanism, that is, if maximum speed or maximum acceleration of the control parameters is exceeded, the respective speed command value generation units47recalculate speed command values vx(i), vy(i) in step S215so as not to exceed the limit.

By way of example, in the case of graph401and graph402shown inFIG. 4, even in the subsequent i+1th control period tc, deviations dx(i), dy(i) indicated as403in the chart still remain as deviations dx(i+1), dy(i+1) indicated as404. It can be understood that, as a result of the checking process indicated by step S214, the recalculations of speed command values vx(i), vy(i) indicated by step S215have taken place.

The respective speed command value generation units47thus control speed in such a manner as to bring deviations dx(i), dy(i) indicated by403in the chart closer to 0. As a result, in the i+1th and subsequent control periods tc, they decrease as in deviations dx(i+1), dy(i+1) indicated by404in the chart. In addition, in the control period tc just before the mth at operation time tm at which target positions xtg, ytg are reached, deviations dx(m), dy(m) and speed command values vx(i), vy(i) thereof become approximately 0.

The respective speed command value generation units47supply to the respective pulse generation units48speed command values vx(i), vy(i) that have been calculated and checked in steps S213to S215. In step S216, the respective pulse generation units48, based on speed command values vx(i), vy(i) thus supplied, convert them into motor drive pulses Px(i), Py(i) for driving the pulse motors27and28, and output them to the pulse motors27and28. Then, in step S217, the pulse motors27and28operate according to motor drive pulses Px(i), Py(i) thus converted, thereby causing the rods19and20attached to the ball screws17and18to advance/retreat, thus moving the X-axis direction moving table15and the Y-axis direction moving table16by pushing/pulling them.

In step S218, laser metrology values x(i), y(i) from step S208, target position command values xtg(i), tg(i) from step S211, speed command values vx(i), vy(i) from steps S213to S215, and motor drive pulses Px(i), Py(i) from step S216obtained or calculated in the present control period tc are collected as log information by the operation log collection unit43, and are stored by the information device70in such a manner as to enable monitoring, or searching at a later time.

Thus, the log information stored in step S218is obtained by the information device70and displayed on the screen of its display70. With respect to the manner of display thereof, by way of example, if laser metrology values and target position command values are to be displayed in contrast to each other, the behavior of the sample table11comprising the X-axis direction moving table15and the Y-axis direction moving table16as represented by graph401and graph402inFIG. 4may be visualized. In addition, by thus visualizing log information, it may be used for behavior analysis in the event of an abnormal operation by the sample table11.

After the log information collection process indicated by step S218has been performed, the X-direction feedback control unit44and Y-direction feedback control unit45of the feedback control unit42of the control device40return to step S208from step S219, and repeatedly execute the processes from step S209to step S218until it is confirmed in step S210that target positions xtg, ytg have been reached.

By thus repeatedly performing, per control period tc, the processes indicated by steps S209to S218based on target position command values xtg(i), ytg(i) of a logical pattern unaffected by drive conditions, it becomes possible to control the movements of the X-axis direction moving table15and the Y-axis direction moving table16in such a manner as to follow the logical pattern.

Further, if, in step S210, it is confirmed by the respective speed command value generation units47that current X-axis direction movement position x(i) and Y-axis direction movement position y(i) have reached target positions xtg, ytg, then in step S220, the respective speed command value generation units47execute operations in which the X-axis direction moving table15and the Y-axis direction moving table16are severed from their corresponding drive mechanisms in order to prevent thermal drift caused by the heat generated from the pulse motors27and28and the ball screws17and18.

In these drive mechanism severing operations, the respective speed command value generation units47generate speed command values that cause the rods19and20to advance/retreat in the opposite direction to the direction in which they were being pushed/pulled up to that point and by a predetermined amount that is less than the difference (e.g., 50 μm) between the groove widths of the guide parts23and24in the X-axis direction moving table15and the Y-axis direction moving table16and the widths of the engagement parts21and22of the X-axis rod19and the Y-axis rod20. They then output these values to the pulse generation units48to perform the drive mechanism severing operations.

As described above, with a sample stage device of the present embodiment, high-speed positioning control may be achieved without being affected by the drive conditions of the sample table11, and such drive conditions as the gap before the table is driven, etc.

In addition, moving to a tentative target position becomes unnecessary, and it becomes possible to move directly to the actual target position. Thus, because such control switching as between high-speed drive for moving to a tentative target position and low-speed drive for moving to the actual target position, etc., becomes unnecessary, high-speed positioning control may be achieved.

All publications, patents, and patent applications cited herein are incorporated by reference in their entirety.

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