JP5002513B2 - Stage positioning control device - Google Patents

Description

  In particular, the present invention relates to an electron microscope apparatus and a stage positioning control method suitable for use in semiconductor inspection and evaluation in the field of semiconductor manufacturing.

  In the semiconductor manufacturing field, a scanning electron microscope having a length measuring function is used to inspect and evaluate whether or not the shape dimension of a pattern formed on a semiconductor wafer is correct. In this scanning electron microscope, a wafer is irradiated with an electron beam, the obtained secondary electron signal is subjected to image processing, and the edge of the pattern is discriminated from the change in brightness to derive the dimension. With the recent miniaturization of semiconductor elements, for example, in order to comply with the design rule of 35 nm node, it is an important issue to obtain a secondary electron image with less noise at an observation magnification of 300,000 times or more. ing. Further, in order to improve the contrast by overlaying a number of images, the stage on which the wafer is mounted and held needs to suppress vibration and drift of the order of nm.

  As a conventional stage positioning control method for an electron microscope apparatus, an example described in Japanese Patent Laid-Open No. 2002-184339 (Patent Document 1) or Japanese Patent Laid-Open No. 2007-80660 (Patent Document 2) is known.

  Of these, Japanese Patent Application Laid-Open No. 2002-184339 discloses two parallel leaf spring mechanisms fixed to a table, two pressurizing members fixed to one of the parallel leaf springs, and the pressurization thereof. Two or more braking mechanisms are provided on each table with a sliding pad fixed to one side of the member and an adjusting means for adjusting the distance between the two pressurizing members, and a sliding surface is provided on the stationary base against which the sliding pad is pressed. It has a configuration. When the table is stopped, the table is fixed by using a static frictional force between the sliding pad and the sliding surface, while at the time of movement, the table is moved by applying a force exceeding the static frictional force.

  Further, JP 2007-80660 A further incorporates a compression coil spring into a leaf spring and a sliding member (sliding pad) of the same table braking principle as in JP 2002-184339 A, and slides with the compression coil spring. A braking force is secured by applying a force in the vertical direction to the transfer surface of the moving member. Furthermore, a gap is provided at the coupling portion between the table and a drive unit such as a ball screw that drives the table, and at the time of fine feed movement, the deviation between the measured value by the position detector and the preset target value is monitored. Position control is performed to stop driving the table when the deviation from the value becomes a certain value or less, and after the table stops, position control for separating the drive shaft is performed using the gap of the coupling portion. Such a configuration is disclosed.

JP 2002-184339 A JP 2007-80660 A

  In the method of fixing the table using the static frictional force between the sliding pad and the sliding surface disclosed in Patent Document 1 and Patent Document 2, the mechanical rigidity of the stage is increased, so that low vibration and drift are reduced during positioning. On the other hand, heat is generated between the sliding pad and the sliding surface because it is always braked with a strong force even when moving the stage. This temperature increase or decrease phenomenon due to heat causes a thermal contraction phenomenon of the member, which causes a drift. In addition, there is a problem that an extra thrust is required for the drive motor to drive the stage while always pressing the sliding pad.

  In Patent Document 2, in order to avoid the occurrence of drift due to a change in the tip position of the drive rod due to the temperature rise of the ball screw, the drive rod is pulled back after the positioning is completed. This pull-back operation is an operation unnecessary for positioning control, and has a problem of causing a reduction in throughput.

  The present invention solves the above-described problems, and suppresses noise caused by drift (a phenomenon in which the stop position shifts as time elapses) and vibration during stage positioning stop, and enables a reduction in positioning time. The purpose is to provide.

  In order to solve the above-described problems, a base including a guide mechanism, a table that moves along the guide mechanism, a drive mechanism that drives the table, and a position detector that measures the position of the table are provided. A stage positioning control device, an actuator that is displaced by applying a voltage, a mechanism that expands the displacement of the actuator, and a braking mechanism that is configured by integrally providing a braking component at a portion that expands the displacement. And a braked rail provided on the base so as to face an upper surface or a side surface of a braking component of the braking mechanism.

  Further, the braking mechanism includes a plurality of compression springs and a brake pad, and the braked rail is pressed by the brake pad.

  Also, the deviation between the measured value by the position detector and the preset positioning set position is monitored, and when the deviation is less than a predetermined allowable deviation, the braking mechanism is activated and the table positioning operation is terminated. It is characterized by comprising a control unit that

  According to the present invention, vibration and drift of the table can be suppressed, and the positioning time can be shortened.

  A stage positioning control apparatus according to an embodiment of the present invention will be described below with reference to FIGS.

  First, an overall configuration of an electron beam microscope apparatus according to an embodiment of the present invention and an outline of a wafer pattern evaluation method will be described. FIG. 1 is a diagram illustrating an overall configuration of an electron beam microscope apparatus. Here, an electron beam microscope apparatus equipped with a sample stage is illustrated. In FIG. 1, a sample stage 3 is mounted inside a sample chamber 2 that can be evacuated by a vacuum pump 1. The sample stage 3 includes a base 4, a center table 5, a top table 6, and the like. The center table 5 is restrained by an X sliding guide member 7 (and a member 8 not shown) as a guide mechanism on the base 4 and can move in one direction (direction indicated by an arrow in FIG. 1: X direction). It has become. The center table 5 is pushed and pulled by an X rod 10 that performs linear motion by rotation of an X ball screw 9 as a drive mechanism, and the tip of the X rod 10 is coupled to the center table 5 by a component (not shown). The X ball screw 9 is coupled to a shaft 11 having a vacuum seal, and can be rotated by a motor 12. On the center table 5, a Y-sliding guide member 13 that intersects with the X-sliding guide member 7 (and 8) at a right angle is similarly configured. 1 in the rear side / front side direction: Y direction). The top table 6 and the Y rod (not shown) are connected. On the other hand, a sample holder 15 is mounted on the top table 6, and a wafer 16 is fixed on the sample holder 15. A bar mirror 17 is mounted on the top table 6 for stage position control, and position measurement is performed using a position detector 18 such as a laser interferometer. The control device 19 controls the motor 12 based on the position of the sample stage 3 measured by the position detector 18 to perform stage position control in the X direction.

  In FIG. 1, only the X-direction stage position control bar mirror 17, the position detector 18, and the X-direction drive motor 12 are shown, but the same bar mirror, position detector, and X-direction are also shown in the Y direction. A drive motor is provided to perform stage position control in the Y direction. The control device 17 functions as “positioning control means” in cooperation with the position detector 16. Specifically, the control device 17 reads a program recorded in a built-in memory, and performs a procedure according to the flowchart of FIG. 3 to be described later. It is a device that includes a main control unit that executes sequentially, a motor control unit, and an on / off command control unit for a brake unit that will be described later.

  On the other hand, in the upper part of the sample chamber 2, an electron gun 20 serving as an electron beam source, a deflector 22 that changes the trajectory of the electron beam 21, an electron lens 23 that converges the electron beam 21, and secondary electrons 24 emitted from the wafer 16. A lens barrel 26 in which a secondary electron detector 25 and the like for taking in are incorporated. The signal of the secondary electron detector 25 is signal-processed by the control unit 27 and sent to the monitor 28 for observation.

  Here, the operation of the electron microscope according to the embodiment of the present invention having the above-described configuration is usually performed as an evaluation method of the pattern shape of the wafer, at which position the desired pattern is in the chip, or on one wafer. For each of the chip patterns to be evaluated, the coordinates are registered in advance. At the time of evaluation, the control device 19 automatically moves the sample stage to the coordinate position based on the registered contents, and then irradiates the electron beam 21 onto the wafer 16 and scans it with the deflector 22 to tens of thousands of times. Hundreds of thousands of times the secondary electron image is acquired and displayed on the monitor 28. Then, the shape of the pattern is discriminated from the change in brightness of the secondary electron image, and the dimension value of the designated shape (pattern line width, pitch, etc.) is calculated. Thereafter, the wafer moves to the coordinate position of the next registered chip, and similarly, image acquisition is repeated to evaluate the shape of the wafer pattern.

  Next, a sample stage positioning control method in the electron microscope apparatus according to the embodiment of the present invention will be described in detail with reference to FIGS. FIG. 2 is a perspective view schematically showing the base 4, the center table 5, the top table 6 and the like on which the sample holder 15 is mounted in the electron microscope apparatus of FIG. The center table 5 is fixed to four sliders 8 slidable on a rail 7 fixed on the base 4, and supported so as to be movable in the X direction by driving a motor 12. Further, the top table 6 is fixed to four sliders 14 slidable on the rail 13 fixed on the center table 5, and supported so as to be movable in the Y direction by driving a motor 29. Further, an X brake rail 35 extending in the X traveling direction is fixed on the base 4. X brake units 30 and 31 to be described later are mounted and fixed to the center table 5 so as to face the X brake rail 35. Similarly, a Y brake rail 36 extending in the Y traveling direction is fixed on the center table 5. Y brake units 32 and 33 are mounted on and fixed to the top table 6 so as to face the Y brake rail 36.

  FIG. 3 is a flowchart showing the contents of stage positioning control in a length-measuring electron microscope equipped with a sample stage according to an embodiment of the present invention. Note that the sample stage is controlled in positioning in the XY directions, but in this flowchart, description will be limited to positioning control in one axis (X) direction.

  First, in step S <b> 10 of FIG. 3, the control device 19 detects the current position of the sample stage 3 using the laser interferometer 18.

  Next, in step S20, the control device 19 reads the positioning target position. As the target position, coordinate data of a position to be evaluated next is registered in advance as a pattern shape evaluation method, and the registered data is read.

  In step S30, a brake operation by a brake unit described later is turned off.

  Next, in step S40, the control device 19 and the motor 12 are driven to move to the target position.

  Next, in step S <b> 50, the control device 19 detects the current position of the sample stage 3 using the laser interferometer 18.

  Next, in step S60, the control device 19 determines whether or not the sample stage is within an allowable range. That is, after moving to the target position, the position of the sample stage at that time is measured by the laser interferometer 18. A value of a positioning tolerance is provided in advance for the target position, and it is determined whether or not the actual position is within the tolerance. If it is not located within the allowable range, the process returns to step S40 and moves to the target position again. If it is within the allowable range, in step S70, the brake by the brake unit is operated, the driving of the motor is stopped, and the positioning is finished.

  In the actual sample stage, positioning control operations in both XY directions are performed simultaneously. That is, steps S10 to S70 are operated in parallel, and the positioning of the sample stage is completed when the positioning operation is finally completed in any of the XY directions.

  In the present invention, the motors 12 and 29 shown in FIGS. 1 and 2 may be of any specifications of a pulse motor or a servo motor, and are not particularly limited. Further, the present invention is not limited to the stage driving system using the motor and ball screw shown in FIG. 1, and a linear motor driving system using a moving magnet system or a moving coil system may be used.

  4 and 5 are a perspective view of the X brake unit 31 and an exploded view of each component of the X brake unit 31, respectively. In FIG. 5, reference numeral 40 denotes a piezo actuator, in which stacked piezo elements (not shown) are mounted, and by applying a voltage to the piezo elements, only the tip 40a expands and contracts in the axial direction. The head 34 is assembled integrally with the distal end portion 40a. The piezo actuator 40 and the holder 42 are assembled together by inserting the piezo actuator 40 into the opening 42 b of the holder 42 and tightening the bolt 47. On the other hand, the sleeve 43 and the head cap screw 44 are inserted into the hole 41C of the link plate 41 and engaged with the hole 42a of the holder 42, whereby the link plate 41 and the holder 42 are assembled together. At this time, the positional relationship is such that the tip of the head 34 provided at the tip of the piezo actuator 40 contacts the vertical plate surface 41 a of the link plate 41. The tip of the head 34 that contacts the vertical plate surface 41a of the link plate 41 is finished in a spherical shape. Reference numeral 45 denotes a ball plunger, which has a spherical tip and is provided with a compression spring (not shown) therein, and is assembled and fixed in the hole 42c of the holder 42. At this time, a constant spring force is applied to the vertical plate surface 41b of the link plate 41 at the tip of the ball plunger 45 in a state where no voltage is applied to the piezo actuator 40, that is, in a state where the head 34 is not displaced. 48 is a brake pad, and 50 is a spring holder. A total of four springs 49 are compressed and assembled in the brake pad 48 and the spring holder 50 so as to have a predetermined pressure. The assembly of the spring 49, the brake pad 48, and the spring holder 50 is assembled to the link plate 41 through the L-shaped bracket 52, whereby the brake unit 31 is finally completed as shown in the perspective view of FIG. To do. The surface of the brake pad 48, which contacts the brake rail side and applies braking, has a spherical shape with a convex central portion.

  FIG. 6 is a schematic view of the mounting relationship between the X brake rail 35 and the X brake units 30 and 31 as viewed from above the table with the base 4, the center table 5, the top table 6 and the like removed in FIG. The X brake units 30 and 31 are arranged so as to be 180 symmetric with respect to the central axis 35 a of the X brake rail 35. That is, each brake pad 48 is arranged to face the side surfaces 35b and 35c of the X brake rail 35. Further, as shown in the figure, the X brake units 30 and 31 are installed with a slight gap (g).

  FIG. 7 is a qualitative graph of the general behavior of an actuator with stacked piezo elements. In the figure, the horizontal axis indicates the generated force of the actuator, the vertical axis indicates the displacement of the actuator, and the relationship between the two is shown. An actuator of a piezo element generates displacement and force when a desired voltage is applied, but has incompatible characteristics. The maximum generated load of the actuator is the force at the time of starting according to the voltage applied when it is fixed at an infinite stiffness theoretically (when the tip is constrained not to be displaced). This force is generally called a blocking force and is approximately proportional to the applied voltage. The generated force is generally proportional to the cross-sectional area of the piezo element. On the other hand, in the no-load state (f = 0), the maximum displacement (δ) occurs according to the applied voltage. The maximum displacement is substantially proportional to the stack length of the piezo elements. The order of the generated displacement is about 0.1% (1/1000) of the total stack length. If the total length of the actuator is 50 mm, the displacement is about 0.05 mm, which is a slight amount. That is, the generated displacement on the vertical axis in FIG. 7 is very small. Therefore, if the brake unit is configured so that the brake pad is attached to the tip of the movable portion of the piezo actuator and is opposed to the brake pad, the gap g must be managed with high accuracy as shown in FIG. Due to the change in the gap, the brake pressing force generated in the piezo actuator changes, and the braking characteristics for the stage are not stable.

  On the other hand, in the present invention, as shown in FIG. 4, the tip displacement generated in the piezo actuator 40 is enlarged to the amount multiplied by (L2 / L1) by the link plate 41 and converted into the surface displacement of the brake pad 48. ing. As a result, the management of the gap (see FIG. 6) between the brake pad 48 and the X brake rail 35 is relatively relaxed. Further, while the displacement is enlarged, the generated force is reduced, on the contrary, the piezo-generated force itself has an area of 10 mm square and can generate a force of several thousand N, which is sufficient. In the present invention, the displacement of the tip of the piezo actuator is changed to the displacement of the surface of the brake pad via the link plate 41 and the spring 49 and is pressed against the brake rail. That is, instead of directly using the force generated at the tip of the piezo actuator, the stage is braked by pressing against the brake rail with the initial spring force previously applied to the spring 49.

  As a general characteristic of an actuator with stacked piezo elements, there is a large resistance to axial force, but it is weak against tension, lateral bending and torsion. On the other hand, as shown in FIGS. 4 to 6, the present invention is not structured to be pressed directly against the brake rail, so that any force other than the axial force is not applied to the actuator. It has become difficult.

  FIG. 8 shows another example of the brake unit structure of the present invention. The brake unit shown in FIGS. 4 to 6 has a structure in which a brake pad 48 constituting the brake unit presses against a side surface of the brake rail to perform braking. On the other hand, the brake unit shown in FIG. 8 changes the L-shaped bracket 52 (see FIG. 5) to the shape of the T-shaped bracket 55 and brakes the upper surface of the X brake rail 35. As described above, in the present invention, when there is a structural restriction or the like when the brake unit or the brake rail is attached, the braking direction can be changed by changing the bracket structure.

  According to the brake unit structure described in the present embodiment, since it is active (ON-OFF) braking, heat is not generated in the brake pad and the brake rail as compared with the method of driving the stage while always pressing the brake pad. In addition, there is an effect that it is possible to avoid problems such as requiring extra thrust in the drive motor.

It is a figure which shows the whole structure of an electron beam microscope apparatus. It is a perspective view of the base and tables in an electron beam microscope apparatus. It is a flowchart which shows the content of the positioning control of a stage. It is a perspective view of a brake unit. It is an exploded view of each component of a brake unit. It is the schematic diagram which looked at the brake rail and brake unit attachment relationship from the table upper direction. It is a figure which shows the general behavior of the actuator which laminated | stacked the piezoelectric element. It is a figure which shows the other example of a brake unit structure of this invention.

Explanation of symbols

4 Base 5 Center table 6 Top table 7 Rail 8 Slider 12, 29 Motor 13 Rail 14 Slider 35 X brake rail 30, 31 X brake unit 32, 33 Y brake unit 36 Y brake rail 40 Piezo actuator 41 Link plate 42 Holder 43 Sleeve 48 Brake pads 49 Spring 50 Spring holder 52 L-shaped bracket

Claims (3)

A base with a guide mechanism;
A table that moves along the guide mechanism;
A drive mechanism for driving the table;
A stage positioning control device comprising a position detector for measuring the position of the table,
An actuator in which piezoelectric elements that are displaced in the guide direction of the table by applying a voltage are stacked ;
A mechanism that has a vertical plate surface that receives the displacement of the actuator in the guide direction of the table, and that expands the displacement around a shaft supported by the table via a support member ;
A braking mechanism configured by integrally providing a braking component on the base side from the vertical plate surface of the mechanism for enlarging the displacement;
A braked rail provided on the base and against which a braking component of the braking mechanism is pressed ,
The stage positioning control device characterized in that the mechanism for enlarging the displacement enlarges the displacement so as to press the braking component from a side surface or an upper surface of the braked rail . The stage positioning control device according to claim 1,
The braking mechanism includes a plurality of compression springs and a brake pad,
A stage positioning control device, wherein the braked rail is pressed by the brake pad. The stage positioning control device according to claim 1 or 2,
Control for monitoring a deviation between a measured value by the position detector and a preset positioning set position, and operating the braking mechanism and ending the table positioning operation when the deviation is less than a predetermined allowable deviation A stage positioning control device comprising a portion.

Images