Abstract:
A driving control apparatus repeats a control cycle of receiving the status value and a target control value of a controlled object and outputting the controlled variable of the controlled object. The driving control apparatus has a detector which detects any one of the position, velocity, and acceleration of the controlled object, and acquires a plurality of detection values from the detector during one control cycle. The driving control apparatus generates a status value to be input to a control unit by using the plurality of detection values.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a driving control apparatus which measures the position of an object or the like and controls the position, rotation, and velocity of the object or the like on the basis of the measured value.  
       BACKGROUND OF THE INVENTION  
       [0002]     To control an object to an arbitrary position or arbitrary rotation or to control to drive an object at an arbitrary velocity, the position of the object is measured by a sensor, and driving of the object is controlled on the basis of the measurement value.  
         [0003]     For example, a semiconductor exposure apparatus comprises a stage which supports a wafer to be exposed to a pattern and can be driven at an arbitrary position, rotation, and velocity. A position measurement sensor for this stage is a laser interferometer (see, e.g., Japanese Patent Laid-Open No. 2002-319541). The current position, rotation, and velocity of the stage are calculated on the basis of the measurement value of the laser interferometer. To control the stage to an arbitrary position, rotation, and velocity, a control system calculates a necessary driving force from information on the current position, rotation, and velocity calculated on the basis of the measurement value of the laser interferometer and information on a target position, rotation, and velocity. The control system controls the stage to an arbitrary position, rotation, and velocity by driving an actuator attached to the stage in accordance with the calculated driving force.  
         [0004]     In stage control, a measurement laser beam irradiates the surface of a bar mirror attached to the side surface of the stage, and reflected light is detected by the laser interferometer, measuring the stage position.  
         [0005]     In this stage position measurement, the bar laser beams having different optical axis positions along the same direction, and the stage position is measured at a plurality of portions. The difference between these measurement values is used to detect the rotation amount and inclination amount of the stage. For example, a plurality of measurement laser beams are arranged side by side in directions parallel and perpendicular to the driving plane of the stage. Calculation is done on the basis of the difference between these measurement values and the distance between the optical axes of the beams. The stage rotation amount is calculated from the difference between two measurement values in the horizontal direction, and the stage inclination amount is calculated from the difference between two measurement values in the vertical direction.  
         [0006]     In a position sensor available at present, an error may be superposed on a measurement value owing to kind of medium (for example, kind of a gas) and fluctuations of magnetic field and electric field or the like in a space between an object to be measured and the sensor main body. An error which makes the output nonlinear may occur also when the actual displacement of an object is a linear change. If the level of the nonlinear error changes depending on the individual difference in sensor, the displacement in the rotational direction is calculated even upon translating the stage in, e.g., only the X direction when the rotation amount and inclination amount are calculated from the above-described difference between a plurality of axes.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention has been made to overcome the above drawbacks, and has as its object to reduce the influence of a sensor measurement error and implement accurate driving control of an object in controlling to drive the object.  
         [0008]     According to one aspect of the present invention, there is provided a driving control apparatus comprising: a control unit configured to repeat a control cycle of receiving a status value and a target control value of a controlled object and outputting a controlled variable of the controlled object; a detector which detects any one of a position, a velocity, and an acceleration of the controlled object; and a generation unit configured to generate the status value to be input to the control unit by using a plurality of detection values by acquiring the plurality of detection values from the detector during one control cycle.  
         [0009]     Also, according to another aspect of the present invention, there is provided a driving control method for a driving control apparatus having a control unit configured to repeat a control cycle of receiving a status value and a target control value of a controlled object and outputting a controlled variable of the controlled object, and a detector which detects any one of a position, a velocity, and an acceleration of the controlled object, comprising: a generation step of generating the status value by using a plurality of detection values by acquiring the plurality of detection values from the detector during one control cycle; and an input step of inputting the status value generated in the generation step to the control unit.  
         [0010]     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
         [0012]      FIG. 1  is a block diagram schematically showing an example of the arrangement of a stage control apparatus according to the first embodiment;  
         [0013]      FIG. 2  is a block diagram for explaining the control loop of a control system associated with the rotation amount of a stage  1  in  FIG. 1 ;  
         [0014]      FIG. 3  is a block diagram showing the arrangement of an input value arithmetic circuit  3  according to the first embodiment;  
         [0015]      FIGS. 4A and 4B  are graphs for explaining ideal measurement values and their arithmetic values;  
         [0016]      FIGS. 5A and 5B  are graphs for explaining measurement values and their arithmetic values when the measurement values vary owing to an error;  
         [0017]      FIGS. 6A and 6B  are graphs for explaining measurement values and their arithmetic values according to the first embodiment;  
         [0018]      FIG. 7  is a block diagram showing the arrangement of an input value arithmetic circuit  3  according to the second embodiment;  
         [0019]      FIGS. 8A and 8B  are graphs for explaining measurement values and their arithmetic values according to the second embodiment;  
         [0020]      FIG. 9  is a graph for explaining application of a bias to an arithmetic value according to the third embodiment;  
         [0021]      FIG. 10  is a graph for explaining a process of excluding a singular value from calculation of an average value according to the fourth embodiment; and  
         [0022]      FIG. 11  is a schematic view showing the schematic arrangement of an exposure apparatus according to the first embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.  
         [0024]     In the following embodiment, an object driving control technique according to the present invention is applied to driving of the stage of a semiconductor exposure apparatus.  
       First Embodiment  
       [0025]      FIG. 11  is a schematic view showing the schematic arrangement of an exposure apparatus according to the first embodiment. In  FIG. 11 , a reticle  111  held on a reticle stage  102  is irradiated with exposure light emitted by an illumination unit  101 . Exposure light having passed through the reticle  111  enters a projection optical system  103 . The projection optical system  103  reduces at a predetermined magnification a pattern image formed by exposure light having passed through the reticle  111 , and the reduced pattern image is projected onto a wafer  112  held by a wafer stage  1 . The wafer stage  1  two-dimensionally moves on a surface plate  104 .  
         [0026]     The position of the wafer stage  1  is measured by laser interferometers  6  and  7  and the like, and measurement values are input to a control unit  120 . The control unit  120  outputs a drive signal to an actuator  12  so as to drive the stage to a target position on the basis of the input measurement values. The actuator  12  controls to drive the wafer stage  1  in accordance with the drive signal from the control unit  120 .  FIG. 11  illustrates a laser interferometer which measures a position along the Y-axis, but a laser interferometer which measures a position along the X-axis may be arranged and utilized to control to drive the wafer stage  1 .  
         [0027]     The following embodiment is related to control of rotation (rotation around the Z-axis) of the stage by measuring a position along the Y-axis. Other driving control operations (stage inclination (rotation around the X- and Y-axes), a position along the X-axis, a position along the Y-axis, and the like) can also be implemented by the same arrangement and method as those for rotation control to be described below.  
         [0028]      FIG. 1  is a block diagram schematically showing an example of the arrangement of a stage control apparatus according to the first embodiment.  FIG. 1  is a schematic view showing an arrangement associated with stage control that is extracted from the arrangement of the exposure apparatus in  FIG. 11  and viewed from the Z-axis. In the following embodiment, the wafer stage  1  will be simply referred to as the stage  1 .  
         [0029]     In  FIG. 1 , the stage  1  can be driven in the X and Y directions within the X-Y plane, a rotational direction centered on the Z-axis perpendicular to the X-Y plane, an inclination direction around the X-axis, and an inclination direction around the Y-axis. As described above, control of the rotational direction of the stage  1  will be explained.  
         [0030]     As shown in  FIG. 1 , a bar mirror  2  is attached to the stage  1 , and irradiated with measurement laser beams  4  and  5 . The measurement laser beams  4  and  5  are so emitted as to be arranged at a predetermined interval d within the same X-Y plane. The Y displacement of the stage  1  is measured by the measurement laser beams  4  and  5  and the interferometers  6  and  7  serving as position detection sensors. An input value arithmetic circuit  3  calculates the current position (rotation amount) of the stage  1  in the rotational direction on the basis of the difference between measurement values obtained by the interferometers  6  and  7  and the interval d between the measurement laser beams  4  and  5 . The input value arithmetic circuit  3  calculates a rotation amount  31  by using a predetermined number of measurement values from the interferometers  6  and  7 , details of which will be described below. A stage controller  10  receives the rotation amount  31  calculated by the input value controlled variable of the stage on the basis of the input value and a separately set target value, and outputs the controlled variable as a stage manipulated variable  11 . An actuator  12  drives the stage  1  in accordance with the input stage manipulated variable  11 .  
         [0031]      FIG. 2  is a block diagram for explaining the control loop of a control system associated with the rotation amount of the stage  1  in  FIG. 1 . In the stage controller  10 , the difference value between a target value  21  and the rotation amount  31  calculated by the input value arithmetic circuit  3  is input to a PID compensator  22 , and the PID compensator  22  outputs a controlled variable (stage manipulated variable  11 ) for driving the stage  1 . The stage manipulated variable  11  is supplied to a controlled object  23  (stage  1  and actuator  12  in  FIG. 1 ), and the stage  1  is driven in accordance with the stage manipulated variable  11 . Measurement values from the interferometers  6  and  7  serving as position detection sensors for the stage  1  are input to the input value arithmetic circuit  3  to calculate the rotation amount  31 .  
         [0032]     The flow of signals in one control cycle of the control system shown in  FIG. 2  when the target value  21  is input to drive the stage to a target rotation position will be considered. The deviation of the input target value  21  from the current value (rotation amount  31 ) is calculated by a subtractor  24 , and input to the PID compensator  22 . The stage controller  10  controls driving of the stage  1  by supplying the stage manipulated variable  11  obtained by the PID compensator  22  to the actuator  12  of the controlled object  23 .  
         [0033]     The position of the stage  1  is measured by the interferometers  6  and  7  serving as position detection sensors. The input value arithmetic circuit  3  calculates the displacement (rotation amount  31 ) in the rotational direction that is obtained from the difference between measurement values from the interferometers  6  and  7 . The calculated rotation amount  31  is sent back to the differentiator  24 , and used to calculate the deviation from the target value. In this manner, one control cycle of the control system is formed. As the control cycle proceeds, the deviation between the target position and the current value decreases and converges to a target value.  
         [0034]     In general, the position of the stage  1  is measured once in one control cycle, and control is executed on the basis of the measurement value. To the contrary, in the first embodiment, the position is measured by the interferometers  6  and  7  a plurality of number of times in one control cycle, and the rotation amount  31  is calculated on the basis of a plurality of measurement values.  
         [0035]      FIG. 3  is a block diagram showing the arrangement of the input value arithmetic circuit  3  according to the first embodiment. The measurement values of the interferometers  6  and  7  are respectively input to average value calculators  82  and  81  in an average value calculation circuit  8  to acquire the average value (to be referred to as a measurement average value hereinafter) of a predetermined number of measurement values. As described above, “a predetermined number of measurement values” mean measurement values acquired in one control cycle by the stage controller  10 . The predetermined number is set on the basis of the time of one control cycle and a time required for measurement by the laser interferometer. Note that the number of measurement values to be acquired may be set by the user via an operation panel or the like. Measurement average values output from the average value calculators  81  and  82  are input to an arithmetic unit  91  in a rotation amount calculator  9  to calculate the rotation amount  31  by using the difference between the measurement average values and the interval d.  
         [0036]     In  FIG. 3 , the averages of measurement values from the interferometers  7  and  6  are respectively calculated by the two average value calculators  81  and  82 . For example, when a measurement value from one interferometer is known in advance to be very stable, the average value of stable measurement values need not be calculated. In the following example, measurement values from the interferometer  7  are stable, and only measurement values from the interferometer  6  are averaged. The average value calculator may be omitted for an interferometer whose measurement value is stable. Also, the user may set whether to validate or invalidate the average value calculation process in each of the average value calculators  81  and  82 . In this case, an “invalid” average value calculator provides a raw measurement value to the rotation amount calculator  9 .  
         [0037]      FIG. 4A  is a graph showing the relationship between the time and an output value from the position sensor when the stage  1  is driven in the Y direction at a predetermined velocity while holding a predetermined rotation angle in  FIG. 1 . The abscissa represents the time, and the ordinate represents the output value (measurement value) of the interferometer. Each arrow along the abscissa indicates a measurement timing in each control cycle. In  FIG. 4A , a represents the measurement value of the interferometer  7 , and b represents that of the interferometer  6 . When the output signal of the sensor is accurately output in response to a change in position, sensor outputs as represented by the measurement values a and b in  FIG. 4A  are ideally obtained upon driving the stage in the Y direction at a constant velocity. The rotation angle in  FIG. 4B  is a value obtained from the difference between the measurement values a and b and the interval d between the measurement laser beams  4  and  5 . When measurement results as shown in  FIG. 4A  are attained, rotation angles shown in  FIG. 4B  are obtained at the measurement timings of respective control cycles. Note that the time axes in  FIGS. 4A and 4B  coincide with each other. As shown in  FIG. 4B , when the stage is driven in the Y direction while keeping a predetermined angle, the rotation angle obtained from the difference between the measurement values a and b and the interval d between the measurement laser beams  4  and  5  is kept constant regardless of the time.  
         [0038]     When, for example, the measurement value of the interferometer  6  has a nonlinear error depending on the Y position, the calculation value of the rotation angle is influenced. This case will be explained with reference to  FIGS. 5A and 5B .  FIGS. 5A and 5B  are graphs showing the relationship between the measurement value by the sensor and the time upon the same driving as that in  FIGS. 4A and 4B . In  FIG. 5A , c represents the measurement value of the interferometer  7 , and d represents that of the interferometer  6 .  FIG. 5B  shows a rotation angle obtained from the difference between the measurement values c and d at the measurement timing of each control cycle and the interval d between the measurement laser beams  4  and  5 . As shown in  FIG. 5B , when the output value of the sensor has a nonlinear error, the rotation angle obtained on the basis of the difference between the measurement values c and d at the measurement timing of each control cycle is so measured as to change in accordance with the Y position though the stage actually keeps a predetermined angle.  
         [0039]      FIGS. 6A and 6B  show an example of the rotation angle obtained using the driving control apparatus according to the first embodiment. In  FIG. 6A , e represents the measurement value of the interferometer  7 , and f represents that of the interferometer  6 . Measurement using the interferometer  6  is performed a plurality of number of times during each control cycle (during the measurement timing of each control cycle). The average value of measurement values is calculated by the average value calculator  82 , and used as a measurement value input at the measurement timing of each control cycle. In  FIG. 6A , g represents the plot of each calculated average value.  FIG. 6B  shows a rotation angle obtained from the difference between the value g and the value e at the measurement timing and the interval d between the measurement laser beams  4  and  5 . In this way, even when an error is superposed on the output of the measurement value, the influence of the error on a calculated rotation angle can be reduced. In controlling to drive the stage, the influence of a sensor measurement error can be reduced to implement accurate driving control of the stage.  
       Second Embodiment  
       [0040]     The average value of measurement values from an interferometer is calculated in the first embodiment, but the average value of rotation amounts may be calculated.  
         [0041]      FIG. 7  is a block diagram showing the arrangement of an input value arithmetic circuit  3  according to the second embodiment. The measurement values of interferometers  7  and  6  are input to a subtractor  92 . The subtractor  92  calculates the difference between the input measurement values, and outputs the difference value. Similar to the first embodiment, a plurality of measurement values are acquired by the interferometers  6  and  7  during one control cycle (during the measurement timing of each control cycle), and a plurality of difference values are output from the subtractor  92 . An average value calculator  83  averages these difference values, and inputs the average value to a rotation amount arithmetic unit  93 . The rotation amount arithmetic unit  93  converts the input difference value into a rotation amount  31  by using the interval d between measurement laser beams, and outputs the rotation amount  31 . The number of difference values corresponds to that of measurement values acquired by the interferometers  6  and  7 , and can be arbitrarily set by the user, similar to the first embodiment.  
         [0042]     The state of each signal (measurement value) in the input value arithmetic circuit  3  will be explained with reference to  FIGS. 8A and 8B . In  FIG. 8A , h represents the measurement value of the interferometer  7 , and i represents that of the interferometer  6 . j represents the result of calculating the difference between the measurement values h and i a plurality of number of times during each control cycle, i.e., represents an output from the subtractor  92 . k represents calculation of the average value during each control cycle for the value calculated by the subtractor  92 , i.e., represents the operation of the average value calculator  83 .  
         [0043]      FIG. 8B  shows a rotation amount obtained by the rotation amount arithmetic unit  93  from an average value calculated by the average value calculator  83 . Similar to the first embodiment ( FIG. 6B ), even when an error is superposed on the output of a measurement value, the influence of the error on a rotation angle can be reduced, implementing high-precision driving control.  
         [0044]     In the second embodiment, the rotation amount is calculated using the interval d and the average value of difference values. In other words, a plurality of values (difference values) corresponding to rotation amounts are calculated, and the rotation amount is calculated from the average value. Alternatively, a plurality of rotation amounts may be calculated from difference values and the interval d to obtain their average value.  
       Third Embodiment  
       [0045]     The rotation amount calculated in the first and second embodiments may be given an arbitrary offset.  FIG. 9  shows this state. The offset is used to correct the rotation amount when the rotation amount has a predetermined offset from a true value upon averaging owing to the output characteristic of a sensor.  
       Fourth Embodiment  
       [0046]     The average value calculator in the first and second embodiments simply calculates the average value of input measurement values or difference values. An average value calculator in the fourth embodiment excludes a singular value from values used to calculate an average value, thereby reducing the influence of noise or the like on driving control. The fourth embodiment will be described with reference to  FIG. 10 . The following embodiment will explain a case in which an average value calculator  83  detects a singular value from difference values obtained by a subtractor  92  in the arrangement according to the second embodiment. It is apparent that average value calculators  81  and  82  may detect and exclude a singular value in the arrangement according to the first embodiment.  
         [0047]     In  FIG. 10 , m represents an output (difference value) from the subtractor  92  in  FIG. 7 . Each averaging section starts immediately after a measurement timing in the control cycle and continues until just before the next measurement timing. An average value is calculated from measurement values in the averaging section, and serves as an input value to a stage controller  10  at the measurement timing. In  FIG. 10 , the abscissa represents the time, and the ordinate represents the difference value. Each arrow along the abscissa indicates the measurement timing of the stage controller  10  in each control cycle. When an input value is supplied at the measurement timing, the stage controller  10  starts the control cycle, and outputs a controlled variable corresponding to the input value.  
         [0048]     As shown in  FIG. 10 , the fourth embodiment can set n representing a tolerance. In calculating an average value during each control cycle, a point exceeding the tolerance n is not used to calculate an average value. In  FIG. 10 , values ( 1001  and  1002 ) exceeding the tolerance n are generated in averaging sections  1  and  3 . Hence, difference values at these points are not used to calculate average values in averaging sections  1  and  3 . That is, the value  1001  in averaging section  1  and the value  1002  in averaging section  3  are excluded from values used to calculate an average value. This can reduce the influence of a singular point generated by noise or the like. The tolerance n can be determined on the basis of a control deviation which can be estimated in advance from the characteristic of a controlled object. As a tolerance setting method, a predetermined fixed range (n/2) from a target control value may be set. Alternatively, the tolerance n may be dynamically changed such that a width of ±n/2 with respect to an average value in the preceding averaging section is set.  
         [0049]     In the above-described embodiments, two measurement beams used to calculate a difference are arranged on the same horizontal plane, and a change of the stage  1  in the rotational direction is calculated. The same signal process as the above one can also be applied when two measurement beams are arranged in a direction (Z direction) perpendicular to the X-Y plane and a change of the stage in the inclination direction is calculated. For a control system which receives a stage position as an input value, the above-described averaging process can be done for position information acquired from one interferometer to exploit an obtained average value as an input value.  
         [0050]     The same arithmetic method can also be employed to calculate distortion from the difference between two measurement beams.  
         [0051]     In the above embodiments, the position of the stage serving as a controlled object is detected to generate an input value to the control system. It is apparent that the present invention can also be applied to an arrangement in which the velocity or acceleration of the stage is detected and used to generate an input value to the control system. For example, the average value of positions or velocities of a controlled object in the translation direction in one control cycle can be calculated and used as an input value to the control system. Further, the present invention can also be applied to a control system which receives as an input value the rotation, inclination, distortion, rotation velocity, or inclination velocity of a controlled object or the like. In this case, the average value of measurement values from, e.g., two velocity sensors in one control cycle is acquired, and the rotation velocity is calculated using the acquired average value and can be used as an input value to the control system. Alternatively, the rotation velocity (or corresponding value) is calculated on the basis of measurement values from two velocity sensors, and the average value of rotation velocities obtained in one control cycle can be used. In this fashion, the present invention can be applied to any control system which receives as an input value the position, velocity, acceleration, rotation, inclination, distortion, rotation velocity, or inclination velocity of a controlled object or the like.  
         [0052]     As has been described above, according to the arrangement of the present invention, a measurement error of an object can be reduced to control to drive the object to a more accurate target value. That is, in controlling to drive an object, the influence of a sensor measurement error can be reduced to control the object to an accurate position, and velocity.  
         [0053]     As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.  
       CLAIM OF PRIORITY  
       [0054]     This application claims priority from Japanese Patent Application No. 2004-099730 filed on Mar. 30, 2004, which is hereby incorporated by reference herein.