Patent Publication Number: US-6337733-B1

Title: Apparatus including a motor-driven stage for exposing a photosensitive substrate, and method of making such apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 09/005,755 filed Jan. 12, 1998 now abandoned, which is a division of application Ser. No. 08/520,245 filed Aug. 28, 1995 now U.S. Pat. No. 5,777,721. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an exposure method and apparatus which exposes a photosensitive substrate with a pattern image of a mask used in a photolithographic process for manufacturing micro devices such as a semiconductor device, liquid crystal display device, image pick-up device (CCD), thin-film magnetic head, opto-magnetic disc, etc. 
     2. Related Background Art 
     Conventionally, a projection exposure apparatus of a step-and-repeat type (stepper, or the like) which positions shot areas in an exposure field of a projection optical system successively by stepping of a wafer and collectively exposes the shot areas with a pattern image of a reticle is used as an exposure apparatus for transferring a reticle pattern serving as a mask onto a wafer (or a glass plate) on which a photosensitive material (photo-resist) is coated. In a projection exposure apparatus of this type, a driving device of a feed screw system was chiefly used as a driving device for driving a wafer stage or a reticle stage, conventionally. Recently, however, in order to improve the throughput (productivity) by reducing a positioning time and to lower an oscillation by a non-contact drive, a linear motor become to be used as a driving device therefor. 
     As an exposure apparatus for transferring a pattern image having a larger space onto a wafer without expanding the exposure field of a projection optical system, a projection exposure apparatus of a step-and-scan type which performs exposure by synchronously scanning a reticle and a wafer with respect to a projection optical system after stepping each shot area on the wafer to a scan start position is employed. The exposure apparatus of the scanning exposure type is disclosed, for example, in U.S. patent application Ser. Nos. 139,803 (Oct. 22, 1993) and 274,037 (Jul. 12, 1994). When the scanning exposure apparatus is of a reduction projection type, since it is required to scan (especially a reticle) with high speed, it is preferably to use a linear motor at least as a driving device for a reticle stage. It is also preferable to also drive a wafer stage by the linear motor in order to perform more stable scanning. 
     Conventionally, a linear synchronous motor of a permanent magnet type, electromagnet type, or the like, is used as a linear motor for driving a reticle stage or a wafer stage of an exposure apparatus. This linear synchronous motor basically consists of an armature coil on the primary side and a field magnet on the secondary side, and is arranged such that a mover side is moved by a moving magnetic field which is generated in said armature coil. In this case, it is required to detect the position of the field magnet on the secondary side in order to correctly determine the phase of the moving magnetic field generated in said armature coil (in order to conduct phase switch correctly). Then, in the conventional exposure apparatus, the linear synchronous motor is provided with a phase switching sensor (consisting of a magnetic sensor of a Hall element type) for detecting a positional relation of the polarity of the field magnet with respect to the standing armature coil. In the exposure apparatus, there is also provided a coordinate measuring device (laser interferometer, or the like) for detecting the position of a stage. However, the coordinate measuring device is provided in parallel to the phase switching sensor in the conventional exposure apparatus. 
     As described above, when the linear motor is used as the driving device for driving the stage in the conventional exposure apparatus, the phase switching sensor is provided separately from the coordinate measuring device for the stage. This phase switching sensor is required to be disposed, for example, periodically, on the entire range in which the field magnet moves, which results in an inconveniently complicated mechanism and wiring of the stage. 
     Since, generally, various mechanisms such as an alignment sensor, a focal position detecting system for autofocusing, and a loader system, for a reticle or a wafer, are incorporated in an exposure apparatus, it is desired to constitute a driving mechanism for the stage as simple as possible and to secure a space around the stage as wide as possible. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is, in an exposure apparatus using a linear motor as a driving device for driving a stage, to drive said linear motor without using a special phase switching sensor. 
     A first exposure apparatus according to the present invention comprises a mask stage for positioning a mask, a linear motor for driving said mask stage, and a position detection system for detecting the position of said mask stage, and uses an output signal from the position detection system as phase control information for said linear motor. 
     A second exposure apparatus according to the present invention comprises a substrate stage for positioning a photosensitive substrate, a linear motor for driving said substrate stage, and a position detection system for detecting the position of said substrate stage, and uses an output signal from the position detection system as phase control information for said linear motor. 
     In the first and second exposure apparatuses, said position detection system is, for example, a laser interferometer. 
     According to the first and second exposure apparatuses of the present invention, the linear motor, such as a linear synchronous motor, is used as a driving device for driving the mask or the photosensitive substrate, and the position detecting system of the stage is used as the phase switching sensor for detecting the position of the field magnet of the linear synchronous motor. Specifically, a positional relation between the armature coil and the field magnet of the linear motor for driving said stage is detected on the basis of an output (a result of measurement) of the position detection system of the stage. For example, when the field magnet and the armature coil of said linear synchronous motor are in a predetermined positional relation, a measured value by said position detection system is reset (or preset), and thereafter the measured value by said position detection system is divided by an alignment pitch of the field magnet to obtain a remainder, whereby the positional relation (phase) between said field magnet and said armature coil can be obtained. Accordingly, said linear motor can be driven without provision of another switching sensor. As a result, the manufacturing cost can be reduced, the stage mechanism can be simplified, and other mechanisms can be loaded easily. 
     In addition, when the laser interferometer is used as the position detection system, the position of the stage can be detected without contact at a high precision, and the phase control between the armature coil and the field magnet of the linear motor can be performed with very high resolving power and a high precision. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic structural view showing a projection exposure apparatus according to an embodiment of the present invention; and 
     FIG. 2 is a structural view showing a part of the wafer stage in FIG.  1  and the control system thereof. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of an exposure apparatus according to the present invention will be described with reference to the drawings. In the embodiment, the present invention is applied to a reduction projection exposure apparatus of the step-and repeat type (stepper) which exposes each shot area on a wafer by a reduced image of a pattern of a reticle. 
     FIG. 1 shows a schematic structure of the projection exposure apparatus according to the present embodiment. Referring to FIG. 1, an exposure light (such as an i beam, excimer laser, or the like) IL emitted from an illumination optical system  1  is reflected by a dichroic mirror  2 , and illuminates a pattern region of a reticle R with substantially uniform intensity of illumination. The Z axis is set to parallel to a main optical line of the exposure light IL reflected by the dichroic mirror  2  (the optical axis of the projection optical system PL), the X axis is set in the direction parallel to the sheet surface of FIG. 1 within the two-dimensional plane perpendicular to Z axis, and the Y axis is set in the direction perpendicular to the sheet surface of FIG.  1 . 
     The reticle R is mounted on a Y stage  3 Y which is movable in the Y direction, and the Y stage  3 Y is mounted on an X stage  3 X which is movable in the X direction on a base  4 . The X stage  3 X is driven in the X direction by a linear motor which consists of a stator  5 A and a mover  5 B (hereinafter called the reticle X-stage linear motor) with respect to the base  4 , and the Y stage  3 Y is driven in the Y direction by a linear motor (not shown) having the same structure as the reticle X-stage linear motor with respect to the X stage  3 X. In the following, a stage system which comprises the Y stage  3 Y, the linear motor for driving said Y stage  3 Y, X stage  3 X, and the reticle X-stage linear motor for driving said X stage  3 X is called a reticle stage. Though the reticle stage in this embodiment has a structure in which the X stage  3 X and the Y stage  3 Y are layered, said reticle stage may have a structure in which reticles are moved in the X direction and the Y direction, respectively, on a base, as disclosed in the U.S. patent application Ser. No. 266,999 (Jun. 27, 1994). 
     On the Y stage  3 Y, a moving mirror  6 X for the X axis and a moving mirror (not shown) for the Y axis are fixed, and an X coordinate X R  of the X stage  3 X is measured by the moving mirror  6 X and a laser interferometer  7 X for the X axis. Though not shown in the drawing, a laser interferometer for the Y axis for applying a laser beam onto the moving mirror for the Y axis is also provided. The Y coordinate of the Y stage  3 Y is measured by said moving mirror and the laser interferometer for the Y axis. A specific configuration of this interferometer system is disclosed in the U.S. patent application Ser. No. 943,808 (Dec. 19, 1986), or the U.S. Pat. No. 4,748,478. The X coordinate X R  and the Y coordinate measured by the laser interferometers for the X axis and the Y axis (hereinafter called the reticle interferometers) are supplied to a central control system  8  which controls the whole operation of the apparatus. 
     The exposure light IL passing through the reticle R enters the projection optical system PL having a projection magnification β (for example, β=⅕), and this projection optical system PL reduces the pattern image of the reticle R to project it onto one shot area on a wafer W. The wafer W is mounted on the Y stage  10 Y which is movable in the Y direction, and this Y stage  10 Y is mounted on the X stage  10 X which is movable in the X direction on a base  11 . The X stage  10 X is driven in the X direction by a linear motor which consists of a stator  12 A and a mover  12 B (hereinafter called the wafer X-stage linear motor) with respect to the base  11 , and the Y stage  10 Y is driven in the Y direction by a linear motor (not shown) having the same structure as the wafer X-stage linear motor with respect to the X stage  10 X. In the following, a stage system which comprises the Y stage  10 Y, the linear motor for driving said Y stage  10 Y, X stage  10 X, the wafer X-stage linear motor for driving said X stage  10 X, and a Z-leveling stage (not shown) for regulating a position and an angle of inclination of the wafer W in the Z direction is called a wafer stage. Though the wafer stage in this embodiment has a structure in which the X stage  10 X and the Y stage  10 Y are layered, said wafer stage may have a structure in which wafers are moved in the X direction and the Y direction, respectively, on a base, as disclosed in the U.S. patent application Ser. No. 221,375 (Apr. 1, 1994). 
     On the Y stage  10 Y, a moving mirror  13 X having a reflection plane extending along the Y direction for the X axis and a moving mirror (not shown) having a reflection plane extending along the X direction for the Y axis are fixed, and an X coordinate X W  of the X stage  10 X is measured by a laser interferometer  14 X for the X axis for applying a laser beam onto the moving mirror  13  along the X direction. Though not shown in the drawing, a laser interferometer for the Y axis for applying a laser beam onto the moving mirror for the Y axis along the Y direction is also provided. A Y coordinate of the Y stage  10 Y is measured by said laser interferometer for the Y axis. A specific configuration of this interferometer system is disclosed, for example, in the U.S. Pat. Nos. 5,003,342 and 5,243,195. The X coordinate X W  and the Y coordinate measured by the laser interferometers for the X axis and the Y axis (hereinafter called the wafer interferometers) are supplied to the central control system  8 . 
     The central control system  8  determines the position of the reticle R by controlling an operation of the linear motors for the X axis and the Y axis on the reticle side, respectively, through a reticle stage drive system  15 , and also determines the position of the wafer W by controlling an operation of the linear motors for the X axis and the Y axis on the wafer side, respectively, through a wafer stage drive system  16 . 
     In the present embodiment, a reference mark member  9  is fixed onto the Y stage  10 Y in such a manner that the surface of said member has the same height as that of the surface of the wafer W. A reference mark which takes, for example, a cross shape is formed on the surface of this reference mark member  9 . This reference mark is normally used for detection of a distance (base line) between the detection center of an alignment sensor and an exposure center, for positioning the reticle R with respect to the wafer stage (reticle alignment) and for detecting the position of a wafer mark (alignment mark) provided in each shot area of the wafer W. Furthermore, in the present embodiment, the reference mark on the reference mark member  9  is used as a reference for the position of the field magnet of the linear motor. 
     As the above-mentioned alignment sensor, an alignment sensor  20  of an off-axis type and an image pick-up type is provided separately from the projection optical system PL in this embodiment. Inside this alignment sensor  20 , a predetermined index mark is arranged at a position conjugated with the surface of the reference mark member  9  (or the wafer W), the image of a mark to be measured and the image of said index mark are simultaneously picked up by an image pick-up device, and an image pick-up signal S 1  therefrom is supplied to the central control system  8 . The central control system  8  processes said image pick-up signal S 1  to obtain an amount of positional displacement of the mark to be measured with respect to said index mark. Specific configurations of the alignment sensor  20  and the reference mark member  9  are disclosed, for example, in the U.S. Pat. No. 5,243,195. Though not shown in the drawing, above the dichroic mirror  2 , there is also provided an alignment sensor of a TTR (Through The Reticle) type for detecting a positional relation between the reticle R and each shot area on the wafer W, as disclosed, for example, in the U.S. Pat. No. 5,214,489 or U.S. Pat. No. 5,204,535. 
     Next, configurations and operations of the linear motor and the control systems thereof in the present embodiment will be described below with reference to the X stage  10 X which constitutes the wafer stage in FIG.  1 . 
     FIG. 2 is a structural view of the wafer stage shown in FIG.  1  and the control system thereof. Referring to FIG. 2, the stator  12 A of the wafer X-stage linear motor is constituted by loading a 3-phase armature coil  19  within a predetermined cover, and the mover  12 B is constituted by fixing four permanent magnets  18  on the bottom of a flat-plate (back yoke)  17  which is fixed on the side of the X stage  10 X in such a manner that the polarities thereof are successively inverted at a polar pitch P M  in the X direction. That is, the wafer X-stage linear motor  12  in the present embodiment is a linear synchronous motor of a moving magnet type, and has a simple structure so that a probability of break down is low and the maintenance thereof is easy. However, a linear motor of a moving coil type which contains an armature coil on the mover side may be used. 
     Next, in the central control system  8  of the present embodiment constituted by computers, the X coordinate X W  of the X stage  10 X which is measured by the wafer interferometer  14 X for the X axis is supplied to an input unit of a differentiator  21  and an input unit on a subtraction side of a subtracter  22 . The differentiator  21  differentiates the supplied X coordinate X W  by time to calculate a velocity VX W  of the X stage in the X direction, and supplies this velocity VX W  to an input unit on a subtraction side of a subtracter  23 . Since the differentiator  21  and the like in the central control system  8  are functions to be executed on software of a computer, a differentiating operation thereof is executed from, for example, a subtracting operation and a dividing operation for dividing a difference obtained from said subtracting operation by a sampling period. 
     On the other hand, an aimed coordinate X Wi  for positioning the X stage  10 X in the X direction is supplied from an aimed position setting device  24  to an addition side of the subtracter  22 . The subtracter  22  subtracts the current X coordinate X W  of the X stage  10 X from the aimed coordinate X Wi  so as to obtain a positional deviation ΔX Wi  (=X Wi −X W ), and supplies this positional deviation ΔX Wi  to an input unit of a positional gain circuit  25 . The positional gain circuit  25  obtains an aimed driving velocity VX Wi  by multiplying the positional deviation ΔX Wi  by a coefficient K P  for obtaining a velocity corresponding to each positional deviation, and supplies this aimed driving velocity VX Wi  to an input unit on an addition side of the subtracter  23 . The subtracter  23  subtracts the measured velocity VX W  of the X stage  10 X from the aimed driving velocity VX Wi  to obtain the velocity deviation ΔVX Wi  in the X direction, and supplied this velocity deviation ΔVX Wi  to a filter circuit  26 . The filter circuit  26  operates, for example, as a low-pass filter, obtains a value for a thrust FWX in the X direction corresponding to a low-frequency component of the supplied velocity deviation ΔVX Wi , and supplies the value for this thrust FWX to one of two input units of each of three multipliers  27 A to  27 C in the wafer stage drive system  16 . 
     Also, the image pick-up signal S 1  from the alignment sensor  20  of FIG. 1 is supplied to the aimed position setting device  24  in the central control system  8 . In this case, a phase θ 0 [rad] of the permanent magnet  18  with respect to the armature coil  19  in FIG. 2 when the image of the reference mark on the reference mark member  9  is coincident with the index mark in the alignment sensor  20  is obtained, and a value obtaining by converting said phase θ 0  into an amount of positional displacement ΔX 0  (=P M •θ 0 /(2π)) in the X direction by use of the polar pitch P M  of the permanent magnet  18  is stored in a memory inside the armed position setting device  24 . Then, when the reference mark of the reference mark member  9  is moved into an observation field of view of the alignment sensor  20  at the initial setting, the aimed position setting device  24  processes said image pick-up signal S 1  to obtain an amount of positional displacement (converted value on the wafer W) ΔX 1  of an image of said reference mark with respect to the index mark in the X direction. Thereafter, the aimed position setting device  24  supplies an amount of positional displacement (ΔX 0 +ΔX 1 ) which is obtained by adding said amount of positional displacement ΔX 1  and the amount of positional displacement ΔX 0  stored in advance to a fraction detecting device  28  inside the wafer stage drive system  16 . 
     Wafer stage drive system  16  is constituted by computers except power amplifiers  30 A to  30 C. In this wafer stage drive system  16 , the X coordinate X W  of the X stage  10 X measured by the wafer interferometer  14 X is supplied to the fraction detecting device  28 . The amount of positional displacement (ΔX 0 +ΔX 1 ) from the aimed position setting device  24  is supplied to the fraction detecting device  28  at the initial setting. This amount of positional displacement (ΔX 0 +ΔX 1 ) represents an amount of positional displacement of the permanent magnet  18  with respect to the armature coil  19  at the initial setting. 
     Then, the fraction detecting device  28  determines an offset value X OFF  such that a coordinate obtained by adding said offset value X OFF  to a value X W0  of the X coordinate X W  of the X stage  10 X at that time turns to be said amount of positional displacement (ΔX 0 +ΔX 1 ). That is, the following relation is established: 
     
       
         X OFF =(ΔX 0 +ΔX 1 )−X W0   (1) 
       
     
     Then, after the initial setting, the fraction detecting device  28  obtains a fraction ΔX W  by dividing a coordinate which is obtained by adding the offset value X OFF  to the X coordinate X W  supplied from the wafer interferometer  14 X by double the polar pitch P M  (2×P M ) of the permanent magnet  18  of the stator  12 B, and supplies this fraction ΔX W  to three phase converting devices  29 A to  29 C. In response to this, the first phase converting device  29 A generates a value for cosθ where θ is a phase obtained by multiplying 2π by a value which is obtained by dividing the fraction ΔX W  by double the polar pitch P M  (2×P M ), and supplies this value for cosθ to the other input unit of the first multiplier  27 A. The second phase converting device  29 B shifts said phase θ by 2π/3 to generate a value for cos(θ−2π/3), and supplies this value for cos(θ−2π/3) to the other input unit of the second multiplier  27 B. In the same manner, the third phase converting device  29 C shifts the phase θ by 4π/3 to generate a value for cos(θ−4π/3), and supplies this value for cos(θ−4π/3) to the other input unit of the third multiplier  27 C. 
     Then, the first multiplier  27 A supplies a current signal corresponding to a thrust which is obtained by multiplying the thrust FWX supplied from the filter circuit  26  by cosθ to a power amplifier  30 A. The second multiplier  27 B supplies a current signal corresponding to a thrust which is obtained by multiplying said thrust FWX by cos(θ−2π/3) to a power amplifier  30 B, and the third multiplier  27 C supplies a current signal corresponding to a thrust which is obtained by multiplying said thrust FWX by cos(θ−4π/3) to a power amplifier  30 C. Each of the power amplifiers  30 A,  30 B and  30 C amplifies the supplied current signal and supplies an exciting current to a coil of a corresponding phase of the 3-phase armature coil  19 . Thus, the X stage  10 X is driven to the X direction through the wafer X-stage linear motor until the X coordinate of the X stage  10 X is convergent on the aimed coordinate set by the aimed position setting device  24 . 
     As described above, in the present embodiment, an amount of positional displacement (phase) of the permanent magnet  18  with respect to the armature coil  19  is calculated in the fraction detecting device  28  on the basis of the X coordinate X W  supplied from the wafer interferometer  14 X, and a phase of the exciting current supplied to the coil of each phase of the armature coil  19  by a servo system is set on the basis of said amount of positional displacement. Therefore, it is no longer required to separately provide a phase switching sensor (consisting of a Hall element, etc.) for detecting the polarity of the permanent magnet  18 . As a result, the stage mechanism can be simplified and various kinds of mechanisms can be easily provided on the stage. 
     In the above-described embodiment, the reference mark member  9  on the Y stage  10 Y is used for obtaining the measured value (X coordinate) of the wafer interferometer  14 X and the correspondence of the armature coil with the phase of the magnet in the linear motor. However, in addition to this, said correspondence may be obtained, for example, by use of a limit switch, or the like, for setting an origin of the wafer interferometer  14 X. 
     The present invention is applicable not only to the exposure apparatus (stepper, etc.) of the step-and-repeat type, but also to the scan exposure apparatus of the step-and-scan type disclosed in the U.S. patent application Ser. Nos. 139,803 (Oct. 22, 1993) and 274,037 (Jul. 12, 1994), in which apparatus the linear motor is used as a driving device for driving the reticle stage or the wafer stage. As seen from the above description, the present invention is not limited to the foregoing embodiment, but can take various structures within the scope of the present invention.