FIG. 9 is a view showing the general arrangement of a wafer stage in an exposure apparatus. FIG. 10 is an exploded view showing the structure of the wafer stage shown in FIG. 9. FIGS. 11A and 11B are views showing the arrangement of a coarse movement stage portion in the wafer stage shown in FIG. 9. FIGS. 12A, 12B, and 12C are views showing the arrangement of a fine movement stage portion in the wafer stage shown in FIG. 9. FIGS. 13A, 13B, and 13C are views showing the arrangement of a fine movement stage linear motor used in the wafer stage shown in FIG. 9. FIG. 14 is a view showing the arrangement of a coarse movement stage linear motor for the wafer stage shown in FIG. 9.
The wafer stage is roughly comprised of a coarse movement stage for long stroke movement in the X-Y direction, and a fine movement stage for precise positioning. The top plate of the fine movement stage is characteristically controlled directly by a linear motor in six-axis directions.
The fine movement stage will be described first.
A wafer top plate 901 serves for placing a wafer as a work on it and positioning the wafer in six degree-of-freedom directions of X, Y, Z, ωx, ωy, and ωz. The wafer top plate 901 is a rectangular plate, and has the wafer chuck 902 at its center to place the wafer on it.
Mirrors 903, 904, and 905 for reflecting laser beams from interferometers are provided to the side surface of the wafer top plate 901, so the position of the wafer top plate 901 can be measured. More specifically, the wafer top plate 901 is irradiated with a total of six light beams, so its six degree-of-freedom positions are measured. With two interferometer beams parallel to the X-axis and having different Z positions, the position in the X direction and the amount of rotation in the ωy direction can be measured. With three interferometer beams parallel to the Y-axis and having different X and Z positions, the position in the Y direction and the amounts of rotation in the ωx and ωy directions can be measured. With a beam irradiated to a C-surface portion (904) of the mirror, the position in the Z direction can be measured. In fact, the measurement values obtained with these beams are not independent of each other but interfere with each other. X, Y, Z, ωx, ωy, and ωz of a typical position can be measured by coordinate transformation as a rigid body.
Seven linear motor movable elements (906 to 912) are attached to the lower surface of the wafer top plate 901. As shown in FIGS. 13A and 13B, each movable element has two sets of yokes (911a and 911d, 906a and 906d) and bipolar magnets (911b and 911c, 906b and 906c) magnetized in the direction of thickness. The two sets of magnets and yokes are connected to each other with side plates to form a box-like structure. The respective movable elements oppose each other to sandwich linear motor stators (918, 913) (to be described later) in a noncontact manner.
Of the seven movable elements, the three movable elements 906 to 908 arranged on the side ends of the rectangular top plate form Z movable elements. In the Z movable element, as shown in FIG. 13A, the bipolar magnets 906b and 906c are arrayed in the Z direction, and mutually act with a current flowing through a Z stator elliptic coil 913b (described later) with a straight portion perpendicular to the Z direction, thereby generating a thrust in the Z direction. These movable elements will be named Z1 to Z3 movable elements (906 to 908).
The four remaining movable elements 909 to 912 are arranged substantially at the center of the rectangular top plate. Of the four movable elements, two form X movable elements. In the X movable element, as shown in FIG. 13C, the bipolar magnets 909b are arrayed in the X direction, and mutually act with a current flowing through an X stator elliptic coil (described later) with a straight portion perpendicular to the X direction, thereby generating a thrust in the X direction. These movable elements will be named X1 and X2 movable elements (909, 910).
The two remaining movable elements form Y movable elements. In the Y movable element, as shown in FIG. 13B, the bipolar magnets 911b and 911c are arrayed in the Y direction, and mutually act with a current flowing through a Y stator elliptic coil (described later) 918b with a straight portion perpendicular to the Y direction, thereby generating a thrust in the Y direction. These movable elements will be named Y1 and Y2 movable elements (911, 912).
The seven linear motor stators 913 to 919 described above for controlling the position of the wafer top plate 901 in the six-axis directions, and one end of a self-weight support spring 921 for supporting the weight of the wafer top plate 901 are fixed to the upper portion of an intermediate plate 920. The stators 913 to 919 support the elliptic coils with peripheral frames, as shown in FIGS. 13A to 13C, and face the linear motor movable elements 906 to 912 (described above) fixed to the lower surface of the wafer top plate 901 in a noncontact manner.
Of the seven stators, the three ones arranged at almost the ends of the sides of the rectangular X stage upper plate form Z stators (913 to 915). In the Z stator, as shown in FIG. 13A, the elliptic coil 913b is arranged such that its straight portion is perpendicular to the Z direction. Thus, the elliptic coil 913b can exert a thrust in the Z direction on those bipolar magnets of the Z movable element (906, 907, or 908) which are arranged in the Z direction. These coils will be named Z1, Z2, and Z3 coils.
The four remaining stators are arranged at the center of the intermediate plate 920. Of the four remaining stators, two form X stators (916, 917). In the X stator, as shown in FIG. 13C, the two straight portions of an elliptic coil 916b are perpendicular to the X direction. The two straight portions are arranged along the X direction. Thus, the elliptic coil 916b can exert a thrust in the X direction on those bipolar magnets of the X movable element 909 or 910 which are arranged along the X direction. These coils will be named X1 and X2 coils.
The two remaining stators are also arranged at the center of the intermediate plate and form Y stators 918 and 919. In the Y stator, as shown in FIG. 13B, the two straight portions of the elliptic coil 918b are perpendicular to the Y direction. The two straight portions are arranged along the Y direction. Thus, the elliptic coil can exert a thrust in the Y direction on those bipolar magnets of the Y movable element which are arranged along the Y direction. These coils will be named Y1 and Y2 coils.
These seven linear motors generate a thrust in accordance with the so-called Lorentz force. In the following description, a linear motor formed of a Z stator and a Z movable element will be referred to as a Z fine movement linear motor, a linear motor formed of an X stator and an X movable element will be referred to as an X fine movement linear motor, and a linear motor formed of a Y stator and a Y movable element will be referred to as a Y fine movement linear motor.
One end of the coil spring 921 is attached to the center of the intermediate plate 920. The other end of the coil spring 921 is coupled to the lower surface of the wafer top plate 901 to support its weight. For this reason, the Z linear motor formed of the Z movable element (906, 907, or 908) and the Z stator (913, 914, or 915) need not generate a thrust for supporting the weight of the wafer top plate 901 but suffices if it generates a small force necessary for correcting a shift from the target position.
The coarse movement stage will be described with reference to FIG. 10 and FIGS. 11A and 11B.
The coarse movement stage is arranged below the intermediate plate 920. The intermediate plate 920 is fixed on an upper plate 921a of an X slider 921 of the coarse movement stage. In other words, the coarse movement stage moves over a long X-Y stroke the intermediate plate 920, serving as part of the fine movement stage and a base for receiving the reaction force of the linear motor that exerts a control force on the wafer top plate 901.
A Y yaw guide 923 is fixed on a base surface plate 922, and a Y slider 924 guided by the side surface of the Y yaw guide 923 and the upper surface of the base surface plate 922 is supported on the base surface plate 922 by an air slide (not shown) to be slidable in the Y direction. The Y slider 924 is mainly comprised of four members, i.e., two X yaw guides 924a, a front end member 924b, and a rear end member 924c. The rear end member 924c faces the side surface of the Y yaw guide 923 and the upper surface of the base surface plate 922 through air pads (not shown) provided to its side and lower surfaces. The front end member 924b faces the upper surface of the base surface plate 922 through an air pad (not shown) provided to its lower surface. Consequently, the Y slider 924 as a whole is supported by the side surface of the Y yaw guide 923 and the upper surface of the base surface plate 922 to be slidable in the Y direction, as described above.
The X slider 921 guided by the side surfaces of the two X yaw guides 924a, which are the constituent components of the Y slider 924, and the upper surface of the base surface plate 922 surrounds the Y slider 924 about the X-axis, and is supported by an air slide (not shown) to be slidable in the X direction. The X slider 921 is mainly comprised of four members, i.e., two X slider side plates 921b and the X slider upper and lower plates 921a and 921c. The X slider lower plate 921c faces the upper surface of the base surface plate 922 through an air pad (not shown) provided to its lower surface. The two X slider side plates 921b face the side surfaces of the two X yaw guides 924a, serving as the constituent members of the Y slider 924, through air pads (not shown) provided to their side surfaces. The lower surface of the X slider upper plate 921a does not come into contact with the upper surfaces of the X yaw guides 924a, and the upper surface of the X slider lower plate 921c does not come into contact with the lower surfaces of the X yaw guides 924a. Consequently, the X slider 921 as a whole is supported by the side surfaces of the two X yaw guides 924a and the upper surface of the base surface plate 922 to be slidable in the X direction, as described above. As a result, the X slider 921 is two-dimensionally slidable in the X-Y direction.
A driving mechanism will be described with reference to FIG. 10, FIGS. 11A and 11B, and FIG. 14. As the driving mechanism, one multi-phase coil switching long distance linear motor (stator 925a, movable element 927a) for X driving, and two multi-phase coil switching long distance linear motors (stators 925b and 925c, movable elements 927b and 927c) for Y driving are used. In these linear motors, as shown in FIG. 14, a stator 925 is formed by inserting a plurality of coils 926 arrayed in the stroke direction in a frame. A movable element 927 is formed by arranging a quadrupole magnet, having a magnetic pole pitch equal to the coil span of the coils 926, on a yoke plate 929. Two movable elements 927 each formed in this manner oppose each other to sandwich the coils 926, thus forming a box-like magnet unit. When a current is selectively supplied to the coils 926 of the stator 925 in accordance with the position of the movable element 927, a thrust is generated. Such a linear motor is a general air-core brushless DC linear motor.
The Y slider 924 is connected to the movable elements 927b and 927c through a front attaching plate 931 and rear attaching plate 930, respectively, and is moved upon movement of the movable elements 927b and 927c. As the X slider upper plate 921a and the movable element 927a (FIG. 11A) are connected to each other, the X slider 921 is moved upon movement of the movable element 927a. The X slider 921 and Y slider 924 have means for measuring the X and Y positions independently of the fine movement stage.
The function of the coarse movement stage is to receive the reaction force of the linear motor of the fine movement stage and to move the intermediate plate 920 to a portion in the vicinity of the target position constantly so the stroke of the linear motor of the fine movement stage is not used up. As the linear motor of the fine movement stage has a stroke of about 1 mm, the coarse movement stage does not perform control operation of particularly measuring the position relative to the fine movement stage and following it, but controls the position independently of the fine movement stage by means of a unique measurement system.
This method is excellent in the following respects. Namely, first, the X, Y and Z fine movement linear motors directly exert forces in six-axis directions on the fine movement top plate as the final control target. In other words, no indirect mechanical transfer elements are present for the fine movement top plate. Hence, the control range of the fine movement top plate can be set very high, and accordingly, the position control precision becomes very high.
Second, vibration from the floor is insulated by the X, Y, and Z fine movement linear motors. As described above, the fine movement linear motor utilizes the Lorentz force, so vibration of the stator is not transferred to the movable element.
The above arrangement realizes high-precision scanning exposure.
The conventional method described above has a problem in that heat generation by the linear motor is large.
First, as the linear motor of the coarse movement stage, a DC brushless linear motor is employed. This linear motor utilizes the Lorentz force, in the same manner as the fine movement linear motor. This linear motor is excellent in response speed and vibration insulating properties, but its heat generation obtained with the same thrust is large. When the linear motor of the coarse movement stage generates heat, ambient air fluctuates, leading to a measurement error of the interferometer. Alternatively, the acceleration may be limited in order to suppress heat generation.
Second, heat generation by the linear motor of the fine movement stage is large. The linear motor of the fine movement stage also utilizes the Lorentz force, and is excellent in response speed and vibration insulating properties, but its heat generation with the same thrust is large. Heat generation becomes an issue during acceleration and deceleration. In scanning exposure, acceleration is performed first. When the maximum speed is reached, exposure is performed while traveling at a constant speed. When exposure is ended, deceleration is performed. This process is repeated. During acceleration or deceleration, a thrust equal to “(the mass of the top plate) x acceleration” must be applied by the X fine movement linear motor when acceleration or deceleration is to be performed in the X direction. When acceleration or deceleration is to be performed in the Y direction, the above thrust must be applied by the Y fine movement linear motor. Therefore, during acceleration or deceleration, the linear motor generates heat to deform the wafer top plate 901. Alternatively, acceleration may be limited in order to suppress heat generation.
Namely, with the conventional method, the acceleration is limited due to heat generation by the coarse movement linear motor and the fine movement linear motor, leading to degradation in productivity.
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