Patent Application
20080100894
1. Field of the Invention
The present invention relates to an apparatus for moving a curved-surface mirror.
2. Description of the Related Art
An exposure apparatus is used in a photolithographic process for the manufacture of a semiconductor element to expose the circuit pattern of a reticle and transfer it to a silicon wafer, by way of example. Owing to demand for higher integration of semiconductor elements, step-and-scan exposure systems now dominate and have supplanted the conventional step-and-repeat exposure systems. A step-and-scan exposure apparatus is a scanning exposure apparatus in which slit-shaped illuminating light is partially emitted from one end of a reticle and the entirety of a circuit pattern is exposed on a wafer (substrate) via a projection optical system while a reticle stage holding the reticle and a wafer stage holding the wafer are driven synchronously.
In an exposure apparatus of this kind, the resolution of the projection optical system has been improved in order to expose and transfer a fine pattern accurately. For example, the apparatus naturally is designed in order to enlarge the numerical aperture (NA) of the optical system and reduce optical aberration, and manufacture, assembly and adjustment employing highly sophisticate measurements have been carried out. Furthermore, it is desired that various optical characteristics (e.g., magnification, distortion and focus) be adjustable during the exposure operation. In addition, it is necessary that the effects of disturbance (e.g., fluctuations in air pressure, fluctuations in temperature and humidity, floor vibration and aging) be eliminated to the maximum degree to achieve stable performance. In order to realize these functions, the positions, attitudes and deformations of the optical elements (e.g., lenses, mirror and prisms) that construct the projection optical system should be adjusted during the exposure operation.
A variety of types of optical element driving apparatuses have been developed from this standpoint. For example, the specification of Japanese Patent Laid-Open No. 2002-131605 discloses an optical element driving apparatus in which the optical elements are capable of being driven through six-degree-of-freedom of motion.
Further, the specification of Japanese Patent Laid-Open No. 2004-064076 discloses an optical element driving apparatus in which a number of focus actuators are deployed on the underside of a mirror to adjust the shape of the reflective surface of the mirror, and position sensors are provided to enable adjustment of rotation about the direction of the optic axis and two other directions that form an orthogonal system with the direction of the optic axis.
In general, if the number of drivable optical elements or number of degrees of freedom of motion is increased, the optical characteristics of a projection optical system can be adjusted to more preferable characteristics. However, unless other components and displacement error can be sufficiently suppressed with respect to drive in a desired direction and drive displacement, optical characteristics will worsen instead. This manifests itself in particular when adjusting and driving a mirror the optical sensitivity of which is greater than that of a lens. Further, if the rigidity of the mechanism declines owing to an increase in degrees of freedom of drive, positional deviation may increase owing to disturbances even if it is possible to adjust drive to the desired position, and optical characteristics may worsen. For these reasons, it is required that driving of the mirror be executed by a driving apparatus having highly sophisticated mechanical and control systems.
The present invention has been made in light of the foregoing background. It is an object of the present invention, for example, to precisely adjust the position of a curved surface mirror.
According to one aspect of the present invention, an apparatus for moving a curved-surface mirror is provided. The apparatus includes at least three actuators configured to move the curved-surface mirror, at least five position sensors configured to sense the position of the curved-surface mirror, and a controller configured to calculate coordinates of a center of curvature of the curved-surface mirror with three-degree-of-freedom based on positions sensed by the at least five position sensors, and to control driving of the at least three actuators in accordance with a difference between the calculated coordinates and predetermined coordinates.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Various exemplary embodiments, features and aspects of the present invention will be described in detail below with reference to the drawings.
A mirror support plate 2 supports the curved-surface mirror 1. Three or more actuators 3 for driving the mirror support plate 2 are deployed in order to make it possible to adjust three-degree-of-freedom, namely along the direction of the optic axis Z of curved-surface mirror 1 and in the θx, θy directions. Examples of the actuators 3 include pneumatic bellows, linear motors, electromagnets, piezoelectric elements, magnetorestrictive elements, piezoelectric thin films formed as an integral part of the curved-surface mirror 1, or compression/decompression chambers formed in the material of the curved-surface mirror as an integral part thereof.
A position sensor 4 is for measuring the position of the curved-surface mirror 1. In order to determine the position and attitude (Xm, Ym, Zm, θxm, θym, θzm) of the curved-surface mirror 1 through six-degree-of-freedom, position sensors 4 are deployed so as to detect at least six points on the curved-surface mirror 1. Alternatively, if the reflective surface of the mirror has rotational symmetry with regard to the optic axis and the θzm value is unnecessary, then five or more position sensors will suffice. Examples of the position sensor are an electrostatic capacitance sensor (electrostatic capacity sensor), a laser interferometer and a wavefront sensor such as a Shack-Hartmann sensor. Reference numeral 5 denotes the base of the overall apparatus. A controller 7 controls the driving of the actuators 3 based upon results of sensing by the position sensors 4. A typical example of the controller 7 is a computer device comprising a CPU, RAM and ROM, etc. (none of which are shown).
Before the operation of the optical element driving apparatus shown in
In
This fact indicates that if at least the position C(Xc,Yc,Zc) of the center of curvature of curved-surface mirror 1 can be held fixed, then the optical characteristics can be held constant. The operation that holds fixed the position of the center of curvature can be executed even by a driving mechanism having the three-degree-of-freedom X, θx, θy and not the degree-of-freedom in the horizontal directions X and Y. That is, it will suffice to construct a control system that compensates for a shift in the center of curvature in the X and Y directions by drive about the angles of rotation θy, θx.
Operation of the optical element driving apparatus of
If the curved-surface mirror 1 is shifted along the X direction owing to a disturbance or the like, naturally the position C of the center of curvature of the mirror also is similarly shifted along the X direction. Fluctuations (ΔXm, ΔYm, ΔZm, Δθxm, Δθym, Δθzm) in position and attitude of the curved-surface mirror 1 through six-degree-of-freedom are calculated by a coordinate transformation from the values detected by the position sensors 4 that measure six or more points on the curved-surface mirror 1. As an operation that is a characterizing feature of this embodiment, displacement (ΔXc, ΔYc, ΔZc) of the position C of the center of curvature of curved-surface mirror 1 (referred to simply as “fluctuation” below) from a target position is calculated by a coordinate transformation from the position and attitude of the curved-surface mirror 1 through six-degree-of-freedom. It should be noted that the fluctuation in the position C of the center of curvature may be calculated directly from measurement values of the position sensors 4 upon combining these two coordinate transformations (step S31).
Next, the actuators 3 are driven and controlled so as to compensate for fluctuation in the position C of the center of curvature by rotating ΔXc through θy and rotating ΔYc through θx. Further, the actuators 3 are driven and controlled so as to compensate for fluctuation in the position C of the center of curvature by a Z translation with regard to ΔZc (step S32). More specifically, the actuators 3 are driven and controlled so as to minimize the fluctuation in the position C of the center of curvature of curved-surface mirror, by way of example.
In a case where the optical element driving apparatus in this embodiment is applied to an exposure apparatus (see the seventh embodiment, described later), the above-mentioned control processing (steps S32 and S33) is executed during the exposure operation and the control processing ends with the end of the exposure operation (step S33).
By virtue of the above-described processing, the position C of the center of curvature of curved-surface mirror 1 is held fixed even if the position of the curved-surface mirror 1 fluctuates owing to disturbance, etc., and therefore the optical characteristics can be held constant.
It should be noted that the scope of application of the technique of this embodiment for controlling the position C of the center of curvature of curved-surface mirror 1 is not limited solely to a case where it is desired to restore the position of the curved-surface mirror 1, which has fluctuated owing to a disturbance, etc., to the original position. For example, in a case where it is desired to move the position C of the center of curvature to a desired target position (e.g., by 10 nm along the +Z direction) in order, for example, to achieve an adjustment to more desirable optical characteristics, the curved-surface mirror 1 and the center of curvature thereof shift horizontally in the X and Y directions owing to other driving components. In this case also, in accordance with the control technique described above, the actuators 3 can be driven and controlled so as to compensate for the shift horizontally in the X and Y directions by θy and θx rotations. Alternatively, even in a case where it is desired to shift the position C of the center of curvature horizontally, the position C of the center of curvature can also be shifted by rotative drive through θy and θx.
Thus, in accordance with this embodiment, a driving mechanism is constructed for applying an adjustment in such a manner that the position C of the center of curvature of the curved-surface mirror 1 will take on a desired value even in a case where the curved-surface mirror 1 has fluctuated from a desired position and attitude owing to other driving components or some disturbance. As a result, an adjustment to more desirable characteristics can be achieved while a decline in the optical characteristics of a projection optical system is prevented effectively even during an exposure operation.
It should be noted that it is possible to adopt an arrangement in which the X, Y, Z directions are the three-degree-of-freedom for driving an optical element driving apparatus as in a second embodiment, described later. However, in a case where the three-degree-of-freedom is made the X, Y, Z directions, the structure becomes a layered structure composed of a plate movable in the X and Y directions and a plate movable in the Z direction, by way of example. Such a structure has a complicated mechanism and tends to have diminished rigidity. By contrast, a driving mechanism whose three-degree-of-freedom is Z, θx, Gy mentioned above is such that it will suffice to dispose three Z-direction driving actuators immediately below the single layer of the mirror support plate 2. Such a mechanism is comparatively simple and tends to assure rigidity. From this standpoint, therefore, the above-mentioned driving mechanism with the three-degree-of-freedom Z, θx, θy is construed to be the best form conceivable at the present time.
The X, Y, Z directions may be the three-degree-of freedom for driving an optical element driving apparatus for performing an adjustment in such a manner that the position C(Xc,Yc,Zc) of the center of curvature of the curved-surface mirror 1 takes on a desired value.
In this case, in a manner similar to the first embodiment, the controller 7 calculates fluctuation (ΔXm, ΔYm, ΔZm, Δθxm, Δθym, Δθzm) in position and attitude of the curved-surface mirror 1 through six-degree-of-freedom by a coordinate transformation based upon the values measured by the position sensors 4 that measure six or more points on the curved-surface mirror 1. Next, the controller 7 calculates fluctuation (ΔXc, ΔYc, ΔZc) in the position C of the center of curvature of curved-surface mirror 1 by a coordinate transformation from the position and attitude of the curved-surface mirror 1 through six-degree-of-freedom. It should be noted that the fluctuation in the position C of the center of curvature may be calculated directly from measurement values of the position sensors 4 upon combining these two coordinate transformations.
Next, the controller 7 drives and controls the actuators 3 so as to compensate for fluctuation in the position C of the center of curvature by X translation of ΔXc and Y translation of ΔYc. Further, the controller 7 drives and controls the actuators 3 so as to compensate for fluctuation in the position C of the center of curvature by a Z translation with regard to ΔZc. As a result, the position C of the center of curvature of curved-surface mirror 1 is held fixed even if the position of the curved-surface mirror 1 fluctuates owing to disturbance, etc., and therefore the optical characteristics can be held constant.
It should be noted that the scope of application of the technique of this embodiment for controlling the position C of the center of curvature of curved-surface mirror 1 is not limited solely to a case where it is desired to restore the position of the curved-surface mirror 1, which has fluctuated owing to a disturbance, etc., to the original position. For example, in a case where it is desired to move the position C of the center of curvature to a desired target position in order, for example, to achieve an adjustment to more desirable optical characteristics, a fluctuation in the directions of rotation θy, θx occurs as other driving components and the center of curvature shifts. In this case also, in accordance with the control technique described above, the actuators 3 can be driven and controlled so as to compensate for this positional deviation by the X and Y translations. Alternatively, even in a case where it is desired to shift the position C of the center of curvature horizontally, the position C of the center of curvature can also be shifted by performing the X and Y translations.
The Z, X directions and rotation θx about the X axis may be the three-degree-of-freedom for driving an optical element driving apparatus for performing an adjustment in such a manner that the position C(Xc,Yc,Zc) of the center of curvature of the curved-surface mirror 1 takes on a desired value.
Let (ΔXc, ΔYc, ΔZc) represent the positional deviation or other driving components of the center of curvature calculated by a coordinate transformation of the values measured by the position sensors 4. In this embodiment, the actuators 3 are driven and controlled so as to compensate for fluctuation of the position C of the center of curvature by an X translation of ΔXc and rotation θx of ΔYc about the X axis. Further, the actuators 3 are driven and controlled so as to compensate for fluctuation of the position C of the center of curvature by a Z translation with regard to ΔZc.
The Z, Y directions and rotation θy about the Y axis may be the three-degree-of-freedom for driving an optical element driving apparatus for performing an adjustment in such a manner that the position C(Xc,Yc,Zc) of the center of curvature of the curved-surface mirror 1 takes on a desired value.
Let (ΔXc, ΔYc, ΔZc) represent the positional deviation or other driving components of the center of curvature calculated by a coordinate transformation of the values measured by the position sensors 4. In this embodiments the actuators 3 are driven and controlled so as to compensate for fluctuation of the position C of the center of curvature by rotation θy of ΔXc about the Y axis and a Y translation of ΔYc. Further, the actuators 3 are driven and controlled so as to compensate for fluctuation of the position C of the center of curvature by a Z translation with regard to ΔZc.
In such an optical element driving apparatus, there are instances where, besides a fluctuation in the center of curvature caused by disturbance or other driving components for which a solution was contemplated in the first and second embodiments, the center of curvature shifts as a result of deforming the curved-surface mirror 1. In this case also a driving mechanism and measurement control system for performing measurement in such a manner that the position C(Xc,Yc,Zc) of the center of curvature will take on the desired value can be constructed.
Specifically, in a manner similar to the first embodiment, the controller 7 calculates fluctuation (ΔXm, ΔYm, ΔZm, Δθxm, Δθym, Δθzm) in position and attitude of the curved-surface mirror 1 through six-degree-of-freedom by a coordinate transformation based upon the values measured by the position sensors 4 that measure six or more points on the curved-surface mirror 1. Next, the controller 7 calculates fluctuation (ΔXc, ΔYc, ΔZc) in the position C of the center of curvature of curved-surface mirror 1 by a further coordinate transformation from the position and attitude of the curved-surface mirror 1 through six-degree-of-freedom. It should be noted that the fluctuation in the position C of the center of curvature may be calculated directly from measurement values of the position sensors 4 upon combining these two coordinate transformations.
Next, the controller 7 drives the actuators 3 so as to compensate for fluctuation in the position C of the center of curvature by rotation θy of ΔXc and rotation θx of ΔYc. Further, the controller 7 drives and controls the actuators 3 so as to compensate for fluctuation in the position C of the center of curvature by a Z translation with regard to ΔZc.
Alternatively, in a manner similar to the second embodiment, the controller 7 calculates fluctuation (ΔXm, ΔYm, ΔZm, Δθxm, Δθym, Δθzm) in position and attitude of the curved-surface mirror 1 through six-degree-of-freedom by a coordinate transformation based upon the values measured by the position sensors 4 that measure six or more points on the curved-surface mirror 1. Next, the controller 7 calculates fluctuation (ΔXc, ΔYc, ΔZc) in the position C of the center of curvature of curved-surface mirror 1 by a further coordinate transformation from the position and attitude of the curved-surface mirror 1 through six-degree-of-freedom. It should be noted that the fluctuation in the position C of the center of curvature may be calculated from measurement values of the position sensors 4 upon combining these two coordinate transformations.
Next, the controller 7 drives and controls the actuators 3 so as to compensate for fluctuation in the position C of the center of curvature by X translation of ΔXc and Y translation of ΔYc. Further, the controller 7 drives and controls the actuators 3 so as to compensate for fluctuation in the position C of the center of curvature by a Z translation with regard to ΔZc.
As a result, the position C of the center of curvature of curved-surface mirror 1 is held fixed even if the position of the curved-surface mirror 1 fluctuates owing to disturbance, etc., and therefore the optical characteristics can be held constant.
In the first to fifth embodiments, the reflective surface of the curved-surface mirror 1 is assumed to be a concave spherical surface. However, the mirror may be a convex spherical mirror. Further, it is not required that the entirety be an accurate spherical surface, and it will suffice if the surface appears spherical optically in the effective area where light is reflected.
Further, the curved-surface mirror 1 may be a cylindrical mirror in which the reflective surface has a concave or convex cylindrical surface. In this case, the center of curvature will be a line rather than a single point. However, it will suffice if drive is controlled so as to move the center line of curvature will to the desired position in a manner similar to that where drive is controlled in such a manner that the center of curvature assumes the desired position in the case of a curved-surface mirror.
Alternatively, the curved-surface mirror 1 may be a toroidal mirror in which the reflective surface is concave or convex and the curvature along the X direction is different from that along the Y direction. In this case, the center of curvature will be two points, depending upon the direction, and not a single point. However, it will suffice if drive is controlled in such a manner that the position of each center of curvature will be a desired position.
Furthermore, an optical element driving apparatus for adjusting the various mirror positions may further be provided with actuators for deforming the mirror.
An exemplary exposure apparatus to which the optical element driving apparatus of the present invention is applied will now be described.
The illuminating device 41 illuminates the reticle 11 in which the circuit pattern has been formed and has a light-source unit and an illuminating optical system (neither of which is illustrated) The light-source unit uses a laser as the light source. The laser can employ an ArF excimer laser having a wavelength of about 193 nm, a KrF excimer laser having a wavelength of about 248 nm, or an F2 excimer laser having a wavelength of about 153 nm. Naturally the type of laser is not limited to an excimer laser and may be, e.g., a YAG laser, and the number of these lasers also is not limited. In a case where a laser is used as the light source, it is preferred to make use of a luminous-flux shaping optical system for shaping collimated light from the laser light source into a desired beam shape, and an optical system for making coherent laser light incoherent. Further, the light source usable in the light-source unit is not limited to a laser, and it is possible to use one or two or more lamps such as mercury lamps or xenon lamps. The illuminating optical system is an optical system for illuminating a mask and includes a lens, a mirror, a light integrator and a diaphragm, etc.
The exposure optical system 10 is a reflecting refractive projection optical system and includes the following in the order traversed by the illuminating light IL from the illuminating device 41: a first lens group 13, a second lens group 14, the curved-surface mirror 1, a first deflecting mirror 17, a third lens group 15, a second deflecting mirror 18 and a fourth lens group 16. The curved-surface mirror 1 is mounted in the optical element driving apparatus 100 shown in
The reticle stage 42 and wafer stage 43 are capable of being moved by a linear motor, by way of example. In the case of a skip-and-scan projection exposure system, these two stages are moved in sync with each other. Further, of the reticle stage 42 and wafer stage 43, at least one is equipped separately with an actuator in order to align the pattern of the reticle with the wafer 12.
Such an exposure apparatus can be utilized to manufacture a semiconductor device such as a semiconductor integrated circuit, a micromachine or a device such as a thin-film magnetic head on which fine patterns have been formed.
Described next with reference to
The circuit for the device is designed at step S1 (circuit design). A mask is fabricated at step S2 (mask fabrication) based upon the circuit pattern designed. A wafer is manufactured using a material such as silicon at step S3 (wafer manufacture). The actual circuit is formed on the wafer by lithography, using the mask and wafer, by means of the exposure apparatus at step S4 (wafer process), which is also referred to as “pre-treatment”. A semiconductor chip is obtained, using the wafer fabricated at step S4, at step S5 (assembly), which is also referred to as “post-treatment”. This step includes steps such as actual assembly (dicing and bonding) and packaging (chip encapsulation). The semiconductor device fabricated at step S5 is subjected to inspections such as an operation verification test and durability test at step S6 (inspection). The semiconductor device is completed through these steps and then is shipped (step S7).
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2006-293153, filed Oct. 27, 2006, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-293153 | Oct 2006 | JP | national |
