1. Field of the Invention
The present invention relates to lithography, and more particularly, to a stage design including a low mass coarse stage that provides support and positions a fine stage capable of movement in six degrees of freedom.
2. Related Art
A typical lithography tool includes a radiation source, a projection optical system, and a substrate stage to support and move a substrate to be imaged. A radiation-sensitive material, such as resist, is coated onto the substrate surface prior to placement onto the substrate stage. During operation, radiation energy from the radiation source is used to project an image defined by an imaging element through the projection optical system onto the substrate. The projection optical system typically includes a number of lenses. The lens or optical element closest to the substrate is often referred to as the “last” or “final” optical element.
The projection area during an exposure is typically much smaller than the imaging surface of the substrate. The substrate therefore has to be moved relative to the projection optical system to pattern the entire surface. In the semiconductor industry, two types of lithography tools are commonly used. With so-called “step and repeat” tools, the entire image pattern is projected at once in a single exposure onto a target area of the substrate. After the exposure, the wafer is moved or “stepped” in the X and/or Y direction and a new target area is exposed. This step and repeat process is performed over and over until the entire substrate surface is exposed. With scanning type lithography tools, the target area is exposed in a continuous or “scanning” motion. The imaging element is moved in one direction while the substrate is moved in either the same or the opposite direction during exposure. The substrate is then moved in the X and/or Y direction to the next scan target area. This process is also repeated until all the desired areas on the substrate have all been exposed.
With both step and repeat and scanning type lithography tools, a substrate stage, commonly called a wafer stage, is used to both secure and position the substrate during exposure. The substrate is typically positioned on a fine stage, which is often positioned on a coarse stage. The coarse stage moves the fine stage and substrate in the X and/or Y directions in coarse increments during the step and repeat or scanning motion, while the fine stage moves the substrate in fine movements. Together, the coarse and fine stages work together to precisely position the correct portion of the substrate in the projection area. With scanning type tools, the imaging element is also moved by a stage, commonly called a reticle stage. In various known reticle stages, either a single stage (one stage holding one reticle), twin stage (two stages, each holding a single reticle), or double stage (one stage holding two reticles) have been considered. In one specific known example, a single reticle stage is used having three degrees of freedom (X, Y and θz). The issue with this type of stage is its movement is limited, and is unable to move in the vertical (Z, θx and θy) degrees of freedom. In the semiconductor industry, there is a constant drive to make the features on semiconductor devices smaller and smaller. To achieve the smaller features, lithography tools with larger and larger numerical apertures are needed. As the numerical aperture increases, the depth of focus becomes smaller, requiring more precise control of the imaging element in the vertical (Z, θx or θy) degrees of freedom. Since the aforementioned single stage does not have six degrees of freedom, its use in future lithography tools may be limited.
In another known design, the imaging element can be moved in six degrees of freedom by the combination of a fine stage supported by a coarse stage. Air pistons are used to support or suspend the fine stage over the coarse stage. At least six voice coil motors (VCMs) are used to move and position the fine stage in the six degrees of freedom. The magnets of all six VCMs are positioned on the fine stage, while the coils are all provided on the coarse stage. The VCM(s) used for moving the fine stage in the scanning direction need to be significantly large to make sure that the imaging element accelerates at the proper rate. In the future, as the throughput of lithography tools increases, the rate of acceleration of the fine stage containing the imaging element will also increase. Consequently the mass of the VCM(s) for accelerating the fine stage will become larger and larger. As the mass of the VCM increases, virtually everything else on the coarse stage will also need to increase in mass. The larger the mass, the more difficult it will become to accelerate the coarse stage. Consequently, the mass of this stage design has made it a limiting factor in increasing the rate of acceleration, and hence throughput, of future lithography tools.
A reticle or wafer stage with six degrees of freedom and a low mass coarse stage is therefore needed.
A reticle or wafer stage mover with six degrees of freedom, a low mass coarse stage, and the ability to move an object in a scanning direction in a lithography tool, is disclosed. The mover includes a coarse stage and a fine stage configured to support the object and supported by the coarse stage. A set of actuators is provided to move the fine stage in six degrees of freedom. All of the actuators contribute to accelerating the object and the fine stage in the scanning direction. With all the actuators generating the necessary force to move the fine stage, a single large actuator to push the fine stage in the scanning direction is eliminated. The size or mass of the coarse stage is therefore reduced. All of the actuators are also capable of generating a second force in either the X or Z directions. The actuators therefore also enable the fine stage and the object it supports to be positioned in six degrees of freedom, as well as moved in the scanning direction.
Like reference numerals in the figures refer to like elements.
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In the embodiment shown, the apparatus 10 is a scanning type tool, which means the first mover 16 moves the patterning element 14 and the second mover 26 supports and moves the wafer 24 during scanning operations, as discussed in the Background of the Invention. In alternative embodiments, the apparatus 10 is a step and repeat type tool. In which case, the first mover 16 can be eliminated and some other type of stationary holder can be used to support the patterning element 14, while the second mover 26 repeatedly steps the wafer during exposure.
The present invention is directed to a novel and useful design for a mover, which supports an object. The mover as described herein can be used to support and position either the patterning element 14 or a substrate upon which an image of the pattern is projected, such as either a semiconductor wafer or a flat panel substrate. Hence, the description of the mover as detailed below is generic in the sense that it can be used to support and position any “object” regardless if it is a patterning element 14, a wafer 24, or flat panel display. The present invention can therefore be used to implement the first mover 16, the second mover 26, or both in apparatus 10.
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The fine stage 42 is movable in six degrees of freedom (6DOF) by a set of actuators. All of the actuators are also used for accelerating the object 45 and the fine stage 42 in the scanning or Y direction. The actuators include a set of movers, typically a permanent magnet or an array of permanent magnets (hereafter generically referred to as “magnets”) located on the fine stage 42 and a set of corresponding stators 50 located on the coarse stage 44. As illustrated in the Figure, the stators 50 are provided on the four sides surrounding the fine stage 42. In one embodiment, the stators 50 on the coarse stage are arrays of electromagnetic coils. The magnets on the fine stage 42 are not visible in the figure, but are described in detail below with regard to other figures. With all the actuators generating the necessary force to move the fine stage in the scanning direction, the need for a single large actuator located, conventionally located on the coarse stage, can be eliminated. The size or mass of the coarse stage 44 of the present invention is therefore reduced relative to prior art movers. All of the actuators are also capable of generating a second force in either the X or Z directions. These actuators therefore enable the fine stage 42 and the object 45 it supports, to be positioned in six degrees of freedom, as well as moved in the scanning direction.
Details of the arrangement of the permanents magnets on the fine stage 42 are provided in
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As noted above, the coils 50 on the coarse stage 44 and the magnets 52, 54A, 54B, 56A and 56B provide a set of actuators. Each actuator is capable of generating (i) a force in the Y or scanning direction; and (ii) in either the X or Z direction as well. With this arrangement, a single large actuator, conventionally located on the coarse stage, can be eliminated. Furthermore, with the actuators each able to generate a force in another direction besides Y, the fine stage 42 and the object 45 it supports, can be moved in 6DOF.
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Semiconductor devices can be fabricated using the above described systems, by the process shown generally in
It should be noted that the particular embodiments described herein are merely illustrative and should not be construed as limiting. For example, the substrate described herein does not necessarily have to be a semiconductor wafer. It could also be a flat panel used for making flat panel displays. Rather, the true scope of the invention is determined by the scope of the accompanying claims.
This application claims priority on Provisional Application Ser. No. 60/801,582 filed on May 18, 2006 and entitled “Maglev Reticle Stage: Fine+Coarse/Carrier Stage”, the content of which is incorporated herein by reference for all purposes.
Number | Date | Country | |
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60801582 | May 2006 | US |