The present invention relates to lithography, and more particularly, to a magnetic levitation lithography apparatus and method that uses magnets to provide a static, gravity opposing force to support a fine stage over a coarse stage and to dynamically control the position of the fine stage in one or more degrees of freedom.
A typical lithography machine includes a radiation source, a patterning element, a projection system, and a wafer table to support a wafer. A radiation-sensitive material, such as resist, is coated onto the wafer surface prior to placement onto the wafer table. During operation, radiation energy from the radiation source is used to project the pattern defined by the patterning element through the projection system onto the wafer.
The projection area during an exposure is typically much smaller than the wafer. The wafer therefore has to be moved relative to the projection system to pattern the entire surface.
In the semiconductor industry, two types of lithography machines are commonly used. With so-called “step and repeat” machines, the entire pattern is projected at once in a single exposure onto a target area of the wafer. 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 wafer surface is exposed. With scanning type lithography machines, the target area is exposed in a continuous or “scanning” motion. The patterning element is moved in one direction while the wafer is moved in either the same or the opposite direction during exposure. The wafer is then moved in the x and y direction to the next scan target area. This process is repeated until all the desired areas on the wafer have been exposed.
With either type of machine, the wafer substrate table is used to move the wafer substrate. Wafer tables typically have two stages, a coarse stage and a fine stage. The coarse stage is used to move the wafer in the x and/or y directions from one target area to the next. The fine stage is used for minute adjustments and is capable of positioning the wafer in six degrees of freedom (x, y, z, ⊖n, ⊖y and ⊖z. Magnetic levitation is one known way to support the fine stage over the coarse stage. For more details on magnetic levitation, see U.S. Pat. Nos. 4,952,858, 5,157,296, 5,294,854, 3,935,486, 5,623,853, U.S. Patent Publications 2003/0173833A1, 2003/0052284 and British Patent Specification 1,424,413, each incorporated by reference herein for all purposes.
Ideally, a magnet levitation fine stage should have no vertical weight. In other words, the upward magnetic force completely offsets or compensates for the effects of gravity, resulting in a static vertical mass of zero for the fine stage. In the real world, a certain amount of stiffness will always be present between the fine and coarse stages. This stiffness, which is analogous to a spring, is problematic for several reasons. Any disturbances in the coarse stage are transmitted to the fine stage through the spring. The force of these disturbances can be modeled using equation [1] below.
[1] F=mg+kz, where
A magnetic levitation lithography machine having a low spring stiffness to minimize disturbances of the fine stage and which is capable of dynamically controlling the fine stage in one or more degrees of freedom is therefore needed.
A magnetic levitation lithography machine having a low spring stiffness to minimize disturbances of the fine stage and which is capable of dynamically controlling the fine stage in one or more degrees of freedom is disclosed. The machine includes a radiation source, a patterning element configured to define a pattern, a projection element, the projection element configured to project the pattern onto a substrate when radiation from the radiation source is projected through the projection element; and a substrate table configured to support the substrate. The substrate table includes a coarse stage, a fine stage, and a magnetic support configured to support the fine stage adjacent the coarse stage. The magnetic support includes a first magnet element, coupled to the fine stage, having a first magnet polarization, a second magnet element, coupled to the course stage, having a second magnet polarization, the first magnet element being separated from the second magnet element by a gap, and an adjustment mechanism configured to adjust the magnetic force used to support the fine stage by varying the gap between the first magnet element and the second magnet element.
Referring to
The apparatus 10 also includes a wafer table 28 that is suspended from frame 22 below the projection system 20. The wafer table 28 includes a fine stage 30 and a coarse stage 32. The fine stage 30 is used to support a wafer 34. The fine stage 30 is limited in travel to fine movements, for example 500 microns in total stroke, in one or more of the six degrees of freedom directions. The coarse stage 32 is used to support the fine stage 30 and is used for coarse positioning. For example, the coarse stage has a capability of traveling 300 mm in the X, and Y directions. The coarse stage may be moved by linear motors that include a fixed member (not shown) and a moving member 38 and positions the coarse stage in three degrees of freedom (in the X, Y directions and about the Z direction). The fine stage 30 may be moved by one or more actuators. The actuators may be, in different embodiments, linear motors, voice coil motors, or a combination thereof. Such actuator may include a fixed member (not shown) connected to the coarse stage 32 and a moving member connected to fine stage 30. The exposure area on the wafer 34 can therefore be precisely controlled by controlling the fine 30 and coarse 32 stages respectively.
Referring to
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A gap 56 is provided between the first magnet 50 and the second magnet 52. By varying the gap 56, the magnetic force applied to the fine stage 30 is controlled. As the gap 56 decreases, the force increases, and vice-versa.
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The annular ring 64 of the second assembly 202 is mounted onto an annular shaped fixed base 205 on the course stage 32. The course stage 32 also includes a second base 206, supported above the surface of the course stage 32, and configured to fit between the ring surface 204A and the plunger 62 and under the bottom surface 203 of the first magnet 50. The second base 206 is also annular shaped and is configured to allow the plunger 62 of the first magnet 50 to move up and down with respect to the course stage 32. The mounts 207 each have an upper pin 207A configured to engage the second base 206 and a lower pin 207b configured to engage the fixed base 205. Together, the pins 207A and 207B allow the mounts 207 to be rotated so that when the annular ring 64 is rotated, the pin 68 can be positioned within the grooves 66 (not illustrated) so that the magnets 52 can be radially moved in and out to vary the size of the gap 56.
In an alternative embodiment, the fine stage 30 can be supported by both the magnet structure 40 and an air bearing. With this embodiment, as illustrated in
In yet another embodiment, the second assembly 202 might be coupled to the fine stage 30 instead of the coarse stage 32. In this case, the flat top surface 60 of the first assembly 201 faces to the coarse stage 32 and an air bearing is formed between the flat top surface 60 and a partial surface of an upper part of the course stage 32 for the horizontal degree of freedom (along the X and Y axes and about the Z axis) of the fine stage 30 relative to the coarse stage 32.
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As described above, a photolithography system according to the above described embodiments can be built by assembling various subsystems, including each element listed in the appended claims, in such a manner that prescribed mechanical accuracy, electrical accuracy and optical accuracy are maintained. In order to maintain the various accuracies, prior to and following assembly, every optical system is adjusted to achieve its optical accuracy. Similarly, every mechanical system and every electrical system are adjusted to achieve their respective mechanical and electrical accuracies. The process of assembling each subsystem into a photolithography system includes mechanical interfaces, electrical circuit wiring connections and air pressure plumbing connections between each subsystem. Needless to say, there is also a process where each subsystem is assembled prior to assembling a photolithography system from the various subsystems. Once a photolithography system is assembled using the various subsystems, total adjustment is performed to make sure that accuracy is maintained in the complete photolithography system. Additionally, it is desirable to manufacture an exposure system in a clean room where the temperature and humidity are controlled. Further, semiconductor devices can be fabricated using the above described systems, by the process shown generally in
At each stage of wafer processing, when the above-mentioned preprocessing steps have been completed, the following post-processing steps are implemented. During post-processing, initially, in step 315 (photoresist formation step), photoresist is applied to a wafer. Next, in step 316, (exposure step), the above-mentioned exposure device is used to transfer the circuit pattern of a mask (reticle) to a wafer. Then, in step 317 (developing step), the exposed wafer is developed, and in step 318 (etching step), parts other than residual photoresist (exposed material surface) are removed by etching. In step 319 (photoresist removal step), unnecessary photoresist remaining after etching is removed.
Multiple circuit patterns are formed by repetition of these preprocessing and post-processing steps.
This invention can be utilized in an immersion type exposure apparatus with taking suitable measures for a liquid. For example, PCT patent application WO 99/49504 discloses an exposure apparatus in which a liquid is supplied to the space between a substrate (wafer) and a projection lens system in exposure process. As far as is permitted, the disclosures in WO 99/49504 is incorporated herein by reference.
In various embodiments of the invention, the magnets 50 and 52 may be either permanent and/or electromagnetic. The present invention may also be used with an illumination system that projects radiation energy in one of but not limited to the following wavelengths 365, 248, 193, 157, 126 nms or EUV in the 5-20 nm range. Also the patterning element 14 may be either a mask or reticle or a programmable LCD array such as described in U.S. Pat. Nos. 5,296,891, 5,523,193 and PCT applications WO 98/38597 and 98/33096, each incorporated by reference herein.
Further, this invention can be utilized in an exposure apparatus that comprises two or more substrate and/or reticle stages. In such apparatus, the additional stage may be used in parallel or preparatory steps while other stage is being used for exposing. Such a multiple stage exposure apparatus are described, for example, in Japan patent Application Disclosure No. 10-163099 as well as Japan patent Application Disclosure No. 10-214783 and its counterparts U.S. Pat. No. 6,341,007, No. 6,400,441, No. 6,549,269 and No. 6,590,634. Also it is described in Japan patent Application Disclosure No. 2000-505958 and its counterparts U.S. Pat. No. 5,969,441 as well as U.S. Pat. No. 6,208,407. As far as is permitted, the disclosures in the above-mentioned U.S. patents, as well as the Japan patent applications are incorporated herein by reference.
This invention can be utilized in an exposure apparatus that has a movable stage retaining a substrate (wafer) for exposing it, and a stage having various sensors or measurement tools for measuring, as described in Japan Patent Application Disclosure No. 11-135400. As far as is permitted, the disclosures in the above-mentioned Japan patent application is incorporated herein by reference.
It should be noted that the particular embodiments described herein are merely illustrative and should not be construed as limiting. Rather, the true scope of the invention is intended to be determined by the accompanying claims.
This application claims priority on Provisional Application Ser. No. 60/580,468 filed on Jun. 17, 2004 and entitled “Permanent Magnet Gravity Compensation Device”. The contents of Provisional Application Ser. No. 60/580,468 are incorporated herein by reference for all purposes.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2005/017945 | 5/20/2005 | WO | 00 | 12/11/2006 |
Number | Date | Country | |
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60580468 | Jun 2004 | US |