Radiation imagery chemistry: process – composition – or product th – Registration or layout process other than color proofing
Reexamination Certificate
2001-06-21
2002-05-21
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Registration or layout process other than color proofing
C430S030000, C430S311000
Reexamination Certificate
active
06391503
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an exposure apparatus and an exposure method. In particular, the present invention relates to an exposure apparatus, especially a scanning exposure apparatus and a scanning exposure method in which a mask held by a mask stage and a photosensitive substrate held by a substrate stage are subjected to scanning in a synchronized manner by using an illumination light beam, so as to transfer, onto the photosensitive substrate, a pattern such as a semiconductor circuit pattern and a liquid crystal circuit pattern formed on the mask via a projection optical system.
BACKGROUND ART
Recently, a scanning type exposure apparatus based on the step-and-scan system (hereinafter referred to as “S&S system”, if necessary), which realizes a resolution line width of not more than 0.5 &mgr;m, has been developed as an exposure apparatus for producing semiconductor elements. The apparatus is being actively improved in order to realize genuine and practical use for the semiconductor production line. The exposure apparatus based on the S&S system is disclosed, for example, in (1) Japanese Laid-Open Patent Publication No. 56-111218, (2) SPIE Vol. 1088 Optical/Laser Microlithography II (1989), pp. 424-433, (3) Japanese Laid-Open Patent Publication No. 2-229423, and (4) Japanese Laid-Open Patent Publication No. 4-277612.
Among them, in order to use mirror projection of 1× magnification in the S&S system, the above-mentioned patent document (1) discloses a system in which the mask is linearly moved in the scanning direction during scanning exposure, while the semiconductor wafer is moved in the scanning direction in a scanning manner, and it is moved in a direction perpendicular thereto in a stepwise manner. The above-mentioned document (2) discloses a reduction projection scanning exposure apparatus of the S&S system which uses a 1/4 reduction projection optical system having a circular arc-shaped slit field constructed by combining an optical lens and a reflecting mirror so as to accurately control the velocity ratio between the mask (or reticle) and the wafer to be 4:1 during scanning exposure. The above-mentioned patent document (3) discloses an apparatus in which an excimer laser is used as an illumination light beam, and an effective projection area is subjected to restriction to a regular hexagon which is inscribed in a circular image field of an ordinary reduction projection lens system to perform exposure based on the S&S system. The above-mentioned patent document (4) discloses an apparatus in which an effective projection area is subjected to restriction to a linear slit-shaped (rectangular) area which is formed along a diameter of a circular image field of an ordinary reduction projection lens system to perform exposure based on the S&S system.
Besides, in order to obtain a higher resolving power, Japanese Laid-Open Patent Publication No. 6-300973 (5) discloses a reduction projection optical system comprising a plurality of optical lenses, a beam splitter, and a concave mirror, the system being applied to an ArF excimer laser having a wavelength of not more than 200 nm as an illumination light beam for exposure. A similar projection optical system is also disclosed in Japanese Laid-Open Patent Publication No. 5-88087 applied by the same applicant as that of the present application.
In the respective conventional techniques described above, the scanning type exposure apparatus based on the use of the reduction projection optical system generally adopts the system in which the reticle stage for holding the reticle and the wafer stage for holding the wafer are moved in a scanning manner at a velocity ratio which coincides with a reciprocal number of a reduction magnification of the projection optical system. Therefore, it has been necessary that a driving source (for example, a linear motor) for the reticle stage and a driving source (for example, a linear motor) for the wafer stage should be individually provided on an apparatus body (for example, a column for fixing the projection optical system thereon) to precisely control the both driving sources in a synchronized manner so that the reticle and the wafer are relatively moved while maintaining a constant velocity ratio. Namely, such a system requires the linear motor for linearly moving the reticle stage with respect to the projection optical system during scanning exposure, the linear motor for linearly moving the wafer stage with respect to the projection optical system, and a servo control circuit for individually and precisely controlling the respective linear motors on the basis of measured values obtained by laser interferometers for individually measuring the position of movement of the respective stages with respect to the projection optical system.
In the case of the scanning type exposure apparatus based on the use of the reduction projection optical system as described above, a method is generally adopted in which a stage having superior characteristics runs after a stage having inferior characteristics, because the reticle stage (mask stage) and the wafer stage (substrate stage) have different dynamic characteristics respectively. However, such a scanning type exposure apparatus has the following inconvenience. Namely, the stage having inferior characteristics is slow in setting adjustment, because it is affected, for example, by fluctuation of the body so serve as a backbone of the apparatus. In order to improve the synchronization performance, it is necessary to use a stage having extremely excellent dynamic characteristics, as the stage having superior characteristics. Moreover, it is necessary and indispensable to use a special unit such as a so-call active vibration-removing apparatus (vibration-preventive apparatus) for reducing fluctuation of the body. Therefore, the system of the apparatus is complicated to that extent, and the cost becomes expensive.
Further, the scanning exposure apparatus based on the use of the reduction projection system, in which the optical axis ranging from the reticle to the wafer is linear, has the following inconvenience, as in the apparatuses described in the foregoing patent documents (3) and (4). Namely, the reticle stage and the wafer stage are generally arranged so that both of them are moved in the horizontal direction. Further, the reticle stage and the wafer stage are disposed so that they are separated from each other in the vertical direction by a distance of about 80 to 150 cm. Accordingly, the reticle stage is arranged at an upper position of the body of the exposure apparatus. Therefore, the entire apparatus may be inclined due to scanning movement of the reticle stage during scanning exposure in some cases. In other cases, excessive stress may be applied to the respective structural components (for example, the column, and the base plate) for constituting the apparatus body.
The conventional apparatus has also involved the following inconveniences. Namely, disorder occurs in synchronous control for the linear motor for the reticle stage and the linear motor for the wafer stage. Further, the transfer magnification becomes non-uniform in relation to the scanning direction concerning the pattern image transferred to the shot area on the wafer if the interferometer suffers measurement error (count mistake).
The present invention has been made considering the inconveniences involved in the conventional technique as described above, an object of which is to provide an exposure apparatus and a scanning exposure apparatus each of which has a simple structure and makes it possible to reduce the stress generated in the structural components for constructing the apparatus, suppress inclination and fluctuation of the entire apparatus, and improve the synchronization performance of the mask stage and the substrate stage.
Another object of the present invention is to provide a scanning exposure method which makes it possible to reduce the stress generated in the exposure apparatus, suppress inclination and fluctuation of the entire apparatu
Nikon Corporation
Oliff & Berridg,e PLC
Young Christopher G.
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