Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2000-09-29
2002-04-30
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S055000, C355S067000
Reexamination Certificate
active
06381004
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus and a device manufacturing method. More particularly, the present invention relates to an exposure apparatus used to manufacture semiconductor devices and liquid crystal display devices in a lithographic process, and a device manufacturing method using the exposure apparatus.
2. Description of the Related Art
Conventionally, in a lithographic process to manufacture devices such as semiconductors and liquid crystal displays, projection exposure apparatus has been used to project and transfer a pattern formed on a mask or a reticle (to be generically referred to as a “reticle” hereinafter) onto a substrate such as a wafer or a glass plate (to be suitably referred to as a “substrate” or a “wafer” hereinafter) coated with a photo resist or the like. As an apparatus of this type, for example, in a manufacturing process for semiconductor devices, a static type (also referred to as a step-and-repeat type) exposure apparatus has been the mainstream. This exposure apparatus mounts a wafer as a substrate on a wafer stage, and after stepping the wafer stage by a predetermined amount XY in a two-dimensional direction, the reticle pattern is transferred onto a shot area on the substrate through an projection optical system. However, as the degree of integration increases in semiconductor devices and the circuit pattern becoming extremely fine, requirements for a higher resolution and exposure preciseness in the performance of exposure apparatus are also increasing. To meet these demands, in recent years, as an exposure apparatus employing a new method, the scanning type exposure apparatus based on a so-called step-and-scan method is becoming widely used. With this type of exposure apparatus, the wafer is illuminated with a slit-shaped illumination light through the reticle and the projection optical system. And along a direction perpendicular to the longitudinal direction of the illumination area of the illumination light, the reticle stage holding the reticle and the wafer stage holding the wafer are moved relatively with respect to the projection optical system, thus the reticle pattern being sequentially transferred onto the wafer.
With the scanning type exposure apparatus described above, when transferring the reticle pattern onto a shot area on the wafer, that is, on exposure, just before performing the exposure the positional information (focus information) of the wafer surface to the optical axis direction of the projection optical system is measured. The information is measured with a focus sensor at the exposure position (the shot area which is subject to exposure). And, scanning exposure is to be performed by positioning a sample holder (Z stage) holding the wafer which finely moves along the optical axis direction so that the surface of the shot area on the wafer coincides within the range of the depth of focus of the projection optical system.
With such a scanning type exposure apparatus, the focus information of the wafer just prior to exposure regarding shot areas excluding the circumferential shot areas of the wafer can be easily detected, therefore do not cause any problems. When exposing circumferential shot areas of the wafer, however, detecting focus information prior to exposure was often difficult, especially when an exposure area, conjugate with an illumination area of the reticle, was exposed with the relative scanning direction proceeding from the circumferential portion of the wafer to the center (the actual exposure is performed with the exposure area fixed and the wafer moving, however, the expressions above are used for the sake of convenience). In such a case, the Z stage movement lagged behind, thus, the reticle pattern was at times, transferred onto the shot area in a defocused state.
Meanwhile, in order to prevent the defocused state, a method is used in some cases where the scanning direction for the circumferential shot areas always proceed from the center of the wafer to the circumferential portion. However, in such a case, since the reticle and the wafer is always relatively scanned in a determined direction, the reticle stage and the wafer stage need to be restored to their original position. This naturally leads to a decrease in the throughput compared with when scanning exposure is performed alternately, to and fro, between one side of the scanning direction and the other side of the scanning direction.
Also, even if the circumferential shot areas were exposed with the scanning direction for the circumferential shot areas proceeding from the center of the wafer to the circumferential portion at all times, the detection points of the focus sensor did not entirely cover the wafer. Consequently, on some of the shot areas, the tilt of the wafer could not be adjusted, resulting at times in a pattern of a defocused state being transferred.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of this situation, and has as its first object to provide an exposure apparatus that is capable of effectively suppressing the critical dimension variation by a macroscopic observation, which is caused by defocus during exposure.
It is the second object of the present invention to provide a device manufacturing method that can contribute to improving the productivity when microdevices with degree of high integration are produced.
With the scanning exposure apparatus, the substrate is relatively scanned with respect to the illumination area that is longitudinal in the non-scanning direction and transversal in the scanning direction. Therefore, in the case of any tilt error of the substrate surface in the scanning direction (pitching) to the image plane of the projection optical system, the contrast of the image transferred decreases, however, due to the averaging effect, defocus is suppressed at a moderate level. On the other hand, when there is a tilt error of the substrate surface in the non-scanning direction (rolling) to the image plane of the projection optical system, this directly becomes the cause of defocus. That is, the influence of the pitching and the rolling of the substrate on the exposure accuracy are not the same. The present invention has focused on this point, therefore has employed the following composition.
According to the first aspect of the present invention, there is provided a first exposure apparatus which relatively scans a mask and a substrate with respect to a projection optical system while the mask having a pattern formed is illuminated with an illumination light to transfer the pattern onto at least one shot area on the substrate via the substrate projection optical system, the exposure apparatus comprising: a focus detection system which detects positional information on the substrate surface in an optical axis direction of the projection optical system at a plurality of detection points; a selection unit capable to set a selection criteria and select detection points according to the selection criteria, the selection criteria including a first type detection point selection criteria to control a tilt of the substrate in a moving direction and a tilt of the substrate in a direction perpendicular to the moving direction, the moving direction being a first direction whereas the direction perpendicular being a second direction, and a second type detection point selection criteria to control the tilt of the substrate with priority on the second direction; and a substrate driving unit which controls a position of the substrate in the optical axis direction and a tilt with respect to a surface perpendicular to the optical axis to adjust a positional relationship between the substrate surface within an illumination area and an image plane of the projection optical system based on positional information of the substrate surface in an optical axis direction of the projection optical system at the detection points selected.
With this apparatus, when the first type detection point selection criteria is set, according
Hagiwara Tsuneyuki
Tashiro Hideyuki
Adams Russell
Nguyen Hung Henry
Nikon Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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