Photocopying – Projection printing and copying cameras – Focus or magnification control
Reexamination Certificate
1999-02-26
2001-08-28
Metjahic, Safet (Department: 2858)
Photocopying
Projection printing and copying cameras
Focus or magnification control
C355S053000
Reexamination Certificate
active
06281966
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates to a projection exposure apparatus and a device manufacturing method using the same. More particularly, the invention is concerned with a projection exposure apparatus which is usable in the field of semiconductor device manufacture and which is called a stepper, having an autofocusing function for automatically adjusting the focus when a pattern of an original, such as a circuit pattern of a reticle, is projected and transferred to the surface of a substrate such as a semiconductor wafer in a reduced scale.
For semiconductor devices, LSI devices and VLSI devices, further miniaturization of the pattern and increasing density of integration have required a projection exposure apparatus having an imaging (projection) optical system with higher resolution. In this stream, the numerical aperture of imaging optical systems is being enlarged and the depth of focus thereof is being narrowed.
With regard to wafers, from the standpoint of flattening work, variation in thickness and warp to some extent have to be accepted. As regards correction of wafer warp, generally a wafer is placed on a wafer chuck having its surface machined with flatness of a submicron order, and the bottom face of the wafer is vacuum attracted whereby flatness correction is performed. However, as regards variation in thickness within a single wafer or deformation of wafers attributable to the wafer attracting method or resulting from wafer processes, flatness correction is difficult to achieve. Therefore, within a picture field to which a reticle pattern is to be projected, a wafer may have surface irregularities. This leads to further narrowing of the effective depth of focus of the optical system.
In reduction projection exposure apparatuses, therefore development of an automatic focusing method for effectively bringing the wafer surface into registration with the focal plane (image plane) of a projection optical system is one of important issues. Examples of a wafer surface position detecting method in a reduction projection exposure apparatus are a method using an air microsensor and a method (optical method) in which light is projected to a wafer surface in an oblique direction without passage through a projection exposure optical system and in which a positional deviation of reflected light is detected.
On the other hand, in projection exposure apparatuses, the focus position (image plane position) may shift due to a change in ambient temperature of a projection optical system, a change in atmospheric pressure, temperature rise caused by irradiation of the projection optical system with light, or temperature rise caused by heat generation in the structure including the projection optical system. This has to be corrected. To this end, a change in ambient temperature of atmospheric pressure is measured by using a detector, or a change in temperature or pressure in a portion of the projection optical system is measured by using a detector, and, on the basis of it, the focus position of the projection optical system is calculated and corrected,
With this method, however, the focus position of the projection optical system is not directly measured. Therefore, there may be a detection error of the detector in the measurement of the temperature or pressure, a variation in temperature of a pressure, or an error in approximation calculation for calculating the focus position of the projection optical system. This obstructs high precision detection of the focus position of the projection optical system,
Japanese Laid-Open Patent Application, Laid Open No. 105514/1990 discloses a Through-The-Lens autofocusing system (TTL-AF) wherein a focusing pattern provided an a reticle is irradiated with light of the same wavelength as exposure light and wherein, while moving an X-Y-Z stage having a predetermined reference flat mirror in an optical axis direction of a redaction projection lens in accordance with a step-and-repeat manner, the quantity of reflected light from the reference flat mirror and an output of a wafer surface position detecting system are measured at plural locations, such that the state of focus of the wafer surface is detected on the basis of the change in light quantity.
SUMMARY OF THE INVENTION
The above-described method, however, involves a problem that, since for each measurement point along the optical axis direction, the stage movement and the measurement have to be repeated to detect the focus state, it takes a long time to complete the focus state detection.
It is an object of the present invention to provide an improved exposure apparatus and/or device manufacturing method by which the image plane position of a projection optical system can be detected quickly so that the device productivity (throughput) can be enlarged significantly.
In accordance with an aspect of the present invention, there is provided an exposure apparatus, comprising: an original stage for supporting an original; a substrate stage for supporting a substrate; exposure illumination means for illuminating the original held by said original stage with exposure light; a projection optical system for projecting a pattern of the original illuminated by said exposure illumination means, onto the substrate held by said substrate stage; substrate position detecting means for detecting the position of the substrate with respect to an optical axis direction of said projection optical system; stage driving means for moving said substrate stage in the optical axis direction; focusing illumination means for illuminating a focusing mark provided on the original with light of substantially the same wavelength as that of the exposure light and for projecting, through said projection optical system, an image of the focusing mark onto a reflection surface provided at a predetermined position on said substrate stage; light receiving means for receiving light reflected by said reflection surface, through said projection optical system and the original; and focal plane detecting means for detecting the image plane position of said projection optical system on the basis of results of reception of light from the focusing mark image reflected by said reflection surface, at different positions along the optical axis direction; wherein said focal plane detecting means is operable, while continuously moving said substrate stage in the optical axis direction, to detect different positions of said reflection surface through cooperation with said substrate position detecting means and also to receive, at the different positions, the reflected light of the focusing mark image through said light receiving means. The focal plane detecting means may include synchronization means for synchronizing the detection of different positions of said reflection surface and the reception of reflected light at the respective positions.
With this arrangement, while the substrate stage is moved continuously along the optical axis direction, at different positions the reflection surface on the substrate stage is detected, and at these positions, the reflection light of the focusing mark image is received by the light receiving means. This enables high speed detection of the image plane position of the projection optical system and, thus, ensures improved device productivity (throughput).
When synchronization means for synchronizing the detection of the reflection surface at different positions and the reception of reflected light at these positions is provided, reception of reflection light can be performed at regular intervals and a precise sampling pitch. This enables high precision measurement of the image plane position.
A device manufacturing method according to the present invention may use an exposure apparatus such as described above, to perform aligning a substrate with respect to an image plane to be detected by focal plane detecting means, and to perform an exposure process to the substrate.
This procedure enables light reception while moving the substrate stage continuously without interruption at re
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
LeRoux Etienne
Metjahic Safet
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