Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2000-01-10
2001-05-15
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S067000, C356S401000
Reexamination Certificate
active
06233043
ABSTRACT:
This application is based on Japanese Patent Applications No. 9-46525, 9-46526, and 9-46527 all filed on Feb. 28, 1997 and No. 9-253786 filed on Sep. 18, 1997, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to position detection techniques using scattered light from edges or apexes, and more particularly to a position detection method, a position detection apparatus and an alignment mark, suitable for improving throughput of proximity exposure.
b) Description of the Related Art
As the position alignment of a wafer and a mask by using an alignment system composed of a lens system and an image processing system, a vertical detection method and an oblique detection method are known. The vertical detection method observes alignment marks along a direction vertical to the mask surface, whereas the oblique detection method observes alignment marks along a direction oblique to the mask surface.
A chromatic bifocal method is known which is used as a focussing method for the vertical detection method. With this chromatic bifocal method, a mask mark formed on a mask and a wafer mark formed on a wafer are observed with light having different wavelengths, and focussed on the same flat plane by utilizing chromatic aberration of the lens system. This method can principally set an optical resolution of a lens high, so that an absolute position detection precision can be made high.
However, since alignment marks (the mask marks and the wafer marks) are observed along the vertical direction, the observing optical system enters an exposure region. If exposure is performed in this state, the optical system intercepts exposure light. It is therefore required to retract the optical system from the exposure region when exposure is performed. The time required for the optical system to retract from the exposure region lowers throughput. Further, during the exposure, the alignment marks cannot be observed and their positions cannot be detected. This may cause a low alignment precision during the exposure.
With the oblique detection method, the optical system is disposed with its optical axis being set oblique to the mask surface so that it can be located at the position not intercepting exposure light. It is therefore unnecessary to retract the optical system during exposure, and alignment marks can be observed even during exposure. It is possible to prevent position misalignment during exposure, without lowering throughput.
With this oblique detection method, however, wafer and mask marks observed obliquely are focussed so that an absolute precision of position detection is lowered by image distortions. Furthermore, since the optical axis of illumination light is not coincident with the optical axis of observation light, it is not possible to coaxially dispose both axes. Therefore, the illumination light axis becomes easy to shift from an ideal optical axis. As the illumination light axis shifts from the ideal optical axis, images are distorted and correct position detection becomes difficult.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide position detection techniques capable of providing high precision alignment without lowering throughput, while allowing position detection during exposure.
According to one aspect of the present invention, there is provided a position detection method comprising the steps of: disposing a wafer having an exposure surface and an exposure mask, with a gap being set between the exposure surface and the exposure mask, the wafer having a wafer mark formed on the exposure surface, the wafer mark having edges for scattering incident light, each edge having a curved portion whose image vertically projected upon a plane in parallel to the exposure surface has a curved shape, the exposure mask having a mask mark formed on the surface thereof, the mask mark having edges for scattering incident light, each edge having a curved portion whose image vertically projected upon a plane in parallel to the surface of the exposure mask has a curved shape; and detecting a relative position of the wafer and the exposure mask by applying illumination light to the curved portions of the edges of the wafer and mask marks and by observing, along a direction oblique to the exposure surface, light scattered from the curved portions.
Since light scattered from edges is observed obliquely, the observing optical system can be configured not to enter the exposure area. It is not necessary to retract the optical system during the exposure and it is possible to observe light scattered from edges even during the exposure. Since the edge has a curved portion, a variation in the shapes and positions of edges to be caused by the influences of manufacture process variation can be reduced.
According to another aspect of the present invention, there is provided a semiconductor substrate having an exposure surface formed with a plurality of aligning wafer marks along a direction perpendicular to a plane of incident of incident light, each wafer mark having an edge for scattering the incident light, and an image of the edge vertically projected upon the exposure surface having at least a curved portion.
According to another aspect of the present invention, there is provided an exposure mask having a plurality of aligning mask marks disposed along a direction perpendicular to a plane of incident of incident lights each mask mark having an edge for scattering the incident light, and an image of the edge vertically projected upon the surface of the exposure mask having at least a curved portion.
Since an edge has a curved portion, a variation in the shapes and positions of edges to be caused by the influences of manufacture process variation can be reduced. Since a plurality of edges are disposed along a direction perpendicular to an incident surface, a plurality of images can be observed at the same time. By moving these images in parallel and superposing the images one upon another, a relative position can be easily detected.
According to another aspect of the present invention, there is provided a position detection method comprising the steps of: disposing a member with an exposure surface to be exposed and an exposure mask, with a gap being set between the exposure surface and the exposure mask, the member having an alignment mark formed on the exposure surface, the alignment mark having edges or apexes for scattering incident light, the exposure mask having a mask mark formed on the surface thereof, mask mark having edges or apexes for scattering incident light; and detecting a relative position of the member and the exposure mask by applying illumination light to the edges or apexes of the alignment and mask marks, by focussing light scattered from the alignment and mask marks on a light reception plane, and by observing images on the light reception plane, whereby a light flux scattered from one of the alignment and mask marks is attenuated or light fluxes scattered from both of the alignment and mask marks are attenuated differently so that a light intensity of an image formed by the light flux scattered from the alignment mark and focussed on the light reception plane becomes near to a light intensity of an image formed by the light flux scattered from the mask mark and focussed on the light reception plane.
Edges or apexes of the alignment and mask marks allow the scattered light to be observed, because an image is formed by a flux of scattered light in the aperture of an objective lens of the observing optical system. Further, even if illumination light is applied along a direction allowing only scattered light from edges to be incident, edge scattered light can be observed because normal reflection light from the alignment and mask marks are not incident upon the observing optical system.
Since the intensities of light scattered from the alignment and mask marks are made near to each other, image signals corresponding to images on a focal plane can be obtained at a
Adams Russell
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Kim Peter B.
Sumitomo Heavy Industrie's, Ltd.
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