Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1999-06-24
2001-01-09
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S067000
Reexamination Certificate
active
06172740
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection exposure apparatus and a method for manufacturing devices such as a semiconductor device including an IC or an LSI, an image pickup device including a CCD, a dispay device including a liquid crystal panel, a magnetic head, etc. The projection exposure apparatus and the device manufacturing method are advantageous for a case where any of these devices is to be manufactured by lithography to have a high degree of integration by projecting an electronic circuit pattern formed on the surface of a mask or a reticle (hereinafter referred to as a reticle) on a wafer through a projection optical system to carry out an exposure or a scanning-exposure action on the wafer. Particularly, the projection exposure apparatus and the device manufacturing method are advantageous for a case where a silicon wafer is to be exposed with an electronic circuit pattern of the reticle by precisely aligning and adjusting the position of the reticle and that of the wafer to each other to obtain a high degree of integration.
2. Description of Related Art
In manufacturing a semiconductor device, a liquid crystal element, etc., by photolithography, a projection exposure apparatus which is called a stepper is used. The projection exposure apparatus is arranged to carry out an exposure by projecting through a projection optical system a pattern formed on a reticle onto a photosensitive substrate which is a wafer or a glass plate coated with a photoresist or the like.
The art of manufacturing semiconductor devices to have a minute and fine circuit pattern has saliently advanced of late. Efforts are being made to have a circuit pattern more minutely defined, for example, down to such a line width measuring less than 0.25 &mgr;m. In respect of those efforts, an art of making optical exposures typically embodied in the stepper is playing the most important role. The performance of a projection lens, i.e., a projection optical system, which is usable as an index for the performance of the art of optical exposure, is considered roughly in three aspects, including a shorter wavelength, a larger image plane and a larger NA (numerical aperture). With respect to having a shorter wavelength, efforts are now ardently exerted to develop as a technique of the next generation a lithographic art of using a laser beam which is obtainable from an ArF excimer laser.
The optical exposure method for manufacturing semiconductor elements (devices) are required to satisfy various factors (requirements) which include, besides a high resolution, a high degree of precision of positional alignment, i.e., position adjustment to each other, of patterns to be superposed on each other in many layers.
Of known position adjusting methods for this purpose, a method called “global alignment” is popularly in use. The error to be made by the global method can be roughly divided into two error components. One is an intershot error component which is an error between one printing shot (exposure shot) and another and an intrashot error component which is an error made within each shot of exposure. Since the size of an image plane is tending to become larger of late, how to suppress the intrashot error component is a serious problem these days.
For example, if there is an error of 2 ppm with respect to magnification or perpendicularity for an image plane size of 22 mm, the alignment error becomes as follows:
22 mm×2 ppm=44 nm.
The value of this error alone is nearly ⅕ times as much as the resolution performance of a line width of 0.25 &mgr;m. In view of a budget for superposition, this value is clearly beyond an allowable limit. It is, therefore, a serious problem for the art of optical exposure to suppress the intrashot error component.
In order to improve the precision of positional alignment of the patterns to be superposed on each other, therefore, the intrashot error component must be adequately controlled. Meanwhile, the projection optical system used for the stepper generally has a function of correcting only such components that are rotationally symmetric with respect to an optical axis.
However, in the actual processes in the manufacture of a semiconductor device, magnifying rates of expansion and contraction of the wafer caused by processes in the x and y directions, i.e., horizontal and vertical directions, sometimes vary and fluctuate among the results of these processes according to the directivity of patterns to be printed. The fluctuations of the rates of expansion and contraction impose some limitation on the efforts to improve the precision of the overall position alignment. As regards the arrangement for correcting the rates of vertical and horizontal expansion and contraction independently of each other, a stepper disclosed in Japanese Laid-Open Patent Application No. Hei 10-242048 is arranged to make correction by shifting an aspheric surface.
Another important subject for improvement in the precision of alignment lies in factors on the side of the reticle. One of the main factors on the side of the reticle is the perpendicularity of a pattern formed on the reticle. The perpendicularity error is not caused by an exposure apparatus or by a wafer process but is caused by fluctuations of the perpendicularity of a reticle pattern drawing apparatus.
BRIEF SUMMARY OF THE INVENTION
It is an object of the invention to provide a projection exposure apparatus arranged to project on the surface of a wafer a pattern formed on a reticle and to permit control over the perpendicularity of the pattern obtained on the reticle as a rotationally asymmetric correction component, and also to provide a method for manufacturing devices with the projection exposure apparatus.
To attain the above object, in accordance with an aspect of the invention, there is provided a projection exposure apparatus, comprising a projection optical system for projecting a pattern of a mask on a substrate, and a stage for the substrate arranged to be movable in directions X and Y each of which is perpendicular to an optical axis of the projection optical system and which are perpendicular to each other, wherein the projection optical system has a pair of aspherical members, at least one of which is displaceable in a direction P which is perpendicular to the optical axis of the projection optical system and which differs from the directions X and Y, wherein a shape of an aspheric surface of each of the pair of aspherical members is determined such that substantially only a refractive power of the pair of aspherical members functioning as one system obtained at a section including the direction P varies accordingly as a positional relation in the direction P between the aspheric surfaces of the pair of aspherical members varies, and wherein substantially only a refractive power at the section of the projection optical system is varied by displacing the at least one of the pair of aspherical members in the direction P.
In the projection exposure apparatus in accordance with another aspect of the invention, the pair of aspherical members are displaceable as much as the same amount in respective opposite directions.
In the projection exposure apparatus in accordance with a further aspect of the invention, the pair of aspherical members are integrally rotatable around a rotation axis being the optical axis of the projection optical system.
In the projection exposure apparatus in accordance with a further aspect of the invention, the projection optical system has a function of varying a magnification thereof in an isotropic manner.
In the projection exposure apparatus in accordance with a further aspect of the invention, the direction P is at an angle of not less than 10 degrees and not greater than 80 degrees with respect to each of the directions X and Y.
In accordance with a further aspect of the invention, there is provided a device manufacturing method, comprising a process of transferring a device pattern of the mask to the substrate by using the projecti
Adams Russell
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Hung Henry
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