Photocopying – Projection printing and copying cameras – Focus or magnification control
Reexamination Certificate
2000-03-23
2003-04-15
Fuller, Rodney (Department: 2851)
Photocopying
Projection printing and copying cameras
Focus or magnification control
C355S053000, C355S057000, C355S060000, C355S066000
Reexamination Certificate
active
06549270
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus and an exposure method, and in particular relates to an exposure apparatus, an exposure method and a method for manufacturing devices, which are used at the time of manufacturing circuit devices for semiconductor elements or liquid crystal display elements and the like using a lithography process.
2. Description of the Related Art
At present, in manufacturing factory for semiconductor devices, circuit devices (64 megabit D-RAM and the like) with a minimum line width of around 0.3 to 0.35 &mgr;m are being mass produced using a reducing projection exposure apparatus, namely a so called stepper, with i-line of a mercury vapor lamp of 365 nm wavelength as the illumination light. At the same time, the introduction of exposure apparatus for mass production manufacture of next generation circuit devices with minimum line widths of less than 0.25 &mgr;m, having integration of the 256 megabit or 1 gigabit bit D-RAM class, has commenced.
As the exposure apparatus used in next generation circuit device manufacture, development is being carried out of a step-and-scan type scanning exposure apparatus, with ultraviolet pulse laser radiation of 248 nm wavelengths from a KrF excimer laser light source, or ultraviolet pulse laser radiation of 193 nm wavelengths from an ArF excimer laser light source as the illumination light. In the step-and-scan type scanning exposure apparatus, a scanning exposure operation and an inter-shot stepping operation are repeated, and at the time of scanning, a mask or reticle (hereunder referred to as “reticle”) on which a circuit pattern is drawn, and a wafer serving as a photosensitive substrate are one dimensionally scanned relatively with respect to a projection field of a reducing projection optical system. As a result, the whole of the circuit pattern of the reticle is transferred to inside one shot region on the wafer.
However, the integration of semiconductor devices is moving prospectively to even higher integration of from 1 gigabit to 4 gigabits. The device rule in this case become 0.1 &mgr;m, that is around 100 nmL/S, and to correspond to this with an exposure apparatus using ultraviolet pulse laser radiation of the aforementioned 193 nm wavelength as the exposure light, there are numerous technical problems.
Recently, the development of an EUV exposure apparatus which uses radiation of the soft X-ray region of 5 to 15 nm wavelength (referred to in the specification of this invention as “EUV (Extreme Ultra Violet) radiation”) is starting to be reached. This EUV exposure apparatus is gaining attention as an effective candidate for next generation exposure apparatus for minimum line widths, where for example with a line-and-space-pattern the pitch thereof is from 100 nm to 70 nm.
However, in such an EUV exposure apparatus, the projection optical system thereof comprises only reflecting type optical elements (mirrors). With such optical elements, the reflectivity is around 60 to 70%. Consequently, the optical elements are heated by the remaining 30 to 40% of energy. If the optical elements are heated, then deformation such as positional displacement and curvature change occur in the reflecting surface due to this, so that the projection optical system changes, resulting in the problem that an adverse effect is exerted on the exposure characteristics.
To address such a problem, cooling by convection of air cannot be hoped for since the projection optical system is in a vacuum. Consequently, conventionally a cooling mechanism is arranged on the attachment part or the rear side or the like of the optical elements, to cool the optical elements and thus suppress changes in the projection optical system.
However, this countermeasure is only for suppressing changes in the respective optical elements constituting the projection optical system, and it is not addressed to correction should a change once occur.
Moreover, in the EUV exposure apparatus, because the illumination optical system is constructed only from a plurality of reflecting type optical elements, there is the risk that a drop in optical characteristics of the illumination optical system may occur due to a change in the reflection surface of the optical elements.
SUMMARY OF THE INVENTION.
It is an object of the present invention to provide an exposure apparatus and exposure method which, even if a change occur in a projection optical system and/or an illumination optical system, can correct the change in order to maintain superior exposure characteristics. It is also an object of the present invention to provide a device manufacturing method which can manufacture stabilized high quality devices using the above exposure apparatus and exposure method.
In order to achieve the abovementioned objects, the exposure apparatus of the present invention is an exposure apparatus which illuminates a pattern formed on a mask with exposure light to transfer the pattern onto a substrate by way of a projection optical system. The projection optical system has at least one reflection type optical element, and is provided with a detection device that detects position information at an irradiation position of the exposure light on the reflection type optical element, and a correction device that corrects the optical element based on the position information.
In the exposure apparatus of the present invention, by detecting with the detection device the irradiation position of the exposure light on the reflection type optical element which constitutes the projection optical system, then position information such as the position, inclination, and deformation of the reflection type optical element can be obtained. Then based on this position information, the position, inclination, deformation and the like of the optical element is corrected with the correction device, thereby enabling the optical element to be corrected to a correct condition. Consequently, even in the case where for example due to heat or the like, the respective optical elements constituting the projection optical system change, these can be corrected. Hence the inherent exposure characteristics can be maintained enabling stabilized exposure to be performed.
In another aspect of the present invention, the detection device detects position information at a plurality of positions with respect to a single reflection type optical element. Therefore, position information for the inclination, deformation or the like of the optical element can also be obtained, and higher accuracy correction is possible.
In another aspect of the present invention, the mask is a reflecting type. Furthermore, in another aspect of the present invention, the exposure light is extreme ultraviolet (EUV) light, and the optical elements which constitute the projection optical system are all reflection type optical elements. As a result, EUV radiation can be used as the exposure light, and high accuracy transfer of extremely fine patterns, for example of fine L/S patterns of from 100 nm to below this, or isolated patterns of 70 nm or below this, are possible. By providing the change correction function of the projection optical system in this exposure apparatus, performance maintenance thereof can be easily affected.
In another aspect of the present invention, an interferometer is provided as the detection device. Hence the position change of the optical element can be measured without requiring contact.
Furthermore, in another aspect of the present invention, the measuring beam of the interferometer is irradiated orthogonal to a reflection surface of the optical element. As a result, position information for the same place as the irradiated position of the illumination light on the optical element can be measured with the interferometer. Hence high accuracy measurement can be performed. Moreover, by irradiating the measuring beam orthogonal to the reflection face of the optical element, the number of turn up mirrors or the like positioned on the optical path of the measuring be
Fuller Rodney
Oliff & Berridg,e PLC
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