Photocopying – Projection printing and copying cameras – Focus or magnification control
Reexamination Certificate
2001-05-02
2004-04-27
Font, Frank G. (Department: 2877)
Photocopying
Projection printing and copying cameras
Focus or magnification control
C355S035000, C355S053000, C355S067000, C355S071000, C355S077000, C359S731000, C359S859000, C430S311000, C430S005000, C430S312000, C356S399000, C356S400000
Reexamination Certificate
active
06727980
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for imprinting mask patterns using photolithography on a substrate base for making semiconductor devices, imaging devices (CCD), or liquid crystal display panels and the like, and also relates to a method for adjusting the exposure apparatus. In particular, the present invention relates to technology for exposing a pattern using illumination light such as extreme ultraviolet light (EUV light) such as soft x-rays.
2. Description of the Related Art
When manufacturing semiconductor devices, various apparatuses are used in photolithography for exposing a pattern, fabricated on a mask such as a reticle, on a wafer (or glass plate) as a substrate base. Traditionally, a base is coated with a photo-resist material and is exposed using a projection type apparatus such as a stepper, or a proximity type apparatus for imprinting a pattern directly on the base. In such apparatuses, ultraviolet light such as the i-line of a mercury lamp (365 nm wavelength), or far ultraviolet light (DUV) such as KrF excimer laser light (248 nm wavelength), has been used as illumination light (exposure light). In recent years, exposure apparatuses utilize other light sources, for example, far ultraviolet light such as ArF excimer light (193 nm wavelength) and vacuum ultraviolet light (VUV light) such as F
2
laser light (157 nm wavelength), have been developed to produce a higher degree of image resolution. Also, illumination or exposure light systems used for the traditional exposure apparatuses include refraction types and reflection/refraction types.
When using light sources in the ultraviolet region, it is not very efficient to use the exposure light for adjusting the optical systems in the illumination or exposure assembly from the initial primary adjustment stage to the final fine adjustment stage. Therefore, conventionally, a different exposure light, for example, a visible light source such as a He—Ne laser is used to perform primary adjustments using methods based on collimators or interferometers, and only the final adjustment is performed using the actual exposure light.
As described above, in the conventional methods based on using adjustment light source such as a visible light source, different from the exposure light source, it is necessary to arrange a special optical path for the adjustment light, using devices such as mirrors, so that the light path of visible adjustment beam coincides approximately with the light path of the exposure beam, so that it has been difficult to perform adjustments involving both the exposure light source and the illumination optics. For this reason, it has been difficult to improve the primary or rough adjustment process, resulting in increasing the time required for final or precise adjustment using the exposure light. There has been the drawback that the assembly time is increased. Furthermore, the exposure apparatus requires periodic maintenance of the illumination and exposure optics, but traditionally, the primary adjustment process performed during the periodic maintenance operation has been quite lengthy because of the special arrangement necessary for checking the illumination optics, such as positioning the guide mirrors, thus resulting in a complex and time-consuming operation.
Also, conventional illumination and projection systems are based on a refraction system or a reflective/refraction system, and because the wavelengths for the exposure light and for the visible light are widely separated, the primary adjustment process performed by using visible light for checking resulted in chromatic aberrations in the illumination and projection optics. Chromatic aberrations cause a large error in the rough adjustment results, and contribute to further lengthening the final adjustment task.
Especially, for the future production of even more microscopic semiconductor devices, development work is underway for an apparatus based on an exposure light of less than 100 nm in the extreme ultraviolet range (EUV light). When using EUV light for exposure, because of the large size of the exposure light source, there has been a need for an adjustment method that allows inclusion of the exposure light source for total optical adjustment of the exposure apparatus.
FIG. 14
shows an example of the projection apparatus based on soft x-rays for exposure light. A laser beam in the infrared range or visible range emitted from a laser source
201
is focused by a laser light focusing optics
201
a
on a focus point
203
. An opening of a nozzle
202
is positioned in the vicinity of the focal point
203
. A target substance such as a gaseous substance ejected from the nozzle
202
is excited by the high intensity laser light at the focal point
203
, and the center portion of the target becomes a plasma, resulting in emission of soft x-ray light. Therefore, the emission point of the x-ray beam is the focal point
203
. Simultaneously, infrared light, visible light, and ultraviolet light are generated as well as soft x-rays light.
The soft x-ray beam emitted from the focal point
203
is converted to a parallel beam by the first focusing optic
204
and the second focusing optic
205
, and is focused by a condenser optic
207
, and after deflecting its optical path by the flat mirror
207
a
, and is superimposed on a reflective type mask
208
. The soft x-ray beam, reflected selectively by the pattern fabricated on the reflective mask
208
, is led to the device surface
210
to be exposed by the projection optics
209
, thereby imprinting the pattern of the mask
208
on the device surface
210
. The portion of the apparatus required for the soft x-rays is located in an evacuated chamber
211
because of the low transmissivity of soft x-rays in air.
In such an apparatus, the nozzle
202
is subjected to some wear because of the plasma generated in its vicinity. Also, the first focusing optic
204
is subjected to contamination from particles worn off the nozzle
202
, thus it is thought that the reflection properties may degrade with use. For this reason, it is necessary to replace the parts
202
and
204
periodically. When exchanging these parts, the new parts must be positioned exactly in their original positions. This is because, in the projection exposure technology field, even the slightest deviation in the illumination optical path will cause distortions in the projected image that demands the highest degree of optical precision.
However, because of the immature state of the current projection exposure technology based on soft x-rays as exposure light, there have been no suggestions of methods dealing with the positioning of replacement parts. It is desirable that the devices used in such replacement process should be as economical as possible in view of the fact that the overall projection exposure system is already extremely expensive.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for adjusting an exposure apparatus that enables to perform adjustments of internal optics quickly and efficiently.
Also, another object of the present invention is to provide a method for adjusting an exposure apparatus using EUV light for exposure that enables to perform adjustment of internal optics quickly and efficiently.
Further, still another object of the present invention is to provide an exposure apparatus designed for the method invented.
A first method is provided for performing optical adjustments on an exposure apparatus provided with: a light source that generates illumination light for exposure, and illumination optics that irradiates a mask with the illumination light and exposes a mask pattern on a substrate base using the illumination light. The method uses a wide bandwidth light source as the light source that generates an exposure light and a non-exposure light having wavelengths different from the wavelengths in the exposure light; and performs optical adjustments on optical components in at least a part of the illumin
Hagiwara Tsuneyuki
Komatsuda Hideki
Mori Takashi
Ota Kazuya
Tanimoto Akikazu
Brown Khaled
Font Frank G.
Nikon Corporation
Oliff & Berridg,e PLC
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