Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2001-03-14
2003-06-24
Font, Frank G. (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S030000, C355S053000, C355S055000, C355S067000, C355S077000, C359S507000, C359S512000, C430S311000, C430S312000
Reexamination Certificate
active
06583857
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus and it making method, and device manufacturing method. More particularly, the present invention relates to an exposure apparatus used to manufacture a semiconductor device and a liquid crystal display device and the like in a lithographic process and its making method, and a device manufacturing method using the exposure apparatus.
2. Description of the Related Art
Conventionally, in the photolithographic process to manufacture a semiconductor device and the like, exposure apparatus such as the so-called stepper or the so-called scanning stepper have been used. As the illuminating light for exposure apparatus such as the stepper, the emission line (g line or i line) in the ultraviolet light region emitted from an ultra-high pressure mercury lamp has been used. In recent years, however, with the requirement for higher integration in the semiconductor device pressing, in order to print a pattern with the highest integration possible on the wafer, the exposure resolution had to be improved. Therefore, inert gas or a halogen laser light source that emits an excimer laser beam having a shorter wavelength such as the KrF excimer laser beam (wavelength: 248 nm) or the ArF excimer laser beam (wavelength: 193 nm) are now becoming used as the exposure light source. It is well known, that in the case of using an excimer laser beam with a short wavelength, materials that can be used for the lens of the projection optical system at this stage are limited to materials made of fluoride crystal such as synthetic quartz, fluorite, or lithium fluoride, mainly due to the problem of transmittance of the material.
In the case of using materials such as quartz or fluorite for the lens of the projection optical system, however, it is difficult to correct the chromatic aberration in actual. Therefore, in order to prevent the image forming characteristics from deteriorating due to the chromatic aberration, what is called narrowbanding of wavelength is required, that is, to narrow the oscillation spectral width of the excimer laser beam. This narrowbanding of wavelength is performed, for example, by using the narrowbanding module (optical elements such as a combination of a prism and a grating (diffraction grating), or etalon are used) provided in the laser resonator. And, to narrowband the wavelength, the spectral width of the wavelength of the excimer laser beam supplied to the projection optical system during exposure is required to be within a predetermined wavelength at all times, and at the same time, the so-called control of wavelength stabilization is required to keep the center wavelength at a predetermined wavelength. With recent exposure apparatus using the excimer laser beam in the far ultraviolet region, the accuracy required in the narrowbanded wavelength bandwidth (spectral width) is around 1 pm (=1×10
−12
) which corresponds to around {fraction (1/300)} of the natural oscillation spectral width before being narrowbanded, and the error of the center wavelength on wavelength stabilization requires the accuracy of around ±0.25 pm. In addition, as a matter of course, exposure amount control is required in these exposure apparatus.
To achieve the wavelength stabilization control, the optical properties (such as the center wavelength and the spectral half-width) of the excimer laser beam need to be monitored. The wavelength monitoring portion of the excimer laser unit is made up of etalon, which is usually a Fabry-Perot spectroscope, and a line sensor to detect its fringe pattern.
In addition, to monitor and feedback control the center wavelength and the spectral half-width of the laser beam, a spectroscopic process called deconvolution is also required. This is because when an emission line spectral emitted from an isotope mercury lamp or an iron lamp serving as a reference wavelength light source is incident on the etalon structuring the wavelength monitoring portion, a fringe pattern corresponding to the center wavelength and the spectral half-width is generated. With the fringe pattern, however, a phenomenon (convolution) occurs in which the width of the spectral half-width detected is thicker than the actual spectral half-width, due to interference of the fringe pattern with the etalon interferometer. The effect of the phenomenon, therefore, must be removed.
With the pressing requirements in recent years for an improvement in throughput, the repetition frequency of the excimer laser is becoming higher, and in order to achieve the higher repetition frequency the pulse compression circuit is becoming larger, leading to a larger excimer laser unit. Thus, the recent exposure apparatus using the excimer laser unit as the exposure light source has an arrangement that houses the main body of the exposure apparatus in a chamber called an environmental chamber where conditions such as the internal pressure, temperature, and humidity are controlled with high precision at a predetermined target value. The excimer laser unit is arranged separately outside the chamber, and is connected to the main body of the exposure apparatus by a light guiding optical system, a part of which includes a beam matching unit that is an optical system for adjusting the optical axis.
However, with the exposure apparatus using the conventional excimer laser unit described above, since the excimer laser unit was arranged separately from the main body of the exposure apparatus, a phenomenon occurred in which the optical properties of the laser beam changed while the laser beam emitted from the excimer laser unit passed through the optical system such as the light guiding optical system and the illumination optical system. This change was due to the difference in environmental conditions such as the difference in temperature and pressure between the interior of the housing of the excimer laser unit and the chamber.
Accordingly, when the spectral half-width and the like was controlled based on the detection of the fringe pattern within the housing of the excimer laser unit as was described above, the center wavelength, the spectral half-width, and the degree of energy concentration of the laser beam guided to the main body of the exposure apparatus could not be maintained at a desirable value. In such a case, since the projection optical system was adjusted only to a predetermined exposure wavelength, as a consequence, chromatic aberration of the projection optical system occurred, as well as the phenomenon of the image forming characteristics such as the magnification, distortion, and focus changing.
In addition, along with the size of the excimer laser unit increasing, to cope with the increase in chip size, the size of the main body of the exposure apparatus size is also increasing due to a larger wafer diameter and a larger stage. Thus, the footprint of the exposure apparatus in the clean room is also increasing. So, to reduce the footprint, methods such as arranging the excimer laser unit in a service room that has a lower degree of cleanliness than the clean room are being employed. With this method, however, since the light guiding optical system becomes longer, the difference in environmental conditions between the chamber where the main body of the exposure apparatus is housed and the interior of the excimer laser unit becomes larger, and the change in the optical properties of the laser beam or the change in the image forming characteristics of the projection optical system becomes more apparent.
Furthermore, when the main body of the exposure apparatus and the excimer laser unit were arranged separately as with the conventional exposure apparatus, the optical axis alignment of the laser unit and the main body of the exposure apparatus had to be performed among the laser unit, the light guiding optical system, and the illumination optical system arranged inside the main body of the exposure apparatus, which made the optical axis alignment operation troublesome and time-consuming. A
Brown Khaled
Font Frank G.
Nikon Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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