Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2000-10-06
2004-11-02
Font, Frank G. (Department: 2877)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S035000, C355S067000, C355S077000, C250S492200, C356S400000, C430S030000, C430S311000
Reexamination Certificate
active
06813004
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure method, an exposure apparatus and making method of the apparatus, and device and manufacturing method of the device. More particularly, the present invention relates to an exposure apparatus used in a photolithographic process in manufacturing a semiconductor device, liquid crystal display device, or the like and its making method, an exposure method using the exposure apparatus, a device manufacturing method using the exposure method and a device manufactured by the exposure apparatus.
2. Description of the Related Art
In a photolithographic process to manufacture a semiconductor device, liquid crystal display device, or the like, conventionally, a projection exposure apparatus such as a reduction projection exposure apparatus based on a step-and-repeat method (so-called stepper) or a scanning exposure apparatus based on a step-and-scan method (so-called scanning stepper) which is an improvement of the stepper is used.
The resolution of a projection optical system of a projection exposure apparatus of this type is expressed by the frequently cited Rayleigh criterion, R=k×&lgr;/N.A. In this case, R is the resolution of the projection optical system, &lgr;is the wavelength of exposure light, N.A. is the numerical aperture of the projection optical system, and k is the constant determined by the process as well as the resolution of the resist.
As the integration degree of semiconductor devices increases, a higher resolution is required for the projection optical system. In order to satisfy this demand, as is obvious from the equation above, efforts have been made to decrease the wavelength of exposure light or increase the numerical aperture of the projection optical system, i.e., to increase the N.A. In recent years, an exposure apparatus having a projection optical system with a numeral aperture of 0.6 or more and using krypton fluoride excimer laser (KrF excimer laser) with an output wavelength of 248 nm as an exposure light source has been put into practice, thus achieving exposure with a device rule (practical minimum line width) of 0.25 &mgr;m.
In the conventional projection exposure apparatus described above, exposure amount control has been performed on the premise that the transmittance of the optical system does not change upon irradiation of exposure light. That is, the amount of exposure light irradiated on a reticle is measured by a light amount monitor (called an integrator sensor) arranged in the illumination optical system before the exposure light passes through the optical system. The amount of exposure light is also measured after the exposure light passes through the reticle and projection optical system by a light amount monitor, e.g., an illuminometer arranged on the wafer stage. The ratio between the output of the integrator sensor and the illuminometer is then calculated prior to exposure. And on exposure, by using the calculated ratio, the illuminance on the wafer surface (image plane) is estimated from the output value of the integrator sensor, and the exposure amount is feedback-controlled so that the illuminance on the image plane is determined at a desired
As a light source succeeding the krypton fluoride excimer laser, an argon fluoride excimer laser (ArF excimer laser) having an output wavelength of 193 nm is beginning to receive attention. If an exposure apparatus using this argon fluoride excimer laser as an exposure light source is put into practice, microdevices having fine patterns with a device rule of 0.18 &mgr;m to 0.13 &mgr;m can be expected to be mass-produced. Therefore, research and development on this technique have been vigorously conducted.
However, with exposure apparatus using an ArF excimer laser as an exposure light source, it was discovered that the transmittance of optical systems (illumination optical system and projection optical system) did change upon irradiation of exposure light at a level in which such changes cannot be neglected. According to recent researches, characteristics have been confirmed that the transmittance of an optical system gradually increases after starting irradiation of exposure light, and saturates when it comes to a certain level.
It is assumed that such changes occur due to a cleaning effect, i.e., removal of moisture and organic material from the surface of optical elements such as lenses and reflecting mirrors upon irradiation of ArF excimer laser light. Such a cleaning effect is also assumed to have occurred in the case of a KrF excimer laser light. With the case of an ArF excimer laser light, however, since the transmittance to substances such as water is low, the transmittance differs greatly when there are drops of water compared with the case when there are no drops of water. In the case of KrF excimer laser light, the difference is not very large, thus does not pose any serious problems.
Accordingly, the conventional exposure amount control method, based on the assumption that the transmittance of optical systems does not change upon irradiation of exposure light, now requires some kind of a modification.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of this situation, and has as its first object to provide an exposure method, which can implement high-precision exposure without being influenced by variations in the transmittance of an optical system.
It is the second object of the present invention to provide an exposure apparatus, which can perform a highly precise exposure without being influenced by the variation in the transmittance of an optical system.
According to the first aspect of the present invention, there is provided a first exposure method performed by an exposure apparatus which has an optical system to transfer a pattern illuminated with exposure light from a light source onto a substrate, the method comprising: setting an exposure amount control target value in accordance with a transmittance of the optical system; and transferring the pattern onto the substrate through the optical system while an exposure amount is controlled based on the set exposure amount control target value.
In this case, an exposure amount control target value is “not a target exposure amount to be provided to an image plane (substrate surface) which is determined in accordance with the sensitivity of a resist coated on a substrate, but is the target value of an exposure amount which is to be controlled in order to provide the target exposure amount to the image plane”. In this specification, the term “exposure amount control target value” is used in this sense.
According to this method, an exposure amount control target value is set in accordance with the transmittance of the optical system, and a pattern is transferred onto the substrate through the optical system while the exposure amount is controlled based on the set exposure amount control target value. That is, the exposure energy tone supplied to the image plane by unit area per unit time changes in accordance with the transmittance of the optical system. Therefore, as in the present invention, if an exposure amount control target value is set in accordance with the transmittance of the optical system and exposure is performed with the set exposure amount; highly precise exposure which is free from the influence of transmittance variations can be performed.
As a countermeasure for transmittance variations, the changes in transmittance can be measured in advance under the same illumination conditions as that of actual exposure, to obtain a transmittance time-varying curve. And on exposure, an elapsed time from the starting of irradiation and the period of time when the apparatus was not operating are measured with a timer. Then by using the time data and the transmittance time-varying curve, the transmittance can be estimated by calculation. By the calculation and an output from the light amount monitor arranged in the illumination optical system, the illuminance on the image plane is estimated, and
Horikoshi Takahiro
Kikuchi Takahisa
Nei Masahiro
Brown Khaled
Font Frank G.
Nikon Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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