Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2001-01-11
2004-04-13
Nguyen, Hung Henry (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000
Reexamination Certificate
active
06721039
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure method, an exposure apparatus and a device producing method, for example, to an exposure method, an exposure apparatus which are used in a lithography process for producing devices such as semiconductor devices, image pickup devices (CCDs etc.), liquid crystal display devices, plasma display devices, thin film magnetic heads, and to a device producing method using the exposure method. The invention is preferably used for controlling exposure amount using a scan exposure type projection exposure apparatus employing a step and scan system using an exposure beam from a pulse light source.
2. Description of the Related Art
Conventionally, as one of basic functions of the projection exposure apparatus used when semiconductor devices or the like are produced, there exists an exposure amount control function for keeping, within an appropriate range, an integrated exposure amount of each point in each shot region of a wafer (or glass plate or the like) as a substrate to be exposed on which photoresist (photosensitive material) is applied. As an exposure amount control in a conventional full field exposure apparatus such as a stepper, even if either of a continuous light source such as a mercury lamp and a pulse laser light source such as an excimer laser light source is used, a cut off control is basically carried out. In the cut off control, exposure is continued until an integrated value of exposure amount on a wafer which is indirectly measured through an integrator sensor comprising a photoelectric detector in an illumination optical system exceeds a predetermined critical level corresponding to a predetermined set exposure amount (target exposure amount). When the pulse laser light source is used as an exposure light source, since each pulse laser light has a variation in its energy, exposure is carried out using a plurality of pulse laser light having a predetermined number of minimum exposure pulses or greater, thereby obtaining a desired control and reproduction precision of exposure amount.
Further, in the scan exposure type projection exposure apparatus such as the step and scan type apparatus used in recent years, a system (open exposure amount control system) for controlling the exposure amount by simply integrating the light amount of each pulse of light as exposure light (exposure, beam) is used. Whereas, as disclosed in U.S. Pat. No. 5,627,627, there is proposed a system (pulse-by-pulse exposure amount control system) for controlling the energy of each pulse of light by measuring the integrated exposure amount with respect to a region included in a slit-shaped exposure region (illumination field) in a scanning direction on a wafer in a pulse-by-pulse manner in real time, and by individually calculating target energy of the next pulse of light based on the integrated exposure amount. In this pulse-by-pulse exposure amount control system, it is possible to reduce the variation in the integrated exposure amount as compared with the open exposure amount control system, and the pulse-by-pulse exposure amount control system can also be applied to the full field exposure type projection exposure apparatus.
By controlling the exposure amount with high precision in this manner, the size precision of pattern (resist pattern) of photosensitive material after development is enhanced, resolution that is more closer to threshold resolution determined in accordance with wavelength (exposure wavelength) of the exposure light, a numerical aperture of the projection optical system and the like can be obtained. The exposure wavelength itself has been further shortened in order to further enhance the threshold resolution, and in recent years, a tendency of using an Arf excimer laser (wavelength of 193 nm) as an exposure light source of the next generation of the KrF excimer laser (wavelength of 248 nm) is increasing.
Under the present circumstances, an optical material having a practical transmittance that can be used as glass material for a refraction member (such as lens) constituting the projection optical system is quartz glass (synthetic quartz) and fluorite. Since the fluorite is expensive, it is possible to reduce the producing cost of the projection optical system by using the quartz glass as much as possible.
However, since the excimer laser light is pulsed light, and if the optical material such as quartz glass is irradiated with the pulsed light of high energy in vacuum ultraviolet region, it is known that its transmittance is varied with time constant on the order of some tens seconds. This phenomenon is reversible to some degree, and if the radiation of pulsed light is stopped, the transmittance of the optical material is restored toward a direction of its initial value with a predetermined time constant. Therefore, when all shot regions on the wafer are sequentially exposed using the pulsed light, the transmittance of the projection optical system is gradually varied.
If the transmittance of the projection optical system is varied in this manner, the relation between the light amount of the exposure light detected by the above-mentioned integrator sensor and the light amount on an image plane of the projection optical system is varied. Therefore, if the exposure amount is controlled based on the relation measured before exposure (correlation between the integrator sensor and the image plane) and the detection result of the integrator sensor, an error is generated in the integrated exposure amount. For this reason, in the projection optical system using the ArF excimer laser light to obtain higher resolution, there is a problem that the target resolution can not be obtained.
Similarly, also when the transmittance variation is generated in an optical member from the integrator sensor to a reticle as a mask in the illumination optical system, the control precision of the exposure amount is lowered.
In this regard, it is known that the variation amount of the transmittance in the short term can be reduced by controlling the doped amount of hydrogen ion (H
+
) in components included in the quartz glass. However, in such a quartz glass, deterioration (compaction) of characteristics due to irradiation of pulsed light over long term is increased. For this reason, although it is possible to use hydrogen ion amount controlled quartz glass where the quartz glass can easily be replaced as in the illumination optical system, but it is preferable not to use the hydrogen ion amount controlled quartz glass where it is difficult to replace the quartz glass, as in the projection optical system. As a result, since there is a tendency that quartz glass whose transmittance is varied in the short term is used especially in the projection optical system, it is desired to develop an exposure method and an exposure apparatus capable of obtaining high control precision of exposure amount even if the transmittance is varied.
When a reflectivity of a reflection member in the projection optical system comprising a catadioptric system for example is also varied in a short term in addition to the transmittance, it is necessary to appropriately control the exposure amount to cope with it.
SUMMARY OF THE INVENTION
In view of the above circumstances, it is a first object of the present invention to provide an exposure method capable of obtaining high control precision of exposure amount on an object to be exposed (such as wafer) even when an optical member whose transmittance or reflectivity is gradually varied is used in an optical system.
It is a second object of the present invention to provide an exposure method capable of obtaining high control precision of exposure amount on an object to be exposed even if the transmittance (the entire, transmittance including the reflectivity) of the optical system when the object is exposed with pulsed light.
Further, it is another object of the invention to provide an exposure apparatus capable of using the above exposure method and a producing method of a device
Nguyen Hung Henry
Nikon Corporation
Oliff & Berridg,e PLC
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