Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2001-02-23
2004-08-03
Rutledge, D. (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S071000
Reexamination Certificate
active
06771350
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus and an exposure method to be used in order to transfer a mask pattern onto a substrate through a projection optical system in the lithography step for producing, for example, semiconductor elements, liquid crystal display elements, plasma display elements, or thin film magnetic heads. In particular, the present invention relates to an exposure apparatus and an exposure method capable of controlling the distribution of illumination generated by an illumination system automatically or precisely.
2. Description of the Related Art
In order to respond to the improvement in the degree of integration and the degree of fineness of the semiconductor device, the exposure apparatus, which is in charge of the lithography step (representatively including the resist application step, the exposure step, and the resist development step) for producing the semiconductor device, is required to further enhance, for example, the resolving power and the transfer faithfulness. In order to enhance the resolving power and the transfer faithfulness as described above, it is necessary that the wavelength of the exposure light beam as the exposure beam is shortened, the projection optical system having a large numerical aperture is used, and the exposure amount is controlled highly accurately in order to expose, with a proper exposure amount, the photoresist applied on the wafer as the substrate. In order to extract the image formation characteristic of the projection optical system to the limit so that the exposure amount is controlled for the photoresist highly accurately, it is necessary to optimize the illumination optical system so as to enhance the illumination characteristic of the illumination optical system for illuminating the reticle as the mask with the exposure light beam as far as possible.
The adjustment to optimize the illumination optical system of the exposure apparatus has been hitherto performed in accordance with the following steps.
(a) An operator measures the illumination characteristic (for example, uneven illuminance) of an adjustment objective of the illumination optical system.
(b) The state (for example, position or angle of inclination) of a predetermined optical member is adjusted by using a driving unit corresponding to the illumination characteristic on the basis of the obtained result of the measurement. The driving amount concerning this process is set so that the illumination characteristic is improved as far as possible by correcting the optical design value on the basis of the experience of the operator.
(c) After the adjustment, the remaining amount of the illumination characteristic is measured again. If the remaining amount exceeds an allowable range, the adjustment is performed again by the aid of the driving unit.
(d) After the completion of the adjustment, the final state (optimum state) of the optical member is stored.
The adjustment steps as described above are repeated for every illumination characteristic of the adjustment objective for each of a plurality of illumination conditions to store the optimum state of the corresponding optical member. When the illumination condition is switched, the corresponding optical member is set to be in the optimum state respectively.
As described above, the adjustment for optimizing the illumination optical system of the conventional exposure apparatus has been performed by the operator, for example, when the exposure apparatus is assembled and adjusted and when the maintenance is performed.
However, when the operator performs the adjustment, an inconvenience arises such that a long period of time is required to perform the adjustment. Further, it is necessary to adjust the illumination optical system for each of the plurality of illumination conditions. Therefore, the overall adjustment time is fairly prolonged. The time required for the optimization is also affected by the degree of skill of the operator. Therefore, there has been also such a fear that the adjustment time is further prolonged depending on the operator.
When the states of a plurality of optical members in the illumination optical system are required to be adjusted, it is necessary to consider, for example, the mutual influence caused by the adjustment as well. Therefore, the adjustment steps have been extremely complicated.
As described above, the adjustment for the conventional illumination optical system has required the complicated steps which take a long period of time. Therefore, for example, it has been difficult to perform such an operation that the allowable level of a predetermined illumination characteristic is changed depending on, for example, the required accuracy for the device to be produced. Further, for example, the uneven illuminance of the illumination characteristic is changed in a time-dependent manner, for example, due to the cloudiness of the optical member in the illumination optical system and the deterioration of the saltpeter material in some cases. However, in such a case, it has been difficult for the conventional adjustment method to make quick response.
The uneven illuminance is principally divided into the uneven illuminance which is axially symmetrical with respect to the optical axis (centro-symmetrical unevenness), i.e., the quadratic function-like unevenness, and the inclination unevenness in which the illuminance is gradually increased or decreased in the area across the optical axis, i.e., the linear function-like unevenness. It is necessary that the uneven illuminance as described above is corrected highly accurately in the orthogonal two directions in the case of the full field exposure type exposure apparatus such as the stepper. On the other hand, in the case of the scanning exposure type exposure apparatus such as those based on the step-and-scan system, the uneven illuminance in the scanning direction is averaged by the scanning exposure operation to such an extent that little problem occurs. Therefore, it is required to especially correct the uneven illuminance in the non-scanning direction perpendicular to the scanning direction highly accurately.
The uneven illuminance has been hitherto corrected in ordinary cases by driving a group of predetermined lenses in the illumination optical system in the optical axis direction, or by driving the group of lenses so that the tilt angle about the two axes is changed. In general, the situation of the uneven illuminance differs depending on the illumination condition. Especially, in the case of the centro-symmetrical unevenness, the degree of concaveness/convexness of the illuminance is changed corresponding to the change of the position through which the light flux passes in the lens group depending on the numerical aperture of the exposure light beam (illumination light beam). Therefore, for example, as for the lens group as the adjustment objective, the optimum position is previously stored for each of the illumination conditions, and the lens group is driven to the optimum position every time when the illumination condition is changed.
A phenomenon is known, in which the cloudy substance adheres to the surface of the optical element when the exposure light beam in the ultraviolet region reacts with a minute amount of organic matter contained in the gas existing around the optical element. Usually, the gas, from which the organic matter or the like is removed, for example, through a chemical filter, is supplied to the surroundings of the respective lenses of the illumination optical system and the projection optical system. However, when the exposure apparatus is used for a long period of time, then a slight amount of remaining organic matter gradually increases the cloudiness of the lens, and the centro-symmetrical unevenness, in which the illuminance is lowered especially at the central portion, is sometimes advanced in a time-dependent manner. In such a case, the operator has adjusted the position of the corresponding lens group again, depending on the deg
Nikon Corporation
Oliff & Berridg,e PLC
Rutledge D.
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