Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2001-05-10
2004-03-09
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S069000, C355S071000
Reexamination Certificate
active
06704090
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure method and an exposure apparatus of the scanning exposure type to be used for transferring a mask pattern onto a substrate in the lithography step for producing devices including, for example, semiconductor elements, liquid crystal display elements, plasma display elements, micromachines, and thin film magnetic heads. In particular, the present invention is preferably used when a pulse light beam is used as an exposure light beam.
2. Description of the Related Art
In order to respond to the improvement in degree of integration and degree of fineness of the semiconductor device, it is demanded to enhance the resolving power and the transfer faithfulness for the exposure apparatus to be used for the exposure step in the lithography step (representatively comprising the resist application step, the exposure step, and the resist development step) in order to produce the semiconductor device. For this purpose, the numerical aperture of the projection optical system has been hitherto gradually increased. Further, the wavelength of the exposure light beam as the exposure beam has been shortened to use the KrF excimer laser (wavelength: 248 nm) and the ArF excimer laser (wavelength: 193 nm). In the present circumstances, only the pulse light source such as the excimer laser is available as the light source of the exposure light beam having the short wavelength as described above. Further, in order to enhance, for example, the resolving power, it is also necessary to enhance the exposure amount control accuracy to expose, with a proper exposure amount, the photoresist applied onto the wafer as the substrate.
Recently, in order to enhance the throughput in the exposure step by increasing the exposure field (respective shot areas on a wafer) without increasing the size of a projection optical system, a scanning exposure type exposure apparatus (hereinafter referred to as “scanning type exposure apparatus”) based on the step-and-scan manner or the like has been developed, in which a reticle as a mask and the wafer are synchronously scanned with respect to the projection optical system. In the case of such a scanning type exposure apparatus, the totalized exposure amount at respective points on the wafer is averaged owing to the integration effect for the scanning direction. However, as for the non-scanning direction perpendicular to the scanning direction, for example, the influence of uneven illuminance in a slit-shaped illumination area in the non-scanning direction directly appears. As a countermeasure for this inconvenience, a method has been suggested, for example, in Japanese Patent Application Laid-Open No. 7-142313 and EP 0,633,506 A1 corresponding thereto. In this method, the shape of an opening of a field diaphragm, which defines the shape of the illumination area, is mechanically changed, or the field diaphragm is mechanically switched, in accordance with an actual totalized exposure amount.
As described above, the method for mechanically switching the shape of the field diaphragm in order to control the exposure amount in the scanning type exposure apparatus is considered to be effective when the exposure light beam is a continuous light beam such as a bright line (i-ray or the like) of a mercury lamp. However, in the present circumstances, a pulse light beam, which has a short wavelength with a relatively low oscillation frequency, is also used gradually in the scanning type exposure apparatus. When such a pulse light beam is used, in order to obtain a uniform totalized exposure amount, it is necessary to define the width of the exposure area on the wafer so that the exposure is performed substantially in an amount corresponding to an integral number of pulses at respective points on the wafer. In this case, if the shape of the opening of the field diaphragm is mechanically switched, it is feared that any area appears on the wafer, in which the condition of exposure in the amount corresponding to the integral number of pulses is not satisfied. Therefore, the method for mechanically switching the shape of the opening of the field diaphragm is not practical so much. For example, U.S. Pat. No. 6,078,381 discloses that the number of pulse light beams radiated onto respective points on the wafer is adjusted to be an integral number.
When the exposure light beam is an ultraviolet light beam, the following inconvenience sometimes arises. That is, any cloudiness gradually appears on a surface of an optical member for constructing the illumination optical system or the projection optical system, for example, due to the reaction between the exposure light beam and organic compounds in the atmosphere. As a result, the transmittance of the optical system is lowered over a long period of time. Further, the following phenomenon is also known. That is, when the exposure light beam is a pulse light beam in a vacuum ultraviolet region at a wavelength of not more than about 200 nm, the refractive member in the illumination optical system or the projection optical system is gradually deteriorated, for example, due to the so-called compaction. As a result, the transmittance is gradually varied. The variation of the transmittance also depends on the optical path for the exposure light beam. Therefore, for example, if the state, in which the distribution of the exposure light beam on the pupil plane is non-axisymmetric (asymmetric with respect to an axis), is continued, for example, when the so-called modified illumination method is used, the variation of the transmittance of the refractive member is also non-axisymmetric. As a result, it is feared that the distribution of illuminance is not uniform in the non-scanning direction in the illumination area (or the exposure area), and the unevenness of the totalized exposure amount is increased. Further, if the variation of the transmittance occurs about the center of any point other than those disposed on the optical axis, it is also feared that the collapse amount of the telecentricity (telecentric property) of the exposure light beam with respect to the reticle or the wafer exceeds an allowable range.
As described above, for example, if any time-dependent variation of the transmittance distribution occurs due to the cloudiness or the deterioration of the optical member, and the illuminance distribution in the illumination area (or the exposure area) is nonuniform in the non-scanning direction, then the nonuniformity can be improved by exchanging the concerning optical member. However, it takes a fairly long period of time to perform the exchange. Further, it is also conceived that any mechanism for exchanging the optical member is provided. However, in such a case, the exposure apparatus has a large size, and the production cost is increased as well.
SUMMARY OF THE INVENTION
Taking the foregoing viewpoints into consideration, a first object of the present invention is to provide an exposure method which makes it possible to enhance the uniformity of a totalized exposure amount on a wafer or the telecentricity of a exposure light beam when the exposure is performed in accordance with the scanning exposure system.
A second object of the present invention is to provide an exposure method which makes it possible to enhance the uniformity of a totalized exposure amount on a wafer when the scanning exposure is performed by using a pulse light beam as an exposure light beam.
A third object of the present invention is to provide an exposure method which makes it possible to easily enhance the uniformity of a totalized exposure amount on a wafer or the telecentricity of a exposure light beam even in the case of the occurrence of any variation in optical characteristic of an optical member or an optical system on an optical path of the exposure light beam up to the wafer, for example, any variation in transmittance (including variation in reflectance) when the exposure is performed in accordance with the scanning exposure system.
Still another object of the pr
Nguyen Henry Hung
Nikon Corporation
Oliff & Berridg,e PLC
LandOfFree
Exposure method and exposure apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Exposure method and exposure apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Exposure method and exposure apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3283380