Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1998-10-26
2001-05-15
Mathews, Alan A. (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C356S401000
Reexamination Certificate
active
06233042
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates to a projection exposure apparatus and a device manufacturing method using the same. The present invention is particularly suitable for printing, through projection exposure, a pattern of a first object onto a second object in a step-and-repeat or step-and-scan method to produce large integration devices of submicron or quarter-micron order, such as semiconductor devices (e.g., IC or LSI), CCDs, liquid crystal panels, for example.
Semiconductor technology is being advanced remarkably, and micro-fabrication techniques are also being advanced notably. Particularly, as regards optical processing techniques using semiconductor projection exposure apparatuses, submicron orders are currently aimed at with 1 MDRAM.
Conventional attempts for enhancement of resolving power in semiconductor projection exposure apparatuses are a method in which the numerical aperture (NA) of a projection optical system is enlarged, and a method in which the wavelength of exposure light is shortened by using i-line in place of g-line, or by using an emission wavelength of an excimer laser (e.g., 248 nm, 193 nm, or 157 nm). Recent attempts are the use of a phase shift mask or a modified illumination method to expand the limitation of optical processing based on optical exposure.
On the other hand, with increases of resolving power, the control of semiconductor processes has become very strict. This causes a notable reduction of process margin, for example, such as tolerance for variation of linewidth in processes or tolerance for total overlay.
SUMMARY OF THE INVENTION
In projection exposure apparatuses, called a stepper, in which a pattern formed on a surface to be illuminated is illuminated by an illumination system with light from a light source and the illuminated pattern is projected and printed on a substrate by means of a projection exposure apparatus, generally the apparatus is set to provide a higher throughput, i.e., a higher yield of semiconductor devices per unit time. For increased yield, the speed of various sequences or the operation time of moving components has to be quickened. This applies also to exposure of a shot. The time necessary for the exposure operation has to be reduced and, to this end, the illuminance of exposure light upon the surface of a wafer has to be increased to quicken sensitization of a resist material.
When higher illuminance is used, while it may depend on the transmissivity of a reticle used, the energy to be applied to a projection optical system in the exposure process per unit time increases. Since the number of wafers to be processed increases, the total amount of energy to be applied to the projection optical system is enormously large. A portion of such energy is absorbed by a glass material used in the projection optical system through which the exposure light passes.
The absorbed energy of exposure light is accumulated, causing thermal deformation, for example, of components of the projection optical system and producing deterioration of the optical characteristic thereof. This is called thermal aberration. This problem becomes more serious particularly with continuing miniaturization of electronic circuit patterns.
Conventionally, in this connection, an optical characteristic of a projection optical system is measured at a certain time interval to monitor any change in optical characteristic, or such change with time is predicted by using software, and a portion of the projection exposure apparatus is actuated to perform correction.
However, if an optical characteristic of a projection optical system is measured at a certain interval, the measurement takes time which directly leads to a decrease of throughput. If software prediction is used, specific parameters have to be prepared and inputted since every machine has its own operational characteristic. This is very cumbersome. Further, prediction by software could not meet a possible deviation of what actually occurs from what is predicted, and it could not monitor the deviation.
It is an object of the present invention to provide a projection exposure apparatus and/or a device manufacturing method using the same, by which any change in optical characteristic of a projection optical system can be detected and corrected in real time to thereby assure high precision projection exposure.
In accordance with an aspect of the present invention, there is provided a projection exposure apparatus, comprising: a projection optical system for projecting a pattern of a first object onto a second object; a correcting mechanism for changing an optical characteristic of said projection optical system; positional information detecting means for detecting a first mark with said projection optical system and for detecting a second mark without said projection optical system to detect a relative positional relationship between the first and second marks which are disposed at different positions; discriminating means operable, after the detection of the relative positional relationship by said positional information detecting means is repeated at a predetermined time interval or successively, to discriminate a relation between first positional information obtained as a result of earlier detection and second positional information obtained as a result of later detection made by said positional information detecting means; and actuating means for actuating said correcting mechanism on the basis of the discrimination made by said discriminating means, to change the optical characteristic of said projection optical system.
In this aspect of the invention, said discriminating means may discriminate whether the second positional information contains a change not less than a predetermined amount as compared with the first positional information.
Said positional information detecting means may detect the relative positional relationship between the first and second marks on the basis of photoelectric conversion of images of the first and second marks, respectively, as formed upon a predetermined plane.
The first mark may comprise a lens monitoring reference mark whose imaging position upon a predetermined plane is shiftable with the optical characteristic of said projection optical system, and the second mark may comprise a reference mark whose imaging position upon a predetermined plane is not shiftable.
Said positional information detecting means may detect imagewise information about the first mark as defined on a predetermined plane to detect a change in imaging plane of said projection optical system.
The apparatus may further comprise a stage for holding the second object, wherein said stage may be moved in accordance with the change in imaging plane of said projection optical system as detected by said positional information detecting means.
In accordance with another aspect of the present invention, there is provided a device manufacturing method, comprising the steps of: transferring a pattern of a reticle onto a surface of a wafer through a projection optical system of a projection exposure apparatus such as recited above; and developing the wafer for production of a device.
Generally, in accordance with the present invention, any change in optical characteristic of a projection optical system can be detected in real time, and on the basis of which the optical characteristic of the projection optical system can be corrected. Thus, the present invention provides a projection exposure apparatus and/or a device manufacturing method using the same by which high precision projection exposure is assured. Further, in accordance with the present invention, the state of a projection lens can be monitored continuously regardless of the sequence in which the projection exposure apparatus is held at that time. Therefore, the optical performance of the projection optical system can be corrected in real time on the basis of the monitoring, such that high precision exposure performance is provided constantly.
REFERENCES:
patent: 5105075 (1992-04-01), Ohta et al.
patent: 5483
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Fuller Rodney
Mathews Alan A.
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