Photocopying – Projection printing and copying cameras – Focus or magnification control
Reexamination Certificate
2001-05-10
2003-01-21
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Focus or magnification control
C355S053000, C355S067000, C355S075000, C355S077000, C430S005000, C430S311000, C430S312000
Reexamination Certificate
active
06509956
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a projection exposure method and a projection exposure apparatus for projecting and exposing a predetermined pattern onto a substrate mounted on a substrate stage via a projection optical system. More specifically, the present invention relates to a projection exposure method and a projection exposure apparatus, which measures a mark formed by exposure in a plurality of shot areas on the substrate, to thereby obtain position information of each shot area by statistical processing.
This application is based on Japanese Patent Application No. 2000-140979, the contents of which are incorporated herein by reference.
BACKGROUND ART
Heretofore, projection exposure apparatus have been used when manufacturing semiconductor devices or liquid crystal display devices by a photolithography process, which projects a pattern image of a photo mask or a reticle (hereinafter generally referred to as a “reticle”) onto each shot area on a photosensitive substrate via a projection optical system. Recently, as such kind of projection exposure apparatus, a so-called step and repeat type exposure apparatus, for example, a reduction projection type exposure apparatus (stepper) has been used in many cases. In this apparatus, a photosensitive substrate is mounted on a two-dimensionally movable stage and the substrate is moved step by step by this stage, to thereby repeat an operation for sequentially exposing a pattern image of the reticle onto each shot area on the photosensitive substrate.
For example, micro devices such as semiconductor devices are formed by overlapping a circuit pattern having multiple layers, on a wafer coated with a photosensitive material, as a photosensitive substrate. Hence, at the time of projection exposure of the circuit pattern in the second or further layers onto the wafer, it is necessary to perform positioning of each shot area on the wafer having a circuit pattern already formed thereon, with a pattern image of a reticle to be exposed next, that is, to perform accurate positioning (alignment) between the wafer and the reticle.
For example, with respect to one wafer having a shot area, on which a circuit pattern is to be exposed, arranged thereon in a matrix, as a method for aligning the wafer at the time of performing overlap exposure, so-called enhanced global alignment (EGA) disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. Sho 61-44429 has become predominant.
The EGA method is a positioning method as described below. That is, at least three areas (hereinafter referred to as “EGA shot”) of a plurality of shot areas formed on the wafer are specified, and the coordinate position of the alignment mark (mark) annexed to each shot area is measured with, for example, an off-axis alignment system. Thereafter, error parameters (offset, scale, rotation and perpendicularity) related to the array characteristics (position information) of the shot area on the wafer are determined based on the measurement and design values, by statistical operation involving the method of least squares. Based on the determined parameter values, the coordinate value for the design is then corrected with respect to all the shot areas on the wafer, and the wafer stage is moved step by step, using a baseline quantity, being a distance between the projection optical system and the off-axis alignment system, in accordance with this corrected coordinate value. As a result, the projected image of the reticle pattern and the plurality of shot areas on the wafer are precisely overlapped and exposed at a working point (a reference point at which the coordinate value is measured or calculated, for example the center of the shot area) set in the shot area.
However, the above described conventional projection exposure method and projection exposure apparatus have problems described below.
In the case where the wafer scaling (scaling of the whole wafer) and shot scaling (scaling for each shot area) of the above error parameters are calculated with the EGA measurement, the shot size on the wafer and the shot size at the time of exposure are controlled so as to coincide with each other, by driving optical lenses in the projection optical system to adjust the projection magnification (hereinafter referred to as “lens magnification drive”), as shown in a flowchart in FIG.
9
. In this case, however, it is found that by performing lens magnification drive, mechanical deviation occurs between lenses in the projection optical system, thereby slightly shifting the optical axis of the projection optical system.
Since positioning of the wafer has been heretofore performed based on the results of EGA performed before the deviation occurs, without taking this deviation of the optical axis into consideration, the pattern image is exposed in a state of being shifted, causing a problem in that the relative position of each shot area formed on the wafer in which the circuit pattern has been already formed and the pattern image of the reticle to, be exposed next is shifted, that is, the overlapping accuracy decreases.
In order to avoid this problem, there has been adopted a method in which evaluation exposure is performed beforehand under predetermined conditions, and the error parameters obtained by the above described EGA measurement are corrected using the evaluation results. However, due reasons such as, hysteresis exists in the lens magnification drive, or conditions at the time of evaluation, such as atmospheric pressure or the like are different at the time of actual exposure, the deviation of the optical axis which actually occurs does not always coincide with the evaluation result, thus leaving a problem in that deterioration of the overlapping accuracy cannot be solved.
The present invention has been completed in view of the above situation, with an object of providing a projection exposure method and a projection exposure apparatus which can prevent deterioration of the overlapping accuracy, even if the optical axis is shifted with the adjustment of the projection magnification of the projection optical system.
BRIEF SUMMARY OF THE INVENTION
In order to achieve the above object, the present invention adopts the following constructions corresponding to
FIG. 1
to
FIG. 7
showing embodiments of the present invention.
The projection exposure method of the present invention is characterized in that in a projection exposure method in which after imaging characteristics of a projection optical system (
9
) are adjusted based on measurement results of marks (YEM, XEM) formed on a substrate (W) mounted on a substrate stage (
10
), the substrate (W) is exposed by a predetermined pattern via the projection optical system (
9
), information related to an imaging position of the projection optical system (
9
) is determined after adjustment of the imaging characteristics and before the exposure of the substrate (W).
In this projection exposure method, since the information related to the imaging position of the projection optical system is determined after adjustment of the imaging characteristics and before exposure of the substrate, positioning error of the substrate attributable to the deviation of the optical axis can be eliminated. As a result, it becomes possible to expose the pattern on the substrate with predetermined accuracy, and hence deterioration in the overlapping accuracy can be prevented beforehand.
If the deviation of the optical axis is measured during the actual exposure processing step, the evaluation result does not differ from the actual exposure, as in the case where the evaluation exposure is performed separately. As a result, there is the effect that the image shift quantity can be obtained accurately and quickly.
In an other embodiment, the projection exposure method is a procedure wherein the imaging characteristics include projection magnification of the projection optical system, and by measuring information related to the imaging position of the projection optical system after adjustment of the imaging
Adams Russell
Brown Khaled
Nikon Corporation
Oliff & Berridg,e PLC
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