Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Reexamination Certificate
2003-04-07
2004-03-16
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Including control feature responsive to a test or measurement
Reexamination Certificate
active
06706456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of determining exposure conditions, an exposure method, a device manufacturing method, and a storage medium, and more specifically to a method of determining exposure conditions in transferring a pattern formed on a mask onto a substrate, an exposure method that exposes under the exposure conditions determined by the determining method, a device manufacturing method that uses the exposure method, and a storage medium that stores the program of determining exposure conditions.
2. Description of the Related Art
To date, in a lithography process for manufacturing semiconductor devices, liquid crystal display devices, or the like, exposure apparatuses have been used which transfer a pattern formed on a mask or reticle (generically referred to as a “reticle” hereinafter) onto a substrate such as a wafer or glass plate (hereinafter, referred to as a “wafer” as needed) coated with a resist, through a projection optical system. As such exposure apparatuses, a reducing projection exposure apparatus of a step-and-repeat type (so-called stepper) and a successive-movement-type exposure apparatus such as a scanning exposure apparatus of a step-and-scan type, that is an improvement on the stepper, are used mainly from the point of view of throughput.
In exposure by such an exposure apparatus, it is known that depending on the energy amount (exposure dose amount) of exposure light irradiating an exposure area on a wafer and the positional relationship between the image plane for a reticle pattern to be transferred onto and the exposure area on the wafer during exposure, that is, a focus error for the exposure area on the wafer, the shapes of the pattern's features transferred onto the wafer vary. If the exposure dose amount is less than a desired one, the exposure of the exposure area on the wafer is not sufficient, and if the exposure dose amount is too much, the neighborhood of the exposure area is also exposed. Further, when the position of the exposure area on the wafer in the direction parallel to the projection optical system's optical axis is not within the depth of focus of the projection optical system's image plane for the reticle pattern, that is, when a focus error exists, an image of the reticle pattern formed in the exposure area on the wafer is blurred, so that an accurate, reduced image of the pattern cannot be formed on the wafer. Therefore, in order to project an accurate, reduced image of the pattern onto a wafer, the exposure dose amount and the position of the wafer in the optical axis direction (hereinafter, called “focus position” as needed) need be optimized.
Moreover, as semiconductor devices (integrated circuits), etc., become more highly integrated year by year, higher resolution, that is, the capability of accurately transferring more detailed dimension features is demanded of projection exposure apparatuses, which are an apparatus for manufacturing semiconductor devices, etc. In order to improve the resolution of a projection exposure apparatus, the projection optical system thereof need be improved in imaging performance, and hence, it is important to accurately measure and evaluate the imaging characteristics of the projection optical system.
In order to accurately measure an imaging characteristic, e.g. the image surface (best imaging surface), of the projection optical system, the best focus position at each measurement point must be accurately measured.
As the method of detecting the above-mentioned optimum exposure conditions and the best focus position simultaneously, a method is known which transfers a predetermined reticle pattern (for example a line-and-space pattern, etc.) as a test pattern onto a test wafer a number of times each time with a different exposure dose amount and with the wafer being at a different focus position, and which views resist images (transferred images of the pattern) obtained through the development of the test wafer by means of a scanning electron microscope (SEM) and determines the forming states thereof. That is, the exposure dose amount and the wafer's position in the projection optical system's optical axis direction under which a resist image has been formed whose forming state is determined to be best by the viewing are determined to be the best exposure dose amount and the best focus position respectively. Alternatively, viewing to check for each field whether or not a transferred pattern exists, the middle point of the exposure dose amount range and the middle point of the wafer's focus position range for which a transferred pattern is determined to exist are determined to be the best exposure dose amount and the best focus position respectively.
In the above prior art method of determining exposure conditions, however, because of viewing to check results of the test exposure, if values of each of the conditions for the test exposure vary coarsely, it is easy to find a pattern in the best forming state in the test exposure wafer or check whether or not a transferred pattern exists in a field, but it is difficult to accurately obtain the best exposure conditions. Meanwhile, if values of each of the conditions for the test exposure vary finely, the time for the exposures of all fields increases, and the number of candidates for a pattern formed in the best exposure conditions is expected to increase, or it is difficult to determine the boundary between fields where a transferred pattern exists and fields where a transferred pattern does not. Hence, it is difficult to determine the best exposure conditions accurately.
Under such circumstances, an invention for solving such difficulty of the above-mentioned method of determining exposure conditions by viewing is disclosed in, for example, Japanese Patent Laid-Open No. 11-233434, where after development of a wafer on which a pattern has been transferred in test exposure, the images of the pattern's resist images developed are picked up, and where pattern matching with a given template is performed on the image data to determine the best exposure conditions based on results of the pattern matching.
Since the invention was made, patterns have become finer in dimension, and when such a pattern is used as the test pattern, depending on the type of template pattern, performing simply pattern matching may take a long time for determining the exposure conditions to increase greatly, and it may be difficult to determine the real, best exposure conditions. Further, while correlation coefficients obtained by the pattern matching are usually compared with a given threshold value, it needs a skill to set the threshold value to an appropriate value. There is much room for improvement therein.
SUMMARY OF THE INVENTION
This invention was made under such circumstances, and a first purpose of the present invention is to provide a method of determining exposure conditions, which method can accurately obtain the best exposure conditions.
Further, a second purpose of the present invention is to provide an exposure method that can exactly perform very accurate exposure under the best exposure conditions.
Yet further, a third purpose of the present invention is to provide a device manufacturing method that can manufacture highly integrated devices with good productivity.
Still further, a fourth purpose of the present invention is to provide a program that automates the process in an exposure apparatus of determining exposure conditions and a storage medium that stores the program.
According to a first aspect of the present invention, there is provided a first exposure condition determining method with which to determine exposure conditions for transferring a pattern arranged on a first plane onto an object arranged on a second plane via a projection optical system, the method comprising the steps of transferring a test exposure pattern including a predetermined measurement pattern and a reference pattern sequentially onto a plurality of part areas on the object via
Mikuchi Takashi
Miyashita Kazuyuki
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