1. Field of the Invention
The present invention relates to a mark detection method and unit, an exposure method and apparatus, and a device manufacturing method and a device, and more specifically to a mark detection method and unit for detecting the positions of marks formed on an object, an exposure method using the mark detection method and an exposure apparatus comprising the mark detection unit, and a device manufacturing method using the exposure method and a device manufactured by using the exposure apparatus.
2. Description of The Related Art
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 “sensitive substrate” or “wafer” as needed), coated with a resist through a projection optical system. As such an exposure apparatus, a stationary-exposure-type projection exposure apparatus such as the so-called stepper, or a scanning-exposure-type projection exposure apparatus such as the so-called scanning stepper is mainly used.
In such an exposure apparatus, it is necessary to highly accurately align the reticle with the wafer before exposure. For the purpose of this alignment, a position detection mark (alignment mark) has been formed (transferred) on each shot area of the wafer in the previous photolithography process, and by detecting the position of this alignment mark, the position of the wafer (or a circuit pattern on the wafer) can be detected. And on the basis of the detection result of the position of the wafer (or a circuit pattern on the wafer), the alignment is performed.
Several methods of detecting the positions of alignment marks on a wafer are actually being used. However, in any of the methods, by analyzing the waveform of a detected signal of an alignment mark obtained by a detector for position detection, the position of the alignment mark on the wafer is detected. For example, in position detection through use of image detection that is mainly being used these days, the position of an alignment mark is detected by picking up an optical image of the alignment mark through use of a picking-up unit and analyzing the light intensity distribution of its picked-up signal, i.e. the image.
As such a method of analyzing a signal waveform, there is a pattern matching (template matching) method which examines correlation between the signal waveform and a beforehand-prepared template waveform by using the position of the alignment mark as a parameter. By analyzing the signal waveform through use of this pattern matching method and obtaining a value of the parameter at which the correlation between the signal waveform and the template waveform is highest, the position of the alignment mark is accurately detected.
In the prior art method of detecting the positions of alignment marks, the image of an alignment mark is picked up such that the image includes the characteristic of the alignment mark needed to detect the position of the alignment mark. Here, for example, the characteristic of an alignment mark needed to detect its position is the state of arrangement of lines when an X-position detection alignment mark comprises lines and spaces which are alternately arranged in an X-direction and extend in a Y-direction, the alignment mark being called a line-and-space mark. Therefore, while the image-pick-up area for the line-and-space mark for X-position detection may be smaller in a dimension in the Y-direction than the line-and-space mark, the image-pick-up area needs to be remarkably larger in a dimension in the X-direction than the line-and-space mark depending on the accuracy in determining the pick-up position in earlier measurement. That is, the pick-up result of the line-and-space mark for X-position detection covers the broad area including the line-and-space mark in the X-direction.
Meanwhile, because it is unknown beforehand where in the X-direction the line-and-space mark for X-position detection is located in the image-pick-up area, pattern-matching is performed over the whole dimension in the X-direction of the image-pick-up area. Therefore, the computation of the pattern-matching becomes enormous in amount and takes a long time, and the prior art has a possibility of mistaking the signal pattern of an area outside the mark-formed area of the X-position detection mark as the signal pattern of the X-position detection mark.
These are true with the line-and-space mark for Y-position detection and other types of position detection marks as well as the line-and-space mark for X-position detection, in the prior art.
This invention was made under such circumstances, and a first purpose of the present invention is to provide a mark detection method and unit that can quickly and accurately detect the positions of marks formed on an object.
Furthermore, a second purpose of the present invention is to provide an exposure apparatus that can improve exposure accuracy in transferring a given pattern onto a substrate and throughput by detecting quickly and accurately the positions of marks formed on the substrate.
Moreover, a third purpose of the present invention is to provide devices on which a fine pattern is accurately formed and a device manufacturing method with which to manufacture such devices with high productivity.