This application claims priority from Japanese Patent Application Serial No. 2009-215305 filed Sep. 17, 2009, the contents of which are incorporated herein by reference in their entirety.
The present invention relates to a method for detecting a workpiece alignment mark for position alignment (method) in which a mask alignment mark formed on a mask and the workpiece alignment mark formed on a workpiece are detected, and both are positioned (aligned) so as to be in a predetermined position relation, and an exposure apparatus using the method for detecting a work alignment mark. Especially, the present invention relates to a method for detecting a workpiece alignment mark, which is suitable for a case where a transparent pattern formed on a transparent workpiece is used as a workpiece alignment mark, and an exposure apparatus using the same.
An exposure apparatus is used in a process of forming, by a photo-lithography, a pattern (s) on a semiconductor device, a printed circuit board, a liquid crystal substrate, etc. The exposure apparatus aligns a mask that has a pattern, which is transferred to a workpiece, with the workpiece to be in a predetermined positional relationship, and then irradiates the workpiece through the mask with light containing exposing light, whereby the pattern of the mask is transferred (exposed) to the workpiece. Generally, in the exposure apparatus, the alignment of the mask and the workpiece is performed as set forth below. An alignment microscope(s) detects a mask alignment mark(s) (hereinafter referred to as a mask mark) formed in the mask, and a workpiece alignment mark(s) (hereinafter referred to as a workpiece mark) formed on the workpiece. Image processing of data of the detected mask mark(s) and the workpiece mark(s) is performed, in order to detect the position coordinate of each mark, and the mask and/or the workpiece is moved so that both marks are in pre-set positional relationship. The mask and the workpiece must be aligned with each other with respect to two directions (X and Y) on a plane, and a rotational direction (θ). Therefore, the mask marks and the workpiece marks are respectively formed at two or more positions.
Next, description of an operation for detecting the workpiece mark WAM by the alignment microscope 10 will be given below referring to
The light, with which the area R is illuminated, is reflected on a surface of the workpiece W, enters the alignment microscope 10, is reflected by the half mirror 10a, passes through the lens L1, and is bifurcated (two branched) by the half mirror 10b. Part of the light (a light component), which is bifurcated by the half mirror 10b, passes through the lens L2 and enters the first CCD camera 13. As a result, the first CCD camera 13 receives a three times magnification image of the area R. On the other hand, the other part of light, which is bifurcated by the half mirror 10b, passes through the lens L3, is reflected by the half mirror 10c, passes through the lens L4, and enters the second CCD camera 14. As a result, the second CCD camera 14 receives a ten times magnification image of the area R. Subsequently, when the images of the area R are received by the first CCD camera 13 and the second CCD camera 14, they are sent to the control unit 11.
The control unit 11 searches and matches the pattern received by the first CCD camera 13 with the registered three times magnification pattern image of the workpiece mark WAM, that is, the control unit 11 searches for the workpiece mark WAM (refer to
Since the workpiece mark WAM has been moved to the center of the view of the alignment microscope 10 as described above, the workpiece mark WAM and its circumference area are enlarged in fact. The control unit 11 searches and matches the pattern received by the 2nd CCD camera 14 with the registered ten times workpiece mark WAM pattern, that is, the control unit 11 searches the workpiece mark WAM. When the workpiece mark WAM is detected, the workpiece mark WAM is aligned with the mask mark MAM based on the position information of the ten times magnification workpiece mark WAM image. In addition, for example, Japanese Patent Application Serial No. H09-82615 teaches such a method of detecting a mask mark.
The reason for detecting the workpiece mark WAM by switching the magnification of the alignment microscope 10 at low magnification (three times) to high magnification (ten times) is that although high magnification alignment microscope is required in order to align the mask and the workpiece with a high degree of accuracy, if the detection is carried out with only the high magnification thereof, the workpiece mark may be out of the view of the alignment microscope 10 so that the alignment may not be performed due to a conveyance error at time of transporting the workpiece to the workpiece stage, and/or an error of at a workpiece mark formation that is a previous stage. Therefore, as described above, the two alignment steps are performed, that is, the first alignment step, in which the workpiece mark is placed within the high magnification view by using a wide view at the low magnification, which may not be out of view thereof even though there are the above described errors, and a second alignment step in which a second alignment is carried out at the high magnification.
In view of the above, the present invention pertains to a method of alignment by detecting, by an alignment microscope, a mask alignment mark formed on a mask and a workpiece alignment mark formed on a workpiece and aligning a mask and a workpiece based on the detected mask alignment mark and workpiece alignment mark. The method comprises detecting a search mark formed on the workpiece by using a first magnification; moving a workpiece stage so that the workpiece alignment mark, which is in a predetermined relative position to a position of the detected search mark, comes within a second magnification view of the alignment microscope; switching magnification between the first magnification and a second magnification, which is higher than the first magnification; and detecting the workpiece alignment mark by using the second magnification.
In the method of alignment, the size of the pattern of the search mark on the workpiece may be larger than that of the pattern of the workpiece alignment mark on the workpiece.
In the method of alignment, material that forms the search mark on the workpiece may be different from that which forms the workpiece alignment mark on the workpiece.
In the method of alignment, the workpiece may transmit visible light, and the search mark may be formed of an opaque pattern which is formed on the transparent workpiece, and the workpiece alignment mark may be a transparent pattern which is formed on the transparent workpiece.
An exposure apparatus that comprises a light emitting unit that emits exposure light; a pattern formed in a mask; a mask stage holding the mask; a workpiece that is irradiated with the exposure light emitted from the light emitting unit through the mask; a workpiece stage holding the workpiece; an alignment microscope that detects a mask alignment mark formed on the mask and a workpiece alignment mark formed on the workpiece; and a control unit that performs alignment of the mask and the workpiece based on a position information of the detected mask alignment mark and a workpiece alignment mark. The exposure apparatus's alignment microscope is capable of switching magnification between a first magnification and a second magnification that is higher than the first magnification.
The exposure apparatus's control unit comprises a storage unit that stores a pattern of a search mark formed on the workpiece and a pattern of the workpiece alignment mark, and an image processing unit that detects the search mark on the workpiece and the workpiece alignment mark by comparing the patterns of the search mark on the workpiece and the workpiece alignment mark, which were both observed by the alignment microscope, with the patterns of the search mark and the workpiece alignment mark that are stored in the storage unit. The control unit switches the magnification of the alignment microscope to the first magnification, detects the search mark formed on the workpiece, moves the workpiece stage so that the workpiece alignment mark that is in predetermined relative position with respect to a position of the detected search mark comes in a second magnification view of the alignment microscope, switches the magnification of the alignment microscope to the second magnification, and detects the workpiece alignment mark at the second magnification.
According to the present invention, the “detection” means an operation of finding a workpiece alignment mark to obtain a position coordinate.
Other features and advantages of the present method for detecting a work alignment mark and the present exposure apparatus using the same will be apparent from the ensuing description, taken in conjunction with the accompanying drawings, in which:
Detection of a workpiece mark, which is performed by an alignment microscope, is carried out, by changing the magnification of the microscope in two steps, as described above. Simply put, as shown in
As described above, the detection of the workpiece mark WAM is performed by finding the pattern, which is matched with the stored pattern, in an actual image of the wafer. Here, the control unit judges whether the stored pattern image is matched with the pattern in the image, based on a degree of matching of the image information thereof. The control unit is configured so that, for example, “when more than 80% of the image information of the stored pattern, is matched with the image pattern of the workpiece, it is detected as the workpiece mark”. When an amount of information as to the image of the workpiece mark WAM in the image of the workpiece is small, even if the workpiece mark WAM exists in the image, the image of the stored pattern and the image of the workpiece mark WAM, are not matched and the workpiece mark WAM cannot be detected. In order to avoid this problem, the matching degree is lowered, for example, “the workpiece mark is detected when the degree of matching is 40%”, as shown in
It may be considered that as a method of solving these problems, an image of the workpiece mark is enlarged so as to increase the amount of image information. However, in such a case, when the workpiece mark is detected at high magnification (ten times), the workpiece mark may not be within the ten times magnification view so that it is impossible to detect the workpiece mark.
The present invention is made in order to solve the above problems. It is an object of the present invention to certainly detect a workpiece mark without any error when a workpiece mark is found at low magnification, and highly accurate alignment is performed at high magnification, by using an alignment microscope, even if the contrast of an image of a pattern formed on the workpiece is low.
In the present invention, a pattern that is detected by using low magnification, may be different from the workpiece mark, which is detected by using high magnification. In a control unit, it is possible to store two patterns, that is, a pattern detected by using the low magnification and a pattern detected by using the high magnification. The pattern detected by using the low magnification is larger or has a higher contrast than the workpiece mark, and it is seen clearly at the low magnification, that is, the pattern includes more image information and a unique shape, and the pattern, whose positional relationship is determined with respect to the workpiece mark, is used. Hereafter, this pattern is also referred to as a search mark. First, the control unit detects a pattern whose positional relationship is determined with respect to the workpiece mark at low magnification, (for example, a positional relationship between the pattern and the workpiece mark is determined, or a positional relationship is found beforehand, etc.), wherein the pattern is larger than the workpiece mark, and/or the pattern has a high contrast so that a large amount information (a search mark) is included. And when the magnification of the microscope is switched to high magnification, the workpiece is moved to a position where the workpiece mark is within a view of the microscope, according to the positional relationship. After that, the position of the workpiece mark is detected at high magnification.
Thus, the pattern whose position is known with respect to the workpiece mark (workpiece alignment mark), and which is large and/or high in contrast even at the low magnification, is used as the pattern detected by using the low magnification. Since the pattern is seen clearly even at the low magnification, the amount of information as to an image thereof becomes large, the stored pattern and the pattern in the image can be matched with each other at a high degree so that it is possible to certainly detect the pattern without a false detection. And since the position of the pattern is known with respect to the workpiece mark, when switching to the high magnification, it is possible to move the workpiece to the position where the workpiece mark is within the view of the microscope so that the position of the workpiece mark can be detected at the high magnification. Since the workpiece mark looks large when it is seen at the high magnification, even if the contrast is somewhat low, the amount of information as to an image becomes larger than that at time of the low magnification. For this reason, the workpiece mark can be detected with certainty alignment started, and even if the contrast of the image of the pattern formed on the workpiece is low, it is possible to detect the pattern without a false detection.
When the size of the pattern of the search mark on the workpiece is made larger than that of the pattern of the workpiece alignment mark on the workpiece, or when the material which forms the search mark on the workpiece is different from the material which forms the workpiece alignment mark on the workpiece, even if the workpiece mark is hardly found, the search mark can be detected certainly, and the workpiece can be moved so as to be within the view of the microscope.
When the workpiece transmits visible light, and the workpiece mark, which is formed on the transparent workpiece, is a transparent pattern, by using the search mark which is a opaque pattern formed on the transparent workpiece, even if the workpiece mark is the transparent pattern which is formed on the transparent substrate, it is possible to certainly detect the pattern.
Next is a description of the present invention involving the figures.
In
The procedure of detection of the workpiece mark in the exposure apparatus will be concretely described, referring to
The operator looks at the displayed image of the workpiece W, and searches a pattern, which is in a predetermined positional relationship with respect to the workpiece mark (a cross shape shown in the figure), which is relatively large (approximately 400 μm to 500 μm), and which has a unique shape (a pattern surrounded by a dotted line in
Next, the surface of the workpiece W (
An operational procedure in case where the workpiece mark is detected in order to actually perform alignment of the mask and the workpiece, will be described below referring to
The control unit 11 switches the magnification of the alignment microscope(s) 10 to ten times magnification. At the same time, the workpiece stage WS is moved by a workpiece stage driving mechanism 4 so that the workpiece mark WAM may be within an image that is displayed as the ten times magnification image. The moving distance of the workpiece stage WS is calculated based on the position coordinate (x2, y2) of the pattern Pw1 detected by using the three times magnification, and the distance (x1, y1) in the X-Y directions from the stored pattern Pw1 to the workpiece mark WAM. Namely, as shown in
An opaque pattern made of a metal film is formed in a circumference area of the glass substrate that forms the transparent electrode, and
Therefore, when the opaque pattern, which is made of metal and formed in the circumference area of the glass substrate, is detected as the first pattern at the low magnification (three times), and the pattern of the transparent electrode, which is made of the ITO film, is detected as the workpiece mark at the high magnification (ten times), and further the positional relationship therebetween is acquired in advance, even if the workpiece mark is a transparent electrode, it is possible to detect them and to perform alignment of the mask and the workpiece.
The preceding description has been presented only to illustrate and describe exemplary embodiments of the present method for detecting work alignment mark and the present exposure apparatus using the same. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. The invention may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope.
Number | Date | Country | Kind |
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2009-215305 | Sep 2009 | JP | national |