Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2000-01-19
2002-10-15
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S055000, C355S077000
Reexamination Certificate
active
06466301
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transfer apparatus and transfer method of fabricating a device by transferring an intricate pattern on a mask onto a substrate such as a wafer, a glass plate or the like.
2. Description of the Related Art
As the degree of integration of semiconductor devices increases and their performance and functions improve, the resolution and field angle of lithography apparatuses increase Also, the transfer method has changed from the wafer full method and the step-and-repeat method to the step-and-scan method. Under the circumstances, a scanning reduction transfer system using a transfer mask has been proposed for an exposure apparatus using a charged particle beam such as an electron beam, which is expected to further increase the resolution.
In apparatuses of this sort, however, the image performance significantly deteriorates when the field angle is increased, and the mask used has its structural limits. Therefore, a desired pattern is obtained by using a divided mask formed by dividing a transfer pattern into a plurality of patterns, and sequentially stitching together and transferring these divided patterns.
The divided mask is formed by arraying divided transfer patterns in predetermined positions on a single mask substrate.
In a transfer method using this divided mask, the stitching accuracy with which adjacent transfer patterns are stitched together is important. Hence, the divided transfer patterns must be arrayed with extremely high accuracy in predetermined positions on a mask. However, when this divided mask is formed by using, e.g., an electron beam lithography apparatus, the divided mask transfer patterns and their array may curve, or the size of each pattern may deviate from its designed value, depending on the method of lithography. Furthermore, errors are also produced by, e.g., strain due to temperature changes of the divided mask, strain due to mechanical stress, and strain due to changes with time. These errors degrade the aforementioned stitching accuracy, resulting in defects in a chip.
One known method of solving this problem is disclosed in Japanese Patent Laid-Open No. 63-73520. In this method, the position of a whole mask is obtained by using a dedicated mark, and a temporary coordinate system based on the data is used to drive a divided pattern to be exposed next to exposure position. After that, an alignment mark dedicated to each divided pattern is used to align each divided transfer pattern. This method is called a die-by-die method and can perform accurate alignment because it separately aligns individual divided patterns.
In the above method, however, each divided pattern is once driven by using a temporary coordinate system, and then an alignment mark dedicated to this divided pattern is used to align the divided transfer pattern. Hence, the measurement and driving for alignment are required whenever a divided pattern is transferred. The measurement time and driving time reduce the throughput of the entire apparatus. The influence that this problem has on the throughput increases as the number of divided patterns of a mask increases.
Also, the method disclosed in Japanese Patent Laid-Open No. 63-73520 cannot correct the curvature of a divided pattern resulting from the lithography method of a lithography apparatus used in the process of forming a divided mask described previously.
Furthermore, in the conventional transfer methods one chip can be transferred by at least one shot. In contrast, in this transfer method using a divided mask the time required to transfer one chip increases with the number of divided patterns of the mask. As an example, when one chip is divided into 5×10 matrix patterns and arranged on a mask, these divided patterns are sequentially transferred and stitched together, and exposure of the chip is not completed unless all these 50 divided patterns are completely transferred. If step-and-scan is simply repeated, the load is 50 times the number of scanning actions and 5 times or more the exposure time.
To save time for extreme acceleration, deceleration, and stoppage of the stage mounting wafers or masks, therefore, a system is possible which can transfer divided patterns at a higher speed by continuously moving the stage from one divided pattern to another without stopping it.
Unfortunately, the abovementioned die-by-die alignment method cannot be used to transfer divided patterns by continuously moving masks or wafers. This is so because, as described earlier, it is necessary to once position each divided pattern by using a temporary coordinate system and then align the divided transfer pattern by using an alignment mark dedicated to the divided pattern.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has as its object to provide a novel transfer apparatus, transfer method, and device fabrication method which improve the accuracy with which partial transfer patterns are stitched together and improve the throughput.
A transfer apparatus according to the present invention is a transfer apparatus for transferring a transfer pattern of a transfer mask while moving the transfer mask and a substrate relative to each other, the transfer pattern being divided into a plurality of partial transfer patterns, and the transfer mask having a plurality of alignment marks for specifying positions of the plurality of partial transfer patterns, comprising a measuring device for measuring all or some of the plurality of alignment marks, and a controller for determining a function indicating an arrangement of the plurality of partial transfer patterns on the basis of the measurements by the measuring device and, during transfer, moving a partial transfer mask to be transferred and the substrate relative to each other while aligning the transfer mask and the substrate in accordance with the function.
According to one preferred embodiment of the present invention, in the above transfer apparatus the controller preferably determines a function indicating an arrangement of partial transfer patterns belonging to each mask stripe composed of a plurality of partial transfer patterns arranged in a direction in which the transfer mask and the substrate are moved relative to each other.
According to another preferred embodiment of the present invention, in the above transfer apparatus the function is preferably a continuous function.
According to still another preferred embodiment of the present invention, in the above transfer apparatus the controller preferably comprises calculating means for calculating a ratio of a size of an actual transfer pattern to a size of a designed transfer pattern on the basis of the measurements by the measuring device, and correcting means for correcting a difference of the size of the actual transfer pattern from the size of the designed transfer pattern, when the transfer mask and the substrate are moved relative to each other, on the basis of the calculation by the calculating means.
According to still another preferred embodiment of the present invention, in the above transfer apparatus the calculating means preferably calculates a ratio of a length of the actual transfer pattern to a length of the designed transfer pattern in the direction in which the transfer mask and the substrate are moved relative to each other.
According to still another preferred embodiment of the present invention, in the above transfer apparatus the correcting means preferably adjusts a speed at which the transfer mask is moved on the basis of the calculated ratio, thereby correcting a difference of the length of the actual transfer pattern from the length of the designed transfer pattern.
According to still another preferred embodiment of the present invention, in the above transfer apparatus the calculating means preferably calculates a first ratio of a length of the actual transfer pattern to a length of the designed transfer pattern in a first direction in which the transfer mask and the subst
Muraki Masato
Yui Yoshikiyo
Adams Russell
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Henry Hung
LandOfFree
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