Radiation imagery chemistry: process – composition – or product th – Registration or layout process other than color proofing
Reexamination Certificate
1999-02-03
2002-09-24
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Registration or layout process other than color proofing
C430S005000
Reexamination Certificate
active
06455211
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a transfer method and apparatus, which use a transfer mask formed with a plurality of partial transfer patterns and a plurality of alignment marks, and which transfer the partial transfer patterns onto a transfer medium in turn, and consequently transfer a pattern obtained by joining the plurality of partial patterns, and a method of manufacturing a device using the transfer method.
As semiconductor devices continue to shrink in feature size and their performance and functions improve, lithography apparatuses now have higher resolutions and larger field angles, and the transfer scheme is changing to the step-and-scan scheme via the full wafer scheme and step-and-repeat scheme. In such a trend, even in an exposure apparatus that uses a charged beam such as an electron beam that can expect higher resolution, a scan reduction transfer system that uses a transfer mask has been proposed.
However, in such apparatus, a divided mask obtained by dividing a transfer pattern into a plurality of partial transfer patterns is used owing to considerable drop of image performance upon broadening of the field angle, limitations on the structure of a mask used, and the like, and these divided patterns are transferred while they are joined in turn, thus obtaining a desired pattern.
The divided mask is obtained by lining up divided partial transfer patterns at predetermined positions on a single mask substrate, and is formed on, e.g., a silicon wafer by the same technique as a semiconductor process such as lithography, etching, or the like.
In a transfer method using the divided mask, since the joint precision between neighboring partial transfer patterns is important, the divided partial transfer patterns must be lined up at predetermined positions on the mask with very high precision. However, these partial transfer patterns of the divided mask and their matrix suffer geometrical errors produced during mask formation, such as a matrix error, rotation error, magnification error, orthogonality error, distortion, and the like. Furthermore, these errors are also caused by distortions of the divided mask due to changes in temperature, mechanical stress, aging, and the like. These errors impair the aforementioned joint precision, and defects are consequently produced in the chip obtained.
In order to solve such problem, as disclosed in Japanese Patent No. 2647835, the position of the overall mask is obtained using dedicated marks, and the next partial transfer pattern to be transferred by exposure is driven to the exposure position using a virtual coordinate system obtained based on the position data of the mask. After that, using alignment marks dedicated to the partial transfer patterns, the patterns are aligned pattern by pattern. Such method is called the dye-by-dye method, and is capable of accurate alignment since it aligns pattern by pattern.
However, with the aforementioned method, after each partial transfer pattern is temporarily driven using the virtual coordinate system, partial transfer patterns are aligned pattern by pattern using alignment marks dedicated to those patterns. Hence, measurement and driving processes for alignment are required upon transferring each partial transfer pattern, and these measurement and driving times lower the throughput of the overall apparatus. This problem has larger influences on the throughput as the number of divisions of the mask increases.
Furthermore, with the aforementioned method, a so-called 2nd layer requires alignment marks on a transfer medium, i.e., a wafer. However, depending on the way the transfer mask is divided, the wafer does not often have any marks corresponding to a partial transfer pattern on the transfer mask. For example, when a transfer pattern is divided into partial transfer patterns in a 5×5 matrix, since partial transfer patterns in a 3×3 matrix near the center of the matrix are present inside the actual element pattern region, it is impossible to transfer alignment marks to this region in advance. Hence, in practice, alignment cannot be done by the above-mentioned method.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a mask pattern transfer method and apparatus, device manufacturing method, and transfer mask, which can improve the joint precision of partial transfer patterns upon obtaining a desired pattern by sequentially transferring a plurality of divided partial transfer patterns onto a transfer medium.
According to the first aspect of the present invention, a transfer method which uses a transfer mask formed with a plurality of partial transfer patterns and a plurality of alignment marks, transfers the partial transfer patterns in turn onto a transfer medium, and consequently transfers a pattern obtained by joining the plurality of transfer patterns, comprises: the measurement step of measuring positions of the alignment marks formed on the transfer mask; the coordinate system determination step of determining an actual coordinate system of the plurality of partial transfer patterns formed on the transfer mask on the basis of measurement results in the measurement step; and the alignment step of sequentially aligning the partial transfer patterns to the transfer medium on the basis of the actual coordinate system determined in the coordinate system determination step, and transfer is done every time alignment is made in the alignment step.
In the transfer method according to the first aspect of the present invention, for example, the alignment step preferably has the parameter calculation step of calculating parameters that represent a relationship between the actual coordinate system of the plurality of partial transfer patterns and a design coordinate system of the plurality of partial transfer patterns, and includes the step of sequentially aligning the partial transfer patterns to the transfer medium on the basis of the parameters.
The transfer method according to the first aspect of the present invention, preferably further comprises the step of calculating a fabrication coordinate system of the plurality of transfer patterns; and correcting the actual coordinate system on the basis of the fabrication coordinate system, and the parameter calculation step includes the step of calculating parameters that represent a relationship between the corrected actual coordinate system and the design coordinate system.
In the transfer method according to the first aspect of the present invention, for example, the correction step preferably includes the step of calculating a difference between an actual position and design position of each of the partial transfer patterns and correcting the actual coordinate system on the basis of the difference.
In the transfer method according to the first aspect of the present invention, for example, the alignment step preferably further has the transfer position determination step of determining positions of the partial transfer patterns and the transfer medium upon transferring the partial transfer patterns onto the transfer medium on the basis of the parameters, and includes the step of moving the corresponding pattern and the transfer medium in turn to the positions determined in units of partial transfer patterns.
The transfer method according to the first aspect of the present invention preferably further comprises the designation step of designating the alignment marks to be measured in the measurement step of the transfer mask, and the measurement step includes the step of measuring the positions of the alignment marks designated in the designation step.
The transfer method according to the first aspect of the present invention preferably further comprises the profile calculation step of calculating profiles that indicate discrepancy levels between design and actual partial transfer patterns in units of partial transfer patterns on the basis of the measurement results in the measurement step, and the alignment step has the correction step of matching the actual partial
Muraki Masato
Yui Yoshikiyo
Huff Mark F.
Mohamedulla Saleha R.
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