Geometrical instruments – Miscellaneous – Light direction
Reexamination Certificate
1998-03-11
2001-02-06
Gibson, Randy W. (Department: 2859)
Geometrical instruments
Miscellaneous
Light direction
C033S503000, C033S504000, C033S702000, C033S706000, C324S758010, C702S094000, C702S095000, C702S150000
Reexamination Certificate
active
06182369
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a pattern forming apparatus for forming a very fine device pattern, such as a semiconductor IC circuit pattern, on a sample, such as a semiconductor wafer and pattern transferring mask, with the use of a beam such as a charged beam.
With a recent high integration of the LSI, a corresponding circuit line's width has been becoming finer and finer in a corresponding semiconductor device. Such semiconductor devices are formed by transferring drawing patterns, that is, desired circuit patterns corresponding to several tens of original patterns, on a mask such as a reticle, sequentially to light exposure areas on a wafer through a high-accurate alignment and performing chemical processing such as etching. Here, as a transferring device use is made of a stepper having a high accurate optical system. The wafer is held in place on a high accurate XY stage so as to allow a whole wafer surface on the transferring side to be exposed with light. The wafer is moved in a step & repeat fashion relative to the optical system and such a transferring apparatus is called a stepper.
The original pattern is formed as a Cr pattern on a glass substrate finished with high accuracy. Upon pattern formation, a glass substrate with Cr evaporated on one side is uniformly coated with a resist and the whole substrate surface is scanned with an energy beam, such as a focusing electron beam or laser beam, in accordance with design data to make a desired area of the resist photosensitized. And the photosensitized resist is developed to provide a resist pattern and then the Cr is etched with the use of the resist pattern to obtain a desired pattern. Since the pattern is formed with the focused spots joined, it is possible to form a high accurate pattern depending upon how the beam is controlled.
The Cr pattern formed on the glass substrate with the use of such a pattern drawing apparatus need be aligned as a high accurate overlay on a circuit pattern on the wafer, so that a pattern transfer is carried out.
However, there are sometimes the cases where the wafer itself may be deformed with a progress of its processing. In order to realize such a pattern transfer process with such high accurate overlay relative to the circuit pattern on the deformed wafer, it is necessary that the circuit pattern on the glass substrate be displaced to achieve an alignment with the deformed wafer.
In the case where a first transfer process of the circuit pattern on the wafer has been made with the use of a deformed-pattern-formed glass substrate, it followed that, in order to achieve a high accurate overlay, it is necessary that a pattern on the glass substrate used at a second and subsequent transfer processes has to be set in a deformed sate as in the case of the circuit pattern used in the first transfer process.
As the method for displacing such a drawing position use is made of a method by which a correction amount at a given point (X, Y) is defined by a function and found through its calculation as, for example, in JPN PAT APPLN KOKAI PUBLICATION NO. 7-52948.
Since, however, the correction value in a given coordinate on a whole drawing surface is calculated, there arises the following problem.
In
FIG. 1
, A represents a grid point showing an ideal drawing position and B a grid point given by correction. If, as shown in
FIG. 1
, a correction amount is locally greater in a portion of the drawing area on the whole drawing section
7
, it is difficult to represent such correction amount, so that correction cannot be achieved with high accuracy. If a higher-degree polynomial equation is used as a function so as to make its approximate precision higher, then the calculation procedure of the correction equation becomes vast and complicated.
Thus, in the case where the whole drawing section of a sample is to be corrected in such a conventional method, for example, the correction amount is locally greater in a portion of the correction area, it has been difficult to make correction with high precision.
BRIEF SUMMARY OF THE INVENTION
It is accordingly the object of the present invention to provide a pattern forming apparatus which can correct a pattern position with high accuracy.
The object of the present invention can be achieved by providing a pattern forming apparatus comprising
a sample base for positioning a sample thereon and moving a drawing position of the sample;
position measuring means for measuring a position of the sample base;
correction means for mutually independently correcting drawing positions at those respective areas into which a whole drawing section of the sample is divided, the drawing position being calculated by the position measuring means at the respective area; and
drawing means for drawing a pattern on the sample on the basis of the position of the sample base measured by the position measuring means and drawing position of the respective area corrected by the correcting means.
According to the present invention, the whole drawing section of the sample is divided into a plurality of areas and the correction of the drawing position at the respective area is made mutually independently for the respective area, whereby, even if, for example, the correction amount is locally greater at a portion of the whole drawing section, it is possible to correct the drawing position with high accuracy.
Further, in the present invention, since the whole drawing section of the sample is divided into a plurality of areas and the correction is made for the respective divided areas, that is, the correction is made, taking the drawing position (drawing coordinate) over the whole drawing section of the sample into consideration, it is possible to effect high accurate correction of the drawing position over a whole surface of the sample, such as a mask and wafer. For example, if any correction amount given at the time of drawing a sub-deflection area (a subfield) on the sample is given to a respective one of a plurality of areas into which a main deflection area (a frame) is divided, correction is made based on only information in the main deflection area irrespective of whether the main deflection area is at a marginal area or at a central area of the sample. That is, such correction is made without giving no consideration to the drawing position (drawing coordinate) over the whole drawing section, so that it is difficult to obtain adequate correction accuracy.
According to the present invention, high accurate correction can be made over a whole drawing section by incorporating, as information, the coordinate in the whole drawing area section.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
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Hideo Yoshihara, SPIE-The International Society for Optical Engineering, vol. 2512, pp. 235-241, “Photomask and X-Ray Mask Technology II”, Apr. 20-21, 1995.
Ryoichi Hirano, et al., American Vacuum Society, Journal of Vacuum Science Technology, vol. 13, No. 6, pp. 2625-2629, “Pattern Positioning Error of Reticle Writing Induced by Reticle Clamping”, Nov./Dec. 1995.
Hirano Ryoichi
Matsuki Kazuto
Tojo Toru
Yoshitake Shusuke
Gibson Randy W.
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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