Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-06-24
2002-06-18
Anderson, Bruce (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492210
Reexamination Certificate
active
06407397
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus using a charged particle beam such as an electron beam, and more particularly to a multi-column electron beam exposure apparatus having a plurality of columns, each containing deflection/scanning means for deflecting and scanning an electron beam across a workpiece (specifically a wafer), and writing a pattern on the wafer by appropriately operating the deflection/scanning means in accordance with exposure pattern data.
2. Description of the Related Art
In recent years, with the increasing density of integrated circuits, exposure methods using charged particle beams such as an electron beam or an ion beam or novel exposure methods using X-rays have been studied and are beginning to be commercially implemented to replace photolithography which has long been the predominant technique for the formation of fine feature patterns. Among these methods, electron beam exposure, which forms a pattern using an electron beam, has the advantageous characteristic that it can focus the electron beam down to a spot of several tens of nanometers, making it possible to form a fine pattern of 1 &mgr;m or less. However, since the exposure using an electron beam is a “single-stroke” writing method, the exposing beam size must be made smaller as the feature size becomes smaller, with the result that the exposure time becomes prohibitively long. To resolve such a deficiency, a block exposure method has been devised and put to practical use.
The block exposure method is one that uses a block mask with openings formed therein corresponding to some of basic patterns which serve as units of repetitive patterns, and that passes a beam through a desired opening, thereby generating unit patterns at a time for writing on the workpiece, the patterns thus written being connected to accomplish the exposure of repetitive patterns. This block exposure method is therefore extremely effective for pattern exposure for 1-Gb (gigabit) DRAMs or 4-Gb DRAMs where most of the fine featured area for exposure consists of the repetition of certain basic patterns.
However, since the conventional known technique is based on the use of a system that controls a single column, the idea of controlling a system equipped with multiple columns (a multi-column electron beam exposure apparatus) has not been embodied yet.
It has also been found that if a multi-column electron beam exposure apparatus were to be realized, various problems would arise. For example, when fabricating a multi-column electron beam exposure apparatus, the columns must be manufactured so that they are as identical to each other as possible, but in reality, there occur variations among the columns in the characteristics of the electrostatic lenses, coils, stages, etc. due to manufacturing variations and other factors. More specifically, the per-shot exposure time and per-shot settling waiting time vary from column to column because of such factors as the amount of the electron beam, mounting conditions of deflectors, wafer warp age, etc. That is, the exposure processing time varies because of inherent variations among the columns. In the description hereinafter given, the term “exposure processing time” refers to the sum of the per-shot exposure time and the waiting time (blanking time) required for the deflectors, etc. to settle to be ready for the next shot.
When there are such variations among the columns, if exposure data is supplied from a common controller at the same timing to the respective columns for the exposure of the same pattern in each column, time variation may occur from column to column, causing a failure to accomplish proper exposure. This results in reduced throughput, contrary to the purpose Of improving the throughput for which the multi-column electron beam exposure is intended.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the problem with the conventional art, and an object of the invention is to provide a charged particle beam exposure apparatus that can achieve proper exposure by achieving perfect synchronization of control between multiple columns and can thus contribute to improving throughput.
To attain the above object, the charged particle beam exposure apparatus according to the present invention is equipped with a plurality of columns, each containing deflection/scanning means for deflecting and scanning a charged particle beam across a sample for exposure, and writing a pattern on the sample by appropriately operating the deflection/scanning means in accordance with exposure pattern data, and comprises: a clock generator for generating an operation processing clock with which the entire charged particle beam exposure apparatus is operated; pattern data correction controllers, one for each column, each controller having a correction operation processing block for performing correction operation processing on the exposure pattern data according to the characteristics of its corresponding column in response to the operation processing clock and for supplying the resulting correction data to the deflection/scanning means contained in the corresponding column, and a data processing block for computing an operation processing time corresponding to an exposure processing cycle, required in the corresponding column, from data indicating a per-shot exposure time, settling waiting time, and exposure time correction value generated based on the correction operation processing; and a maximum value detector for detecting a maximum value from among the operation processing times computed by the data processing blocks in the respective pattern data correction controllers, and wherein the clock generator generates the operation processing clock based on the operation processing time of the maximum value detected by the maximum value detector.
According to the configuration of the charged particle beam exposure apparatus of the present invention, the pattern data correction controller provided for each column performs correction operation processing on the exposure data according to the characteristics of the corresponding column and, based on the correction operation processing, computes the operation processing time corresponding to the exposure processing cycle required in that column; next, the maximum value detector detects the maximum value from among the operation processing times computed by the respective pattern data correction controllers, and the clock generator generates the operation processing clock based on the operation processing time of the maximum value thus detected. The generated operation processing clock is supplied to the correction operation processing blocks in the respective pattern data correction controllers. That is, the correction operation processing blocks corresponding to the respective columns operate in unison by responding to the common operation processing clock. This operation processing clock corresponds to the longest operation processing time of all the operation processing times corresponding to the exposure processing cycle required in the respective columns, that is, the exposure processing time of the column that requires the longest time for exposure processing.
Accordingly, even if there is a variation in the exposure processing time due to manufacturing variations among the columns, the operation processing clock generated by the clock generator is supplied with the same timing (that is, synchronized to the exposure cycle of the column that requires the longest time for exposure processing) to the correction operation processing blocks corresponding to the respective columns. This-achieves perfect synchronization of control between the respective columns, making it possible to project the same pattern for exposure simultaneously in all the columns. As a result, proper exposure can be achieved in all the columns, and throughput can thus be improved.
REFERENCES:
patent: 5384463 (1995-01-01), Honjo
patent: 5528048 (1996-06-01), Oae et al.
patent: 5614725 (1997
Advantest Corporation
Christie Parker & Hale LLP
Quash Anthony
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