Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Electron beam imaging
Reexamination Certificate
2000-03-07
2001-12-25
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Electron beam imaging
C430S942000
Reexamination Certificate
active
06333138
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a technique to image an LSI pattern onto an energy-sensitive material on a substrate and more specifically to an exposure system and method in which an exposure area is divided into subareas and the subareas are exposed in a step and repeat fashion using shaped beams.
With conventional various exposure techniques, an area to be exposed is generally larger than a unitary area that can be covered by exposure systems. For this reason, each area to be exposed is divided into subareas and each of the subareas is exposed in sequence. In the case that an area corresponding to a transferred pattern is constituted by a plurality of divided areas, it is very important how well the boundary portions of adjacent exposure areas are to be connected.
It has been known that in a system in which an exposure area is exposed by using light and combining unitary exposure areas, mask patterns are transferred so that adjacent exposure areas overlap each other in their boundary portions. According to this method, a problem of pattern failure is eliminated in which exposure dosage and position change in step-like manner in the overlapping zone of the exposure areas. To be specific, when two exposure areas are arranged to overlap each other in their boundary portions, the exposure dosages are adjusted so that the exposure in the overlapping zone of one exposure area is decreased progressively toward the end of that area and, in the other exposure area, the exposure is decreased in the opposite direction. As a result, at the termination of exposure, the sum of exposure dosages at any point in the overlapping zone of two exposure areas becomes constant. It therefore becomes possible to prevent pattern size and position from changing in step-like manner in the overlapping zone.
However, such a method as described above has not been able to be used with a step and repeat exposure system that controls exposing energy based on beam blanking time management.
In the step and repeat exposure system, each of shots, the minimum unit of exposure, is exposed in a different size but with a predetermined exposure dosage, by a predetermined or shaped beam. The system suffers from a limitation on the minimum beam irradiation time. The exposure dosages are treated as digital data (as opposed to analog data) and hence set in steps.
Having such features, the step and repeat (including step and scan) exposure system has no ability to, in exposing the overlapping zone, change progressively the exposure dosages from a constant value to zero as in photolithography. In electron-beam step and repeat lithography, therefore, the use of the overlap exposure as utilized in photolithographic techniques has been limited to the following ways.
One of conventionally proposed methods is to, in exposing each of overlapping adjacent exposure areas, expose shots of a pattern that resides across the boundary between the areas with half of exposing energy for the non-overlapping portions of the exposure areas, thereby improving the exposure accuracy in the boundary portion of the exposure areas. With this method, additional data processing is required to select patterns that reside across the boundary, making the overall data processing complex. In addition, there is a limit on the effectiveness of improvement in accuracy.
Another approach has been adopted which reduces and makes uniform the effects of the boundary portion by changing the boundary position and making multiple exposure. With this method, the degree to which exposure dosages change in steps in the boundary portion is reduced. However, as the multiplicity of exposure increases, the time required for exposure processing increases. In addition, the effect of step-like changes in exposure dosage still remains. Thus, a sufficient reduction of pattern failures cannot be effected.
Thus, there have been various proposals in the field of step and repeat lithography for improving the accuracy of connection between patterns in the boundary portion of exposure areas. However, these methods cannot be applied to the step and repeat lithography without modifications or cannot achieve sufficient effectiveness in the step and repeat lithography.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a step and repeat exposure system and method which permits the accuracy of connection between exposure areas to be improved and makes a contribution to the improvement of pattern accuracy.
According to an aspect of the present invention, there is provided an exposure method for making a desired pattern onto the surface of a sample by dividing an exposure area into a plurality of subareas, subjecting the subareas to exposure in a step and repeat fashion and subjecting the boundary portion between adjacent fields to multiple exposure, characterized by setting the total exposure dosage (at any exposure position) in the boundary portion subjected to multiple exposure equal to an exposure dosage (at any exposure position) in the other portions of the exposure areas, and setting the percentage exposure dosage in the boundary portion of each of the adjacent exposure areas to change in steps, decreasing from a predetermined value to the minimal value for available exposure dosage in the apparatus.
The exposure method of the present invention is preferably practiced by:
(1) Producing a variable- or non-variable-shaped beam based on exposure data including pattern information, pattern placement information and exposure dosage information, directing the shaped beam to a predetermined position for a time corresponding to a predetermined exposure dosage to make a beam shot as a unit, and repeating the beam shot sequentially.
(2) Using at least two-stage deflection type of exposure equipment in which a main deflection area covered by a main deflector is separated into sub-deflection areas covered by a at least one-stage sub-deflector, a sub-deflection area is specified by the main deflector, and a beam is directed to a predetermined position in the specified sub-deflection area by the sub-deflector, and determining an area subjected to the multiple exposure in sub-deflection area units. Alternatively, an apparatus of one-stage deflection type may be used, where an area subjected to multiple exposure process is defined by a given deflection width of the apparatus.
(3) Setting each exposure dosage in the multiple-exposure area on the basis of a minimum exposure dosage available in exposure equipment.
(4) As a beam for exposure, using an optical beam, or a charged beam such as an electron beam or ion beam, and the exposure dose of each beam shot given by the beam is controlled a blanking element.
(5) Allowing the exposure data to contain information for correcting the proximity effect associated with electron-beam lithography, the information including at least exposure dosage correction data, and using different exposure dosage data in part of patterns.
According to the first aspect of the invention, there is provided an exposure method for forming a desired pattern on the surface of an object by exposing the surface with an exposure apparatus, comprising the steps of: dividing an area to be exposed into a plurality of fields; applying a sequential exposure process to each of the plurality of fields by using a shaped beam, wherein: an area where adjacent fields overlap each other is subject to multiple exposure process, the exposure dosage given by the shaped beam is controlled in a manner such that the total exposure dosage at any exposure unit in the boundary portion for multiple exposure is set equal to an exposure dosage used when single exposure process is applied. And the exposure dosage in the boundary portion of each of the adjacent fields is increased in steps, within the range between a least exposure dose and an exposure dose less than a predetermined exposure dose by the least exposure dose (i.e., an exposure dose obtained by subtracting the least exposure dose from a predetermined exposure dose), in th
Abe Takayuki
Higashikawa Iwao
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Young Christopher G.
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