Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-01-28
2001-11-20
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S022000
Reexamination Certificate
active
06319637
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of forming a pattern by transferring an original mask onto a substrate such as a photomask to be exposed to light. More particularly, the present invention relates to a method of forming a pattern for preventing a defect produced in the original mask from being transferred to the substrate to be exposed to light. Furthermore, the present invention relates to a photomask for use in the method of forming a pattern.
In a lithography technique widely used in manufacturing processes of semiconductor devices and the like, it is a great matter of concern to reduce defects as well as to improve accuracy in size and arrangement of the pattern. In the light exposure technique for preparing and transferring the original mask, defects of the original mask are transferred throughout light exposure process as common defects. Therefore, conventionally, accurate inspection and repair have been made.
In a typical light-exposure technique called an optical reduction projection exposure method, a fifth- or fourth-fold mask is usually used. In the manufacturing steps of the photomask, a raster or vector scan exposure method using an electron beam or a laser beam is generally used. Furthermore, it is known that an photomask is manufactured by applying a technique in which an LSI pattern is reduced and transferred from an original mask using an optical reduction projection exposure method.
The defects in the original mask have been repaired by using various repair techniques to a level having no effect upon the transfer results. However, as a size of the LSI pattern comes closer to a resolution limit of the optical projection exposure method with miniaturization of the semiconductor devices, it has been difficult to repair the defects to the level having no effect upon the transfer results.
To repair the defects of the photomask, employed are a method of removing an opaque film by a laser beam, a method for forming an opaque film by depositing of a carbon film using a focused ion beam (FIB) and so forth. However, it is difficult to repair defects with an accuracy of 50 nm or less due to limitations in size and alignment of the beam. Furthermore, in the case where Ga ions etc. are implanted into a quartz substrate for repair, optical characteristics of the repaired portion and the peripheral region thereof are degraded. Alternatively, in the repaired portion, the opaque film is not formed with a desired sectional profile of the end portion. As a result, a transferred image is degraded.
In a conventional pattern formation method for forming an LSI pattern on the substrate to be exposed to light (hereinafter, simply referred to as “substrate”) such as a photomask by use of the original mask, repairing the defects is a great matter of concern. It has become more difficult to repair the defects so as not to have an effect upon the transfer results with the miniaturization of the device. It is difficult to repair the defects with a sufficient repair accuracy after being transferred to the substrate because of limitations of a beam in size and alignment. In addition, some regions are degraded in optical characteristics after repair, or when an image is transferred onto the repaired portion, the transferred image is degraded. In particular, due to limitations in the defect repair technique, it is difficult to repair the defects produced in the pattern edge portion with a high accuracy.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of forming a pattern capable of preventing a defect produced in an original mask from being transferred to a substrate to be exposed and capable of repairing a defect produced at an edge portion of the pattern with a high accuracy without limitations given by a conventional defect repair technique.
Another object of the present invention is to provide a photomask for use in the method for forming a pattern.
To attain the aforementioned objects, the method of forming a pattern according to a first aspect of the present invention comprises the steps of:
selectively forming an opaque film on defective portions including defects of a main pattern region of an original mask on which an LSI pattern is formed, to prevent the defective portions from being transferred;
transferring the main pattern region of the original mask to a substrate to be exposed; and
transferring at least one spare pattern to a portion of the substrate corresponding to each of the defective portions of the original mask.
The step of forming the opaque film includes the steps of:
forming an LSI pattern at least in the main pattern region of the original mask on the basis of a design data;
performing defect inspection for the LSI pattern formed on the original mask to detect positions and types of the defects;
repairing a repairable defect of the defects; and
forming the opaque film on each of the defective portions including a non-repairable defect of the defects to prevent the non-repairable defect from being transferred onto the substrate.
The step of forming then opaque film includes the steps of:
forming a large main pattern on the main pattern region of the original mask on the basis of a design data;
performing defect inspection for the main pattern formed on the original mask to detect positions and types of the defects; and
forming the opaque film on each of the defective portions including a defect selected from the defects of the main pattern to prevent the defective portions from being transferred onto the substrate, and
the step of transferring at least one spare pattern on the substrate includes the steps of:
obtaining data on figure patterns and positions of the defects under the opaque film from one of the design data and an original mask pattern data of the defective region, thereby obtaining a light exposure data for the at least one spare pattern; and
projecting at least one of the figure patterns of the defects onto a selected region of one of the original mask and another original mask to form the at least one spare pattern.
The method of forming a pattern according to a second aspect of the present invention comprises the steps of:
preparing light exposure data of an LSI pattern including a large main pattern and at least one small spare pattern, the at least one small spare pattern being constituted of at least one simple figure pattern;
forming the large main pattern and the at least one small spare pattern on at least one original mask;
performing defect inspection for the large main pattern to determine positions and types of the defects;
forming an opaque film on a defective portion including a defect selected from the defects of the large main pattern, to prevent the defect selected from being transferred onto the substrate;
transferring the large main pattern of the at least one original mask onto a predetermined region of the substrate; and
selectively transferring the at least one small spare pattern onto the defective portion of the at least one original mask with the opaque film formed thereon, to recover a desirable figure.
The at least one simple figure pattern is desirably at least one figure pattern repeatedly emerging in the main pattern.
In the first and second aspects, the substrate to be exposed is desirably a photomask.
The photomask according to a third aspect of the present invention comprises
a mask substrate;
a large main pattern formed on a region of the mask substrate;
at least one small spare pattern formed on another region of the mask substrate, the at least one small spare pattern being constituted of at least one simple figure pattern; and
an opaque film covering a predetermined region including a defect of the large main pattern.
The at least one simple figure pattern includes at least one figure pattern repeatedly emerging in the large main pattern.
In the present invention, desirable embodiments are as follows:
1. The at least one spare pattern may be formed on a spare pattern region or on another original mask but not on the main pattern region of
Higashikawa Iwao
Kyoh Suigen
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Rosasco S.
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