Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-08-04
2002-04-23
Anderson, Bruce (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492230
Reexamination Certificate
active
06376847
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to charged particle lithography method and system for writing a design pattern formed on a mask onto a substrate by using charged particles in fabrication of a semiconductor device, a liquid crystal display device or a thin film magnetic head device.
In photolithography now used in fabrication of a semiconductor device and the like, a KrF excimer laser beam with a wavelength of 248 nm is used as a light source. Furthermore, lithography using an ArF excimer laser beam with a wavelength of 193 nm is planned to be adopted as the next generation photolithography. However, for further refinement of devices, there is a limit in the resolution between design patterns attained by the photolithography.
Therefore, various types of lithography techniques have been proposed, among which lithography technique using charged particles, such as ions and electrons, particularly an electron beam, is regarded promising. The electron beam lithography method is divided into a method using a mask bearing a design pattern and a method not using a mask.
Now, a conventional electron beam lithography method using a mask will be roughly described with reference to drawings.
FIG. 19
is a diagram for illustrating the conventional electron beam lithography method in which an electron beam
103
is scanned across a mask
101
bearing a desired circuit pattern
102
. As is shown in
FIG. 19
, an electron beam emitted from an electron gun is allowed to pass through a shaping aperture (not shown) to be shaped into an electron beam with a section of, for example, approximately 1 mm×1 mm, and the mask
101
bearing the desired circuit pattern
102
is exposed to the shaped electron beam. The electron beam having passed through the mask
101
is reduced by an electron lens, and exposes a substrate (not shown) coated with a resist. In general, the circuit pattern
102
is sufficiently larger than the dimension of the shaping aperture. Accordingly, as is shown in
FIG. 19
, by repeating scanning of the circuit pattern
102
from one end to the other end thereof with the mask
101
continuously moved by using the effective width of the shaping aperture as a pitch P, the entire circuit pattern
102
is exposed zonally to the electron beam
103
.
The conventional electron beam lithography method, however, has the following problem: As is shown in
FIG. 20
, during the repeated scanning of the electron beam
103
, there arises a connection error between partial exposure areas
104
A,
104
B and
104
C, each of which corresponds to an area exposed in one of the repeated scanning. In the case shown in
FIG. 20
, the first partial exposure area
104
A and the second partial exposure area
104
B are away from each other and the second exposure area
104
B and the third exposure area
104
C overlap each other. This problem occurs depending upon alignment accuracy of a stage for supporting the substrate or the mask and stability of the used electron beam.
The connection error caused between the partial exposure areas leads to the following problems in wiring a pattern across the connection between the partial exposure areas: When the partial exposure areas are away from each other, disconnection is caused as is shown in FIG.
21
(
a
), and when the distance therebetween is small, a line width failure where the line width is locally reduced is caused as is shown in FIG.
21
(
b
), and hence there is fear of disconnection. Furthermore, when the partial exposure areas overlap each other, a line width failure where the line width is locally increased is caused as is shown in FIG.
21
(
c
). In any case, a failure can be caused in the resultant circuit pattern.
SUMMARY OF THE INVENTION
In view of the aforementioned conventional problems, an object of the invention is preventing fatal deformation of a circuit pattern without lowering throughput even when there arises a connection error between partial exposure areas.
In order to achieve the object, according to the invention, respective exposure areas are exposed to be partially overlapped in repeating partial transfer of a design pattern formed on a mask, so that an exposure dose in a double exposure portion and an exposure dose in a normal exposure portion that is not doubly exposed can be equal to each other.
Specifically, the charged particle lithography method of this invention comprises a beam shaping step of shaping an output beam emitted from a charged particle producing source into a predetermined shape; and a design pattern transferring step of transferring a design pattern formed on a mask onto a substrate by repeating partial transfer for transferring a part of the design pattern onto the substrate by allowing the shaped beam to transmit the part of the design pattern and exposing a part of the substrate to the transmitted beam, wherein the design pattern transferring step includes, in conducting the partial transfer, a step of forming a double exposure portion that is doubly exposed in an exposure area on the substrate exposed to the beam, and exposing the exposure area so that an exposure dose in the double exposure portion and an exposure dose in a non-double exposure portion that is not doubly exposed are substantially the same.
In the charged particle lithography method of this invention, a double exposure portion that is doubly exposed in repeated partial transfer is formed in an exposure area on the substrate. Therefore, a margin for moving the beam can be so large that exposure areas are difficult to be away from each other. Also, the exposure is conducted so as to attain substantially the same exposure dose in the double exposure portion and the non-double exposure portion that is not doubly exposed in the exposure area. Therefore, a line width failure can be prevented from being caused in a design pattern in the double exposure portion. Furthermore, even when the exposure areas are away from each other, the exposure dose is prevented from being 0, and even when the exposure areas are largely overlapped, the exposure dose is not doubled. Accordingly, disconnection and deformation of a resist pattern derived from a connection error occurring in repeating the partial exposure can be prevented, resulting in improving the performance and the yield of semiconductor devices.
In the charged particle lithography method, the beam shaping step preferably includes a step of shaping the output beam so that an exposure dose of the output beam at a center of a line extending between an end of the double exposure portion closer to the non-double exposure portion and the other end of the double exposure portion farther from the non-double exposure portion is approximately a half of an exposure dose in the non-double exposure portion, and the design pattern transferring step preferably includes a step of scanning the shaped beam across the mask and the substrate zonally. In this manner, even when the exposure is conducted by the scanning method, the exposure dose in the double exposure portion can be substantially the same as the exposure dose in the non-double exposure portion.
In the charged particle lithography method, the beam shaping step preferably includes a step of continuously changing the output beam so that an exposure dose of the output beam in the double exposure portion is 0 at an end thereof farther from the non-double exposure portion and is a predetermined dose at the other end closer to the non-double exposure portion, and the design pattern transferring step preferably includes a step of scanning the shaped beam across the mask and the substrate zonally. In this manner, even when the exposure is conducted by the scanning method, the exposure dose in the double exposure portion can be substantially the same as the exposure dose in the non-double exposure portion.
In the charged particle lithography method, the beam shaping step preferably includes a step of shaping the output beam so that an exposure dose of the output beam in the double exposure portion is approximately a half of an exposure
Anderson Bruce
Matsushia Electric Industrial Co., Ltd.
Robinson Eric J.
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