Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Reexamination Certificate
2001-01-11
2001-09-18
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Including control feature responsive to a test or measurement
C430S296000, C430S942000
Reexamination Certificate
active
06291119
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electron beam lithography, and more particularly, to a method of compensating for pattern dimension variation caused by a re-scattering effect of the electron beam occurring when a resist is exposed to the electron beam.
2. Description of the Related Art
Electron beam lithography is a technique used in patterning a material layer formed on a substrate in a desired pattern. This entails the process of coating an electron beam resist on a material layer; writing a desired pattern with an electron beam (referred to in the art as an “exposure”); developing the electron beam resist; and etching the material layer by using the electron beam resist pattern formed using the desired pattern as a mask. Electron beam lithography can be used to form a predetermined material layer pattern directly forming an integrated circuit on the substrate, however, in general, electron beam lithography is used to fabricate a photomask for use in photolithography.
Referring to
FIG. 1
, the process for fabricating the photomask will be described in greater detail. The process comprises the steps of: coating an electron beam resist
130
on an opaque film
120
(in the case of a phase shift mask, a phase shifting layer is available, hereinafter described simply as an opaque film) formed on a transparent substrate
110
; writing a desired pattern with an electron beam
150
; developing the electron beam resist
130
by using a difference of solubility depending on writing of the electron beam; and etching the opaque film
120
by using the formed resist pattern as a mask.
However, the electron beam
150
does not only expose the desired portion of the electron beam resist
130
, as the electron beam
150
is reflected on the surface of the opaque film
120
or scattered by collisions with atoms of a resist material in the electron beam resist
130
as marked
170
in FIG.
1
. Also, the electron beam
150
is reflected in the electron beam resist
130
or on the surface of the electron beam resist
130
and at the lower plane of an objective lens
140
of an electron beam writer and, as a consequence, the electron beam
150
exposes an undesired portion of the electron beam resist
130
as marked
160
in FIG.
1
.
A quantity (a dose) by which the electron beam resist
130
is exposed an extra amount by scattering of the electron beam
150
as described above, is shown in FIG.
2
. As shown in
FIG. 2
, the electron beam resist can be additionally exposed from a region in which a pattern is written with the electron beam, that is, from an edge of the pattern to a maximum distance of 10 cm. Close to the edge of the pattern, the dose can be as high as 25% of the original exposure dose. In
FIG. 2
, an additional exposure
210
affecting from the region in which a pattern is written with the electron beam, to approximately 10 &mgr;m, is caused by forward scattering and backward scattering of the electron beam indicated by reference numeral
170
in
FIG. 1
, and an additional exposure
220
affecting to approximately 10 cm is caused by re-scattering of the electron beam indicated by reference numeral
160
in FIG.
1
. In conclusion, these additional exposures deteriorate the accuracy of the opaque film pattern, and cause a critical dimension (CD) error. The pattern dimension variation caused by the former additional exposure
210
is referred to as a proximity effect, and the pattern dimension variation caused by the latter additional exposure
220
is referred to as a re-scattering effect (multiple scattering effect or a fogging effect) of the electron beam.
The re-scattering effect of the electron beam affects a wide range (Considering the integration of a current integrated circuit, 10 cm is a very wide range.), and since a dose caused by the additional exposure
220
is relatively small, the effect has not been ascertained, and no compensation method is well-known. However, the pattern dimension variation of the photomask caused by the re-scattering effect of the electron beam is estimated to be about 10~20 nm when an electron beam dose is 8 &mgr;C/cm
2
at an accelerating voltage of 10 keV, and the pattern dimension variation of the photomask greatly affects the manufacture of more highly-integrated circuits.
On the other hand, the re-scattering effect of the electron beam is introduced, and a method for forming the lower plane of the objective lens in which the re-scattered electron beam is reflected, of a material with a low atomic number, as a method for reducing this effect is disclosed in, Norio Saitou et al., “Multiple Scattered E-beam Effect in Electron Beam Lithography”, SPIE Vol. 1465, pp. 185-p. 191, 1991. That is, it is reported in the paper that an additional dose caused by the re-scattering effect of the electron beam when the lower plane of the objective lens is formed of copper, aluminum, and carbon, respectively, was measured, and the re-scattering effect of the electron beam was lowest when carbon was adopted. However, it is shown in
FIG. 2
that the re-scattering effect is not remarkably reduced even if carbon is adopted. In
FIG. 2
, the chart of symbol “∘” applies to the case where aluminum is adopted, and the chart of symbol “□” applies to the case where carbon is adopted.
Also, a method for reducing the re-scattering effect by absorbing the re-scattered electron beam by attaching an absorber plate in which a honeycomb groove is formed at the lower plane of the objective lens, is disclosed in Naoharu Shimomura et al., “Reduction of Fogging Effect caused by Scattered Electron in an Electron Beam System”, SPIE Vol. 3748, pp. 125-p. 132, 1999. However, it is also not possible for all re-scattered electrons to be absorbed by this method, and there is a limitation in reducing the re-scattering effect.
SUMMARY OF THE INVENTION
To address the above limitation, it is an object of the present invention to provide a method of compensating for pattern dimension variation caused by a re-scattering effect of an electron beam.
Accordingly, to achieve the above object, there is provided a method of compensating for pattern dimension variation caused by a re-scattered electron beam, the method comprising the steps of: dividing original exposure patterns into square sections; determining a dose of additional exposure (referred to herein as a “supplemental exposure dose”) to the re-scattered electron beam for each section; and compensating the electron beam resist so that the supplemental exposure dose may be the same for all sections. That is, the method of compensating for pattern dimension variation caused by a re-scattered electron beam comprises the steps of: dividing original exposure pattens into square sections; determining a dose of supplemental exposure to the re-scattered electron beam when adjacent sections are exposed, for each section; determining a compensation exposure dose for each section by deducting supplemental exposure doses of each section from a predetermined reference value; and compensation-exposing the electron beam resist according to the compensation exposure dose of each section.
The method of compensating for pattern dimension variation caused by a re-scattering effect of an electron beam according to the present invention can be provided in the form of a recording medium on which a program to be read and performed by a commercial computer is recorded. That is, a recording medium on which a program for obtaining compensation exposure data for compensating pattern dimension variation is recorded includes a program module for dividing original exposure patterns into square sections and determining a dose of supplemental exposure to the re-scattered electron beam when adjacent sections are exposed, for each section, a program module for determining a compensation exposure dose for each section by deducting the supplemental exposure dose of each section from a predetermined reference value, and a program module for setting-up compensation exposure patterns for each secti
Choi Ji-hyeon
Ki Won-tai
Mills & Onello LLP
Samsung Electronics Co,. Ltd.
Young Christopher G.
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