Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Reexamination Certificate
2001-05-24
2003-08-12
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
06605397
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of preparing pattern data for combined use of two different exposure methods to a single resist so called to as “intra-level mix & match”, and more particularly to a method of avoiding any disconnection due to misalignments or displacements between the two different exposure methods.
2. Description of the Related Art
The combined use of two different exposure methods to a single resist is so called to as “intra-level mix & match”, wherein the two different exposure methods may be an electron beam exposure and a light beam exposure. The electron beam exposure is superior in resolving power, whilst the light beam exposure is superior in throughput. The electron beam exposure is carried out for forming fine patterns or small size patterns with high resolving power. The electron beam exposure is then carried out for forming remaining patterns with high throughput.
It is necessary for the “intra-level mix & match” to provide an overlapping margin to at least one of two sets of the exposure pattern data for the light and electron beam exposures in consideration of an unavoidable displacement or misalignment of the exposure patterns. If no overlapping margin is provided to the two sets of the exposure pattern data, an unavoidable displacement or misalignment of the exposure patterns results in disconnection of the patterns.
A method of preparing exposure pattern data with any overlapping margin in the “intra-level mix & match” is disclosed in “Microelectronic Engineering” vol. 27, pp. 231-234, which was published in 1995 from ELSEVIER, and entitled “Electron beam/DUV intra-level mix-and-match lithography for random logic 0.25 &mgr;m CMOS” and reported by R. Jonckheere.
Fine patterns with a smaller size than 0.4 micrometers are formed by the electron beam exposure with the high resolving power and then the remaining patterns are formed by an KrF exposure with the high throughput. This “intra-level mix & match” lithography is applied to form gate electrodes of the CMOS devices. On boundary regions between the KrF exposure patterns and the electron beam exposure pattern, the KrF exposure pattern has an overlapping margin which overlaps the electron beam exposure pattern by 0.1 micrometer.
The conventional method is to provide the overlapping margin to the electron beam exposure with the high throughput and low resolving power, wherein the overlapping margin makes the actual pattern size different from the designed size. The overlapping margin reduces the alignment margin to a base.
Japanese laid-open patent publication No. 11-204407 discloses another intra-level mix-and-match lithography, wherein fine patterns with smaller sizes than 0.25 micrometers are formed by the electron beam exposure and then the remaining patterns are formed by the KrF exposure, provided that the overlapping margin is provided to the electron beam exposure with the high resolving power. The intra-level mix-and-match lithography processes will be described hereafter.
FIG. 1
is a flow chart illustrative of a conventional intra-level mix-and-match lithography, provided that the overlapping margin is provided to the electron beam exposure with the high resolving power.
The preparation of the electron beam exposure pattern data will be described. In a first process PI, larger patterns than a predetermined reference size “Lth” are extracted from pattern data D
1
to prepare light pattern data D
2
which will be converted to a reticule formation data for forming a reticule for the electron beam exposure.
The preparation of the electron beam exposure pattern data will subsequently be described. In a process P
2
, design pattern data D
1
are modified to reduce pattern widths by &Dgr;W
1
which is more than zero. In a process P
3
, a reference size is set to be Lth−2&Dgr;W
1
, so that smaller patterns than the reference size of Lth−2&Dgr;W
1
are extracted to prepare electron beam exposure pattern bare data D
3
which are free of any overlapping margin. In a process P
4
, the electron beam exposure pattern bare data D
3
are modified to increase pattern widths by &Dgr;W
2
which is more than zero, thereby preparing electron beam exposure pattern modified data D
4
with overlapping margins. The electron beam exposure pattern modified data D
4
are then converted into data for an electron beam writer.
FIGS. 2A through 2C
are views of patterns in sequential processes for preparing electron beam exposure pattern data D
4
with the overlapping margin. With reference to
FIG. 2A
, there are two different design patterns
1
and
2
. The design pattern
1
has a minimum size L
1
which is less than 2&Dgr;W
1
. The design pattern
2
has a minimum size L
2
which is more than 2&Dgr;W
1
. The minimum sizes L
1
and L
2
are smaller than Lth which is the critical size for isolating the electron beam exposure pattern and the electron beam exposure pattern.
With reference to
FIG. 2B
, the design patterns
1
and
2
are modified to reduce the individual widths by &Dgr;W
1
. Slender stripe portions of the designed patterns
1
and
2
correspond to portions to be patterned by the electron beam exposure. Square shaped portions of the designed patterns
1
and
2
correspond to portions to be patterned by the light beam exposure. Since the minimum size L
1
of the design pattern
1
is smaller than 2&Dgr;W
1
, then the slender stripe portion of the designed pattern
1
disappears, whilst the square shaped portions of the designed pattern
1
remain with size reductions. The slender stripe portion
7
and the square shaped portions
5
and
6
of the designed pattern
2
remain with size reductions, wherein the reference size is set to be Lth−2&Dgr;W
1
. The slender stripe portion
7
is to be patterned by the electron beam exposure, whilst the square shaped portions
5
and
6
are to be patterned by the light beam exposure. The slender stripe portion
7
is free of any overlapping margin.
With reference to
FIG. 2C
, only the stripe portion
7
of the designed pattern
2
is increased in width by &Dgr;W
2
, to form an electron beam exposure pattern
8
having overlapping margins
9
and
10
with a size of &Dgr;W
1
+&Dgr;W
2
. If &Dgr;W
1
=&Dgr;W
2
, the size of the electron beam exposure pattern is not changed.
The electron beam exposure pattern data D
4
with the overlapping margin are prepared from the designed pattern data D
1
. If the minimum size of the design pattern is not more than 2&Dgr;W
1
, then the above conventional method is not applicable because at least the minimum size part of the pattern disappears. It is possible that &Dgr;W
1
is so set that 2&Dgr;W
1
is not more than the critical size. In this case, however, the overlapping margin size is &Dgr;W
1
+&Dgr;W
2
, for which reasons it is difficult to obtain a sufficient overlapping margin. If &Dgr;W
1
is size-reduced and &Dgr;W
2
is size-increased, then it is possible to obtain a sufficient overlapping margin. In this case, however, the design size of the portion other than overlapping margin portion is changed.
In order to have solved the above problems, another countermeasure was proposed.
FIG. 3
is a flow chart of another conventional exposure processes. This processes are disclosed in Japanese laid-open patent publication No. 11-204407. &Dgr;W
1
is size-reduced, provided that the minimum-size portion of the pattern is not disappeared even allowing the disadvantage in size-reduction of the overlapping margin. However, a short side of the electron beam exposure pattern data is shifted by &Dgr;W
3
in a process P
5
, in order to obtain the sufficient overlapping margin of &Dgr;W
1
+&Dgr;W
2
+&Dgr;W
3
. This method can not be implemented by the CAD system because the CAD system is incapable of shifting only the short sides of all the patterns.
The electron beam exposure pattern data are variable in long-side length. It is, actually, however, difficult to replacing the electron beam exposure pattern data into the modifi
Foley & Lardner
NEC Corporation
Young Christopher G.
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