Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1998-04-07
2001-04-03
Berman, Jack (Department: 2878)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492230
Reexamination Certificate
active
06211528
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron beam drawing method suitable for forming a fine pattern on a resist on a semiconductor substrate surface by an electron beam and more particularly, to an electron beam drawing method in which patterns of substantially the same size can be formed on a resist on a semiconductor substrate in a cell projection manner enabling a high speed formation of a fine pattern and in a conventional variably shaped beam manner.
2. Description of the Related Art
In company with progress of LSI, miniaturization of a pattern, which is used for a semiconductor device fabrication process, has also been rapidly advanced. A drawing method utilizing an electron beam is effective to cope with a future requirement for a width of a pattern as small as 0.25 &mgr;m or less in fabrication of a semiconductor device.
FIG. 1A
is a schematic drawing showing a conventional electron beam exposure system and
FIG. 1B
is a schematic drawing showing a beam path passing through an aperture. It should be noted that hatching is made on a drawn latent image in FIG.
1
B. In the electron beam exposure system, a sample stage
92
, on which a semiconductor wafer
91
coated with a resist on its surface is mounted, is disposed and an electron gun
81
is disposed above the sample stage
92
which gun generates an electron beam
100
being irradiated on the semiconductor wafer
91
. There are provided, between the electron gun
81
and the sample stage
92
in the sequential order from the top, a blanking electrode
82
, which controls ON/OFF of irradiation of the electron beam
100
to the semiconductor wafer
91
, a first aperture
83
, which has an opening
83
a
of a rectangular shape for transforming the electron beam
100
to an electron beam
100
a
of a rectangular shape in section, a beam shaping lens
84
, which suppresses spreading of the electron beam
100
a
which has passed through the first aperture
83
, a shaping deflector
85
, which deflects the electron beam
110
a
, a second aperture
86
, which has an opening for variably shaped beam drawing
86
f
of a rectangular shape and plural openings for cell projection drawing
86
a
to
86
e
for transforming the electron beam
100
a
in section to a cell projection beam
100
b
or a variably shaped beam
100
c
, a demagnifying lens
87
, which suppresses spreading the cell projection beam
100
b
and the variably shaped beam
100
c
which have passed through the second aperture
86
, a main deflector
88
and an auxiliary deflector
89
, which deflect the cell projection beam
100
b
and the variably shaped beam
100
c
, and a projection lens
90
, which controls focuses of the cell projection beam
100
b
and the variably shaped beam
100
c.
The openings for cell projection drawing
86
a
to
86
e
have different shape from one another. In
FIG. 1B
, the cell projection beam
100
b
is an electron beam after the electron beam
100
a
has passed through the opening
86
c.
A controlling unit
96
, which controls the blanking electrode
82
, the shaping deflector
85
, the main deflector
88
and the auxiliary deflector
89
, is connected to those portions. Besides, there are connected to the controlling unit
96
, a calculator
94
, in which processing such as expansion of data, sorting thereof and the like through a data bus
93
are conducted and an intensity of an electron beam is calculated, a storage unit
95
, in which a graphical data to be drawn on the resist on the semiconductor wafer
91
is stored, and a graphical data memory
97
, which temporarily stores the graphical data.
In an electron beam exposure system constituted in such a manner, the graphical data to be drawn on the resist on the semiconductor
91
is stored in the storage unit
95
and necessary processing such as expansion of data, sorting thereof and the like is performed in the calculator
94
. At this point, a part of the processing result is temporarily stored in the graphical data memory
97
and is read out therefrom. The result of processing by the calculator
94
is transmitted to controlling unit
96
and the blanking electrode
82
, the shaping deflector
85
, the main deflector
88
and the auxiliary deflector
89
are controlled by the controlling unit
96
. Thereby, the cell projection beam
100
b
or the variably shaped beam
100
c
of a desired shape can be irradiated to a desired position on the surface of the semiconductor substrate
91
.
One or more patterns are transferred to form latent images in one shot of exposure by irradiating the cell projection beam
100
b
having plural patterns on the resist on the surface of the semiconductor wafer
91
by use of the above mentioned electron beam exposure system. Thereby, the throughput can be improved. A sectional area of the variably shaped beam
100
c
is determined by a degree of superposition between the opening
83
a
of the first aperture
83
and the opening for variably shaped beam drawing
86
f
of the second aperture
86
. Thus, a pattern of an arbitrary sectional area can be formed as a latent image on the resist coated on the semiconductor wafer
91
.
For example, an exposure process in fabricating a Dynamic Random Access Memory (DRAM) will be described.
FIG. 2
is a schematic drawing showing a structure of DRAM. DRAM is constructed with a memory cell array section
101
, in which the same patterns in shape are disposed in a repeated manner and a peripheral circuit section
102
, in which patterns are disposed in an irregular manner.
In the case where such a pattern of DRAM is exposed by use of the electron beams exposure system, the opening for variably shaped beam drawing
86
f
is selected to form the peripheral circuit section
102
and drawing in the variable shaped beam manner is performed. On the other hand, drawing in the cell projection manner is performed by selecting the opening for cell projection drawing
86
a
,
86
b
,
86
c
,
86
d
or
86
e
for formation of the memory cell array section
101
.
In a conventional electron beam drawing method, a graphical data of a pattern is produced in the following way.
FIG. 3
is a flow chart showing a conventional production process for a graphical data. First, a density of a drawing pattern present in a predetermined area is calculated based on a CAD data
68
(step S
51
). Then, a proximity effect correction is conducted based on the density to calculate an optimum exposure dose (step S
52
). Thereafter, an exposure dose D
0
is set regardless of whether the drawing pattern is transferred in the cell projection manner or the variably shaped beam manner (step S
53
). In such a manner, a data for direct drawing
69
is produced. The data for direct drawing
69
is the graphical data of the pattern. Electron beam drawing is performed by use of the data for direct drawing
69
(step S
54
).
However, there is a difference between an optimum exposure dose for a pattern drawn in the cell projection manner and an optimum exposure dose for a pattern drawn in the variably shaped beam manner. Therefore, when drawings are conducted with the same exposure doses D
0
, difference in size arises between patterns drawn in the cell projection manner and the variably shaped beam manner.
FIG. 4
is a schematic drawing showing a pattern formed by a conventional electron beam drawing method. It should be noted that hatching is made on a drawn latent image in FIG.
4
. For example, in the case where a cell projection drawing region
71
in which plural repetitions of a basic portion
73
are disposed and a variably shaped beam drawing region
72
in the surrounding thereof are drawn with the same exposure doses D
0
, a size L
4
of a pattern
72
a
drawn in the variably shaped beam manner is narrower than a size L
3
of a pattern
71
a
drawn in the cell projection manner.
There has been proposed a pattern formation method in which a fluctuation of a line width of a pattern is suppressed in a process step of developing or the like after drawing in Japanese Unexamined Patent
Berman Jack
McGinn & Gibb PLLC
NEC Corporation
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