Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1998-09-24
2001-01-16
Anderson, Bruce C. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492200
Reexamination Certificate
active
06175121
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to block masks and charged particle beam exposure methods and apparatuses which use such masks, and more particularly to a block mask having repeating basic unit patterns and to a charged particle beam exposure method and a charged particle beam exposure apparatus which use such a block mask to expose the unit patterns in one shot.
Conventionally, the photolithography technique was popularly used to form patterns on a semiconductor wafer. But because the integration density of integrated circuits have recently become high, the exposure technique used to form patterns on the semiconductor wafer is about to change from the photolithography technique to the charged particle beam exposure technique which uses a charged particle beam such as an electron beam.
There are various kinds of charged particle beam exposure techniques such as the variable rectangular exposure technique and the block exposure technique, depending on the shapes of the patterns that may be generated at one time. The variable rectangular exposure technique varies the size of the exposed pattern by varying the overlap of an aperture for use in variable rectangular exposure and the beam spot of the charged particle beam. According to the block exposure technique, the charged particle beam is transmitted through a mask having repeating basic unit patterns, and the unit patterns are exposed in one shot even for complicated patterns. Hence, the block exposure technique is particularly effective when exposing patterns which are fine but most of the area to be exposed consists of repeating basic patterns, such as the case of the patterns of a 256 Mbit dynamic random access memory (DRAM).
FIG. 1
shows an example of a conventional electron beam exposure apparatus employing the block exposure. The electron beam exposure apparatus shown in
FIG. 1
generally includes an electron gun
101
, an electron lens system L
1
a
, a plate
102
with a rectangular opening, an electron lens system L
1
b
, a beam shaping deflector
103
, a first mask deflector MD
1
, a dynamic mask stigmator DS, a second mask deflector MD
2
, a dynamic mask focus coil DF, an electron lens system L
2
a
, a mask stage
105
mounted with a block mask
104
, an electron lens system L
2
b
, a third mask deflector MD
3
, a blanking deflector
106
, a fourth mask deflector MD
4
, a reduction electron lens system L
3
, a circular aperture
107
, a projection electron lens system L
4
, a main deflector (electromagnetic deflector)
108
, a sub deflector (electrostatic deflector)
109
, a projection electron lens system L
5
, a wafer stage
111
mounted with a wafer
110
, and a control system.
The control system includes a central processing unit (CPU)
121
, a clock unit
122
which generates various kinds of clock signals including an exposure clock signal, a buffer memory
123
, a control unit
124
, a data correction unit
125
, a mask memory
126
, and a main deflector setting unit
127
. The CPU
121
which controls the operation of the entire electron beam exposure apparatus, the clock unit
122
, the mask memory
126
and the main deflector setting unit
127
are coupled via a bus
128
.
For the sake of convenience, the data correction unit
125
and the main deflector setting unit
127
are shown in
FIG. 1
as including the functions of a digital-to-analog converter and an amplifier. In addition, a laser interferometer which measures the position of the wafer stage
111
and a stage moving mechanism which moves the wafer state
111
are respectively known from U.S. Pat. No. 5,173,582 and No. 5,194,741, for example, and an illustration and description thereof will be omitted in this specification.
An electron beam emitted from the electron gun
10
passes through the rectangular hole of the plate
102
, and is deflected by the first and second deflectors MD
1
and MD
2
before passing a desired pattern portion of the block mask
104
. The cross sectional shape of the electron beam is shaped depending on the desired pattern portion, and the electron beam is swung back to an optical axis of the system by the converging functions of the electron lens systems L
2
a
and L
2
b
and the deflecting functions of the third and fourth deflectors MD
3
and MD
4
. Thereafter, the cross section of the electron beam is reduced by the reduction electron lens system L
3
, and irradiated on the wafer
110
via the projection electron lens systems L
4
and L
5
, thereby exposing the desired pattern on the wafer
110
.
Exposure pattern data related to the patterns to be exposed on the wafer
110
, block data related to mask patterns on the block mask
104
and the like are stored in the buffer memory
123
. The exposure pattern data includes main deflection data to be supplied to the main deflector
108
and the like. In addition, data related to the relationships of the deflection data and the mask pattern positions which are measured in advance prior to the exposure, correction data for correcting the deflection data to be supplied to the dynamic mask stigmator DS and the dynamic mask focus coil DF and the like are stored in the mask memory
126
.
The exposure pattern data received by the CPU
121
from a host unit (not show) or the like and stored in the buffer memory
123
includes a pattern data code PDC which indicates which mask pattern of the block mask
104
is to be used for the exposure. The control unit
124
uses this pattern data code PDC to read from the mask memory
126
the deflection data for deflecting the electron beam to the position of the mask pattern to be used. The control unit
124
supplies the read deflection data to the first through fourth deflectors MD
1
through MD
4
which are used for the pattern selection. In addition, the deflection data read from the mask memory
126
are also supplied to the data correction unit
125
. The deflection data are read from the mask memory
126
based on an exposure clock signal which is generated by the clock unit
122
.
On the other hand, the main deflector setting unit
127
reads from the buffer memory
123
the main deflection data of the main deflector
108
based on the clock signal from the clock unit
122
, and supplies the read main deflection data to the main deflector
108
. In addition, the deflection data of the sub deflector
109
, the deflection data of the beam shaping deflector
103
, and the deflection data of the blanking deflector
106
are decomposed into shot data in the control unit
124
depending on the data stored in the buffer memory
123
. The shot data are supplied to the corresponding sub deflector
109
, the beam shaping deflector
103
and the blanking deflector
106
via the data correction unit
125
. In other words, the control unit
124
depending on the data stored in the buffer memory
123
, the control unit
124
obtains and supplies to the data correction unit
125
the size of the electron beam for the case where the variable rectangular exposure is to be made and the deflection position of the electron beam on the block mask
104
. The data correction unit
125
corrects each of the deflection data of the electron beam which are dependent on the patterns to be exposed and are supplied from the control unit
124
, based on the correction data read from the mask memory
126
. The deflection data of the beam shaping deflector
103
determine the variable rectangular size of the electron beam, and the deflection data of the blanking deflector
196
are set for each exposure shot.
FIGS. 2A and 2B
show an example of the block mask
104
for a memory. As shown in
FIG. 2A
, the block mask
104
is made up of a substrate
104
a
which is made of a semiconductor such as silicon or a metal, and a plurality of deflection areas
104
-
1
through
104
-
12
provided on this substrate
104
a
. A plurality of mask patterns are formed in each of the deflection areas
104
-
1
through
104
-
12
. In the electron beam exposure apparatus that employs the block exposure, the range of the mask patterns which are
Yamada Akio
Yasuda Hiroshi
Anderson Bruce C.
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
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