Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-10-18
2003-08-26
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S3960ML, C250S492100, C250S492200, C250S492210, C250S492230
Reexamination Certificate
active
06610988
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charged particle beam drawing apparatus for directly drawing a pattern onto a sample wafer using a charged particle beam such as an electron beam, and, in particular, a charged particle beam drawing method for drawing a repeating pattern, such as a cell array pattern, by a partial blank drawing method.
This application is based on Japanese Patent Application No. Hei 11-294718, the contents of which are incorporated herein by reference.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
A blank drawing method is used as an example of an electron beam drawing method for lithography in a process for preparing a capacity contact in a DRAM manufacturing process, or the like. In this method, when the same patterns are sequential, a part of the repeating pattern is provided as a cell projection exposure aperture on the second mask (which is also called “the second aperture”), the electron beam penetrates the first mask (which is also called “the first aperture”) on which a rectangular hole is provided, and the electron beam penetrates the second mask having the cell projection exposure aperture. As a result, plural patterns are simultaneously drawn on a sample wafer. That is to say, the blank drawing method is executed so that the electron beam penetrates the cell projection exposure aperture on the second mask, wherein the area of the cell projection exposure aperture of the second mask is the same as an irradiation area of the electron beam which has already penetrated the rectangular hole on the first mask, as a result, the cell projection exposure aperture pattern formed on the second mask is sequentially drawn on the sample wafer. This method particularly reduces drawing time for periodic patterns.
When a repeating pattern is drawn by the partial blank drawing method, in a preparation step of data of the repeating pattern, a repeating pattern is selected from design data as a basic cell for a partial blank drawing and the repeating pattern is output as partially blank direct drawing data. However, a number of the periodic repeating pattern may not agree with an integer multiple of the number of a pattern of the basic cell for the partial blank drawing. Conventionally, to solve this problem, the partial blank drawing method was controlled as follows:
(1) A size of the basic cell for the partial blank drawing is adjusted and selected not so as to generate an excess pattern.
(2) To improve throughput, a pattern group having a maximum size within an area in which the partial blank drawing can be carried out, is selected as the basic cell for the partial blank drawing. On the other hand, the excess pattern, as a fraction which is generated at the end of a cell array pattern and cannot be in the maximum area is drawn using an aperture of a single pattern provided on the second mask or using a variable rectangular drawing method by combining the pattern of the first mask and the pattern of the second mask.
(3) To improve the throughput, a pattern group having a maximum size within an area in which the partial blank drawing can be carried out is selected as a first basic cell for partial blank drawing. On the other hand, the excess pattern as a fraction which is generated at the end of a cell array pattern and cannot be in the maximum area is selected as a second basic cell for partial blank drawing, an aperture for a partial blank drawing for the excess pattern is provided in addition to an aperture for a main partial blank drawing, and a cell array pattern is drawn using plural type apertures for a partial blank drawing.
FIG. 5
illustrates the above methods (2) and (3).
FIG. 5A
shows an aperture pattern of the first mask, FIGS.
5
B and
5
B′ show aperture patterns of the second mask, and
FIG. 5C
shows a cell array pattern on a semiconductor wafer to be formed by the cell projection exposure.
As shown in
FIG. 5A
, a rectangular aperture
12
a
is provided on the center of the first mask
12
1
. As shown in
FIG. 5B
, a rectangular aperture
13
a
and cell projection exposure apertures
13
a
and
13
d
to
13
g
are provided on the second mask
13
1
which is used in the above method (2). Furthermore, a cell projection exposure aperture
13
h
is provided on the second mask
13
2
which is used in the above method (3) for the cell projection exposure aperture
13
g
having a single pattern on the second mask
13
1
, wherein plural patterns corresponding to an excess pattern are formed on the cell projection exposure aperture
13
h
. As shown in
FIG. 5C
, a cell array pattern
11
is composed of a center portion pattern
11
a
drawn using the cell projection exposure aperture
13
b
as a standard, and an excess pattern
11
b
without the center portion pattern
11
a.
In the above method (2), as shown in
FIG. 6A
, the center portion pattern
11
a
is drawn using the cell projection exposure aperture
13
b
on the second mask
13
1
(a blank shot area
1
aa
is then shown), and, as shown in
FIG. 6B
, the excess pattern
11
b
is drawn one after the other using the cell projection exposure aperture
13
g
which exposes the single pattern (a blank shot area
1
bb
is then shown). Furthermore, by combining the rectangular aperture
12
a
of the first mask
12
1
, and the rectangular
13
a
of the second mask
13
1
, a rectangular pattern is formed and patterns for the excess pattern
11
b
are exposed one after the other.
In the above method (3), as shown in
FIG. 6A
, the center portion pattern
11
a
is drawn using the cell projection exposure aperture
13
b
on the second mask
13
2
, and, as shown in FIG.
6
B′, the excess pattern
11
b
is drawn for each blank shot area
11
bc
using the cell projection exposure aperture
13
h.
However, when the above method (1) is used, the size of a cell selected as the basic cell for the cell projection exposure is small, therefore, the number of partial blank shots increases and, as a result, the throughput decreases. When the above method (2) is used, since the excess pattern is exposed one after one, the number of partial blank shots also increases and the throughput decreases. When the above method (3) is used, since the throughput is improved, both the cell projection exposure aperture
13
b
for the center portion pattern and the cell projection exposure aperture
13
h
for the excess pattern have to be simultaneously prepared on the second mask (wherein a necessary type of cell projection exposure aperture for the excess pattern is not always one), therefore, the number of the cell projection exposure patterns which can be exposed on the second mask, is limited. Normally, the number of pattern types of the cell projection exposure aperture which can be provided on the second mask, is several to dozens.
As a method to solve the above problems, a method in which an excess pattern is drawn by controlling deflection of the electron beam is disclosed in Japanese Unexamined Patent Application, First Publication, No. 7-211609 (Kokai) (which is hereafter called JP 7-211609).
FIG. 7
is a schematic diagram showing an overview of the drawing apparatus disclosed in JP 7-211609. The apparatus is composed of an electron beam source
21
, an electron beam
22
, the first mask
23
, a shaping lens
24
, a shaping deflector
25
, the second mask
26
, a reducing lens
27
, a locating deflector
28
, an objective lens
29
, and a semiconductor wafer
30
. A cell array pattern
31
composed of the center portion pattern
31
a
and the excess pattern
31
b
is drawn on the semiconductor wafer
30
.
When the center portion pattern
31
a
is drawn, the electron beam, after penetrating the first mask
23
, is irradiated on all apertures to be exposed. When the excess pattern
31
b
is drawn, the electron beam, after penetrating the first mask
26
, is deflected using the shaping deflector
25
and irradiated on a part of apertures on the second mask
26
to be exposed.
Similarly, the above drawing method is
Hayes & Soloway P.C.
Lee John R.
NEC Electronics Corporation
Souw Bernard E.
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