Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1998-08-12
2001-08-14
Bella, Matthew C. (Department: 2621)
Image analysis
Applications
Manufacturing or product inspection
C382S144000, C382S173000, C382S199000, C382S203000, C430S005000, C430S313000, C430S328000, C430S333000
Reexamination Certificate
active
06275604
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to semiconductors, and, more particularly, to method and apparatus for generating exposure data of use in a design pattern of a semiconductor integrated circuit on an exposure medium.
FIG. 1
is a schematic diagram of an electron beam (EB) exposure apparatus. The EB exposure apparatus has a stencil mask (or block mask)
12
and a plate
11
having a rectangular opening
13
. As shown in
FIG. 2
, the stencil mask
12
has a plurality of first transmission apertures
14
having rectangular shapes, and a plurality of block areas
15
.
Second transmission apertures
16
are formed in some block areas
15
, and third transmission apertures
17
are formed in the other block areas
15
. The second transmission apertures
16
take the shapes of “recursive patterns” which are acquired by extracting common portions from layout pattern data of LSI circuits. The recursive patterns include plural kinds of patterns. The block areas
15
in which the second transmission apertures
16
are formed are called “recursive blocks”. The third transmission apertures
17
take the shapes of predetermined “segmental patterns” including oblique sides. That is, segmental patterns include oblique sides corresponding to the size of the block areas
15
. The block areas
15
in which the third transmission apertures
17
are formed are called “segmental blocks”.
Referring again to
FIG. 1
, an electron beam
10
is deflected by a first electromagnetic deflector
19
before passing the plate
11
. The electron beam
10
is then deflected by a second electromagnetic deflector
20
before passing any one of the first to third transmission apertures
14
-
17
of the stencil mask
12
. Accordingly, the cross-sectional shape of the electron beam
10
or the shape of its exposure pattern is changed. The electron beam
10
after it has passed the stencil mask
12
is further deflected by a third electromagnetic deflector
21
. As a platform or stage
22
is moved along the X and Y axes, a desired pattern is exposed on a predetermined area of a wafer
23
located on the stage
22
.
The size of a rectangular pattern exposed on the wafer
23
is determined by adjusting the degree of overlapping of the beam passing through the plate
11
with the associated first transmission aperture
14
. This exposure scheme is called a variable rectangular system. As the electron beam
10
passes any second transmission aperture
16
, the associated recursive pattern is exposed by a single shot. In a block exposure scheme using “recursive blocks”, the third electromagnetic deflector
21
and the stage
22
are controlled to expose recursive patterns of the same shape on a plurality of areas of the wafer
23
. As this block exposure involves fewer shots, the exposure time is decreased. In a block exposure scheme using “segmental blocks”, as an electron beam passes any third transmission aperture
17
, the associated segmental pattern is exposed by a single shot. Combining some segmental patterns permit a pattern of a desired shape to be exposed on the wafer.
As shown in
FIG. 3A
, in a case where the variable rectangular system is used to expose a pattern with an oblique side
24
, on a wafer
23
, for example, the pattern is formed by shooting a plurality of rectangular patterns
25
at a time. This scheme however increases the number of shots and elongates the exposure time. Further, this scheme exposes the oblique side
24
of the pattern in a stepwise form. To make the oblique side
24
as straight a line as possible, the rectangular patterns
25
constituting the pattern should have relatively narrow widths. This approach would result in an undesirable increase in the number of rectangular patterns
25
or the number of shots.
FIG. 3B
shows a pattern formed by combining triangular patterns
26
a
and
26
b
and rectangular patterns
27
a
and
27
b
to improve the linearity of the oblique side
24
of the pattern. The triangular patterns
26
a
and
26
b
are formed by the third transmission aperture
17
formed in the stencil mask
12
. The third transmission aperture
17
has a right-triangular shape including an oblique side which has the same inclination as the oblique side
24
of the pattern. The pattern can be formed with fewer shots than is required by the scheme in
FIG. 3A
by individually shooting the triangular patterns
26
a
and
26
b
and the rectangular patterns
27
a
and
27
b
. The triangular pattern
26
b
having a relatively small size is obtained by adjusting the degree of overlapping of the beam
10
, which has passed the plate
11
, with the associated third transmission aperture
17
. The rectangular patterns
27
a
and
27
b
are obtained by adjusting the degree of overlapping of the beam
10
, which has passed the plate
11
, with the associated first transmission aperture
14
.
An exposure data generating apparatus receives layout pattern data from a CAD system (not shown) and performs a graphics process on the layout pattern data. The graphics process includes a sizing process, a shrinking process and a rounding process which converts the coordinates of the layout pattern data to the grids (coordinates) of data the exposure apparatus handles. The exposure data generating apparatus then determines if exposure using the layout patterns on the stencil mask
12
is possible. Exposable layout patterns include, for example, a rectangular pattern
29
a
in
FIG. 4A
, right-triangular patterns
29
b
to
29
e
in
FIG. 4B
, parallelogram patterns
29
f
to
2
i
in
FIGS. 4C and 4D
, trapezoidal patterns
29
j
to
29
n
in
FIGS. 4E and 4F
and the patterns of the third transmission apertures
17
shown in FIG.
2
. When exposure is possible, the exposure data generating apparatus converts the format of the layout pattern data to an adequate format for the exposure apparatus.
Patterns that cannot be exposed using the patterns on the stencil mask
12
are layout patterns which do not include horizontal and/or vertical sides. The exposure data generating apparatus segments such layout pattern data to produce plural pieces of rectangular pattern data. The exposure data generating apparatus then performs format conversion on the plural pieces of rectangular pattern data and supplies the converted rectangular pattern data to the exposure apparatus. The exposure apparatus carries out divided shot exposure using a plurality of rectangular patterns instead of the patterns on the stencil mask
12
.
Depending on the shapes of the layout pattern, the layout pattern data after the graphics process may differ from the layout pattern data before the graphics process. This difference or error leads to an incoincidence between the coordinates of the layout pattern data before processing (format conversion) and the coordinates of the layout pattern data after processing. This leads to a probable case where although the original layout pattern is exposable using the patterns on the stencil mask
12
, exposure is actually conducted using plural pieces of rectangular pattern data. This increases the number of shots by the exposure apparatus, increasing the exposure time for a single wafer. Particularly, specific triangular layout patterns excluding triangles having one angle of approximately 45 degrees are likely to be affected by the error. That is, since the graphics process may cause the inclination of the oblique side of a triangle to be varied by the error, the pattern data of the third transmission apertures
17
previously prepared cannot be used for such a specific triangular layout pattern. Therefore, exposure is executed using plural pieces of rectangular pattern data in place of the pattern data of the third transmission apertures
17
. This results in an increased number of shots by the exposure apparatus.
Accordingly, it is an objective of the present invention to provide an efficient exposure data generating method and apparatus capable of decreasing the exposure time.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a method for gene
Ito Yoshio
Miyajima Masaaki
Bella Matthew C.
Chawan Sheela
Fujitsu Limited
Staas & Halsey , LLP
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