Computer-aided design and analysis of circuits and semiconductor – Nanotechnology related integrated circuit design
Reexamination Certificate
2002-02-28
2004-05-04
Siek, Vuthe (Department: 2825)
Computer-aided design and analysis of circuits and semiconductor
Nanotechnology related integrated circuit design
C378S034000, C716S030000, C716S030000
Reexamination Certificate
active
06732351
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of forming a mask used for the charged particle beam exposure and a program for processing pattern data for forming a mask for the charged particle beam exposure, and more particularly to a method of forming a mask used for the EPL (Electron-beam Projection Lithography) and a program for processing pattern data therefor.
BACKGROUND OF THE INVENTION
In recent years, accompanying progress in the degree of integration of semiconductor devices, miniaturization of the patterns to be projected into semiconductor wafers have been further advancing, and for the projection of such minute patterns, exposure methods with charged particle beams such as electron beams or ion beams have been employed.
In the exposure methods, using charged particle beams, for example, electron beams, stencil masks are generally utilized as masks for the pattern projection. The stencil mask has a structure in which openings in the form of a prescribed pattern is set in a thin substrate made of silicon or similar material. With such a stencil mask being used, in the electron beam exposure method, an electron beam consisting of electrons which pass through the openings in the form of a prescribed pattern travels through a projection optical system and forms an image on a wafer, and thereby projection of the pattern is made. An electron beam consisting of electrons which, in irradiation, fall on a region of the stencil mask other than the openings is thereby blocked from reaching the wafer by the mask substrate through absorption, reflection or heavy scattering. Having traversed the mask substrate, some rays of the electron beam are heavily scattered and are cut off by a limiting aperture in the projection optical system, and they do not arrive on the wafer.
Meanwhile, in the electron beam exposure method, there is also utilized a membrane-type mask (referred to as a “continuous membrane mask” hereinafter) in which an electron-beam scatterer in a prescribed shape is set on an electron-beam transmittable thin film with a small electron-beam scattering power. In the electron beam exposure method utilizing such a continuous membrane mask, electrons which traverse the thin film region of the mask where no electron-beam scatterer is formed form an image on a wafer, and thereby projection of the pattern is made. The electrons, having traversed the electron-beam scatterer of the mask, are heavily scattered and cut off by a limiting aperture so that they cannot arrive on the wafer.
As against the continuous membrane mask of this sort, the afore-mentioned stencil mask is widely used. The reason lies in a fact that, with the stencil mask, electrons to form an image on the wafer pass through the opening thereof so that, compared with the continuous membrane mask with which image-forming electrons have to traverse a thin film thereof, no energy loss by the mask occurs or the resolution is not lowered by chromatic aberration, and, thus, a high resolution can be obtained. Moreover, fabrication of stencil masks is also relatively easy.
For the stencil mask of this sort, however, the pattern must be formed by the layout of openings. This gives rise to a problem that the pattern shape possible to be formed becomes limited.
For example, because a structure with a pattern (referred to as a “doughnut pattern” hereinafter) in which a screening region to block the electron beam is completely surrounded by an opening, as shown in FIG.
1
(
a
), cannot itself support its screening region that is like an isle surrounded by an opening, and this region will fall out, it is impossible to form a stencil mask with this pattern. Furthermore, in a structure with a pattern (referred to as a “leaf pattern” hereinafter) wherein an opening is not set around the entire perimeter of the inner screening region but formed in such a way that the inner screening region is linked with the peripheral screening region by a part of its perimeter, as shown in FIG.
1
(
b
) (leaf type) and FIG.
1
(
c
) (tongue type), the linking section has a substantially low mechanical strength so that the inner screening region is bound to fall off, while the mask is in use or even in fabrication. In addition, for a structure with a pattern (referred to as an “L-shaped pattern” hereinafter) in which an opening is in the shape of the letter “L” or the shape that the letters “Ls” are joined together, the stress is liable to center at both ends of corner sections of the screening region which extends into the opening, and thus the mask may be easily damaged at those sections.
Accordingly, to overcome these problems, there has been employed a method in which a prescribed pattern is divided into a plurality of sections and, by distributing these sections onto two masks, complementary opening patterns are formed in respective masks, and, using these two complementary masks, pattern transcription is carried out twice and, at the end, a prescribed pattern is transcribed onto a wafer (J. Vac. Sci. Technol. B (1993) Vol. 11(6), pp. 2400-2403).
For instance, in Japanese Patent Application Laid-open No. 132206/1994, there is disclosed a method wherein a doughnut pattern shown in FIG.
2
(
a
) is divided into two, and, using alternately a first mask with an opening pattern shown in FIG.
2
(
b
) and a second mask with an opening pattern shown in FIG.
2
(
c
), and a doughnut pattern is transcribed.
Further, in U.S. Pat. No. 5,166,888, a method of splitting a pattern in formation of complementary masks is disclosed. An example of this method is described below, with reference to FIG.
3
. In FIG.
3
(
a
), a prescribed pattern (H) that is to be transcribed onto a wafer is shown, and a set of cutting lines for the pattern is each shown in FIGS.
3
(
a
-
1
) and (
a
-
2
). The cutting lines shown in FIG.
3
(
a
-
2
) are the ones selected to use. FIG.
3
(
b
) shows a stencil mask having an opening in the form of a pattern corresponding to FIG.
3
(
a
). Further, FIGS.
3
(
b
-
1
) and (
b
-
2
) show a set of two complementary masks, which are used alternately to transcribe, at the end, the pattern of FIG.
3
(
a
).
Firstly, all corners of a polygon (
100
), an outline of which is in the form of the prescribed pattern (H), are determined. Next, all inside corners
102
,
103
,
104
and
105
are determined. Herein, all corners other than inside corners are called outside corners.
Next, as shown in FIG.
3
(
a
-
1
), cutting lines
107
,
108
,
109
and
110
are laid down from each inside corner to its opposing sides. Although cutting lines are, here, laid down from all inside corners, only an inside corner whose specifically assigned stability value does not satisfy a specific criterion can be selected for the inside corners from which cutting lines are actually laid down. Next, among these sets of possible cutting lines, a set of cutting lines which have the shortest lengths and do not intersect one another are chosen (
112
,
113
,
114
and
115
of FIG.
3
(
a
-
2
)). The prescribed pattern (H) is, then, split by these chosen cutting lines into a plurality of sections (H′), and a plurality of these sections (H′) are distributed to two masks. That is, in one mask, as shown in
FIG. 3
(
b
-
1
), there are formed opening patterns
117
,
119
and
120
, each of which corresponds to a section (H′) distributed to this mask, out of a plurality of sections (H′), while, in the other mask, as shown in FIG.
3
(
b
-
2
), there are formed opening patterns
118
and
121
, each of which corresponds to a section (H′) distributed to this second mask, out of a plurality of sections (H′).
Although the above disclosure has been made to propose a splitting technique for the projection of patterns that may bring about a problem to the stencil mask, any effective method capable to extract singular patterns such as a doughnut pattern, a leaf pattern and an L-shaped pattern systematically from a group of various patterns has not been known. For that reason, even a pattern which hardly requires splitting is
Do Thuan
NEC Electronics Corporation
Siek Vuthe
Whitham Curtis & Christofferson, PC
LandOfFree
Method of forming mask for charged particle beam exposure... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of forming mask for charged particle beam exposure..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of forming mask for charged particle beam exposure... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3220581