Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-08-30
2002-04-23
Berman, Jack (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S505100, C430S005000, C430S296000
Reexamination Certificate
active
06376849
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mask (in the present specification, the concept of “mask” includes reticles) to be used for a charged particle beam (for example, an electron beam) exposure apparatus and a charged particle beam exposure apparatus on which the mask is installed, and more particularly to a charged particle beam exposure apparatus mask whose transfer accuracy remains unchanged even if the pattern formed on the mask is deformed by the internal tension stress of the mask, and a charged particle beam exposure apparatus on which the mask is mounted.
2. Description of Related Art
A projection exposure apparatus for manufacturing semiconductors project-transforms a circuit pattern formed on a mask surface onto a substrate such as a wafer via an image forming device. A resist is coated on the substrate. When the resist coated on the substrate is exposed to an electron beam, a resist pattern is formed on the substrate. According to the electron beam exposure, which forms a pattern using an electron beam, the width of the electron beam can be reduced to several Angstroms. Therefore, a fine pattern of line width less than or equal to 1 &mgr;m can be formed, which is a primary characteristic of the projection exposure apparatus.
According to the conventional direct drawing type electron beam exposure system, a fine pattern is drawn by scanning an electron beam that converges to a micro size smaller than the line width of the pattern to be drawn. However, this method requires a long drawing time, and cannot obtain a high throughput, which is a major drawback. In order to solve this problem, an electron beam exposure apparatus which project-transfers a circuit pattern formed on a mask surface onto a wafer using an electron beam optical system has been developed as exemplified by the partition transfer system. This type of electron beam exposure apparatus achieves a higher throughput than the conventional straight drawing type electron beam exposure apparatus.
FIG. 5
shows the configuration of a conventional projection transfer type electron beam exposure apparatus. This apparatus is constituted of at least a mask
13
, an irradiation device
11
which irradiates an electron beam
12
onto the mask
13
, and an electron beam image forming device
15
which projects the electron beam
14
that has passed through the mask onto a substrate
17
. The electron beam
12
emitted from the irradiation device
11
hits and passes through the mask
13
. The electron beam
14
that has passed through the mask
13
is transformed into an electron beam
16
by the electron beam image forming device
15
. This electron beam
16
forms an image of the pattern formed on the mask
13
on the substrate
17
. The substrate
17
is, for example, a silicon wafer on which a resist is coated. The resist on the substrate
17
is then exposed to the projected electron beam
16
.
The electron beam image forming device
15
reduce-projects the circuit pattern formed on the mask onto the substrate
17
. As a result, the fine circuit pattern is exposed on the resist. In general, the electron beam image forming device
15
can obtain a high resolution only within a small area of size, for example, 1 mm×1 mm square, due to its optical limitation. On the other hand, the size of a semiconductor chip is about 20 mm×20 mm square. Therefore, the entire semiconductor chip cannot be transferred by a single exposure. Hence, the conventional electron exposure apparatus exposes the desired exposure region by irradiating with the electron beam
12
a portion of the mask, and scanning the electron beam
12
. In the case the mask
13
is scanned in addition to the scan of the electron beam
12
, the mask
13
is mounted on a scanning stage, and the scanning stage is scanned. For example, by scanning the electron beam
12
in a specific direction and scanning the mask
13
in a direction perpendicular to the specific direction, a wide area of the mask
13
can be exposed. In the case the mask
13
is scanned, the substrate
17
is scanned in the opposite direction in synchronization with the scanning direction of the mask
13
.
FIG. 6
shows a portion of a cross section of the mask
13
. The mask
13
has a self-supporting membrane member
18
(hereafter, this will be referred to as membrane
18
.) as its principal portion. Penetration holes
19
are formed on the membrane
18
to form a pattern of the mask
13
. The electron beam portions
12
′ that travel toward the penetration holes
19
pass through the penetration holes
19
. However, the electron beam portions
12
″ that travel toward the other portion of the mask
13
are scattered or absorbed by the membrane
18
. The electron beam image forming device
15
causes the electron beam portions
12
′ that pass through the penetration holes
19
to form an image of the pattern on the substrate
17
.
In the above-described mask, the portion of the electron beam absorbed by the membrane portion of the mask generates heat. As a result, the mask is thermally expanded and deformed. This causes the shape of the pattern formed on the mask to be deformed also, which is a problem. To cope with this problem, the thickness of the membrane of the conventional electron beam exposure apparatus mask is made less than 10 &mgr;m so that a very small portion of the electron beam will be absorbed. That is, by making the membrane thin, a major portion of the electron beam is made to transmit through the membrane. This transmitting electron beam is scattered by the membrane. Hence, the transmitting electron beam can be removed by the electron beam image forming device so that only those electron beams that pass through the pattern portion will form an image on the substrate.
However, when the membrane is made so thin, the membrane is deflected by it own weight, which is a problem. In order to reduce the degree of this deflection cause by its own weight, an internal tensile stress is pre-applied to the membrane, for example, by adding an additive to the membrane.
In order to form a pattern on the mask, for example, a resist pattern is formed on the surface of the membrane, a removal process by dry-etching is applied to the membrane, and the resist pattern is transferred to the membrane. In this case, when penetration holes are formed on the membrane having an internal tensile stress, the membrane is deformed by the internal tensile stress, which is a problem. For example, in the case a rectangular circuit pattern
20
shown in FIG.
7
(
a
) is exposed, if a penetration hole
21
similar to the circuit pattern as shown in FIG.
7
(
b
) is formed on the membrane
18
, the penetration hole
21
is deformed into a barrel-shape
21
′ as shown in FIG.
7
(
c
) due to the internal tensile stress of the membrane
18
. Therefore, the exposure pattern also becomes a barrel-shape.
In other words, due to the internal tensile stress that is applied to prevent the deflection generated by the weight of the membrane itself, the shape of the circuit pattern that is actually formed differs from the intended shape. The deformation of the mask pattern distorts the shape and position of the exposure pattern, which is a problem.
In exposing a circuit pattern of a semiconductor or the like, the position distortion of the exposure pattern needs to be suppressed to a low degree. For example, in the case a circuit pattern whose minimum line width is 130 nm is exposed, it is desirable that the position distortion of the mask having a reduction rate of 4 be set approximately below 28 nm.
Given these problems, it is an object of the present invention to provide a charged particle beam exposure apparatus mask such that, even if an internal tensile stress is applied to the mask, the degree of deformation of the circuit pattern remains within a range in which the transfer accuracy remains satisfactory, and a charged particle beam exposure apparatus on which such a mask is mounted.
SUMMARY OF THE INVENTION
The first means for sol
Berman Jack
Chapman and Cutler
Nikon Corporation
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