Computer-aided design and analysis of circuits and semiconductor – Nanotechnology related integrated circuit design
Reexamination Certificate
2000-11-01
2003-04-08
Siek, Vuthe (Department: 2825)
Computer-aided design and analysis of circuits and semiconductor
Nanotechnology related integrated circuit design
C716S030000, C716S030000
Reexamination Certificate
active
06546544
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a partial one-shot transfer exposure technique, used in electron beam exposure or the like, for preparing a plurality of small mask patterns (block patterns) as an exposure pattern, exposing each small pattern by selecting the masks and exposing all the pattern by connecting the small patterns or, in particular, to a technique for preparing a mask for the small pattern.
With the recent great progress in the semiconductor techniques, the integration and functions of semiconductor integrated circuits (ICs) have been improved remarkably. Thus semiconductor techniques are expected to play central roles in technological development in all industries including the computer and the communication machine control industries. The integration of the IC has increased about four times every two or three years. The storage capacity of the dynamic access memory (DRAM), for example, has increased from 1 M, to 4 M, to 16 M, to 256 M and to 1 G. The high degree of integration of the IC depends to a large measure on the progress of micro patterning techniques for semiconductor production.
The limit of micro patterning techniques is currently defined by the pattern exposure technique (lithography). As a technique for pattern exposure, an optical exposure apparatus called a stepper is now used. In the optical exposure apparatus, the minimum width of the pattern that can be formed is defined by the wavelength of the exposure light source due to diffraction. A light source emitting ultraviolet light is used, and it is difficult to use light of a shorter wave length. To realize finer processing successfully, therefore, a new exposure method, other than the optical exposure apparatus, is now being planned.
In charged beam exposure and, especially, electron beam exposure, micro patterning less than 0.05 &mgr;m can be realized with the positioning accuracy of 0.02 &mgr;m. Charged beam exposure, however, is lower in throughput than the stepper and has, thus far, been thought to be unusable for mass production of LSIs. An electron beam exposure method will be explained as an example.
In an optical exposure apparatus, a photo mask corresponding to the pattern of the whole layer of the IC and the whole layer is exposed with one shot, thus leading to a high throughput. The high degree of integration of the IC, however, has made the production of the photo mask very difficult and has given rise to the problem of an increased cost and time required for producing the photo mask.
In the electron beam exposure method, various techniques including the blanking aperture array (BAA) method and the partial one-shot transfer exposure method have been proposed for improving the throughput.
The pattern of the whole layer of the IC cannot be exposed by the electron beam exposure method. Therefore, a partial one-shot transfer exposure method has been introduced in which the whole pattern is segmented into a plurality of small patterns, and a plurality of mask patterns (block patterns) corresponding to the small patterns are prepared for connecting the small patterns, followed by exposing the whole pattern. It is both difficult and deteriorates the efficiency to prepare block patterns corresponding to all the small patterns. Block patterns are prepared, therefore, only for the small patterns which repeatedly appear, while the other small patterns are scanned and exposed by a small beam or by exposing a pattern shaped by a method called the variable rectangle method described later. The partial one-shot transfer exposure method is generally called, and referred to hereinafter as, the block exposure method.
The block exposure method, as compared with the one-shot transfer exposure method for exposing the whole pattern with one shot, is low in throughput for production but has the advantage of a lower cost and a shorter time required for mask production. The block exposure method is used for the charged particle beam exposure method as well as for the electron beam exposure method and also is applicable to the optical exposure method. The electron beam exposure method will be referred to as an example in the description that follows.
FIG. 1
is a diagram showing a basic configuration of the optical system of the electron beam exposure apparatus of block exposure type. In
FIG. 1
, an electron beam emitted from an electron gun
11
is shaped in a first rectangular aperture
12
and, after being converted into a parallel beam by an electromagnetic lens and the like, enters a block mask
20
where it is shaped into the pattern of the block mask. A blanker
14
is an electrostatic deflector for deflecting the beam when shutting off the beam that has been passed through the block mask
20
. When deflected, the beam is shut off by the last aperture
15
while, when it is not deflected, the beam passes through and is turned on. The beam that has passed through the last aperture
15
is deflected by a subdeflector
16
and a main deflector
17
and radiated onto a predetermined position on a sample (wafer)
18
placed on a stage. At the same time, the beams are focused on the sample
18
by an electromagnetic lens (configured with the coil
19
and a pole piece not shown). Specifically, the beam radiated on the sample
18
has a shape corresponding to the pattern of the block mask. The elements described above are encased in a housing called an optical column of which the part traversed by the electron beam is reduced in pressure to a vacuum.
The actual electron beam exposure apparatus comprises electron control circuits, not shown, such as an exposure control circuit for generating a signal for controlling the selection of one of a plurality of block patternson the block mask
20
in accordance with an exposure pattern and generating a deflection signal to be applied to the subdeflector
16
and the main deflector
17
, a drive circuit for applying the signals output from these units to the various parts and a stage control circuit for controlling the movement of the stage.
FIG. 2A
is a diagram for explaining the principle of the block exposure system, and
FIG. 2B
is a diagram for explaining the variable rectangular exposure system. As shown in
FIG. 2A
, in the block exposure system, the beam that has passed though a square opening
21
, for example, is shaped into the shape of the opening
21
. The beam thus shaped is deflected by the deflector
22
in such a manner as to pass through one of a plurality of block patterns arranged on the block mask
20
. The block patterns have various opening shapes as shown.
As shown in
FIG. 2B
, in the variable rectangular exposure system, the beam that has passed through a first square opening
31
is shaped into the shape of the opening
321
, deflected by a deflector
32
, and enters a second square opening base
33
. By changing the amount of deflection in the deflector
32
, the position incident to the second opening base
33
is changed so that the shape of the beam that has passed through the second opening base
33
is changed. In this way, the beam is shaped into the desired rectangle. The IC pattern can be formed by combining rectangles, in all cases, and therefore any IC pattern can be exposed by the variable rectangle exposure system.
As described above, black patterns corresponding to all the small IC patterns are prepared, and the remaining small patterns are exposed by another method. The variable rectangle exposure method is also employed to expose such remaining small patterns with as high an efficiency as possible.
FIG. 3
is a diagram showing a configuration of the block mask
20
of an electron beam exposure apparatus. As shown, the block mask
20
has
12
mask areas
41
. A plurality of block patterns
42
are arranged in each mask area
41
. An opening
43
for changing the rectangle is formed at the four corners of each mask area
41
. Comparison between
FIGS. 2A and 2B
apparently shows that the beam-shaping mechanism of the block exposure system is analogous with that of the variable rectangle system. I
Advantest Corporation
Christie Parker & Hale LLP
Siek Vuthe
Tat Binh
LandOfFree
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