Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
2002-06-17
2004-03-23
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
active
06709880
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device, which forms semiconductor integrated circuit patterns by using charged particle beams.
2. Description of the Related Art
A lithography technology has been used for pattern formation of a semiconductor integrated circuit. In such a case, a light, an electron beam or the like is used as an energy beam to expose a photo-sensitive film. In photolithography using a light as an energy beam, in order to deal with microfabrication of a semiconductor device, a wavelength of a light source has been made shorter from a g line (436 nm) to an i line (365 nm), and to KrF (248 nm). This has been carried out because of the fact that resolution of a micro pattern is increased in inverse proportion to a wavelength. In the photolithography, resolution has accordingly been increased by a shorter wavelength. However, performance of a photolithography device has become insufficient for a pattern size required as device performance. Thus, further shortening of a wavelength of the light source has been pursued so as to increase resolution. However, not only light sources but also new lens materials and resists must be developed, necessitating enormous development costs. Consequently, device prices and process costs are increased, creating a problem of a high price of a manufactured semiconductor device.
On the other hand, electron beam lithography using an electron beam as an energy beam has an advantage of high resolution capability compared with the photolithography. In the case of a conventional electron beam lithography device, however, writing was carried out on a resist on a wafer by coating (direct writing) with a point (rectangular) beam or connecting a mask pattern of only several &mgr;m×several &mgr;m. In the case of the conventional electron beam, an electron source for obtaining high-density electron beams was not provided, and uniform electron beams were not provided in a wide range. Alternatively, aberration occurred between a center portion and a peripheral portion in the case of projecting an area of a large area. Consequently, resolution was deteriorated, making it impossible to project patterns of large areas all at once. Therefore, in a conventional electron beam writing method, since writing is carried out while connecting very small areas, many shots are necessary for writing on one wafer. In addition, since time is necessary until stabilization after an electron beam is deflected to a predetermined position for each shot, the increased number of shots causes a reduction in throughput. For such a reason, throughput has conventionally been low, about several pieces per hour (in 8-inch wafer), proving the method to be unsuitable as a mass-production technology.
As one of the measures to improve throughput of the electron beam lithography, for example as described in pp. 6897 to 6901, Japan Journal Applied Physics, vol., 39 (2000), electron projection lithography has been presented, which forms all patterns on a mask original plate (referred to as a reticle, hereinafter), and then projects/transfers the patterns by using electron beams. In this electron beam projection lithography, a lens was developed, which prevents aberration from being generated even when high-density electron means are provided uniformly in a wide range, and large-area irradiation is carried out. As in the case of the photolithography, the development of the lens enables the mask to be irradiated with electron beams, and scanned, greatly reducing the number of shots. Thus, the electron projection lithography is similar to the photolithography in terms of projection, its image being similar to a change of a light source from a light to an electron beam. Compared with several pieces/hour of the conventional electron beam lithography, throughput of one digit higher, i.e., 35 pieces/hour (in 8-inch wafer) is estimated.
A shape of the reticle for electron beam projection is descried in, for example pp.214 to 224 of Proceedings of SPIE vol. 3997 (2000).
FIG. 2A
is a bird's eye view of a reticle for electron beam projection,
FIG. 2B
an expanded view of a area
203
of
FIG. 2A
, and
FIG. 2C
a view of the reticle seen from the above. The electron beam lithography has a limited projection range. Accordingly, circuit patterns constituting an LSI chip are divided at sizes 1000 &mgr;m
□
on the reticle, and these circuit patterns are connected to form a pattern of the entire chip during projection. Hereinafter, one of such divided areas, i.e., a area on which the patterns are projected all at once, is referred to as a “subfield”
201
. A wafer, on which the circuit patterns are projected, is continuously moved, and each pattern projection is carried out by mechanically moving a reticle stage and deflecting electron beams corresponding to the wafer movement. A thickness of silicon (Si) of a pattern portion of the reticle is thin, 0.5 to 2 &mgr;m, and consequently breaking easily occurs. Thus, a mechanical strength is increased by providing a silicon beam called a strut
202
between the subfields.
Now, a manufacturing flow of a reticle for electron beam projection is described by referring to
FIGS. 3A
to
3
D. As shown in
FIGS. 3A
to
3
D, a silicon-on-insulator (SOI) wafer having SiO
2
buried in a Si substrate is used. The substrate has a thickness of about 400 to 800 &mgr;m and, thereon, SiO
2
is deposited by 0.1 to 0.5 &mgr;m, and Si by 0.5 to 2 &mgr;m. As methods of manufacturing a reticle for electron beam projection, there are available a preceding back etching method for carrying out back etching of the substrate before formation of a reticle pattern to manufacture the strut
202
, and a succeeding back etching method for carrying out back etching of the substrate later. Here, the preceding back etching method is described. In the preceding method, first, a area of the strut
202
is subjected to patterning, and dry etching is carried out. According to the preceding back etching method, a reticle pattern is formed after blanks for a stencil mask are made. Thus, since blanks for a stencil mask can be made and stored, and only surface machining is needed thereafter, turn around time (TAT) can be shortened.
On the other hand, in the succeeding back etching method, patterning is carried out on a normal thick substrate. Accordingly, the number of special steps for manufacturing an EPL mask is relatively small. However, if mismatching is present in membrane stress between an oxide film of an intermediate layer and silicon on the surface by execution of etching of back-side Si, which makes TAT longer, mask deformation may occur, causing a shift in projection position. This positional shift is prevented by adding boron or the like to an oxide film on the surface to generate tensile stress on the substrate surface as well, and reducing stress between the oxide film and the substrate. Both methods have own features different from each other as described above, and the preceding back etching method enabling TAT to be shortened is considered to be more suitable. The oxide film is removed after the execution of the back etching. Accordingly, membrane blanks for the reticle for electron beam projection are made (FIG.
3
B). Then, circuit patterns are divided into predetermined subfields, and a resist pattern
301
is formed on the reticle for electron beam projection by a resist process (FIG.
3
C). A predetermined pattern is formed by further carrying out dry etching. Lastly, the reticle for electron beam projection is made by carrying out cleaning (FIG.
3
D). As described herein, the reticle having an opening pattern for passing the energy beam is called a stencil type.
SUMMARY OF THE INVENTION
Representative features of the present invention can be summarized as follows.
In the case of using the electron projection lithography device, throughput can be greatly improved up to 35 pieces/hour compared with the electron beam direct writing method. Compared with the
Murai Fumio
Terasawa Tsuneo
Yamamoto Jiro
Yamamoto Tosiyuki
Hitachi , Ltd.
Le Thao Phuong
Miles & Stockbridge P .C.
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