Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Electron beam imaging
Reexamination Certificate
1999-07-01
2001-01-09
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Electron beam imaging
C430S302000, C430S942000
Reexamination Certificate
active
06171760
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a lithography method and a lithography system using a charged particle beam, and more particularly, to a lithography method and system in which a photoresist film is irradiated with light while the charged particle beam is applied. More specifically, the present invention is applied to a character projection method and system for a mask pattern using an electron beam.
Recently, in a photolithography technology for LSI, shorter-wavelength light has been increasingly used for obtaining a micro pattern. Furthermore, lithographic techniques using a charged particle beam and X-rays have been proposed to attain a direct writing of the micro pattern.
FIG. 1
is a schematic view of a conventional lithography system using an electron beam. The system shown in
FIG. 1
comprises a thermal cathode
401
, a wehnelt electrode
402
, an aperture
403
having a rectangular opening for shaping a beam, a first beam-shaping electron lens
404
, a beam deflector
405
, a second beam-shaping electron lens
406
, a mask stage
407
, a transfer mask
408
mounted on the mask stage, a demagnification lens
409
, an objective lens
410
, a beam deflector
411
, a wafer stage
413
, and a wafer
412
mounted on the wafer stage and having a photoresist film coated on the upper surface thereof.
In the lithography system having the aforementioned structure, electrons emitted from an electron gun, which is composed of the thermal cathode
401
and the wehnelt electrode
402
, are allowed to pass through the aperture
403
to form a rectangular beam. Furthermore, the electron beam is applied onto the transfer mask
408
by the function of the beam-shaping electron lenses
404
and
406
. At this time, by using the beams deflector
405
interposed between the beams shaping electron lenses
404
and
406
, an arbitrarily chosen position on the transfer mask
408
can be irradiated. The transfer mask
408
has an opening portion whose shape is obtained by synthesizing a rectangular and an ellipse. Therefore, if the opening portion on the transfer mask
408
is irradiated with the rectangular shaped beam, the resultant beam is obtained in a desired shape.
In addition, owing to the functions of the beam deflector
405
and the mask stage
407
, the electron beam can be applied to an arbitrarily chosen cell pattern portion within the transfer mask
408
.
The electron beam passed through the transfer mask
408
is demagnified and projected onto the wafer
412
by means of the demagnification lens
409
and the object lens
411
, and then applied to the photoresist film coated on the wafer
412
. In this case, the entire surface of the wafer
412
can be irradiated by combining beam deflection by the beam deflector
411
with the movement of the wafer
412
by the wafer stage
413
.
According to the direct writing technique on the wafer performed by using the electron-beam lithography system, a micro pattern of 0.2 &mgr;m or less can be formed.
However, the direct writing technique on the wafer has problems. The most significant problem is a low productivity. To describe more specifically, the throughput of wafer in the pattern exposure step is low. This is because, in the direct writing technique, a desired beam shape is obtained by applying the rectangular beam to the opening portion of the transfer mask, so that writing has to be made by dividing all patterns to be written in accordance with the rectangular beam shapes. In this method, even if repetition patterns are employed, the patterns are divided and then writing is made. As a result, the number of beam shots drastically increases. It is therefore impossible to improve the throughput. To improve this problem, recently proposed is a cell projection method in which an image of a repetition pattern previously formed on the transfer mask, is transferred onto the wafer. This method suggests the possibility of the high-speed writing using the electron beam.
When pattern exposure of a semiconductor memory is performed by using the electron beam, if the cell array portion is written by the cell projection method (since the cell array portion has a repeat pattern) and the peripheral circuit portion is written by a variable shaped beam varied in shape and size, the number of beam shots can be drastically reduced. As a result, high-speed writing can be attained.
However, even if the aforementioned high speed writing method is used, a beam shot density comes up to 10
4
to 10
5
shots/mm
2
. Therefore, the shot number (density) will restrict the throughput of the wafer. Since the size of the beam shot is determined by characteristics of the electron beam optical system in the lithography system, the low throughput inevitably occurs in the case where the pattern on the transfer mask is demagnified and projected.
On the other hand, as a micro patterning technique more suitable than the optical lithography, X-ray lithography is known. The X-ray lithography has many advantages including linearity and non-interference, over the conventionally-used lithography using visible light and ultraviolet light. However, it has a problem of a low throughput due to a low photosensitivity of resist, difficulty in alignment, and difficulty in mask material selection and in processing thereof.
To solve the low sensitivity of a resist in the X-ray lithography, proposed is a method for increasing an effective sensitivity of the resist by use of a secondary radiation from the fluorescent film (Japanese Patent Application KOKAI Publication No. 63-53922). In this method, since the fluorescent material layer is arranged above the mask material holding thin film (on the X-ray source side), the sensitivity of the resist for X-rays can be auxiliarily increased by application of the secondary radiation generated from the fluorescent material layer. However, the X-ray lithography has many problems to be solved, such as a cost, safety of the X-ray source and an improvement of productivity.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a lithography method and a lithography system capable of applying light onto a large area region of the wafer in a one-shot, thereby increasing a throughput of the wafer in a lithography step and improving a productivity.
To attain the aforementioned object, there is provided a lithography method comprising:
preparing a lithography system having
a charged particle beam generation section for generating a charged particle beam,
a mask stage for holding a transfer mask to which the charged particle beam is applied, and
a wafer stage for holding a wafer to be processed so as to face the charged particle beam generation section via the transfer mask;
setting the transfer mask on the mask stage;
setting the wafer coated with a photoresist on the wafer stage;
providing a fluorescent film between the transfer mask and the wafer coated with the photoresist;
irradiating the fluorescent film with the charged particle beam which passes through an opening portion of the transfer mask; and
applying a light to the photoresist film formed on the wafer by a light emitted from the fluorescent film.
The step of providing the fluorescent film between the transfer mask and the wafer coated with the photoresist film desirably includes a step of providing the fluorescent film on a surface of the transfer mask facing the wafer so as to face the wafer in close proximity or in contact with the wafer.
The step of providing the fluorescent film between the transfer mask and the wafer coated with the photoresist film may include a step of providing the fluorescent film on a surface of the wafer facing the transfer mask, with the photoresist interposed therebetween.
It is desirable that the fluorescent film emits an ultraviolet light and the photoresist is a resist for the ultraviolet light.
The transfer mask may have a same size pattern as that to be projected to the photoresist.
In the opening portion of the transfer mask, an opening aperture of a surface of the transfer mask facing the wafer is desir
Miyoshi Motosuke
Yamazaki Yuichiro
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Young Christopher G.
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