Charged particle beam exposure system

Details Charged particle beam exposure system Charged particle beam exposure system

2001-08-03

2004-11-09

Pham, Hai (Department: 2853)

Radiant energy

Irradiation of objects or material

Irradiation of semiconductor devices

C250S492100, C250S492210

Reexamination Certificate

active

06815698

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application claims benefit of priority under 35USC §119 to Japanese patent application No.2000-237163, filed on Aug. 04, 2000, the contents of which are incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a charged particle beam exposure system, such as an ion or electron beam exposure system which is used in a process for fabricating semiconductors such as LSIs or VLSIs. More specifically, the invention relates to a low-accelerating-voltage charged particle beam exposure system.
2. Description of the Prior Art
Charged particle beam exposure systems have the function of being capable of forming a high resolution pattern since it is possible to write at a resolving power of a wavelength level of electrons (or ions) which is shorter than light wavelength. On the other hand, since a complete pattern is directly written with small divided pattern beams unlike a mask writing system based on light exposure, there is a problem in that charged particle beam exposure systems take a lot of time to write. However, in view of characteristics that accurate fine line patterns can be formed, the charged particle beam exposure technique has been developed as the next technique to the lithography technique of the light exposure system, or as an important tool to the fabrication of semiconductors in a multi-product small-lot production such as ASIC.
A method for direct-writing a pattern with electron beams mainly uses two systems. That is, there is a system for writing a pattern by scanning the whole surface of a wafer while on-off-controlling small round beams, and a VSB writing system for writing a pattern with electron beams passing through a stencil aperture. As the electron beam writing technique developed from the VSB writing, there has been developed a bulk writing system for preparing a stencil on which repeated patterns are formed as one block and for selecting one of the patterns of the stencil to enable a high-speed writing.
First, as a conventional charged particle beam exposure system, a typical example of an electron beam lithography system of a VSB writing system is shown in
FIG. 10
(H. Sunaoshi et al.; Jpn. J. Appl. Phys. Vol. 34 (1995), pp. 6679-6683, Part 1, No. 128, December 1995). Furthermore, in the following drawings, the same reference numbers are given to the same portions to suitably omit the descriptions thereof.
Electron beams
7
emitted and accelerated from an electron gun
11
are arranged as uniform electron beams by means of an illumination lens
15
and pass through a first forming aperture
85
to be formed as rectangular electron beams, and thereafter, projected on a second shaping aperture
89
of a rhombic or rectangular shape by means of a projection lens
87
. At this time, the beam irradiation position on the second shaping aperture
89
is controlled by a shaping deflector
21
so that the shape and the area of the second shaping aperture
89
is irradiated with the pattern beams in accordance with CAD data. The beams passing through the second shaping aperture
89
are reduced and projected by means of a reducing lens
64
and an objective lens
66
, and a position of the beams on a region of a wafer
14
to be written is controlled by means of a main deflector
95
and a sub deflector
93
. In this case, the main deflector
95
controls the interior of a stripe of an irradiation region to be written (main field) with respect to the wafer
14
referring to the position of an XY stage (not shown), and the sub deflector
93
controls the position of a range to be written which is obtained by finely dividing the interior of the stripe (sub-field). Below the objective lens
66
, there is an electron detector
33
for detecting secondary electrons and back-scattered electrons (which will be hereinafter referred to as secondary electrons and so forth) which are produced when the wafer
14
is irradiated with the electron beams
7
. By processing the detected signals acquired by the electron detector
33
, various control parts (not shown) detect an image of SEM, and controls such as adjustment of the trajectories of the beams based thereon are carried out.
Since the electron optical system of an electron beam lithography system
120
shown in
FIG. 10
comprises electromagnetic lenses and electrostatic deflectors, it is required to design the electron optical system while sufficiently taking account of the influence of the total optical characteristics of the lenses, the deflectors, the precision of mechanical assembly and contamination. In addition, in order to improve the resolution of beams, there has been widely adopted a system for driving highly accelerated electron beams
7
into a resist on the wafer
14
. For that reason, there is caused the proximity effect which is a phenomenon that the incident electron beams
7
reflect on various multilayer thin films deposited on the bottom face of the resist of the wafer
14
to travel above the resist again. This proximity effects causes blurring and deterioration of resolution on the written pattern. Therefore, in the design of the electron beam lithography system, it is essential that the control for correcting the proximity effect be carried out, so that it is required to provide a large-scale system in a control part in addition to the electron optical system. Thus, there is a problem in that the system is complicated and troubles are induced, so that precision is lowered. Moreover, since highly accelerated electrons are used, there is the possibility that the surface of the wafer may be damaged.
In order to eliminate the above described problems in the VSB system of high-accelerating-voltage charged particle beams, an electron beam lithography system of an aperture system using low-accelerating-voltage electron beams has been proposed (Japanese Patent Application No. 10-363071, J. Vac. Sci. Technol. B14 (6), 1996, 3802). The electron beam lithography system proposed in Japanese Patent Application No. 10-363071 is shown in
FIG. 11. A
first aperture
13
having a rectangular or circular opening is irradiated with electron beams
67
which are emitted and accelerated from an electron gun
11
. The electron beams
67
passing through the first aperture
13
travel toward a second shaping aperture
19
comprising the arrangement of a plurality of bulk exposure cell apertures. The beam diameter of the electron beams
67
is adjusted by means of illumination lenses
15
a
and
15
b
to such a size which is sufficiently larger than that of any one of cell apertures and in which the electron beams
67
do not interfere with adjacent cell patterns. The illumination lenses
15
a
and
15
b
comprise two electrostatic lenses (Einzel lenses), and a negative voltage is applied to the central electrode to use the illumination lenses
15
a
and
15
b
. The beams passing through the second illumination lens
15
b
are controlled to be deflected toward a target position by means of a first shaping deflector
17
so that a target cell aperture of the plurality of cell apertures formed in the second shaping aperture can be selected. The electron beams
67
passing through the second shaping aperture
19
start as cell pattern beams leaving the second shaping aperture
19
, and pass through a reducing lens
64
in a state that the beams are returned to an optical axis by a second shaping deflector
21
. Above the reducing lens
64
, a third shaping aperture
62
is provided for cutting undesired beams scattered by the second shaping aperture
19
and so forth. The electron beams reduced by the reducing lens
64
pass through a pre sub deflector
93
′, a pre main deflector
95
′, a sub deflector
93
, a main deflector
95
and an objective lens
66
to be reduced and projected on the top face of the wafer
14
which is mounted on an XY stage (not shown). The position irradiated with the beams with respect to the position of a pattern to be written on the wafer is controlled by means of th

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