Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1998-09-02
2001-06-12
Berman, Jack (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
Reexamination Certificate
active
06246065
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron beam exposure technique in a pattern exposure process in the manufacture of semiconductor elements and, more particularly, to an electron beam projection transfer exposure apparatus which assures high use efficiency of electron beams and has high productivity.
2. Description of the Related Art
In the manufacturing process of semiconductor memory elements, light exposure that can assure high productivity is used. However, in the manufacture of semiconductor memory elements such as 1G and 4G DRAMs, which require processing an exposure pattern having a minimum line width of 0.2 &mgr;m or less, electron beam exposure with higher resolution is beginning to gain attention as an alternative exposure technique to light exposure.
In recent years, a transfer electron beam exposure apparatus which aims at improving productivity as compared to a conventional Gaussian or variable shaped electron exposure apparatus, i.e., an exposure apparatus which irradiates an electron beam onto a mask surface formed with a desired pattern and transfers the electron beam transmitted through the mask in a reduced scale to project the pattern on the mask onto a wafer, has been developed.
FIG. 7
shows the arrangement of a conventional electron beam projection exposure apparatus. In the conventional electron beam projection exposure apparatus shown in
FIG. 7
, an electron beam emitted by an electron gun
101
is condensed by a condenser lens
102
formed with a rectangular aperture
121
, and uniformly illuminates the surface of a mask
104
via a field lens
103
. As the mask
104
, either a scattering type mask prepared by forming a scattering pattern for scattering the electron beam on a membrane that transmits the electron beam, or a stencil type mask prepared by forming an absorbing pattern for absorbing the electron beam on a membrane may be used. The electron beam which is neither scattered nor absorbed by the pattern on the mask
104
is imaged and irradiated on a wafer
107
via reduction projection lenses
105
and
106
, thus forming an image of the pattern on the mask
104
onto the wafer
107
by exposure. Since the electron beam is transmitted through the rectangular aperture
121
, an electron beam irradiation region
110
on the wafer
107
also has a rectangular shape, as shown in FIG.
8
. The mask
104
is mounted on an X-Y stage which can be scanned in the X- and Y-directions, and the wafer
107
is mounted on a wafer stage. By scanning the X-Y stage in synchronism with the wafer stage, the entire surface of the wafer
107
is exposed.
One of the major factors that determine the productivity of the above-mentioned electron beam projection exposure apparatus is the exposure area (irradiation area) of an electron beam on the wafer surface. Especially, the exposure width (stripe width) W (see
FIG. 8
) of an electron beam in a direction perpendicular to the scanning direction of the wafer stage is an important factor. The exposure area is determined by off-axis aberrations of a projection lens of an electron optical system. In the manufacture of 1G or 4G DRAMs, the allowable value of the blur amount of an electron beam on the exposure surface is 20 to 30 nm. Hence, the allowable value of the blur amount due to aberrations of the electron optical system must be set to be equal to or smaller than this value, and a status quo numerical value example of the exposure area is around 0.25 mm×0.25 mm. The throughput in this case is five 8″ wafers/hour, and sufficient performance is not obtained in terms of productivity (J. Alexander Liddle et al., Jpn. J. Appl. Phys. Vol. 34 (1995) pp. 6663-6671).
As for the intensity of the electron beam, the electron gun requires an emittance of around 10
−5
to 10
−4
(cm•rad) if off-axis aberrations can be reduced and the exposure area is several ten mm square. This value is one to two orders of magnitudes larger than that obtained by a LaB6 emitter electron gun used in the electron beam exposure apparatus. Therefore, when the exposure region is broadened while prescribed current density conditions of the electron gun determined by the resist sensitivity and stage scanning speed are satisfied, the intensity of the electron beam is limited by the emittance of the electron gun. Hence, a sufficiently high electron beam intensity cannot be obtained if the exposure region is broadened.
As described above, in the conventional electron beam exposure apparatus, it is hard to broaden the exposure region while maintaining the electron beam intensity required for obtaining a throughput with high productivity.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has as its object to provide an electron beam projection exposure apparatus which can obtain a large exposure width while maintaining an electron beam intensity required for exposure.
An electron beam projection exposure apparatus according to one aspect of the present invention comprises an electron gun, and a projection lens for projecting, onto a wafer, an electron beam which has been emitted by the electron gun and transmitted through a mask, and an intensity distribution of the electron beam emitted by the electron gun in a section perpendicular to an optical axis includes a ring-shaped region as a high intensity region.
According to a preferred embodiment of the present invention, the electron gun preferably has an electron source, an electron emission surface of which has a circularly recessed central portion.
According to a preferred embodiment of the present invention, the electron gun preferably has an electron source, an electron emission surface of which has a circularly recessed central portion and a ring-shaped peripheral portion.
According to a preferred embodiment of the present invention, the electron beam projection exposure apparatus preferably further comprises a slit member which is inserted between the electron gun and mask, and has a slit for shaping a sectional shape of the electron beam emitted by the electron gun.
According to a preferred embodiment of the present invention, the slit preferably has an arcuated shape.
According to a preferred embodiment of the present invention, the slit preferably has a shape defined by two arcs which substantially have the optical axis as a center.
According to a preferred embodiment of the present invention, the electron beam projection exposure apparatus preferably further comprises an electron optical system which is inserted between the electron gun and mask and irradiates an image formed by the electron beam group transmitted through the slit onto the mask while magnifying the image to a predetermined size.
According to a preferred embodiment of the present invention, the electron optical system preferably includes a condenser lens and field lens.
According to a preferred embodiment of the present invention, the slit member is preferably located in the condenser lens.
According to a preferred embodiment of the present invention, the electron beam projection exposure apparatus preferably further comprises a control circuit for adjusting a size of an image formed by the electron beam irradiated onto the mask by controlling the electron optical system.
According to a preferred embodiment of the present invention, the electron beam projection exposure apparatus preferably further comprises a measurement device for measuring a current distribution of the electron beam which becomes incident at a position of the mask, and the control circuit operates on the basis of a measurement result of the measurement device.
According to a preferred embodiment of the present invention, the electron beam projection exposure apparatus preferably further comprises a bias circuit for adjusting a bias voltage to be applied to the electron gun.
According to a preferred embodiment of the present invention, the electron beam projection exposure apparatus preferably further comprises a measurement
Berman Jack
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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