Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-09-08
2003-01-14
Anderson, Bruce (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S491100, C250S397000
Reexamination Certificate
active
06507034
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-257280, filed Sep. 10, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a charge beam exposure apparatus, a charge beam exposure method, and an charge beam exposure mask for adjusting beams and exposing patterns according to patterns to be exposed.
Conventionally, a character projection exposure system (referred to hereafter as a CP exposure system) and a scanning exposure system are designed as exposure systems using an electron beam.
First, the following explains the CP exposure system using a schematic diagram in FIG.
1
. As shown in
FIG. 1
, a region as large as several micrometers including a plurality of figures is formed as CP apertures
101
a
through
101
e
on a second formation aperture
101
. The CP exposure system collectively exposes these CP apertures
101
a
through
101
e
. This exposure system is assumed to be promising as means for improving throughput. Specifically, an electron beam irradiated from an electron gun
11
is formed to a specified shaped through a first aperture
13
. The shaped electron beam enters a second aperture
101
. Specified CP apertures
101
a
through
10
l
e
are selected from the second aperture
101
, forming an electronic image having a pattern composed of the selected CP apertures
101
a
through
101
e
. This electronic image is collectively exposed on a wafer
19
.
When the CP exposure is used, a total electric current amount for beams varies with an opening area or an area for collective exposure. When a CP aperture which is 5 by 5 micrometers square is used for exposure, for example, a focus position fluctuates approximately up to 30 micrometers compared to an ordinary Variable Shaped Beam (VSB). Accordingly, the CP exposure requires the focus position optimization which is unnecessary for the VSB system.
For example, Jpn. Pat. Appln KOKAI Publication No. 2837515 discloses a beam adjustment method for such an electron beam exposure apparatus.
FIG. 2
shows a structure of the second aperture used for the adjustment method described in this Jpn. Pat. Appln KOKAI Publication. A second aperture
201
is provided with a rectangular aperture
203
and an optical axis adjustment opening
204
in addition to a pattern exposure opening
202
. In the conventional method, the optical axis adjustment opening
204
is used to adjust an optical axis.
However, this beam adjustment method has the following problems.
The conventional method uses an optical axis adjustment opening
204
to perform a beam adjustment for adjusting a beam focus and a beam deflection amount depending on a change in beam currents by varying an amount of beams that pass through rectangular apertures
203
.
However, this beam adjustment method is available only when an unsimplified electro-optic system is used.
FIG. 3A
illustrates an apparatus structure for an unsimplified electro-optic system.
FIG. 3B
illustrates an apparatus structure for a simplified electro-optic system. These figures use an electron gun
161
, a capacitor lens
162
, a first aperture
163
, a formation lens
164
, a second aperture
165
, a reduction lens
166
, an objective lens
167
, and a sample
168
.
The simplified electro-optic system in
FIG. 3B
can be used when the scanning exposure system is used or the CP system is used for exposing all patterns. Namely, when the scanning exposure system is used or the CP system is used for exposing all patterns, it is unnecessary to form a first aperture image on a second aperture image. Accordingly, the formation lens
164
in
FIG. 3A
is unnecessary.
Here, an external edge of a rectangular aperture is referred to as an aperture edge. An edge of an electron beam is referred to as a beam edge. For decreasing a beam amount, a beam is irradiated to only part of the aperture edge. When the beam is irradiated so as to overlap the rectangular aperture, the beam edge is shaded by the rectangular aperture. When the beam is irradiated to only part of the aperture edge, the electron beam at the beam edge is also transferred onto the wafer
19
. A beam at this beam edge is defocused on the wafer
19
. This beam defocusing degrades the beam adjustment accuracy. Namely, the conventional beam adjustment is applicable only for the electro-optic system in
FIG. 3A
, in which the formation lens
164
is used for forming the first aperture image and the projection lens
166
and the objective lens
167
are used for forming the second aperture image on the sample surface. Apparently, the method in
FIG. 3A
is incapable of a beam adjustment according to variations in beam current amounts for the optical system in FIG.
3
B.
The following describes a second problem with reference to
FIGS. 4A and 4B
. When the exposure apparatus in
FIG. 1
is used for beam adjustment, a heavy metal dot
111
in
FIG. 4A
is provided on the wafer
19
or a stage (not shown) where the wafer
19
is placed. A CP-shaped electron beam
12
is applied to this heavy metal dot
111
through the use of surface scanning. The electron beam
12
is irradiated to shaded regions. An operation is performed to find a two-dimensional beam intensity distribution obtained by this surface scanning. Further, an operation is performed to find an ideal two-dimensional beam intensity distribution.
After the surface scanning, a beam adjustment is performed using this ideal intensity distribution as a template based on the actually obtained beam intensity distribution and the correlational method. Alternatively, it is possible to perform a beam adjustment and the like with respect to an edge position of the electron beam
12
.
FIG. 4B
shows a two-dimensional intensity distribution of a reflected electron signal. The abscissa axis represents beam scanning positions. The ordinate axis represents reflected electron signal amounts.
However, the use of the above-mentioned signal processing method creates the following problem. Compared to the ordinary VSB, it takes a long time to find a two-dimensional beam intensity distribution using the surface scanning. Further, when the focus position is displaced for dozens of micrometers, not only the focus, but also a beam position or a beam rotation is affected. Consequently, the beam adjustment requires a lot of additional works.
To solve these problems, a method is designed to form a pattern having the same shape as the electron beam shape on the sample surface and to detect marks and adjust beams using this pattern. This method is examined with respect to an electron beam exposure apparatus for the scanning exposure system.
FIGS. 5A and 5B
illustrate this beam adjustment method. As shown in
FIG. 5A
, the electron beam
12
is scanned in the direction of an arrow with reference to a CP alignment mark
121
formed on the sample surface. Then an operation is performed to find an intensity distribution for reflected electron signals before and after the electron beam
12
passes the CP alignment mark
121
. The electron beam
12
is irradiated to a shaded region which is same as a pattern shape of the CP alignment mark
121
. As shown in
FIG. 5B
, a resulting reflected electron signal becomes maximum when the CP alignment mark
121
completely coincides with the electron beam
12
. Applying this beam adjustment method to beam adjustment, say, for CP exposure eliminates at least the need for the surface scanning and accompanying image processing and the like, making the beam adjustment simple.
However, when there are more than 100 types of CP apertures, for example, the beam adjustment for CP exposure would consume a vast amount of time in view of different numerical apertures or CP areas.
The following describes problems in the scanning exposure system.
FIG. 6A
is a schematic diagram of the scanning exposure system. The scanning exposure system exposes the electron beam
12
irradiated from the electron gun
11
on the
Anderson Bruce
Kabushiki Kaisha Toshiba
LandOfFree
Charge beam exposure apparatus, charge beam exposure method,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Charge beam exposure apparatus, charge beam exposure method,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Charge beam exposure apparatus, charge beam exposure method,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3009870