Radiant energy – Irradiation of objects or material – Ion or electron beam irradiation
Reexamination Certificate
2000-03-23
2003-06-03
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Ion or electron beam irradiation
C250S492200
Reexamination Certificate
active
06573520
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron beam lithography system for drawing circuit patterns to a wafer and a mask by utilizing the electron beam and particularly to an electron beam lithography system which is just suitable for shortening the drawing time and improving the rate of the apparatus operation.
2. Description of the Related Art
In an electron beam lithography system, an X-Y stage for moving a sample is required to draw a pattern on the entire part of the sample such as wafer and mask because the drawing area of the sample on which a pattern is drawn is larger than the deflection range of electron beam. Moreover, since the drawing by the electron beam is conducted under the vacuum condition, the XY stage must be placed within a vacuum chamber which is called a stage-chamber.
In the electron beam lithography system, two or more vacuum chambers are necessary to realize effective pattern drawing, because the stage chamber has a large volume and longer time will be required until the predetermined degree of vacuum required for drawing by electron beam can be attained from the atmospheric condition. Therefore, in an ordinary electron beam lithography system, the stage chambers maintain the low pressure atmosphere and the other chambers change the atmosphere of sample for the vacuum/atmospheric conditions.
Structure of such electron beam lithography system will be explained with reference to
FIGS. 10 and 11
.
FIG. 10
is an upper cross-sectional view illustrating an example of structure of an electron beam lithography system of the related art.
FIG. 11
is a side cross-sectional view of an electron beam lithography system of FIG.
10
.
This example is described in the “Journal of Vacuum Science and Technology B, Vol. 10, No.6, November/December 1992, P.2759” and is composed of three vacuum chambers.
In this technology, a sample exchange chamber
12
and an evacuation chamber
20
are also provided in addition to the stage chambers
2
a
. In the sample exchange chamber
12
provided adjacently to the stage chamber
2
a
via a vacuum valve
11
, two sheets of sample having completed or not completed the drawing are loaded by a loader mechanism consisting of an elevator
14
or the like while the evacuation atmosphere is maintained for the purpose of cross-exchange. The inside of this sample exchange chamber
12
has the structure to accommodate two sheets of sample and this chamber is moved upward and downward for selection of samples.
Moreover, in the evacuation chamber
20
adjacent to the sample exchange chamber
12
via a vacuum valve
13
, the work for evacuating the sample to the predetermined degree of vacuum condition from the atmospheric condition with a vacuum pump
22
or the work for returning the sample which has completed the drawing to the atmospheric condition with a leaking valve
21
are conducted.
With employment of such structure, the time required for the work to increase or evacuate the pressure between the vacuum condition and atmospheric condition and for loading of sample can be shortened and thereby the total number of sheets of samples for the drawing process of the electron beam lithography system can be increased.
Next, sample loading profiles will be explained. When a wafer
26
is used as the sample, following two kinds of techniques are proposed to load the sample to the stage chamber
2
a
from the evacuation chamber
20
. One is a direct wafer loading technique to load independently the wafer
26
placed on a top table
5
of the XY stage from the evacuation chamber
20
and the other is a pallet loading technique to load the wafer
26
together with a pallet
18
to the stage chamber
2
a
from the evacuation chamber
20
by providing a plate type board called the pallet within the evacuation chamber
20
and then placing the wafer
26
on the pallet
18
.
In the examples of FIG.
10
and
FIG. 11
, the wafer
26
is loaded together with the pallet
18
, while the wafer
26
is placed on the pallet
18
, between the stage chamber
2
a
and sample exchange chamber
12
using three pallets
18
.
However, the in-vacuum loading technique using such pallet
18
has following problems to be solved.
1) A pallet
18
is heavy and loading velocity is lowered.
Namely, a recent pallet
18
is provided with an electrostatic chuck to attract the wafer
26
. Since this electrostatic chuck is formed of ceramics which is mainly composed of alumina or the like, it is heavier in several times or several tens of times the weight of the wafer
26
. In addition, since the chuck is also provided with a ground pin
6
and a rotation positioning mechanism
8
of the wafer
26
, the weight of the pallet
18
reaches, as a result, about 1 kg to 5 kg. Therefore, it is difficult to realize the loading velocity identical to that for independently loading a wafer
26
and it has been considered as a cause for drop of total throughput of the electron beam lithography system.
2) Compatibility among the pallets
18
, namely error of warp of the wafer
26
during the holding thereof will give influence on the drawing accuracy.
In other words, an electrostatic chuck attracts the wafer
26
along the chuck surface, however, if a plurality of sheets of pallet
18
are used, differences in shape of attracting surface of electrostatic chuck among each pallet
18
and in mounting positions of structural elements give influence on reproducibility among wafers
26
of alignment accuracy to lower the accuracy.
The technique to load in direct the wafer
26
is capable of taking an adequate measure to such problem. In this technique, throughput can be improved because the sample loading velocity can be improved.
Moreover, since a plurality of pallets are not used, the wafer attracting surface always becomes constant on the XY stage and warp of the wafer due to the difference in the processing shape of attracting surface of each pallet is eliminated, drawing alignment accuracy can also be improved.
However, the technique to load in direct the wafer
26
also has the following problem.
3) Exchange of ground pin
6
lowers the rate of the apparatus operation.
In other words, if unwanted electric field or magnetic field is generated in the area near the trajectory of electron beam in the electron beam lithography system, the electron beam is bent to result in the fault of drawing pattern. Therefore, the sample must be kept within the equal potential. Therefore, the sample surface is maintained in the equal potential by pricking the sample with a stylus type projection called a ground pin
6
.
However, in the course of drawing the patterns on many samples, the end point of the ground pin
6
is worn out not to maintain the equal potential. Therefore, the ground pin
6
must be exchanged periodically. Since this ground pin
6
is set on the XY stage, the stage chamber
2
a
must be set to the atmospheric condition on the occasion of replacing the ground pin. Accordingly, the rate of the apparatus operation may be lowered.
4) It is difficult to remove particles deposited on the electrostatic chuck.
Namely, the wafer
26
must be fixed on the X-Y stage at the time of drawing a pattern, but there is an example that warp of 50 &mgr;m or more is generated on the wafer
26
coming to electron beam lithography process. If the wafer
26
warped as explained above is fixed for the drawing purpose, the alignment accuracy will be lowered. Therefore, an electrostatic chuck utilizing the electrostatic attracting phenomenon is used in order to fix such wafer under the good flatness condition.
However, if particles are adhered on the surface of electrostatic chuck, the wafer
26
is deformed to lower, on the contrary, the accuracy. In this case, therefore, the particles must be removed from the surface of chuck. The stage chamber
2
a
is also required to be set under the atmospheric condition while the particles are removed. Thereby, the rate of the apparatus operation may also be lowered.
The problem to be solved in the electron beam lithogr
Harada Kunio
Satoh Hidetoshi
Sohda Yasunari
Tsuji Hiroshi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Lee John R.
Quash Anthony
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