Radiant energy – Irradiation of objects or material – Ion or electron beam irradiation
Reexamination Certificate
2000-11-29
2003-12-02
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Ion or electron beam irradiation
Reexamination Certificate
active
06657212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an electron beam measurement method that measures the amount of electron beams radiated from a vacuum tube type of electron beam tube that is used in curing resists applied to semiconductor wafers, etc. and in drying ink applied to various types of printed material. The present invention also relates to an electron beam irradiation processing device that processes aforementioned processed material by irradiating it with electron beams.
2. Description of Related Art
The use of electron beam irradiation has been proposed to cure resists applied to semiconductor wafers as well as to dry or cure paint, ink, adhesive, protective resin, etc., applied to substrates.
In recent years, electron beam tubes provided with a window have been marketed. The structure of such electron beam tubes comprises a thermo-ionic unit and an electron beam acceleration unit mounted in a vacuum container provided with a window which is permeable to electron beams. The thermo-ionic electrons radiated from the thermo-ionic unit are accelerated by an electron beam acceleration unit and radiated.
Electron beams are radiated into the atmosphere from the window when such an electron beam tube is used. Conventional electron beam irradiation processing devices have depressurized the atmosphere in which the irradiated material is disposed. However, this is unnecessary when using aforementioned electron beam tube thereby eliminating the need for vacuum pumps and vacuum chambers for depressurization, and consequently, simplifying the structure of the electron beam irradiation processing device.
FIG. 7
is a diagram that shows the diagrammatic structure of a vertical type of electron beam tube provided with a window (hereinafter abbreviated EB tube) and its power source circuit.
EB tube
1
is provided with filament
1
a
and grid
16
. High voltage of 30 to 70 kV, for example, is applied to filament
1
a
and grid
1
b
from direct current high-voltage power source
2
via terminal
1
f
. Furthermore, filament power source
3
is connected to filament
1
a
via terminal
1
f
. Filament
1
a
is heated by current that is provided from said filament power source
3
and thermo-ionic electrons are radiated. Electrons that are radiated are arranged in beam shape by an electric field that is created by grid
1
b
. In addition, grid power source
4
is connected to grid
1
b
via terminal
1
f
and electron emission from grid
1
b
can be controlled by controlling the voltage that is applied to grid
1
b.
The arranged electron beam (hereinafter termed “electron beam”) is output outside of EB tube
1
from window
1
d
that is set in flange
1
c
. The electron beams that are output from EB tube
1
are irradiated on processed material such as semiconductor wafers that are not illustrated or on various types of printed material to complete curing of resists or drying of ink, etc.
EB tube
1
has a sealed structure comprising quartz tube wall
1
e
, flange
1
c
and window
1
d
. The internal pressure is depressurized to 10
−4
to 10
−6
Pa (10
−6
to 10
−8
Torr) to ensure that the electron beams that were created are not attenuated.
Window
1
d
is a film of special material containing silicon of several &mgr;m thickness (for example, 3 &mgr;m) to ensure that the electron beams are not attenuated while passing through the window
1
d.
The electron beams that are created can be output outside of EB tube
1
more efficiently by enlarging the area of window
1
d
. However, the window is extremely thin (several &mgr;m), as indicated above, and it must serve as a partition between the atmospheric pressure outside of EB tube
1
and the pressure (10
−4
to 10
−6
Pa) within EB tube
1
. Accordingly, the area of one window cannot be too large because of the danger of breakage. Thus, a plurality of windows, each having a small area with a size of 1 to 2 mm per side, are aligned in the longitudinal direction of the filament so as to match the shape of the electron beams, as shown in FIG.
8
.
A prescribed amount of electron beams must be irradiated onto processed material when processing the processed material (workpiece) using electron beams that are output from EB tube
1
. If the processed material is not irradiated with the prescribed amount of electron beams and the amount of irradiation is inadequate or excessive, the processing of the processed material would fail.
The following two methods of outputting a fixed amount of electron beams have been available. Both effect controls so that a fixed amount of power is provided to EB tube
1
.
[1] Method of control in which the tube current is detected and controlled so as to be constant. This is a method in which the tube current (the current flowing from direct current high-voltage power source
2
to EB tube
1
in
FIG. 7
, denoted by broken line in the diagram) is detected by current detection unit
5
and is controlled so as to be constant by controlling the current flowing through filament
1
a
, as shown in FIG.
7
. This is control in which the power supplied to EB tube
1
is kept constant by holding the tube current constant so long as the voltage of direct current high-voltage power source
2
is constant. This method is usually used in X-ray tubes.
[2] Method in which the filament input power is held constant. This is a method in which the power input to filament
1
a
is controlled to be constant by controlling the current (and the voltage of filament
1
a
) that flows through filament
1
a
. The amount of thermo-ionic electrons that are emitted is controlled by controlling the power of filament
1
a
to be constant. More specifically, the tube current is controlled to be constant and the power supplied to EB tube
1
is held constant. Despite the control methods described above, the amount of electron beams output from EB tube
1
changes even if the tube current is controlled to be constant and a fixed level of power is supplied to EB tube
1
, as shown in FIG.
7
. The present inventors believe that the reasons for this are follows:
[1] Filament
1
a
and grid
1
b
within EB tube
1
are fixed within so that their positions would not change. However, the shapes of the filament
1
a
and of the nearby grid
1
b
change due to thermal expansion since the temperature of the heated filament reaches about 1900° C. during thermo-ionic electron output.
[2] The shape and direction of the electron beams change due to the effects of the electrostatic charge that develops within the tube.
As mentioned above, window
1
d
that captures electron beams outside of EB tube
1
comprises a set of windows about 1 mm wide, each aligned in the longitudinal direction of the filament. Accordingly, electron beams are emitted beyond window
1
d
when the shape and direction of the generated electron beams change within EB tube
1
for aforementioned reasons [1] and [2], and those electron beams are no longer captured. As a result, the amount of output electron beams changes.
Accordingly, the present inventors believe that even if EB tube
1
could be controlled so that a constant power would be provided, the amount of electron beams output from EB tube
1
could not be held constant.
Therefore, there exists an unfulfilled need for an electron beam irradiation processing device and a method of control thereof that overcomes the above noted disadvantages.
SUMMARY OF THE INVENTION
The present inventors have found that the amount of electron beams could be controlled to be constant if the power supplied to EB tube
1
could be controlled in a manner that the amount of electron beams output from EB tube
1
were constant by measuring this electronic beam output from the EB tube
1
. However, no method of accurately measuring the amount of electron beams output from EB tube
1
had been available. In particular, the atmospheric gases turn into plasma as a result of electron beam irradiation, resulting in secondary
Komori Minoru
Yamaguchi Masanoru
Lee John R.
Nixon & Peabody LLP
Safran David S.
Smith II Johnnie L
Ushiodenki Kabushiki Kaisha
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