Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2003-02-26
2004-06-22
Wells, Nikita (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S251000, C250S492300
Reexamination Certificate
active
06753539
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ion implantation apparatus and an ion implantation method.
2. Description of the Related Art
The following will describe a typical configuration of an ion implantation apparatus with reference to FIG.
1
. In
FIG. 1
, ions are extracted as an ion beam
52
by an extraction electrode
51
from an ion source
50
. The extracted ions are analyzed by a mass analysis magnet
53
and a resolving aperture member
54
and a required ion species is selected. The selected ions are implanted into a wafer
55
. The resolving aperture member
54
serves as a mass analysis slit. On a beam line, a shower tube
56
for showering plasma is arranged between the resolving aperture member
54
and the wafer
55
. The shower tube
56
is mounted with an arc chamber
57
. The arc chamber
57
has an opening therein which faces the beam line side. A Faraday cup
58
for use in measurement of a beam current is provided in such a manner that it can advance onto and retreat from the beam line. That is, the Faraday cup
58
is placed on the beam line when the ion beam is set up (as indicated by a dash-and-dot line in
FIG. 1
) and placed off from the beam line at the position of a solid line in
FIG. 1
when the ions are being implanted. On the back side of the wafer
55
, a Faraday cup
59
is arranged so that measurement may be possible during ion implantation.
FIG. 2
is an enlarged view for showing the downstream side of the resolving aperture member
54
in FIG.
1
. Although not shown in
FIG. 1
, components shown in
FIG. 1
are arranged in a vacuum chamber
60
as shown in FIG.
2
. The arc chamber
57
incorporates therein a filament
57
-
1
. To the filament
57
-
1
are there connected a filament power source
57
-
2
and an arc power source
57
-
3
. Furthermore, the arc chamber
57
is arranged in such a manner that a predetermined gas can be introduced into it from a gas supply system
57
-
4
. The shower tube
56
, the arc chamber
57
, and the arc power source
57
-
3
are each connected to the ground. In this configuration, in the immediate vicinity of the downstream side of the resolving aperture member
54
is there arranged at least one aperture member
61
. The Faraday cup
58
can be advanced onto and retreated from the beam line by a drive device
63
which is mounted outside the vacuum chamber
60
.
The following will describe a method of extraction of electrons from the plasma shower. The electrons are specifically extracted from the plasma shower as follows.
(1) Generation of Arc
When a large current is flown through the filament
57
-
1
, the filament
57
-
1
is heated to 2000° C. or higher, to emit thermions. The arc chamber
57
is supplied with a gas such as Ar from the gas supply system
57
-
4
and also supplied with an arc voltage of a few tens of volts with respect to the filament
57
-
1
. Then, the thermions are accelerated to collide with atoms of the gas, thus generating new thermions. This electron amplification action generates plasma between the filament
57
-
1
and the arc chamber
57
.
(2) Extraction of Electrons by Use of Beam Potential
When an ion beam passes by outside the opening in the arc chamber
57
in a condition where plasma is being generated stably in the arc chamber
57
, a positive potential of the ion beam extracts electrons from the plasma which is present in the arc chamber
57
. These extracted electrons are accelerated toward the ion beam. These electrons collide with neutral gas atoms which have not been ionized in the arc chamber
57
and ejected through the opening in the arc chamber
57
, thus generating plasma again between the arc chamber
57
and the ion beam. This is called a plasma bridge (which is indicated by a reference numeral
65
) and has an effect of supplying the ion beam with such a quantity of electrons as to exceed a space charge limited current.
Next, characteristics of extraction of electrons from a plasma shower are described. For example, if the magnitude of a beam current increases, the positive potential of the ion beam increases. As a result, the quantity of electrons which are extracted from the arc chamber
57
increases, thus increasing also the quantity of electrons which are supplied to the ion beam. By such autonomous control, in a plasma shower system, electrons which are abundant enough to neutralize the positive charge of the ion beam are extracted from the plasma shower, thus restraining the positive charging of the wafer
55
. That is, the plasma shower system comprised of the shower tube
56
and the arc chamber
57
serves as a charge neutralization apparatus which is for restraining charge.
The following will describe various problems of the above-mentioned conventional technologies.
(1) Effects of Ion Beam Diameter
An ion implantation apparatus employs an ion beam of a variety of ion species, energy levels, and beam currents. The diameter of such an ion beam varies with beam conditions and beam generating conditions.
The arc chamber
57
is mounted at such a position that it may not be collided with an ion beam which has the maximum design diameter. This is done so in order to prevent such a problem from occurring that the beam current would decrease or particles would be generated if the ion beam collides with the arc chamber
57
.
If a beam diameter D
1
varies at the position of the arc chamber
57
, a distance between the opening in the arc chamber
57
and the ion beam also varies and hence the magnitude of an electric field varies. Accordingly, if the beam diameter D
1
varies, the quantity of electrons which are supplied to the ion beam varies. For example, if such beam conditions are applied that the beam diameter D
1
is liable to decrease, there occurs an insufficiency in quantity of electrons which are supplied from the plasma shower, thus making it impossible to sufficiently suppress positive charging of the wafer
55
in some cases. In order to solve this problem, there may be considered such a method as to vary the power of the plasma shower corresponding to the beam diameter D
1
. This method, however, requires for its implementation a beam diameter measurement mechanism, a feedback circuit, etc., thus complicating the plasma shower system more than necessary.
(2) Effects of Position of the Arc Chamber
57
The plasma shower is normally arranged on the downstream side of the resolving aperture member
54
where the ion beam is converged, for example, between the wafer
55
and a suppression electrode, that is, the aperture member
61
. The plasma shower, however, may be arranged in some cases in the immediate vicinity the wafer
55
so that the wafer may be supplied with electrons easily.
As is clear from
FIG. 2
, a variation d
1
in value of the beam diameter D
1
at the position of the plasma shower increases as the plasma shower becomes more distant from the resolving aperture member
54
in a beam axial direction. Accordingly, as the distance between the arc chamber
57
and the ion beam increases in a condition where the arc chamber
57
is separated from the resolving aperture member
54
, the quantity of electrons which are supplied from the plasma shower becomes insufficient, thus making it impossible to suppress positive charging of the wafer
55
in some cases.
Next, the Faraday cup
58
is described.
(1) Device Layout Along the Beam Line
As described above, on the downstream side of the resolving aperture member
54
is there arranged the Faraday cup
58
to measure a beam current when the ion beam is set up. The Faraday cup
58
is intended to monitor the beam current, to adjust ion source parameters, thus obtaining a desired ion beam. Furthermore, on the downstream side of the Faraday cup
58
, that is, between the Faraday cup
58
and the wafer
55
is there arranged the shower tube
56
to shower plasma, which serves as a charge neutralization apparatus.
When the ion beam is set up completely, the Faraday cup
58
is moved off from the beam line. Then, the ion beam passes through
Arent & Fox PLLC
Sumitomo Eaton Nova Corporation
Wells Nikita
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