Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2002-08-09
2003-10-28
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492100, C250S492200, C250S492210, C250S3960ML, C250S281000, C438S510000, C438S514000, C438S506000, C438S527000
Reexamination Certificate
active
06639233
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus and a method for implanting ions on a target, and more particularly relates to the apparatus and the method for preventing impurity ions, which are different from desired ions in at least one of mass number and energy, from being implanted on a target.
2. Description of the Related Art
FIG. 2
shows an example of an ion implantation apparatus of the related art. The ion implantation apparatus includes an ion source
2
having a plasma production chamber
4
for electrostatically extracting ions
8
therefrom, a mass segregation magnet
10
for selectively deriving specific ions (which are specified by a mass number and valence) from the ions
8
extracted from the ion source
2
, an acceleration pipe
12
for electrostatically accelerating the ions
8
derived from the mass segregation magnet
10
, and a momentum segregation magnet
14
for selectively deriving the ions having a specific momentum (which is specified by a mass number and energy) from the ions
8
derived from the acceleration pipe
12
. The ion implantation apparatus is constructed so that only the desired ions derived from the momentum segregation magnet
14
are implanted on a target (e.g. substrate such as a semiconductor wafer)
16
.
The target
16
is held on a holder
18
at a ground potential. A scanner for scanning ions
8
and others not shown are usually provided between the momentum segregation magnet
14
and the target
16
. A path of the ions
8
from the outlet of the ion source
2
to the holder
18
is included in a vacuum chamber. The vacuum chamber is not shown.
The ion source
2
includes the plasma production chamber
4
for generating plasma and an extraction electrode
6
for extracting the ions
8
. The plasma production chamber has a positive potential, and then an extraction voltage V
E
applied therebetween from a DC extraction electrode
20
. The ions
8
are electrostatically generated from the plasma production chamber
4
by the extraction voltage.
The acceleration pipe
12
has a plurality of electrodes
13
. The acceleration pipe
12
has a positive potential, and then a voltage V
A
is applied between an inlet and outlet electrode
13
from a DC accelerating power source
22
. The ions
8
are electrostatically accelerated by the accelerating voltage V
A
so that the ions
8
has target energy.
Assuming that the valence of the desired ions is Z
I
, the total energy E
T
of the desired ions incident on the target
16
is expressed by the following equation.
E
T
=(
V
E
+V
A
)×
Z
I
[eV]
[Equation 1]
Since the following phenomenon occurs between the outlet of the mass segregation magnet
10
and the inlet of the acceleration pipe
12
, impurity ions which are different from the desired ions may be mixed into the desired ions in the ion implantation apparatus.
(1) The energy accelerated by the acceleration pipe
12
is changed by charging conversion in which the desired ions collide with a residual gas. For example, when doubly charged ions are converted into singly charged ions by the charging conversion, the energy accelerated by the acceleration pipe
12
becomes half of that in the case of the doubly charged ions, if the Voltage V
A
is constant.
(2) Where the desired ions are molecular ions, by molecular dissociation, the desired ions change into different ions. For example, when BF
2
ions dissociate into BF ions and F ions, or B ions and F ions, the BF
2
ions no longer are the desired ions.
(3) A part of the ions
8
collides with the member which constitutes an apparatus such as the vacuum chamber so that atoms or molecules of the member are out of the surface of the member by a sputtering to become impurity ions.
(4) A part of the ions
8
collides with the member which constitutes an apparatus such as the vacuum chamber so that atoms or molecules deposited on or implanted in the member during previous operation of the ion implantation apparatus are out of the member surface by sputtering to become impurity ions.
(5) The gas or vapor used to generating plasma in the plasma production chamber
4
of the ion source
2
flows out from the plasma production chamber
4
into a passage of the ions
8
, and then the flown gas or vapor is ionized on the passage to the inlet of the acceleration pipe
12
, or otherwise the flown gas or vapor reacts with the atoms or molecules generated owing to the phenomena of the above items (3) and (4) thereby to become impurity ions.
In the ion implantation apparatus, it is not desired that the impurity ions which are different from the desired ions in at least one of mass number and energy are implanted into the target
12
together with the desired ions. Accordingly, a desired implantation characteristic of the target cannot be obtained.
Therefore, when ion implantation with high purity is required as in the example shown in
FIG. 2
, the momentum segregation magnet
14
as described above as well as the mass number segregation magnet
10
is provided behind the acceleration pipe
12
in order to derive only the ions having a specific momentum selectively.
The momentum segregation magnet
14
permits the impurity ions generated by the phenomena of the above items (1) and (2) to be removed. The impurity ions having a different momentum from that of the desired ions are generated in the phenomena of (1) and (2).
However, in case the impurity ions are generated by the phenomena of the above items (3) to (5), the impurity ions which satisfy the following Equation 2 cannot be separated and removed from the desired ions by means of the momentum segregation magnet
14
. This applies to the case where the left side≈the right side in Equation 2 (that means, the left side of the Equation 2 is equal or about equal to the right side thereof). Now it is assumed that M
T
denotes the mass number of the desired ions, Z
I
denotes the valence thereof, M
C
denotes the mass number of the impurity ions at issue, and Z
C
denotes the valence thereof. V
E
and V
A
have been already defined.
M
I
·(V
E
+V
A
)/Z
I
=M
C
·V
A
/Z
C
Assuming that B is a magnetic flux density, V
T
is an entire acceleration voltage, m is a mass, and q is a charge, the circling radius R of the ions in the momentum segregation magnet
14
is expressed by a following Equation 3. Now, assuming that M is the mass number of the ions and m
P
is the mass of a proton, m=M·m
P
. Further, Z is the valence of the ions and e is an electron weight, q=Z·e. In short, Equation 3 implies that the ions with the same M·V
T
/Z provides the same circling radius R.
R=B
−1
{square root over ((2
mV
T
/q
))} [Equation 3]
Therefore, if the above Equation 2 is satisfied, in the momentum segregation magnet
14
, the circling radii of the desired ions and impurity ions are equal to each other, both cannot be separated from each other. As a result, even with the momentum segregation magnet
14
, the impurity ions as well as the desired ions are implanted into the target
16
. This applies to the case where the left side≅the right side of the Equation 2 (that means, the left side of the Equation 2 is equal or about equal to the right side thereof).
A case where the valence Z
I
of the desired ions and the valence Z
C
of the impurity ions at issue are equal to each other (i.e. where Z
I
=Z
C
) is typical. For example, both are singly charged ions. In this case, the above Equation 2 can be represented by the following equation.
M
I
·(
V
E
+V
A
)=
M
C
·V
I
[Equation 4]
If the ion implantation is carried out for the target
16
on the condition of the Equation 4, the desired ions as well as the impurity ions will be implanted into the target
16
. This applies to the case where the left side≅the right side (that means, the left side of the Equation 2 is equal or about equal to the right side thereof). Such implantation is not preferable.
It can be supposed that the m
Finnegan Henderson Farabow Garrett & Dunner LLP
Lee John R.
Nissin Electric Co. Ltd.
Souw Bernard E.
LandOfFree
Apparatus for implanting an ion on a target and method for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for implanting an ion on a target and method for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for implanting an ion on a target and method for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3146591