Ion implanter with impurity interceptor which removes...

Details Ion implanter with impurity interceptor which removes... Ion implanter with impurity interceptor which removes...

1999-01-21

2001-01-23

Nguyen, Kiet T. (Department: 2881)

Radiant energy

Irradiation of objects or material

Irradiation of semiconductor devices

Reexamination Certificate

active

06177679

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ion implanter for use in semiconductor manufacturing, and more particularly to an ion implanter equipped with an interceptor which intercepts undesired impurities in an ion beam.
2. Background of the Related Art
An ion implantation process, which facilitates control of impurity concentration and junction depth, is widely used to form an impurity layer in a semiconductor device, e.g., a source/drain area of a transistor. The ion implantation process involves ionizing a gas containing desired impurities, accelerating the ionized impurities, and implanting the result into a predetermined area of a semiconductor wafer.
Referring to
FIG. 1
, in a conventional ion implanter, an ion beam emitted from an ion source
10
passes through a pre-analyzing magnet
12
to remove undesired types of ions. Since ions having identical energies in a magnetic field exhibit different bending effects due to their mass, only those beams of the desired ions pass through the pre-analyzing magnet
12
.
After passing through the pre-analyzing magnet
12
, the ion beam is accelerated to a desired energy by an accelerator
14
. Meanwhile, negative ions accelerated by the accelerator
14
reach a stripper canal (not shown). Here, the negative ions are changed into positive ions by a charge exchange process involving collisions with a gas such as N
2
gas. The positive ions pass through a post-analyzing magnet
16
and finally reach a wafer
18
.
However, during the ion implantation process, undesired impurities can be generated at a main acceleration portion of the accelerator
14
. The impurities generally have a different radius of curvature as compared to the high energy ion beam in the post-analyzing magnet
16
, so that they are prevented from reaching the wafer
18
. However, on occasion, the product of the mass M and the energy E of some impurities can be the same as that of the ion beam. In such cases, since the impurities have the same radius of curvature as the ion beams, they are likely to pass through the post-analyzing magnet
16
and reach the wafer
18
. For example, impurities accelerated to several tens of kilo electron volts (KeV) can have the same radius of curvature as ions accelerated to hundreds of KeV, depending on the type of impurities. Thus, undesired impurities can pass through the post-analyzing magnet
16
.
Even if the impurities reach the wafer
18
, it is not easy to verify the arrival of the impurities. Also, even if only a very small amount of undesired impurities reach the wafer
18
and are present on the surface of the wafer
18
, the undesired impurities can degrade the quality of a gate oxide film formed thereon and cause the gate oxide film to grow to an undesired thickness. As a result, the reliability of the semiconductor device is deteriorated, and the yield is reduced.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide an ion implanter including an impurity interceptor for preventing impurities from reaching a wafer.
Accordingly, to achieve the above objective, there is provided an ion implanter comprising: an ion source for producing an ion beam which is to be implanted into a wafer; an accelerator for accelerating the ion beam; and an impurity interceptor installed downstream of the accelerator, for intercepting impurities generated in the accelerator to prevent the impurities from reaching the wafer. It is preferable that the accelerator is a tandem accelerator.
The impurity interceptor comprises an intercepting plate installed in a path of the ion beam, and a high voltage power supply having an output port electrically connected to the intercepting plate. Here, a high voltage output from the high voltage power supply is applied to the intercepting plate in the form of a floating voltage. Also, the intercepting plate has an opening formed at its center for allowing desired ions in the ion beam to pass.
The impurity interceptor is located in the path of the ion beam, and may be self-contained, or may be installed in an output portion of the accelerator.
The ion implanter further comprises a pre-analyzing magnet and a post-analyzing magnet. The pre-analyzing magnet is installed between the ion source and the accelerator. The post-analyzing magnet may be installed downstream of the impurity interceptor, or the post-analyzing magnet may be installed between the accelerator and the impurity interceptor.


REFERENCES:
patent: 5130552 (1992-07-01), Bright et al.
patent: 5134307 (1992-07-01), Kamata et al.
patent: 5300891 (1994-04-01), Tokoro
patent: 5306922 (1994-04-01), O'Connor
patent: 5311028 (1994-05-01), Glavish
patent: 5438203 (1995-08-01), Glavish et al.
patent: 5932882 (1999-08-01), England et al.
patent: 9-115850 (1997-05-01), None
patent: 92-18839 (1992-09-01), None

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