Ion beam mass separation filter, mass separation method...

Details Ion beam mass separation filter, mass separation method... Ion beam mass separation filter, mass separation method...

2003-03-04

2004-10-12

Vu, David (Department: 2821)

Radiant energy

Irradiation of objects or material

Irradiation of semiconductor devices

C250S492210, C315S111810

Reexamination Certificate

active

06803590

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ion source used in an ion implanter, and in particular, a mass separation filter for extracting ions with a desired mass provided in the ion source.
2. Related Art
An ion source generates plasma from a gas introduced into a vacuum vessel to extract as an ion beam. It is used in areas such as the introduction of impurities to semiconductors, TFT for liquid crystal, solar cells, and the like, processing through etching and sputter by an ion beam, and furthermore, in deposition and reforming by ions.
In particular, large area ion beams are greatly used in the ion implantation of semiconductors and reforming of materials, obtaining high productivity when producing products such as flat panels on a large scale.
The ion beam for a semiconductor wafer in general ion implantation is smaller than the above ion beams. This ion beam implants only one ionic species undergoing mass spectrometry onto a substrate thereof. To use a large area ion beam in this preferred method, it is necessary to increase scale across the board, but increasing the size of the device is difficult. In addition, large sector dipole magnets used for the wafer would become costly.
As a related art, there is a mass separation device disclosed in Japanese Patent Journal No. 2920847. This device, as shown in
FIG. 7
, includes an incidence plate
31
having a plurality of through holes
30
with mutually parallel axis lines, and an ion incidence plate
33
which is arranged in parallel with the incidence plate and has a plurality of through holes
32
with axis lines at a predetermined angle &thgr; with respect to the axis line of the through holes of the incidence plate
31
. This device is also provided with field generating means B that generates a magnetic field perpendicular to the axis lines of the respective through holes.
With this mass separation device, it is possible to simultaneously separate mass across a wide area since mass separation is performed through only a difference in the curving angle of the ions. However, in this device, the direction of ions incident to the implantation incidence plate differs the direction of the ions emitted from the ion incidence plate, therefore, the incidence direction and the emitting direction of the ion beam passing via an extraction electrode cannot be made uniform, and it is difficult to arrange the plasma electrode, extraction electrode, acceleration electrode, and ground electrode in parallel at the bottom portion of the plasma chamber to extract ions of a desired mass in a fixed direction.
Also, a mass separation system from Aitken is disclosed in the specification of European Patent No. 1090411. In this system, two dipole magnets sequentially placed along a beam axis form a quadrupole type lens. The two magnets are oriented such that their magnetic fields are not parallel and face in opposite directions perpendicular to the beam axis. This quadrupole lens forms a linear ion beam extracted from a slit in the plasma electrode, and ions linearly converge at the exit portion of the lens thereof.
Therefore, since this focus position changes according to ionic mass, mass selection becomes possible and ions with a necessary mass can be separated. However, this device requires a large space, and the beam has a long trajectory direction. The mass separation filter should prevent the beam from impinging on the internal portion of the filter and must collimate, therefore maintaining the beam in parallel is difficult. Accordingly, the space of the ribbon ion beam must be widened, and the horizontal space of the mass separation filter needs to be made larger.
Further, a mass separation filter
40
using a Wien filter that separates mass through the action of electric and magnetic fields is disclosed in Japanese Patent Laid-Open Publication No. 5-82083 (corresponding U.S. Pat. No. 5,189,303 specification). This device, as shown in
FIG. 8A
, has a plasma electrode
41
, an extraction electrode
42
, an acceleration electrode
44
, and a ground electrode
45
arranged on an ion source exit side. The extraction electrode
42
at which ionic speed is at a low stage is constituted by an extraction electrode
42
a
and a mass separation electrode
43
. A Wien filter
50
is respectively provided on each through hole
52
of the extraction electrode
42
a.
Expanding a portion of the extraction electrode
42
a
, as evident in detailed views of
FIG. 8
, a vertical section in
FIG. 8B and a
horizontal section in
FIG. 8C
, it includes magnets
48
disposed facing each other on segmented electrode plates
46
, and structures a Wien filter generating an electric field E in direction x, and a magnetic field B in direction y. Further, a mass separation electrode
43
with little voltage conforming to a position of a through hole is provided immediately rearward of the extraction electrode
42
a
, thereby enabling the mass separation of a large area ion beam. In this case, ions of a desired mass pass through holes without change, while ions with undesired masses do not pass through the through holes. In other words, ions with excessively large or small masses are eliminated, therefore resolution is high and size reduction is possible.
However, the Wien filter adds an electric field applied parallel to the beam direction to accelerate ions, and furthermore, requires an electric field perpendicular to the beam direction which generates a filtering effect through the electric field and the magnetic field. In addition, much of that plate/electrode area necessitates structures for generating the crossed electric fields and magnetic field, which limit the electrode release area relating to beam transport, therefore in addition to restricting total beam current, it is difficult to obtain satisfactory homogeneity.
SUMMARY OF THE INVENTION
In view of the foregoing situation, it is an object of the present invention to provide a mass separation filter and a mass separation method thereof, as well as an ion source using the same, in order to generate a large area ion beam from ions with a desired mass, allowing the selective rejection of unnecessary ions, in addition to simplifying and reducing the size of the electrode structure of the ion source.
In order to achieve the above-mentioned object, the present invention has a structure as described in the claims. The mass separation filter of the present invention is characterized by having a first magnet forming a first magnetic field in a direction orthogonal to a beam axis of an ion beam; a second magnet provided in series to the first magnet along the beam axis, forming a second magnetic field which is orthogonal to the beam axis and in parallel with and opposite the first magnetic field; and a collimator wall for forming a beam channel having a first and a second curved channels formed within the first and second magnetic fields such that selected ions of a desired mass can pass from the first curved channel slanted by the first magnetic field to the second curved channel which is slanted in a direction the reverse of the first magnetic field by the second magnetic field.
According to this structure, it is possible to extract ions of a desired mass from ions entering the mass separation filter and passing through a beam channel with a channel that is inversely curved by the magnetic fields of the first and second magnets, in addition to allowing the directions in which ions enter and are emitted to be identical to the direction of the beam axis.
Also, according to the first aspect of the present invention, a large area ion beam of the present invention includes a plasma chamber; means for introducing gas with a controlled flow into the plasma chamber; an energy source for ionizing the gas within the plasma chamber; a plasma electrode that forms a plasma chamber wall with an oblong opening, and extracts positive ions from the opening; an extraction electrode for setting a controllable value of the kinetic energy of the ions, and provided parallel to and wit

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