Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2002-12-27
2004-09-28
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492300, C250S3960ML
Reexamination Certificate
active
06797968
ABSTRACT:
This application claims priority to prior application JP 2001-397817, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an ion beam processing method and an ion beam processing apparatus.
There are various types of usage for the ion beam processing apparatus. For example, it is used as an ion implantation system. The ion implantation system is for implanting ions in semiconductor devices. For recent ion implantation system, following development and progress in a microfabrication technology of a semiconductor device, the energy of implanted ions is decreasing in order to implant the ions shallowly in the semiconductor substrate. However, in low ion energy range, in the midway of a beam line structure from an ion source to the semiconductor substrate, ion beam spreads because of charges of their own. This is because repulsion is attributed to a space charge effect. Therefore, in the low ion energy range, transport efficiency of ion beam is reduced, which causes a problem not to get sufficient ion beam current.
In ion beam, because of the electrical repulsive force: space charge effect, each positive ion bears off other positive ions. As a result, the ion beam is diffused. The space charge effect works more strongly as ion beam energy is lower, and also as ion beam current is higher.
Thus, especially in the low energy ion implantation, in order to obtain higher ion beam current, it is important to reduce the space charge effect and to prevent from diffusion of ion beam.
The space charge effect by ions having positive charges is mitigated by an amount equal to cancellation of total charges in a space if there are electrons or ions having negative charges. For example, as shown by P
1
to P
6
of
FIG. 1
, secondary electrons generated from a surface of a structure when ion beam collide with the structure in the beam line structure, electrons emitted when ion beam collide with gas remaining in the beam line structure to ionize the residual gas, or negative ions generated by electron impartation act to mitigate the space charge effect.
The space charge effect by positive ions is mitigated by amount of electrons secondarily emitted by ion impact to the beam line structure, by ion collisions with residual gas in the beam line structure or so. Negative ions, generated by capture of the secondary electrons, also mitigate the space charge effect.
Referring to
FIG. 1
, ions are generated by an ion source
200
, and are extracted by an extraction electrode
201
as ion beam. The ion beam is transported in a vacuum chamber
202
and passes through an analysis slit
203
and are irradiated to a target semiconductor substrate
204
. A mass analysis magnet unit is arranged outside the vacuum chamber
202
, which is not shown here.
In
FIG. 1
, P
1
denotes collision of ion beam with the extraction electrode
201
, P
2
collision of heavier ions than target ions with the inner wall of the vacuum chamber
202
, P
3
collision of ions with residual gas, P
4
collision of lighter ions than the target ions with the inner wall of the vacuum chamber
202
, P
5
collision of ion beam with the analysis slit
203
, and P
6
collision of ion beam with the semiconductor substrate
204
.
The following method is known, which actively induces the above-described operation in order to reduce the space charge effect and to increase beam current ultimately. Gas is intentionally introduced into the vacuum chamber constituting the beam line structure, and the space charge effect is reduced by electrons ejected by collision ionization of the gas with ions. This method is disclosed in, for example Japanese Patent No. 2765111. Simply put, when gas is introduced into an ion beam transport line, collision of ions of ion beam with the gas molecules is increased. As a result, the amount of electrons present in the ion beam is substantially increased to mitigate the space charge effect of the ion beam.
In addition to the above method, another method is known using the neutralization by the molecules that are easily turned to negative ions or are easily polarized, e.g., water (H
2
O). This method serves the same purpose as that of the above, and disclosed in Japanese Patent Application Laid-Open No. Hei 11 (1999)-96961.
The method based on the gas introduction increases the amount of generated electrons, results in loss of ion beam by collision with the gas. Generally, a beam current is maximized under a certain gas pressure and, even if more gas is introduced, ion beam current will decrease.
Thus, the amount of electrons is decided by balance of generation and disappearance of electrons. In order to completely cancel the space charge effect, this balance must be changed and the number of electrons must be increased.
From another standpoint, to substantially increase the amount of electrons, necessary for neutralization of ion beam, without any losses of ion beam themselves, a method of extending the life time of electrons or negative ions which have been present from generation to disappearance is effective.
In addition, for the conventional ion implantation system, between the both poles of the mass analysis magnet unit, a detachable/separable mass analysis magnet unit beam line vacuum chamber is arranged to transport ion beam while analyzing mass. The ion beam passed in the mass analysis magnet unit beam line vacuum chamber are diffused to reduce beam current.
Especially, in the low ion energy range, a reduction in beam current is significant. As a method of obtaining much more beam current in the low energy range, a deceleration mode is known. However, even by the deceleration mode, diffusion of ion beam cannot be suppressed.
As a method of suppressing diffusion of ion beam, application of a continuous cusp field in the ion beam is known to be effective. However, in the conventional ion implantation system, it is difficult to secure space for forming a cusp field.
Further, in the conventional ion implantation system, to use an apparatus with deceleration mode, the analysis magnetic pole surfaces of the mass analysis magnet unit, the magnets for forming the cusp field, and the beam line vacuum chamber must be set to different potentials. However, it is difficult to secure a space for arranging the magnets for forming the cusp field, and then a space for arranging its insulating material. The insulating material can be arranged by increasing a distance between the analysis magnetic pole surfaces of the mass analysis magnet unit. However, when the distance between the both pole surfaces of the mass analysis magnet unit is increased, electric power consumption necessity for analyzing mass of ion beam will increase.
At present, demand for space and energy conservation grows in the industrial field, and increases in size of the apparatus and electric power consumption run counter to such demand.
SUMMARY OF THE INVENTION
Therefore, a purpose of the present invention is to enable acquisition of higher beam current by forming a cusp field in a beam line structure of an ion beam processing apparatus in order to suppress diffusion of ion beam, and to transport much more ion beam.
Another purpose of the present invention is to increase the ion beam current easily in low energy range in an ion implantation system for implanting ions in semiconductor substrate such as silicon wafer.
Yet another purpose of the present invention is to provide an effective supporting method and an effective supporting structure of a set of magnets for forming a cusp field in a beam line structure.
An ion beam processing method of the present invention subjects ions extracted from an ion source by an extraction electrode to mass analysis by a mass analysis magnet unit and by a mass analysis slit, and are drifted or accelerated/decelerated to implant the ions in a substrate.
According to a first aspect of the present invention, a set of magnets for forming continuous cusp fields is continuously disposed in a continuous beam line structure from front part of the mass analysis magn
Amano Yoshitaka
Kabasawa Mitsuaki
Matsushita Hiroshi
Murooka Hiroki
Sugitani Michiro
Arent Fox PLLC.
Fernandez Kalimah
Lee John R.
Sumitomo Eaton Nova Corporation
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