Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1998-08-28
2001-02-20
Anderson, Bruce C. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C251S315040
Reexamination Certificate
active
06191427
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to an ion implantation system and method, and more particularly to an ion implantation system and method suitable for implantation by a low energy ion beam.
b) Description of the Related Art
High integration of CMOS semiconductor integrated circuit devices nowadays is associated with some problem of short channel effects which may cause a lowered performance of MOS transistors, a lowered drain current, a threshold value shift and the like. Shallow source and drain regions are effective for suppressing the short channel effects. In order to form shallow source and drain regions, it is desired to use a low energy ion beam for ion implantation.
When ions are implanted at a low energy, a process time per unit doping amount becomes long because the ion beam current is small. In order to avoid a prolonged process time, it is necessary to increase the ion beam current at a low energy. As the beam current is increased, the ion beam becomes likely to be diverged by the space-charge effects. In order to prevent ion beam divergence, a method has been proposed which converges an ion beam by disposing an electrostatic lens along a beam line.
The present inventors have found that ion implantation with a low energy ion beam converged by an electrostatic lens is not, however, sufficient for forming shallow source and drain regions.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ion implantation system suitable for forming shallow impurity doped regions.
It is another object of the present invention to provide an ion implantation method suitable for forming shallow impurity doped regions.
According to one aspect of the present invention, there is provided an ion implantation system comprising: ion beam generating means for generating and emitting an ion beam containing ions of a target impurity element; a mass analyzing system for receiving the ion beam emitted from the ion beam generating means and deriving desired ions from the received ion beam to output an ion beam containing the desired ions; a beam line for defining an internal cavity upon which the ion beam emitted from the mass analyzing system becomes incident and outputting the Ion beam propagated in the internal cavity; an electrostatic lens disposed in the inner cavity of the beam line for converging the ion beam incident upon the inner cavity; substrate holding means for holding a substrate into which impurities are to be implanted, in such a manner that the ion beam emitted from the beam line becomes incident upon the substrate; and evacuating means coupled to the beam line for evacuating the inner cavity of the beam line.
According to another aspect of the present invention, there is provided an ion implantation method comprising the steps of: generating an ion beam containing ions of a target impurity; making the ion beam be incident upon an inner cavity of a beam line and converging the incident ion beam with an electrostatic lens disposed in the inner cavity, the ion beam being converged while an inside of the inner cavity is maintained evacuated with evacuating means coupled to the beam line; and impinging the converged ion beam upon a substrate to implant the ions into the substrate.
Since the inner cavity in which the electrostatic lens is disposed is evacuated, the ion beam propagating through the electrostatic lens becomes hard to be influenced by the residual gas in a space near the ion beam. Ions become hard to be neutralized by the residual gas, so that each ion is accelerated or decelerated with the electrostatic lens reliably by a predetermined amount. Therefore, a disturbance of the energy distribution of the ion beam to be caused by the electrostatic lens can be suppressed.
According to another aspect of the present invention, there is provided an ion implantation system comprising: ion beam generating means for generating and emitting an ion beam containing ions of a target impurity element; a mass analyzing system for receiving the ion beam emitted from the ion beam generating means and deriving desired ions from the received ion beam to output an ion beam containing the desired ions; a beam line for defining an internal cavity upon which the ion beam emitted from the mass analyzing system becomes incident and outputting the ion beam propagated in the internal cavity; an electrostatic lens disposed in the inner cavity of the beam line for once accelerating and converging and thereafter decelerating the ion beam incident upon the inner cavity, an energy of the ion beam after the acceleration being controlled to have an energy three time or higher than an energy of the ion beam before the acceleration; and substrate holding means for holding a substrate into which impurities are to be implanted, at a position where the ion beam emitted from the beam line becomes incident upon.
According to another aspect of the present invention, there is provided an ion implantation method comprising the steps of: generating an ion beam containing ions of a target impurity; making the ion beam be incident upon an inner cavity of a beam line and converging the incident ion beam with an electrostatic lens disposed in the inner cavity, the electrostatic lens accelerating and converging the ion beam to have an energy three time or higher than an energy of the ion beam before the ion beam becomes incident upon the electrostatic lens, and thereafter decelerating the ion beam; and impinging the decelerated ion beam upon a substrate to implant the ions into the substrate.
If ions after once accelerated by the electrostatic lens are changed to neutral atoms, these atoms are not thereafter affected by a downstream electric field. Therefore, the atoms are emitted from the electrostatic lens without being decelerated. Since the energy of the accelerated ion beam is set three times or more than that before the acceleration, the energy of the neutral atoms emitted from the electrostatic lens is as high as about three times the decelerated ions, even if the ions are changed to neutral atoms. Accordingly, implantation into a deep region of high energy neutral atoms can be suppressed.
According to another aspect of the present invention, there is provided an ion implantation method comprising the steps of: generating an ion beam containing ions of a target impurity having an energy of 5 keV or lower; making the ion beam be incident upon an inner cavity of a beam line and converging the incident ion beam with an electrostatic lens disposed in the inner cavity; and impinging the converged ion beam upon a single crystal semiconductor substrate to implant the ions into the semiconductor substrate without passing the ion beam through an amorphous layer made of elements constituting the semiconductor substrate.
Shallow implantation is possible by using an ion beam having an energy of 5 keV or lower. Since the ion beam is converged by the electrostatic lens, the ion implantation amount can be prevented from being reduced by the divergence of the ion beam. If a crystal substrate without an amorphous surface layer is used, an impurity distribution generally the same as that without the active electrostatic lens can be obtained.
As above, when ions are implanted by using an ion beam converged by the electrostatic lens, the ions can be prevented from being implanted into a substrate deep region. With this method, shallow source and drain regions of a MOS transistor can be formed so that the short channel effects can be alleviated.
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patent: 5818040 (1998-10-01), Kinoshita et al.
patent: 5892236 (1999-04-01), Takahashi et al.
Kase Masataka
Niwa Yoshiyuki
Anderson Bruce C.
Armstrong, Westermen, Hattori, McLeland & Naughton
Fujitsu Limited
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