Ion source head

Details Ion source head Ion source head

1999-10-02

2001-10-09

Berman, Jack (Department: 2881)

Radiant energy

Ion generation

Arc type

C250S427000, C250S42300F, C250S310000, C250S311000

Reexamination Certificate

active

06300636

ABSTRACT:

TECHNICAL FIELD
The present invention generally relates to ion implantation machines used in fabricating semiconductor devices, and deals more particularly with an improved ion source head that reduces material build-up and flaking in the arc chamber.
BACKGROUND OF THE INVENTION
Semiconductor fabrication processes often use a high current ion implantation machine to implant impurity ions into semiconductor substrates in order to form doped regions, such as sources and drains. The ion implanter delivers a beam of ions of a particular type and energy to the surface of a silicon substrate. Such machines typically include an ion source supply, normally a gas source, and an ion source power supply which is connected to an ion source head. A small quantity of the gas is passed through a vaporizer oven and then into an arc chamber which includes a heated filament, and an anti-cathode. The filament is directly heated by passing electric current through it, derived from the power supply. This heating causes thermionic emission of electrons from the surface of the filament. An electric field, typically 30 to 150 volts is applied between the filament and the arc chamber walls using the power supply. The field accelerates the electrons in the filament area to the arc chamber walls. A magnetic field is then introduced to perpendicular to the electric field and causes the electrons to spiral outward, increasing the path length and chances for collisions with the gas molecules. The collisions break apart many of the molecules and ionize the resultant atoms and molecules by knocking outer shell electrons out of place. As charged particles, these atomic or molecular ions can now be controlled by magnetic and/or electric fields. Source magnets are employed to change the ion path from a straight path to a helicoid path. With one or more electrons missing, the particles carry a net positive charge. An extraction electrode (anti-cathode) placed in proximity to a slit and held at a negative potential attracts and accelerates the charged particles out of the chamber through the slit opening in the top of the chamber. Ions exiting the chamber are passed through an acceleration tube where they are accelerated to the implantation energy as they move from high voltage to ground. The accelerated ions form a beam well collimated by a set of apertures. The ion beam is then scattered over the surface of a wafer using electrostatic deflection plates.
After operation over a period of time, the processing of gasses in the arc chamber results in the accumulation of materials deposited from the gas, causing the formation of a conductive coating on the filament, chamber walls and anti-cathode. This coating eventually flakes, causing the filament to short out such that its can no longer produce electrons and the implantation machine becomes inoperable. This shorting phenomena is a result of arc-outs and typically occurs during boron implanting. When the arc chamber shorts out, it is necessary to clean the chamber, the anti-cathode and filament, which is a time consuming procedure since the machine is operated at a high vacuum pressure. This procedure is not only time consuming and costly, but the machine down time reduces throughput.
Accordingly, there is a clear need in the art to provide an improved arc chamber that reduces or eliminates arcing and shorting within the arc chamber.
SUMMARY OF THE INVENTION
In accordance with the present invention, an improved ion source head is provided for use in an ion implantation machine comprising an arc chamber, a source of gas, arc means for generating an ion plasma within the chamber, and a bottom liner in the chamber having the plurality of spaced apart through holes therein for allowing the evenly distributed introduction of gas into the chamber, thus tending to avoid concentrated material buildup or coating on elements within the chamber. The bottom liner includes at least four, but preferably six thru-holes therein communicating with a feed chamber beneath the bottom liner which is coupled with the gas source. Each of the through-holes is preferably greater than 4 mm but less than 8 mm in diameter. The through-holes are desirably arranged in two groups thereof respectively lying along parallel axes, and thus are disposed symmetrically in a bottom of the arc chamber.
According to another aspect of the invention, an ion source is provided for generating ions, comprising: and arc chamber defined by a top, a bottom, opposing sides and opposing ends; a source of ions in the form of a selected gas; a heated filament on one of the chamber ends; and an anti-cathode on the other of the chamber ends; and a plurality of openings in the bottom of the chamber coupled with the gas source and allowing evenly distributed introduction of gas into the chamber between the filament and the anti-cathode.
Accordingly, it is a primary object to provide an improved ion source head which reduces arcing and shorting within the arc chamber caused by coating build-up on elements within the chamber.
Another object of the invention is to provide an improved ion source head of the type described above which reduces down time necessary for cleaning the arc chamber.
A still further object of the invention is to provide an improved ion source head of the type described above which allows for the even distribution of an ion source gas flowing into the arc chamber.
Another object of the invention is to provide an improved ion source head which significantly reduces coating and flaking of ion source materials on the anti-cathode, and undesired arcing which results from such flaking.
These, and further objects and advantages of the invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the invention.


REFERENCES:
patent: 5886355 (1999-03-01), Bright et al.

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