Ion implantation process

Details Ion implantation process Ion implantation process

1998-12-09

2001-02-06

Anderson, Bruce C. (Department: 2881)

Radiant energy

Irradiation of objects or material

Irradiation of semiconductor devices

C250S492100, C250S492200, C250S42300F

Reexamination Certificate

active

06184536

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to an ion implantation process, particularly ion implantation of phosphorus into a semiconductor substrate using ion implanting equipment having mass separation.
Ion implantation is an important technique used in the manufacture of semiconductor devices. Ion shower systems are commonly used for implantation into a larger area of semiconductor material. Alternatively, an ion implantation apparatus is known using mass-analysed ion implantation, which effects selection by mass of ions desired for implantation into the semiconductor substrate. A mass spectrometer typically performs the mass separation using a static magnetic field generated by an electron magnet, wherein selected ion species are obtained by controlling the electric current in the magnetic coil so that the selected ion species pass through a resolving slit. Mass separation is suitable for narrow ion implantation beams, which can be scanned to cover a large area semiconductor layer.
One common donor atom implanted into semiconductor material to create an n-type doped semiconductor is phosphorus, and it is known to use an ion source of phosphine (PH
3
) for phosphorus doping. A problem with conventional ion shower implantation is that a number of ion species are implanted into the semiconductor substrate during the implantation process. Mass separation systems may also not have the resolution to discriminate between individual ion species. For example, phosphorus hydride ions (present in ionised phosphine) have very similar atomic masses to phosphorus ions, so that accurate mass analysis is required in order to separate the phosphorus ion species. Implantation of some hydrides may not be considered to be a problem, particularly in the case of poly-silicon or single crystal silicon semiconductor substrates. However, for doping of amorphous silicon layers the effects of hydride impurities is more pronounced. It has been recognised that implantation of hydrogen ions should be avoided, and the ion implantation system described in U.S. Pat. No. 4,533,831 seeks to avoid implantation of hydrogen ions. This is achieved generally by separating heavier ions from lighter ions. U.S. Pat. No. 4,533,831 does not eliminate the implantation of phosphorus hydride ions.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an ion implantation process comprising performing mass separation of ions from an ionised source of phosphorus so as to select P
2
ions and reject phosphorus hydride ion species and implanting the P
2
ions into a semiconductor material.
The implantation process of the invention selects P
2
ions. When beam current analysis is performed on the ion species derived from a phosphine (PH
3
) ion source, it is revealed that there are no hydride ions surrounding (on the mass axis) the P
2
ion species. Consequently, a rough mass separation procedure may enable efficient separation of the P
2
ions, with the result that the ion implantation process can be controlled to eliminate any hydrogen implantation into the semiconductor substrate. The invention is therefore particularly suited to the use of gaseous phosphine as the ion source and which is readily available and already conventionally used in phosphorus implantation procedures.
The invention provides particular advantages for implantation into amorphous silicon, because it has been found that the introduction even of hydride ions into amorphous silicon significantly deteriorates the properties of the amorphous silicon semiconductor devices.
The invention also provides a method of manufacturing thin film transistors using an ion implantation process of the invention. In particular, the ion implantation process is used to define drain and source regions of the thin film transistors in an amorphous silicon layer.


REFERENCES:
patent: 4533831 (1985-08-01), Itoh et al.
patent: 4881817 (1989-11-01), Kim et al.
patent: 4904616 (1990-02-01), Bohling et al.

Affiliated with

Also associated with

Rating

Ion implantation process does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Ion implantation process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ion implantation process will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2614919