1. Field of the Invention
This invention relates to ion implantation and more particularly to a non-mass-analyzed ion implantation process wherein ions of non-selected species are accelerated and implanted into a target.
2. Description of Prior Art
Today, ion implantation is evaluated as one of important techniques, especially, in the semiconductor industry. Conventionally, most ion implantation apparatus for processing semiconductors have been based on mass-analyzed ion implantation wherein mass analysis is effected by utilizing a static magnetic field generated by a magnet and an ion of one selected species is used as an ion source. The mass-analyzed ion implantation has an advantage of high purity of implanted impurities but it requires a mass analyzer and suffers from a disadvantage that the apparatus is costly and running cost is high.
On the other hand, non-mass-analyzed ion implantation has been proposed especially for formation of a pn junction of solar batteries and it eliminates the above disadvantage (Japanese Patent Application Kokai (Laid-Open) No. 130975/78). In the non-mass-analyzed ion implantation, ions are accelerated and without being subjected to mass analysis, implanted into a target. This ion implantation process dispenses with the mass analyzer so that not only apparatus cost and running cost can be reduced but also travel path of ion beams can be reduced to reduce loss of ions due to collision and scattering of the ion beams at the inner wall of the apparatus. The reduction in loss leads to an increase in implantation current which in turn increases implantation processing speeds.
The conventional non-mass-analyzed ion implantation, however, simply implants all the ions of nonselected species into the target and has difficulties with the use of compound source materials. Further, even with an elemental source material such as for example red phosphorus, a phosphorus vaporizer is required and it is necessary to prevent solidification of vaporized phosphorus by heating an atmosphere between the phosphorus vaporizer and the ion source up to about 400.degree. C.