Ion implantation is a well-known and widely used process for injecting atoms into a solid material to selected depths and concentrations in selected areas. Ion implant accelerators are similar to isotope separators but typically have an added acceleration stage and field controls for precisely locating the beam of ions and controlling the energy anf flux of the beam of ions to cause the desired penetration and concentration. Atoms of the selected chemical element to be ionized are ionized by collisions with electrons in an electrical discharge in a gas at low pressure and pass through an orifice into a high-vacuum region where they are accelerated by an electric field to a an intermediate energy, typically from 10 to 30 keV, where they are analyzed by a magnetic field based upon the e/m ratio, i.e. the ratio of electronic charge over mass. The selected ion beam passes through an analyzer slit, and the ions are accelerated to the desired energy, and the beam passes through a refocussing field, typically a quadrupole lens, is deflected by a scanner system, and collimated by a defined aperture and allowed to strike the target. When the ions penetrate the target lattice, they lose energy through collisions with lattice atoms and come to rest as part of the target. There are, of course, a large number of variations between specific ion implant system but the foregoing principles apply generally to ion implant proceses. The ion implant technique is described, inter alia, in U.S. Pats. Nos. 2,750,541, 2,787,564 and 2,842,466, which are incorporated herein. The ion implant method is also described in many texts, encylopedias and scientific journals; see, e.g. Encyclopedia of Semiconductor Technology, "Ion Implantation" pp. 397-410, John Wiley & Sons (1984) and the numerous references cited therein; see also, Kirk Othmer Concise Encyclopedia of Chemical Technology, "Ion Implantation", p. 666 et seq., John Wiley & Sons (1985); and Ion Implantation, J. K. Hirvonen, ed., Academic Press, Inc., (1980). Since the equipment and methods of ion implantation are so thoroughly described and widely used in the semiconductor industry, those skilled in the art are familiar with these methods and devices and may refer to any of the many excellent journal, text and patent descriptions for details. Manufacturer's manuals, provided with specific items of equipment are the best source for details as to a given piece of equipment.
This invention relates to the use of a particular class of chemicals as ion source materialss and, consequently, to a modified method; i.e. a method which is modified in that it utilizes a novel source of ions.
Ions are introduced into the ion implant equipment periodially. This generally requires cooling the implant equipment down, opening the high vacuum to at least some atmospheric exposure, introducing the new charge of ion source material into a receptacle, closing up the equipment, pumping the ion implant and accelerator chambers down to a high vacuum, and placing the equipment into operation again. This procedure is necessarily very expensive in terms of lost production and wasted time in a very expensive piece of equipment. Ion implant devices not infrequently cost over one million dollars and it is necessary to maximize production time to recoup the investment in saleable product.
While the ion implant equipment is very precise, elegant and complex in design and operation, the introduction of ion source materials is a relatively simple, largely manual operation. Basically, the charge of ion source material is, according to the prior art, simply pushed, poured or dropped into a small chamber in a Source Vaporizor which is then closed, after which the entire system is pumped down using well-known rotory and oil diffusion vacuum pumps. Source Vaporizers of the type under consideration are sold by various manufacturers, one of which is described as a Nova NV-10.TM. Series Source Vaporizer. This, however, is merely exemplary and other source vaporizers are well-known to those skilled in the art.
For more than a decade, ion implantation has been a chief step in the industrial processing of semiconductor devices; in particular, large-scale integrated circuits; see, for example, Ion Implantation in Semiconductors, Sartwell, et al., editors, Plenum Press, New York (1977). It is within this art that the present invention lies and to which it is an improvement.