Plasma doping dosimetry

Plasma immersion ion implantation (PIII) is a large-area doping technique that can provide very high implant current at very low implant energy. Multiple ion species, plasma conditions, and implanter current-voltage waveforms in PIII lead to an exponential implant profile which is different from conventional implant profiles. A methodology is developed for using in situ measurements of the implanter current (I) and implant voltage (V) to derive an energy spectrum for a single implant pulse. The advantage of this technique is that a per-pulse profile may be determined experimentally, even in the presence of substrate etching, without any need for an implant model. If the ion species concentrations in the plasma are known, the energy spectrum found from the ion current and voltage waveforms can be used to construct a per-pulse implant profile. If the ion species distribution is not known a priori for a multispecies plasma, secondary ion mass spectroscopy (SIMS) data from an implanted sample can be used to estimate the ion species distribution and calibrate the IV-generated profile within a factor of two. Data from 1-5 kV, 2.5-5 kHz BF/sub 3/ PIII implants are used to demonstrate the concept. The implant profile for a single pulse can then be used to project the final implant profile and total implanted dose as a function of implant time, Pm pulse frequency, and substrate etching. In this work, an estimated secondary electron yield function is used to separate the total implant current into ion and secondary electron current components. The 25% dose variation error introduced by this effective secondary electron yield function could be avoided in a system which can measure ion current directly.