Characterization of Boron Contamination in Fluorine Implantation using Boron Trifluoride as a Source Material

Abstract

Fluorine implantation process purity was considered on different types of high current implanters. It was found that implanters equipped with an indirectly heated cathode ion source show an enhanced deep boron contamination compared to a high current implanter using a cold RF-driven multicusp ion source when boron trifluoride is used for fluorine implantations. This contamination is directly related to the source technology and thus, should be considered potentially for any implanter design using hot cathode/hot filament ion source, independently of the manufacturer.The boron contamination results from the generation of double charged boron ions in the arc chamber and the subsequent charge exchange reaction to single charged boron ions taking place between the arc chamber and the extraction electrode. The generation of the double charged boron ions depends mostly on the source parameters, whereas the pressure in the region between the arc chamber and the extraction electrode is mostly responsible for the charge exchange from double charged to single charged ions. The apparent mass covers a wide range, starting at mass 11. A portion of boron ions with energies of (19/11) times higher than fluorine energy has the same magnetic rigidity as fluorine beam and cannot be separated by the analyzer magnet. The earlier described charge exchange effects between the extraction electrode and the entrance to the analyzer magnet, however, generates boron beam with a higher magnetic rigidity compared to fluorine beam and cannot cause boron contamination after mass-separation.The energetic boron contamination was studied as a function of the ion source parameters, such as gas flow, arc voltage, and source magnet settings, as well as analyzing magnet aperture resolution. This allows process optimization reducing boron contamination to the level acceptable for device performance.Keywords: Ion implantation, high current single wafer implanter, high current batch implanter, spot ion beam.

Purity of Ion Beams: Analysis and Simulation of Mass Spectra and Mass Interferences in Ion Implantation

“…Because of the variables z ex and z sp , the apparent mass is not limited to discrete values but can take values from a continuous range. Equation (3), therefore, is appropriate to describe tails of peaks in a mass spectrum, such as the Al tail in Figure 4 in the next section or to model contamination problems where the charge exchange occurs in section [Src-Ex] [8].…”

“…The simultaneous implantation of unwanted ions with the same mass to charge ratio as the desired ion species might appear to be a manageable contamination risk, but it is only a special case. When ions undergo a charge exchange or dissociate between the ion source and the analyzer magnet, surprising contamination issues may arise [6][7][8]. This paper illustrates by means of mass spectrum analysis (which is not only essential in order to check which elements are present in the ion source) that charge exchange events and dissociation processes between the ion source and the analyzer magnet of an implanter are fairly common.…”