Detection and reduction of tungsten contamination in ion implantation processes

Abstract In this paper, we review the results of some studies addressing the problem of tungsten contamination in implantation processes. For some tests, the implanter was contaminated by implantation of wafers with an exposed tungsten layer, resulting in critical contamination conditions. First, DLTS (deep level transient spectroscopy) measurements were calibrated to measure tungsten contamination in ion‐implanted samples. DLTS measurements of tungsten‐implanted samples showed that the tungsten concentration increases linearly with the dose up to a rather low dose (5×10 10 cm –2 ). Tungsten deactivation was observed when the dose was further increased. Under these conditions, ToF‐SIMS revealed tungsten at the wafer surface, showing that deactivation was due to surface segregation. DLTS calibration could therefore be obtained in the linear dose regime only. This calibration was used to evaluate the tungsten contamination in arsenic implantations. Ordinary operating conditions and critical contamination conditions of the equipment were compared. A moderate tungsten contamination was observed in samples implanted under ordinary operating conditions. This contamination was easily suppressed by a thin screen oxide. On the contrary, implantations in critical conditions of the equipment resulted in a relevant tungsten contamination, which could be reduced but not suppressed even by a relatively thick screen oxide (up to 150 Å). A decontamination process consisting of high dose implantations of dummy wafers was tested for its efficiency to remove tungsten and titanium contamination. This process was found to be much more effective for titanium than for tungsten. Finally, DLTS proved to be much more sensitive that TXRF (total reflection X‐ray fluorescence) in detecting tungsten contamination. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)