Mass spectrometric study of low-pressure inductively coupled plasma for chemical vapor deposition of cubic boron nitride films

Chemical species in plasma are crucial for understanding the mechanism of cubic boron nitride film vapor phase deposition and controlling the film structure. In this study, the plasma condition for cubic boron nitride deposition by low-pressure inductively coupled plasma-enhanced chemical vapor deposition using B₂H₆, N₂, and Ar as reactant gases has been diagnosed by a quadrupole mass spectrometer with an ion energy analyzer. The ionization potentials of B_XH_Y (X=1–2, Y=0–6) decomposed from B₂H₆ have been measured to be between 11.6 and 18.9 eV. B₂H₆ was totally ionized to B⁺ together with small amounts of BH⁺, BH₂⁺ and B₂H_Y⁺ in plasma above the 2 kW input power. N₂ was only partially ionized, and the degree of ionization increased with increasing Ar partial pressure. Neutral species under the present plasma environment were N₂, Ar and He, but N and H were not detected even by appearance mass spectrometry. Our results demonstrate that the main sources for cubic boron nitride formation are ions produced in plasma. The interaction between N₂ and the growth surface suppresses the cubic boron nitride formation by enhancing the tBN growth, and this surface interference can be reduced by introducing Ar into the system.