Plasma-Enhanced Chemical Vapor Deposition of High Quality Cubic BN Films with an Intermediate Layer of Turbostratic BN T
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Plasma-Enhanced Chemical Vapor Deposition of High Quality Cubic BN Films with an Intermediate Layer of Turbostratic BN Thinner than 3 nm Hangsheng Yang 1), Chihiro Iwamoto 2), and Toyonobu Yoshida1) 1) Department of Materials Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan. 2) Engineering Research Institute, School of Engineering, The University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-8656, Japan. ABSTRACT Cubic boron nitride (cBN) thin films were deposited on silicon wafers by low-pressure inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD). By using special substrate pre-treatment processes including positive biasing treatment in H2 plasma or 1200 K pre-heating in H2 atmosphere followed by an N2 plasma treatment, turbostratic BN (tBN) intermediate layer was revealed to directly grow on Si substrates without an initial amorphous layer. The thickness of the tBN transition layer can be reduced to less than 3 nm. INTRODUCTION The synthesis of cBN films has attracted extensive research interest due to their excellent physical and chemical properties. Both chemical vapor deposition (CVD) and physical vapor deposition (PVD) techniques are used for cubic phase BN thin film deposition with the assistance of ion bombardment1-8. Recently, cBN films thicker than 1µm have been deposited by DC jet plasma CVD9. However, cBN films still grow with a unique three-layered structure10 consisting of layers of amorphous BN (aBN), sp2-bonded turbostratic (tBN) and cBN with only a few exceptions11-13. Recently, we found that using a time-dependent biasing technique (TDBT) from a sputtering mode to a film deposition mode with an appropriate substrate bias, cBN films with a 98% (volume%) cubic phase, and an initial layer thickness as thin as 3 nm can be achieved by an inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD) technique13-15. In this paper, we report the elimination of an initial aBN layer by using special substrate pre-treatment processes. EXPERIMENTAL DETAILS The cBN films were deposited on (111)-oriented Si wafers by ICP-CVD using a TDBT15. In this study, three kinds of pre-treatments of the substrate were applied, namely, (i) 30 mTorr H2 plasma treatment with –40 V biasing for 10 min, (ii) 30 mTorr H2 plasma treatment with +40 V biasing for 120 min, and (iii) 1200 K heating in 20 mTorr H2 for 120 minutes, respectively, followed by the same treatment: 1 mTorr pure N2 plasma treatment with biasing the substrate at -150 V for 30 minutes. After the series of the pretreatments, plasma gas composition was changed from pure N2 to 95% Ar +5% N2 by adjusting each flow rate, 19 and 1 sccm, respectively. 10% B2H6 diluted with He was introduced gradually from an injection probe into the 95% Ar + 5% N2 plasma with keeping the same –150 V biasing condition and the substrate temperature at 600 K. Within a three-minute time span, the source gas flow rate was increased up
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to 10 sccm. After stabilizing the plasma at 1 mTo
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