Lowering of the Substrate Bias Voltage for Deposition of Cubic Boron Nitride in Microwave Plasma

A moderate-pressure microwave plasma is used to deposit boron nitride (BN) films by employing boron trifluoride as a source gas. In the deposition conditions, the ion flux onto a negatively biased substrate is measured to be on the order of 10
¹⁶
cm
^-2
s
^-1
depending upon the bias voltage. The films consisting of both hexagonal BN and cubic BN (cBN) phases are deposited on silicon substrates by applying a bias voltage ranging from -85 to -200 V. The film deposited at -85 V shows the higher crystallinity and larger roughness and grains of cBN due to a decrease in mean ion impact energy. The results suggest that the bias voltage for cBN phase formation is lowered by increasing the ion to depositing boron flux ratio even in collisional moderate-pressure conditions.