A transparent boron-nitrogen thin film formed by plasma CVD out of the discharge region

A transparent boron-nitrogen thin film of thickness 550 nm was successfully deposited out of the discharge region by rf plasma CVD. The deposition was performed with diborane (4.8 vol % in N₂) as the reactant gas and argon as the carrier gas by an inductively coupled reactor at a frequency of 13.56 MHz. The transparent films could be obtained at a low pressure of about 30 Pa, at a discharge power level of 30 W, and at room temperature without heating the substrate. The thin films obtained by rf plasma are compared with those obtained by microwave plasma. Both the refractive index and the deposition rate for the films deposited by microwave plasma are discussed according to the deposition conditions.