Cubic boron nitride (c-BN) layers were deposited by a plasma activated process in a hollow cathode are deposition device. The deposition process is analyzed by in situ polarized infrared reflection spectroscopy. The s-polarized infrared reflectance spectra of a growing BN film show the structure of the in-plane vibration of sp(2) bonded BN at 1370 cm(-1) for film thicknesses greater than 20 nm. At thicknesses greater than 50 nm, the out of plane vibration at 780 cm(-1) can be observed also. The signature of the cubic phase can be detected at a thickness of 95 nm. By simulation of the spectra, the damping constant of the c-BN oscillator was estimated to be 170 cm(-1), nearly independent of the thickness. The transverse optical mode frequency of the c-BN phonon starts at 1090 cm(-1), decreases to a minimum of 1070 cm(-1) at a film thickness of 300 nm and increases at higher thicknesses. Up to a film thickness of 300 nm the oscillator strength increases from 5 x 10(5) cm(-2) to 22 x 10(5) cm(-2) and remains constant during further growth. The c-BN layer growth was investigated in situ during the variation of the DC bias voltage. At a bias voltage of -275 V a reflectance feature can be observed at 1360 cm(-1) corresponding to the in-plane vibration of sp(2) bonded material.