Electronic and optical investigation of hydrogenated amorphous carbon (a-C:H) by X-ray photoemission spectroscopy and spectroscopic ellipsometry

Hydrogenated amorphous carbon (a-C:H) films were prepared by low-pressure PECVD of CHI in a dual electron cyclotron resonance (ECR)-radio frequency (RF) discharge by applying an independently controlled RF substrate bias voltage from 0 to -200 V. The films were analyzed with core-level and valence band (VB) X-ray photoemission spectroscopy (XPS) as well as spectroscopic ellipsometry. A progressive change from soft transparent polymer-like to hard absorbing diamond-like was observed with increasing bias voltage in this range. The C 1s core-level spectra were fitted by using a Doniach-Sunjic photoemission line-shape. The C Is spectra showed the enhanced asymmetric behavior with increasing bias voltage. In addition, the VB spectra exhibited distinct pi density of states according to the bias. Such XPS features were analyzed and interpreted in terms of the pi --> pi* electron transition model on amorphous carbon through spectroscopic ellipsometry. (C) 2000 Elsevier Science B.V. All rights reserved.