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 P ECVD of CHI in a dual electron cyclotron resonance (ECR)-radio frequency (R F) discharge by applying an independently controlled RF substrate bias volt age from 0 to -200 V. The films were analyzed with core-level and valence b and (VB) X-ray photoemission spectroscopy (XPS) as well as spectroscopic el lipsometry. A progressive change from soft transparent polymer-like to hard absorbing diamond-like was observed with increasing bias voltage in this r ange. The C 1s core-level spectra were fitted by using a Doniach-Sunjic pho toemission line-shape. The C Is spectra showed the enhanced asymmetric beha vior with increasing bias voltage. In addition, the VB spectra exhibited di stinct pi density of states according to the bias. Such XPS features were a nalyzed and interpreted in terms of the pi --> pi* electron transition mode l on amorphous carbon through spectroscopic ellipsometry. (C) 2000 Elsevier Science B.V. All rights reserved.