a-C : H thin films deposited by radio-frequency plasma: influence of gas composition on structure, optical properties and stress levels

a-C:H thin films are deposited by plasma-enhanced chemical vapor deposition (PE-CVD) at 13.56 MHz at room temperature. Three different precursor gas m ixtures are used (CH4, CH4/He, CH4/Ar). Structure, optical properties and s tress levels are evaluated by elastic recoil detection analysis (ERDA), IR absorption, UV/vis spectrometry, Raman spectroscopy. We observe a loss of h ydrogen content (bonded and not bonded) from 38 to 24 at.%, as well as an i ncreasing of sp(2) content (from 14 to 29%) with the increase of self-bias voltage for all mixtures. Argon and helium addition to methane induce a gre ater graphitization of a-C:H thin films. These modifications induce a decre ase of the optical gap which is set between 1.4 and 1.1 eV and an increase of the Urbach gap from 0.6 to 0.8 eV. The internal stresses are controlled by subplantation model and decrease from 4 to 1 GPa with the increase of th e bias voltage. The use of argon and helium as carrier gas induce lower str ess in the films. (C) 2001 Elsevier Science B.V. All rights reserved.