Etching characteristics of low-k SiCOH thin films under fluorocarbon-based plasmas

Abstract

Low dielectric constant (low-k) SiCOH thin films were prepared on silicon (Si) wafers using plasma enhanced chemical vapor deposition (PECVD) of the precursor tetrakis(trimethylsilyloxy)silane (TTMSS). The deposition RF plasma power was 20 and 100 W. The k-values were 2.14 and 3.2 for the films deposited at 20 and 100 W, respectively. The deposited films then underwent an inductively coupled plasma-reactive ion etching (ICP-RIE) using fluorocarbon-based etching gas of CF4, CF4+O2, and CF4+Ar. After etching, the etch rate and refractive index for the films deposited at 100 W were higher than those at 20 W. The surface roughness decreased for the films at 20 W but increased for those at 100 W after etching. Contact angles decreased indicating a hydrophilic surface after etching. Prominent absorption bands from the Fourier transform infrared (FTIR) spectra were observed as C–Hx stretching, Si–CH3 bending, Si–O–Si stretching, and Si–(CH3)x bending vibration modes. X-ray photoelectron spectroscopy (XPS) showed a significant fluorine concentration on the film surface. From high resolution scans for C1s and F1s in the XPS, dominant peaks were observed as C–H/C–C and C–F3 after etching, respectively. After etching, the k-values and leakage current densities increased from those of as-deposited films.