Mechanisms Involved in the Conversion of ppHMDSO Films into SiO₂‐Like by Oxygen Plasma Treatment

Abstract

Summary: Thin ppHMDSO plasma polymer films deposited in a low pressure hexamethyldisiloxane plasma have been exposed to oxygen plasmas ignited in the same reactor at different pressures. The time evolution of the ppHMDSO film during the oxygen plasma treatment (30 s to one hour) was monitored in situ by multi‐wavelength ellipsometry. The treated films were analysed ex situ by X‐ray reflectometry, spectroscopic ellipsometry and infrared spectroscopy. On the other hand, the oxygen atom density as well as the oxygen ion density and energy were measured by actinometry and Langmuir probe measurements, respectively. For all the investigated oxygen plasma conditions, the film thickness and extinction coefficient significantly decrease. If the O 2+ ion energy is low enough (typically less than 10 eV) the 65nm ppHMDSO can even be transformed into a 45 nm‐thick carbon free SiO2‐like film. In contrast, if the ion energy is higher than 10 eV, the ppHMDSO is only partially oxidised. Based on the oxygen atom flux measurement, it is concluded that the number of oxygen atoms impinging on the ppHMDSO film is not the only parameter which governs the treatment. The oxygen ion energy appears to have a key role as far as energetic ions are likely to induce the formation of a dense superficial SiO2 layer which prevents the diffusion of O atoms in the film and the out diffusion of volatile oxidation products.

GC‐MS Investigation of Hexamethyldisiloxane–Oxygen Fed Cold Plasmas: Low Pressure Versus Atmospheric Pressure Operation

“…Organosilicon compounds, such as hexamethyldisiloxane (HMDSO) and tetraethoxysilane (TEOS) in mixture with oxidants (i.e., O 2 and N 2 O) and/or noble gases (i.e., Ar and He), are widely used both in low pressure (LP) and in atmospheric pressure (AP) plasma‐enhanced chemical vapor deposition (PE‐CVD) of silicon‐based thin films. In particular, the extensive investigations performed during the last decades on LP organosilicon‐containing plasmas1–20 have clearly shown the versatility of these reactive systems due to the tunability of the chemical composition of the deposited coatings from silicone‐like to SiO 2 ‐like1, 11, 12, 16, 19 for applications in several technological fields 16, 21–25. The general deposition mechanism proposed for LP plasmas rationalizes the published experimental evidences, that is, the effect of process parameters, such as feed composition, power density, substrate temperature, substrate bias voltage, etc..…”

Effect of ion bombardment on the structural and optical properties of TiO2 thin films deposited from oxygen/titanium tetraisopropoxide inductively coupled plasma

“…When no substrate bias voltage is applied, the ion energy corresponds to E i = e(V p -V f ), where V p is the plasma potential and e is the electron charge. On the basis of Langmuir probe measurements previously carried out in pure oxygen plasma at the same pressure [36], E i can be estimated to be 15 eV. In the presence of RF bias, E i , is equal to e(V p -V b ), with a value of V p which is expected to be around 25 V, as previously measured in pure oxygen plasmas.…”

Influence of Ion Bombardment and Annealing on the Structural and Optical Properties of TiOx Thin Films Deposited in Inductively Coupled TTIP/O2 Plasma

“…Thanks to Langmuir probe measurements, performed in pure oxygen plasma at 4 × 10 −3 mbar for a rf power of 300 W, the electron density and temperature close to the substrate holder were measured to be 5 × 10 9 cm −3 and 4 eV, respectively 9. The ion energy, equal to the difference between plasma and floating potentials, did not exceed 20 eV.…”