Antoine Goullet

A comparative study of oxygen/organosilicon plasmas and thin SiOxCyHz films deposited in a helicon reactor

Thin SiOxCyHz films have been prepared by plasma enhanced chemical vapor deposition (PECVD) on silicon substrates at low pressure (2 mTorr) and 300 W rf power, using tetraethoxysilane (TEOS) or hexamethyldisiloxane (HMDSO) as a monomer and oxygen as a reactive gas. The plasma composition, the structure and properties of the deposited films are studied as a function of the organosilicon fraction (Xorg). Optical emission spectroscopy is carried out in order to identify the species in the plasma. The layers are characterized by in situ spectroscopic ellipsometry and by several ex situ diagnostics including infra-red spectroscopy, X-ray photoelectron spectroscopy, gravimetry and chemical etching. At low values of Xorg, the structure and properties of the films and optical emission spectra are very similar whatever the organosilicon precursor. At high values of Xorg, the structure and properties of the deposited films and emitting species significantly depend on the organosilicon precursor.

Diagnostics in helicon plasmas for deposition

and helicon plasmas used for plasma enhanced chemical vapour deposition of films are investigated in the 1 - 10 mTorr pressure and 0 - 800 W rf power ranges. The positive oxygen ions are analysed by energy selective mass spectrometry and Langmuir probes. The oxygen atom concentration is monitored by actinometry and ionization threshold mass spectrometry. In oxygen plasmas it is shown that is the major positive ion, and that the oxygen molecules are far from being completely dissociated, due to a very high oxygen atom recombination frequency on the reactor walls. The dissociation degree increases with the rf power reaching 10% at 500 W. In plasmas, the plasma density and electron temperature decrease as the TEOS fraction increases. In contrast, the degree of oxygen dissociation increases sharply with the addition of a few per cent TEOS, is maximum for about 5% TEOS and decreases as TEOS fraction is further increased. In a 95:5 plasma (5 mTorr, 300 W) the fluxes of oxygen positive ions and atoms impinging onto a floating substrate are estimated to be and respectively. Under these plasma conditions, near-stoichiometric films, with low OH content, are deposited at ambient temperature. The corresponding atom to ion flux ratio is about 250, which suggests the dominant role of oxygen atoms in the deposition kinetics. The comparison of the compositions of layers grown in a 5 mTorr 95:5 plasma at two rf powers confirms the major role of oxygen atoms.

Inorganic to organic crossover in thin films deposited from O2/TEOS plasmas

The structure of thin films prepared from O2/TEOS plasmas in an rf helicon reactor has been investigated using in situ UV-visible spectroscopic ellipsometry and ex situ X-ray, reflectivity, Fourier transform infrared, photoelectron and Rutherford backscattering spectroscopy. It is shown how the structure of the films evolves from an inorganic silica-like structure towards an organic SiOxCyHz framework when the relative proportion of TEOS in the plasma increases. On the one hand, the structure and properties of the silica-like films are shown to be very close to those of a thermal oxide. On the other hand, the organic films have larger refractive index and extinction coeAcient but are less dense than the SiO2-like films. It is shown that the increase in the refractive index and extinction coeAcient is correlated to the carbon incorporation into the film. It is further established that the O/Si content ratio is enhanced from about 2 to 2.5 with increasing TEOS volume fraction. This evolution is explained by the increasing number of Si‐O‐H and Si‐O‐CxHy bonds in the material at the cost of the number of ‐Si‐O‐Si‐ bonds. It is furthermore shown that the abrupt character of the transition between silica-like and organic films is likely to be correlated to the depletion in oxygen atoms in the plasma. ” 2000 Elsevier Science B.V. All rights reserved.

Silicon dioxide deposition in a microwave plasma reactor

Abstract SiO x C y H z films were deposited using hexamethyldisiloxane (HMDSO) in a 2.45 GHz microwave plasma reactor. The plasma was characterised by optical emission spectroscopy as a function of the HMDSO-to-oxygen ratio. The emission of species resulting from the dissociation and recombination of the monomer was identified. The film structure was investigated by means of FTIR spectroscopy and ellipsometry was used to determine the thickness and refractive index of the layer. The infrared spectrum and the deposition rate are strongly dependent on the HMDSO-to-O 2 ratio, whereas the refractive index is quite constant and lower than expected.

Ellipsometry and Raman study on hydrogenated amorphous carbon (a-C:H) films deposited in a dual ECR-r.f. plasma

Abstract Hydrogenated amorphous carbon ( a -C:H) films were deposited from methane in a dual microwave electron cyclotron resonance (ECR) – radio frequency (r.f.) plasma by applying an independently controlled r.f. substrate bias voltage. In situ real-time ellipsometry was used to monitor the evolution of the film growth during the deposition. The combined in situ/ex situ ellipsometry and Raman spectroscopy measurements show that the deposited film properties change from polymer-like to diamond-like depending on the presence of the applied bias voltage. The spectroscopic ellipsometry analysis exhibits a decrease in the optical bandgap energy and an increase in the sp 3 / sp 2 ratio with the r.f. bias voltage. Raman spectra have been analyzed using a four-Gaussian deconvolution procedure which allowed the assignment of the two D and G peaks as well as two additional bands at around 1170 and 1480 cm −1 suggesting the presence of a diamond phase enhanced by the presence of the r.f. bias voltage.

Impedance and electric modulus study of amorphous TiTaO thin films: highlight of the interphase effect

The influence of phases and phase’s boundaries of TiO2 and Ta2O5 in the dielectric and electric response of TiTaO (100 nm thick) elaborated by RF magnetron sputtering was highlighted by complex impedance spectroscopy. Dielectric and electric modulus properties were studied over a wide frequency range (0.1–10 5 Hz) and at various temperatures (−160 to 120 ◦ C). The diagram of Argand (e �� versus e � ) shows the contribution of phases, phases’ boundaries and conductivity effect on the electric response of TiTaO thin films. Moreover, the resistance of the material decreases when the temperature increases, thus the material exhibits a negative temperature coefficient of resistance. The electric modulus plot indicates the presence of two peaks of relaxation. The first relaxation process appears at low temperature with activation energy of about 0.22 eV and it is related to the first ionization energy of oxygen vacancies. The second relaxation process appears at high temperature with activation energy of about 0.44 eV. This second peak is attributed to the Maxwell–Wagner–Sillars relaxation. The plots of the complex dielectric modulus and the impedance as a function of frequency allow concluding to a localized relaxation due to the long-range conductivity in the TiTaO film. (Some figures may appear in colour only in the online journal)

Analysis of Low-k Organosilicon and Low-Density Silica Films Deposited in HMDSO Plasmas

Low-dielectric constant (low-k) films have been prepared by plasma-enhanced chemical vapor deposition from hexamethyldisiloxane (HMDSO). The films are analyzed by ellipsometry, infrared absorption spectroscopy while their electrical properties are deduced from C–V and I–V measurements performed on metal/insulator/silicon structures. First, it is shown that the carbon-containing silicon oxide films deposited in HMDSO and HMDSO/Ar plasmas have a dielectric constant equal to 3.0 ± 0.1 and are thermally stable at 400°C. The leakage current densities measured for an electric field of 1 MV/cm are less than 10−9 A/cm2 and the breakdown fields are in the range of 6–7 MV/cm. Then, a low-density silica film was obtained by exposing a film deposited in an HMDSO plasma to an O2 plasma. The dielectric constant of this low-density silica film is 3.5 and its breakdown field is close to 6 MV/cm.

In situ ellipsometry and infrared analysis of PECVD SiO2 films deposited in an O2/TEOS helicon reactor

Copyright (c) 1997 Elsevier Science B.V. All rights reserved. Silicon dioxide thin films have been deposited at room temperature on silicon substrates in oxygen/tetraethoxysilane (O 2 /TEOS) helicon diffusion plasmas at low pressure (5 mTorr) and 300 W rf power. The properties of the films have been measured by in and ex situ ellipsometry, ex situ infrared spectroscopy, and chemical etching (p-etch) as a function of the TEOS flow rate (Q TEOS ). The growth rate (V d ) is determined in situ using an ultra violet-visible phase modulated spectroscopic ellipsometer (1.5 to 5 eV). Two different kinetic regimes appear: at low TEOS flow rate (Q TEOS <5 sccm) V d increases linearly and no carbon species are detected while the OH content rises strongly. For higher values of Q TEOS , V d saturates at 11 nm. The change in the kinetics corresponds to the appearance of carbon impurities. The increase in the deposition rate is accompanied by a decrease in the refractive index and an increase in the p-etch rate. The Bruggeman effective medium approximation (BEMA) is used to determine the fraction of voids incorporated in the layer. It is shown that porous films incorporate water when exposed to the atmosphere. Based on this result, an explanation is proposed for the insensitivity of the stretching peak of Si-O-Si to the deposition conditions. Good quality SiO 2 films with optical properties close to that of a thermal oxide can be obtained at low deposition rates (V d <5 nm/min).

Structure and properties of silicon oxide films deposited in a dual microwave-rf plasma reactor

The characterisation of SiOx thin films deposited from hexamethyldisiloxane in a microwave plasma reactor showed they were carbon containing and porous. With the aim of improving the film quality, the substrate holder was biased with the use of a 13.56-MHz radio-frequency power supply. Results on chemical structure, deposition rate and optical emission spectroscopy are reported. The rf-induced negative bias voltage affected both gas phase reactions and film composition. Moreover, it induced change in the deposition rate.

Optical characterization of hydrogenated amorphous carbon (a-C:H) thin films deposited from methane plasma

Abstract Hydrogenated amorphous carbon ( a -C:H) thin films are deposited at low-pressure (0.35 Pa) on c -Si substrates from methane plasmas. The plasma enhanced chemical vapor deposition (PECVD) process is operated in a dual electron cyclotron resonance (ECR) – radio frequency (r.f.) reactor using an independently controlled r.f. substrate bias. The film growth and substrate temperature are monitored in situ using real time kinetic ellipsometry and fluoroptometry. The deposited films are investigated by means of ex situ UV–Visible (1.5–5.0 eV) spectroscopic ellipsometry and Fourier transform infrared spectroscopy (500–4000 cm −1 ). The dielectric functions are determined from the ellipsometric spectra using Jellison and Modines dispersion model whereas the structure of the films is examined through the use of absorption spectra. Complementary Raman measurements performed at 457 nm reveal the presence of the two main graphitic G and D peaks as well as two additional bands located at about 1170 and 1470 cm −1 . It is shown that a -C:H film optical properties change from polymer-like to diamond-like depending on the energy and flux of the hydrocarbon species impinging on the substrate.