Deposition of silicon nitride thin films by hot-wire CVD at 100ºC and 250ºC

Silicon nitride thin films for use as passivation layers in solar cells and organic electronics or as gate dielectrics in thin-film transistors were deposited by the Hot-wire chemical vapor deposition technique at a high deposition rate (1-3 Ǻ/s) and at low substrate temperature. Films were deposited using NH3/SiH4 flow rate ratios between 1 and 70 and substrate temperatures of 100º C and 250ºC. For NH3/SiH4 ratios between 40 and 70, highly transparent (T ~ 90%), dense films (2.56 - 2.74 g/cm3) with good dielectric properties and refractive index between 1.93 and 2.08 were deposited on glass substrates. Etch rates in BHF of 2.7 Ǻ/s and 10 MV cm−1.Fundação para a Ciência e Tecnologia (FCT) - FCT/CNRS programa com o contracto no. 20798, bolsa de investigaçao e projecto PTDC-CTM-66558-200

The effect of argon plasma treatment on the permeation barrier properties of silicon nitride layers

In this work we produce and study silicon nitride (SiNx) thin films deposited by Hot Wire Chemical Vapor Depo- sition (HW-CVD) to be used as encapsulation barriers for flexible organic photovoltaic cells fabricated on poly- ethylene terephthalate (PET) substrates in order to increase their shelf lifetime. We report on the results of SiNx double-layers and on the equivalent double-layer stack where an Ar-plasma surface treatment was performed on the first SiNx layer. The Ar-plasma treatment may under certain conditions influences the structure of the interface between the two subsequent layers and thus the barrier properties of the whole system. We focus our attention on the effect of plasma treatment time on the final barrier properties. We assess the encapsulation barrier properties of these layers, using the calcium degradation test where changes in the electrical conductance of encapsulated Ca sensors are monitored with time. The water vapor transmission rate (WVTR) is found to be ~3 × 10−3 g/m2·day for stacked SiNx double-layer with 8 min Ar plasma surface treatment.FCT - CNRS PICS (French–Portuguese no: 5336) projectDirection des Relations Extérieures, Ecole Polytechniqu

Effect of argon ion energy on the performance of silicon nitridemultilayer permeation barriers grown by hot-wire CVD on polymers

One of the authors (S.M.) acknowledges Direction des Relations Extérieures of Ecole Polytechnique for financial support.Permeation barriers for organic electronic devices on polymer flexible substrates were realized by combining stacked silicon nitride (SiNx) single layers (50 nm thick) deposited by hot-wire chemical vapor deposition process at low-temperature (~100°C) with a specific argon plasma treatment between two successive layers. Several plasma parameters (RF power density, pressure, treatment duration) as well as the number of single layers have been explored in order to improve the quality of permeation barriers deposited on polyethylene terephthalate. In this work, maximumion energy was highlighted as the crucial parameter making it possible to minimize water vapor transmission rate (WVTR), as determined by the electrical calcium test method, all the other parameters being kept fixed. Thus fixing the plasma treatment duration at 8 min for a stack of two SiNx single layers, a minimum WVTR of 5 × 10−4 g/(m2 day), measured at room temperature, was found for a maximum ion energy of ~30 eV. This minimum WVTR value was reduced to 7 × 10−5 g/(m2 day) for a stack of five SiNx single layers. The reduction in the permeability is interpreted as due to the rearrangement of atoms at the interfaces when average transferred ion energy to target atoms exceeds threshold displacement energy.The authors are grateful to Dr. R. Cortes (PMC, Ecole Polytechnique) for XRR analysis, to Dr. P. Chapon (HORIBA Jobin Yvon) for GD-OES analysis and Dr. J. Leroy (CEA Saclay) for XPS analysis. This work was partly supported by the PICS (FrenchPortuguese) project No. 5336. One of the authors (S.M.) acknowledges Direction des Relations Extérieures of Ecole Polytechnique for financial support

Crystal and magnetic structure of LaTiO3 : evidence for non-degenerate t2gt_{2g}-orbitals

The crystal and magnetic structure of LaTiO3 ~ has been studied by x-ray and neutron diffraction techniques using nearly stoichiometric samples. We find a strong structural anomaly near the antiferromagnetic ordering, T$_N$=146 K. In addition, the octahedra in LaTiO3 exhibit an intrinsic distortion which implies a splitting of the t2g-levels. Our results indicate that LaTiO3 should be considered as a Jahn-Teller system where the structural distortion and the resulting level splitting are enhanced by the magnetic ordering.Comment: 4 pages 5 figure

High density plasma enhanced chemical vapor deposition of optical thin films

Deposition of pure and Ge-doped silica as well as silicon oxynitride films has been studied in a recently developed matrix distributed electron cyclotron resonance (MDECR) reactor. Process parameters were optimized in order to obtain optical quality thin films at low substrate temperatures and high deposition rates without post-deposition treatment. The choice of injection system is shown to be of crucial importance for the deposition of high quality materials in low pressure PECVD. It has been found that injecting silane near the surface allows to obtain films with a low OH absorption independently of silane flow i.e. growth rate in a certain range of process parameters. On the contrary, in the case of uniform distribution of silane in the reactor volume the hydrogen content increases with silane flow, which affects the quality of films deposited at higher rates. With the optimized injection system, stress-free silica films with a low absorption have been deposited at the rates up to 70 nm/min at temperatures lower than 150 °C. Non-absorbing oxynitride films with a controllable refractive index ranging from 1.46 to 1.86 have been obtained from SiH4/O2/N2 mixtures. Ge-doped silica films with a Ge content of up to 4% has been deposited using a mixture GeH4 in H2 as a dopant. The properties of deposited films have been studied as a function of process parameters. The results show that the MDECR concept, that permits, in principle, unlimited scaling of substrate size, can be technology of choice for the deposition of optical thin films and functional coatings

Hydrogenated amorphous and nanocrystalline silicon solar cells deposited by HWCVD and RF-PECVD on plastic substrates at 150 °C

International audienc

Control and monitoring of optical thin films deposition in a Matrix Distributed Electron Cyclotron Resonance reactor

A range of silicon-based optical thin films have been deposited in a matrix distributed electron cyclotron resonance (MDECR) reactor. Process parameters were optimized in order to obtain optical quality thin films at low substrate temperatures and high deposition rates without post-deposition treatment. Stoichiometric silica films have been deposited at the rates up to 70 nm/min at temperatures lower than 150 °C. Oxynitride films with a controllable refractive index ranging from 1.46 to 1.86 have been obtained from SiH4/O2/N2 mixtures. Real time process control by multichannel ellipsometry has been implemented and successfully applied for the deposition of silica, silicon oxynitrides and amorphous silicon. Better than 0.3% in thickness accuracy was achieved in high rate deposition of silica layers of various predefined thickness. Refractive indices were determined in real-time with an absolute precision of 0.005–0.02. The control algorithm was used for fabrication of multilayer optical filters. The results show that the MDECR concept coupled with real-time process control by ellipsometry can be technology of choice for the deposition of interference coatings