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International audience

International audience

International audience

International audience

28th European Photovoltaic Solar Energy Conference and Exhibition; 1831-1834, A new method to obtain antireflection and passivation coatings of silicon solar cells is presented. In this method hydrogenated silicon nitride (SiNx:H) films are obtained by atmospheric pressure plasma-enhanced chemical vapor deposition (AP-PECVD). This process could entail an augmentation of the throughput and yield of the silicon solar cell processing and thus reduce the cost of photovoltaic systems. The chemical composition and optical properties of the AP-PECVD SiNx:H films are determined. The passivation behavior of the SiNx:H films is also characterized. To evaluate the interest of these films for the photovoltaic industry, solar cells coated with AP-PECVD SiNx:H films are obtained and compared with reference cells.

26th European Photovoltaic Solar Energy Conference and Exhibition; 2154-2160, In regards to standard low- (LF) or radio-frequency (RF) low pressure PECVD processes industrially used for antireflection and passivating coatings of silicon solar cells, very high frequency (VHF) plasmas appear as an alternative to reduce production costs. When coupled to the use of liquid precursors to replace SiH4/NH3 usual gases, they appear to be candidates for cost effective safety systems limitations. Such association is in this work employed to grow hydrogenated silicon carbide layers, oxide and nitride derivates that can present varying refractive index n that can be close to SiN:H antireflection coating. Chemically stable liquid precursors, tetramethylsilane (TMS) and tetramethyl-cyclotetrasiloxane (TMCTS), and NH3 are employed in argon, to manage Si-C, C-C, Si-O and Si-N bondings as well as bonded hydrogen content (SiHx, CHx, NHx) in SiC(N,O):H material grown on 2” silicon substrates. High plasma density PECVD using a “dual” Microwave (2.45 GHz coaxial applicators) / Low Frequency (50 kHz to apply DC bias VDC) excited plasma device was employed. Three material families are identified by varying gas mixture content (%TMS/%TMCTS/%NH3) in argon, surface DC bias and temperature for growth. In SiCN:H growth conditions (Ar/TMS/NH3 discharges with or without applied VDC), films material can be varied from carbide-like form (TMS/NH3>>) to nitride-like (TMS/NH3<>) to high oxygen content SiCO:H films (TMCTS/TMS >>) using ion bombardment that controls O rate through oxygen selective sputtering leading to n increase (1.7 < n < 2.2 at 350 °C). Carbon rich nitrides and oxides (TMS/NH3 >> or TMCTS/TMS <

26th European Photovoltaic Solar Energy Conference and Exhibition; 2161-2164

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 2101-2106, In this work, silicon carbide nitride (SiCN:H) antireflection and passivating coatings realized by plasma enhanced chemical vapor deposition (PECVD) of tetramethylsilane (TMS) / ammonia mixtures are discussed. The PECVD process parameters (pressure, total flow, precursor ratio, power, plasma modulation and deposition temperature) were varied in order to obtain homogeneous and thermally stable coatings with convenient optical index and enhanced passivating properties. The optical index and the deposition velocity are given by ellipsometry measurements and a discussion of the films chemical structure from infrared spectrometry is proposed. Lifetime measurements are made on p+nn+ structures realised on 5 inches polycrystalline n-type wafers.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 1800-1804, As an alternative to the standard industrial Low Pressure Plasma Enhanced Chemical Vapor Deposition (LP PECVD) process, an Atmospheric Pressure PECVD (AP PECVD) is under development to deposit amorphous silicon nitride SiNx:H on silicon solar cells. Due to its online integration capability, this process should improve industrial productivity. The laboratory scale reactor allows deposition in two modes: in static mode, only a limited area of the silicon substrate is covered, whereas in dynamic mode, amorphous silicon nitride is deposited on the whole substrate. Dynamic mode is representative of an industrial configuration. Compared to standard industrial low pressure PECVD silicon nitride layer, for the same refractive index, atmospheric pressure silicon nitride presents higher extinction coefficient than low pressure one. Higher silicon content coupled with lower mass density in atmospheric pressure silicon nitride could explain these results, particularly because of the presence of powders included in the atmospheric layer. To investigate these points, the morphology of the deposited layers is first studied by AFM and SEM in dynamic mode. Then, to determine the origin of the observed structure, static mode is considered.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1660-1664, This work is a comparative study of the optical and chemical properties of Hydrogenated Silicon Nitride films (SiNx:Hy) made with an atmospheric pressure PECVD (AP - Plasma Enhanced Chemical Vapor Deposition) process under development and an industrial Low Pressure (LP) PECVD reactor. The AP-PECVD films are deposited with a laboratory scale reactor using Ar, SiH4 and NH3 gas mixtures whereas the LP-PECVD silicon nitride is obtained in a Centrotherm reactor with NH3 and SiH4 as reactive gases. The optical parameters (refractive index and extinction coefficient) of the two silicon nitrides are compared before and after Rapid Thermal Annealing (RTA) by means of ellipsometric measurements and New Amorphous dispersion law. To compare the different chemistries of the layers, FTIR measurements are done, also before and after RTA. Si-H and N-H absorption peaks are related to the refractive index showing that the same optical properties are obtained with different chemical compositions. To finalize the comparison between LP and AP-PECVD, coatings have been processed on multicrystalline silicon solar cells.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1617-1622, Hydrogenated silicon carbide and silicon carbide nitride are widely studied for their good antireflective and passivating properties on both p-type and n-type crystalline silicon-based solar cells. Such materials are mainly prepared by PECVD processes using silane-hydrocarbon mixtures such as SiH4/CH4. We report the use of tetramethylsilane (TMS), a friendly-use and chemically stable liquid precursor, as a possible alternative to the wellknown dangerous and pyrophoric silane. The first aim of this work is to show the feasibility of TMS to obtain thermally stable thin layers with good antireflective properties for industrial photovoltaic applications. Deposition rate and optical properties of the films are determined by spectroscopic ellipsometry. Results are discussed as a function of the plasma composition and parameters and are correlated to the layer composition determined by FTIR spectroscopy. The surface passivation quality on crystalline FZ silicon wafers is determined by the quasi steady-state photoconductance decay (QSSPC) technique. The process leads to the deposition of homogeneous, adhesive and thermally stable layers with high growth rate (up to 70 nm/mn) and a wide range of optical index (1.6 – 2.8). However, the films do not present good passivation properties. Further understanding and optimisation is necessary.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 1576-1580, This study describes a new deposition technique of silicon nitride Antireflection Coating (ARC) at atmospheric pressure on silicon substrate. The depositions are carried out in a direct-PECVD reactor using a homogeneous Dielectric Barrier Discharge (DBD) in Ar/SiH4/NH3 gas mixture. First, deposition rate and optical properties (refractive index n) of such nitride films are determined by spectroscopic ellipsometry in regards to precursor gases ratio (R= NH3/SiH4). For R varying from 1 to 10, the refractive index changes from 2,5 to 1,8. Then, films are analysed by Fourier Transformed InfraRed (FTIR) spectroscopy in order to establish a correlation between SiNx:H chemical composition and optical properties. Refractive index variation is linked to the Si-H bonds density. Finally, the plasma phase is characterised by Optical Emission Spectroscopy (OES), and SiH peak intensity is related to refractive index to develop an in-situ control of the plasma.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 1581-1585, This work is the first step of a study of antireflecting and passivating properties of Hydrogenated Silicon Nitride films (SiNx:Hy) made with a new atmospheric pressure PECVD process. Photovoltaic properties are correlated with physico-chemical ones. Films are deposited with a laboratory scale system of Atmospheric Pressure Plasma Enhanced Chemical Vapor Deposition (AP-PECVD) using Ar, SiH4 and NH3 gas mixtures. According to experimental parameters such as the ammonia to silane ratio and the substrate temperature, the surface passivation is determined on FZ silicon wafer by photoconductance decay measurements. The evolution during the days following the deposit realization is also studied. The refractive index and the extinction coefficient are determined from ellipsometry measurements. The chemical composition of the SiNx:Hy is studied by Fourier Transformed InfraRed spectroscopy (FTIR), Secondary Ion Mass Spectroscopy (SIMS), X-ray Photoelectron Spectroscopy (XPS), and Elastic Recoil Detection Analysis (ERDA). Scanning Electron Microscopy (SEM) photographs coupled to the other diagnostics gives informations on the layer morphology. SiNx:Hy films deposited at atmospheric pressure passivate the surface of silicon wafers even if there is presence of porosity, dense layers are achieved for deposit temperatures above 330°C with a good chemical and morphological homogeneity.