An Expanding Thermal Plasma for Deposition of a-Si:H

1995 ◽  
Vol 377 ◽  
Author(s):  
R. J. Severens ◽  
G. J. H. Brussaard ◽  
H. J. M. Verhoeven ◽  
M. C. M. Van de Sanden ◽  
D. C. Schram
Keyword(s):  
Hydrogen Content ◽  
Hydrogen Plasma ◽  
Hydrogen Abstraction ◽  
Dissociative Recombination ◽  
Operating Conditions ◽  
Refractive Indices ◽  
Hydrogenated Silicon ◽  
Amorphous Hydrogenated Silicon ◽  
20 Nm

ABSTRACTA remote argon/hydrogen plasma is used to deposit amorphous hydrogenated silicon. The plasma is generated in a DC thermal arc (typical operating conditions 0.5 bar, 5 kW) and expands into a low pressure chamber (20 Pa) thus creating a plasma jet with a typical flow velocity of 103 m/s. Pure silane is injected into the jet immediately after the nozzle, in a typical flow mixture of Ar:H2:SiH4=55:10:6 scc/s. The electron temperature in the jet is low (typ. 0.3 eV) : silane radicals are thought to be produced mainly by hydrogen abstraction, but also by a sequence of dissociative charge exchange and consecutive dissociative recombination. In-situ ellipsometry yields refractive indices of 3.6–4.2 at 632.8 nm and growth rates of 10–20 nm/s. FTIR analysis yields a hydrogen content of 9–25 at.% and refractive indices of 2.7–3.3 in the infrared. The SiH density decreases with increasing hydrogen content, whereas the SiH2 density increases. Above 11 at.%, the majority of hydrogen is bonded in the SiH2 configuration. The optical bandgap remains constant at approximately 1.72 eV. The photoconductivity is of the order 101–6 (Ωcm) 1–6 and the photoresponse 106.

scholarly journals On the Effect of Substrate Temperature on a-Si:H Deposition Using an Expanding Thermal Plasma

1996 ◽  
Vol 420 ◽  
Author(s):  
R. J. Severens ◽  
M. C. M. Van De Sanden ◽  
H. J. M. Verhoeven ◽  
J. Bastiaanssen ◽  
D. C. Schram
Keyword(s):  
Growth Rate ◽  
Substrate Temperature ◽  
Urbach Energy ◽  
Hydrogen Plasma ◽  
Hydrogen Abstraction ◽  
Plasma Jet ◽  
Hydrogenated Silicon ◽  
Amorphous Hydrogenated Silicon ◽  
Simple Kinetic Model ◽  
S Deposition

AbstractFast (7 nm/s) deposition of amorphous hydrogenated silicon with a midgap density of states less than 1016 cm-3 and an Urbach energy of 50 meV has been achieved using a remote argon/hydrogen plasma. The plasma is generated in a dc thermal arc (0.5 bar, 5 kW) and expands into a low pressure chamber (20 Pa) thus creating a plasma jet with a typical flow velocity of 103 m/s. Pure silane is injected into the jet immediately after the nozzle, in a typical flow mixture of Ar:H2:SiH4=55:10:10 scc/s. As the electron temperature in the recombining plasma is low (typ. 0.3 eV), silane radicals are thought to be produced mainly by hydrogen abstraction.Material quality in terms of refractive index, conductivity, microstructure parameter and optical bandgap was found to increase monotonously with substrate temperature, even up to 350 °C; for practically all low growth rate deposition schemes an optimum around 250 °C is observed. It will be argued that this behavior is consistent with a simple kinetic model involving physisorption and hopping, growth on dangling bonds and thermal desorption of hydrogen.

Characterization and Optimization of The Tco/a-Si:H(,B) Interface for Solar Cells by In-Situ Ellipsometry and Sims/XPS Depth Profiling

1994 ◽  
Vol 336 ◽  
Author(s):  
H.N. Wanka ◽  
E. Lotter ◽  
M.B. Schubert
Keyword(s):  
Solar Cells ◽  
Light Trapping ◽  
Hydrogen Plasma ◽  
Depth Profiling ◽  
Trapping Efficiency ◽  
Force Microscopy ◽  
Hydrogen Plasmas ◽  
Atomic Force ◽  
20 Nm

ABSTRACTThe chemical reactions at the surface of transparent conductive oxides (SnO2, ITO and ZnO) have been studied in silane and hydrogen plasmas by in-situ ellipsometry and by SIMS as well as XPS depth profiling. SIMS and XPS of the interface reveal an increasing amount of metallic phases upon lowering a-Si:H growth rates (controlled by plasma power), indicating that the ion and radical impact is more than compensated by protecting the surface by a rapidly growing a-Si:H film. Hence, optical transmission of TCO films as well as the efficiency of solar cells can be improved if the first few nanometers of the p-layer are grown at higher rates. Comparing a-Si:H deposition on top of different TCOs, reduction effects on ITO and SnO2 have been detected whereas ZnO appeared to be chemically stable. Therefore an additional shielding of the SnO2 surface by a thin ZnO layer has been investigated in greater detail. Small amounts of H are detected close to the ZnO surface by SIMS after hydrogen plasma treatment, but no significant changes occur to the optical and electrical properties. In-situ ellipsometry indicates that a ZnO layer as thin as 20 nm completely protects SnO2 from being reduced to metallic phases. This provides for shielding of textured TCOs, and hence rising solar cell efficiencies, too. Regarding light trapping efficiency we additionally investigated the smoothing of initial TCO texture when growing a-Si:H on top by combining atomic force microscopy and spectroscopie ellipsometry.

Investigations on the Real-Time Monitoring of the Crystallinity of Hydrogenated Microcrystalline Silicon Films

2003 ◽  
Vol 762 ◽  
Author(s):  
Christoph Ross ◽  
Friedhelm Finger ◽  
Reinhard Carius
Keyword(s):  
Spectroscopic Ellipsometry ◽  
Time Resolution ◽  
Deposition Process ◽  
Silicon Films ◽  
Microcrystalline Silicon ◽  
Hydrogenated Silicon ◽  
20 Nm ◽  
Good Agreement ◽  
Uv Range

AbstractA method for monitoring the evolution of the crystallinity during the deposition of thin hydrogenated silicon films by using in situ spectroscopic ellipsometry is presented. The crystallinity of the topmost 10-20 nm of a film is derived from the analysis of the shape of ellipsometric spectra in the UV range. The values are closely related to parameters of the deposition process and in good agreement with Raman scattering results. Examples of different kinds of microcrystalline silicon films are shown. Improvements of the time resolution and/or accuracy are discussed. The method turns out to be well suited for process control.

An Investigation of Photo-Induced Degradation by Means of Photothermal Deflection Spectroscopy

1987 ◽  
Vol 95 ◽  
Author(s):  
M. S. Bennett ◽  
S. Wiedeman ◽  
J. L. Newton ◽  
K. Rajan
Keyword(s):  
Optical Absorption ◽  
Fermi Level ◽  
Single Peak ◽  
Defect States ◽  
Hydrogenated Silicon ◽  
Photothermal Deflection Spectroscopy ◽  
Amorphous Hydrogenated Silicon ◽  
Measured Absorption ◽  
Photothermal Deflection

AbstractAbsorption measurements of as deposited and photodegraded intrinsic amorphous hydrogenated silicon films were made using photothermal deflection spectroscopy (PDS). The films were light-soaked in situ using HeNe laser light to simulate AM1 illumination. An increase in subbandgap absorption occurred predominantly near energies of 1.2eV. A simple model was developed in which a density of states function is hypothesized and the resulting optical absorption at subgap energies is calculated. The measured absorption could be well matched in all cases by assuming a single peak of defect states at or slightly below the Fermi level. Further, the observed changes in optical absorption due to degradation could be modeled by increasing the density of the single peak of defect states and moving the Fermi level towards the valence band.

A Plasma Chemistry and Surface Model for the Deposition of a–Si:H from RF Glow Discharges: A Study of Hydrogen Content

1986 ◽  
Vol 68 ◽  
Author(s):  
Mark J. Kushner
Keyword(s):  
Hydrogen Content ◽  
Electron Distribution Function ◽  
Plasma Chemistry ◽  
Chemical Vapor ◽  
Rf Discharge ◽  
Surface Model ◽  
Plasma Parameters ◽  
Surface Deposition ◽  
Hydrogenated Silicon ◽  
Amorphous Hydrogenated Silicon

AbstractAn integrated electron kinetics, plasma chemistry, and surface deposition model has been developed to study the relationship between film characteristics and plasma parameters in the plasma enhanced chemical vapor deposition (PECVD) of amorphous hydrogenated silicon (a–Si:H) in low pressure parallel plate RF discharges.The integrated model consists of a Monte-Carlo simulation for the electron distribution function in the RF discharge, a time and spatially dependent plasma chemistry model, and a model for the surface deposition process.The surface model consists of an accounting of the surface density of adsorbed species, and the fractional distribution of various types of bonds (e.g.Si–Si, Si–H, Si–.) in the film.The calculated distribution of radicals in silane discharges will first be discussed.The computed hydrogen content and deposition rates of a-Si:H films from silane and disilane discharges are next discussed and compared to experiment.The dependence of hydrogen content on Rf power and substrate temperature is calculated and agrees well with experiment.Mechanisms are proposed to explain these dependencies.

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