Plasma deposition of optical films and coatings: A review

Abstract

Plasma enhanced chemical vapor deposition (PECVD) is being increasingly used for the fabrication of transparent dielectric optical films and coatings. This involves single-layer, multilayer, graded index, and nanocomposite optical thin film systems for applications such as optical filters, antireflective coatings, optical waveguides, and others. Beside their basic optical properties (refractive index, extinction coefficient, optical loss), these systems very frequently offer other desirable “functional” characteristics. These include hardness, scratch, abrasion, and erosion resistance, improved adhesion to various technologically important substrate materials such as polymers, hydrophobicity or hydrophilicity, long-term chemical, thermal, and environmental stability, gas and vapor impermeability, and others. In the present article, we critically review the advances in the development of plasma processes and plasma systems for the synthesis of thin film high and low index optical materials, and in the control of plasma–surface interactions leading to desired film microstructures. We particularly underline those specificities of PECVD, which distinguish it from other conventional techniques for producing optical films (mainly physical vapor deposition), such as fabrication of graded index (inhomogeneous) layers, control of interfaces, high deposition rate at low temperature, enhanced mechanical and other functional characteristics, and industrial scaleup. Advances in this field are illustrated by selected examples of PECVD of antireflective coatings, rugate filters, integrated optical devices, and others.

Characterisation and optimisation of PECVD SiNx as an antireflection coating and passivation layer for silicon solar cells

“…Changing the deposition pressure and plasma power has a strong effect on the gas phase dissociation rate and the shape of the electron distribution function. 30,31 As pressure decreases, μW plasma becomes less confined near the quartz tubes and approaches the downstream SiH 4 gas injection region. 11 The decrease of pressure therefore enhances the dissociation of SiH 4 but suppresses the dissociation of NH 3 , leading to an increase in [Si-H] and a decrease in [N-H].…”

“…31 The main purpose of the RF plasma in our system is to create a bias voltage between the plasma and the substrate, thereby enhancing the flux of radicals onto the substrate surface. Based on the discussion above, we are not surprised to see in Figure 3 Without sufficient information on the relative amount of gas phase consumption of a precursor, also called depletion, we cannot postulate how an increase of total gas flow causes an increase of [Si-H] and a decrease of [N-H].…”

Relationship between scaling behavior and porosity of plasma-depositedTiO2thin films

“…9 This situation contrasts with the fact that through the adjustment of a wide range of experimental parameters ͑i.e., type of plasma gas, pressure, temperature, etc.͒ PECVD provides great flexibility to control the microstructure of the thin films. [10][11][12][13][14][15] The present paper aims at describing and explaining the reasons why different microstructures and porosities are obtained for TiO 2 thin films prepared by PECVD as a function of the composition of the plasma gas used for the deposition. Studies about the microstructure and porosity of TiO 2 thin films are of importance for the control of their optical properties 11,12 or their photoactivity when used as photoactive materials.…”

“…[10][11][12][13][14][15] The present paper aims at describing and explaining the reasons why different microstructures and porosities are obtained for TiO 2 thin films prepared by PECVD as a function of the composition of the plasma gas used for the deposition. Studies about the microstructure and porosity of TiO 2 thin films are of importance for the control of their optical properties 11,12 or their photoactivity when used as photoactive materials. 11 On the other hand, in the last years there has been an increasing interest in the analysis of the scaling behavior of the surface roughness and its relationship with the growing mechanisms of the thin films.…”

Hybrid C-nanotubes/Si 3D nanostructures by one-step growth in a dual-plasma reactor

“…For the generation of such nanostructures, we obtained more interesting results using Plasma Enhanced Chemical Vapour Deposition (PE-CVD) reactors, in particular a dual mode microwave/radio frequency plasma system [11][12][13][14]. Indeed, as already reported, this technique connects the advantages of microwave discharge, such as homogeneity of plasma and high concentration of active chemical species, with the ability to control ion energy by proper biasing of the substrate [14], and makes it possible to obtain many different carbon materials [15].…”