A. Amassian

Mechanical and optical properties of hard SiCN coatings prepared by PECVD

Novel amorphous SiCN coatings are becoming increasingly attractive because of their mechanical, optical and electronic properties. In the present work, SiCN films were fabricated by PECVD from SiH4/CH4/N2/Ar gas mixtures at a temperature of 400 °C. Mechanical properties such as hardness, Youngs modulus, friction coefficient and stress were evaluated, respectively, by depth-sensing indentation, pin-on-disk, micro-scratch and curvature methods. Films deposited under optimized conditions exhibited a hardness >30 GPa, Youngs modulus >190 GPa, elastic rebound of 85% and a compressive stress of approximately 1 GPa. A friction coefficient against Al2O3, ranging from 0.75 to 0.25 and a low surface roughness of approximately 1 nm were found to be accompanied by a refractive index ranging from 1.85 to 2.10 (at 550 nm) and an extinction coefficient between 1.0×10−4 and 4.5×10−2. The film behavior is correlated with the microstructure and composition determined by SEM, XPS, AFM and broad-range UV–VIS–NIR–IR spectroscopic ellipsometry.

Growth of vacuum evaporated ultraporous silicon studied with spectroscopic ellipsometry and scanning electron microscopy

Using a combination of variable-angle spectroscopic ellipsometry and scanning electron microscopy, we investigated the scaling behavior of uniaxially anisotropic, ultraporous silicon manufactured with glancing angle deposition. We found that both the diameter of the nanocolumns and the spacing between them increase with film thickness according to a power-law relationship consistent with self-affine fractal growth. An ellipsometric model is proposed to fit the optical properties of the anisotropic silicon films employing an effective medium approximation mixture of Tauc-Lorentz oscillator and void. This study shows that the optical response of silicon films made at glancing incidence differs significantly from that of amorphous silicon prepared by other methods due to highly oriented nanocolumn formation and power-law scaling.

Plasma treatment of porous SiNx:H films for the fabrication of porous-dense multilayer optical filters with tailored interfaces

Porous and dense silicon nitride films with low (1.58) and high (1.88) refractive indices were prepared by using successively microwave and radio frequency (rf) plasma-enhanced chemical vapor deposition. Surface treatments were performed on porous layers using argon and nitrogen rf plasmas in order to densify and flatten their surface, and hence to obtain an abrupt transition between porous and dense films. The processes during deposition and interface treatment were studied by in situ real-time spectroscopic ellipsometry as well as by other characterization techniques. We show that besides the densification effect, preferential sputtering and annealing phenomena occur during plasma treatments at high bias (∣VBtreat∣>400V), leading to silicon enrichment at the film surface and chemical stabilization of the film bulk. Using atomic force microscopy, we observed a significant reduction of the thickness of the surface roughness layer after treatment for single layers (≈70% reduction) and multilayer stacks (≈6...

Optical depth profiling of strontium titanate and electro-optic lanthanum-modified lead zirconium titanate multilayer structures for active waveguide applications

Transparent polycrystalline strontium titanate (STO) and lanthanum-modified lead zirconium titanate (PLZT) thin films were deposited, respectively, on Si and on indium-doped tin oxide (ITO) coated glass by pulsed laser deposition (PLD). PLZT films are shown to exhibit electro-optic properties close to the bulk material when deposited on ITO in specific process conditions. The refractive index depth profile was determined by using a combination of variable angle spectroscopic ellipsometry and spectrophotometry, and the multisample analysis approach. PLZT films deposited at high O2 pressure, PO2, and annealed at 700°C were found to be more porous and inhomogeneous than low PO2 films. The optical properties of STO films strongly depend on PO2 as well: low PO2 depositions lead to denser film growth with homogeneous, bulk-like refractive index profile, while high PO2 depositions lead to porous and highly inhomogeneous films, exhibiting band-gap variation and formation of a 60-nm-thick interdiffusion layer on S...

Interface broadening due to ion mixing during thin film growth at the radio-frequency-biased electrode in a plasma-enhanced chemical vapor deposition environment

The authors show that ion bombardment in the range of tens to a few hundreds of eV, used in ion- and plasma-assisted deposition processes, can lead to thin film growth dominated by subsurface deposition due to subplantation (shallow implantation). This can cause significant interface broadening during the initial stages of film deposition as a result of ion mixing. First, by studying the modifications of a c-Si(100) target exposed to an O2 plasma at the radio-frequency (rf)-biased electrode using in situ real-time spectroscopic ellipsometry (RTSE), the authors detect implantation, damage, and oxidation to a depth of up to ∼10nm. They validate these results using high resolution transmission electron microscopy and simulate the effects of ion-surface interactions at the rf-biased electrode by using Monte Carlo TRIDYN simulations. The simulation code, which was modified specifically to consider a broadband ion energy source, enabled the authors to reproduce depth and time relevant experimental results with ...

Ion-surface interactions on c-Si(001) at the radiofrequency-powered electrode in low-pressure plasmas: Ex situ spectroscopic ellipsometry and Monte Carlo simulation study

We use variable-angle spectroscopic ellipsometry (VASE) to investigate oxide and interface formation during plasma-oxidation of monocrystalline Si(001) at the radiofrequency (rf) powered electrode of a plasma-enhanced chemical vapor deposition reactor. HF-etched c-Si(001) wafers were exposed to an oxygen plasma under conditions similar to those used in optical coatings deposition in order to ascertain the effects of plasma-bulk interactions, and to gauge to what depth O2+ and O+ ions interact with and alter the structure and composition of the target in the presence of negative self-bias, VB. From VASE analyses, modifications are best described using a two-layer model: A top layer consisting of SiO2 and a defective interfacial layer (DL) composed of a mixture of c-Si, a-Si, and SiO2. The saturation value of the modification depth (oxide and DL thickness) increases from 3.4±0.4to9.6±0.4nm, for VB ranging from −60to−600V, respectively, and scales with Emax1∕2, where Emax is the maximum energy of ions from a...

Dynamics of ion bombardment-induced modifications of Si(001) at the radio-frequency-biased electrode in low-pressure oxygen plasmas: In situ spectroscopic ellipsometry and Monte Carlo study

Low-pressure O2 plasma exposures were performed on c-Si(001) at a radio frequency (rf)-powered electrode in the presence of substrate self-biasing (VB) from VB=−60to−600V, in order to evaluate ion-surface interactions at the growth surface under ion bombardment conditions suitable for the fabrication of high quality optical coatings. The plasma-surface interactions were monitored in situ using real-time spectroscopic ellipsometry (RTSE), which reveals time- and ion-fluence-resolved information about depth-dependent modifications, such as damage and oxidation below the c-Si substrate surface. RTSE analysis indicates almost immediate damage formation (⪡1s) to a depth of a few nanometers below the surface after exposure to a low oxygen ion fluence (∼5×1014Ocm−2). Oxide growth is detected at intermediate fluence (∼1015–1016Ocm−2) and is attributed to O subplantation (shallow implantation); it forms near the surface of the target on top of an O-deficient interfacial damage layer (DL). Both layers experience a ...

Plasma deposition of anti-reflective coatings on spherical lenses

Plasma-enhanced chemical vapor deposition (PECVD) was used to fabricate multilayer anti-reflective coatings (ARCs) on spherical fiber couplers. Two- and four-layer designs were applied for single- and double-band ARCs centered at 1300 nm and 1550 nm, respectively. The systems consist of SiO2 as a low index material, and SiN1.3 or TiO2 as high index materials, obtained from different precursors (SiH4, SiCl4, and TiCl4). The deposition was controlled in-situ by single wavelength (632.8 nm) reflection monitoring. The optical and mechanical performance of the lenses was evaluated and related to the deposition conditions and the film microstructure.

Study of the growth and interface engineering of dense/porous SiN x optical coatings by real-time spectroscopic ellipsometry

We study the growth of dense and porous SiNx:H films deposited in radiofrequency and microwave plasmas. Ion bombardment is used to densify and flatten the surface of porous films, thus improving the quality of interfaces.