Characterization of SiNx:H films deposited by rapid thermal chemical vapor deposition

Hydrogenated silicon nitride films were deposited with NH₃, SiH₄ and N₂ gas mixture at 700 °C by rapid thermal chemical vapor deposition (RTCVD) system. The NH₃/N₂ flow ratio and deposition pressure are found to influence the film properties. The stress of SiN_x:H films deposited by RTCVD is tensile, which can reach ~ 1.5 GPa in our study. The stress of SiN_x:H films is dependent on the deposition parameters, which can be associated with chemical configuration of the film. It is suggested that the presence of hydrogen atoms will relax the Si-N network, which results in the decrease of tensile stress of the SiN_x:H film.     

Properties of plasma enhanced chemical vapor deposited silicon nitride for the application in multicrystalline silicon solar cells

Hydrogenated films of silicon nitride (SiNx:H) were investigated by varying the deposition condition in plasma enhanced chemical vapor deposition (PECVD) reactor and annealing condition in infrared (IR) heated belt furnace to find the optimized condition for the application in multicrystalline silicon solar cells. By varying the gas ratio (ammonia to silane), the silicon nitride films of refractive indices 1.85-2.45 were obtained. Despite the poor deposition rate, silicon wafer with the film deposited at 450 °C showed the best minority carrier lifetime. The film deposited with the gases ratio of 0.57 showed the best peak of carrier lifetime at the annealing temperature of 800 °C. The performance parameters of cells fabricated by varying co-firing peak temperature also showed the best values at 800 °C. The multicrystalline silicon (mc-Si) solar cells fabricated in conventional industrial production line applying the optimized film deposition and annealing conditions on large area substrate (125 mm × 125 mm) was found to have the conversion efficiency of 15%.     

Visible electroluminescence from silicon nanoclusters embedded in chlorinated silicon nitride thin films

Visible electroluminescence (EL) has been obtained from devices with active layers of silicon nanocrystals embedded in chlorinated silicon nitride (Si-nc/SiN_x:Cl) thin films, deposited by remote plasma enhanced chemical vapour deposition, using SiCl₄/NH₃/H₂/Ar. The active nc-Si/SiN_x:Cl film was sandwiched between Al contacts and a transparent conductive contact of ZnO_x:Al deposited by the pyrosol process. White EL centred at around 600 nm was observed, with a turn-on voltage of 5 V, and the intensity increasing as a function of voltage. Recombination between electron-hole pairs generated in the Si-nc by electron impact ionization is proposed as the EL mechanism.     

Effect of hydrogen on SiNx films deposited by Cat-CVD method

This study is aimed at improving the characteristics of silicon nitride (SiNx) film deposited by catalytic chemical vapor deposition (Cat-CVD) method. Cat-CVD method can deposit SiNx films that have low hydrogen content and high density at low temperature without any plasma damage to substrates. Usually silane (SiH₄) and ammonia (NH₃) are used for source gases. Then adding hydrogen (H₂) gas to source gases makes characteristics of Cat-CVD SiNx improved. When using H₂ gas, hydrogen content in SiNx film becomes lower and electronic reliability becomes higher.     

Characterization of SiNx/a-Si:H crystalline silicon surface passivation under UV light exposure

One of the most promising solution for crystalline silicon surface passivation in solar cell fabrication consists in a low temperature (< 400 °C) Plasma Enhanced Chemical Vapor Deposition of a double layer composed by intrinsic hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon nitride (SiN_x). Due to the high amount of hydrogen in the gas mixture during the double layer deposition, the passivation process results particularly useful in case of multi-crystalline silicon substrates in which hydrogenation of grain boundaries is very needed. In turn the presence of hydrogen inside both amorphous layers can induce metastability effects. To evaluate these effects we have investigated the stability of the silicon surface passivation obtained by the double layer under ultraviolet light exposure. In particular we have verified that this double layer is effective to passivate both p- and n-type crystalline silicon surface by measuring minority carrier high lifetime, via photoconductance-decay. To get better inside the passivation mechanisms, strongly connected to the charge laying inside the SiN_x layer, we have collected the Infrared spectra of the SiN_x/a-Si:H/c-Si structures and we have monitored the capacitance-voltage profiles of Al/SiN_x/a-Si:H/c-Si Metal Insulator Semiconductor structures at different stages of UltraViolet (UV) light exposure. Finally we have verified the stability of the double passivation layer applied to the front side of solar cell devices by measuring their photovoltaic parameters during the UV light exposure.     

Effect of NH3 flow rate on growth, structure and luminescence of amorphous silicon nitride films by electron cyclotron resonance plasma

In this paper, hydrogenated amorphous silicon nitride (a-SiN_x:H) films have been deposited using an electron cyclotron resonance chemical vapor deposition system. The effect of NH₃ flow rate R on the deposition rate, structure and luminescence were studied using various techniques such as optical emission spectroscopy, Fourier Transform Infrared absorption (FTIR), X-ray photoelectron spectroscopy (XPS) and fluoro-spectroscopy, respectively. Optical emission behavior of SiH₄ + NH₃ plasma shows that atomic Si radical concentration determines the film deposition rate. Structural transition of a-SiN_x film from Si-rich one to near-stoichiometric/N-rich one with R was revealed by FTIR and the two phase separation of a-Si and a-Si₃N₄ was also convinced in Si-rich SiN_x films by XPS. Either photo- or electroluminescence for all the SiN_x films with R > 3 sccm shows a strong light emission in visible light wavelength range. As R < 6 sccm, recombination of electrons and holes in a-Si quantum dots is the main mechanism of photo/electroluminescence for Si-rich SiN_x films, however, for photoluminescence, gap states' luminescence is also in competition; as R > 6 sccm, light emission of the SiN_x film originates from defect states in its band gap.     

Bulge testing and fracture properties of plasma-enhanced chemical vapor deposited silicon nitride thin films

The mechanical properties and fracture behavior of silicon nitride (SiN_x) thin film fabricated by plasma-enhanced chemical vapor deposition is reported. Plane-strain moduli, prestresses, and fracture strengths of silicon nitride thin films deposited both on a bare Si substrate and on a thermally oxidized Si substrate were extracted using bulge testing combined with a refined load-deflection model of long rectangular membranes. The plane-strain moduli and prestresses of SiN_x thin films have little dependence on the substrates, that is, for the bare Si substrate, they are 133 ± 19 GPa and 178 ± 22 MPa, respectively, while for the thermally oxidized substrate, they are 140 ± 26 GPa and 194 ± 34 MPa, respectively. However, the fracture strength values of SiN_x films grown on the two substrates are quite different, i.e., 1.53 ± 0.33 GPa and 3.08 ± 0.79 GPa for the bare Si substrate and the oxidized Si substrate, respectively. The reference stresses were computed by integrating the local stress of the membrane at the fracture over the edge, surface, and volume of the specimens and fitted with the Weibull distribution function. For SiN_x thin film produced on the bare Si substrate, the volume integration gave a significantly better agreement between data and model, implying that the volume flaws are the dominant fracture origin. For SiN_x thin film grown on the oxidized Si substrate, the fit quality of surface and edge integration was significantly better than the volume integration, and the dominant surface and edge flaws could be caused by buffered HF attacking the SiN_x layer during SiO₂ removal.     

Hot Wire CVD for thin film triple junction cells and for ultrafast deposition of the SiN passivation layer on polycrystalline Si solar cells

We present recent progress on hot-wire deposited thin film solar cells and applications of silicon nitride. The cell efficiency reached for μc-Si:H n-i-p solar cells on textured Ag/ZnO presently is 8.5%, in line with the state-of-the-art level for μc-Si:H n-i-p's for any method of deposition. Such cells, used in triple junction cells together with hot-wire deposited proto-Si:H and plasma-deposited SiGe:H, have reached 10.5% efficiency. The single junction μc-Si:H n-i-p cell is entirely stable under prolonged light soaking. The triple junction cell, including protocrystalline i-layers, is within 3% stable, due to the limited thicknesses of the two top cells. The application of SiN_x:H at a deposition rate of 3 nm/s to polycrystalline Si wafer solar cells has led to cells with 15.7% efficiency. We have also achieved record high deposition rates of 7.3 nm/s for transparent and dense SiN_x;H. Hot-wire SiN_x:H is likely to be the first large commercial application of the Hot Wire CVD (Cat-CVD) technology.     

Deposition of device quality silicon nitride with ultra high deposition rate (> 7 nm/s) using hot-wire CVD

The application of hot-wire (HW) CVD deposited silicon nitride (SiN_x) as passivating anti-reflection coating on multicrystalline silicon (mc-Si) solar cells is investigated. The highest efficiency reached is 15.7% for SiN_x layers with an N/Si ratio of 1.20 and a high mass density of 2.9 g/cm³. These cell efficiencies are comparable to the reference cells with optimized plasma enhanced (PE) CVD SiN_x even though a very high deposition rate of 3 nm/s is used. Layer characterization showed that the N/Si ratio in the layers determines the structure of the deposited films. And since the volume concentration of Si-atoms in the deposited films is found to be independent of the N/Si ratio the structure of the films is determined by the quantity of incorporated nitrogen. It is found that the process pressure greatly enhances the efficiency of the ammonia decomposition, presumably caused by the higher partial pressure of atomic hydrogen. With this knowledge we increased the deposition rate to a very high 7 nm/s for device quality SiN_x films, much faster than commercial deposition techniques offer [S. von Aichberger, Photon Int. 3 (2004) 40].     

Post deposition annealing temperature effect on silicon quantum dots embedded in silicon nitride dielectric multilayer prepared by hot-wire chemical vapor deposition

The preparations of the 20-period of a Si quantum dot (QD)/SiN_x multilayer in a hot-wire chemical vapor deposition (HWCVD) chamber is presented in this paper. The changes in the properties of Si-QDs after the post deposition annealing treatment are studied in detail. Alternate a-Si:H and SiN_x layers are grown in a single SiN_x deposition chamber by cracking SiH₄, and SiH₄ + NH₃, respectively at 250 °C. The as-deposited samples are annealed in the temperature range of 800 °C to 950 °C to grow Si-QDs. All the samples are characterized by confocal micro Raman, transmission electron microscope (TEM), and photoluminescence (PL) to study the changes in the film structures after the annealing treatment. The micro Raman analysis of the samples shows the frequency line shifting from 482 cm^− 1 to 500 cm^− 1 indicating the Si transition from an amorphous to a crystalline phase. The TEM micrograph inspection indicates the formation of Si-QDs of size 3 to 5 nm and a density of 5 × 10¹²/cm². The high resolution TEM micrographs show an agglomeration of Si-QDs with an increase in the annealing temperature. The PL spectra show a peak shifting from 459 nm to 532 nm with increasing the annealing temperature of the film.     

Protection of organic light-emitting diodes over 50 000 hours by Cat-CVD SiNx/SiOxNy stacked thin films

Silicon oxynitride (SiO_xN_y) films have been formed by adding proper amount of oxygen gas to usual forming condition of silicon nitride (SiN_x) films in catalytic chemical vapor deposition (Cat-CVD) method. The composition and refractive index of the film can be systematically controlled by changing oxygen flow rate. Organic light-emitting diodes (OLEDs) covered with SiN_x/SiO_xN_y stacked films have been completely protected from damage due to oxygen and moisture and their initial emission intensity is maintained over 1000 hours under 60 °C and 90% RH, which is equivalent to 50 000 hours in normal temperature and humidity conditions.     

Influence of N2 flow rate on the mechanical properties of SiNx films deposited by microwave electron cyclotron resonance magnetron sputtering

Hydrogen-free amorphous silicon nitride (SiN_x) films were deposited at room temperature by microwave electron cyclotron resonance plasma-enhanced unbalance magnetron sputtering. Varying the N₂ flow rate, SiN_x films with different properties were obtained. Characterization by Fourier-transform infrared spectrometry revealed the presence of Si-N and Si-O bonds in the films. Growth rates from 1.0 to 4.8 nm/min were determined by surface profiler. Optical emission spectroscopy showed the N element in plasma mainly existed as N⁺ species and N₂⁺ species with 2 and 20 sccm N₂ flow rate, respectively. With these results, the chemical composition and the mechanical properties of SiN_x films strongly depended on the state of N element in plasma, which in turn was controlled by N₂ flow rate. Finally, the film deposited with 2 sccm N₂ flow rate showed no visible marks after immersed in etchant [6.7% Ce(NH₄)₂(NO₃)₆ and 93.3% H₂O by weight] for 22 h and wear test for 20 min, respectively.     

Evolution of optical properties with deposition time of silicon nitride and diamond-like carbon films deposited by radio-frequency plasma-enhanced chemical vapor deposition method

The paper presents investigations of the optical properties of thin high-refractive-index silicon nitride (SiN_x) and diamond-like carbon (DLC) films deposited by the radio-frequency plasma-enhanced chemical vapor deposition method for applications in tuning the functional properties of optical devices working in the infrared spectral range, e.g., optical sensors, filters or resonators. The deposition technique offers the ability to control the film's optical properties and thickness on the nanometer scale. We obtained thin, high-refractive-index films of both types at deposition temperatures below 350 °C, which is acceptable under the thermal budget of most optical devices. In the case of SiN_x films, it was found that for short deposition processes (up to 5 min long) the refractive index of the film increases in parallel with its thickness (up to 50 nm), while for longer processes the refractive index becomes almost constant. For DLC films, the effect of refractive index increase was observed up to 220 nm in film thickness.     

Double layer SiNx:H films for passivation and anti-reflection coating of c-Si solar cells

In this report, we present a cost effective simple innovative approach to fabricate double layer anti-reflection (DLAR) coatings using a single material which can provide high qualities of passivation and anti-reflection property. Two layers of SiN_x:H films with different refractive indices were deposited onto p-type c-Si wafer using plasma enhanced chemical vapor deposition reactor by controlling the NH₃ and SiH₄ gas ratio. Refractive indices of top and bottom layers were chosen as 1.9 and 2.3 respectively. The effect of passivation at the interface was investigated by effective carrier lifetime, hydrogen concentration and interface trapped density (D_it) measurements. The optical characteristic was analyzed by reflectance and transmittance measurements. A superior efficiency of 17.61% was obtained for solar cells fabricated with DLAR coating when compared to an efficiency of 17.24% for cells with SLAR coating. Further, J_sc and V_oc of solar cell with DLAR coating is increased by a value of ~ 1 mA/cm² and 4 mV respectively than cell with SLAR coating.     

Characteristics of bottom-gate low temperature nanocrystalline silicon thin film transistor fabricated by hydrogen annealing of gate dielectric layer

Thin film transistors having nanocrystalline silicon as an active layer were fabricated by catalytic-CVD at a low process temperature (≤ 200 °C). The tri-layer of the bottom-gate TFT was deposited continuously inside the Cat-CVD reactor. In order to improve the quality of the gate dielectric layer an in-situ hydrogen annealing step was introduced in between the silicon nitride and the nanocrystalline silicon deposition steps. The in-situ hydrogen annealing was effective in reducing the hysteresis in the C-V characteristics and in enhancing the breakdown voltage by decreasing the defects inside the SiN_x film.     

Intrinsic stress effect on fracture toughness of plasma enhanced chemical vapor deposited SiNx:H films

The apparent fracture toughness for a series of plasma enhanced chemical vapor deposition SiN_x:H films with intrinsic film stress ranging from 300 MPa tensile to 1 GPa compressive was measured using nanoindentation. The nanoindentation results show the measured fracture toughness for these films can vary from as high as > 8 MPa⋅√m for films in compression to as low as < 0.5 MPa⋅√m for the films in tension. Other film properties such as density, Young's modulus, and hydrogen content were also measured and not observed to correlate as strongly with the measured fracture toughness values. Various theoretical corrections proposed to account for the presence of intrinsic or residual stresses in nanoindent fracture toughness measurements were evaluated and found to severely underestimate the impact of intrinsic stresses at thicknesses ≤ 3 μm. However, regression analysis indicated a simple linear correlation between the apparent fracture toughness and intrinsic film stress. Based on this linear trend, a stress free/intrinsic fracture toughness of 1.8 ± 0.7 MPa⋅√m was determined for the SiN_x:H films.     

The effect of composition on the bond structure and refractive index of silicon nitride deposited by HWCVD and PECVD

Silicon nitride (SiN_x) is a material with many applications and can be deposited with various deposition techniques. Series of SiN_x films were deposited with HWCVD, RF PECVD, MW PECVD and LF PECVD. The atomic densities are quantified using RBS and ERD. The influence of the atomic densities on the Si-N and Si-Si bond structure is studied. The density of N-N bonds is found to be negligible. New Si-N FTIR proportionality factors are determined which increase with increasing N/Si ratio from 1.2 · 10¹⁹ cm^− 1 for Si rich films (N/Si = 0.2) to 2.4 · 10¹⁹ cm^− 1 for N rich films (N/Si = 1.5). The peak position of the Si-H stretching mode in the FTIR spectrum is discussed using the chemical induction model. It is shown that especially for Si-rich films the hydrogen content affects the Si-H peak position. The influence of the composition on the refractive index of the films is discussed on the basis of the Lorentz-Lorenz equation and the Kramers-Kronig relation. The decreasing refractive index with increasing N/Si ratio is primarily caused by an increase of the band gap.     

Amorphous silicon carbide thin films (a-SiC:H) deposited by plasma-enhanced chemical vapor deposition as protective coatings for harsh environment applications

We investigated amorphous silicon carbide (a-SiC:H) thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) as protective coatings for harsh environment applications. The influence of the deposition parameters on the film properties was studied. Stoichiometric films with a low tensile stress after annealing (< 50 MPa) were obtained with optimized parameters. The stability of a protective coating consisting of a PECVD amorphous silicon oxide layer (a-SiO_x) and of an a-SiC:H layer was investigated through various aging experiments including annealing at high temperatures, autoclave testing and temperature cycling in air/water vapor environment. A platinum-based high-temperature metallization scheme deposited on oxidized Si substrates was used as a test vehicle. The a-SiO_x/a-SiC:H stack showed the best performance when compared to standard passivation materials as amorphous silicon oxide or silicon nitride coatings.     

Formation of gold nanoparticles in silicon suboxide films prepared by plasma enhanced chemical vapour deposition

Nanostructured materials fabricated by dispersing metal particles on the dielectric surface have potential application in the field of nanotechnology. Interfacial metal particles/dielectric matrix interaction is important in manipulating the structural and optical properties of metal/dielectric films. In this work, a thin layer of gold (Au) was sputtered onto the surface of silicon oxide, SiO_x (0.38 < x < 0.68) films which was deposited at different N₂O/SiH₄ flow rate ratios of 5 to 40 using plasma enhanced chemical vapor deposition (PECVD) technique prior to the annealing process at 800 °C. FTIR spectra demonstrate the intensity and full-width at half-maximum (FWHM) of Si-O-Si stretching peaks are significantly dependent on the N₂O/SiH₄ flow-rate ratio, η. The films deposited at low and high N₂O/SiH₄ flow rate ratios are dominated by the oxygen and silicon contents respectively. The size and concentration of Au particles distributed on the surface of SiO_x films are dependent on the N₂O/SiH₄ flow-rate ratio. High concentrations of Au nanoparticles are distributed evenly on the surface of the film deposited at N₂O/SiH₄ flow-rate ratio of 30. Crystallinity and crystallite sizes of Au are enhanced after the thermal annealing process. Appearance of surface plasma resonance (SPR) absorption peaks at 524 nm for all samples are observed as a result of the formation of Au particles. The annealing process has improved SPR peaks for all the as-deposited films. The energy gap of the as-deposited Au/SiO_x films are in the range of 3.58 to 4.38 eV. This energy gap increases after the thermal annealing process except for the film deposited at η = 5.