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.     

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.     

Hard BCxNy thin films grown by dual ion beam sputtering

Boron carbonitride thin films were deposited by sputtering of a B₄C target with Ar-N₂ ion assistance. BC_xN_y films were grown onto Si (001) at room temperature. The chemical composition and the type of bonding were determined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The hardness of the films was measured with a nanoindenter. The chemical analysis of the samples indicates the formation of two different compounds, a ternary BC_xN_y and a binary carbonitride CN_x. All the films showed high hardness, in the range 16-33 GPa, which clearly increases as the BC_xN_y content in the sample increases. In this study the highest hardness (i.e. 33 GPa) was obtained when the BC_xN_y content in the sample was 50%. The average composition of this BC_xN_y was estimated by XPS as 20 at.% carbon and 12 at.% nitrogen.     

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.     

SiNx/a-SiCx:H passivation layers for p- and n-type crystalline silicon wafers

In this work we present a detailed investigation of Si surface passivation obtained by a PECVD double dielectric layer, composed of intrinsic hydrogenated amorphous silicon-carbon (a-SiC_x:H), followed by a silicon nitride (SiN_x). The double layers have been deposited on p- and n-type of mono- and multi-crystalline silicon wafers. IR spectra have been carried out to evaluate the structure of a-SiC_x:H layers on monocrystalline wafers. The passivation effects have been studied performing the following measurements: the photoconductance decay, to measure contactlessly the effective lifetime of passived mono and multi Si wafers; the capacitance voltage profile of Al/SiN_x/Si, Al/a-SiC_x:H/Si and Al/SiN_x/a-SiC_x:H/Si MIS structures, to estimate the field effect at the dielectric/silicon interface and individuate the passivation mechanism on silicon surfaces. It has been found that the mechanism of the surface passivation depends on the doping type of the silicon wafer. Indeed from C-V measurements it has been realized that the great amount of positive charge within the SiN_x is able to promote an inversion layer if it is deposited on a-SiC_x:H/Si p-type and an accumulation if it is grown on a-SiC_x:H/Si n-type.     

Excellent passivation effect of Cat-CVD SiNx/i-a-Si stack films on Si substrates

We have demonstrated that the surface recombination velocity can be lowered to as low as 1.3 cm/s for n-type c-Si wafers and to 9.0 cm/s for p-type wafers by using amorphous Si (a-Si) and Si nitride (SiN_x) stacked films prepared by catalytic chemical vapor deposition (Cat-CVD). These values are much lower than those of c-Si wafers passivated by same stacked structures formed by low-damage remote plasma-enhanced CVD (PECVD). It is revealed that Cat-CVD a-Si insertion layers play an important role to improve interface quality, and also SiN_x films are also essential for reducing the surface recombination velocity down to such low levels.     

Hydrophobic properties of the ion beam deposited DLC films containing SiOx

Diamond like carbon (DLC) films received considerable interest due to outstanding mechanical and tribological properties as well as chemical inertness and hydrophobicity. That combination is particularly interesting for possible application of the DLC as anti-sticking layers in novel lithographic techniques such as nanoimprint lithography, because Si, quartz and Ni - the most often used materials for imprint stamp formation - have high surface energy and, as a result, bad anti-adhesive properties. In present study, SiO_x containing DLC thin films were synthesized from hexamethyldisiloxane vapor and hydrogen gas mixture by direct ion beam deposition. Anti-sticking properties of the grown DLC thin films were evaluated measuring surface contact angle with water. Chemical composition and structure of the deposited films were investigated by X-ray photoelectron spectroscopy and FTIR spectrometry. Morphology of the films was measured by atomic force microscopy. Effects of hexamethyldisiloxane flux on structure, anti-sticking properties and surface morphology of the SiO_x containing DLC thin films were defined.     

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.     

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.     

Preparation of ZrNxOy films by magnetron sputtering using air as a reactive gas

Zirconium oxynitride (ZrN_xO_y) thin films were prepared by d.c. magnetron sputtering using air as a reactive gas. Replacing conventionally used N₂/O₂ with air as a reactive gas allows the process to perform at high base pressures (low vacuum), which could drastically reduce the processing time. The color of the obtained films changed from light golden and dark golden for low air/Ar flow ratios, to dark violet and bright cyan for high air/Ar ratios. X-ray diffraction patterns show that the films transformed from ZrN and Zr₂ON₂ mixed phases to a Zr₂ON₂ phase, and then an m-ZrO₂ phase. The thickness of the films decreased slightly with increasing the air/Ar flow ratio. ZrN_xO_y films possessed a mixture of Zr-N-O, Zr-N and Zr-O chemical binding states determined from X-ray photoelectron spectroscopy. ZrN_xO_y films with mainly a Zr₂ON₂ phase exhibited the band gap of 1.96-2.26 eV, while the m-ZrO₂ films with slight nitrogen incorporation had a band gap of 2.32 eV, evaluated from transmittance spectra. By varying the air/Ar ratio during deposition, the nitrogen/oxygen content of the films could be controlled and hence, the color, crystal structure, atomic composition, and band gap of the films could be tailored.     

双离子束溅射法制备铁氮薄膜

使用双离子束溅射法制得了铁氮薄膜,随着基片温度的变化,薄膜的成分是ε－Fe2-3N,γ′－Fe4N或是二相的混合物,薄膜的晶粒尺寸随基片温度的升高而增大。以振动样品磁强计（VSM）测定了薄膜的磁性能。另外,研究了在基片温度为160℃时,改变主源中通入N2／Ar的比例对薄膜成分的影响。     

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 annealing on the composition, structure and mechanical properties of carbon nitride films deposited by middle-frequency magnetron sputtering

Carbon nitride films were deposited by middle-frequency reactive magnetron sputtering and annealed at different temperatures in nitrogen ambient. X-ray photoelectron spectroscopy, Raman scattering, transmission electron microscopy, and nano-indenter were used to characterize the as-deposited and annealed films. The analysis showed that annealing resulted in the dissociation of N and C in the films. The dissociation of C happened after 500 °C and lagged behind that of N. With the increase of annealing temperature, the disorder of sp² C decreased and the films were gradually graphitized. The microstructure changed from amorphous to fullerene-like CN_x with the annealing temperature increasing to 500 °C, and then to nitridized graphite nanocrystals at 600 °C. The graphitization resulted in a drastic decreasing of hardness and modulus of the films.     

Stepwise functionalization of SiNx surfaces for covalent immobilization of antibodies

A stepwise functionalization of silicon nitride surfaces is followed by X-ray photoelectron spectroscopy (XPS). The first step involves a silanization reaction leading to the formation of a silane film with a thickness estimated by XPS of one or two molecular layers. A monoprotected homobifunctionalized linker is then used to avoid the formation of bridge structures on the surface. The linker reacts quantitatively with the amino groups of the surface as outlined by the absence of residual unreacted CNH₂/CNH₃⁺ groups in XPS analyses. Deprotection of the ester groups of the immobilized linker and subsequent reaction with N-hydroxysuccinimid lead to N-hydroxysuccinimid activated surfaces able to react with biological species. These surfaces were then incubated with anti-transferrin antibodies. As seen by XPS and atomic force microscopy analyses, the concentration and incubation conditions of antibodies are important to obtain a compact layer of antibodies on the surface. All chemical steps of the procedure are compatible with microelectronic process on silicon. Moreover, antibodies introduced under native conditions at physiological pH, in the last step of the immobilization process, recognized specifically antigens, as shown by fluorescence competitive assay.     

Deposition and properties of ZrNx films produced by radio frequency reactive magnetron sputtering

Thin ZrN_x films have been prepared by reactive radio frequency magnetron sputtering. The radio frequency power has been chosen as a sputtering parameter and the effect on the compositional and optical properties of the films was systematically studied. The films have been analyzed by X-ray photoelectron spectroscopy. The reflectance and transmittance of the samples have been recorded by a spectrophotometer in the UV-Vis-IR range. The effects of the different powers (in the range 100-400 W) on the stoichiometry of ZrN_x films have been studied. The components revealed on N 1s photoelectron peaks were correlated with different bounding states for the zirconium nitride. The threshold power value between N-rich ZrN_x films and Zr-rich ZrN_x ones is 270 W. A correlation has been observed between the optical properties and the stoichiometry of the films. In fact, the samples catalogued as N-rich by X-ray photoelectron spectroscopy analyses are optically insulating and the Zr-rich ones show a metallic behaviour. A simple growth model has been set up in order to explain the different chemical states detected from the compositional measurements.     

A new fabrication method of low stress PECVD SiNx layers for biomedical applications

A new fabrication method to produce low residual stress PECVD SiN_x layers at high deposition rates was developed and their biomedical applications were reported in this paper. This new method employed up to 600 W high power to fabricate low stress SiN_x layers in high frequency (13.56 MHz). By adjusting the composition of reactant gases, the residual stress can be lowered to 4 MPa and high deposition rate up to 320 nm/min can be achieved. In addition, this paper also investigated the influence of other important parameter, such as pressure, power and gases flow rates. Moreover, by using this optimized process, an 11 μm thick low stress SiN_x layer was produced, which will be used to fabricate large window area for cell culture. Finally, a successful cell culture test involving cultivating mouse stem cells onto the porous membrane made of these low stress PECVD SiN_x layers indicated that these layers are biocompatible and are suitable for biomedical applications.     

Mechanical properties and bonding structure of boron carbon nitride films synthesized by dual ion beam sputtering

The BCN films were synthesized on Si (110) wafers by using dual ion beam sputtering deposition from boron carbide target. The influences of ion assist source energy and N₂ relative flow rate on the surface roughness, mechanical properties and chemical bonding structure of BCN films were investigated systematically. The surface roughness was measured using non-contact optical surface profilometer and the mechanical properties of BCN films were evaluated with nano-indenter. The BCN films were characterized by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. The results showed that the BCN films' surface roughness varied in the range of 5–15 nm, and their hardness and reduced elastic modulus fluctuated in the scope of 18–29 GPa and 192–229 GPa, respectively. When the BCN films' surface roughness varied in the range of 8–12 nm, the values of hardness and reduced elastic modulus were fluctuated slightly. The BCN films with the smoothest surface (R_a = 5 nm) and the highest hardness of 28 GPa were obtained at the ion assist source energy of 200 eV and the N₂ relative flow rate of 50%. The BCN films were amorphous and contained several bonding states such as B–N, B–C and C–N with B–C–N hybridization.     

Influence of assistant ion beam on the opto-electrical properties of molybdenum doped zinc oxide films deposited on polyethersulfone via dual ion beam sputtering

An alternative transparent conductive oxide, molybdenum doped zinc oxide (MZO) was deposited onto a flexible polyethersulfone (PES) substrate by using a dual ion beam sputtering system. One argon ion beam was used to sputter a MZO target and another assistant argon ion beam was for bombarding deposits simultaneously. The assistant ion source discharge voltage and current were changed respectively for investigating their influences on the conductivity of deposited MZO films. Changing the discharge voltage shows that, the film crystallinity, carrier concentration and mobility in films all increase with the discharge voltage and subsequently decrease when the applied voltage is over 100 V. Changing the discharge current also shows a similar trend. The film crystallinity and carrier concentration initially increase with the discharge current, and thereafter a minimum for 1.4 A, and a subsequent increase in resistivity is observed. According to the results, properly raising the discharge voltage and current of assistant ion source can improve both electrical conductivity and optical transparency of deposited MZO films, but the excess discharge voltage and current will cause the grain refinement which may retard the carrier mobility and result in the lower conductivity of MZO films.     

Effect of the microstructure of Si3N4 on the adhesion strength of TiN film on Si3N4

The effect of the microstructure of silicon nitride, which was used as a substrate, on the adhesion strength of physical vapor deposited TiN film on Si₃N₄ was investigated. Silicon nitride substrates with different microstructures were synthesized by controlling the size (fine or coarse), the phase ( or β) of starting Si₃N₄ powder, and sintering temperature. The microstructure of Si₃N₄ was characterized in terms of grain size, aspect ratio of the elongated grain, and β-to- phase ratio. For a given chemical composition but different mechanical properties, such as toughness, elastic modulus, and hardness of Si₃N₄ were obtained from the diverse microstructures. Hertzian indentation was used to estimate the yield properties of Si₃N_4, such as critical loads for yield (P_y) and for ring cracking (P_c). The effect of the microstructure of Si₃N₄ on adhesion strength evaluated by scratch test is discussed. TiN films on Si₃N₄ showed high adhesion strengths in the range of 80–140 N. Hardness and the P_y of Si₃N₄ substrate were the primary parameters influencing the adhesion strength of TiN film. In TiN coating on Si₃N₄, substrates with finer grain sizes and higher phase ratios, which show high hardness and high P_y, were suitable for higher adhesion strength of TiN film.     

Reactively sputtered GaAsxN1−x thin films

Thin films of GaAs_xN_1−x alloys were deposited by reactive rf magnetron sputtering of GaAs target with a mixture of argon and nitrogen as the sputtering gas. Growth rate was found to decrease from ∼ 7 μm/h to ∼ 2 μm/h as the nitrogen content increased from 0% to 40%. XRD and TEM studies of the films reveal the presence of hexagonal GaN with a significant increase of the lattice parameters in a narrow range of composition of the sputtering gas (5-10% nitrogen), which is attributed to the incorporation of arsenic. The limited availability of nitrogen in the sputtering atmosphere is found to encourage the incorporation of arsenic in the alloy films. Optical absorption coefficient spectra of the films were obtained from reflection and transmission data. The effect of arsenic incorporation is seen in the optical absorption spectra of the films, which show a continuous shift of the absorption edge to lower energies with respect to that of gallium nitride.