Si-nanostructures formation in amorphous silicon nitride SiNx:H deposited by remote PECVD

The formation of silicon nanoclusters embedded in amorphous silicon nitride (SiN_x:H) can be of great interest for optoelectronic devices such as solar cells. Here amorphous SiN_x:H layers have been deposited by remote microwave-assisted chemical vapor deposition at 300 °C substrate temperature and with different ammonia [NH₃]/silane [SiH₄] gas flow ratios (R=0.5−5). Post-thermal annealing was carried out at 700 °C during 30 min to form the silicon nanoclusters. The composition of the layers was determined by Rutherford back scattering (RBS) and elastic recoil detection analysis (ERDA). Fourier transform infrared spectroscopy (FTIR) showed that the densities of SiH (2160 cm⁻¹) and NH (3330 cm⁻¹) molecules are reduced after thermal annealing for SiN:H films deposited at flow gas ratio R>1.5. Breaking the SiH bonding provide Si atoms in excess in the bulk of the layer, which can nucleate and form Si nanostructures. The analysis of the photoluminescence (PL) spectra for different stoichiometric layers showed a strong dependence of the peak characteristics (position, intensity, etc.) on the gas flow ratio. On the other hand, transmission electron microscopy (TEM) analysis proves the presence of silicon nanoclusters embedded in the films deposited at a gas flow ratio of R=2 and annealed at 700 °C (30 min).     

X-ray photoelectron spectroscopy investigations of Si in non-stoichiometric SiNx LPCVD multilayered coatings

Si nanocrystals were formed in the non-stoichiometric Si-enriched SiN_x low-pressure chemical vapor deposited (LPCVD) coatings on Si wafers treated by various modes. The coating structure as a function of technological conditions was investigated by ellipsometry and X-ray photoelectron spectroscopy (XPS) depth profiling. It was found that nanocomposites on base of SiN_x films enriched by Si have a complex multilayered structure varying in dependence of deposition and annealing parameters. Analysis of the XPS spectra and Si 2s peaks shows the existence and quantity of four chemical structures corresponding to the Si–O, Si–N states, nanocrystalline and amorphous Si. The XPS results show evolution of the chemical structure of silicon nitride and formation of Si nanocrystals. It was found:

• The LPCVD technology of nanocrystals formation allows to get enough high concentration of Si nanocrystals on different depths from the sample surface.

• The volume fraction of nanocrystalline and amorphous Si is changed with depth; this relation depends from SiN_x composition and annealing parameters.

• XPS detects these two phase compositions of Si nanoparticles in SiN_x and SiO₂ layers. The ellipsometry, HR-TEM, and XPS results are in good agreement.

Effective surface passivation of crystalline silicon using ultrathin Al2O3 films and Al2O3/SiNx stacks

We measure surface recombination velocities (SRVs) below 10 cm/s on p‐type crystalline silicon wafers passivated by atomic–layer–deposited (ALD) aluminium oxide (Al₂O₃) films of thickness ≥10 nm. For films thinner than 10 nm the SRV increases with decreasing Al₂O₃ thickness. For ultrathin Al₂O₃ layers of 3.6 nm we still attain a SRV < 22 cm/s on 1.5 Ω cm p‐Si and an exceptionally low SRV of 1.8 cm/s on high‐resistivity (200 Ω cm) p‐Si. Ultrathin Al₂O₃ films are particularly relevant for the implementation into solar cells, as the deposition rate of the ALD process is extremely low compared to the frequently used plasma‐enhanced chemical vapour deposition of silicon nitride (SiN_x). Our experiments on silicon wafers passivated with stacks composed of ultrathin Al₂O₃ and SiN_x show that a substantially improved thermal stability during high‐temperature firing at 830 °C is obtained for the Al₂O₃/SiN_x stacks compared to the single‐layer Al₂O₃ passivation. Al₂O₃/SiN_x stacks are hence ideally suited for the implementation into industrial‐type silicon solar cells where the metal contacts are made by screen‐printing and high‐temperature firing of metal pastes. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interface property of silicon nitride films grown by inductively coupled plasma chemical vapor deposition and plasma enhanced chemical vapor deposition on In0.82Al0.18As

Au/silicon nitride/In_0.82Al_0.18As metal insulating semiconductor (MIS) capacitors were fabricated and then investigated by capacitance voltage (C–V) test at variable frequencies and temperatures. Two different technologies silicon nitride (SiN_x) films deposited by inductively coupled plasma chemical vapor deposition (“ICPCVD”) and plasma enhanced chemical vapor deposition (“PECVD”) were applied to the MIS capacitors. Fixed charges (N_f), fast (D_it) and slow (N_si) interface states were calculated and analyzed for the different films deposition MIS capacitors. The D_it was calculated to be 4.16 × 10¹³ cm⁻² eV⁻¹ for “ICPCVD” SiN_x MIS capacitors, which was almost the same to that of “PECVD” SiN_x MIS capacitors. The D_it value is obviously higher for the extended wavelength In_xGa_1−xAs (x > 0.53) epitaxial material as a result of lattice mismatch with substrate. Compared to the results of “PECVD” SiN_x MIS capacitors, the N_si was significantly lower and the N_f was slightly lower for “ICPCVD” SiN_x MIS capacitors. X-ray photoelectron spectroscopy (XPS) analysis shows good quality of the “ICPCVD” grown SiN_x. The low temperature deposited SiN_x films grown by “ICPCVD” show better effect on decreasing the dark current of In_xGa_1−xAs photodiodes.     

Growth and characterization of silicon nitride films on various underlying materials

Characteristics of silicon nitride (SiN_x:H) films, grown by plasma enhanced chemical vapor deposition (PECVD) on various metals such as Ta, IrMn, NiFe, Cu, and CoFe at various temperatures down to 100 °C, were studied using measurements of BHF etch rate, surface roughness and Auger electron spectroscopy (AES). The results were compared with those obtained for SiN_x:H films on Si. The deposition rate of SiN_x:H films increased slightly as deposition temperature decreased, and showed a weak dependence on the underlying materials. The surface of the nitride films deposited on all underlying materials at lower temperatures (below 150 °C) became rougher. In particular, a bubble-like surface was observed on the nitride film deposited on NiFe at 100 °C. At higher deposition temperatures (above 200 °C), SiN_x:H films on all the above metals had small RMS values, except for films on Cu which cracked at 250 °C. BHF (10:1) etch rate increased dramatically for nitride films deposited below 150 °C. For different underlying films, the BHF etch rate was quite different, but exhibited the same trend with decrease in deposition temperature. AES measurements showed that Si and N concentrations in the SiN_x:H films were only slightly different for the various deposition temperatures and underlying materials. AES depth profile of nitride films indicated that both surface O content and the depth of oxygen penetrating into SiN_x:H increased for low temperature-deposited films. However, there was no observed oxygen signal from within the films, even for films deposited at 100 °C, and both Si and N concentrations were uniform throughout the film. Received: 26 October 2001 / Accepted: 2 March 2001 / Published online: 20 June 2001     

Influence of SiNx:H film properties according to gas mixture ratios for crystalline silicon solar cells

The Hydrogenated silicon nitride (SiN_x:H) using plasma enhanced chemical vapor deposition is widely used in photovoltaic industry as an antireflection coating and passivation layer. In the high temperature firing process, the SiN_x:H film should not change the properties for its use as high quality surface layer in crystalline silicon solar cells. For optimizing surface layer in crystalline silicon solar cells, by varying gas mixture ratios (SiH₄ + NH₃ + N₂, SiH₄ + NH₃, SiH₄ + N₂), the hydrogenated silicon nitride films were analyzed for its antireflection and surface passivation (electrical and chemical) properties. The film deposited with the gas mixture of SiH₄ + NH₃ + N₂ showed the best properties in before and after firing process conditions.The single crystalline silicon solar cells fabricated according to optimized gas mixture condition (SiH₄ + NH₃ + N₂) on large area substrate of size 156 mm × 156 mm (Pseudo square) was found to have the conversion efficiency as high as 17.2%. The reason for the high efficiency using SiH₄ + NH₃ + N₂ is because of the good optical transmittance and passivation properties. Optimized hydrogenated silicon nitride surface layer and high efficiency crystalline silicon solar cells fabrication sequence has also been explained in this study.     

Photoluminescence properties of SiNx/Si amorphous multilayer structures grown by plasma-enhanced chemical vapor deposition

Very thin (nanometric) silicon layers were grown in between silicon nitride barriers by SiH₂Cl₂/H₂/NH₃ plasma-enhanced chemical vapor deposition (PECVD). The multilayer structures were deposited onto fused silica and silicon substrates. Deposition conditions were selected to favor Si cluster formation of different sizes in between the barriers of silicon nitride. The samples were thermally treated in an inert atmosphere for 1 h at 500 °C for dehydrogenation. Room-temperature photoluminescence (RT-PL) and optical transmission in different ranges were used to evaluate the optical properties of the structures. UV-VIS absorption spectra present two band edges. These band edges are well fitted by the Tauc model typically used for amorphous materials. RT-PL spectra are characterized by strong broad bands, which have a blue shift as a function of the deposition time of the silicon layer, even for as-grown samples. The broad luminescence could be associated with the confinement effect in the silicon clusters. After annealing of the samples, the PL bands red shift. This is probably due to the thermal decomposition of N-H bonds with further effusion of hydrogen and better nitrogen passivation of the nc-Si/SiN_x interfaces.     

Improved resistive switching phenomena observed in SiNx‐based resistive switching memory through oxygen doping process

The improvement of resistive switching (RS) phenomena of silicon‐nitride (SiN_x)‐based resistive random access memory (ReRAM) cells through oxygen doping process was investigated. As a result, compared to un‐doped SiN_x films, the oxygen doped SiN_x (SiN_x:O₂)‐based ReRAM cells show a lower current (～0.3 μA) level at a high resistance state and a smaller variation of operating voltage through the reduction of leakage current in the SiN_x:O₂ film by combining silicon dangling bonds and doped oxygen ions. Therefore, we believe that the oxygen doping process in SiN_x films can effectively improve the RS characteristics of SiN_x‐based ReRAM cells. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Silicon nitride/silicon oxide interlayers for solar cell passivating contacts based on PECVD amorphous silicon

This Letter demonstrates improved passivating contacts for silicon solar cells consisting of doped silicon films together with tunnelling dielectric layers. An improvement is demonstrated by replacing the commonly used silicon oxide interfacial layer with a silicon nitride/silicon oxide double interfacial layer. The paper describes the optimization of such contacts, including doping of a PECVD intrinsic a‐Si:H film by means of a thermal POCl₃ diffusion process and an exploration of the effect of the refractive index of the SiN_x. The n⁺ silicon passivating contact with SiN_x /SiO_x double layer achieves a better result than a single SiN_x or SiO_x layer, giving a recombination current parameter of ～7 fA/cm² and a contact resistivity of ～0.005 Ω cm², respectively. These self‐passivating electron‐selective contacts open the way to high efficiency silicon solar cells. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Excellent organic/inorganic transparent thin film moisture barrier entirely made by hot wire CVD at 100 °C

We present a silicon nitride/polymer hybrid multilayer moisture barrier for flexible electronics made entirely by hot wire chemical vapor deposition (HWCVD) at substrate temperatures below 100 °C. Using the initiated CVD (iCVD) variant of HWCVD for the polymer layers, these can be extremely thin, while efficiently decoupling the defects in consecutive inorganic layers. Although a single layer of low temperature SiN_x is more prone to have pinholes than its state‐of‐the‐art high temperature equivalent, we have achieved a simple three‐layer structure consisting of two low‐temperature SiN_x layers with a polymer layer in between, which is pinhole free and shows a water vapor transmission rate (WVTR) as low as 5 × 10^–6 g/m²/day at a temperature of 60 °C and a relative humidity of 90%. This WVTR is low enough for organic devices. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

硅片及其太阳电池的光衰规律研究

采用氙灯模拟太阳光源,将光强调至1000 W/m2,研究常规太阳能级单晶硅片、多晶硅片和物理提纯硅片的原片、去损减薄片、热氧化钝化片、双面镀氮化硅(SiN x:H)膜钝化片、碘酒钝化片以及太阳电池的光衰规律.利用WT-2000少子寿命测试仪以及太阳电池I-V特性测试仪分别对硅片的少子寿命和太阳电池的I-V特性参数随光照时间的变化进行了测试.结果表明:所有硅片以及太阳电池在光照的最初60 min内衰减很快随后衰减变慢,180 min之后光衰速率变得很小,几乎趋于零.     

Gas-Phase Synthesis of Silicon-Rich Silicon Nitride Nanoparticles for High Performance Lithium–Ion Batteries

The practical application of silicon-based anodes is severely hindered by continuous capacity fade during cycling. A very promising way to stabilize silicon in lithium–ion battery (LIB) anodes is the utilization of nanostructured silicon-rich silicon nitride (SiN_x), a conversion-type anode material. Here, SiN_x with structure sizes in the sub-micrometer range have been synthesized in a hot-wall reactor by pyrolysis of monosilane and ammonia. This work focusses on understanding process parameter–particle property correlations. Further, a model for the growth of SiN_x nanoparticles in this hot–wall–reactor design is proposed. This synthesis concept is of specific interest regarding simplicity, flexibility, and scalability: A way utilizing any mixtures of precursor gases to build multi-functional nanoparticles that can be directly used for LIBs instead of focusing on modification of nanostructures after they have been formed. Lab-scale production rates as high as 30 g h⁻¹ can be easily achieved and further scaled. SiN_0.7 nanoparticles provide a first cycle coulombic efficiency of 54%, a specific discharge capacity of 1367 mAh g⁻¹, and a capacity retention over 80% after 300 cycles at 0.5 C (j = 0.68 mA cm⁻²). These results imply that silicon-rich silicon nitrides are promising candidates for high-performance LIBs with very high durability.     

Structural evolution of SiNx films deposited by ECR and its light emission

Structural and optical properties of a-SiN_x films deposited by electron cyclotron resonance chemical vapor deposition (ECRCVD) have been investigated. The Fourier transform infrared (FTIR) spectroscopy shows the structural evolution of the SiN_x films, which are defined as Si-rich SiN_x and N-rich SiN_x films, also confirmed by Raman spectroscopy. The origin of the light emission for SiN_x films may be attributed to two mechanisms, i.e., quantum confinement effect (QCE) and transition of defect energy levels. The correlation between light emission and structures of SiN_x films is discussed.     

基于等离子体增强化学气相沉积技术的光电子器件多层抗反膜的设计和制作

针对光电子器件端面抗反镀膜的要求,研究了基于等离子体增强化学气相沉积(PECVD)技术的多层抗反膜的设计和制作.首先,对影响SiN_x折射率的因素进行了实验研究,确定了具有大折射率差的SiO₂/SiN_x材料的PECVD沉积条件.根据理论计算分析,设计了四层SiO₂/SiN_x抗反膜结构,能够在70 nm的波长范围内实现低于10^-4的反射率     

The relationship between the macroscopic properties of PECVD silicon nitride and oxynitride layers and the characteristics of their networks

Silicon nitride and oxynitride films have been deposited on silicon wafers using plasma-enhanced chemical vapour deposition. Various amounts of ammonia, silane and nitrous oxide gases were applied at fixed total gas flow and at the same deposition temperature. The dependence of the macroscopic properties of the layers such as refractive index, internal stress and etch rate on the reaction atmosphere during deposition has been demonstrated. The chemical structure of amorphous layers was studied using infrared spectroscopy. The network was found to be characterised by SiN_xO_yH_z tetrahedra, joined to each other by common corners. The characteristic vibrational bands due to species that join tetrahedral units (N(-Si≡)₃, ≡Si-N-Si≡, ≡Si-O-Si≡) and species that stop this interconnection (Si-H, N-H) were determined and discussed with reference to the corresponding species available during deposition. The analysis resulted in the determination of the relationship between the chemical structure of the network and the layer’s refractive index, internal stress and etch rate. Received: 24 July 2000 / Accepted: 30 May 2001 / Published online: 30 August 2001     

The effect of Si surface nitridation on the interfacial structure and electrical properties of (La2O3)0.5(SiO2)0.5 high-k gate dielectric films

Thermal stability, interfacial structures and electrical properties of amorphous (La₂O₃)_0.5(SiO₂)_0.5 (LSO) films deposited by using pulsed laser deposition (PLD) on Si (1 0 0) and NH₃ nitrided Si (1 0 0) substrates were comparatively investigated. The LSO films keep the amorphous state up to a high annealing temperature of 900 °C. HRTEM observations and XPS analyses showed that the surface nitridation of silicon wafer using NH₃ can result in the formation of the passivation layer, which effectively suppresses the excessive growth of the interfacial layer between LSO film and silicon wafer after high-temperature annealing process. The Pt/LSO/nitrided Si capacitors annealed at high temperature exhibit smaller CET and EOT, a less flatband voltage shift, a negligible hysteresis loop, a smaller equivalent dielectric charge density, and a much lower gate leakage current density as compared with that of the Pt/LSO/Si capacitors without Si surface nitridation.     

Electric-stress reliability and current collapse of different thickness SiNx passivated AlGaN/GaN high electron mobility transistors

This paper investigates the impact of electrical degradation and current collapse on different thickness SiNx passivated AlGaN/GaN high electron mobility transistors.It finds that higher thickness SiNx passivation can significantly improve the high-electric-field reliability of a device.The degradation mechanism of the SiNx passivation layer under ON-state stress has also been discussed in detail.Under the ON-state stress,the strong electric-field led to degradation of SiNx passivation located in the gate-drain region.As the thickness of SiNx passivation increases,the density of the surface state will be increased to some extent.Meanwhile,it is found that the high NH 3 flow in the plasma enhanced chemical vapour deposition process could reduce the surface state and suppress the current collapse.     

Photoinduced non-linear optical diagnostic of SiNxOy/Si111 interfaces

Anisotropic (elliptically polarized) photoinduced second harmonic generation (PISHG) in SiN_xO_y/Si1 1 1 films was proposed for contact-less monitoring of specimens with different nitrogen to oxygen (N/O) ratios. As a source for the photoinducing light, we used a nitrogen Q-switched pulse laser at wavelengths of 315, 337 and 354 nm as well as doubled frequency YAG–Nd laser wavelength (λ=530 nm). The YAG : Nd pulse laser (λ=1.06 μm; W=30 MW; τ=10–50 ps) was used to measure the PISHG. All measurements were done in a reflected light regime. We found that the output PISHG signal was sensitive to the N/O ratio and the film thickness. Measurements of the PISHG versus pumping wavelengths, powers, incident angles as well as independent measurements of the DC-electric field induced second harmonic generation indicate the major role played in this process by axially symmetric photoexcited electron–phonon states. The SiN_xO_y films were synthesized using a technique of chemical evaporation at low pressures. Films with thickness varying between 10 and 30 nm and with an N/O ratio between 0 and 1 were obtained. Electrostatic potential distribution at the Si1 1 1–SiN_xO_y interfaces was calculated. Comparison of the experimentally obtained and quantum chemically calculated PISHG data are presented. High sensitivity of anisotropic PISHG to the N/O ratio and film thickness is revealed. The role of the electron–phonon interactions in the dependencies observed is discussed. We have shown that the PISHG method has higher sensitivity than the traditional extended X-ray absorption fine structure spectroscopic and linear optical method for films with the N/O ratio higher than 0.50.     

Si-rich SiNx rear passivated c-Si solar cell with a novel antimony Local Back Surface Field formed by Laser Fired Contact

Local Back Contact (LBC) crystalline silicon solar cell with novel antimony (Sb) Local Back Surface Field (LBSF) are reported. The Sb LBSF is formed at low temperature with a Laser Fired Contacts (LFC) process. To improve the solar cell parameters of Sb LBSF, the rear passivation layer with SiN_x is optimized by varying the refractive index. The Si-rich SiN_x with a refractive index (n) of 2.7 possesses high lifetime of 2 ms with reduced absorption at a longer wavelength. The increase in lifetime is analyzed with Si–H bond concentration by FTIR. A 100 nm thick Sb layer with low laser power of 44 mW resulted in a junction depth of 500 nm with a carrier concentration of 5 × 10²⁰ cm^?3. The improved rear passivation with Si-rich SiN_x, the optimized Sb thickness yielded the best electrical results, with open circuit voltage (V_oc) of 643 mV and efficiency of 19.25%, compared to the reference cell with V_oc of 625 mV and efficiency of 18.20%.     

Enhanced rear‐side reflection and firing‐stable surface passivation of silicon solar cells with capping polymer films

Low refractive index polymer materials have been investigated with a view to form the back surface mirror of advanced silicon solar cells. SiO_x:H or AlO_y SiO_x:H polymer films were spun on top of an ultra‐thin (<10 nm) atomic‐layer‐deposited (ALD) Al₂O₃ layer, itself deposited on low‐resistivity (1 Ω cm) p‐type crystalline silicon wafers. These double‐layer stacks were compared to both ALD Al₂O₃ single layers and ALD Al₂O₃/plasma‐enhanced chemical vapour deposited (PECVD) SiN_x stacks, in terms of surface passivation, firing stability and rear‐side reflection. Very low surface recombination velocity (SRV) values approaching 3 cm/s were achieved with ALD Al₂O₃ layers in the 4–8 nm range. Whilst the surface passivation of the single ALD Al₂O₃ layer is maintained after a standard firing step typical of screen printing metallisation, a harsher firing regime revealed an enhanced thermal stability of the ALD Al₂O₃/SiO_x:H and ALD Al₂O₃/AlO_y SiO_x:H stacks. Using simple two‐dimensional optical modelling of rear‐side reflection it is shown that the low refractive index exhibited by SiO_x:H and AlO_y SiO_x:H results in superior optical performance as compared to PECVD SiN_x, with gains in photogenerated current of ～0.125 mA/cm² at a capping thickness of 100 nm. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)