Vapor Deposited Silicon Nitride Research Articles

Hydrogen diffusion in silicon from plasma-enhanced chemical vapor deposited silicon nitride film at high temperature

The stable hydrogen isotope deuterium (D), which is released during the annealing of deuterated silicon nitride films, diffuses through the crystalline silicon and is captured by a thin, amorphous layer of silicon sputtered on the rear surface. We report on the measurement of the concentration of “penetrated” D by secondary ion mass spectrometry to monitor the flux of D diffusing through single-crystalline silicon wafers. The penetrated D content in the trapping layer increases with the annealing time. However, the flux of D injected into the silicon from the silicon nitride layer decreases as annealing time increases.

Red-shifting the surface plasmon resonance of silver nanoparticles for light trapping in solar cells

AbstractSurface plasmons in metallic nanoparticle arrays have been shown to increase the absorption of an underlying silicon substrate. This has wide ranging applications, not least in the photovoltaic industry. Incident light excites localised surface plasmons in the silver nanoparticles and is coupled into the silicon in trapped modes. The radiative behaviour of the nanoparticle film is changed by the proximity of a high refractive index surface, causing radiation to be directed into the silicon and providing a light-trapping layer. We investigate a simple and effective method of tuning the surface plasmon resonance frequency, and hence the spectral region at which the absorption enhancement is seen, by varying the underlying dielectric. The particle geometry and distribution are modified by the surface conditions provided by the dielectric layer, and both this and the change in refractive index alter the resonance position. Three common dielectrics used in the photovoltaic industry were investigated as surfaces on which to form arrays of self-assembled silver nanoparticles atmospheric pressure chemical vapour deposited titanium dioxide (APCVD TiO2), low pressure chemical vapour deposited silicon nitride (LPCVD Si3N4) and thermally grown silicon dioxide (SiO2). We show, by optical and electrical measurements, that the red-shifted resonances produced by nanoparticle films on APCVD TiO2, and LPCVD Si3N4 with relatively high refractive indices, correspond to an increase in optical absorption and external quantum efficiency in thin, crystalline solar cells at longer wavelengths.

Process condition dependence of mechanical and physical properties of silicon nitride thin films

This study uses a resonance method to determine Young’s modulus (E), shear modulus (G), and Poisson’s ratio (ν) of plasma-enhanced chemical vapor deposited silicon nitride (SiNxHy) thin films deposited under varying process conditions. The resonance method involves exciting the bending and torsional vibration modes of a microcantilever beam fabricated from a film. The E and G values can be extracted directly from the bending and torsional vibration modes, and the ν value can be determined from the calculated E and G values. The density (ρ) of the films was determined using a quartz crystal microbalance method. In order to determine the validity of the resonance method, finite element modeling was used to determine its dependence on microcantilever beam dimensions. Over a deposition temperature range of 100–300°C, measured E, G, and ν values varied within 54–193GPa, 22–77GPa, and 0.20–0.26 with changes in process conditions, respectively. Over the same deposition range, measured ρ values varied within 1.55–2.80g∕cm3 with changes in process conditions.

A comparison of zinc oxide thin-film transistors on silicon oxide and silicon nitride gate dielectrics

We compared the properties of ZnO thin-film transistors in the inverted coplanar geometry on thermally grown silicon oxide gate dielectric to devices on silicon nitride, grown by plasma-enhanced chemical vapor deposition at 150 °C or magnetron sputtering at room temperature. The ZnO semiconductor was sputtered without substrate heating at oxygen partial pressures in the range of 10−5−10−4 Torr. At the lowest oxygen partial pressure, transistor characteristics were similar for all dielectrics. The field-effect mobility approached ∼5 cm2/V s and devices generally operated in depletion mode. With increasing oxygen partial pressure, the mobility decreased by 1000× on SiO2, whereas the decrease on silicon nitride was considerably smaller. On SiO2 the threshold voltage was >30 V but <5 V on silicon nitride. Devices on SiO2 operated in enhancement mode, whereas they operated in depletion mode on PECVD silicon nitride. Photoluminescence of ZnO revealed that deep-level emission depended on the specific dielectric on which ZnO was grown. Green emission for ZnO on chemically vapor-deposited silicon nitride was consistent with the presence of oxygen vacancies in ZnO. Yellow emission for ZnO on silicon oxide was associated with electron acceptor defects, such as oxygen adsorbed in grain boundaries or interstitially in ZnO. We concluded that differences in transistor properties were attributable to modification of ZnO defect chemistry, mediated by growth on a specific dielectric.

Poisson's Ratio of Low-Temperature PECVD Silicon Nitride Thin Films

In this paper, the Poisson's ratio of low-temperature plasma-enhanced chemical vapor deposited silicon nitride thin films has been determined by a modified double-membrane bulge test. This test method utilizes a square membrane and a large-aspect-ratio rectangular membrane that is fabricated alongside from the same thin film. The Poisson's ratio is determined from the ratio of the bulge deflections of the two membranes under an applied pressure. The method is suitable for determining of either stress-free thin films or those containing low tensile residual stresses. Poisson's ratio values of 0.23 0.02 and 0.25 0.01 were measured for films that were deposited at 125 and 205 , respectively.

Reactive Ion Etching of Titanium Tungsten Thin Films

Reactive ion etching processes on titanium tungsten thin films have been investigated with , , and feed gases. Process parameters such as feed gas composition, radio-frequency power, and pressure showed tremendous effects on the etch rate and the etch selectivity. Both F and Cl are effective etchants for the titanium tungsten film. The etch rate is chemically controlled by the F concentration in the plasma, and by the sum of Cl and F concentrations in the and plasmas. The etch rate is a function of both the plasma phase etchant concentration and the ion bombardment energy. The peak etch rate was obtained at the medium pressure range, e.g., , due to the combination of the above two factors. The F residue was detected on the plasma etched surface, while a trace amount of Cl was detected on the plasma etched surface. Although the plasma-enhanced chemical vapor deposition silicon nitride was etchable with the same type of plasma, an etch selectivity of greater than 2 was achieved under the low ion bombardment condition.

Dynamic NBTI characteristics of PMOSFETs with PE-SiN capping

Negative-bias-temperature instability (NBTI) characteristics of strained p-channel metal–oxide–semiconductor field-effect transistors (PMOSFETs) under dynamic and AC stressing were investigated in this work. The compressive strain in the channel was deliberately induced by a plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiN) capping layer in this study. It was found that the capping would degrade the NBTI characteristics, although the degradation is relieved when the stress frequency increases. The aggravated NBTI behaviors are ascribed to the higher amount of hydrogen incorporation during SiN deposition.

The effect of low pressure chemical vapor deposition of silicon nitride on the electronic interface properties of oxidized silicon wafers

AbstractThe effect of LPCVD Si3N4 film deposition on oxidized Si wafers, to form Si3N4/SiO2/Si stacks, is studied using capacitance–voltage and carrier lifetime measurements. The deposition of a nitride film leads to an increase in the density of defects at the Si–SiO2 interface, with the increase being greater the thinner the oxide. However, even the presence of a very thin intermediate oxide results in a dramatic improvement in interface properties compared to the direct deposition of the Si3N4 film on Si. The interface degradation occurs in the initial stages of nitride film deposition and appears to be largely the result of increased interfacial stress. Subsequent thermal treatments do not result in significant further degradation of the Si–SiO2 interface (except for a loss of hydrogen), again in contrast to the case where the nitride films is deposited onto Si. Copyright © 2007 John Wiley & Sons, Ltd.

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%.

Improved Silicon Nitride Surfaces for Next-Generation Microarrays

This work reports how the use of a standard integrated circuit (IC) fabrication process can improve the potential of silicon nitride layers as substrates for microarray technology. It has been shown that chemical mechanical polishing (CMP) substantially improves the fluorescent intensity of positive control gene and test gene microarray spots on both low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) silicon nitride films, while maintaining a low fluorescent background. This results in the improved discrimination of low expressing genes. The results for the PECVD silicon nitride, which has been previously reported as unsuitable for microarray spotting, are particularly significant for future devices that hope to incorporate microelectronic control and analysis circuitry, due to the film's use as a final passivating layer.

Oxidation of PECVD SiN x thin films

The effect of heat treatment on the chemical structure of low-temperature plasma-enhanced chemical vapor deposited silicon nitride thin films is presented. The deposited films were heat treated to temperatures up to 1373 K in air. The chemical composition of the films was analysed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. It was found that the as-deposited films contained Si, N and H in varying proportions, depending on deposition and post-deposition treatment conditions. Upon heating to elevated temperatures, N lost from the films in two stages by different mechanisms. The decrease in N concentration at relatively low heat treatment temperatures (<673 K) is due to loss of N–H bonded N, whereas, the decrease at higher temperatures is due to the oxidation conversion of the SiN x matrix. Heating to high temperatures also resulted in the removal of H.

Radio frequency magnetron sputtering of Au and low temperature plasma enhanced chemical vapor deposition of silicon nitride for ring ultramicroelectrodes fabrication

A procedure of fabricating ring ultramicroelectrodes (UMEs) is presented that employs radio frequency (RF) magnetron sputtering and low temperature plasma enhanced chemical vapor deposition (PECVD) technique. Specially, the fabrication of Au ring UMEs is described. The 125 μm diameter optical fibers are concentrically coated by RF magnetron sputtering with Au films of 300 nm thickness and then insulated by low temperature PECVD with silicon nitride films of 0.7 μm thickness. The silicon nitride films are found to be free of microcracks and characterized with excellent adhesion at the interfaces of Au films/silicon nitride films and silicon nitride films/optical fibers by scanning electron microscopy (SEM). In the electrochemical experiments the optical fiber scribe is used to produce tip surface. The electrochemical responses are sigmoidal in shape at different scan rates and indicate that the fabricated Au ring electrodes exhibit electrochemical response of UMEs. The diffusion-limited steady-state currents show that microgaps or microcracks of silicon nitride thin film at the electrode tip may be developed or that the quality of adhesion at the interfaces of silicon nitride thin film/Au thin film and Au thin film/optical fiber may be destroyed in the process of producing the electrode tip surfaces with the carbide fiber scribe, so a polishing fixture should be specifically developed to produce the electrode active surface for the quantitative analyses of ring UMEs with small overall size base on the RF magnetron sputtering and PECVD techniques.

Passivation of air-exposed AlGaAs using low frequency plasma-enhanced chemical vapor deposition of silicon nitride

The authors report on the development of a simple passivation technique of air-exposed AlxGa1−xAs using (NH4)2S treatment and low frequency plasma-enhanced chemical vapor deposition of silicon nitride. Metal-insulator-semiconductor capacitors were fabricated on p-AlxGa1−xAs substrates and characterized using capacitance-voltage and conductance-frequency measurements. Modulation of the surface potential is observed and unpinning of Fermi level is demonstrated. The minimum interface state density as estimated using conductance method is in the order of (2–3)×1012cm−2eV−1. The passivation potential of the low frequency plasma may be explained by the high level of hydrogen bombardment of the substrate.

Defect generation at SiO2∕Si interfaces by low pressure chemical vapor deposition of silicon nitride

Low pressure chemical vapor deposition of Si3N4 on oxidized Si (111) surfaces causes a change in the properties of the dominant interface defect, the Pb center, observed by electron paramagnetic resonance. The change in the signature of the Pb center is consistent with the formation of an oxynitride layer at the interface, which could be formed during the initial stages of nitride layer deposition. Photoconductivity decay measurements show a concomitant increase in the minority carrier recombination rate at the Si surface. The modified Si surface shows a worse thermal stability than the as-oxidized Si surface.

Passivation of boron emitters on n-type silicon by plasma-enhanced chemical vapor deposited silicon nitride

A well-passivated emitter is crucial to making high efficiency solar cells. With several reported potential benefits in using n-type silicon compared to p-type silicon for solar cell applications, there is a need to investigate silicon nitride passivation on boron-diffused emitters. The passivation of plasma-enhanced chemical vapor deposited silicon nitride with different refractive indices on a variety of boron doping profiles on 1Ωcm, float zoned, n-type silicon is studied. Contrary to the general perceptions that silicon nitride provides relatively poor passivation on boron-diffused surfaces, our results show that for some diffusion sheet resistances and with sufficient annealing, silicon nitride can be particularly well suited for passivating boron emitters. One-sun implied open circuit voltages of 663 and 718mV and dark saturation current densities of 25 and 13fA∕cm2 per side are achieved by silicon nitride passivation on moderately doped boron emitters (100Ω∕sq) and lightly doped boron emitters (240Ω∕sq), respectively.

Device Characteristics and Aggravated Negative Bias Temperature Instability in p-Channel Metal–Oxide–Semiconductor Field-Effect Transistors with Uniaxial Compressive Strain

P-channel metal–oxide–semiconductor field-effect transistors (PMOSFETs) featuring poly-SiGe gates and compressive strain channels were investigated. The compressive strain in the channel was deliberately induced in this study by a plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiN) capping layer over the gate. Our results indicate for the first time that, while strain channel engineering serves as an effective method to enhance drive current for scaled complementary metal–oxide–semiconductor (CMOS) devices consistent with literature reports, it also simultaneously aggravates the negative bias temperature instability (NBTI) of scaled devices. The aggravated NBTI behavior is ascribed to a higher amount of hydrogen incorporation during SiN deposition as well as a higher strain energy stored in the channel. Saturation phenomena in the shift of threshold voltage and generation of interface states are observed at high stress temperatures and long stress times. Moreover, transconductance degradation in devices with SiN capping is greatly aggravated under high temperature stress.

Environmental stability and cryogenic thermal cycling of low-temperature plasma-deposited silicon nitride thin films

Stress in low-temperature plasma-enhanced chemical vapor deposited silicon nitride (SiNx) thin films subject to cryogenic thermal cycling (100–323K) has been measured. It is observed that the SiNx deposition temperature strongly influences the thin film characteristics. For films deposited between 200 and 300°C, the thermal expansion coefficient is similar to that of silicon over the 180–323K temperature range. The room temperature thermal expansion coefficient of SiNx films is found to decrease sublinearly from 5.2×10−6to2.6×10−6K−1 as the temperature of the deposition process is increased from 50to300°C. The negative correlation between deposition temperature and thin film thermal expansion coefficient, and the positive correlation between deposition temperature and the thin film Young’s modulus inferred from nanoindentation are postulated to be associated with the local bonding environment within the thin film. The stress state of SiNx films deposited above 150°C is stable under atmospheric conditions, in contrast to SiNx films deposited below 100°C, which under atmospheric storage conditions become more tensile with time due to oxidation. In addition, SiNx thin films deposited below 100°C exhibit higher tensile stress values in vacuum than at atmospheric pressure, and vacuum annealing at 50°C of films deposited below 100°C introduces further tensile stress changes. These stress changes have been shown to be fully reversible upon reexposure to high purity nitrogen, helium, argon, oxygen, or laboratory atmosphere, and are likely to be associated with thin film porosity.

A High-Yield Fabrication Process for Silicon Neural Probes

There is a great need for silicon microelectrodes that can simultaneously monitor the activity of many neurons in the brain. However, one of the existing processes for fabricating silicon microelectrodes-reactive-ion etching in combination with anisotropic KOH etching-breaks down at the wet-etching step for device release. Here we describe a modified wet-etching sidewall-protection technique for the high-yield fabrication of well-defined silicon probe structures, using a Teflon shield and low-pressure chemical vapor deposition (LPCVD) silicon nitride. In the proposed method, a micro-tab holds each individual probe to the central scaffold, allowing uniform anisotropic KOH etching. Using this approach, we obtained a well-defined probe structure without device loss during the wet-etching process. This simple method yielded more accurate fabrication and an improved mechanical profile.

Hot-wire CVD a-Si:H TFT on Plastic Substrates

AbstractFabrication of hot-wire chemical vapor deposition (HWCVD) of amorphous silicon (a-Si) thin film transistors (TFT) on thin polyamide sheets is reported. A single graphite filament at 1500 °C was used for HWCVD and device quality amorphous silicon films were deposited with no thermal damage to plastic substrate. Top-gate staggered thin film transistors (TFTs) were fabricated at 150°C using hot-wire deposited a-Si channel, Plasma enhanced chemical vapor deposition (PECVD) silicon nitride gate dielectric, and microcrystalline n+ drain/source contacts. Low leakage current of 5×10-13 A, high switching current ratio of 1.3×107, and small sub threshold swing of 0.3 V/dec was obtained for TFTs with aspect ratio of 1300μm/100μm. The field effect mobility was extracted to be 0.34 cm2/V.s.

Reversing the hydrogen silsesquioxane image by silicon nitride and silicon oxide chemical mechanical polishing

Patterns, e-beam written in hydrogen silsesquioxane (HSQ), have been reversed in tone by chemical mechanical polishing of silicon nitride deposited on top of these HSQ patterns. First, high-resolution patterns have been written in an 80nm thick HSQ layer on a 6in. silicon wafer. After development, 200nm thick plasma enhanced chemical vapor deposited silicon nitride has been deposited at 300°C on top of these patterns. Next, the silicon nitride has been Syton polished down to 50nm thickness. Finally, the HSQ has been removed wet chemically from in between the nitride features using buffered oxide etch (7:1). Features of 50nm wide have been resolved, but even smaller isolated spaces are feasible. The same method has been tested with silicon oxide obtained from boron doped tetraethyl orthosilicate. Although the wet-chemical removal of HSQ is less selective in this case, still 50nm wide features have been resolved in silicon oxide this way.