Plasma-enhanced Chemical Vapor Deposition SiNx Research Articles

Islands stretch test for measuring the interfacial fracture energy between a hard film and a soft substrate

We present a technique for measuring the interfacial fracture energy, Γi, between a hard thin film and a soft substrate. A periodic array of hard thin islands is fabricated on a soft substrate, which is then subjected to uniaxial tension under an optical microscope. When the applied strain reaches a critical value, delamination between the islands and the substrate starts from the edge of the islands. As the strain is increased, the interfacial cracks grow in a stable fashion. At a given applied strain, the width of the delaminated region is a unique function of the interfacial fracture energy. We have calculated the energy release rate driving the delamination as a function of delamination width, island size, island thickness, and applied strain. For a given materials system, this relationship allows determination of the interfacial fracture energy from a measurement of the delamination width. The technique is demonstrated by measuring the interfacial fracture energy of plasma-enhanced chemical vapor deposition SiNx islands on a polyimide substrate. We anticipate that this technique will find application in the flexible electronics industry where hard islands on soft substrates are a common architecture to protect active devices from fracture.

Physical model of dielectric charging in MEMS

Dielectric charging is a key failure mechanism in radio frequency (RF) microelectromechanical systems (MEMS). To date we lack suitable physical models for the prediction of long-term behavior of RF MEMS switches, susceptible to dielectric charging. In this paper, we present an original approach of studying dielectric charging including modeling of long-term behavior of RF MEMS switches based only on physical dielectric properties that are experimentally characterized. For the first time, we introduce explicitly the trapping kinetics in the model of charging in RF MEMS. In this study, the conduction mechanism and trapping properties of the plasma enhanced chemical vapor deposition (PECVD) SiNx and SiO2 dielectric layers used for the fabrication of RF MEMS switches are characterized. The conduction is determined from I–V sweeps in metal–insulator–metal (MIM) capacitors, whereas the trapping properties are determined from constant current injections in MIM capacitors. The SiNx material shows Poole–Frenkel conduction while Schottky conduction is found to be the best fitting model for the SiO2 dielectric material. The trapping properties of the SiNx layer is best fitted with a logarithmic model of repulsive trapping, while SiO2 fits better with an exponential model of first-order trapping. These extracted physical properties serve as input parameters to our model of pull-in voltage drift in RF MEMS switches. The results of modeling are verified against the pull-in voltage drifts measured on real fabricated capacitive-type RF MEMS switches. It is concluded that the simulated switch lifetime results are very consistent with experimental data obtained for electrostatic MEMS switches either made with PECVD SiNx or SiO2 dielectric materials.

Characterisation and optimisation of PECVD SiNx as an antireflection coating and passivation layer for silicon solar cells

In this work, we investigate how the film properties of silicon nitride (SiNx) depend on its deposition conditions when formed by plasma enhanced chemical vapour deposition (PECVD). The examination is conducted with a Roth & Rau AK400 PECVD reactor, where the varied parameters are deposition temperature, pressure, gas flow ratio, total gas flow, microwave plasma power and radio-frequency bias voltage. The films are evaluated by Fourier transform infrared spectroscopy to determine structural properties, by spectrophotometry to determine optical properties, and by capacitance–voltage and photoconductance measurements to determine electronic properties. After reporting on the dependence of SiNx properties on deposition parameters, we determine the optimized deposition conditions that attain low absorption and low recombination. On the basis of SiNx growth models proposed in the literature and of our experimental results, we discuss how each process parameter affects the deposition rate and chemical bond density. We then focus on the effective surface recombination velocity Seff, which is of primary importance to solar cells. We find that for the SiNx prepared in this work, 1) Seff does not correlate universally with the bulk structural and optical properties such as chemical bond densities and refractive index, and 2) Seff depends primarily on the defect density at the SiNx-Si interface rather than the insulator charge. Finally, employing the optimized deposition condition, we achieve a relatively constant and low Seff,UL on low-resistivity (≤1.1 Ωcm) p- and n-type c-Si substrates over a broad range of n = 1.85–4.07. The results of this study demonstrate that the trade-off between optical transmission and surface passivation can be circumvented. Although we focus on photovoltaic applications, this study may be useful for any device for which it is desirable to maximize light transmission and surface passivation.

Overcoming over-plating problems for PECVD SiNx passivated laser doped p-type multi-crystalline silicon solar cells

Effective self-aligned metallisation schemes, such as the electroless and light induced plating techniques have been well-characterised and used in photovoltaic devices for many decades. However, application of these plating techniques to standard acid-textured, phosphorus-diffused, p-type multi-crystalline silicon (Si) wafers with a plasma enhanced chemical vapour deposition (PECVD) silicon nitride (SiNx) coated surface can be problematic due to over-plating. In this paper, we identify the two main causes of over-plating on these wafers: the physical properties of the deposited SiNx layer and the topology of the acid-textured multi-crystalline wafer surfaces. It is shown that the implementation of an innovative acid rounding or alkali etch process prior to the PECVD process can eliminate over-plating problems and, thus, improve the performance of the final cell devices resulting in an average efficiency of 16.8% and an average fill factor (FF) of 78% for laser-doped selective emitter cells fabricated on commercial grade wafers with nominal resistivity of 1Ωcm.

Accelerated deactivation of the boron–oxygen-related recombination centre in crystalline silicon

A significant acceleration of the permanent deactivation of the boron–oxygen-related recombination centre in crystalline silicon is observed if the samples are exposed to the plasma during plasma-enhanced chemical vapour deposition (PECVD) of a hydrogen-rich silicon nitride (SiNx) layer. Similar deactivation rate constants are measured in samples passivated with hydrogen-rich SiNx deposited without plasma exposure and hydrogen-lean aluminium oxide (Al2O3) deposited with plasma-assisted atomic layer deposition, suggesting that the critical parameter responsible for the acceleration is not the hydrogen content in the dielectric layer. Instead, we propose increased in-diffusion of hydrogen during or after the deposition of the PECVD SiNx layer, for example due to surface damage caused by plasma exposure, as the cause for the acceleration.

Effect of a SiNx insulator on device properties of pentacene-TFTs with a low-cost copper source/drain electrode

We fabricated different SiNx insulators at a 150–350 °C deposition temperature by plasma-enhanced chemical vapor deposition (PECVD) and investigated the effect of SiNx insulator on the device properties of pentacene-TFTs with a low-cost copper source/drain electrode. A pentacene-TFT with a SiNx insulator at a deposition temperature of 300 °C exhibited the highest saturation mobility of 0.29 cm2 (V s)−1, the lowest threshold voltage of −8.9 V and an on/off current ratio of 5.3 × 106. The best performance of the device with a SiNx insulator at a 300 °C deposition temperature can be attributed to the electrical properties and a relatively large water contact angle of insulator, smooth insulator surface and better crystallinity of the pentacene active layer. The present organic thin-film transistors (OTFTs) with the PECVD SiNx insulator and the low-cost Cu electrode could be a significant step toward the commercialization of OTFT technology.

A comparative study of effects of SiNx deposition method on AlGaN/GaN heterostructure field-effect transistors

The effects of thin SiNx deposition on AlGaN/GaN heterostructure field-effect transistors were systematically studied by comparing their electrical and device characteristics. Two aspects of the thin SiNx film deposition were investigated: (i) the increase in two-dimensional electron gas (2DEG) density at the heterointerface and (ii) its capability as a gate insulating layer. Three different SiNx deposition methods were studied: catalytic chemical vapor deposition (Cat-CVD), metalorganic chemical vapor deposition (MOCVD), and plasma enhanced chemical vapor deposition (PECVD). A large increase in 2DEG density was obtained after SiNx deposition for all methods. The devices with MOCVD SiNx gate insulator showed a larger gate leakage current than those with the Cat-CVD and PECVD SiNx, implying that a thinning of the AlGaN surface barrier occurred due to Si diffusion into the AlGaN barrier during the high-temperature MOCVD process.

A comparative study of plasma-enhanced chemical vapor gate dielectrics for solution-processed polymer thin-film transistor circuit integration

This paper considers plasma-enhanced chemical vapor deposited (PECVD) silicon nitride (SiNx) and silicon oxide (SiOx) as gate dielectrics for organic thin-film transistors (OTFTs), with solution-processed poly[5,5′-bis(3-dodecyl-2-thienyl)-2,2′-bithiophene] (PQT-12) as the active semiconductor layer. We examine transistors with SiNx films of varying composition deposited at 300 °C as well as 150 °C for plastic compatibility. The transistors show over 100% (two times) improvement in field-effect mobility as the silicon content in SiNx increases, with mobility (μFE) up to 0.14 cm2/V s and on/off current ratio (ION/IOFF) of 108. With PECVD SiOx gate dielectric, preliminary devices exhibit a μFE of 0.4 cm2/V s and ION/IOFF of 108. PQT-12 OTFTs with PECVD SiNx and SiOx gate dielectrics on flexible plastic substrates are also presented. These results demonstrate the viability of using PECVD SiNx and SiOx as gate dielectrics for OTFT circuit integration, where the low temperature and large area deposition capabilities of PECVD films are highly amenable to integration of OTFT circuits targeted for flexible and lightweight applications.

Formation of a Porous Silicon Layer by Electrochemical Etching and Application to the Silicon Solar Cell

SiNx thin film grown by plasma-enhanced chemical vapor deposition (PECVD) has conventionally been used as an antireflection layer of the silicon solar cell. In this work, a porous silicon (PS) layer formed by electrochemical etching was shaped on the surface of a crystalline silicon wafer for a simple alternative of anti-reflection coating (ARC). The etching solution was prepared by mixing HF and ethanol for efficient bubble elimination on the silicon surface during the etching process. The anodization of the silicon surface was performed under a constant current, and the process parameters, such as current density and etching time including volume fraction of HF to ethanol in the solution, were carefully tuned to minimize the surface reflectance of the CZ silicon wafer with sheet resistance of 35-40 Ω/□. The PS layer as an anti-reflection coating in the solar cell was compared with conventional PECVD SiNx thin film by measuring the surface reflectance of the cell. Also, Photovoltaic I-V properties and the quantum efficiencies of the cells with PS layers were measured.

Effect of oxidation on the chemical bonding structure of PECVD SiNx thin films

This study investigated the effect of oxidation on the chemical bonding structures of silicon nitride thin films synthesized by a low-temperature plasma-enhanced chemical vapor deposition (PECVD) method. These films were heat treated to different temperatures up to 1373 K. The bonding structures were studied by means of x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. It was found that the amorphous PECVD SiNx films were subjected to oxidation in air at elevated temperatures. The oxidation caused the formation of crystalline silicon dioxide within the matrix of amorphous silicon nitride, conforming to the “random mixing” model. The crystalline silicon dioxide formed is believed to be stoichiometric SiO2, whereas the remaining matrix is believed to be a nonstoichiometric silicon oxynitride with a structure conforming to the “random bonding” model.

Evaluation of Thin Dielectric-Glue Wafer-Bonding for Three Dimensional Integrated Circuit-Applications

AbstractThe critical adhesion energy of benzocyclobutene (BCB)-bonded wafers is quantitatively investigated with focus on BCB thickness, material stack and thermal cycling. The critical adhesion energy depends linearly on BCB thickness, increasing from 19 J/m2 to 31 J/m2 as the BCB thickness increases from 0.4 μm to 2.6 μm, when bonding silicon wafers coated with plasma enhanced chemical vapor deposited (PECVD) silicon dioxide (SiO2). In thermal cycling performed with 350 and 400 oC peak temperatures, the significant increase in critical adhesion energy at the interface between BCB and PECVD SiO2 during the first thermal cycle is attributed to relaxation of residual stress in the PECVD SiO2 layer. On the other hand, the critical adhesion energy at the interface between BCB and PECVD silicon nitride (SiNx) decreases due to the increase of residual stress in the PECVD SiNx layer during the first thermal cycle.

Al-enhanced PECVD SiNx induced hydrogen passivation in string ribbon silicon

The effectiveness of manufacturable gettering and passivation technologies is investigated for their ability to improve the quality of a promising Si photovoltaic material. The results of this study indicate that a lifetime enhancement of 30 μs is attained when a backside screen-printed aluminum layer and a thin film of SiNx, applied by plasma-enhanced chemical vapor deposition (PECVD), are simultaneously annealed at 850°C in a lamp-heated belt furnace. Based on the results of this study, a model is proposed to describe the Al-enhanced SiNx induced hydrogen defect passivation in String Ribbon silicon due to the simultaneous anneal. According to this model, three factors play an important role: i) the release of hydrogen from the SiNx film into the substrate; ii) the retention of hydrogen at defect sites in silicon; and iii) the generation of vacancies at the Al−Si interface due to the alloying process which increases the incorporation of hydrogen and creates a chemical potential gradient which enhances the migration of hydrogen in the substrate. A PC1D device simulation indicates that screen-printed cell efficiencies approaching 16% can be achieved if the gettering and passivation treatments examined in this study are employed, the substrate thickness is reduced, and a high-quality surface passivation scheme is applied.

Dependence of crystallographic tilt and defect distribution on mask material in epitaxial lateral overgrown GaN layers

We have investigated the dependence of crystallographic tilt and defect distribution on mask material in metalorganic chemical vapor deposition grown GaN layers formed utilizing an epitaxial lateral overgrowth (ELO) technique using x-ray diffraction and transmission electron microscopy. Crystallographic tilt in the ELO GaN layer was suppressed by changing the mask material from electron beam (EB)-evaporated SiO2 to plasma enhanced chemical vapor deposition (PECVD) grown SiO2 and PECVD SiNx. Defect distribution also changes in accordance with mask materials. By depositing a thin PECVD SiNx layer on the PECVD SiO2 mask, the crystalline quality of the ELO layer changes from that used with the SiO2 mask to that used with the SiNx mask. These results suggest that the interface between the ELO GaN layer and the mask has a significant effect on crystallographic tilt and defect distribution.

Heat transport in thin dielectric films

Heat transport in 20–300 nm thick dielectric films is characterized in the temperature range of 78–400 K using the 3ω method. SiO2 and SiNx films are deposited on Si substrates at 300 °C using plasma enhanced chemical vapor deposition (PECVD). For films >100 nm thick, the thermal conductivity shows little dependence on film thickness: the thermal conductivity of PECVD SiO2 films is only ∼10% smaller than the conductivity of SiO2 grown by thermal oxidation. The thermal conductivity of PECVD SiNx films is approximately a factor of 2 smaller than SiNx deposited by atmospheric pressure CVD at 900 °C. For films <50 nm thick, the apparent thermal conductivity of both SiO2 and SiNx films decreases with film thickness. The thickness dependent thermal conductivity is interpreted in terms of a small interface thermal resistance RI. At room temperature, RI∼2×10−8 K m2 W−1 and is equivalent to the thermal resistance of a ∼20 nm thick layer of SiO2 .

Investigation of a High Quality and Ultraviolet-Light Transparent Plasma-Enhanced Chemical Vapor Deposition Silicon Nitride Film for Non-Volatile Memory Application

A high quality and ultraviolet-light transparent (UV-transparent) plasma enhanced chemical vapor deposition (PECVD) silicon nitride ( SiNx ) film is developed to form passivation layer for non-volatile memory devices. Comparing to the conventional PECVD SiNx film known to have tensile stress and opacity to ultraviolet-light (UV-light), the proposed SiNx film with very low compressive stress ( <1×109 dyn/cm2) and excellent UV-transmittance (>70% for 1.6 µ m-thick film) can be achieved. The film stress is strongly related to RF input power during deposition process. The UV-transmittance is influenced by pressure and SiH4/NH3 flow ratio. It is also shown that the UV-transmittance is closely correlated to refractive index (RI), film density as well as N/Si ratio inside the film. This SiNx film has been successfully applied to erasable programming read-only memory (EPROM's) devices, and very good UV-erasability and reliability performances are demonstrated.

Silicon nitride encapsulation of sulfide passivated GaAs/AlGaAs microdisk lasers

SiNx encapsulation of sulfide passivated GaAs/AlGaAs surfaces was examined with respect to the SiNx deposition conditions and applied to GaAs/AlGaAs microdisk lasers. The SiNx encapsulation is a method for preserving the positive effects (e.g., reduced surface recombination velocity, Sv) of the sulfide passivation by inhibiting the oxidation process of the air-exposed semiconductor. GaAs-based microdisks, with diameters of 2–10 μm, provide a very sensitive probe of the surface recombination since the resonator mode is in close proximity to the edge of the disk (∼&amp;lt;0.5 μm) and the carrier diffusion length is typically several microns. An ammonium sulfide solution was used for the S passivation. The SiNx was deposited by plasma-enhanced chemical vapor deposition (PECVD) at 50 or 300 °C, with and without post-deposition annealing (300–400 °C), or by electron cyclotron resonance chemical vapor deposition (ECR-CVD) at 100 °C. Photoluminescent measurements of GaAs/InGaP epitaxial structures provided an indication of the relative change in Sv. The GaAs/AlGaAs microdisks do not lase without sulfide treatment when optically pumped at 77 K. With the sulfide treatment alone, cw lasing was achieved but the lifetime was only several seconds. A dramatic increase in the laser lifetime was obtained using PECVD-deposited SiNx at 300 °C. The laser output for the PECVD SiNx (300 °C) encapsulated microdisks could be increased by nearly an order of magnitude by annealing at 400 °C for 300 s or by cw operation for several hours. Initial results using the ECR-deposited SiNx films suggest improved performance (lower threshold, stability) compared to the PECVD SiNx. The laser performance is correlated with the photoluminescence results.

Stability of a-Si:H TFTs Employing APCVD SiO2 with N2 Plasma Treatment as a Gate Dielectric

ABSTRACTWe have investigated the stability of the hydogenated amorphous silicon thin film transistors (a-Si:H TFTs) employing silicon dioxide (SiO2) with N2 plasma treatment as a gate dielectric, where SiO2 was deposited by atmospheric pressure chemical vapor deposition (APCVD). Their stability was compared with those of a-Si:H TFTs whose gate dielectric was silicon nitride (SiNx) deposited by plasma enhanced chemical vapor deposition (PECVD). Two kinds of stresses, gate bias and light illumination, were applied. The threshold voltage shin (AVu,) and the inverse subthreshold slope shift (ΔVth) were measured as a function of the bias voltage and the light stress time. For the positive bias stress, the ΔVth, of the a-Si:H TFTs with the N2 plasma treated SiO2 dielectric is smaller than that with the PECVD SiNx gate dielectric. For the negative bias stress and light stress, however, the ΔVth of TFT with N2 plasma treated SiO2 dielectric is larger than that with the SiNx dielectric

Effects of stress on the electrical activation of implanted Si in GaAs

The effects of various plasma-enhanced chemical vapor deposition SiNx encapsulating films on the electrical activation of ion-implanted 29Si+ in GaAs were investigated. Films inducing the most tensile stress in the GaAs resulted in the lowest activation efficiency and films inducing the most compressive resulted in the highest. The results suggest that ratio of donors to acceptors, SiGa:SiAs, is a sensitive function of the stress state during the activation anneal.

Control and Variation of Stress in Pecvd SiNx Films on InP

AbstractStress in plasma enhanced chemical vapor deposited (PECVD) SiNx films on InP has been evaluated as a function of source gases (NH3 /SiH4 or N2/SiH4) and plasma operating frequency (high, » 1 MHz or low, « 1 MHz). All films were deposited at 300°C in the same parallel-plate, radial flow plasma reactor. Levels of stress in PECVD SiNx on InP within a continuous range from moderately high tensile (∼ 5 × 109 dyne cm−2) to very high compressive (2 × 1010 dyne cm−2 ) were obtained from appropriate choices of deposition parameters. Deposition from NH3/SiH4 at high frequency produces tensile stress, of magnitude increasing with NH3/SiH4 flow ratio. Deposition from N2/SiH4 at high frequency produces zero to low compressive stress. At low frequency compressive stress is always produced; for N2/SiH4 increasing the gas flow ratio from 25:1 to 500:1 reduces the compressive stress from 1.8 X 1010 to 7 × 108 dyne cm−2. The ability to vary the stress in a dielectric film of approximately constant chemical composition over such a broad range is beneficial for assessing the effects of stress on device performance.