Plasma-enhanced Chemical Vapor Deposition Silicon Research Articles

Recess-Free E-Mode AlGaN/GaN MIS-HFET with Crystalline PEALD AlN Passivation Process

We utilized a plasma-enhanced atomic layer deposition (PEALD) process to deposit an AlN passivation layer on AlGaN/GaN surface to enhance the polarization effects, which enabled the fabrication of an enhancement-mode (E-mode) AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistor (MIS-HFET) without the need for a gate recess process. The AlN film deposited by PEALD exhibited a crystalline structure, not an amorphous one. The enhanced polarization effect of introducing the PEALD AlN film on a thin AlGaN barrier was confirmed through electrical analysis. To fabricate the E-mode AlGaN/GaN MIS-HFET, the PEALD AlN film was deposited on a 4.5 nm AlGaN barrier layer and then a damage-free wet etching process was used to open the gate region. The MIS-gate structure was formed by depositing a 15 nm plasma-enhanced chemical vapor deposition (PECVD) silicon dioxide (SiO2) film. The fabricated thin-AlGaN/GaN MIS-HFET demonstrated successful E-mode operation, with a threshold voltage of 0.45 V, an on/off ratio of approximately 109, a specific on-resistance of 7.1 mΩ·cm2, and an off-state breakdown voltage exceeding 1100 V.

Selectively patterned Mg-doped GaN by SiNx-driven hydrogen injection

We demonstrate a method to achieve selectively patterned Mg-doped GaN layers using hydrogen drive-in through plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiNx) films. Activated Mg-doped GaN layers were selectively deactivated by patterned PECVD SiNx films with low-temperature annealing and showed high-resistive behavior. Spatially resolved photoluminescence measurements were used to optically verify the deactivation of Mg acceptors and showed distinct features corresponding to activated and deactivated Mg in GaN. The method suggested here provides a simple and effective method to achieve patterned Mg-doped GaN regions without thermal and plasma damage, which could cause degradation of device performance. The proposed method could provide a way to achieve future high-performance GaN lateral and vertical devices that rely on laterally patterned doping.

Demonstration of DC Kerr effect induced high nonlinear susceptibility in silicon rich amorphous silicon carbide

In this study, we demonstrate the DC Kerr effect in plasma-enhanced chemical vapor deposition silicon rich amorphous silicon carbide (a-SiC). Using the resonance shift of the transmission spectra of a ring resonator, we experimentally extract the third order nonlinear susceptibility χ3 to be 6.90×10−19 m2/V2, which is estimated to be more than six times higher than previous reported values in stoichiometric a-SiC. The corresponding induced second order nonlinear susceptibility χ2 of 44.9 pm/V is also three times higher than the reported value in silicon and silicon rich nitride utilizing the DC Kerr effect. The high nonlinearity makes silicon rich a-SiC a good materials candidate for nonlinear photonic applications.

Dispersion Optimization of Silicon Nitride Waveguides for Efficient Four-Wave Mixing

Silicon nitride waveguides have emerged as an excellent platform for photonic applications, including nonlinear optical signal processing, owing to their relatively high Kerr nonlinearity, negligible two photon absorption, and wide transparent bandwidth. In this paper, we propose an effective approach using 3D finite element method to optimize the dispersion characteristics of silicon nitride waveguides for four-wave mixing (FWM) applications. Numerical studies show that a flat and low dispersion profile can be achieved in a silicon nitride waveguide with the optimized dimensions. Near-zero dispersion of 1.16 ps/km/nm and 0.97 ps/km/nm at a wavelength of 1550 nm are obtained for plasma-enhanced chemical vapor deposition (PECVD) and low-pressure chemical vapor deposition (LPCVD) silicon nitride waveguides, respectively. The fabricated micro-ring resonator with the optimized dimensions exhibits near-zero dispersion of −0.04 to −0.1 ps/m/nm over a wavelength range of 130 nm which agrees with the numerical simulation results. FWM results show that near-zero phase mismatch and high conversion efficiencies larger than −12 dB using a low pump power of 0.5 W in a 13-cm long silicon nitride waveguide are achieved.

Bistable Threshold Humidity Sensor Switch with Rectangular Bimorph Bending Plate.

Energy-autonomous bistable threshold sensor switches have the potential to reduce costs because they do not need any electrical energy supply for monitoring physical quantities, such as relative humidity. In previous work, a bistable beam-like sensor switch with switching hysteresis was manufactured from sheet metal and a partially coated water vapor-sensitive hydrogel (poly(vinyl alcohol)/poly(acryl acid)). Based on the beam theory, a corresponding mechanical model was developed. However, bending plates should be used instead of bending beams to separate the humidity to be measured from the electrical contacts. For this reason, this work deals with the development and realization of a mechanical model based on the plate theory to describe the deflection of a silicon bimorph bending plate partially coated with hydrogel that swells with increasing humidity. For implementing a switching hysteresis a plasma-enhanced chemical vapor deposition silicon dioxide (SiO2) layer is used, which was deposited and structured on top of the silicon plate. The hydrogel layer itself is patterned on the surface of the bending plate using a stamp technique. To validate the mechanical model, the switching hysteresis of the miniaturized sensor switch was measured optically by a camera measurement device.

Evaluation of Argon as a Carrier Gas of Liquid Material Vaporization During the Plasma-Enhanced Chemical Vapor Deposition (PECVD) Silicon Oxide Process

This paper investigated the potential use of argon (Ar) as an alternative carrier gas to helium (He) during the tetraethyl orthosilicate–silicon dioxide (TEOS–SiO2) process using a plasma-enhanced chemical vapor deposition (PECVD) system. Due to the shortage or depletion of conventional He gas, it is important to find alternative gases. This study investigated the effects of the Ar carrier gas on the vaporization efficiency and properties of SiO2 film in the PECVD TEOS–SiO2 process for different process conditions, such as flow rate and plasma power. Ar showed a much higher vaporization efficiency and faster deposition rate than He due to its higher molecular weight and plasma density, indicating that SiO2 film can be deposited considerably faster with less Ar gas. While changes in the film density and residual film stress were also noted depending on the types of carrier gas and amounts or types of plasma power, these changes were insignificant and within the controllable process range during the PECVD process. Therefore, the use of Ar gas can reduce costs and contribute to improvements in productivity without affecting the quality of SiO2 film.

Gettering of interstitial iron in silicon by plasma-enhanced chemical vapour deposited silicon nitride films

It is known that the interstitial iron concentration in silicon is reduced after annealing silicon wafers coated with plasma-enhanced chemical vapour deposited (PECVD) silicon nitride films. The underlying mechanism for the significant iron reduction has remained unclear and is investigated in this work. Secondary ion mass spectrometry (SIMS) depth profiling of iron is performed on annealed iron-contaminated single-crystalline silicon wafers passivated with PECVD silicon nitride films. SIMS measurements reveal a high concentration of iron uniformly distributed in the annealed silicon nitride films. This accumulation of iron in the silicon nitride film matches the interstitial iron loss in the silicon bulk. This finding conclusively shows that the interstitial iron is gettered by the silicon nitride films during annealing over a wide temperature range from 250 °C to 900 °C, via a segregation gettering effect. Further experimental evidence is presented to support this finding. Deep-level transient spectroscopy analysis shows that no new electrically active defects are formed in the silicon bulk after annealing iron-containing silicon with silicon nitride films, confirming that the interstitial iron loss is not due to a change in the chemical structure of iron related defects in the silicon bulk. In addition, once the annealed silicon nitride films are removed, subsequent high temperature processes do not result in any reappearance of iron. Finally, the experimentally measured iron decay kinetics are shown to agree with a model of iron diffusion to the surface gettering sites, indicating a diffusion-limited iron gettering process for temperatures below 700 °C. The gettering process is found to become reaction-limited at higher temperatures.

Electronic Properties of a-SiO<inline-formula> <tex-math notation="LaTeX">${}_{x}$</tex-math> </inline-formula>N<inline-formula> <tex-math notation="LaTeX">${}_{y}$</tex-math> </inline-formula>:H/SiN<inline-formula> <tex-math notation="LaTeX">${}_{x}$</tex-math> </inline-formula> Stacks for Surface Passivation of P-Type Crystalline Si Wafers

The surface passivation quality of plasma-enhanced chemical vapor-deposited silicon oxynitride/silicon nitride (a-SiO ${}_{x}$ N ${}_{y}$ :H/SiN ${}_{x}$ ) stacks has been investigated for p-type float-zone crystalline silicon wafers. The effective lifetime $\tau _{\rm{eff}}$ , density of fixed charge $Q_{{f}}$ , and density of interface defects $D_{\rm{it}}$ were measured as a function of the a-SiO ${}_{x}$ N ${}_{y}$ :H layer thickness both before and after firing at 800 °C for 3 s. Photoluminescence imaging under applied bias has been used to characterize $Q_{{f}}$ and the surface recombination parameters ${\rm S}_{\rm 0n}$ and ${\rm S}_{\rm 0p}$ through fitting $\tau _{\rm{eff}}$ versus voltage curves to an extended Shockley–Read–Hall (SRH) model. The results are in good agreement with values measured using capacitance–conductance–voltage measurements. Good surface passivation has been obtained with a peak effective lifetime of 2.41 ms. For both as-deposited and fired samples, $Q_{{f}}$ and $D_{\rm{it}}$ decrease with increasing a-SiO ${}_{x}$ N ${}_{y}$ :H layer thickness up to ∼18 nm. The results indicate that the field-effect passivation is weakened as the a-SiO ${}_{x}$ N ${}_{y}$ :H thickness increases and that chemical passivation from a-SiO ${}_{x}$ N ${}_{y}$ :H/SiN ${}_{x}$ plays a prominent role. Increasing the a-SiO ${}_{x}$ N ${}_{y}$ :H/SiN ${}_{x}$ thickness to 50 nm produces similar results, indicating that an 18-nm interlayer is enough to obtain the desired passivation properties. Compared with as-deposited samples, fired samples exhibit lower $D_{\rm{it}}$ , indicating that the firing process enhances chemical passivation of the a-SiO ${}_{x}$ N ${}_{y}$ :H/SiN ${}_{x}$ stacks.

Silicon Surface Passivation by Gallium Oxide Capped With Silicon Nitride

Advances in the passivation of p-type and $p^{+}$ surfaces have been one of the main developments in crystalline silicon solar cell technology in recent years, enabling significant progress in p-type solar cells with partial rear contacts, and n-type solar cells with front-side boron diffusions. In this contribution, we demonstrate improvements in the passivation of p-type and boron diffused $p^{+}$ surfaces with plasma-enhanced atomic layer deposition (PEALD) gallium oxide (Ga2O3) with the addition of plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiNx). On 1.6 Ωcm p-type wafers, we measure an improvement in the upper limit surface recombination velocity ( $S_{{\rm eff, \text{UL}}}$ ) from 2.5 to 1.4 cm/s on optimized Ga2O3 passivated samples before and after SiNx capping. We also show an improvement in the passivation of boron diffused $p^{+}$ surfaces over previously reported data, measuring a recombination parameter ( $J_{0}$ ) of 26 fA/cm2 on a Ga2O3 passivated 85 Ω/sq boron diffusion, approaching the Auger limit of ∼21 fA/cm2 for this diffusion. In addition, we show that initial studies on the thermal stability of the Ga2O3/SiNx stack indicate that it is compatible with conventional screen-printed metallization firing procedures.

Thermal annealing effects on the stress stability in silicon dioxide films grown by plasma-enhanced chemical vapor deposition

The stress stability in plasma-enhanced chemical vapor deposition (PECVD) silicon dioxide (SiO2) films is a key factor of device performance. In this study, the PECVD SiO2 films are annealed at 400–1000 °C in a nitrogen (N2) or oxygen (O2) ambience for 2 h. The influences of annealing parameters on the stress state and stress stability in PECVD SiO2 films are investigated. The bonding nature and surface morphology of the films are also studied to analyze the physical mechanism involved. It is demonstrated that the stress stability is first deteriorated and then improved with increasing annealing temperature. In addition, O2 ambience is more appropriate to improve stress stability than N2, and the stress in PECVD SiO2 film can be stabilized when it is annealed at 1000 °C in O2 ambience. These results should be able to provide important insights into the design of device fabrication processes.

Thin-Film Multichip Packaging for High-Temperature Geothermal Application

A thin-film multichip module substrate technology has been developed and evaluated for packaging high-temperature (300 °C) geothermal well instrumentation. The base substrate technology selected was AlN to minimize the difference in the coefficient of thermal expansion between the substrate and the SiC digital die. The conductor was vacuum deposited Ti/Ti:W/Au followed by an electroplated Au. A plasma-enhanced chemical vapor-deposited silicon nitride was used for the interlayer dielectric. The substrate was characterized as a function of temperature and after aging at 300 °C. The electrical properties and adhesion remained stable after 2000 h at 300 °C.

Reliability of platinum electrodes and heating elements on SiO2 insulation layers and membranes

In this work, failure mechanisms of Pt electrodes including adhesion problems, material migration due to thermally induced compressive stress and electromigration that could occur in the platinum electrodes and heater structures at temperatures above 600°C have been systematically studied, after the deposition. Lifetime determination, scanning electron microscopy and XRD analysis have been applied for samples which have experienced different loading conditions in order to qualitatively and quantitatively understand the phenomena. Electromigration testing is performed with the aim to enable time-to-failure prediction for sensor elements and compare different platinum layers in terms of their stability. Dedicated, application-related test structures are used so that the results are applicable to sensor lifetime estimations. Furthermore, a method for the determination of thermal conductivity of thin insulating films has been adapted for the characterization of plasma-enhanced chemical vapor deposition (PECVD) silicon oxide and successfully applied on two materials with different deposition recipes. These two materials are used for the fabrication of platinum-based heating elements with PECVD SiO2 as insulation or membrane layer. The results for the two recipes are similar but with a significant difference. A slight increase of the conductivities has been observed due to a thermal anneal of the test structures at temperatures above 700°C.

Study of the a-Si:H/c-Si Heterointerface by Ex-Situ Spectroscopic Ellipsometry, Infrared Spectroscopy, and Solar Cell Modeling

The interface formation between plasma-enhanced chemical vapor-deposited (PECVD) silicon thin films and H-terminated, p-type c-Si was investigated. The formation of hydrogenated amorphous silicon (a-Si:H), epitaxial Si, and mixed phase Si was detected through spectroscopic ellipsometry (SE) and high-resolution transmission electron mi- croscopy (HRTEM). The evolution of the hydrogen content and hydrogen bonding configurations in the films were monitored by attenuated total reection infrared spectroscopy (FTIR-ATR). The dependence of the hydrogen binding configuration on the film morphology was observed. Even with an observed epitaxial layer in the structure of the intrinsic a-Si:H, a silicon heterojunction (SHJ) solar cell with 9.2% efficiency was obtained, which is the largest-active-area (72 cm^2) SHJ cell on p-type c-Si. The numerical simulation tool AFORS-HET was used to model the layers and interface properties of the cell. The simulation results were consistent with the experimental results, demonstrating the importance of interface defect passivation in SHJ solar cells.

PECVD low stress silicon nitride analysis and optimization for the fabrication of CMUT devices

Two technological options to achieve a high deposition rate, low stress plasma-enhanced chemical vapor deposition (PECVD) silicon nitride to be used in capacitive micromachined ultrasonic transducers (CMUT) fabrication are investigated and presented. Both options are developed and implemented on standard production line PECVD equipment in the framework of a CMUT technology transfer from R & D to production. A tradeoff between deposition rate, residual stress and electrical properties is showed.The first option consists in a double layer of silicon nitride with a relatively high deposition rate of ~100 nm min−1 and low compressive residual stress, which is suitable for the fabrication of the thick nitride layer used as a mechanical support of the CMUTs. The second option involves the use of a mixed frequency low-stress silicon nitride with outstanding electrical insulation capability, providing improved mechanical and electrical integrity of the CMUT active layers. The behavior of the nitride is analyzed as a function of deposition parameters and subsequent annealing. The nitride layer characterization is reported in terms of interfaces density influence on residual stress, refractive index, deposition rate, and thickness variation both as deposited and after thermal treatment. A sweet spot for stress stability is identified at an interfaces density of 0.1 nm−1, yielding 87 MPa residual stress after annealing. A complete CMUT device fabrication is reported using the optimized nitrides. The CMUT performance is tested, demonstrating full functionality in ultrasound imaging applications and an overall performance improvement with respect to previous devices fabricated with non-optimized silicon nitride.

CMUTs with high-K atomic layer deposition dielectric material insulation layer.

Use of high-κ dielectric, atomic layer deposition (ALD) materials as an insulation layer material for capacitive micromachined ultrasonic transducers (CMUTs) is investigated. The effect of insulation layer material and thickness on CMUT performance is evaluated using a simple parallel plate model. The model shows that both high dielectric constant and the electrical breakdown strength are important for the dielectric material, and significant performance improvement can be achieved, especially as the vacuum gap thickness is reduced. In particular, ALD hafnium oxide (HfO2) is evaluated and used as an improvement over plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (Six)Ny)) for CMUTs fabricated by a low-temperature, complementary metal oxide semiconductor transistor-compatible, sacrificial release method. Relevant properties of ALD HfO2) such as dielectric constant and breakdown strength are characterized to further guide CMUT design. Experiments are performed on parallel fabricated test CMUTs with 50-nm gap and 16.5-MHz center frequency to measure and compare pressure output and receive sensitivity for 200-nm PECVD Six)Ny) and 100-nm HfO2) insulation layers. Results for this particular design show a 6-dB improvement in receiver output with the collapse voltage reduced by one-half; while in transmit mode, half the input voltage is needed to achieve the same maximum output pressure.

A Sub-Critical Barrier Thickness Normally-Off AlGaN/GaN MOS-HEMT

A new high-performance normally-off gallium nitride (GaN)-based metal-oxide-semiconductor high electron mobility transistor that employs an ultrathin subcritical 3 nm thick aluminium gallium nitride (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.25</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.75</sub> N) barrier layer and relies on an induced two-dimensional electron gas for operation is presented. Single finger devices were fabricated using 10 and 20 nm plasma-enhanced chemical vapor-deposited silicon dioxide (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) as the gate dielectric. They demonstrated threshold voltages (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) of 3 and 2 V, and very high maximum drain currents (IDSmax) of over 450 and 650 mA/mm, at a gate voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GS</sub> ) of 6 V, respectively. The proposed device is seen as a building block for future power electronic devices, specifically as the driven device in the cascode configuration that employs GaN-based enhancement-mode and depletion-mode devices.

High efficiency large area n -type front junction silicon solar cells with boron emitter formed by screen printing technology

In this paper, we report on commercially viable screen printing (SP) technology to form boron emitters. A screen-printed boron emitter and ion-implanted phosphorus back surface field were formed simultaneously by a co-annealing process. Front and back surfaces were passivated by chemically grown oxide capped with plasma-enhanced chemical vapor deposition silicon nitride stack. Front and back contacts were formed by traditional SP and firing processes with silver/aluminum grid on front and local silver back contacts on the rear. This resulted in 19.6% efficient large area (239 cm2) n-type solar cells with an open-circuit voltage Voc of 645 mV, short-circuit current density Jsc of 38.6 mA/cm2, and fill factor of 78.6%. This demonstrates the potential of this novel technology for production of low-cost high-efficiency n-type silicon solar cells. Copyright © 2014 John Wiley & Sons, Ltd.

Hot-wire polysilicon waveguides with low deposition temperature

We fabricated and measured the optical loss of polysilicon waveguides deposited using hot-wire chemical vapor deposition at a temperature of 240°C. A polysilicon film 220 nm thick was deposited on top of a 2000 nm thick plasma-enhanced chemical vapor deposition silicon dioxide layer. The crystalline volume fraction of the polysilicon film was measured by Raman spectroscopy to be 91%. The optical propagation losses of 400, 500, and 600 nm waveguides were measured to be 16.9, 15.9, and 13.5 dB/cm, respectively, for transverse electric mode at the wavelength of 1550 nm. Scattering loss is expected to be the major contributor to the propagation loss.

Back-End Deposited Silicon Photonics for Monolithic Integration on CMOS

We present the vision of back-end deposited silicon photonics (BDSP) and review works that have been done in this field. Individual aspects of BDSP platform including excimer-laser-annealed polycrystalline silicon, low-loss plasma-enhanced chemical vapor deposition silicon nitride waveguide, modulator, detector, electrical interface, back-end CMOS compatibility, and benefits of the platform are discussed in detail.

Near-Infrared Grating Couplers for Silicon Nitride Photonic Wires

Silicon nitride is a promising high-index material for dense photonic circuits and applications in the visible-midinfrared wavelength regime. Design, fabrication, and optical characterization of silicon nitride waveguides at visible-near-infrared wavelength are presented. Finally, design and experimental results are presented for the first time for linear and focused grating couplers (GCs) at near-infrared wavelength (900 nm) for plasma-enhanced chemical vapor deposition silicon nitride wires (220 × 500 nm) and compared with theoretical simulations. An experimental efficiency of 5.7 and 6.5 dB and 1-dB bandwidth of 26 and 40 nm are reported for the linear and focused GCs, respectively.