Chemical Vapor Deposition Silicon Research Articles

3D Free‐Form Patterning of Silicon by Ion Implantation, Silicon Deposition, and Selective Silicon Etching

AbstractA method for additive layer‐by‐layer fabrication of arbitrarily shaped 3D silicon micro‐ and nanostructures is reported. The fabrication is based on alternating steps of chemical vapor deposition of silicon and local implantation of gallium ions by focused ion beam (FIB) writing. In a final step, the defined 3D structures are formed by etching the silicon in potassium hydroxide (KOH), in which the local ion implantation provides the etching selectivity. The method is demonstrated by fabricating 3D structures made of two and three silicon layers, including suspended beams that are 40 nm thick, 500 nm wide, and 4 μm long, and patterned lines that are 33 nm wide.

Chemical Vapor Deposition of Silicon by the Reaction of Bromosilanes and Hydrogen

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Development of Crystal Growth Simulator Based on Tight-Binding Quantum Chemical Molecular Dynamics Method and Its Application to Silicon Chemical Vapor Deposition Processes

We have developed a crystal growth simulator based on tight-binding quantum chemical molecular dynamics (TB-QCMD) method and applied it to plasma-enhanced chemical vapor deposition (PECVD) processes for silicon thin-film growth via SiH3 radicals on hydrogen-terminated Si(001). We successfully simulated the abstraction of a surface hydrogen atom by irradiated SiH3 radical and the formation of a dangling bond on the hydrogen-terminated Si(001) surface. SiH3 radical was subsequently adsorbed on this dangling bond. When these processes were repeated, the thin film grew. Thus, a detailed mechanism was successfully found for the chemical reaction and electron transfer dynamics of silicon thin film growth by PECVD.

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.

Measurement technique for the thermal properties of thin-film diaphragms embedded in calorimetric flow sensors

In diaphragm-based micromachined calorimetric flow sensors, convective heat transfer through the test fluid competes with the spurious heat shunt induced by the thin-film diaphragm where heating and temperature sensing elements are embedded. Consequently, accurate knowledge of thermal conductivity, thermal diffusivity, and emissivity of the diaphragm is mandatory for design, simulation, optimization, and characterization of such devices. However, these parameters can differ considerably from those stated for bulk material and they typically depend on the production process. We developed a novel technique to extract the thermal thin-film properties directly from measurements carried out on calorimetric flow sensors. Here, the heat transfer frequency response from the heater to the spatially separated temperature sensors is measured and compared to a theoretically obtained relationship arising from an extensive two-dimensional analytical model. The model covers the heat generation by the resistive heater, the heat conduction within the diaphragm, the radiation loss at the diaphragm’s surface, and the heat sink caused by the supporting silicon frame. This contribution summarizes the analytical heat transfer analysis in the microstructure and its verification by a computer numerical model, the measurement setup, and the associated thermal parameter extraction procedure. Furthermore, we report on measurement results for the thermal conductivity, thermal diffusivity, and effective emissivity obtained from calorimetric flow sensor specimens featuring dielectric thin-film diaphragms made of plasma enhanced chemical vapor deposition silicon nitride.

Simulation of Boron-doped Silicon Film Thickness within Holes on the Wafer

A reaction model is discussed for in-situ boron-doped silicon chemical vapor deposition that uses Si2H6 and B2H6. First, the elementary reactions were studied by using an ab initio molecular orbital method and the first-principle molecular dynamics method. These showed that the B2H6 decomposes into BH3 easily and that BH3 has a high probability of sticking to silicon film. Therefore, the boron was doped in the silicon film by BH3. The desorption energy of H2 terminated silicon film surface was lower due to the boron doping in the silicon film. Then, an increase in the boron concentration of the silicon film increased the sticking probability of the Si2H6. Next, a deposition model was made on the basis of these results, and reaction constants were determined by using experimental results. Finally film thickness distribution was simulated by using a flow-diffusion-reaction analysis and an integrated method on the above deposition model. The result shows that our reaction model can replicate experimental step coverage.

Structural evolution of a Ta-filament during hot-wire chemical vapour deposition of Silicon investigated by electron backscatter diffraction

We report on the application of electron backscatter diffraction to investigate the structural changes of a tantalum filament operated at typical hot-wire chemical vapour deposition conditions for the synthesis of hydrogenated nanocrystalline silicon. Various tantalum-silicides, identified by electron backscatter diffraction, form preferentially along the length of the filament. The filament has a recrystallized Ta inner core and a TaSi2 layer encapsulated with a Si layer at the cooler ends. The αTa5Si3, metastable Ta5Si3 and Ta2Si phases formed in addition to recrystallized Ta and TaSi2 at the centre regions. Cracks and porosity were prevalent throughout the length of the filament. The microstructural evolution of the aged tantalum filament can be ascribed to the thermal gradient along the filament length, recrystallization of Ta and the variation of silicon content within the filament.

Enhancing the Wettability of High Aspect-Ratio Through-Silicon Vias Lined With LPCVD Silicon Nitride or PE-ALD Titanium Nitride for Void-Free Bottom-Up Copper Electroplating

One of the critical steps toward producing void-free and uniform bottom-up copper electroplating in high aspect-ratio (AR) through-silicon vias (TSVs) is the ability of the copper electrolyte to spontaneously flow through the entire depth of the via. This can be accomplished by reducing the concentration gradient of cupric ions from the via mouth to the via bottom by enhancing the wettability of the vias sidewalls. In this paper, we report on a new dry technique to enhance the hydrophilicity in high AR (~15) TSVs as one of the key solutions to face the mass transport limitation, low pressure chemical vapor deposition silicon nitride and atomic layer deposition titanium nitride of composition SiN0.95 and TiN11, respectively, are used as both barrier layers and wetting surfaces in these vias. Ammonia plasma immersion is used to treat silicon nitride. X-ray photoelectron spectroscopy shows both a partial oxidation and grafting of hydrophilic components. Alternatively, a rapid flood ultraviolet exposure step in order to photocatalytically activate the surface and induce a partially oxidized titanium nitride is used to create a highly wettable interface with a contact angle close to zero. These wettability enhancement steps were incorporated in a TSV process to produce 3-D cross-Kelvin structures using bottom-up copper electroplating. The vias lined with silicon nitride and titanium nitride exhibited a low average resistance of 25 mΩ and 50 mΩ, respectively, making them very suitable for radio-frequency signal transmission. This all-dry technology to achieve superhydrophilic barrier layers can be employed in both high and low thermal budget processing, thus enabling via-last or via-first flowchart schemes for advanced 3-D interconnects.

Hollow Waveguides With Low Intrinsic Photoluminescence Fabricated With PECVD Silicon Nitride and Silicon Dioxide Films

A new type of integrated hollow core anti-resonant reflecting optical waveguide (ARROW) with low intrinsic photoluminescence (PL) fabricated with plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiN) and silicon dioxide (SiO2) films is demonstrated. The waveguide is fabricated by surrounding the hollow core with alternating layers of SiN and SiO2. The thicknesses and indices of the layers are designed to meet an anti-resonance condition. Compared to earlier ARROW structures made by depositing high-temperature (HT) SiN (250 °C), the PL background decreases by a factor of ~ 10 when low-temperature (LT) SiN (100 °C ) films are used. Therefore, LT SiN ARROWs are attractive platforms for sensitive fluorescence and Raman spectroscopy measurements of biomolecules.

Nanotribology-based novel characterization techniques for the dielectric charging failure mechanism in electrostatically actuated NEMS/MEMS devices using force–distance curve measurements

The work presents a comprehensive package of novel nanoscale characterization techniques to study dielectric charging in electrostatic nano- and microelectromechanical systems (NEMS and MEMS). The proposed assessment methodologies are based on the force–distance curve (FDC) measurements performed using an atomic force microscope (AFM) to measure, for the first time, the induced surface potential and adhesive force over charged dielectric films. They were employed to study plasma enhanced chemical vapor deposition (PECVD) silicon nitride films for application in electrostatic capacitive RF MEMS switches. Three different techniques were introduced including the application of FDC measurements to study charging in bare SiN x films, metal–insulator–metal (MIM) capacitors, and MEMS switches. The results from the three methods were correlated and compared with the published data from other characterization techniques, mainly charge/discharge current transient (C/DCT) and Kelvin probe force microscopy (KPFM). The unique advantages of the proposed FDC-based characterization techniques are twofold. First, they can measure the multiphysics coupling between the dielectric charging phenomenon and tribological issues at the interface between the switch bridge and the dielectric surface. Second, the FDC-based techniques can measure larger levels of induced surface potential over charged dielectric films which results from the high electric field normally used to actuate MEMS switches. Based on the proposed FDC techniques, the influence of several parameters on dielectric charging/discharging processes was investigated: the dielectric film thickness, deposition conditions, substrate, and electrical stress conditions.

Linking the Operating Parameters of Chemical Vapor Deposition Reactors with Film Conformality and Surface Nano-Morphology

A multiscale modeling framework is used to couple the co-existing scales, i.e., macro-, micro- and nano-scale, in chemical vapor deposition (CVD) processes. The framework consists of a reactor scale model (RSM) for the description of the transport phenomena in the bulk phase (macro-scale) of a CVD reactor and two models for the micro- and nano-scale: (a) A feature scale model (FSM) describing the deposition of a film inside features on a predefined micro-topography on the wafer and (b) a nano-morphology model (NMM) describing the surface morphology evolution during thin film deposition on an initially flat surface. The FSM is deterministic and consists of three sub-models: A ballistic model for the species' transport inside features, a surface chemistry model, and a profile evolution algorithm based on the level set method. The NMM is stochastic and is based on the kinetic Monte Carlo method. The coupling of RSM with FSM is performed through a correction of the species consumption on the wafer. The linking of RSM with NMM is performed through "feeding" of the deposition rate calculated by RSM to the NMM. The case study is CVD of Silicon (Si) from Silane. The effect of the reactor's operating parameters on the Si film conformality inside trenches is investigated by the coupling of RSM with FSM. The formation of dimmers on an initially flat Si (001) surface as well as the periodic change of the surface nano-morphology is predicted.

New insights into reliability of electrostatic capacitive RF MEMS switches

Among other reliability concerns, the dielectric charging is considered the major failure mechanism which hinders the commercialization of electrostatic capacitive radio frequency micro-electro-mechanical systems (RF MEMS) switches. In this study, Kelvin probe force microscopy (KPFM) surface potential measurements have been employed to study this phenomenon. Several novel KPFM-based characterization methods have been proposed to investigate the charging in bare dielectric films, metal–insulator–metal (MIM) capacitors, and MEMS switches, and the results from these methods have been correlated. The used dielectric material is plasma-enhanced chemical vapor deposition (PECVD) silicon nitride. The SiNxfilms have been charged by using a biased atomic force microscope (AFM) tip or by electrically stressing MIM capacitors and MEMS switches. The influence of several parameters on the dielectric charging has been studied: dielectric film thickness, deposition conditions, and under layers. Fourier transform infra-red (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) material characterization techniques have been used to determine the chemical bonds and compositions, respectively, of the SiNxfilms. The data from the physical material characterization have been correlated to the KPFM results. The study provides an accurate understanding of the charging/discharging processes in dielectric films implemented in electrostatic MEMS devices.

Modifications of an HY zeolite for n-octane hydroconversion

Solids based on HY zeolite were modified by either dealuminization (D) followed by chemical vapour deposition of silicon (CVD). Additionally, impregnation of Pt or Ni was performed over selected D and CVD solids. Samples were characterized by XRD, 27Al and 29Si NMR, acidity measurements, N 2 adsorption/desorption isotherms, Raman analysis and evaluated in n-octane hydroconversion at P = 1 atm and T = 300 °C. In comparison with the CVD and pure D series of solids, Pt impregnation on dealuminated HY resulted in a high level of isomerization products. Although the conversion upon using Ni-containing dealuminated HY was elevated, cracking products were predominant over this solid. The trends in the activity can be explained by the accessibility of acidic sites and their acidity. The catalytic activity follows the order PtCVD1 > NiD > PtD ∼ D > CVD1. The combined effect of moderate acidity and Pt dispersion resulted in better catalytic performance for the PtCVD1 catalyst, which was active in the hydroisomerization reaction (conversion of 30%) with almost no coking on the sample, whereas cracking products were predominant over other solids. The characterization of spent catalysts showed no loss in activity, with low coke deposition on solid surface over the CVD1 sample in comparison with the D series of solids. Furthermore, mechanistic insights demonstrated that on PtCVD1, the adsorbed carbon species were formed via the cracking and oligomerization of n-octane precursors.

Investigation of silicon nitride charging

The TSDC spectra of MIM capacitors with different SiN film thicknesses were analyzed assuming a minimum number of three charging mechanisms, which are attributed to dipolar and space charge polarization. Two relatively narrow contributions appear in the low temperature region and a broad contribution appears in high temperature region. All these contributions exhibit a relatively small dependence on the film thickness. The paper investigates the charging mechanisms of plasma enhanced chemical vapor deposition (PECVD) silicon nitride films, which are used in MEMS capacitive switches. The assessment has been carried out in metal-insulator-metal (MIM) capacitors with symmetric metal contacts and film thicknesses from 100nm to 500nm, with the aid of thermally stimulated depolarization currents (TSDC) method. Various polarization fields with intensities from 20kV/cm to 1MV/cm and of both field polarities were applied and the stored charge measured in the external circuit was calculated. The decomposition of TSDC spectra revealed the contribution of discrete polarization mechanisms, attributed to dipolar and space charge polarization. In low field intensities the TSDC spectra were attributed to domination of dipolar polarization and in high fields to space charge polarization.

Nanoscale characterization of the dielectric charging phenomenon in PECVD siliconnitride thin films with various interfacial structures based on Kelvin probe forcemicroscopy

This work presents a novel characterization methodology for the dielectric chargingphenomenon in electrostatically driven MEMS devices using Kelvin probe force microscopy(KPFM). It has been used to study plasma-enhanced chemical vapor deposition (PECVD)silicon nitride thin films in view of application in electrostatic capacitive RF MEMSswitches. The proposed technique takes the advantage of the atomic force microscope(AFM) tip to simulate charge injection through asperities, and then the induced surfacepotential is measured. The impact of bias amplitude, bias polarity, and bias durationemployed during charge injection has been explored. The influence of various parameters onthe charging/discharging processes has been investigated: dielectric film thickness,SiNx material deposition conditions, and under layers. Fourier transform infrared spectroscopy(FT-IR) and x-ray photoelectron spectroscopy (XPS) material characterization techniqueshave been used to determine the chemical bonds and compositions, respectively, of theSiNx films being investigated. The required samples for this technique consist only of thindielectric films deposited over planar substrates, and no photolithography steps arerequired. Therefore, the proposed methodology provides a low cost and quitefast solution compared to other available characterization techniques of actualMEMS switches. Finally, the comparison between the KPFM results and thedischarge current transients (DCT) measurements shows a quite good agreement.

Mechanical property characterization of sputtered and plasma enhanced chemical deposition (PECVD) silicon nitride films after rapid thermal annealing

In this paper, the mechanical and fracture properties of silicon nitride films subjected to rapid thermal annealing (RTA) have been systemically tested. The residual stress, Young's modulus, hardness, fracture toughness, and interfacial strength of both sputtered and plasma-enhanced chemical vapor deposition (PECVD) silicon nitride films deposited on silicon wafers were measured and compared. The results indicated that the Young's modulus and hardness of both types of silicon nitride films significantly increased when the RTA temperature increased. Furthermore, RTA processes could also alter the state of residual stress. The initial residual compressive stress of sputtered silicon nitride film was gradually relieved, and the film became tensile after the RTA process. For PECVD silicon nitride, the tensile residual stress reached its peak after a 600 °C RTA, then dropped after further increases in RTA temperature, due to stress relaxation. The tendency of the equivalent fracture toughness was to exhibit a strong correlation with that shown in the residual stress of silicon nitride. By considering the effect of residual stress, the real fracture toughness of both types of silicon nitride films were slightly enhanced by using RTA processes. Finally, experimental results indicated that the interfacial strength of PECVD silicon nitride could also be significantly improved by RTA processes at 600–800 °C. On the other hand, the initial interfacial strength of the sputtered silicon nitride was sufficiently strong, and the RTA processes only resulted in minor improvements. The characterization flow could be applied to other brittle films, and these specific test results should be useful for improving the structural integrity and process optimization of related MEMS and IC applications.

Effect of Boundary Layers on Polycrystalline Silicon Chemical Vapor Deposition in a Trichlorosilane and Hydrogen System

This paper presents the numerical investigation of the effects of momentum, thermal and species boundary layers on the characteristics of polycrystalline silicon deposition by comparing the deposition rates in three chemical vapor deposition (CVD) reactors. A two-dimensional model for the gas flow, heat transfer, and mass transfer was coupled to the gas-phase reaction and surface reaction mechanism for the deposition of polycrystalline silicon from trichlorosilane (TCS)-hydrogen system. The model was verified by comparing the simulated growth rate with the experimental and numerical data in the open literature. Computed results in the reactors indicate that the deposition characteristics are closely related to the momentum, thermal and mass boundary layer thickness. To yield higher deposition rate, there should be higher concentration of TCS gas on the substrate, and there should also be thinner boundary layer of HCl gas so that HCl gas could be pushed away from the surface of the substrate immediately.

On the influence of environment gases, relative humidity and gas purification ondielectric charging/discharging processes in electrostatically driven MEMS/NEMSdevices

In this paper, we investigate the impact of environment gases and relative humidity ondielectric charging phenomenon in electrostatically actuated micro- and nano-electromechanicalsystems (MEMS and NEMS). The research is based on surface potential measurementsusing Kelvin probe force microscopy (KPFM). Plasma-enhanced chemical vapor deposition(PECVD) silicon nitride films were investigated in view of applications in electrostaticcapacitive RF MEMS switches. Charges were injected through the atomic forcemicroscope (AFM) tip, and the induced surface potential was measured using KPFM.Experiments have been performed in air and in nitrogen environments, both underdifferent relative humidity levels ranging from 0.02% to 40%. The impact of oxygengas and hydrocarbon contaminants has been studied for the first time by usingdifferent gas purifiers in both air and nitrogen lines. Voltage pulses with differentbias amplitudes have been applied during the charge injection step under allinvestigated environmental conditions in order to investigate the effect of biasamplitude. The investigation reveals a deeper understanding of charging anddischarging processes and could further lead to improved operating environmentconditions in order to minimize the dielectric charging. Finally, the nanoscaleKPFM results obtained in this study show a good correlation with the devicelevel measurements for capacitive MEMS switches reported in the literature.

Use of Neural Network to Model the Refractive Property of PECVD Silicon Nitride Films used to Prevent Water Permeability of Piezoresistive Pressure Sensor

A plasma-enhanced chemical vapor deposition (PECVD) silicon nitride is used for the passivation layer of ICs and sensors. For example, in blood pressure sensor, the piezoresistive pressure sensor is immerged into liquid and the silicon nitride film is expected to prevent water permeability into it. In this paper, we first applied a design of experiment (DOE) and neural network to discover the relationship between input parameters and refractive indexes of PECVD silicon nitride films. Later we introduced the metrology developed to quantify the water permeability into the film based on the resistance test structure measurement and the break down measurement. These two performance tests could further use to identify the optimal silicon nitride deposition recipe which could prevent water permeability of piezoresistive pressure sensor.

Comparison of charge generation from hot wires between AC and DC power supply and its effect on deposition behavior during hot-wire chemical vapor deposition of silicon

The generation behavior of electric charges was different between DC and AC powered wires of hot-wire chemical vapor deposition (HWCVD), which is attributed to the different electric fields formed around the hot wire powered by DC and AC. When the AC and DC powers were used to heat the wire, the currents measured 1.5 cm below the input position of the hot wire were −3.65×10 4 and −0.11 nA/cm 2, respectively, under the same processing conditions of the wire temperature of 1800 °C, reactor pressure of 40 Pa and a reactant gas mixture of 5% SiH 4–95% H 2. Deposited thin films showed different crystalline fraction depending on the type of power supply. The AC power produced more negative current and a thin film with a higher crystalline fraction than the DC power. When the additional DC bias was applied to the hot wire with respect to the ground, the electric field around the hot wire changed, which affected both the measured current and deposition behavior. Thin films with a higher crystalline fraction could be deposited when the negative wire bias was applied for both AC and DC powers. In this case also thin films deposited under AC power showed higher crystallinity than those under DC power.