SiOC Films Research Articles

Hierarchical microstructure growth in a precursor‐derived SiOC thin film prepared on silicon substrate

AbstractSilicon oxycarbide film deposited on a silicon substrate has shown superior electrical conductivity relative to its monolithic counterpart. In this work, the evolution of different microstructures detected on the SiOC film reveals its hierarchical microstructure. The existence of sp2‐hybridized carbon domains has been unambiguously confirmed by means of Raman spectroscopy and transmission electron microscopy corroborated with electron energy loss spectroscopy. The diffusion coefficient of carbon in silica and its dependence on temperature were studied by assessing energy‐dispersive X‐ray spectroscopy profiles taken from the cross‐sections of samples annealed at temperatures in the range from 1100°C to 1400°C. The activation energy for diffusion of carbon in silica was determined to be approximately 3.05 eV, which is significantly lower than the values related to the self‐diffusion of silicon and oxygen. The microstructural evolution of precursor to SiCnO4‐n and SiC serves as migration path of sp2‐hybridized carbon to the SiOx layer. With increasing temperature, the formation of microscale carbon‐rich segregation is promoted while the SiOC film becomes thinner.

Etching kinetics and dielectric properties of SiOC films exposed to Ar and CF4 plasmas

The investigation of both etching and damage mechanisms for SiOC thin films treated in Ar and CF4 plasma was carried out. It was found that CF4 plasmа provides systematically higher SiOC etching rates (due to the domination of chemical etching pathway) as well as is featured by decreasing effective reaction probability for F atoms toward higher input powers (due to a decrease in the fraction of free adsorption sites for F atoms and/or in their sticking coefficient). It was shown that any SiOC etching process always leads to an increase in the dielectric constant, and the situation appears to be worse in the case of Ar plasma. From plasma damage evaluation experiment, it was suggested that the main damage mechanism is the destruction of Si–C bonds by the ion bombardment and ultra-violet (UV) radiation. In the case of CF4 plasma, the fluorination of SiOC surface enforces the destructive impact of ion bombardment through a decrease in the corresponding threshold energy.

Properties of Carbon-coated SiO-C Negative Electrodes for Sulfide-type All-solid-state Batteries

Carbon-coated SiO (SiO-C) sheet-type electrodes without sulfide-based solid electrolytes on a current collector worked as negative electrode materials for all-solid-state batteries. The SiO-C sheet-type electrodes exhibited the high capacity (ca. 1500 mAh g−1), good cycle and high-rate discharge performance for all-solid-state batteries using sulfide solid electrolytes at room temperature. It is notice that SiO-C film electrodes are expected to promote new ionic-electronic conducting interface for sulfide-based solid electrolytes in all-solid-state batteries.

Etching Characteristics of Low-k Dielectric Using C5H2F10 Liquefied Gas Plasma for Mitigating of Global Warming Potential

In this work, we studied the etch characteristics and dielectric constant change of SiOC thin films by plasma etching for the fabrication of nanoscale devices to evaluate the C5H2F10 as alternative etching gas. We performed plasma etching of SiOC films with inductively coupled plasma using the CF4+X+O2 mixed gas, where X = CHF3 and C5H2F10. Plasma diagnosis such as optical emission spectroscopy and double Langmuir probe measurements were carried. We analyzed the chemical compositions of residues on the etched SiOC film surface using X-ray photoelectron spectroscopy. After the process, contact resistance was measured using the transmission line method to analyze the degree of polymer on the surface of the silicon. Ellipsometry were used to evaluate the change in the dielectric constant of the thin film due to plasma exposure. It was confirmed that the etched profile was more vertical than that of the CHF3 gas plasma, and the increase in the dielectric constant of the SiOC thin film by C5H2F10 gas plasma is less than that of CHF3 gas plasma. These results confirmed that C5H2F10 gas was a powerful alternative to CHF3 gas in semiconductor processing for the fabrication of nanoscale devices.

Compressive thermal stress and microstructure-driven charge carrier transport in silicon oxycarbide thin films

This work correlates the charge carrier transport mechanism of silicon oxycarbide-based thin films with their morphology and thermal stress. Segregation of highly-graphitized carbon-rich, oxygen-depleted C/SiC areas homogeneously dispersed within an oxygen-rich C/SiOC matrix was seen on the 500 nm-SiOC thin films. Compressive biaxial stress induced by the mismatch with the Si-substrate thermal expansion coefficient was calculated at 109 MPa. Through Hall measurements, p-type carriers were shown dominating the SiOC film similar to monolithic samples. Thin films and monoliths have comparable carrier concentrations while the carrier mobility in SiOC thin films was 2 magnitudes higher than that of monolithic samples and is considered a consequence of the compressive thermal stress acting on the film. Improved conductivity of 16 S cm -1 is measured for the SiOC thin film sample which is assumed considering the enhanced carrier mobility alongside the reduced percolation threshold ascribed to the phase-separated morphology of the thin film.

Electrically conductive silicon oxycarbide thin films prepared from preceramic polymers

AbstractThis work focuses on silicon oxycarbide thin film preparation and characterization. The Taguchi method of experimental design was used to optimize the process of film deposition. The prepared ceramic thin films with a thickness of c. 500 nm were characterized concerning their morphology, composition, and electrical properties. The molecular structure of the preceramic polymers used for the preparation of the ceramic thin films as well as the thermomechanical properties of the resulting SiOC significantly influenced the quality of the ceramic films. Thus, an increase in the content of carbon was found beneficial for the preparation of crack‐free thin films. The obtained ceramic films exhibited increased electrical conductivity as compared to monolithic SiOC of similar chemical composition. This was shown to correlate with the unique hierarchical microstructure of the SiOC films, which contain large oxygen‐depleted particles, mainly consisting of highly graphitized carbon and SiC, homogeneously dispersed in an oxygen‐containing amorphous matrix. The matrix was shown to also contain free carbon and to contribute to charge carrier transport between the highly conductive large particles. The ceramic thin films possess electrical conductivities in the range from 5.4 to 8.8 S/cm and may be suitable for implementation in miniaturized piezoresistive strain gauges.

Surface Analysis of TMCTS-Based SiOC(H) Low-k Dielectrics in Post-Etch Strip of ACL Hardmask.

The miniaturization of devices requires the introduction of a high aspect ratio through patterning in the Damascene copper interconnect process. The high aspect ratio etch process employs hardmasks, such as amorphous carbon, that can withstand high-powered plasma exposure. When an etch hardmask is removed after patterning, the properties of the underlying film can be altered by the effect of plasma exposure during the strip process. In this study, surface properties of SiOC(H) are investigated after an amorphous carbon strip with O2/Ar plasma. Since the low-k film of SiOC(H) structure shows characteristics according to the Si-O internal bonding structure, the Si-O bonding ratio of the ring, network and cage structure was analyzed through Fourier-transform infrared (FT-IR) analysis to measure changes in thin film properties. X-ray photoelectron spectroscopy (XPS) was also used to add reliability to the SiOC(H) film structure. In addition, the end point of the strip process was obtained using an optical emission spectroscopy sensor and variations in thin film characteristics over the plasma exposure time were analyzed. These results revealed the structural modification of the SiCO(H) thin film in the post-etch strip of the amorphous carbon layer (ACL) hardmask.

Erratum to “Chemical bonding structure in porous SiOC films (k < 2.4) with high plasma-induced damage resistance” [Micro and Nano Engineering Vol. 3 (2019) 1–6

Erratum to “Chemical bonding structure in porous SiOC films (k < 2.4) with high plasma-induced damage resistance” [Micro and Nano Engineering Vol. 3 (2019) 1–6

Chemical bonding structure in porous SiOC films (k < 2.4) with high plasma-induced damage resistance

Abstract The chemical bonding structure of porous low-k carbon-doped silicon oxide (SiOC) films (k Si( CH3)2) is crucial for resistance to plasma-induced damage (PID) and prevention of moisture uptake after the plasma treatment. The mix of di-methyl bonds is believed to be the key to protecting the films from PID because the films retain their hydrophobic characteristics even after plasma treatment. Thus, control of the ratio of di-methyl bonds to mono-methyl bonds ( Si CH3) in the as-deposited SiOC film is necessary. Selection of trimethyl silane as a precursor for film matrix formation resulted in excellent control of this ratio to obtain highly reliable low-k/Cu interconnects for high-performance logic devices.

Strength and plasticity of amorphous silicon oxycarbide

Amorphous SiOC films were synthesized by magnetron sputtering at room temperature with/without radio frequency (RF) bias and further improved in terms of mechanical properties by ion irradiation. As-deposited SiOC films without RF bias exhibit catastrophic failure at a low stress and strain, which is ascribed to microstructural heterogeneities associated with the formation of voids during deposition, as evidenced by transmission electron microscopy. Ion irradiation unifies microstructure accompanied with eliminating the voids, resulting in a simultaneously increase in strength and plasticity (ultimate strength of 5–7 GPa and the strain to shear instability of over 20%). Homogeneous microstructures are demonstrated to ensure high strength and plasticity of amorphous SiOC, as observed in SiOC that are deposited with RF-bias. Thus, microstructural homogeneous amorphous SiOC exhibits intrinsically high strength and plasticity, making them promising as structural engineering materials.

Adhesion enhancement and amine reduction using film redeposited at the interface of a stack of plasma-enhanced CVD dielectrics for Cu/low-k interconnects

The dielectric interface for a stack of SiOC and SiCN films in Cu/low-k interconnects is engineered using Ar plasma pretreatment of the top surface of SiCN, which prevents oxidization during SiOC film deposition. Oxidized SiCN causes delamination of the SiOC film and resist poisoning through amines generated during resist baking, which can lead to undeveloped photoresist. The Ar plasma pretreatment in the plasma-enhanced chemical vapor deposition chamber modifies the interface by redepositing a thin pre-coated SiOC film from the upper electrode surface. This redeposited SiOC film acts as a buffer for oxygen plasma during SiOC film deposition.

Optical model for spectroscopic ellipsometry analysis of plasma-induced damage to SiOC films

We propose a new optical model for assigning the physical structure of plasma-damaged SiOC films examined by spectroscopic ellipsometry. A two-parameter Bruggeman’s effective medium approximation is used for estimating the thickness and volume fraction of a low-dielectric (ε) region (ε ∼ 1) in the SiO2 background. We introduced an optical model consisting of damaged and undamaged layers. The thickness and fraction of the damaged layer are fitted. Prediction was performed using this model for SiOC samples exposed to various plasmas, and the results were compared with those of scanning electron microscopy. We further applied this model to estimating the depth of damaged region in combination with a layer-by-layer wet-etching technique. In the case of He plasma exposure, the structural change induced by the damage extends 90–130 nm in depth. Since the degradation of interlayer dielectrics affects the circuit performance, the proposed optical model should be used for designing plasma processes.

Synthesis, Characterization and Optical Constants of Silicon Oxycarbide

High refractive index glasses are preferred in integrated photonics applications to realize higher integration scale of passive devices. With a refractive index that can be tuned between SiO 2 (1.45) and a-SiC (3.2), silicon oxycarbide SiOC offers this flexibility. In the present work, silicon oxycarbide thin films from 0.1 – 2.0 μm thickness are synthesized by reactive radio frequency magnetron sputtering a silicon carbide SiC target in a controlled argon and oxygen environment. The refractive index n and material extinction coefficient k of the silicon oxycarbide films are acquired with variable angle spectroscopic ellipsometry over the UV-Vis-NIR wavelength range. Keeping argon and oxygen gases in the constant ratio, the refractive index n is found in the range from 1.41 to 1.93 at 600 nm which is almost linearly dependent on RF power of sputtering. The material extinction coefficient k has been estimated to be less than 10 -4 for the deposited silicon oxycarbide films in the visible and near-infrared wavelength regions. Morphological and structural characterizations with SEM and XRD confirms the amorphous phase of the SiOC films.

Preparation of Sioc Li-Ion Capacitor By TEOS Based Sol-Gel Method with Different Silicones Precursors

Since the development of Li ion battery, carbonous materials e.g. graphite had been widely used in commercial lithium-ion batteries. However, the practical capacity of graphite reached an almost theoretical limit. Therefore, promising anode materials, such as Sn, Si etc. have been considered to replace the graphite though they are not stable during charge-discharge cycles. It was recently reported that amorphous SiOC anode performs high capacity and superior cycling durability. SiOC material has high chemical stability and mechanical strength. In this study, we used a TEOS based sol-gel method with different silicones precursorsto synthesize SiOC directly on the Cu foil as a simple and cheap way. The silicones used in this study were PDMS(dimethylpolysiloxane), silanol- terminated PDMS, Cyclotetrasiloxane, polyether-modified silicone, alkyl-modified silicone and phenol-modified silicone. They were mixed respectively with TEOS (Tetraethyl orthosilicate), which was considered to perform a sol-gel reaction, and water in ethanol. The mole ratio of the TEOS/ silicone / H2O was 1:1:4, and the volume ratio of the mixture and ethanol was 1:1. 10 μl of HCl(37wt%) was added as catalyst before stirring. The sol solution was spin-coated onto the Cu foil. We evaluated these kinds of anode by battery charge-discharge test. Pore distribution and composition was measured by small angle X-ray scattering (SAXS) and X-ray photoelectron spectrometry, respectively. Amorphous SiOC thin films with all precursors showed a high cycling durability. The SiOC film from PDMS sol solution which was heated to 50ºC for 30 minutes during stirring achieved a best specific discharge capacity of about 1050 mAh/g even after 100 cycles, others are distributed from 150-400mAh/g. The SAXS of this sample shows a stronger peak of micropores(pore size <6 nm)than other samples. As a contest, we repeated the experiment without TEOS, and it became pyrolysis of silicones. The anodes made during the contest experiment showed low cycling durability but higher average specific capacity.

Effects of dilution gas on characteristics of SiOC(H) films synthesized by atmospheric pressure plasma CVD

In this study, we synthesized SiOC(H) films by atmospheric pressure plasma enhanced CVD from trimethylsilane and oxygen gas diluted by helium, argon and nitrogen. We changed the oxygen flow rate and investigated the effect of dilution gas on the hardness of the films. The deposition rate for both helium and argon dilution increased with increasing the oxygen flow rate up to 100 ml/min. The hardness of the films diluted by argon gradually increased from 0.2 GPa to 1.1 GPa with an increase of oxygen flow rate while that of the films diluted by helium was hardly changed about 0.6 GPa. The films diluted by nitrogen exhibited high hardness at 2.3 GPa, which was highest value among the samples. The FT-IR spectra of the films showed the peaks corresponding to terminal methyl and hydroxyl bonds along with the stretching vibrations of SiOSi network bonding were observed and their intensities varied with the hardness of the films. As the oxygen flow rate increased, intensity of methyl bond decreased and that of hydroxyl bond was not increased different from the result of the films diluted by argon or helium gas. The methyl bonds are likely to prevent oxygen atom from forming SiOSi structures. The existence of terminated bonds such as methyl bond and hydroxyl bond lead to low hardness of the films. From the result of optical emission spectroscopy, peaks of nitrogen-oxygen radicals were observed at plasma diluted by nitrogen, while a large amount of oxygen radical were generated in the plasma diluted with noble gas.

Evaluation technique for plasma-induced SiOC dielectric damage by capacitance–voltage hysteresis monitoring

We propose an electrical method, named capacitance–voltage (C–V) monitoring, for quantifying plasma-induced damage (PID) to interlayer dielectrics. By this method, we measure the C–V hysteresis loops to assign carrier trap sites created by PID, and simultaneously obtain the change in the dielectric constant and thickness. We optimized the bias-sweep configuration for measuring the hysteresis curves. It is found that the C–V curve shifted in the negative direction during the optimized voltage sweep from accumulation to inversion in a pseudo-metal–oxide–semiconductor (MOS) structure. This implies the appearance of net positively charged sites owing to PID, presumably near the surface of the SiOC film. We estimate the density of defects created near the surface by monitoring the obtained C–V hysteresis curve shift. Since the degradation of interlayer dielectrics affects the circuit performance, the proposed quantitative method should be used for plasma process designs.

Effects of Precursor Flow Rates on Characteristics of Low-K SiOC(H) Film Deposited by Plasma-Enhanced Chemical Vapor Deposition

In this study, low-dielectric constant (low-k) SiOC(H) films deposited using conventional plasma-enhanced chemical vapor deposition (PECVD) by varying flow rates of the deposition precursors were investigated through various characterization techniques. The used deposition precursors were DEMS and ATRP, which acted as a network matrix and a sacrificial porogen, respectively. Experimental results indicate that the flow rates of both DEMS and ATRT precursors influenced the properties of the resulting porous low-k SiOC(H) films, but the former caused a larger impact. For porous low-k SiOC(H) films deposited with an increase of DEMS flow rate, an enhanced cross-linking was formed, leading to a higher hardness, smaller pore size, better electric performance, and stronger dielectric breakdown strength. However, a higher dielectric constant (k) was the cost. The k values of porous low-k SiOC(H) films with various ATRP flow rates (1700~2500 sccm) remained unchanged, although, the optimized electrical characteristics and reliability were obtained as ATRP flow rate was 2100 sccm.

Effects of Precursor Flow Rates on Characteristics of Low-K SiOC(H) Film Deposited by Plasma-Enhanced Chemical Vapor Deposition

In this study, low-dielectric constant (low-k) SiOC(H) films deposited using conventional plasma-enhanced chemical vapor deposition (PECVD) by varying flow rates of the deposition precursors were investigated through various characterization techniques. The deposition precursors were DEMS and ATRP, which acted as a network matrix and sacrificial porogen, respectively. Experimental results indicated that both DEMS and ATRT precursors influence the properties of resulting porous low-k SiOCH films. But matrix DEMS precursor causes greater impact. With an increase of DEMS flow rate, an enhanced cross-linking was formed, leading to a higher hardness, smaller pore size, better electric performance, and stronger dielectric breakdown strength. However, a higher dielectric constant (k) is the cost. The k values of the porous low-k SiOCH films with various ATRP flow rates (1700~2500 sccm) remained unchanged, although, the optimized electrical characteristics and reliability were obtained as ATRP flow rate was 2100 sccm.

Tunneling Characteristics Depending on Schottky Barriers and Diffusion Current in SiOC.

To obtain a diffusion current in SiOC, the aluminum doped zinc oxide films were deposited on SiOC/Si wafer by a RF magnetron sputtering. All the X-ray patterns of the SiOC films showed amorphous phases. The level of binding energy of Si atoms will lead to an additional potential modulation by long range Coulombic and covalent interactions with oxygen ions. The growth of the AZO film was affected by the characteristics of SiOC, resulting in similar trends in XPS spectra and a shift to higher AZO lattice d values than the original AZO d values in XRD analyses. The charges trapped by the defects at the interlayer between AZO and SiOC films induced the decreased mobility of carriers. In the absence of trap charges, AZO grown on SiOC film such as the sample prepared at O2 = 25 or 30 sccm, which has low charge carrier concentration and high mobility, showed high mobility in an ambipolar characteristic of oxide semiconductor due to the tunneling effect and diffusion current. The structural matching of an interface between AZO and amorphous SiOC enhanced the height of Schottky Barrier (SB), and then the mobility was increased by the tunneling effect from band to band through the high SB.

Multicolor Depth-Resolved Cathodoluminescence from Eu-Doped SiOC Thin Films.

A very bright room-temperature cathodoluminescence (CL) signal, tunable in the visible range by changing the Eu(2+) concentration, has been observed in Eu-doped SiOC films. Depth-resolved CL measurements demonstrate that a bilayer consisting of two SiOC films containing different Eu concentrations allows the continuous tuning of the Eu(2+) emission from blue to green by changing the energy of the exciting electrons. Furthermore, the proper control at the nanoscale of the electron penetration depth allows to obtain a high-quality white light emission. The compatibility of SiOC films with Si technology opens the way to promising applications of Eu-based materials in lighting and display technologies.