Cyclotron Resonance Chemical Vapor Deposition Research Articles

Mechanical behavior related to various bonding states in amorphous Si–C–N hard films

A series of amorphous Si–C–N hard films were prepared by an electron cyclotron resonance chemical vapor deposition method. Microstructure characterization revealed that amorphous Si–C–N hard films contained various bonding states. Among them, SiN and SiC bonds played a leading role in determining the microstructure of amorphous Si–C–N hard films. Mechanical measurements showed that the hardness of these films varied between 17GPa and 28GPa as a function of the tetramethylsilane flow rate. A close relation between various bonding states and hardness was found. The variation of hardness was dominated by the bond fraction that corresponded to various bonding states. Macroscopic mechanical properties of a material were illustrated from the perspective of microscopic structural characterization.

Highly Stable Micromorph Tandem Solar Cells Fabricated by ECRCVD With Separate Silane Gas Inlets System

In this paper, hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon ( \(\mu \) c-Si:H) films are deposited by electron cyclotron resonance chemical vapor deposition with two separate silane gas inlets. One of the silane gases (S2) is introduced near the substrate region. Effects of S2 flow rate on film properties and solar cell performance are investigated in comparison to traditional plasma-enhanced chemical vapor deposition (PECVD). The results show that the introduction of S2 gas leads to: 1) significant reduction of higher order silane radicals participating film growth; 2) dense film structure with a low microstructure factor of 0.06; and 3) lower surface roughness of the interface between top a-Si:H and bottom \(\mu \) c-Si:H subcells of micromorph tandem cells, favoring bottom \(\mu \) c-Si:H deposition. Single-junction amorphous silicon solar cells show light-induced degradation (LID) of 7.8%, almost half of that observed in PECVD cells. Micromorph tandem solar cells show a 13.3% initial conversion efficiency and a 12.7% stabilized efficiency. Highly stabilized micromorph tandem solar cell with 4.7% LID can be achieved.

Comparative and integrative study of Langmuir probe and optical emission spectroscopy in a variable magnetic field electron cyclotron resonance chemical vapor deposition process used for depositing hydrogenated amorphous silicon thin films

An electron cyclotron resonance chemical vapor deposition (ECR-CVD) system applied in a hydrogenated amorphous silicon (a-Si:H) thin-film deposition process was diagnosed in-situ by using optical emission spectroscopy (OES) and a Langmuir probe. The optical actinometry technique was used to obtain the ratio of species concentration to the concentration of a trace gas (Ar). The electron temperature (Teoes) was estimated according to the spectrum intensity ratio of Hβ to Hα or that of Si* to SiH*, and the two estimation approaches were evaluated by comparing the results (TeLP) of Langmuir probe measurement. The probe surface contaminants (a-Si:H) produced during in-situ measurement created errors in the measurement of parameters such as the electron temperature and density (Ne). The results indicated that, when a-Si:H was coated on the probe at thicknesses less than 150nm, the errors were negligible. OES and Langmuir probe measurement were integrated and used to determine the dependence of the processing pressure and resonance magnetic field configuration on the properties of an a-Si:H film grown using ECR-CVD. When the process pressure was increased, the Ne, Teoes and TeLP decreased; moreover, the Fourier-transform infrared spectroscopy results indicated that structure factor (R*) increased, and both the photosensitivity and hydrogen content (CH) decreased. An analysis conducted using OES and Langmuir probe measurement revealed, that the decreased concentration of the H radical reduced the passivation effect, and surface diffusion decreased. Furthermore, the gas partial pressure exerted a substantial influence on OES measurement. The volatility of the Ar spectrum intensity equaled the product of the volatility of Ne and TeLP when the partial pressure effect is eliminated. Regarding the resonance magnetic field, the effects of plasma resonance position on film characteristics were substantial. The Ne decreased greatly when the distance between quartz and the resonance zone was increased.

Investigation of hydrogenated amorphous silicon as passivation layer by high density plasma

In this study, we use an electron cyclotron resonance chemical vapor deposition to deposit hydrogenated amorphous Silicon (a-Si:H) by different process parameters. We investigated the structure and passivation quality of a-Si:H by tuning the hydrogen dilution ratio and thermal annealing. The properties of films were measured by spectroscopic ellipsometry, optical emission spectroscopy, Fourier transform infrared spectrometer, and quasi-steady-state photoconductance methods. The best passivation quality results from films are consistent with a low microstructure parameter, abundant hydrogen content, and high photosensitivity. The maximum value of τeff at about 1182μs at an injection level of 10−15cm−3 was obtained on single-side polished p-type Cz (100) substrates after thermal annealing around 270°C. The high passivation quality can be obtained at the onset of the amorphous–crystalline transition, while the thin film remains in the amorphous phase.

Investigation of a-Si:H Films as Passivation Layer in Heterojunction Interface at Low Temperature

In this study, hydrogenated amorphous silicon (a-Si:H) thin films that were deposited by the high density plasma electron cyclotron resonance chemical vapor deposition (ECRCVD) were used to study the passivation effect on the surface of c-Si substrate. We investigated the structural, optical, and passivation qualities of a- Si:H as a heterojunction interface by modulating the parameters of microwave power, substrate temperature, and post-deposition annealing. With increasing the microwave power leading to more dangling bonds, such that the longer lifetime and lower microstructure factor R* were demonstrated at 500W. When raising the substrate temperature, the hydrogen content (CH) will be decreased but the lifetime will be increased because this R* is the a dominated factor. It indicates that exceeding 120ºC in the substrate temperature has better absorption to the light. In addition, the post-deposition annealing of a-Si:H was an effective method to improve the minority carrier lifetime, and we can obtain better passivation with the carrier lifetime of 883μsec after 2 minutes annealing at 270ºC.

Electrical and Optical Characterization of Boron-doped Microcrystalline SiH Films Prepared by ECR-CVD for Solar Cell

In this study, boron doped p-type hydrogenated silicon films were prepared by Electron Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD) at lower temperature (＜200℃) for solar cell. In order to analyze the optical and electrical property of the film, the film’s absorption coefficient and imaginary part of the pseudo-dielectric function 〈ε2〉 as well as resistivity and dopant concentration were obtained by spectroscopic ellipsometry (SE) and Hall measurement respectively. The Optical Emission Spectroscopy (OES) is used as a diagnostic tool for analyzing the plasma spectra, and we try to find out the correlation between plasma spectra and film properties. Based on the above results, we can build up the database from plasma spectra corresponding to film properties, and the processing time required for optimization of process can be reduced significantly. In addition, it was found that the applications of these results can be used for the phase transition in the boron doped hydrogenated silicon film from amorphous to microcrystalline structure.

CVD Characteristics and Mechanism of a-Si:H thin Films in Electron Cyclotron Resonance H2-Ar-SiH4 Plasma

This study investigated the use of quadrupole mass spectrometer (QMS), optical emission spectrometer (OES) and Langmuir probe to diagnose the H2-Ar-SiH4 plasma characteristics in cyclotron resonance chemical vapor deposition (ECR-CVD) process. The plasma physical characteristics such as electron density (Ne), electron temperature (Te), plasma and floating potential were obtained by Langmuir probe. The QMS and OES were used to identify the radicals in the plasma. Furthermore, the relative concentration and consumption of SiH4 in ECR-CVD process could be estimated by the TIMS (threshold ionization mass spectrometry) method based on the QMS results. The relationship between the film and plasma characteristics with varying process parameters was also discussed. As results shown, besides the degree of ionization, the consumption of SiH4 and the sheath potential (Vs) were key factors to affect thin film deposition rate (DR). When microwave power density rose from 1 w/cm2 to 3w/cm2, the DR has increased 194%, and it was nearly equal to the product of 104% in SiH4 consumption and 187% in Vs increase. The high hydrogen dilution ratio (H2/SiH4) would lead to higher electron temperature, density and Vs, but decrease the SiH4 consumption and DR. Moreover, the declining extent of DR was significantly greater than SiH4 consumption and Vs increase. It seems that the effect of hydrogen etching plays an important role due to the increase of high hydrogen dilution ratio (H2/SiH4), This interpretation can be received from supporting evidence in OES measurements.

Integrating the Quadrupole Mass Spectrometer, Optical Emission Spectroscopy and Langmuir Probe as a Plasma Characterization Tools for ECR-CVD with a-Si:H

We present the application of quadrupole mass spectrometer (QMS), optical emission spectroscopy (OES), and Langmuir probe (LP) as an integrated technique for plasma characterization of the process during electron cyclotron resonance chemical vapor deposition (ECR-CVD) of hydrogenated amorphous silicon (a-Si:H). The main aim of this study was to investigate the use of QMS to determine the relationship between plasma and thin film characteristics, in particular microstructure parameter (R*) and hydrogen content (CH). The OES was used to assist the QMS in measuring the light and simple radicals, such as the H, Si and SiH, and the associated physical plasma properties which include electron density (Ne), electron energy (Te) and sheath potential (Vs) would be studied with the Langmuir probe. The effects of the two ECR-CVD parameters, namely the power density (1 ~ 4 w/cm2) and hydrogen dilution ratio (H2/SiH4, 0 ~ 25) were discussed. The results indicated that there is a very obvious difference in QMS analysis between plasma and gas, and it is due to the fact that the QMS analysis of plasma is accompanied with the vapor and surface reactions. Therefore, the consumption of parent molecule (SiH4) needed to be considered. The TIMS (Threshold ionization mass spectrometry) method which is usually applied to estimate the relative density trends of the ground-state silane radicals (SiHx, x < 4) was used in this study. It was found that increasing power density and hydrogen dilution ratio would lead to higher electron density and more SiH2 generated in the plasma. Furthermore, when comparing with the TIMS analysis reported by other authors, we found the ratio of SiH2 to SiH3 from QMS could be considered as a better indicator of film quality for R*.

Scalable Graphite/Copper Bishell Composite for High-Performance Interconnects

We present the fabrication and characterizations of novel electrical interconnect test lines made of a Cu/graphite bishell composite with the graphite cap layer grown by electron cyclotron resonance chemical vapor deposition. Through this technique, conformal multilayer graphene can be formed on the predeposited Cu interconnects under CMOS-friendly conditions. The low-temperature (400 °C) deposition also renders the process unlimitedly scalable. The graphite layer can boost the current-carrying capacity of the composite structure to 10(8) A/cm(2), more than an order of magnitude higher than that of bare metal lines, and reduces resistivity of fine test lines by ∼10%. Raman measurements reveal that physical breakdown occurs at ∼680-720 °C. Modeling the current vs voltage curves up to breakdown shows that the maximum current density of the composites is limited by self-heating of the graphite, suggesting the strong roles of phonon scattering at high fields and highlighting the significance of a metal counterpart for enhanced thermal dissipation.

Kinetic Study of the Thermal Crystallization Behavior of Hydrogenated Amorphous Silicon Prepared by ECRCVD

Hydrogenated amorphous silicon (a-Si:H) thin films were deposited at low temperature by electron cyclotron resonance chemical vapor deposition (ECRCVD). A furnace annealing (FA) treatment was applied to the as-grown thin films to initiate solid-phase crystallization (SPC) in nitrogen atmosphere and oxygen atmosphere. Raman spectroscopy and X-ray diffraction (XRD) were used to investigate the crystallization and grain growth behaviors in the annealed films in N2. The crystalline fraction of the annealed films can reach ∼80%, and a grain size of up to 17 nm can be obtained from the FA treatment at high temperatures. The surface morphologies and microstructures of annealed films were observed using transmission electron microscopy (TEM). The evolution of crystallization with the nucleation and grain growth processes in the annealed film was described by classical thermal kinetics. The activation energies for the incubation time and grain growth of the ECRCVD film were 3.51 ± 0.09 eV and 2.54 ± 0.13 eV, respectively. The results indicate that the ECRCVD deposited films exhibited more voids which would lead to lower nucleation barrier for crystallization and faster rate for grain growth when compared to other different fabrication methods. This was also the reason for the ease of grain growth. Furthermore, the chemical states of silicon in thermally oxidized a-Si:H films were examined by X-ray photoelectron spectroscopy (XPS). The crystalline fraction of annealed films in oxygen atmosphere is higher than that of film in nitrogen atmosphere due to the Si daggling bonds easily form bonding reaction with O atoms for the amorphous phase in oxygen atmosphere. Overall this study provided not only a better understanding of crystallization kinetics in ECRCVD-grown a-Si:H films in N2 vs. O2 atmosphere but also this investigation provided a good understanding on the enhancing effect of crystallization behavior related to mechanism and characteristics of ECRCVD-grown a-Si:H films being oxidized at high annealing temperatures.

Low Temperature (180°C) Growth of Smooth Surface Germanium Epilayers on Silicon Substrates Using Electron Cyclotron Resonance Chemical Vapor Deposition

This paper describes a new method to grow thin germanium (Ge) epilayers (40 nm) on c-Si substrates at a low growth temperature of 180°C using electron cyclotron resonance chemical vapor deposition (ECR-CVD) process. The full width at half maximum (FWHM) of the Ge (004) in X-ray diffraction pattern and the compressive stain in a Ge epilayer of 683 arcsec and 0.12% can be achieved. Moreover, the Ge/Si interface is observed by transmission electron microscopy to demonstrate the epitaxial growth of Ge on Si and the surface roughness is 0.342 nm. The thin-thickness and smooth surface of Ge epilayer grown on Si in this study is suitable to be a virtual substrate for developing the low cost and high efficiency III-V/Si tandem solar cells in our opinion. Furthermore, the low temperature process can not only decrease costs but can also reduce the restriction of high temperature processes on device manufacturing.

The effects of substrate self-biasing on the growth of Sn-catalysed silicon nanowires grown at low pressure

We describe the fabrication of silicon nanowire arrays on silicon substrates using Sn as a catalyst metal and electron cyclotron resonance chemical vapour deposition as the growth method. This technique features low deposition pressures and long mean-free paths, allowing the ability to control the ion bombardment energies at the substrate with the application of RF power to the substrate. The applied RF signal generates a DC self-bias across the substrate. Wires have been grown under differing levels of DC self-bias from 0 to −100 V. The impact on wire density, morphology and catalyst stability is described.

Low temperature growth of highly conductive boron-doped germanium thin films by electron cyclotron resonance chemical vapor deposition

The effect of the doping ratio (B2H6/GeH4) on the structural and electrical properties of boron doped hydrogenated germanium films deposited by the electron cyclotron resonance chemical vapor deposition process has been investigated. By increasing the flow rate of B2H6/GeH4 from 0.025 to 0.125, more boron related radicals are available to desorb hydrogen atoms from the growing surface. This leads to degradation of the structure of the amorphous phase identified by Raman and X-ray diffraction spectroscopy. The incorporation of boron enhances the carrier concentration from 1.65×1019cm−3 to 2.25×1020cm−3 and reduces the resistivity from 0.131Ω·cm to 0.018Ω·cm as measured by Hall measurement. These highly conductive boron-doped hydrogenated Ge films can be useful as low resistance doped layer in devices to achieve better performance. Moreover, we are able to deposit highly conductive boron-doped Ge films at a low growth temperature (180°C) and low hydrogen dilution ratio (H2/GeH4=33), in this study. Such a low temperature process can overcome some problems with high temperature deposition process that limit application in devices. Furthermore, the low hydrogen dilution ratio can minimize an ion bombardment effect on the films.

Fabrication of Si heterojunction solar cells using P-doped Si nanocrystals embedded in SiN x films as emitters

Si heterojunction solar cells were fabricated on p-type single-crystal Si (sc-Si) substrates using phosphorus-doped Si nanocrystals (Si-NCs) embedded in SiNx (Si-NCs/SiNx) films as emitters. The Si-NCs were formed by post-annealing of silicon-rich silicon nitride films deposited by electron cyclotron resonance chemical vapor deposition. We investigate the influence of the N/Si ratio in the Si-NCs/SiNx films on their electrical and optical properties, as well as the photovoltaic properties of the fabricated heterojunction devices. Increasing the nitrogen content enhances the optical gap E04 while deteriorating the electrical conductivity of the Si-NCs/SiNx film, leading to an increased short-circuit current density and a decreased fill factor of the heterojunction device. These trends could be interpreted by a bi-phase model which describes the Si-NCs/SiNx film as a mixture of a high-transparency SiNx phase and a low-resistivity Si-NC phase. A preliminary efficiency of 8.6% is achieved for the Si-NCs/sc-Si heterojunction solar cell.

Nanoscratch properties of extremely thin diamond-like carbon films

Scratch properties of extremely thin (targeted at 0.03–5.0-nm-thick) diamond-like carbon (DLC) films deposited by the filtered cathodic vacuum arc (FCVA) and electron cyclotron resonance chemical vapor deposition (ECR-CVD) methods are investigated. The difference in profiles and friction coefficients of scratches in both the corn and edge directions are evaluated. The difference of scratch properties between deposition methods is clearly evaluated by the scratching in the corn direction. When scratching in the corn direction, the friction coefficient and wear depth of the FCVA-DLC film increased rapidly at critical load, whereas those of the ECR-CVD-DLC film increased gradually even beyond this critical load. These results are deduced to be caused by the differences in the hardness and brittleness of the films. The dependence of nanoscratch friction force and scratch profile on DLC film thickness can reveal differences in mechanical properties that correspond to atomic-scale thickness.

Optical Emission Spectroscopy Studies in ECR Plasma Used for the Deposition of Silicon Oxide Film

The Optical Emission Spectroscopy (OES) is used as a diagnostic tool for analyzing the plasma spectrum of Electron Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD) in solar silicon oxide thin film process. In this study, the correlation between spectrum variation trend and a-SiOx film properties will be discussed. The results reveal when the total flow rate and working pressure are fixed, the silicon oxide deposition rate can be interpreted by SiH* spectroscopy. On the premise that the bond energy of reaction species is lower than the bond energy of Si-O bond, the O* spectroscopy intensity tends to to be a positive correlation with oxygen content of thin film. Based on the above results, we can develop and use the database from plasma spectra corresponding to film properties, and the processing time required for optimization of silicon oxide process can be reduced significantly. In addition to the film properties, it is noted that a different and opposite finding compared with PECVD is that the photo-conductivity of a-SiOx film increases and dark-conductivity decreases when microwave power augments. Finally, in 800W power, 200°C process temperaure and 5mTorr working pessure, it is found that the hydrogenated amorphous silicon oxide will transform to the crystalline phase when CO2/SiH4 ratio was less than 0.2 and H2/SiH4 ratio greater than 10.

Influence of phosphorous doping on silicon nanocrystal formation in silicon-rich silicon nitride films

Phosphorus-doped silicon nanocrystals (Si-NCs) embedded in a silicon nitride matrix were fabricated by post-annealing of silicon-rich silicon nitride (SRN) films deposited by electron cyclotron resonance chemical vapour deposition. The effects of phosphorus addition on the Si crystallization behaviour in SRN films were investigated. From the experimental results, the existence of phosphorus enhances phase separation in SRN and thus Si crystallization rate. As the phosphorus content increases, the Si-NC size increases under the same annealing conditions. The x-ray photoelectron spectroscopy P 2p signal attributed to Si–P or P–P bonds indicates that the phosphorus may exist inside Si-NCs. It was also found that the crystallization temperature decreases when phosphorus concentration is increased, and could be as low as 800 °C.

Low pressure plasma assisted silicon nanowire growth from self organised tin catalyst particles

We present results on the growth of silicon nanowires from self organised tin catalyst particles by electron cyclotron resonance chemical vapour deposition (ECRCVD), a technique utilising process pressures in the mTorr range with the allied long mean free path. The formation of tin catalyst particles from layers with initial thicknesses of 6, 12 and 24 nm is studied along with nanowire growth parameters of silane partial pressure, microwave power and process pressure. Preliminary observations on the effects on wire growth of a radio frequency (RF) generated direct current (DC) sample self bias are also reported. Observations are made on the mechanisms influencing nanowire growth along with catalyst stability.

Crystalline silicon interface passivation improvement with a-Si1−xCx:H and its application in hetero-junction solar cells with intrinsic layer

Excellent passivation of an n-type Czochralski crystalline silicon surface is made possible by the deposition of hydrogenated silicon carbide (Si1−xCx:H) layers in the electron cyclotron resonance chemical vapor deposition. We investigate the structural effect with various CH4/SiH4 dilution ratios, and the lowest effective surface recombination velocity (21.03 cm/s) that can be obtained. We also demonstrate that the Voc can be improved more than 200 mV by inserting Si1−xCx:H layers to form hetero-junction with intrinsic thin layer (HIT) solar cells. The conversion efficiency of the planar HIT solar cell with μc-Si emitter can reach 13%.

Investigation of the amorphous to microcrystalline phase transition of thin film prepared by electron cyclotron resonance chemical vapor deposition method

Hydrogenated silicon (Si:H) thin film growth by hydrogen dilution method and its phase transition were investigated in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system. These amorphous and microcrystalline structured silicon thin films were deposited on glass and silicon substrates. The structure, optical and electrical properties of these films were identified by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscope (SEM), UV–visible spectroscopy, and dark/photo conductivity measurements. The dilution ratio (H2/SiH4) was varied to obtain different qualities of silicon thin films and we found that a phase transition from amorphous to microcrystalline could be obtained when dilution ratio (H2/SiH4) is above 0.71. These films with lower microstructure parameter (R*=0.07) and hydrogen content (CH=18%) have low optical gap (1.85), and exhibit the highest photo conductivity (σph) of 2.2E−5Ω−1cm−1 and lowest dark conductivity (σd) of 1E−9Ω−1cm−1 at the phase transition boundary. Due to proper atomic hydrogen could break the weaker SiSi and SiH bonds to form the rigid structure, and then the lower microstructure parameter and hydrogen content could be achieved. The lower hydrogen content in films makes the optical gap to be lower for absorbing more photons which is the reason why there is a better photo response at the phase transition boundary. Furthermore, high-quality hydrogenated silicon thin films are realized through the diluted control of both silane and hydrogen flow rates. Finally, we demonstrate that high quality intrinsic hydrogenated silicon thin films deposited with high growth rate (~1nm/s) using ECR-CVD, are suitable as absorber in a-Si solar cells.