Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition Research Articles

Optical and Mechanical Properties of Si-Based Thin Films for Photonic Applications

In this talk, we will review recent advances in the fabrication and characterization of silicon-based thin film structures for photonic applications, including rare earth doped silicon oxynitrides and luminescent silicon carbonitrides.For Si-based materials to be used in solid-state lighting (SSL) and silicon photonics schemes it is necessary to have precise control of the optical emission from these materials. This can be accomplished using rare earth dopants such as Ce, Tb, and Eu to obtain blue, green, and red emissions, respectively. After a brief review of the latest developments in the field, this talk will focus on Eu-doped films, which are attractive for silicon photonic applications due to their intense emission in the visible spectral region [1]. The films are fabricated by electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD) and doping is accomplished using a novel hybrid radio frequency (RF) magnetron sputtering source in the ECR-PECVD reactor chamber [2]. This approach contrasts with traditional doping methods which use metal-organic precursors to introduce rare-earth dopant species into the host matrix. We will discuss the relationship between the photoluminescence, elasticity, and hardness of Eu doped silicon oxynitride (SiON) thin films.As the efficiency of photonic devices can be influenced by the mechanical properties of the deposited films, a good understanding of their mechanical properties is required for the integration of these films in photonic devices. SiNx thin films, for example, play an important role in strain engineering of active photonic devices, such as diode lasers fabricated on GaAs or InP substrates. We will discuss results of a collaboration between McMaster and the Université de Rennes in France, aimed at quantifying the effects of structured dielectric thin films on the generation of a mechanical strain field in the semiconductor through tuning the amount of mechanical stress present in the dielectric thin film, as a function of the details of the deposition process [3].[1] Fahmida Azmi et al., “Tunable Emission from Eu:SiOxNy Thin Films Prepared by Integrated Magnetron Sputtering and Plasma Enhanced Chemical Vapor Deposition”, J. Vac. Sci. Technol. A 40, 043402 (2022); https://doi.org/10.1116/6.0001761[2] J.W. Miller et al., “Integrated ECR-PECVD and Magnetron Sputtering System for Rare-Earth-Doped Si-Based Materials”, Surface and Coatings Technology 336, 99 (2018); doi: 10.1016/j.surfcoat.2017.08.051[3] Brahim Ahammou et al., “Strain engineering in III-V photonic components through structuration of SiNx films”, J. Vac. Sci. Technol. B 40, 012202 (2022); doi: 10.1116/6.0001352

Optical and Structural Properties of Europium-Doped Silicon Oxide Fabricated Using Integrated Sputtering and Chemical Vapour Deposition

Europium (Eu) doped silicon oxide (SiOx) thin films containing Eu concentrations of 0.2 to 6.4 at% were fabricated using a hybrid deposition system combining a magnetron sputtering gun serving as the doping source with electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD). The influence of annealing conditions on the structural and luminescence properties was thoroughly studied. The optical properties of the films were investigated by performing variable angle spectroscopic ellipsometry (VASE) and photoluminescence (PL) measurements. The Eu-related emission was found to be highly dependent on the deposition parameters and annealing conditions. Eu2+ and Eu3+ emissions, which are attributed to blue and red light emissions, respectively, were observed. The structural properties were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses, and the formation of nanoclusters was confirmed. At annealing temperatures of 900 °C and beyond, EuxSiyOz crystals were formed, and Eu ions were optically activated. As the light emissions of these thin films are in the blue and red wavelength range, they are promising candidates to be used as greenhouse covers and transparent solar cells.

Nucleation of cubic boron nitride on boron-doped diamond via plasma enhanced chemical vapor deposition

Cubic boron nitride (c-BN), with a small 1.4% lattice mismatch with diamond, presents a heterostructure with multiple opportunities for electronic device applications. However, the formation of c-BN/diamond heterostructures has been limited by the tendency to form hexagonal BN at the interface. In this study, c-BN has been deposited on free standing polycrystalline and single crystal boron-doped diamond substrates via electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD), employing fluorine chemistry. In situ x-ray photoelectron spectroscopy (XPS) is used to characterize the nucleation and growth of boron nitride (BN) films as a function of hydrogen gas flow rates during deposition. The PECVD growth rate of BN was found to increase with increased hydrogen gas flow. In the absence of hydrogen gas flow, the BN layer was reduced in thickness or etched. The XPS results show that an excess of hydrogen gas significantly increases the percent of sp2 bonding, characteristic of hexagonal BN (h-BN), particularly during initial layer growth. Reducing the hydrogen flow, such that hydrogen gas is the limiting reactant, minimizes the sp2 bonding during the nucleation of BN. TEM results indicate the partial coverage of the diamond with thin epitaxial islands of c-BN. The limited hydrogen reaction is found to be a favorable growth environment for c-BN on boron-doped diamond.

A Comparative Study of a:SiCN:H Thin Films Fabricated with Acetylene and Methane

In this paper we present a comparative study of the properties of amorphous hydrogenated silicon carbonitride (SiCN:H) thin films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD). The elemental composition, growth rate, density, and refractive index values of the SiCN:H thin films were analyzed as functions of flow rates of pure acetylene (C2H2) and methane (CH4) hydrocarbon precursors. The mechanical properties were studied with nanoindentation measurements to compare hardness and Young’s modulus of the SiCN:H thin films deposited with different carbon sources. Variable angle spectroscopic ellipsometry (VASE), elastic recoil detection (ERD), and Rutherford backscattering spectrometry (RBS) were used to determine thin film properties. Higher carbon content in the thin films was achieved by acetylene compared to methane at the same flow rate due to its lower ionization energy during the deposition. Infrared (IR) absorption spectra of the thin films deposited with acetylene precursor were analyzed to determine the correlation between the hydrocarbon flow rate and the intra-molecular bond intensities in the thin films. We found that the major contribution to the hardness comes from hydrogen (H) in the SiCN matrix which makes the films less dense. Carbon improves the hardness, however, H introduced by the hydrocarbon reduces the mechanical strength.

(Student Award, 2nd Place) Optical and Mechanical Properties of Europium-Doped Sicn Thin Films Prepared By Integrated Ecr-PECVD and Magnetron Sputtering

Silicon carbonitride (SiCN) is a wide bandgap semiconductor material that has drawn significant interest over the past few decades due to its excellent optical, electrical, and mechanical properties[1]. Rare earth doping in wide bandgap semiconductors has several prospective applications in the field of photoelectric devices, solid-state lasers, flat panel displays, and high-energy radiation detectors [2]. Among the various rare earth materials, europium (Eu) is particularly interesting due to its optically active divalent and trivalent states capable of emitting in different visible spectral ranges [3].In this work, Eu-doped SiCN thin films were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) with integrated magnetron sputtering [4] on p-type 3” Si (100) substrates. Silane (diluted in 90% argon), nitrogen (diluted in 90% argon) and ethane (C2H6) were used as precursor gases, and a 99.9% pure Eu sputtering target was used as a sputtering source. To understand the effect of C incorporation in the Eu-doped SiCN matrix, we have prepared a set of samples without C. The as-deposited samples were annealed over a wide range of temperatures from 600 to 1100° C in an internet N2 environment. Rutherford backscattering spectrometry (RBS) was performed to determine the atomic concentration of the constituents. Variable angle spectroscopic ellipsometry (VASE) analysis was performed to investigate the optical properties of the films. The room temperature photoluminescence (PL) experiments were carried out with a laser diode excitation source, operating at a wavelength of 375nm. Finally, we performed nanoindentation measurements to understand the deformation behavior of SiCN films as a function of the incorporation of C. The indentation hardness and Young’s modulus of the films were investigated for different Eu and C concentrations.

Design and Fabrication of Multiple-Color-Generating Thin-Film Optical Filters for Photovoltaic Applications

The use of electric vehicles (EVs) can reduce greenhouse gas emissions, air pollution, dependency on fossil fuels, and their adverse health effects on humans. But, we can only utilize the full environmental benefits of EVs when they are charged with renewable energy sources with zero or low carbon emissions. As a solution, Mobarak et al. [1] suggested integrating low-cost, flexible, and thin-film copper indium gallium selenide (CIGS) solar cells directly onto the steel of all the upward-facing body parts of the vehicles. But, this integration of solar cells comes with an aesthetic drawback. Previously, colorful photovoltaics (PVs) have been designed with one-dimensional (1D) photonic crystals or various 1D and 2D metallic nanostructures for aesthetic building-integrated photovoltaics (BIPVs) [2, 3]. However, the functionality of our application differs from that of BIPV as we need maximum absorption of the solar spectrum to obtain maximum conversion efficiency. Thus, we propose replacing the anti-reflective coating (ARC) present in the solar cells with a notch filter (a narrow high-reflection region in the visible range along with high transmission for the rest of the solar spectrum) to obtain colors.High-performance notch filters with a narrow and ultra-steep notch are well known in literature [4, 5]. Generally, high-performance notch filters are designed with a minimum of 45 layers. It is challenging to use filters with many layers on solar cells due to fabrication and thickness complexities. Thus, we created designs with a maximum of 27 layers for possible integration with photovoltaics. We used OptiLayer [6] to simulate our designs and the gradual evolution technique was used to optimize the designs. We performed our simulations with a multilayer structure of alternating high and low refractive indices of 2.09 and 1.45, respectively, on top of a silicon substrate. We optimized this multilayer structure for three reference wavelengths (400 nm, 550 nm, and 700 nm) resembling three colors. Our designs have notch widths of less than 100 nm for all the reference wavelengths with an average of 70% reflection in the high-reflection region and less than 20% reflection in the high-transmission area.To fabricate our designs, we need materials that are transparent to the solar spectrum targeted by the active material of the solar cells. The materials also need to have refractive indices closer to our simulation. Thus, we chose the combination of silicon nitride and silicon dioxide as our high and low refractive index material, respectively [7, 8]. To better understand our designs’ optical characteristics, we fabricated a scaled-down version of our structure with 5-10 layers. We used electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) to deposit the multilayer structure on silicon wafers. To obtain the silicon nitride and silicon dioxide layers, we used a SiH4/N2/O2/Ar precursor mixture. By tuning the gas flow rate in the reactor chamber, we tuned the stoichiometry and obtained the required refractive index for each layer. To characterize the refractive index and thickness for each layer, we used variable angle spectroscopic ellipsometry (VASE). We made a detailed comparison of our simulation and fabrication results.

Influence of Nitrogen on the Luminescence Properties of Ce-Doped SiOxNy

We report wideband photoluminescent emission from cerium-doped silicon oxynitride (Ce-doped SiOxNy) thin films deposited using electron cyclotron resonance plasma enhanced chemical-vapor deposition (ECR-PECVD). The in situ doping with Cerium (Ce) was performed using a volatile metal organic powder, (Ce[tmhd]4). Oxygen was gradually substituted by nitrogen to produce SiOxNy thin films with varying nitrogen to oxygen ratio, to explore the effect of nitrogen on the photoluminescence (PL) of the thin films. Thin film composition and optical constants were determined using Rutherford back scattering and ellipsometry techniques, respectively. Samples subjected to post-deposition thermal annealing yielded considerably stronger blue/white PL emission than as-deposited ones, due to the formation of Ce-containing clusters at a temperature of 1000 °C and above. X-ray diffraction (XRD) revealed no crystalline structure in samples annealed at elevated temperatures. The optimum layer composition and annealing condition to produce SiOxNy thin films with maximized Ce3+ emission was determined. Besides, hydrogen fluoride etching along with hydrogen passivation demonstrated the enhancement of the PL emission of the thin films.

Mechanical and Optical Properties of Amorphous SiN-Based Films Prepared By ECR PECVD and CCP PECVD

Hydrogenated amorphous silicon nitride (a-SiN:H) and silicon carbonitride (a-SiCN:H) films grown by plasma enhanced chemical vapor deposition (PECVD) are widely investigated for their interesting optical and electrical properties [1]. In this work, we discuss the effect of the deposition power on SiN-based films during plasma deposition. The influence on the optical and mechanical properties of the films was investigated. In order to study this issue on a broader basis, two types of plasmas were applied to deposit 0.5 to 1.5 μm a-SiN:H and a-SiCN:H films. First, a-SiN:H and a-SiCN:H films were deposited by electron cyclotron resonance (ECR) PECVD using the same deposition parameters for all films. During the deposition process, the carbon content in the a-SiCN:H thin films was introduced into the chamber through a pure CH4 gas source to avoid any perturbation on the deposition pressure. Second, a-SiN:H films were deposited by a capacitively coupled plasma reactor CCP PECVD using a SiH4/NH3/N2/Ar precursor mixture. In both deposition processes, the ion bombardment energy was tuned only by the deposition power. The mechanical properties of the films were determined ex-situ by profilometry to evaluate the residual stress using the wafer curvature method and by nanoindentation to determine Young’s modulus and hardness of the films. The thickness and the refractive index were measured by variable angle spectroscopic ellipsometry (VASE). It was observed that the evolution of the residual stress according to the deposition power in the ECR PECVD was different from the CCP PECVD. Besides, we notice a slight increase in the refractive index when the residual stress becomes more compressive as illustrated in figure 1 for a-SiN:H and a-SiCN:H films. Through this discussion, we try to have a better understanding of the different interactions taking place when the deposition power increases in terms of ion bombardment energy. Then, we will study the effect of ion bombardment on the film structure based on the composition and structure of the films and the hydrogen bond concentration measured by Fourier transmission infrared spectroscopy (FTIR). In addition, we have also investigated the influence of carbon incorporation on a-SiN:H thin film properties. We notice a decrease in the refractive index and an increase in the compressive residual stress caused by the carbon incorporation.[1] A. Abdelal, Z. Khatami, and P. Mascher, “Optical and Electrical Properties of ECR-PECVD Grown SiCN Thin Films,” ECS Meet. Abstr., vol. MA2018-01, no. 17, p. 1189, Apr. 2018, doi: 10.1149/ma2018-01/17/1189. Figure 1

Investigation of Thin Film Properties of SiCN:H deposited by ECR PECVD with Acetylene and Ethane Hydrocarbon Sources

Silicon carbonitride (SiCN) thin films have drawn considerable interest among the ternary compounds due to the combination of unique properties such as high hardness, wide band gap, high photosensitivity in the ultraviolet (UV) region and low dielectric coefficient (k). In the last few decades various fabrication methods including reactive sputtering and plasma-enhanced chemical vapour deposition (PECVD) have been intensively studied to achieve SiCN thin films having attractive mechanical, tribological and optoelectronic features. Applications range from hard, wear-resistant coatings, low-k interconnects, UV photodetectors to gas separation membranes [1].The properties of thin films are not only influenced by the deposition method, which mainly determines the energy of bombarding ions, but also the choice of source gas [2]. In PECVD processes, silicon (Si), carbon (C) and nitrogen (N) can either be introduced separately as silane (SiH4), methane (CH4), and molecular nitrogen (N2) or ammonia (NH3), or alternatively using organic single precursors such as methylsilazanes [3]. In this work we deposited our thin films with the electron cyclotron resonance (ECR) PECVD method, which differs from other PECVD methods due to it is capability of generating a dense, highly ionized plasma (1011 ions/cm3) and ion impingement energies on the substrate as low as 20 eV [4]. We present the compositional and mechanical properties of hydrogenated SiCN (SiCN:H) thin films which were deposited with two different C precursors, acetylene (C2H2) and ethane (C2H6). The stoichiometry, density of the thin film, optical constants, and the bonding structure of SiCN:H thin films as a function of hydrocarbon carbon gas source have been explored. Due to the hydrogen-containing precursors used, the silicon carbonitride films deposited by CVD methods contain a significant amount of hydrogen (H). From Rutherford backscattering spectrometry (RBS), elastic recoil detection (ERD) analysis, quantitative elemental composition distributions including H were found for films deposited with both carbon sources. For further investigation of bonding structure of SiCN:H, Fourier Transform Infrared (FTIR) Spectroscopy and X-ray Photoelectron Spectroscopy (XPS) measurements were performed. Furthermore, we studied the hardness and Young’s modulus by nanoindentation, and variable angle spectroscopic ellipsometry (VASE) measurements were performed to extract optical constants. To interpret the measurements further, nearly stoichiometric silicon nitride and silicon carbide thin films were also prepared.[1] C.W. Chen, C.C. Huang, Y.Y. Lin, L.C. Chen, K.H. Chen, W.F. Su, Optical prop- erties and photoconductivity of amorphous silicon carbon nitride thin film and its application for UV detection, Diamond Relat. Mater. 14 (3-7) (2005) 1010–1013.[2] Schwarz-Selinger, T., Von Keudell, A., & Jacob, W. (1999). Plasma chemical vapor deposition of hydrocarbon films: The influence of hydrocarbon source gas on the film properties. Journal of Applied Physics, 86(7), 3988-3996.[3] V.I. Ivashchenko, A.O. Kozak, O.K. Porada, L.A. Ivashchenko, O.K. Sinelnichenko, O.S. Lytvyn, T.V. Tomila, V.J. Malakhov, Characterization of SiCN thin films: experimental and theoretical investigations, Thin Solid Films 569 (2014) 57–63.[4] M. G. Boudreau, "SiOxNy Waveguides Deposited by ECR-PECVD", M.Eng. thesis, McMaster University, 1993.

Effect of Sputtering Parameters on the Optical Properties of Luminescent Eu-Doped SiOx Thin Films

Luminescent silicon (Si) based structures that are compatible with the existing complementary metal oxide semiconductor industry has drawn significant interest with the vision of developing an integrated optoelectronic platform on monolithic Si [1]. Such luminescent structures find several applications in inter- and intra-chip optical interconnects, microdisplay, biological detections, and solid-state lighting [2, 3]. The outstanding optical properties and chemical stability of rare earth materials make doping Si with rare earths a promising approach to obtain bright emission from Si-based structures [4].In this work, we have investigated the influence of sputtering power and argon (Ar) partial pressure on the optical properties and the composition of europium (Eu) doped silicon oxide (SiOx) thin films. For this purpose, the thin films were fabricated by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) with in-situ magnetron sputtering on a p-type 3" Si (100) substrate. Silane (SiH4) and oxygen (O2) were used as precursor gases, and a solid 99.9% pure Eu as the sputtering target. Ar was used as the sputtering gas and brought into the chamber through a gas injection ring. A set of samples was prepared by changing the Ar flow rate ranging from 10 to 40 cubic centimeters per minute at standard temperature and pressure (sccm) in steps of 10 sccm. Another set of samples was fabricated by varying the sputtering power from 20 to 30W in steps of 5W. Post-deposition annealing was performed at a higher temperature from 900°C to 1200°C in ambient nitrogen and a mixture of nitrogen (95%) and hydrogen (5%) atmosphere. The effect of hydrogen passivation has also been studied in this work. The compositional analysis was performed by Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA). We found that the doping concentration was strongly influenced by the sputtering power, and it is slightly affected by the Ar partial pressure. The thickness, refractive index, and absorption coefficient of the thin films were obtained from variable angle spectroscopic ellipsometry (VASE) analysis. The dependency of the thickness and the optical parameters on sputtering power and Ar partial pressure was also analyzed. In addition, the luminescence properties of Eu doped SiOx films have been investigated. A bright white emission was observed due to the transition between 4f65d and 4f7energy levels of Eu2+ ion from all the films, which can be seen by the naked eye under daylight conditions. The relation between intensity and doping concentration was also discussed.[1] Lin, R. Huang, H. Wang, Y. Wang, Y. Zhang, Y. Guo, ... and H. Li, “Dense nanosized europium silicate clusters induced light emission enhancement in Eu-doped silicon oxycarbide films,” J. Alloys Compd., vol. 694, pp. 946–951, 2017, doi: 10.1016/j.jallcom.2016.10.132.[2] D. Thomson, A. Zilkie, J. E. Bowers, T. Komljenovic, G. T. Reed, L. Vivien, ... and J. M. Hartmann, , “Roadmap on silicon photonics,” J. Opt. (United Kingdom), vol. 18, no. 7, pp. 1–20, 2016, doi: 10.1088/2040-8978/18/7/073003.[3] H. Jeong, S. Lee, G. Y. Sung, and J. H. Shin, “Design and fabrication of Tb3+-doped silicon oxy-nitride microdisk for biosensor applications,” IEEE Photonics Technol. Lett., vol. 23, no. 2, pp. 88–90, 2011, doi: 10.1109/LPT.2010.2091268.[4] L. Li, J. Zheng, Y. Zuo, B. Cheng, and Q. Wang, “Strong Eu2+ light emission in Eu silicate through Eu3+ reduction in Eu2O3/Si multilayer deposited on Si substrates,” Nanoscale Res. Lett., vol. 8, no. 1, p. 194, 2013, doi: 10.1186/1556-276x-8-194.

Low-Temperature and Low-Pressure Silicon Nitride Deposition by ECR-PECVD for Optical Waveguides

We report on low-temperature and low-pressure deposition conditions of 140 °C and 1.5 mTorr, respectively, to achieve high-optical quality silicon nitride thin films. We deposit the silicon nitride films using an electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD) chamber with Ar-diluted SiH4, and N2 gas. Variable-angle spectroscopic ellipsometry was used to determine the thickness and refractive index of the silicon nitride films, which ranged from 300 to 650 nm and 1.8 to 2.1 at 638 nm, respectively. We used Rutherford backscattering spectrometry to determine the chemical composition of the films, including oxygen contamination, and elastic recoil detection to characterize the removal of hydrogen after annealing. The as-deposited films are found to have variable relative silicon and nitrogen compositions with significant oxygen content and hydrogen incorporation of 10–20 and 17–21%, respectively. Atomic force microscopy measurements show a decrease in root mean square roughness after annealing for a variety of films. Prism coupling measurements show losses as low as 1.3, 0.3 and 1.5 ± 0.1 dB/cm at 638, 980 and 1550 nm, respectively, without the need for post-process annealing. Based on this study, we find that the as-deposited ECR-PECVD SiOxNy:Hz films have a suitable thickness, refractive index and optical loss for their use in visible and near-infrared integrated photonic devices.

Europium Doped Silicon Oxide Thin Films Using an Integrated PECVD and Sputtering System

Over the last decades, silicon-based materials have exhibited outstanding electronic properties and been used in photovoltaic and electrical devices such as transistors [1]. However, due to their indirect band gap nature and poor light emitting properties, they are not satisfying candidates when it comes to photonics. One way through which this poor performance is sorted out is doping of rare earth (RE) elements into the silicon nanostructure thin film to enhance the light emission. The reason for the use of RE elements in silicon-based materials is the fact that they showed well-defined emission peaks and 4f electron shielding making them independence of the host matrix [2].In this study, luminescence properties of Europium (Eu) doped oxygen rich silicon oxide (ORSO) materials using two fabrication techniques are discussed as well as controlling of the Eu concentration, argon partial pressure and sputtering power. In addition, the effect of different annealing atmospheres is observed as here pure nitrogen (N2) and forming gas (N2+5% H2) are tested at a variety of deposition temperatures ranging between 300 °C and 1350 °C. In particular, samples subjected to the higher annealing temperatures of 1200 °C and 1350 °C behave differently in comparison with lower annealing temperatures where their structural and photoluminescence (PL) properties are investigated in more details.The introducing of Eu into ORSO host matrix was performed by two different deposition methods with the first one being the conventional method of metal organic powders where RE elements are introduced using electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) system. The second method involves the use of a novel and custom-made integration of ECR-PECVD and magnetron sputtering [3]. The investigation of a variation of optical and structural properties of the samples made with similar deposition parameters using these two different techniques resulted in insignificant light emission of the ones fabricated with metal organic precursor and remarkable emission of the samples produced using the integrated ECR-PECVD and sputtering method.Variable angle spectroscopic ellipsometry (VASE) measurements are carried to comprehend the refractive index and thin films thicknesses, and their dependence on the deposition parameters such as the sputtering power. Rutherford backscattering spectrometry (RBS) measurements provide the film composition and verify a good control of the Eu concentration using the second deposition method (integrated ECR-PECVD and sputtering). X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) confirm the formation of nanostructures in the Eu-ORSO thin films following post-deposition annealing beyond 1200 °C. The PL studies are performed to study the light emission properties of Eu-ORSO thin films and the changes introduced by the hydrogen passivation. Figure 1 shows the influence of hydrogen passivation on one of the Eu-ORSO thin films containing 0.1 ± 0.01 at. % of Eu. The sample is annealed at 1200 °C and 1350 °C using N2 and N2+H2 atmospheres for 1 hour in the quartz tube furnace. The hydrogen passivation enhances the PL emission by one order of magnitude possibly due to the passivation of the defects and dangling bonds.

Optoelectronic Properties of Ce3+ Doped Silicon Oxide and Oxynitride Electroluminescent Devices

In this work, we propose a new type of silicon-based electroluminescent device. The thin film emitting layers of the device were deposited using Electron-Cyclotron-Resonance Plasma Enhanced Chemical-Vapor Deposition (ECR-PECVD) with in-situ Ce3+ doping on a P-type silicon substrate. Oxygen was gradually substituted by nitrogen to produce silicon oxynitride thin films with different layer compositions. Refractive indices extracted from variable-angle spectroscopic ellipsometry (VASE) measurements classified the thin films into two main groups, silicon oxide (SiOx) and silicon oxynitride (SiOxNy). The thin film composition was studied by Rutherford Backscattering Spectrometry (RBS), verifying the gradual increase in oxygen content. Photoluminescence (PL) spectroscopy of the emitting layer was obtained using a 375 nm laser as an excitation source. All samples were subjected to the post-deposition annealing treatment for 1 hour at different temperatures varying from 600 to 1200°C in 95% N2 and 5% H2 ambient gas environment, yielding considerably stronger blue PL emission than as-deposited ones. PL intensity of SiOx showed a sudden increase due to the formation of Ce2Si2O7 clusters when annealed at 1200°C. Internal Quantum Efficiency (IQE) and External Quantum Efficiency (EQE) were measured using an integrating sphere and a UV-Vis-NIR spectrometer. The optimum layer composition and annealing condition to produce SiOxNy thin films with maximized Ce3+ excitation efficiency were obtained. To further investigate the electrical performance of the produced samples, the thin films were coated with indium tin oxide (ITO) and aluminum (Al) on the top and bottom side of the thin film respectively. Current-Voltage (I-V) measurements showed improved charge injections in SiOxNy compared to SiOx, due to the reduction of the bandgap upon the incorporation of nitrogen.

Characterization of Europium Doped Silicon Oxide, Silicon Oxynitride, and Silicon Nitride Films Prepared By Integrated Ecr-PECVD and Magnetron Sputtering

The compatibility of Si-based light sources with mainstream metal-oxide semiconductor technology has become very interesting over the past decades due to their potential in integrated optoelectronics circuits of monolithic Si [1]. A very promising approach to improve the light emission from silicon-based materials is doping silicon with rare earth elements, and numerous research is involved in this field [1]. However, there are only a few works on europium (Eu) doped silicon-based matrix. In this work, Eu doped silicon oxide, silicon oxynitride, and silicon nitride thin films were deposited on P (100) Si substrates using integrated electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) and magnetron sputtering. Silane (SiH4), oxygen (O2), and Nitrogen(N2) gases were used as precursors and solid Eu as the sputtering target. The integrated ECR-PECVD and sputtering system allows tunable and highly consistent Eu doping concentration, better control of the layer stoichiometry along with less hydrogen incorporation in the deposited film compared to conventional CVD systems [2]. Several thin films were investigated using room temperature photoluminescence (PL) and X-ray diffraction (XRD). A detailed investigation of the effect of annealing on the PL was performed. The annealing temperature was varied from 500 OC to 1200 OC in nitrogen and a mixture of nitrogen and hydrogen atmospheres. It was observed that the intensity of the PL spectra increased with increasing annealing temperature. Besides, the hydrogen passivation effect has been studied in this work, which shows that hydrogen passivation increases the intensity of the peak. Based on the XRD measurements, we have found that the amorphous silicon oxide structure changes to a crystalline structure by adding nitrogen in the film. Interestingly silicon oxynitride and silicon nitride films do not show any luminescence at room temperature. The influence of the precursors' gases in the atomic percentage of the thin films was analyzed by Rutherford Backscattering spectrometry (RBS). In addition to it, the thickness and the index of refraction were characterized by variable angle spectroscopic ellipsometry (VASE).Reference: 1. Lin, Z., Huang, R., Wang, H., Wang, Y., Zhang, Y., Guo, Y., ... & Li, H. (2017). Dense nanosized europium silicate clusters induced light emission enhancement in Eu-doped silicon oxycarbide films. Journal of Alloys and Compounds, 694, 946-951.2. Miller, J. W., Khatami, Z., Wojcik, J., Bradley, J. D. B., & Mascher, P. (2018). Integrated ECR-PECVD and magnetron sputtering system for rare-earth-doped Si-based materials. Surface and Coatings Technology, 336, 99-105.

X-ray Absorption Spectroscopy of Silicon Carbide Thin Films Improved by Nitrogen for All-Silicon Solar Cells

Synchrotron-based experiments in combination with optical measurements were used to explore the potential of a photovoltaic material based on silicon carbonitride (SiCN) thin films, in particular for the use in space solar cells. The large bandgap, SiCN films were fabricated using electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD) followed by low-temperature annealing processes. X-ray absorption near edge structure (XANES) with excitations at the carbon, nitrogen, and silicon K-edges verifies that the presence of nitrogen tends to disrupt Si–C networks. This results in the enhancement of light absorption and bandgap widening, which is desirable for front emitters in all-silicon tandem solar cells. The ternary structure of SiCN allows bandgap engineering and tuning of the light absorption and refractive index through careful design of the composition. XANES showed that the thermal annealing at a medium temperature (500 °C) using N2 ambient promoted the formation of Si–Si and C–N sp2 bonds before disappearing in higher annealing temperatures. In our opinion unlocking the potential of robust SiC mixed with nitrogen in SiCN matrix has appeal in radiation-resistant solar cells, where it can serve as the top emitter layer in all-silicon tandem solar cells and at the same time benefits the antireflection properties.

Optical and Electrical Properties of ECR-PECVD Grown SiCN Thin Films

Recent progress in scaling down the metal-oxide semiconductor (MOS) devices accompanied limitations arising from quantum effects, which leads to a search for new materials. Silicon oxide (SiO2) thin films have been a favourable dielectric for more than 4 decades. Their usage have become impractical due to the power dissipation and delay in interconnects. To increase the electrical performance, low extinction coefficient (low-k) dielectric materials are being developed as a substitute to SiO2. Those materials draw considerable attraction due to their advances in the integrated circuit technology to increase the transistor density. Among numerous materials, silicon carbonitride (SiCN), which is an intermediate compound between silicon nitride (SiN) and silicon carbide (SiC), has become noteworthy with its unique properties as low-k, robustness, high thermal stability, and wide bandgap of 2.2eV- 5eV1. In this work we present the optical, structural, and electrical analysis of SiCN thin films grown using electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD). The influence of the precursors (SiH4, C2H2, and N2 gases) on the composition and electronic structure of thin films which were characterized by Rutherford backscattering spectroscopy (RBS) and Fourier transmission infrared spectroscopy (FTIR). Furthermore, current-voltage characteristics were studied in dark and illuminated environment at room temperature. We studied the variation of photodiode characteristics with the thin film compositions. These results were also compared with the SiCN thin films growth using identical parameters except for the carbon source (CH4 gas) which has been reported in earlier studies2. Our findings showed that the hydrogen content influenced the optical coefficients of these two set of samples. Index of refraction and extinction coefficients were characterized by variable angle spectroscopic ellipsometry (VASE). In addition to our works on developing low-k matrix to enhance the performance of the integrated circuits, the wide gap feature of SiCN thin films enable us to consider the ultraviolet (UV) photo responsivity effect which is studied for photodetector device application.

Effect of Temperature on the Microstructure and Electrical Conductivity of Microcrystalline Si Films

Micro-Si films were deposited using Ar diluted SiH4 gaseous mixture by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD). The effects of the substrate temperature on microstructure and electrical conductivity of micro-Si film were investigated. The results show that, with the increasing of substrate temperature, crystallinity and grain size increased monotonously, of which a competing balance would determine the electrical conductivity of micro-Si films. Based on these results, relatively small grain size and appropriate crystallinity would be beneficial to improve the electrical properties of micro-Si films.

In-Situ Rare Earth Doping of Silicon-Based Nanostructures By Plasma Enhanced Chemical Vapour Deposition

In order for Si-based materials to be used in solid-state lighting (SSL) schemes it is necessary to have precise control of the optical emission from these materials. This can be accomplished through the use of rare earth dopants such as Ce, Tb, and Eu to obtain blue, green, and red emissions, respectively. After a brief review of the latest developments in the field, this talk will focus on several in-situ doping approaches to achieving very high, optically active concentrations of the rare earths. The methodologies include electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD), inductively coupled plasma (ICP) CVD as low thermal budget processes for film deposition, reactive sputtering, as well as the use of a recently installed Circular High Vacuum Magnetron Sputtering source attached to the ECR-PECVD tool. We will describe the salient features of the deposition systems and correlate important process parameters with the observed luminescence. Finally, we will discuss some of the challenges in developing electrically driven lighting cells suitable for SSL and in particular, for the development of widely tuneable Si-based light sources.This work has been supported by the Natural Sciences and Engineering Research Council (NSERC) under its Discovery Grants Program.

Microcrystalline silicon thin films deposited by matrix-distributed electron cyclotron resonance plasma enhanced chemical vapor deposition using an SiF4 /H2 chemistry

For the growth of hydrogenated microcrystalline silicon (μc-Si:H) thin films by low temperature plasma-enhanced chemical vapor deposition (PECVD), silicon tetrafluoride (SiF4) has recently attracted interest as a precursor due to the resilient optoelectronic performance of the resulting material and devices. In this work, μc-Si:H films are deposited at high rates (7 Å s−1) from a SiF4 and hydrogen (H2) gas mixture by matrix-distributed electron cyclotron resonance PECVD (MDECR-PECVD). Increased substrate temperature and moderate ion bombardment energy (IBE) are demonstrated to be of vital importance to achieve high quality μc-Si:H films under such low process pressure and high plasma density conditions, presumably due to thermally-induced and ion-induced enhancement of surface species migration. Two well-defined IBE thresholds at 12 eV and 43 eV, corresponding respectively to SiF+ ion-induced surface and bulk atomic displacement, are found to be determinant to the final film properties, namely the surface roughness, feature size and crystalline content. Moreover, a study of the growth dynamics shows that the primary challenge to producing highly crystallized μc-Si:H films by MDECR-PECVD appears to be the nucleation step. By employing a two-step method to first prepare a highly crystallized seed layer, μc-Si:H films lacking any amorphous incubation layer have been obtained. A crystalline volume fraction of 68% is achieved with a substrate temperature as low as 120 °C, which is of great interest to broaden the process window for solar cell applications.

Calibration of a Circular HV Magnetron Sputtering Source for in-Situ RE Doping of Ecr-PECVD Si-Based Thin Films

Rare-Earth doped silicon based luminescent materials have become an attractive solution in some key areas of technological development. For instance, in the field of silicon photonics there is a drive to replace electronic on-chip components with photonic counterparts [1-2]. One of the major challenges thus far has been to provide the monolithic integration of an efficient reliable electrically driven light source. Such an element could also be used for solid state lighting, and avoid expensive III-V compounds that cannot be fully integrated into electronic drivers in a CMOS line [3]. In-situ doping of Eu3+ions in silicon oxides and oxynitrides fabricated by electron-cyclotron-resonance plasma enhanced chemical vapour deposition (ECR-PECVD) is performed. Doping is achieved by using a Circular High Vacuum Magnetron sputtering source attached to the ECR-PECVD tool. The doping concentration is varied by varying the distance of the sputtering source to the target. The hot matrix composition is varied through varying oxygen and nitrogen gas flows. The effects on the doping concentrations of the sputtering source distance to target is determined through Rutherford Backscattering Spectrometry and Variable Angle Spectroscopic Ellipsometry. Preliminary luminescence measurements are discussed. [1] Jalai, B., and Fothpour, S. “Silicon photonics,” Journal of Lightwave Technology 24, 4600-4615(2006) [2]Liu, A. Jones, R., Liao, L., Samarah-Rubio, Rubin, D., Cohen, O. Nicolaescu, R., and Paniccia, M., “A high-speed silicon optical modulator based on a metaloxide-semiconductor capacitor,” Nature 427, 615-618 (2004) [3] Ponce, F.A., Bour, D.P., “Nitride-based semiconductors for blue and green light-emitting devices”, Nature 386 (6623), 351-359 (1997)