Deposition and Characterization of Indium Nitride and Aluminum Nitride Thin Films by Reactive Sputtering

Intensive research has been carried out on III-V semiconductors for over a century due to their various applications in the field of Microelectronics, Optics, and Photonics. Among III-V materials, the III-nitrides, for example Aluminum Nitride, Indium Nitride, Gallium Nitride and their ternary alloys are known for their unique properties. All the III-Nitride Compounds are direct bandgap semiconductors with a bandgap ranging from 0.7 eV to 6.2 eV covering the entire visible region and extending to the UV region as well. Despite having many applications, fabricating good quality thin films without defects is quite a challenge. They are typically grown using a process called Molecular Beam Epitaxy (MBE) on substrates, such as sapphire or silicon carbide (SiC), but the process and materials are not very economical. The main aim of this thesis is to deposit high quality III-Nitrides thin films with the help of Reactive Magnetron Sputtering on various substrates. Various characterization techniques are used to analyze the samples and understand the effect of various deposition parameters on the quality of the films

Control of the properties of semiconducting thin films deposited using magnetron sputtering

The objective of the work was to deposit semiconducting thin films with controlled properties using unbalanced reactive magnetron sputtering. It was decided to utilise this technique because it offers high deposition rate and controllable in-situ ion bombardment of the growing film, desirable attributes from both research and production perspectives. Sputtering from a metal cathode in a reactive gas atmosphere introduces process instabilities which can result in a low degree of control over the stoichiometry, optical, electrical and structural properties of the films. Whilst the focus of the study was to achieve repeatable control over semiconducting film properties, additional areas of interest associated with the reactive sputtering process were investigated as the project developed. Improvements in magnetron design have been made to remove iron contamination from the extended poles, at the same time improving cathode utilisation. A new technique of bonding polycrystalline silicon cathodes to cooling shims has been developed using a sputtered threemetal multilayer process. DC sputtering of silicon in the presence of oxygen, nitrogen, nitrogen and oxygen, and nitrogen and air has been used to produce films of refractive index between 2.27 and 1.45 at rates between 0.5 and 2 nms-1 depending on composition. Refractive index and optical transmittance of the films have been closely controlled by varying gas flow and composition, and substitution of air for oxygen increased the sensitivity so that indices of oxy-nitride films could be tailored to one decimal place. The deposition of Indium-tin-oxide (ITO) onto glass substrates has been investigated, using a feedback control loop to control the otherwise unstable process...cont'

Nanostructured Vanadium Oxide Uncooled Bolometers and Method of Fabrication

The present invention relates to uncooled microbolometers which can be integrated in future thermal instruments engaged in land imaging on future observatories. The present invention includes: (1) developing and characterizing a microstructured VOx thin film, and, (2) fabricating an uncooled microbolometer array over the 8-14 micron spectral band

Effect of interface fields on the piezoelectric response of aluminum nitride thin films

Group III-Nitride wide bandgap semiconductors have attracted much attention in the optoelectronic and electronic research areas recently. III-Nitride semiconductor materials are attractive materials for use in optoelectronic and high speed electronics devices because they are direct bandgap semiconductors and the bandgap can be varied over a wide range. It has also been shown that the III-Nitride group of materials function exceptionally well in harsh environments. The piezoelectric properties of the III-Nitride material system have been studied and several of the III-Nitride compounds have been found to have non zero piezoelectric coefficients. This work shows that the observed piezoelectric coefficient of Aluminum Nitride (AlN) is directly related to the metal used as the topside contact. The data and preliminary analysis presented here indicate that AlN cannot be treated as an insulating material and must be treated as a semiconductor in order to model its piezoelectric behavior

Investigation Of Reactively Sputtered Boron Carbon Nitride Thin Films

Research efforts have been focused in the development of hard and wear resistant coatings over the last few decades. These protective coatings find applications in the industry such as cutting tools, automobile and machine part etc. Various ceramic thin films like TiN, TiAlN, TiC, SiC and diamond-like carbon (DLC) are examples of the films used in above applications. However, increasing technological and industrial demands request thin films with more complicated and advanced properties. For this purpose, B-C-N ternary system which is based on carbon, boron and nitrogen which exhibit exceptional properties and attract much attention from mechanical, optical and electronic perspectives. Also, boron carbonitride (BCN) thin films contains interesting phases such as diamond, cubic BN (c-BN), hexagonal boron nitride (h-BN), B4C, β-C3N4. Attempts have been made to form a material with semiconducting properties between the semi metallic graphite and the insulating h-BN, or to combine the cubic phases of diamond and c-BN (BC2N heterodiamond) in order to merge the higher hardness of the diamond with the advantages of c-BN, in particular with its better chemical resistance to iron and oxygen at elevated temperatures. New microprocessor CMOS technologies require interlayer dielectric materials with lower dielectric constant than those used in current technologies to meet RC delay goals and to minimize cross-talk. Silicon oxide or fluorinated silicon oxide (SiOF) materials having dielectric constant in the range of 3.6 to 4 have been used for many technology nodes. In order to meet the aggressive RC delay goals, new technologies require dielectric materials with

Fabrication and Characterization of AlN-based, CMOS compatible Piezo-MEMS Devices

This paper details the development of high-quality, c-axis oriented AlN thin films up to 2 {\mu}m thick, using sputtering on platinum-coated SOI substrates for use in piezoelectric MEMS. Our comprehensive studies illustrate how important growth parameters such as the base Pt electrode quality, deposition temperature, power, and pressure, can influence film quality. With careful adjustment of these parameters, we managed to manipulate residual stresses (from compressive -1.2 GPa to tensile 230 MPa), and attain a high level of orientation in the AlN thin films, evidenced by < 5deg FWHM X-Ray diffraction peak widths. We also report on film surface quality regarding roughness, as assessed by atomic force microscopy, and grain size, as determined through scanning electron microscopy. Having attained the desired film quality, we proceeded to a fabrication process to create piezoelectric micromachined ultrasound transducers (PMUTs) with the AlN on SOI material stack, using deep reactive ion etching (DRIE). Initial evaluations of the vibrational behavior of the created devices, as observed through Laser Doppler Vibrometry, hint at the potential of these optimized AlN thin films for MEMS transducer development

Boron nitride thin films deposited by magnetron sputtering on Si3N4

Mestrado em Ciência e Engenharia de MateriaisO Nitreto de boro é um material polimorfo, sendo as fases hexagonal (h-BN) ecúbicas (c-BN) as predominantes. A fase hexagonal do nitreto de boro apresenta uma estrutura em camadas sp2, semelhante a grafite, enquanto que a fase cúbica do nitreto de boro tem forte ligações sp3, como o diamante. O h- BN apresenta boas propriedades dieléctricas, é um material refractário, resistente a corrosão, é conhecido por ser um lubrificante sólido que tem aplicações na protecção de moldes de injecção e em outros processos mecânicos de elevadas temperaturas ou lubrificação em ambientes de elevada humidade. Contudo, o h-BN é extremamente macio. Em contraste, o c-BN apresenta excelentes propriedades térmicas, eléctricas e ópticas, sendo ainda um dos materiais conhecidos com dureza mais elevada (70 GPa). Além disso, c-BN apresenta propriedades superiores em relação ao diamante quando aplicado em ferramentas de corte na maquinagem de materiais ferrosos, devido a sua alta estabilidade química a altas temperaturas durante a maquinagem. Essa combinação de propriedades faz dele um forte candidato no campo das ferramentas de corte e em dipositivos electrónicos. No presente trabalho, filmes finos de nitreto de boro foram depositados por DC e RF magnetron sputtering, utilizando alvos de B4C e h-BN prensados a quente, numa atmosfera de deposição contituída por misturas de Ar e N2. Os filmes finos de BN foram depositados simultâneamente em dois tipos de substratos: cerâmicos de Si3N4 com diferentes acabamentos superficiais e em discos de Si(100). A influência dos parâmetros de deposição, tais como a temperatura do substrato, composição da atmosfera de deposição na espessura dos filmes, taxa de deposição, cristalinidade, tensão residual, fases presentes e dureza, foram sistematicamente investigados usando técnicas como, SEM, XRD, FT-IR e nanodureza. O h-BN foi a principal fase observada nas análises dos espectros de FT-IR e nos difractogramas de XRD. O estado de tensão dos filmes finos de BN films é estremamente afectado pela temperatura do substrato, composição do gás de trabalho e pelo acabamento superficial dos substratos. O estudo da influência da temperatura mostraram que a taxa de deposição aumenta com o aumento da temperatura do substrato. Tensões residuais elevadas ocorrem para altas concentrações de árgon e para substratos polidos em suspensão de diamante 15 μm. Nos espectros de FT-IR, a forma das bandas de vibração variam de uma forma alargada para uma configuração estreita, correspondendo a uma menor desordem da fase hexagonal do BN, devido a variação da composição da atmosfera de deposição. Os valores de dureza obtidos estão numa faixa que vai desde os valores do h-BN macio (6 GPa) até valores próximos dos limites encontrados para filmes contendo a fase cúbica (16 GPa ), acima de 40%. ABSTRACT: Boron nitride is a polymorphic material, the hexagonal (h-BN) and the cubic (c- BN) being its main crystalline structure. The hexagonal boron nitride has a layered sp2-bonded structure, similar to graphite, while the cubic boron nitride has a hard sp3-bonded diamond-like structure. h-BN presents good dielectric properties, refractoriness, corrosion-resistant characteristics, low friction and low wear rate, and it is a well-known solid lubricant which has wide applications in metal-forming dies and other metal working processes at high temperatures or lubrication in high relative humidity environments. However, h-BN is mechanically soft. In contrast, c-BN presents excellent thermal, electrical and optical properties, with a hardness up to 70 GPa. Moreover, c-BN is superior to diamond as cutting tool for ferrous materials due to its high thermal chemical stability during machining. In the present work, thin films of boron nitride have been deposited by D.C. and R.F. magnetron sputtering from hot-pressed B4C and h-BN targets, using mixtures of Ar and N2, as working gases. The BN thin films were deposited simultaneously on two different substrates: Si3N4 ceramics with different surface finishing and Si(100) wafers. The influence of parameters such as substrate temperature and working gas composition ratio, on film thickness, deposition rate, cristallinity, residual stress, phase composition and hardness, were systematically investigated using techniques like SEM, XRD, FT-IR and nanohardness. h-BN was the main observed phase. The stress-state of the thin BN films is largely affected by the substrate temperature, working gas composition and the substrate surface finishing. The substrate temperature studies show that the deposition rate increases with an increasing of the substrate temperature. Large high residual stresses are developed for higher argon ratios and for substrate finishing with 15 μm diamond paste. In the FT-IR spectra, the shape of the vibration band changes from broad to narrow, corresponding to a less disorder h-BN phase, due to the working gas composition. The hardness values obtained are typical in the range of a soft h-BN (6 GPa) to values approaching the limit of the range reported for films containing a fraction of cubic phase (16 GPa ) up to 40%

Deposition and characterization of magnetron sputtered BCC tantalum

The goal of this thesis was to provide scientific and technical research results for developing and characterizing tantalum (Ta) coatings on steel substrates deposited by DC magnetron sputtering. Deposition of tantalum on steel is of special interest for the protection it offers to surfaces, e.g. the surfaces of gun barrels against the erosive wear of hot propellant gases and the mechanical damage caused by the motion of launching projectiles. Electro-plated chromium is presently most commonly used for this purpose; however, it is considered to be carcinogenic in its hexavalent form. Tantalum is being investigated as non-toxic alternative to chromium and also because of its superior protective properties in these extreme environments. DC magnetron sputtering was chosen for this investigation of tantalum coatings on steel substrates because it is a versatile industrial proven process for deposition of metals. Sputter deposited Ta films can have two crystallographic structures: 1) body center cubic (bcc) phase, characterized by high toughness and high ductility and 2) a tetragonal beta phase characterized by brittleness and a tendency to fail under stress. It was found in this work that the bcc Ta coatings on steel can be obtained reliably by either of two methods: 1) depositing Ta on a submicron, stoichiometric TaN seed layer reactively sputtered on unheated steel and 2) depositing Ta directly on steel heated above a critical temperature. For argon sputtering gas this critical temperature was found to be 400°C at a pressure of 5 mtorr. With the heavier krypton gas, this critical temperature is reduced to 350°C. X-ray diffraction (XRD) was used to investigate the structure of tantalum and nitride films, and the composition of the nitride films was measured by nuclear reaction analyses (NRA), which were used to study in detail the enhancement of the bcc phase of Ta on steel. The scratch adhesion tests performed with a diamond hemispherical tip of radius 200 µm under increasing loads revealed high critical load values for failure (\u3e15 N) for the bcc coatings versus the low load values (\u3c9 N) for the beta coatings. The coating deposited on TaN interlayers on sputter-etched steel had better adhesion than those on steel surface without sputter etching. The results for this work have demonstrated that by controlling the various process parameters of dc magnetron sputtering, high quality bcc Ta coatings of multimicron thickness with excellent adhesion to steel can be made. An important contribution of this dissertation is in the enhancing an understanding of this process. The impact of this research will be in a number of fields where superior protective castings are needed. These include military applications, electronic components, chemical processing, and others