Thin, high atomic weight refractory film deposition for diffusion barrier, adhesion layer, and seed layer applications

Thin, nearly conformal films are required for semiconductor applications to function as diffusion barriers, adhesion layers and seed layers within trenches and vias. The deposition of high mass refractory films with conventional, noncollimated magnetron sputtering at low pressures shows better-than-expected conformality which is dependent on the degree of directionality of the depositing atoms: the conformality increases as the directionality increases. The primary cause appears to be a strongly angle-dependent reflection coefficient for the depositing metal atoms. As the deposition is made more directional by increasing the cathode-to-sample distance, the depositing atoms are more likely to reflect from the steep sidewalls, leading to better conformality as well as a less columnar film structure. © 1996 American Vacuum Society.S. M. Rossnagel et al., Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena 14, 1819 (1996) https://doi.org/10.1116/1.58856

Study of Tantalum nitride diffusion barrier films for coppper interconnect technology

As technology progressed to ultra - large scale integration leading to smaller and smaller devices, there are continuous challenges in the fields of materials, processes and circuit designs. Copper is the interconnect material of choice because of its low electrical resistivity and high electromigration resistance. However, copper is quite mobile in silicon at elevated temperatures. Therefore, to prevent the diffusion of copper into silicon, a diffusion barrier layer that has fewer grain boundaries, good adhesion to Si and Si02, high thermal and electrical stability with respect to Cu is necessary. Tantalum nitride compounds have been investigated as potential barrier materials. TaN has a very high melting point of 2950C. It is thermodynamically stable with respect to Cu and has good adhesion to the substrate. It has a dense microstructure and shows good resistance to heavy mobility of Cu in Si and has electrical stability at temperatures upto 750 C. The diffusion barrier properties of Ta and its nitrides for copper metallization at RIT have been investigated. The TaNx films were reactively sputter deposited on Si02 substrates at various N2/AJ- ratios. The influence of nitrogen partial pressure on the electrical and structural properties of the films is studied. It has been observed that as deposited pure Ta is tetragonal, which becomes bcc-Ta with small increase in N2 flow to 5% of the sputtering gas mixture. When the nitrogen flow is increased from 12 up to 20%, amorphous and a mixture of amorphous and crystalline Ta2N phase is formed. The amorphous phase crystallizes when annealed to higher temperatures. An fee- TaN phase is formed at N2 flow of 30%. At higher concentrations of N2; nitrogen rich compounds like Ta5N6, Ta3N5 are formed. During backend semiconductor processing, both Cu and TaN films are subjected to various annealing treatments in N2, 02, and Ar at relatively high temperatures. Since these treatments influence the stability of the metallization it was important to establish the effect of the ambients on the integrity of the copper interconnect. The Cu/TaN/Si02 films were annealed to various temperatures up to 600 C in N2, Ar ambients for 20 min and the thermal stability and barrier effectiveness of the films was studied. Annealing the films to temperatures above 500 C cause de-lamination of films at the Cu/TaN interface, which is attributed to the formation of copper oxides with a high density of voids. This was observed by XRD analyis and SEM. RBS spectra showed diffusion of tantalum into the surface of copper at temperatures ~ 500 to 600 C. Therefore we can conclude that cubic TaN films act as stable barrier films up to 500 C in an inert ambient

Chemical vapor deposition of thin films for ULSI interconnect metallization

We have studied the kinetics of copper chemical vapor deposition (CVD) for interconnect metallization using solution delivery of Cu(hfac)2 (Cu(II) hexafluoroacetyl-acetonate) dissolved in isopropanol. We observe a growth rate of 17.7 „b 1.5 nm/min at reference conditions of 300„aC substrate temperature, 0.025 Torr Cu(hfac)2 partial pressure, 1.6 Torr isopropanol (reducing agent), and 80 Torr H2 (carrier gas). The film resistivity approaches the bulk value of copper for film thickness greater than 100 nm. Reaction order experiments show first-order kinetics with respect to Cu(hfac)2 partial pressure and zero-order with respect to isopropanol. A series reaction mechanism including three kinetically significant steps (adsorption of Cu(hfac)2, dissociation of (hfac) ligand, and desorption of (hfac)) is used to describe the observed kinetic results. The proposed rate determining step is the dissociation of (hfac) ligand when the pressure ratio of Cu(hfac)2 to isopropanol is low, and becomes the desorption of (hfac) when the pressure ratio is high. We also examined a low temperature chemical vapor deposition process for the growth of tantalum thin films using SiH4 reduction of TaF5. Using a temperature of 350„aC and reactant partial pressures of 0.2 Torr TaF5 and 0.3 Torr SiH4, we obtain a growth rate of 2.2 ¡Ó 1.7 nm/min. The XPS analysis results show that the Ta film is Si free, but contains relatively high oxygen concentration because of residual gas contamination. Lastly, we have studied a batch CVD process for palladium seed layer deposition using H2 reduction of Pd(hfac)2 (Pd(II) hexafluoroacetylacetonate). Nano-sized Pd particles with nuclei density between 1 to 14 clusters/ƒÝm2 are observed using AFM. The quality of the Pd seed layer is examined by depositing electroless copper film. We have investigated the influence of CVD operating conditions (deposition time, activation temperature, and precursor concentration) on the activity of the Pd seed layers (i.e., by monitoring visual appearance and deposition rates of the ELD Cu films). At the optimized conditions we can deposit uniform Cu films at a rate of 3.4 „b 1.4 nm/s. Additional work is needed to improve the resistivity and adhesion of the films

Adhesion Enhancement of Diamond Coating on WC-Co Substrates Through Interlayer Design

Diamond coating with sufficient adhesion on WC-Co cutting tools is expected to significantly increase their cutting performance. However, the adhesion is always limited by the formation of graphitic soot in the interface due to the catalytic effect of Co on graphite formation. Moreover, the low nucleation density and the high thermal stress in the coatings also result in poor adhesion. The introduction of interlayer is one of the available approaches to enhance the coating-substrate interfacial adhesion. The goal of this project is to improve the adhesion through the optimization of interlayer design. The Al2O3 and Ta mono-interlayer, Al-Al2O3, Al-AlN, Al2O3-Ta and Al-Ta duplex interlayer systems have been developed in this study. These interlayer materials were prepared using a magnetron sputtering method, and diamond coating were deposited on them using microwave plasma enhanced chemical vapor deposition. In addition, different diamond seeding conditions have been studied to increase the diamond nucleation density. Grazing incident X-ray diffraction was carried out to determine the phase components in the Al-Al2O3 and Al-AlN interlayers. Raman spectroscopy and scanning electron microscopy were used to evaluate the quality, morphology and microstructure of the deposited diamond coatings. Rockwell C indentation testing was performed to evaluate the adhesion of the coatings. To elucidate the coating failure mechanism, the compositions around the delaminated spots of diamond coatings after indentation were identified by Energy-dispersive X-ray spectroscopy. To evaluate the tribological properties of the diamond coatings, the diamond coated WC-Co sheets were rubbed against steel and alumina balls respectively. The results show that continuous diamond coatings were achieved on Al2O3, Al-Al2O3, Al-AlN and Al-Ta interlayered substrates, whereas a graphite layer was still formed with the Ta monolayer or Al2O3-Ta duplex layer accompanied by an easy spallation of diamond coatings. The Al interlayer has played an important role in obtaining high purity diamond by in-situ forming an alumina barrier layer. Especially, the diamond coating deposited with an Al-AlN interlayer exhibits superior interfacial adhesion in comparison with all the other interlayers. Meanwhile, seeding with nano-diamond particles is more efficient than micro-diamond particles for improving the diamond nucleation density on Al-AlN interlayered substrates. Furthermore, the diamond coated WC-Co sheets possess lower coefficient of friction and wear rate than bare sheets when rubbing against either steel or alumina balls

Nano-derived sensors for high-temperature sensing of H2, SO2 and H2S

The emission of sulfur compounds from coal-fired power plants remains a significant concern for air quality. This environmental challenge must be overcome by controlling the emission of sulfur dioxide (SO2) and hydrogen sulfide (H2S) throughout the entire coal combustion process. One of the processes which could specifically benefit from robust, low cost, and high temperature compatible gas sensors is the coal gasification process which converts coal and/or biomass into syngas. Hydrogen (H2), carbon monoxide (CO) and sulfur compounds make up 33%, 43% and 2% of syngas, respectively. Therefore, development of a high temperature (\u3e500°C) chemical sensor for in-situ monitoring H2, H2S and SO2 levels during coal gasification is strongly desired. The selective detection of SO2/H2S in the presence of H2, is a formidable task for a sensor designer. In order to ensure effective operation of these chemical sensors, they must inexpensively function within the gasifier\u27s harsh temperature and chemical environment. Currently available sensing approaches, which are based on gas chromatography, electrochemistry, and IR-spectroscopy, do not satisfy the required cost and performance targets.;There is also a substantial necessity for microsensors that can be applied inexpensively, have quick response time and low power consumption for sustained operation at high temperature. In order to develop a high temperature compatible microsensor, this work will discourse issues related to sensor stability, selectivity, and miniaturization. It has been shown that the integration of nanomaterials as the sensing material within resistive-type chemical sensor platforms increase sensitivity. Unfortunately, nanomaterials are not stable at high temperatures due to sintering and coarsening processes that are driven by their high surface to volume ratio. Therefore, new hydrogen and sulfur selective nanomaterial systems with potentially highly selective and stable properties in the proposed harsh environment were investigated. Different tungstates and molybdates (WO3, MoO3, MgMoO4, NiMoO4, NiWO4, Sr2MgWO6 (SMW), Sr2MgMoO6 (SMM), SrMoO4, and SrWO4) were investigated at the micro- and nano-scale, due to their well-known properties as the reversible absorbents of sulfur compounds. Different morphologies of aforementioned compounds as well as microstructural alterations were also the subject of the investigation. The fabrication of the microsensors consisted of the deposition of the selective nanomaterial systems over metal based interconnects on an inert substrate. This work utilized the chemi-resistive (resistive-type) microsensor architecture where the chemically and structurally stable, high temperature compatible electrodes were sputtered onto a ceramic substrate. The nanomaterial sensing systems were deposited over the electrodes using a lost mold method patterned by conventional optical lithography.;Development of metal based high temperature compatible electrodes was crucial to the development of the high temperature sensor due to the instability of typically used noble metal (platinum) based electrode material over ceramic substrates. Therefore, the thermal stability limitations of platinum films with various adhesion layers (titanium (Ti), tantalum (Ta), zirconium (Zr), and hafnium (Hf)) were characterized at 800 and 1200°C. Platinum (Pt)-zirconium (Zr)-hafnium (Hf) were investigated. The high-temperature stable composite thin film architecture was developed by sequential sputter deposition of Hf, Zr and Pt. In addition to this multilayer architecture, further investigation was carried out by using an alternative DC sputtering deposition process, which led to the fabrication of a functionally-gradient platinum and zirconium composite microstructure with very promising high temperature properties. The final process investigated reduced labor, time and material consumption compared to methods for forming multilayer architectures previously discussed in literature.;In addition to electrical resistivity characterization of the different thin film electrode architectures, the chemical composition, and nano- and micro-structure of the developed nanomaterial films, as well as sensing mechanism, were characterized by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS), atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), Raman spectroscopy, temperature programmed reduction (TPR) and transmission electron microscopy (TEM). The macro-configurations of the sensors were tested and analyzed for sensitivity and cross-sensitivity, response time and recovery time, as well as long term stability. The microsensor configuration with optimized nanomaterial system was tested and compared to a millimeter-size sensor platform in terms of sensitivity and accuracy. Electrochemical relaxation (ECR) technique was also utilized to quantify the surface diffusion kinetics of SO2 over the chosen sensor material surface. The outcomes of this research will contribute to the economical application of sensor arrays for simultaneous sensing of H2, H2S, and SO2

Metal Nitride Diffusion Barriers for Copper Interconnects

Advancements in the semiconductor industry require new materials with improved performance. With the introduction of copper as the interconnect material for integrated circuits, efficient diffusion barriers are required to prevent the diffusion of copper into silicon, which is primarily through grain boundaries. This dissertation reports the processing of high quality stoichiometric thin films of TiN, TaN and HfN, and studies their Cu diffusion barrier properties. Epitaxial metastable cubic TaN (B1-NaCl) thin films were grown on Si(001) using an ultra-thin TiN (B1-NaCl) seed layer which was as thin as 1 nm. The TiN/TaN stacks were deposited by Pulsed Laser Deposition (PLD), with the TiN thickness systematically reduced from 15 to 1 nm. Microstructural studies included X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Preliminary Cu diffusion experiments showed that the TiN seed layer thickness had little or no obvious effect on the overall microstructure and the diffusion barrier properties of the TaN/TiN stacks. Epitaxial and highly textured cubic HfN (B1-NaCl) thin films (~100 nm) were deposited on MgO(001) and Si(001) using PLD. Low resistivities (~40 mu omega-cm) were measured with a four point probe (FPP). Microstructural characterizations included XRD, TEM, and HRTEM. Preliminary Cu diffusion tests demonstrated good diffusion barrier properties, suggesting that HfN is a promising candidate for Cu diffusion barriers. Cubic HfN (B1-NaCl) thin films were grown epitaxially on Si(001) substrates by using a TiN (B1-NaCl) buffer layer as thin as ~10 nm. The HfN/TiN stacks were deposited by PLD with an overall thickness less than 60 nm. Detailed microstructural characterizations included XRD, TEM, and HRTEM. The electrical resistivity measured by FPP was as low as 70 mu omega-cm. Preliminary copper diffusion tests showed good diffusion barrier properties with a diffusion depth of 2~3 nm after vacuum annealing at 500 degrees C for 30 minutes. Additional samples with Cu deposited on top of the cubic HfN/TiN/Si(001) were vacuum annealed at 500 degrees C, 600 degrees C and 650 degrees C for 30 minutes. The diffusivity of copper in the epitaxial stack was investigated using HRTEM. The measured diffusion depths, 2 Dt , were 3, 4 and 5 nm at 500 degrees C, 600 degrees C and 650 degrees C respectively. Finally, the diffusivity of Cu into epitaxial HfN was determined to be D=D0 exp(-Q/kT)cm2s-1 with D0=2.3x10-14cm2s-1 and Q=0.52eV

Frontiers of Cu electrodeposition and electroless plating for on-chip interconnects

In the electronics industry, interconnect is defined as a conductive connection between two or more circuit elements. It interconnects elements (transistor, resistors, etc.) on an integrated circuit or components on a printed circuit board. The main function of the interconnect is to contact the junctions and gates between device cells and input/output (I/O) signal pads. These functions require specific material properties. For performance or speed, the metallization structure should have low resistance and capacitance. For reliability, it is important to have the capability of carrying high current density, stability against thermal annealing, resistance against corrosion and good mechanical properties

New Chemistry For The Growth Of First-Row Transition Metal Films By Atomic Layer Deposition

Thin films containing first-row transition metals are widely used in microelectronic, photovoltaic, catalytic, and surface-coating applications. In particular, metallic films are essential for interconnects and seed, barrier, and capping layers in integrated circuitry. Traditional vapor deposition methods for film growth include PVD, CVD, or the use of plasma. However, these techniques lack the requisite precision for film growth at the nanoscale, and thus, are increasingly inadequate for many current and future applications. By contrast, ALD is the favored approach for depositing films with absolute surface conformality and thickness control on 3D architectures and in high aspect ratio features. However, the low-temperature chemical reduction of most first-row transition metal cations to their zero-valent state is very challenging due to their negative electrochemical potentials. A lack of strongly-reducing coreagents has rendered the thermal ALD of metallic films an intractable problem for many elements. Additionally, several established ALD processes for metal films are plagued by low growth rates, impurity incorporation, poor nucleation, high surface roughness, or the need for hazardous coreagents. Finally, stoichiometric control of ternary films grown by ALD is rare, but increasingly important, with emerging applications for metal borate films in catalysis and lithium ion batteries. The research herein is focused toward the development of new ALD processes for the broader application of metal, metal oxide, and metal borate thin films to future nanoscale technologies. These processes display self-limited growth and support the facile nucleation of smooth, continuous, high-purity films. Bis(trimethylsilyl) six-membered rings are employed as strongly-reducing organic coreagents for the ALD of titanium and antimony metal films. Additionally, new processes are developed for the growth of high-purity, low-resistivity cobalt and nickel metal films by exploiting the redox non-innocent nature of a series of recently-reported 1,4-di-tert-butyl-1,3-diazabutadienyl complexes. Other metal complexes using the same ligand system are subsequently evaluated for use as ALD precursors. Finally, a novel approach is described for the stoichiometric control of first-row transition metal manganese and cobalt borate films, whereby the film composition is governed by the elements present in a single precursor. Computational techniques such as density functional theory (DFT) using nucleus-independent chemical shift (NICS) are used to determine the electronic structure and predict the relative reducing power of organic coreagents. Potential ALD precursors are analyzed by 1H and 13C NMR, IR, thermogravimetric and differential thermal analyses (TGA/DTA), melting point and solid state decomposition measurements, magnetic susceptibility measurements, preparative sublimation studies, and solution-screening reactions. Deposition parameters are optimized for successful ALD processes. The composition and surface morphology of the resultant films are studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), X-ray diffractometry (XRD), time-of-flight elastic recoil detection analysis (TOF-ERDA), ultraviolet-visible spectroscopy (UV-Vis), and four-point probe resistivity measurements

Synthesis and characterization of Titanium Nitride Nanowires for neural-electrode coatings for improving electrode/neuron interface in the brain

In neurophysiological measurements, a neural-electrode interface material plays a critical role in delivering adequate charge to elicit action potentials without damaging the tissue of interest. However, the need to minimise electrode dimensions to reduce invasiveness and increase selectivity, demands the use of materials that are able to handle larger current and charge densities than traditional noble electrodes such as platinum. Since charge density is directly affected by the surface area of the electrode, nanoscale materials have shown a great deal of potential for not just improving the electrochemical properties, but the biocompatibility at reduced electrode dimensions. Titanium Nitride thin film (TiN) has been implemented previously in neural-electrode application due to its apposite properties. The work described here is aimed towards the synthesis of a novel TiN Nanowire interface (TiN-NW) as a potential neural-electrode material. The synthesis of the nanowires involved a three-step approach: (1) sputter of TiN thin film onto a substrate to act as a seed layer for the growth of NWs, (2) the growth of titanium dioxide nanowires (TiO2-NWs) of high aspect ratio and crystallinity followed by (3) a novel plasma nitridation step using Plasma Enhanced Chemical Vapour Deposition (PECVD) which offered a lower synthesis temperature than the conventional processing temperature reported in the literature. An optimised TiN thin film, grown through Radio Frequency (RF) non-reactive magnetron sputtering, was used as a seeding layer for the growth of NWs. The properties of the seed layer and the grown NWs were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-Ray diffraction (XRD), Raman spectroscopy, X-Ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) while the suitability of the grown TiN-NWs as an electrode material was tested by studying their electrochemical performance through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In addition, the biocompatibility of both structures were tested by culturing glioblastoma cells (GBM) in vitro, and cell viability and behaviour were studied and compared to that on TiN thin film. xv XPS and TEM results showed that TiO2-NWs were converted to TiN-NWs at a temperature of 600 °C. Electrochemical results showed 5-fold of capacitance enhancement of the synthesised TiN-NWs as compared to that of the optimised TiN film. Additionally, TiN-NWs have shown greater cyclic stability, with capacitance retention of almost 99%, and lowered susceptibility to oxidation compared to TiN thin films. The impedance of TiN-NWs electrode at low frequencies, corresponding to ion diffusion, was noticeably lower than that of the film electrode. The in vitro test showed that cells were viable and attached to both structures and the cells on NWs formed dense 3D structures and had a greater spatial distribution than those cultured on the thin film layer. These findings not only highlighted the potential use of TiN-NWs as a neural-electrode interface material but also suggested a way of reducing the nitridation temperature to obtain TiN through PECVD process, which can improve existing electrodes or be integrated into next-generation neural-electrode structures.Royal Embassy of Saudi Arabia Cultural Bureau

Study of Interactions Between Diffusion Barrier Layers and Low-k Dielectric Materials for Copper/Low-k Integration

The shift to the Cu/low-k interconnect scheme requires the development of diffusion barrier/adhesion promoter materials that provide excellent performance in preventing the diffusion and intermixing of Cu into the adjacent dielectrics. The integration of Cu with low-k materials may decrease RC delays in signal propagation but pose additional problems because such materials are often porous and contain significant amounts of carbon. Therefore barrier metal diffusion into the dielectric and the formation of interfacial carbides and oxides are of significant concern. The objective of the present research is to investigate the fundamental surface interactions between diffusion barriers and various low-k dielectric materials. Two major diffusion barriers¾ tatalum (Ta) and titanium nitride (TiN) are prepared by DC magnetron sputtering and metal-organic chemical vapor deposition (MOCVD), respectively. Surface analytical techniques, such as X-ray photoelectronic spectroscopy (XPS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) are employed. Ta sputter-deposited onto a Si-O-C low dielectric constant substrate forms a reaction layer composed of Ta oxide and TaC. The composition of the reaction layer varies with deposition rate (1 Å-min-1 vs. 2 Å-sec-1), but in both cases, the thickness of the TaC layer is found to be at least 30 Å on the basis of XPS spectra, which is corroborated with cross-sectional TEM data. Sputter-deposited Cu will not wet the TaC layer and displays facile agglomeration, even at 400 K. Deposition for longer time at 2 Å-sec-1 results in formation of a metallic Ta layer. Sputter deposited Cu wets (grows conformally) on the metallic Ta surface at 300 K, and resists significant agglomeration at up to ~ 600 K. Cu diffusion into the substrate is not observed up to 800 K in the UHV environment. Tetrakis(diethylamido) titanium (TDEAT) interactions with SiO2, Cu and a variety of low-k samples in the presence (~ 10-7 Torr or co-adsorbed) and absence of NH3 result in different products. TDEAT interactions with SiO2 are dominated by Ti interactions with substrate oxygen sites, and that Ti oxide/sub-oxide bond formation can proceed with relatively low activation energy. No Ti carbide or Si carbide formation is observed. Co-adsorption of TDEAT and NH3 on SiO2 at 120K followed by annealing to higher temperature results in enhanced Ti-N bond formation, which is stable against oxidation up to 900K in UHV. Similarly, continuous exposures of TDEAT on SiO2 at 500K in the presence of NH3 exhibit a relatively enhanced Ti-N spectral component. Co-adsorption of NH3 and TDEAT on Cu (poly) surface at 120K, followed by annealing to 500K, results in complete desorption of Ti, N or C-containing species from the Cu substrate. Reaction of TDEAT with a Cu surface at 500K yields a Ti-alkyl species via a b-hydride elimination pathway. TDEAT/Cu interactions are not observably affected by overpressures of NH3 of 10-7 Torr. TDEAT interaction with a porous carbon doped oxide low-k substrate at 700K demonstrates undissociated or partly dissociated Ti-NR species trapped in the dielectrics matrix due to its high porosity. In addition, carbide formation is observed from C(1s) XPS spectra. For a hydrocarbon low-k film, the majority sites (carbon) are highly unreactive towards TDEAT even at higher temperature due to a lack of functional groups to initiate the TDEAT/low-k surface chemistry