Composition profiles of CVD platinum and platinum silicide by Auger electron spectroscopy and secondary ion mass spectrometry

Phosphorus, platinum, silicon and oxygen profiles have been studied in thin film Pt formed on Si by chemical vapor deposition (CVD) from Pt(PF₃)₄, and in the platinum silicide formed by interdiffusion at 450° and 625°C. Low voltage sputtered Pt and its silicide have also been studied. Two profiling techniques have been used: inert ion sputtering with sequential Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS).Phosphorus in as-deposited (225°C) Pt formed by chemical vapor deposition (CVD Pt) was found to be non-uniformly distributed, indicating that some diffusion had already occurred even under these mild conditions. There was a high concentration (10–20 at.%) at the surface, decreasing rapidly to the 0.1% range at a depth of about 50 Å. At the interface with the silicon substrate there was a broad peak with a P concentration of about 1 at.%. When platinum silicide was formed, most of the phosphorus from the interior migrated to the surface, resulting in an enhanced P zone now 150–200 Å thick. The phosphorus did not appear to impede silicide formation in any way. The same $\text{Pt}\text{Si}$ ratio was found in platinum silicide formed from CVD Pt at either 450° or 625°C, in silicide from sputtered Pt and in single-crystal PtSi. The composition of the silicide was essentially constant through most of the film. A strong oxygen signal combined with an Si peak shift was present within 100–200 Å of the surface of the silicide. This is the layer of SiO₂ which has been detected by independent methods earlier, and which protects PtSi from attack by the aqua regia used to remove unreacted Pt from insulator areas. The surface silica coincided with the enhanced phosphorus zone when CVD Pt was used, and thus in this case should be considered as a phosphosilicate glass.     

Oxidation behavior of silicide coating on Ti3SiC2-based ceramic

A silicide coating was prepared on Ti₃SiC₂-based ceramic by pack cementation to improve the oxidation resistance of Ti₃SiC₂, which is a technologically important material for high temperature applications. The microstructure, phase composition and oxidation resistance of the coated sample were investigated. The results demonstrated that the silicide coating was mainly composed of TiSi₂ and SiC. A single layer of a mixture of SiO₂ and TiO₂ was formed on the surface of the coated sample during isothermal oxidation at 1100 °C and 1200 °C for 20h. Compared to Ti₃SiC₂, the parabolic rate constant of silicide coated Ti₃SiC₂ decreased by 2~3 orders of magnitude. Furthermore, the coated sample showed much better cyclic oxidation resistance than Ti₃SiC₂ during the cyclic oxidation at 1100 °C for 400 times. However, during the preparation of the coating, a number of fine cracks formed in the outer layer of the coating. When these cracks penetrated the whole coating during the cyclic oxidation, the oxidation rate was accelerated, which degraded the oxidation resistance. Electronic Publication     

Ion-induced transformations of a W–Si interface

Tungsten silicide formation in multilayer tungsten/silicon structure was investigated. The W–Si multilayers were deposited on thermally oxidized silicon wafers using the dual-target magnetron sputtering. Deposition of the whole stack of sublayers was carried out without breaking vacuum in order to eliminate contamination or oxidation of the interfaces between sublayers. Samples were annealed in the RTA furnace at temperatures ranging from 700 °C up to 1050 °C. Some of the structures were irradiated with argon ion beam before annealing. Reactions between sublayers were studied using SEM imaging of cross-sectional cleavages and by X-ray diffraction analysis. Influence of the irradiation with argon ion beam on structural transformations was investigated using RBS analysis. It has been found that tungsten silicide formation depends on the deposition sequence. The reaction was more effective on interfaces between silicon layer deposited on tungsten then on interface between tungsten deposited on silicon. Ion beam mixing experiment showed that ion–target interaction promotes formation of the WSi₂ phase.     

Properties of indium tin oxide films prepared by ion-assisted deposition

Conducting transparent films of indium tin oxide were deposited by 100 eV oxygen-ion-assisted deposition. A refractive index of 2.13 at 550 nm was obtained for films deposited onto ambient temperature substrates. The refractive index decreased with increasing substrate temperature to a value of 2.0 at 400°C. The sheet resistance of films 135 nm thick decreased from 800 Ω/□ for layers deposited onto room temperature substrates to around 25 Ω/□ at 400°C. Structural studies revealed that ion-assisted deposition onto ambient temperature substrates produced amorphous films, and that at temperatures above 100°C the films exhibit In₂O₃ crystallinity. In addition, it was found that the number of voids in the ion-bombarded films was reduced relative to that in films produced by conventional reactive evaporation.     

Improvement of the properties and electrical performance on TiCl4-based TiN film using sequential flow chemical vapor deposition process

Sequential flow chemical vapor deposition (SFCVD), utilizing TiCl₄/NH₃ as reactants and immediate NH₃ treatment after film deposition, is applied to produce TiN barrier films in the contact process. Secondary ion mass spectroscopy results indicate that the SFCVD TiN film can effectively block the diffusion of WF₆ into the underlying Ti layer during W deposition. NH₃ treatment immediately after film deposition causes SFCVD TiN films to be less contaminated with carbon than TiN films that are formed by metallic organic compounds chemical vapor deposition (MOCVD) and to contain less chlorine residue than conventional TiCl₄/NH₃ CVD TiN layers even at a low reaction temperature. According to the resistance measurement of Kelvin contacts, the SFCVD process yields a lower resistance and a more uniform distribution than the MOCVD or CVD process. Transmission electron microscopic observations demonstrate that WF₆ can diffuse through the MOCVD TiN to react with the underlying Ti layer, causing a rupture at the Ti/TiN interface and poor W adhesion. The SFCVD TiN can serve as a sufficient diffusion barrier against WF₆ penetration during W CVD deposition.     

Self-Formation of a Ru/ZnO Multifunctional Bilayer for the Next-Generation Interconnect Technology via Area-Selective Atomic Layer Deposition

This study suggests a Ru/ZnO bilayer grown using area-selective atomic layer deposition (AS-ALD) as a multifunctional layer for advanced Cu metallization. As a diffusion barrier and glue layer, ZnO is selectively grown on SiO₂, excluding Cu, where Ru, as a liner and seed layer, is grown on both surfaces. Dodecanethiol (DDT) is used as an inhibitor for the AS-ALD of ZnO using diethylzinc and H₂O at 120 °C. H₂ plasma treatment removes the DDT adsorbed on Cu, forming inhibitor-free surfaces. The ALD-Ru film is then successfully deposited at 220 °C using tricarbonyl(trimethylenemethane)ruthenium and O₂. The Cu/bilayer/Si structural and electrical properties are investigated to determine the diffusion barrier performance of the bilayer film. Copper silicide is not formed without the conductivity degradation of the Cu/bilayer/Si structure, even after annealing at 700 °C. The effect of ZnO on the Ru/SiO₂ structure interfacial adhesion energy is investigated using a double-cantilever-beam test and is found to increase with ZnO between Ru and SiO₂. Consequently, the Ru/ZnO bilayer can be a multifunctional layer for advanced Cu interconnects. Additionally, the formation of a bottomless barrier by eliminating ZnO on the via bottom, or Cu, is expected to decrease the via resistance for the ever-shrinking Cu lines.     

The growth and physical properties of low pressure chemically vapour-deposited films of tantalum silicide on n+-type polycrystalline silicon

Bilayer films of tantalum silicide on n⁺-type polycrystalline silicon prepared by low pressure chemical vapour deposition (LPCVD) were fabricated from SiH₄ and TaCl₅ in a single standard hot-wall LPCVD reactor. The main advantages over conventional co-sputtered films are reduced wafer handling, improved conformal deposition, increased wafer throughput and the use of only one piece of process equipment. Both films of the bilayer structure are deposited at 575°C and annealing is carried out in the deposition reactor at 900°C. The amorphous deposited silicon films were doped in situ with PH₃. The stoichiometry of the as-deposited tantalumrich Ta₅Si₃ films is shifted to the desired low resistivity TaSi₂ during the annealing process, in which the additional silicon required is supplied from the underlying polycrystalline silicon. The resistivity of annealed LPCVD tantalum silicide films is 60–70μΩ cm which is comparable with that of films prepared by co-sputtering. The peak-to-valley surface roughness of 30 nm is at present typically a factor of 2 larger than that for co-sputtered films. Wet oxidation experiments indicate that there is no large difference in the thermal SiO₂ formation between LPCVD and co-sputtered tantalum silicide.     

Aluminum contact to nickel silicide using a thin tungsten barrier

An aluminum film in contact with NiSi is not stable in the temperature range around 450 °C usually applied for aluminum contact sintering. We used thin (about 2 kÅ) self-supported silicon substrates to investigate the interaction of aluminum films with NiSi by mega-electronvolt ⁴He⁺ backscattering spectrometry. The thin substrate enables us to distinguish between the aluminum and the silicon signals, to isolate them, and to analyze the reaction. It is found that the aluminum reacts with the silicide and forms an NiAl₃ layer in direct contact with the silicon substrate. Simultaneously, a rise in the Schottky barrier height of the contact is observed. A thin layer (250 Å) of tungsten placed as a barrier between the aluminum and the silicide is shown to inhibit the aluminum-silicide reaction. A process is described to prepare a reliable aluminum contact to NiSi on a silicon substrate in a single annealing step.     

Chemical Fluid Deposition: A Hybrid Technique for Low‐Temperature Metallization

Chemical fluid deposition (CFD) is a novel approach to metal deposition that involves the chemical reduction of organometallic compounds in supercritical carbon dioxide to yield high purity films at low temperature. Since supercritical CO₂ can exhibit densities that approach those of a liquid solvent while retaining the transport properties of a gas, CFD is essentially a hybrid technique that uniquely blends the advantages of chemical vapor deposition (CVD) and electroless plating. Here, we describe the deposition of high‐purity films of Pt, Pd, Au, and Rh onto inorganic and polymer substrates by the reduction of appropriate precursors in CO₂ at 60 °C.     

Effect of filament temperature and deposition time on the formation of tungsten silicide with silane

The effect of filament temperature and deposition time on the formation of tungsten silicide upon exposure to the SiH₄ gas in a hot wire chemical vapor deposition process was studied using the techniques of cross-sectional scanning electron microscopy and Auger electron spectroscopy. At a relatively low temperature of 1500 °C, the decomposition of WSi₂ phase and the diffusion of Si towards the silicide/W interface produce a thick W₅Si₃ layer. The diffusional nature leads to a parabolic rate law for silicide growth. An exponential decrease of silicide thickness with temperature between 1600 and 2000 °C illustrates the dominance of Si evaporation at higher temperatures (T ≥ 1600 °C) over the silicide formation.     

Properties of chemically vapor-deposited Tungsten thin films on silicon wafers

Tungsten thin films were deposited onto silicon wafers by the thermal decomposition of W(CO)₆. The non-corrosive nature of W(CO)₆ and its decomposition products, tungsten and CO, allows deposition without damage to the wafer surface. The deposition rate is dependent on such parameters as the wafer temperature and the pressure of W(CO)₆. The effects of annealing on film characteristics were studied.The tungsten films show good uniformity and adhesion after deposition and also after annealing. The resistivity depends on the film thickness and, for a film 2200 Å thick, is 15 x 10^-5 ω cm. Wafer annealing is done at 800–900°C under vacuum in an atmosphere of forming gas. After the films have been annealed for 30 min, the resistivity decreases to 1.5 x 10^-5 ω cm.Auger analysis of the films shows that some CO is trapped in the tungsten matrix after deposition at a ratio of about one CO molecule to every four tungsten atoms. Annealing for 30 min drives off the CO, reducing the ratio to less than one CO molecule per 30 tungsten atoms.     

Formation and characterization of semiconductor Ca2Si layers prepared on p-type silicon covered by an amorphous silicon cap

Formation of calcium silicide on three types of templates: Si(111)7 × 7, 2D Mg₂Si, and 3D Mg₂Si, was studied during Ca deposition at 120 °C in situ by Auger and electron energy loss spectroscopy, and by differential optical reflectance spectroscopy. A continuous Ca₂Si layer is formed on 2D and 3D Mg₂Si templates; but, on an atomically clean silicon surface (Si(111)7 × 7), a mixture of Ca₂Si with another Ca silicide was found. The growth of a Si cap layer over the Ca silicide layers at about 100 °C studied by in situ methods demonstrated the full embedding of Ca silicide in amorphous silicon, independent of the used template. Transmission electron microscopy, Rutherford backscattering spectrometry, atomic force microscopy, and electrical characterization of Schottky junctions revealed the Ca₂Si and Mg₂Si nanoparticles and the redistribution of Mg and Ca during the silicon cap growth and its effect on the electronic properties of the structures. Reproduction of the experiments on higher doped and better purity substrates is needed to understand better the role of Mg- and Ca-related defects, and defects of silicon generated by the growth process.     

Degradation and silicidation of Ta- and W-filaments for different filament temperatures

Using typical conditions for hot wire chemical vapour deposition (HWCVD) of high quality thin silicon films in a UHV deposition chamber, we studied the silicidation of different filaments mainly varying the filament temperatures between 1700 °C and 2130 °C. The experiments were done with constant current, running the filament for 5 to 8 h and even longer. The changes of filament resistance and filament temperature with time will be shown and discussed. We investigated the material changes over the whole filament by Scanning Electron microscopy (SEM), especially the thickness of the formed silicide layers. The change of filament resistance depending on the filament temperature was also monitored, pointing out the different behaviour of tungsten and tantalum filaments. As a result, optimum temperature regimes for tantalum and tungsten filaments could be derived with respect to the filament degradation reducing the filament lifetime. Using a specially developed protection for the cold ends, a tungsten filament could be run for more than 139 h under silane with a filament temperature of T_fil ≈ 2000 °C.     

A simple chemical vapour deposition method for depositing thin TiO2 films

Thin films of TiO₂ were produced at 130–250°C by chemical vapour deposition (CVD) involving the hydrolysis of TiCl₄. An apparatus was developed which gives good control and reproducibility. The reaction takes place on a heated disc that rotates the silicon substrate. Premature reaction between the gases, TiCl₄ and water vapour is prevented by appropriate temperature control and careful design of the gas delivery system. With this apparatus the thickness of the TiO₂ films is controlled to within ±5% of the target value. Attention is also directed to reducing the pinhole density of the resulting films. The refractive index of the TiO₂ films was found to increase with increasing deposition temperature, from 2.1 at around 130°C to 2.4 at 250°C. From capacitance-voltage measurements the surface charge at the TiO₂-Si interface of films deposited at 200°C was found to be negative. Hence these TiO₂ films are good antireflection coatings for n-type metal/insulator/semiconductor inversionlayer solar cells.     

Growth of GaN on SiC/Si substrates using AlN buffer layer by hot-mesh CVD

GaN films were grown on SiC/Si (111) substrates by hot-mesh chemical vapor deposition (CVD) using ammonia (NH₃) and trimetylgallium (TMG) under low V/III source gas ratio (NH₃/TMG = 80). The SiC layer was grown by a carbonization process on the Si substrates using propane (C₃H₈). The AlN layer was deposited as a buffer layer using NH₃ and trimetylaluminum (TMA). GaN films were formed and grown by the reaction between NH_x radicals, generated on a tungsten hot mesh, and the TMG molecules. The GaN films with the AlN buffer layer showed better crystallinity and stronger near-band-edge emission compared to those without the AlN layer.     

MicroRaman spectroscopy of protective coatings deposited onto C/C–SiC composites

Abstract

MicroRaman spectroscopy has been used in the present work to investigate the structure and composition of pyrolytic carbon (PyC) and SiC protective coatings formed under various chemical vapour deposition conditions. Analysis of spectra obtained during Raman line mapping experiments on samples with graded Si_xC_y layer in the region of about 700–1000 cm^?1 allows information to be extracted on different SiC polytypes. It was found that the graded SiC layered sample contained a mixture of 3C–SiC and 6H–SiC polytypes at the film/substrate interface, but for the major part of this layer the 3C–SiC (β-SiC) phase predominates. For pure PyC films, it was found that the formation of PyC layer begins at 1200°C and the layer formed at this temperature is more uniform with slightly larger crystallite size (～3 nm) compared to that in the layer formed at 1300°C.     

Interfacial reactions between Sn-3.5 Ag solder and Ni–W alloy films

Nickel based alloys are currently being investigated in an effort to develop stable barrier films between lead free solder and copper substrate. In this study, interfacial reactions between Ni–W alloy films and Sn-3.5 Ag solder have been investigated. Ni–W alloys films with tungsten content in the range of 5.0–18.0 at.% were prepared on copper substrate by electrodeposition in ammonia citrate bath. Solder joints were prepared on the Ni–W coated substrate at a reflow temperature of 250 °C. The solder joint interface was investigated by Cross-sectional scanning electron microscopy, energy dispersive X-ray spectroscopy and electron back scatter diffraction. It has been observed that a Ni₃Sn₄ layer with faceted morphology formed on the Ni–W alloy film after reflow. The thickness of the bright layer was found to decrease with the increase of tungsten content in the Ni–W film. An additional layer with a bright appearance was also found to form below the Ni₃Sn₄ layer. The bright layer was identified to be a ternary phase containing Sn, W and Ni. The bright layer is found to be amorphous and is suggested to have formed through solid state amorphization caused by anomalously fast diffusion of Sn into Ni–W film.     

Formation and microstructure of various thin film chromium silicide phases

The formation of the various chromium silicide phases, as predicted by the Cr-Si phase diagram for bulk materials, was studied when thin Cr/a-Si (where a-Si is amorphous silicon) bilayers were annealed in situ in a transmission electron microscope using a limited supply of a-Si. These results are compared with the silicide formed when unlimited a-Si or single-crystal silicon was used. The specimens were analysed using electron micrographs and diffraction patterns.The detailed studies of the bilayers were preceded by studies of single layers of chromium and a-Si. The chromium single layers proved to be continuous for films as thin as approximately 2 nm. The as-deposited films with thickness in excess of about 5 nm were crystalline with b.c.c. structure and comprised very small grains. A phase change occured at about 450°C from the b.c.c to a simple cubic lattice structure. The silicon single layers were completely amorphous in their as-deposited state and crystallized around 600°C. Very large grains formed.The self-supporting Cr/a-Si bilayers with a typical total thickness of about 50 nm, where the relative film thickness were adjusted to yield Cr:a-Si atomic ratios of 1:2, 1:1, 5:3 and 3:1, were prepared by sequential electron gun vacuum deposition of chromium and silicon onto photoresist-covered glass slides. In the early stages of phase formation, when both unreacted chromium and silicon were present, the CrSi₂ phase was formed at about 450°C for all of these specimens. This was the end phase for the 1:2 ratio specimen. For all the other specimens the metal- rich Cr₅Si₃ phase was next to grow at about 550°C. For the 5:3 ratio specimen this was the end phase.Upon further heating of specimens with a Cr:a-Si atomic ration of 3:1, a more chromium-rich phase of Cr₃Si was formed at about 650°C. In the 1:1 ratio specimen, however, the next and end phase observed was CrSi, also growing at about 650°C. The end phase was thus determined by the availability of chromium and silicon during the reactions and could be predicted from the phase diagram.When using an unlimited supply of a-Si (or of single-crystal silicon), instead of limiting it to the thickness necessary for the predetermined ratios mentioned above, the only phase that ever formed was CrSi₂.The grain sizes observed in the various final phase specimens were as follows: CrSi₂, 25 nm; Cr₃Si, 40 nm; Cr₅Si₃, 50 nm; CrSi, 100 nm.     

Characterization of titanium silicide films formed by composite sputtering and rapid thermal annealing

Titanium silicide films were prepared by sputtering from a single composite TiSi_x source followed by rapid thermal annealing in N₂. The composition, resistivity, crystal structure and microstructure were investigated using Auger electron spectroscopy, Rutherford backscattering spectrometry, scanning and transmission electron microscopy, X-ray and electron diffraction and a four-point resistivity probe. As-deposited and fully annealed films were found to possess a TiSi_2.2 stoichiometry and to contain 6–7 at.% O and significant amounts of several metallic impurities (copper, iron and tungsten). Rapid thermal annealing at 850–1000°C for 10 s forms a polycrystalline equilibrium orthorhombic phase TiSi₂ structure with 0.25-0.50 μm grains. The annealed layer resistivity was reduced to 28 μΩ cm, i.e. 1.4Ω/▭ for a 0.20 μm film. No expulsion of silicon was observed after annealing, and it appears that excess silicon has trapped oxygen within the film in the form of silicon oxide precipitates. Titanium polycide layers were unable to be etched successfully in an SF₆-CCl₄ plasma because of the presence of the non-volatile copper and iron impurities within the silicide.     

Preparation of CdTe films by electrodeposition

Single-phase CdTe thin films have been prepared by depositing sequentially a layer of tellurium and a layer of cadmium on a molybdenum substrate followed by a short thermal treatment. Deposition of tellurium films was done in an aqueous solution containing TeO₂ at a current density of ≈ 1 mA/cm². An aqueous solution containing cadmium sulfate was used for cadmium deposition with a current density of ≈1 mA/cm². Solution temperature was ≈ 95°C for tellurium film deposition and was 50°C for cadmium deposition. It was found that after a heat treatment at ≈ 370°C for 10 min the deposited Te/Cd layers were converted to CdTe thin films with a cubic structure. Compositional uniformity of the films was also investigated by electron probe microanalysis.