Physical model and numerical results of dissociation kinetics of hydrogen-passivated Si/SiO2 interface defects

A simple model of thermal dissociation and recovery of hydrogen-passivated silicon defects at the Si/SiO₂ interface, such as P_b - centers, during vacuum thermal annealing has been suggested. his model considers reactions of hydrogen with defect states at the Si/SiO₂ interface and diffusion of liberated atomic and molecular hydrogen in a silicon dioxide film. The rate constants were calculated in diffusion approximation. A good agreement was obtained between the experimental and numerical simulation results for oxides with different thickness (204–1024 Å), grown, both, (111) and (100) samples and annealed in the temperature range (480–700°C).     

Effect of N2O/SiH4 ratio on the properties of low-temperature silicon oxide films from remote plasma chemical vapour deposition

Silicon oxide films have been deposited with remote plasma chemical vapour deposition (RPCVD) at low temperatures (<300 °C) from SiH₄---N₂O. The effect of a gas-phase reaction on the SiO₂ film properties and Si/SiO₂ interface was investigated. As the partial pressure ratio was increased above N₂O/SiH₄ = 4, a gas-phase reaction with powder formation was observed, which degraded film properties, increased surface roughness, and decreased deposition rate. When N₂O/SiH₄ <4, there was no detectable IR absorption in the film associated with hydrogen-related bonds (Si---OH and Si---H) but when N₂O/SiH₄ >4, the incorporation of Si---OH bond became significant and Si¹⁺, intermediate state silicon at the interface, was more abundant. The oxide fixed charge, interface trap density, surface roughness and leakage current were increased when there was powder formation in the gas phase. High plasma power also favoured the powder formation in the gas phase. C---V and I---V characteristics were measured and it was shown that these electrical properties were directly related to the process condition and material properties of the oxide and the Si/SiO₂ interface.     

Loss of material from TiSi2 films during annealing in hydrogen

Annealing of co-evaporated TiSi₂ layers on bare and oxidized silicon substrates at high temperatures (above 900 °C) in a hydrogen ambient may lead to loss of silicon from the film. Such a weight loss is caused by the formation of volatile SiO by reaction with trace impurities (of the order of 1 ppm) of oxygen of water vapour in the hydrogen. As well as the weight loss a decrease in the film thickness and an increase in the resistance of TiSi₂ layers on SiO₂/Si is observed. Such effects do not occur in hydrogen at lower temperatures or in an argon ambient. The residual contamination of argon with oxygen and hydrogen vapour leads to a passivation of the annealed samples with SiO₂ but has no measurable effect on the resistance of the TiSi₂ film.     

Preparation of strontium titanate thin films by mirror-confinement-type electron cyclotron resonance plasma sputtering

Using mirror-confinement-type electron cyclotron resonance (ECR) plasma sputtering method, strontium titanate (SrTiO₃) thin films have been prepared on Si and Pt/Ti/SiO₂/Si substrates at a low substrate temperature (below 450 K) in a low pressure (2.7×10⁻² Pa) environment of pure Ar and Ar/O₂ mixture. Prepared film surfaces were very smooth regardless of high deposition rate (8.5 nm/min). The composition ratio Sr/Ti of Sr to Ti in the films varied with the distance between the target and the substrate. All as-deposited films on Si substrates were found to be amorphous and were crystallized by post-deposition annealing using an electric furnace at 650 K, i.e. approximately 250 K lower than annealing for films obtained by conventional RF magnetron sputtering. Post-deposition annealing of these films using millimeter-wave radiation decreased the crystallization temperature to a value of 550 K. Furthermore, all as-deposited films on Pt/Ti/SiO₂/Si substrates by a plasma of Ar and O₂ gas mixture were found to be crystallized regardless of no substrate heating.     

Characterization of intermetallic phases and oxides formed in annealed Ni/Al multilayer structures

Two different multilayer structures composed of ten alternating Ni and Al thin films were sputter deposited on Si (111) substrates. These multilayers with individual Ni and Al thin film thicknesses of about 25 nm and 38 nm and of 25 nm and 13 nm, respectively, have the average compositions of Ni_0.50Al_0.50 and Ni_0.75Al_0.25. The samples were heat treated in a differential scanning calorimeter instrument with a constant heating rate of 40 °C min ⁻¹ in Ar from room temperature to 550 °C. The compositions of as-deposited and heat-treated samples were studied with high-resolution Auger electron spectroscopy (AES) rotational depth profiling. X-ray photoelectron spectroscopy (XPS) analyses show an excess of Ni in both annealed samples. X-ray diffraction measurements of annealed multilayers show the formation of Ni₂Al₃ and NiAl₃ phases in the Ni_0.50Al_0.50 sample and the presence of Ni₃Al and Ni A1₃ phases with some excess of Ni in the Ni_0.75Al_0.75 sample. AES and XPS investigations of the reacted layers after 15 min annealing in air at 500 °C disclose considerably different surface oxide thin films: on the Ni_0.50Al_0.50 layer the oxide thin film consists of Al₂O₃ with a small amount of NiO, whereas that on the top of the Ni_0.75Al_0.25 layer is thicker and consists of NiO on top and some Al₂O₃ below.     

High concentration erbium doping of silicon-rich SiO2 thin films on silicon

In this work, high concentration erbium doping in silicon-rich SiO₂ thin films is demonstrated. Si plus Er dual-implanted thermal SiO₂ thin films on Si substrates have been fabricated by using a new method, the metal vapor vacuum arc ion source implantation with relatively low ion energy, strong flux and very high dose. X-Ray photoelectron spectroscopy measurement shows that very high Er concentrations on the surfaces of the samples, corresponding to 10 at.% or the doping level of 10²¹ atoms cm⁻³, are achieved. This value is much higher than that obtained by using other fabrication methods such as the high-energy ion implantation and molecular beam epitaxy. Reflective high-energy electron diffraction, atomic force microscopy and cross-section high-resolution transmission electron microscopy observations show that the excess Si atoms in SiO₂ matrix accumulate to form Si clusters and then crystallize gradually into Si nanoparticles embedded in SiO₂ films during dual-ion implantation followed by rapid thermal annealing. Er segregation and precipitates are not formed. Photoluminescence at the wavelength of 1.54 μm exhibits very weak temperature dependence due to the introduction of Si nanocrystals into the SiO₂ matrix. The 1.54-μm light emission signals from annealed samples decrease by less than a factor of 2 when the measuring temperature increases from 77 K to room temperature.     

Texture of copper films on Ta35Si18N47 and Ti33Si23N44 underlayers

The crystallographic texture and the grain size have been measured by X-ray diffraction techniques for about 200 nm-thick Cu films sputter-deposited on amorphous Ta₃₅Si₁₈N₄₇ and Ti₃₃Si₂₃N₄₄ underlayers, and for comparison also on TiN underlayers and oxidized silicon, all on Si (100) substrates. The (111) texture of the as-deposited Cu films increases in the sequence TiN233Si₂₃N₄₄35Si₁₈N₄₇. Amorphous Ta₃₅Si₁₈N₄₇ and Ti₃₃Si₂₃N₄₄ layers evidently promote quite effectively the growth of highly (111) textured Cu films. After vacuum annealing at 450°C for 30 min the texture of Cu rises on Ti₃₃Si₂₃N₄₄, falls on Ta₃₅Si₁₈N₄₇, while that on TiN and on SiO₂ changes little and the sequence becomes TiN235Si₁₈N₄₇33Si₂₃N₄₄. The grain size of the as-deposited Cu films increases in the sequence Ti₃₃Si₂₃N₄₄235Si₁₈N₄₇47N₅₃ and rises moderately upon annealing, least for TiN and most for SiO₂ and Ti₃₃Si₂₃N₄₄.     

Synthesis of AlN by reactive sputtering

We present a systematic study of the sub-band gap optical absorption coefficients (hν) in the range 1.2–6 eV vs. deposition-temperature (T_s from 27 to 450°C) films deposited on silica by 13.6 MHz magnetron sputtering of an Al target with 53 and 72% N₂ in the reactive mixture. X-ray diffraction, infrared absorption and Raman diffusion are also presented, mainly on films deposited on Si in the same run to help in the characterisation of the films. All signals are specific of AlN polycrystalline films, which are of better quality when deposited with 72% N₂. The lowest sub-band gap optical absorption around 5×10² cm⁻¹ is obtained for deposition on silica at T_s=300°C with 72% N₂ and is close to that of heteroepitaxial films deposited on sapphire.     

退火气氛对镶嵌在SiO2中Ag纳米颗粒热演变影响效应的研究

将70 keV的Ag离子以5×10¹⁶ cm^-2的剂量注入到SiO₂基底中, 随后分别在400~800℃的Ar、N₂、空气气氛中退火, 详细研究了样品的表面形貌、光吸收特性、结构及成分随退火气氛及退火温度的变化规律。原子力显微镜、紫外-可见分光光度计及掠入射X射线衍射仪的测试结果显示: Ar气氛退火样品中形成的Ag纳米粒子(NPs)细小均匀, 其颗粒密度在700℃时达到最大值, 光吸收性能最佳; N₂气氛退火引发Ag纳米颗粒的团聚生长, 在样品近表面形成较大的Ag NPs, 其颗粒密度也在700℃时达到最大值; 而空气中退火后, 由于AgO的形成、分解, 样品的光吸收强度随退火温度升高持续下降。最后, 卢瑟福背散射研究结果表明, 样品的这些变化主要归因于Ag原子在不同退火气氛下随退火温度的扩散行为不同。     

The effect of rapid thermal annealing on structural and electrical properties of TiB2 thin films

This work reports on the effect of post-deposition rapid thermal annealing on the structural and electrical properties of deposited TiB₂ thin films. The TiB₂ thin films, thicknesses from 9 to 450 nm, were deposited by e-beam evaporation on high resistivity and thermally oxidized silicon wafers. The resistivity of as-deposited films varied from 1820 μΩ cm for the thinnest film to 267 μΩ cm for thicknesses greater than 100 nm. In the thickness range from 100 to 450 nm, the resistivity of TiB₂ films has a constant value of 267 μΩ cm.

A rapid thermal annealing (RTA) technique has been used to reduce the resistivity of deposited films. During vacuum annealing at 7 × 10⁻³ Pa, the film resistivity decreases from 267 μΩ cm at 200 °C to 16 μΩ cm at 1200 °C. Heating cycles during RTA were a sequence of 10 s. According to scanning tunneling microscopy analysis, the decrease in resistivity may be attributed to a grain growth through polycrystalline recrystallization, as well as to an increase in film density.

The grain size and mean surface roughness of annealed films increase with annealing temperature. At the same time, the conductivity of the annealed samples increases linearly with grain size. The obtained results show that RTA technique has a great potential for low resistivity TiB₂ formation.     

A method for the measurement of thin film optical constants with a spectral photometer from 230 nm to 850 nm and its application to plasma silicon (oxy) nitride

A technique to measure the complex index of refraction of thin solid films in the visible and near-UV range with a spectral photometer using polarized light is introduced. The complex index of refraction of amorphous silicon (oxy)nitride films deposited in a glow discharge with different gas flow ratios of NH₃:SiH₄ and N₂O:SiH₄ at 270°C was measured as a function of wavelength. The real part of the index of refraction at 632.8 nm of the films investigated varies from 1.5 to 2.5. The results could be confirmed by scanning ellipsometry.     

Electrical characterization of Ta2O5 films deposited by laser reactive ablation of metallic Ta

Tantalum oxide films have been deposited by 355 nm pulsed laser ablation of metallic Ta target in O₃/O₂ ambient. The structure and the composition of as-deposited and annealed films were examined by X-ray diffraction and Fourier transform infrared spectroscopy. The measurements of the current–voltage and capacitance–voltage characteristics of the Al/Ta₂O₅/Si capacitors were performed to reveal the electrical properties of the Ta₂O₅ films. The effects of annealing temperature on the characteristics of thin films have been studied. The results suggest that the films annealed above 700°C have the structure of orthorhombic β-Ta₂O₅, thc annealing treatment at high temperature decreases the bulk trap charge, the border trap, and the interface trap densities of as-deposited films, and improves significantly the dielectric and electrical properties of Ta₂O₅ film.     

Fabrication of robust Bi3.25La0.75Ti3O12 thin film resistant to hydrogen damage

Ferroelectric bismuth lanthanum titanate (Bi_3.25La_0.75Ti₃O₁₂; BLT) thin films were deposited on Pt/TiO₂/SiO₂/Si substrate by chemical solution deposition method. The films were crystallized in the temperature range of 600–700 °C. The spontaneous polarization (P_s) and the switching polarization (2P_r) of BLT film annealed at 700 °C for 30 min were 22.6 μC/cm² and 29.1 μC/cm², respectively. Moreover, the BLT capacitor did not show any significant reduction of hysteresis for 90 min at 300 °C in the forming gas atmosphere.     

Densification and Grain-Growth Behavior of Various Amounts of SiO2 Doped 8YSCZ/SiO2 Composites

The effect of SiO₂ addition on densification and grain-growth behavior of 8YSCZ/SiO₂ composites was investigated using high purity 8 mol% yttria-stabilized cubic zirconia powders (8YSCZ) doped with 0, 1, 5, 10 wt% SiO₂. The specimens were sintered at 1400°C for 1 hour. It was seen that the sintered density increased with SiO₂ content up to 1 wt% and further increase in SiO₂ content led to a decrease in density. The enhanced density with increasing SiO₂ content up to 1 wt% could be mainly attributable to liquid phase sintering. For grain growth measurements, the specimens sintered at 1400°C were annealed at 1400, 1500, and 1600°C for 10, 50, and 100 hours. The experimental results showed that the grain growth in 8YSCZ/SiO₂ composites occurred more slowly than that in undoped 8YSCZ. Also, the grain growth rate decreased with increasing SiO₂ content. The grain growth exponent value and the activation energy for undoped 8YSCZ were found to be 2 and 289 kJ/mol, respectively. The addition of SiO₂ raised the grain growth exponent value to 3, and activation energy for the grain growth process was increased from 289 to 420 kJ/mol for the addition of SiO₂ from 0 to 10 wt%.     

Low temperature plasma-assisted oxidation and thin-film deposition processes for forming device-quality SiO2/Si and composite dielectric-SiO2/Si heterostructures

In the high-temperature thermal oxidation of Si, the SiO₂/Si interface is continuously regenerated as the bulk oxide grows. This paper describes an alternative low temperature, 200–300 °C, plasma-assisted process that optimizes electrical properties of SiO₂/Si interfaces and bulk SiO₂ layers by separately controlling interface formation and bulk oxide deposition. Composite dielectrics, oxide/nitride (ON) and oxide (ONO), have been fabricated by extending the low temperature plasma-assisted processes to include deposition of Si₃N₄ films. The electrical properties of SiO₂/Si structures formed by the two-step, low temperature oxidation-deposition process are essentially the same as those of SiO₂/Si structures formed by high temperature, 850–1050 °C, thermal oxidation. The electrical properties of devices incorporating ON and ONO composite dielectrics are degraded with respect to the SiO₂/Si structures, but are similar to those of composite dielectrics formed by combinations of high temperature processing.     

Structural, dielectric and optical properties of Ba(Ti, Zr)O3 thin films prepared by chemical solution deposition

Ba(Ti_0.95Zr_0.05)O₃ (BTZ) thin films grown on Pt/Ti/SiO₂/Si(100) substrates were prepared by chemical solution deposition. The structure and surface morphology of BTZ thin films has been studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). At 100 kHz, the dielectric constant and dissipation factor of the BTZ film are 121 and 0.016, respectively. The ellipsometric spectrum of the BTZ thin film annealed at 730 °C was measured in the range of wavelength from 355 to 1700 nm. Assuming a five-layer model (air/surface roughness layer/BTZ/interface layer/Pt) for the BTZ thin films on platinized silicon substrates, the optical constant spectra (refractive index n and the extinction coefficient k) of the BTZ thin films were obtained.     

Arsenic distribution in bilayers of TiSi2 on polycrystalline silicon during heat treatment

The diffusion behaviour of arsenic in bilayers of TiSi₂ on polycrystalline silicon (poly-Si) was investigated by the He⁺ backscattering technique and sheet resistance measurements. The TiSi₂ films were sputtered from a stoichiometric compound target onto poly-Si prepared by low pressure chemical vapour deposition. X-ray diffractometry was used to identify the phases present after the samples had been annealed at various temperatures. The as-deposited silicide layers were found to be amorphous and to recrystallize into orthorhombic TiSi₂ (C54 structure) on heat treatment at and above 800 °C. Arsenic was either implanted into the already formed TiSi₂ films or directly implanted into the poly-Si layer prior to silicide deposition. In the former case the arsenic was observed to redistribute solely within the silicide film without any significant out-diffusion into the underlying poly-Si layer on subsequent heat treatment. The arsenic initially present in the poly-Si layer, however, was found to migrate into the silicide film at temperatures in the vicinity of 900 °C. This feature makes arsenic incompatible with a particular metal/oxide/semiconductor process, where it is desired to carry out poly-Si drain-source doping by a single ion implantation step if TiSi₂/poly-Si is used as the gate level interconnection material. It is concluded that the behaviour of arsenic in a bilayer of TiSi₂/poly-Si is completely different from that reported for the WSi₂/poly-Si system.     

Temperature-dependent resistivity measurements on polycrystalline SiO2-covered thin gold films

The influence of a thin SiO₂ top layer on the resistivity of gold films with thicknesses ranging from 10 to 80 nm is studied. It is found that the resistivity of both as-deposited and annealed samples can be analysed solely in terms of the grain boundary scattering model of Mayadas and Shatzkes. A lower value of the reflection coefficient is derived than that reported earlier for polycrystalline gold films. No change in the amount of surface scattering resulting from the SiO₂ top layer was found.     

反应烧结法制备高强度多孔氮化硅陶瓷

以硅粉(Si)为起始原料, 氧化钇(Y₂O₃)为烧结助剂, 利用干压成型工艺制备出不同气孔率的多孔硅坯体, 通过反应烧结得到高强度多孔氮化硅(Si₃N₄)陶瓷. 研究了Y₂O₃添加量在不同升温制度下对于氮化率的影响, 以及1500~1750℃后烧结对多孔材料强度的影响. 结果表明: 添加9%Y₂O₃的样品具有较高的氮化率, 主要是Y₂O₃与Si粉表面的SiO₂在较低的温度下反应生成了Y₅Si₃O₁₂N. 在不同的反应条件下可得到气孔率为30%~50%, 强度为160~50MPa的样品. 在1750、 0.5MPaN₂气压下对样品进行后处理, α-Si₃N₄完全转变成柱状β-Si₃N₄, 晶型转变有利于强度提高,气孔率为46%的多孔Si₃N₄其强度可达140MPa.     

Deposition of HfO2 thin films on ZnS substrates

HfO₂ thin films with columnar microstructure were deposited directly on ZnS substrates by electron beam evaporation process. SiO₂ thin films, deposited by reactive magnetron sputtering, were used as buffer layers, HfO₂ thin films of granular microstructure were obtained on SiO₂ interlayer by this process. X-ray diffraction patterns demonstrate that the as-deposited HfO₂ films are in an amorphous-like state with small amount of crystalline phase while the HfO₂ films annealed at 450 °C in O₂ for 30 min and in Ar for 150 min underwent a phase transformation from amorphous-like to monoclinic phase. Antireflection effect in certain infrared wave band, such as 3–6 μm, 4–12 μm, 4–8 μm and 3–10 μm, can be observed, which was dependent on the thickness of thin films. The cross-sectional images of HfO₂ films, obtained by field emission scanning electron microscopy, revealed that there was no distinct morphological change upon annealing.