Deposition and characterization of Pb TiO3 thin films on silicon wafers using metalorganic sources

Ferroelectric PbTiO₃ thin films were deposited on bare silicon and Pt/SiO₂/Si substrates by metalorganic chemical vapor deposition in a temperature range from 270 to 550°C. The deposition of a single phase PbTiO₃ thin film did not occur on bare silicon substrates. Instead a double layer of lead-silicate and PbTiO₃ was formed owing to a serious diffusion of lead and oxygen ions into silicon substrates. But on Pt/SiO₂/Si substrates, a single phase PbTiO₃ oriented parallel to a-and c-axis was grown at a substrate temperature as low as 350°C even without a high temperature post-annealing. To get an optimal film, a precise control of input gas composition and also a deposition in a low temperature range from 350 to 400°C are necessary.     

The effect of post-deposition thermal processing on MOS gate oxides formed by remote PECVD

The effects of post-deposition thermal exposure, at temperatures typical of MOS fabrication processes, on gate oxides formed by remote plasma enhanced chemical vapor deposition (RPECVD) is discussed. SiO₂ films were prepared by (1) thermal oxidation of silicon at temperatures from 700 to 1150° C, and (2) by RPECVD at a substrate temperature of 350° C. Post deposition thermal processing was achieved by rapid thermal annealing for 100 sec from 850–1200° C. Film properties were studied by infrared spectroscopy (IR), ellipsometry, and by measurements of stress, capacitance voltage characteristics, and dielectric breakdown. Post-formation, thermal processing in the range of 850–1200° C was shown to modify both thermally grown and deposited oxides, but it has been shown that RPECVD films could be stabilized against post-deposition changes by rapid thermal annealing at temperatures of about 900° C for periods of at least 100 sec.     

Plasma-enhanced chemical-vapor deposition oxide prepared at low-flow conditions for course wavelength-division multiplexing optical-waveguide devices

Silicon oxide (SiO_x) films grown by plasma-enhanced chemical-vapor deposition (PECVD) were investigated for applications in a course wavelength-division multiplexing (CWDM) network. The SiO_x films were deposited on 4-in. silicon wafers based on the reaction of N₂O/SiH₄ precursors. After postdeposition annealing at 1,150°C, the transmission spectra of the films prepared at different flow rates of the precursor were compared. We found that the transmission spectrum of the films deposited at the low-flow conditions can be flattened to a ripple of less than 0.5 dB ranging from visible up to 1,470 nm. In addition, the material losses at wavelengths around 1,500 nm caused by absorption of Si-H and N-H bonds were significantly reduced.     

基于PECVD的SiO2薄膜制备研究进展

二氧化硅(SiO₂)薄膜因其卓越的光学性能,在半导体器件、集成电路、光学涂层等领域具有巨大的应用潜力。然而,SiO₂薄膜制备过程中面临表面粗糙度、杂质控制和致密性等问题。为解决这些问题,研究者们通过工艺改进和表面修饰等手段来提高SiO₂薄膜的性能。在众多SiO₂薄膜制备技术中,等离子体增强化学气相沉积(Plasma-Enhanced Chemical Vapor Deposition, PECVD)技术由于沉积SiO₂薄膜所需温度低、原位生长等优势,成为制备SiO₂薄膜最常用的方法。综述了用PECVD技术制备SiO₂薄膜的发展历程,并探讨了关键工艺参数和后处理工艺对薄膜质量的影响。对PECVD技术的深入研究,有助于实现对SiO₂薄膜生长的更精准控制,进一步拓展其广泛的应用前景。     

Low-Temperature Pulsed-PECVD ZnO Thin-Film Transistors

We report high-quality ZnO thin films deposited at low temperature (200°C) by pulsed plasma-enhanced chemical vapor deposition (pulsed PECVD). Process byproducts are purged by weak oxidants N₂O or CO₂ to minimize parasitic CVD deposition, resulting in high-refractive-index thin films. Pulsed-PECVD-deposited ZnO thin-film transistors were fabricated on plasma-enhanced atomic layer deposition (PEALD) Al₂O₃ dielectric and have a field-effect mobility of 15 cm²/V s, subthreshold slope of 370 mV/dec, threshold voltage of 6.6 V, and current on/off ratio of 10⁸. Thin-film transistors (TFTs) on thermal SiO₂ dielectric have a field-effect mobility of 7.5 cm²/V s and threshold voltage of 14 V. For these devices, performance may be limited by the interface between the ZnO and the dielectric.     

Influence of the annealing temperature on the ferroelectric properties of niobium-doped strontium–bismuth tantalate

Characteristics of ferroelectric thin films of niobium-doped strontium–bismuth tantalate (SBTN), which were deposited by magnetron sputtering on Pt/TiO₂/SiO₂/Si substrates, are investigated. To form the ferroelectric structure, deposited films were subjected to subsequent annealing at 700–800°C in an O₂ atmosphere. The results of X-ray diffraction showed that the films immediately after the deposition have an amorphous structure. Annealing at 700–800°C results in the formation of the Aurivillius structure. The dependences of permittivity, residual polarization, and the coercitivity of SBTN films on the modes of subsequent annealing are established. Films with residual polarization 2P_r = 9.2 µC/cm², coercitivity 2E_c = 157 kV/cm, and leakage current 10^–6 A/cm² are obtained at the annealing temperature of 800°C. The dielectric constant and loss tangent at frequency of 1.0 MHz were ε = 152 and tan δ = 0.06. The ferroelectric characteristics allow us to use the SBTN films in the capacitor cell of high density ferroelectric random-access non-volatile memory (FeRAM).     

Effect of Rapid Thermal Annealing on Sputtered CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> Thin Films

Calcium copper titanium oxide (CaCu₃Ti₄O₁₂, abbreviated to CCTO) films were deposited on Pt/Ti/SiO₂/Si substrates at room temperature (RT) by radiofrequency magnetron sputtering. As-deposited CCTO films were treated by rapid thermal annealing (RTA) at various temperatures and in various atmospheres. X-ray diffraction patterns and scanning electron microscope (SEM) images demonstrated that the crystalline structures and surface morphologies of CCTO thin films were sensitive to the annealing temperature and ambient atmosphere. Polycrystalline CCTO films could be obtained when the annealing temperature was 700°C in air, and the grain size increased signifi- cantly with annealing in O₂. The 0.8-μm CCTO thin film that was deposited at RT for 2 h and then annealed at 700°C in O₂ exhibited a high dielectric constant (ε′) of 410, a dielectric loss (tan δ) of 0.17 (at 10 kHz), and a leakage current density (J) of 1.28 × 10⁻⁵ A/cm² (at 25 kV/cm).     

Atomic Layer Deposition of Aluminum Nitride Using Tris(diethylamido)aluminum and Hydrazine or Ammonia

Aluminum nitride (AlN _x ) films were obtained by atomic layer deposition (ALD) using tris(diethylamido) aluminum(III) (TDEAA) and hydrazine (N₂H₄) or ammonia (NH₃). The quartz crystal microbalance (QCM) data showed that the surface reactions of TDEAA and N2H4 (or NH₃) at temperatures from 150 to 225°C were self-limiting. The rates of deposition of the nitride film at 200°C for systems with N₂H₄ and NH₃ coincided: ~1.1 Å/cycle. The ALD AlN films obtained at 200°C using hydrazine had higher density (2.36 g/cm³, 72.4% of bulk density) than those obtained with ammonia (2.22 g/cm³, 68%). The elemental analysis of the film deposited using TDEAA/N2H4 at 200°C showed the presence of carbon (~1.4 at %), oxygen (~3.2 at %), and hydrogen (22.6 at %) impurities. The N/Al atomic concentration ratio was ~1.3. The residual impurity content in the case of N₂H₄ was lower than for NH₃. In general, it was confirmed that hydrazine has a more preferable surface thermochemistry than ammonia.     

Electrical characteristics of very thin SiO2deposited at low substrate temperatures

Very thin (≲ 100-Å) films of SiO2have been deposited by a modified plasma-enhanced chemical-vapor deposition (PECVD) process at very low substrate temperatures (≲ 350°C). Low flow rates of reactive gases and a high flow of inert carrier gas were used to lower the deposition rate, ensuring improved dielectric properties and good control over film thickness. Measurements made on MOS capacitors of current-voltage characteristics, electrical breakdown, interface trap density, and mobile ion drift indicate that these very thin PECVD films are approaching thermally grown SiO2in quality and may be suitable as gate dielectrics in device applications.     

Formation of aluminum oxide films from aluminum hexafluoroacetylacetonate at 350–450° c

A study of the thermally activated decomposition of Al(hfa)₃ (aluminum hexafluoroacetylacetonate) from the gas phase to form Al₂O₃ on silicon substrates is reported. The decomposition process was carried out in an open tube atmospheric pressure reactor in either argon or oxygen/argon mixtures in the temperature range, 350–450° C. The chemical vapor deposition process resulted in the formation of aluminum oxide films in all instances. The dielectric strength of Al/Al₂O₃/Si capacitors which received a post-metal anneal, but did not receive a high temperature annealing treatment, with aluminum oxide films prepared from Al(hfa)₃ in argon, was found to be in the range 2–6 MV/cm. The difference between the flatband voltage of the MOS structures and the metal-silicon work function difference was positive, indicative of a net negative oxide charge with a density of approximately 3 × 10¹¹ – 3 × 10¹² cm^-2, assuming the charge is located at the oxide-silicon interface. Decomposition of Al(hfa)₃ was also carried out in oxygen/argon mixtures with the oxygen concentration in the range 10–60 vol %. This process led to the deposition of aluminum oxide films with breakdown fields in the range 8–9 MV/cm. However, the flatband voltages of the Al/Al₂O₃/Si capacitors were even more positive than those obtained with Al₂O₃ formed in pure argon. High temperature (800–1000° C) oxygen or nitrogen annealing treatments of alumina films deposited in either argon or oxygen/argon mixtures were evaluated from the point of view of their influence on the oxide film properties. In particular, an annealing process in oxygen at 1000° C for 15 min was found to result in a reduction of the net negative oxide charge, and an improvement of the dielectric strength of films deposited in argon. Films formed in oxygen/argon mixtures did not change appreciably following oxygen annealing, as far as breakdown fields are concerned, but the oxide net negative charge was reduced. As in an earlier study by the authors, of copper film deposition from Cu(hfa)₂, it was found that essentially carbon free films could be obtained under appropriate conditions.     

Characteristics of thin film transistors fabricated in polysilicon films deposited by plasma enhanced chemical vapor deposition

Thin-film transistors (TFTs) fabricated in polysilicon films deposited by plasma enhanced chemical vapor deposition (PECVD) were characterized. The transistors were fabricated using a low temperature process (i.e., <- 700° C). The characteristics of the devices were found to improve as the deposition temperature of the polysilicon film increased. The best characteristics (μ _FE of 15 cm²/V _s andV _TH of 2.2V) were measured in the devices fabricated in the film deposited at 700° C. The devices fabricated in the PECVD polysilicon films were compared to those fabricated in polysilicon films deposited by thermal CVD in the same reactor in order to decouple the effect of the plasma. A coplanar electrode structure TFT with adequate characteristics (μ _FE of 8 cm²/V _s) was also demonstrated in the PECVD polysilicon films.     

Preparation of PbTiO3 thin films by plasma enhanced MOCVD and the effect of rapid thermal annealing

Dielectric PbTiO₃-thin films were prepared on p-Si(100) substrate by plasma enhanced metalorganic chemical vapor deposition using high purity Ti(O-i-C₃H₇)₄, Pb(tmhd)₂, and oxygen. As-deposited films were post-treated by rapid thermal annealing method, and the effect of annealing was examined under various conditions. The deposition process was controlled by mixed-control scheme at temperatures lower than 350°C, but controlled by heterogeneous surface reaction at temperatures greater than 350°C. The as-deposited films showed PbO structure at 350∼400°C, but (100) and (101) PbTiO₃ orientations started to appear at 450°C. The deposition rate was increased with rf power due to the enhanced dissociation of Ti and Pb precursors. It was found that the concentration of oxygen plays an important role in crystallization of PbTiO₃ during the rapid thermal annealing. A linear relationship was obtained between the dielectric constant of PbTiO₃ films and the annealing temperature. However, the surface roughness and leakage current density increased mainly due to the defects caused by volatilization of lead and the interface layer formed during the high temperature annealing.     

Zinc telluride films by photoenhanced metalorganic chemical vapor deposition

Polycrystalline films of zinc telluride (ZnTe) have been deposited on glass and conducting semiconductor coated glass substrates at 270°-350° C by photoenhanced metalorganic chemical vapor deposition (PECVD) using the reaction of dimethylzinc (DMZn) or diethylzinc (DEZn) and diisopropyltellurium (DIPTe) in hydrogen under atmospheric pressure. The deposited films are always ofp-type conductivity. Their properties are affected by the DMZn/DIPTe or DEZn/DIPTe molar ratio in the reaction mixture. The optimum DMZn/DIPTe ratio has been found to be approximately 0.9 on the basis of the open-circuit voltage of ZnTe/CdS heterojunctions and photoconductivity measurements. Without intentional doping, the deposited films are of high resistivity (>10⁷ ohm-cm) at room temperature, and the resistivity of these films has been controlled by using arsine as a dopant. The structural, optical, and electrical properties of ZnTe films have been characterized. Supported by the Solar Energy Institute under Subcontract XL-8-18091-1.     

Integration of high dielectric Ba0.5Sr0.5TiO3 films into amorphous TaSiN barrier layer structures

The high-k dielectric material (Ba,Sr)TiO₃ has been intensively investigated for possible applications in dynamic random access memory circuits. During the BST deposition process in O₂ ambient, typically at 650°C, the diffusion of oxygen through the bottom electrode into the poly Si plug must be prevented. Amorphous TaSiN films are excellent candidates as oxygen barrier layers. Ba_0.5Sr_0.5TiO₃ (BST) films with thickness of 100 nm were deposited on the electrode structure SiO₂/TaSiN/Pt. The sol–gel method was used to grow the BST films. The barrier effect for oxygen diffusion is studied in TaSiN layers with thickness of 50 nm, which were deposited by a reactive sputter process. X-ray photoemission spectroscopy results confirm that this amorphous material is a suitable barrier against oxygen diffusion at 650°C. The BST films, deposited at 650°C and post-annealed at 650°C show a dielectric constant of 100 at 100 kHz and a dissipation factor of less than 5%.     

The electrical properties of Hg-sensitized “photox”-oxide layers deposited at 80°C

This paper deals with the electrical properties of low-pressure CVD SiO₂ deposited at 80°C. The deposition rate is enhanced by UV radiation in the presence of Hg vapor. The photo-enhanced low-pressure chemical-vapor-deposited oxide, known also as “photox,” offers a good quality oxide deposited at temperatures as low as 80°C. The films are deposited in a batch-load “photox” barrel reactor and subsequently annealed at 950°C for 30 min in a conventional hot-wall furnace. Cold-sputtered aluminum-gate guard-ring capacitors are fabricated on the oxide films. High-frequency and quasi-static capacitance measurements indicate the interfacial properties of “photox” are comparable to those of thermal oxide. Fast interface states density are less than 2 × 10¹⁰ cm⁻² eV⁻¹ and a light negative interfacial charge could just be detected. The dielectric breakdown field is typically 4–5 MV/cm.Deep-depletion transient-capacitance measurements were performed at temperatures between 20 and 100°C to investigate the possible impact of “photox” processing on the generation lifetime. The Hg in particular might be suspected as a heavy-metal contaminant. Typical recovery times observed at 20°C were in the range of 10–15 min. The generation lifetime derived from such measurements ranges from 140 to 200 μs which is comparable to values for control samples made with standard thermal oxide. The magnitude and temperature dependence of the generation lifetime suggest that the same G-R centers are present in both “photox” and thermal oxide devices. The only apparent electrical effect of the Hg vapors used in the deposition process is a small negative fixed interface charge, 2 × 10¹⁰cm⁻².     

Metalorganic chemical vapor deposition of silver thin films for future interconnects by direct liquid injection system

Deposition of Ag films by direct liquid injection-metal organic chemical vapor deposition (DLI-MOCVD) was chosen because this preparation method allows precise control of precursor flow and prevents early decomposition of the precursor as compared to the bubbler-delivery. Silver(I)-2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionato-triethylphosphine [Ag(fod)(PEt₃)] as the precursor for Ag CVD was studied, which is liquid at 30 °C. Ag films were grown on different substrates of SiO₂/Si and TiN/Si. Argon and nitrogen/hydrogen carrier gas was used in a cold wall reactor at a pressure of 50–500 Pa with deposition temperature ranging between 220 °C and 350 °C. Ag films deposited on a TiN/Si diffusion barrier layer have favorable properties over films deposited on SiO₂/Si substrate. At lower temperature (220 °C), film growth is essentially reaction-limited on SiO₂ substrate. Significant dependence of the surface morphology on the deposition conditions exists in our experiments. According to XPS analysis pure Ag films are deposited by DLI-MOCVD at 250 °C by using argon as carrier gas.     

Piezoelectric and electrical properties of PZT-PSN thin film ceramics for MEMS applications

Piezoelectric and electrical properties of PZT-PSN ceramics have been investigated as a function of WO₃ addition from 0 to 6.0 wt%. The dielectric and piezoelectric characteristics of PZT-PSN ceramics have been investigated at different calcination (800–900°C) and sintering (1100–1300°C) temperatures. The grain size increased in proportion to adding the amount of WO₃ and increasing the sintering temperatures. Anisotropic properties of electromechanical coupling coefficient and piezoelectric coefficient are proven to be dependent on processing temperatures and amount of addition. For the specimen with 0.6 wt% WO₃ addition, using a calcination temperature of 800°C and a sintering temperature of 1100°C, the mechanical quality factor and electromechanical coupling coefficient were 1560 and 0.48, respectively. Thin films were deposited in situ onto Pt/Ti/SiO₂/Si substrates by pulsed laser deposition using a Nd:YAG laser. The microstructure, dielectric, electrical, and piezoelectric properties of thin films with the compound ceramics have been systematically investigated for microtransformer and MEMS applications.     

Optimization of saturation current density of PECVD SiN coated phosphorus diffused emitters using neural network modeling

Emitter surface passivation by low temperature plasma enhanced chemical vapor deposition (PECVD) silicon nitride is investigated and optimized in this paper. We have found that the saturation current density of a 90±10 μ/sq phosphorus diffused emitter with N_s ≈3 x 10¹⁹ and X_j ≈0.3 μm can be lowered by a factor of eight by appropriate PECVD silicon nitride deposition and photoassisted anneal. PECVD silicon nitride deposition alone reduces the emitter saturation density (J_oe) by about a factor of two to three, and a subsequent photoanneal at temperatures ≥350°C reduces J_oe by another factor of three. In spite of the larger flat band shift for direct PECVD silicon nitride coating, the silicon nitride induced surface passivation is found to be about a factor of two inferior to the thermal oxide plus PECVD silicon nitride passivation due to higher interface state density at the SiN/SiO₂ interface compared to SiO₂/Si interface. A combination of statistical experimental design and neural network modeling is used to show quantitatively that lower radio frequency power, higher substrate temperature, and higher reactor pressure during the PECVD deposition can reduce the J_oe of the silicon nitride coated emitter.     

Mechanical stress in PECVD a-SiC:H: aging and plasma treatments effects

Hydrogenated amorphous silicon carbide (a-SiC:H) deposited by PECVD is one of the most promising dielectric diffusion barrier available in Cu—Ultra low k interconnections due to its low dielectric constant and good barrier ability. In this work, the mechanical stress evolution with time of a-SiC:H film exposed to room atmosphere is studied and compared with the behavior observed on other PECVD dielectrics (SiN, SiO₂, SiCN). For as-deposited a-SiC:H samples, a strong stress evolution with time toward compression is observed and the results are interpreted mainly in terms of surface reactivity and silanol buildup. Infrared spectroscopy analysis allows to confirm that the mechanical stress evolution and the OH content are linked. An oxidation of the hydrogenated amorphous silicon carbide film with time is also observed. Different plasma treatments (He, O₂ or H₂) are tested on a-SiC:H films to limit the stress drift with time. Each plasma treatments are able to limit the stress evolution of a-SiC:H films but the mechanisms are different in each case: densification of the film with He plasma treatment, formation of a dense oxide at the surface with O₂ plasma treatment and passivation of dangling bonds with H₂ plasma treatment.     

High-quality conformal silicon oxide films prepared by multi-step sputtering PECVD and chemical mechanical polishing

High-quality conformal oxide films were obtained by using multi-step sputtering (MSSP) plasma enhanced chemical vapor deposition (PECVD) process with argon ion sputtering and chemical mechanical polishing (CMP). The repeated deposition by plasma enhanced chemical vapor deposition (PECVD) and anisotropic etching of oxide films by multi-step sputtering PECVD improve the step coverage and gap filling capability significantly. The argon plasma treatment enhances the binding energy of Si-O in the SiO₂ network, and the temperature dependence of stress for MSSP oxide film showed no hysteresis after the heating cycle up to 440 °C. The stress-temperature slope of MSSP oxide film was found to be much less than that of conventional PECVD oxide film. The slope for 1.1 μm thick film is about 5.8×10⁵ dynes/cm²/°C which is smaller than that of thermally grown oxide film. It seems that MSSP oxide film reduces stress-temperature hysteresis and becomes more dense and void-free in the narrow gaps with inter-metal spacing of 0.5 μm. After filling of the narrow gap, we adopted the CMP process for global planarization and obtained good planarization performance. The uniformity of the film thickness was about 4% and the degree of the planarization was over 95% after CMP process.