A physically based phenomenological model using boltzmann-matano analysis for boron diffusion from polycrystalline Si into single crystal Si

The diffusion of boron in single crystal Si from a BF₂-implanted polycrystalline Si film deposited on single crystal Si has been accurately modeled. The effective diffusivities of boron in the single crystal Si substrate have been extracted using Boltzmann-Matano analysis and the new phenomenological model for B diffusivity has been implemented in the PEPPER simulation program. The model has been implemented for a range of furnace anneal conditions (800 to 950°C, from 30 min to 6h) and implant conditions (BF₂ doses varied from 5×10¹⁵ to 2×10¹⁶ cm⁻² at 70 keV).     

PMOS integrated circuit fabrication using BF3 plasma immersion ion implantation

The feasibility of plasma immersion ion implantation (PHI) for multi-implant integrated circuit fabrication is demonstrated. Patterned Si wafers were immersed in a BF₃ plasma forp-type doping steps. Boron implants of up to 3 × 10¹⁵ atoms/cm² were achieved by applying microsecond negative voltage (-2 to -30 kV) pulses to the wafers at a frequency of 100 Hz to 1 kHz. After implantation the wafers were annealed using rapid thermal annealing (RTA) at 1060° C for 20 sec to activate the dopants and to recrystallize the implant damaged Si. For the PMOS process sequence both the Si source-drain and polycrystalline Si (poly-Si) gate doping steps were performed using PIII. The functionality of several types of devices, including diodes, capacitors, and transistors, were electrically measured to evaluate the compatibility of PIII with MOS process integration.     

Secondary ion mass spectrometry characterization of D2O and H2 18O steam oxidation of silicon

Silicon wafers were steam oxidized at temperatures of 550–1000°C and pressures of 0.05–8 atm with H₂ ¹⁶O, H₂ ¹⁸O, and D₂ ¹⁶O. Deuterium (D) and¹⁸O profiles in 100–200 nm thick oxide films were measured with Cs⁺ beam secondary ion mass spectroscopy (SIMS). The use of D and¹⁸O isotopes enabled analysis of these elements without interference from the sputtering ambient. Peaks in the D profiles near the interface are due predominantly to abrupt changes in the ion yield and charging conditions as the interface is approached. Although the D concentration is nearly constant at ∼ 1 × 10²⁰ cm⁻³ for 700–1000°C oxidations, it rises to a non-equilibrium value of 6 × 10²⁰ cm⁻³ at 600°C. Analysis of steam indiffusions below 800°C indicates that the OD concentration is proportional to the (steam pressure)^1/2, in agreement with earlier results on as-oxidized wet thermal oxides. The results of sequential isotope oxidations indicate that there is rapid exchange ofboth the hydrogen and oxygen species during transport of “water” to the SiO₂. Si interface. We examine these results in terms of the concentrations of the interacting species in the oxide films, and our results are compared to similar reported studies.     

Mg2Si buffer layers on Si(100) prepared by a simple evaporation method

The formation of Mg₂Si(100), a_o= 6.39Å, on Si(100) substrates has been investigated. Mg was first evaporated onto Si(100) surfaces and Mg₂Si (100) films were formed in a subsequent annealing process. The Mg₂Si layers were characterized by x-ray diffraction and transmission electron microscopy analysis. Optical and scanning electron microscopy analysis show the surface morphology to be smooth. The films are stable under thermal cycling and exhibit low resistivity. Epitaxial films of Mg₂Si on Si(100) could be an ideal substrate for mercury cadmium telluride and antimonide based III-V semiconductor for mid-infrared devices because of its close lattice matching (the lattice misfit factor is less than 1.5%).     

Low temperature cleaning of Si by a H2/AsH3 plasma prior to heteroepitaxial growth of GaAs by metalorganic chemical vapor deposition (MOCVD)

A method using a H₂/AsH₃ plasma to clean the Si surface before GaAs heteroepitaxy was investigated and the dependence of the effectiveness of this treatment on arsine partial pressure was studied. Thin GaAs-on-Si films deposited on the plasma-cleaned Si were analyzed using plan-view TEM, HRXTEM and SIMS. Although not optimized, this method of Si cleaning makes heteroepitaxial deposition of GaAs possible. Some roughening of the Si surface was observed and a possible explanation is offered. Using the results of this study, thick (2.5–3.0μm) epitaxial GaAs films were then deposited and their quality was evaluated using RBS, XTEM and optical Nomarski observation. All Si surface cleaning and GaAs deposition were carried out at temperatures at or below 650°.     

The effect of hydrogen on boron diffusion in SiO2

The diffusivity of boron in silicon dioxide may be increased by the introduction of hydrogen into the annealing atmosphere. In this paper we report on the diffusion characteristics of boron ion-implanted into thermally grown SiO₂. A sensitive technique was used in which the boron atoms redistributed into the substrate are characterized by electrical methods. The diffusivity of boron in thermal SiO₂ was measured over the temperature range of 950-1150°C with hydrogen partial pressure from 0 to 0.2 atm. It was found that the diffusion coefficient of boron in oxide at 1150° C increases as the square root of the hydrogen partial pressure. At fixed pressure the temperature dependence of the diffusion coefficient obeys a single-activation-energy exponential rule. At 0.1 atm partial pressure of H₂ the activation energy is 3.0 eV and the preexponential factor is 6 x 10⁵ [cm²/sec.].     

Effects of annealing conditions on the properties of tantalum oxide films on silicon substrates

The formation of a SiO₂ layer at the Ta₂O₅/Si interface is observed by annealing in dry O₂ or N₂ and the thickness of this layer increases with an increase in annealing temperature. Leakage current of thin (less than 40 nm thick) Ta₂O₅ films decreases as the annealing temperature increases when annealed in dry O₂ or N₂. The dielectric constant vs annealing temperature curve shows a maximum peak at 750 or 800° C resulting from the crystallization of Ta₂O₅. The effect is larger in thicker Ta₂O₅ films. But the dielectric constant decreases when annealed at higher temperature due to the formation and growth of a SiO₂ layer at the interface. The flat band voltage and gate voltage instability as a function of annealing temperature can be explained in terms of the growth of interfacial SiO₂. The electrical properties of Ta₂O₅ as a function of annealing conditions do not depend on the fabrication method of Ta₂O₅ but strongly depend on the thickness of Ta₂O₅ layer.     

Epitaxial Ge layers on Si via GexSi1-xO2 reduction: The roles of the hydrogen partial pressure and the Ge content

The epitaxial growth of an epi-Ge layer via Ge_xSi_1-xO₂ reduction in hydrogen annealing is reported. Ge_xSi+_1-x alloys with x = 0.52 and 0.82 were first grown epitaxially on Si substrates. They were then oxidized in a wet ambient and subsequently annealed in 5% or 100% H₂. The reduction of Ge from its oxide state is observed in both samples with both ambients. However, an epitaxial Ge growth is only observed in the sample with x = 0.82 after the 5% H₂ annealing. The other three cases result in the formation of polycrystalline Ge. The roles of the hydrogen partial pressure and the Ge content are discussed and conditions under which this novel mode of solid-phase epitaxy can occur are explained.     

Optical absorption studies of Si implanted SiO2

Optical absorption of Si implanted SiO₂ is characterized as a function of implant dose and energy upon annealing in N₂, H₂ and O₂ ambients. Interpretation of optical data yields information regarding the structure of defects due to excess Si. These defects are responsible for the memory effect and enhanced conductivity previously reported for Si implanted SiO₂. A correlation between E-band absorption (Si-Si ‘wrong’ bond defect) intensity and the amount of excess Si was established. Annealing of this band in O₂ is diffusion-limited with a reaction cross-section of 5.10⁻¹⁵ cm². Compressive strain-induced, oxygen diffusivity-retardation was observed. The C-band absorption (relaxed oxygen vacancy defect) observed in this study is unique in its response to heat treatment in N₂ and H₂ since it does not anneal in these ambients. C-band annealing kinetics in O₂ closely parallel those of E-band. B₂-band absorption (unrelaxed oxygen vacancy defect) produced by Si implantation is very similar in its annealing properties to the published data.     

Radiation sensitivity of buried oxides

Capacitance-voltage (C-V) techniques have been used to examine the 10-keV x-ray radiation sensitivity of buried oxides that are created by the implantation of oxygen into silicon. Buried oxide to substrate interfaces have been studied by using samples implanted with different oxygen implant doses from a 100 mA-class implanter. Fiatband voltage (Vfb) shift for the buried oxide to the substrate interface has been used to monitor charge buildup as a function of radiation dose and applied electrical bias. The Vfb shift of the buried oxides indicate a oxide trapping behavior that is different than that of thermal oxides.     

Characterization of Si homoepitaxial films grown with and without surface photoactivation by ArF excimer laser-induced photodissociation of Si2H6

Silicon homoepitaxial films have been grown by photodissociation of Si₂H₆ by the 193 nm line of an ArF excimer laser in an ultra-high vacuum system. Silicon epitaxy has been achieved in two ways: one, in which the laser shines into the chamber parallel to the substrate and another, in which the laser is directly incident on the substrate at grazing angles (87° with respect to the substrate normal). Controllable growth rates of 0.5–4Å/min have been achieved for crystalline films by the first method using substrate temperatures as low as 250° C, Si₂H₆ partial pressures of 20 mTorr and photon flux densities of 10¹⁶ photons/pulse.cm². In the second method, where the laser beam is directly incident on the wafer at grazing angles, very high growth rates of up to 80Å/min have been achieved at 300° C, 20 mTorr Si₂H₆ partial pressure and a photon flux density of 2 × 10¹⁵ photons/pulse.cm². A comparison of the microstructure of the films grown by the two methods is presented on the basis ofin situ reflection high energy electron diffraction (RHEED) analysis and selected area transmission electron microscopy (TEM) studies. In both cases, the growth rates are found to be linearly dependent on the photon flux density for the process parameter ranges studied.     

MIS characterization and modeling of the electrical properties of the epitaxial Caf2/Si(111) interface

CaF₂ layers have grown by molecular beam epitaxy on bothn-type andp- type Si(111). Capacitance-voltage (C-V) and current-voltage (I-V) measurements have been made on metal-insulator-semiconductor (MIS) capacitors to characterize these structures. For devices onp-type Si, C-V characteristics show only the insulator value of the capacitance over a wide range of applied voltages, indicating an accumulated surface. At room temperature, C-V characteristics ofn-type devices show the minimum value of the capacitance (corresponding to inversion) for small voltages, but modulation of the capacitance at larger voltages. At 200 K, this modulation is no longer present in the C-V curves. I-V curves show a rapid increase in the leakage current at relatively low fields at room temperature, and this leakage decreases dramatically with temperature. These results are largely independent of cleaning procedure, growth temperature, and the degree of misalignment of the substrate. The characteristics are modeled by assuming the Fermi level to be pinned at the valence-band edge, and the modulation in the C-V characteristics ofn-type samples to be driven by leakage currents. Work done at GE while a graduate student in the School of Electrical Engineering, Cornell University. Present address: Jet Propulsion Laboratory, 4800 Oak Grove Dr., Pasadena, CA 91109.     

The diffusion of ion-implanted arsenic in thermally grown SiO2

The diffusivity of ion-implanted As in SiO₂ is investigated as a function of the implanted dose, oxide type and ambient in the 1000–1200° C temperature range. The As diffusivity in oxide is extracted, using electrical methods, from the profiles of As diffused into the substrate. Secondary-ion-mass-spectroscopy depth profiles of some of the samples are in agreement with the results of the electrical methods. Two types of oxide are investigated: Dry oxide grown in O₂ and wet oxide grown in steam. The diffusivity is characterized as a function of the temperature for dry oxide annealed in N₂, and for wet oxide annealed both in N₂ and in N₂/H₂ (10%). The measured As diffusivity vs temperature is fitted to a single activation energy exponential model. For the wet-grown oxide, the extracted activation energy for the N₂/H₂ (10%) annealed sample is 4.4 ± 0.5 eV and for the N₂ annealed oxide it is found to be 5.5 ± 0.5 eV. For oxide grown in dry oxygen the As diffusivity is characterized also as a function of the implant dose. It is found to be independent of the implanted dose, for ion energy of 40 keV and dose in the 10¹²–10¹⁵ cm^-2 range, and its activation energy equals 4.7 ± 0.5 eV. The extracted parameters were installed in the SUPREM-III process simulation program and correctly predict ion-implanted As diffusion behavior in SiO₂.     

Applications of electron paramagnetic resonance to studies of defects in insulators and semiconductors

Electron paramagnetic resonance (EPR) which is the absorption of electromagnetic waves in the microwave frequency domain has been used for many years to study magnetic dipoles in crystals subjected to magnetic fields. These magnetic dipoles arise from electrons in the material whose intrinsic spin is exposed due to processes such as doping with transition metal ions, doping with ions whose spin is not locked up with chemical bonding and irradiation with bond breaking energy. The sensitivity of the EPR technique depends on such experimental parameters as, incident microwave power, size of the sample, quality of the microwave cavity, number of paramagnetic spins participating in the absorption, width of the EPR resonance line, temperature of the sample and relaxation time of the spin system to the lattice. The experimental spectrum is described by parameters which by the application of basic quantum mechanics can be related to properties of the wave function of the electron spin in the crystal environment such as bonding directions to neighboring ions in the crystal lattice. Some examples of this analysis will be presented to show how EPR is used in the study of defects in Si and SiO₂.     

Improved Gettering Efficiency of Ni from Nickel-Mediated Crystallization Silicon Using Phosphorus-Doped Amorphous Silicon

Ni-metal-induced lateral crystallization (NILC) has been utilized to fabricate polycrystalline silicon thin-film transistors. However, the NILC process often leads to Ni and NiSi₂ precipitates being trapped. In this study, two kinds of films were used as gettering layers: (1) amorphous Si and (2) phosphorus-doped amorphous Si. After annealing at 550°C for 12 h, it was found that phosphorous dopant did improve the gettering efficiency of amorphous Si.     

SiO2/Si上石墨烯薄膜的化学气相沉积法制备及其性能表征

以铜为催化剂,采用聚甲基丙烯酸甲酯(PMMA)和甲烷为碳源的化学气相沉积两步法,在SiO₂/Si衬底上制备了石墨烯薄膜。利用拉曼光谱分析了薄膜的层数和质量,利用光学显微镜(OM)和扫描电子显微镜(SEM)分析了薄膜的尺寸与表面形貌。实验探究了生长时间、氢气流量和气体总压强等工艺参数对石墨烯薄膜层数和质量的影响,最终在优化条件下制得10μm级质量较高的多层石墨烯薄膜。     

Laser-induced self-organization of nano-wires on SiO2/Si interface

Original observation of new graded band gap structures formed on the surface of elementary Si semiconductor at studying the optical properties of Si nano-hills formed at the SiO₂/Si interface by pulsed Nd:YAG laser irradiation is reported. The self-organized nano-hills on Si surface are characterized by a strong photoluminescence in the visible range of spectrum with a shoulder extended to the long-wave part of the spectrum. The feature is explained by the quantum confinement effect in nano-hills-nano-wires of gradually changing diameter.     

Highly concentrated ozone gas supplied at an atmospheric pressure condition as a new oxidizing reagent for the formation of SiO2 thin film on Si

We have investigated the characteristics of silicon oxidation by concentrated ozone gas through the comparison of the oxidation by oxygen molecules. A sophisticated high-concentration ozone generator, which exploits the ozone/oxygen gas separation technique with silica gel, has been developed for the study. The generator can continuously supply ozone-oxygen mixtures with ozone concentrations up to 30 at.% at one atmospheric pressure. Ozone gas with a concentration of 25 at.% from the generator formed SiO₂ films as thick as 2 nm and 6 nm on Si for a 30 min. exposure at 200°C and 600°C, respectively. On the other hand, oxygen gas by itself could form SiO₂ films with only 1 nm and 3 nm thickness, respectively, at the same conditions. Moreover, in the oxide film formation at 600°C, the oxide film growth by ozone was proceeded with an oxidation time in excess of 240 min., while it saturated within very short time in the oxidation by oxygen. These phenomena verify the strong oxidation power of ozone. In addition, we confirmed that the growth rate of the silicon oxide with ozone dramatically changed when the substrate temperature was over 500°C, and this suggested the change of oxidation mechanism at this point. However, such a characteristic was not found in oxidation with oxygen.     

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.     

Plasma enhanced chemical vapor deposition of SiO2 films at low temperatures using SiCl4 and O2

Silicon dioxide films have been deposited by Plasma-Enhanced Chemical Vapor Deposition (PECVD) technique using SiCl₄ and O₂ as reactive materials. Infra-red transmittance, Auger electron spectroscopy analysis, ellipsometry, electrical, and chemical etch measurements have been used to characterize these films. It is possible to obtain good quality oxides at a substrate temperature of 200° C using a low flow of reactant gases. High flow of reactant gases results in highly non-homogeneous porous films. The best oxide films obtained show destructive breakdown at electrical fields above 4 MV/cm and a fixed charge density of the order of 2.6 × 10¹¹ charges/cm².