Non uniform recombination in thin silicon-on-sapphire films

Recombination parameters of SOS films are deduced from the study of the magnetoconcentration effect in double-injecting structures. The method of measurement is based on an original theory succintly developed; it takes into account general SRH bulk and surface recombination laws; moreover inhomogeneous distributions of recombination centers are considered.Experimental results (current-voltage characteristics of such “magnetodiodes”), when analysed according to the proposed method, lead to more realistic values of the global recombination parameters (τ_v, S₁, S₂) of the SOS film. It is proved, for example, that the previous simplified analysis overestimates the carrier recombination velocity on the Si-Al₂O₃ surface. On the contrary our method gives both a moderate value for this recombination velocity and a lower carrier lifetime near the Sapphire interface, which well agrees with the continuity of recombination rates at the surface and in the underlying bulk; the higher recombination region is found to be 100–1000 Å thick.     

IMMA applications to ion implantation in silicon-on-sapphire

Application of ion-microprobe mass analysis (IMMA) technique for the characterization of the silicon-on-sapphire (SOS) epitaxial layers and ion implantation in SOS axe described. A significantly high level of aluminum and oxygen concentration was observed in the thin (O.5-µm) epitaxial film. Ion-implant profiles of boron and phosphorus before and after high-temperature activation and oxidation procedures commonly used in SOS fabrication process are characterized and correlated to SUPREM calculations, spreading resistance, and resistivity measurements.     

晶态InSb薄膜在脉冲YAG激光作用下的熔化与再结晶过程的研究

观察了不同能量的YAG激光脉冲辐照引起的晶态InSb薄膜熔化与再结晶的瞬态过程,分析了InSb薄膜在激光作用下发生相变的时间过程和微观机制。     

Neutralization of electrically active aluminum in recrystallized silicon-on-sapphire films

We report the effect of steam oxidation at 875° C on the electrical resistivity, crystalline quality (measured by ion channeling), and Al concentration (measured by secondary ion mass spectrometry) in 0.25 μm thick, Si-implanted and recrystallized, Si-on-sapphire films. After a deep Si implantation (180 keV, 1.4×l0¹⁵ Si/cm²) at room temperature, and solid-phase epitaxial regrowth from the non-amorphized, 0.03 μm thick surface region, the initially undoped SOS films become doped p-type, and their resistivity decreases from (1−5)xl0¹⁴ ficm to 0.5 Ωcm. The doping is due to electrically active Al, released from the A1₂O₃ by the Si implantation, and present in the recrystallized films at a concentration of ≃2×l0¹⁶ Al/cm³ . After a 75 min steam oxidation at 875 °C, which consumes 0.06 Μm of Si, the resistivity of the recrystallized films increases to over 40 Ωcm, but the Al concentration is unchanged. The oxidation also uncovers higher quality material below the non-recrystallized surface layer. A semi-quantitative model is proposed to explain the electrical data, based on the diffusion of oxygen from the Si/SiO₂ interface into the SOS film during oxidation, and the formation of Al-O-Si neutral complexes. Data on the stability of the high-resistivity films against high-temperature annealing or re-amorphization and annealing is given.     

Energy distribution of recoil atoms and formation of radiation defects in silicon carbide films under proton irradiation

Proton scattering in a silicon carbide film has been numerically simulated. Distribution histograms of the energy imparted to recoil atoms are obtained. Two energy ranges are considered when analyzing the histograms. In the first range of “low” energies, individual Frenkel pairs with closely spaced components are created. In the second range, recoil atoms have energies sufficient for generating a cascade of displacements. This gives rise to microscopic regions with high density of vacancies and vacancy complexes of various kinds.     

Defect formation in epitaxial GaP junctions under heat treatment

A theoretical and experimental investigation is reported into the influence of hydrogen heat treatment on the electrical and electroluminescent characteristics of GaP LEDs. It is shown that electrical transport in processed specimens is mainly by tunneling. The tunneling rate as a function of some properties is examined. A mechanism of electrical transport in the LEDs is proposed. The role of hopping conduction is discussed, and its parameters are determined. Electroluminescence spectra are measured and explained in terms of thermally induced structural changes in defects.Translated from Mikroelektronika, Vol. 34, No. 1, 2005, pp. 43–50.Original Russian Text Copyright © 2005 by Boulyrskii, Groushko, Kazakov.     

Effect of ion irradiation of amorphous-silicon films on their crystallization

The change in the structure of amorphous Si films implanted with inert-gas ions and chemically active impurity was investigated by transmission electron microscopy and electron diffraction methods. It was shown that as a result of radiation-induced formation of thermally stable vacancy complexes, Si films irradiated with Ar⁺ and P⁺ ions with doses above 7×10¹⁵ cm⁻² do not crystallize up to temperature 680 °C. It was established that crystallization of Si films after implantation of lower doses of P⁺ ions accelerates the growth of grains in the films as a compared with the unirradiated films. A model of the mechanism by which the ion irradiation influences the crystallization of Si films is discussed. Fiz. Tekh. Poluprovodn. 32, 349–352 (March 1998)     

Improved subthreshold characteristics of n-channel MOS transistorsfabricated in solid phase epitaxially regrown silicon-on-sapphire films

Subthreshold characteristics of n-channel silicon-on-sapphire (SOS) MOSFETs have been measured following solid-phase epitaxial regrowth of the epitaxial film. Results obtained from planar n-channel transistors show that an increase in the subthreshold current slope can be obtained by improving the quality of the silicon layer. These results are explained in terms of a reduction in the density of interface traps present at the Si/SiO₂ interface     

Ge-nanocluster formation in Ge-doped polysilicon films under oxidation and heat treatment

An experimental investigation is conducted into the formation Ge nanoclusters by heat treatment of germanosilicate-glass (Si _x Ge _y O _z ) films that are produced by oxidation of Ge-doped nanostructured polysilicon. It employs Auger and IR spectroscopy, high-resolution electron microscopy, and x-ray diffraction. The process by which Ge atoms in the films are transported toward the substrate is found to include the following stages: (1) the formation of a GeO₂ and a SiO₂ phase, (2) the reduction of GeO₂ to Ge by Si, (3) Ge-crystallite nucleation, and (4) Ge-crystallite growth. Heat treatment in humid oxygen at ≥ 800°C is found to increase Ge-nanocluster size, the point of crystallization being 500°C. It is established that heat treatment at a temperature close to the Ge melting point results in complete aggregation of the germanium into clusters, with a twofold increase in both the mean size and the number of clusters. Germanium is found to accumulate at the interface between oxidized and unoxidized polysilicon.     

Defect formation in PbTe under the action of a laser shock wave

Mechanisms of the defect formation in PbTe thin films on BaF₂ substrates under shock-wave action are studied, and the kinetics of the annealing of the resulting nonequilibrium crystal defects at room temperature is analyzed. The respective roles of the first-and second-order annealing reactions in settling of the equilibrium state of the defects are estimated. The contributions of Frenkel pair annihilation in both sublattices and migration of interstitials to sinks to a change in the total concentration of nonequilibrium defects at different stages of annealing are considered.     

Modification of electrical and optical properties of ZnO films under ultraviolet irradiation

The effect of ultraviolet radiation of polycrystalline zinc oxide films (with a thickness of 200 nm) on their resistivity, transparency, and luminescence in the visible and violet spectral regions is studied. It is shown that, under irradiation of the films in air and vacuum, the conductivity, transmittance, and edge luminescence intensity increase with characteristic times of about 100 min. It is established that the corresponding processes controlled by desorption of oxygen atoms and molecules from the surface of nanocrytals in the ZnO films are reversible.     

A short-channel CMOS/SOS technology in recrystallized 0.3-µm-thick silicon-on-sapphire films

CMOS/SOS devices and circuits were fabricated in 0.3-µm-thick epitaxial silicon-on-sapphire (SOS) films. Two solid-phase epitaxial recrystallization techniques double solid-phase epitaxy (DSPE) and solid-phase epitaxy and regrowth (SPEAR) reduced the total microtwin concentrations in the Si layers more than tenfold, while increasing electron and hole inversion-layer mobilities between 30 and 45 percent. Leakage currents were substantially reduced in all SPEAR devices and in n-channel DSPE transistors, with some increase observed for p-channel DSPE devices. Drive currents and subthreshold slopes also showed significant improvement in both n- and p-devices. Propagation delays below 75 ps were obtained for CMOS/SOS inverters with Loff= 0.5 µm. The application of DSPE and SPEAR techniques to 0.3-µm SOS films will extend the scaling of CMOS/SOS to circuits with VLSI complexity.     

Performance of CMOS devices in silicon-on-sapphire films after solid-phase epitaxial growth with rapid electron-beam heating

The crystal quality of 0.3-µm-thick as-grown epitaxial silicon-on-sapphire (SOS) was improved using solid-phase epitaxy (SPE) by implantation with silicon to 10¹⁵ions/cm²at 175 keV and rapid annealing using electron-beam heating, n-channel and p-channel transistor mobilities increased by 31 and 19 percent, respectively, and a reduction in ring-oscillator stage delay confirmed that crystal defects near the upper silicon surface had been removed. Leakage in n-channel transistors was not significantly affected by the regrowth process but for p-channel transistors back-channel leakage was considerably greater than for the control devices. This is attributed to aluminum released by damage to the sapphire during silicon implantation.     

激光辐照下金纳米缺陷诱导光学玻璃损伤特性

采用离子束溅射的方式,在K9玻璃基片表面引入金纳米杂质缺陷,通过原子力显微镜(AFM)测得金纳米尺寸直径在50~100 nm之间。采用不同能量密度的激光对样品进行点阵式的单脉冲辐照(1-on-1)并且对损伤阈值及典型损伤形貌进行了实验及理论分析。损伤阈值采用零几率处的损伤密度。结果表明:引入金纳米杂质缺陷后其抗激光损伤阈值由裸基片的26.6 J/cm2下降为15.5 J/cm2。通过微分干涉显微镜,随着激光能量的增加,损伤呈爆炸坑形貌,主要呈现纵向加剧损伤。金纳米杂质缺陷在K9玻璃基片上形成了强吸收中心(引入金纳米杂质K9玻璃基片的弱吸收(47.33 ppm,1 ppm=10-6)是裸K9玻璃基片(3.57 ppm)的13倍)造成局部高温,这是造成损伤的诱因。通过计算,金纳米杂质对K9玻璃基片的作用包括两部分:当激光辐照在K9玻璃基片上,首先是热应力引起玻璃的破裂;随后杂质汽化产生的蒸汽压加剧材料的破坏,引起局部炸裂。     

Defect formation in epitaxial crystal growth

Factors affecting the nucleation and propagation of dislocations, stacking faults, microtwins, and inversion domain boundaries in epitaxially grown semiconductor layers are reviewed, with examples for heteroepitaxial MBE-grown layers on substrates having varying degrees of mismatch or different crystal symmetry. Mechanisms for generation of defects at the heterointerface and in the epilayer are discussed. For epilayers with bulk mismatch from 0 to 4%, methods for reducing defect density in the epitaxial layer are considered. Examples of structural details in the epilayers and at heterointerfaces, particularly those which may be revealed by transmission electron microscopy, are given.     

Properties of buried SiC layers produced by carbon ion implantation in (100) bulk silicon and silicon-on-sapphire

Buried layers of SiC were formed in (100) single-crystal bulk silicon and silicon-on-sapphire by ion implantation of 125–180 keV, (0.56-1.00) × 10¹⁸ C/cm² at 30–40 μA/ cm² into samples held at 450-650° C. The as-implanted and 950° C annealed samples were characterized by differential infra-red absorbance and reflectance, Rutherford backscattering and channeling spectrometry, x-ray diffraction, four-point probe measurements, Dektak profilometry, I-V measurements, spreading resistance measurements and secondary ion mass spectrometry. Work done while affiliated with Rockwell International Corporation, Microelectronics Research & Development Center, 3370 Miraloma Avenue, Anaheim, CA 92803 and a Visiting Associate at the California Institute of Technology, Department of Applied Physics, Mail Code 116-81, Pasadena, CA 91125.     

Estimation of the efficiency of the introduction of a porous layer into a silicon-on-sapphire structure substrate to enhance the reliability of devices under irradiation

We investigate the efficiency of the introduction of a porous layer into the substrate of a silicon-onsapphire structure by the implantation of He ions to enhance the radiation resistance of devices. The properties of the introduced layer and its parameters affecting the concentration of minority charge carriers generated by irradiation are analyzed. The reported results of the analysis and calculations can be used to optimize He-ion implantation conditions during the formation of a porous layer.     

Effect of Ar ion irradiation on structural and optical properties of e-beam evaporated cadmium telluride thin films

CdTe thin films were prepared using e-beam evaporation technique. The prepared films were irradiated by Ar⁺ ions at different fluencies using multipurpose aluminum (Al) probe as in-situ. This could also be used in ion bombardment for cleaning the substrate prior to coating. The as grown and Ar⁺ ion irradiated films were confirmed to be of polycrystalline nature with X-ray technique. Ar⁺ ion irradiation enhances the growth of (1 1 1) oriented CdTe crystals and the Cd enrichment on the surface of CdTe thin films. Higher Ar⁺ ion flux helps to grow (2 2 0) oriented CdTe thin film. A considerable change in structural parameters like crystallite size, lattice parameter, internal strain, etc. could be observed as a result of high Ar⁺ ion flux. The applied in-plan stress in both as grown and irradiated film was identified to be of tensile nature. The applied stress was observed between 0.016 and 0.067 GPa for all Ar⁺ ion irradiated samples. As a result of the Ar⁺ ion irradiation, the in-plan stress varies between 1.38×10⁹ and 5.58×10⁹ dyn/cm². The observed bad gap was increased for higher Ar⁺ ion flux. It shows the effect of Ar⁺ ion irradiation on the modifications of optical properties. The observed results were encouraging on the use of simple multipurpose Al probe for Ar⁺ ion irradiation process as in-situ.     

Quasi-stationary electron and ion processes in dielectric films and diagnostics of films

The principle of quasi-equilibrium in the study of the structures that contain semiconductors and insulators, in particular, dielectric films in the metal-insulator-semiconductor (MIS) structures is discussed. A possibility of the simultaneous measurements of the averaged convection currents in an insulator and the current flows through the semiconductor-insulator interface in the MIS structures is considered. The methods for the measurement of the concentration of mobile ions in a dielectric film are analyzed.