Investigation of Si/SiGe/Si heterostructure implanted by H ion and annealed in vacuum and dry O2 ambient

The 20-nm-thick Si cap layer/74-nm-thick Si_0.72Ge_0.28 epilayer/Si heterostructures implanted by 25 keV H⁺ ion to a dose of 1×10¹⁶ cm⁻² were annealed in ultra-high vacuum ambient and dry O₂ ambient at the temperature of 800 °C for 30 min, respectively. Rutherford backscattering/ion channeling (RBS/C), Raman spectra, high-resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) were used to characterize the structural characteristics of the Si_0.72Ge_0.28 layer. Investigations by RBS/C demonstrated that the crystal quality of the Si/Si_0.72Ge_0.28/Si heterostructure sample implanted by 25 keV H⁺ in conjunction with subsequent annealing in dry O₂ ambient is superior to that of identical sample annealing in ultra-high vacuum ambient. The less strain relaxation of SiGe layer of the Si/Si_0.72Ge_0.28/Si heterostructures implanted by H ion and annealed in dry O₂ ambient at the temperature of 800 °C for 30 min could be doublechecked by Raman spectra as well as HRXRD, which was compared with that in an identical sample annealed in ultra-high vacuum ambient for identical thermal budget. In addition, the SiGe layer of the H-implanted Si/SiGe/Si heterostructural sample annealed in dry O₂ ambient accompanied by better crystal quality and less strain relaxation made its surface morphology superior to that of the sample annealed in ultra-high vacuum ambient at the temperature of 800 °C for 30 min, which was also verified by AFM images.     

Study of porous silicon obtained by krypton ion implantation and laser annealing

An ellipsometric technique is used to study the formation of a finely porous layer saturated with atoms of an inert gas in a crystalline silicon lattice that has been doped by high doses of krypton and then irradiated by nanosecond laser pulses. The changes in the complex refractive index of this layer induced by laser pulses at different powers are studied. A scanning field ion microscope is used to follow the transformation of the pores, as the energy per unit area of the annealing laser light is varied, and to estimate their sizes. Fiz. Tekh. Poluprovodn. 31, 1130–1134 (September 1997)     

Effect of annealing on the structural, optical and electrical properties of ITO films by RF sputtering under low vacuum level

Indium tin oxide (ITO) thin films were prepared by RF sputtering of ceramic ITO target in pure argon atmosphere at a high base pressure of 3×10⁻⁴ mbar without substrate heating and oxygen admittance. The use of pure argon during deposition resulted in films with high transparency (80-85%) in the visible and IR wavelength region. The films were subsequently annealed in air in the temperature range 100-400 °C. The annealed films show decreased transmittance in the IR region and decreased resistivity. The films were characterized by electron microscopy, spectrophotometry and XRD. The predominant orientation of the films is (2 2 2) instead of (4 0 0). The transmission and reflection spectra in the wavelength range 300-2500 nm are used to study the optical behaviour of the films. The optical transmittance and reflectance spectra of the films were simultaneously simulated with different dielectric function models. The best fit of the spectrophotometric data was obtained using the frequency-dependent damping constant in the Drude model coupled with the Bruggeman effective medium theory for the surface roughness. It has been found that the sputtering power and the chamber residual pressure play a key role in the resulting optical properties. This paper presents the refractive index profile, the structure determined from the XRD and the electrical properties of ITO films. It has been found from the electrical measurement that films sputtered at 200 W power and subsequently annealed at 400 °C have a sheet resistance of 80 Ω/□ and resistivity of 1.9×10⁻³ Ωcm.     

Characterization of electroplated copper self-annealing with investigations focused on incorporated impurities

At room temperature electroplated copper exhibits changes in microstructure widely known as self-annealing. To investigate this phenomenon we simultaneously determined resistivity, residual stress, microstructure evolution, and behavior of organic impurities in three Cu layers of 600, 1000, and 2000 nm thickness. The examination of Cu layer impurities presupposed an extensive work of identification and elimination of contamination sources. After developing and applying several cleaning procedures it was possible to qualify and quantify incorporated C as indicator for organic impurities. The investigation of Cu self-annealing led to the conclusion that the microstructure evolution has to be divided into two periods. The first period of inhibited grain growth shows an impurity diffusion out of the metallization layer combined with a significant stress relaxation. In the following second period a forced grain growth evolution starts forming up a coarse grain microstructure.     

GaInAs junction FET with InP buffer layer prepared by selective ion implantation of Be and rapid thermal annealing

GaInAs JFETs were fabricated on VPE-grown GaInAs layers. The pn junctions have been realised with Be ion implantation and rapid thermal annealing. The devices show a high transconductance of 130 mS/mm and an electron saturation velocity of 1.8 × 107 cm/s. Channel mobilities measured at the complete device are as high as 6800 cm2/Vs. These excellent device properties are due to the use of an undoped InP buffer layer which avoids the diffusion of Fe from the substrate into the active layer. The data were supported by S-parameter measurements which gave a frequency limit of 20 GHz for gate dimensions of 1.6 by 200 ?m2.     

Formation of Ge nanocrystals in a silicon dioxide layer using pulsed plasma-immersion ion implantation

Pulsed plasma-immersion ion implantation (PIII) or Pulsed PLAsma Doping (P²LAD) is known as a cost effective solution for ultra shallow junction formation due to its capability to implant doping species at ultra-low energies (0.05–5 keV), the advantages of P²LAD, high concentration and sharp distribution of the implanted species, also make this technique a good candidate to fabricate nanocrystals (NCs) within silicon dioxide (SiO₂) layer. In this work, we report Ge NC fabrication within a SiO₂ layer by using the pulsed PIII technique for the first time. GeH₄ (4 sccm) and He (100 sccm) gases were flown to the plasma chamber, and a voltage of 4.5 kV was applied. After pulsed PIII process, furnace annealing was performed at 900 °C in nitrogen atmosphere for Ge agglomeration. By using such a process, we fabricated non-volatile memory devices and obtained relevant program/erase, retention, and cycling characteristics.     

Redistribution of ytterbium and oxygen in annealing of silicon layers amorphized by implantation

The redistribution of ytterbium and oxygen was studied in silicon layers that were implanted with 1-MeV Yb⁺ ions at a dose of 1×10¹⁴ cm^?2, which exceeds the amorphization threshold, and 135-keV O⁺ ions at a dose of 1×10¹⁵ cm^?2 and that were subsequently annealed at 620 and 900°C. The redistribution of Yb is due to segregation at the interface between the amorphous and single-crystal layers in solid-phase recrystallization of the buried amorphized layer. The redistribution of oxygen and its accumulation in regions with the highest concentration of Yb is associated with oxygen diffusion and the formation of YbO_n complexes with n varying from 1 to 6. The parameters characterizing the dependence of the Yb segregation coefficient on the thickness of the recrystallized layer and the formation of YbO_n complexes were determined.     

Fabrication of thick, high-quality strained SiGe layer on ultra-thin silicon-on-insulator and modeling of film strain

Fabrication of a thick strained SiGe layer on bulk silicon is hampered by the lattice mismatch and difference in the thermal expansion coefficients between Si and SiGe, and a high Ge content leads to severe strain in the SiGe film. When the thickness of the SiGe film is above a critical value (90 nm for 18% Ge), drastic deterioration of the film properties as well as dislocations will result. In comparison, a silicon-on-insulator (SOI) substrate with a thin top Si layer can mitigate the problems and so a thick SiGe layer with high Ge concentration can conceivably be synthesized. In the work reported here, a 110 nm thick high-quality strained Si_0.82Ge_0.18 layer was fabricated on an ultra-thin SOI substrate with a 30 nm top silicon layer using ultra-high vacuum chemical vapor deposition (UHVCVD). The thickness of the SiGe layer is larger than the critical thickness on bulk Si. Cross-sectional transmission electron microscopy (XTEM) reveals that the SiGe layer is dislocation-free and the atoms at the SiGe/Si interface are well aligned, even though X-ray diffraction (XRD) data indicate that the SiGe film is highly strained. The strain factors determined from the XRD and Raman results agree well.     

Dislocation-related luminescence in silicon,caused by implantation of oxygen ions and subsequent annealing

Multiple implantation of oxygen ions with energies of 0.1–1.5 MeV at doses of 7 × 10¹³?2 × 10¹⁴ cm^?2 and subsequent annealing in a chlorine-containing atmosphere at 900°C for 4 h give rise to dislocation-related luminescence in p-Si. A p → n conductivity-type conversion is also observed in this case in the surface layer of Si, which indicates that electrically active donor centers are formed in the process. Preliminary heat treatment of wafers covered with an erbium-doped film of tetraethoxysilane (TEOS) in argon at 1250°C for 1 h does not preclude the appearance of dislocation-related luminescence, but affects the parameters of the dislocation-related lines (peak positions and intensities).     

Formation of a buried collector layer in RF-bipolar devices by ion implantation

High-dose implantation of arsenic (As) buried collector layer formation for bipolar/BiCMOS processes has been studied. Wafers with and without screen oxide were subjected to high-dose implants with different energies. Some wafers were given a low-temperature anneal before XTEM and SIMS analyses. Defects observed after As implants of 6E15 cm⁻² through screen oxide after low-temperature anneal were annihilated at the subsequent high-temperature steps, but the direct implant of As into the silicon is preferred since fewer defects are generated and there is no knock-on of oxygen into the material. Fabricated devices showed excellent electrical performance. However, the upper limit (dose and/or energy) at which perfect recrystallization does no longer occur has not been defined and the process limit is consequently not established.     

Defect-engineering in SiC by ion implantation and electron irradiation

Three examples are given, which show that ion implantation and electron irradiation can drastically modify the electrical properties of SiC and SiC-based MOS capacitors. (1) It is demonstrated that sulphur ions (S⁺) implanted into 6H-SiC act as double donors with ground states ranging from 310 to 635 meV below the conduction bandedge. (2) Co-implantation of nitrogen (N⁺) - and silicon (Si⁺) - ions into 4H-SiC leads to a strong deactivation of N donors. Additional experiments with electron (e⁻)-irradiated 4H-SiC samples (E(e⁻) = 200 keV) support the idea that this deactivation is due to the formation of an electrically neutral (N_x-V_C, y)-complex. (3) Implantation of a surface-near Gaussian profile into n-type 4H-SiC followed by a standard oxidation process leads to a strong reduction of the density of interface traps D_it close to the conduction bandedge in n-type 4H-SiC/SiO₂ MOS capacitors.     

A study of the ion implantation damage and annealing behavior in GaSb

The effects of damages produced by implantation of Te, Er, Hg, and Pb ions into undoped (100) GaSb single crystals and their recovery by Rutherford backscattering (RBS)/channeling were investigated. The implantations with dosages in the range of 10¹³ to 10¹⁵ ions/cm² were carried out at liquid nitrogen temperature, at energies corresponding to a projected range of 447Å in GaSb. Near surface damage equivalent to that of an amorphous layer was observed even at lower doses. The samples were annealed at 600°C for different durations, with the Te implanted sample of the lowest dosage exhibiting the best recovery (Χ_min = 11%) compared to others. This value of Χ^min nearly corresponds to that of the virgin crystal. Examination of the surface morphology as a function of mass, dosage, and annealing duration revealed that it was strongly influenced by the dosage of the implanted ions.     

Planar nucleation and crystallization in the annealing process of ion implanted silicon

According to thermodynamic and kinetic theory,considering the variation of bulk free energy and superficial energy after nucleation as well as the migration of atoms,we study systematically the planar nucleation and crystallization that relate to two possible transition mechanisms in the annealing process of ion implanted S i:(1) liquid/solid transition:the critical nucleation work is equal to half the increased superficial energy and inversely proportional to the supercoolingΔT.Compared with bulk nuclea...     

The influence of dose and protecting mask on electrically active defects induced by ion implantation in silicon

We present a study of electrically active defects induced by ion implantation, for two dopants: arsenic and phosphorous. Our analysis technique is Deep Level Transient Spectroscopy (D.L.T.S.). We have studied the generation of defects by direct implantation, and indirect implantation, that is through an SiO₂ layer. We follow the defect spectrum evolution for different doses (10⁸ to 10¹⁴ atoms/cm²) and for different annealing temperatures (from room temperature up to 800° C). The comparison of our results with other published ones allows us to improve the knowledge about the role of a protecting oxide layer, the influence of moderate thermal annealing, and the effect of oxygen on deep centers produced by ion bombardment.     

Photovoltaic effect in a structure based on amorphous and nanoporous silicon formed by plasma immersion ion implantation

A p-i-n structure with photovoltaic properties was proposed and fabricated by plasma immersion ion implantation. Implantation of helium ions with an energy of 1 to 5 keV with subsequent annealing creates a region of nanoporous silicon at a depth of ～20 to 80 nm from the silicon substrate surface. A nanocrystalline structure of this layer results in high light absorption and a change in the band-gap energy, which leads to the formation of a heterojunction. The upper layer of the modified region was additionally doped with boron to create a p region. The resulting structure showed a photovoltaic effect (0.15 V, 6.4 mA/cm²) under illumination with light equivalent to sunlight in terms of the spectral range and intensity.     

The effect of oxygen on segregation-induced redistribution of rare-earth elements in silicon layers amorphized by ion implantation

A model of segregation-induced redistribution of impurities of rare-earth elements during solid-phase epitaxial crystallization of silicon layers amorphized by ion implantation is developed. This model is based on the assumption that a transition layer with a high mobility of atoms is formed at the interphase boundary on the side of a-Si; the thickness of this layer is governed by the diffusion length of vacancies in a-Si. The Er concentration profiles in Si implanted with both erbium and oxygen ions are analyzed in the context of the model. It shown that, in the case of high doses of implantation of rare-earth ions, it is necessary to take into account the formation of R_m clusters (m = 4), where R denotes the atom of a rare-earth element, whereas, if oxygen ions are also implanted, formation of the complexes RO_n (n = 3–6) should be taken into account; these complexes affect the transition-layer thickness and segregation coefficient.     

Effects of predoping and implantation conditions on diffusion of silicon in gallium arsenide subjected to electron-beam annealing

Measurements of capacitance-voltage characteristics and Rutherford backscattering were used to study the parameters of silicon diffusion from preliminarily formed n-type layers into semi-insulating GaAs under electron-beam annealing and conventional heat treatment. The layers were doped with either sulfur or silicon. The degree of ²⁸Si electrical activation and ²⁸Si diffusion coefficient are found to depend on the dopant used to form the n-type layer and on the implantation conditions (continuous or pulsed-repetitive, with a pulse width of 1.3×10^?2 s and duty factor of 100).     

Characterization of hafnium oxide grown on silicon by atomic layer deposition: Interface structure

Ultra-thin films of hafnium oxide deposited on Si(1 0 0) substrates by means of atomic layer deposition using tetrakis(diethylamino)hafnium as the hafnium precursor are characterized. These films and interface structures are probed using Fourier transform infrared spectroscopy along with Z-contrast imaging and electron energy loss spectroscopy (EELS) of a scanning transmission electron microscope. The interface structure of HfO₂/Si(1 0 0) is further investigated using angle resolved X-ray photoelectron spectroscopy to probe the core level orbitals (Hf 4f, Si 2p, O 1s) at high resolution. The interfacial differences are also examined by probing the Hf 4f bonding with normal incidence XPS in thin and thick films. The XPS studies show that the binding energies remain unchanged with film depth and that there is no apparent signature of silicate structure in the as-deposited films. EELS spectra taken at the interface and XPS measurements suggest the interface is mainly silicon oxide. Two different cleaning methods used show difference only in the thickness of the silicon oxide interlayer.     

Influence of AlN buffer layer thickness on the properties of GaN epilayer on Si(1 1 1) by MOCVD

The effect of thickness of the high-temperature (HT) AlN buffer layer on the properties of GaN grown on Si(1 1 1) has been investigated. Optical microscopy (OM), atomic force microscopy (AFM) and X-ray diffraction (XRD) are employed to characterize these samples grown by metal-organic chemical vapor deposition (MOCVD). The results demonstrate that the morphology and crystalline properties of the GaN epilayer strongly depend on the thickness of HT AlN buffer layer, and the optimized thickness of the HT AlN buffer layer is about 110 nm. Together with the low-temperature (LT) AlN interlayer, high-quality GaN epilayer with low crack density can be obtained.