Quantum-confinement effect in silicon-on-insulator films implanted with high doses of hydrogen ions

280-nm-thick silicon-on-insulator films are implanted with high doses of hydrogen with the energy 24 keV and the dose 5 × 10¹⁷ cm^?2. Peaks corresponding to optical phonons localized in the silicon nanocrystals 1.9?C2.5 nm in size are observed in the Raman spectra. The fraction of the nanocrystal phase is ??10%. A photoluminescence band with a peak at about 1.62 eV is detected. The intensity of the 1.62 eV band nonmonotonically depends on the measurement temperature in the range from 88 to 300 K. An increase in the radiative recombination intensity at temperatures <150 K is interpreted in the context of a two-level model for the energy of strongly localized electrons and holes. The activation energy of photoluminescence enhancement is 12.4 meV and corresponds to the energy of splitting of the excited state of charge carriers localized in the silicon nanocrystals.     

Special features of photoluminescence in silicon-on-insulator structures implanted with hydrogen ions

The special features of photoluminescence spectra of silicon-on-insulator structures implanted with hydrogen ions are studied. An increase in the photoluminescence intensity with increasing hydrostatic pressure P during annealing and the formation of narrow periodic photoluminescence peaks in the spectral range from ～500 to 700 nm are revealed for the structures annealed at P > 6 kbar. It is shown that the fine structure of the photoluminescence spectra correlates with the slowing-down of hydrogen effusion from the implanted samples and with the suppression of the formation of hydrogen microbubbles in the surface layer. These processes promote the formation of an optical resonator, with the mirrors formed by the “silicon-on-insulator-air” and “silicon-on-insulator-SiO₂” interfaces and with the optically active layer formed by hydrogen ion implantation and subsequent annealing.     

Effect of hydrostatic pressure during the annealing of silicon-on-insulator films implanted with a high hydrogen-ion dose

The properties of silicon-on-insulator films implanted with high hydrogen-ion doses (～50 at %) and annealed under a pressure of 10.5 kbar are studied using the Raman scattering (RS) method. A high degree of optical-phonon localization is detected in the films under study, which is retained to an annealing temperature of ～1000°C and is explained by the formation of silicon nanocrystals. It is found that the activation energy of annealing of the structural relaxation of dangling bonds in films with a high hydrogen content is independent of the annealing pressure. The activation energy of growth of the crystalline phase, calculated from RS spectra is ～1.5 eV and is independent of pressure. The effect of hydrostatic pressure consists only in a decrease in the frequency factor limiting Si-Si bond relaxation during ordering.     

Rapid thermal annealing of gallium arsenide implanted with sulfur ions

Sulfur ions were implanted into semi-insulating GaAs. A SiO₂ film was deposited by either of two methods onto the implanted surface. The samples were then subjected to either rapid thermal annealing (using halogen lamps) for 10–12 s at 805°C or to conventional thermal annealing for 30 min at 800°C. The content of GaAs components in the film was determined from the spectra of Rutherford backscattering. The electron-concentration profiles were plotted using the measurements of the capacitance-voltage characteristics. It is shown that sulfur diffuses in two directions, i.e., towards the surface and into the GaAs bulk. The former process is stimulated by vacancies formed near the semiconductor surface during the deposition of SiO₂. The coefficients of the “volume” diffusion of S and of the diffusion of S towards the surface are two orders of magnitude larger upon rapid thermal annealing than upon conventional thermal annealing, with the degree of S activation also being higher.     

Transformation of interface states in silicon-on-insulator structures under annealing in hydrogen atmosphere

Changes induced by annealing the spectrum of states on a Si/SiO₂ interface obtained by direct bonding and on a Si(substrate)/〈thermal SiO₂〉 interface in silicon-on-insulator (SOI) structures were investigated by charge-related deep-level transient spectroscopy. The structures were formed by bonding silicon wafers and slicing one of the wafers along a plane weakened by hydrogen implantation. The SOI structures were annealed at 430°C for 15 min in hydrogen, which corresponded to the conventional mode of passivation of the Si/SiO₂-interface states. The passivation of interface states by hydrogen was shown to take place for the Si/〈thermal SiO₂〉 interface, as a result of which the density of traps substantially decreased, and the continuous spectrum of states was replaced by a band of states in the energy range E _c=0.1–0.35 eV within the entire band. For the traps on the bonded Si/SiO₂ interface, the transformation of the centers occurs; namely, a shift of the energy-state band is observed from E _c=0.17–0.36 to 0.08–0.22 eV. The trapping cross section decreases by about an order of magnitude, and the density of traps observed increases slightly.     

Magnetic ordering in crystalline Si implanted with Co ions with intermediate doses

Crystalline Si implanted with the 380-keV cobalt ions with the dose Φ = 10¹⁴?10¹⁶ cm^?2 is studied. The method of Rutherford backscattering is used to determine the Si amorphization threshold (Φ = 3 × 10¹⁴ cm^?2). A quasi-resonance anisotropic line with a width of approximately 170 mT is observed at a temperature of T = 78 K in the spectrum of the electron spin resonance of silicon implanted with Co⁺ ions with Φ ≥ 3 × 10¹⁴) cm^?2. A resonance signal of paramagnetic centers in amorphous Si regions (g = 2.0057 and δB = 0.74 mT) is observed against the background of the above line. A quasi-resonance line of the electron spin resonance related to Co atoms and intrinsic Si defects was not observed at T = 300 K.     

Rapid thermal annealing of ion implanted 6H-SiC by microwave processing

Rapid thermal processing utilizing microwave energy has been used to anneal N, P, and Al ion-implanted 6H-SiC. The microwaves raise the temperature of the sample at a rate of 200°C/min vs 10°C/min for conventional ceramic furnace annealing. Samples were annealed in the temperature range of 1400-1700°C for 2-10 min. The implanted/annealed samples were characterized using van der Pauw Hall, Rutherford backscattering, and secondary ion mass spectrometry. For a given annealing temperature, the characteristics of the microwave-annealed material are similar to those of conventional furnace anneals despite the difference in cycle time.     

真空还原制备的VO_2热致相变薄膜光学性质研究

本文对不同衬底制备的VO2 薄膜进行了表面形貌测试 ,对其红外透射光谱和Raman光谱进行了研究 ,并进行 370nm -90 0nm波段的光透射测试以及 90 0nm波长的热滞回线特性测试 ,表明所制备VO2 薄膜具有优良的热致相变光学特性 ,薄膜为纳米结构 ,并且结晶状态不同的薄膜其Raman谱位置有明显改变 ,室温时的红外光谱表现出较好的红外振动特性。讨论了薄膜结晶状态对Raman位移的影响以及VO2 薄膜的红外光谱     

Magnetism in SiC implanted with high doses of Fe and Mn

High concentrations (0.1–5 at.%) of Mn or Fe were introduced into the near-surface region (≤2000 Å) of 6H-SiC substrates by direct implantation at ～300°C. After annealing at temperatures up to 1000°C, the structural properties were examined by transmission electron microscopy (TEM) and selected-area diffraction pattern (SADP) analysis. The magnetic properties were examined by SQUID magnetometry. While the Mn-implanted samples were paramagnetic over the entire dose range investigated, the Fe-implanted material displayed a ferromagnetic contribution present at <175 K for the highest dose conditions. No secondary phases were detected, at least not to the sensitivity of TEM or SADP.     

Rapid thermal annealing of zirconia films deposited by spray pyrolysis

Zirconia (8 mol% yttria) (YSZ) amorphous layers were deposited by spray pyrolysis on Si oxidized substrates and crystallized by rapid thermal treatment in a home-made halogen lamps furnace. Uniform films were obtained by depositing up to six layers, followed by the thermal treatment. X-ray analysis showed that the cubic phase is obtained during the initial stage of the annealing process. No significant differences with increasing annealing time nor interaction between the YSZ film and the substrate were observed. Ionic conduction in air, with activation energies comparable to those of bulk YSZ ceramics, was observed. The electrical characteristics of the films make them suitable for microelectronics applications.     

Silicon nanocrystal formation upon annealing of SiO2 layers implanted with Si ions

The formation of silicon nanocrystals in SiO₂ layers implanted with Si ions was investigated by Raman scattering, X-ray photoelectron spectroscopy, and photoluminescence. The excess Si concentration was varied between 3 and 14 at. %. It was found that Si clusters are formed immediately after implantation. As the temperature of the subsequent annealing was raised, the segregation of Si accompanied by the formation of Si-Si₄ bonds was enhanced but the scattering by clusters was reduced. This effect is attributed to the transformation of loosely packed clusters into compact, separate-phase nanoscale Si precipitates, with the Raman peak observed at 490 cm^?1 being related to surface scattering. The process of Si segregation was completed at 1000°C. Nevertheless, characteristic nanocrystal photoluminescence was observed only after annealing at 1100°C. Simultaneously, scattering in the range 495–520 cm^?1, typical of nanocrystals, appeared; however, the “surface-related” peak at 490 cm^?1 persisted. It is argued that nanocrystals are composed of an inside region and a surface layer, which is responsible for their increased formation temperature.     

Properties of silicon implanted with boron ions through thermal silicon dioxide

The properties of silicon implanted with boron ions through thermal SiO₂ films were studied using sheet resistivity measurements (corroborated by Hall data). Electrical properties for implants through 0.1 μm of SiO₂, as compared to bare silicon, showed no unusual behavior as a function of anneal temperature. Sheet resistivity measurements as a function of SiO₂ thickness for fixed ion energy, and as a function of energy for fixed oxide thickness were made after 525 and 925°C anneals, for boron doses of 10¹³, 10¹⁴ and 10¹⁵ ions/cm². The profile of boron ions in SiO₂ is near Gaussian for the energy range investigated and the stopping power is 0 to 20% lower than the theoretical value currently in the literature. Considerations for device manufacture are discussed in light of the results.     

Bonding and thermal stability of implanted hydrogen in silicon

The behavior of implanted hydrogen in Si has been investigated by differential infrared transmittance measurements using multiple-internal-reflection (MIR) plates. Si-H bonding of implanted hydrogen is detected by seven absorption bands between 4.5 and 5.5 μm after implantation with 10¹⁶ H⁺/cm² at ion energies between 70 and 400 keV. The absorption bands are close in frequency to those for SiH stretching modes for silane, and they are produced only by hydrogen implantation. Implantation with deuterium gave absorption bands shifted to lower frequencies in accord with the square root of the reduced mass ratio for Si-H relative to Si-D. The multiplicity of hydrogen-associated bands is apparently a consequence of defects in the implanted layer. A dependence of the hydrogen-associated bands on the disorder is suggested by the annealing loss of five of the initial seven bands, and a growth of the other two, for the same temperatures (100–300°C) as those for annealing out the broad divacancy band at 1.8 μm. A disorder dependence of the Si-H vibrational frequencies is further demonstrated by a regeneration of the bands annealing below 300°C when a hydrogen-implanted MIR plate annealed at 300°C was subsequently bombarded with neon. In addition to the seven resolved bands after H⁺ implantation, five other bands in the same range of frequencies grow in and anneal out between 100 and 700°C. Annealing at 700°C eliminates all SiH bands, and they cannot be regenerated by bombardment with other ions. It is suggested that implanted hydrogen in Si is bonded at defect sites, and that a loss of an SiH band is caused by either a change in charge state of a defect or by the loss of a defect. This work was supported by the United States Atomic Energy Commission     

Short-wavelength photoluminescence of SiO2 layers implanted with high doses of Si+, Ge+, and Ar+ ions

The short-wavelength (400–700 nm) photoluminescence (PL) spectra of SiO₂ layers implanted with Si⁺, Ge⁺, and Ar⁺ ions in the dose range 3.2×10¹⁶–1.2×10¹⁷ cm⁻² are compared. After Ar⁺ implantation an extremely weak luminescence, which vanishes completely after annealing for 30 min at 400 °C or 20 ms at 1050 °C, was observed. After implantation of group-IV elements the luminescence intensities were 1 to 2 orders of magnitude higher, and the luminescence remained not only with annealings but it could also increase. The dose and heating dependences of the luminescence show that it is due to the formation of impurity clusters and this process is more likely to be of a percolation than a diffusion character. For both group-IV impurities an intense blue band and a weaker band in the orange part of the spectrum were observed immediately after implantation. The ratio of the excitation and emission energies of the blue luminescence is characteristic of oxygen vacancies in SiO₂; its properties are determined by the direct interaction of group-IV atoms. On this basis it is believed that the centers of blue PL are chains of Si (or Ge) atoms embedded in SiO₂. The orange luminescence remained after annealings only in the case of Si⁺ implantation. This is attributed directly to the nonphase precipitates of Si in the form of strongly developed nanometer-size clusters. Fiz. Tekh. Poluprovodn. 32, 439–444 (April 1998)     

Formation of photoluminescence centers during annealing of SiO2 layers implanted with Ge ions

Photoluminescence (PL), Raman scattering, and the Rutherford backscattering of α-particles were used to study the formation of the centers of radiative-recombination emission in the visible region of the spectrum on annealing of the SiO₂ layers implanted with Ge ions. It was found that the Ge-containing centers were formed in the as-implanted layers, whereas the stages of increase and decrease in the intensities of PL bands were observed following an increase in the annealing temperature to 800°C. The diffusion-related redistribution of Ge atoms was observed only when the annealing temperatures were as high as 1000°C and was accompanied by formation of Ge nanocrystals. However, this did not give rise to intense PL as distinct from the case of Si-enriched SiO₂ layers subjected to the same treatment. It is assumed that, prior to the onset of Ge diffusion, the formation of PL centers occurs via completion of direct bonds between the neighboring excess atoms, which gives rise to the dominant violet PL band (similar to the PL of O vacancies in SiO₂) and a low-intensity long-wavelength emission from various Ge-containing complexes. The subsequent formation of centers of PL with λ_m～570 nm as a result of anneals at temperatures below 800°C is explained by agglomeration of bonded Ge atoms with formation of compact nanocrystalline precipitates. The absence of intense PL following the high-temperature anneals is believed to be caused by irregularities in the interfaces between the formed Ge nanoc-rystals and the SiO₂ matrix.     

Microstructure and electrical properties of high power laser thermal annealing on inkjet-printed Ag films

In this work, a high power continuous-wave (CW) Nd:YAG laser was used for thermal treatment of inkjet-printed Ag films - resulting in the elimination of organic additives (dispersant, binder, and organic solvent) in the Ag ink and annealing of Ag nano-particles. By optimizing laser parameters such as laser power and defocusing value, the laser energy can be totally converted into heat energy, which is used for thermal treatment of inkjet-printed Ag films. This results in the microstructure and the resistivity of the films to be controlled. We investigated the thermal diffusion mechanisms during laser annealing and the resulting microstructures. The impact of high power laser annealing on microstructures and electrical characteristics of inkjet-printed Ag films was compared to those of the films annealed by a conventional furnace annealing. Focused ion beam (FIB) channeling images show that the laser annealed Ag films have large columnar grains and a dense void-free structure, while furnace annealed films have much smaller grains and exhibit void formation. As a result, the laser annealed films have better electrical properties (low resistivity) compared to furnace annealed samples.     

Role of thermal annealing on SiGe thin films fabricated by PECVD

Amorphous Silicon Germanium (a-SiGe) thin films of 500 nm thickness are deposited on silicon substrates using Plasma Enhanced Chemical Vapour Deposition (PECVD). To obtain polycrystalline nature of films, thermal annealing is done at various temperature (450–600 °C) and time (1–10 h). The surface morphology of the pre- and post-annealed films is investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The crystallographic structure of the film is obtained by X-ray diffraction method. Raman spectroscopy is carried out to quantify the Ge concentration and the degree of strain relaxation in the film. Nano-indentation is performed to obtain the mechanical properties of the film. It is found that annealing reduces the surface roughness of the film and increases the Ge concentration in the film. The grain size of the film increases with increase in annealing temperature. The grain size is found to decrease with increase in annealing time up to 5 h and then increased. The results show that 550 °C for 5 h is the critical annealing condition for variation of structural and mechanical properties of the film. Recrystallization starts at this condition and results in finer grains. An increase in hardness value of 7–8 GPa has been observed. Grain growth occurs above this critical annealing condition and degrades the mechanical properties of the film. The strain in the film is only relaxed to about 55% even for 10 h of annealing at 600 °C. Transmission Electron Microscopy (TEM) observations show that the strain relaxation occurs by forming misfit dislocations and these dislocations are confined to the SiGe/Si interface.     

Formation of nanocrystalline silicon films using high-dose H<Superscript>+</Superscript> ion implantation into silicon-on-insulator layers with subsequent rapid thermal annealing

The formation of nanocrystalline Si films as a result of rapid thermal annealing of silicon-on-insulator structures implanted with high doses of H⁺ ions is studied. It is ascertained that the process of formation of Si nanocrystals is active even at temperatures of 300–400°C and is controlled by the hydrogen content in the silicon film and by the duration of annealing. It is concluded that the formation of nuclei of the crystalline phase occurs in silicon islands surrounded by microvoids and is caused by the ordering of Si-Si bonds in the course of release of hydrogen from the bound state. It is important that microvoids do not coalesce at temperatures up to ～900°C in conditions of rapid thermal annealing. It is found that synthesized films exhibit luminescence in the green-orange region of the spectrum at room temperature.     

Dynamics of nonequilibrium gratings induced in silicon films by femtosecond laser pulses

Relaxation of the dynamic gratings formed by nonequilibrium charge carriers in thin single-crystal silicon films during femtosecond laser excitation was studied. The case of the ultimate concentration of carriers (N≈10²¹ cm^?3) is considered. Ambipolar diffusion and Auger recombination contributions to the grating decay are estimated. The observation of a long-lived grating at pump intensity above 5×10¹¹ W/cm² is reported.     

Redistribution of Al in implanted SiC layers as a result of thermal annealing

The experimental Al concentration profiles formed on implantation of Al into SiC at room temperature with subsequent high-temperature annealing are analyzed. It is shown that, at doses above the amorphization threshold, the profiles exhibit a number of specific features: a shift of the maximum of the distribution, accumulation of dopants at the surface, and formation of box-shaped profiles. To describe quantitatively the redistribution of Al dopants in the SiC layers implanted with high doses, the segregation-diffusion model is suggested for the first time. The model takes into account segregation of dopants between the α and c phases during solid-state epitaxial crystallization followed by diffusion of dopants and their evaporation from the surface The formation of box-shaped Al profiles as a result of short-term thermal annealing is attributed to the origination of highly damaged single-crystal and polycrystalline SiC layers in the recrystallized region, with a high diffusion coefficient of dopants, and to the suppression of the enhanced transient diffusion in the remaining single-crystal part of the implanted layer.