Evolution of microstructure during annealing of low-dose SIMOX wafers implanted at 65 keV

The microstructural changes that occur during annealing of ultra-thin oxygen-implanted silicon-on-insulator have been studied using transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and Auger electron spectroscopy (AES). Silicon substrates were implanted at 65 keV with a dose of 4.5×10¹⁷ O⁺ cm^–2, followed by annealing at various temperatures. TEM results show that the defects observed in the as-implanted material (stacking faults and {1 1 3} defects) were reduced after annealing at 900 °C for 2 h and were eliminated after annealing at 1100 °C for 2 h. A continuous buried oxide (BOX) layer was formed after annealing at 1300 °C for 6 h. Numerous silicon islands were present in the BOX layer. The silicon islands can be traced to a precursor structure that developed at the implantation step. RBS results indicate that the crystallinity of the top Si layer is significantly restored after annealing at 1100 °C for 2 h and is completely restored after annealing at 1300 °C for 6 h. It was also found through AES analysis that the redistribution of oxygen during annealing is initiated at 1100 °C.     

HI-ERDA, Micro-Raman and HRXRD studies of buried silicon oxynitride layers synthesized by dual ion implantation

Silicon oxynitride (Si_xO_yN_z) buried insulating layers were synthesized by dual implantation of nitrogen (¹⁴N⁺) and oxygen (¹⁶O⁺) ions sequentially into single crystal silicon in the ratio 1:1 at 150 keV to ion-fluences ranging from 1 × 10¹⁷ to 5 × 10¹⁷ cm⁻². Heavy ion elastic recoil analysis (HI-ERDA) studies of as implanted samples show Gaussian like distributions of nitrogen and oxygen. After annealing at 800 °C, both the nitrogen and oxygen distributions appear as flat plateau like regions near projected range showing the formation of a continuous buried oxynitride layer. Micro-Raman study of as implanted samples shows a broad peak at 480 cm⁻¹ for all fluences. It signifies a complete amorphization of silicon due to high fluence implantation. The annealing at 800 °C results in the reduction of the intensity of the broad peak observed at 480 cm⁻¹ and also gives rise to an additional peak at 517 cm⁻¹. It shows partial recrystallization of damaged silicon due to annealing. The X-ray rocking curves studies from high-resolution X-ray diffraction (HRXRD) of the samples implanted with different fluences have also further confirmed partial recrystallization of damaged silicon on annealing.     

Dependence of photoluminescence and electrical properties with rapid thermal annealing in nitrogen-implanted ZnO films

Undoped (as-grown) ZnO films grown by pulsed laser deposition on Al₂O₃ (0001) substrates were doped with nitrogen by means of an ion implantation process. Post-implantation annealing behavior in the temperature range between 500 and 700 °C has been studied by photoluminescence and Hall effect measurements. The implanted films show no peak other than the excitonic recombination emission in the as-implanted state, however, after rapid thermal annealing at 700 °C they reveal a nitrogen acceptor related emission at 3.273 eV. The as-implanted ZnO films show more electron concentrations than the as-grown, unimplanted ZnO film. In contrast, after annealing, the electron concentration in the implanted films is significantly reduced, indicating that the incorporated nitrogen becomes activated after the thermal annealing, then produces holes and eventually compensates for certain amount of electrons. The results imply that a proper nitrogen implantation and subsequent annealing may be a way to produce p-type ZnO films.     

Optical and nuclear characterization of Xe-induced nanoporosity in SiO2

We performed RBS, infrared (IR) and C-V measurements in order to follow the evolution of Xe, bubbles/cavities and other defects (with a focus on NBOHC: non-bridging oxygen hole center) and dielectric constant (k), in high dose Xe implantation in SiO₂. As-implanted sample provides the lowest value of k which increases with post thermal annealing. In the meantime, the concentration of negatively charged defects decreases with annealing while Xe out-diffuses after annealing at 1100 °C leaving Xe free cavities in the sample. By combining these results one can determine the contribution of nanoporosity in dielectric constant evolution.     

Tuned photoluminescence from Si-implanted SiO2 films with rapid and conventional thermal annealing

In this study, by using a conventional thermal annealing (CTA), the obviously near-infrared shift and intensity amplification of room-temperature photoluminescence (PL) spectrum could be observed from the 3 × 10¹⁶ cm⁻² Si⁺-implanted 400-nm-thick SiO₂ films after rapid thermal annealing (RTA) at 1150 °C in dry nitrogen. For isothermal RTA durations ≥20 s at the heating rate of 100 °C/s, the PL peaks from the only RTA-treated films were detected around 1.7 eV and, for 1050 °C CTA durations between 1 and 3 h, no significant PL could be found from the only CTA-treated films. However, when annealing the RTA-treated films with the CTA for only 1 h, then, we varied the terminal PL-peak from 1.7 to 1.5 eV and obviously increased their respective intensities from the films. These results are attributed to the variation of silicon nano-crystals embedded in SiO₂ film.     

Optical properties of ion-implanted silicon and separation by implantation of oxygen silicon-on-insulator substrates in the infrared: Study of B and P2 implantation doping

The optical properties of ion implanted silicon and silicon-on-insulator substrates have been studied by Fourier transform infrared spectroscopy. The influence of the implanted-ion mass in changing the refractive index of a silicon target has been examined by implanting 80 keV ¹¹B⁺ and ⁶²P₂⁺ ions respectively. A refractive index rise not exceeding 2% and total amorphization were observed respectively in the vicinity of the Si surface after boron and phosphorous implantations. Free carrier profiles generated after thermal annealing at 950 °C/30 min and 1150 °C/120 min were modeled by Pearson and half-Gaussian distributions respectively. The phosphorous implantation was also performed in silicon-on-insulator substrates, yielding after annealing nearly homogeneous free-carrier profiles in the top-Si layer and optical mobility values comparable to those of bulk-Si.     

NEXAFS and XPS study of GaN formation on ion-bombarded GaAs surfaces

Interaction of low-energy nitrogen ions (0.3-2 keV N₂⁺) with GaAs (100) surfaces has been studied by X-ray photoemission spectroscopy (XPS) around N 1s and Ga 3d core-levels and near-edge X-ray absorption fine structure (NEXAFS) around the N K-edge, using synchrotron radiation. At the lowest bombardment energy, nitrogen forms bonds with both Ga and As, while Ga-N bonds form preferentially at higher energies. Thermal annealing at temperatures above 350 °C promotes formation of GaN on the surface, but it is insufficient to remove disorder introduced by ion implantation. We have identified nitrogen interstitials and anti-sites in NEXAFS spectra, while interstitial molecular nitrogen provides a clear signature in both XPS and NEXAFS. The close similarity between NEXAFS spectra from thin GaN films and ion-bombarded GaAs samples supports our proposition about formation of thin GaN films on ion-bombarded GaAs.     

Structural and electrical characterization of TiO2 films grown by spray pyrolysis

The sol-gel spray pyrolysis method was used to grow TiO₂ thin films onto silicon wafers at substrate temperatures between 315 and 500 °C using pulsed spray solution feed followed by annealing in the temperature interval from 500 to 800 °C in air. According to FTIR, XRD, and Raman, the anatase/rutile phase transformation temperature was found to depend on the film deposition temperature. Film thickness and refractive index were determined by Ellipsometry, giving the refractive indexes of 2.1-2.3 and 2.2-2.6 for anatase and rutile, respectively. According to AFM, film roughness increases with annealing temperature from 700 to 800 °C from 0.60 to 1.10 nm and from 0.35 to 0.70 nm for the films deposited at 375 and 435 °C, respectively. The effective dielectric constant values were in the range of 36 to 46 for anatase and 53 to 70 for rutile at 10 kHz. The conductivity activation energy for TiO₂ films with anatase and rutile structure was found to be 100 and 60 meV, respectively.     

Investigation of microstructure and chemical composition of Ni contacts to n-type 4H–SiC

Structure and chemical compositions of the interface layer obtained after nickel deposition on silicon carbide surface and subsequent annealing have been analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray diffraction (XRD) and Raman spectroscopy. Nickel silicide (Ni₂Si) were characterized as the main product of reaction between nickel and silicon carbide after annealing at temperatures range 700–1000 °C. Raman spectroscopy and TOF-SIMS profiling results confirmed carbon precipitation within contact layer. Obtained results indicate graphitic form of carbon and its non-uniform distribution in the contact layer. Moreover, TOF-SIMS analysis showed modification of nitrogen distribution in the contact area upon Ni/SiC contact annealing.     

Thermal stability of advanced gate stacks consisting of a Ru electrode and Hf-based gate dielectrics for CMOS technology

Metallic Ru and Hf-based dielectrics such as HfO₂, HfSiO_x and HfSiON, are promising materials for the gate electrode and gate dielectrics, respectively. This paper reports on the thermal stability of gate stack systems comprised of Ru/Hf-based dielectrics. Layers of both types of material were prepared on Si substrate by metal-organic chemical vapour deposition (MOCVD). The stacks underwent exposure by rapid thermal annealing (RTA) in pure nitrogen ambience at temperatures 800, 900, and 1000 °C for 10 s. The samples were analysed using Rutherford backscattering spectrometry (RBS). Small changes were found in the stacks treated at 800 and 900 °C. The most stable stack was found to be one with a HfSiON dielectric layer, which was resistant also at temperature 900 °C. However, the annealing at 1000 °C induced massive diffusion at both interfaces for all types of stack. The results imply a limited thermal stability of the Ru/Hf-based dielectric gate stacks during the source/drain activation step.     

Practical realization of dual-gate-oxide technology concept using ultra-shallow nitrogen r.f. plasma implantation with plasma and thermal oxidation

In mixed logic/memory circuits manufactured as a system on chip, two different thicknesses of dielectric layers are required. Simultaneous formation of both layers is possible if oxidation of a silicon layer is preceded by local nitrogen implantation, since the rate of oxidation depends on the nitrogen implantation dose and its profile.Experiments presented in this work show a possibility and an attempt of practical realization of controlling a very thin dielectric layer's thickness by preceding the oxidation with an ultra-shallow nitrogen implantation from r.f. plasma.As opposed to the methods presented in the literature so far, where classical implanters or the ion immersion implantation plasma (IIIP) technique were used for ultra-shallow implantation, our process is performed in a typical PECVD planar plasma reactor.The r.f. plasma nitrogen implantation has been carried out from NH₃ plasma and then immediately followed by the thermal- or plasma-oxidation process.The electrophysical properties of the obtained layers and systems (ultrathin dielectric layer, silicon) were characterized by electrical methods. Results of ellipsometric, XPS and ULE-SIMS measurements are also presented and discussed.     

Internal oxidation of Mo-Ru coatings

The current experiment deposits Mo-Ru coatings with a Ti interlayer on silicon wafers by sputtering at 400 °C. The annealing treatments were conducted at 600 °C under atmospheres consisting of controlled oxygen contents with balanced nitrogen. After annealing in a 10 ppm O₂-N₂ atmosphere, surface roughness increased, apparently due to the formation of external island oxides. While annealing in a 220 ppm O₂-N₂ atmosphere, the relatively smooth surface was accompanied by the internal oxidation zone consisting of alternated oxygen rich and deficient layers.     

Visible light emission from silicon dioxide with silicon nanocrystals

An electroluminescent MOS structure was developed using silicon wafers covered by thermal silicon dioxide containing silicon nanocrystals. Efficiency of the structure was sufficient for observation to be possible with the naked eye in daylight conditions under DC polarization. Silicon nanocrystals were produced using silicon ion implantation followed by subsequent annealing at 1100 °C in a nitrogen atmosphere. Three separate bands of emitted light at wavelengths of ∼400-500 nm (blue), ∼500-600 nm (green), and ∼650-850 nm (red) were observed and found to be related to specific regions of the implanted silicon concentration profile. For a single energy implant, each of the emitted light bands originated from a separate depth region of the silicon dioxide layer containing silicon nanocrystals. The spectrum of the emitted light was found to depend on the excess silicon concentration profile. For practical applications, the color of the emitted light can be controlled by adjustment of the implantation parameters and MOS structuring process.     

Role of La0.5Sr0.5CoO3 template layers on dielectric and electrical properties of pulsed-laser ablated Pb(Nb2/3Mg1/3)O3-PbTiO3 thin films

Relaxor ferroelectric thin films of 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-PT) deposited on platinized silicon substrates with and without template layers were studied. Perovskite phase (80% by volume) was obtained through proper selection of the processing conditions on bare Pt/Ti/SiO₂/Si substrates. The films were initially grown at 300 °C using pulsed-laser ablation and subsequently annealed in a rapid thermal annealing furnace in the temperature range of 750-850 °C to induce crystallization. Comparison of microstructure of the films annealed at different temperatures showed change in perovskite phase formation and grain size etc. Results from compositional analysis of the films revealed that the films initially possessed high content of lead percentage, which subsequently decreased after annealing at temperature 750-850 °C. Films with highest perovskite content were found to form at 820-840 °C on Pt substrates where the Pb content was near stoichiometric. Further improvement in the formation of perovskite PMN-PT phase was obtained by using buffer layers of La_0.5Sr_0.5CoO₃ (LSCO) on the Pt substrate. This resulted 100% perovskite phase formation in the films deposited at 650 °C. Dielectric studies on the PMN-PT films with LSCO template layers showed high values of relative dielectric constant (3800) with a loss factor (tan δ) of 0.035 at a frequency of 1 kHz at room temperature.     

Microstructure and electrical properties of Al2O3-ZrO2 composite films for gate dielectric applications

Al₂O₃-ZrO₂ composite films were fabricated on Si by ultrahigh vacuum electron-beam coevaporation. The crystallization temperature, surface morphology, structural characteristics and electrical properties of the annealed films are investigated. Our results indicate that the amorphous and mixed structure is maintained up to an annealing temperature of 900 °C, which is much higher than that of pure ZrO₂ film, and the interfacial oxide layer thickness does not increase after annealing at 900 °C. However, a portion of the Al₂O₃-ZrO₂ film becomes polycrystalline after 1000 °C annealing and interfacial broadening is observed. Possible explanations are given to explain our observations. A dielectric constant of 20.1 is calculated from the 900 °C-annealed ZrO₂-Al₂O₃ film based on high-frequency capacitance-voltage measurements. This dielectric characteristic shows an equivalent oxide thickness (EOT) as low as 1.94 nm. An extremely low leakage current density of ∼2×10⁻⁷ A/cm² at a gate voltage of 1 V and low interface state density are also observed in the dielectric film.     

Effect of annealing on the electrical and optical properties of electron beam evaporated ZnO thin films

Zinc oxide thin films have been grown on (100)-oriented silicon substrate at a temperature of 100 °C by reactive e-beam evaporation. Structural, electrical and optical characteristics have been compared before and after annealing in air by measurements of X-ray diffraction, real and imaginary parts of the dielectric coefficient, refractive index and electrical resistivity. X-ray diffraction measurements have shown that ZnO films are highly c-axis-oriented with a full width at half maximum (FWMH) lower than 0.5°. The electrical resistivity increases from 10⁻² Ω cm to reach a value about 10⁹ Ω cm after annealing at 750 °C. The FWHM decreases after annealing treatment, which proves the crystal quality improvement. Ellipsometer measurements show the improvement of the refractive index and the real dielectric coefficient after annealing treatment at 750 °C of the ZnO films evaporated by electron beam. Atomic force microscopy shows that the surfaces of the electron beam evaporated ZnO are relatively smooth. Finally, a comparative study on structural and optical properties of the electron beam evaporated ZnO and the rf magnetron deposited one is discussed.     

Effect of post-annealing treatment in oxygen on dielectric properties of K0.5Na0.5NbO3 thin films prepared by chemical solution deposition

K_0.5Na_0.5NbO₃ thin films were prepared on Pt/Ti/SiO₂/Si substrates by chemical solution deposition method with different annealing temperatures of 550 °C, 600 °C, 700 °C. The post-annealing treatment was introduced at 550 °C for 3 min in oxygen ambient. It is found that the films were composed of pure provskite phase, and the post-annealing treatment promoted the crystallization and improved the quality of the films, which resulted in the enhancement of the dielectric property of the films. The effect of the post-annealing on the dielectric properties of the films was also discussed.     

Thermal evolution and optical properties of Cu nanoparticles in SiO2 by ion implantation

SiO₂ samples were implanted by 45 keV Cu ions at a dose of 1 × 10¹⁷ /cm², and subjected to furnace annealing at temperatures ranging from 200 to 600 °C in nitrogen atmosphere. The results indicate that the Cu nanoparticles have been synthesized by Cu ion implantation, and subsequent annealing induces the diffusion and nucleation of nanoparticles partially. The results from XPS measurements show that the Cu⁰ is the dominate charge state in the implanted and subsequent annealed samples. With increasing annealing temperature, the size and distribution of Cu nanoparticles have been modified gradually. The surface plasmon resonance (SPR) of Cu nanoparticles at 570 nm has been observed by optical transmission spectroscopy. The strongest SPR signal at 400-600 °C indicates that lots of Cu nanoparticles have grown and show good optical properties. Moreover, the luminescence has been investigated in Cu implanted and subsequent annealed samples. Possible luminescence mechanisms, such as radiation induced defects, Cu (ions or atoms) related luminescence centers, etc., have been discussed.     

Preparation of phosphorus-containing silica glass for radiotherapy by co-implantation of phosphorus and nitrogen ions

P-31 can be activated to -emitter P-32 with 14.3 days half-life by neutron bombardment. A chemically durable glass containing a large amount of phosphorus is believed to be useful for in situ irradiation of cancers. When they are subjected to neutron bombardment and injected around the tumor, they can irradiate directly a cancer without giving radiation to normal tissues. In this study, a pure silica glass was implanted with phosphorus and nitrogen ions by a dose of 5×10¹⁶ cm^-2 at 30 and 14 keV, respectively, and subjected to two-step heat treatments at 400°C in H₂ and then at 900°C in O₂. In the first step, phosphorus colloids were grown in the silica glass. In the second step, the colloids were encapsulated in a SiO₂–P₂O₅ glass film formed at their surfaces and the structural damage produced by ion implantation was healed. It is speculated that the implanted nitrogen forms silicon oxynitride in the glass, strengthening the silica network and suppressing the evaporation of phosphorus during heat treatment. The prepared glass did not dissolve phosphorus or silicon, even after soaking in distilled water at 95°C for 7 days, and hence is believed to be useful for radiotherapy of cancers.     

Effect of annealing temperature on growth of Ce-ZnO nanocomposite thin films: X-ray photoelectron spectroscopy study

Ce-doped ZnO nanocomposite thin films with Ce/Zn ratio fixed at optimum value (10 at.%) have been prepared via sol-gel method at different annealing temperatures varied from 180 to 500 °C. The synthesized samples were characterized employing atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) techniques. According to AFM analysis, the average grain size increased from about 70 nm to 150 nm by increasing the annealing temperature from 300 to 500 °C. Moreover, based on the XPS data analysis, it was found that three major metal ions namely Ce³⁺, Ce⁴⁺, and Zn²⁺ coexist on the surface of the nanocomposite films. XPS data analysis also revealed that Ce³⁺ ion is oxidized to Ce⁴⁺ ion with increasing annealing temperature. Due to oxidation, the ratio of [Ce^3±]/[Ce total] changed from 68.8 to 38.1% by increasing the annealing temperature from 180 to 500 °C. In addition, the Ce/Zn ratio increased from 0.21 to 0.42 when increasing the annealing temperature from 180 to 500 °C indicating migration of Ce ions toward the surface at higher temperatures. Finally, the XRD measurements determined that the ZnO thin films have a hexagonal wurtzite structure and CeO₂ crystallites are formed at 500 °C in the Ce-doped ZnO nanocomposite thin films.