High temperature high dose C ion implantation in epitaxial SiGe

Si_{1 − x}Ge_x epitaxial layers fully strained (x = 0.27) and relaxed (x = 0.55) have been implanted with C ions at 500°C. Implantation energy and doses were selected to obtain the C peak in the central region of the SiGe layer, with a concentration similar to the Ge content. The implanted layers have been analyzed by Raman scattering, X-ray diffraction, transmission electron microscopy and secondary ion mass spectroscopy. The data obtained show the direct synthesis of β-SiC precipitates aligned in relation to the SiGe lattice after the implantation, as well as a Ge enrichment and stress relaxation of the SiGe lattice. For the relaxed layer a significant Ge redistribution from the implanted region is observed.     

Characterization of Si/GexSi1 − x heterojunction bipolar transistors formed by Ge ion implantation in Si

Epitaxial Si/Ge_xSi_{1 − x} heterojunctions were formed by high dose Ge ion implantation in Si followed by rapid thermal annealing at 1000°C for 10 s. This technique was adopted to fabricate Si/Ge_xSi_{1 − x} heterojunction n-p-n bipolar transistors (HBT) using a self-aligned, double polycrystalline silicon process commonly used for fast Si bipolar transistors. The devices are characterized by a 60 nm wide neutral base with a Ge concentration peak of ≈ 7 at.% at the base-collector junction. Good static and dynamic electrical characteristics are demonstrated and discussed.     

Evaluation and control of defects, formed by keV-MeV implantation

Ion implantation has been used in shallow junction formation, well formation, buried layer formation, etc. Ultra-shallow junction formation at energies below several keV and gettering-sites formation at several MeV with a high dose have been investigated. However, problems for these applications are defect formation, which induces dopant-enhanced diffusion and junction leakage current increase. In this paper, two topics, related to these applications, are presented. The first topic is the evaluation of dopant-enhanced diffusion in source/drain formation by preamorphization. The second topic is the defect reduction in MeV implantation by RTA with a high ramping rate above 50°C/s. These results suggest that applications of ion implantation would spread in wider regions, if enhanced diffusion at ultra low energies and/or defect formation at MeV could be reduced.     

高剂量N^＋注入碳膜形成氮化碳CNx的研究

研究了利用高剂量的Ｎ＾＋注入碳膜形成氮化碳ＣＮｘ的可能性，对这种新材料进行了城叶变换红外吸收光谱、Ｘ射线光电子能说、Ｘ射线衍射和薄膜的维氏显微硬度等测量。结果表明，在１００ｋｅＶ高剂量Ｎ＾＋注入碳膜过程中形成了含有碳氮共价键成分的ＣＮｘ化合物。     

Photoluminescence induced by Si implantation into Si3N4 matrix

Up to the present, photoluminescence (PL) was obtained from near stoichiometric or amorphous Si nitride films (SiN_x) after annealing at high temperatures. As a consequence, the existence of PL bands has been reported in the 400–900 nm range. In the present contribution, we report the first PL results obtained by Si implantation into a stoichiometric 380 nm Si₃N₄ film. The Si excess is obtained by a 170 keV Si implantation at different temperatures with a fluence of Φ = 10¹⁷ Si/cm². Further, we have annealed the samples in a temperature range between 350 and 900 °C in order to form the Si precipitates. PL measurements were done using an Ar laser as an excitation source, and a broad PL band basically centered at 910 nm was obtained. We show that the best annealing condition is obtained at T_a = 475 °C for the samples implanted at 200 °C, with a PL yield 20% higher than the obtained at room temperature implantation. Finally, we have varied the implantation fluence and, consequently, the Si nanocrystals size. However, no variation was observed nor in the position neither in the intensity of the PL band. We concluded that the PL emission is due to radiative states at the matrix and the Si nanocrystals interface, as previously suggested in the literature.     

Real-time in situ study of hydrogen diffusion in amorphous Si formed by ion implantation

The diffusion of hydrogen in amorphous silicon formed by ion implantation is studied using real-time elastic recoil detection analysis. An activation energy for H diffusion of 1.82 eV is determined in a single ramped anneal. This activation energy is consistent with diffusion studies in the high H concentration regime. The low beam current employed is found to have a negligible influence on the H diffusion within the sensitivity of the measurement. Further refinements for increased accuracy of this technique are discussed.     

Stability of defects created by high fluence helium implantation in silicon

Stability of extended defects created by high fluence helium implantation (50 keV, 5 × 10¹⁶ cm⁻²) from room temperature to 800 °C has been studied using transmission electron microscopy. Our results clearly show that the cavities behave as good sinks for interstitial type defects generated during ion implantation, leading in some cases to the cavity dissolution. A three-dimensional “phase diagram” related to the formation and evolution of interstitial-type defects is also proposed. It is plotted in terms of quantity of damage, annealing time and implantation temperature.     

Characterization of high energy ion implantation into Ti-6Al-4V

Ion implantation is a surface modification process that can improve the wear, fatigue, and corrosion resistance for several metals and alloys. Much of the research to date has focused on ion energies less than 1 MeV. With this in mind, Ti-6Al-4V was implanted with Al²⁺, Au³⁺, and N⁺ ions at energies of 1.5 and 5 MeV and various doses to determine the effects on strengthening of a high energy beam. A post heat treatment on the specimens implanted with Al²⁺ samples was conducted to precipitate Ti_xAl type intermetallics near the surface. Novel techniques, such as nanoindentation, are available now to determine structure-mechanical property relationships in near-surface regions of the implanted samples. Thus, nanoindentation was performed on pre-implanted, as-implanted, and post heat treated samples to detect differences in elastic modulus and hardness at the sub-micron scale. In addition, sliding wear tests were performed to qualitatively determine the changes in wear performance. The effect of this processing was significant for samples implanted with Al²⁺ ions at 1.5 MeV with a dose higher than 1 × 10¹⁶ ions/cm² where precipitation hardening likely occurs and with N⁺ ions.     

高剂量注入中离子溅射的影响

在离子注入材料改性的研究过程中(金属、绝缘材料和光学材料等),在许多场合下,要求注入的元素(如Fe中注入N、Y、Ph和Sn等)在靶子中占百分之几的含量,这就要求注入剂量高达10~(17)/cm~2到10~(12)/cm~2。由于离子注入的溅射效应在低能和大剂量注入中是相当明显的,因此,对这些元素高剂量注入后的杂质分布、溅射系数、溅射厚度和靶子中杂质的收集量做一分析是十分重要的。     

Effect of forming gas anneals on the photoluminescence from nanocrystalline silicon formed by Si implantation into SiO2 matrix

The blue region of the room temperature photoluminescence spectrum from Si nanocrystallites formed in SiO₂ by Si⁺ ion implantation has been observed for the first time after annealing in a forming gas (10% H₂ + 90% N₂) ambient. Thermally grown SiO₂ on Si substrates were implanted with a dose of 2 × 10¹⁷ Si⁺ cm⁻² at energies of 200 keV and 400 keV. For reference purposes, quartz silica was implanted also with the same dose of 200 keV Si⁺ ions. The implanted samples were annealed in nitrogen and forming gas at 900°C for 3 to 180 min. Both the SiO₂ and quartz samples exhibited luminescence at about 380 nm which was weak, but detectable, before annealing. During extended anneals in forming gas, the intensity increased by a factor of about 2 above that recorded after a nitrogen anneal but the peak position was unchanged. The intensity was greater in samples annealed in forming gas which is due to the additional hydrogen. It would seem that this blue luminescence originates from new luminescent centres in the matrix caused by the Si⁺ ion implantation.     

离子注入SOI薄膜材料的制备及性能

ＳＯＩ－ＣＭＯＳ电路具有高速度、低功能、抗辐照等优点。用氧、氮离子注入硅中,得到性能良好的ＳＩＭＯＸ和ＳＩＭＮＩ薄膜材料。用扩展电阻、霍耳效应和深能级瞬态谱等多种方法研究了ＳＯＩ材料表面界面的电学性能。并对各种方法进行了讨论。结果显示,用分步注入和分步退火制备的ＳＯＩ材料大大地改善了材料的电学性能。     

EPR study of defects produced by MeV Ag ion implantation into silicon

The damage produced by implanting (1 1 1) Si wafers with 4 MeV Ag ions at implantation temperatures of 210, 350 and 400 K has been investigated by electron paramagnetic resonance as a function of implantation fluence in the range 5 × 10¹²–2 × 10¹⁵ Ag cm⁻². For each implantation temperature, at low ion fluences the EPR spectra show the presence of the point defect centres Si-P3 (neutral 4-vacancy) and Si-P6 (di-interstitial) as well the so-called Σ defect complexes. As the implantation fluence is raised the population of P3 centres goes through a maximum while the Σ centre resonance is gradually replaced by the spectrum of the well-known Si-D centre of a-Si. For implantation at 210 K the total Σ+D centre concentration increases linearly with implantation fluence up to the point at which an amorphous layer is formed; however raising the implantation temperature causes the dependence of the Σ+D concentration on implantation fluence to become increasingly sublinear with the result that the production of a given level of damage requires a larger implantation fluence. The results are discussed in the context of a previous study of the implantation damage in the same samples by optical reflectivity depth profiling [Mat. Res. Soc. Symp. Proc. 540 (1999) 31].     

Ohmic contacts on n-type layers formed in GaN/AlGaN/GaN by dual-energy Si ion implantation

Electrical properties of Si-implanted n-type GaN/AlGaN/GaN layers and contact resistances of ohmic electrodes (TiAl) formed on these layers have been examined. Experimental results have clearly shown that ohmic electrodes with a low specific-contact resistance of 1.4 × 10^?7 Ω cm² can be fabricated on the n-type layer having a low sheet resistance of 145 Ω/sq, which has been formed by the dual-energy Si ion implantation (80 keV:1.01 × 10¹⁵/cm² + 30 keV:1.6 × 10¹⁴/cm²) and subsequent annealing at 1200 °C for 2 min using a Si₃N₄ layer as an encapsulant.     

Thermal redistribution of Al implanted in Si: evidences for interactions with extended defects

Al was implanted at 180 keV to a dose of 4.5 × 10¹⁴ cm⁻². Various anneals were performed in the temperature range (900–1100°C), for times varying from 15 min up to several hours. The SIMS measurements reveal anomalous redistribution of the aluminium profiles. The bulk side of the profiles diffuses normally at a rate in agreement of the Al intrinsic diffusivity, but two peaks of apparently immobile atoms are formed near the surface. Cross observations by Transmission Electronic Microscopy (TEM) prove that there is no Al precipitation, and reveal the existence of two extended defects bands, the position of which is perfectly correlated with Al peaks. This strongly suggests that these peaks are due to Al trapping on the extended defects. First simulations also support this assumption.     

Birefringence in optical fibers formed by proton implantation

Birefringence can be induced in silica-based optical fibers by ion implantation. In the present research, protons were implanted in single-mode optical fibers with two different energies, one being the energy with which the protons can just reach the center of the optical fiber core and the other being a slightly lower energy. The degree of birefringence was evaluated by measuring reflection spectra of Bragg gratings formed at the proton-implanted region of the optical fibers. The results confirmed that birefringence is induced by unidirectional densification along the projected range of protons formed in the fiber core and by densification of the fiber cladding. The induced birefringence reached three to ten times higher than that of a conventional birefringent fiber. The birefringence caused by ion implantation can be a versatile tool for manufacturing various optical fiber devices.     

Temperature effect study of silicon-on-insulator structures prepared by high dose implantation of nitrogen

The temperature effect on the microstructure of the N⁺-ion implantation-induced Si₃N₄ buried layer was investigated. The underlying silicon nitride layers were formed in a Si (1 1 1) wafer after implantation of 50 keV nitrogen ions (fluence: 1 × 10¹⁷, 2 × 10¹⁷ and 5 × 10¹⁷ ions/cm²). It was observed that a continuous amorphous layer of about 200 nm thickness was formed in all implanted samples due to the irradiation damage. After 30 min annealing at 900 °C, poly-crystalline Si₃N₄ products were found by TEM examination in the specimen implanted with 5 × 10¹⁷ ions/cm² dose. In the case of annealing at 1200 °C a continuous single-crystalline α-Si₃N₄ buried layer was formed indicating that the amorphous layer in the implanted samples could be transformed into three successive layers, which are amorphous SiO₂, single-crystal α-Si₃N₄ and retained defects from surface to inner substrate, respectively.     

Temperature and dose dependences of nitrogen implantation into aluminium

It has been established that nitrogen implantation into metals can alter their surface properties such as friction, wear, corrosion, etc. Recent studies have shown that nitrogen implantation into aluminium leads to the formation of aluminium nitride which has interesting tribological, electronic and optical properties. For a given implantation energy, the characteristics of the nitrogen profile, e.g. thickness, shape and concentration, depend strongly on the experimental conditions during the implantation. In order to study the influence of the implantation parameters, aluminium samples have been bombarded with ¹⁵N⁺₂ of 100 keV to different doses ((1–20) × 10¹⁷ N⁺/cm²), at several temperatures (25–300° C). Distributions of the implanted species were investigated by nuclear reaction analysis (NRA) and by Rutherford backscattering spectroscopy (RBS). The chemical bonds of aluminium in the matrix were studied by using low-energy electron-induced X-ray spectroscopy (LEEIXS). It is shown that aluminium nitride is formed and that the nitrogen distribution presents a surface peak when the implantation temperature is higher than 200° C.     

Monitoring interstitial fluxes by self-assembled nanovoids in ion-implanted Si/SiGe/Si strained structures

We report on the effect of the rapid thermal annealing (RTA) ambiance on evolution of self-assembled voids of nanometer size. The spherically shaped voids are produced in molecular beam epitaxially grown Si/SiGe/Si strained structures with in-situ implantation of 1 keV Ge ions followed by RTA at 800 or 900 °C. The voids are of nanometer size and are exclusively assembled in the narrow SiGe layer. During the RTA, the voids grow in size in a nitrogen ambiance and shrink in an oxygen ambiance. The evolution of the voids correlates well with oxidation-induced injection of excess interstitials. Prospects for point defect monitoring are discussed.