Transient effects in SIMS analysis of Si with Cs+ at high incidence angles: Secondary ion yield variations

Secondary ion mass spectrometry (SIMS) depth profile analysis of Si wafers using 1 keV Cs⁺ primary ions at large incidence angles (80°) is plagued by unusually strong transient effects (variations in both sputter and ion yields). Analysis of a native oxide terminated Si wafer with and without the aid of an O₂ leak, and an Ar⁺ pre-sputtered wafer revealed correlations between the implanted Cs content and various secondary ion intensities consistent with that expected from a resonance charge transfer process (that assumed by the electron tunneling model). Cs concentrations were defined through X-ray photoelectron spectroscopy of the sputtered surface from SIMS profiles terminated within the transient region. These scaled with the surface roughening occurring under these conditions and can be explained as resulting from the associated drop in sputter rates. An O induced transient effect from the native oxide was also identified. Characterization of these effects allowed the reconstruction of the XPS derived Cs concentration profiles, which in turn, allowed enhancement effects resulting from O and Cs to be approximated.     

Observation of nano-indent induced strain fields and dislocation generation in silicon wafers using micro-Raman spectroscopy and white beam X-ray topography

In the semiconductor manufacturing industry, wafer handling introduces micro-cracks at the wafer edge. During heat treatment these can produce larger, long range cracks in the wafer which can cause wafer breakage during manufacture. Two complimentary techniques, micro-Raman spectroscopy (μRS) and White Beam Synchrotron X-ray Topography (WBSXRT) were employed to study both the micro-cracks and the associated strain fields produced by nano-indentations in Si wafers, which were used as a means of introducing controlled strain in the wafers. It is shown that both the spatial lateral and depth distribution of these long range strain fields are relatively isotropic in nature. The Raman spectra suggest the presence of a region under tensile strain beneath the indents, which can indicate a crack beneath the indent and the data strongly suggests that there exists a minimum critical applied load below which cracking will not initiate.     

SiC辐照损伤对耐高温氧化性能的影响

碳化硅（SiC）材料在高温氧化时会生成SiO2保护膜,但经辐照后高温氧化,材料结构和氧化速率会发生变化,影响材料性能。为研究其晶格损伤与氧化规律之间的关系,利用6H-SiC单晶片和烧结SiC多晶片,开展了在室温下经过能量为5 MeV、注量为5×1014 cm-2的Xe20+离子辐照后再进行1 300 ℃氧化1 h的实验。利用X射线衍射、拉曼光谱、傅里叶变换红外光谱、扫描电镜、透射电镜进行表征,对比了不同晶型的SiC氧化前后辐照与未辐照区域。结果显示：辐照破坏了晶格有序度,造成了晶格损伤,这些损伤在氧化过程中促进了多种SiO2基团的形成;生成的SiO2形成氧化层,由于与SiC基体热膨胀系数的差异,以及重结晶作用,导致碳化硅产生内应力,使氧化膜破裂;截面TEM图像显示,辐照引起的层错致使氧化程度加深,这是导致氧化速度加快的重要原因。     

Xenon-ion irradiation of Co/Si bilayers: Effects of interface structure and ion energy

Heavy-ion irradiation of ferromagnetic thin layers changes their micromagnetic and microstructural properties, due to the production of defects, relaxation or build-up of stress, or changes of grain size. When the ion range exceeds the layer thickness, ion mixing processes take place, leading to the formation of silicide phases. The present study deals with Co(30 or 55 nm)/Si bilayers irradiated at room temperature with 100- or 200 keV Xe ions to fluences of up to 15 × 10¹⁵/cm². The Si(1 0 0) wafers were either crystalline or pre-amorphized by 1 keV Ar⁺ implantation. Rutherford backscattering spectroscopy, in-plane magneto-optical Kerr effect, and X-ray diffraction served to analyse the samples before and after irradiation. The results will be compared with those obtained for other heavy-ions for Co/Si bilayers and in similar studies on Fe/Si bilayers.     

Structural changes of Si surfaces by nitrogen implantation using plasma based ion implantation

Nitrogen ion implantation to Si wafers is carried out by a plasma based ion implantation (PBII) and the compositional and structural changes of the Si surfaces are examined as a function of implantation time by energy dispersive X-ray spectrometer (EDX), Raman and Fourier Transform Infrared (FT-IR) spectroscopy. The implantation time is varied from 10 min to 7 h. From the results of EDX measurements, the N concentration is increased with increasing implantation time up to 1 h, but it is not significantly increased at further increase of implantation time. In the Raman spectra, the sharp peak from Si crystal is decreased in intensity and the small peaks from a-Si and/or a-SiN_x appear after N ion implantation. On the other hand, in the FT-IR spectra, a broad peak assigned to Si–N bonds appears after N ion implantation. The result of RBS measurement indicates that the N/Si ratio is approximately 1.3. Judging from these results, it is suggested that a-SiN_1.3 is formed as a surface layer on Si wafer by N ion implantation using PBII system.     

Ionizing Radiation Effects in Inversion Layer Silicon Solar Cells

Ionizing irradiation experiments on a new inversion layer solar cell have been carried out to determine its potential for space applications. A scanning electron microscope was used as a source of low energy (2-12 keV) electrons in doses up to 1014 e/cm2. Phototopographic scanning and C-V analysis were used to determine the effects of the radiation on the Si02-Si system. The electron irradiation results are validated by comparison with those of a conventional X-ray experiment. The operation, fabrication and electrical characteristics of the cell are also discussed. Large increases in both the oxide charge and surface state density were observed, but little change occurred in the cells' output characteristics below 105 rads (Si). A drop-off in power at higher doses is explained in terms of surface recombination and series resistance increases. The results of isochronal and UV annealing experiments on these effects are also presented. The cells are concluded to have potential for use in space.     

Is there an effect of the proximity of a “free-surface” on the formation of End-Of-Range defects?

We have studied the effect of the proximity of the wafer surface on the formation of End-Of-Range defects. These experiments are aimed at elucidating the behavior, upon annealing, of the Si self-interstitial supersaturation responsible for transient enhanced diffusion of boron in pre-amorphized silicon wafers. By implanting with Ge at constant energy while carefully etching away increasing thicknesses of the amorphous layer the nucleation and growth of End-Of-Range defects have been studied by transmission electron microscopy. Clearly, no influence in the loop population can be shown even when using state-of-the-art “quantitative” electron microscopy. These results are explained by considering that the c/a interface is a diffusion barrier for the Si self-interstitial atoms during the nucleation stage, i.e., when the supersaturation is high. Only after the solid phase epitaxial regrowth, i.e., during the coalescence of the loops when the supersaturation is already low, the surface can interact with the loops. However, this interaction is not measurable through the observation of extended defects and this leads to simplifying assumptions for the simulation of Transient Enhanced or Retarded Diffusion in pre-amorphized Si wafers.     

The surface charge effect by using boron ions implantation in p-channel MOSFETs fabricated

This article reports on the effects of surface charge on bare wafers and p-channel MOSFETs by a positive ion beam accompanied by an electron beam current for surface charge neutralization. Without the negative electron beam the films show a higher sheet resistance and the pMOSFETs exhibit a lower threshold voltage, a lower breakdown voltage and a lower gain factor. If the electron beam current is equal to or higher than the ion beam current of 6 mA, the uniformity of sheet resistance, fluctuations of breakdown voltage and gain factor are significantly improved by controlling the charge neutralization in this experiment. It prevents the positive charges from penetrating the poly-gate and causing catastrophic damage in the gate oxide layer. The sheet resistance deviation for the samples with a capped photoresist is higher than that for the bare wafer because the insulating property of the photoresist enhances the wafer surface charge accumulation and thus repels the subsequently implanted ions. The thinner gate oxide layer leads to larger deviations of threshold voltage, breakdown voltage and gain factor due to the imbalance of surface charge.     

Effect of oxygen on ion-beam induced synthesis of SiC in silicon

The properties of Si-structures with a buried silicon carbide (SiC) layer created by high-dose carbon implantation into Cz–Si or Fz–Si wafers followed by high-temperature annealing were studied by Raman and infrared spectroscopy. The effect of additional oxygen implantation on the peculiarities of SiC layer formation was also studied. It was shown that under the same implantation and post-implantation annealing conditions the buried SiC layer is more effectively formed in Cz–Si or in Si (Cz-or Fz-) subjected to additional oxygen implantation. So we can conclude that oxygen in silicon promotes the SiC layer formation due to SiO_x precipitate creation and accommodation of the crystal volume in the region where SiC phase is formed. Carbon segregation and amorphous carbon film formation on SiC grain boundaries were revealed.     

Spectroscopic and microscopic study of the corrosion of iron–silicon steel by lead–bismuth eutectic (LBE) at elevated temperatures

The performance of iron–silica alloys with different silicon composition was evaluated after exposure to an isothermal bath of lead–bismuth eutectic (LBE). Four alloys were evaluated: pure iron, Fe–1.24%Si, Fe–2.55%Si and Fe–3.82%Si. The samples were exposed to LBE in a dynamic corrosion cell for periods from 700 to 1000 h at a temperature of 550 °C. After exposure, the thickness and composition of the oxide layer were examined using optical microscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS), including sputter depth profiling. Particular attention was paid to the role, spatial distribution, and chemical speciation of silicon. Low-binding-energy silicon (probably silicates or ) was found in the oxide; while elemental silicon (Si) was found in the metal as expected, and silica (SiO₂) was found at the bottom of the oxide layer, consistent with the formation of a layer between the oxide and the metal. Alloys with low concentrations of Si contained only silicate in the oxide. Alloys with higher concentrations of Si contained a layer of silica at the boundary between the oxide and the bulk metal. All of the alloys examined showed signs of oxide failure. This study has implications for the role of silicon in the stability of the oxide layer in the corrosion of steel by LBE.     

μm-resolved high resolution X-ray diffraction imaging for semiconductor quality control

We present a method and an equipment for performing μm-resolved X-ray diffraction area maps, and apply it to wafer defect analysis and industrial wafer quality inspection. The method determines simultaneously the macroscopic warpage, the mesoscopic curvature and the microscopic defect structure of semiconductor wagers. It is based on X-ray diffraction rocking curve imaging of the whole wafer with down to 1 μm² resolution. The new wafer testing equipment determines the maximal and integral peak intensities, the peak position and the half width of the rocking curves with a microscopic resolution, thus imaging simultaneously the macroscopic quality parameters and the microscopic defect structure. This permits to establish a direct one-to-one correlation between the microscopic defects and the resulting macroscopic effects. As an example, wafers of different materials, fabrication technology and resulting perfection are studied. When investigating layered samples, the technique allows furthermore to determine the influence of the wafer quality on the layer properties. The method can be applied generally to characterize non-destructively the quality of all kinds of crystalline structures, like, e.g. microelectronic and optoelectronic devices.     

Recovery of Heat-Generating Nuclides in Eluted Solutions

To study about microstructure and chemical composition of oxide films formed on surface of stainless steel is most important for understanding of stress corrosion cracking (SCC) and irradiation assisted stress corrosion cracking (IASCC). In this work, a new sample preparation method for microstructure observation of oxide films was developed. To prevent to break oxide films during fabrication, surface of specimens were protected with plating. Focused ion beam (FIB) processing was conducted to prepare thin foil samples of cross section of oxide films. After sample preparation, microstructure of cross section of oxide films was observed by transmission electron microscope (FE-TEM), and microscopic chemical composition was analyzed by energy dispersed X-ray spectrometer (EDS). From the results, effects of silicon (Si) doping for oxide film formation in two oxidation conditions are discussed.     

Structural analysis of DC magnetron sputtered and spin coated thin films using RBS, TEM and X-ray reflectivity methods

Metallic thin films such as Au, Cr, Ag, etc., on silicon substrate have many technologically important applications as contact layers in microelectronic industry, as reflecting mirrors in synchrotron radiation research, etc. The native oxide layer on crystalline silicon surface inhibits wetting of few nm thick Au or Ag on native oxide/silicon systems. To obtain continuous thin metallic films (a few nm thick), a Cr layer was first deposited as a adhesion layer on the Si substrate. In this paper, Rutherford backscattering analysis (RBS) of Si/Cr/SiO₂/Si, Si/Au/SiO₂/Si, Si/Au/Cr/SiO₂/Si and Polystyrene (PS) polymer coated on some of these bi- or tri-layer structures has been reported. The X-ray reflectometry and transmission electron microscopy studies were carried out to complement the RBS measurements. The thickness, surface and interface roughness, and crystalline quality have been determined.     

COMPETING REACTIONS OF EXISTING Ni SILICIDE AND Ni OR Si INDUCED BY THERMAL ANNEALING AND MeV Si ION BEAM MIXING

The competing reactions between existing Ni silicides surrounded by Si and Ni were investigated by thermal annealing and MeV Si ion beam mixing. With high energy irradiation, the energy deposition at both interfaces, Ni/Ni silicide and Ni silicide/Si, is equal. Two MeV He~- RBS and TEM were used to obtain the reacted layer composition and epitaxial orientation, respectively. Also glancing angle Co K_a. X-ray diffraction was utilized to identify phase formation. The main results indicate that the existing silicides preferentially react with Ni layer, and that there are pronounced differences of Ni silicide phase transition between thermal annealing and MeV Si ion beam mixing, even though the mixing was performed in radiation enhanced diffusion regime. The results can be explained in term of the heat of silicide formation and surface energy change.     

X-ray irradiation of ion-implanted MOS capacitors

He⁺ ion-implanted metal-oxide-semiconductor (MOS) capacitors with two different oxide thickness have been irradiated by X-rays and the depth distribution of the implant damage in the Si–SiO₂ structures have been examined. The efficiency of X-ray annealing of electronic traps caused by implantation and changes in charge populations are reported. The experiment shows that (in the case when defects introduced by implantation are located at the Si–SiO₂ interface) only defects corresponding to the deep levels in the Si can be affected by X-ray irradiation. When defects introduced by ion implantation are located deeper within the Si substrate complete annealing of these defects is observed.     

钝化层结构对氚辐伏电池转换性能的影响

在辐射伏特效应同位素电池(辐伏电池)中,器件的辐伏转化性能不仅受限于换能器件所用的半导体材料、结构或加载放射源的种类,还受换能器件表面钝化层结构的影响。为在氚化钛源加载的平面单晶硅PN结辐伏电池(氚辐伏电池)中得到最佳的钝化效果,本文设计了3种不同的钝化层结构,考察其初始输出性能和抗辐射性能,并单独研究了氚化钛源出射的X射线对单晶硅换能器件的辐射损伤。结果显示:在辐伏电池初始输出性能方面,Si/SiO2/Si3N4结构Si/B-Si glass/Si3N4结构Si/Si3N4结构;在抗氚化钛源辐射损伤方面,Si/Si3N4结构Si/B-Si glass/Si3N4结构Si/SiO2/Si3N4结构,Si/B-Si glass/Si3N4结构具有最佳的抗X射线辐射衰减性能。氚化钛源出射的X射线对辐射损伤效应起主要作用,XPS结果显示,X射线长时间辐照造成了单晶硅表面平整性的破坏。     

Range distributions of 50–400 keV Hg+in amorphous silicon and Si-Ar binary targets

Range distributions of 50–400 keV Hg⁺ in amorphous Si and Si-Ar binary targets have been investigated by Rutherford backscattering spectrometry. The Si(100) wafers were amorphized by means of 150 keV Ar⁺ irradiation to a dose of 2 × 10¹⁵ ions/cm². To produce Si-Ar binary targets, the Si(100) wafers were implanted with 150 keV Ar⁺ to a dose of 3 × 10¹⁷ ions/cm². 50–400 keV Hg⁺ were introduced into amorphous Si and Si-Ar binary targets in increments of 50 keV. Parallel scanning of the Hg⁺ beams was used. The measured ranges and range stragglings have been compared to the Biersack theory. The results show that good agreements are found between the experimental and theoretical projected ranges for both Si and Si-Ar, but the predicted range straggling for both Si and Si-Ar are systematically lower than the experimental results in the case of a first order treatment. After correcting for second order energy loss terms, a better agreement for the range straggling is obtained.     

A broad beam ion source used for planar sputter-etching of shallow layers from flat samples and determination of their mass density

A special UHV device for sputter-etching of large planar samples is presented, which is based on a broad beam ion source of the Kaufman type. It is designed for a beam of Ar⁺ ions with an energy of only 600 eV and a heat load per area of about 0.17 W cm⁻². The equipment is suitable for a planar removal of nanometer thin layers from the surface of flat samples especially of wafers. In a circular area of 2 cm diameter a homogeneous sputtering was reached with ±5% in depth. By means of an atomic force microscope the surface roughness of highly polished wafers was shown to keep on the sub-nanometer level. The sputtered depth was determined by a Tolansky microscope, the sputtered mass was measured by differential weighing on a calibrated microbalance. Depending on the sputtered target (Si, Ge, GaAs) the sputtering yield was in the range of 0.9–2.0 atoms per ion and was very similar for modified materials like oxidised or Co- and As-implanted samples of Si (±10%). For validation of the method, the mass density of thin layers consisting of pure crystalline Si, GaAs, Ge and of As-implanted Si was determined. Precision and accuracy were shown to be <3% and <6%, respectively. The method was also used successfully for depth profiling of a Si and a GaAs wafer sample by repeated sputter-etching and differential weighing. Density/depth profiles were recorded with 35 and 50 nm steps but the actual depth resolution can be reduced to 5–10 nm and possibly to only 2–3 nm.     

Suppression of charge carrier collection in diode with retrograde well and epitaxial layers for soft-error immunity

One of the solutions to the reduction of soft errors is suppression of carrier collection generated by an energetic particle emitted from typical contaminants of packaging or wiring materials. Suppression of carrier collection by a retrograde well or an epitaxial layer has been investigated by nuclear microprobes to clarify the validity of various well structures against soft errors in dynamic random access memories (DRAMs). The carrier collection efficiency of a retrograde well, a retrograde well with a buried layer on a Si wafer, and on an epitaxial wafer has been investigated for DRAM application using the ion-beam-induced-current (IBIC) measurement. The collection of carriers induced by proton microprobe irradiation could be reduced by the retrograde well formed at different boron doses. n⁺p diodes with retrograde well structures were fabricated by B⁺ implantation at 0.4–1.3 μm and to doses of 3.5 × 10¹⁶–3.4 × 10¹⁷ ions/cm³. It should be noted that an increase in the B⁺ implantation dose effetively reduces carrier collection efficiency, though a buried layer implanted with a higher dose degrades the characteristics of devices by the increase in leakage current. The carrier collection efficiency of the n⁺p diode with the higher dose retrograde well can be reduced by more than half compared to the diode with a retrograde well in an epitaxial layer.     

XPS characterization of different thermal treatments in the ITO–Si interface of a carbonate-textured monocrystalline silicon solar cell

In this work we have applied the X-ray photoelectron spectroscopy (XPS) in depth to study, for the first time, the influence of different thermal treatments in the ITO–Si interface of a monocrystalline Si-based solar cell where the Si surface is carbonate-textured and covered by an ITO sputtered layer. The efficiency of the solar cells significantly increases when thermal treatments are applied just after the ITO deposition. The efficiency is also dependent on the characteristics of the pyramidal relief of the silicon surface previously obtained by immersion of the Si wafers in a sodium carbonate/bicarbonate solution. An efficiency of 15.5% has been obtained with an optimized texturization of the silicon substrates and an annealing treatment of the solar cells at 400 °C just after the ITO deposition.