Si Surface Layer Research Articles

Analysis of the Influence of Formation of Pd Silicides on Surface Layers of Si on the Diffusion of Atoms of Contacting Metal

4-probe measurements of surface resistivity, measurements of dark and light current-voltage characteristics, the possibilities of using a thin PdSi film to obtain perfect nano-sized ohmic contacts on the Si(111) surface have been investigated using Auger electron spectroscopy methods in combination with ion etching of the surface. It has been shown that the depth of Ni diffusion in the Ni-Si (111) system is 400 ‑ 500 Å at indoor temperature, and 70 – 80 Å in the Ni-PdSi-Si (111) system. The quality of the ohmic contact in the latter case does not change up to T = 800 K and withstands luminous flux illumination up to F = 1100 lux. It is shown that the resistivity of the PdSi film passes through a minimum at T = 900 – 1000 K. An analysis of the results obtained will be given in the article.

Study of the dependence of the degree of disordering of the surface layers of Si(111) and Ge(111) single crystals upon bombardment with low-energy ions

Study of the dependence of the degree of disordering of the surface layers of Si(111) and Ge(111) single crystals upon bombardment with low-energy ions

Athermal annealing of pre-existing defects in crystalline silicon

Systematic investigations of electronic energy loss (Se) effects on pre-existing defects in crystalline silicon (Si) are crucial to provide reliance on the use of ionizing irradiation to anneal pre-existing defects, leading to successful implementation of this technology in the fabrication of Si-based devices. In this regard, the Se effects on nonequilibrium defect evolution in pre-damaged Si single crystals at 300 K has been investigated using intermediate-energy ions (12 MeV O and Si ions) that interact with the pre-damaged surface layers of Si mainly by ionization, except at the end of their range where the nuclear energy loss (Sn) is no longer negligible. Under these irradiation conditions, experimental results and molecular dynamics simulations have revealed that pre-existing disorder in Si can be almost fully annealed by subsequent irradiation with intermediate-energy incident ions with Se values as low as 1.5–3.0 keV/nm. Selective annealing of pre-existing defect levels in Si at room temperature can be considered as an effective strategy to mediate the transient enhanced diffusion of dopants in Si. This approach is more desirable than the regular thermal annealing, which is not compatible with the processing requirements that fall below the typical thermal budget.

Phase transformation pre-treatment of diamond wire-sawn multi-crystalline silicon wafers for metal-assisted chemical etching of solar cells

Phase transformation by the heat treatment, prior to metal-assisted chemical etching (MACE) of solar cells, has been proposed and studied, as a pre-treatment approach for diamond wire sawn (DWS) Si wafers. The results of the study show that the phase transformation pre-treatment can modify the microstructure of amorphous Si surface layers of DWS multi-crystalline (mc) Si wafers. The modified surface layer proved to be more reactive to the chemical etching solution, which was the primary factor for the improvement in the treated solar cells. A significant improvement on the surface uniformity and morphology of the textured Si wafer was achieved, subsequent to the pre-treatment, during the MACE texturization process. These solar cells based on the treated DWS mc-Si wafers displayed a gain of about 0.18% (absolute value), in the overall photoelectric conversion efficiency (η), when compared to the solar cells of the same batch, for the untreated wafers, on the same production line. It is hence, proven that this pre-treatment method, when used as a supplementary technique to the wet-chemical texturization process, has great potential as an effective application technology for solar cells based on DWS mc-Si wafers.

Microstructural evolution and hardness of rapidly solidified hypereutectic Al-Si surface layers by laser remelting

ABSTRACT Selective laser melting technique is used to manufacture Al-25 wt.%Si and Al-30 wt.%Si surface layers with a thickness of 0.5–0.6 mm followed by a laser rapid solidification process to refine the silicon to a nano-size and increase the hardness. The as-produced alloyed layers were heterogeneous and composed of clustered aggregates of primary Si crystals of size 5–7 µm, decorated with α-Al cells/dendrites, and embedded in a matrix consisting of α-Al dendritic crystals and Al-Si eutectic. However, after several remelting scanning treatments at a fast speed and low power, significant refinement of all phases was achieved, and a dramatic increase in the proportion of the interwoven nano-sized Al-Si fibrous eutectic. The primary Si sizes were reduced to ≤1 µm, while the eutectic spacing decreased and approached as low as 10–15 nm at the highest cooling rate. The high cooling rate significantly reduced the size and the amount of the α-Al cells/dendrites especially those surrounding the primary Si, thereby stimulating ultrafine Al-Si fibrous eutectic to grow adjacent to the primary Si crystals and spread massively, which in turn contributed to the increase in hardness. Transmission electron microscopy revealed block-like primary Si, worm-like Si, and nanoscale fibrous eutectic Si, which was internally nano-twinned.

Composition and electronic structure of hidden nanoscale phases and layers of BaSi-=SUB=-2-=/SUB=- formed in the near-surface of Si

For the first time, nanoscale phases and layers of BaSi2 were obtained by implantation of Ba+ ions with an energy of E0=20-30 keV in the surface layer of Si(111). In particular, it is shown that at a dose of D~1015 cm-2 nanophases with a band gap Eg~0.85 eV are formed, and at D~1017 cm-2 a BaSi2 nanolayer with Eg=0.67 eV. The composition and structure of the barium disilicide nanostructure were investigated by light absorption spectroscopy by Auger electron spectroscopy, and the X-ray surface morphology was studied by scanning electron microscopy. The optimal modes of ion implantation and annealing for obtaining nanoscale phases and layers of BaSi2 in the near-surface region of Si have been established. Using the method of light absorption spectroscopy, the band gap and the degree of coverage of the layer with BaSi2 nanophases were estimated. It has been shown that at a dose of D≥6·1016 cm-2 the nanolayer of BaSi2. Keywords: ion implantation, nanostructure, nanophase, annealing, barium disilicide, Auger electrons, degree of coverage.

Ultra-refined primary and eutectic silicon in rapidly solidified laser produced hypereutectic Al–Si alloys

ABSTRACT A series of laser-produced Al–Si surface layers of composition 35, 50, and 60 wt%Si was prepared and analysed for microstructure and hardness. Also, laser remelting at different scanning speeds was performed to obtain nano-sized silicon crystals. The results indicated that all the laser fabricated Al–Si layers consisted of fine primary silicon (PSi) crystals of average size 10 µm, surrounded by α-Al cells/dendrites and distributed in dendritic structure of α-Al and Al–Si eutectic. The results of laser remelting at speeds of 10 and 50 mm/s showed slight microstructural refinement. However, a significant reduction of the amount and size of the PSi to <1 µm as well as a favourable change in the morphology of the eutectic have resulted in the sample processed at a speed of 120 mm/s. The high cooling rate led to a dramatic reduction in the amount of the α-Al dendrites and triggers the eutectic silicon fibres to grew from the existing PSi crystals and ramify around its perimeter. The nanoindentation hardness increased as the interlamellar eutectic spacing decreased. The refinement of the PSi crystals and the modification of the eutectic silicon were attributed to the high density of twins which facilitate rapid and directional growth.

Force analysis of stress-strain state of surface layer of ground Si&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt;‒TiC ceramics

С использованием базовых положений компьютерной инженерии изучено напряженное состояние поверхностного слоя шлифованной Si3N4‒TiC-керамики под действием силовой нагрузки. Выявлено формирование микроструктурных концентраторов напряжений в точке приложения сосредоточенной силы, приводящих к изменению структуры керамики за счет образования несплошностей.

Isotopic enrichment of silicon by high fluence 28Si− ion implantation

Spins in the `semiconductor vacuum' of silicon-28 ($^{28}$Si) are suitable qubit candidates due to their long coherence times. An isotopically purified substrate of $^{28}$Si is required to limit the decoherence pathway caused by magnetic perturbations from surrounding $^{29}$Si nuclear spins (I=1/2), present in natural Si (nat Si) at an abundance of 4.67%. We isotopically enrich surface layers of nat Si by sputtering using high fluence $^{28}$Si$^-$ implantation. Phosphorus (P) donors implanted into one such $^{28}$Si layer with ~3000 ppm $^{29}$Si, produced by implanting 30 keV $^{28}$Si$^-$ ions at a fluence of 4x10^18 cm^-2, were measured with pulsed electron spin resonance, confirming successful donor activation upon annealing. The mono-exponential decay of the Hahn echo signal indicates a depletion of $^{29}$Si. A coherence time of T2 = 285 +/- 14 us is extracted, which is longer than that obtained in nat Si for similar doping concentrations and can be increased by reducing the P concentration in future. The isotopic enrichment was improved by employing one-for-one ion sputtering using 45 keV $^{28}$Si$^-$ implantation. A fluence of 2.63x10^18 cm^-2 $^{28}$Si$^-$ ions were implanted at this energy into nat Si, resulting in an isotopically enriched surface layer ~100 nm thick; suitable for providing a sufficient volume of $^{28}$Si for donor qubits implanted into the near-surface region. We observe a depletion of $^{29}$Si to 250 ppm as measured by secondary ion mass spectrometry. The impurity content and the crystallization kinetics via solid phase epitaxy are discussed. The $^{28}$Si layer is confirmed to be a single crystal using transmission electron microscopy. This method of Si isotopic enrichment shows promise for incorporating into the fabrication process flow of Si spin qubit devices.

The Effect of Stepwise Postimplantation Annealing on the Composition and Structure of Silicon Surface Layers Implanted with Alkali Metal Ions

The dynamics of changes in the crystal structure and in the elemental and chemical composition of Si surface layers implanted with Na+, Rb+, and Cs+ ions in the process of stepwise annealing under different temperature conditions has been studied. It is shown that, on the surface implanted with Na+ ions, a NaSi2 film is formed after annealing it at a temperature of T = 900 K, a single-layer NaSi2 coating is formed at T = 1000 K and the surface and near-surface Si layers are completely cleansed of the atoms of the alloying element, oxygen, and carbon at T = 1100 K.

Влияние поэтапного постимплантационного отжига на состав и структуру поверхностных слоев кремния, имплантированного ионами щелочных металлов

Studies of the dynamics of changes in the crystal structure, elemental and chemical composition of the surface layers of Si implanted with Na + , Rb + and Cs + ions during gradual heating in various temperature conditions. In the case of Na + ions, after heating at a temperature of T = 900 K, a NaSi 2 film is formed on the surface, at T = 1000 K, a monolayer coating of NaSi 2 and at T = 1100 K the surface layers of Si are completely cleaned of atoms of the alloying element, as well as oxygen and carbon.

Analysis of Surface Morphology and Chemical Composition of Silicon Implanted with Copper Ions

We report on the results of analysis of the structure and chemical composition of the surface of c-Si single crystal substrates implanted with Cu+ ions with energy of 40 keV and doses in a range of 3.1 × 1015–1.25 × 1017 ions/cm2 for a current density of 8 μA/cm2 in the ion beam. It has been established using scanning electron microscopy and probe microscopy combined with X-ray photoelectron and Auger spectroscopy that at the initial stage, the implantation with Cu+ ions to a dose of 6.25 × 1016 ions/cm2 induces the formation of Cu nanoparticles with an average size of 10 nm in the Si surface layer. Upon a further increase in the implantation dose, beginning with 1.25 × 1017 ions/cm2 and higher, the nucleation of the η phase of copper silicide (η-Cu3Si) is observed. This is due to heating of the surface layer of the Si substrate during its irradiation to a temperature facilitating the formation of the η-Cu3Si phase.

Pulse ion annealing of silicon layers with silver nanoparticles formed by ion implantation

The paper presents the results of Si surface modification created by implantation with Ag+ ions at energy of 30 keV, current density of 8 μA/cm2 for various doses from 6.0·1015 to 7.5·1016 ion/cm2 and annealed by powerful beam pulses (C+, H+) of nanosecond duration. Scanning electron microscopy and optical reflection measurements showed that after ion implantation an amorphous a-Si layer on the surface of c-Si substrates with Ag nanoparticles was formed. Followed pulse ion beam annealing of sample obtained at lowest dose of 6.0·1015 ion/cm2 leads to melting and recrystallization of the Si surface layer with segregation of Ag nanoparticles. For samples implanted with doses higher than 2.5·1016 ion/cm2 after annealing an epitaxial cellular breakdown structures are fabricated on the Si surface decorated at the cell boundaries by Ag nanoparticles.

Mechanism study of SiO2 layer formation and separation at the Si die sidewall during nanosecond laser dicing of ultrathin Si wafers with Cu backside layer

Laser dicing of ultrathin dies is promising and is gaining importance because of its cost and quality advantages over mechanical and plasma dicing. However, the effects of laser dicing on the mechanical strength and microstructure of ultrathin Si dies need to be further understood, especially when dicing through Si wafers with backside Cu layer. A critical phenomenon effecting the Si die sidewall strength after nanosecond laser dicing of Si wafers with backside Cu is the formation and separation of a SiO2 layer at the sidewall. The mechanisms behind the SiO2 layer formation and separation were studied in this work. Si wafer samples without and with backside Cu layer were prepared by dicing with nanosecond laser using standard production parameters. The microstructure and phases formed were investigated by energy dispersive spectroscopy and nanobeam diffraction in a transmission electron microscope. In die samples without backside Cu, the sidewall consists of a thin surface layer of amorphous Si, followed by a polycrystalline Si layer, and finally an epitaxial Si layer. In die samples with backside Cu, the sidewall microstructure was observed to be vastly different. At the upper region of the sidewall, a surface layer of polycrystalline Cu was found, followed by a polycrystalline Cu3Si layer, a SiO2 layer mixed with Cu3Si, and finally a thick SiO2 layer. The Cu3Si catalyzes the growth of the SiO2 through an oxidation step of the Cu3Si on the sidewall surface as well as at the SiO2/Si interface. In the lower region of the sidewall, the microstructure is similar to the upper region, but there is a separation of the SiO2 layer from the crystalline Si. The SiO2 undergoes a decomposition reaction at the SiO2/Si interface, releasing volatile SiO which causes microvoids to form and grow laterally at the interface. The growth and coalescence of the microvoids eventually lead to the separation of the SiO2 layer from the crystalline Si, leaving behind a clean and rough crystalline Si surface with a peak-to-peak roughness of 100–200 nm. In the areas where the SiO2 layer has separated from the Si die sidewall, the fracture strength of the sidewall is dependent on the material property and surface roughness of the crystalline Si, and not on the SiO2 layer. In the sidewall region near the die frontside, the SiO2 thickness is more than regions near the die backside, and no microvoiding and separation at the SiO2/Si interface were detected. This is hypothesized to be due to a higher O2 pressure at the upper region of the narrow dicing trench which is open to the atmosphere compared to the lower regions where there could be O2 deprivation and lower O2 pressure.

Исследование морфологии поверхности и химического состава кремния, имплантированного ионами меди

This paper presents the results of studies of the structure and chemical composition of the surface of single-crystal silicon c-Si substrates implanted with Cu^+ ions with an energy of 40 keV and doses in the range of 3.1 · 10^15 - 1.25 · 10^17 ions/cm^2 at a current density in the ion beam of 8 μA/cm^2. Using scanning electron and probe microscopy in combination with X-ray photoelectron and Auger electron spectroscopy it was found that at the initial stage of irradiation with Cu^+ ions up to a dose of 6.25 · 10^16 ions/cm^2 Cu metal nanoparticles with an average size of 10 nm are formed in the surface layer of Si. With a further increase in the implantation dose starting from a value of 1.25 · 10^17 ions/cm^2 and higher the η-phase of copper silicide η-Cu3Si nucleates. This circumstance is due to the heating of the near-surface layer of Si substrate during its irradiation to a temperature conducive to the phase formation of η-Cu3Si.

Origin of Degradation of the CaF2/BaF2 Buffer Layers on Si(111)

The growth temperature dependences of the capacitance–voltage characteristics and chemical stability of the CaF2/BaF2 buffer layers formed on Si by molecular beam epitaxy have been investigated. Secondary ion mass spectrometry and X-ray photoelectron spectroscopy studies of the CaF2/Si interface suggest that the observed variations can be caused by the enrichment of the Si surface layer with calcium.

Change of electrophysical properties of the Si(111) and Si(100) surface in the process of ion implantation and next annealing

The change in the electrical properties of the Si(111) and Si(100) surfaces during ion implantation and subsequent annealing was studied. The possibilities of controlling of the electrophysical properties of the Si(111) and Si(100) surface layers by the implantation of ions of alkaline and alkaline-earth elements are analyzed. Some electrophysical properties of semiconductors containing p- and n-structures and the possibilities of their application in electronics are discussed.

Ga2O3/Si and Al2O3/Si Room-Temperature Wafer Bonding Using in-Situ Deposited Si Thin Film

Recently, β-Ga2O3 has caught attentions in the field of high-voltage power-device applications due to its excellent material properties and suitability for mass production1). Thermal conductivity of Ga2O3 is, however, low, and bonding Ga2O3 to high-thermal conductivity substrate material is desired to improve heat dissipation of power devices. For the bonding between dissimilar materials, low temperature process is desirable to avoid the problems caused by thermal expansion mismatch. Surface activated bonding (SAB), which can achieve strong bonding without any heat treatments, is one of the candidates for the purpose, however bonding strength of oxide materials is low compared to metals and semiconductors2). In this paper, we propose bonding process using in-situ deposition of Si thin film on oxide materials, which can be performed by a standard SAB apparatus without any modification. By the process, we tried bonding of Ga2O3 and Al2O3 to Si. In the bonding experiments, a 15 x 10-mm2, 500-μm-thick, single-side polished chip of (010) β-Ga2O3 (TAMURA Corporation) was used. 100-mm-diameter, 650-μm-thick, single-side-polished, c-face sapphire wafers and 100-mm-diameter, 400-μm-thick, double-side-polished, (100) Si wafers were also used. A pair of Ga2O3 and Si specimens were introduced into an apparatus for the surface activated bonding (MWB-12ST, Mitsubishi Heavy Industries Machine Tool Co. Ltd.). After setting specimens on stages in the bonding chamber, Ar fast atom beam was irradiated to the Ga2O3 chip for 10 seconds to remove adsorbed surface contaminants. Then, the Ar fast atom beam was irradiated to the Si wafer for 60 seconds to remove surface contaminants and an oxide layer. During this surface activation step for Si, some of sputtered Si atoms were deposited on the Ga2O3 surface and form a thin Si layer. Immediately after the surface activation and Si layer deposition step, Ga2O3 and Si specimens were mated in the vacuum and pressed. Sapphire and Si wafers were bonded by the same procedure. The Ga2O3 chip was successfully bonded to the Si wafer except the area near the edge of the chip as shown in figures. The unbonded area is supposed to be caused by the edge-sagging formed during polishing process. Sapphire wafers were also successfully bonded to Si wafers. The Ga2O3/Si bonded specimen was cut into two pieces at the center of the Ga2O3 chip by dicing saw, and strength of Ga2O3/Si bonded specimen was evaluated by the dicing test from Si side. No cleavage from the bonding interface was observed after dicing test (lower-left in figures). Sapphire/Si bonding strength was evaluated by the blade test 3) as well as the dicing test. The bonding was so strong that no crack initiated at the bonding interface and Si wafer was cracked by blade insertion. Micro structure of the Ga2O3/Si and sapphire/Si interface was investigated by TEM. No cleavage was observed in low magnification images. In a HRTEM image of Ga2O3/Si interface (lower-right in figures), an amorphous intermediate layer was observed. Considering bonding step, the intermediate layer was resulted from deposited Si layer on Ga2O3 surface and damaged layer on Si surface formed during Ar fast beam irradiation4). In-situ deposition of Si thin film on oxide wafer is proved to be effective for strong bonding formation at room-temperature. Ga2O3 and sapphire were successfully bonded to Si wafers. This process is expected to provide a promising method to improve heat dissipation in Ga2O3 devices, as well as integration of oxides to other materials with large thermal expansion mismatch. This work is partly supported by International Joint Research Program for Innovative Energy Technology, METI. 1) M. Higashiwaki, K. Sasaki, T. Kamimura, M. Hoi Wong, D. Krishnamurthy, A. Kuramata, T. Masui, and S. Yamakoshi, Appl. Phys. Lett., 103(2013), 1. 2) H. Takagi, R. Maeda, T. R. Chung, and T. Suga, Sensors Actuators, A 70(1998), 164. 3) W. P. Maszara, G. Goetz, A. Caviglia, and J. B. McKitterick, J. Appl. Phys., 64(1988), 4943. 4) H. Takagi, R. Maeda, N. Hosoda, and T. Suga, Japanese J. Appl. Physics, 38(1999), 1589. Figure 1

Formation of Precipitates in Si Implanted with 64Zn+ and 16O+ Ions

The results of studying the surface Si layer and precipitate formation in CZ n-Si(100) samples sequentially implanted with 64Zn+ ions with a dose of 5 × 1016 cm2 and energy of 100 keV and 16O+ ions with the same dose but an energy of 33 keV at room temperature so that their projection paths Rp = 70 nm would coincide are presented. The post-implantation samples are annealed for 1 h in an inert Ar medium in the temperature range of 400–900°C with a step of 100°C. The profiles of the implanted impurities are studied by time-of-flight secondary ion mass spectrometry. The Si surface is visualized using a scanning electron microscope, while the near-surface layer is visualized with the help of maps of elements formed by Auger electron spectroscopy with profiling over depth. The ZnO(002) texture is formed in an amorphized Si layer after the implantation of Zn and O ions. ZnO(102) crystallites of 5 nm in size are found in a recrystallized single-crystalline Si layer after annealing in Ar at 700°C.

Structural evolution of thermal annealed Si(0 0 1) surface layers fabricated by plasma immersion He+ implantation

Abstract Structural evolution in Si(0 0 1) surface layers after high-dose (D = 5 × 1017 cm–2) low-energy (2 and 5 keV) plasma immersion He+ ion implantation (He+ PIII) and subsequent annealing at 853 and 1073 K was studied by complementary structural sensitive methods (TEM, XRR, RBS, and AFM). Formation of a three-layer structure (amorphous a-SiOx sublayer at the surface, amorphous a-Si sublayer with large size helium-filled bubbles, and heavily damaged crystalline c-Si sublayer containing small-size bubbles and Si nanocrystallites) was observed for both implantation energies. This three-layer structure is retained after annealing. It was shown that the thickness of the oxide sublayer does not depend on implantation energy and does not change after annealing. This amorphous oxide sublayer together with dense top part of the a-Si sublayer forms a cap layer with a thickness of 15 nm that can be considered as a protective layer for the sublayers containing He-filled bubbles and Si nanocrystallites. The Si nanocrystallites were revealed at the boundary of the a-Si and the c-Si sublayers both in as-implanted at 5 keV and annealed samples.