Cu In Si Research Articles

Hydrogen Embrittlement Characterization of 1.4614 and 1.4543 Martensitic Precipitation Hardened Stainless Steels

Hydrogen embrittlement (HE) of 1.4614 and 1.4543 maraging stainless steels is characterized with fine structural TEM-ASTAR, hydrogen electrochemical permeation, thermodesorption and tensile testing (with slow strain rate during H cathodic charging) experiments. Both solutions annealed and 550 °C aged states are studied. When aged, 1.4614 grade contains nanometric hexagonal Ni3Ti precipitates whereas 1.4543 grade contains three families of nanometric precipitates, namely, hexagonal Ni3Ti, non fcc-rich Cu and G-phase rich in Si, Ti and Ni with cube-cube relations with martensite. From the permeation and thermodesorption results, it appears that austenite and nanometric precipitates seem to constitute deep traps for hydrogen in both grades. From tensile tests with in situ H charging, 1.4614 and 1.4543 maraging grades show a high susceptibility to HE with relative reduction of area (RRA) strictly superior to 80% for both metallurgical states. The presence of retained austenite does not seem to bring any HE resistance because of its transformation into martensite during deformation.

Formation Mechanism of ZrB2 in a Si–Cu Melt and Its Potential Application for Refining Si and Recycling Si Waste

Based on (i) the low liquidus temperature of Si–Cu systems, (ii) low solubility of Cu in solid Si, and (iii) a strong affinity of Zr to B for the enhanced boride formation, a novel method to remove...

Thermodynamic modelling of fast dopant diffusion in Si

In the present study, nickel and copper fast diffusion in silicon is investigated in the framework of the cBΩ thermodynamic model, which connects point defect parameters with the bulk elastic and expansion properties. All the calculated point defect thermodynamic properties (activation Gibbs free energy, activation enthalpy, activation entropy, and activation volume) exhibit temperature dependence due to the non-linear anharmonic behavior of the isothermal bulk modulus of Si. Calculated activation enthalpies (0.15–0.16 eV for Ni and 0.17–0.19 eV for Cu) are in agreement with the reported experimental results. Small values of calculated activation volumes for both dopants (∼4% of the mean atomic volume) are consistent with the interstitial diffusion of Ni and Cu in Si.

Hybrid-Functional Calculations of the Copper Impurity in Silicon

Unsurprisingly, considering its significance to electronics, the impact of copper impurities on the electrical properties of silicon has been widely studied. Surprisingly, there is still marked disagreement, both among and between experiments and calculations. The remarkable disagreement between various theoretical studies is mainly due to the band-gap error in basic versions of density functional theory. This study revisits the problem using the nuanced HSE06 hybrid functional. Its model for the electronic structure of Cu in Si yields results that agree well with experimental transition levels and solubilities.

Applying Biogeochemistry to Identify the Geographic Origins of Insects-A Model Using Prostephanus truncatus

application of geochemical screening for tracking insects and other organisms is poorly understood. We explored multi-elemental profiles of an insect pest and its food from different locations in order to identify intrinsic markers of geographic origin. ICP-AES screening was completed for soil, maize grains and Prostephanus truncatus of different geographic origin, with insects collected in the field or reared on maize under controlled conditions. Background level geochemical data are presented with concentrations of Cu, S and Sr in maize, and Al, Ba, Ca, Fe, S, Si, Sr, Ti and Zn in insects differing according to their origin, or that of their food. Cu, Fe and Zn determinations of insects were 20, 6.5 and 11.5 times the concentrations of the maize they were reared on. A Linear Discriminant Analysis (LDA) based on Al, Fe, Sr and Zn successfully assigned 78% of laboratory-reared P. truncatus and 94% of field-caught insects to their origin (68% and 75% respectively after jacknifing). There was excellent discrimination between insects reared on maize from Guanajuato and Nuevo Leon, and Guanajuato and Michoacan, good separation between Sonora and Nuevo Leon but overlap for Sonora, Guanajuato and Michoacan, and Michoacan and Nuevo Leon. The same LDA for field-caught insects gave complete separation between Michoacan and Sonora, but some overlap between Michoacan and Nuevo Leon. This robust ICP-AES technique successfully identified a combination of elements able to classify insects according to their origin. The model was restricted to elements showing a normal distribution but non-parametric tests suggest other elements may act as intrinsic markers. This shows the potential of atomic spectroscopy for remotely tracing insects and other biological materials, with applications including providing provenance data for species routinely captured for surveillance and to track natural enemies and wildlife.

Thermal Decomposition of Tungsten Nitrido Precursors for Low Temperature MOCVD of WNxCy

As the feature size of electronic devices continues to shrink, the integrated circuit device density increases. This not only modifies the RC time delay to severely limit the device performance, but also places increased demand on Cu metallization effectiveness (1). The extremely high diffusivity of Cu in Si and its ‘killer’ effect on devices has led to the requirement of a barrier layer to prevent Cu transport into the underlying Si. Among various candidates, W-based nitrides have shown promise as replacements of current barrier layers due to their good thermal stability, low resistivity, and the possibility of one-step CMP with Cu slurry (2, 3). In addition, a single barrier layer process is simpler than the Ta-based barrier layer, which needs a double layer of TaN and Ta. The performance of W-based nitrides increases when they are alloyed with carbide to make WNxCy due to its higher crystallization temperature and possibility to adjust film resistivity to lower values. The tungsten nitrido complex WN(NMe2)3 was demonstrated to serve as a single-source precursor for metal organic chemical vapor deposition (MOCVD) of WNxCy films at temperatures as low as 125 ˚C (4). The goal of this study is to understand decomposition mechanisms and their kinetics for the WN(NMe2)3 precursor, and furthermore, to optimize conditions for deposition of the WNxCy film. To elucidate the mechanism and kinetics of thermal decomposition of WN(NMe2)3, in-situ Raman spectroscopy was used to quantitatively measure the disappearance of precursor and appearance of products. An up-flow, cold-wall MOCVD reactor was designed to perform Raman scattering experiments along the centerline of the reactor (5). The system design allows the CVD reactor to translate along three-dimensionally, to permit the laser to focus on any spot in the reactor. In-situ Raman experiments were performed using a heater set point temperature of 650 ˚C. Axial centerline temperature profiles in the reactor are measured by analysis of the rotational bands of the diatomic N2 carrier gas. Due to the low volatility of the precursor, it was dissolved in liquid pyridine and delivered to the reactor as an aerosol with N2 carrier gas (6). The 532 nm line of a Nd:YVO4 solid-state laser at 1.5 W was used as the light source to excite the molecules in the sample. Raman spectra were measured at various distances below the heated susceptor surface and thus various temperatures from 159 ˚C to 474 ˚C. Density Functional Theory (DFT) calculations (using the B3LYP functional and LanL2DZ basis sets) were performed to assess possible pathways of thermal decomposition of WN(NMe2)3 and to assign observed Raman peaks to the decomposition products. The results of this study are consistent with proposed mechanistic steps for the thermal decomposition of the precursor, including dimerization of the precursor and loss of the amine. In addition to gas phase data, liquid phase Raman experiments were performed to better define additional species that are Raman active but not detected in the lower density gas phase experiments and to find vibrational frequencies before the molecule is decomposed.

On copper diffusion in silicon measured by glow discharge mass spectrometry.

Copper contamination occurs frequently in silicon for photovoltaic applications due to its very fast diffusion coupled with a low solid solubility, especially at room temperature. The combination of these properties exerts a challenge on the direct analysis of Cu bulk concentration in Si by sputtering techniques like glow discharge mass spectrometry (GDMS). This work aims at addressing the challenges in quantitative analysis of fast diffusing elements in Si matrix by GDMS. N-type, monocrystalline (Czochralski) silicon samples were intentionally contaminated with Cu after solidification and consequently annealed at 900 °C to ensure a homogeneous distribution of Cu in the bulk. The samples were quenched after annealing to control the extent of the diffusion to the surface prior to the GDMS analyses, which were carried out at different time intervals from within few minutes after cooling onward. The Cu profiles were measured by high-resolution GDMS operating in a continuous direct current mode, where the integration step length was set to ∼0.5 μm over a total sputtered depth of 8-30 μm. The temperature of the samples during the GDMS analyses was also measured in order to evaluate the diffusion. The Cu contamination of n-type Si samples was observed to be highly material dependent. The practical impact of Cu out-diffusion on the calculation of the relative sensitivity factor (RSF) of Cu in Si is discussed.

Upper limit on room-temperature diffusion of metal impurities interstitially dissolved in amorphous Si

Impurity profiles of Cu and Ag in amorphous silicon were studied before and after one year storage at room temperature and found to be indistinguishable. Since just before storage, hydrogen had been ion implanted into the uniformly metal doped layer, a diffusivity in excess of 3 × 10−24 m2/s would have led to an observable change in the impurity profile. Therefore the room-temperature diffusivity must be less than that (3 × 10−24 m2/s), which in turn implies one of two possibilities: either the interstitial diffusivity is much lower than previously determined, or the metal impurities were not fully detrapped by the implanted hydrogen. A subsequent thermal anneal at 450 °C confirmed that the detrapping and diffusion of Ag and Cu in H-implanted amorphous Si conforms to its normal behaviour. The low value of the room-temperature diffusivity is important for the interpretation of forthcoming measurements on high-energy ion tracks in amorphous Si.

Novel Low-Temperature-Sintering Type Cu-Alloy Pastes for Silicon Solar Cells

This paper describes a novel Cu paste for low temperature sintering, which is required to fabricate electrodes on transparent conductive films in heterojunction solar cells. For this, glass-fritless Cu-alloy pastes containing a low melting point alloy (LMPA) were prepared. The pastes were evaluated in terms of printability, contact resistance, line resistance, adhesive property, diffusion of Cu in Si, and oxidation resistance. It was concluded that the pastes could be applicable to silicon solar cells requiring low temperature processes.

Transition from exo to endo Cu absorption in CuSi n clusters: a genetic algorithms density functional theory study

The characterisation and prediction of the structures of metal silicon clusters is important for nanotechnology research because these clusters can be used as building blocks for nanodevices, integrated circuits and solar cells. Several authors have postulated that there is a transition between exo and endo absorption of Cu in Si n clusters and showed that, for n larger than 9, it is possible to find endohedral clusters. Unfortunately, no global searches have confirmed this observation, which is based on local optimisations of plausible structures. Here, we use parallel genetic algorithms (GAs), as implemented in our modified genetic algorithms (MGAC) software, directly coupled with density functional theory energy calculations to show that the global search of CuSi n cluster structures does not find endohedral clusters for n < 8 but finds them for n ≥ 10.

Deposition of WNxCy from the Tungsten Piperidylhydrazido Complex Cl4(CH3CN)W(N-pip) as a Single-Source Precursor

The tungsten piperidylhydrazido complex Cl4(CH3CN)W(N-pip) (1) was used as a single-source precursor for film growth of tungsten carbonitride (WNxCy) by metal-organic chemical vapor deposition (CVD) in H2 carrier. Multiple spectroscopic techniques were used for preliminary evaluation of the suitability of 1 as a precursor and to suggest possible fragmentation pathways. The microstructure of films deposited below 500°C was X-ray amorphous, with the highest N content in the film occurring for growth at 400°C. The chemical bonding state of films deposited at 400°C was WNxCy, while tungsten oxide (WO3) was observed for films deposited at 300°C. Film growth rates varied from 2.7 Å/min (300°C) to 29.4 Å/min (700°C) with deposition temperature. The lowest measured resistivity value is 0.9 mΩ cm for a film grown at 550°C. The diffusion barrier properties were investigated using Cu/WNxCy/Si stacks consisting of Cu deposited by reactive sputtering on WNxCy films deposited at 400°C. The Cu/WNxCy/Si stacks annealed at 500°C for 30 min maintained the integrity of both Cu/WNxCy and WNxCy/Si interfaces as determined by x-ray diffraction measurement, detection of etch-pits, and the Auger electron spectroscopy depth profile. These results support the conclusion that WNxCy deposited from 1 is a viable barrier material to prevent diffusion of Cu in Si for Cu interconnect technology.

The Stable Site and Diffusion of Impurity Cu in Si

The Stable Site and Diffusion of Impurity Cu in Si

Changes in Concentrations of Copper and Nickel on Boron-Doped Czochralski-Grown Silicon Surface at Room Temperature

In the diffusion of metal impurities in single-crystal silicon (c-Si), it is well known that Cu and Ni atoms diffuse very quickly within the crystal matrix. From various studies on diffusivity in bulk Si, it is clear that such elements can easily move through the Si matrix. In this paper, the time-dependent change in the concentrations of Cu and Ni metals on the Si surface at room temperature is reported. In this study, this change is evaluated by wet chemical analysis, and it is shown that this change results from the high diffusivity of Cu and Ni in Si at room temperature. Furthermore, it is shown that the Ni atoms move independently of the B concentration in Si, and it is possible to predict the diffusion behavior of Cu and Ni in p-type Si at room temperature on the basis of using the conventional thermal diffusion theory.

Atomic Diffusion in Cu/Si (111) and Cu/SiO2/Si (111) Systems by Neutral Cluster Beam Deposition

The Cu films are deposited on two kinds of p-type Si (111) substrates by ionized cluster beam (ICB) technique. The interface reaction and atomic diffusion of Cu/Si (111) and Cu/SiO2/Si (111) systems are studied at different annealing temperatures by x-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). Some significant results are obtained: For the Cu/Si (111) samples prepared by neutral clusters, the interdiffusion of Cu and Si atoms occurs when annealed at 230°C. The diffusion coefficients of the samples annealed at 230°C and 500°C are 8.5 × 10-15 cm2·s-1 and 3.0 × 10-14 cm2·s-1, respectively. The formation of the copper-silicide phase is observed by XRD, and its intensity becomes stronger with the increase of annealing temperature. For the Cu/SiO2/Si (111) samples prepared by neutral clusters, the interdiffusion of Cu and Si atoms occurs and copper silicides are formed when annealed at 450°C. The diffusion coefficients of Cu in Si are calculated to be 6.0 × 10-16 cm2·s-1 at 450°C, due to the fact that the existence of the SiO2 layer suppresses the interdiffusion of Cu and Si.

Fe and Cu in Si: Lattice sites and trapping at implantation-related defects

We have used the emission channeling technique in order to study the lattice sites of radioactive 59Fe and 67Cu following 60keV ion implantation into Si single crystals at fluences around 1012–1014cm−2. We find that in the room temperature as-implanted state in high-resistivity Si both Fe and Cu occupy mainly lattice sites displaced around 0.05nm (0.5Å) from substitutional positions. Both are released from these positions during annealing at temperatures between 300°C and 600°C. Fe is then found mainly on near-tetrahedral interstitial sites and further annealing causes it to be increasingly incorporated on ideal substitutional sites, on which it is stable to around 800°C. We have strong indications that during annealing around 600°C, along with the dominance of interstitial Fe, a redistribution towards the surface takes place, suggesting that the subsequent formation of ideal substitutional Fe may be related to the trapping of Fe at Rp/2, half of its implanted depth. Possible Rp/2 trapping might also have taken place in our Cu experiments but appears to be less efficient since Cu tended to escape to the bulk of the samples.

Electronic state of interstitial Cu in bulk Si: Density functional calculations

The behavior of the interstitial Cu atom in an otherwise clean Si crystal has been examined by means of density functional calculations. It is found that Cu basically stays at the tetrahedral site with hardly any electrons promoted from the 3d to the 4sp shells. Our calculations confirm the well-known fact that interstitial Cu in Si donates its 4s electron to the surrounding lattice. The 4s state is found to be very diffuse as the resulting Cu+ ion is effectively screened by the Si environment. When the precision in calculations is lowered, Cu starts moving away from the tetrahedral site. The results of our calculations with atomic-type orbitals emphasize the importance of using a consistent basis set: if Si atoms in the vicinity of the impurity are treated differently from remaining Si atoms and the basis sets are not both sufficiently complete, artificial confinement of electrons will occur.

Activity measurements of Al and Cu in Si–Al–Cu melt at 1273 and 1373 K by the equilibration with molten Pb

For the effective control of Al introduction to solidified Si during the solidification refining of Si with the Si–Al-based melt for the solar cell material or the LPE Si film growth processes from the Si–Cu–Al solvent, thermodynamic properties of the Si–Al–Cu melt were investigated at 1273 and 1373 K. Activities of Al and Cu in the Si–Al–Cu melt were measured by the equilibration with molten Pb. Also, the excess Gibbs energy of the melt was studied by the ternary regular solution model. The evaluated thermodynamic properties of the Si–Al–Cu melt indicated that Cu addition to the Si–Al melt brings the smaller activity coefficient of Al and is effective for reducing the Al content of solidified Si from the melt more effectively than its dilution effect for Al.

2808 金属/セラミックスの超音波接合に関する研究 : 第6報 消費エネルギーの比較(S35-2 溶接・接合の動向とその展開(2),S35 溶接・接合の動向とその展開)

The Ultrasonic welding has made possible to weld various ceramics to various metals at room temperature, quickly and easily compared to other welding methods. In addition, the weldability is improved by preheating. This paper shows to be possible to weld Al, Cu, Ag, and Mg (AZ31) in Si_3N_4 directly used ultrasonic vibration. Using the low melting metal, the weldability is better, welding strength is higher, and welding energy is lower. The welding energy used by ultrasonic welding is less than that used for resistance welding.

Thermodynamics of solid silicon equilibrated with Si–Al–Cu liquid alloys

For discussing the addition of copper to the Si–Al solvents in the LPE growth of silicon and that in the solidification refining of silicon, the solubilities of aluminum at 1173, 1273, and 1373 K and copper at 1273 and 1373 K in solid silicon in equilibrium with liquid Si–Al–Cu alloys were investigated. Solubilities of aluminum and copper were determined by employing the temperature gradient zone melting method and diffusion experiment, respectively. The activity coefficient of copper in solid silicon at infinite dilution relative to the pure solid state was determined as follows R T ln γ Cu ( s ) in solid Si 0 = 166 , 000 ( ± 3500 ) − 47.6 ( ± 2.8 ) T ( J / mol ) ( 975 – 1602 K ) Copper additions to the Si–Al solvents decreased aluminum solubilities in solid silicon effectively and the contents of copper introduced into solid silicon were found to be fairly small.

Copper related diffusion phenomena in germanium and silicon

This paper concerns diffusion related properties of Cu in Ge and Si. In Ge, Cu prefers to occupy a substitutional lattice site whereas Cu in Si is mainly dissolved on an interstitial position. This difference in the lattice site occupancy is also reflected in the diffusion behaviour. Whereas Cu diffusion in Ge is accurately described on the basis of the dissociative mechanism, which involves Ge vacancies for the conversion of Cu from interstitial to substitutional sites, the diffusion of Cu in Si is mainly mediated by the direct interstitial mechanism. The specific diffusion behaviour of Cu in Ge and Si as well as its electronic properties strongly affect other diffusion related phenomena such as the precipitation and gettering of Cu. Detailed understanding of the latter processes are of fundamental technological significance to keep the contamination of electronic devices during processing to a harmless level. The various aspects of Cu in Ge and Si, which are the result of former and recent experiments, are reviewed in this paper.