Materials Science Forum Vol. 815

Abstract: Silver nanoparticles (Ag NPs) thin film were fabricated by radio-frequency (RF) magnetron sputtering on the quartz substrates in different sputtering time, then covered with a layer of rubrene by means of thermal evaporation. The sputtering time for preparation of Ag NPs could be tuned to increase the spectral overlap between the emission spectra of rubrene and surface plasmon resonance spectra, so that the surface plasmon enhancement was improved. Using a Fluorescence spectrophotometer (FLS920), the photoluminescence (PL) intensity of the rubrene/Ag NPs thin film was up to 22 times higher than that as-deposited rubrene thin film. It is attributed to the energy transfer effect in the surface plasmon resonance coupling, the surface plasmons mediated emission, and light scattering.

Abstract: High-purity precious metal and its alloy targets make a very important role in semiconductor manufacturing. In this paper, the preparation methods of high performance sputtering targets (including silver, platinum and its alloy, ruthenium materials) for advanced semiconductor manufacturing were introduced. The relationships between deposited film behaviors and sputtering target properties in some applications were also discussed. In order to acquire high quality thin film, the properties of sputtering target such as density, alloy composition homogeneity, grain size and uniformity et al. have to be well controlled by proper fabrication techniques.

Abstract: In the present study, epoxy based composite filled with meso and non-porous silica microspheres with similar size were prepared respectively and their rheological and thermo-mechanical properties were studied systematically. The results showed that the mesoporous silica/epoxy composites showed much higher viscosity, storage modulus and glass transition temperature (Tg) while lower coefficient of thermal expansion (CTE) than did epoxy composites with nonporous silica particles, which could be attributed to the stronger interface interaction between the mesoporous silica filler with larger specific surface area (BET) and the epoxy matrix.

Abstract: The center of czochralski (CZ) wafer for solar cell often has black center, due to the existence of high impurities content, many defects such as dislocations. This has serious effect on solar cells’ conversion efficiency. To solve this problem, we developed a new kind of material-czochralski and floating zone (CFZ) silicon. But there is still black center in the CFZ-Si wafer with conventional process. In order to solve this problem successfully a new technology-alternant forward and reverse rotation was introduced. By testing the crystal defects, metal and oxygen impurities content, it has been found that the black center is related to oxygen distribution in the wafer. However since the content was very low and not enough to affect the solar cells’ conversion efficiency, which has been testified in solar cell. Therefore CFZ technology offers a new kind of silicon material, which can avoid the black center problem in CZ silicon wafer.

Abstract: A method for detecting impurities in high purity BCl₃ was described in the present work. GC, ICP-MS, FTIR and colorimetric method were applied to analyze high-purity BCl₃. The quantitative results of the impurities such as N₂, CO, CO₂ and Fe demonstrated that these methods had excellent repeatability (RSD<3%), reproducibility. The ICP-MS detection accuracy can achieve ppb limiter. The FTIR method provided opportunities for the determination of HCl, COCl₂, which have difficulties in quantification with other method.

Abstract: To find the optical properties of Cu₂ZnSnS₄ (CZTS) absorber in two crystal structures (kesterite and stannite) which are key factors determining solar cell performance and are based on the electronic structures, a systematical calculation of electronic and optical properties were calculated using density functional theory. The results suggested that the optical properties of CZTS had a rather weak dependence on the (Cu, Zn) cation ordering. Kesterite and stannite CZTS both suited for photovoltaics with large light absorption coefficient ( > 10⁴ cm^-1 ) in the visible light region that is the most important part for photovoltaics, and kesterite CZTS had larger light absorption than stannite CZTS exhibiting a more obvious advantage. In the visible light region the reflectivity of CZTS was lower than that of silicon, the absorber material used most widely, which might be in favor of light absorption and cell efficiency. Ground-state structure, electronic transitions relevant to solar light absorption, static dielectric constant and plasma frequency were also investigated.

Abstract: Highly (100)-oriented LaNiO₃ (LNO) thin films were prepared on p-type Si (100) substrates by metal organic solution deposition (MOSD). The LNO thin films were driven by series precursor solutions with different ratio of acetic acid to deionized water (R_aaw) and pH values. The dependences of viscosity, pH value and the thermal property of the gel-derived powders of the precursor solution on R_aaw values were systematically investigated. AFM images showed that R_aaw can dramatically influence the surface roughness. When R_aaw changed from 7:1 to 1:1, the surface roughness decreased from 3.695 nm to 1.488 nm. The resistivities of all the films are less than 2.1×10^-3Ω·cm. It shows that the precursor solution has strong effect on the microstructure of the thin films and relatively slight effect on the resistivity.

Abstract: In the present study, Cobalt nanoparticles were synthesized and mixed with Sn-3.0Ag-0.5Cu solder (SAC305). The effect of 0.05 wt.%, 0.2 wt.%, 0.5 wt.% and 1.0 wt.% Co nanoparticles on the wettability, the shear strength as well as the growth of intermetallic compounds (IMCs) at composite solder/Cu interface during thermal cycling were investigated. Results show that Co nanoparticle addition can considerably improve wettability, increase the shear strength and suppress the growth of interfacial IMCs. The addition amount of Co nanoparticles have the consistent relation with the improvement extent of the wettability, shear strength and the growth rate of interfacial IMCs. Slight addition (0.05 wt.% and 0.2 wt.%) can significantly improve the properties of nanocomposite solder in all the three aspects. However, with excessive addition amount (0.5 wt.% and 1.0 wt.%) of Co nanoparticles, the improvement extent will decline. The Cross-section images of the interface of nanocomposite solder/Cu joint show that Co can form reinforcement particles in the solder and can act as the sacrificial element to substitute Cu to react with Sn. Excessive Co nanoparticles would form large amount of hard and brittle intermetallics which leads to decreasing shear strength of the composite solder.

Abstract: In the present study, the effect of addition of Ni nanoparticles on the growth of the intermetallic compound (IMC) layer between low-silver lead-free solder and Cu substrate was investigated. Ni nanoparticles were synthesized and smelted with pure Sn, Ag to prepare Sn-1.0Ag-xNi (x=0, 0.05, 0.1, 0.2) solder alloy. Sn-1.0Ag-xNi was soldered on a copper substrate, and then the solder/Cu couples were isothermally aged at 423K for 360h.The Cross-section images of IMCs layer were obtained to observe the morphology of IMC and to measure the thickness of Cu₆Sn₅ and Cu₃Sn layers respectively. The results show that, during aging, addition of Ni can remarkably improve the morphology of IMC, level the scalloped IMC, facilitate the growth of the total interfacial IMCs and inhibit the growth of Cu₃Sn. Moreover, the rate change of thickness of the Cu₃Sn reduced obviously with the increase of Ni nanoparticles. Comprehensive analysis shows that the addition of Ni promotes the nucleation and growth of Cu₆Sn₅. The thermodynamics calculation on the solder alloy was identical with the experiment result.

Abstract: The research on a new low-Ag lead-free solder has become a hot spot in the field of electronic packaging. In this work, the effects of Bi addition on microstructure, melting temperature, wettability of low-Ag solder, shear strength of solder joint and the growth of interfacial intermetallic compound (IMC) before and after thermal cycling were investigated. A moderate amount of Bi element resulted in the microstructural refinement and melting temperature reduction of Sn-0.2Ag-0.7Cu solder. Wetting test results showed that a small amount of Bi produced the significant effect on improving the wettability. In addition, it is shown that the thickness of interfacial IMC during thermal cycling decreased first and then increased; the shear strength of solder joint increased with the increase of Bi.