Papers by Author: Li Li

Abstract: With the developing of integrated circuit(IC) technique, improving of integration level, reducing of feature size and increasing the wafer size, the stringent requirements for global planarization during IC fabrication are raised. During chemical mechanical polishing(CMP) of multilevel interconnect for IC, there are obvious influence of the polishing quality on performances of the device．CMP slurry is one of the important factors of influencing the polishing quality. In this work, the stability of tungsten plug CMP slurry for IC multilevel interconnect was studied. Through experiment, interaction between the components in the CMP slurry was analyzed, and stable slurry with optimized polishing parameters to achieve higher removal rate were defined．

Abstract: In the present paper, hot uniaxial compression at elevated temperatures on the samples which had been hot isostatically pressed to 70%-100% relative densities was carried out to investigate the deformation behaviours of porous Ti-6Al-4V alloy. The results show that the flow stress and densification of Ti-6Al-4V alloy have a greater sensitivity on the deformation temperature and strain rate. The flow stress will increase as strain rate increases at the same temperature and the increasing of deformation temperature can lead to a decline in the flow stress at a specific rate. As the deformation temperature rises or the strain rate decreases, the relative density of compressed samples are higher. Moreover, the initial density affects the thermal deformation of powder compact to a certain extent. At the same strain, the greater the initial relative density of Ti-6Al-4V alloy is, the greater the flow stress will be. The flow stress sensitivity to relative density is much less than that to the temperature and strain rate. In addition, the higher the deformation temperature is, the more sufficient the process of alloy spheroidization will be. As the deformation rate decrease, the lamellar organization in the titanium alloy will convert into the equiaxed grains. The lower the deformation rate is, the more obvious the phenomenon of alloy globalization will be. There is not significant transition of the widmanstatten structure in the sample compressed for 2mm. When the sample was compressed for 5.6mm, a few equiaxed grains occurred. When the sample was compressed for 7mm, a large number of equiaxed grain occurred.

Abstract: The forward extrusion experiments of homogenized AZ80 magnesium alloy were conducted in the extrusion temperature range of 300°C to 420°C and extrusion ratios between 15 and 75 to study the effect of plastic deformation on the mechanical properties and microstructure. The microstructure and mechanical properties of extrudate were measured by tensile tests and optical microscopy. The results demonstrated that the alloy grains were small, and small amounts of black hard and brittle second-phase precipitated at 330°C. When the extrusion temperature was up to 390°C, the grain size increased significantly, but the second phase precipitation became continuous. And then, in the case of the extrusion ratio of 60, the tensile strength of the alloy reached the peak value of 390 MPa. Inhomogeneous precipitation of the second-phase increased with the increasing of extrusion temperature. At the same temperature, the tensile strength increased firstly and then decreased with increasing extrusion ratio. With the gradual increase of the grain refinement, the dispersed precipitates increased and the tensile strength and plasticity reached their peaks when the extrusion temperature was 390°C. As the grain grew, the second phase distribution became inhomogeneous, and the strength and plasticity gradually decreased.

Abstract: In the present paper a research has been made on the effect of aging on the microstructure and mechanical properties of AZ80 and ZK60 wrought magnesium alloys by virtue of optical microscope, electronic scanning microscope and mechanical testers. The research indicates that both the tensile strength and elongation of AZ80 alloy first increase and then decrease as the aging temperature rises, and that, at 140°C-170°C aging temperature, the alloy has good performances in both tensile strength and elongation, they both reaching their peak values at 170°C aging temperature. It has been proved in these researches that while the hardness of ZK60 alloy first increase and then decrease as the aging temperature rises and that the hardness reaches its peak value at 170°C aging temperature, the impact of toughness of the alloy is just the opposite. ZK60 alloy has good performances in both impact toughness and other properties at 140-200°C aging temperature. Constrastive researches have shown that, at the same aging temperature, ZK60 alloy has a better performance than AZ80 alloy.

Abstract: TiO2 sol containing nano anatase crystalline grains was prepared using Ti(OC4H9)4 as a precursor in a water-excessive reaction system. The processes of hydrolytic-polymeric reactions and the structures of the products were analyzed. It was found that the -OC4H9 radicals previously linked to Ti atom in Ti (OC4H9) 4 molecular are broken, and there is no organic radicals linked to Ti atoms in the final sol. The structure of particles in the sol changes along with time from tetrahedral [TiO4] to octahedral [TiO6], with the coordination number changing from 3.14 to 5.18, accordingly. Therefore, the structure becomes closer to an anatase, which is octahedral [TiO6] with a coordination number of 6.0. Transmission electron microscope micrograph also reveals the foursquare projection shape of crystalline grains with a size of 200 nm in the sol. As the particles in the sol have a quasi anatase structure, the TiO2 sol can directly photodegrade Rhodamine B under Ultraviolet illumination with a rate of 62.35%.

Abstract: Ag+-doped TiO2 films on stainless steel were prepared by a sol-gel method and their microstructures and compositions were studied with X-Ray Diffractometer, Scanning Electron Microscope (SEM) and X-ray Photoelectron Spectroscopy. It was shown that Fe atoms in untreated stainless steel react with Ag+ in the TiO2 film and form FeTiO3, which has an acicular crystal form under SEM observation. As a result, Ag+ in the film is reduced to the silver atom, which degrades the antibacterial property of the film. However, after an oxidization of the substrate, a layer of ferric oxide is formed, which reacts with Fe atoms that would otherwise react with and reduce Ag+, and then forms FeTiO3. Thus, the penetration of Fe atoms is stopped and Ag+ in the anatase-structure TiO2 film is protected from the reduction, which enhanced antibacterial property of the film.

Abstract: The effect of aluminium sol on the properties and microstructure of corundum-mullite ceramics was investigated. The sample with 1.5 wt% aluminium sol possessed higher room-temperature and high-temperature strengths, while the sample with 3 wt% aluminium sol had higher bulk density, lower apparent porosity and better thermal shock resistance. Aluminium sol not only acts as a binder instead of some polyvinyl alcohol (PVA), but also reacts with silica to form mullite, which improves the properties and microstructure of the ceramics by increasing corundum and mullite phases.

Abstract: The ultra-fine treatment of industrial SiC powder was carried out by fluidized bed opposed jet milling (QLM-100K), and the influences of grinding parameters on the ultra-fine treatment were studied. A better grinding result is achieved through a higher crushing pressure and a higher sorter frequency and the ultra-fine treated SiC powder possesses a smaller particle size, a narrower particle-size distribution, a higher specific surface area and reduced agglomeration. The effects of ultra-fine treatment on the compaction behaviors, sintering behaviors, properties and microstructure of SiC ceramics were investigated. The compact with ultra-fine treated powder has a higher density and a lower sintering temperature. The densification and mechanical properties of the ceramics can be ameliorated obviously and the microstructure defects of the ceramics decrease.

Abstract: The mechanism of the effect that zircon additive had on the properties of 95-alumina ceramic was studied and compared with that of zirconia additive. The results show that zircon additive can decrease the sintering temperature of 95-alumina ceramic, the suitable content of zircon additive is 3% and the suitable sintering temperature is1630°C; under these conditions, the 95-alumina composite ceramic can obtain satisfactory sintering and mechanical properties. Compared with zirconia additive, besides the stress-induced-phase-transformation of ZrO2 and micro-cracks, the toughened mechanism of 95-alumina ceramic with zircon additive also includes zirconia secondary crystallization in the liquid phase.

Abstract: The aim of the present study is to investigate the physical properties and antibacterial performances of Ag+-doped TiO2 film on stainless steel and effects of surface oxidization. In the experiment, the surface of stainless steel was been oxidized by heat treatment (550°C, 1 hour) before the Ag+-doped TiO2 (anatase) film being formed by sol-gel method. Sample A (filmed after surface oxidization), B (filmed without surface oxidization), C (only surface oxidization) and D (neither oxidized nor filmed) were respectively tested for corrosive resistance, abrasive resistance and adhesiveness, and the samples with different content of argentine was tested for antibacterial performance. Results: 1) Corrosion rates of sample A, B, C and D in 10% FeCl3 solution are respectively 1.65%, 1.87%, 2.02% and 3.28%, suggesting that the film has protected the stainless steel from the corrosion; 2) Scratching using a loaded (150 g) pin makes no crack on surface of sample A, while it results a slight scuffing on surface of sample B, suggesting that the surface oxidization has enhanced the abrasive resistance and adhesiveness of the TiO2 film, which may be due to the bridge-like function of the oxidation film; 3)Antibacterial performance is enhanced as the content of doping argentine increases, exceeding 90% when the argentine reached 3%, and the TiO2 film on the oxidized stainless steel performs better in antibacterial test than untreated one.