Guihai Luo

Effects of mixed inhibitors in copper chemical mechanical polishing at a low down pressure

The individual and synergistic effects of benzotriazole and sodium dodecyl sulfonate on copper disc are investigated at a down pressure of 3.4 kpa. The corrosion rate is reduced by using benzotriazole, but the surface quality is poor owing to the slow formation rate of copper–benzotriazole protection film. For sodium dodecyl sulfonate, the corrosion rate is further reduced, but slight corrosions can be still observed due to the incomplete coverage of sodium dodecyl sulfonate molecules. The combination of sodium dodecyl sulfonate and benzotriazole leads to the maximum decrease of corrosion rate. Under the benzotriazole/sodium dodecyl sulfonate ratio of 1:3, the average roughness achieves as low as 1.025 nm owing to the soft and dense coverage of benzotriazole/sodium dodecyl sulfonate molecules. Besides, the trends of removal rate, roughness and friction coefficient are proved to be similar for copper discs and copper wafers in slurries with different inhibitors. Therefore, the results presented here are relevant for further developments in the area of low-pressure chemical mechanical planarization of copper lines overlying fragile low-k dielectrics in the new interconnect structures.

Synthesis of dual-doped non-precious metal electrocatalysts and their electrocatalytic activity for oxygen reduction reaction

Abstract The pyrolyzed carbon supported ferrum polypyrrole (Fe-N/C) catalysts are synthesized with or without selected dopants, p -toluenesulfonic acid (TsOH), by a facile thermal annealing approach at desired temperature for optimizing their activity for the oxygen reduction reaction (ORR) in O 2 -saturated 0.1 mol/L KOH solution. The electrochemical techniques such as cyclic voltammetry (CV) and rotating disk electrode (RDE) are employed with the Koutecky-Levich theory to quantitatively obtain the ORR kinetic constants and the reaction mechanisms. It is found that catalysts doped with TsOH show significantly improved ORR activity relative to the TsOH-free one. The average electron transfer numbers for the catalyzed ORR are determined to be 3.899 and 3.098, respectively, for the catalysts with and without TsOH-doping. The heat-treatment is found to be a necessary step for catalyst activity improvement, and the catalyst pyrolyzed at 600 °C gives the best ORR activity. An onset potential and the potential at the current density of – 1.5 mA/cm 2 for TsOH-doped catalyst after pyrolysis are 30 mV and 170 mV, which are more positive than those without pyrolized. Furthermore, the catalyst doped with TsOH shows higher tolerance to methanol compared with commercial Pt/C catalyst in 0.1 mol/L KOH. To understand this TsOH doping and pyrolyzed effect, X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) are used to characterize these catalysts in terms of their structure and composition. XPS results indicate that the pyrrolic-N groups are the most active sites, a finding that is supported by the correspondence between changes in pyridinic-N content and ORR activity that occur with changing temperature. Sulfur species are also structurally bound to carbon in the forms of C–S n –C, an additional beneficial factor for the ORR.

The effects of ultra-smooth surface atomic step morphology on CMP performances of sapphire and SiC wafers

Whether sapphire or SiC wafer, clear and regular atomic step morphology could be observed all over the ultra-smooth wafer surface via atomic force microscopy (AFM) using our CMP technology. However, towards sapphire and SiC wafers, the variations of atomic step widths and step directions on the whole of wafer surface are different. The step widths and step directions on the different positions of sapphire wafer are uniform, while that on SiC wafer are distinct. Thus, the effects of atomic step width on CMP removal rate of sapphire and SiC wafers were studied. On the other side, the CMP removal model of super-hard hexagonal crystalline wafer to realize atomically ultra-smooth surface is proposed. The variations of atomic step morphology towards different defects on sapphire and SiC wafers surface are analyzed, and the formation mechanism of the defects is discussed.