A controlled atmosphere polishing ͑CAP͒ system was used to determine the effects of various chamber gases on copper chemical mechanical polishing ͑CMP͒ in the presence and absence of NH 4 OH and H 2 O 2 . Using 500 kPa oxygen or nitrogen has only slight effects on copper removal rates in the presence of 1 wt % H 2 O 2 . Polishing without H 2 O 2 , performed with controlled oxygen partial pressure, demonstrates removal rates that are 4 times higher than using nitrogen. Polishing using inert gases alone demonstrates an oxidant-starved system that reflects little dependence on wafer pressure or velocity. Addition of NH 4 OH ͑pH 10͒ to experiments using oxidizing gases, such as oxygen and air, increases removal rates up to 3ϫ. Removal rates vary linearly with oxygen partial pressure using oxidizing gases for experiments using NH 4 OH at pH 10. A trend indicating a transition from chemical to mechanical control is observed when NH 4 OH concentration is increased at constant oxygen pressure. A copper removal mechanism in the presence of dissolved oxygen has been developed that highlights a buildup of oxidized copper at the wafer surface. The ability to perform CMP in a pressurized gaseous environment has shown that copper removal is a process of mechanical removal, dissolution of abraded material, and copper-oxygen reactions at the wafer surface.
A controlled atmosphere polishing system ͑CAP͒ was used to identify differences in copper chemical mechanical polishing ͑CMP͒ removal characteristics by changing oxygen partial pressure. A two-step kinetic mechanism was proposed, including a copper surface passivation layer formation and subsequent removal. A semiempirical, two-parameter model has been developed to simulate removal rates for multiple wafer pressures, pad-wafer velocities, and oxygen concentrations. The model accurately predicts removal trends with calculated root-mean-square errors of 77-125 A/min. A major advantage of the CAP system is that a point-of-use gaseous oxidant was successfully used to polish copper substrates, and slight changes in oxidant partial pressure were found to significantly affect removal rate trends.
An innovative dilatancy polishing pad of which characteristics are controlled with processing conditions is proposed to establish high-efficiency, high-quality polishing of hard-to-machine materials for next-generation high-power devices. To make the best use of the property of the dilatancy pad, a highly durable polishing machine which enables high-pressure, high-speed, and immersed polishing was developed. Dilatancy properties were evaluated for various viscoelastic materials to select appropriate materials for a pad. The selected viscoelastic material was mixed with a special filler and abrasive particles, and integrated into a conventional polishing pad to form a dilatancy pad. Application of the dilatancy pad to polishing of SiC realized a smart polishing which achieves both high efficiency and high quality in any processing conditions. In addition, it was demonstrated that the processing conditions could be selected for the purpose of each polishing step, i.e. mid- to high-speed conditions for high-efficiency polishing and low-speed condition for high-quality finishing. A newly developed highly durable polishing machine is capable of achieving wide range of processing conditions. To avoid overheating under high load conditions, the machine can polish a work piece in slurry fluid. The material removal rate using the dilatancy pad showed superlinear dependence on the rotation speed, which outperforms the conventional polishing following the Preston's law. This innovative process can significantly reduce the polishing time of hard-to-machine materials for next-generation semiconductor devices.
We synthesized a series of polysilanes -[Si(CH 3)2SiR2]n-[R ) C2H5, n-C4H9, n-C6H13, n-C8H17, n-C10H21] end-grafted on a quartz surface by utilizing the anionic polymerization of the corresponding source materials. We first confirmed that these symmetrically alkyl-substituted polysilanes exhibited reversible thermochromism in isooctane solution. When the polysilanes were end-grafted on the quartz surface, they also exhibited reversible thermochromism in a vacuum and reversible solvatochromism as the ratio of the isooctane/ethanol cosolvent was varied. In all of these experiments, we observed the transition between two clearly distinguishable phases. No side chain effect was observed for the peak wavelengths of the absorption band. However, the side chain effect appeared at a critical temperature and a critical cosolvent ratio for the transitions. The packing force between the alkyl chains in the highly ordered structure of the polysilane plays a dominant role in these transitions. We also discuss the difference in the transition behavior in solution, in the solid state, and in the end-grafted state.
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