Study On The SiO₂ Water-based Polishing Slurry By Experiments

With the rapid development of communication and network, the integrated circuit ( IC ) is becoming increasingly demanding. So it is developing continuously in high speed, high integration, high density and high performance ways. On the chip manufacturing side, on the one hand, the wafer size increases in order to reduce the production cost; on the other hand, the line width decreases to improve the integration of the circuit. Because of the increasingly stringent requirements of the Silicon wafer surface flattening and the requirements of material removal rate, surface roughness and surface / subsurface non injury in polishing behavior, CMP was currently widely used as a recognized global planarization of practical technology in IC manufacturing. In the traditional CMP, as the material consumption, the polishing slurry accounted for 40 percent of total costs of CMP process, but the utilization rate was only 20 percent. So the overuse of polishing slurry was not only one of the main reasons of IC high cost, but it produced considerable quantities of slurry waste contributing to polluting the environment. In view of above problems, in allusion to the improvement about the conventional CMP liquid application method, the ultrasonic fine atomized CMP process was put forward.This paper aimed to develop a kind of alkaline slurry for ultrasonic fine atomized CMP. For improving material removal rate, reducing the metal ion pollution and improving the utilization rate of slurry, the paper made the component selection and content optimization analysis through many experiments. Also the ultrasonic atomization characteristics and slurry removal mechanism were analyzed. Finally the slurry prescription was found which a little slurry could obtain a higher material removal rate and good surface topography.Firstly, the principle of ultrasonic fine atomization CMP and the slurry polishing mechanism have been studied, and the slurry component selection and content optimization have been established upon them. In the ultrasonic atomized CMP, the fine spray, which from the slurry through the high frequency oscillation of atomizing piece in the ultrasonic atomizer, was rapidly guided onto the polishing pad to full contact surface of the silicon wafer under the action of the negative pressure. As a result of the alternant action of chemical corrosion and mechanical grinding, the material was removed and ultra smooth precision surface was formed. Study found that the abrasive, pH value regulator, surfactants, and antioxidant in the slurry have an important effect on polishing quality.Then, analyze the components in slurry and find the best ones by the single factor experiment. Silica particles were selected as the abrasive because of the good polishing selectivity and good dispersion. Without the metal ion, the organic alkali was chose to the slurry's pH value regulator. After ultrasonic fine atomized CMP, the slurry containing three ethylamine had the best results that the material removal rate was 476 nm/min and the surface roughness was 3.2 nm. The alkylphenol polyoxyethylene got the best static test effect to be the surfactant. Hydrogen peroxide was selected as the oxidant since no metal ion and the oxidation in the alkaline environment. Finally, by orthogonal test, the slurry component content was optimized and the slurry prescription which had high material removing rate and good surface topography was found. And compare with the conventional polishing effect parameters of the purchased SSP-L suspension slurry. The result shows that the MRR is 490 nm/min and the Ra of the silica wafer is 2.7 nm when the components ratio of the self-made slurry as the following: SiO2 accounted for 20 wt%, pH was 11, surfactant accounted for 0.5 wt% and oxidant accounted for 2 wt%. The polishing effect of the self-made slurry in the atomization CMP closed to that of the SSP-L slurry in the conventional CMP, but the dosage of the atomization CMP was less than one-tenth of the conventional CMP. The reason may be that the atomized liquid is helpful to remove the material and form the ultra precision surface, because of the homogeneous chemical composition, the high activity and strong adsorption on the interface of chemistry reaction.