We examined the effect of the molecular weight of surfactants in ceria slurry during chemical mechanical polishing (CMP) for shallow trench isolation (STI). We found that for a surfactant with a higher molecular weight, the oxide removal rate decreased drastically as the surfactant concentration increased, but in the case of a lower molecular weight, it only slightly decreased. In addition, slurries whose surfactants had lower molecular weights maintained a higher nitride removal rate with increasing surfactant concentration. The results showed that the molecular weight and surfactant concentration have complex effects on the oxide removal rate and the oxide-to-nitride removal selectivity.
Through chemical mechanical polishing (CMP) tests using polycrystalline silicon (polysilicon) and oxide blanket film wafers, the effects of alkaline agents added to colloidal silica slurries were investigated. With increasing concentration of the alkaline agent, a decreasing trend after an initial increase in the polysilicon removal rate was found, along with a low oxide removal rate, enabling high selectivity. The surface roughness similarly became worse and then better with increasing concentration of the alkaline agent. The results suggest a mechanism in which hydroxide bonds to the Si surface of the abrasives in the slurry and OH- attaches to the polysilicon surface. The silanol group induces high polarization and thus weakens the Si–Si back bonds. These results can be qualitatively explained in terms of the chemical reaction between the polysilicon surface and the alkaline agent in the slurry, according to the hydrophobicity and hydrophylicity as indicated by contact angle measurements.
We have investigated how controlling the pH, molecular weight, and concentration of the surfactant in ceria slurry affects the nitride film loss and oxide-to-nitride selectivity in the shallow trench isolation (STI) chemical mechanical polishing (CMP) process. We found that for a surfactant with a higher molecular weight, the oxide removal rate markedly decreased as the surfactant concentration increased, but in the case of a lower molecular weight, the removal rate only slightly decreased. In addition, with increasing surfactant concentration and addition of surfactant with the same molecular weight, the nitride removal rates for all slurries markedly decreased and very quickly saturated at a lower surfactant pH. Moreover, with an increase in the surfactant concentration from 0.1 to 0.3 wt %, the slurries whose surfactants had a medium or the lowest molecular weight maintained higher nitride removal rates than did the slurry whose surfactant had the highest molecular weight.
This paper proposes a novel contrast enhancement method which determines the stretching ranges based on the distribution densities of segmented sub-histogram. In order to enhance the quality of image effectively, the contrast histogram is segmented into sub-histograms based on the density in each brightness region. Then the stretching range of each sub-histogram is determined by analysing its distribution density. The higher density region is extended wider than lower density region in the histogram. This method solves the over stretching problem, because it stretches using density rate of each area on the histogram. To evaluate the performance of the proposed algorithm, the experiments have been carried out on complex contrast images, and its superiority has been confirmed by comparing with the conventional methods.
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