Device fabrication using high density, small pattern size shallow trench isolation ͑STI͒ processes requires material removal selectivity during chemical mechanical polishing ͑CMP͒ steps for optimum product processing and quality control. To improve the selectivity of STI CMP processes, surfactants were applied to selectively polish silica as opposed to silicon nitrides surfaces. A ten-fold increase in selectivity over conventional colloidal silica slurry was achieved by the addition of sodium dodecyl sulfate ͑SDS͒ and pH adjustment. Adsorption characteristics of SDS on silica and silicon nitride were measured as a function of slurry pH and concentration of SDS. As indicated by streaming potential measurements and solution depletion adsorption experiments under acidic pH conditions, SDS adsorption on silicon nitride was significantly higher than silica primarily due to the electrostatic interactions. It was concluded that the preferential adsorption of SDS on silicon nitride results in the formation of a materialselective self-assembled passivation ͑lubrication͒ layer leading to selective polishing. Effects of different alkyl chain length of surfactants were tested. Various mixed surfactant systems were tested and it is believed that the addition of second surfactants promotes the adsorption on silica diminishing selectivity. The material-targeted boundary layer lubrication concept may be used to develop selective CMP polishing slurries.The fabrication of next-generation devices will require advances in shallow trench isolation ͑STI͒ technology. 1-3 STI chemical mechanical polishing ͑CMP͒ is particularly challenging due to the highly integrated and variable pattern density as well as smaller pattern sizes. Less than optimal CMP system can cause several defects such as dishing, nitride erosion, and failure to clear oxide that are detrimental to global planarization. To minimize such defects, current STI CMP processes comprised multistep or raw structure modification such as reverse mask, dummy active area, and additional active area. 1 For better productivity and process simplicity, a minimum number of processing steps is highly desirable. Accordingly, "high selectivity single-step" slurry designs are being widely investigated. 4,5 The term "selectivity" in this paper is defined as the ratio of material removal rate ͑MRR͒ of silica to that of silicon nitride as described below. It is the slurry property as to how much more it can polish silica than silicon nitride Selectivity = Material Removal Rate of Silica Material Removal Rate of Silicon Nitride ͓1͔In general, conventional silica-abrasive-based STI CMP slurries exhibit selectivity in the range of 3-4. 5 Besides its influence on planarization, high selectivity slurries are known to provide more reliable endpoint detection capability. Generally, if the oxide to nitride selectivity is greater than 15, monitoring wafer carrier motor current can be utilized for efficient endpoint detection. 6 In recent years, ceria-based abrasives have shown potential for high selec...

Among various properties of chemical mechanical polishing (CMP) slurry, selectivity plays a key role in global planarization of high density and small pattern size shallow trench isolation (STI) process. Lack of adequate selectivity can lead to defects such as dishing and erosion. To improve the selectivity of STI CMP process, CMP characteristics of silica and silicon nitride wafer were investigated using colloidal silica slurry as a function of slurry pH. Sodium dodecyl sulfate (SDS), an anionic surfactant, was added to increase the selectivity of the slurry. As a result, selectivity increased from 3 to 25. It was concluded that selective passivation layer formed on silicon nitride wafer surface at acidic slurry pH range was responsible for the observed selectivity increase. Adsorption characteristics of SDS on silica and silicon nitride were measured as a function of slurry pH and concentration of SDS. As indicated by zeta potential behavior under acidic pH conditions, SDS adsorption on silicon nitride was significantly higher han silica due to the electrostatic forces. Significantly higher SDS coating on silicone nitride seems to have resulted in lubrication layer leading to increased polishing selectivity.