No abstract

No abstract

No abstract

A colloidal AFM-based method was used to understand the role of diallyldimethyl ammonium chloride (DADMAC) molecules in non-Prestonian silicon dioxide removal obtained using ceria-based slurries. A series of force-distance measurements between silicon dioxide films, polyurethane IC1000 polishing pad and ceria abrasives in liquid media with and without DADMAC molecules were made. It was shown that at 15 mM concentration, DADMAC molecules yield non-Prestonian behavior by interfering between ceria particles and the oxide film. The effects of the DADMAC additive on the removal rates of the oxide films and their corresponding coefficients of friction (COFs) values were also investigated. Finally, the correlation between AFM force measurements, removal rates and COF values measured during polishing are discussed. Interestingly, below a threshold COF value of ∼0.23 to 0.24, corresponding to a threshold down pressure of ∼2psi for both 15 mM and 25 mM DADMAC concentration, no oxide film removal was observed. Chemical Mechanical Planarization (CMP) is a critical step during the fabrication of ultra large scale integrated circuits (ULSICs) in the semiconductor industry. Since the feature dimensions of current ICs are continually scaling down (latest technology node of 14 nm was recently announced by Intel corp.), the demands on surface planarity of various films have become more stringent. An improved understanding of polishing mechanisms can help to achieve the desired polishing requirements. These requirements include minimizing defects such as surface roughness, micro-scratches, etc. 1,2One of the main applications of CMP in the front-end-of-the-line is shallow trench isolation (STI) fabrication. The STI 3 structure isolates two adjacent semiconductor device components (transistors, diodes, etc.) preventing electrical current leakage between them. Application of CMP for fabricating these STI structures has been widely studied. However, precise end-point detection during the fabrication of these structures remains a challenge. As a result, due to the non-uniform polishing of the oxide film across the wafer, 4 over-polishing time is almost always required to remove any residual oxide from the nitride areas. This can result in considerable dishing in the oxide-filled trenches in the STI structure. Dishing takes place if the oxide material inside the trenches is polished, especially at the low pressures created by contact with the polishing pad. One efficient method that can minimize dishing is to use a non-Prestonian polishing slurry [5][6][7] which causes negligible removal below a threshold applied downward pressure. Recently, it was shown that a ceria-based slurry containing 15 mM diallyldimethyl ammonium chloride (DADMAC) as an additive resulted in non-Prestonian oxide removal 7 with negligible removal below ∼2 psi applied pressure. Based on the measurements of the adsorption strength of DADMAC molecules on ceria and silica surfaces, using various techniques including thermo-gravimetric analysis (TGA) and UV-visible sp...

No abstract