Formulation of slurry for chemical mechanical polishing of Cu substrates

Abstract

The present study focuses on polishing of the Copper (Cu) metal by exploring various oxidizers in the presence of fumed silica slurry. Screening of oxidizers was done in order to get a desired polish rate for copper metal at two extreme pH regimes. Slurry is formulated to find robust polish rate for Cu Chemical Mechanical Planarization (CMP). The removal rate was investigated by using ammonium peroxydisulphate, potassium persulphate and potassium hydrogen phthalate in fumed silica slurry. Potassium persulphate showed highest material removal rate (RR) among all oxidizers at pH 9. For polishing Cu, alkaline slurry is always preferred due to the accumulation of passive layer on surface, which restricts direct dissolution of metal ions, which is prevalent in acidic region. Cu polishing done after addition of fumed silica abrasive in potassium persulphate solution at all pH values enhanced polishing rate due to the added mechanical abrasion to the chemical action. Addition of benzotriazole (BTA) as corrosion inhibitor to the slurry decreased polishing rate for complete pH range, attributed to the deposition of insoluble Cu compounds on the Cu metal surface. With increase in pressure and turntable speed an increase in removal rate was observed signifying that the proposed slurry follows non-Prestonian behaviour.