Characterization of Abrasives on Chemical-Mechanical Polishing Silicon Oxide and Aluminum Thin Films
Dr. George C. Tu
Dr. Ming-Shih Tsai
In the integrated circuit (IC) industry, global planarization of the wafer is an important process to achieve 0.35 um linewidths and multilevel interconnections; chemical-mechanical polishing (CMP) is the most effective technology for global planarization. Abrasives in the slurry play important roles in the CMP process, they are responsible not only for the mechanical abrasion of the materials being polished, but also some interactions related to surface charges between the abrasives and the polishing surface being polished are critical in CMP. In this study, alumina and silica polishing powders are employed in polishing oxide and aluminum films to explore their influences on the chemical-mechanical polishing (CMP) performance. In the case of polishing film with abrasive of the same material, it has been found the mechanical abrasion would dominate the overall material removal. (It should point out that in the present work, aluminum film was assumed as the same material of alumina, since it usually present a passive oxide layer during CMP operation) The removal rate would be strongly depended upon the geometry factors of abrasives, that means higher removal rate could be obtained by polishing with larger and sharp-edged abrasive than that with small and rounded one. The electrostatic interaction between the abrasive and the film tends to dominate the CMP removal rate when the abrasives and the polished films are of different isoelectric points (I.E.P.). The maximum removal rate is obtained at the slurry pH values being between the I.E.Ps. of the polished film and the abrasive. Polishing at this range of slurry pH value, electrostatic attraction exists between abrasives and the films being polishing, which results in the enhancement of impinging frequency of abrasives on the films and absorbing of dissolved materials onto the abrasives. The surface roughness after polishing would depend upon the abrasive size and the pad hardness. Polishing with larger particle size and harder pad would result in rougher surface.