Effect of La doping of ceria abrasives for STI CMP

Abstract

The nitride removal rate by ceria abrasives in presence of amino acids is altered by the purity of ceria. Commercial ceria obtained from Sigma-Aldrich with low purity (<90%) and with high purity (99.95%) were employed in the study. Polishing experiments showed that in presence of lanthanum in the abrasive, proline does not suppress nitride removal. In order to verify that the effect is mainly due to presence of lanthanum, ceria particles were synthesized with and without lanthanum doping. Three types of amino acids viz. proline, alanine and glutamic acid were used with the ceria particles. The removal rate results show that proline is sensitive to presence of lanthanum impurity in abrasive, while alanine and glutamic acid suppress the nitride removal irrespective of the purity of the abrasives. The abrasives were characterized using XRD. The adsorption of amino acids on abrasive was characterized by differential thermal analysis