Chemical mechanical polishing of thermal oxide films using silica particles coated with ceria
- PDF / 282,500 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 96 Downloads / 179 Views
Thermal oxide covered silicon wafers were polished with slurries containing either nano-sized ceria (CeO2) or newly prepared uniform colloidal silica particles coated with ceria. The polish rate of the latter was significantly higher than that of pure ceria. The experiments were carried out using different concentrations of the abrasives at pH 4 and 10. Little effect on the polishing rates was noted when the conditions of the slurries were varied, which was explained by the compensation of two opposite polishing mechanisms.
I. INTRODUCTION
Ceria slurries have been commonly used in polishing silicon oxide films. The CeO2 particles offer certain advantages, such as high polish rates due to their chemical reactivity with the silica substrate. In spite of these advantages, ceria-based slurries have not yet gained widespread commercial acceptance. The reasons include their cost, as well as the broad size distribution and irregular shape of the particles. In addition, the commercial ceria abrasives contain several contaminants that influence negatively their polishing performance, since they can alter the surface morphology, the charge characteristics, and the roughness of the particles, resulting in the excessive scratches and defects of the polished films. Finally, the stability of the slurries can also be affected. So far, limited information has been given on the properties of ceria used in chemical mechanical polishing (CMP). Indeed, in the reported studies data on the characterization of the slurries are either nonexistent or incomplete.1–4 More recently, America5 employed two commercial particles of approximately 440 and 140 nm in diameter and Jindal6 used mixed abrasives of nano-sized ceria and alumina in polishing silicon oxide wafers. Depending on the size and the structural properties of the abrasives, different mechanisms may be operational in the CMP processes. Thus, it is important to carry out experiments with slurries of well-defined morphological characteristics. In this study experiments were carried out with uniform ceria particles. For this purpose, two different dispersions were prepared, one consisting of nano-sized ceria particles of narrow size distribution
a)
On leave from Korea Institute of Ceramic Engineering and Technology, Seoul, South Korea. b) Address all correspondence to this author. 2744
http://journals.cambridge.org
J. Mater. Res., Vol. 17, No. 10, Oct 2002 Downloaded: 14 Mar 2015
and the other of monodispersed colloidal silica coated with ceria. The latter dispersion was chosen because methods for the preparation of uniform larger ceria yielded only very low concentrations of solids,7 insufficient for polishing experiments. In contrast, uniform silica cores are available in large amounts and could be coated with ceria by a process described in this work. This approach makes it possible to control the size of the dispersed abrasives, yet having the desired surface and other characteristics, in this case of ceria. The actual CMP experiments were conducted at two pH values with diff
Data Loading...