Effects of mixed abrasives in chemical mechanical polishing of oxide films
- PDF / 335,155 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 3 Downloads / 159 Views
Thermal oxide covered silicon wafers were polished with slurries containing (i) only nano-sized particles of ceria, monodispersed colloidal spherical silica, or hematite of different shapes, (ii) a binary mixture of the same nano-sized and uniform colloidal particles, and (iii) the same colloids coated with nano-sized ceria. The procedures for the preparation of the coated particles are described in this article. The polish rates and surface qualities were in all cases higher with mixed slurries, and even more so with coated particles. The performance of composite systems also depended on the shape of the particles, cubic ones being the most and spheres least efficient. Experimental results indicated that ceria in mixtures was responsible for the enhanced polish process, while core materials enhanced a closer contact of nano-sized particles with the wafer. In general, the polish rates were higher with the larger contact area between the abrasives and the wafer. This mechanism was further verified by polishing oxide wafers on 3-M fixed abrasive pads, which have cylindrical structures with flat surfaces.
I. INTRODUCTION
A key requirement of all present and future chemical mechanical polishing (CMP) processes is planarization across multilength scales (nanometers to several centimeters) with appropriate selectivity and defect-free finish of surfaces, consisting of composite regions of dielectric and metal films, followed by complete particle removal during post-CMP cleaning. These goals can be best achieved, independent of the polish tool and the geometry used, if the characteristics of the abrasive particles, such as their size, shape, hardness, chemical functionalities, and adhesion properties, are tailored to the nature of surfaces being planarized and to the chemical environment present during the CMP process. The common abrasive particles used in the CMP are usually irregularly shaped and of broad size distributions. It is, therefore, of general interest to carry out polishing experiments with slurries, consisting of uniform particles of different morphologies, sizes, and other properties. A previous study, in which copper and tantalum wafers and/or disks were polished with such well defined slurries, offered useful information on the mechanism of the processes involved.1 It is well known that ceria particles (unlike silica) have, as a rule, rough surfaces, which may contribute to polishing efficiency. The high removal rates of oxide a)
On leave from the Korea Institute of Ceramic Engineering and Technology, Seoul, South Korea. b) Address all correspondence to this author. J. Mater. Res., Vol. 18, No. 10, Oct 2003
http://journals.cambridge.org
Downloaded: 21 Mar 2015
films have been usually attributed to their ability to interact with the surface of the silica layer. Cook2 coined the term “chemical tooth,” referring to the chemical bonds between the abrasive particles and the wafer, which should increase the shear stress and, therefore, improve the removal rate. Ceria-based slurries are also desirable for th
Data Loading...
