Diamond Particles for Copper CMP
The abrasive particles in slurries used for Chemical Mechanical Polishing (CMP) typically have a well-defined particle size distribution. Within the distribution there are some large (> 1mm) particles and agglomerations due to manufacturing processes, usage systems, and transportation or storage conditions. These oversized entities affect the surface defectivity of the wafer during the CMP process. Professor Yuzhuo Li and his group are addressing this problem. One method for reducing oversized particles is Point of Use (POU) filtration. POU filtration is positioned next to or within a polisher to provide the last line of defense to remove defect-causing particles from the polishing slurry. Prior to POU filtration, several filtration options are often considered to protect the POU filter from premature clogging, optimize filtration performance, minimize total filtration costs, and maximize tool uptime. These filtration opportunities include a recirculation loop in the slurry delivery system, a post mixing/blending before transfer to the day tank, and transferring from shipping drum to the slurry delivery system.
Working with Dr. Michael Tseng at CUNO Incorporated, Professor Yuzhuo Li and his graduate student John Westbrook and undergraduate student Krista Manno have studied the effectiveness of a POU system for the filtration of Alumina slurries in copper CMP. More specifically, the direct impact of the filtration system on the copper material removal rate and surface quality has been measured. In addition, particle size distribution and over particle counting are also compared before and after filtration. They will use the filtration system to study the impact of an over sized particle on scratching in Copper CMP.
Professor Yuzhuo Li and collaborators are studying the factors that affect the smoothness of poilshed disks. The fast development of computer industries requires fast-running CPU as well as high-speed high-density storage media. The storage density reached 52.5 gigabits per square inch at the beginning of this year. The storage density is to reach 80-100 gigabits per square inch in two years. This requires the development of methods to prepare a very smooth substrate surface for dot packing layers of magnetic particles. The current method to obtain a smooth surface for a hard drive disc, which has an aluminum substrate and on top a layer of Ni-P before other thin layers of magnetic materials, involves a polisher, a pad, and a slurry (containing abrasive particles and chemicals). The basic principles are the same as CMP of IC chips and other microelectronic devices. The surface quality and smoothness of the Ni-P surface will control the finishing quality of the final layer of magnetic materials. Working with Mark Mayton, Dan Dunn and Ki Sohn at Ferro Microelectronics, Professor Yuzhuo Li and Research Assistant Professor Gary Yu have investigated the factors affecting the material removal rate, surface quality, and smoothness of the polished discs. They found that during the polishing of the discs, the chemistry of the slurries and the mechanical effect must be balanced to reach the best surface finish. As a result, they have developed a qualitative model for the development of future useful slurries.
of Surfactants on CMP