MICRO: Ultrapure Fluid/Slurry Delivery- McMillan (January 2001)

A microprocessor-based flow controller system has shown several advantages over the traditional peristaltic pump setup in tests run on polishing tools at AMD's Fab 25. Advanced Micro Devices' Fab 25 in Austin, TX, is a high-volume, state-of-the-art microprocessor device production facility. Like other such facilities, Fab 25 has numerous chemical- mechanical planarization (CMP) tools, each of which uses a system of peristaltic pumps for process fluid delivery. At various times during each CMP process, these pumps may be delivering tungsten or oxide slurries, DI water, or ammonium hydroxide. These fluids are dispensed onto the polishing substrate, and mechanical force is applied to create the desired planarized surface. The chemical interaction and the mechanical force combine to achieve the desired effect on each wafer. Peristaltic pumps have been used to dispense the necessary chemicals since the development of CMP tools. Before the advent of fabwide chemical delivery systems, many chipmakers simply pumped slurry and other chemicals out of nonpressurized drums, and the peristaltic pumps provided the necessary pressure to dispense the slurry onto the wafers. However, with the coming of state-of-the-art pressurized chemical delivery systems, pressure no longer needs to be provided by each tool. Although proved to be functional, peristaltic pumps create several problems when used in a CMP process. First, tubing breakdown caused by the pump design generates particles, which are detrimental to any semiconductor process. Second, the pumps do not provide consistent flow control and therefore introduce potential process variability. Third, peristaltic pumps require significant maintenance to keep functioning properly, which leads to tool downtime and excessive repair costs. Fourth, the pumps used on most CMP tools do not incorporate any type of closed-loop feedback system. Lack of feedback can lead to dry polishing or inconsistent flow rates, either of which can cause wafer surface microscratching or even breakage.