Mechanism and an empirical model of the fixed abrasivepolishing process on a web-format tool
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Laertis Economikos IBM Microelectronics, East Fishkill Facility, Hopewell Junction, New York 12533
S.V. Babu Department of Chemical Engineering and Center for Advanced Materials Processing, Clarkson University, Potsdam, New York 13699 (Received 20 January 2003; accepted 14 April 2003)
Several chemical–mechanical planarization characterization test wafers were polished to understand the polishing mechanism of the fixed abrasive process. Oxide thickness removal in the “active” (up) and the “recessed” (down) regions of the wafer was monitored for different times of polish. It was found that there was no significant removal in the recessed areas until the step height was reduced to about 100 Å, and the polish rate in the active area decreased rapidly once this critical step height had been attained. At this critical step height, the polish rate of the down areas started to increase and approached that of the up area, with both eventually reaching the negligibly low removal rate of the blanket wafer. The drop in the polish rate of the up area, after planarity had been attained, was fitted to an exponential model.
I. INTRODUCTION
Over the last ten years, chemical–mechanical planarization (CMP) has become one of the most widely used planarization techniques in the silicon integrated circuit manufacturing industry.1,2 However, as the planarization needs to continue to evolve with each new generation of devices, it is becoming increasingly difficult to use the same kind of CMP tool for all the different planarization steps in the manufacturing process. CMP tool manufacturers have made innovative modifications to meet these challenges. One such innovation in tool design is the development of a fixed abrasive polishing platform. A schematic of a fixed abrasive tool, also called a web-format tool, is shown in Refs. 3 and 4. In conventional rotary CMP tools,5 a polishing pad (usually polyurethane foam) is glued to a table that rotates at a given speed. The slurry, typically consisting of abrasive particles and the chemicals needed to polish the material from the wafer, is dispensed onto the pad by a slurry delivery system, also attached to the tool.5 In contrast, in a fixed abrasive process, the abrasive particles are embedded in the pad while the slurry consisting only of the chemicals is dispensed onto the pad. A magnified image
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Presently at IBM Microelectronics, East Fishkill Facility, Hopewell Junction, NY 12590. J. Mater. Res., Vol. 18, No. 7, Jul 2003
of a fixed abrasive pad is shown in Refs. 3 and 6. Although in both cases the wafer contacts both the abrasive particles and the chemicals during polishing, there are significant differences in the polishing mechanism of the two processes. These differences are discussed later. Fixed abrasive polishing has special significance for shallow trench isolation (STI) planarization. STI has become the isolation method of choice at 0.25 m and lower nodes of technology.7,8 As improvements in integrated circuit (IC) device fabrication technology are reducing the device dime
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