Polish profile control using magnetic control head
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Polish profile control using magnetic control head Manabu Tsujimura1, Yu Ishii1, Norio Kimura1 and Masahiro Ota2, 1
Precision Machinery Group, Ebara Corporation 4-2-1 Honfujisawa Fujisawa Japan Department of mechanical engineering, graduate school of eng. Tokyo Metropolitan University 1-1, Minami-Oosawa, Hachi-oji, Tokyo, Japan
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ABSTRACT Magnetic bearing technology is widely used in various technical fields, and is particularly appreciated in the semiconductor industry, where it is applied to the turbo molecular pump and wafer transfer system due to the excellent controllability it provides, even at speeds as high as 50,000 rpm. This report discusses the adoption of magnetic bearing technology to control the wafer carrier tilt angle during polishing. When the wafer is polished on a viscoelastic pad, the wafer carrier is inclined and pressed into the pad. Therefore, the reaction force on the wafer from the pad is concentrated at the wafer edge, increasing the polish rate at the edge relative to the rest of the wafer. Modification of the tilt angle is thought to offer a possible means of normalizing the distribution of the reaction force from the pad and correcting the nonuniformity of the polish rate. The wafer carrier was confirmed to press slightly into the pad and to be tilted 18 x 10-5 rad by the viscoelasticity of the pad (without tilt angle control). Constant current control led to better control of the polish rate profile relative to feedback control. The polish rate in the outer area of the wafer was increased by tilting the carrier to the positive side, and the polish rate of the wafer center area could be reduced by tilting it to the negative side. The best profile was obtained with control current of Im = -0.4 A. When the wafer carrier was tilted in the reverse direction, the polish rate became almost zero. It was concluded that hydro-planing occurred between the wafer and the pad. Accordingly, this report demonstrates the possibility of improving the polish rate profile by maintaining the wafer carrier in a horizontal position using magnetic control. INTRODUCTION Semiconductor devices are currently developed in accordance with the worldwide “roadmap” of the ITRS （ International Technology Roadmap for Semiconductors）１）. CMP (Chemical Mechanical Polisher) is now adopted in several processes involving the ILD (Inter Layer Dielectric), W-plugs, STI (Shallow trench Isolation) and Cu wire. The CMP stipulates greater uniformity within the wafer and higher planarization performance within the die. It is possible to improve these characteristics by controlling load distribution on the wafer, as the polish rate is in accordance with Preston’s law. This control of load on the wafer is accomplished by the wafer carrier head; several manufacturers have focused on the design of this component, recognizing the critical importance of load control as a key CMP technology.
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Although magnetic bearing technology is well known in a number of technical fields, its use is particularly important in the semic
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