Design and fabrication of a high precision wafer polishing machine

Abstract

The objective of this project is to design and fabricate a full-scale Chemical- Mechanical Polishing machine, whose performance is much higher than that of the existing technology. The machine consists of a lower structure, an upper structure, and a polishing head. This thesis covers the design of the upper structure in detail. The machine was recently built and tested. The upper machine frame, which is the moving component of this polishing tool, was designed for maximum rigidity using FEA analysis. Vibrational analysis was also performed to design a mechanically quiet system. All of the associated components were designed with extreme precision in mind. In addition to the upper structure, a loading mechanism was also designed for the polishing head. Two high-precision linear drive mechanisms, the z-axis and the x-axis, were designed as the two major axes of motion for this machine tool. The z-axis applies the normal polishing force of 1500 lbs. This axis has a travel of 8", maximum velocity of 4 in/sec, resolution of 50 nm, and a repeatability of 0.0005". The z-axis applies the load using a pneumatic piston, in parallel with a "rotary" ball screw. The x-axis moves the upper machine structure, which weighs over 2000 lbs. The x-axis has a travel of 82", a maximum velocity of 12 in/sec, a maximum acceleration of 0.2g's, a resolution of 10 microns, and a repeatability of 0.002". The x-axis is driven on both sides with two separate motors and ball screws.