Dynamics of the Formation of the Subambient Pressure Distribution During Chemical-Mechanical Polishing

Chemical-Mechanical Polishing is used to polish silicon wafers in the manufacturing of integrated circuits. Wafers are pressed, electronics side down, onto a rotating pad that is flooded with a slurry containing abrasive particles. The slurry is entrained in the interface and the abrasive particles slide against the silicon and polish it. Our previous work has shown that subambient pressures develop at the silicon/pad interface and we have measured this pressure and its distribution over the wafer surface (1). However, our experiments have been limited to those conditions where the pad rotates and the wafer slides on the pad but the wafer itself does not rotate. Our experiments showed a skewed pressure distribution. This paper describes experiments and pressure distribution measurements where the wafer, as well as the pad/platen is rotated (2). Specifically-designed wireless electronic transmitters and receivers were built and used to measure the interfacial pressures at the silicon/pad interface. Subambient stress maps and temperatures have been measured and Figure 1 shows an example of a skewed pressure distribution when the silicon is not rotated and Figure 2 shows the pressure distribution for the same wafer while it is rotating. The subambient pressures develop over a 2 second time period from when the rotation started. The pressure distributions are symmetric in spite of the lean and tilt of the wafers. The rotational speed and other variables have a big influence on the polishing rate and this will be discussed in the talk.