| A polishing platform was developed to study slurry behavior beneath a wafer during chemical mechanical polishing processes. This polishing platform was approximately a 1:2 scale model of an industrial polisher and was meant to emulate the polishing characteristic of a full-scale polisher. Polishing parameters were scaled appropriately to insure the scale model's accuracy. Parameters that were investigated using this model included slurry flow rate, platen and wafer rotation rates, wafer down force, different pad types and pad topographies, and different in situ conditioning recipes. The slurry behavior was characterized using an optical technique known as dual emission laser induced fluorescence (DELIF). By tagging slurry with fluorescent dyes, quantitative in situ measurements of slurry mixing and slurry fluid depth beneath a wafer are possible, The slurry laver beneath the wafer varied from 17 to 35 microns in height depending on the platen speed and wafer pressure. The slurry depth appeared to follow Reynolds' solution of hydrodynamic lubrication over the range of pressures and speeds examined. Friction measurements of the wafer drag on a flat polishing pad revealed that above 100 rpm, the coefficient of friction became independent of down force and platen speeds to within the resolution of the transducer. Below 100 rpm the coefficient of friction demonstrated a complex dependency on platen speed, wafer down force, and slurry flow rate. Polishing, rates of the glass substrates fell within the acceptable industry standard of approximately 1000–2000 angstroms/min. The polishing rates increased towards the edge of the wafer as compared to the center of the wafer. The effects of five major CMP parameters were investigated to determine how they affect slurry transport beneath the wafer in a designed experiment. These parameters include platen speed, slurry flow rate, wafer down force, pad manufacturer and pad grooving. All of the parameters except wafer down force affected the slurry transport and many of the parameters demonstrated non-linear interactions with other factors. In situ conditioning had a large effect on slurry transport compared with ex situ conditioning. |
