CHEMICAL MECHANICAL POLISHING PAD PROFILE OPTIMIZATION

Abstract

The complexity of established microelectronic devices demands global planarity at different metallization levels. Chemical mechanical polishing (CMP) has the potential in offering solution to such stringent requirements over a step height of several micrometers. Thus, CMP provides advantages of global planarity, wide windows for etching and photolithography and yield enhancement. From manufacturing point of view, however, stable CMP process is difficult to achieve because of its complicated consumables being used. In CMP, uniformity of polishing pad is important factor to maintain a stable operation. Currently, due to the pad non-uniformity of tungsten polishing process, problem such as pad balding at the edge, wafers de-chuck and instability of wafer removal rate occurred. In this report, various pad conditioning parameters and their important characteristics for the pad wear during conditioning are explored. To maintain a uniform pad profile, current conditioning recipe has to be modified. The report demonstrated a successful attempt in changing both conditioning retention time of specific zones as well as the pad conditioner sweeping range to address above-mentioned problem. To have more efficient and effective pad profile evaluation process, mathematical models using Preston’s equation and actual conditioning time calculation for pads wear were developed and simulated. Conditioning recipe was modified where the pad non-uniformity was improved from originally 5mils to 2mils. Actual conditioning time calculation show strong relationship with the pad wear rate (WR). It was used to verify the pad non-uniformity across the used pad. Again the simulated actual conditioning time matches closely to the experimental results. Having improved tungsten-polishing process, similar methods can be used to improve other polishing process such as oxide, shallow trench isolation under different operating ambient.