Toshihiro Morisawa

Polishing time calculation method to reduce oxide-film-CMP send-ahead works

In order to obtain higher throughput maintaining high precision in the CMP process, it is important to reduce send-ahead work and rework related to film thickness over the within-wafer distribution. This paper presents a new polishing time calculation method that ensures film thicknesses at all measurement positions satisfy the control limit, and gives a judgment on whether send-ahead work is necessary, with the margin of variation of film thicknesses from the control limits after CMP based on the within-wafer distribution of the removal rate and film thickness before CMP. The CMP-APC system applying these methods reduces the defects in film thickness after CMP, along with the amount of send-ahead work, which is half that of the former CMP-APC run-to-run control system.

Non-Linear Process Model for CMP-APC

For Si dioxide-film CMP process in semiconductor manufacturing, which requires high precision, run-to-run control has been developed. The run-to-run control is a kind of repetitive control to adjust polishing time at every start of work in a work sequence. This control is based on a process model, which expresses the relation between polishing time and polished thickness. The model is non-linear for Si dioxide-film CMP with Ceria slurry and it contains many parameters. However the parameters must be determined by product type. Therefore, a modeling method of nonlinear process models is developed for multi-product high-volume manufacturing. In this method, model is determined by selecting the optimum combination of arbitrary terms, whose parameter values satisfy constraints of non-linear polishing process. The result shows that the model can be selected using more than 10 samples. Calculated polishing time achieves high precision in film-thickness after CMP. The standard deviation of film-thickness after CMP is less than 1% of target film-thickness.