Endpoint detection of Ge2Sb2Te5 during chemical mechanical planarization

In this paper, the in situ end-point detection (EPD) technique of Ge2Sb2Te5 (GST) chemical mechanical planarization (CMP) is investigated by the optical methods. It is shown that the intensity of optical reflectance for GST is much higher than that of oxide and the end-point of GST CMP is successfully captured using optical signal for the pattern wafer with damascene trench structure. In order to evaluate process stability, 5 pieces pattern wafer are polished in different periods under the same condition. The polishing time matches well with a great variation of the removal rate (RR) when the EPD technique is applied. The variation of GST thickness with wafer-to-wafer is less than 7.2%. The dishing of GST polished is also evaluated. It is shown that the average dishing of GST is less than 3.5 nm and the wafer-to-wafer variation is less than 8.0%, which meets well the requirements of mass production.