Feasibility of a Real-Time Method in Determine the Extent of Pad Break-In during Copper Chemical Mechanical Planarization

Material removal rate, shear force and variance of shear force during copper polishing are studied as a function of pad break-in time. Results show that copper removal rate and variance of shear force increase within 30 min of pad break-in. Spectral analysis of raw shear force data is employed to help elucidate the fundamental physical phenomena during copper chemical mechanical planarization. Fast Fourier transform is performed to convert the shear force data from time domain to frequency domain. The energy distribution of copper polishing is quantified which sheds light on the effect of pad break-in time. Spectral analysis indicates that as pad break-in progresses, newly formed pad asperities dominate the interaction with the wafer and therefore shifting the spectral amplitudes to the higher frequency peaks (i.e. 101-108 Hz). Further spectral analysis also confirms that such increases in the high-frequency range dominate the distribution of energies. This study shows that a combination of unique spectral fingerprinting and analysis of force variance can be used to monitor the progress of pad break-in in real-time. This work underscores the importance of real-time detection and non-destructive method in chemical mechanical planarization process to quantify the extent of pad break-in.