Investigation of Diamond Grit Size and Conditioning Force Effect on CMP Pads Topography
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Investigation of Diamond Grit Size and Conditioning Force Effect on CMP Pads Topography Ting Sun1, Leonard Borucki2, Yun Zhuang1,2, and Ara Philipossian1,2 1 University of Arizona, Tucson, AZ, 85721 2 Araca Inc., Tucson, AZ, 85750 ABSTRACT In this study, incremental loading and interferometry analysis were performed on Rohm and Haas IC1000 plain pad surfaces to investigate the effects of diamond size and conditioning force on pad topography. The Rohm and Haas IC1000 plain pad was conditioned by Mitsubishi Materials Corporation 100-grit and 325-grit diamond discs under 3.6 and 8.0 lb. Two pad samples were taken for each disc and each conditioning force test. For each pad sample, a custom-made incremental loading device (ILD) was used to measure pad surface mechanical response under different loads. When loads were applied to the pad sample surface, the pad surface displacement was measured. A decay length was extracted from the log plot of the pressure ratio vs. the change in pad surface displacement. The decay length generally increased with the diamond size and conditioning force. Both dry and wet pad samples were analyzed by the incremental loading device. Results showed that wet pad samples had higher decay lengths than dry pad samples. Separately, optical interferometry was used to probe dry pad sample surfaces without contact and produce surface height probability density functions (PDFs). For all pad samples, the pad surface height PDFs exhibited an exponential tail and a decay length was extracted, which represented the distance over which the pad surface height probability dropped by a factor of 1/e. The decay lengths extracted from the optical interferometry analysis were consistent with those extracted from the incremental loading experiments, indicating that the optically measurable pad surface characteristic had a practical interpretation in terms of the pad surface mechanical response.
INTRODUCTION Chemical mechanical planarization (CMP) is an essential technology for reaching the high levels of global and local planarity required by the microelectronics industry. Polishing pads play a crucial role in the process and the performance of pads is greatly affected by pad conditioning. In this study, incremental loading and interferometry analyses were performed on Rohm and Haas IC1000 plain pad surface to investigate the effects of diamond size and conditioning force on pad topography. The Rohm and Haas IC1000 plain pad was conditioned by Mitsubishi Materials Corporation 100-grit and 325-grit diamond discs under 3.6 and 8.0 lb. A custom-made incremental loading device was used to measure pad surface mechanical response under different loads. Decay lengths were extracted from the log plots of the pressure ratio vs. the change in pad surface displacement and the values were compared among pad samples. Both dry and wet pad samples were analyzed by the incremental loading device to investigate the impact of moisture on pad surface. Separately, optical interferometry was used to probe dry pad sampl
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