Surface Chemical Characteristics of CMP Polyurethane Pads
- PDF / 122,258 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 111 Downloads / 209 Views
0991-C01-03
Surface Chemical Characteristics of CMP Polyurethane Pads Hongqi Xiang, Abaneshwar Prasad, and Edward E. Remsen Cabot Microelectronics Corporation, 870 North Commons Drive, Aurora, IL, 60504 ABSTRACT Attenuated total reflection FT-IR spectroscopy coupled with a hydrogen-deuterium exchange technique is employed to investigate the surface chemistry of two polishing pads, a thermoplastic polyurethane (TPU) pad and a commercial cast urethane (PU) pad. A time/temperature-dependent reduction of nitrogen-hydrogen stretching modes (νN-H) was observed when the pads were immersed in deuterium oxide (D2O). Compared to TPU pads, the PU pads showed an ambiguous correlation between dependence of the band intensity changes and D2O-immersion time/temperature. For both types of pads, a sharp decrease in νN-H band intensity and an unexpected rebound in νN-H band intensity were observed within 24 hrs after immersing the pads in D2O. However, a comparable rebound in νN-H band intensity was not observed for conditioned TPU pad samples. This phenomenon is proposed to be due to a rearrangement of polar groups at the pad surface when the pad is immersed in water, which may influence pad performance on the asperity level. INTRODUCTION Chemical-mechanical planarization (CMP) is an enabling technology for reaching the high levels of global and local planarity required by the microelectronics industry. CMP relies on both chemical and mechanical polishing processes, the performance of which is dependent on the properties of the slurry and the polishing pad; and processing parameters [1, 2]. Polishing pads, as a key consumable component, are well known to play a crucial role in both the mechanical and the chemical polishing steps. The elastic properties and surface morphology of the pad influence the material removal rate [2] and the pad conditioning process is regarded as a key driver in the creation of the desired pad surface morphology for CMP [3, 4]. It had also been reported that the interactions of the pad’s surface with slurry or water can reduce the modulus of the pad by as much as 30% [2, 5, 6]. Some studies suggest that pad - slurry interactions may disrupt hydrogen bonding within the pad and increase the local concentration of hard polyurethane segments at the pad surface [7, 8]. Studies of the polishing pads surface, therefore, provide fundamental knowledge needed to optimize CMP processes. In this presentation, interactions between water and two types of CMP pads, a TPU pad and a PU pad, are characterized using two complementary techniques. Attenuated total reflection (ATR) FT-IR spectroscopy is employed to monitor the surface chemistry of the polishing pads during water diffusion into the pads. An isotopic exchange technique is applied to mark the spectroscopic change as a result of the H-D exchange at the N-H groups of the urethane polymers. The time dependence of the water diffusion and H-D exchange into the pads is studied at different temperatures. The effect of pad conditioning process on the diffusion and exchang
Data Loading...
