Paper PS+AS+SS-WeA10
Role of Plasma Density in Damage Characterization and its Impact on Low-Damage Plasma Process Design

Wednesday, October 21, 2015, 5:20 pm, Room 210B

Plasma process-induced damage (PID) is one of critical issues in designing metal−oxide−semiconductor field-effect transistors (MOSFETs) with higher performance and reliability. The damage creation mechanisms—plasma-induced physical damage (PPD) and charging damage (PCD) [1]—have been characterized by various techniques so far [2] to design low plasma processes. In this study, conflicting results leading to erroneous conclusions in designing future plasma processes are presented, where ion flux and charge injection from plasma (~ plasma density) play a key role in these conventional characterizations. Firstly, regarding PPD, n-type (100) Si wafers were exposed to Ar-based ICP and CCP discharges [3] and the localized defects were created in the Si substrates by ion bombardment. It is found that, although the average energy of incident ions (E_ion) is larger for the case of CCP, the latent defect density (n_dam) of CCP-damaged samples is smaller than that of ICP, even after the damaged-layer removal. This observation is in sharp contrast to previous pictures, i.e., the larger E_ion leads to the larger PPD. Secondary, MOSFETs with "high-k" (HfSiO_x) gate dielectric were damaged by the Ar-based ICP plasma and the high-k damage (~ carrier trap site generation) by PCD is evaluated by time-dependent dielectric breakdown (TDDB) measurement [4]. We identify that the TDDB lifetime becomes longer under a certain amount of charge injection by plasma-induced current. This finding implies that one might be misled to an erroneous design rule of future LSIs. We propose a model explaining these conflicting results, where both ion flux and charge injection from plasma and the nature of the analysis techniques are taken into account. Since modern FinFETs with high-k dielectrics [5] are susceptible to PPD and PCD, the present model should be intensively implemented in designing future "low-damage" plasma processes.

This work was supported in part by a Grant-in-Aid for Scientific Research (B) 25630293 from the Japan Society for the Promotion of Science.

[1] For example, K. Eriguchi and K. Ono, J. Phys. D 41, 024002 (2008).

[2] M. Fukasawa et al., Dry Process Symposium, 183, (2013).

[3] Y. Nakakubo et al., ECS J. Solid State Sci. Technol., 4 N5077 (2015).

[4] M. Kamei et al., IEEE Int. Integrated Reliability Workshop Final Report, 43 (2014).

[5] For example, I. Ferain et al., Nature 479, 310 (2011).