| AVS 54th International Symposium | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS1-TuA |
| Session: | Plasma Etching for Advanced Interconnects II |
| Presenter: | M. Fukasawa, Sony Corporation, Japan |
| Authors: | M. Fukasawa, Sony Corporation, Japan T. Tatsumi, Sony Corporation, Japan K. Nagahata, Sony Corporation, Japan S. Uchida, Nagoya University, Japan S. Takashima, Nagoya University, Japan M. Hori, Nagoya University, Japan Y. Kamide, Sony Corporation, Japan |
| Correspondent: | Click to Email |
Reducing the damage to low-k dielectrics caused by plasma is one of the key issues for achieving high-performance devices. We report the root cause of the dielectric constant increase (Δk) of SiOCH that occurs after N2/H2 plasma exposure. The plasma damage of SiOCH (k=2.65) was investigated in a dual-frequency (60/2 MHz) capacitively coupled plasma reactor equipped with a surface wave probe, quadruple mass spectrometer, high-voltage probe and optical emission spectroscope. Measurements were performed as a function of an N2/H2 flow rate ratio, while maintaining total ion and neutral fluxes, and ion energies. The amount of moisture uptake during air exposure, Δk, water contact angle, and chemical bonding were analyzed. The behavior of Δk strongly depends on the N2/H2 flow rate ratio. Thermal disorption spectroscopy revealed that the Δk is almost proportional to the amount of moisture uptake.1 The amount of Si-CH3 bond in the bulk SiOCH measured by FT-IR decreased monotonically with an increasing H2 flow rate ratio. These results suggest that the Si-CH3 bonds were broken by H, and the dangling bond (or one weakly terminated by H) was generated during plasma exposure. During air exposure, the Si-H bonds are replaced with Si-OH bonds, which then adsorb moisture. However, in the case of H-rich plasma, the Δk decreased, while the total number of adsorption sites increased. We analyzed the depth profile of incident ions since the SiOCH damage gradually varies from the surface depending on the depth distribution of ion, light, and radical diffusion from the surface. In relatively H-rich plasma, the small mass number of dominant ion species (H3+) results in the deeper damage caused by the longer projected range (10 nm). Thus, more Si-CH3 bonds remained on the surface and generated more hydrophobic surface, compared with that generated by relatively N-rich plasma. The hydrophobic surface was found to suppress the moisture permeability and lead to the Δk reduction. To suppress Δk, it is important to precisely control the incident radical/ion flux ratios and ion energies thus reducing the adsorption sites in the bulk and keeping the hydrophobic surface that suppresses the water permeation during air exposure.
1M. Fukasawa et al., in Proceedings of International Conference on Dry Process, Nagoya, Japan (2006) p.5.