Paper PS+TF-MoA8
PECVD, Rf vs Dual Frequency : Investigation of Plasma Influence on Metalorganic Precursors Decomposition and Material Characteristics

Monday, October 28, 2013, 4:20 pm, Room 102 B

In the last decade, Dual Frequency (DF) reactors have been considerably developed as fine etching tool for microelectronic manufacturing. In this case, the CCP source is driven by a high frequency (HF) and a LF sources attached on either one electrode or two electrodes separately. Usually one frequency is chosen to be much higher than the other in order to achieve an independent control of ion bombardment and electron density (i.e. ion flux). In the case of deposition process, it has been observed for Silicon Nitride deposition that the HF to LF ratio in the plasma modify the ion flux and energy and so the mechanical properties of the material [3]. Moreover, addition of LF to HF can modify the sheath thickness of the plasma and so increase the electron temperature of the gas [4]. In this way, the precursor fragmentation can be tuned by tuning the LF power what will impact the deposition rate and thin film properties.

In this study we compare RF and Dual frequency deposition of materials for metal gate applications such as TiCN and TaCN. The reactor used is a 300 mm Metal Organic PECVD industrial tool in which the plasma is sustained capacitively by a RF power supply (13.56 MHZ) and a LF (350 kHz) source. Impact of LF addition on the metal composition and its physical properties is analyzed and correlated to plasma modification observed by OES (Optical Emission Spectroscopy). For both metalorganic precursors we observe a strong modification of the metal properties and deposition rate when adding 25 to 100 W LF to a 200 W RF plasma. As an example, in case of TiN, with 50 W LF added to a 200 W RF, the deposition rate increased more than twice, the film appears to be less resistive (50%) and denser. These modifications highlight the change of deposition mechanisms/reactions. The beneficial effect of adding a weak LF power to the RF power can be correlated to a modification of the precursor fragmentation as observed by OES. These results are less pronounced and not obtained when only RF plasma is used, whatever the increasing power (from 200 to 300 W). Finally, with LF addition, we also hope, to reduce the RF plasma impact on the dielectric leading to a regrowth of Equivalent Oxide Thickness (EOT) observed previously in our p-like metal MOS capacitors [5].

[1] H. N. Alshareef et al, Electrochemical and Solid-State Letters 11 (2008) H18

[2] H. Zhu et al, Phys. Review B 80 (2009) 201406

[3] W.S. Tan et al, Journal of Electronic Materials 33 (2004) 400-407

[4] W-J Huang et al, Phys. Plasmas 16 (2009) 043509