A Comprehensive Study on Chemical Bonding and Open Spaces with Silicon Carbon Nitride Films for Direct Bonding

Abstract

Wafer-to-wafer (W2W) direct bonding has been extensively developed as a key unit process for BS-PDN, CFET and advanced chiplet. As a bonding dielectric layer, CVD-SiO2 has been comprehensively studied for direct/hybrid bonding. SiCN is emerging dielectric bonding layer due to its unique properties such as high bonding strength at low annealing temperatures, suppressing void formation after Post Bond Annealing (PBA) and barrier properties against Cu diffusion [1][2]. However, the bonding mechanism for SiCN has not yet been clearly described. In this study, we investigated the mechanism from several kinds of perspectives by analyzing the properties of different films under various conditions. From those results, SiCN is characterized and compared to SiO2.SiO2 and SiCN films were deposited on 300mm Si wafers using plasma-enhanced chemical vapor deposition (PECVD). Subsequently, the wafers were polished and bonded.Atomic level open spaces in dielectric films were analyzed by positron annihilation spectroscopy (PAS). For the SiO2 samples after plasma activation, the S parameter did not show significant changes. This indicates the open spaces in SiO2 were not significantly influenced by plasma. On the contrary, the S parameter of SiCN samples increased after post deposition annealing (PDA) and decreased after plasma activation. This atomic level open spaces might be contributed the unique properties of SiCN for direct bonding.Since the analysis by PAS is one of the examples, we will report the overall results of the analysis on SiCN, e.g. TDS, XPS, AFM, and so on, then discuss the bonding mechanism for SiCN-SiCN.[1] F. Inoue, et. al., ECS Journal of Solid State Science and Technology 8(6), P346(2019)[2] F. Nagano, et. al., ECS Journal of Solid State Science and Technology 9 123011(2020) Figure 1