Invited Paper: Low-Temperature SiO₂/SiO₂ Wafer Direct Bonding by N₂ Plasma Activation

Direct bonding is a promising technology in the semiconductor industry for achieving material stack integration. Traditional high-temperature bonding methods can introduce thermal stresses and defects that affect device performance and reliability. This paper proposes a low-temperature SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> wafer bonding technique based on non-oxidizing nitrogen plasma activation. Here, we show that $\mathbf{N}_{2}$ plasma treatment significantly enriches the surface with functional groups, improving the chemical reactivity and surface energy, thus achieving a high bonding strength of $\sim 2.0 \mathrm{~J} / \mathrm{m}^{2}$. The mechanism of nitrogen plasma activation on surface modification and interfacial bonding was revealed by surface analysis and mechanical strength testing. This study is of great significance for the development of component fabrication, micro-electro-mechanical systems (MEMS) and optoelectronic devices.