Catalytic nickel silicide as an alternative to noble metals in metal-assisted chemical etching of silicon.

Metal-assisted chemical etching (MACE) has received much attention from researchers because it can be used to fabricate plasma-free anisotropic etching profiles for semiconductors. However, the etching mechanism of MACE is based on the catalytic reaction of noble metals, which restricts its use in complementary metal oxide semiconductor (CMOS) processes. To obtain process compatibility, we developed catalytic Ni after alloying it with Si as a substitute for noble metals in the MACE of Si substrates. Nickel silicide is a material commonly used as a contact electrode in CMOS processes. When NiSi was used as the catalyst, the anisotropic etching of Si with a smooth surface was successfully demonstrated. Silicidation increased the standard reduction potential of the Ni alloy and enhanced the electrochemical stability in the MACE of Si. In contrast, when pure Ni was used as the catalyst, a rough-etched surface was fabricated because of the low standard reduction potential. Based on the experimental results, the factors affecting the MACE of Si were systematically analyzed to optimize the catalytic NiSi properties. The implementation of the NiSi alloy potentially eliminates the use of noble metals in MACE and allows the technology to be adopted in contemporary CMOS processes.

Comprehensive Assessments in Bonding Energy of Plasma Assisted Si-SiO2 Direct Wafer Bonding after Low Temperature Rapid Thermal Annealing.

Direct wafer bonding is one of the most attractive techniques for next-generation semiconductor devices, and plasma has been playing an indispensable role in the wider adoption of the wafer bonding technique by lowering its process temperature. Although numerous studies on plasma-assisted direct wafer bonding have been reported, there is still a lack of deep investigations focusing on the plasma itself. Other than the plasma surface treatment, the wafer bonding process includes multiple steps such as surface cleaning and annealing that require comprehensive studies to maximize the bonding strengths. In this work, we evaluate the various process steps of Si-SiO2 wafer bonding through case-by-case experimental studies, covering factors including the plasma conditions for surface treatment and secondary factors such as the time intervals between some process steps. The results show that plasma treatment with increasing input power has a trade-off between bonding strengths and interfacial voids, requiring the optimization of the plasma conditions. It is also noticeable that the effects of plasma treatment on wafer bonding can be improved when the plasma-treated wafers are stored in ambient atmosphere before the subsequent process step, which may suggest that wafer exposure to air during the bonding process is advantageous compared to processing entirely in vacuum. The results are expected to allow plasma-assisted direct wafer bonding technology to play a bigger role in the packaging process of semiconductor device manufacturing.