Recently, the uniformity in the wafer edge area that is normally abandoned in the fabrication process has become important for improving the process yield. The wafer edge structure normally has a difference of height between wafer and electrode, which can result in a sheath bend, distorting important parameters of the etch, such as ionic properties, resulting in nonuniform etching. This problem nowadays is resolved by introducing the supplemented structure called a focus ring on the periphery of the wafer. However, the focus ring is known to be easily eroded by the bombardment of high-energy ions, resulting in etch nonuniformity again, so that the focus ring is a consumable part and must be replaced periodically. Because of this issue, there are many simulation studies being conducted on the correlation between the sheath structural characteristics and materials of focus rings to find the replacement period, but the experimental data and an analysis based on this are not sufficient yet. In this study, in order to experimentally investigate the etching characteristics of the wafer edge area according to the sheath structure of the wafer edge, the etching was performed by increasing the wafer height (thickness) in the wafer edge area. The result shows that the degree of tilt in the etch profile at the wafer edge and the area where the tilt is observed severely are increased with the height difference between the wafer and electrode. This study is expected to provide a database for the characteristics of the etching at the wafer edge and useful information regarding the tolerance of the height difference for untilted etch profile and the replacement period of the etch ring.

This paper proposes the use of environmentally friendly alternatives, C₆F₆ and C₄H₂F₆, as perfluorocarbon (PFC) and hydrofluorocarbon (HFC) precursors, respectively, for SiO₂ plasma etching, instead of conventional precursors C₄F₈ and CHF₃. The study employs scanning electron microscopy for etch profile analysis and quadrupole mass spectrometry for plasma diagnosis. Ion bombardment energy at the etching conditions is determined through self-bias voltage measurements, while densities of radical species are obtained using quadrupole mass spectroscopy. The obtained results compare the etch performance, including etch rate and selectivity, between C₄F₈ and C₆F₆, as well as between CHF₃ and C₄H₂F₆. Furthermore, greenhouse gas (GHG) emissions are evaluated using a million metric ton of carbon dioxide equivalent, indicating significantly lower emissions when replacing conventional precursors with the proposed alternatives. The results suggest that a significant GHG emissions reduction can be achieved from the investigated alternatives without a deterioration in SiO₂ etching characteristics. This research contributes to the development of alternative precursors for reducing global warming impacts.

One of the cleaning processes in semiconductor fabrication is the ashing process using oxygen plasma, which has been normally used N₂ gas as additive gas to increase the ashing rate, and it is known that the ashing rate is strongly related to the concentration of oxygen radicals measured OES. However, by performing a comprehensive experiment of the O₂ plasma ashing process in various N₂/O₂ mixing ratios and RF powers, our investigation revealed that the tendency of the density measured using only OES did not exactly match the ashing rate. This problematic issue can be solved by considering the plasma parameter, such as electron density. This study can suggest a method inferring the exact maximum condition of the ashing rate based on the plasma diagnostics such as OES, Langmuir probe, and cutoff probe, which might be useful for the next-generation plasma process.

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.

As the importance of ion-assisted surface processing based on low-temperature plasma increases, the monitoring of ion energy impinging into wafer surfaces becomes important. Monitoring methods that are noninvasive, real-time, and comprise ion collision in the sheath have received much research attention. However, in spite of this fact, most research was performed in invasive, not real-time, and collisionless ion sheath conditions. In this paper, we develop a noninvasive real-time IED monitoring system based on an ion trajectory simulation where the Monte Carlo collision method and an electrical model are adopted to describe collisions in sheaths. We technically, theoretically, and experimentally investigate the IED measurement with the proposed method, and compared it with the result of IEDs measured via a quadrupole mass spectrometer under various conditions. The comparison results show that there was no major change in the IEDs as radio-frequency power increased or the IED gradually became broad as gas pressure increased, which was in a good agreement with the results of the mass spectrometer.