3D plasma sheath tailoring for micro structuring of silicon and glasses

• Applicant: Professor Dr. Achim von Keudell
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 543807415

The project aims to develop a concept to 3D etch microstructured devices in silicon and glasses for optics and microfluidics on the 10s of micrometer scale using a typical plasma etching device such as an ICP plasma with an additional RF-bias. Such systems are regularly employed in microstructuring equipment. The concept involves steering the incident ion flux onto a material surface to create an accurate 3D etching process in a low-pressure reactive RF plasma. This should be achievable by designing metal masks and a static magnetic field parallel to the wafer surface, where the plasma sheath boundary is distorted dynamically during the RF cycle so that the direction of ion incidence can be adjusted. These metal masks are also intentionally biased to enhance the flexibility of the concept. The electric field in the sheath is further manipulated by generating secondary electrons at the grid surface by light illumination to balance the charging process by the incident ions. Such an effect would correspond to optical control of the ion steering and is easier to implement than direct electronic biasing. The experimental investigation is based on the evaluation of etch profiles in CF4 ICP plasmas with additional RF biasing of the substrate holder and metallic masks with permanent magnets in front of silicon and glass surfaces. In addition, the dynamic variation of the incident ion flux will be monitored in-situ by a multi channel plate (MCP) behind the etch masks. This is complemented with ex-situ analysis of the etch structures. The experiments are complemented by 2d3c particle-in-cell (PIC) modeling of the ion dynamics in the plasma sheath region, which also includes the chemical effects during chemical sputtering in fluorine containing discharges. The following research questions will be answered: Is it possible to monitor the distribution of ions behind these metal masks also in situ by an optical technique? What is the maximum achievable 3D control of the incident ions using tapered metal masks and a static magnetic field? Can the ion steering effect be actively controlled by applying a bias to the grids or manipulating it with photoelectrons from UV illumination? Can the ion steering effect be predicted based on PIC modeling of the plasma sheath region in combination with a chemistry model to cover the etch layer and the re-deposition profile? What are the differences in the etching dynamics for standard silicon wafers and quartz glass?

• DFG Programme: Research Grants