Plasma etching of the trench pattern with high aspect ratio mask under ion tilting

In this study, we developed a method to qualify the plasma etching result in high-aspect-ratio trench with ion tilting using the natural sheath curvature at the wafer edge. Etching was performed using a patterned wafer with trenches composed of an amorphous carbon mask/SiO2/Si in a radio-frequency-biased inductively coupled plasma with an Ar/C4F6 mixture. It is revealed that even a slight ion tilt (1–2°) induces dramatic changes in etch characteristics, such as etch-stop, asymmetric and vertical etching, which strongly depend on the arrangement, location, and aspect ratio of the trench. These phenomena were analyzed using the relationship between the electric field angle (θE) at the sheath curvature and the critical angle (θc) for ions reaching the trench bottom. It was confirmed that: i) bottom etch stops when θE>θc, ii) asymmetric etching occurs when θE<θc, and iii) vertical etching occurs when θE≈0°. This study provides a new concept for quantifying the etching performance at the wafer edge, as well as the etching mechanism of high-aspect-ratio trench in the situation of ion tilting, which is a central issue in current and next-generation etch processes.