The features of surface charging on rectangle mask holes in plasma etching

In the plasma etching technique, acquiring a high-quality transfer from the mask pattern onto the substrate under the suppression of the charging effects is of great significance. Most previous publications only focus on studying the charging phenomena on round mask holes. This work shifted the target to an isolated rectangle mask hole and two types of mask arrays (quadrangle and hexagonal arrays). A classical particle simulation program was used. This study first shows that rectangle holes with various ratios of length and width present different electric field (E-field) strength distribution around the long and short sides. The larger the ratio, the stronger the E-field in the long side is than that in the short one. In addition, the E-field shows a quite weak distribution at the vertexes, which is due to the low curvature of the vertexes. Based on the evolutions of E-field and the simulated profile with time, it is indicated that ions would give priority to bombard the long side rather than the short side and vertexes, forcing the sides to deform outward as arcs. Unlike an isolated mask hole, the mask array has a remarkable influence on the charging effects in case of the close distance between holes. Simply put, the quadrangle and hexagonal arrays relieve and worsen the non-uniformity of the distribution of the E-field at the edge of a rectangle mask hole, respectively. The simulated profile evolution further proves those speculations based on the E-field distribution. Possible mechanisms behind this have been discussed in detail. The findings of this work help arrange an appropriate mask pattern according to the specific mask shape, which would shed light on a way of maintaining the pattern integrity.