High aspect ratio tilted gratings through local electric field modulation in plasma etching

The anisotropic nature of plasma etching is usually exploited to realize vertical nano-/micro- silicon structures by deep reactive ion etching. However, some applications require tilted instead of perpendicular profiles with respect to the substrate. Here, a controlled tilted etching is realized by introducing a set of metal electric field modulator(s), which modify the near sample surface potential. The ions from the plasma body are accelerated under the influence of the distorted electric field, and hit the silicon surface with a certain incident angle. A model is built with finite elements method, taking into account the geometry of the experiment and the chamber conditions during the etching process. The thickness and the inter-distance of Al slabs have been varied in a range of 0.5–3 mm and 10–25 mm, respectively. A tilt angle ranging from 0° to 22.6° has been measured and validates the simulation results, showing that a desired tilt profile can be achieved with a proper parameters tuning. Examples of 1D and 2D modulations are reported with linear and chessboard slanted gratings for X-ray imaging applications.