Variable isotropy Deep RIE process for through wafer via holes manufacturing

Abstract

This paper reports a method on the manufacturing of through wafer via holes in silicon with tapered walls by Deep Reactive Ion Etching (DRIE) using the opportunity to change the isotropy in the DRIE equipments during processing. By using consecutively anisotropic and isotropic etching steps it is possible to enlarge the dimension of via holes on one side of the wafer, while on the other side dimension is set by the initial etching window.The method was used for two etching windows sizes (100μm and 20μm respectively) on 200μm and 300μm thick wafers. The aim was to manufacture tapered walls via having a good control over the walls angle. Different Bosch process recipes providing different walls roughness were used. Via holes with tapered walls (2° to 22°) were manufactured using this method. An angle deviation smaller than 10% of the manufactured via holes along the wafers was observed.

Fabrication of through-wafer interconnections by gold electroplating

“…The whole manufacturing process resides in successive anisotropic and isotropic etching cycles, step by step reaching the depth and enlarging via. To achieve the tapered walls, a supplementary step is necessary before isotropic etching -oxygen plasma cleaning; this step is needed to remove the passivation deposit on the walls during the anisotropic etching [6].…”

“…TWV were manufactured using a DRIE variable isotropy process [6]. The manufacturing method consists in alternatively using of anisotropic and isotropic etching processes: anisotropic etching is used to achieve the depth, while the isotropic etching main role is to enlarge via's on one side in order to obtain the desired angle.…”