This paper presents the design and fabrication of a 2nd order L/S band filter used as a test vehicle for the development of a fabrication technology for cavity microwave filters based on micromachining in order to preliminary explore all the technological constraints on a simpler structure. The multilayered 2nd order pseudo-elliptic L/S band filter is based on λ/4
TEM mode resonators which are patterned on a dielectric layer. For convenience 500 μm thick Si wafers have been used even if this limits the simulated Q factor of the 2nd order L/S band filter to about 200. The test structures presented here
amount to the more sophisticated 4th order filters in an extended technological concept (i.e. 1500 μm thick Si wafer and two additional modules) but still based on similar resonating elements aiming to replace the existing bulky metallic
waveguide filters installed in many satellite transceivers. A five mask fabrication process is employed for the realization of the elements of said filter which is based on three
modules. Module A and B are fabricated on the same wafer while module C which served as ground is fabricated on a separate wafer. A 2 μm high sealing ring is etched on the back of module A and B by DRIE (Deep Reactive Ion Etching) while cavities and TSVs (Through Silicon Vias) are etched by TMAH (TetraMethylAmmonium Hydroxide). The surface
mounting compatibility of the filter is obtained by adopting vertical via holes to connect the external feeding lines (e.g.
microstrip or coplanar) with the filter resonators. Such a transition separates the input/output from the filter input/output coupling mechanism. The final wafers are diced and specimens are vertically stacked and bonded through
thermocompression bonding. The overall filter dimensions are 48x20x1.5 mm<sup>3</sup>.
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