Isotropic etching of 111 SCS for wafer-scale manufacturing of perfectly hemispherical silicon molds

High temperature micro-glassblowing process demonstrated on fused quartz and ULE TSG

“…With the emergence of novel fabrication techniques batch fabrication of 3-D wineglass structures are becoming possible. For instance, hemispherical shells fabricated by deposition of polysilicon [3] or silicon nitride [4] thin films into isotropically etched cavities have recently been demonstrated. Alternative fabrication techniques include "3-D SOULE" process for fabrication of mushroom and concave shaped spherical structures [5], as well as blow molding of bulk metallic glasses into pre-etched cavities [6].…”

Micromachined polycrystalline diamond hemispherical shell resonators

“…The 1 mm diameter hemispherical shell mold is then formed via EDM process, after which a HNA (HF/Nitric/Acetic acid) etch chemically polishes the inside surface of the machined hemispherical mold while the metal hard mask protects the top surface of the silicon substrate. Image analysis demonstrates that the finished shell mold exhibits high symmetry, having a radial standard deviation below 6 µm for a 500 µm radius shell [3] and a surface roughness of 4 nm measured at the inside of the silicon mold. After stripping the etch mask, a 2 µm thick SiO 2 sacrificial layer is grown conformally on the shell mold via CVD.…”

“…To achieve mode-matching and high-Q performance in a hemispherical resonator, geometric uniformity and symmetry in combination with low thermoelastic damping structural material are critical. Many different methods such as wafer scale glass blowing [2], traditional silicon etching [3,4] and integrating precision machining with standard silicon microfabrication [5,6] have been employed to create 3D spherical or hemispherical shells. Materials such as polysilicon, and glass have also been used as the isotropic structural material for the shell itself.…”

Demonstration of sub-1 Hz structural symmetry in micro-glassblown wineglass resonators with integrated electrodes

“…Both of the lithography steps are performed while the device is still in 2-D, eliminating the need for more challenging patterning techniques such as 3-D lithography, shadow masks or laser ablation of the 3-D structure. Finally, anisotropic dry etching was used to define both the substrate cavity and the outer perimeter of the structure, eliminating etch asymmetries that may occur due to crystalline orientation of silicon [5].…”

“…Diamond hemispherical shells were also fabricated, using microcrystalline diamond deposition into hemi-spherical molds, a frequency split of ~770 Hz was reported at ~35 kHz center frequency [4]. A similar process based on deposition of silicon nitride thin films and isotropic etching of silicon has also been explored by [5], minimum etch non-uniformity of 1.4 % was observed inside the molds due to the crystalline orientation dependent preferential etching in silicon. This effect may be a contributing factor in frequency asymmetry observed in [3] and [4].…”