Through vias on silicon or suspended membrane on a silicon substrate have aroused interest in various disciplines of science and engineering. Resources and effort are being devoted to research towards the realization of through vias in refined scale and possible applications of such vias....[ Read more ]

Through vias on silicon or suspended membrane on a silicon substrate have aroused interest in various disciplines of science and engineering. Resources and effort are being devoted to research towards the realization of through vias in refined scale and possible applications of such vias.

A process to fabricate nanoscale vias on layers of silicon oxide, which are subsequently suspended to form a membrane, was developed with photolithography steps. The process involves a photolithography pattern of a via pattern on layers of silicon oxide with an offset between the via pattern on different layers of silicon oxide. Due to partial overlapping caused by the offset, an array of nanoscale vias can be achieved.

Polysilicon was incorporated to enable formation of the membrane by acting as a protective layer for etching via patterns on different layers of silicon oxide allowing independent pattern of the layers forming the offset pattern. Polysilicon was also utilized as etch mask for etching of via patterns onto the 3 μm thick oxide layer. The polysilicon mask endured oxide dry etching and opened a window for etching the via patterns onto the thick oxide layer by extending the life of the etch mask.

Results have shown resultant vias with equivalent diameter down to 103nm. Membranes containing nanoscale vias were suspended with DRIE from the back of the substrate. The via structure, cross section of via and the build-up of the suspended membrane were observed under SEM. Challenges in DRIE for etching trenches for suspending the membrane were also discussed.

The existence of nanoscale through vias was observed under SEM with cross sections of vias. Trans-membrane diffusion of ink and copper (II) sulphate revealed mass transport from one side of the membrane to the other through the nanoscale vias. Furthermore, the diffusion rate of copper (II) sulphate across the membrane with nanoscale through vias was characterized.