Silicon Micro-Channel Definition via ICP-RIE Plasma Etching Process Using Different Aluminum Hardmasks

In this work, thermally evaporated aluminum (Al) was used as hardmask (HM) to obtain silicon microchannels (SiMCs), using an Inductively Coupled Plasma - Reactive Ion Etching (ICP-RIE) system, in SF6/Ar gas mixture environment. The channel depth must be greater than 50 μm, with a high aspect ratio. For this, Al HM lines were defined by photolithography and by Al wet etching on a silicon substrate. To improve the resistance against the ICP-RIE etching process, the Al HMs were treated with four different conditions: i) Al HM without treatment step (control sample); ii) with plasma nitridation (AlN/Al structure); iii) with thermal annealing (annealed Al film); iv) with plasma nitridation and annealing (annealed AlN/Al structure). After 100 min of ICP-RIE etching process, SiMC with depths of 90.6 μm, 95 μm, 91.2 μm, and 109 μm, respectively, were measured using a scan profiler system. As the main result, the annealed AlN/Al structure presented a high resistance against the ICP-RIE etching for 100 minutes. Furthermore, Scanning Electron Microscopy (SEM) images indicate an etch uniformity on the walls and bottom of the channels for all the samples. This parameter is a mandatory requirement to obtain the integrated microchannel liquid-cooling technology for heat sinks in photovoltaic cells and Complementary Metal-Oxide-Semiconductor microprocessors.