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 mu m, 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 mu m, 95 mu m, 91.2 mu m, and 109 mu m, 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.

Automated summary

In this study, thermally evaporated aluminum was used as a hardmask to fabricate silicon microchannels using an ICP-RIE system in SF6/Ar gas mixture. The treated aluminum hardmasks demonstrated high resistance against the etching process, leading to successful fabrication of SiMCs with desired depths. SEM images showed uniform etching on the channel walls and bottom, indicating good etch uniformity for all samples.