Evidences for redox reaction driven charge transfer and mass transport in metal-assisted chemical etching of silicon

Abstract

In this work, we investigate the transport processes governing the metal-assisted chemical etching (MacEtch) of silicon (Si). We show that in the oxidation of Si during the MacEtch process, the transport of the hole charges can be accomplished by the diffusion of metal ions. The oxidation of Si is subsequently governed by a redox reaction between the ions and Si. This represents a fundamentally different proposition in MacEtch whereby such transport is understood to occur through hole carrier conduction followed by hole injection into (or electron extraction from) Si. Consistent with the ion transport model introduced, we showed the possibility in the dynamic redistribution of the metal atoms that resulted in the formation of pores/cracks for catalyst thin films that are ≲30 nm thick. As such, the transport of the reagents and by-products are accomplished via these pores/cracks for the thin catalyst films. For thicker films, we show a saturation in the etch rate demonstrating a transport process that is dominated by diffusion via metal/Si boundaries. The new understanding in transport processes described in this work reconcile competing models in reagents/by-products transport, and also solution ions and thin film etching, which can form the foundation of future studies in the MacEtch process.

Interfacial Contact is Required for Metal‐Assisted Plasma Etching of Silicon

“…Si covered by the noble metal catalyst etches significantly faster than uncovered Si, transferring the pattern of the deposited metal catalyst to the underlying Si. MACE proceeds through electrochemical and mass transport reactions predicated on the reduction of H 2 O 2 at the metal surface and extraction of electrons from underlying Si, thus injecting holes, at the Si–metal interface to create electron‐poor depletion regions in Si that are more susceptible to etching by HF …”

“…MACE proceeds through electrochemical and mass transport reactions predicated on the reduction of H 2 O 2 at the metal surface and extraction of electrons from underlying Si, thus injecting holes, at the Si–metal interface to create electron-poor depletion regions in Si that are more susceptible to etching by HF. [ 46 – 51 ]…”

“…The difference in the catalytic effect between MACE and MAPE suggests that the mechanism of MAPE deviates from that of MACE, although the exact reason why a metal will function as a catalyst in MACE but not MAPE is not currently fully understood. Unlike in MACE, where the reduction potential of the metal catalyst in relation to the Si ionization potential predicts whether a metal will function as a MACE catalyst,[ 51 ] reduction potential does not correctly predict the noncatalytic behavior of Pt and Cu in MAPE. Although shown not to correlate with MACE activity, previous studies have demonstrated that changing the work function of metals can enhance their catalytic activity.…”

General corrosion during metal-assisted etching of n-type silicon using different metal catalysts of silver, gold, and platinum

“…2 shows one of the models of the etching process. [28][29][30] The oxidizing agent is reduced on the metal catalysts and positive holes are injected into the metal/Si interface. Basically, the injected holes react with the uoride species near the metal/Si interface, and hence, the Si surface under the metal catalysts is preferentially etched.…”

Metal-Assisted Plasma Etching of Silicon: A Liquid-Free Alternative to MACE

“…This reaction causes electrons to be extracted from the underlying Si, thus injecting holes, to create electron-poor depletion regions in Si that are more susceptible to etching by HF. For thin metal layers, pores generated in the metal during etching facilitate transport of the HF through the film to enable etching of the underlying oxidized Si, with reactant byproducts carried away in solution 36 . For thick metal layers, this process happens at the Si/metal interface.…”