Patterning of platinum (Pt) thin films by chemical wet etching in Aqua Regia

Abstract

The chemical and physical properties of platinum (Pt) make it a useful material for microelectromechanical systems and microfluidic applications such as lab-on-a-chip devices. Platinum thin-films are frequently employed in applications where electrodes with high chemical stability, low electrical resistance or a high melting point are needed. Due to its chemical inertness it is however also one of the most difficult metals to pattern. The gold standard for patterning is chlorine RIE etching, a capital-intensive process not available in all labs. Here we present simple fabrication protocols for wet etching Pt thin-films in hot Aqua Regia based on sputtered Ti/Pt/Cr and Cr/Pt/Cr metal multilayers. Chromium (Cr) or titanium (Ti) is used as an adhesion layer for the Pt. Cr is used as a hard masking layer during the Pt etch as it can be easily and accurately patterned with photoresist and withstands the Aqua Regia. The Cr pattern is transferred into the Pt and the Cr mask later removed. Only standard chemicals and cleanroom equipment/tools are required. Prior to the Aqua Regia etch any surface passivation on the Pt is needs to be removed. This is usually achieved by a quick dip in dilute hydrofluoric acid (HF). HF is usually also used for wet-etching the Ti adhesion layer. We avoid the use of HF for both steps by replacing the HF-dip with an argon (Ar) plasma treatment and etching the Ti layer with a hydrogen peroxide (H 2 O 2) based etchant.

Resistive switching and its suppression in Pt/Nb:SrTiO3 junctions

“…All samples were post-Pt deposition annealed at 800 °C in flowing O 2 to eliminate any possible contributions from oxygen vacancies that may have formed during Pt deposition. Square 30 × 30 μm 2 Pt electrodes were patterned by standard photolithography, following by selective oxidation of the top Pt surface by a room temperature plasma in 300 mTorr O 2 at 100 W. The Pt oxide was then used as a hard mask for wet etching Pt in Aqua Regia at 60 °C 40 . A ground-signal-ground electrode configuration was then completed with Ohmic Al contacts made to the Nb:SrTiO 3 , which was defined by a standard lift-off process (see Fig.…”

Chemical compatibility of fused filament fabrication-based 3-D printed components with solutions commonly used in semiconductor wet processing

“…Aqua regia is a mix of HCl and HNO3, often used in a 4:1 HCl 37% : HNO3 69% volumetric ratio. Specifically, Aqua regia is used to remove even noble metals like Au and Pt [38,39]. Aqua regia is also used as a semiconductor surface treatment for example in obtaining low contact resistance p-GaN [40,41], which is important for high efficiency white LEDs and blue lasers.…”

Metallization of Organically Modified Ceramics for Microfluidic Electrochemical Assays

“…To integrate metal elements with Ormocomp microchannels, case-specific processes were developed for each of Pt, Au, silver (Ag), and aluminum (Al) by using Cr (for Al and Pt) or Ti (for Au and Ag) as the adhesion layers on the basis of prior literature [21,22,23,24]. The adhesion layer was first deposited on top of the microchannels by evaporation (Ti, 5 nm, IM-9912 evaporator, Instrumentti Mattila, Mynämäki, Finland) or sputtering (Cr, 17 nm, PlasmaLab 400, Oxford Instruments, Bristol, UK) (Figure 1D).…”