CHALLENGES: Advanced cleanroom compatible TiN probes for Tip-Enhanced Raman Spectroscopy

TERS (Tip-Enhanced Raman Spectroscopy) is a technique that is very attractive for the nanocaracterisation of various materials and devices. Its major advantages are its very high resolution (down to the single molecule), non-destructiveness and speed. Several factors, however, contribute to the non-applicability of this technique to the industrial sector. This research, carried out as part of the H2020 Challenges (Real-time nano CHAracterisation reLatEd techNloGiEeS) project (https://www.challenges2020.eu/), aimed to develop TiN-coated tips for tip-enhanced Raman spectroscopy (TERS), addressing the incompatibility of Ag and Au tips in semiconductor cleanrooms. The three main application contexts of the Challenges project were: Nanoscale strain characterisation, defect analysis in photovoltaic silicon and 2D material characterisation using TERS.Indeed, Silver (Ag) and gold (Au) TERS (Tip-Enhanced Raman Spectroscopy) tips are typically avoided in high-end silicon cleanroom environments for two main reasons: 1) Silver and gold are chemically reactive metals. They can oxidise when exposed to air, moisture or certain chemicals while the clean room environment requires non reactive materials to maintain the better conditions necessary for semiconductor manufacturing; 2) Ag and Au are soft metals and their tips can wear or shed particles during TERS measurements and contamination by metal particles is a critical issue in cleanroom environments as even the smallest impurities can severely interfere with the device’s functionality resulting in electrical shorts, altered circuit behaviour or other undesirable effects. In contrast, the use of tips made from materials such as titanium nitride (TiN) offers a combination of chemical stability, wear resistance and non-conductive properties that make it suitable for use in clean room environments. The TiN-coated tips maintain the integrity of the cleanroom conditions while providing the functionality required for effective TERS measurements. Precise stoichiometry control was critical to maintain optical resonance intensity and wavelength. ScanSens GmbH achieved reliable and manufacturable tip shapes from unconventional materials, allowing TiN-based tips to be used in clean room environments. Using this approach, TiN coated tips tested by La Sapienza University of Rome showed comparable performance to standard Ag and AgAu TERS tips. This achievement opens up avenues for advancing nanoscale characterisation in contributing to the evolution of semiconductor manufacturing processes.