Evaluation of photoresist-based nanoparticle removal method for recycling silicon cantilever mass sensors

Photoresist-based nanoparticle (NP) removal is evaluated as an approach to extend the life time of silicon resonant cantilever-based mass sensors for airborne NP monitoring. Integrated with a miniaturized electrostatic NP sampler, the cantilever can collect and detect airborne NP mass. Prior to airborne NP sampling, the cantilever surface is covered by a sacrificial layer of photoresist. Within a lift-off process of wet cleaning, the photoresist layer is removed together with the trapped NPs with cleaning efficiencies of ~95 - 99%. The resonant frequencies and the quality factors (Q-factors) of the cantilevers are characterized for different thicknesses of the photoresist layers given by their viscosities. The proposed recycling technique is found to be most effective when a thin photoresist film is used. By using higher order resonant modes, Q-factors of more than 1000 in air are maintained even after the photoresist coating. As necessary for an application under workplace conditions, the limitations of the sensor sensitivity influenced by the environment, i.e., ambient temperature and relative humidity (rH), are also measured.