Competence Center for Micro- and Nanotechnologies

Microfabricated silver deposited two-dimensional quartz gratings are developed for the use as plasmonic arrays for surface enhanced Raman spectroscopy (SERS). The SERS technique provides enormous signal intensity and fingerprint specificity and is a powerful tool in chemical and biological applications [1]. However, the acceptance and the employment of the SERS technique for (bio)analytical devices depends on the availability of suitable substrates with reproducible field enhancement properties. Our earlier work on micro fabricated SERS substrates was focused on the reproducible formation of large-scale arrays of very small and sharp-edged metallic nanostructures made in gold on quartz [2]-[4]. With this contribution we present some aspects of the micro fabrication that provides regularly patterned SERS arrays using silver. In particular, the influences of the silver evaporation rate, the silver thickness as well as pattern geometries are discussed. On 4” wafers 2-d gratings with a size of 1 mm² and a pitch of 436 nm are produced by means of electron beam lithography and etched 50 nm deep into the quartz surface using reactive ion beam etching (Figure 1). Compared to gold, silver yields larger surface enhancement of Raman scattering. Unfortunately, non-protected thin silver films tend to corrode when exposed to air. Therefore the 40 nm thick silver film is thermally evaporated on top of the quartz chips shortly before the SERS measurement (Figure 2). SERS investigations have shown a reproducible signal enhancement across the whole grating area (Figures 3 and 4). The estimated enhancement factor is in the range of 6 orders of magnitude.