The application of reactive ion etching in producing free-standing microstructures and its effects on low-temperature electrical transport

Abstract

We have developed a reliable method of fabricating free‐standing metallic microstructures with dimensions down to 50 nm. This technique is compatible with virtually any metal and can be used to fabricate samples that should be low‐dimensional with respect to both electron and phonontransport. Unlike earlier schemes that effect substrate removal from the front, our technique calls for reactive‐ion etching (RIE) from the reverse side of a Si3N4 membrane substrate, onto which microstructures have been previously patterned by standard methods. By carefully controlling the etching times, the extent of invasive damage of the etch on the microstructures is minimized. We have also performed resistance measurements for etched and unetched Al films on bulk substrates to characterize the effect of etching damage and its consequence on low‐temperature transport. By measuring the low‐field magnetoresistance(MR), the inelastic scattering rate and its dependence on temperature can be determined by fitting data to theoretical models. For short etch times, we have found that RIE does not alter the low‐frequency electrical transport properties of these supported films in any significant fashion. The only discernible difference between the etched and the unetched samples appears to be a small, temperature‐independent contribution to the inelastic rates, which can be attributed to surface damage. Thus, we conclude that our technique can be used to effectively decouple microstructures from substrate effects without introducing appreciable process related artifacts.