Apr 12, 2013
New sequential process delivers pure Pt EBID structures
Electron beam induced deposition (EBID) is a direct-write process used for rapid prototyping of three-dimensional nanodevices. This process allows fabrication of nanostructures of a variety of materials and of desired dimensions at pre-defined locations on a substrate in a scanning electron microscope (SEM). However, the low purity of the deposits is a significant shortcoming of the process. For instance, use of MePtCpMe3 as a precursor typically leads to a carbon-rich Pt EBID structure (approx. 15 at. % of Pt) and a resistivity of the order 107 µΩ.cm. This negatively affects application of Pt EBID structures as nanocontacts.
Different post-treatments like electron beam post-irradiation and annealing (300 °C to 550 °C) in oxygen atmosphere have been reported to increase the Pt content up to 35 at.% and 70 at.% maximum, respectively. In addition, the shape and size distortion of the structure increases with annealing temperature. We have developed a new post-treatment: in situ annealing with electron beam irradiation under oxygen flux, which leads to complete purification of Pt EBID structure at annealing temperatures as low as 120 °C. The lateral dimensions of the structure are observed to be the least affected while the height reduces to 33% of the as deposited height.
Furthermore, we have followed a sequential deposition and purification approach to fabricate a pure Pt structure. A Pt EBID structure is deposited on a previously purified structure and it is purified sequentially. In this way, a pure Pt structure of final dimensions 2 µm × 2 µm × 160 nm was fabricated by stacking up eight individually purified Pt structures (figures A and B). The corresponding EDX line profile confirms the purity of the structure (figure C). The resistivity of a 15 µm × 1 µm × 200 nm thick pure Pt contact fabricated by this method is determined to be 70 ±8 µΩ.cm – only six times higher than that of pure bulk Pt (10.62 µΩ.cm). However, the time required for fabrication of this contact is typically hundreds of minutes.
Further experiments towards increasing the speed of the process and applying the same method for purification of other carbon-rich structures of noble metals are in progress.
More information can be found in the journal Nanotechnology.
About the author
Shruti Mehendale is a postdoctoral research scientist working together with senior scientists Dr J J L Mulders and P H F Trompenaars at FEI Electrons Optics, Eindhoven. This work is supported by NanoNextNL, a micro and nanotechnology programme of the Dutch Government and 130 partners.