X-rays feel the strain

Nano Lett. doi:10.1021/nl2013289 (2011)

Strain is often employed in the semiconductor industry to increase the speed of transistors, but it is difficult to measure the strain fields in devices after they have been fabricated. X-ray nanodiffraction is a promising technique for this task because it offers good resolution, elemental sensitivity and the large penetration depths needed to 'see' inside devices containing many layers of different materials. Now Nina Hrauda of Johannes Kepler University in Linz and co-workers have used this approach to measure the strain fields inside a working field-effect transistor.

Hrauda and co-workers focussed hard X-rays from the European Synchrotron Radiation Facility in Grenoble to produce a beam with a diameter of 400 nm. This X-ray beam was then directed at devices in which a nanoscale island of SiGe was used to induce tensile strain in the silicon channel above it. The team found that various nanostructures in their devices, notably the gatestack (which contains a thin layer of SiO_xN_y and a thicker layer of Al) and a SiO₂ isolation layer, tend to reduce the strain induced by the island. An improved understanding of the strain distributions inside devices should lead to improvements in performance.