The Back-End-Of-Line (BEOL) Compatible Antiferromagnet PtMn

Back-end-of-line (BEOL) processes in device fabrication often require thermal annealing up to 400°C for 3 hours. This is too high for most antiferromagnetic (AFM) materials, such as the ubiquitous IrMnx alloys, where Mn diffusion happens too readily for BEOL compatibility. Hence, there is significant interest worldwide to identify suitable alternative AFM materials many of which have an L10 structure. One such material is the equiatomic alloy Pt50Mn50. However, this stoichiometry has two stable phases: a low temperature paramagnetic face-centred cubic (fcc) phase and a higher energy face-centred tetragonal (fct) phase, where the latter has the needed AFM ordering. The thermal energy applied during BEOL processes can be used to trigger the phase transformation from fcc to fct. As such the AFM no longer needs to be robust to the BEOL process, as it becomes part of it. Optimising and controlling this phase transition is key – often achieved with long, high temperature anneals. We have used a wide range of experimental techniques to characterise a set of PtMn samples deposited on different seed layers. The seed layers (Pt, Ru and Nb) were chosen so as to manipulate the crystallisation of a PtMn layer through lattice mismatch and intermixing effects. Polarised Neutron Reflectometry (PNR) will be used as a complementary technique to validate or disprove our current interpretation of our results. The collected data would contribute towards a peer reviewed publication.