C54-TiSi 2 formation using nanosecond laser annealing of A-Si/Ti/ A-Si stacks

Low resistive Ti-based contacts are required to reach the targeted performances of 3D imaging devices. To fulfill this request, the C54-TiSi 2 phase appears to be the most efficient. However, in view of monolithic integration, the temperature needed to form C54-TiSi 2 must be drastically reduced by at least 100 degrees C in order to avoid damage in other parts of the device. Indeed, as these 3D imaging devices require the co-integration of Ti and Ni based silicides, it is crucial to develop a thermal treatment which allows to form the C54-TiSi 2 phase without agglomerating the NiSi layer (i.e. at temperatures lower than 600 degrees C). In this work, a three-layer stack made of a Ti layer in between two amorphous Si thin films deposited on (100) Si substrate has been studied. Nanosecond laser annealing (NLA) followed by rapid thermal annealing (RTA) from 500 to 800 degrees C were performed on those stacks. Sheet resistance and X-Ray Diffraction measurements showed that the C54-TiSi 2 phase could be formed with a RTA treatment at a temperature as low as 600 degrees C in this case. In line with some previous work, this was due to another phase sequence involving the C40-TiSi 2 during the laser annealing. The most favorable microstructure to form C54-TiSi 2 by a subsequent RTA treatment seemed to be a matrix made of amorphous titanium silicide containing grains of the C40-TiSi 2 template phase. This hypothetical microstructure was formed by laser annealing at a lower energy density when layers of amorphous Si were used.