Optically inducing and probing the local crystallization of ultra-thin GeSbTe films by single-pulse laser irradiations

GeSbTe alloys are among the basic elements for high-performance electrically-programmable phase change memories. In this context, technology advances rely on complex material analyses in extremely miniaturized devices and so require numerous and tedious tasks. In this work, we optically emulate and measure the phase change of GeSbTe alloys without the need for device integration. Using microsecond laser pulses, we crystallize multilayer thin-film systems. The irradiated materials are then investigated using microscopy and spectroscopy methods. By comparing measurements with optical simulations, we demonstrate that quantitative descriptions are achievable and thus that local phase changes of ultrathin films relevant for microelectronics applications can be directly monitored, compared and evaluated. An improved detection sensitivity is found for the infrared region of the spectrum leading to the use of a transmission microscopy arrangement operated at 1200-nm wavelength for insitu studies. With appropriate laser conditions under damage threshold, we demonstrate the ability of the pulses to selectively crystallize Ge 2 Sb 2 Te 5 layers while leaving untouched other germanium-rich layers due to distinct crystallization temperatures. The optical detection scheme is shown to detect phase changes of single ultrathin films with thicknesses as small as 5 nm. This opens a way for all-optical methods complementing advanced material analyses for the study of GeSbTe-based microelectronics technologies and the development of the next generations of high-density phase change memories.