Temperature And Stress Study On Crystallization Behavior Of Ge₂Sb₂Te₅ Thin Films Induced By Laser

Phase-change memory?PCM? has been widely employed with the forms of rewritable CDs, DVDs, and Blu-ray discs based upon the reversible switching between the amorphous and crystalline phases of chalcogenide alloys. As induced by laser, the reason of ultrafast phase-change were not clear. There are two main reasons for it: 1.The time of phase change is short and the area of phase change is small. 2. The theoretical calculations were based on the annealing process, the characteristics of laser-induced phase-change were not well performed. In order to solve these problems, we calculate the crystallization process of phase-change induced by laser using the finite element method calculation. And then we analyzed the temperature and the stress distribution of Ge₂Sb₂Te₅ thin film induced by short laser.In the study, we used a 3D FEM model to investigate the temperature field and stress distribution of GST thin film induced by an excimer KrF laser. A typical significance laser influence of 53.3mJ/cm3 was employed in the simulation. Based on the simulated result, we divided the whole process into four part: temperature-rise period, thermal equilibrium phase, cooling stage and temperature stable stage. The heating rate at first 5ns and the cooling rate were calculated. Through the analysis of heating rate and cooling rate induced by laser, the crystallization process mainly take place in the cooling stage. The effect of laser influence on temperature field was also studied. Both the heating rate and cooling rate were increased with the increase of laser influence.The elastic modulus and hardness of amorphous and crystalline GST films were determined by nanoindentation. The thermal stress as well as phase-change stress distribution were exhibited through the FEA simulation, it was found that the magnitude of thermal stress is bigger than the phase-change stress, and the gradient of phasechange is higher than the thermal stress. And the stress mainly distributed in the top surface and ground contact area. Mechanical failure accompanied by volumetric change and hillock of PRAM devices can therefore be attributed to the phase-change stress, both the thermal stress and phase-change stress should be taken into consideration for understanding the mechanism of mechanical failure and optimizing the mechanical reliability of the PRAM device.In the paper, we calculated the temperature field and stress filed induced by laser of different pulse width. Then we proved the temperature and stress play an important role to the crystallization process of GST film, and made contribution to understand the mechanism of phase-change.