Laser-Induced Self-Propagating Reaction In Ti/α-Si Multilayer Films

The processes of nanometer devices, for example, micro-joining, need very preciseheat source. Some induced nano-structure multilayer films can rlease a amount of heatrapidly, and act as a heat source for nano-devices, especially for heat susceptible devices.The most important thing is how to control the speed and heat-output of the reaction inorder to reduce or avoid damage to the nano-meter units.First of all, we fabricate19kinds of Ti/α-Si multilayer systems with differentstructure parameters (N-number of layers, λ-thickness of bilayer, w-thickness of SiO2)and character surface roughness, cross section feature and compostion of the materialsystem. The second part is inducing19kinds of multilayer systems with proper lowenergy provided by laser in order to get the relationship between structure parametersand E-inducing energy or v-reaction speed. In addition, we use XRDand SEM toanalyze the composition and surface feature of the reaction product. The third part ismainly about exothermic process of the reaction. We make use of DTA method to getthe reaction peorid and its product in order to obtain the reaction mechanism of Ti/α-Simultilayer system. Furthermore, finite element analysis simulation method is taken tostudy the dynamic exothermic process of reaction.Results show:(1)Theory adiabatic temperature of reaction between Ti and Si withTi5Si3as the only reaction product is about2403K, which is higher than the criticalvalue-1800K of self-propagating reaction. Besides, the Ti/α-Si multilayers are fabricatedwith very clear layer structure and the average surface roughness is only4.14nm. Noapparent reaction between Ti and α-Si layers were found during XRD test.(2)Thicknessof SiO2–w is the most critical structure parameter for the reason that almost all kinds ofTi/α-Si film systems cannot be induced when w is very low. If other structureparameters are constant, reaction speed-v will increase both with the increase of laserenergy-E, numbers of bilayers-N or Thickness of SiO2–w and the decrese of bilayerthickeness-λ, decrease with the prediffusion thickness. In addition, Ti5Si3is the mainproduct of self-propagating reaction.(3)All exothermic peaks will be sharper withhigher heating rate and exothermic peaks appear when temperature is500C、600C、700C、1000C or1300C which means there are solid diffusion reactions between Tiand α-Si layers. By analyzing the composition and cross-sectional morphology of theproduct at each exothermic peak, we obtain the product trend is TiSi2�'TiSi�'Ti5Si4�'Ti5Si3, the reaction mechanism of which can be described by “Disk Growth” model.(4)ANSYS results show: during the process, high-temperature region is concentrated in thefilm and high SiO2layer due to the thermal barrier effect of the SiO2; the heating rateand cooling rate of A1, which is located in Si basement with10μm distance to the SiO2 layer, is as high as6.6×105K/s and4.3×105K/s. It means the heat affected zone is smalland the process is suitable for heat treatment of heat-sensitive device.