The Thermal Effect During KrF Laser Interaction With SOI And Application Of Melting Finishing On Nano Optical Waveguide

Silicon-on-Insulator(Silicon-on-insulator,SOI)has became one of important material in micro-opto-electro-mechanical systems(MOEMS),because it has many advantages in the field of microelectronics and optoelectronics field,such as optical communication system,optical interconnect system,digital image processing system and the military field.Further more,benefiting from the large refractive index difference of Si and SiO2,nano optical waveguide based on SOI has the ability to focuse optical field in a cramped space,which is expected to be primary part in quantum communication system.At present,it is a goal of advanced manufacturing to achieve low cost and mass production of SOI device.UV laser micro-machining is no mechanical stress and flexible method,and its small beam size,large absorption coefficient and maskless processing make it widely used in SOI optoelectronics.In particular,UV laser surface melting finishing technology can reduce waveguide sidewall roughness and manufacture ultra-low loss nano optical waveguide,which has become crucial for the development of several fields including optical communication,biosensor and high sensitive detection.Based on the mechanism of interaction between laser and material and the heat conduction theory,in this thesis,melting and vaporization threshold and temperature distribution of SOI induced by KrF excimer laser are studied.The paper discusses small heat-affected zone of SOI under radiation of KrF excimer laser and application in laser micro processing.Meanwhile,a systematical analysis for the self-heating effect of SOI was given.On this basis,KrF excimer laser reformation as a sidewall smoothing technique is studied with the theoretical analysis and finite element method.On the basis of distribution rule of temperature field,morphology of melting pool is precisely controlled by the controlling laser technics parameters.Finally,combined with relevant knowledge,new technological process is put forward and the process parameter is optimized.To clarify the temperature field evolution law of SOI induced by KrF excimer laser,a two dimensional finite element numerical model is established on the analysis of time and space distribution of laser energy.Meanwhile,the model has taken into account the effects of temperature dependences of material parameters and latent heat.Melting and vaporization threshold of SOI are obtained to use different average energy density laser irradiation on material.The temperature variation in radius suggest that the high temperature zone is observed in only certain range around light spot,and temperature decreases rapidly away from irradiated zone.The temperature variation in axial suggest that more heat conserve in silicon layer and the temperature of silica layer is low,which is due to low thermal conductivity of silica.Aiming at the problem of waveguide sidewall large roughness leading to larger scattering loss,a two dimensional finite element numerical model is established.Several investigations have been made about the relationships between the carry behavior forward of melting pool boundary and different processing parameters.Simulation results indicate that melting pool begin developing in the corner between the upper surface of waveguide and the laser-facing sidewall surface.At a given laser incidence angle,the depth of melting pool is correlated positively with the average energy density.Melting pool shape is mainly controlled by laser incident angle: with the decreasing of incidence angle,the shapes of melting pool appear in first single-edge U-shaped,then single-edge V-shaped,and finally single-edge V-shaped with an obtuse angle.Analysis shows that melting pool shape induced by a larger laser incidence angle is more favourable to the finishing process of waveguide sidewall.Based on this,a new process method is proposed that determinating laser incident angle to optimize the shapes of melting pool and then selecting the appropriate laser energy density to obtain the sufficient melting depth.Result of this thesis may provide theoretical basis for the thermal effect on SOI induced by laser and UV laser processing of SOI devices.Meanwhile,it may accelerate the development and application of laser melting finishing on SOI nano optical waveguide.