Numerical Calculation Of Thermal Effect Of 4H-SiC Irradiated By Nanosecond Laser

Lasers are becoming the main tool for manufacturing SiC devices,such as micro-switches,tunable capacitors,micro-machined inductors,micro-machined antennas and resonators,etc.Compared with silicon-based devices,SiC-based devices have advantages in operating frequency,power handling capability and reliability.At present,the researches on laser and SiC devices are mainly limited to the experimental part,the systematic investigations on theoretical calculation is still blank.Therefore,the thermal effect of 355 nm and 248 nm lasers irradiation on SiC is systematic study in this thesis.The calculation results show that the heat conduction-coupling model is chosen to explore the carrier concentration changes;however,the heat conduction model must be adopted for the temperature variation when 355 nm laser irradiates SiC.Different pulse width determines the application of laser.Small pulse width is suitable for ion implantation annealing,while large pulse width is suitable for Ohmic contact fabrication.When the pulse width is 4 ns and the energy density is in the range from0.35 to 0.75 J/cm²,the irradiation temperature is 1903～3100 K,which is very suitable for ion implantation annealing.If the corresponding laser parameters are 40ns and 1.75～2.75 J/cm²,respectively,the temperature is 1806～2680 K,Ohmic contact can be successfully fabricated for Ni/SiC system.The temperature distribution of laser irradiation based on pulse width and energy density provides the basis for selecting laser parameters for different laser applications.The effects of laser irradiation times on the composition and thickness of SiC near surface were studied experimentally.When the laser irradiation times are 50,70and 1000,the thickness of SiC damage layer is about 370 nm,in which the thickness of carbon-rich layer is about 100 nm and the thickness of the mixture of Si_1-xC,Si and C is about 270 nm.The basic physical model of the damage layer of SiC irradiated by laser is established in view of the experiment.The calculation results show that the temperature of the damage layer in the thickness range of 101 nm is higher than 5100K,which is higher than the boiling points of Si and C.It is approximately considered that all the damage layers of this thickness have been sublimated;the 368 nm-thick damage layer is in the range of 3100-5100 K.There exists partial decomposition of SiC at this temperature range.The experimental results are in good agreement with the theoretical calculation.The results of temperature distribution calculation deepen the understanding of delamination phenomenon caused by SiC irradiation.