Optimization And Exploration Of Laser Annealing Process For Micro-nano Devices

With the rapid development of big data and cloud computing,the amount of data that integrated circuits need to process continues to increase,and the storage of data becomes extremely important.In order to meet the market demand for high-performance and high-density storage devices and to alleviate the technical bottleneck of planar NAND flash memory,3D NAND flash memory structures have been proposed.Due to the characteristics of the 3D NAND flash structure,a lower thermal budget is required to reduce temperature damage to the device layer.Therefore,the study of 3D architecture annealing process has very important practical significance for the new generation of devices.In order to understand in more detail the thermal field situations during the crystallization of amorphous silicon under laser irradiation and optimize laser annealing process and improve semiconductor memory performance,the temperature field changes in the device under nanosecond laser annealing condition and the phase transition mechanism of femtosecond laser irradiation on semiconductor materials have been deeply studied in this paper.The purpose is to more thoroughly grasp the change of thermal field in the process of laser amorphous silicon annealing,optimize the laser annealing process and provide a certain data reference for laser annealing to prepare polysilicon channel.The first part mainly introduces the thermal field distribution in 3D NAND flash memory cells under the action of nanosecond laser pulses with COMSOL software.Establish laser annealing simulation model by parameter setting,model creation,meshing,phase change processing,etc.A Gaussian heat source is applied to the model,and then change the polysilicon channel thickness,laser energy density and pulse width for numerical simulation.Simulation results show that:the temperature of the sample surface is proportional to the laser energy density and inversely proportional to the pulse width.Besides,the temperature and temperature gradient along the radial direction and along the axis gradually decrease.When the laser energy density isU = 1500mJ/cm2,the amorphous silicon material on the surface of the channel layer first reaches the phase transition temperature;when U ? 1500mJ/cm2,the temperature of the bottom amorphous silicon material can be stabilized in the amorphous silicon.The phase transition temperature;at the same time,in order to avoid melting of the adjacent Si02 material layer,the laser energy used in the laser annealing process should be limited to 3000mJ/cm2.In addition,the thickness of the polysilicon channel is nonlinearly related to the interface temperature,and the temperature at the interface is the lowest when the thickness of the channel layer is about 13 nm.The results of this study can provide an important reference for the optimization of 3D NAND flash annealing process.The second part mainly studies the interaction between femtosecond laser and solid materials from theoretical analysis,numerical simulation and experimental methods.In the theoretical part,the physical mechanism of the interaction between femtosecond laser femtosecond laser and solid materials is introduced,which lays a theoretical foundation for the understanding of the femtosecond laser cold action process.In the numerical calculation part,the interaction process between the femtosecond laser and the semiconductor material is studied by introducing and solving the two temperature model.Solution results show that:electron-lattice coupling time is far less than femtosecond laser pulse duration.Therefore,the electron temperature and the lattice temperature are always in a non-equilibrium state.The penetration depth of the laser in the semiconductor sample is on the order of microns.When the laser energy density is constant and the pulse laser width increases,the maximum value of electron temperature and the lattice equilibrium temperature decreases,and the lattice temperature rise rate becomes slower.In the experimental part,an amorphous silicon film is prepared on two different substrates by using PECVD process,and then crystallization of amorphous silicon is achieved by irradiating the film with femtosecond laser at room temperature.Observed byscanning electron microscope and atomic force microscope,after annealing,nano-grains appear on the surface of the amorphous silicon film and the surface roughness increases more evenly.Besides,the oxide substrate has little effect on annealing.According to Raman spectroscopy,the femtosecond laser realizesthe phase transition from amorphous silicon to polycrystalline silicon.The above results show that the femtosecond laser non-thermal annealing process is suitable for large-scale preparation of polycrystalline silicon films on room temperature non-heat-resistant substrates.