Research On Key Technology Of Laser Recrystallization Of Ge Epitaxial Film On Si

With the development of microelectronics and optoelectronic,new materials and new technologies are emerging.Both of the advantages of Si substrate and Ge semiconductor are available for Ge on Si technology（Ge/Si）,which has great potential applications in the field of microelectronics and optoelectronics.However,it is difficult to obtain high-quality Ge epitaxial layers on a Si substrate due to the 4.2%lattice mismatch between Si and Ge.Although the high quality Ge/Si epitaxial layer can be prepared by a two-step process combined with cyclic thermal annealing,the method still has the following disadvantages:（1）The Ge epitaxial layer usually prepared by the process is about 1 micron thick,and the thin Ge epitaxial layer has poor applicability;（2）the process still has the disadvantage of long cycle and high thermal budget.Laser recrystallization technology provides an effective way to solve this problem.The essence of this technology is a thermally induced phase change process.By controlling the laser process parameters,a certain thickness of the Ge epitaxial layer is melted and lattice rearrangement and recrystallization are achieved.Laser recrystallization technology is fast,simple in process and precise in control,enabling high quality thin Ge/Si preparation.Based on the finite difference time domain method,the absorption and reflection model of Ge epitaxial layer on Si irradiated by 808nm continuous laser is established.Based on the model,the effects of SiO₂ capping layer thickness and Ge epitaxial layer thickness on the reflectivity and absorptivity of 808nm continuous laser irradiated Ge epitaxial system on Si are studied.The results show that when the thickness of SiO₂ is 150nm,the reflectivity is the lowest and the absorption of laser by Ge epitaxial layer is the highest.With the increase of the thickness of Ge layer,the reflectivity of the system fluctuates and gradually stabilizes.The rate fluctuates with the increase of Ge thickness,and the absorption rate of Si laser decreases with the increase of Ge thickness.The above results can provide a theoretical reference for the selection of SiO₂ capping layer thickness and Ge thickness,and can provide important parameters for the establishment of subsequent models.Based on the principle of heat transfer and finite element method,a thermophysical model of laser recrystallization process parameters and temperature distribution of Ge epitaxial layer on Si was established.The effects of process parameters such as initial temperature,Ge epitaxial layer thickness,laser output power and effective laser radius on laser recrystallization of Ge epitaxial layer on Si are studied.The selection of laser recrystallization parameters for Ge epitaxial layer on Si are proposed:The SiO2 capping layer has a thickness of 150 nm,and the system is preheated at 873 K before laser recrystallization.The thickness of the Ge epitaxial layer is 400 nm,the continuous laser output power of 808 nm is 60 W,and the effective laser radius is 75μm.The thermal physical model of laser recrystallization of Ge epitaxial layer on Si can be used as a technical reference for laser recrystallization to provide high quality thin Ge epitaxial layer on Si substrate.In addition,using the above method,the laser absorption model and laser recrystallization thermal physics model of SiO₂/Ge/sapphire system are also studied.By optimizing the process parameters and melting the Ge epitaxial layer,it can provide an important technical reference for the laser recrystallization technology to assist in the preparation of high quality GeOI.Laser recrystallization is a thermal process,and there may be a problem of Si-Ge interdiffusion in the process.In this paper,the mechanism of Si-Ge interdiffusion is studied.Based on Fick's law of diffusion,a numerical model for Si-Ge interdiffusion of Ge epitaxial layer on Si is established.The process simulation software Sentaurus Process is used to study Si-Ge interdiffusion during rapid thermal annealing and laser recrystallization.The results show that compared with rapid thermal annealing,Ge on Si does not undergo Si-Ge interdiffusion during laser recrystallization.Reasonable control of the laser recrystallization process parameters,so that the thin layer Ge near the Si-Ge interface does not melt,which can improve the crystal quality of the Ge epitaxial layer,and effectively avoid the Si-Ge interdiffusion during laser recrystallization.In this paper,the research on the thermal physics model of the Ge epitaxial layer on Si substrate and the interdiffusion of Si-Ge can provide an important technical reference for the laser recrystallization process to assist in the preparation of high quality Ge epitaxial layers on Si.