泡生法蓝宝石生长过程优化数值模拟研究

发布时间：2018-08-21 10:26

【摘要】：蓝宝石是一种有着良好性能的人工晶体,在军事光学材料、半导体衬底、智能手机上应用广泛。泡生法是生长蓝宝石晶体最主要的方法之一,本文主要运用Fluent数值模拟软件,对泡生法生长蓝宝石过程中的温度场、流场及固液界面形状进行模拟分析,研究了不同生产工艺及系统结构对晶体生长过程的影响。本文总结了蓝宝石的生长理论,建立泡生法生长蓝宝石过程的物理模型和数值模型,对晶体生长过程中放肩、等径初期、等径后期三个主要生长阶段进行数值模拟研究。研究发现,在籽晶上方通水冷却和坩埚周围加热器加热作用下,三个阶段系统内等温线呈上高下低分布,熔体内的等温线凸向坩埚底部分布,熔体沿坩埚壁面向上流动到固液界面中心位置后沿对称轴中心向下流动,进而形成一个逆时针漩涡。随着晶体生长过程的持续,系统内的等温线与熔体内漩涡中心向下移动,熔体内对流效应减弱,熔体内最大流速降低,晶体生长至等径后期,熔体内最大流速的位置由对称轴中心向坩埚侧壁偏移。泡生法生长蓝宝石过程中,工艺参数与热场结构的选择对晶体质量影响巨大。本文研究了放肩角、坩埚底部倒角半径和侧部与底部加热器功率配比变化对于泡生法生长蓝宝石系统内温度场、流场、固液界面形状的影响。研究发现:随着放肩角度的减小,系统内的平均温度降低,轴向温度梯度增大,熔体内的最大流速减小,熔体对流效应减弱,固液界面的凸度随之减小;随着坩埚底部倒角半径的增大,系统内的等温线上移,熔体平均温度升高,结晶前沿附近的最大流速降低,流场漩涡的形状随着坩埚底部倒角出现而变得圆滑,固液界面的凸度随着坩埚倒角半径的增大而减小,较小的凸度有利于保持自由界面的稳定;减小侧部与底部加热器功率配比后,系统内的等温线下移,固液界面附近的熔体径向温度降低,径向温度梯度减小,熔体内的最大流速降低,固液界面凸度增大。
[Abstract]:Sapphire is a kind of intraocular crystal with good performance, which is widely used in military optical materials, semiconductor substrates and smart phones. Bubble growth method is one of the most important methods for the growth of sapphire crystals. In this paper, the temperature field, flow field and solid-liquid interface shape of sapphire growth process are simulated and analyzed by Fluent numerical simulation software. The effects of different production processes and system structure on crystal growth were studied. In this paper, the growth theory of sapphire is summarized, and the physical and numerical models of the growth process of sapphire by bubble method are established. The three main growth stages of sapphire growth in the process of crystal growth, such as shoulder placement, initial equidiameters and late equidiameters, are studied numerically. It is found that under the action of water cooling above seed crystal and heating around crucible, the isotherms in the three stages are distributed up, down and down, and the isotherms in the melt protrude to the bottom of the crucible. The melt flows upward along the crucible wall to the center of the solid-liquid interface and then flows down along the center of the symmetry axis, thus forming an anticlockwise vortex. With the continuous growth of the crystal, the isotherm and the center of the vortex in the melt move downward, the convection effect in the melt weakens, the maximum velocity in the melt decreases, and the crystal grows to the late equidiameters. The position of the maximum velocity in the melt shifted from the center of the symmetry axis to the lateral wall of the crucible. The choice of process parameters and thermal field structure has a great influence on the crystal quality during the growth process of sapphire by bubbling method. In this paper, the effects of shoulder angle, bottom chamfer radius of crucible and power ratio of side to bottom heater on temperature field, flow field and solid-liquid interface shape of sapphire growth system are studied. It is found that with the decrease of shoulder angle, the average temperature in the system decreases, the axial temperature gradient increases, the maximum velocity in the melt decreases, the convection effect weakens, and the convexity of the solid-liquid interface decreases. With the increase of the chamfer radius at the bottom of the crucible, the isotherm of the system moves up, the average temperature of melt increases, the maximum velocity of flow near the crystallization front decreases, and the shape of the swirl becomes smooth with the appearance of the chamfer at the bottom of the crucible. The convexity of the solid-liquid interface decreases with the increase of the crucible chamfer radius, and the smaller crown is conducive to maintaining the stability of the free interface, and the isotherm line in the system moves down when the power ratio of the side part to the bottom heater is reduced. The radial temperature and radial temperature gradient of the melt near the solid-liquid interface decrease, the maximum velocity of flow in the melt decreases, and the convexity of the solid-liquid interface increases.
【学位授予单位】：河北工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ164.2

【共引文献】