大尺寸蓝宝石泡生单晶炉温场模拟研究

发布时间：2019-04-03 16:47

【摘要】：由于蓝宝石晶体良好的光学特性、稳定的化学结构和较强的机械强度,使其广泛应用于卫星空间技术、红外军事装置、高强度激光的窗口等军事领域;因其晶格常数与GaN接近,生长工艺成熟,使蓝宝石单晶广泛应用于SOS微电子电路、LED灯珠等衬底行业;因其硬度高、介电常数符合电容屏要求,使蓝宝石单晶应用于可穿戴设备窗口领域;又因其原子能级跃迁的特殊性质,使掺钛蓝宝石单晶应用于高功率激光器增益介质。随着这些行业的快速发展,蓝宝石的需求量日益增加,生长大尺寸、高质量蓝宝石单晶变得尤为迫切。因此,大尺寸蓝宝石泡生单晶炉温场的研究具有重大的应用价值。本论文利用CGSim模拟软件,并结合实际长晶实验的结果,探究了单晶炉温场老化的原因。利用金相显微镜、扫描电子显微镜(SEM)和干涉仪测试老化单晶炉钼屏的成分、微结构和反射率,结果表明单晶炉上、中、下层钼屏老化的机理明显不同:上部钼屏老化的机理是由于钼屏长期工作在低温区而被Al、O、Mo、W等挥发物附着,形成凸凹不平、大小不一的黑色附着物,吸附在钼屏表面的黑色挥发物改变了钼屏的反射率,降低了其保温效果;中部钼屏因工作区域温度没有达到其最高工作温度,表面形貌变化不大,反射率也没有太多变化;下层钼屏由于长期工作在高温区而造成钼元素挥发,在其表面形成了许多方向混乱、大小不一的微镜面,因微镜面的散射而降低钼屏的保温效果。将测得老化温场钼屏各部分反射率的结果导入计算机,模拟计算发现,由于钼屏保温效果改变,其温场温度梯度、固液面、熔体液流也发生了改变。通过实验长晶,晶体品质检测,发现与原温场对比晶体品质出现严重下降。利用蓝宝石单晶模拟软件CGSim,研究了氧化锆、氧化铝和金属组合温场的性能。首次提出了下部由钼屏与锆石结合、侧部由钼屏与氧化铝结合的保温系统。模拟结果显示:在保持侧屏厚度不变的情况下,将等厚度的钼屏更替为氧化铝后,温场的保温效果反而变差;在保证内部钼屏层数不变的情况下,不断增加锆石或氧化铝厚度,温场保温效果明显增强,功耗下降。但增加到一定厚度后,功耗下降趋缓。通过模拟相同温场构造、不同坩埚尺寸的单晶炉温场,探究120kg、200kg和300kg级的温场性能,结果显示:随着坩埚尺寸的增大,温场的保温效果变差、功耗增加;生长角变大、应力变大并出现应力富集现象;温度梯度减小;熔体液流保持不变。设计大尺寸单晶炉时,增强侧保温和下保温效果,扩大引晶与晶体交界面,防止应力富集现象出现。
[Abstract]:Because of its good optical properties, stable chemical structure and strong mechanical strength, sapphire crystal is widely used in military fields such as satellite space technology, infrared military devices, high-intensity laser windows and so on. Because its lattice constant is close to that of GaN and its growth process is mature, sapphire single crystal is widely used in SOS microelectronics circuit, LED lamp bead and other substrate industries. Because of its high hardness and dielectric constant, sapphire single crystal is applied to the window field of wearable devices, and because of its special properties of atomic level transition, Ti-doped sapphire single crystal is used in gain medium of high power laser. With the rapid development of these industries, the demand for sapphire is increasing day by day. It is very urgent to grow sapphire single crystal with large size and high quality. Therefore, the study of large size sapphire bubble single crystal furnace temperature field has great application value. In this paper, the reason of temperature field aging of single crystal furnace is investigated by using CGSim simulation software and the results of practical long crystal experiment. The composition, microstructure and reflectivity of molybdenum screen in aging single crystal furnace were measured by metallographic microscope, scanning electron microscope (SEM) and interferometer. The results showed that, in the single crystal furnace, the composition, microstructure and reflectivity of molybdenum screen were measured. The mechanism of molybdenum screen aging in the lower layer is obviously different: the aging mechanism of the upper molybdenum screen is that the molybdenum screen is attached by volatiles such as Al,O,Mo,W because the molybdenum screen works in low temperature for a long time, resulting in uneven black attachments of varying sizes. The black volatiles adsorbed on the surface of the molybdenum screen changed the reflectivity of the molybdenum screen and reduced its thermal insulation effect. Because the temperature of the middle molybdenum screen did not reach its highest working temperature, the surface morphology did not change much, and the reflectivity did not change much. Molybdenum element volatilization is caused by long-term work in the high temperature region of the lower molybdenum screen. There are many disordered micromirrors with different sizes on the surface of the molybdenum screen, which reduces the thermal insulation effect of the molybdenum screen due to scattering of the micro-mirror surface. The results of measuring the reflectivity of the molybdenum screen in the aging temperature field are introduced into the computer. The simulation results show that the temperature gradient of the temperature field, the solid liquid level and the melt liquid flow also change due to the change of the thermal insulation effect of the molybdenum screen. It was found that the crystal quality decreased seriously compared with the original temperature field through the experiment of long crystal and crystal quality test. The temperature fields of zirconia, alumina and metal have been studied by using the sapphire single crystal simulation software CGSim,. For the first time, a thermal insulation system is put forward, in which the lower part is bonded with zircons and the lateral part is bonded by molybdenum screen and alumina. The simulation results show that when the thickness of the side screen is kept constant, the thermal insulation effect of the temperature field becomes worse when the molybdenum screen of equal thickness is replaced by alumina. Under the condition of keeping the number of layers of molybdenum screen constant, the thickness of zircon or alumina is continuously increased, the thermal insulation effect of temperature field is obviously enhanced, and the power consumption is decreased. However, after increasing to a certain thickness, the power consumption decreases slowly. By simulating the temperature field of single crystal furnace with the same temperature field structure and different crucible sizes, the temperature field performance of 120 kg, 200 kg and 300kg grades is investigated. The results show that with the increase of crucible size, the thermal insulation effect of the temperature field becomes worse and the power consumption increases. The growth angle becomes larger and the stress increases and stress enrichment occurs; the temperature gradient decreases and the melt flow remains unchanged. In the design of large size single crystal furnace, the effect of side and bottom heat preservation is enhanced, the interface between crystal and crystal is enlarged, and the phenomenon of stress enrichment is prevented.
【学位授予单位】：深圳大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O78

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