大尺寸HVPE反应器寄生沉积的数值模拟与优化

发布时间：2018-03-03 03:23

本文选题：HVPE反应器　切入点：GaN　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

【摘要】：GaN是重要的宽禁带半导体材料,氢化物气相外延(Hydride Vapor Phase Epitaxy,HVPE)是制备GaN同质衬底的主要方法。在GaN的HVPE生长中,存在严重的气相寄生反应,使反应腔壁面产生大量的寄生沉积,严重影响薄膜生长速率及质量。本文针对自制的大尺寸垂直式HVPE反应器,通过数值模拟与实验对比,研究了反应腔壁面寄生沉积以及GaN生长速率的分布规律,特别是寄生沉积分布与载气流量的关系。通过改变反应腔几何模型,讨论了原始模型与新模型之间的差异,以及在不同操作参数下对寄生沉积和生长速率的影响。论文的主要结论如下:1.在基准条件下,顶壁寄生沉积速率由中心向边缘逐渐降低,与实验结果吻合;侧壁出现8个高寄生沉积区域,对应喷头边缘处排布的GaCl管,说明沉积主要取决于GaCl的浓度输运。模拟得出的石墨托表面生长速率低于实验速率,但趋势一致。2.保持其他条件不变,增大NH_3管载气N_2流量,顶壁和侧壁的寄生沉积速率及分布区域均随之增大,石墨托表面生长速率随之减小而均匀性随之提高;增大GaCl管载气N_2流量,顶壁和侧壁的寄生沉积速率及分布区域均随之减小,石墨托表面生长速率随之增大,而均匀性随之降低。增大托盘转速后,对顶壁寄生沉积分布影响不大,对侧壁影响较大,能显著提高生长速率。3.针对目前反应腔结构的参数调整,不能明显抑制寄生沉积。为进一步减少寄生沉积,改变原顶壁处改为隔离N_2入口后,继续调整气体流量、改变重力矢量方向、改变入口温度等,再次进行模拟,寻求减少寄生沉积的最佳方法。模拟结果表明:(1)改进反应腔几何模型以后,GaCl与NH_3之间引入额外的隔离N_2,能够有效减少寄生沉积;(2)增大隔离N_2流量,侧壁寄生沉积速率及分布区域均随之减少,生长速率降低,但均匀性提高;(3)增大GaCl管载气N_2流量,侧壁寄生沉积速率及分布区域随之减少,生长速率增大,均匀性提高;(4)增大NH_3管载气N_2流量,侧壁寄生沉积及分布区域随之增大,生长速率降低,均匀性提高;(5)改变重力矢量方向后,对寄生沉积的影响。发现侧壁寄生沉积速率及分布区域增大,生长速率降低,均匀性提高;(6)结合实际情况,当入口温度低于理论温度时,对寄生沉积的影响。发现侧壁寄生沉积随之降低,生长速率随之降低,生长均匀性不变。
[Abstract]:GaN is an important wide band gap semiconductor material, and hydride vapor phase epitaxy (Vapor Phase EpitaxyHVPE) is the main method for the preparation of homogeneous GaN substrates. In the HVPE growth of GaN, there is a serious vapor phase parasitic reaction, which results in a large amount of parasitic deposition on the wall of the reaction chamber. The film growth rate and quality are seriously affected. In this paper, the parasitic deposition on the wall of the reaction chamber and the distribution of the GaN growth rate are studied by numerical simulation and experimental comparison for the large scale vertical HVPE reactor. In particular, the relationship between parasitic deposition distribution and carrier gas flow is discussed. The difference between the original model and the new model is discussed by changing the geometric model of the reaction chamber. The main conclusions of this paper are as follows: 1. Under the reference condition, the parasitic deposition rate of the top wall decreases from the center to the edge, which is consistent with the experimental results. There are 8 high parasitic deposition areas on the lateral wall, corresponding to the GaCl tube arranged at the edge of the nozzle, which indicates that the deposition mainly depends on the concentration transport of GaCl. The simulated surface growth rate of graphite bracket is lower than the experimental rate. However, the trend is the same. 2. Keeping the other conditions unchanged, increasing the flow rate of NH_3 tube carrier gas, the parasitic deposition rate and distribution area of the top wall and side wall increase, the growth rate of graphite substrate surface decreases and the uniformity increases. The parasitic deposition rate and distribution area of the top wall and the side wall decrease with the increase of the flow rate of GaCl tube carrier gas N _ 2, and the growth rate of graphite bracket surface increases, and the uniformity decreases with the increase of the rotating speed of the tray. It has little effect on the distribution of parasitic deposition in the apical wall, but a great influence on the lateral wall, which can significantly increase the growth rate .3.To further reduce the parasitic deposition, the parasitic deposition can not be significantly inhibited by adjusting the parameters of the current reaction cavity structure. After changing the original top wall to isolate the entrance of Nflesh 2, continue to adjust the gas flow, change the direction of the gravity vector, change the inlet temperature, and conduct the simulation again. The simulation results show that the introduction of extra isolation between GaCl and NH_3 can effectively reduce parasitic deposition and increase the flow of isolated N2. The parasitic deposition rate and distribution area of lateral wall decreased, but the growth rate decreased, but the homogeneity increased) the flow rate of GaCl pipe carrier gas N2 increased, the deposition rate and distribution region of lateral wall parasitic deposition decreased, and the growth rate increased. After increasing the flow rate of NH_3 tube carrier gas N2, the parasitic deposition and distribution area of the lateral wall increases, the growth rate decreases, and the homogeneity increases after changing the direction of gravity vector. It is found that the parasitic deposition rate and distribution area of the lateral wall increase, the growth rate decreases, and the homogeneity increases in combination with the actual situation, when the inlet temperature is lower than the theoretical temperature, It is found that the lateral parasitic deposition decreases, the growth rate decreases and the growth uniformity remains unchanged.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN304.05

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