大尺寸HVPE反应器寄生沉积的数值模拟研究

在氢化物气相外延(HVPE)生长GaN厚膜中,反应腔壁面总会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.研究发现: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;侧壁沉积出现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.保持其他条件不变,增大NH3管载气N2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却随之提高;增大GaCl管载气N2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却随之降低.研究结果为大尺寸HVPE反应器生长GaN的工艺优化提供了理论依据.

Numerical Simulation Study on Parasitic Deposition in Large-size HVPE Reactor

In the growth of thick GaN films by hydride vapor phase epitaxy (HVPE), severe parasitic depositions occur on the reactor walls, which will decrease the growth rate and the quality of films.Numerical modelings were conducted for the parasitic depositions of GaN growth in a large-size vertical HVPE reactor.Through comparison of modeling results with experimental data, the distribution of the parasitic deposition on reactor walls and the GaN growth rate were investigated, especially, the relationship between the flow rate of N2 carrier gas and the parasitic deposition were determined.The results show that at the base condition, the top wall parasitic deposition rate decreases gradually from center to edge, in agreement with the experimental result.For the side wall deposition there are eight high parasitic deposition zones, corresponding to GaCl nozzle tubes, indicating that the deposition mainly depends on the GaCl mass transport.The predicted growth rate at graphite susceptor is lower than the experimental one, but the trend is consistent.Keeping other conditions unchanged, increasing the flow rate of the NH3 carrier gas N2, the parasitic deposition rates and distribution areas of both top and side walls increase, while the growth rate on graphite susceptor decreases and uniformity has been increases;increasing the flow rate of the GaCl carrier gas N2, the parasitic deposition rate and the distribution area are reduced both on top and side walls, while the growth rate on graphite susceptor increases and uniformity has been decreases.The results provide theoretical reference for the optimization of GaN growth in large-size HVPE reactor.