坩埚位置对PVT生长AlN晶体过程中物质传输的影响

Influences of Crucible Position on Mass Transport during AlN Crystal Growth Process by PVT Method

摘要:

使用FEMAG晶体生长模拟仿真软件以及自主开发的PVT法有限元传质模块对全自动、双电阻加热物理气相沉积炉开展了AlN晶体生长工艺过程中不同坩埚埚位对温度场、过饱和度场及烧结体升华速率等影响的模拟仿真分析研究。模拟仿真结果表明:在给定工艺条件下,坩埚埚位较低时烧结体温度较高且内部温差较小,烧结体升华表面存在较大的Al蒸气分压梯度,各表面升华速率较快且均匀,籽晶衬底生长前沿温度场呈微凸分布,有利于晶体扩径及生长高质量晶体。随着坩埚埚位的上升,低温区向坩埚壁扩展,预烧结体内轴向及径向温度梯度增加,籽晶衬底附近径向温度梯度逐步降低,过饱和度区域扩大且增强。在坩埚埚位较高情况下,坩埚内原料升华变得不均匀,坩埚侧壁存在高过饱和区域,极易在坩埚壁上发生大量的AlN多晶沉积。模拟分析结果与大量实际晶体生长实验后的坩埚壁处沉积现象及剩余烧结体原料形态相符,较好地验证了模拟仿真分析结果的准确性。

Abstract:

In this paper, the influences of crucible position on the mass transport during AlN crystal growth process by the physical vapor transport method were investigated by numerical modeling and simulations. The temperature field of the whole growth chamber was solved with FEMAG simulation software, while the mass transport in the growth chamber was simulated by using an in-house mass transport code by the finite element method. The simulation results show that under a low crucible position, the temperature was quite high and uniform as well inside the pre-sintered AlN source. A high Al vapor gradient was observed above the evaporation surface of the AlN powder source and a concave temperature field was formed near the crystal growth deposition surface, which were beneficial to grow large-size and high-quality AlN crystals. With the increasing crucible position, a low-temperature region was extended from the crucible top to the crucible periphery and both the thermal gradient along the axis and radial direction were increased. The evaporation rates along the AlN powder source surfaces became non-uniform, and a high supersaturation region near the crucible wall was founded. Accordingly, small polycrystalline AlN crystals normally would nucleate with high density at the high supersaturation region. The simulation results were in good agreement with experimental results when compared to the shape of residual AlN power source after the crystal growth.