掺锗直拉硅体单晶的生长

Bulk Single Crystal Growth of Silicon-Germanium

为了控制锗在硅中的分凝和分布的均匀性 ,抑制熔体中因重力场引起的无规律热对流和质量对流 ,文中设计制造了一种新型的环型永磁场直拉炉 ( PMCZ法 ) ,生长了掺锗量 0 .1～ 5 .0 % ( Ge∶Si重量比 )、 65 mm和 5 2 mm的硅锗体单晶 ,拉速一般控制在 0 .2～ 0 .5 mm/分。当磁场强度较高时 ,熔体中由于重力场引起的热对流和质量对流在一定程度上被抑制 ,类似于空间微重力环境生长晶体的条件 ,晶体中锗和氧杂质分布均匀性的问题得到了较好地控制。文中利用扫描电子显微镜 ( SEM)能谱分析和二次离子质谱 ( SIMS)等方法观测了PMCZ法生长的掺锗 Si单晶中锗的分布状况。发现用 PMCZ法生长的锗硅晶体比常规 CZ法生长的晶体杂质均匀性要好些。同时发现 ,由于晶体生长速率很低 ,使得掺锗硅中产生了大量的过饱和氧的微沉淀。这些微沉淀经过 1 2 5 0°C热处理后会溶解消失。在晶体尾部 ,由于锗在硅中的分凝系数小于 1 ,使得锗在熔体中高度富集 ,产生了“组份过冷现象”,出现了枝状结晶生长。

Si single crystals of doping Ge up to 0.1～5.0wt% were grown using ring permanent magnetic Czochralski technology (PMCZ method). The diameter of crystal is 65 mm and  52 mm. In order to control homogeneity of Ge distribution in Si, the crystal growth rate was lowed to less than 0.5 mm/min. Distribution of Ge in crystal was observed by SEM and SIMS. The results indicate that the homogeneity of Ge distribution was improved with magnetic field than without a magnetic field, because thermal convection was inhibited to a certain extent by magnetic. We also observed oxygen micro-precipitation in the SiGe crystal. The phenomenon is different from that CZSi without doped Ge resulted from a larger growth rate of 1～ 1.5～2.0 mm/min and cooling rate for the CZSi without doped Ge. Presented is the crystallization of branch type in the tail of crystal owing to a very high concentration of Ge in Si melt leading to the constitutional super-cooling.