Lower-Temperature Deposition of Poly-crystalline Silicon Film by High-Density Plasma

多晶硅是未来薄膜晶体管的候选材料之一。然而，满足大面积、高速、低温的沉积技术尚未建立。本研究的目的是建立符合上述要求的新技术。以下是本研究项目的主要成果。1)电感耦合等离子体对多晶硅的实验验证。利用天线内电感耦合等离子体，我们演示了多晶硅的沉积。采用x射线衍射分析（XRD）和透明电子显微镜（TEM）对薄膜进行了评价。XRD结果表明，该薄膜的晶向为（220）取向，晶粒尺寸达150nm。透射电镜结果表明，该薄膜具有柱状形貌。2)等离子体中离子组成的研究利用四极杆质谱仪，我们研究了高密度硅烷等离子体中的离子组成，发现SiHx+离子成分足够高，足以解释薄膜沉积速率。此外，还发现SiHx+离子组成与硅烷流量比无关，基本保持恒定。这表明薄膜的结晶不依赖于SiHx+离子组成。3)膜结晶的再现性我们发现通过控制容器壁条件可以提高膜结晶的再现性。这表明薄膜结晶的关键物质（可能是H原子）主要取决于壁条件。

Poly-crystalline silicon is one of candidate of the future materiel for thin film transistor. However, deposition technique which satisfies large area, high-speed, lower temperature is not yet established. Purpose of this research is to establish new technique which meets with the above requirement.Followings are main results of this research project.1) Experimental demonstration of poly-crystalline silicon by inductively-coupled plasma.By using an internal-antenna inductively-coupled plasma, we have demonstrated deposition of poly-crystalline silicon deposition. Film evaluation is carried out by using X-ray diffraction analysis (XRD) and transparent electron microscopy (TEM). The XRD result have indicated that the crystalline of the film is (220) oriented and that the grain size is up to 150nm. The TEM result have shown that the film has columnar morphology.2) Investigation of ionic composition in the plasmaBy using quadrupole mass spectrometer, we have investigated ionic composition in the high-density silane plasma, and have found that the SiHx+ ionic component can be sufficiently high enough to explain the film deposition rate. Furthermore, it is also found that the SiHx+ ionic composition is roughly constant irrespective to silane flow rate ratio. This suggests that the crystallization of the film does not depend on the SiHx+ ionic composition.3) Reproducibility of film crystallizationWe have found that the reproducibility of the film crystallization can be improved by controlling the vessel wall condition. This suggests that the key species (presumably H atom) for the film crystallization critically depends on the wall condition.