Fabrication of Large-Grained Polycrystalline Si Thin Films by Controlling Nucleation Sites on Glass Substrates

玻璃衬底上的大晶粒多晶硅（poly-Si）薄膜对于高性能薄膜晶体管（TFT）和成本有效的太阳能电池的制造是有意义的。为了获得大晶粒的多晶硅薄膜，重要的是在膜沉积之前控制玻璃表面上的硅晶体生长的成核位点的形成。对于非晶硅（a-Si）薄膜的固相结晶化（SPC）而言，特别需要具有定制性质（例如尺寸和间距）的成核位点的玻璃基板。在这项工作中，我们提出了一种新的工艺来制造结晶锗岛与控制的大小和密度在定制的范围内，形成核SPC的a-Si薄膜。该工艺包括在室温下在玻璃衬底上沉积a-Ge薄膜，随后对沉积的a-Ge薄膜进行真空退火以形成自组装的结晶Ge岛，以及控制Ge岛的尺寸和密度的氧蚀刻。用微束反射高能电子衍射观察了以Ge为核的部分晶化a-Si薄膜，证实了Ge岛作为Si晶化的核。在玻璃衬底上沉积的含锗a-Si：H薄膜的退火实验中观察到晶化时间和晶化温度的显著降低。此外，还发现常压等离子体CVD沉积的a-Si：H的晶体生长速率远大于电子束蒸发沉积的a-Si。为了实现锗原子核在玻璃衬底上的位置控制，提出了一种利用锗晶体针尖阵列的纳米压印技术。

Large-grained polycrystalline silicon (poly-Si) thin films on glass substrates are of interest for the fabrication of high-performance thin-film transistors (TFT) and cost-effective solar cells. To obtain large-grained poly-Si thin films, it is important to control the formation of nucleation sites for Si crystal growth on a glass surface prior to film deposition. Glass substrates having nucleation sites with tailored properties, such as size and spacing, are particularly desirable for the solid-phase crystallization (SPC) of amorphous silicon (a-Si) thin films. In this work, we have proposed a new process to fabricate crystalline Ge islands with controlled size and density in a tailored range to form nuclei for SPC of a-Si thin films. The process consists of the deposition of a-Ge thin films on glass substrates at room temperature, the subsequent vacuum annealing for SPC of the deposited a-Ge thin films to form self-assembled crystalline Ge islands, and the oxygen etching for controlling the size and density of Ge islands. From the micro beam reflection high-energy electron diffraction observation of the partially crystallized a-Si thin film using Ge nuclei, we have confirmed that Ge islands act as nuclei for Si crystallization. Marked reductions of the crystallization time and temperature are observed in the annealing experiments of a-Si : H thin films deposited on glass substrates with Ge nuclei. Moreover, it is found that the crystal growth rate of a-Si : H deposited by atmospheric pressure plasma CVD is much larger than that of a-Si deposited by E-beam evaporation. For the location control of Ge nuclei on glass substrates, a nano-imprint technique using crystalline Ge tip array has been demonstrated.