氢等离子体退火对氢化非晶硅结构有序度的影响

Influence of Hydrogen Plasma Annealing on the Microstructural Ordering of Hydrogenated Amorphous Silicon

室温下利用氢等离子体退火技术对氢化非晶硅 (a_Si:H)薄膜进行处理 ,通过傅立叶红外、光吸收、拉曼光谱 3种测试手段对非晶硅的微结构进行了分析 ,发现不同的退火时间对a_Si:H的微结构影响很大 ,氢等离子体在与薄膜的化学反应过程中主要表现为原子氢 (H0 )与薄膜的反应 .化学势很高的H0 能将Si_Si弱键转变成Si_Si强键 .硅网络结构发生弛豫 ,使结构由无序向有序转变 ,从而能够降低晶化温度与退火时间 .

Amorphous and nanocrystalline silicon (a-Si and nc-Si)currently are of great interest due to their potential applications in various optoelectronic devices, such as thin film transistors (TFT) and solar cells. Due to the low mobility of carriers in a-Si film, various technologies have been applied to crystallize the amorphous silicon films to improve the performance of Si-based devices and the low-temperature crystallization process is highly desired. It is reported that hydrogen plays a critical role in enhancing the ordering of the film network in a-Si, which can increase nucleation sites and reduce the crystallization temperature effectively.In this paper, a series of a-Si:H thin films with about 100 nanometers in thickness were deposited on double polished-silicon wafers in the plasma-enhanced chemical vapor deposition facilities and subsequently dehydrogenated in furnace at 500 ℃ for 30 minutes. Then, post-hydrogen plasma annealing was carried out at room temperature on a-Si samples for 10,20,30,40 minutes respectively, and the changes of structures were characterized by the Raman and FT-IR spectra as well as the absorption spectra. Experimental results show that the hydrogen induces the transition from disorder to order in a-Si thin films. It is demonstrated that there is an intermediate stage in the transformation from the weak Si-Si bonds to the strong Si-Si bonds that generates the bonds of Si-H-Si. With time passing by, the atomic hydrogen can remove the hydrogen from the intermediates, which results in the strong Si-Si bonds. So we can improve the structural ordering of the amorphous silicon by selecting the suitable HPA conditions to realize low-temperature crystallization process.