Role of Seed Crystal Layer in Two-Step-Growth Procedure for Low Temperature Growth of Polycrystalline Silicon Thin Film from SiF₄ by a Remote-Type Microwave Plasma Enhanced Chemical Vapor Deposition

Abstract

Role of seed crystal layer which played in low temperature growth of polycrystalline silicon (poly-Si) thin films was investigated by two-step-growth (TSG) process. The TSG involves two different deposition processes, which are called as `seed process' and `growth process'. In order to satisfy the conflicting demands such as low temperature, high rate and high quality crystal growth, the deposition conditions in the seed and growth processes were examined. As a result, it is confirmed that the seeding of high quality crystal layer is effective to improve crystallinity of growing poly-Si film, especially for the case grown at lower temperature than 300°C. In order to fully promote crystallinity, some thick and high crystallinity seed layer is needed. In addition, epitaxial-like growth on the seed layers can be realized by optimizing deposition conditions both during the seed and growth processes. When H2/SiF4 flow ratios larger than those used during the seed process were used during the growth process, lower growth temperatures were possible with maintaining a smooth interface between the seed and the grown poly-Si layers. In essence, the hydrogen mixing ratio and deposition temperature are complementary parameters, thus it was possible to reduce deposition temperatures with maintaining large crystal fraction and oriented structure, if the hydrogen mixing ratio was increased to an appropriate amount. Furthermore, in situ ellipsometry analysis indicated that, under optimal conditions, the interface between the seed and the growing film can indeed be smooth and epitaxial-like. TSG is a promising technique by which to fabricate high quality poly-Si thin films on glass substrates at low temperatures.

Effects of Chemical Composition and Morphology of Substrate Surfaces on Crystallinity of Ultrathin Hydrogenated Microcrystalline Silicon Films

“…7,8) It has been well known that increasing the H 2 dilution ratio not only facilitates transition from the incubation-layer growth to the microcrystallinefilm growth, 4,5) but also helps increase the crystalline volume fraction (called crystallinity in this paper) of the film. 2) Our previous study showed that a dilution ratio as high as SiH 4 /H 2 ∼ 0.003 is also effective to reduce the thickness of the incubation layer to a large extent.…”

“…4) The initial layer near the substrate, however, remains amorphous and is called an incubation layer. There have been many studies on the mechanisms of nucleation of the microcrystalline Si after the incubation layer is formed, 5) as well as on grain growth of the nucleated microcrystals. 6) On the other hand, little is understood regarding the formation mechanism of the incubation layer itself, although this layer is undesirable for most device applications.…”

From amorphous to microcrystalline silicon: Moving from one to the other by halogenated silicon plasma chemistry

“…Therefore, many attempts have been made to improve crystallinity during the early stage of growth using fluorinated plasmas, e.g. SiF 4 -H 2 plasmas [86,87] and CF 4 -He plasmas [88]. Film structure, including grain size and orientation, and crystalline fraction, can be controlled even at the early stage of growth by pre-treatments and modification of the substrate surface.…”

Structural evolution optimization at p/i interface and in the bulk intrinsic‐layer for high efficiency microcrystalline silicon solar cells

“…3 Results and discussions 3.1 High-quality initial seed layer In order to decrease the a-Si:H incubation layer thickness in the initial growth of µc-Si:H i-layer, a two-step growth method has been widely employed, where an initial seed layer was formed firstly, and subsequently, the rest part of film [10,11]. The general way to deposit the initial seed layer is just to decrease silane concentration while retaining other parameters.…”