利用電子迴旋共振化學氣相沉積法沉積氫化非晶矽薄膜探討其應力與結晶行為

Stress and crystallization of hydrogenated amorphous silicon films grown by electron cyclotron resonance chemical vapor deposition

王榆茜(Yu-cian Wang)

指導教授 ： 陳一塵

國立中央大學/工學院/材料科學與工程研究所/碩士(2011年)

摘要

以高頻之ECRCVD成長氫化非晶矽薄膜，具有低溫成膜性質及沉積速率較快等優勢，將有效降低製作元件成本。然而，氫化非晶矽薄膜為矽氫所組成，其結構相對於結晶矽鬆散，且矽氫鍵結斷裂形成缺陷，易發生光衰退效應，為提高薄膜穩定度使得元件壽命增加，故各國研究目標為將薄膜由非晶結構轉至微晶或多晶結構，調整SiH4與H2流量比例，直接成長微晶矽結構薄膜；或是經由熱處理使氫化非晶矽薄膜結晶化，得到多晶矽薄膜，以提升薄膜太陽能電池之效率與穩定度。
本研究利用ECRCVD成長不同SiH4流量之薄膜，為要得到不同R* 薄膜，以了解其微結構對於薄膜在退火前後應力與結晶行為之影響。利用OM、FTIR、Raman、XRD與NMR分別利用Stoney Equation進行應力計算、Si-H與Si-H2之鍵結型為與氫含量計算、薄膜結晶率與中短程有序結構、結晶尺寸與結晶方向與氫分布之行為探討。在ECRCVD成長氫化非晶矽薄膜時，隨著流量上升，薄膜R*下降而氫含量上升，薄膜之壓縮應力與R*並非成比例之變化。因此我們提出一假設，認為具有氫鈍化的孔洞表面微薄膜中應力集中處，隨著R*上升，薄膜壓縮應力提高，然而當氫已無法全部鈍化孔洞表面時，這種被部分鈍化的孔洞反而成為應力釋放處，因此薄膜的壓縮應力下降。另一方面，在R*愈大的薄膜結晶速率愈慢，是因其薄膜內部氫分布較為鬆散且空孔密度大有機會使其孕核時的障壁能提高。

關鍵字

電子迴旋共振化學氣相沉積法、氫化非晶矽、R*、薄膜應力、氫含量、部分鈍化孔洞

並列摘要

Due to its high mobility and high stability under light soaking, polycrystalline silicon (Poly-Si) is a promising material candidate for thin film solar cells and transistors. Solid phase crystallization (SPC) of hydrogenated amorphous silicon (a-Si:H) is a simple and attractive method to fabricate poly-Si at a low temperature. However, the evolution of stress and hydrogen effusion of a-Si:H films during SPC have not been well-understood.
In this study, the relationship between the stress and crystallization behavior of the annealed films were investigated. a-Si:H thin films with various microstructure parameter (R*) values were prepared using electron cyclotron resonance chemical vapor deposition (ECRCVD) by adjusting the feed gas ratio. The crystallization of the a-Si:H films were then carried out by the thermal annealing process at a temperature range from 200 °C to 800 °C under nitrogen ambient. The microstructure properties of the films were evaluated using Raman spectroscope, scanning electron microscope and Infrared spectroscope. From our experimental results, the as-grown sample with R* = 0.54 may have largest compressive stress. After annealing above 300 °C, the film stress is changed to tensile stress due to hydrogen effusion, and reaches a maximum around 400 °C. Different mechanisms of stress formation and relaxation, such as bond reconstruction and microstructure evolution during crystallization at higher temperatures were also discussed.

並列關鍵字

a-Si:H ； ECRCVD ； R* ； stress ； hydrogen content ； crystallization

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