以準分子雷射退火改善於高分子基板上之氧化銦錫薄膜與基板對光學能隙影響之探討

Abstract

近幾年在軟性微電子元件科技發展過程中，以沉積氧化銦錫薄膜於高分子基材之技術引起了最多的研究興趣與關注。因此，發展一個新穎的後退火技術用以改善氧化銦錫薄膜之特性同時不破壞高分子基板，對於其做為透明導電材料是否能成功的應用於軟性電子是一個十分重要的議題。 在此研究中，我們使用KrF準分子雷射作為退火源，分別處理ITO薄膜於不同的高分子基板(PET與ODPA-BADB PI)。經由雷射處理後它們的光、電等性質將進一步探討。微結構而言，雷射後退火處理的ITO薄膜由初沉積的非晶相轉變為結晶相。對於室溫沉積於PET的ITO薄膜而言，經雷射退火，表面粗糙度下降、電阻率也下降了42% (4.3×10-4 Ω-cm) 並且增進14倍的载子濃度(5×1021 cm-3)。對於200 oC高溫沉積於ODPA-BADB PI的ITO薄膜而言，經雷射退火後，其電阻率更低，約為3.2×10-4 Ω-cm。 我們也探討基材效應如何影響ITO薄膜的光學能隙變化。實驗發現，ITO薄膜的光學能隙不只有被薄膜本身的特性所決定(如過多载子濃度和缺陷等)，基材也是另一個決定的因素。結果指出，ITO薄膜與基材之間的熱膨脹係數差異會誘發張應力，而進一步改變ITO薄膜的光學能隙。

For the development of flexible microelectronic device technology, indium-tin-oxide (ITO) on polymer substrates has attracted interest recent years. Therefore, development of a novel post treatment method to improve properties of ITO film without damage polymer substrate is an important key issue for successful application as a transparent electrode material. In this study, a KrF excimer laser source has been used to anneal ITO deposited on polymer substrates, which are polyethylene terephthalate (PET) and ODPA-BADB polyimide (PI). The electrical and optical properties of ITO films following various laser shots number were further investigated. For microstructure, after laser irradiation, the ITO film from amorphous phase changes to crystalline phase. For room temperature ITO deposited on PET following laser irradiation, the ITO films show reduced surface roughness, 42% reduction of resistivity (4.3×10-4 Ω-cm) and enhanced carrier concentration of 5×1021 cm-3 (14 times increase). For higher temperature ITO deposited on ODPA-BADB PI substrate at 200oC following laser irradiation, it shows very low resistivity, which around 3.2×10-4 Ω-cm. The substrate effect on optical band gap shift of ITO films was also investigated. It has been shown that, the optical band gap of ITO film does not only depend on ITO films itself such as heavy carrier concentration and impurity, but also be affected by different substrates. The different in tensile stress induced by the ITO film and polymer substrate due to the different of coefficient thermal expansion (CTE) mismatch leads the optical band gap shift of ITO film.