金屬觸媒在液晶顯示器及場發射顯示器之應用­用金屬觸媒促進低溫複晶矽及奈米碳管之成長

Abstract

本研究中，我們探討了金屬觸媒於製作低溫複晶矽薄膜及誘發碳管成長兩方面之應用。在金屬觸媒用於低溫複晶矽薄膜製作方面， 我們採用金屬誘發非晶矽結晶化之方法製備低溫複晶矽薄膜，研究不同金屬型態及各種退火參數對金屬誘發非晶矽結晶化速率之影響，利用這些結果建立起模型。 主要是利用無電鍍鎳之方式取代傳統物理氣相蒸鍍方式來鍍覆金屬層。相較於物理氣相蒸鍍方式，無電鍍鎳之方式具有製程迅速簡單且製程設備便宜及適用於大面積基板之好處。經由材料分析可得知利用無電鍍鎳方式鍍覆之鎳金屬也具有低溫誘發複晶矽結晶之現象。在製作複晶矽薄膜之前，控制不同之無電鍍時間尋找出最佳退火條件，而製作出之複晶矽薄膜電晶體也具有相當優異之電性表現，所以表示了無電鍍鎳之方式能夠取代傳統物理氣相蒸鍍方式。 為了提高金屬誘發非晶矽結晶化製作複晶矽薄膜電晶體之電特性，針對金屬誘發非晶矽結晶化製作之複晶矽薄膜做後續的退火處理，本研究中採取兩種方式第一種為高溫爐管退火結晶化，利用高溫過程使得針狀之複晶矽晶粒進行合併成長並且修補薄膜中之缺陷。由於高溫退火會限制玻離基板之使用，所以提出第二種方式─利用在室溫進行之後續雷射退火製程。在本論文中，後續雷射退火製程又稱為金屬誘發雷射後續製程。此項製程同樣能夠使得針狀之複晶矽晶粒進行合併成長並且修補薄膜中之缺陷。但是其成長機制與傳統雷射退火不同，所以本論文會有深入之研究並且提出金屬誘發複晶矽薄膜經雷射退火之成長模型。兩種再結晶化之退火方式皆製作出薄膜電晶體。兩種薄膜電晶體之電性皆有明顯提升。 此外，場發顯示器也是屬於平面顯示器的一種。根據先前文獻指出場發射顯示器由碳管及薄膜電晶體俎成之陰極元件，能夠提高場發射顯示器之性能及可靠度。但是當碳管要併入薄膜電晶體時會遇到一些問題。分別是低溫(低於600 ℃)、碳管可自動選區成長、碳管密度可以控制。只要達到以上三項需求就可以使得碳管應用於場發射顯示器擁有製程簡單、場發射性質良好以及可靠度佳等特性。針對此三項需求本論文提出利用無電鍍鎳方式製備鎳金屬觸媒。另外針對低溫成長碳管的需求，根據文獻可以得知碳管溫度與金屬觸媒之顆粒尺寸有關，當金屬觸媒尺寸縮小至數百奈米以下則可以降低製程溫度低於600 ℃。而在無電鍍製程中鎳顆粒之尺寸可以利用無電鍍的時間控制，隨無電鍍鎳金屬鍍複時間增加鍍覆出之鎳金屬顆粒尺寸分佈可由20 nm增加到150 nm另外鎳金屬顆粒分佈密度也會隨之增加，所以本研究已經成功的於580 ℃下製備出奈米碳管。除此之外這些試片經過奈米碳管製程之合成同樣也會製備出不同大小尺寸及分佈密度之碳管，碳管的尺寸及佈密度皆會影響碳管所表現出之場發射性質，所以藉由控制無電鍍鎳金屬鍍覆時間可以得到不同場發射性質之奈米場發射元件。

In this study, the metal catalysts were used for the application of Low temperature poly-Si (LTPS) films and carbon nanotubes (CNTs). For fabrication process of LTPS, the metal induced crystallization of amorphous Si (a-Si) and metal induced lateral crystallization of a-Si (MIC/MILC) methods were used to fabricate the LTPS films. In this study, the effects of thickness and crystallinity of a-Si films, width of a-Si channel, feature of metal pattern and furnace annealing parameters for MILC rate were studied and a kinetic model of MIC/MILC was built. Electroless plating (EP) method was supposed to replace the conventional physical vapor deposition (PVD) during MIC/MILC process. Compared to PVD method, the EP method is easier, faster, more convenient and requires lower equipment cost. The a-Si films were crystallized by EP Ni and the crystallized Si films were analyzed by SEM, TEM and XRD. Various EP and furnace annealing parameters were used to produce high quality poly-Si films in a short period of time. The high performance poly-Si was fabricated by electroless plating Ni induced lateral crystallization of a-Si (EPILC). To enhance the performance of MILC TFT, a post annealing method was used after MILC process. Two kinds of post annealing methods were used. The first method is high temperature furnace annealing. During the high temperature annealing, the needlelike MILC poly-Si grains were recombined and the defect structure was repaired. However, high temperature furnace annealing is not suitable for glass substrates. The other method is room temperature laser annealing. This method is done in the room temperature so it is suitable for glass substrates. In this thesis, the method is called NILC-ELA method. The function of NILC-ELA method is the same as that of high temperature furnace annealing. However the growth mechanism of NILC-ELA process is different from that of conventional ELA process. In this study, the growth mechanism of NILC-ELA was discussed. The performance of poly-Si TFTs was enhanced by two kinds of recrystallization process. Field emission display (FED) is one of the flat panel displays. According to previous studies, the reliability and performance of emitter could be enhanced by the combination of carbon nanotubes and TFT. However some problems were found when synthesis process of CNT was incorporated into the TFT process on the glass substrates. CNTs synthesis needs to meet three requirements in order to apply in field emission display. (Three requirements of for application of field emission display.) These three requirements are: low temperature process (＜600 ℃), selective area growth and controllable site density. In this study, an electroless plating Ni method was introduced to make CNTs synthesis more compatible with application of field emission display. According to previous studies, to synthesize CNTs at low temperatures, the size of metal catalysts should be smaller than hundreds of nm. The sizes of Ni catalysts with various plating time range from 20nm to 150nm. The CNTs were successfully synthesized at 580 ℃ in this study. Therefore, the size and density of CNTs could both be controlled by plating time. Since these two parameters could affect the field emission properties of CNTs, it could be stated that plating time could control the field emission properties of CNTs.