空間電荷限制電晶體中奈米金屬網之製程改善

Abstract

有機電晶體的發展在近年來已越趨活躍，其同時擁有無機半導體製程所欠缺的低成本與製程簡單、可撓性與大面積化等優點。本論文將進行垂直式空間電荷限制電晶體(SCLT)製程上的兩大改善。在過去的研究中，我們利用非緊密堆積的奈米球作為金屬基極蒸鍍遮罩的製程製作，使其具隨機排列孔洞之金屬基極，然而奈米球的隨機排列將容易出現因球聚集而造成孔洞過大的問題，並使基極對孔洞中心區域的控制能力降低，進而導致垂直通道結構電晶體的漏電流。因此我們的第一大主軸是利用規則奈米球沉積技術，將奈米球在氣液界面上面產生緊密堆積，並用氧電漿進行縮球使其產生規則排列，在本研究中，我們已成功利用此技術替換原本的非緊密堆積技術，產生大範圍的規則奈米球排列，並使元件具有開電流0.59 mA/cm2以及開關電流比5000之元件特性。而關於沉積奈米球聚集的問題，我們將利用氧電漿對奈米球進行乾式蝕刻，將原本聚集的球縮小分離。除此之外，在沉積奈米球的步驟中常會因為其中需要應用的異丙醇(IPA)的高沸點而使得兩顆或數顆奈米球產生「熔化現象」(並非聚集)，我們將異丙醇用較低沸點的乙醇代替，成功的改善此現象，卻也造成奈米球密度過低的問題。因此我們另外用了聚環氧乙烷(poly(ethylene oxide),PEO)在沉積奈米球之前先處理基板，發現的確可以在沉積奈米球之後的提高奈米球密度。結合了以上氧電漿縮球、乙醇替換、PEO修飾的三部份即為本論文所提出的第二大主軸。相信經過適當的製程改良後，更佳的元件特性將可被預期，並將有助於空間電荷限制電晶體在未來之應用與發展。

The organic transistor has become more and more active in recent years due to its advantages such as lower cost, simplicity in process, flexibility and high uniformity in large area which can hardly be found in the silicon transistor. This study focused on two major improvements in vertical polymer space-charge-limited transistor(SCLT) process. In the past, the non-close-packed polystyrene spheres(Nano balls) were used as the evaporation mask for the metal base. However, the cluster of Nano balls was easily found under the random permutation. Our first task of improvement was to produce close-packed Nano balls in the gas-liquid interface by applying the well-ordered nano balls. A large area of well-ordered Nano balls were produced and both an on current as 0.59 mA/cm2 and an on/off current ratio around 5000 at VCE as 0.6 V. were successfully obtained in this study. Regarding the problem of the cluster of Nano balls, the etching to the Nano balls by oxygen plasma was done to shrink and separate the originally-clustered spheres. Furthermore, the molten, not cluster, phenomenon on two or more Nano balls was found due to the high boiling point of IPA which is one of the necessary steps in the process of Nano ball coating. The problem was resolved by applying ethanol, which has lower boiling point, as the replacement of IPA. However, the low density of Nano balls was found because of the replacement. The poly ethylene oxide (PEO) was used to modify the substrate and it did improve the density of the Nano balls .The combination of the oxygen plasma for sphere shrinkage, the ethanol for the replacement of IPA, and the PEO for the modification of the substrate was the second major task of improvement in this study. It was believed that after the appropriate process improvement, a better component feature can be expected and be conductive the future application and development of SCLT.