具閘極圓錐狀鑽石場發射矩陣之製作與特性研究

Abstract

電子場效發射元件應用在平面顯示器上，必須具備低功率消耗及高場效發射電流的特性，而鑽石則是具有這些特性的最佳材料。而且鑽石環具有較好的負電子親和力（Negative Electron Affinity），能夠輕易的經由電場激發而發射電子，因此降低了工作的電壓、功率的損耗以及提高場效發射電流之功效。 因此，本實驗室利用半導體製程製作 MIS （metal-insulator-semiconductor）結構的技術，以及微影（Photolithography）和活性離子蝕刻（Reactive Ion Etching, RIE）技術，製作孔徑8um的圓形場效發射陣列。並採用偏壓輔助微波電漿化學氮相沈積系統（BAMPCVD System）及二階段（two-step）沈積技術，以甲烷－氫氣混和為反應氣體源，將圓錐狀鑽石選擇性的沈積在圓孔內的矽晶片上。沈積後的圓錐狀鑽石的表面型態、品質和電性以掃瞄式電子顯微鏡（SEM）、拉曼光譜儀（Raman）、歐傑電子光譜儀（AES）及I-V量測系統來觀察、鑑定與分析。 經實驗結果顯示，圓錐狀鑽石的密度會因為負偏壓的增高而增加，這可能是因為負偏壓能夠促進電漿中反應氣體的解離，使得圓錐狀鑽石在基材上的沈積密度增加。而圓錐狀鑽石的品質則隨著甲烷濃度的增加而變差，其結構逐漸趨向於類鑽石碳組織（Diamond-like carbon）或石墨組織（Graphite）。甲烷的濃度較低時所形成的圓錐狀鑽石比較尖銳且細長，而甲烷的濃度較高時所形成的圓錐狀鑽石則比較鈍且粗大。經I-V特性的量測結果顯示，在高甲烷濃度（CH4/H2=5/95）之條件下所合成的圓錐狀鑽石的場發射電流值（電壓30V時電流141uA）比低甲烷濃度（CH4/H2=1/99）的電流值（電壓30V時電流82uA）大，這可能是因為存在於圓錐狀鑽石的晶粒介面中的非晶質鑽石或石墨組織所造成的結果。有關圓錐狀鑽石之成長機制、場發射電流之產生原理及微結構之詳細，將是本實驗室往後的研究重點。 根據上述的結論，今後我們將著手在縮小圓形場效發射陣列的孔徑、閘極與尖錐之間距，以及摻雜硼、磷等元素來改善與提高場效發射電流、降低工作電壓之目標。我們實驗室更期待在近期內，完成理優良的I-V特性及更實用性之FED元件製作技術。

Vacuum microelectronic devices with field emitters possess many advantages over vacuum devices and solid-state devices. Applications of field emitter devices can be largely found in flat panel displays and RF power amplifiers. For such applications, the field emitters must have a high yield and relatively low cost. Among the various field emitter structures, gated cone-type emitters provide the highest emission current density. For various applicatios in microelectonics and in particular vacuum microelectronics, negative electron affinity (NEA) is a highly desired property of the material used in devices. Either obtaining the NEA property or lowering surface and interface barriers can substantially increase the operational efficiency and reduce the power consumption of the entire device. Selecting proper materials such as a diamond can cahieve such an objective. In light of above concerns, this investingation fabricates the gated cone-shaped diamond field emitter array by using bias-assisted microwave plasma chemical vapoor deposition system (BAMPCVD) with a two-step deopositon method. A cone-shaped diamond is grown on 8μm gated circle patterned silicon substrates, which are fabricated with. standard photolithography and RIE techniques. the reactive gases used in depostiton are a mixture of CH4-H2 Scanning electron microscopy (SEM), Raman spectroscopy, Auger electron spectroscopy (AES) are used to examine the morphology, crystallity and quality of the as-deposited cone-shaped diamond. According to our results. the cone-shaped diamond's density increases with an increasing negative bias Voltage. In addition, the change of methane concentration influences the quality of conic diamond, deposition rate and size. Also discussed herein is the possible mechanism and some phenomena associated with the formation of a cone-shaped diamond by BAMPCVD system.