奈米針尖的製備與場發射研究

Abstract

本研究主要以電子迴旋共振氣相沉積系統(electron cyclotron resonance chemical vapor deposition, ECR-CVD) ，以乾蝕刻方式製備具有高對直性之奈米針尖陣列(nanotip arrays)。反應氣體為矽甲烷(SiH4)、甲烷(CH4)、氬氣(Ar)及氫氣(H2)；其中矽甲烷與甲烷氣體在反應腔體中形成碳化矽奈米微粒(SiC nanoclusters)以作為奈米遮蔽物(nanomasks)，進而阻擋氬及氫電漿的乾蝕刻。以此自組遮蔽機制(Self-masked mechanism)，多種材料如：矽、氮化鎵、磷化鎵、鋁金屬等，皆可製備為句有高深寬比(aspectratio)之奈米針尖。 研究發現，在相同的反應條件下，奈米針尖的長度隨反應溫度升高而有所降低。本論文將會以動力學角度進行討論其內在機制。 本文亦將討論奈米針尖材料的場發射特性(field emission properties)，結果顯示：矽奈米針尖之場發射具可調整(tunable)的特性，可經由改變奈米針尖之長度及針尖間距而得到不同的場發射特性。在最佳條件下，其起始電場為0.35 V/μm，其遠低於目前文獻中所報導之值。再者，我們首先發現了磷化鎵一維奈米材料的場發射特性。其起始電場雖比矽奈米針尖為高，但相較於文獻報導之化合物半導體一維奈米材料，磷化鎵奈米針尖具有較佳之場發射特性。 此乾蝕刻技術除通用於各式基材，其低溫及大面積製程更提供了工業化的最佳潛力。

Well-aligned nanotip arrays were fabricated by electron cyclotron resonance plasma process using gas mixtures of silane, methane, argon and hydrogen. Nanotip arrays with high aspect ratios (~ 50) and sharp apexes (~ 1 nm) were achieved by direct etching from a variety of substrates such as silicon, gallium nitride, gallium phosphide and aluminum with the simultaneous formation of silicon carbide (SiC) protecting caps on the tips. Two competing mechanisms, namely the formation of the SiC nanomask on the surface and the preferential etching of the unmasked substrates, coexist during this process and proceed simultaneously in the plasma, forming the nanotips. Further investigation showed that the length of nanotips decreases with an increasing temperature. A comprehensive discussion will be proposed explaining this phenomenon. Tunable field emission property is achieved by changing the intertip distance. In an optimal case, a 0.35 V/μm turn-on field to draw a 10 μA/cm2 current density was demonstrated, which is much lower than other materials reported to date. Moreover, the first demonstration of field emission from GaP nanotips is reported. In the case of GaP we observed a relative higher tune-on field than the Si nanotips, but substantially lower than that of 1-D compound nanostuctured materials. This one-step self-masked dry etching technique makes it possible to fabricate uniform nanotip arrays on various substrates over large area at low process temperatures, therefore, possesses a high potential for practical industrial application.