準分子雷射加工玻璃表面形貌探討及其應用於微探針製作之研究

Study on surface morphology of excimer laser micromachined glasses and its application in fabricating micro-tip array

陳盈同(Ying-Tung Chen)

指導教授 ： 廖運炫

國立臺灣大學/工學院/機械工程學研究所/博士(2006年)

https://doi.org/10.6342/NTU.2006.00673

摘要

玻璃材料具有高透光性、高硬度、高剛性及化學穩定性佳等優異性質，廣泛的被應用於微機電、半導體、光電、光通訊與生物醫學產業。但玻璃材料具有硬脆性，以傳統機械式加工法進行微細加工時容易產生脆性破壞，本研究利用高能量密度的ArF (λ = 193 nm)準分子雷射加工不同光學玻璃（BK7、Soda lime及Zerodur®），探討其加工產生V型溝槽之機制，並利用改變加工參數控制加工後的表面形貌，建立加工參數與形貌之關係，提出製作V型溝槽之最佳參數。經由實驗觀察，準分子雷射加工玻璃表面形貌形成V字形的主要原因是由於玻璃的導熱係數低，溫度的分佈型態為高斯分佈，加工區中心點的溫度較高所造成。在高的脈衝頻時會造成電漿遮蔽效應，減弱蝕刻效率，也會造成表面的蝕傷區較大；低的脈衝頻率會造成微結構崩裂，不適合高脈衝數加工玻璃。光罩特徵尺寸變小時（>10 μm），因為高溫的電漿造會造成玻璃表面熱蝕傷，加工的尺寸精度不易控制且蝕刻效率變差，形貌容易形成V字形的結構，而光罩尺寸越大時，蝕刻深度較深，易獲得U字形的凹槽結構。經由雷射加工玻璃獲得之結果，本研究提出一個創新的微陣列探針製程技術(Laser-LIGA)，以ArF 準分子雷射鑽孔BK7玻璃作為模具，利用雷射加工參數及光罩特徵尺寸控制模具的表面形貌及密度，並結合微電鑄技術製作高密度的Ni-Co 合金微陣列探針，探針密度高達4901/mm2，且針尖半徑小於100 nm；由於高密度及針尖尖銳的微陣列金屬探針，有利於電子放電，因此在場發射上有極大的應用潛力，本研究將Ni-Co合金的微陣列探針製作成Spindt 型的場發射陣列（FEA），為降低其有效功函數，於Ni-Co合金的微陣列探針上沈積一層非晶鑽石薄膜（DLC），討論在不同的探針密度、表面型貌及環境溫度下微陣列探針的場發射特性，研究結果發現，Ni-Co合金之FEA上沉積一層DLC鍍膜，在外加電場110 V/μm時，發射電流密度由0.027 mA/cm2 增加到31.42 mA/cm2，高於其他研究學者所量測發射電流密度。本研究製作之Spindt 型FEA擁有很高的密度及尖銳的針尖，可以獲得很高的發射電流密度(83.48 mA/cm2)。當FEA的陣列探針密度由2500/mm2 增加到4901/mm2時(增加2倍)，最低動電場(Turn on)並沒有降低，但是發射電流密度由21.6 mA/cm2增加到31.42 mA/cm2(增加45%)。研究結果顯示Ni-Co合金Spindt型的FEA具有很低的啟動電壓及很高發射電流密度，非常適合作為場發射結構之應用。

關鍵字

準分子雷射 ； 微細加工 ； 玻璃 ； 微陣列探針 ； 場發射

並列摘要

Glass materials, which have been widely employed in MEMS, semi-conductor, optical communications and bio-medical technology, are superb for its high transparency, high rigidity and high chemical stability. However, the brittleness of glass materials makes them easily crack with traditional machining process. In this research, various glass materials including BK7, Soda lime and Zerodur glass, are micro-machined by ArF (λ= 193 nm) excimer laser. The relation between the surface morphology and machining parameters is studied. The results show that the main factor for the V-shape trenches on the laser-machined surface is due to the low thermal conductivity of the glass materials, which brings about the Gaussian distribution of the surface temperature with the highest temperature at the center of the machining zone. The ablation rate is reduced by the plasma shielding effect resulted from the high repetition rate– which also enlarges the thermo-erosion area. On the other hand, the microstructure of the glass is cracked with low repetition rate of the laser. When the machining depth becomes deeper, the tape angle of the trenches becomes sharper and the aspect rate becomes higher as well. When the feature size of the mask is less than 10 μm, the accuracy of the machining dimension is not easy to be controlled, because of the plasma thermo-erosion, and this makes the trenches more likely to be V-shaped. When the feature size of the mask becomes larger, the etching depth becomes deeper, and the more likely U-shaped trenches are formed. Base on this study, a novel process for fabricating micro-tip array by means of glass mode engraved by ArF excimer laser micromachining is proposed. The surface morphology and the dimension density of the glass work-piece are controlled by laser parameter, and the Ni-Co micro tip is formed by microforming technology. The micro-tip array with dimension density as high as 4901/mm2 and the radius of the tip is less than 100 nm, is successfully fabricated. Because the emission of electrons is facilitated with higher density and sharper tipping of micro-tip array, this research has a high potential in the application of field emission. A Spindt-type field emission array( FEA)of Ni-Co alloy is manufactured with the proposed techniques. In order to reduce the work function of field emission, the micro-tip array of Ni-Co alloy is deposited a layer of amorphous diamond(DLC）. The FEA emission properties under different density of micro-tip, surface morphology and surrounding temperature are then studied. The result shows that the current density is increased form 0.027 mA/cm2 to 31.42 mA/cm2–about 11000 folds amplified, when the FEA of Ni-Co alloy is coated with a DLC under the applied voltage of 110 V/μm. The FEA of Spindt-type developed in this research consists of high density and sharp tips, allowing high current density (83.48 mA/cm2), which is much higher than what can be obtained with FEA of CNTs-type. When the density of micro-tip array of FEA is elevated from 2500/mm2 to 4901/mm2, the lowest turn on field does not suppressed but the current density is increased from 21.6 mA/cm2 to 31.42 mA/cm2, an increase by over 45%. In summary, the fabricated FEA of Ni-Co alloy is very suitable for field emission device for its low turn on field and high current density.

並列關鍵字

excimer laser ； micromachining, ； glass, ； micro-tip array, ； field emission

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