以微機電製程技術製作應用於多電子束微影之場發射元件

Abstract

現今的微影製程之最小圖形半間距，在45nm以下且能應用於業界的微影技術仍未有定論。而單一電子束微影技術已有相當的研究基礎，若將其推廣成多電子束平行寫入的方式便能提高產能，極有機會成為下一世代的微影技術。本論文即以微機電製程技術製作產生多電子束的場發射元件，材料選用製作上方便且便宜的矽。 場發射元件的製作分為矽針陣列、矽針之閘極層、陽極板的製作。矽針的形成機制主要為反應式離子蝕刻等向性蝕刻矽，過蝕刻大致上仍能維持小的針尖半徑，僅對矽針外型與矽針均勻度有較大影響；調整反應式離子蝕刻中壓力的大小以及稀釋氣體與主要氣體的比例，可做出不同高寬比及頂端圓錐角的矽針結構。在矽針之閘極層的部分主要為標準製程的製作，觀察到了在濕蝕刻完成結構時，閘極層產生崩塌的現象，以及提出一個以旋塗光阻來決定閘極孔徑大小的可能製作方法。在陽極板的製作方面，利用舉離製程的技術，設計了可使陰極與陽極導電層維持數個微米尺寸距離之陽極板的微機電製程，理想上可完全阻隔陽極與陰極的漏電，並可改變陽極板的蝕刻凹槽深度，調整陰極與陽極層的距離。 最後將製作的矽針陣列及陽極板組裝成場發射元件，在約10-5torr的真空度下做初步的場發射實驗，將實驗結果以金屬場發射電流公式分析，得到電場增強因子 、場發射面積 以及場發射起始電場Estart，與他人的場發射實驗比較，大致上為一個合理的數值。

Currently, the lithography which has critical dimension small than 45nm and can be applied to industry is not presented. However, single beam e-beam lithography has been developed for years. If the disadvantage of low throughput can be overcome by extending single beam to multiple beams, it will be the next generation of lithography. This thesis is about MEMS design and fabrication of field emission device as the source of parallel electron beams. Silicon is chosen to be the material of field emission device. Fabrication of field emission device includes Si tips array, gated Si tips array, and anode plate. First, Si tips array are formed mainly by RIE. The effect of over-etched on the apex of Si tip is not evident. It has mainly effect on the shape and the uniformity of Si tips. The aspect ratio and the cone angle of apex can be modified by varying the pressure and the ratio of flow rate of etching gas and diluted gas. Second, for gated Si tips array, the standard fabrication process of etched-gate Si tips array is performed. The collapse of gate layer is observed. A possible fabrication process defining the gate aperture by PR spin coating is presented. Third, we design a fabrication process utilizing the “lift-off” technique for anode plate. By this anode plate, anode and cathode can be separated at micrometers, and the leakage current can be totally blocked ideally. The distance can be modified by varying the etched depth in the fabrication process. Finally, experimental field emission device is constituted by the Si tips and the anode plate. The experiment on field emission is performed in a vacuum system with residual gas pressure about 10-5torr. The results are analyzed by theory of field emission from metal to obtain field factor,β, effective emission area,α, and turn-on electric field, Estart. Reasonable data is obtained.