單一聚焦離子束斑點研磨及其重疊行為之研究

Abstract

本論文研究聚焦離子束(Focused ion beam, FIB)砰擊矽基板後所產生的腫起(swelling)和研磨(milling)的現象，研究著重在不同參數下研磨後的形貌變化。實驗過程，首先必須先調整FIB像差(stigmator)及焦距，讓FIB輪廓為圓形且砰擊於樣品時會是最集中的離子束，FIB以掃描單點(single-spot)的方式加工於基板，接著用原子力顯微鏡(Atomic force microscope, AFM)測量經過FIB加工過的矽基板形貌輪廓。單點研磨後基板會有一深度似高斯分布的凹洞，隨駐留時間(dwell time)增長凹洞會加深且變寬，可以從實驗結果觀察到在一定駐留時間範圍內，研磨深度和駐留時間程線性關係，並可得到FIB單點研磨速度的函數，而此函數是高思函數。 不同加速電壓(Accelerate voltage)、離子束電流(beam current)會改變研磨速率分布的影響。當離子束電流變高研磨速度會變快，整體的高思函數會變高變寬，加速電壓則會影響單點研磨的寬度，低電壓時高斯函數會變寬。本論文會展示使用FIB研磨速度函數，去預測FIB研磨單點、兩點、線、方形微結構後的形貌，並和實驗結果做比較，解釋預期深度和實驗結果的差距來自能量累積，能量累積造成非晶化但尚未造成濺射，因此AFM無法量測到。最後研究如何控點距(pitch)設計線結構達到波浪(fluctuation)能變小。

In this thesis, we investigated the swelling and milling due to FIB impinging, primary research is the milling topography contours. In Experiments, before FIB patterns, we adjusted FIB stigmator and focus to obtain a circular FIB profile and tight FIB. FIB scanned on the silicon substrate using single-spot, after that Atomic force microscope (AFM) measured topography of patterned silicon substrate. The substrate surface showed a Gaussian shape crater caused by FIB milling a single spot and the crater increased depth and width with longer dwell time. We observed that milling depth is linear to dwell time in limited dwell time and calculated the FIB milling speed. FIB milling speed is a Gaussian function. Accelerate voltage and beam current affect milling speed. The higher milling current results in higher milling speed, and Gaussian function became taller and broad. Accelerate voltage affects width of milling single spot, lower Accelerate voltage wider Gaussian shape is. This thesis presents the predicted topography of FIB milling single spot, two spots, line and square fabrication by milling speed function. The predicted topography are compared with experiments. We did the double spot experiments to explain the deviations occurs because of energy accumulation. At the end of thesis, we show adjusting pitch reduce the fluctuate of line fabrication bottom.