應用在雷射直寫微影的光學頭之研究

Study of the optical pickup head for direct laser writing lithography

李源欽(Lee, Yuan Chin)

指導教授 ： 趙煦

國立清華大學/電機資訊學院/光電工程研究所/博士(2015年)

摘要

本論文旨在研究如何設計及應用光學頭做為雷射直寫微影製程的光源。一般商用光學頭很難被應用在雷射直寫微影製程，主要原因有二，首先，一般光學頭的致動器因為使用6條銅線懸吊機構，造成水平方向的剛性不足。其次，光學頭連續聚焦伺服的能量可能會造成點與點之間光阻不必要的曝光。
為解決上述問題。首先，本論文提出一個特殊的單軸致動器設計，利用2個3臂式黃銅彈片結合物鏡承載機構使得致動器水平方向的剛性大幅強化。在實際完成致動器製作後，由於物鏡的工作距離僅有0.56 mm，很難量測該致動器水平方向的穩定性。為此，我們提出原創的修正式推挽法(Modified push-pull method)克服此問題。實驗結果顯示，致動器在水平面兩個垂直方向的偏擺量都在2 nm以下。其次，為了解決聚焦伺服光會曝光光阻的問題，本論文提出一個使用405 nm及650 nm兩種光源的雙波長光學頭設計，405 nm波長做為曝光光源，而650 nm波長則做為聚焦伺服光，該系統使用數值孔徑0.85的藍光物鏡，並且兩種波長的聚焦光點共焦。相關的共焦調整步驟，論文中也會詳細說明。另外，該光學頭設計為可以曝光有機光阻與無機光阻，有鑑於無機光阻為熱敏感材料，因此，建議兩個波長的聚焦光點應該相距至少1.58 um，以避免650 nm光點的能量影響405 nm光點的曝光過程。關於曝光實驗，使用工研院開發的GeSbSnO無機光阻與永光化學所生產的EPG 512有機光阻塗佈於4吋矽晶圓測試，其中無機光阻膜厚65 nm，最小曝光光點直徑為0.19 um。有機光阻模厚為1 um，全穿透最小曝光光點直徑為0.52 um。半穿透最小曝光光點直徑0.29 um，曝光深度0.24 um。由曝光結果顯示，前述共焦調整步驟是有效且準確的，並且該雙波長光學頭確實可以應用在次微米尺度的雷射直寫微影製程。

關鍵字

光學頭 ； 雷射直寫微影 ； 致動器 ； 物鏡 ； 推挽法 ； 聚焦伺服 ； 共焦 ； 無機光阻 ； 有機光阻

並列摘要

The purpose of this dissertation is to design and implement an optical pickup head to be the light source for direct laser writing lithography. It is difficult to use the commercial optical pickup head as the light source for direct laser writing lithography due to two reasons. Firstly, the lateral stability of the actuator of the optical pickup head is not good since it adopts the six-wired suspension structure. Secondly, the optical power from continuous focusing servo of the optical pickup head may expose the photoresist between two successive exposed spots.
To solve the first problem, a special design of a single-axial actuator was proposed. By using two planar springs with three-armed structure, the lateral stability of the actuator was improved. For solving the difficulty of the measurement of the lateral stability of the actuator while the focusing servo is activated, the original “modified push-pull method” was proposed. The measurement results showed that the lateral jitters of the actuator in two orthogonal directions were less than 2 nm. To solve the second problem, a new design of the dual-wavelength optical pickup head with both 405 nm and 650 nm wavelengths was proposed and implemented. The 405 nm beam was used to expose the photoresist, including inorganic and organic photoresists, while the 650 nm beam was used to execute the focusing servo. Numerical aperture of the objective lens was 0.85 at 405 nm. Both focused spots of the two beams by the objective lens were confocal and the detailed procedure of the confocal adjustment was also given. However, since the inorganic photoresist is heat sensitive, we suggest the two focused spots should be separated by at least 1.58 m to prevent from the optical power of the 650 nm spot affecting the exposure of the inorganic photoresist. Finally, the dual-wavelength optical pickup head with the single-axial actuator was used to expose both GeSbSnO inorganic photoresist and EPG 512 organic photoresist. The photoresist was coated on a 4” Si wafer and was spin with the linear velocity of 1 m/s. For the exposure of GeSbSnO photoresist, the minimum diameter of the pierced exposed spots was 0.19 um with 65 nm in depth. For the exposure of EPG512 photoresist, the minimum diameter of the pierced exposed spots was 0.52 um with 1um in depth. Besides, exposed spots with diameter of 0.29 um and with 0.24 um in depth were obtained. The exposure results showed that the procedure of the confocal adjustment was effective, and the dual wavelength optical pickup head was suitable to be used as the light source to expose those devices with feature size near 1 um or below.

並列關鍵字

Optical pickup head ； Direct laser writing lithography ； Actuator ； Objective lens ； Push-pull method ； Focusing servo ； Confocal ； Inorganic photoresist ； Organic photoresist

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