奈米壓印對位光學系統之研製

Abstract

當全球各大半導體商努力追求製造出更小線寬的晶片時，對於次世代微影製程設備的需求也逐漸增加。但是傳統紫外光顯影技術由於複雜的光源與光學系統，造成微影製程設備的成本也隨之提高。在100奈米以下線寬的需求下奈米壓印，奈米壓印提供了一個高精密度，高解析度，高產量與低成本的替代方案。但是對位精度必須達到解析度的範圍之內才能符合商業量產的需求。對位誤差主要源自於壓印過程中壓模面與晶圓面的平行度誤差，儘管如此，由於壓模面與晶圓面之間的極小間距，使得壓印對位系統的光學誤差大幅減少，並且可提升線寬的解析度。奈米壓印提供了一條已證明CD(critical dimension)可達到10奈米以下的另一路徑。但是無論是步進掃描的系統或是奈米壓印的方式，其相關定位技術仍必須一起進步以實現10奈米的尺寸之下之製程。 論文主體在於設計一個適用於奈米壓印製程的對位(alignment)光學系統，當光路調校理想的情況下，母模面與晶圓面之間的對位僅包含二維平面以及Z軸旋轉共三個自由度的調整。壓印系統之對位重點有二：其一為對位光學系統的調校，包含入射光零度入射、對焦控制以及光柵面平行度校正，其中將採用輔助的光路控制機構使之自動平行校準；其二為壓印母模與晶圓本身之二軸精密對位，論文將使用類似於目前掃描步進機的對位控制方式，使用兩段式控制 (dual-stage control)，第一階段使用下層的位移平台配合傳統的對位記號與白光顯微術做微米等級的粗定位，第二階段的對位系統採用近場量測(near-field measurement)模式配合壓電致動器作奈米等級的精準對位。近場量測模式採用光柵耦合原理，以正負一階光強變化的曲線作為檢測的依據。我們將量測結果與G-solver模擬做比較，發現誤差來源主要為位移平台振動以及光柵結構缺陷，兩者只要控制得宜，系統就可以在光柵週期之內得到高靈敏度的光電訊號變化，突破傳統的對位精度限制。

The main subject of this thesis is to design an optical system applied to the alignment of nano-imprint lithography. Under the premise of all optical elements being well-aligned, the alignment between the mold plane and the wafer plane only involves 2-D plane and rotation of z axis. There are two emphases on the thesis. The first is the alignment procedure of the entire optical elements, including zero-degree incidence, focus control and the horizontal adjustment of grating planes. The second emphasis is two-axis alignment setup between the mold and the wafer. A scanner-like, dual-stage control method is used . In the first stage we use the underneath position stage along with traditional alignment marks and white light microscopy to achieve micron-level coarse alignment. In the second stage, we adopt the near-field measurement along with piezo-electric actuator in the alignment system to achieve nano-range positioning. The near-field measurement is based on grating-coupled principle, using the curve of first-order light intensity variation as the alignment reference. We compare the results with G-solver simulation and found out that the error sources are primarily from vibration of the position stages and defects of the grating structure. From the experiment results, the clear signal variation within a grating pitch movement can be obtained while both factors are under control. The signal can then used for second stage fine alignment, and break the limitation of convertional optical