Research and Design of Semiconductor Lithography Overlay Metrology Simulation System

在半導體製程中，微影技術是決定半導體線寬尺寸的關鍵技術，而覆蓋誤差量的控制又是微影製程的關鍵。隨著半導體製程的發展，積體電路的元件線寬越來越小，覆蓋誤差（Overlay error）量的控制也越來越重要。產生覆蓋誤差的原因是光罩之對位不正以及光源經過透鏡组與光罩後，因為電磁場與表面結構之近場交互作用的效應以及遠場之光學像差影響，造成晶圓表面的光學量測幾何圖案偏移與變形。為了能有效控制覆蓋誤差量，除了利用測量儀器做精確定位以減少對位產生之誤差之外，對於圖案線寬小於波長等級之結構，使用數值模擬的方法在電腦上進行計算，以事先了解光罩圖案在近場因繞射效應產生之圖案變形，做最佳之光罩圖樣設計以減少覆蓋誤差量是較經濟且有效的做法。 本論文採用OptiFDTD軟體，使用時域有限差分法之運算方式，將空間直接格點化，藉由時間變化疊代出每個時間的場變化，可以得到暫態以及穩態之結果，在運算上與實際狀況較為符合。而本論文除了利用OptiFDTD軟體模擬近場的空間格點電磁波性質外，在遠場部份則採用LightTools軟體來模擬計算。LightTools可以取代傳統在遠場使用繁複的傅立葉轉換積分計算，以非序列光線追蹤的方式，使用非常龐大的光線數量來計算光在遠場的光強分佈，兩種軟體之間的結合則以VBA做為媒介。藉由模擬 業界廣泛使用的BiB疊對標記圖樣與實驗的驗證，來建立一個可以自行開發的微影疊對量測模擬平台。最後我們發現以線（line）來做光罩標的圖樣會比溝槽（trench）來的好。Photolithography is the key technology driving the advancement of the semiconductor industry and directly influences the critical dimension (CD) of Ultra-Large Scale Integration chips. The reduction of CDs creates more strictly overlay control requirements. In order to control and minimize overlay metrology errors, we have to deal with a number of design parameters both on the metrology tools and on the overlay targets. For speeding the rate of performance improvement, optical simulation can be used to model the effects of target designs on the ultimate metrology performance. Optical simulation on the computer can aid R&D efforts to improve metrology methods. In this thesis, a overlay metrology simulation platform will be presented, developed in-house. The main idea of this platform is to simulate the overlay metrology which integrating with finite difference time domain and non-sequential ray tracing software package. Finite difference time domain method program is used to calculate the overlay target as an amplitude/phase-object in the near-field. And non-sequential ray tracing method program is used to calculate the power of the overlay target in the far-field. The simulation validation test with simulation standard overlay mark BiB（Bar-in-Bar）will also be detailed in this thesis..誌謝…....................................i文摘要.................................ii文摘要................................iii錄.....................................iv目錄...................................vi目錄...................................ix一章 緒論..............................1.1前言...................................1.2研究動機...............................1.2文獻回顧...............................2.3.1微影疊對量測簡介.....................2.3.2微影疊對量測模擬技術.................6.3 論文架構及概要.......................12二章 模擬與實驗原理介紹...............14.1光學成像原理..........................14.1.1光的數學表示式......................14.1.1基本成像原理........................15.2 OptiFDTD理論介紹.....................20 2.2.1 FDTD 的基本架構.................21 2.2.2 Yee的FDTD演算法.................22 2.2.3穩定準則.........................26 2.2.4激發源...........................27.2.6 吸收邊界（Absorbing Boundary Condition）的處理....29.3 LightTools 之理論介紹...............................41.3.1光的反射與折射…....................42.3.2輻射度學（Radiometry）與光度學（Photometry）.......43.3.3非序列性光線追蹤（Non-sequential Ray Tracing）.....46三章 系統模擬架構與結果...............47.1模擬實施架構..........................47.2模擬近場光學行為......................50.3模擬遠場光學行為......................64.4模擬結果比較..........................68.5模擬實務的疊對標記圖樣................71四章 實驗架構與結果分析...............73.1實驗方法..............................73.1.1晶圓軌道機（Track）掃瞄機（Scanner）整合系統......73.1.2疊對（Overlay）量測機台運作原理...................77.2實驗結果與分析........................79五章 結論與未來展望...................86.1結論..................................86.2未來展望..............................87考文獻.................................88錄…….................................9