雙鑲嵌（Dual Damascene）製程結構已廣泛用於銅金屬連線，而製作方式有很多種，目前最常用的有中介窗優先（via first）、溝漕優先（Trench first）以及內嵌硬質罩幕（Buried hard mask），然而不論使用哪種方式製作總是會用到蝕刻中止層或硬質罩幕層搭配低介電（low k）材料使得整個製程複雜。不管用何種方法製作雙鑲嵌結構，都需要兩面光罩及兩次曝光程序，在現今先進製程的光罩一面需要兩百萬元，而ㄧ層金屬層就需要兩面光罩將增加晶片製造成本。而隨著晶片尺寸的縮小，也增加了中介窗與溝漕的對準誤差（misalignment）導致微影失敗需重新微影。隨著金屬層數的增加以上問題的出現增加了製程花費，也降低了生產速度與良率。
本論文主要是研究以不同光穿透度的金屬薄膜，製作一片光罩同時具有中介窗與溝漕圖樣，並設計光罩的中介窗與溝漕有不同的能量穿透，其中的溝漕我們以鉻(Cr)薄膜減少曝光能量造成部分曝光，中介窗的部份以全透光方式處理，因此達到一次曝光能形成光阻雙鑲嵌(Dual Damascene)結構，最後利用乾蝕刻使光阻雙鑲嵌結構轉移至下面的基板。光罩設計及曝光模擬部分此研究以KLA-Tencor 公司的Prolith v.9.2模擬軟體來進行。
我們可以藉此單一光罩取代傳統兩面光罩來製作雙鑲嵌結構，降低光罩成本，而在製程上也僅需ㄧ次微影、蝕刻、灰化及清洗，降低很多的生產成本且簡化製程並降低對準誤差問題。

Dual damascene process has been used for copper interconnect.There are many schemes to fabricate dual damascene structure. The most common integration approaches for the dual damascene architecture are via first, trench first and buried hard mask. Which mask
first, using etch stop and hard masks or not and the use of ultra low k materials in advanced interconnect make dual damascene process very complicated.
No matter which dual damascene scheme used all of them need two masks and two lithography process. One advanced mask cost about two million NT$ and one metal layer needs two masks. With the increasing trend of metal layers of modern IC, the mask cost will add additional burden on already high manufacture cost. With rapidly decreasing chip feature size, the misalignment tolerance is not that far from critical dimension (CD). The existence of misalignment between via and trench mask will cause more rework on lithography steps. The increases of metal layers and higher rework rate on high cost lithography steps can only make things worse. Misalignment will also degrade the process and product yield. It is also a reliability killer.
This thesis is to develop a differential exposure lithography process between via and trench using partial transmission on trench. On the mask, it combines via and trench pattern layout. To achieve one exposure having dual damascene shape on photo resist, we need different exposure energy settings or conditions at via and trench areas at the same time. This thesis used light’s partial transmission technique to weaken the exposure energy on trench to obtain partial exposure. Semi-transparent chromium(Cr) film on trench area was used to absorb
some energy of the exposure light to create partial exposure on trench.Via area can be simply clear (no Cr for positive resist) to obtain full exposure. Dry etching was then used to transfer the dual damascene shape photoresist to underlying substrate.
The thesis also used KLA Tencor’s Prolith v.9.2 to simulate the combined mask structures to optimize mask design and exposure conditions.
Using this unique single mask instead of two traditional masks, we can obtain photoresist dual damascene structure in one exposure. This dual damascene structure can be transferred to underlying dielectric via selective etch process. This cuts the high mask cost in half. With
one mask, we need only one lithography step, one etch, one ash and one clean instead of two each. It saves process cost a lot, simplifies the complicated two mask dual damascene processes and completely removed two masks’ misalignment problems. Besides saving mask and process cost, without misalignment’s issues. It will also boost yield and improves product reliability.

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