新式電子束直寫圖案化多孔性低介電常數材料之研究

Abstract

本論文研究一多孔隙低介電常數材料POSG(porous organic Silsesquoxane glass) 薄膜，使用電子束微影系統直寫定義圖案，其性質及其在積體電路(IC)製程上之應用。低介電常數材料POSG(porous organic Silsesquoxane glass)為一種有機類之高分子矽酸聚合物，類似Methylsilsesquixane(MSQ)，也是一種旋塗式塗佈的低介電常數材料。由於在IC製程中，微影是製造流程的核心，而且製程繁瑣複雜，而其中光罩的對準、光阻的去除…等，任何一個步驟都有可能造成誤差，而影響整個產品的良率；所以，如果能夠減少製程的步驟，也可減少每個製程可能造成的誤差。 本文提出用電子束直接定義低介電常數材料薄膜,用以取代傳統的微影流程。研究實驗結果顯示此多孔性薄膜只需要如商用光阻般小劑量的的電子束劑量即可使其完成圖案的定義。而不同於傳統爐管加熱成膜,我們發現使用電子束將POSG薄膜曝光成膜的動作是一種“部分交聯硬化”的動作。這表示電子束的能量只夠將部分的鳥籠狀(cage-like)單體鍵結成聚合體型式。而經過顯影劑(TMAH加甲醇)顯影之後，顯影劑將未交聯硬化的小單體帶走，留下大分子的聚合體。並且顯出我們使用電子束所定義的圖案。而整體薄膜的孔隙度，由於小單體的消失而變得更大，同時也使得介電值得以更低至1.89。此外，在經歷過顯影與再次固化的作用之後，薄膜的漏電流密度與可靠度也變得更佳。 另外，我們也對使用傳統爐管固化的標準製程POSG薄膜，及使用電子束固化的POSG薄膜做漏電機制的分析；得知爐管固化的POSG薄膜為Schotty 型的漏電機制；而使用電子束固化的POSG薄膜則為空間電荷(space charge limit current)型的漏電機制。 由此可知，在新世代積體電路製程中，POSG薄膜使用電子束微影系統直寫定義圖案，為一有潛力之新製程方法。

Low-k/Cu integration with low-cost process is an important issue for Cu multilevel interconnection in future. The nanodevices such as single-electron transistor attract much attention in recent years. The electron beam (EB) lithography and direct patterning of low-k materials are two potentially novel technologies for nanodevice fabrication process. In this thesis, we propose direct patterning of porous organosilicate glass (POSG) films to replace the traditional lithography processes. The results demonstrated that the dosage of electron-beam used in POSG film just needs as small as commercial electron-beam photoresist. Comparing with traditional curing process, the effect of electron-beam treatment to POSG film is just a partial curing. Although the energy of e-beam is not large enough to evaporate the solvent of as-baked POSG, but it could patterning the film by crosslink the chemical structure. After undergoing development process, a few portion of cage-like monomer in post-exposed POSG will be carried out by utilizing the developer of methanol mixing with TMAH. As a result, the porosity of the POSG film will become higher than standard one and make the dielectric constant of the POSG film decrease significantly to 1.89. In addition, the dielectric properties of POSG film after e-beam exposure and develop process, no matter the dielectric constant, leakage current and the reliability will be improved through thermal annealing process. Therefore, the POSG film with e-beam curing is a potential technology to manufacture multilevel interconnection in Cu damascene process.