CMP鑽石修整器修整聚胺酯拋光墊表面特性之研究

Abstract

化學機械拋光是半導體製程中不可或缺的關鍵技術，為了讓化學機械拋光製程穩定且持續進行及維持晶圓品質，拋光墊必須適當的以鑽石修整器來進行修整，以恢復其表面形貌與特性。本研究從最基本現象開始了解，首先以單顆鑽石於拋光墊表面進行刮削實驗，研究過程中，改變不同鑽石方位、修整參數及修整路徑，探討其對拋光墊表面形貌的影響。結果顯示鑽石方位對拋光墊表面形貌有顯著的影響，修整後材料會於溝槽兩旁堆積而形成隆起現象。面部朝下之鑽石修整後之拋光墊材料的變形模式以犁削為主。而尖點朝下之鑽石修整後之拋光墊材料的變形模式以切削為主。當改變不同修整參數及修整路徑時，亦發現尖點朝下之鑽石修整後之拋光墊表面隆起變動最為平緩。因此尖點朝下之鑽石的切削能力最佳且隆起的變動亦最小，最適合推薦用於鑽石修整器。實驗亦發現溝槽深度遠低於刺入深度，意味著在修整過程中，拋光墊存在有極大的材料回彈。 文中亦探討隆起高度隨拋光時間累積的變化及其對於晶片移除率的影響，結果顯示晶片移除率首先會隨著刺入深度增加而逐漸增加，但是當刺入深度超過某一臨界值時，晶片移除率有逐漸下降的趨勢。而尖點朝下之鑽石修整後之晶片拋光率隨著刺入深度增加的變動量最為平緩。此外過多的隆起材料不易被拋光行為所去除，導致少許的隆起材料殘留於拋光墊表面，其亦導致晶片移除率的下降。因此若希望不要於拋光墊表面殘留隆起材料及可產生較高且穩定的晶片移除率，尖點朝下之鑽石比較合乎要求。 由於尖點朝下之鑽石是適合推薦用於鑽石修整器，文中亦使用鑽石尖峰在同一高度且形狀相同之鑽石修整器(ADD)來修整拋光墊，探討於修整過程中之拋光墊表面特性，並且與傳統的鑽石修整器(DG)作一比較。結果顯示ADD修整後之拋光墊表面較平整、均勻且修整率較低，但是達到拋光墊穩定的表面粗糙度之時間並不遜於DG。另外ADD修整後之晶片拋光率較高且拋光墊消耗量較少，並且晶片拋光率隨拋光時間增加而下降之變動幅度亦較小，是未來值得推薦的鑽石修整器。

The wafer performance is often determined by the texture of the pad surface which is controlled by a diamond pad conditioner in the CMP process. In the thesis, the fundamental characteristics of dressing action on the polyurethane pad are investigated first via dressing by single diamond of different orientations, under various dressing parameters and dressing path. Experimental results show that a groove with pile-up on both side walls forms as the diamond moves over the pad. Plowing is found to be the major mechanism responsible for this surface topology if dressing is conducted by the face of a diamond. On the contrary, cutting action dominates when the point of a diamond is responsible for dressing. The depth of the groove is smaller than the dressing depth due to the spring back of the pad. There is less variation of ridge with the dressing depth and dressing path for point dressing. These results imply that the use of point dressing is recommended. The second part of the thesis study the effects of ridges on the polishing rates of silicon dioxide are investigated. Experimental results reveal that there exists an optimal dressing depth. Below this value, the polishing rate decreases with the reduction of the dressing depth. Above this value, the polishing rate saturates and then decreases gradually. The use of point dressing is beneficial since it results in a higher but less variation polishing rate. As a result, the point dressing is recommended to the design of diamond pad conditioner. Finally dressed by a novel advanced diamond disk (ADD) containing the same height and identically shaped tip diamond are studied. They are compared those dressed by with conventional diamond disk (DG). Experimental results demonstrate that the ADD can dress asperities of the pad more uniformly than the DG. The dressing rate of the ADD is reduced by about 30% and the pad is less worn during the polishing process, and hence the pad life is extended. As a result, reduction of the cost CMP is expected. The polishing rate of the ADD is higher than that of the DG. There is less variation of polishing rate with the polishing time for ADD as compared with that of DG.