銅金屬化學機械研磨漿料之研究

Abstract

由於元件尺寸縮小，閘極傳送的時速度提昇，進而凸顯出元件間導線上信息傳送的延遲現象的嚴重性;這就是一般所謂的RC delay的問題，其必須以低電阻金屬導線及低介電常數介電材料來建構多層金屬連線來加以改善。而要建立這結構，平坦的表面是必須的；尤其在臨界尺寸已在0.18微米以下，微影曝光解析度的要求更加的嚴苛時。銅製程的化學機械研磨 (CMP, Chemical Mechanical Polishing) 是目前唯一可達到全面平坦化技術。 CMP的技術目前能有許多的問題急待研究；例如，刮痕、研磨粉體的殘留、銅、介電層及擴散障礙層選擇率等。 在本文中主要是針對不同的添加劑對化學機械研磨的粉體及晶圓表面的研磨行為和影響加以探討。 本實驗採用的研磨粉體是 "膠體的二氧化矽(colloidal silica)"。它與氧化鋁粉末相比，具有高活性、好的懸浮性、較小的粒徑、圓球狀不易對表面造成刮痕而且便宜的特點。 由此研究中我們發現 CMP的研磨行為與研磨液的pH值及研磨粉體跟被研磨物的表面電荷有很大的關係。一方面是由於不同的pH會導致不同相的產物生成，而且研磨物與被研磨物的溶解度也隨pH的不同也有所不同。另一方面，研磨粉體與晶圓表面所帶的電性為相反相互吸引或研磨液中的離子濃度越強造成越薄的電雙層厚度，則粉體較易與晶圓表面作用會有比較大的研磨率。這的確與我們的實驗結果相互吻合，對鉭及二氧化矽薄膜之研磨而言，添加KOH的研磨液的確有較大的研磨率。 羧酸的添加在雙氧水系統中對銅有鉗合的作用以至於加入的量越多，其研磨速率越快；但在硝酸系統中反而隨之減少，因其可產生一保護層去抑制銅腐蝕。 總而言之我們可以藉由這colloidal silica 為研磨粉體的拋光液晶由添加有機酸以滿足高選擇率（銅對tantalum及thermal oxide）之需求；再利用不同鹼液添加獲得的鉭高移除率以滿足Cu-CMP第二研磨步驟。

In order to overcome sever limitation of DOP (deep of focus) in deep sub-micro lithography would be necessary to eliminate surface topography a globe planarization technology only by CMP. And based on the problem of RC delay, Cu process must be the major tendency for deep-submicro semiconductor manufacturing; and Cu-CMP takes an important role. Material polished by Cu CMP contains upper copper film and diffusion barrier layer. Because of differences of material properties, it's difficult to use a single slurry to remove copper barrier layer and stop on the underlying dielectric. In the past, it does not work well especially in the removal selectivity of copper to barrier layer. Thus, it is an avenue for Cu-CMP research. In our study, we major focus on the polishing behavior and mechanism of various additives to our abrasive and wafers, which contain copper, oxide, and tantalum films. A different abrasive "colloidal silica " is adopted here. It has four advantages, high activity, well dispersion, smaller particle size, and cheaper as abrasives of CMP. In this search, the polishing behavior of CMP is deeply involved by slurry pH and the surface-charge-related interactions between the slurry and polishing surface. The slurry pH of slurries is an important factor of removal rate. Because in different pH value, the films of metal or silica will has different phases and lead different removal behaviors. Besides, the solubility of metal, metal oxide and silica depended on pH value. The surface-charge-related interactions between the slurry and polishing surface is related to the pH. Besides, the collision frequency of abrasive and the surface of wafer affects by the attraction and expulsive Force. It will depend on adsorption of cations and ion strength of slurry. So, in KOH added slurry has the smaller size of cations and complete dissolution constant than TMAH, NH4OH to reduce the width of diffusion layer; increase collision frequency and then get higher removal rate. Carboxylic acids form complexeing of copper in acid solution, and lead to the increase of copper film removal rate. But it is not the same in slurries taking HNO3 as oxidizer. With increasing the citric acid concentration in slurry, the removal rate of copper is decreasing. Based on citric acid inhibits the removal rate of copper by forming a passivation layer of CuO, Cu2O, Cu(OH)2. Combined all result, we can use this colloidal based slurries to achieve high or low any selectivity during all polishing step in Cu CMP just adding proper different alkaline and organic solution.