研磨粉體對二氧化矽與鋁薄膜之化學機械研磨特性研究

Abstract

在積體電路的製程中，為了要達到0.35um的線寬與多重金屬連線，全面平坦化是必須的，而化學機械研磨（CMP）是現在的平坦化技術中，最能夠達到全面平坦化的要求的技術。研磨液中的研磨粉體(abrasive）在CMP過程中，扮演著舉足輕重的角色，但目前尚不十分明瞭其實際的反應機制。除了機械的磨耗部份，研磨粉體與晶圓(wafer)表面的作用力亦不容忽視。 本實驗中利用不同的氧化鋁研磨粉體研磨二氧化矽與鋁薄膜，試著找出粉體的相組成如何影響化學機械研磨。此外，利用氧化鋁及二氧化矽粉體在鋁與二氧化矽薄膜上作研磨，以此比較及探討粉體/研磨層在化學機械研磨上的相互作用。當研磨粉體與研磨薄膜屬於同材質時（因鋁薄膜在進行化學機械研磨時，表面易生成一層氧化鋁，在本文中視為與氧化鋁同材質），此時磨除作用主要受到機械磨耗的影響。其研磨速率與研磨粉體的幾何形狀有很大的關連，當粉體呈稜角狀與粒徑較大時會有高的研磨速率。 而在研磨粉體與研磨薄膜屬不同材質時，靜電作用力主導了化學機械研磨的磨除率，當研磨液的pH值落於研磨粉體於薄膜的等電位點間時會有最大的磨除率，此時粉體與薄膜間存在靜電吸引力，而使粉體撞擊薄膜表面的頻率增加，造成溶解物質吸附在粉體上的量增加。 在研磨後的表面粗糙度方面，表面粗糙度受粉體的粒徑與研磨墊的硬度影響，在較大粒徑的研磨粉體與較硬的研磨墊上會造成較大的表面粗糙度。

In the integrated circuit (IC) industry, global planarization of the wafer is an important process to achieve 0.35 um linewidths and multilevel interconnections; chemical-mechanical polishing (CMP) is the most effective technology for global planarization. Abrasives in the slurry play important roles in the CMP process, they are responsible not only for the mechanical abrasion of the materials being polished, but also some interactions related to surface charges between the abrasives and the polishing surface being polished are critical in CMP. In this study, alumina and silica polishing powders are employed in polishing oxide and aluminum films to explore their influences on the chemical-mechanical polishing (CMP) performance. In the case of polishing film with abrasive of the same material, it has been found the mechanical abrasion would dominate the overall material removal. (It should point out that in the present work, aluminum film was assumed as the same material of alumina, since it usually present a passive oxide layer during CMP operation) The removal rate would be strongly depended upon the geometry factors of abrasives, that means higher removal rate could be obtained by polishing with larger and sharp-edged abrasive than that with small and rounded one. The electrostatic interaction between the abrasive and the film tends to dominate the CMP removal rate when the abrasives and the polished films are of different isoelectric points (I.E.P.). The maximum removal rate is obtained at the slurry pH values being between the I.E.Ps. of the polished film and the abrasive. Polishing at this range of slurry pH value, electrostatic attraction exists between abrasives and the films being polishing, which results in the enhancement of impinging frequency of abrasives on the films and absorbing of dissolved materials onto the abrasives. The surface roughness after polishing would depend upon the abrasive size and the pad hardness. Polishing with larger particle size and harder pad would result in rougher surface.