多層導體連線結構中介層洞與介電層之研究

Abstract

在元件的尺寸進入深次微次微米的時代後，在後段多層導體的連線中，RC delay的問題愈趨重要，本篇論文乃對如何降低多層導體連線中之RC delay 做一深入的探討，本文大致圍繞著如何降低電容或電阻兩個方向來探討，在降低電容方面，我們是針對一種低介電材料對各種電漿處理之探討，在本文之低介電材料為一含有機官能基之聚合物methysilsesquioxane（MSQ），其製作方式為旋塗（spin coating）後，進行軟烤（baking）及固化（curing）的過程，來達到做為積體電路導體連線間介電材料之應用。此種MSQ高分子聚合物，除有機官能基之存在而具低介電常數，並在預烤的過程中，富良好的流動性，因此，有極佳的局部平坦化能力，並能填入高aspect ratio的洞中。此外，經過固化處理後，此高分子聚合物（polymer）薄膜具有較低的應力而不易龜裂。 本篇研究對MSQ低介電薄膜進行一系列之電漿處理，包括：H2，O2， N2O及NH3，其處理時間依序為：as cured，3分鐘，6分鐘及9分鐘。實驗結果顯示，氫電漿能量最弱，對MSQ薄膜內部結構並不影響，並可填補其表面矽原子之懸浮鍵（dangling ing bond），因而使其漏電流下降，是理想之電漿處理。而氣電漿對MSQ薄膜則持續造成氣化作用，減弱其低介電材料之特性。含氮原子的電漿處理（N2O，NH3），可於MSQ表面形成鈍化膜，保護MSQ薄膜整體結構，並可抵擋後續氧電漿處理之傷害性。 一般而言，物質介電常數的大小是由偶極矩（dipole moment）的強度及物質的密度（density）所決定。從上述討論的結果，可知MSQ薄膜具有較低的密度，再加上薄膜中的Si-CH3鍵取代了高極性的Si-O鍵，因此使得MSQ薄膜具有較低的密度，再加上薄膜中的Si - CH3鍵取代了高極性的Si - O鍵，因此使得MSQ薄膜具有低介電材質的特性〔4〕，然而在經過我們其它電漿（plasma）後續處理過後的MSQ薄膜，其對於氧電漿的抵抗性（O2plasma-resistance）都比沒有處理過的MSQ薄膜來的好。也因為其對於氧電漿的抵抗性（O2plasma-resistance）之特性有明顯的提昇，所以此種處理方式，將非常值得被廣泛運用在一般積體電路的製造上。 另外，在降低電阻方面，我們致力於研究一種清潔介層洞之溶液-(NH2OH)2H2SO4，透過此溶液的使用，我們發現其效果可以大幅降低介層洞的接觸電阻（via resistance）。之後我們於清潔溶液中再加入CuSO4其目的是希望加入溶液的銅離子（Cu2+）會在（NH2OH）2H2SO4，清潔的過程中的同時與新鮮的鋁產生化還原的反應。藉以在介層洞底部表面形成銅的鈍化層，如此，一層薄薄的銅便在介層洞底部的鋁上生成， 而使化層以下的金屬不致與空氣接觸以致被氧化。如此一來介層洞的電阻(via resistance)便可得到明顯的改善。

In this thesis, we will study how to reduce RC time delay. The following investigation is dvided into two major topics. The first topic, we investigate a kind of low dielectric constant materials such as methylsilsesquioxane (MSQ) which is treated by various plasma. There are four kinds of plasmas were used H2, O2, N2O and NH3. After H2 plasma treatment, the dangling bonds of silicon atom in the surface of MSQ film were eliminated, thus the dielectric constant of MSQ film wre improved, also the leakage current become smaller than those untreated films. Due to the silicon-methyl bonds of the MSQ film were continuously broken during the O2 plasma treatment process, both the dielectric constant and the leakage current of MSQ film were increased. In addition, after the MSQ film were treated by N2O and NH3 plasma. Passivation behaviors were observed on the MSQ surface. The passivation layer on the MSQ surface prevent MSQ which is under the passivation layer from O2 plasma damage. Thus, when MSQ film treated by N2O or NH3 plasma and following by O2 plasma treatment, the lower dielectric constant and leakage current could be gotten. The second topic, we investigated the clean capability of solutions. In the new cleaning solution development, we investigate the cleaning capability of (NH2OH)2H2SO4 combined with CuSO4 Low via resistance of electrical test structre is obtained if the via is cleaned by this new cleaning solution. The role of CuSO4. The cleaning capability of (NH2OH)2H2SO4 combined with CuSO4 is better than that of (NH2OH)2H2SO4. Low via resistance of electrical test structure is obtained if the via is cleaned by this new cleaning solution. The role of CuSO4 in the new solution is provide Cu to passive the Al surfaced. The copper is more stable than aluminum in the environment. The copper is hard be oxidated. The (NH2OH)2H2SO4 in this new solution can efficient ot remove AL3O2 and leave the clean Al on the surface of via. Then, the Cu ion in this new solution will immediately react with clean Al and form a copper passivated layer on the surface of via. Therefore, (NH2OH)2H2SO4 combined with CuSO4 can provide excellent cleaning capability for aluminum via hole Finally, we find that one step clean process is better than two step clean process for selectivity of W-CVD and the lower via resistance could be achieved. To clean via hole, for clean temperature, 50℃ is the optimal clean temperature and 1 min is the optimal clean time.