利用非水溶液製備銅錳薄膜之研究

Abstract

遵循摩爾定律下，積體電路不斷的微縮，在導線線寬180 nm以後由原本銅線取代鋁線，因使用鋁線本身導線電阻高會有嚴重的RC延遲效應，且鋁線有嚴重的電遷移效應使導線壽命嚴重縮短，因此使用銅可改善上述現象，目前以銅做為導線已經為一種趨勢，而製程中以銅取代鋁做為金屬導線材料後，為了克服銅與矽基材間相互擴散的問題，必須在銅與矽基材之間沉積具有高熱穩定性及良好界面附著性的擴散阻障層。本實驗利用金屬錳具有較大的擴散係數及在升溫時與二氧化矽有高度反應能力，因此在高溫驅動下能與二氧化矽層相互作用，自行形成擴散阻障層，以防止銅與矽基材互相擴散。 本研究利用兩種非水溶液，分別為有機溶劑和深共晶溶劑，進行銅錳薄膜的脈衝電鍍，將銅錳薄膜沉積在銅晶片上，並以不同環境進行銅錳薄膜的熱處理，以觀察金屬錳是否與二氧化矽層反應，形成擴散阻障層。銅錳薄膜分析以掃描式電子顯微鏡(SEM)觀察銅錳薄膜之表面形貌和橫截面；能量散射光譜儀(EDS)進行銅錳薄膜的定性及定量；X-ray繞射儀(XRD)進行相的分析鑑定；X-ray光電子能譜(XPS)分析表面形貌各元素價態；利用交流阻抗分析(EIS)、循環伏安法(CV)、極化曲線(polarization curve)和熱重分析儀(TGA)等電化學分析非水溶液電解液之特性。 本研究結果顯示有機溶液添加冰醋酸後，電解液之導電度大幅提升，且解離的醋酸根離子會與銅錳錯合，使銅錳薄膜較好還原與沉積，但添加的冰醋酸後有微量水分，因此所沉積的銅錳薄膜為氧化錳顆粒，且在400 oC熱處理時氧化錳顆粒無法順利擴散至二氧化矽層形成擴散阻障層，故將電鍍用的電解液由有機溶液改為深共晶溶液。深共晶溶液具有非常良好的導電性，在電解液之銅錳比例為1:10 (Cu:Mn=0.006 M:0.03 M)、電流密度為1 mA/cm2及電鍍15分鐘可沉積出均勻且平整的銅錳薄膜，經分析確認薄膜成為金屬銅與微量氧化錳，且銅薄膜中固溶著錳原子。將銅錳薄膜在400 oC下熱處理後，固溶於銅薄膜中的錳原子順利擴散至下層形成擴散阻障層，故利用深共晶溶液成功製備銅錳薄膜且熱處理後也使錳擴散形成擴散阻障層。

The feature size of integrated circuit is constantly miniaturized as predicted by Moore’s law. As the wire dimension was reduced to less than 0.18 µm, aluminum wire was replaced by copper which exhibits higher conductivity and reduced RC delay. However, rapid diffusion of copper to the underneath silicon layer is a serious issue, resulting in excessive defects. Therefore, a robust diffusion barrier is required. Desirable barriers should meet certain criteria such as high thermal stability and sufficient adhesion with Cu interconnect and dielectric layer. In this study, manganese is chosen as the model material for self-forming diffusion barrier due to its large diffusion coefficient and strong reactivity toward the dielectric layer at elevated temperature. By co-deposition of Cu-Mn alloyed film followed by thermal annealing, Mn atoms diffuse faster than Cu atoms to the dielectric, and an ultra-thin film of Mn-silicate is formed at the interface between the Cu interconnect and dielectrics.

In this work, two different non-aqueous solvent systems, organic solvent and deep eutectic solvent, are employed as the deposition baths. Pulse-current electrodeposition is applied for the deposition of copper-manganese films on Cu@Si wafers. A Mn-silicate thin layer is formed by heat treatment with controlled temperature profile. Surface morphologies, film thickness and composition of the deposited Cu-Mn films are examined by SEM and EDS; further compositional analysis is conducted by XRD and XPS. Characterization of the performance for electrolytes are performed by EIS, CV, TGA, and polarization curve.

For organic solvent based deposition bath, it is proven that the electrical conductivity is greatly improved with the addition of some acetic acid. The acetic acid is also complexing metal ions and hence renders better film quality with a layer amount of deposits. However, trace amount of water exhibited in acetic acid resulted in the oxidation of as-deposited films. These oxide particles were reluctant toward diffusion and thus no barrier material was formed. Therefore, deep eutectic solvent was then adopted for electrodeposition baths. DES baths showed much better conductivity, hence improved morphology control and current efficiency could be expected. Several parameters were examined, and optimized results were obtained. The as-deposited films were then characterized and confirmed with solid-soluted Mn atoms in copper lattices. Under 400 ˚C, these Mn atoms were successfully diffused to the underneath dielectric layer and formed a diffusion barrier layer as expected previously.