銅內連線及低介電常數材料製程整合於高介電常數薄膜電容

Abstract

本研究探討及研發具有高效能及穩定性的銅金屬內連線於先進高介電常數金屬-絕緣層-金屬(MIM)薄膜電容元件應用。以金屬鋁/鉭/金屬銅/鉭 (Al/Ta/Cu/Ta) 作為Ta2O5薄膜電容的底電極，可降低漏電流密度至1x10-9 A/cm2並提升崩潰電壓至5.2 MV/cm。因金屬鋁自身形成緻密且均勻氧化鋁，所以超薄金屬鋁成功地阻絕Ta2O5中的氧熱擴散至金屬銅層形成氧化銅。此外以低溫短時間的高密度N2O電漿處理Ta2O5薄膜能有效提升電容效能及元件熱穩定性，降低漏電流密度至4x10-10 A/cm2。 本研究並研究高介電常數材料鈦酸鍶鋇薄膜(BST)於先進MIM薄膜電容的應用。以銅鎂合金[Cu(Mg)]取代金屬銅成為金屬電極，因退火後會生成超薄MgO薄膜，能阻絕氧擴散，所以大幅降低漏電流密度。以氮化鉭/銅/氮化鉭(TaN/Cu/TaN)為電極應用於先進高介電常數BST MIM電容，結果顯示電容元件具有超高電容密度(11.5 fF/µm2)。此外，高介電常數材料 BST薄膜蝕刻及圖型定義亦是研究重點。以氯為反應氣體雖能有效蝕刻BST薄膜，但會殘留含鋇及鍶的化合物，降低元件電容特性。本實驗以氧電漿做蝕刻後處理能修補因蝕刻所造成的薄膜缺陷，降低漏電流密度至3.0□10-8 A/cm2及提升崩潰電場強度至2 MV/cm。 本實驗亦研究銅導線系統中，擴散阻障層與低介電常數材料SiOC:H薄膜間的交互作用及穩定性分析，藉銅離子漂移程度探討擴散阻障層效能及元件穩定性。因為在以金屬銅為電極的金屬層-絕緣層-半導體(MIS)結構中，施加正電場於金屬銅會使其分解為銅離子加速擴散至元件中。因此，高穩定性的MIS的結構是以金屬銅/氮化鉭/金屬鉭(Cu/TaN/Ta)多層薄膜為電極。此外，研究N2O電漿後處理對擴散阻障層氮化鎢及金屬鎢薄膜的阻障效能影響。結果顯示經電漿後處理的擴散阻障層具有奈米結構表面，能增加元件熱穩定性及阻障效能。本研究並以Whipple及Fick’s第二定律深入分析銅擴散在擴散阻障層的晶粒及晶界擴散因子。

We have investigated the characteristics and reliability of high dielectric constant metal-insulator-metal capacitors with copper interconnects. The properties of tantalum oxide (Ta2O5) metal-insulator-metal (MIM) capacitors with Al/Ta/Cu/Ta bottom electrodes were investigated. An ultra thin Al film successfully suppresses oxygen diffusion in the Ta2O5 MIM capacitor with the Cu-based electrode. The decrease in leakage current is attributed to formation of a dense and uniform Al2O3 layer, which has self-protection property and stops further oxygen diffusion into the tantalum contact. Moreover, the electrical characteristics of Ta/Ta2O5/Ta capacitors are improved by the treatments with inductively coupled N2O plasma. To integrate the high dielectric constant (Ba,Sr)TiO3 (BST) film in the advanced MIM capacitor, Cu(Mg) alloy films have replaced pure Cu films as bottom electrodes for BST capacitors used in high-frequency devices. High-quality characteristics probably follow the formation of a self-aligned MgO layer following the deposition of a Cu(Mg) alloy by annealing in an oxygen ambient, yielding an electrode with an excellent diffusion barrier and electrical characteristics, which is therefore effective in a BST thin-film capacitor. MIM capacitors made from a BST high-k dielectric film with Cu-based electrodes were also fabricated and demonstrated. The MIM capacitor has a high capacitance density of 11.5 fF/μm2, a low dissipation factor below 0.03 and small frequency dependence. Furthermore, BST thin films were patterned for fabricating BST capacitors in a helicon-wave plasma system. Some etching residues consisting of Ba and Sr were found after the BST films were etched and increased leakage current density. Oxygen surface plasma treatment can effectively repair surface damage caused by etching, and reduce the leakage current density and increase the breakdown field of the BST capacitor. To study the high performance Cu metallization in ULSI technology, the interactions between low-k material SiOC:H and barrier layers have been investigated. The drift mobility of the Cu+ ions in the Cu/TaN/Ta-gated capacitor was lower than that in a Cu-gated capacitor. The electric field in the Cu-gated MIS capacitor in the cathode region is believed to be increased by the accumulation of positive Cu+ ions, which determines the breakdown acceleration. Good Cu+ ions drift barrier layers are required as reliable interconnects using thin TaN and Ta layers. Thermal stabilities of Cu-contacted n+-p junctions with tungsten nitride (WNx) diffusion barriers deposited at various nitrogen flow ratios are investigated. N2O plasma treatment is applied to improve thermal stability and barrier performance of WNx film. Meanwhile, N2O plasma-treated W barrier has a nanostructured surface layer and shows high thermal stability and best barrier properties. Also investigated herein are the lattice and grain boundary diffusivities extracted from the Cu penetration depth profiles using the Whipple analysis of grain boundary diffusion and Fick’s second law of diffusion.