評估錸膜與含氧錸膜應用於銅金屬化之擴散阻障層特性研究

Abstract

在未來超大型積體電路元件中，銅導線因其具有更佳的導電性及抗電致遷移的能力而將取代鋁導線，但銅極容易擴散進入矽基材，為克服此一問題，必須在矽與銅之間尋求一具有低電阻係數、高熱穩定性及良好界面附著性的擴散阻障層。本實驗主要是在探討以Re與Re(O)薄膜做為銅與矽之間擴散阻障層的反應，由擴散、相變化的觀點來討論其變化。所採用的鍍膜結構如下： Cu (100 nm) / Re (50 nm) / SiO2 (20nm) / Si Cu (100 nm) / Re (20 nm) / SiO2 (20nm) / Si. Cu (100 nm) / Re(O)-4﹪O2 (20 nm) / SiO2 (20nm) / Si Cu (100 nm) / Re(O)-1﹪O2 (20 nm) / SiO2 (20nm) / Si 銅膜及阻障層以濺鍍法沉積。對試片做300~800℃/ 30分鐘的氮氣氣氛退火處理，以四點探針量測片電阻，掃瞄式電子顯微鏡（SEM）用來觀察銅膜表面型態，歐傑電子能譜儀（AES）做成分縱深分析，X光繞射儀（XRD）做相的鑑定，並利用穿透式電子顯微鏡（TEM）做鍍膜截面的觀察，分析各層結構的變化。 研究結果顯示這幾種不同的結構在退火後有不同的行為，Cu (100 nm) / Re (50 nm) / SiO2 (20nm) / Si結構與Cu (100 nm) / Re(O)-4﹪O2 (20 nm) / SiO2 (20nm) / Si結構在800 ℃/30分鐘退火後片電阻值明顯上升，Cu (100 nm) / Re (20 nm) / SiO2 (20nm) / Si.結構在750 ℃/30分鐘退火後片電阻值有明顯的上升，Cu (100 nm) / Re(O)-1﹪O2 (20 nm) / SiO2 (20nm) / Si在700 ℃/30分鐘退火後片電阻值開始上升，其造成電阻上升的原因為表面銅膜產生球化不連續的結團所導致。比對XRD、AES、TEM的結果，各結構在退火溫度750 ℃以上，阻障層與銅膜並無產生反應，顯示阻障層仍能維持其熱穩定性。 由實驗結果可知Cu / Re / SiO2 / Si 結構與Cu / Re(O) / SiO2 / Si皆具有低電阻、高熱穩定性，其鍍膜結構變化將於本文中討論。

In future ULSI devices copper will replace aluminum as the conducting metal due to their better conductivity and superior resistance to electromigration. The difficulty is that copper diffuses with extreme ease into silicon and this cannot be tolerated. The problem to be solved here is to find a diffusion barrier between copper and silicon which should have low resistivity, high thermal stability, and good adhesion with copper and substrate. In this study, we investigated the diffusion barrier properties of Re and Re(O) thin films for Cu metallization in ULSI circuit devices. The following structures , Cu (100 nm) / Re (50 nm) / SiO2 (20nm) / Si, Cu (100 nm) / Re (20 nm) / SiO2 (20nm) / Si, Cu (100 nm) / Re(O)-4﹪O2 (20 nm) / SiO2 (20nm) / Si, Cu (100 nm) / Re(O)-1﹪O2 (20 nm) / SiO2 (20nm) / Si, were deposited by DC sputtering. Annealing was carried out in nitrogen at temperatures ranging from 300 to 800 ℃ for 30 min. Sheet resistances were measured by a four-point probe method. Copper surface morphplogy was inspected by scanning electron microscopy. Auger electron spectroscopy was used to evaluate the inter-diffusion across the interfaces by the compositional depth profile. The phase identification was performed by XRD. The microstructure was investigated by cross-sectional transmission electron microscopy with X-ray energy dispersive spectroscopy. Sheet resistance measurement and microstructural characterization show that these structures have different behaviors after annealing. The sheet resistance of Cu (100 nm) / Re (50 nm) / SiO2 (20nm) / Si and Cu (100 nm) / Re(O)-4﹪O2 (20 nm) / SiO2 (20nm) / Si increased steeply after 800 ℃/30 min annealing. The sheet resistance of Cu (100 nm) / Re (20 nm) / SiO2 (20nm) / Si and Cu (100 nm) / Re(O)-1﹪O2 (20 nm) / SiO2 (20nm) / Si increased after annealing at 750 ℃ and 700 ℃ respectively. The resistance increase was due to the spheroidization of Cu thin film. The results of XRD, AES, and TEM analyses indicated all barriers remains stable up to 750 ℃/30 min annealing. From these results, the both structures of Cu / Re / SiO2 / Si and Cu / Re(O) / SiO2 / Si have low resistivity, high thermal stability. The difference between all structures will be discussed.