銅導線之鈦及氮化鉭複合層擴散障礙特性研究

Abstract

摘 要 在目前超大型積體電路的發展中，以銅取代鋁，做為連接導線材料已成為必然的趨勢。為了克服銅與矽基材間相互擴散的問題，必須在銅與矽間鍍上具有高熱穩定性、良好界面接合性及低電阻係數的擴散阻障層。本實驗在探討以Ti及TaN複合層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： 1. SiNx /Cu(100nm) /TaN(10nm) /Ti(10nm) /(SiO2 20nm) /Si 2. SiNx /TaN(20nm) /Ti(20nm) /(SiO2 20nm) /Si 3. SiNx /TaN(50nm) /Ti(50nm) /(SiO2 20nm) /Si 銅膜及阻障層以濺鍍法沈積後，對試片做400~800 ℃ / 30分鐘的氮氣氣氛退火處理，以四點探針量測片電阻，歐傑電子能譜儀(AES) 做成分縱深分析，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 /TaN /Ti /SiO2 /Si在400-600 ℃退火後電阻降低，650 ℃ / 30分鐘退火後電阻明顯上升，阻障層產生變化；TaN(50nm)/ Ti(50nm)/ SiO2 /Si、TaN(20nm) /Ti(20nm) / SiO2 /Si在450 ℃電阻上升，500-800 ℃退火後電阻降低。 由實驗結果可知TaN(20nm)比TaN(10nm) /Ti(10nm) /SiO2 /Si結構有較佳的熱穩定性，因退火過程中，TaN/Ti阻障層產生變化，變化原因將於本文中討論，氮與氧兩種元素在其中扮演主要的角色。

Abstract Cu is expected to be adopted in deep submicron ultra-large scale integration metallization due to its lower resistivity and better reliability than conventional Al alloys. Since copper diffuses fast in Si and introduce deep-level traps, a proper diffusion barrier is needed. The barrier should have high thermal stability, low resistivity, and good adhesion with Cu and substrate. In this study, we investigate the diffusion barrier properties of TaN/Ti bilayers for Cu metallization in ULSI circuit device. The following structures are used: SiNx /Cu(100nm) /TaN(10nm) /Ti(10nm) /SiO2(20nm) /Si SiNx /TaN(50nm) /Ti(50nm) /SiO2(20nm) /Si SiNx /TaN(20nm) /Ti(20nm) /SiO2(20nm) /Si Copper and barriers were deposited by DC sputtering. Annealing was carried out in nitrogen at temperatures from 400 ℃ to 800 ℃ for 30 min. Sheet resistance was measured by a four-point probe method. Auger electron spectroscopy was used to evaluate the inter-diffusion across interfaces by the compositional depth profile. The phase identification of layers 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 barriers of Cu/TaN/Ti/SiO2/Si were failed after 650 ℃/30 min annealing as a result of barrier phase change. Sheet resistances of TaN(50nm) /Ti(50nm) /SiO2 /Si and TaN(20nm) /Ti(20nm) /SiO2 /Si increased after 450 ℃ and decreased after 500 ℃ to 800 ℃ annealing . From these results, TaN(20 nm) is better than TaN(10nm) / Ti(10nm) on the thermal stability. Barrier was changed during annealing .It is suggested that nitrogen and oxygen elements play important roles on the thermal stability.