Barrier properties of Ta and TaN bilayers in Integrated Circuit Cu Metallization System
|關鍵字:||銅金屬化;擴散障礙層;copper metallization;diffusion barrier|
1. Cu(100nm)/TaN(20nm)/(SiO2 20nm)/Si
2. Cu(100nm)/TaN(10nm)/Ta(10nm)/(SiO2 20nm)/Si
3. Cu(100nm)/Ta(10nm)/TaN(10nm)/(SiO2 20nm)/Si
銅膜及障礙層以濺鍍法沈積後，對試片做450~850℃ / 30分鐘的真空退火處理，以四點探針量測片電阻，歐傑電子能譜儀(AES)、二次離子質譜儀（SIMS）做成分縱深分析，場發射電子顯微鏡（FE-SEM）觀察表面銅膜的變化，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/Ta /TaN/Si、Cu/Ta/TaN/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，障礙層產生氧化；Cu/TaN/Ta/Si、Cu/TaN/Ta /SiO2/Si在700℃退火後仍能保持其熱穩定性，750℃/30分鐘退火後，Cu/TaN/Ta/Si 在表面及矽基材中已有反應物析出，Cu/TaN/Ta/SiO2/Si 的銅與障礙層界面情況改變。
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/Ta and Ta/TaN bilayers for Cu metallization in ULSI circuit device. The following structures, Cu(100nm)/TaN(10nm)/Ta(10nm)/Si, Cu(100nm)/TaN (10nm)/Ta(10nm)/SiO2(20nm)/Si, Cu(100nm)/Ta(10nm)/TaN(10nm)/Si, and Cu(100nm)/Ta(10nm)/TaN(10nm)/SiO2(20nm)/Si, were deposited by DC sputtering. Annealing was carried out in a vacuum furnace at temperatures from 450℃ to 850℃ for 30min. Sheet resistance was measured by a four-point probe method. The morphologies of the surfaces of the Cu films were observed by scanning electron microscopy. Auger electron spectroscopy and secondary ion mass spectrometry were used to evaluate the inter-diffusion across interfaces by the compositional depth profile. The interfacial reaction between layers were 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/Ta/TaN/Si and Cu/Ta/TaN/SiO2/Si were failed after 650℃/30min annealing as a result of oxidation, while those of Cu/TaN/Ta/Si and Cu/TaN/Ta/SiO2/Si can be stable up to 700℃. After 750℃/30min annealing, precipitates were observed in the Cu film and within the Si matrix in Cu/TaN /Ta/Si structure, and the interface between Cu and barrier in the Cu/TaN/Ta SiO2/Si structure also changed. From these results, TaN/Ta is a better choice than Ta/TaN because its higher thermal stability. The reasons for the difference between these two barrier structures will be discussed. It is suggested that nitrogen and oxygen elements play important roles on the thermal stability.