氧化效應在銅／鉭／矽基材和銅／鉭／二氧化矽／矽基材之界面反應影響研究

The effect of oxygen on the interfacial reactions of Cu/Ta/Si and Cu/Ta/SiO2/Si multilayers

本研究目的是以離子化金屬電漿沈積法（IMP）成長奈米晶粒β相金屬鉭膜，作為積體電路上金屬銅導線製程的擴散障礙層之熱穩定性研究；且分別成長(1)銅／鉭／二氧化矽／矽基材，(2)銅／鉭／矽基材和氮化矽／銅／鉭／矽基材等兩大類不同的結構。所有試片在不同氧含量環境下及不同退火溫度下退火30分鐘後，作成電鏡試片放入配有X射線能量分佈儀（EDS）和能量過濾器（Energy Filter）的場發射穿透式電子顯微鏡（FEGTEM）進行觀察。結果在銅／鉭／二氧化矽／矽基材和在銅／鉭／矽基材的退火試片中均發現退火爐中少量的氧氣氛會經由銅的晶界擴散到銅／鉭界面上，由於鉭的親氧性而形成非晶質的氧化鉭薄膜，此氧化層會隨退火溫度上升而增厚、隨較佳的真空度而減薄。在有氮化矽膜隔絕氧的作用下，其鉭的主要失效機制由鉭膜與矽產生的矽化反應所主導。而鉭膜可以承受600℃退火三十分鐘而不失效。在沒有氮化矽膜隔絕氧的作用下，則氧會加強鉭矽界面的矽化反應導致擴散障礙層失效溫度降低和失效行為嚴重。因此氧在退火中所扮演的角色是在失效溫度之下以氧化形式出現，在失效溫度則會加強矽化反應導致銅提早穿過擴散障礙層引發失效行為。

This study investigates the thermal stability of the Ta diffusion barrier layer grown by IMP deposition on VLSI Cu metallization process. Two types of structures: (1) Cu/Ta/SiO2/Si, (2) Cu/Ta/Si and silicon nitride/Cu/Ta/Si were examined after annealed 30 minute at different temperatures and/or in different oxygen ambients by the field-emission transmission electron microscopy equipped with X-ray energy dispersive spectrometer and energy filter. According to the results, the residual oxygen in the furnace was found to be able to diffuse toward to the interface of the Ta and Cu via grain boundaries of Cu grains, and then reacted with Ta to form an amorphous Ta oxide layer. The thickness of the amorphous Ta oxide layer increased with increasing annealing temperature but decreased with better vacuum. Moreover, Ta layer could resist the oxidation under 30 minute annealing at 600C with the silicon nitride capped layer. It indicates that the silicidation of the Ta and Si can dominate the failure mechanism in this case. On the other hand, oxygen would enhance the silicidation and thus lead to a significant failure of the diffusion-barrier layer without the silicon nitride capped layer. Consequently, oxygen would react with Ta barrier layer to form a oxide phase below the failure temperature but enhanced the silicidation to activate Cu to diffuse through the diffusion barrier layer and resulted in the failure above the failure temperature.