毒化效應對銅電遷移的影響

Abstract

使用低電阻之導體和低介電常數之金屬佈局能解決RC延遲以及增進電遷移的抵抗能力。本研究中，使用純銅當導線及低介電常數的聚亞醯胺或二氧化矽當介電材質的結構來量測電遷移現象。由TGA，DTA，和DSC觀察聚亞醯胺的熱穩定性且從FTIR瞭解聚亞醯胺在熱處理過程中的鍵結變化。 由SIMS的原子縱向分析，可以觀察到在聚亞醯胺的固化處理時(curing)也對銅金屬造成破壞(毒化效應)。毒化效應會降低銅的導電性質即增強銅的電遷移破壞。因此本實驗中用一層二氧化矽來當擴散阻障層以降低毒化效應。 銅的電遷移實驗是在爐管中進行。使用聚亞醯胺或二氧化矽當保護層來防止在高溫電遷移實驗可能產生的氧化現象。電流密度為2x106A/cm2以避免因焦耳效應而混淆了電遷移實驗。電遷移的機制及活化能也將在本實驗中討論。

The use of low resistivity conductors and low dielectric constant interlevel dielectrics has been proposed to reduce the RC time delay and to improve electromigration (EM) damage. In this work, the metallization system with Cu and low K material, polyimide (PI), was prepared for electromigration tests. TGA, DTA and DSC revealed the thermal stability of polyimide and FTIR revealed the chemical structure transformation of polyimide in thermal process. Poison effect was observed during curing of polyimide and was investigated by secondary ion mass spectrometer (SIMS). It is observed that poison effect degraded the electric property of copper line and enhanced electromigration damage (EMD). Hence, a layer of thin SiO2 as diffusion barrier was deposited between polyimide and Cu in order to reduce poison effect. Electromigration of Cu interconnection was studied by an isothermal electrical resistance method. Electromigration of copper line with polyimide/SiO2, polyimide and SiO2 as passivation layers had been proposed to inhibit oxidation during high temperature electromigration measurement. As current density was below 2x106A/cm2, the raising temperature resulted from joule heating was too small to induced thermomigration. The activation energy and the mechanisms of electromigration were discussed. Keyword: Electromigration, Poison effect, Thermomigration,