摘 要
本研究是利用場發射式電子顯微鏡(FEG-TEM)、X光繞射儀(XRD)與四點探針(Four point probe)來探討銅鎂合金之抗氧化性、熱穩定性與電性。製程上首先以熱氧化法生成一厚度約300 nm的二氧化矽介電層,接著以離子電漿沈積法(IMP)成長奈米晶粒結構的TaNX擴散阻礙層,最後再以濺鍍的方式沈積銅(2at.%鎂)合金。本次實驗將銅鎂合金施以4種不同氣氛或程序的退火處理,研究不同的熱處理方式對於結構特性的影響。
單純氮氣退火熱處理的合金試片在退火溫度達700℃之際仍有效的阻擋氧與試片的作用,由XRD繞射圖中並無發現銅或鉭的氧化物特徵峰;而800℃退火後,銅膜則由於表面能因素已經聚集成團狀。沒有了氧化鎂鈍化層保護,阻礙層Ta2N會先氧化成Ta2O5再與氧化鎂作用產生MgTa2O6的氧化物。
試片若先行進行400℃氮氣氛圍、30分鐘的預退火處理,則可於試片表面成長一層氧化鎂鈍化層,如此一來能更有效的阻擋氧與試片間的作用;再者預退火試片經800℃退火後,由於氧化鎂層有較低的表面能,以致於高溫退火後仍能保持相當的平整同時可明顯的降低銅膜結團的情形。
真空下退火銅鎂合金試片則可以獲得最佳的熱穩定性與電性。真空中退火即使在800℃時,Ta2N仍十分的穩定,並無氧化的現象,並且銅膜也維持非常的平整,惟局部位置銅已經穿越阻礙層到達阻礙層/二氧化矽之介面。推論Ta2N相較於MgTa2O6或Ta2O5與銅膜間有更好的附著性或較高之表面能,因此高溫熱處理後銅膜依舊可擁有平整的型態。
而真空預退火理論上可加速鎂原子往銅表面移動,所以可更快速、有效的形成氧化鎂鈍化層,降低氧與試片之作用並且增加結構的熱穩定性,然而實際的效果卻十分有限。由於在真空環境中退火氧化鎂無法形成足夠抵擋氧化所需的厚度,因此阻礙層在800℃退火後一樣會有氧化的情況發生。阻礙層氧化會降低與銅膜間的附著性又無氧化鎂層來抑制銅膜的凝聚、結團,因此就如同單純氮氣退火的例子,在800℃高溫退火後結構會完全的崩潰。
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