無電鍍鈷鎢磷與鎳磷薄膜之微觀結構對擴散阻障能力影響之研究

Abstract

本論文研究不同微觀結構之無電鍍鈷鎢磷（Electroless Co（W,P））與鎳磷（Electroless Ni（P））薄膜對銲錫（Solder）之擴散阻障性質及界面反應，以了解其應用於銅製程覆晶接合（Flip-chip Bonding，FC）之底部金屬化（Under Bump Metallurgy，UBM）之可行性。實驗先在預鍍鈦、銅的矽晶片上長成無電鍍Co(W,P)或Ni(P)薄膜，藉由改變鍍液的溫度、pH值等條件製成不同磷含量之非晶（Amorphous）與複晶（Polycrysatlline）等無電鍍層，接著鍍上錫銀銅（Sn-3.0Ag-0.5Cu）或共晶錫鉛（37Pb-63Sn）銲錫，經250□C、1小時之液態時效（Liquid-state Aging）與150□C、1000小時之固態時效（Solid-state Aging）後，再分析無電鍍層與銲錫之界面反應以了解其擴散阻障性質。經液態時效後，複晶Co(W,P)與SnAgCu界面形成約5 □m厚之CoSn3介金屬化合物（Intermetallic Compound，IMC），且其隨熱處理時間增長而增厚，IMC與複晶Co(W,P)界面則出現富鎢層；在Co(W,P)為非晶時，介金屬相則球化（Spallation）進入銲錫區，IMC與非晶Co(W,P)界面則出現富磷層；在固態時效部分，複晶與非晶Co(W,P)與SnAgCu界面均形成約2至3 □m厚之(Cu,Co)6Sn5。在Ni(P)薄膜部分，無論其結構為何，經液態時效後其與PbSn界面均形成約2至3 □m厚之Ni3Sn4介金屬相，但1小時後不再增厚；介金屬相與Ni(P)之間出現富磷層，磷的累積量與Ni(P)之原始磷含量有關。在固態時效之各種Ni(P)薄膜試片中亦見到類似結果。無論Co(W,P)或Ni(P)薄膜結構為何，其阻擋銲錫的擴散均以犧牲型阻障層為主要機制，但以非晶結構之消耗率最慢，故為最理想之阻障層微觀結構。

This work studies the diffusion barrier properties of electroless Co(W,P) and Ni(P) layers to lead-free SnAgCu or eutectic PbSn solder so as to explore their applicability to under bump metallurgy (UBM) for flip-chip Cu-ICs. First, Co(W,P) or Ni(P) layers with various phosphorous contents i.e., the electroless layers with various microstructures including amorphous, or polycrystalline, was grown on the Si substrate coated with a Ti/Cu layer. After depositing the SnAgCu or PbSn solder, the samples were subjected to liquid-state aging at 250□C for 1 hr and solid-state aging at 150□C up to 1000 hrs, respectively. Interfacial reactions between electroless layers and solder were then analyzed and the diffusion barrier mechansim was discussed. For the samples subjected to liquid-state aging, annealed at 250□C, about 5-□m thick CoSn3 intermetallic compound (IMC) formed at SnAgCu/poly-Co(W,P) interface and its thickness increased with the time of aging treatment. A tungsten-rich (W-rich) layer formed in between IMC and poly-Co(W,P). As to the SnAgCu/amorphous-Co(W,P), the CoSn3 IMC spalled into the solder and a phosphorous-rich (P-rich) layer formed in between IMC and morphous-Co(W,P). In the Co(W,P) samples subjected to solid-state aging, about 2~3 □m thick (Cu,Co)6Sn5 IMC formed at interface regardless of the microstructure of Co(W,P). In the case of Ni(P), about 2~3 □m Ni3Sn4 IMC formed at PbSn/Ni(P) interface regardless of the microstructure of Ni(P) and aging test type. A P-rich layer was also observed in between IMC and Ni(P) and its phosphorous content was related to that in Ni(P) layer. Analytical results indicated that both Co(W,P) and Ni(P) mainly serve as the sacrificial type barrier; however, the amorphous layers the preliminary choice of diffusion barrier since it exhibited the slowest consumption rate in comparison with the polycrystalline layers.