三維積體電路技術之銅/銦金屬低溫接合面研究

Abstract

本論文主要為研究三維積體電路中銅銦接合面的形成機制。在用穿透式電子顯微鏡儀器來元素分析時，發現在銅銦接合面有異常的變化。本研究利用設計的兩種接合結構Cu-O-Cu/In 和Cu/In-O-In確定原生氧化物是造成接合面的主要原因，並了解了原生氧化物不只在固態接合上會造成影響，在固液態接合上也會影響。此外，在這兩種結構中，氧化銦和氧化銅都會造成這樣的現象，氧化銅會因為活性的關係被還原成銅，銦被氧化成氧化銦。 接合完成以後，除了接合面有氧化銦外，其餘銅銦金屬形成合金。但是，氧化銦在沒有破裂的情況下會阻礙銅銦擴散，同時在沒有破裂的氧化銦之後有一塊沒有形成合金的金屬。本研究結果顯示，良好的接合強度其接合時的壓力必須大到讓氧化膜破裂，所以如果氧化層太厚，將導致無法接合。另外，接合前使用表面清理和或是減少表面在大氣下暴露的時間將有助於提升接合的品質。

This thesis focuses on the mechanism of interface behavior between copper and indium during low temperature bonding in three-dimension integrated circuits (3D IC). The phenomenon of the unusual atomic percentage variations at the bonding interface is investigated by TEM. Two bonding schemes, Cu-O-Cu/In and Cu/In-O-In, verify that the native oxide on metal surface influences on not only solid-solid bonding but also solid-liquid bonding. In addition, it is found that both indium (III) oxide In2O3 and cuprous oxide Cu2O will cause the phenomenon. Using EELS, there is only In2O3 at the bonding interface due to redox reaction between Cu2O and In to form In2O3 and pure Cu because of higher active energy of indium than copper’s. During bonding, Cu and In react and form the intermetallic compounds (IMC); however, the existence of amorphous indium oxide at the bonding interface will block the diffusion of copper and indium unless the plastic deformation and crack of oxide film during bonding. When indium diffusion is blocked by oxide, the regions of copper behind the oxide film will not turn into IMC. An area of pure Cu surrounded by IMC is found in origin copper region. According to this research, the bond pressure and thickness of oxide film are important to make sure the crack of oxide film. Finally, the surface treatment and ambient time are both significant to decide the bond quality.