三維積體電路技術之銅/銦金屬低溫接合研究

Abstract

銅，具有低電阻率、高電子遷移電阻抗等特性，在半導體產業中被廣泛應用作為連線(interconnect)的材料，並被研究、發展於三維整合結構中，以提供尺寸小及高效能的元件。銅-銅接合可提供良好的電性及接合強度以因應後續半導體製程之應用，但所需的接合溫度高於300 ℃，容易導致殘留熱應力 (residual thermo-stress)及熱損害(thermal damage)，使應用受到限制，因此極需發展低溫接合(<180 ℃)的技術以利其在三維整合結構上之應用。 本論文主要為研究金屬材料在低溫下之接合，銦具有低熔點(156.6 ℃)的特性，被選用作為低溫接合的材料。銅-銦接合形成之合金結構，其熔點高，可承受後續半導體產業之高溫製程，且具有阻值低(0.03Ω)、穩定性高等特性，經過一系列可靠性分析，其中包含長時間電流、溫度循環及溼度測試，證明此設計的銅-銦結構可提供良好的接合品質，並期望未來能發展、應用於3DIC相關產品上。

Copper, the mainstream interconnect material used in semiconductor industry with low resistivity and high electro-migration resistance, has been developed for 3D integration in order to fabricate devices with small form factor and high performances for different applications. Direct Cu-Cu bonding can provide good electrical connection and sufficient bonding strength for follow-up processes; however, the required bonding temperature is higher than 300 ℃, which may lead to residual thermo-stress and thermal damages. Therefore, it will be more beneficial to develop a low temperature bonding at less than 180 ℃ for 3D IC integration The main study is focused on the investigation of metal to metal bonding at low temperature. Indium, owing to its low melting temperature (156.6 ℃), can be an attractive option for low temperature bonding technology. The intermetallic compounds formed in the Cu-In bonded structures with high melting temperature can endure a higher following processing temperature; besides, the bonded structure has the characteristics of low contact resistance (~0.03 Ω) and high electrical stability. Through a series of reliability tests, including current stressing, temperature cycling, and humidity tests, the results prove that the Cu-In bonded structure can provide good bonding quality. We expect that this bond scheme may provide useful guidelines and information for low temperature bonding (<180 ℃) in 3D interconnects.