利用結構設計進行先進低溫銅對銅直接接合技術並用於三維異質整合之模擬研究與製程開發

Abstract

在過去四十年中摩爾定律在半導體產業發展中扮演相當重要的推力。當電子元件微縮時，在傳統二維積體電路就會遇到物理極限以及高製程成本等問題。因此，三維積體電路就被發展以延伸摩爾定律。同時三維積體電路擁有較低的功率損耗以及高異質整合能力。在三維積體電路各項關鍵技術中，金屬與金屬接合可以達成垂直方向電性連接及穩固的機械強度，因而廣泛被使用在先進封裝。考慮材料特性後，銅與銅接合因為擁有良好的導電及導熱特性，因此被選為這篇論文中接合的材料。 在傳統銅與銅直接接合中， 300°C的高溫會造成電子元件的損壞以及對準精度下降等問題。因此插入接合等低溫銅對銅直接接合被發展以解決高溫接合的問題 可是這種低溫接合仍有其缺點，因此這篇論文主要研究低溫銅柱和銅凹洞銅銅接合同時達到低成本以及更廣泛的使用。 本篇論文成功展示在達到在一大氣壓下、200°C的接合溫度、接合時間十分鐘的環境中，利用銅柱和銅凹洞，結合在矽基板上的高分子層，使低溫的銅-銅直接接合開發成功。同時本篇論文利用有限元素分析模擬方法，探討銅柱和銅凹洞在製程過程中的非理想效應，其所造成的銅柱直徑改變和銅凹洞側壁斜度改變，對於接合的影響。為了增加接合良率，銅柱直徑、銅凹洞側壁斜度、銅凹洞開口形狀、添加額外高分子層、熱壓溫度以及銅柱銅凹洞結構的間距等參數均包括在模擬內。相較於傳統接合以及前述的低溫銅對銅直接接合方法，此篇論文提出的結構能夠達到低溫接合，未來可應用於各式基板、可簡化製程、具高表面粗糙容忍度，以及未來應用於無焊錫上。

Three-dimensional integrated circuits (3D ICs) is explored with the advantages of low RC delay and potential heterogeneous integration applications. Among key technologies in 3D integration, metal-to-metal direct bonding using especially Cu is a favorable choice in consideration of cost, electrical performance, reliability, and thermal conductivity. In traditional thermal-compression bonding including low temperature Cu-Cu direct bonding methods, concerns such as high cost still exist. This thesis investigates Cu-Cu direct bonding using pillar-concave structure to realize low bonding temperature with lower cost and wider applications. Direct Cu-to-Cu bonding at low temperature of 200°C for 10 min under atmospheric pressure using pillar-concave structure on silicon with polymer layer has been developed and investigated for 3D integration. As compared to pillar-concave structure on silicon without polymer layer, the proposed method can greatly reduce the bonding duration. In order to discuss the influence of bonding parameters variations on the bonding result, FEM simulations are also presented on both condition of silicon with and without polymer layer. Changes of parameters in FEM simulations are also investigated for further enhancement on the bonding outcome. Simulation parameters include the pillar diameter, the sidewall angle of concave, the shape of the concave opening, the addition of extra material above original polymer or silicon layer, the bonding temperature, and the pitch of the pillar-concave structure. The deviation of pillar diameter and the concave sidewall angle would not aggravate Cu-Cu direct bonding result. The alteration of concave opening and the addition of multilayer can enhance the bonding outcome. For future low temperature Cu direct bonding, the main requirement is the growth of recrystallized grains. The pillar-concave bonding method presented in this thesis is helpful for the future fine pitch application. As compared to the mentioned traditional Cu bonding structure and approaches, method proposed in this thesis can achieve low temperature bonding with promising applicability on various kinds of substrates along and high tolerance of Cu surface for future manufacturing of solder free interconnect.