SiC 晶背金屬層優化與銀奈米孿晶低溫接合研究

Abstract

本研究針對SiC與Sapphire基板的晶背金屬層架構進行優化。SiC是功率元件所採用的基板，晶背金屬層的品質成為決定元件可靠度的要素之一，因此本研究針對Ti/Ni/Ag、Ti/Ni/Ag/Sn、Ti/Ni/Cu/Ag與Ti/Ni/Cu/Ag/Sn 結構進行探討，分析濺鍍與蒸鍍製程的差異。而Sapphire是LED所用的基板材料，本研究將探討銀奈米孿晶在Sapphire基板上沉積與低溫直接接合的影響。 薄膜的品質會受到原子動能影響，原子動能不足或太大可能會造成金屬層孔洞、甚或導致應力累積並導致成長突起。根據結構區域理論，提升基板溫度可以改變原子的擴散能力、施加基板偏壓與調整濺鍍功率能夠改變原子的動能甚至薄膜的應力，透過上述參數的調整可以調整金屬層與界面品質。此外，由於Ni/Cu互相固溶，因此會比不固溶的Ni/Ag界面有更好的剪力強度、提供元件更好的可靠度。蒸鍍製程因為原子動能較低，因此可以得到較為緻密平整的金屬層。 Sapphire是LED元件的基板材料，在Sapphire基板上添加反射層可以增加元件的發光效率，由於銀具有所有金屬中最高的反射率，因此常被用作反射層材料。 銀具有低疊差能，容易製作出可以提升整體反射力的孿晶，並提高元件的光析出率，加上孿晶具有低移動力、低電阻與熱穩定性，可以提供元件可靠度、增加導電能力並且抑制電遷移的特性。本研究將利用濺鍍法製備銀奈米孿晶結構，並添加Ti薄膜作為黏著層來增加材料附著度，接著將銀奈米孿晶與Au-finished DBC基板進行250℃以下的低溫直接接合。由於Ag-Au可以互相固溶，加上高溫能夠提供原子更大的移動力，因此接合界面可靠度與品質會直接受到接合溫度影響，在250℃接合時可以得到最緻密的界面與最高的剪力強度。

This study focuses on optimizing the metal layer structure of SiC and Sapphire substrates. SiC is a substrate used in power devices, and the quality of the metal layer on the backside of the substrate is one of the determining factors for device reliability. Therefore, this study investigates the structures of Ti/Ni/Ag, Ti/Ni/Ag/Sn, Ti/Ni/Cu/Ag and Ti/Ni/Cu/Ag/Sn and analyzes the differences between sputtering and evaporation processes. Sapphire is a substrate material used in LEDs, and this study examines the deposition of silver nanotwinned crystals on Sapphire substrates and low-temperature direct bonding. The quality of thin films is influenced by atomic kinetic energy. Insufficient or excessive atomic kinetic energy may result in voids in the metal layer or even lead to stress accumulation and hillock growth. According to the theory of structural zones model, increasing the substrate temperature can change the diffusion capability of atoms. Applying substrate bias and adjusting sputtering power can alter the atomic kinetic energy and even the stress of the thin film. By adjusting these parameters, the quality of the metal layer and interface can be controlled. In addition, since Ni and Cu are mutually solid soluble, the Ni/Cu interface provides better shear strength compared to the non-soluble Ni/Ag interface. Besides, the evaporation process results in a denser and smoother metal layer due to lower atomic kinetic energy. Sapphire is a substrate material for LED devices, and adding a reflective layer on Sapphire substrates can increase the device's light-emitting efficiency. Silver has the highest reflectivity among all metals and is commonly used as a reflective layer material. Silver has low stacking fault energy, making it easy to produce nanotwinned crystals that enhance overall reflectivity and increase the light extraction efficiency of the device. Moreover, nanotwinned crystals exhibit low mobility, low resistance, and thermal stability, contributing to device reliability, improved conductivity, and suppression of electromigration. This study focuses on the preparation of silver nanotwinned crystals structures and adds a Ti thin film as an adhesive layer to enhance material adhesion. Subsequently, the silver nanotwinned films are directly bonded to Au-finished DBC substrates at temperatures below 250°C. Since Ag and Au can form a solid solution, and higher temperatures provide greater atomic mobility, the reliability and quality of the bonding interface are directly influenced by the bonding temperature. The densest interface and highest shear strength can be achieved when bonding at 250°C.