碳化矽背晶研磨拋光與Ti/Ag奈米孿晶鍍膜及其與DBC陶瓷基板固晶接合

Abstract

隨著積體電路電子元件的蓬勃發展，在高溫高電力的電子裝置產業，如電動汽車、風力發電機、5G通訊領域等領域，對於元件的能源轉換效率問題越來越重視，傳統的矽逐漸無法滿足新興科技的需求，使得寬能隙半導體備受重視，如碳化矽與氮化鎵，在元件設計上，由於高功率元件為滿足耐高壓的需求，多採取垂直結構，晶圓後端在背晶研磨(BG)與背晶金屬化(BM)製程的品質與性能，將是影響功率模組可靠性的重要因素。 本研究首先探討拋光漿料使用不同磨粒種類、磨粒尺寸對化學機械拋光後晶圓性質的影響，結果顯示需要存在硬度較高的氧化鋁磨料作為主要材料移除源，此外同時使用氧化鈰大尺寸磨料會造成材料表面粗糙值提升，低濃度的氧化鋁和氧化鈰組合可以達成最佳品質的表面粗糙度，並以此為關鍵因素選用適當濃度的15%wt氧化鋁，深入分析添加氧化鈰對拋光製程的影響，結果發現添加氧化鈰的拋光漿料可上升一倍才料移除率，且同時能維持在中心位置有1.9 Å的高表面粗糙度品質，最後研究還發現晶圓邊緣位置由於翹曲會使表面粗糙度上升，本研究使用雙面研磨拋光方法降低晶圓邊緣處的翹曲程度，最終在邊緣處表面粗糙度可以大幅下降，能得到2.73 Å的表面粗糙度值。 此外本研究利用磁控濺鍍法製備(111)高密度銀奈米孿晶，藉由改變製程基板偏壓進行微結構的觀察，結果顯示基板偏壓在一定限度內，會因為給予沉積薄膜的壓應力提升，而產生較高比率的(111)奈米孿晶，結果顯示在-175 V基板偏壓可濺鍍出最高密度之奈米孿晶結構，但是當基板偏壓高到-200 V，氬離子攜帶過多的動能也可能會破壞孿晶結構，形成過強的再濺鍍效應，降低沉積速率同時讓孿晶結構無法穩定成長，因此薄膜中孿晶的比例又下降，透過EBSD技術分析可得知該薄膜內部有高比例的孿晶結構且表面呈現(111)取向的晶格，由於同時存在高擴散速率的(111)晶格取向與孿晶的熱穩定性結構，銀奈米孿晶薄膜是一種具有低溫接合與高溫運用的特殊結構，在工業接合應用上具有巨大的潛力。 本研究根據先前得到銀孿晶薄膜特性，為了驗證其低溫接合的可行性，與樂鑫公司合作使用在碳化矽晶圓蒸鍍高(111)銀奈米孿晶薄膜，並利用納美仕公司開發奈米銀燒結膏，與DBC陶瓷基板進行低溫固晶接合研究，結果發現在250℃時，銀奈米薄膜能與銀奈米顆粒形成良好的燒結作用，在介面處僅存在微小且獨立的小孔隙，接合強度更是高達38.8MPa，相較一般使用的Ti/Ni/Ag背晶金屬化結構，介面處仍存在明顯空隙且接合強度僅為28.2MPa，證明銀奈米孿晶薄膜有更好的低溫接合性能，再加上FIB離子影像觀察孿晶結構仍然存在，因此證明銀奈米孿晶在背晶金屬化製程具有極大的可行性與應用價值。

The vigorous development of integrated circuit and discrete electronic components, in the high-temperature and high-power electronic devices industry, such as electric vehicles, wind turbines, 5G communications and other fields, more and more attention is paid to the energy conversion efficiency. Traditional silicon is gradually unable to meet the needs of emerging technologies. Wide bandgap semiconductors, such as silicon carbide and gallium nitride, have attracted much attention. In terms of component design, since high-power components often adopt vertical structures to sustain the demand for high voltage, the back-end of the wafer is also important key process. The quality and performance of the back grinding (BG) and back metallization (BM) processes will be important factors affecting the reliability of power modules. This study first explores the impact of different abrasive grain types and abrasive grain sizes used in polishing slurries on the properties of SiC after chemical mechanical polishing. The results show that aluminum oxide abrasives with higher hardness are required as the main material removal source, and cerium oxide is also used. Large-sized abrasives will increase the surface roughness of the material. The combination of low-concentration alumina and cerium oxide can achieve the best quality surface roughness. Using this as a key factor, select an appropriate concentration of 15%wt alumina, and conduct an in-depth analysis of the addition of oxide. The impact of cerium on the polishing process. It was found that adding cerium oxide to the polishing slurry can double the material removal rate while maintaining a high surface roughness quality of 1.9 Å at the center. Finally, the study also found that the wafer edge The surface roughness will increase due to warping. This study uses double-sided grinding and polishing method to reduce the degree of warpage at the edge of the wafer. Finally, the surface roughness at the edge can be greatly reduced, and a surface roughness value of 2.73 Å can be obtained. In addition, this study used magnetron sputtering to prepare (111) high-density silver nanotwins. The microstructure was observed by changing the substrate bias in the process. The results showed that within a certain limit, the substrate bias would cause the deposition of thin films to the compressive stress increases, resulting in a higher ratio of (111) nanotwins. The results show that the highest density nanotwin structure is visible at -175 V substrate bias. However, when the substrate bias reaches -200 V, argon Excessive kinetic energy carried by ions may also destroy the twin structure and form an excessively strong re-sputtering effect, which reduces the deposition rate and prevents the stable growth of the twin structure. Therefore, the proportion of twins in the film decreases. Analysis through EBSD technology It can be seen that the film has a high proportion of twin structures inside and a (111) oriented lattice on the surface. Due to the simultaneous existence of a high diffusion rate (111) lattice orientation and the thermal stability structure of twins, silver nanotwins thin film is a special structure capable of low-temperature bonding and high-temperature application, and has great potential in industrial bonding applications. Based on the previously obtained characteristics of silver twinned films, this study cooperated with Espressif to evaporate high (111) silver nanotwinned films on silicon carbide wafers to verify the feasibility of low-temperature bonding, and used Namex Developed nano-silver sintering paste and conducted low-temperature bonding research with DBC ceramic substrates. It was found that at 250°C, the silver nanofilm can form a good sintering effect with the silver nanoparticles, and there are only tiny and independent lags at the interface. Small pores, the joint strength is as high as 38.8MPa. Compared with the commonly used Ti/Ni/Ag backside metallization structure, there are still obvious gaps at the interface and the joint strength is only 28.2MPa, proving that the silver nanotwin film has better The good low-temperature bonding performance, coupled with the fact that the twin structure still exists according to FIB ion imaging, proves that silver nanotwins have great feasibility and application value in the backside metallization process.