碳化矽背晶鍍等軸粗晶與奈米孿晶Cu 薄膜及其與DBC陶瓷基板銀燒結固晶接合

Abstract

本研究的主要目標涉及利用磁控濺鍍製備具高密度（111）方向的奈米雙晶銅結構。這包括最佳化製程條件，從理論上解釋製程參數對奈米雙晶銅形成的影響，以及透過改變負基板偏壓和厚度來評估結構變化對薄膜性能的影響。此外，該研究還調查了接著層（鉻和/或鎳）對奈米雙晶銅生長的影響。其目的是確定沉積高品質奈米雙晶銅薄膜的最佳濺鍍參數。本研究也探討了此製程在碳化矽晶圓上生長（111）奈米雙晶銅結構的應用，以進行後續改進。 透過施加基板偏壓可以控制奈米雙晶結構和（111）表面取向的形成。具有高密度奈米雙晶結構的濺鍍銅薄膜，特別是在 -150 V 下在 SiC 基板上預塗鉻（Cr）的薄膜，表現出很大比例的 （111）取向。研究顯示 -150 V偏壓濺鍍的奈米雙晶銅薄膜具有用作低溫直接鍵結中間層的潛力。 擴展了先前濺鍍實驗的見解，樂鑫材料科技股份有限公司展開合作，目標是開發離子束輔助電子束蒸鍍，成功在4英寸碳化矽晶圓上製備高密度（111）取向奈米雙晶銅薄膜。微觀結構分析表明，晶圓上的薄膜具有優異的均勻性，表面（111）晶粒取向超過90%。 此外，本研究廣泛研究了燒結溫度和壓力對碳化矽/奈米雙晶銅（ SiC/nt-Cu）與使用 銀燒結（Ag-sintering）的 DBC 基板的鍵結特性的影響。研究內容包括不同燒結條件下鍵結SiC/nt-Cu/Ag-sintering/DBC 和SiC/Cr/nt-Cu/Ag-sintering/DBC 組件的結構完整性、空隙形成和界面特徵。研究結果強調了高密度（111）織構奈米雙晶銅薄膜對鉻/銅金屬化 SiC 晶片與 DBC 氧化鋁基板的銀燒結晶片黏接的顯著影響。 傳統細晶粒鉻/銅非奈米雙晶金屬化 SiC 晶片與奈米雙晶銅薄膜的銀燒結之間的比較揭示了顯著的差異。 微觀結構橫截面的掃描式電子顯微鏡影像顯示，與細長晶粒鉻/銅非奈米雙晶晶片相比，銀燒結高密度 (111) 取向 奈米雙晶銅結構的孔隙率降低了三倍。 令人印象深刻的是，在壓力下，與在相同條件下燒結的SiC/Cr/Cu 晶片相比，銀燒結的SiC/Cr/nt-Cu 晶片表現出明顯更高的剪切強度(42.8 MPa) ，相差18.5 MPa。 這些結果強調了高密度（111）織構奈米雙晶銅薄膜對銀燒結晶片鍵結的有利影響。

The continual escalation in demand for high power and high frequency in modern electronic devices has driven innovation in packaging technology and materials. Consequently, wide-bandgap semiconductors have gained prominence. In response to this evolution, the Backside Metallization process for wafers has been developed. The quality and performance of the metal layer on the wafer''s backside now play critical roles in ensuring the reliability of power modules. This research focuses on enhancing the reliability and performance of components through the investigation of backside metalized copper nanotwinned on SiC substrate. It aims to evaluate the performance and strength of die attach materials during low-temperature die bonding Ag sintering on DBC substrate. The primary objectives of this research involve utilizing magnetron sputtering to prepare high-density (111) copper nanotwinned structures. This includes optimizing process conditions, theoretically explaining the impact of process parameters on copper nanotwin formation, and assessing the effects of structural changes on film properties by varying negative substrate biases and thicknesses. Additionally, the study investigates the influence of adhesion layers (chromium and/or nickel) on copper nanotwin growth. It aims to determine optimal sputtering parameters for depositing high-quality copper nanotwinned films. The research also explores the application of this process to grow (111) copper nanotwinned structures on silicon carbide wafers for subsequent improvements. Controlled formation of a nano-twinned structure and (111) surface orientation is achievable through applied substrate bias. Sputtered Cu films with high-density nanotwinned structures, particularly those pre-coated with Cr on SiC substrates at -150 V, exhibit a significant proportion of (111) orientation. It is suggested that Cu nanotwinned films sputtered with a -150 V bias voltage possess potential for use as interlayers in low-temperature die bonding. Expanding on insights gained from previous sputtering experiments, a collaboration was initiated with Ag materials technology co., Ltd. The objective was to develop ion beam-assisted electron beam evaporation, successfully preparing high-density (111)-oriented copper nanotwinned films on 4-inch silicon carbide wafers. Microstructure analysis demonstrated excellent uniformity of the film on the wafer, with surface (111) grain orientation exceeding 90%. Moreover, this research extensively examined the effects of sintering temperature and pressure on the bonding characteristics of SiC/nt-Cu with DBC substrates using Ag sintering. Investigations encompassed structural integrity, void formation, and interfacial characteristics of bonded SiC/nt-Cu/Ag sintering/DBC and SiC/Cr/nt-Cu/Ag sintering/DBC assemblies at various sintering conditions. The findings highlight the significant influence of high-density (111) textured Cu nanotwinned films in Ag-sintered die bonding of Cr/Cu metallized SiC chips with DBC alumina substrates. A comparison between Ag sintering of conventional coarse grain Cr/Cu non-nanotwinned metallized SiC chips and those with Cu nanotwinned films revealed substantial differences. SEM microstructure cross-sections depicted a threefold decrease in porosity in the Ag-sintered high-density (111)-oriented Cu nanotwinned configurations compared to coarse grain Cr/Cu non-nanotwinned chips. Impressively, under pressure, Ag sintering of SiC/Cr/nt-Cu chips exhibited significantly higher shear strength (42.8 MPa) compared to SiC/Cr/Cu chips sintered under identical conditions, marking an 18.5 MPa difference. These results underscore the advantageous impact of high-density (111) textured Cu nanotwinned films on silver-sintered die bonding.