HSQ的熱學性質及HSQ和擴散金屬鉭(Ta)對銅電致遷移的影響

Abstract

隨著元件尺寸的縮小, RC延遲限制了電路的傳輸速度。 解決方式便是使用低介電材料如HSQ和低阻率的銅。 在本實驗中, 主要探討擴散層鉭(Ta)在HSQ和SiO2基材上對銅遷移的影響。 而且,對Cu/Ta金屬膜在HSQ和SiO2基材上的特性及HSQ的熱學性質也有所探討。 從TG/DTA, FTIR和折射率分析, 固化溫度在400 ℃可以獲得較低的介電常數。 使用擴散層鉭(Ta)不但可以改善銅和HSQ的接合強度,而且可以阻擋銅擴散到HSQ中。 並且, 擴散層鉭(Ta)可以改善銅的結晶性,進而增強銅在高溫下的電致遷移。 另外, 比較銅/鉭(Cu/Ta)金屬膜在HSQ和SiO2 基材上的特性和電遷移的影響, 發現HSQ基材的粗糙度和氫會影響銅/鉭(Cu/Ta)金屬膜的阻率和抗電致遷移的能力。 除此之外, 在高電流密度下, 具有較差的熱傳導係數的HSQ會導致嚴重的焦耳效應,進而降低抗電致遷移的能力。

As device scaling down to sub-micron, the RC time delays become the limitation to circuit speed. The solution is the use of low dielectric materials (such as HSQ) and low resistivity materials (such as copper). In this work, the influence of underlying barrier Ta on Cu electromigration (EM) performance for HSQ and SiO2 substrate was investigated. The properties of Cu/Ta on HSQ coated Si substrate and the thermal properties of HSQ were also studied. From TG/DTA , FTIR, and refractive index analysis, curing at around 400℃ is desired to obtain lower dielectric constant property. The presence of a Ta barrier not only improves the adhesion between Cu and dielectrics, but also blocks the Cu diffusion into dielectrics. And the presence of a Ta barrier can enhance the microstructure and improve the Cu electromigraton at high temperatures. The hydrogen from HSQ may affect the resistivity of metal films and electromigration performance. The roughness of HSQ may influence the resistivity of metal films for as-deposited condition. The poor thermal conductivity of HSQ substrate enhances Joule heating effects and then degrades the EM performance. Abstract…………………………………………………………………… i Acknowledgement iii Contents iv List of Tables vi Figures Caption vii Chapter 1 Introduction 1 Chapter 2 Literature Review 3 2-1 Advanced interconnect schemes 3 2-2 Damascene structure 3 2-3 Materials option 6 2-3-1 Requirements for IC industry 6 2-3-2 Properties of hydrogen silsesquioxane (HSQ) 6 2-3-3 Properties of copper 19 2-3-4 Properties of Ta barrier metal 21 2-4 Electromigration mechanism 27 2-5 Factors Influencing the Electromigration 36 2-5-1 Geometry factors 36 2-5-2 Barrier metal (adhesion/diffusion barrier) 36 2-5-3 Impurities in metal 41 2-5-4 Joule heating effect 41 2-5-5 Stress effect 44 2-5-6 Oxidation 46 Chapter 3 Experimental Procedures 47 3-1 Sample preparation 47 3-2 Measurements and analyses 52 3-2-1 Properties of HSQ film analysis 52 3-2-2 Metal films analysis 54 3-2-3 Electromigration measurement 55 Chapter 4 Results and Discussion 56 4-1 Thermal Properties of HSQ 56 4-2 Influence of Barrier Ta for Cu/Ta/SiO2 Structure 61 4-3 Influence of HSQ for Cu/Ta/HSQ/Si Structure 78 4-3-1 Properties of Cu/Ta/HSQ/Si films 78 4-3-2 Activation Energy for Electromigration 86 4-3-3 Current Exponents (n) for Electromigration 95 Chapter 5 Conclusions 99 References 101 Vita 110