在化學機械研磨中研磨液添加劑對於鍺研磨性質之影響

Abstract

近年來鍺(Germanium，Ge)開始被考慮用來取代在互補式金氧半導體(Complementary Metal-Oxide-Semiconductor，CMOS)中使用已久的矽(Silicon，Si)。Ge是一種具有高電子遷移率的材料，其特點是電子和電洞遷移速度比Si更快。因此從原理上來說，Ge能比Si發揮更高速的運作。 在先進製程裡，利用磊晶鍺(Epi-Ge)來進行溝槽填充時，Epi-Ge會過度生長並覆蓋在整個結構之上，故須利用化學機械研磨製程(Chemical Mechanical Polishing，CMP)來移除結構上多餘的Ge並停止在氧化矽(SiO2)層上。一般在CMP後，常會發生淺碟型凹陷(Dishing)現象，這在10 nm以下的先進製程裡必須盡量避免。在研磨過程中Ge會氧化成為氧化鍺(GeO2)，其易溶於水的性質使得研磨後易產生嚴重的淺碟型凹陷現象，所以急需開發具有高研磨速率選擇比(Selectivity)且不會造成嚴重的淺碟型凹陷現象的Ge-CMP研磨液(Slurry)。針對不同的應用研磨液中可添加特殊的添加劑(Additive)來增強其研磨效果，本研究使用膠體二氧化矽(Colloidal Silica)為研磨料(Abrasive)，並添加兩種不同濃度的添加劑於研磨液中來觀察其對於Ge研磨性質的影響，使用生長在Si基板上的Ge、SiO2等晶圓控片來驗證各種研磨液特性，包括材料靜態溶解速率(Static Etching Rate，SER)、材料移除速率(Material Removal Rate，MRR)、晶圓表面缺陷 (Defectivity)和表面粗糙度(Roughness)等。 研究發現添加添加劑A可增加Ge的MRR，提高Ge/SiO2之研磨速率選擇比，但其Ge的SER也跟著增加，代表著在研磨完後晶圓上之圖形容易產生淺碟型凹陷現象。加入添加劑B的研磨液可有效的降低SER並仍保持Ge/SiO2之高研磨速率選擇比，代表著其具有有效的Ge平坦化並且在晶圓上之圖形不易產生淺碟型凹陷現象，且此研磨液也觀察到有低表面缺陷和低表面粗糙度等研磨特性。

In recent years the high carrier mobility materials have been considered to replace the silicon (Si) in complementary metal-oxide-semiconductor (CMOS) devices. Carrier mobility of germanium (Ge) is known to be higher than that of Si and, hence, the utilization of Ge is able to improve the operation speed of integrated circuits. After the trench filling of epitaxy-Ge (epi-Ge), chemical mechanical polishing (CMP) has to be carried out to remove the overgrown Ge so that the smooth surface can be obtained. Nevertheless, CMP process usually results in the dishing defects which must be avoided in 10-nm node semiconductor processes. During CMP, Ge tends to form the GeO2 which has high solubility in water and, consequently, causes the severe dishing defects. The development of slurry with high selectivity for CMP of Ge to diminish the dishing defects is hence an urgent issue for advanced semiconductor processes. Additive is commonly added in CMP slurry to improve its polishing capability. This study adopts colloidal silica as the abrasive and added two different kinds of additives with various concentrations in CMP slurry for Ge. Si wafers containing Ge and SiO2 layers were utilized for the experiments to investigate the static etching rate (SER), material removal rate (MRR), defectivity and roughness of CMP for Ge. Analytical results indicated the addition of additive A in CMP slurry increases the MRR of Ge and the selectivity of polishing rate of Ge/SiO2; however, the SER of Ge simultaneously increased which implies the emergence of dishing defects after CMP. Addition of additive B in CMP slurry might reduce the SER of Ge and maintain the high selectivity of polishing rate of Ge/SiO2. This means the planarization of Ge can be achieved with the effective suppression of dishing defects. The polished surface with low defectivity and roughness was also observed in the sample subjected to the CMP utilizing the slurry containing additive B.