利用電漿輔助原子層氣相沉積法在多孔性超低介電薄膜製備銅導線擴散阻障層之研究

Abstract

隨著半導體元件的微小化，現行的製程技術與材料皆面臨極大的挑戰且已無法滿足先進製程需求，因此對奈米結構原子級薄膜製程設備的需求極為殷切。原子層沉積(atomic layer deposition, ALD)技術同時具有大面積、高階梯覆蓋率、高厚度均勻性、低溫製程及原子級膜厚控制等優點，除了應用於銅導線擴散阻障層外，亦可有效解決超薄高介電材料鍍膜需求，同時可用於複雜的DRAM電容結構與微機電元件等技術所需的高深寬比均勻鍍膜製程。 本論文利用電漿輔助原子層氣相沉積法(plasma-enhanced atomic layer deposition, PEALD)製備銅導線擴散阻障層，期能應用於半導體32奈米以下之IC製程。研究中乃利用ALD之自我侷限(slef-limited)特性製備出具有可靠的熱穩定性TaNx擴散阻障層，探討其應用於有機模板分子多孔性二氧化矽(mesoporous SiO2)超低介電薄膜的製程整合，由於其開放性孔洞表面易於吸附水氣並且使得沉積TaNx擴散阻障層之TaCl5氣態前趨物擴散進入mesoporous SiO2層中，造成其介電特性的影響，因此利用高密度電漿化學氣相沉積系統的氧氣或氬氣電漿前處理mesoporous SiO2使得其多孔性薄膜表面緻密化，可有效地改善水氣吸附和氣態前趨物的擴散。 此外，本研究亦對於TaNx擴散阻障層以及其與銅導線的疊層，進行薄膜附著力方面的研究與探討。在PEALD製備TaNx擴散阻障層中，氮化物擁有較佳的阻障特性與較高的熱穩定性質，然而TaNx擴散阻障層的氮化表面並不利於後續的銅導線製程並且與其附著性不佳等問題，研究中發現，TaNx擴散阻障層的氮化表面可經由氫氣電漿表面處理或氫氣氛圍的快速退火(rapid thermal anneal, RTA)處理，藉由增加Ta/N原子成份比例的表面還原處理，可提升擴散阻障層與銅導線的附著力與熱穩定性將大幅提升。 本論文亦採用二階段的PEALD連續製程，沉積Ru/RuNx得到可直接銅導線電鍍的擴散阻障層，Ru是一個過渡金屬且擁有低的電阻係數，但金屬Ru沒有TaNx的擴散阻障特性，利用二階段的PEALD連續製程沉積3.5奈米的PEALD RuNx再沉積0.5奈米的metallic Ru成為Ru/RuNx，金屬Ru層可有效地減緩RuNx的熱裂解並提供直接銅導線電鍍所需的低電阻係數，以此方式所沉積的Ru/RuNx擴散阻障層可成功地電鍍銅導線，並具有可靠的熱與介電穩定性，膜薄疊層也顯示有良好的附著性，利於將來進行銅鑲嵌之後段製程整合。

With the dimensional shrinkage of microelectronic devices, atomic layer deposition (ALD) becomes a very attractive method for the deposition of ultrathin films. Beacuse ALD can deposit uniform ultrathin thin films on substrates with high aspect ratio structures, it has been implemented in the Cu interconnect process, whcin requires diffusion barriers of high conformality and precise thickness. In addition, ALD also meets challenging requirements in many other IC processes, such as the deposition of high quality dielectrics to fabricate trench capacitors for DRAM. We use plasma-enhanced ALD (PEALD) to deposit TaNx diffusion barriers on mesoporous SiO2 low-k dielectrics. The self-limiting nature of the surface reactions can produce uniform TaNx films of high thermal stability on the mesoporous SiO2 low-k dielectrics. However, the porous nature of the porous dielectrics leads to a difficulty for the integration of the dielectrics into Cu interconnect technology. Surface pores are penetration pathway of adverse impurities into the porous dielectrics, such as moisture uptake during cleaning and plasma species diffusion during etching. O2 and Ar plasmas were used to modify the surface of the mesoporous dielectric in a high density plasma chemical vapor deposition (HDP-CVD) system, and both of the treatments produced a densified oxide layer a few nanometer thick. The pore sealing treatment could effectively prevent metallic atoms from diffusing into the mesoporous dielectric during the PEALD process and enhance retardation of moisture uptake. Adhesion properties of PEALD diffusion barriers with the Cu interconnect were also studied. The TaNx nitride barrier usually exhibit good diffusion barrier properties, but they often has a poor mechanical strength at the interface with the Cu layer. In the study, we used hydrogen plasma treatment and rapid thermal annealing (RTA) in hydrogen ambient to reduce the nitrogen content in the surface layer of the PEALD-TaNx barrier layer. The surface treatment greatly improved adhesion of the TaNx barrier layer with Cu and the thermal stability of the TaNx/Cu film stack. We also deposited Ru/RuNx bilayer barriers on mesoporous SiO2 dielectrics by an in situ two-step PEALD process for the application of seedless Cu electroplating. Ru is a stable transition metal in air and has low electrical resistivity, but it has worse diffusion barrier properties than RuNx. We sequentially deposited 3.5 nm thick RuNx and 0.5 nm thick metallic Ru on the mesoporous dielectric by PEALD. The metallic Ru capping layer can retard thermal decomposition of the underlying RuNx layer and provides the barrier surface a low electrical resistance for direct Cu electroplating. The Ru/RuNx bilayer exhibits satisfactory thermal stability and electrical characteristics, and is suitable for the seedless Cu electroplating process in nanometer scale interconnect technology.