INTRODUCTION The increasing demand for faster and more reliable integrated circuits (ICs) has driven the procedure of integration of Cu-based metallization. 1 The success- ful manufacturing of this new metallization relies on major technological progress in a variety of develop- mental areas by overcoming difficult materials and process challenges. One of the most important devel- opmental achievements for Cu-based metallization is the incorporation of the damascene process in con- junction with the use of the electroplating technique. This process has an advantage over conventional processes, because its capability of fabricating deep submicron Cu lines and vias is much better than common physical vapor deposition or chemical vapor deposition (CVD) techniques. On the other hand, elec- troplated Cu films demonstrate an intriguing phe- nomenon known as “self-annealing”; the as-plated films are not stable and their microstructure evolves even at room temperature over a period of hours or days through secondary recrystallization. 2 The kinet- ics of self-annealing are very complex and difficult to control, affected by various parameters such as film thickness, trench or via configuration, substrate to- pography, and electroplating bath chemistry. 2,3 Hence, implementing a self-annealing step into IC manufacturing is not considered as a realistic way to stabilize the microstructural property of Cu intercon- nects. Generally, the microstructure of electroplated films is controlled by performing a brief anneal at rel- atively high temperatures (200–400°C). This work is concerned with understanding the ef- fect of postelectroplating anneals on the microstruc- tural evolution and reliability of electroplated Cu films. The microstructural evolution is examined as Journal of ELECTRONIC MATERIALS, Vol. 30, No. 12, 2001 Special Issue Paper Effect of Annealing on the Surface Microstructural Evolution and the Electromigration Reliability of Electroplated Cu Films S.H. KANG, 1 Y.S. OBENG, 1 M.A. DECKER, 1 M. OH, 1 S.M. MERCHANT, 1 S.K. KARTHIKEYAN, 1 C.S. SEET, 1,2 and A.S. OATES 1 1.—Agere Systems, 9333 S. John Young Parkway, Orlando, FL 32819. 2.—Permanent address: Chartered Semiconductor, Singapore. This paper presents the effects of annealing, performed over a temperature range from 200°C to 400°C, on the surface microstructural evolution and the electromigration reliability of electroplated Cu films. After annealing, a sub- stantial increase in surface roughness was observed, while variations in mean grain size and nanoindentation hardness were minor. Given the annealing temperature, the surface roughness was larger for the films annealed in form- ing gas, due to the existence of hydrogen. In particular, the films annealed at 400°C in forming gas demonstrated severe grain-boundary grooving and sur- face voiding. The defective nature of the annealed surface can be alleviated by chemical-mechanical polishing (CMP), when annealing is conducted prior to the CMP. However, it appears that a sequential thermal excursion at relatively high temperatures re-aggravates the integrity of the Cu surface. This argu- ment may be supported by the electromigration-test results on dual-dama- scene interconnects fabricated using two different thermal profiles. The elec- tromigration lifetimes were longer by more than a factor of two for the interconnects that skipped a post-passivation anneal at 400°C. The experi- mental evidence presented in this work suggests that controlling the integrity and quality of the Cu surface is an important step in ensuring good electromi- gration reliability. Key words: Cu interconnects, annealing, electroplating, surface roughness, electromigration, and nanoindentation (Received March 5, 2001; accepted October 4, 2001) 1506