An Isothermal Annealing Study of Spontaneous Morphology Change in Electrodeposited Copper Metallization

Abstract

A systematic investigation of the effect of annealing time and temperature on the incubation period for spontaneous morphology change ͑SMC͒ in electrodeposited copper metallization is reported. Based on an additivity principle derived by Mittemeijer for transformations with an Arrhenius-type dependence of kinetics on temperature, it is shown that the remaining incubation time for SMC at room temperature following annealing at a given temperature should be linearly related to the annealing time. By repeatedly scanning atomic-force microscopy images at room temperature, the time at which SMC occurred was determined for films annealed for various times at temperatures ranging from 32 to 60°C. At each temperature studied, the remaining incubation time at room temperature was found to decrease approximately linearly with increasing annealing time, thus experimentally verifying the behavior predicted by the additivity principle. An Arrhenius plot of the measured rates of decrease showed good linearity and yielded a value of 0.48 eV for the activation energy. This is consistent with a vacancy diffusion mechanism for the process occurring during the incubation period, and supports our proposed mechanism for SMC.Copper has been widely adopted as an interconnection material in ultralarge-scale integrated ͑ULSI͒ circuits. 1-3 Electrodeposition is the technology of choice for the fabrication of copper interconnects because of factors such as the ability to fill dual damascene architectures without voids, lower cost, and better electromigration performance. As a consequence of its rapid growth, the technology has in many respects outpaced fundamental scientific understanding, and many important questions need to be investigated if technological progress is to be maintained. Thus, the study of the deposition and properties of copper metallization films is of major importance to the semiconductor industry. In particular, understanding and controlling the microstructure of electrodeposited copper 4-22 metallization is increasingly important.It has been observed that the microstructure of both sputtered and electrodeposited copper can change considerably with time, even at room temperature. 4,23-33 The effects of additives to the plating bath on the electrodeposition and properties of copper metallization have been studied extensively. 15,18,19 Scanning probe microscopy, including atomic force microscopy ͑AFM͒ and scanning tunneling microscopy ͑STM͒, has proved to be a useful tool to study copper electrodeposition; [4][5][6][7][8][11][12][13][14][15][16][17][18][19][20][32][33][34][35][36][37][38][39][40][41][42][43] mechanistic studies, the effect of additives, and the influence of the substrate on microstructure have been reported. The influence of various additives on the roomtemperature recrystallization of electrodeposited copper has been investigated by Stafford et al. 22 using X-ray diffraction and resistance measurements. Lingk and Gross 27 demonstrated the influence of damascene topography and showed that initiation of r...

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Effects of Temperature and Composition on Catholyte Stability in Vanadium Flow Batteries: Measurement and Modeling

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Vacancy-Induced Plastic Deformation in Electrodeposited Copper Films

“…During this event, smaller particles appear on top of the existing smooth rounded features on the surface of the deposit typically after 0.5-2 h of room-temperature aging. [1][2][3][4][5][6][7][8][9] The metallurgical phenomenon characteristic of such an event, occurring after a short period of time at low temperatures, is generally a recovery process, which involves the activity of point defects, primarily vacancies. Thin films often contain a high concentration of excess vacancies 10 and thus the early stages of thin-film relaxation is probably dominated by a recovery process.…”

“…A recent in situ atomic force microscope ͑AFM͒ study revealed that, during room-temperature aging, the surface of freshly electrodeposited polycrystalline copper films can undergo a spontaneous morphology change ͑SMC͒. [1][2][3][4][5][6][7][8][9] Typically, this takes place within a period of 30 min to 2 h after the deposition and occurs suddenly in many cases. We investigated why such a sudden morphology change occurs within a short period of time after the deposition and concluded that this particular film behavior appears to be stress-related.…”