Characterization of Vacancy Defects in Electroplated Cu Films by Positron Annihilation and its Impact on Stress Migration Reliability

Abstract

Articles you may be interested inVacancy reactions near the interface between electroplated Cu and barrier metal layers studied by monoenergetic positron beams Room-temperature microstructural evolution of electroplated Cu studied by focused ion beam and positron annihilation lifetime spectroscopy Defects introduced into electroplated Cu films during room-temperature recrystallization probed by a monoenergetic positron beam J. Appl. Phys. 98, 043504 (2005); 10.1063/1.2009813 Vacancy-type defects in electroplated Cu films probed by using a monoenergetic positron beam J. Appl. Phys. 95, 913 (2004);Abstract. Positron annihilation was used to evaluate vacancy concentrations in electroplated Cu films with different kinds of electrolytes. The influence of various electrolytes on the impurities, grain boundaries, and micro-voids were also investigated. We found a higher impurity concentration and larger micro-voids were observed in copper films with higher vacancy concentrations. We reduced the failure rate in our stress migration results using a copper film with a higher concentration of vacancy and impurity. The stress migration performance improved because impurity nucleated vacancy clusters act as effective traps for diffusing vacancies.

Electrolyte Additive Chemistry and Feature Size-Dependent Impurity Incorporation for Cu Interconnects

“…7 The poor stress migration performance for the "doped" Cu in this study appears to contradict the trend found by Suzuki et al, where Cu having a relatively higher level of impurities showed fewer stress migration failures compared a "low impurity" Cu. 8 But in Reference 8, the "low impurity" chemistry showing higher stress migration failure rates had S and Cl impurity levels in blanket Cu films of about ∼10 16 atom/cm 3 , about a factor of 10 lower than that found for the "pure" Cu in the current study. As the time to fail is also not specified in Reference 8, the trend found by Suzuki et al does not necessarily conflict with the current results.…”

“…5,6 Stress migration (sometimes referred to as stress induced voiding), a failure mode where voids in plated Cu coalesce in a line or wide plate beneath a narrow via at elevated temperatures, 7 has been shown to be sensitive to the impurity content of the electrodeposited Cu. 8 An example of such a defect is shown in Figure 1; this type of metallization failure is especially problematic, since the void typically spans the entire via width, breaking electrical continuity. Hence, a detailed understanding of the behavior of impurities over a range of damascene features sizes is required to engineer interconnect microstructure for optimum yield and reliability performance.…”

Electrolyte Additive Chemistry and Feature Size-Dependent Impurity Incorporation for Cu Interconnects

“…Control of impurity levels is important in that an excessive impurity content may adversely affect plated Cu stability during subsequent damascene processing steps (e.g., during chemical mechanical polishing or CMP) (5)(6). Stress migration (sometimes referred to as stress induced voiding), a failure mode where voids in plated Cu coalesce in a line or wide plate beneath a narrow via at elevated temperatures (7), has been shown to be sensitive to the impurity content of the electrodeposited Cu (8). An example of such a defect is shown in Figure 1; this type of metallization failure is especially problematic, since the void typically spans the entire via width, breaking electrical continuity.…”