Stress migration phenomenon in narrow copper interconnects

Abstract

Stress migration ͑SM͒ behavior in Cu damascene interconnects was investigated in detail using different kinds of test patterns. SM failure was found in narrow lines that are very long, or connecting to a wide line. In the pattern in which narrow lines are connected to wide metal, the failure rate decreased as the narrow metal becomes longer. It was found that the failure rate in minimum 0.14 m wide lines is more than that in 0.2-0.42 m wide lines. The result of the test patterns with different via arrangements clarified that the placing of the vias at the edge of the M1 line plays an important role in the SM phenomenon in narrow copper lines. Failure analysis using scanning transmission electron microscopy revealed voiding beneath the via at the failure points for all test patterns. It is shown that the enhanced failure rate in the minimum wide lines and the via arrangement effect cannot be understood by the previous diffusion mechanism. Based on these results, the effect of the via arrangement close to the edge of the lower lines on SM failure in narrow lines is discussed.

Effect of Layout Variation on Stress Migration in Dual Damascene Copper Interconnects

“…When the linewidth is the same as the via size, a top-corner edge, where the barrier metal, Cu, and cap dielectric intersect may serve as the dominant diffusion path for vacancies. 11,12) This means that vacancies may migrate directly to the via bottom along a top-corner edge in the form of one-dimensional diffusion, J c , as illustrated in Fig. 5(b).…”

“…11) In addition, we have reported the enhanced failure rate in minimum-width lines, and found a via arrangement effect that cannot be explained by the previous diffusion mechanism. 12) In the present work, we focus on the study of SM behavior using the extrusion pattern in which narrow lines are connected to a wide line at both the M1 and M2 levels as shown in Fig. 1(b).…”

Lifetime prediction model of stress-induced voiding in Cu/low-κ interconnects

“…However, in actuality, a very high failure probability was reported for via chain structures. [1][2][3][4][5][6][7][8][9][10][11] In particular, the geometry dependence of the failure probability is significantly different from that of Al lines. A comparably high failure probability is observed at vias connected to wide lines.…”

Effect of stress migration on electromigration for nano scale advanced interconnects

“…Geometrical effects in terms of the width and length of the wide metal line are also found to have a significant influence on SM [32,95,113]. It is reported that SM failure is more rampant in wider metal lines because the larger metal plates serve as a better vacancy reservoir within one diffusion length of the via.…”

“…It is reported that SM failure is more rampant in wider metal lines because the larger metal plates serve as a better vacancy reservoir within one diffusion length of the via. Voiding in narrow lines appears to occur only at extremely long stressing time of 12,000 hours (>1 year) [113]. Therefore, the current understanding is that SM is a risk factor in large metal plates and not so much of a critical concern for further downscaled structures.…”