Temperature determination methods on copper material for highly accelerated electromigration tests (e.g. SWEAT)

Abstract

Highly accelerated electromigration tests conducted at wafer level require meaningful measurements of the stress temperature of the test line. Estimates of the test temperature can he made with the use of the temperature coefficient of resistance, TCR, before significant electromigration damage occurs and with the use of the thermal resistance of the test line as electromigration damage progresses to line failure. Each approach depends on an assumption of linearity; for the use of TCR it is the linear dependence of resistance on temperature, and for the use of the thermal resistance it is the linear dependence of temperature on power dissipation. For testing aluminum test structures, these assumptions are adequately well obeyed to approximately 300 OC. This is not the case for testing copper test lines. Stress temperatures as high as 600 "C are encountered in highly accelerated electromigration tests. At such high temperatures, the assumptions of linearity are not valid, and large overestimates of the stress temperature will result. We show how to correct TCR estimates of the stress temperature by the use of recommended values for the resistivity of pure, bulk copper with temperature. We obtain a suitable value for the thermal resistance of the test structure from the slope of the temperatureversus-power-dissipation curve at temperatures near the desired stress temperature. Use of the approaches are demonstrated. MotivationHighly accelerated electromigration tests conducted at wafer level require meaningful measurements of the stress temperature of the test line. Estimates of the stress temperature can he made with the use of the temperature coefficient of resistance (TCR)

Electromigration Reliability Assessment of Cu-based Metallization Systems by a Wafer-Level Approach

“…We were able to estimate for these samples the parameters of Black's equation [7]: shows the calculation of E a = 0.84 eV (left) and n = 1.27 (right), referred to the Metal-1 downstream structures with 1-via. These values are quite close to the values reported in the literature for PLR tests (13,14), suggesting that the flow of dislocated ions is mainly located at the upper interface, between copper and the silicon nitride cap.…”

“…[2] is not feasible, because of the complex dependence of R th on the temperature delta T test -T chuck . However, doing some empirical check, it is possible to realize a matrix of stress conditions (T test , J test ), suitable to calculate the parameters of the Black's equation [7], i.e. E a , the activation energy, and n. , 8 (1) 157-162 (2007) …”

Electromigration behavior of Cu metallization interfacing with Ta versus TaN at high temperatures

“…12 The hot chuck was set at different temperatures ranging from RT up to 350 C. At each temperature, a low current of 2 mA was applied, so as to avoid Joule heating, to the line structure and the resistance value was recorded. An external thermometer attached to the wafer surface and close to the structure was used for accurate temperature calibration.…”