Effect of tungsten incorporation in cobalt tungsten alloys as seedless diffusion barrier materials

Seedless Cu Electroplating on Co-W Thin Films in Low pH Electrolyte: Early Stages of Formation

“…The average current density, J , which can be calculated dividing Equation (1) by t , is much higher in DC, J = 20 mA·cm −2 , than in PC, J = 0.77 mA·cm −2 . A similar J value was reported using a similar electrolyte in DC mode (1 mA·cm −2 ) [ 15 ], resulting in incomplete substrate coverage, similar to Figure 5 a, suggesting that higher values of J are required to achieve better substrate coverage. Exposure time to the electrolyte is also substantially shorter in DC than in PC for the same transferred charge, reducing the extent of nuclei and substrate dissolution.…”

“…Co-W films near equimolar composition were selected in this work for subsequent Cu electrodeposition. Su et al [ 15 ] demonstrated that equimolar Co-W films display the best plating behaviour while being effective as a diffusion barrier. GIXRD confirms the amorphous structure of the film, allowing it to adequately function as a diffusion barrier layer ( Figure 1 c).…”

“…These nuclei disappear either by direct dissolution into the electrolyte or by dissolution of the substrate underneath them. The acidic nature of the electrolyte herein used (pH ≈ 1.8) can dissolve Cu but is particularly aggressive to the Co-W substrate [ 15 , 24 ]. The nucleation and growth mechanism for Cu and the effects of the substrate dissolution are illustrated in Figure 6 .…”

“…Another possible explanation for a lower nuclei density in PC deposition is that the number of active sites for nucleation decreases with the immersion time. It has been reported that the number of electrodeposited Cu nuclei decreases with increasing W content in Co-W and Ru-W substrates [ 15 , 26 ]. Accordingly, in this case, the selective dissolution of Co leads to substrate enrichment in W, rendering it difficult to nucleate further as the immersion time increases.…”

“…From a manufacturing point of view, Co-W is an interesting alternative to Ta/TaN as well, because it can be synthesised by electrochemical routes that produce a high film uniformity and step coverage in narrow vias and lines. Additionally, Co-W can function as both a diffusion barrier and seed layer, whereupon Cu can be directly electroplated [15]. Electroless methods used for the synthesis of Co-W-based thin films have been reported in the literature [16][17][18], but the direct electroplating of Cu on Co-W-based thin films is frankly unaddressed.…”