Thermal Stability of Copper–Nickel and Copper–Nickel Silicide Contacts for Crystalline Silicon

Abstract

Copper is a low-cost, low-damage alternative to Ag paste for front-side metallization of crystalline Si (c-Si) solar cells, but requires conductive diffusion barriers like Ni or NiSi. Thermal stability of these barriers during postmetallization anneal is critical for performance. In this study, we address the structural and chemical stability of Cu contacts with both Ni and NiSi barrier layers, identifying interfacial reactions responsible for their degradation. Superior thermal and chemical stability of single-phase NiSi barrier as compared to Ni is made evident by XRD, Auger, and Raman spectroscopies. Moreover, the commonly used Cu− Ni−Si contact stack does not convert to more stable Cu−NiSi−Si stack upon thermal treatment. Instead, Cu readily alloys with the Ni layer and reacts with the underlying c-Si to form Cu 3 Si, with no evidence for the formation of Ni x Si phases. Also, even the superior NiSi barrier slowly dissolves into Cu at elevated temperatures.

Formation of nanoflowers: Au and Ni silicide cores surrounded by SiOx branches

“…This can also be proved by the plateau of Ni in EDS results of line structures. A number of works about self-assembled epitaxial Ni silicide have been published [41][42][43][44][45][46], and some works pointed out that the Ni 2 Si phase formed first, followed by NiSi and NiSi 2 after annealing [47][48][49]. Generally, NiSi 2 forms above 600 °C [42][43][44][45]48].…”

Transformation and Control of Crystal Structures on Electronic Thin Films

“…For example, the Ni-based alloys fabricated by sputter and PLD were applied to the interconnects to Li storage materials. − The Ni films deposited on steel substrates by the PVD technique promoted the corrosion and wear resistance . Owing to the low resistivity and interfacial stress of Ni silicides, the studies of Ni deposition on Si substrates as interconnects in MOS devices were also carried out. ,,− In addition, the fabrication of Ni–Ti - based shape memory alloy thin films on Si substrates was achieved by sputtering from Ni–Ti alloy targets, − alternative Ni/Ti sputtering, − or simultaneous sputtering from Ni and Ti targets. The Ni-based thin films on the Si substrate still hold a large amount of potential in various fields of applications.…”

Control of Large‐Scale Single‐Phase Ni Silicide Formation from Reactive Multilayers

“…[17,18] Nonetheless, the applications of Ni silicides as electrodes still draw a lot of attention recently. [19][20][21][22] As a result, the combustion and thermal behavior of large-area Ni/Si RMLs with different compositions were studied in this research.…”