manufacturing costs [99, 100]. It is not possible to effectively deposit thick Cu layers on
complex geometries with PVD or CVD techniques [101].
However, Cu electroplating (CE) is an inexpensive and straight forward process.
Besides performance and cost-related reasons, CE can be carried out at ambient conditions
of temperature and pressure, which, in combination with its ability to produce high quality
layers [101], makes CE a very promising candidate for the fabrication of metal contacts in
wafer-based solar cells.
Even though CE itself is a simple process, the implementation of Cu as a
metallization material is challenging. This is primarily because Cu diffuses extremely fast
into Si which leads to the creation of impurities and hence defects [102]. These defects act
as traps for Shockley–Read–Hall recombination (see Section 7.3) and lead to a decrease of
the minoritycarrier lifetime and ultimately degrade the electrical characteristics of the Si
devices [103]. Furthermore, studies on the impact of Cu contamination in Si have shown a
substantial increase in the leakage current of p-n junctions [102]. The introduction of Cu
as metallization material is possible by introducing thin-film diffusion barriers that prevent
Cu from diffusing into Si. These diffusion barriers can also act as seed layers of high
conductivity that facilitate CE. Several investigations have shown that titanium (Ti),
nickel (Ni), tantalum (Ta) or alloys of these metals with nitrogen such as TaN or TiN are
efficient Cu seed layers and Cu diffusion barriers [99, 103, 104]. They can be deposited
with PVD and CVD methods. Their utilization for the fabrication of the front metal
contacts with subsequent CE in c-Si and SHJ solar cells has improved their performance
[100].
complex geometries with PVD or CVD techniques [101].
However, Cu electroplating (CE) is an inexpensive and straight forward process.
Besides performance and cost-related reasons, CE can be carried out at ambient conditions
of temperature and pressure, which, in combination with its ability to produce high quality
layers [101], makes CE a very promising candidate for the fabrication of metal contacts in
wafer-based solar cells.
Even though CE itself is a simple process, the implementation of Cu as a
metallization material is challenging. This is primarily because Cu diffuses extremely fast
into Si which leads to the creation of impurities and hence defects [102]. These defects act
as traps for Shockley–Read–Hall recombination (see Section 7.3) and lead to a decrease of
the minoritycarrier lifetime and ultimately degrade the electrical characteristics of the Si
devices [103]. Furthermore, studies on the impact of Cu contamination in Si have shown a
substantial increase in the leakage current of p-n junctions [102]. The introduction of Cu
as metallization material is possible by introducing thin-film diffusion barriers that prevent
Cu from diffusing into Si. These diffusion barriers can also act as seed layers of high
conductivity that facilitate CE. Several investigations have shown that titanium (Ti),
nickel (Ni), tantalum (Ta) or alloys of these metals with nitrogen such as TaN or TiN are
efficient Cu seed layers and Cu diffusion barriers [99, 103, 104]. They can be deposited
with PVD and CVD methods. Their utilization for the fabrication of the front metal
contacts with subsequent CE in c-Si and SHJ solar cells has improved their performance
[100].