Subject Number: S-19-JI-0001
Support Type: Technical support
Proposal Title (English): Barrier properties of ITO for copper metallization in silicon solar cells
Username (English): Wen Jauh Chen
Affiliation (English): National Yunlin University of Science and Technology (Taiwan)

1. Summary
A thin indium tin oxide (ITO) barrier layer and copper were deposited on textured (001) silicon by a sputtering. The structures of Cu/ITO/Si characterized by scanning transmission electron microscope (STEM) and energy dispersive X-ray spectrometer. The results show that the sputtering ITO layer with a thickness of 35 nm was found to be an excellent diffusion barrier against Cu up to 600°C. The failure of Cu/ITO/Si can be attributed to copper agglomeration t.

2. Experimental
Single crystal phosphorus-doped pyramid textured silicon wafers were used as substrate. The copper and ITO films were sputter-deposited onto textured silicon substrates in a dc/rf-magnetron sputtering system. All as-deposited samples were annealed in the furnace at 300-800°C for 10 min in Ar/H2 atmosphere. A scanning transmission electron microscope (STEM) was performed on a JEM-ARM200F. A STEM equipped with an energy dispersive X-ray spectrum (EDS, JEOL Ltd.). To determine the chemical composition and STEM-EDS compositional maps of all samples.

3. Results and Discussion
Figure 1 is a high magnification of STEM micrograph and EDS maps of Cu, ITO, and Si for the sample annealed at 300 °C for 10 min in the Ar/H2 environment. Figure 1 (a) is a STEM micrograph of a layer structure of showing the Cu/ITO/Si. Fig. 1 (b) shows an overlap of Cu, In, Sn, and Si maps. The intensity of the layer with red color in Fig. 1 (b) show that it is constituted of Cu. Fig. 1 (b) also indicated that the ITO layer was presented between copper and silicon. It is evident that the Cu/ITO/Si structure preserved after annealing at 300 °C from the analysis of elemental map. The thicknesses are about 35 nm and 80 nm for the ITO layer and Cu film, respectively.

Figure 1
STEM bright-field micrograph of Cu/ITO/Si sample annealed at 800 °C is presented in figure 2 (a). The particles with about one micrometer were observed at this temperature. And the particles located at the valley of the textured structure. Fig. 2 (b) shows the overlap of Cu, In, Sn, and Si maps. From figure 2 (b), the elemental map reveals the main component in the particles is Cu, which shows that the Cu thin film was agglomerated at 800 °C. For the Cu/ITO/Si system, the failure seems to be induced by copper agglomeration.

Figure 2
4. Others
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5. Publication/Presentation
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6. Patent
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