Subject Number : S-19-JI-0045
Support Type : Technical Surrogate
Proposal Title (English) : Thermal stability of electroplating cobalt alloy in silicon
Username (English) : Wen Jauh Chen
Affiliation (English) : Graduate School of Materials Science, National Yunlin University of Science and Technology, Douliu, Yunlin, Taiwan.

1. Summary
In this report, using the electroless method, nickel metal is plated on the textured silicon substrate. Low-resistance nickel silicides (Ni2Si and NiSi) formed after 10 minutes of annealing at heat treatment of 500 ℃. The cobalt tungsten alloy and copper layer electroplated on the silicon substrate with nickel silicides. The sample is designed the structure of Cu/CoxW1-x/NiSiy/Si. The thermal stability of CoxW1-x was investigated.
2. Experimental
The silicon wafer used in this report is p-type monocrystalline silicon. The experimental process details are as follows: First, the cleaning of the textured silicon substrate, the substrate in acetone completely degreased, the use of H2SO4/H2O2 solution to remove metal ions and form silicon oxide. By immersion in hydrogen fluoride solution to remove silicon oxide from the silicon substrate. After sensitization and activation, the nickel film is plated on the textured silicon substrate by the electroplating method. The nickel-plated sample formed nickel silicide through heat treatment. The sample is designed as NiSiy/Si after annealing. Cobalt tungsten film is electroplated on the NiSiy/Si as a diffusion barrier layer for copper diffusion. Finally, the electroplating copper used commercial electroplating copper solution. The sample is designed as Cu/CoxW1-x/NiSiy/Si after CoW and Cu electroplating. The Cu/CoxW1-x/NiSiy/Si is annealed at 300 to 800 ℃ in an atmosphere of Ar/H2 (95% Ar and 5% H2). The surface morphology is observed using the JEOL scanning electron microscope (SEM). A scanning transmission electron microscope (STEM) was performed on a JEM-ARM200F. A STEM that equipped with an energy dispersive X-ray spectrum (EDS, JEOL Ltd.), which we used to determine the chemical composition and STEM-EDS compositional maps of all samples.
3. Results and Discussion
Figure 1 (a) is the surface morphology of the sample after electroplating cobalt tungsten alloy. Figure 1 (b) is cross-section view of figure 1 (a). The pyramid structure is preserved completely, indicating that the cobalt tungsten alloy layer is a continuous film. Co: W ratio is approximately 8:2 atomic percentage as shown in the inset of figure 1 (b) by elements analysis of SEM-EDS. Figure 2 is a STEM bright-field micrograph and EDS mapping that show the typical microstructure of a Cu/CoxW1-x/NiSiy/Si for the sample annealed at 500 °C for 10 min.

(a) (b)
Figure 1 SEM micrograph of (a) plan-view and (b) cross-sectional view for CoxW1-x/NiSiy/Si sample.

(a) (b)
Figure 2 STEM micrograph of (a) bright-field and (b) EDS mapping for CoxW1-x/NiSiy/Si sample.

4. Others
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5. Publication/Presentation
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6. Patent
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