Shibaura Institute of Technology New Technology Presentation Meetings!
Cu wiring is formed by use of Cu complex and laser irradiation

July 4, 2017“Shibaura Institute of Technology New Technology Presentation Meetings!” was held in JST. In this here, oral presentation by Prof. Ooishi of Shibaura Institute of Technology is picked up.

In this research, glyoxylate Cu complex (GACu) is used as a material of Cu wiring. As you know, Nano size metal paste or ink is generally used for a low thermal resistance substrate, such as plastic film, because of low melting point. Nano size Cu grain is reasonable and has nonoccurrence property of migration, but it is easy to be oxidized and difficult to treat in atmosphere environment. As a result, if Nano size Cu is used in the wiring forming process, total cost is not inexpensive. For this reason, the research group has developed a new patterning process by use of GACu, which is inexpensive, chemically stable, and easy to be synthesized and treated.

Picture 1. Comparison of Cu precipitation state1)

Figure 1 shows molecule structure of GACu. It is easy to prepare ink and paste because of existence of OH2 region, which is easy to join together various solvents. And also, GA is easy to be thermally decomposed, as a result, after deposition; residue is not remained in the coating film.

For this reason, pure Cu wiring is formed by direct patterning process using CO2 laser (wavelength 10.6μm). Concretely, first of all, GACu ink is coated on the substrate by various coating methods, and then, CO2 laser is irradiated into the substrate. As a result, Cu in irradiated area is precipitated. The next, GACu film in non-irradiated area is removed selectively by use of ethanol solvent. As a result, Cu pattern is gained. In this process, Cu is precipitated by its mechanism (Cu²⁺＋2e^-→Cu) , on the other hand, ligand is eliminated as a gas.

Picture 1 shows comparison of Cu precipitation state. In the case of the conventional annealing process (500℃) at N2 environment, conductive property was gained, on the other hand, in annealed sample at atmosphere environment, conductive property was not gained. By contrast, laser treated sample had conductive property in both environments.

Figure 2 shows relationship of laser power and specific resistance. If laser power is 4W and over, conductive property was developed, and in the case of 12W, lowest resistance such as 3×10^-5Ω･cm was gained. In short, if laser power is increased, conductive property is enhanced. This is reason why ligand was eliminated and micro Cu grains were generated by laser irradiation, and also, Cu grains grow greatly by thermal fusion of micro Cu grains. On the other hand, in the case of atmosphere annealing process, Cu is oxidized; as a result, this film becomes to be Cu-oxide.

Furthermore, GACu film was directly printed by the micro contact printing method, and then, it was treated by laser irradiation. In this experiment, fine Cu pattern such as 5μm width was formed. And also, Cu pattern was formed on the alumina substrate by the above process, and then, thick Cu film grew by the electroless plating method. This new process is confirmed to have high general versatility against substrates and manufacturing processes.　

Reference
1)Ooishi：Forming technology of Cu fine wiring in atmosphere by making use of laser irradiation and Cu complex, Shibaura Institute of Technology New Technology Presentation Meetings!, pp.3-7(2017.7)
※This title is translated arbitrarily by Stella News Site because of without English edition of presentation material.