Aluminum Foil/Si Direct Bonding as Prototypes of Ultra-Thick Metal Contacts in Devices

We bonded aluminum (Al) foils to Si substrates to fabricate Al/p-Si, Al/n-Si, Al/p+-Si, and Al/n+-Si junctions by surface activated bonding (SAB) method and investigated the effects of the annealing process on the electrical properties of the junctions by measuring their current - voltage (I-V) characteristics. It was found that the leakage current of the reverse bias voltage in the bonded Al/n-Si junctions significantly decreased and the interface resistance of the bonded Al/p-Si junctions dramatically decreased with the annealing temperature. The smallest interface resistances of the bonded Al/p+-Si and Al/n+-Si junctions were obtained to be 0.021 and 0.032 Ω·cm2, after annealing at 300 and 400°C, respectively. We demonstrated the fabrication of Al foil mesa-structures and micro wiring with complex structures on Si substrates. The sheet resistance of the bonded micro wiring was found to be more than two orders of magnitude lower than that of the evaporated micro wiring. In addition, Al foil mesa structures revealed a good thermal stability at the annealing temperature lower than 600°C. These results indicated that the fabrication of the thick metal electrode in devices could be realized by SAB.