| Summary: | 碩士 === 國立中興大學 === 精密工程學系所 === 94 === An electroless plating technique is used to deposite the Au electrode pads on GaN light-emitting diodes (LEDs) by applying photolithography and lift-off processes. It was found that the metallic seed layer on the pre-determined electrode region played an important role in the electroless plating process. The existence of photoresist passivation was confirmed to be necessary in order to achieve a successful plated Au pads. Details of the GaN LED performance were investigated, where the Au pads were fabricated by the present electroless plating or conventional electron-beam (EB) evaporation processes.
For the electroless plating experiments, the GaN LED wafer was immersed in the constant temperature bath at 53°C and a linear growth rate versus time can be achieved. A typical growth rate of 1.1 µm/hr was obtained by using a refresh plating solution. For a plated Au thickness grow ranged from 10 nm to 1 µm, the surface roughness can maintain 8 nm. Once the plated thickness increased above 1.2 µm, the surface roughness gradually increased and became rougher than that coated by EB evaporation. From the wire bonding tests, the pulling strength test of each pad was greater than 8 g with a pad thickness of 1 µm. The current versus voltage curves are same for the GaN LED with electroplated and EB evaporated electrodes. A reliability test was performed by 55°C/50 mA for 526 hours, the electroplated GaN LED samples show only 8% degradation in the luminous intensities. These results indicate that the Au bonding pads of GaN LEDs deposited using the electroless plating process have high potential in the capability of cost down. As compared with the none-selective deposition by the EB evaporation, the electroless plating process only uses 20% area of the two inch wafer, corresponding to a more efficient gold usage.
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