Comparison of Radio Frequency and Microwave Plasma Treatments on LED Chip Bond Pad for Wire Bond Application

The efficiencies of argon radio frequency [Ar(RF)] and argon microwave [Ar(MW)] plasma treatments were compared in terms of contaminant removal and wire bond interfacial adhesion quality in this paper. The efficiency in contaminant removal was analyzed by applying Ar(RF) and Ar(MW) plasma treatments with operating frequencies of 13.56 MHz and 2.45 GHz, respectively, onto the light-emitting diode chip bond pad prior to the wire bonding process. Surface characterization results show that Ar(MW) plasma treatment is able to remove the bond pad surface contaminant and improve the bond pad surface roughness more effectively than Ar(RF) plasma treatment. Moreover, contact angle measurement results show that bond pad samples after Ar(MW) plasma treatment have higher surface free energy compared with Ar(RF) plasma treatment. To study the improvement of wire bond interfacial adhesion after Ar(RF) and Ar(MW) plasma treatments, the bond pad samples were wire-bonded via the thermosonic wire bonding method and examined with the ball shear test. The ball shear test results show that Ar(MW) plasma treatment leads to a better improvement of wire bond interfacial adhesion compared with Ar(RF) plasma treatment.