Research On Wafer Bonding Technology Of GaN Based LED

Gallium nitride-based light emitting diode has always been the focus in the field of solid state lighting. For the growth of GaN films, hetero-epitaxial method (typically based on sapphire substrate) is a better choice in industrialization, compared with homo-epitaxial method which is difficult and costly. Although widely used, hetero-epitaxial method induces the problems of large lattice mismatch (13.4%) and great difference in thermal expansion (25.5%). which greatly enhances the difficulty to achieve high efficiency, high power LED. Silicon has excellent thermal conductivity as well as relatively good electrical conductivity, which could be an ideal substrate for high efficiency and high power LED. But higher lattice mismatch (16.9%) and greater thermal difference (54%) made Si substrate GaN a even more difficult method.Over the years, the IC industry has evolved towards wafer-level packaging (WLP) processes in order to reduce the costs in package step. Wafer bonding is a key technology in the field of wafer level package. With the help of wafer bonding technology, GaN film can be transferred from Al2O3 substrate to Si substrate. Using this substrate transfering method, high power and high efficiency LED could be achieved.In this paper, Au-Si eutectic bonding method was used to complete Si-Si, Si-GaN wafer bonding. Main work of this paper is listed as follows:1. Au, Ni/Au, and Ti/Au layers were deposited and annealed on Si substrates to investigate the influence of adhesion (barrier) layer on low temperature silicon diffusion in Si/Au eutectic system. We demonstrated that the adhesion layer acts as a diffusion barrier which reduces the diffusion of Si into Au. However this fails at relatively low temperature. We observed that annealing ambient has significant influence on the breaking down of diffusion barrier. Potential barrier model was proposed to explain the failure mechanism.2. Si-Si, Si-GaN wafer bonding was completed using Au-Si eutectic bonding method. Through altering of bonding recipe and adding of eutectic diffusion step, high quality bonding with single sided thin metal layer was achieved.