Fabrication Technology of Metal Bumps for Ultra-high Resolution Micro-display

Ultra-high density micro-nano display devices impose stringent requirements on interconnect bumps, including ultra-fine pitch and high uniformity. In this work, ultra-fine pitch copper (Cu) bump arrays were fabricated by combining electrochemical deposition, the core process, with ultraviolet laser direct writing technology. The photolithography process was optimized to obtain high-resolution micropore masks, and a copper sulfate-based acidic electroplating solution was adopted for bump growth. The effects of current density, deposition time and other parameters on bump morphology, height uniformity, internal structure and interfacial bonding performance were systematically investigated. Finally, ultra-high density bumps with a pitch of 2 μm were efficiently fabricated. The array scale reached 5000 × 5000, and the bump height was up to 2 μm, with the array height non-uniformity as low as 2.92%. The as-prepared copper bump arrays featured smooth and regular surfaces without short-circuit bridging, as well as dense internal structures free of voids, impurities and other defects. The bump structures remained stable even after the removal of the redundant seed layer. Using the proposed process, 250 × 250 light-emitting arrays were successfully fabricated on gallium nitride light-emitting diode (GaN-LED) epitaxial wafers, which verified the feasibility of achieving a pixel density of 12700 PPI. This study provides a valuable reference for the interconnection and bonding technology of ultra-high resolution micro-display devices, as well as the research, development and industrial application of high-efficiency light-emitting devices.