Selective Electroless Plating Of Copper By Laser And A Mathematical Model For Deposition

With the rapid development of the electronic technical products, the size of theirs tends to the microscale and high reliability is very necessary. Thus, the electroless plating becomes a key technology for the fabrication of micro electromechanical systems (MEMS) and microelement for its particular characteristics. Laser has a good prospect of application in the fabrication of MEMS and other micro or nano-systems duo to its unique advantages, such as very high laser pulse intensity with low pulse energy, a very small heat diffusion region, machining objects at atomic or molecular scale and modifying and processing some important properties of structures in microscopic areas.This paper describes a surface micromachining process for selective electroless plating of copper on N-type silicon. A copper- hypophosphite bath is considered in the deposition process. Before the electroless plating, it is necessary to treat the silicon surface to be plated. In this work, this pretreatment consists of degreasing, etching, sensitization and activation. After that YAG laser ablation of Pd thin metal films on the silicon surface was carried out. In this process, in order to produce the final copper microstructures over the silicon substrate, the laser was used to ablate metal micro-patterns, and the created micro-pattern worked as mould for deposition copper through electroless deposition process. The residual patterned Pd film on the silicon surface acts as an excellent catalyst for electroless copper plating. The nickel ion acting re-activator was added into the electroless plating solution for hypophosphite acted as reducing agent in this work. Finally the metal film is copper-nickel alloy evenly.A mathematical model for the electroless deposition of copper on planar substrates from a copper-tartrate-formaldehyde bath is presented in this paper. The model takes into account mass transport by diffusion. A finite difference approach is used to solve the equations, and the resultant model is used to predict the concentration profiles of various reactive as a function of time from the bulk to the surface. The copper deposit thickness is plotted as a function of time which increases linearly with time going on.