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Next Level of Enhanced Isotropic Etchants
Keywords: Differential Etching , Semi-Additive-Processing , Enhanced Isotropic Etchants
By the trend towards miniaturization IC-manufacturers are permanently requested to increase the density of interconnects generating conductors featuring finer lines and spaces. Advanced manufacturing technologies such as Semi-Additive-Processing (SAP) and (advanced) Modified-Semi-Additive-Processing were devised, realized and implemented in order to satisfy these needs. According to the roadmaps of the major Original Equipment Manufacturers, Line/Space requirements Copper conductors become increasingly finer and will be below 5/5µm for the future packaging substrates. As an alternative etching solution a recyclable ferric sulfate based process was introduced to the market by Atotech. Firstly this type of etchant does not exhibit undercut as found for the POR. A second advantage is the fact that by utilization of an electrolytic regeneration unit the process becomes nearly waste water free. No feed & bleed operation is required to maintain constant bath parameters in contrast to the POR, with a big impact on the overall process costs. The small dosing required is mainly governed by the drag-out loss. In addition the etched copper is reclaimed on-site as pure copper and can be used to the economic benefit of the customer. Based on the described first-generation product and in order to maintain the cost (recyclable, less waste water), and functional advantages (no undercut formation) and to further improve the performance of ferric sulfate based etching solutions EcoFlash™ was developed. Herein we report about the performance of the new developed EcoFlash™ process with the focus on fine line capability in comparison to hydrogen peroxide etchants. The additive package developed for EcoFlash™ is able to change/impact the intrinsic solution characteristics and mimic a hydrogen peroxide like etching behavior. That means EcoFlash™ performance is also nearly unresponsive to solution agitation/flow like hydrogen peroxide based etchants and hence etch attack in areas with dense conductors is the same then in areas with isolated tracks. Beside the vanished agitation dependency EcoFlash™ fulfills all performance demands from IC-substrate manufacturers. The process offers minimized etching on the conductor tracks (minimized line width reduction) combined with a fast and complete seed layer removal. In contrast to hydrogen peroxide based systems no undercut formation will occur even with strong over-etching, what means the interfacial integrity and mechanical stability of the conductors can be ensured. Furthermore the ferric sulfate based EcoFlash™ process is operated with a recovery unit which offers the possibility to regenerate the solution in by-pass equipment and therefore eliminating the need for feed and bleed operation. This concept greatly reduces the amount of copper contaminated waste water and hence process costs. Besides regenerating the oxidizer pure copper is plated, which can either be re-used internally or sold to recyclers. EcoFlash™ as a new differential etching process is in line with Atotech’s global commitment to reduce the environmental footprint associated with clear economic benefits in day to day operation
R. Haidar, P. Brooks, F. Michalik, Global Product Manager
N. Luetzow, G. Schmidt, T. Huelsmann, M. Kloppisch Atotech Deutschland GmbH
Berlin, Germany

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