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Direct Metal Replenishment - Cost-effective novel method of replenishing electrolytic plating baths
Keywords: Wafer level packaging, Low alpha tin, Electrodeposition
Continuous technology development and the onset of new Si technology nodes require further scaling and cost reduction per transistor/ IO. At the current technology development junction, approaching the sub 10 nm nodes, the cost and complexity of the traditional semiconductor FEOL equipment manufacturing are increasing exponentially. Faced with this challenge, more and more companies are turning to investment in novel packaging solutions, as a way of differentiating their technology offerings. Many of those new interconnect solutions, including multiple Fan-out methodologies, as well as 2.5 / 3D IC, RDL-type integration schemes, require novel electrolytic plating applications. To effectively meet marketplace performance and price pressure requirements, these new plating methods face an additional challenge of being higher throughput and lower costs, than their predecessors. These requirements are specifically pertinent for copper, nickel, and tin-silver plating - metals ubiquitous and omnipresent in all generations of interconnects - past, present, and future. In this paper we report on the novel method of delivery of the bath component replenishment to the electrolytic plating bath, using powdered materials. Tested for several unique applications, this methodology delivers a dramatic reduction in the cost of ownership, environmental personnel exposure, process robustness, and stability, compared to the liquid replenishment out of metal salts. The system is an addition to the ancolyzer - ancosys -proprietary chemical analysis and control system, controlling and maintaining the bath and all of its components within the specification. The direct metal replenishment (DMR) system provides gravity-fed delivery of the powdered components directly into the bath and is fully integrated into the bath control scheme. The methodology uses ancosys-proprietary powder containers, fully compatible with the traditional packaging clean room requirements, and delivering state of the art reporting on the replenished component quality, as well as full reporting on the efficiency of material replenishment in the bath. We concentrate on the details of the qualification of the DMR using low alpha tin oxide material for low alpha tin-silver applications. For the low alpha tin-silver plating, we demonstrate cost savings of at least 50-60% over conventional replenishment, by using powdered low alpha tin oxide for tin replenishment in the bath. Most of this cost reduction is due to the fact this technology allows significant waste reduction over a full bath lifetime. We also show an improved process stability, where DMR-replenished baths perform better than POR replenished baths, as demonstrated by on-wafer reliability data. Using this DMR methodology also dramatically improves overall process uptime, by increasing bath lifetime (up to 4x), as well as reducing the environmental impact of plating operation by reducing the amount of bath waste produced. We explain the mechanism of the observed improvements and benefits seen. For fast copper plating, using the DMR methodology to replenish copper oxide directly into the plating bath offers an opportunity to use plating baths with high copper concentrations. This allows avoiding additional bath dilution commonly associated with traditional liquid replenishment methods. High-speed plating applications, like RDL mega pillars or Fan-out, work best with inert anodes, which are critical for enabling the best equipment uptime and plating results. State of the art PCB and panel plating for high-end applications traditionally uses copper oxide as a replenisher. With DMR from ancosys, we enable semiconductor WLP manufacturers to utilize the advantages of copper oxide in a clean room environment. Using DMR allows the end user to drastically reduce process cost of ownership by using shelf-stable copper oxide powder at an improved price point. Plated nickel barriers are essential for achieving high reliability in plated WLP structures. Boric acid is a critical component of the majority of commonly used nickel baths and needs to be tightly controlled. With the newly available DMR technology, ancosys enables its customers to replenish boric acid in powder format directly into the plating bath and ensure tight process control. We demonstrate that using a DMR system for delivery of powdered boric acid, allows manufacturers to eliminate employee exposure to and contact with both liquid and powdered boric acid material and enables effective utilization of high boric acid electrolytic nickel baths, which often require high temperatures and extensive handling to effectively maintain. In summary, ancosys presents a set of field- tested and qualified in high volume manufacturing examples using DMR (direct metal replenishment) - an ancosys- proprietary novel system of chemical process control, offering significant cost of ownership and process stability benefits, compared to the current industry standard options. Utilizing DMR methodology in conjunction with ancolyzer analysis and replenishment systems, allows WLP device manufacturers, chemical and electroplating equipment suppliers to meet the ever increasing cost and capability demands of the marketplace.
I. Popova, Senior Director in R&D
Ancosys GMBH
Hopewell Jctn, NY
United States

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