In-Situ Analysis of Chronopotentiometry Data to Predict Electrodeposition Rates

Abstract

Often in MEMS or NEMS microfabrication R&D, many single layer “test” samples are created prior to committing more complex multiple layer “device” samples which require more time and effort to create. Ideally, much of the R&D can focus on less critical test samples and the experimental results can then be applied to more valuable device wafers. We investigated tin electroforming into patterned polymer molds creating Meissner-Effect Transition-Edge-Sensor (ME-TES) devices1 and found multiple variables changed between the test and device samples making it difficult to target a desired tin metal thickness. These variables were analyzed and distilled down to two: (I) area and (II) the measured voltage at constant current 30 seconds after plating started. In addition to the underlying analysis, a Graphical User Interface (GUI)2 was developed in R to quickly calculate and predict in-situ tin electroplating rates regardless of uncontrolled variables in the sample.ME-TES devices required a final tin plating feature height of 8-12 microns for 50-micron diameter discs coupled with patterned niobium electrical traces3. During chronopotentiometry experiments, two samples were plated for 1 minute and 18 minutes, respectively – both achieving the target height of 10 microns. This extreme variability in rate caused the height to undershoot or overshoot within just a few minutes of plating. Many variables were collected into a database and analyzed including wafer design layout, electrochemical methods, chemistry make-up, electrochemical setup, the use of a reference electrode, current density, voltage, mounting technique, height, device size, and surface roughness across the substrate. The resulting GUI resulted in fewer necessary test samples, reduced processing time, and improved accuracy in plating thickness.(1) Finnegan, P. Packaging & Solid-state Materials and Fabrication Processes. In Packaging & Solid-state Materials and Fabrication Processes, June 2023.(2) St. John, C. “R Shiny User Interface for Electrochemical Development.” In CoDA, Santa Fe NM, March 2023.(3) Arrington, C.L. Optimizing Tin Electroplating for MEMS Meissner-Effect Transition Edge Sensors. In 243rd ECS Meeting with SOFC-XVIII, Boston, MA, 2023.Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.SAND2022-10287A