Nondestructive Methods for Characterizing Copper Electrofilled through Silicon Vias

Abstract

Developments in through silicon via (TSV) fabrication and filling have allowed for significant advancements in the microelectronics industry by enabling compact 3D integration. Copper, due to its desirable electrical properties, is the most commonly used metal for TSVs filling. TSVs are filled electrochemically by selectively reducing solvated metal ions in an electrolyte solution to confined TSV geometries via the addition of organic and inorganic additives (halides, suppressors, accelerators, levelers). Optimization of this mechanism can often be temperamental requiring alterations in the solution’s chemical makeup as well as electrical bias and fluid flow parameters. Therefore, consistent and reliable methods of characterizing electrochemical copper fill quality is critical to provide feedback necessary for process adjustments. Historically, characterizing TSV fill profile has relied on physical cross sectioning by mechanical grinding, planarization and polishing (Figure 1). These methods are effective in that they offer direct visualization of the TSV fill quality; however, they have certain inherent drawbacks. The most critical drawback is that mechanical cross sectioning is a destructive process and can only be used in process development and not on deliverable parts. Also, mechanical material removal can often be time consuming and inconsistent requiring significant effort by process technicians to generate desirable results. Implementing non-destructive methods for characterization is necessary for the advancement of TSV technology and has been explored in an effort to make TSV research more streamline and efficient. Recent work at Sandia National Laboratories has evaluated non-destructive TSV characterization processes through X-Ray Computed Tomography (CT), digital radiographs and X-ray Phase Contrast Imaging (XPCI). The benefit of X-ray evaluation of TSV filling is batch level processing of many TSVs at once (Figure 2A), digital model rendering for multidimensional analysis (Figure 2B), and complete preservation of the physical integrity of test pieces and deliverables. Each nondestructive technique for TSV characterization will be directly compared and contrasted to conventional grinding and polishing on the merits of defect detection, resolution, time consumption and reproducibility. This talk will outline the development of non-destructive methods for TSV characterization and evaluate the reliability and consistency of these approaches. Sandia National Laboratories, a multimission laboratory managed and operated by National Technology and 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-NA-0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. Figure 1