Rapid characterization and modeling of pattern-dependent variation in chemical-mechanical polishing

TLDR

Pattern‑dependent effects in chemical‑mechanical polishing cause interlevel dielectric thickness variations across a die and wafer, degrading circuit performance and yield. This study introduces test mask designs and measurement methods to rapidly characterize and model polishing behavior as a function of layout pattern factors. The approach uses these masks to analyze interconnect oxide planarization, comparing pattern‑dependent variation models for two polishing pads across various CMP applications. Pattern density dominates polishing variation, while structure area, pitch, and perimeter/area have only minor influence.

Abstract

Pattern-dependent effects are a key concern in chemical-mechanical polishing (CMP) processes. In oxide CMP, variation in the interlevel dielectric (ILD) thickness across each die and across the wafer can impact circuit performance and reduce yield. In this work, we present new test mask designs and associated measurement and analysis methods to efficiently characterize and model polishing behavior as a function of layout pattern factors-specifically area, pattern density, pitch, and perimeter/area effects. An important goal of this approach is rapid learning which requires rapid data collection. While the masks are applicable to a variety of CMP applications including back-end, shallow-trench, or damascene processes, in this study we focus on a typical interconnect oxide planarization process, and compare the pattern-dependent variation models for two different polishing pads. For the process and pads considered, we find that pattern density is a strongly dominant factor, while structure area, pitch, and perimeter/area (aspect ratio) play only a minor role.