Ultra-fast correlative chemical-mechanical-polishing (CMP) metrology: integrating phase shifting interferometry with active-probe scanning probe microscopy

This paper presents the development of an Ultra-Fast Correlative Metrology method that integrates high-accuracy phase-shifting interferometry (PSI) with active probe-atomic force microscopy (AP-AFM). PSI is a widely used optical metrology technique for precise surface roughness measurements, refractive index mapping, and other optical parameter evaluations. Its advantages: high accuracy, full-field capability, high speed, and non-destructive nature make it indispensable for semiconductor wafer inspection, particularly in Chemical Mechanical Polishing (CMP) control, where the dishing effect must be carefully monitored. However, its effectiveness is often compromised by phase-shift errors, vibrations, detector non-linearity, stray reflections, quantization errors, frequency instability, and intensity fluctuations, especially when measuring topographic profiles with varying refractive indices. To overcome these limitations, we propose a novel approach that combines PSI with AFM, leveraging the high imaging resolution of AFM. Unlike PSI, the performance of AFM is independent of the probe material’s refractive index. Moreover, the construction of optical beam deflection (OBD)-based AFM is incompatible with this integration within the PSI system due to space limitations. Instead, the AFM technology developed by nano analytik GmbH utilizes active probes (AP) with integrated piezoresistive readout and autonomous actuation, eliminating the need for the OBD-system. These active probes incorporate durable hard-material tips, such as GaN and diamond, ensuring long-lasting performance with atomic resolution. This hybrid metrology system bridges the gap between high-speed optical metrology and atomic-scale resolution, enabling near real-time inspection with traceable defect review capabilities. By merging PSI’s speed with AFM’s precision, this approach enhances metrology accuracy for semiconductor manufacturing and beyond.