纳米级金属薄膜厚度电涡流检测方法研究

As integrated circuit (IC) manufacturing technologies advance and feature sizes reduce to the nanoscale, the chemical mechanical polishing (CMP) process is imposed by increasingly stringent precision requirements. This is because slight variations in material removal can cause device failure. In particular, for metal CMP processes, achieving accurate real-time endpoint detection is essential for ensuring controllable material removal and maintaining high-quality process outcomes. Compared with other conventional endpoint detection methods based on frictional or optical principles, the eddy-current method has emerged as an optimal solution for detecting the copper film thickness variation during copper CMP process. As a non-destructive testing technique characterized by high sensitivity, rapid response, and high resistance to environmental interference, the eddy-current method provides a reliable approach for in-situ thickness measurements under complex polishing conditions. Focusing on the challenges in detecting nanoscale metal film thicknesses, a simulation model of the eddy-current sensor is established in this study by coupling an electromagnetic field and an electrical circuit. Based on the numerical simulations, the effects of fundamental parameters, including coil parameters (e.g., excitation frequency, wire diameter, inner radius, turns, and diameter–height ratio), and signal-conversion module parameters of the detection-circuit (e.g., parallel capacitance, voltage division resistance, and bridge arm resistance) on sensor performance are systematically revealed. Then the coil parameters are further optimized. And the optimal parameter values are determined specifically for CMP applications under a lift-off distance of 2 mm (corresponding to the typical thickness of a polishing pad). Subsequently, the detection circuit is optimized with emphasis on the signal-conversion module, including two fundamental circuit topologies, i.e., an LC resonant circuit and an AC bridge circuit, by determining their respective optimal values of key electrical parameters, meanwhile, the other modules, such as the signal-generation module and peak-detection module are well accomplished for a good measurement performance. Furthermore, the influences of environmental parameters, particularly lift-off distance and temperature, on the output characteristics of the detection coil is revealed. To quantify the influence of lift-off distance variations, a quantitative thickness-error assessment model is developed that correlates the film thickness, measurement error, and lift-off distance. Additionally, a decoupling calculation method is proposed by establishing a mathematical relationship correlating the output voltage, film thickness, and temperature, thereby diminishing the influence of temperature variations on the thickness measurement. Finally, a nanoscale metal film thickness eddy-current detection system is developed. The system comprises an eddy-current sensor, precision displacement modules, and a vacuum-based wafer-holding module featuring a microporous ceramic vacuum chuck. The probe is mounted on a non-metallic cantilever beam fixed to the linear-displacement module to minimize lift-off distance variations, whereas the vacuum chuck ensures stable wafer holding on the rotary-displacement module. The coordinated motion of the linear-and rotary-displacement modules enables precise thickness measurements at multiple locations on the wafer surface. According to the experimental testing at a lift-off distance of 2 mm, the self-developed detection system demonstrates a sensitivity of 1.38 mV/nm and a linearity coefficient of 0.986 9 within a measurement range of approximately 1.5 μm. And a comprehensive evaluation of the measurement performance, based on the output-voltage fluctuation and sensitivity, shows that the detection system can achieve a nanoscale precision measurement of copper film thickness over a wide range. This study facilitates advancements in high-precision in-situ detection technology for high-quality polishing processes.