Computational investigation of a novel metal thickness measurement system with coaxial triple-coil sensor for chemical mechanical polishing

• Published in: International journal of advanced manufacturing technology 2024-06, Vol.132 (11-12), p.5249-5258
• Main Authors: Wang, Chengxin, Tian, Fangxin, Wang, Tongqing, Liu, Bangxu, Lu, Xinchun
• Format: Article
• Language: English
• Subjects: Accuracy; Advanced manufacturing technologies; Amplitudes; CAE) and Design; Chemical-mechanical polishing; Coils; Computer simulation; Computer-Aided Engineering (CAD; Copper; Dimensional analysis; Eddy currents; Electric potential; Electromagnetic fields; Electromagnetism; Engineering; Film thickness; Finite element analysis; Finite element method; Industrial and Production Engineering; Magnetic fields; Manufacturing; Mathematical models; Mechanical Engineering; Media Management; Metal films; Original Article; Permeability; Real time; Sensors; Simulation; Thickness measurement; Time measurement; Voltage
• ISSN: 0268-3768; 1433-3015
• DOI: 10.1007/s00170-024-13677-7

The eddy-current method has been employed to realize the real-time measurement of thickness distribution and polishing endpoint detection of metal films during the metal chemical mechanical polishing (CMP) process. However, accuracy and sensitivity in thickness measurement can be significantly impacted by a variation in lift-off distance (about 3.5 mm), attributable to the progressive wear of the polishing pad. This paper proposes a novel triple-coil sensor system, integrated with an alternating-current bridge and designed for high-precision metal film thickness measurement. Subsequently, the measurement performance of the bridge output voltage was scrutinized using a theoretical model and a trans-dimensional finite element analysis model of electromagnetic fields and circuit coupling. The correlations between the amplitude, phase, and the ratio of the real part to the imaginary part of the output voltage, in context with film thickness, were determined at assorted excitation frequencies and lift-off distances. Both theoretical equations and simulation results affirmed that the phase and ratio were more resistant to lift-off distance variations than the amplitude, and a linear relationship was identified between the ratio and film thickness. Furthermore, the thickness measurement performance of the amplitude and phase, when the triple-coil was imbalanced, was dissected via numerical simulation. A profound understanding of the proposed system was provided and beneficial for the practical applications in real-time thickness measurements of metal films during the metal CMP process.