Study on Nanoparticle Movement using Multi-wavelength Evanescent Fields for Chemical Mechanical Polishing

In the wet semiconductor process, abrasive nanoparticles have been being widely used in the chemical mechanical polishing （CMP） process to polish a wafer surface for high planarization. During polishing, nanoparticles move with a high-speed three-dimensional （3D） position in the solution. In the 3D nanoparticle's moving positions, X and Y positions are parallel to the surface, which can be measured by general microscopy. However, Z is a perpendicular distance between the surface to the nanoparticle, which could not be measured by general microscopy without longitudinal scanning, which is our research challenge. To understand nanoparticle phenomena near-surface, we have proposed and developed the apparatus with real-time fast-motion tracking on optical multi-wavelength evanescent fields microscopy to measure the 3D motion of an individual nanoparticle in water without scanning. The proposed method could measure height Z in one shot, suitable for high-speed measurement. There were three main experiments performed in this thesis. The first experiment focuses on the verification of measurement in the z-direction. A piezoelectric actuator was employed to control the nanoparticle displacement in height Z. Standard polystyrene φ100 nm particles randomly adhered to a spherical tip connected with the piezoelectric actuator. The spherical tip was essentially made from an optical adhesive （n=1.348） with a refractive index close to the water to decrease the tip self's unnecessary signal during nanoparticle observation in the water. The proposed method could obtain the multi-wavelength scattering lights from the observed nanoparticles by an 8-bit color camera with higher than 50 frames per second recording to investigate the 3D nanoscale tracking. The X and Y positions of nanoparticles were determined by the centroid of the scattering light intensities. The height Z was determined from the logarithm ratios between the detected scattering light intensities of both wavelengths. The measurement repeatability of the absolute difference in height between nanoparticles could be measured less than ±16 nm by using the proposed method. The uncertainty measurement of height Z of nanoparticles was less than that of ± 17 nm （2σ from 400 measurements）. The penetration height measurability range was approximately 250 nm from the reference surface. In the second experiment, we have therefore developed an invisible nano-step pattern in water to verify the absolute distance Z of an individual nanoparticle. The invisible nano-step height in water is made from an optical adhesive with a refractive index of 1.348. The invisible nano-step height in various heights was approximately less than 100 nm on a glass surface. Polystyrene φ100 nm standard particles were used to adhere to the invisible nano-step height and glass surface in water to verify the absolute distance Z. As a result, the measurement uncertainty of the absolute distance Z of nanoparticles was approximately less than ±10 nm （2σ from 100 measurements）. The third experiment used polystyrene （PS） standard φ100 nm particles and gold （Au） standard φ50 nm particles to investigate our three-dimensional tracking method. The 3D tracking results of PS φ100 nm particles were used to analyze the nanoparticle diffusion in the water. As a result, we found that the diffusion rapidly decreased when the height Z of the nanoparticles was nearer to nanoparticle size D （Z < 100 nm）. Finally, the outcomes of this study can provide information explaining some of the phenomena during the nanoscale process on a surface （Z < 100 nm）, such as a wet semiconductor process.