A tool for uniform coating of 300-mm wafers with nanoparticles

We report a laminar flow thermophoretic aerosol deposition tool suitable for depositing nanoparticles on flat substrates such as silicon wafers up to 300 mm in diameter. The essential features were found to be a high aerosol flow rate, an inlet designed to minimize flow separation (a hyperbolic design in this case), and heating the aerosol inlet gas flow. A high flow rate reduces the residence time, thereby limiting particle agglomeration. The hyperbolic design of the aerosol inlet nozzle maintains the dynamic pressure that is needed to prevent flow recirculation, and is robust up to flow rates of 15 SLM without flow separation. Finally, heating the inlet gas flow ensures uniform particle deposition over the entire surface of the substrate. Particle deposition is quite uniform in both radial and azimuthal directions, with less than ±5.5 % variation of particle density on a 150-mm wafer, as characterized using non-contact AFM imaging. Computational fluid dynamics simulations predict that similar uniformity can be attained on larger (300 mm diameter) wafers.