Aerosol jet cleaning of silicon wafers

Submicron particles, ionic and metallic impurities, and organic residue are the major surface contaminants in microelectronics fabrication. These contaminants result in more than seventy-five percent of the yield loss in advanced device manufacturing. Contamination control involves both prevention of contaminant deposition on wafer surfaces and removal of deposited contaminants from wafer surfaces. Because complete prevention of contaminant deposition is unattainable, wafer cleaning is the most common operation performed during device fabrication. With continued reduction of line width and feature sizes in microelectronics devices, current surface cleaning techniques are inherently unable to meet the demanding requirements for surface purity.;The main objective of this research is to develop a novel wafer cleaning technique, termed aerosol jet cleaning (AJC), using a high-speed aerosol jet. Both theoretical and experimental studies were conducted. In order to understand ultrafine droplet impingement from supersonic jets, a two-step Taylor-Galerkin finite element method with flux corrected transport algorithm (FEM-FCT) was used to calculate the flow fields of highly underexpanded two dimensional planar symmetric impinging jets. The trajectories and impaction efficiencies of ultrafine aerosol droplets were calculated with the known flow fields.;In the experimental work, an apparatus for the AJC system was designed and constructed. By combining a pure vapor stream of the chemicals and a cold stream of non-reactive gas, ultrafine aerosol droplets are produced by homogeneous nucleation in the aerosol generation chamber. The aerosol droplets grow by coagulation and condensation in the aerosol growth chamber. Then this aerosol expands through a slit nozzle into a low pressure chamber, accelerates to supersonic velocities, and impinges on the wafer surface which is maintained perpendicular to the jet centerline. A series of experiments with several different operating parameters were studied to confirm theoretical predictions. Cleaning efficacy of AJC for different contaminants on a variety of substrates, including patterned wafers, was investigated with a Nomarski optical microscope and a Scanning Electron Microscope (SEM). Additionally, an atomic force microscope (AFM) was used to study the surface roughness of the wafer surfaces subjected to AJC.