Modeling and experiment of concave microlens array on silicon wafer by grinding-polishing process with diamond slurry

Silicon wafers with micro patterns were evaluated as one of the promising molds to fabricate microlens arrays for its high hardness. This study presents an efficient yet flexible manufacturing method for microlens array silicon mold by a polishing method. Unlike conventional processes for microstructures on silicon wafers such as diamond machining and photolithography, this research demonstrates a low-cost and high efficient chemical mechanical polishing (CMP) process with steel balls and diamond slurries for precision microlenses manufacturing. During the CMP process, polishing parameters for each micro cavity need to be accurately calculated and controlled to obtain microlenses with specific apertures. Therefore, a micro wear model for micro cavity CMP process was established to calculate cavity sag height with the knowledge of down force, polishing time and relative velocity between ball and silicon wafer. Several groups of microlenses polishing were then conducted under the same conditions to validate the micro wear model. Guided by the micro wear model, a 5×5 microlens array was fabricated on silicon surfaces. The shape accuracy and surface texture of the microlens arrays were evaluated by using a white light interferometer. This research demonstrates an alternative lowcost and efficient method for microstructure fabrication on silicon wafers and possible follow up optical molding processes.