Improvement of thickness uniformity of bulk silicon wafer by numerically controlled local wet etching

We have developed numerically controlled local wet etching (NC-LWE) as a novel deterministic subaperture figuring and finishing method, which is suitable for fabricating various optical components and for finishing functional materials. In this method, a chemical reaction between the etchant and the surface of the workpiece removes the surface without degrading the physical properties of the workpiece material. Furthermore, the processing properties of NC-LWE are insensitive to external disturbances, such as the vibration or thermal deformation of the machine or the workpiece, because of its noncontact removal mechanism. By applying the NC-LWE process using a HF/HNO3 mixture to etch silicon, we corrected the thickness distribution of a bulk silicon wafer with a diameter of 200 mm and achieved a total thickness variation of less than 0.23 μm within a diameter of 190 mm.