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 technique, which is suitable for fabricating various optical components and finishing functional materials. In this technique, a chemical reaction between the etchant and the surface of the workpiece removes the surface without causing the degradation of 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 HF/HNO3 mixtures to etch the silicon, we corrected the thickness distribution of the bulk silicon wafer with a diameter of 200 mm and achieved the total thickness variation of less than 0.23 µm within the diameter of 190 mm.