Apparatus and method for wafer thinning in advanced packaging applications

A method for wet-etching a wafer having a fan-out wafer level packaging (FOWLP) construction with at least one metal interconnect pad located within a redistribution layer (RDL) beneath a surface of the wafer to produce a processed wafer with the at least one metal interconnect pad being at least partially exposed the method comprising the steps of:

• measuring, at a measurement station, an initial thickness of the wafer at each of a plurality of radial locations along the wafer;
• calculating, by a process controller, a respective first etch depth for each of the plurality of radial locations, wherein the respective first etch depth for a particular radial location is the amount of material to be removed at the particular radial location during the first etching step and is a function of the measured initial thickness of the particular radial location and a prescribed respective residual substrate material thickness (RST) which is a thickness of a layer of residual wafer material left over the at least one interconnect pad after the first etching step, and wherein the respective first etch depths are non-uniform;
• generating, with the process controller, a first-etch recipe based on the calculated respective first etch depths, wherein the first etch recipe controls movement of a nozzle during the first etching step causing the nozzle to selectively dispense a first etchant onto each of the plurality radial locations thereby thinning the wafer at each radial location the respective first etch depths, wherein the first etch depths are depths that do not reveal the at least one interconnect pad;
• etching, at a first etching station, the surface of the wafer according to the first etch recipe and using the first etchant;
• etching, at a second etching station, the surface of the wafer according to a second etch recipe using a second etchant to thin the wafer material such that a respective portion of the at least one interconnect pad is exposed;
• and
• wherein the first etching step is an isotropic wet-etching step, the second etching step is an anisotropic wet-etching step, and the first and second etchants comprise different chemical compositions.