Integrated circuits (ICs 110) are attached to a wafer (120W). A stabilization layer (404) is formed over the wafer to strengthen the structure for further processing. Unlike a conventional mold compound, the stabilization layer is separated from at least some wafer areas around the ICs by one or more gap regions (450) to reduce the thermo- mechanical stress on the wafer and hence the wafer warpage. Alternatively or in addition, the stabilization layer can be a porous material having a low horizontal elastic modulus to reduce the wafer warpage, but having a high flexural modulus to reduce warpage and otherwise strengthen the structure for further processing. Other features and advantages are also provided.