After the Upper On-Chip Lens (UOCL) is patterned and thermally reflowed into a hemispherical shape, it must be permanently solidified (Engineering Practice).This step prevents any further deformation of the critical optical profile during subsequent backend processing (Engineering Practice).By highly crosslinking the polymer matrix, the lens material achieves the necessary mechanical and thermal stability to withstand the subsequent Upper OCL protective oxide coating and pre-lithography cleaning