HARMONI is the ELT first light visible and near-infrared (0.45 to 2.45 μm) integral field spectrograph over a range of resolving power from R~3500 to R~18000. It will provide 4 different spatial scales from 4*4mas to 30*60mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews. This paper depicts the final design of the Integral Field Unit in charge of splitting, slicing and rearranging the rectangular field of view into 4 long slits (~540mm) to feed the 4 spectrographs. The manufacturing of sensitive optics such as the field splitter or the image slicer are detailed. The mechanical and alignment design strategy is explained as well as the design of some dedicated integration tools, developed for cryogenic environment. The performances of the full unit are deeply discussed in terms of image quality, straylight analysis, tolerancing.
