These files are generated by the Lotus Incremental Installer. They are backups of the files that the Incremental Installer changed. You can delete these files if you are satisfied with the incremental upgrade. If not, run the same Incremental Installer again and it will ask if you want to uninstall the upgrade.
Note: If you're running a CF incremental, do *not* delete the IIB files. When Lotus releases another normal incremental, it will try backing out the CF incremental by using the IIB files; if they don't exist, the incremental will fail.