WebSphere does not have a built in feature that can be used to archive a checkpoint. Instead, archiving a checkpoint is a manual process where you copy the checkpoint files to a backups directory on one of your servers. Then, if you ever need to restore a checkpoint that has been archived, you simply move the checkpoint files back into the appropriate location on your WebSphere server and restore the checkpoint.
When a full or delta checkpoint is created, two files will be created. One is a metadata file, and the other is the actual contents of the checkpoint. The metadata file is located at was_home/profiles/profile_name/config/cells/cell_name/repository/checkpoints/checkpoint_name/checkpoint.xml and the actual contents file is located at was_home/profiles/profile_name/checkpoints.