There are some fonts which do have those superscripts built in. You may have to see how you can access those characters (most likely via their Unicode ID).
If this is not the case, you will have to use the richText property of the field. There is a good code sample in the Acrobat JavaScript documentation (part of the Acrobat SDK, downloadable from the Adobe website), if you look for the Span Object, and go to the superscript property.
Hope this can help.
Max Wyss.