Contact the authors at ULVAC Technologies, 401 Griffin Brook Drive, Methuen, MA 01844. Richard Bersin is a senior member of technical staff, 978-686-7550, ext. 251, fax: 978-689-6302, dbersin@ulvac.com; Han Xu is director of process technology, 978-686-7550 ext. 253, fax: 978-689-6300,