(19)

(11)

EP 0 555 402 A1

(12)

(43) Date of publication: 18.08.1993 Bulletin 1993/33 (21) Application number: 92902033.0 (22) Date of filing: 24.10.1991

(51) International Patent Classification (IPC):  H01L 31/ 09( . ) H01L 31/ 10( . ) H01L 31/ 0352( . ) H01L 31/ 101( . ) (86) International application number: PCT/US1991/008004 (87) International publication number: WO 1992/008250 (14.05.1992 Gazette 1992/11)

(84) Designated Contracting States: DE FR GB IT (30) Priority: 31.10.1990 US 19900606285 (71) Applicant: Martin Marietta Corporation Bethesda Maryland 20817 (US)	(72) Inventor: LITTLE, John, William, Jr. Ellicott City, MD 21043 (US) (74) Representative: Cotter, Ivan John, et al  D. YOUNG & CO. 21 New Fetter Lane London EC4A 1DA London EC4A 1DA (GB)