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H. -C. HUANG, A. SEGMULLER, F. A. SUGERMAN, and P. A. TOTTA

E.

TURENE,

IBM T. J. Watson Research Center*, Yorktown Heights, N. Y. 10598, and IBM East Fishkill Facility, Hopewell Junction, N. Y. 12533 ABSTRACT PtSi films have been formed using sputtered Pt and different annealing sequences and ambients. A clear dependence on the annealing sequence and ambient is observed for both the PtSi films and the passivating oxide layers formed. The single-temperature process at 550"C using forming gas (N 2 -H 2 9:1), nitrogen and oxygen shows incomplete reactions between Pt and Si, with a surface oxide layer of poor resistance against etching in aqua regia. A three-temperature process using forming gas is shown to provide complete reactions between Pt and Si, with a surface oxide layer of excellent resistance against aqua regia. The three-temperature process using nitrogen or oxygen, however, fails to provide films of high quality, and the results are similar to those obtained by the single-temperature process in various gases. INTRODUCTION The silicide contact has been extensively used in very large scale integrated circuits, both as Schottky and ohmic contacts. Among the silicide contacts of interest, PtSi has been widely used both as a high barrier Schottky contact and as an ohmic one (1). Many studies have been devoted to understanding the various aspects of this silicide, including formation kinetics (2), ambient effects on the silicide formation (3-10), surface oxide formation (11), electrical characteristics (12), and effects of deposition techniques of Pt (13). Little is known, however, of the effects of annealing conditions for the silicide on the quality of the silicide and the passivating oxide layers formed on it. In this paper we report our studies of the effects of the annealing process on the formation of PtSi and the passivating oxide layer needed for the protection of the silicide layer in device processing. We show that both the annealing sequence for the Pt/Si system and the ambient gases used have profound effects on the quality of the silicide and the passivating oxide layers formed. EXPERIMENTAL PROCEDURES AND RESULTS Pt films, 430,k thick, were deposited by sputtering on (100) Si wafers precleaned by buffered HF cleaning and deionized water rinsing. Two annealing sequences were used, a single-temperature one at 550 0 C for 30 min,

Mat. Res. Soc. Symp. Proc. Vol. 54. c 1986 Materials Research Society

776

and a three-temperature one at 2000(lhr)-3000 (lhr)-550°C(30min) (14). For the latter, the samples remained in the annealing tube during the temperature rise from 200 to 300'C and from 300 to 550 0 C. Three annealing ambients were compared: forming gas (N 2 -H 2 9:1), nitrogen and oxygen at a The samples were either loaded into the cooling flowrate of 1 liter/min. zone outside the furnace, purged and moved into the furnace, or directly loaded into the furnace. Similar results were obtained for the corresponding annealing conditions. The samples were analyzed by x-ray diffraction and transmission e