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AMORPHOUS PHASE FORMATION AND RECRYSTALLIZATION

C.A.

HEWETT*,

I.

SUNI**,

S.S.

LAU*,

L.S.

HUNG***,

IN ION-IMPLANTED SILICIDES AND D.M.

SCOTT*

University of California at San Diego, La Jolla, CA 92093. **Caltech, Pasadena, CA 91125. ***Cornell University, NY 14853. ABSTRACT Ion implantation induced phase transformations and recrystallization during post-annealing in CoSi , CrSi 2, and Pd2Si are studied. All three silicides are found to reorder at about 1/3 the melting point of the silicide. We speculate that ionimplanted silicides recrystallize by the same mechanism and that amorphous phases produced by implantation are unstable rather than metastable. INTRODUCTION The self-aligned gate technology is commonly used in MOSFET fabrication. The gate electrode, usually a metal or a metal silicide, is used as a mask to protect the conducting channel during the implantation of source and drain regions. The phase transformations during ion implantation and subsequent annealing are thus of fundamental interest. One qualitative measure of the ability of a material to withstand ion bombardment is its radiation hardness. Radiation soft materials are easily damaged, while radiation hard materials are much more resistant to ion beam induced damage. In this study we investigate amorphous phase formation and recrystallization of silicon ion implanted CoSi and CrSi believed to be radiation soft materials, and Pd Si a radiation hard material. These silicites are of interest as each is capable of forming good crystalline quality epitaxial silicidce layers on Si substrates; in addition, Co, Cr, and Pd silicide layers may be oxidized to form SiO 2 films on their surface without significantly altering the composition of the silicide layer [I]. EXPERIMENTAL Thin layers of Co or Pd were e-beam deposited onto chemically cleaned < Ill> Si substrates. Cr layers were evaporated onto chemically cleaned SiO 2 substrates. Depositions were carried out in a vacuum chamber equipped with ion pumps. The pressure during evaporation was _ 10-7 Torr. Tlhe substrate temperature was held at -600'C for the Co evaporation; Pd and Cr were deposited onto the substrates without intentional heating. After deposition, samples were annealed in vacuum (-3x10,7 Torr). Co samples were annealed at 950'C for one hour, Pd samples were annealed at 700'C for one hour, and Cr samples were annealed at 500'C for 30 minutes, forming CoSi 2. Pd2Si. and CrSi2 , respectively. Pd2Si was observed to be highly textured and CrSi 2 was observed to be poradiation). CoSi layers were observed to lycrystalline by x-ray diffraction (Read Camera 121,CuKa 4 be epitaxial by x-ray diffraction as well as by MeV tte+ channeling measurements. The samples were then bombarded in a random direction with 60 keV to 250 keV Si+ ions at liquid nitrogen temperatures (LNT) for all cases in this study. a+channeling surFor an investigation of regrowthMekinetics, 2 111 4, +- epitaxial CoSi - 1130 A thick with Si• face minimum yield of 5.50/,, (1.5 MeV tte) was implanted with either 2x10 Si /cm or