Epitaxial Growth Of Nickel and Cobalt Germanides On Germanium
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EPITAXIAL GROWTH OF NICKEL AND COBALT GERMANIDES ON GERMANIUM Y.F. HSIEH*, L.J. CHEN*, E.D. MARSHALL** AND S.S. LAU** * Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Republic of China ** Department of Electrical Engineering and Computer Science, University of California, San Diego, La Jolla, CA 92093 ABSTRACT Transmission and scanning electron microscopy, Rutherford backscattering-channeling and Read camera glancing angle x-ray diffraction techniques have been applied to study the epitaxial growth of nickel and cobalt germanides on germanium. NiGe, Co5Ge7 and CoGe2 were found to grow epitaxially on both (001) and (lll)Ge. More extensive epitaxy on (lll)Ge is correlated with better lattice matches at the germanide/Ge interfaces than those on (001)Ge for these epitaxial germanides. I.
INTRODUCTION
Compared to the extensive studies of silicide formation, germanide formation has received relatively little attention. (1-10] Renewed interest in the development of germanium technology for radiation detector systems and integrated circuits, in recent years, has provided an impetus to study the metal-germanium interactions. Previous studies have found that the germanide formation characteristics such as first phase nucleation, sequence of phase formation, kinetics and moving species are similar to those of the corresponding silicides. [4,9] It is therefore anticipated that the investigation of gerrnanides be benefited greatly from past experiences gained in studying silicides. The study of metal-semiconductor interaction using an elemental semiconductor other than silicon is also of fundamental interest. In addition to the generally known NiSi 2 , CoSi2, PtSi, and Pd2Si, a number of other transition metal silicides were also found to grow epitaxially on silicon. (11] Among these silicides exhibiting epitaxial relationships with respect to the substrate silicon, only NiSi 2 epitaxy on (001), (111) and (011)Si and CoSi2 epitaxy on (lll)Si were reported to be grown to be truly single-crystalline. The importance of crystallographic directions on the Schottky barrier formation between metal and silicon has been demonstrated for single-crystalline NiSi2 films on silicon. [12] Owing to the considerable similarity between germanide and silicide formation, epitaxial growth of germanide on germanium is therefore of significant interest. In this paper, we report the results of a study on the epitaxial growth of nickel and cobalt germanides on germanium, II.
EXPERIMENTAL PROCEDURES
Germanium wafers, 2 in. in diameter, were cleaned by organic solutions in an ultrasonic cleaner. After etching in a solution of HF, HNO3 and CH3COOH (3:5:3) for 30 s, rinsed in deionized water, the samples were etched in a dilute HF solution immediately before loading into an electron gun evaporation chamber. Nickel or cobalt thin films, 30-60 nm in thickness, were then electron-gun deposited onto the Ge substrate at room 6 temperature.
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