Vacuum/volume 46/number 516lpages 531 to 53511995 Copyright 0 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0042-207x/95 $9.50+.00 0042-207x(94)001235 Direct observation of rare-earth silicide epilayer formation by RHEED technique P Mazurek, 2 Mitura, K Paprocki, M Subotowicz and P Mikoiajczak, Institute of Physics, M. Curie-Sklodowska University, pl. M. Curie-Skfodowskiej I, 20-031 Lublin, Poland The solid phase reaction of yttrium thin film and silicon substrate was investigated in situ with help of RHEED technique. For the first time, ye have measured directly yttrium silicide formation temperature which can be as low as 120°C for a thin (60 A) metal layer deposited on a Si(l1 I) substrate. For this purpose, we developed a new experimental technique. A study of rhe growth of thin (l&150 A) silicon over-layers on yttrium and dysprosium silicide films epiraxially grown on Sill 1 I) was also made. In this paper, an in situ reflection high energy electron diffraction (RHEED) pattern and also azimuthal plot investigation of Si/RE-silicide/Si double heterostructures grown by solid phase epiraxy and reactive deposition method are presenred. 1. Introduction Rare-earth (RE) silicide films have attracted attention because of their unusual electrical conduction and formation properties. They form contacts with n-type silicon with the lowest known Schottky barrier height (0.34.4 eV). RE silicides are usually prepared by a contact reaction method’, with the RE metal deposited on a precleaned silicon surface and then heated. Almost all RE silicides are known to form an epitaxial layer on Si. The RE thin films are extremely reactive mainly with oxygen, thus zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA in situ annealing is recommended. Here, we report experimental study of the formation of RE silicides on silicon surface between room temperature and 600°C using in situ RHEED intensity measurements. There is also currently much interest in the Si/RESi,_JSi double heterostructure2,’ because it can give both new information about the physics in the single-crystal-metal/semiconductor4 system and be a fabrication tool of novel devices such as permeable base transistors (PBT)5 or tuneable infrared sensors. High quality single-crystal YSi, , and DySi, 7 films can now be fabricated on Si(ll1) with a high degree of perfection either by room tem- perature deposition and reaction at higher temperature or by MBE under ultrahigh vacuum conditions. In this report we also describe the system we have used to extend our qualitative RHEED studies of rare-earth silicides. By utilizing a CCD-based RHEED detection system and a sophisticated data reduction scheme, we can measure in situ, simultaneous, time-resolved specular and integral-order intensity, streak linewidth and epi- taxial layer lattice constants. After the process, the samples were removed from the MBE chamber for further ex situ analysis. The microstructure was revealed by X-ray diffraction. Scanning electron microscopy (SEM) was used to view the surface top- ography. 2. Statement of the problem Let us first recall the main properties of epitaxial yttrium and dysprosium silicides. These silicides crystallize in AlB, (hex- agonal) system and are formed of planes of rare-earth (RE) atoms separated by planes of Si. Yttrium subgroup silicides are characterized by a rather large homogeneity interval (0 < x < 0.4), that is, x varies without changing the disilicide crystal structure. This hexagonal phase is formed with 15-20% vacancies on the Si sublattice, about 1 of 6 Si atoms are missing, giving the composition REB, ,. The arrangement of Si atoms in a plane normal to the silicide c axis is essentially identical to that on the (111) surface of Si, resulting in a nearly ideal epitaxial arrangement. In epitaxy on Si( 111) the (0001) plane of the silicide is parallel to the substrate surface. Solid phase epitaxy method is the simplest one and has been widely used to prepare, with success, a great number of metal silicides. Previous studies reported different aspects of RE silicide formation but we did not find accurate information in the litera- ture about formation temperature of epitaxial RE silicides formed by solid phase epitaxy (SPE). The reaction between a Y overlayer and an Si(l11) substrate has been reported6 to nucleate between 300 and 400°C. This wide range is not acceptable from a technological point of view. So far, various material characterization techniques such as Rutherford backscattering spectroscopy, transmission and scan- ning electron microscopy, and X-ray rocking curve, as well as X- ray photoelectron spectroscopy and low energy electron diffrac- tion have been used to study the structural properties, kinetics of formation and morphology of epitaxial RESi, , films. However, not much work has been performed using in situ reflection high energy electron diffraction (RHEED) analysis to monitor the YSi, , and zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJ DySi, , material growth. In this work, we aimed to 531