The Effect of Ion Implantation on the Interdiffusion in Si/Ge Amorphous Artificial Multilayers
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THE EFFECT OF ION IMPLANTATION ON THE INTERDIFFUSION IN Si/Ge AMORPHOUS ARTIFICIAL MULTILAYERS B. PARK1 , F. SPAEPEN 1 , J.M. POATE 2 , F. PRIOLO 2 , D.C. JACOBSON 2 , C.S. PAI 2 , A.E. 2 wHrIE 2 AND K.T. SHORT 1 Division of Applied Sciences, Harvard University, Cambridge, MA 02138 2 AT&T Bell Laboratories, 600 Mountain Road, Murray Hill, NJ 07974 ABSTRACT Amorphous Si/Ge artificial multilayers have been implanted with Si and B at liquid nitrogen temperature, and partially ion mixed with Ar at different temperatures. In all cases, the square of the mixing length was found to be proportional to the dose. Annealing of Si-implanted samples showed that after relaxation the diffusivity appeared unaffected by the implantation process. Annealing of the B-implanted samples showed an enhancement of the diffusivity at the higher dose. The diffusive component of the square of the mixing length in the Ar-ion mixed samples has an Arrhenius-type temperature dependence, with an activation enthalpy of 0.22 eV. INTRODUCTION Diffusion in amorphous covalent network formers, such as Si and Ge, is governed by structural defects (broken bonds, vacancies or interstitials) that are present as a result of growth or implantation processes. The presence of dopants may also affect the diffusivity of the host atoms. It is therefore of interest to study the effects on the diffusivity of processes that change these defect concentrations: self-implantation, implantation of dopants, and noble gas ion mixing. Since these amorphous systems must be kept below the temperature at which they crystallize rapidly, the values of the diffusivities to be measured are necessarily small. Techniques based on determining the broadening of a single composition profile, such as Rutherford backscattering, have a resolution limit of about 20A, which allows measurements of diffusivities as low as 10-19 cm 2/s. An artificial multilayer, on the other hand, contains several
hundred identical diffusion couples and changes in their composition profile can be detected by x-ray diffraction with a resolution of 0. IA; diffusivities down to 10- 23cm 2 /s can therefore be measured by this technique [1]. Last year we presented a first report on a study of self-implantation on the interdiffusion of amorphous Si/Ge multilayers of equiatomic average composition [2]. We demonstrated there that the artificial multilayer technique can be used for very accurate determinations of ion beam mixing lengths, and that the interdiffusivity of implanted and unimplanted samples was the same. In this paper we present further data on the effects of self-implantation, as well as on the effects of implantation of boron and of ion mixing with high energy argon. EXPERIMENTAL TECHNIQUE The artificial multilayers were prepared by ion beam sputtering from alternating elemental targets onto a (100) polished and oxidized Si substrate [3]. The layer repeat lengths were around 60A, and were kept constant within 4%. The total film thickness was usually around 2000A, and the films were capped with a 150A Si
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