Heteroepitaxial Si 1-x-y Ge x C y Layer Growth on (100)Si by Atmospheric Pressure Chemical Vapor Deposition
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ABSTRACT Thin heteroepitaxial films of Sil-x-yGexCy have been grown on (100)Si substrates using atmospheric pressure chemical vapor deposition at 550 and 700'C. The crystallinity, composition and microstructure of the SiGeC films were characterized using Rutherford backscattering spectrometry (ion channeling), secondary-ion-mass-spectrometry and cross-sectional transmission electron microscopy. SiGeC films with up to 2% C were grown at 700'C with good crystallinity and very few interfacial defects, while misfit dislocations at the SiGe/Si interface were observed for SiGe films grown under the same conditions. This difference indicates that the presence of carbon in the SiGe matrix increases the critical thickness of the grown layers. SiGeC thin films (>110 nm) with up to 3.5% C were grown at 550'C with good crystallinity. The crystallinity of the films grown at lower temperature (550'C) was less sensitive to the flow rate of the C source (C2 H4 ), which enabled growth of single crystal SiGeC films with higher C content. INTRODUCTION The significant successes of semiconductor electronic devices are closely connected to the concept of band gap engineering. The band gap of Si-based materials has been successfully engineered by alloying with Ge and by forming strained-layer superlattices.[1] However, the presence of compressive strain in pseudomorphic Sil-xGex films grown epitaxially on (100)Si substrates causes stability problems that limit film thickness. Moreover, in many applications, it is desirable to have a wider band gap than that of pure Si. Adding substitutional carbon into SiGe alloy layers may increase the band gap[2] and, at the same time, result in strain compensation.[3,4] In fact, strain in Sil-x-yGexCy alloy layers can in principle be adjusted over a wide range from compressive all the way to tensile, depending on the Ge/C concentration ratio. If Vegard's law is applied to the SiGeC ternary system, then we expect compensation of 8.2 at% Ge by 1.0 at% C in the pseudomorphic Silx-yGexCy film.[5] This paper is focused on the growth layers on (100)Si substrates using atmospheric pressure of pseudomorphic Si1 xi GexC chemical vapor deposition (APCVD). EXPERIMENTAL Silx yGexCy layers were epitaxially grown at 550 and 700'C on (100)Si in an EPSILON ONE, model E-2 single wafer, automated APCVD reactor using SiH 2 Cl 2 as the Si source, GeH 4 as the Ge source, and C2 H4 as the C source at atmospheric pressure. A reference SiGe sample was also grown at 700'C in order to determine the influence of carbon on the microstructure and the growth behavior. Point-of-use purifiers on the gas lines provide purity levels in the parts-perbillion range in the process chamber. Nitrogen-purged load locks exclude air from the system. The growth conditions and some preliminary results have recently been published.[6] Rutherford
117 Mat. Res. Soc. Symp. Proc. Vol. 399 01996 Materials Research Society
backscattering spectrometry (RBS) in the channeling mode and the 12 C(a,a) 12C elastic resonance reaction at 4.265 MeV were used
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