Strain Measurements of Sigec Heteroepitaxial Layers On Si(100) Using Ion Beam Analysis
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ABSTRACT The strain in SiGeC heteroepitaxial films grown on Si(100) substrates has been quantified using ion channeling. The films were grown both by combined ion beam and molecular beam epitaxy (CIMID) and chemical vapor deposition (CVD). Rutherford backscattering spectrometry (RBS) was used to quantify the Ge concentration as well as the film thickness, nuclear resonance elastic ion scattering was used to quantify the carbon concentration, and ion channeling was utilized to measure film quality. Channeling angular scans across an off normal major axis were used to quantify the strain. Part of the film was removed by using a solution of HF, HNO 3 and CH 3COOH in order to obtain a reliable scan in the substrate. The results indicate that C may be compensating for the strain introduced by Ge.
INTRODUCTION It is well known that commensurate Sil. Ge, films can be grown on Si substrates up to a maximum thickness for a given fraction of Ge. ' 2 For films grown within these limits, the misfit caused by lattice mismatch between substrate and film is taken up by strain. In such films grown beyond this thickness, misfit dislocations occur at the interface which relieve strain in the film. The lattice mismatch is due to the 4.2 % larger lattice constant of Ge relative to Si. Pseudomorphic strained layers of Sil-yCy alloys (with a few percent carbon concentration) have been grown on Si and it was shown that the lattice constant was reduced in the alloy compared to the lattice constant of Si when the C was substitutional. 3 It is estimated that because the lattice constant of Sil-yCy alloys reduces with substitutional C and the lattice constant of SiixGex increases with Ge, it should be possible to control strain in a film of Sil-.xyGexCy grown on Si by adjusting x/y. From Vegard's law, It is estimated that each C atom can compensate for the strain introduced by approximately nine Ge atoms in Si.4 For compositions that vary from this, strain or strain relaxation should be present in the film depending on the C to Ge concentration ratio and film thickness. The present work measures the strain in films with varying C and Ge concentrations and film thicknesses. The results show that the measured strain in films that contain carbon is different than in the films that do not. 461 Mat. Res. Soc. Symp. Proc. Vol. 354 01995 Materials Research Society
EXPERIMENTAL The films were grown in a UHV combined ion beam and molecular beam deposition (CIMD) system at Arizona State University 5 and in a chemical vapor deposition (CVD) apparatus at Lawrence Semiconductor Research Laboratory Inc.6 Films were grown on 100 mm diameter Si (100) wafers. Growth temperatures were controlled over a range of 450 'C to 625 °C and growth times were determined to provide a range of thicknesses from 35 nm to 210 nm. Ion beam analysis was done at the Facility for Ion Beam Analysis of Materials (IBeAM) at Arizona State University. The facility includes a 1.7 MV Tandetron ion accelerator which produces a well-collimated beam of mono-energetic helium ions over
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