An epitaxial SixGey layer on a silicon substrate was quantitatively evaluated using rocking curve (RC) and reciprocal space map (RSM) obtained by powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) in conjunction with transmission electron microscopy (TEM), and EDS in conjunction with scanning electron microscopy (SEM). To evaluate the relative deviation of the quantitative analysis results obtained by the RC, RSM, SEM/EDS, and TEM/EDS methods, a standard sample comprising a Si0.7602Ge0.2398 layer on a Si substrate was used. The correction factor (K-factor) for each technique was determined using multiple measurements. The average and standard deviation of the atomic fraction of Ge in the Si0.7602Ge0.2398 standard sample, as obtained by the RC, RSM, TEM/EDS, and SEM/EDS methods, were 0.2463 ± 0.0016, 0.2460 ± 0.0015, 0.2350 ± 0.0156, and 0.2433 ± 0.0059, respectively. The correction factors for the RC, RSM, TEM/EDS, and SEM/EDS methods were 0.9740, 0.9740, 1.0206, and 0.9856, respectively. The SixGey layer on a silicon substrate was quantitatively evaluated using the RC, RSM, and EDS/TEM methods. The atomic fraction of Ge in the epitaxial SixGey layer, as evaluated by the RC and RSM methods, was 0.1833 ± 0.0007, 0.1792 ± 0.0001, and 0.1631 ± 0.0105, respectively. After evaluating the results of the atomic fraction of Ge in the epitaxial layer, the error was very small, i.e., less than 3%. Thus, the RC, RSM, TEM/EDS, and SEM/EDS methods are suitable for evaluating the composition of Ge in epitaxial layers. However, the thickness of the epitaxial layer, whether the layer is strained or relaxed, and whether the area detected in the TEM and SEM analyses is consistent must be considered.
Over the past several decades, heteroepitaxial structures composed of silicon-germanium on a silicon substrate (SixGey/Si) have been investigated and successfully applied in complementary metal oxide semiconductors (CMOS) [
An epitaxial SixGey layer was deposited onto a Si substrate by ultrahigh vacuum chemical vapor deposition (UHVCVD) under a base pressure of 2 × 10−8 Torr. The reactive gases for the growth of Si and Ge were disilane (Si2H6) and germane (GeH4), respectively. The SixGey layer was grown on the silicon substrate at 400˚C and then annealed at 750˚C/15min to improve the crystallinity. The thickness of the deposited film was approximately 50 nm. The epitaxial SixGey was quantitatively analyzed using a high-resolution X-ray diffractometer (PANalytical MRD X’Pert) equipped with a Cu-Kα1 radiation source (λ = 1.5406 Å), a transmission electron microscopy (model JEM 2010Fx, JEOL, Ltd., Tokyo, Japan) equipped with an energy-dispersive X-ray spectrometer (model X-Max 80, Oxford Instruments, Inc., London, UK), and a scanning electron microscope (JEOL JSM 6500-F) also equipped with an energy-dispersive X-ray spectrometer (model X-Max 80). The cross-sectional TEM specimen of epitaxial SixGey on Si was prepared using a focused ion beam (FIB, FEI NovaLab 600). The rocking curve (RC) and reciprocal spacing map (RSM) of XRD have been performed to evaluate the composition of SixGey. As for SEM and TEM, the thickness of the detected areas should be consistent in order to decrease the error. To evaluate the relative deviation of the quantitative analysis results for SixGey obtained by XRD, TEM/EDS, and SEM/EDS, the analyses of the SixGey layer were performed multiple times for comparison. Moreover, a standard sample―an Si0.7602Ge0.2398 layer with a thickness of 5 μm on Si (reference #8095, National Institute of Standards and Technology (NIST))―was used to evaluate and compare the quantitative errors associated with the aforementioned techniques.
In Vegard’s law, the relaxation (R) of the layer is strained (R = 0%) or relaxed (R = 100%) to simulate the experimental RC. Thus, in the case of the standard specimen, R was assumed to be 100% because the thickness of the epitaxial layer (4 µm) exceeded the critical thickness, resulting in the lack of interference fringes in the RC pattern in