A. E. Bair

Chemical vapor deposition of heteroepitaxial Si1−x−yGexCy films on (100)Si substrates

Thin heteroepitaxial films of Si1−x−yGexCy have been grown on (100)Si substrates using atmospheric pressure chemical vapor deposition at 625 °C. The crystallinity, composition, and microstructure of the SiGeC films were characterized using Rutherford backscattering spectrometry, secondary‐ion‐mass spectrometry, and cross‐sectional transmission electron microscopy. The crystallinity of the films was very sensitive to the flow rate of C2H4 which served as the C source. Films with up to 2% C were epitaxial with good crystallinity and very few interfacial defects. Between 800 and 900 sccm of 10% C2H4 in He, the C content increased dramatically from 2% to 10% and the as‐grown films changed from crystalline to amorphous. In order to establish deposition conditions for the crystalline‐amorphous phase transformation, one SiGeC film was deposited as the 10% C2H4 flow was increased linearly from 500 to 1500 sccm during growth. When the C content reached ∼4%, the film developed considerable stacking defects and diso...

Band offsets in Si/Si1–x–yGexCy heterojunctions measured by admittance spectroscopy

We have used admittance spectroscopy to measure conduction-band and valence-band offsets in Si/Si1–xGex and Si/Si1–x–yGexCy heterostructures grown by solid-source molecular-beam epitaxy. Valence-band offsets measured for Si/Si1–xGex heterojunctions were in excellent agreement with previously reported values. Incorporation of C into Si1–x–yGexCy lowers the valence- and conduction-band-edge energies compared to those in Si1–xGex with the same Ge concentration. Comparison of our measured band offsets with previously reported measurements of energy band gaps in Si1–x–yGexCy and Si1–yCy alloy layers indicate that the band alignment is Type I for the compositions we have studied and that our measured band offsets are in quantitative agreement with these previously reported results.

Cu enhanced oxidation of SiGe and SiGeC

A study of the effects of C and Ge additions on the Cu catalyzed oxidation of Si has been performed. It was found that the addition of Ge alone resulted in a marked slowdown in the rate of oxygen incorporation; during the first three days of the experiment the rate of oxygen incorporation was 25 times higher in the Si reference sample. The Ge was incorporated into the oxide. Small amounts of C added to the SiGe compound have a more pronounced effect. Carbon concentrations of less than 2% prevent oxidation of SiGeC for periods of at least one month. Copper enhanced oxidation of Si(100) has produced oxides of several hundred nanometers in under one month.

Strain measurements of SiGeC heteroepitaxial layers on Si(001) using ion beam analysis

The strain in SiGeC heteroepitaxial films grown on Si(001) substrates by chemical vapor deposition is quantified using ion channeling. Rutherford backscattering spectrometry was used to quantify the Ge concentration as well as the film thickness, nuclear resonance elastic ion scattering was used to quantify the C concentration, and ion channeling was utilized to measure film quality and C substitutionality. Channeling angular scans across an off‐normal major axis were used to quantify the strain. The results confirm that addition of C compensates for the strain introduced by Ge.

Wet oxidation of amorphous and crystalline Si1-x-yGexCy alloys grown on (100)Si substrates

The oxidation of amorphous Si0.65Ge0.27C0.08 and single‐crystal Si0.63Ge0.36C0.01 in wet ambient at 700 and 900 °C has been studied using Rutherford backscattering spectrometry and transmission electron microscopy. A reference sample of Si0.63Ge0.37 was also oxidized in order to determine the influence of carbon on the oxidation behavior. The low C content alloy behaved similar to the SiGe alloy: uniform Si1‐xGexO2 was obtained at 700 °C whereas SiO2 was formed at 900 °C, and Ge piled up underneath the oxide. In both cases, carbon was not detected in the oxide layer. The amorphous Si0.65Ge0.27C0.08 alloy behaved significantly different at both oxidation temperatures in comparison with the crystalline Si0.63Ge0.36C0.01 and Si0.65Ge0.37. Negligible oxidation occurred at 700 °C whereas SiO2 was obtained at 900 °C and the rejected Ge distributed uniformly throughout the SiGeC alloy. It is proposed that fast Ge diffusion during oxidation at 900 °C resulted from diffusion at grain boundaries, since crystallizat...

Quantification of carbon in Si1-x-yGexCy with uniform profiles

Methods to quantify the carbon concentration of CVD grown Si1−x−yGexCy (0.25 < x < 0.37 and 0.01 < y < 0.12) layers on (100) Si with uniform composition profiles were investigated. Two analysis techniques were used: Rutherford backscattering spectrometry (RBS) using a 4.295 MeV He+2 incident ion and elastic recoil detection (ERD) using a 24 MeV Si+5 incident ion. For the RBS measurements the 12C(α,α)12C elastic resonance reaction near 4.265 MeV was used to enhance the scattering cross section of carbon. These carbon concentrations were calculated by either integrating the resonant scattering cross section across the energy width of the layer or by using a Lorentzian fit to estimate the area. The backscattering data were additionally analyzed with the program RUMP. These different analysis techniques resulted in a large scatter in the RBS predictions for the carbon concentrations depending on how the resonant cross sectional area was calculated. The appropriateness of each technique was judged by comparing the predicted concentrations to those obtained by ERD. The divergence between the carbon concentration predicted by using the Lorentzian approximation and the ERD values was great enough to deem this method as inappropriate. The values obtained by RUMP were systematically greater than the ERD concentrations, however the percent difference was never more than 20. The predicted carbon concentration that had the closest correlation to ERD was found by integrating an appropriate scattering cross section across the energy width of the layer.

Guidelines to the application of nuclear resonance to quantitative thin film analysis

Abstract The use of elastic nuclear resonances, including 12 C(α, α) 12 C, 14 N(α, α) 14 N and 16 O(α, α) 16 O, provide a useful means of enhancing the sensitivity toward light elements using the same experimental setup as for Rutherford backscattering. Quantitative information about light element concentrations is only obtainable under certain conditions, and the use of simulation programs in conjunction with resonance analysis may often lead to erroneous results. By using resonance near the peak value of the cross section one may enhance sensitivity; however, this may result in a loss of precision, defined as day-to-day repeatability of the measurement. Conversely, using resonance in an energy regime in which the cross section varies less rapidly may more accurately predict the actual composition than standard RBS but prove less useful for low concentrations. We explore the importance of film thickness and composition and the variation in the incident beam energy toward the selection of the appropriate resonance regime, as well as discuss common sources of error.

WET OXIDATION OF AMORPHOUS SI0.67GE0.25C0.08 GROWN ON (100) SI SUBSTRATES

Wet oxidation annealing of thin films of amorphous Si0.67Ge0.25C0.08 was performed over the temperature range from 700 to 950 °C. Changes in composition and microstructure were assessed using Rutherford backscattering spectrometry and transmission electron microscopy. A nearly pure layer of SiO2 with approximately 1 at. % carbon was formed, with Ge being rejected from the oxide at all temperatures. At low temperatures, the oxide formed was very thin. Ge piled up at the oxide/film interface and the thin film microstructure remained amorphous. At higher temperatures, a network of nanocrystals was observed which was believed to provide a grain boundary diffusion path for Ge which had redistributed throughout the remaining layer. It is proposed that the Ge layer had inhibited oxidation at the lower temperatures, whereas its removal resulted in increased oxidation rates at higher temperatures. Annealing at 950 °C for 5 and 6 h resulted in an epitaxial transformation and a single crystal structure. This process...

Control of composition and crystallinity in the molecular beam epitaxy of strain-compensated Si1-x-yGexCy alloys on Si

In this paper, we present a mass-spectrometry-based approach to the control of C concentration during molecular beam epitaxy (MBE) of Si 1-x-y Ge x C y /Si superlattices. High-resolution X-ray diffraction, ion beam analysis, and transmission electron microscopy (TEM) were used to characterize composition and crystallinity in a series of superlattices for which the average strain condition was designed to range from biaxial compression to biaxial tension. For each sample, secondary ion mass spectrometry and Rutherford backscattering spectrometry confirmed that the average composition of each Si 1-x-y Ge x C y layer was constant during growth. However, TEM revealed strain contrast variations within the Si 1-x-y Ge x C y layers, leading to the conclusion that the presence of C on the wafer surface leads to laterally inhomogenous incorporation of C (and possibly Ge). TEM also showed that all samples were essentially free of extended defects except for short microtwins observed in the tensile-strained sample, that originated in the Si 1-x-y Ge x C y . layers and terminated in the Si layers directly above.

Comparison of elastic resonance and elastic recoil detection in the quantification of carbon in SiGeC

Abstract The carbon concentrations of chemical vapor deposition grown Si 1− x − y Ge x C y (0.25 x y 0.12) layers on (100) Si with uniform composition profiles were quantified by two ion analysis techniques. Measurements made with backscattering spectrometry using a 4.295 MeV He 2+ incident ion were compared to compositions predicted by elastic recoil detection (ERD) using a 24 MeV Si 5+ incident ion. To enhance the carbon scattering cross section for the backscattering measurements, the 4.265 MeV 12 C(α, α) 12 C elastic resonance reaction was used. The carbon concentrations of the films were calculated by integrating the resonant scattering cross section using the energy width of the layer as the limits of integration. The results of this backscattering analysis technique were compared to the predicted carbon concentrations obtained by ERD. It was found that the predictions of these techniques correlated within the uncertainty of each method.