D. J. Godbey

Low-temperature cleaning processes for Si molecular beam epitaxy

Hydrogen‐terminated surface cleaning techniques of silicon substrates were investigated by using x‐ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and transmission electron microscopy (TEM). Either a 4% HF dip or an HF‐terminated abbreviated Shiraki clean was used as the cleaning technique. Shiraki‐cleaned samples were grown as control samples. XPS was used to measure the C, O, and F remaining on the surface at various stages of the cleaning/growth process, including after a 1 h bake at 200 °C prior to growth. XPS did not detect a significant difference in the adsorbate concentrations between the baked and unbaked samples. From SIMS, the lowest impurity concentrations at the epitaxial/substrate interface were achieved with the abbreviated Shiraki clean, approximately at the same levels as obtained with the standard Shiraki clean, 1.3×1013, 5.4×1012, 1.6×1010, and 4.2×1011/cm2 for C, O, F, and N, respectively. This was achieved without the 850 °C anneal required to desorb the ...

Surface segregation and structure of Sb-doped Si(100) films grown at low temperature by molecular beam epitaxy

Abstract Sb surface segregation and doping during Si(100) molecular beam epitaxy were studied for growth temperatures of 320–500°C. Surface segregation was analyzed by depth profiling with secondary ion mass spectrometry and the results indicate the existence of several distinct dopant concentration- and temperature-dependent surface segregation regimes: (1) For dilute Sb surface concentrations the measurements reveal a region where bulk and surface concentrations are linearly related, and the surface segregation is described by a constant. However, the experimentally determined temperature dependence of the segregation does not follow simple kinetics theory, and appreciable surface segregation is observed at temperatures ≤ 400°C. (2) At temperatures ≥ 350°C, the surface segregation reaches a maximum for Sb surface concentrations of 0.5 monolayers. (3) For surface concentrations near 1 monolayer, the surface segregation decreases with increasing surface Sb coverage due to dopant interaction within surface and subsurface layers. In cases where films were grown under very high dopant fluxes, we have identified cone-like defects and stacking faults that are the result of the apparent surface concentration exceeding 1 monolayer.

Ge profile from the growth of SiGe buried layers by molecular beam epitaxy

X‐ray photoelectron spectroscopy measurements were obtained and interpreted by a kinetic simulation to determine the germanium concentration profile of thin Si/SiGe heterostructures grown at 500 °C using elemental source molecular beam epitaxy. The primary finding is that there are significant segregation effects in these commonly grown structures which affect both the ‘‘leading’’ and ‘‘trailing’’ interfaces. Upon opening of the germanium shutter, the surface monolayer must be built up to a germanium composition of greater than 96% before the composition of the deposited alloy layer is equal to the flux composition for a Ge ratio of 0.3. This buildup causes the germanium depletion at the leading interface. Upon termination of the germanium flux, the incorporation of the germanium rich monolayer into the growing silicon cap layer causes a corresponding degradation of the trailing interface.

Ge surface segregation at low temperature during SiGe growth by molecular beam epitaxy

The temperature dependence of germanium surface segregation during growth by solid source SiGe molecular beam epitaxy (MBE) was studied by x‐ray photoelectron spectroscopy and kinetic Monte Carlo (KMC) modeling. Germanium segregation persisted at temperatures 60 °C below that predicted by a two‐state exchange model. KMC simulations, where film growth, surface diffusion, and surface segregation are modeled consistently, successfully describe the low temperature segregation of germanium. Realistic descriptions of MBE must follow the physical rates of the growth, surface diffusion, and surface segregation processes.

Copper diffusion in organic polymer resists and inter-level dielectrics

Abstract In future generation microelectronic devices, it is anticipated that back end of the line processing may incorporate interconnects composed of Cu metal, and inter-level dielectrics composed of organic polymers. In this study, we examined a number of commercially available and new NRL synthesized organic polymer systems towards Cu metal incorporation in the film during application. All the polyimides examined transported Cu, in large part due to the ability of the solvent, 1-methyl-2-pyrrolidinone (NMP), to dissolve Cu. We report examples where the solvent is largely responsible for Cu incorporation into the polymer film, and examples where the polymer and not the solvent is responsible for Cu transport into the film polymethyl methacrylate. Three preparations examined in this study, polystyrene, Teflon AF, and 1,3,5-tris (2-allyloxy-hexafluoro-2-propyl) benzene/poly methyl hydrosiloxane, were found to resist Cu diffusion.

Sb surface segregation and doping in Si(100) grown at reduced temperature by molecular beam epitaxy

X‐ray photoelectron spectroscopy, depth profiling with secondary ion mass spectrometry, and conductivity measurements have been performed on Sb‐doped Si(100) films grown at low temperature (350 °C) by molecular beam epitaxy. The measurements reveal two important effects: (1) a significant increase in the surface segregation of Sb as the dopant concentration approaches 1×1020 cm−3, and (2) a decrease in surface segregation as the surface concentration of Sb reaches one monolayer. We believe that the presence of this monolayer of Sb is responsible for the surface segregation becoming self‐limited and the associated bulk concentration exceeding 1×1020 cm−3.

Analysis of Ge segregation in Si using a simultaneous growth and exchange model

Abstract Ge segregation data is analyzed using a simultaneous growth and exchange model in the limit of infinite surface diffusion. This model is found to predict a longer leading edge, an enlarged surface Ge storage reservoir, and a better temperature dependence than the previously described two-layer model. This suggests that surface diffusion and rearrangement plays a more important role in Ge segregation than believed heretofore.

Interfacial point defects in heavily implanted silicon germanium alloys

Comparing electron paramagnetic resonance (EPR) spectra from samples of two different alloy compositions we develop a structural model for SG1, a Ge dangling bond defect in O implanted SiGe. Analysis of the angular dependence of EPR spectra from measurements of 10% and 40% Ge alloys reveals that in both cases the defect exhibits 〈111〉 symmetry of the Si lattice; however, the defect in the 40% alloy exhibits a larger g⊥ and broader linewidth than the defect in the 10% alloys. From these observations we propose that for both alloy compositions SG1 is a trivalently bonded Ge atom, and we suggest that the center in the 40% Ge alloy involves a greater number of Ge backbonds than the center in 10% Ge samples. That implantation with Ne does not produce SG1 provides evidence to suggest that the defect is located at interfaces between the SiGe alloy and SiO2 precipitates formed by oxygen implantation.

Post‐growth annealing of low temperature‐grown Sb‐doped Si molecular beam epitaxial films

Sb‐doped Si films have been grown on (100) Si substrates at low temperature (∼350 °C) by molecular beam epitaxy. Through coevaporation with Sb, very high doping efficiencies were achieved over a carrier concentration range of 1×1017 to 1×1020 cm−3. Through calibration of the beam flux we found that the incorporation of Sb was very near unity up to a concentration of ∼5×1019 cm−3. As‐grown films are of good quality. However, furnace annealing was shown to improve the mobility and completely activate the Sb. Temperature dependent Hall measurements were used to further characterize the films.

Parametric Investigation of Si1-xGex/Si Multiple Quantum Well Growth

Si0.8Ge0.2/Si multiple quantum wells (3 nm/30 nm) have been grown by molecular beam epitaxy and have been characterized using photoluminescence (PL), secondary ion mass spectrometry, and transmission electron microscopy. A parametric investigation relating the growth conditions to the PL was carried out. The existence of phonon-resolved band-edge PL appears to be strongly related to the background impurity concentration. The connection between phonon-resolved band-edge PL and higher substrate growth temperatures is probably due to the temperature-dependent incorporation of impurities. In the as-grown samples a correlation of the broad PL with platelet density in the quantum wells was observed. The broad PL may be associated with Cr at the platelets since a high temperature ( 710° C) anneal extinguished the broad PL and caused a reduction in the Cr found in the quantum wells, but had no effect on the platelet density.