D. Krüger

Suppressed diffusion of boron and carbon in carbon-rich silicon

Transient enhanced diffusion of boron in silicon can be suppressed by substitutional carbon. We show here that diffusion of boron and carbon is strongly reduced in carbon-rich silicon, even when no supersaturation of interstitials due to implantation is present. Pronounced non-Fickian diffusion behavior was found for epitaxially grown-in carbon at concentrations well above its solid solubility. The experimentally observed suppression of B and C diffusion at high C concentrations is explained in terms of a recently proposed model that predicts an undersaturation of Si self-interstitials caused by diffusion of C out of C-rich regions.

Novel collector design for high-speed SiGe:C HBTs

We describe a novel collector design for high-frequency SiGe:C HBTs without deep trenches and with low-resistance collectors formed by high-dose ion implantation after shallow trench formation. f/sub T/ values of 200 GHz at BV/sub CEO/=2.0 V and ring oscillator delays of 4.3 ps are obtained. Excellent static characteristics and high yield were achieved for the HBT module integrated in a 0.25 /spl mu/m CMOS platform.

Dopant diffusion in C-doped Si and SiGe: physical model and experimental verification

We show that B and P exhibit suppressed, and As and Sb enhanced diffusion in C-rich Si. This can be well described by coupled diffusion of C and Si point defects. We present a physical model for the impact of C on dopant diffusion in Si and SiGe and demonstrate its reliability in the context of device characteristics of heterojunction bipolar transistors, which constitute a most sensitive tests for dopant diffusion on the nm scale.

The impact of supersaturated carbon on transient enhanced diffusion

Transient enhanced diffusion of B is strongly suppressed in C-rich Si. We show that the physical mechanism for this suppression is out-diffusion of C from regions of high C concentration. B doping superlattices with background C concentrations between 1018 and 1020 cm−3 were grown by molecular beam epitaxy and implanted with BF2 ions. The measured dependence of transient B diffusion on the C profile is explained by coupled diffusion for C and Si point defects. The proposed model is supported by the observation of transient enhanced diffusion of C.

Strain compensation in Si1−xGex by heavy boron doping

Strain compensation in SiGe by heavy boron doping was demonstrated. For this purpose, SiGe layers containing up to several percent of boron were deposited using rapid thermal chemical vapor deposition. The strain compensation effect was evaluated by double crystal x‐ray diffraction measuring the difference between the diffraction peak distances of the boron doped samples and a reference sample without boron which can be directly related to the decrease of the lattice constant in Si1−x−yGexBy due to the incorporation of boron. The films were characterized by cross‐sectional transmission electron microscopy (XTEM), Auger electron spectroscopy (AES), and secondary ion mass spectroscopy (SIMS).

Influence of carbon incorporation on dopant surface segregation in molecular-beam epitaxial growth of silicon

We describe the effect of carbon incorporation into Si on dopant surface segregation during molecular-beam epitaxial growth. Low concentration of carbon can significantly reduce the surface segregation of boron and phosphorus. Combining the surface diffusion model with a two-state exchange process, we are able to model the experimental results over the whole temperature range between 350 and 800 °C. Each exchange process alone is not sufficient to describe surface segregation at all investigated temperatures. Our results show that the presence of carbon lowers the energy difference for boron in subsurface and surface states. The energy barriers for surface diffusion as well as for the two-state exchange process are not affected by carbon.

HEAVY PHOSPHORUS DOPING IN MOLECULAR BEAM EPITAXIAL GROWN SILICON WITH A GAP DECOMPOSITION SOURCE

Doping with phosphorus in solid source silicon molecular beam epitaxy is possible using a GaP decomposition source. This source evaporates solid GaP and is combined with an efficient mass separator system. Homogeneous P doping up to concentrations higher than 1019 cm−3 was realized. Surface accumulation of phosphorus was not observed for the low growth temperature of 400 °C used in this study. The parasitic Ga incorporation is about three orders of magnitudes below the P concentration. This new phosphorus doping technique is suitable for n‐type doping in the range of 1017–1020 cm−3.

Cost-effective high-performance high-voltage SiGe:C HBTs with 100 GHz f/sub T/ and BV/sub CEO/ /spl times/ f/sub T/ products exceeding 220 VGHz

High performance HBTs with f/sub T/, f/sub max/ and BV/sub CEO/ values of 100 GHz, 130 GHz, and 2.5 V, respectively, are demonstrated in a 0.25 /spl mu/m BiCMOS technology without epitaxially-buried subcollector, and deep trench isolation. High voltage devices with BV/sub CEO/ values of up to 9 V and BV/sub CEO/ /spl times/ f/sub T/ products above 220 VGHz can be produced on the same chip with no special mask.

Formation of shallow source/drain extensions for metal-oxide-semiconductor field-effect-transistors by antimony implantation

Shallow Sb and As junctions have been investigated with regard to their applicability in complementary metal–oxide–semiconductor (CMOS) technologies. Replacing As source/drain extensions by Sb with the same implanted depth facilitates the formation of about 20 nm shallower junctions and even lower sheet resistance. This is due to the absence of transient enhanced diffusion effects and less dose loss for Sb. Sb source/drain extensions with a final junction depth of 40 nm and a sheet resistance of 320 Ω/sq have been integrated in a standard CMOS process with 130 nm gate length. The same low leakage current level is demonstrated for Sb and As extensions.

Boron‐controlled solid phase epitaxy of germanium on silicon: A new nonsegregating surfactant

10‐nm‐thick germanium layers have been grown on Si(100) with boron as a surfactant with three different growth procedures, and investigated with reflection high‐energy electron diffraction, transmission electron microscopy, and secondary ion mass spectroscopy. We obtained smooth and completely closed epitaxial germanium layers only by depositing the boron on top of the amorphous germanium layer followed by a post‐annealing step. The surface energy anisotropy of the germanium will be affected by the presence of boron in this equilibrium process. The islanding observed in all other growth processes can be understood by taking into account that boron is a typical nonsegregating material in Ge below 600 °C and a surfactant acts mainly due to its presence in the growing front.