St. Lenk

Effect of helium ion implantation and annealing on the relaxation behavior of pseudomorphic Si1−xGex buffer layers on Si (100) substrates

The influence of He implantation and annealing on the relaxation of Si0.7Ge0.3 layers on Si (100) substrates is investigated. Proper choice of the implantation energy results in a narrow defect band ≈100 nm underneath the substrate/epilayer interface. During annealing at 700–1000 °C, He-filled bubbles are created, which act as sources for misfit dislocations. Efficient annihilation of the threading dislocations is theoretically predicted, if a certain He bubble density with respect to the buffer layer thickness is maintained. The variation of the implantation dose and the annealing conditions changes density and size of spherical He bubbles, resulting in characteristic differences of the dislocation structure. Si1−xGex layers with Ge fractions up to 30 at. % relax the initial strain by 70% at an implantation dose of 2×1016 cm−2 and an annealing temperature as low as 850 °C. Simultaneously, a low threading dislocation density of 107 cm−2 is achieved. The strain relaxation mechanism in the presence of He fi...

Schottky barrier height modulation using dopant segregation in Schottky-barrier SOI-MOSFETs

The effect of dopant segregation (DS) on the electrical behavior of silicon-on-insulator Schottky barrier MOSFETs (SB-MOSFETs) is investigated. Ion implantation with arsenic and boron and subsequent silicidation is used to create highly n- and p-doped interface layers at the silicide-silicon interface. As a result, a strong band bending occurs at the silicide-silicon interface giving rise to a lowering of the effective Schottky barrier height. In turn, an increased electron as well as hole injection into the channel leads to improvements of the off- and on-state of the SB-MOSFETs. Using dopant segregation n-type as well as p-type SB-MOSFETs with nickel silicide source/drain electrodes have been fabricated exhibiting an inverse sub-threshold slope close to the thermal limit and showing one order of magnitude higher on-currents if compared to SB-MOSFETs without DS. In essence, the use of dopant segregation allows the fabrication of high performance Schottky barrier MOSFETs.

Effective Schottky barrier lowering in silicon-on-insulator Schottky-barrier metal-oxide-semiconductor field-effect transistors using dopant segregation

We present an investigation of the use of dopant segregation in Schottky-barrier metal-oxide-semiconductor field-effect transistors on silicon-on-insulator. Experimental results on devices with fully nickel silicided source and drain contacts show that arsenic segregation during silicidation leads to strongly improved device characteristics due to a strong conduction/valence band bending at the contact interface induced by a very thin, highly doped silicon layer formed during the silicidation. With simulations, we study the effect of varying silicon-on-insulator and gate oxide thicknesses on the performance of Schottky-barrier devices with dopant segregation. It is shown that due to the improved electrostatic gate control, a combination of both ultrathin silicon bodies and gate oxides with dopant segregation yields even further improved device characteristics greatly relaxing the need for low Schottky barrier materials in order to realize high-performance Schottky-barrier transistors.

Gadolinium scandate thin films as an alternative gate dielectric prepared by electron beam evaporation

Gadolinium scandate thin films deposited on silicon substrates using electron beam evaporation were investigated. Measurements with Rutherford backscattering spectrometry, high temperature x-ray diffraction, x-ray reflectometry, transmission electron microscopy, and atomic force microscopy were performed. A stoichiometric transfer of material from the source to the substrate in high vacuum could be demonstrated. Homogeneous, amorphous, and smooth films (root mean square surface roughness <1A) stable up to 1000°C were obtained. Electrical characterization of capacitor stacks revealed a dielectric constant of ≈23, C-V curves with small hysteresises and low leakage current densities (770μA∕cm2 for a capacitance equivalent thickness of 1.5nm).

Morphology and structure of laser-modified Ge2Sb2Te5 films studied by transmission electron microscopy

Abstract The morphology and crystal structure of laser-modified areas in an amorphous Ge2Sb2Te5 film have been investigated by transmission electron microscopy (TEM) and selected area electron diffraction (SAD). Two different types of crystallized areas are found by TEM. Low power laser irradiation leads to crystallization out of the solid phase. Whereas these crystalline areas are characterized by a fine grained morphology (dgrain=5–25 nm), the grain distribution of melt crystallized areas is rather different. It resembles the well known pattern of solidified alloy ingots but is formed on a different length- and timescale. The crystal structure of both the fine-grained crystalline area as well as of the melt-crystallized area is shown to be cubic and not the more complex hexagonal equilibrium structure of Ge2Sb2Te5. These findings enable a deeper understanding of fast nucleation and growth processes in phase change media.

Effects of annealing on the electrical and interfacial properties of amorphous lanthanum scandate high-κ films prepared by molecular beam deposition

Amorphous LaScO3 thin films were grown on (100) Si by molecular beam deposition and the effects of postdeposition thermal treatments on the film properties were studied after anneals in O2 or inert Ar atmosphere at 400 or 650 °C. Rutherford backscattering spectrometry, transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy (XPS) were employed to investigate the samples. Capacitance-voltage and current-voltage measurements allowed their electrical characterization. Postdeposition annealing in O2 reduces hysteresis, flatband voltage, and also leakage current density. In contrast, films treated in Ar ambient revealed a different behavior. The observations were associated with the interface evolution as studied by XPS, which verify that an O2 atmosphere favors the formation of a SiO2-rich interface between the film and the Si substrate, while a La-Sc-silicate-like compound predominates in this region after treating the samples in Ar. Additionally, postdeposition annealing re...

SmScO3 thin films as an alternative gate dielectric

Samarium scandate thin films deposited on (100) Si have been investigated structurally and electrically. Rutherford backscattering spectrometry and transmission electron microscopy results show that the films are stoichiometric, amorphous, and smooth. X-ray diffraction analysis indicates that SmScO3 starts to crystallize at 900 °C. Capacitance and leakage current measurements reveal C-V curves with negligible hysteresis, a dielectric constant around 29 for 6 nm thick films, low leakage current densities in the range of 10−7 A/cm2, an effective oxide charge density of ∼5×1011 cm−2, and an interface trap density of 4.5×1011 (eV cm2)−1.

Asymmetric strain relaxation in patterned SiGe layers: A means to enhance carrier mobilities in Si cap layers

Strain relaxation in patterned Si0.77Ge0.23 stripes grown on Si(001) by chemical vapour deposition was investigated after He+ ion implantation and annealing. Ion channeling measurements indicate asymmetric strain relaxation with a significantly higher residual strain parallel to the stripes than perpendicular to the stripes. These results are confirmed by plan view transmission electron microscopy showing a much higher density of misfit dislocations running along the stripes than across the stripes. Estimates based on a piezoresistivity model indicate significant enhancements of electron and hole mobilities for asymmetrically strained Si cap layers on such SiGe stripes.

Segregation of ion implanted sulfur in Si(100) after annealing and nickel silicidation

Diffusion of sulfur (S) in S+ ion implanted Si(100) was investigated after rapid thermal annealing as well as after nickel silicidation. At lower S doses, S segregates to the Si(100) surface when the defects created by the S implantation are reduced during annealing. If the S dose exceeds the amorphization threshold, two heavily damaged regions with dislocation loops appear after annealing. It seems that S atoms form stable complexes with dislocation loops that survive even after high-temperature anneals at 900 °C. In contrast, when silicidation comes into play, S atoms appear more mobile. Even during Ni silicidation at 550 °C, segregation yields an enrichment of S at the NiSi/Si interface while the defect density and the S content in the deeper Si regions decrease.

Strain relaxation of pseudomorphic Si1-xGex/Si(100) heterostructures after Si+ ion implantation

The strain relaxation of pseudomorphic Si1−xGex layers (x=0.21,…,0.33) was investigated after low-dose Si+ ion implantation and annealing. The layers were grown by molecular-beam epitaxy or chemical vapor deposition on Si(100) or silicon-on-insulator. Strain relaxation of up to 75% of the initial strain was observed at temperatures as low as 850°C after implantation of Si ions with doses below 2×1014cm−2. We suggest that the Si implantation generates primarily dislocation loops in the SiGe layer and in the underlying Si which convert to strain relaxing misfit segments. The obtained results are comparable to strain relaxation achieved after He+ implantation with doses of 1–2×1016cm−2.