Leakage current study of Si1−xCx embedded source/drain junctions

This work investigates the impact of various processing parameters on the leakage current of in situ P-doped Si_1−xC_x embedded source/drain (S/D) junctions, i.e., the carbon content x (%) and the thermal budget used either before or after the selective epitaxial deposition. It is shown that while the area leakage current density, generated by defects in the depletion region is not affected by the epitaxial process or the strain in the substrate, the perimeter leakage current density (J_P) increases with x. From the stronger reverse bias dependence of J_P, it is derived that a higher electric field exists along the junction periphery. This is confirmed by capacitance-voltage (C-V) measurements, demonstrating a higher p-well B doping density for increasing x. It is believed that this originates from the strain dependence of the B diffusivity in the p-well region. No evidence of electrically active extended defect formation was found, so it is expected that the off-state current of embedded Si_1−xC_x S/D nMOSFETs will not be adversely affected by the selective epitaxial deposition.     

Chemical vapor deposition of ZrxTi1−xO2 and HfxTi1−xO2 thin films using the composite anhydrous nitrate precursors

Zr-Ti and Hf-Ti composite nitrates were successfully developed as single-source precursors for the chemical vapor deposition (CVD) of Zr_xTi_1−xO₂ and Hf_xTi_1−xO₂ thin films. The Zr-Ti nitrate can be assumed as a solid solution of the individual Zr and Ti nitrates, and the Zr/Ti molar ratio in the deposited Zr_xTi_1−xO₂ films is consistent with that in the precursor. The Hf-Ti nitrate appears to be a mixture of the Hf and Ti nitrates and the composition of the deposited Hf_xTi_1−xO₂ films depends remarkably on the heating time of precursor. Both Zr_xTi_1−xO₂ and Hf_xTi_1−xO₂ films exhibit trade-off properties between band gap and dielectric constant. The obtained results suggest that Zr_xTi_1−xO₂ and Hf_xTi_1−xO₂ films are promising candidates for gate dielectric application to improve the scalability and reduce the leakage current of the future complementary metal-oxide-semiconductor (CMOS) devices.     

Structural and surface properties of Si1−xGex thin films obtained by reduced pressure CVD

This paper investigates the structure and surface characteristics, and electrical properties of the polycrystalline silicon-germanium (poly-Si_1−xGe_x) alloy thin films, deposited by vertical reduced pressure CVD (RPCVD) in the temperature range between 500 and 750 °C and a total pressure of 5 or 10 Torr. The samples exhibited a very uniform good quality films formation, with smooth surface with rms roughness as low as 7 nm for all temperature range, Ge mole fraction up to 32% (at 600 °C), textures of 〈2 2 0〉 preferred orientation at lower temperatures and strong 〈1 1 1〉 at 750 °C, for both 5 and 10 Torr deposition pressures. The ³¹P⁺ and ¹¹B⁺ doped poly-Si_1−xGe_x films exhibited always lower electrical resistivity values in comparison to similar poly-Si films, regardless of the employed anneal temperature or implantat dose. The results indicated also that poly-Si_1−xGe_x films require much lower temperature and ion implant dose than poly-Si to achieve the same film resistivity. These characteristics indicate a high quality of obtained poly-Si_1−xGe_x films, suitable as a gate electrode material for submicron CMOS devices.     

Magnetoresistance in La1−xCaxMnO3 (0≤x<0.4)

The magnetic and transport properties of La_1−xCa_xMnO₃ (0≤x<0.4) have been systematically studied. The magnetoresistance (MR) maximum appears at x=0.2-0.25 and the temperature dependence of MR for x>0.25 shows a much broader profile than that of samples for x=0.2-0.25. Based on a scenario in which there is a short-range charge ordering (CO) state coexisting in the ferromagnetic state matrix for x>0.25, and the least or even no short-range CO state exists in samples for x=0.2-0.25, the above observations can be understood.     

Growth dynamics of C-induced Ge dots on Si1−xGex strained layers

We address the growth mechanism of Ge quantum dots (QDs) on C-alloyed strained Si_1−xGe_x layers by in situ reflection high-energy electron-diffraction (RHEED). We show that C-induced growth on a Si-rich surface leads to a high density (about 10¹¹ cm⁻²) of small dome-shaped islands. On surfaces up to ≈65% richer in Ge we observe a decrease of the dot density by two orders of magnitude, which is associated to the increase of the adatom diffusion. Based on quantitative RHEED analysis, the islands are believed to grow in a Volmer-Weber mode even though their spotty electron transmission pattern is not detectable in the initial stages of growth due to the reduced size of the three-dimensional nucleation islands.     

Formation of Ge self-assembled quantum dots on a SixGe1−x buffer layer

Ge self-assembled quantum dots (SAQDs) grown on a relaxed Si_0.75Ge_0.25 buffer layer were observed using an atomic force microscopy (AFM) and a transmission electron microscopy (TEM). The effect of buried misfit dislocations on the formation and the distribution of Ge SAQDs was extensively investigated. The Burgers vector determination of each buried dislocation using the g·b = 0 invisibility criterion with plane-view TEM micrographs shows that Ge SAQDs grow at specific positions related to the Burgers vectors of buried dislocations. The measurement of the lateral distance between a SAQD and the corresponding misfit dislocation with plane-view and cross-sectional TEM images reveals that SAQDs form at the intersections of the top surface with the slip planes of misfit dislocations. The stress field on the top surface due to misfit dislocations is computed, and it is found that the strain energy of the misfit dislocations provides the preferential formation sites for Ge SAQDs nucleation.     

Adsorption and decomposition of triethylsilane on Si(1 0 0)

The adsorption and decomposition of triethylsilane (TES) on Si(1 0 0) were studied using temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), electron stimulated desorption (ESD), and X-ray photoelectron spectroscopy (XPS). TPD and HREELS data indicate that carbon is thermally removed from the TES-dosed Si(1 0 0) surface via a β-hydride elimination process. At high exposures, TPD data shows the presence of physisorbed TES on the surface. These species are characterized by desorption of TES fragments at 160 K. Non-thermal decomposition of TES was studied at 100 K by irradiating the surface with 600 eV electrons. ESD of mass 27 strongly suggests that a β-hydride elimination process is a channel for non-thermal desorption of ethylene. TPD data indicated that electron irradiation of physisorbed TES species resulted in decomposition of the parent molecule and deposition of methyl groups on the surface that desorbed thermally at about 900 K. Without electron irradiation, mass 15 was not detected in the TPD spectra, indicating that the production of methyl groups in the TPD spectra was a direct result of electron irradiation. XPS data also showed that following electron irradiation of TES adsorbed on Si(1 0 0), carbon was deposited on the surface and could not be removed thermally.     

Self-limited growth of Si on B atomic-layer formed Ge(1 0 0) by ultraclean low-pressure CVD system

Utilizing BCl₃ reaction on Ge(1 0 0) and subsequent Si epitaxial growth by SiH₄ reaction at 300 °C, B atomic-layer doping in Si/Ge(1 0 0) heterostructure was investigated. Cl atoms on the B atomic-layer formed Ge(1 0 0) scarcely affect upon the SiH₄ reaction. It is also found that Si atom amount deposited by SiH₄ reaction on Ge(1 0 0) is effectively enhanced by the existence of B atomic layer and the deposition rate tends to decrease at around 2-3 atomic layers which is three times larger than that in the case without B. The results of angle-resolved X-ray photoelectron spectroscopy show that most B atoms are incorporated at the heterointerface between the Si and Ge.     

Behavior of N atoms in atomic-order nitrided Si0.5Ge0.5(1 0 0)

Behavior of N atoms in atomic-order nitrided Si_0.5Ge_0.5(1 0 0) by heat treatment in Ar at 600 °C was investigated by X-ray photoelectron spectroscopy (XPS). For thermal nitridation by NH₃ at 400 °C, nitridation of surface Si atoms tends to proceed preferentially over nitridation of surface Ge atoms. It is also clear that, with the heat treatment, nitridation of Si atoms proceeds by transfer of N atoms from Ge atoms. Angle-resolved XPS results show that Ge fraction beneath the surface nitrided layer increases significantly at 600 °C compared to the initial surface. These results indicate that preferential nitridation of Si atoms at surface over Ge atoms induces Ge segregation beneath the surface nitrided layer at higher temperatures above 400 °C.     

Composition dependent structural modification in relaxed Si1−xGex films by 100 MeV Au beam

We report the modification of molecular beam epitaxy grown strain-relaxed single crystalline Si_1−xGe_x layers for x=0.5 and 0.7 as a result of irradiation with 100 MeV Au ions at 80 K. The samples were structurally characterized by Rutherford backscattering spectrometry/channeling, transmission electron microscopy (TEM) and high-resolution X-ray diffraction before and after irradiation with fluences of 5×10¹⁰, 1×10¹¹ and 1×10¹² ions/cm², respectively. No track formation was detected in both the samples from TEM studies and finally, the crystalline to amorphous phase transformation at 1×10¹² ions/cm² was examined to be higher for Si_0.3Ge_0.7 layers compared to Si_0.5Ge_0.5 layers.     

Reply to the comment on: ‘Magnetoresistance in La1−xCaxMnO3(0≤x<0.4)’

The author of the comment objects to the characterization and the interpretation of magnetoresistance (MR) effects observed by us in La_1−xCa_xMnO₃ (0≤x<0.4) samples. In this reply, arguments are used to show that the samples' characterization and explanation of the MR by considering the role of the short-charge ordering (CO) regions and magnetic domains are reasonable and acceptable.     

New fabrication of a strained Si/Si1−yGey dual channel on a relaxed Si1−xGex virtual substrate using a Ge-rich layer formed by oxidation

This paper presents a new method of forming a Si/SiGe dual channel on a Si_0.8Ge_0.2 virtual substrate. Generally, in a CMOS process using a Si/SiGe dual channel, due to several processes involving ion-implantation, annealing and dry-etching after the deposition of the Si/SiGe dual channel, the surface can be damaged, leading to reduced electrical properties. However, if the dual channel is formed during a specific stage of the CMOS process, the defects of the dual channel can be reduced and the thermal stability will be excellent. Therefore, in this paper, a method for minimizing the defects of the dual channel is presented. This method uses the segregation of the Ge in the oxidation process of a SiGe. A Si/SiGe dual channel formed using this method achieved results that were identical to a dual channel deposited using the chemical vapor deposition (CVD) method.     

Scanning tunneling microscopy observation of initial growth of Sn and Ge1−xSnx layers on Ge(0 0 1) substrates

We have investigated the initial growth of Sn and Ge_1−xSn_x layers on Ge(0 0 1) surface by using scanning tunneling microscopy. After the growth of a 0.035 ML-thick Sn layer at room temperature, Sn clusters lining vertically to a dimer row was observed. In the case of the 0.035-0.018 ML-thick Sn growth at 250 °C, the characteristic surface reconstruction with the step-edge undulation like a comb was observed. In the growth of a Ge_0.994Sn_0.006 layer at 250 °C, the multilayer polynuclear growth with a lot of two-dimensional small domain was observed. These surface reconstructions should be accounted for by the large compressive stress induced in the surface layer due to the incorporation of Sn atoms.     

Structural studies of evaporated CoxCr1−x/Si (1 0 0) and CoxCr1−x/glass thin films

Series of Co_xCr_1−x thin films have been evaporated under vacuum onto Si (1 0 0) and glass substrates. Chemical composition and interface properties have been studied by modelling Rutherford backscattering spectra (RBS) using SIMNRA programme. Thickness ranges from 17 to 220 nm, and x from 0.80 to 0.88. Simulation of the energy spectra shows an interdiffusion profile in the thickest films, but no diffusion is seen in thinner ones. Microscopic characterizations of the films are done with X-ray diffraction (XRD) measurements. All the samples are polycrystalline, with an hcp structure and show a 〈0 0 0 1〉 preferred orientation. Atomic force microscopies (AFM) reveal very smooth film surfaces.     

Effect of a LaSrCoO3 buffer layer on Pb1 − xLaxTi1 − x/4O3 films studied by polarized Raman spectroscopy

A confocal Raman investigation of Pb_1 − xLa_xTi_1 − x/4O₃ (PLT) thin films grown by RF magnetron sputtering on PbO_x/Pt/Ti/SiO₂/Si substrates with an intermediate LaSrCoO₃ (LSCO) layer was performed. The influence of the LaSrCoO₃ buffer layer was analyzed taking advantage of the observed Raman spectral band variation, which varied according to different manufacturing procedures. In the presence of a LSCO layer, the A1(1TO) Raman mode, which was indicative of tetragonal distortion, was pronouncedly enhanced, and a slight deviation from the (0 0 1) plane of the film was observed from the angular dependence of the polarized Raman spectral intensity. Furthermore, the spectral band variation as well as the residual stress along the in-depth direction was measured in the film from cross-sectional spectral line scans. This latter measurement showed a relaxation of the lattice mismatch in the presence of LSCO and PbO layers.     

Annealing of thin Zr films on Si1−xGex(0≤x≤1): X-ray diffraction and Raman studies

X-ray diffraction experiments have been combined with Raman scattering and transmission electron microscopy data to analyze the result of rapid thermal annealing (RTA) applied to Zr films, 16 or 80 nm thick, sputtered on Si_1−xGe_x epilayers (0≤x≤1). The C49 Zr(Si_1−xGe_x)₂ is the unique phase obtained after complete reaction. ZrSi_1−xGe_x is formed as an intermediate phase. The C49 formation temperature T_f is lowered by the addition of Ge in the structure. Above a critical Ge composition close to x=0.33, a film microstructure change was observed. Films annealed at temperatures close to T_f are continuous and relaxed. Annealing at T>T_f leads to discontinuous films: surface roughening resulting from SiGe diffusion at film grain boundaries occurred. Grains are ultimately partially embedded in a SiGe matrix. A reduction in the lattice parameters as well as a shift of Raman lines are observed as T exceeds T_f. Both Ge non-stoichiometry and residual stress have been considered as possible origins for these changes. However, as Ge segregation has never been detected, even by using very efficient techniques, it is thought that the changes originate merely from residual stress. The C49 grains are expected to be strained under the SiGe matrix effect and shift of the Raman lines would indicate the stress is compressive. Some simple evaluations of the stress values indicate that it varies between −0.3 and −3.5 GPa for 0≤x≤1 which corresponds to a strain in the range (−0.11, −1.15%). X-ray and Raman determinations are in good agreement.     

A note on TiN/Si (1 0 0) contacts

The contact properties of TiN on p- and n-type Si (1 0 0) obtained by magnetron reactive sputtering were investigated. Schottky diode characteristics were observed on p-type Si (1 0 0) as determined by forward current-voltage (I-V) measurements, but on n-type Si (1 0 0) the reverse I-V relation has shown a nonsymmetrical character. The zero-bias barrier heights evaluated by I-V on both type diodes were in the range of ∼0.60-0.64 V within the range of a few mVs, not more than ∼±(10-30) mV from each other. Incorporation of the effect of the series resistance in the I-V analysis resulted in a significant reduction in the magnitude of the ideality factor of the TiN/p-type specimen. Almost no change has occurred in the barrier height values. The contradictory reports on the TiN/n-type Si (1 0 0) diode characteristics in earlier works have been explained in terms of surface passivation of Si by the HF cleaning solution. It was stated in these reports that following annealing at 673 K the diodes have shown rectifying behavior. It has been speculated, that the nonsymmetrical nature of the TiN/n-Si (1 0 0) showing an intermediate behavior between Ohmic and rectifying behavior is a result of the specimen being exposed to a temperature lower than 673 K during sputtering where no complete depassivation took place. In order to obtain a rectifying behavior of TiN on both n-type and p-type Si surface passivation has to be eliminated.     

Surface anisotropy of CrxN1−x films prepared on an inner wall by magnetic sputtering

The Cr_xN_1−x films were prepared by magnetic sputtering on an inner wall of a column. Their surface morphologies were studied by atomic force microscopy (AFM) and found to be anisotropic. The 3-D AFM images indicate the grains grow upward along the rotational axis of the system. The AFM top views show a mosaic-like pattern for all samples. Analysis of the height-height correlation function demonstrates that correlation length along the rotational axis of the system is longer than that vertical to the axis. The correlation length and RMS roughness increase with the flow rate of N₂. A deposition model proposed that the shadowing effect of the reactive gas N₂ is the dominant factor for surface anisotropy. The bias added on the substrate is regarded to modulate the grain direction to the rotation axis and enhance roughness and defects.     

Heavy atomic-layer doping of B in low-temperature Si epitaxial growth on Si(1 0 0) by ultraclean low-pressure chemical vapor deposition

Electrical characteristics of B atomic-layer doped Si epitaxial films on Si(1 0 0) formed by B atomic-layer formation on Si(1 0 0) at 180 °C and subsequent capping Si deposition at 500 °C using ultraclean low-pressure chemical vapor deposition were investigated. From evaluation results of carrier concentration in the films, by low-temperature SiH₄ exposure at 180-300 °C before the capping Si deposition at 500 °C, 70% improvement of B electrical activity was confirmed, and it is suggested that lowering the temperatures for B atomic-layer formation on Si(1 0 0) as well as SiH₄ exposure before the capping Si deposition is effective to suppress B clustering and to achieve B atomic-layer doped Si films with extremely high carrier concentration.