Characterization of strained silicon on relaxed SiGe layer made by H ion implantation and annealing in ultra-high vacuum ambient

Twenty-nanometer-thick Si cap layer/74-nm-thick Si_0.72Ge_0.28 epilayer/Si heterostructural sample was implanted by 25 keV H⁺ ion to a dose of 1 × 10¹⁶ cm⁻² and subsequently annealed in ultra-high vacuum ambient at the temperature of 800 °C for 30 min. Rutherford backscattering/ion channeling (RBS/C), Raman spectra, high resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) were used to characterize the structural characteristic of Si/SiGe/Si heterostructure. Investigations by RBS/C demonstrate that the Si_0.72Ge_0.28 layer show good crystal quality (21.1% of channel minimum yield). The relaxation degree of partially relaxed Si_0.72Ge_0.28 layer was around 74%, which was obtained by HRXRD. The computation process of the relaxation degree of strain in SiGe layer according to HRXRD rocking curve was also thoroughly introduced. Raman analysis revealed that stress, σ and strain, ε in the thin strained-Si layer were around 1.2 Gpa and 0.52%, respectively. In addition, the small surface roughness in the formed strained-Si/relaxed Si_0.72Ge_0.28 layer/Si heterostructural sample was observed via AFM image.     

Role of a Si0.95Ge0.05 epilayer cap on boron diffusion in silicon under inert and dry oxidizing ambient annealing

Silicon (Si) and Si with a 60 nm Si_0.95Ge_0.05 epilayer cap (Si_0.95Ge_0.05/Si) were implanted with 60 keV, 1×10¹³ cm⁻² boron (B) followed by annealing in nitrogen (N₂) or dry oxygen (O₂) in two different anneal conditions. B⁺implantation energy and dose were set such that the B peak is placed inside Si in Si_0.95Ge_0.05/Si samples and concentration independent B diffusion is achieved upon annealing. For samples annealed above 1075 °C, Ge diffusing from the Si_0.95Ge_0.05 epilayer cap in Si_0.95Ge_0.05/Si samples reached the B layer inside Si and resulted in retarded B diffusion compared to the Si samples. For annealing done at lower temperatures, diffusion of Ge from Si_0.95Ge_0.05 epilayer cap does not reach the B layer inside Si. Thus B diffusion profiles in the Si and Si_0.95Ge_0.05/Si samples appear to be similar. B diffusion in dry oxidizing ambient annealing of Si_0.95Ge_0.05/Si samples further depends on the nature of Si_0.95Ge_0.05 oxidation which is set by the duration and the thermal budget of the oxidizing anneal.     

Interaction of ion-implantation-induced interstitials in B-doped SiGe

B-doped Si_0.77Ge_0.23 of various surface-doping levels was used to investigate the evolution of implant damage and the corresponding transient enhanced diffusion of boron as a function of boron concentration. These layers were implanted with a non-amorphizing 60 keV, 1×10¹⁴ cm⁻² Si, and annealed at 750 °C. Plan-view transmission electron microscopy (PTEM) confirmed the formation and dissolution of dislocation loops. Transient enhanced diffusion (TED) is evident in the surface doped SiGe, but the low diffusivity of interstitials in Si_0.77Ge_0.23 and the presence of interstitial traps inhibited TED at the deeper B marker layer.     

Electronic properties of Si/Si-Ge Alloy/Si(100) heterostructures formed by ECR Ar plasma CVD without substrate heating

By using our low-energy Ar plasma enhanced chemical vapor deposition (CVD) at a substrate temperature below 100 °C during plasma exposure without substrate heating, modulation of valence band structures and infrared photoluminescence can be observed by change of strain in a Si/strained Si_0.4Ge_0.6/Si(100) heterostructure. For the strained Si_0.5Ge_0.5 film, Hall mobility at room temperature was confirmed to be as high as 660 cm² V⁻¹ s⁻¹ with a carrier concentration of 1.3×10¹⁸ cm⁻³ for n-type carrier, although the carrier origin was unclear. Moreover, good rectifying characteristics were obtained for a p⁺Si/nSi_0.5Ge_0.5 heterojunction diode. This indicates that the strained Si-Ge alloy and Si films and their heterostructures epitaxially grown by our low-energy Ar plasma enhanced CVD without substrate heating can be applicable effectively for various semiconductor devices utilizing high carrier mobility, built-in potential by doping and band engineering.     

Characterization of reduced pressure chemical vapor deposited Si0.8Ge0.2/Si multi-layers

We have investigated the Si_0.8Ge_0.2/Si multi-layer grown directly onto the Si (001) substrates using reduced pressure chemical vapor deposition. The thicknesses of the Si_0.8Ge_0.2/Si multi-layer were determined using transmission electron microscopy. From the results of energy-dispersive X-ray spectroscopy and X-ray diffraction analyses on the Si_0.8Ge_0.2/Si multi-layer, Ge composition in the Si_1?xGe_x layers was determined as ～20% and the value of residual strain ε of the Si_0.8Ge_0.2 layer is calculated to be 0.012. Three peaks are observed in Raman spectrum, which are located at approximately 514, 404, and 303 cm^?1, corresponding to the vibration of Si–Si, Si–Ge, and Ge–Ge phonons, respectively. The photoluminescence spectrum originates from the radiative recombinations both from the Si substrate and the Si_0.8Ge_0.2/Si multi-layer. For the Si_0.8Ge_0.2/Si multi-layer, the transition peaks related to the quantum well region observed in the photocurrent spectrum were preliminarily assigned to e–hh and e–lh fundamental excitonic transitions.     

Photophysical properties of nano Si/SiOx composites in Al/composite/mono Si structures for green light emitting and photodetector-Schottky diodes

The concept of the self-formation of a nanocrystallite (nc-) Si/SiO_x : Si_zO_yAl nanocomposite at the Al/oxidized porous silicon interface in the result of solid-phase processes between Al and oxidized porous Si (PS) and the influence of its composition on photophysical properties were developed and experimentally confirmed for the Si chip with optical intra-chip interconnect consisting of light emitting and photodetector diodes and alumina waveguide on oxidized PS surface with aluminum electrodes. The peculiarities of nanocomposite photophysical properties (the refractive index, photoluminiscence (PL) peak situation, PL spectrum shape in the green range) have been shown to be due to the quantum confinement effects (revealed by XPS, Raman spectroscopy) and depend on the Al presence in the nanocomposite (obtained by XPS, IR spectroscopy). The experimental confirmation of this concept is (i) the shift of the nc-Si valence band relatively to that of monocrystalline Si (c-Si) on 0.2–0.7 eV for nc-Si size in 2.5–6.5 nm range; (ii) the decrease of Si nanocrystallite size in the Al presence; (iii) the approach of the value of the refractive index of nc-Si : SiO : Si₂O₃ : Si_zO_yAl nanocomposite at λ=236 nm to that of porous Si with 45% porosity and (iv) the stable green PL spectra in the Si_zO_yAl presence in the nanocomposite.     

Structural,magnetic and electrical properties of Fe/Si system

Interface studies in metal/semiconductor systems are important due to their potential technological application in microelectronics. A total of 80 nm Fe film was deposited on Si(1 1 1) substrate using electron beam evaporation technique at a vacuum of 2×10⁻⁷ Torr. The samples were annealed at temperatures 500 and 600 °C for 1 h in 3×10⁻⁵ Torr for the formation of silicide phases. GIXRD results show a stable disilicides FeSi₂ formation at the interface at annealing temperature 600 °C. The coercivity determined from MOKE hysteresis curves for as-deposited and annealed samples are 14.91, 29.82 and 31.01 Oe. The Schottky barrier height, as estimated by the current–voltage measurement is 0.59, 0.54 and 0.49 eV for pristine and annealed samples at 500 and 600 °C, respectively, and concludes that the barrier height values as a function of the heat of formation of the silicides.     

Paramagnetic Ge dangling bond type defects at (1 0 0)Si1−xGex/SiO2 interfaces (Invited Paper)

The work addresses the occurrence of Ge dangling bond type point defects at Ge_xSi_1?x/insulator interfaces as evidenced by conventional electron spin resonance (ESR) spectroscopy. Using multifrequency ESR, we report on the observation and characterization of a first nontrigonal Ge dangling bond (DB)-type interface defect in SiO₂/(1 0 0)Ge_xSi_1?x/SiO₂/(1 0 0)Si heterostructures (0.27 ? x ? 0.93) manufactured by the condensation technique, a selective oxidation method enabling Ge enrichment of a buried epitaxial Si-rich SiGe layer. The center, exhibiting monoclinic-I (C_2v) symmetry is observed in highest densities of ～7 × 10¹² cm^?2 of Ge_xSi_1?x/SiO₂ interface for x ～ 0.7, to disappear for x outside the ]0.45–0.87[ interval, with remarkably no copresence of Si P_b-type centers. Neither are trigonal Ge DB centers observed, enabling unequivocal spectral analysis. Initial study of the defect passivation under annealing in molecular H₂ has been carried out. On the basis of all data the defect is depicted as a Ge P_b1-type center, i.e., distinct from a trigonal basic Ge P_b(0)-type center (Ge₃Ge). The modalities of the defect’s occurrence as unique interface mismatch healing defect is discussed, which may widen our understanding of interfacial DB centers in general.     

Direct bonding of Si wafer pairs with SiO2 and Si3N4 films with a fast linear annealing

2000 Å-SiO₂/Si(1 0 0) and 560 Å-Si₃N₄/Si(1 0 0) wafers, that are 10 cm in diameter, were directly bonded using a rapid thermal annealing method, so-called fast linear annealing (FLA), in which two wafers scanned with a high-power halogen lamp. It was demonstrated that at lamp power of 550 W, corresponding to the surface temperature of ∼450°C, the measured bonded area was close to 100%. At the same lamp power, the bond strength of the SiO₂∥Si₃N₄ wafer pair reached 2500 mJ/m², which was attained only above 1000°C with conventional furnace annealing for 2 h. The results clearly show that the FLA method is far superior in producing high-quality directly bonded Si wafer pairs with SiO₂ and Si₃N₄ films (Si/SiO₂∥Si₃N₄/Si) compared to the conventional method.     

Determination of boron concentration in heavily doped p-type Si1−xGex/Si heterostructure by infrared ellipsometric spectroscopy

Si_1−xGe_x/Si heterostructures play a primary role in the Si-based fast electronics developments of today. In this work, we will present the experimental results of infrared spectroscopic ellipsometry (IRSE) for structural determination of the boron heavily doped SiGe/Si sample grown by ultra-high vacuum chemical vapor deposition (UHVCVD) (the Ge atomic percent, the thickness of SiGe film and boron concentration). Especially, the principle of boron concentration in p-type SiGe film layer determined by IRSE was elucidated in detail. In addition, in order to corroborate the validity of IRSE for determining dopant concentration, secondary ion mass spectroscopy (SIMS) experiment has also been carried out. The close experimental agreement between IRSE and SIMS demonstrate that IRSE as a contactless, and non-destructive technology can be used in-line tools in production used for measuring the Ge content, the thickness of SiGe layer and boron concentration in p-type dopant SiGe/Si heterostructure, which often used the base layer of SiGe hetero-junction bipolar transistor (HBT) devices.     

Thermal stability of compressively strained Si/relaxed Si1-xCx heterostructures formed on Ar ion implanted Si (100) substrates

Thermal stability of compressively strained Si/relaxed Si_1-xC_x heterostructure formed with the defect control by Ar ion implantation was investigated. It was found that compressive strain is sustained up to 900 °C without prominent change in surface roughness. From the X-ray diffraction reciprocal space mapping, it was found that relaxed Si_1-xC_x layer is stable up to at least 800 °C, and compressively strained Si_1-xC_x with relatively large thickness is formed by annealing at temperatures higher than 900 °C owing to redistribution of C atoms. These results indicate that the compressively strained Si/relaxed Si_1-xC_x heterostructure formed by Ar ion implantation technique is available up to at least 800 °C and has a potential to be used at more than 900 °C.     

Optical study of germanium nanostructures grown on a Si(118) vicinal substrate

Photoluminescence (PL) measurements were carried out on Si/Ge(n)/Si_0.7Ge_0.3/Si structures (n is varying from 1 to 7 ML) deposed by gas source molecular beam epitaxy (GS-MBE) on Si(100) surfaces and high index Si(118) vicinal surfaces. Ge nanostructures were confined on the top of the undulation of the Si_0.3Ge_0.7 wetting layer, according to the Stranski–Krastanov growth mode. PL measurements reveal a correlation between the substrate orientation and the island morphology: square dots for (001) and wires for (118) surface orientation. The results suggest that the SiGe wetting layer is required to ensure a good dot size uniformity. The dependence of the luminescence on the excitation power and the PL decay time indicate that the luminescence transitions likely occur in a type-II band line up. Finally, the dot-related PL persists up to room temperature which is very promising for optoelectronic device applications.     

Improvement in negative differential conductance characteristics of hole resonant-tunneling diodes with high Ge fraction Si/strained Si1−xGex/Si(1 0 0) heterostructure

Hole resonant-tunneling diodes (RTD) with Si/strained Si_1?xGe_x heterostructures epitaxially grown on Si(1 0 0) have been fabricated and improvement in negative differential conductance (NDC) characteristics for high Ge fraction such as x = 0.5 was investigated. It is clearly shown that SiH₄ exposure at low temperatures of 400–450 °C just after Si_1?xGe_x epitaxial growth is effective to suppress surface roughness in atomic order. In the case of the RTD with x = 0.48, NDC characteristics for 1.4-nm thick Si barriers were observed at higher temperatures around 270 K than that for 2.4-nm thick Si barriers. By increasing the Ge fraction to x = 0.58, NDC characteristics were also observed at higher temperatures around 290 K than that with x = 0.48.     

Effect of high-temperature annealing on lanthanum aluminate thin films grown by ALD on Si(1 0 0)

Amorphous lanthanum aluminate thin films were deposited by atomic layer deposition on Si(1 0 0) using La(ⁱPrCp)₃, Al(CH₃)₃ and O₃ species. The effects of post-deposition rapid thermal annealing on the physical and electrical properties of the films were investigated. High-temperature annealing at 900 °C in N₂ atmosphere leads to the formation of amorphous La-aluminosilicate due to Si diffusion from the substrate. The annealed oxide exhibits a uniform composition through the film thickness, a large band gap of 7.0 ± 0.1 eV, and relatively high dielectric constant (κ) of 18 ± 1.     

Growth temperature dependence of epitaxial Gd2O3 films on Si(1 1 1)

This article reports on the epitaxy of crystalline high κ oxide Gd₂O₃ layers on Si(1 1 1) for CMOS gate application. Epitaxial Gd₂O₃ thin films have been grown by Molecular Beam Epitaxy (MBE) on Si(1 1 1) substrates between 650 and 750 °C. The structural and electrical properties were investigated depending on the growth temperature. The C–V measurements reveal that equivalent oxide thickness (EOT) equals 0.7 nm for the sample deposited at the optimal temperature of 700 °C with a relatively low leakage current of 3.6 × 10^?2 A/cm² at |V_g ? V_FB| = 1 V.     

Optical properties of Si0.8Ge0.2/Si multiple quantum wells

The optical property was studied on the Si_0.8Ge_0.2/Si strained multiple quantum well (MQW) structure grown using ultra-high vacuum chemical vapor deposition (UHV-CVD). Three peaks are observed in Raman spectrum, which are located at about 510, 410, and 300 cm⁻¹, corresponding to the vibration of Si–Si, Si–Ge, and Ge–Ge phonons, respectively. The photoluminescence (PL) spectrum originates from the radiative recombinations both from the Si substrate and the Si_0.8Ge_0.2/Si MQW. For Si_0.8Ge_0.2/Si strained MQW, the transition peaks related to the MQW region observed in the photocurrent (PC) spectrum were preliminarily assigned to electron–heavy hole (e–hh) and electron–light hole (e–lh) fundamental excitonic transitions.     

Low-temperature crystallization of Ge-rich GeSn layers on Si3N4 substrate

Solid phase crystallization (SPC) of amorphous GeSn (a-GeSn) layers with a Sn content of 2% on various insulating substrates of Si₃N₄, sapphire, and Y₂O₃ have been investigated. We found that Si₃N₄, which has almost same value of a higher surface energy with sapphire and the value is about twice as high as Y₂O₃, could be reduced the SPC temperature of a-GeSn layers (to 400 °C) compared with the other cases. We can see that a maximum grain size as large as 0.9 µm was achieved for polycrystalline GeSn layers on Si₃N₄ by the annealing at 450 °C for 5 h. Correspondingly, a relatively higher Hall hole mobility (180 cm²/Vs) was obtained.     

Composition,structure and electrical properties of DC reactive magnetron sputtered Al2O3 thin films

Thin films of alumina (Al₂O₃) were deposited over Si 〈1 0 0〉 substrates at room temperature at an oxygen gas pressure of 0.03 Pa and sputtering power of 60 W using DC reactive magnetron sputtering. The composition of the as-deposited film was analyzed by X-ray photoelectron spectroscopy and the O/Al atomic ratio was found to be 1.72. The films were then annealed in vacuum to 350, 550 and 750 °C and X-ray diffraction results revealed that both as-deposited and post deposition annealed films were amorphous. The surface morphology and topography of the films was studied using scanning electron microscopy and atomic force microscopy, respectively. A progressive decrease in the root mean square (RMS) roughness of the films from 1.53 nm to 0.7 nm was observed with increase in the annealing temperature. Al–Al₂O₃–Al thin film capacitors were then fabricated on p-type Si 〈1 0 0〉 substrate to study the effect of temperature and frequency on the dielectric property of the films and the results are discussed.     

Influence of the Germanium content on the amorphization of silicon–germanium alloys during ion implantation

We have studied by transmission electron microscopy the amorphization of silicon–germanium (SiGe) alloys by Ge⁺ implantation. We show that when implanted with the same amorphization dose, the resulting amorphous layers get narrower when the Ge content increases. The experimental results can be simulated using the critical damage energy density model assuming that the amorphization threshold rises linearly with the Ge content from 3 eV/at for pure Si to 5 eV/at for pure Ge. These results and simulations are needed to optimize the fabrication of highly doped regions in SiGe alloys.     

Ultra flexible SiGe/Si/Cr nanosprings

The electrical and mechanical properties of Si/SiGe rolled-up nanosprings have been investigated. Micromanipulation has been employed to investigate the mechanical properties. For nanosprings under investigation, a linear dependence between applied force and extention is found until the spring is extended to 91% of its original length, moreover, the springs could be reproducibly extended to more than 180% of their original length. An extremely small spring constant of 0.003 N/m has been determined, which is an order of magnitude smaller than that of the most flexible available atomic force microscope (AFM) cantilever (～10^?2 N/m). Thus, it is expected that these springs can be used as ultra-sensitive force sensors. A simple estimation assuming an imaging resolution of approximately 1 nm is adopted for displacement measurement and reveals that using a nanospring fabricated from a 300 nm wide mesa as a visual-based force sensor, a resolution of 3 pN/nm can be provided. The conductivity of nanospirals was analysed and current densities up to 530 kA/cm² were measured. Structures with metallic wires on top of the mesa structures were successfully employed to activate mechanical movements of the structure.