Reduced Pressure Chemical Vapor Deposition Research Articles

High-quality Ge/Si0.4Ge0.6 multiple quantum wells for photonic applications: growth by reduced pressure chemical vapour deposition and structural characteristics

Strain-symmetrized Ge/SiGe multiple quantum wells have been grown on a thin (2.1 µm) relaxed Si0.2Ge0.8/Ge/Si(1 0 0) virtual substrate (VS) by reduced pressure chemical vapour deposition. Such structures are of interest in optoelectronic applications for which the structural integrity of the quantum well layers, after processing, is critical. The layer composition, thickness and interface quality have been studied for wafers both as-grown and after annealing between 550 and 700 °C. Transmission electron microscopy indicated precise thickness control of ±0.1 nm and sharp abruptness between the Ge QWs and SiGe barrier layers. A smooth surface was observed, with an average rms roughness of 1.5 ± 0.1 nm determined by atomic force microscopy. High-resolution x-ray diffraction (HR-XRD) indicated that both the QWs and barriers were fully strained compared with the relaxed VS. The thermal stability of the epilayers was investigated both by ultra low energy secondary ion mass spectroscopy of post-growth annealed layers and by in situ annealing in a high temperature HR-XRD stage. No obvious interdiffusion and strain relaxation was observed provided the annealing temperature was below 600 °C, but significant atomic rearrangement was evident for greater thermal budgets, thereby setting an upper processing temperature for this type of structure.

X-ray characterization of Ge epitaxially grown on nanostructured Si(001) wafers

Selective growth of Ge on nanostructured Si(001) wafers is studied to evaluate the applicability of nanoheteroepitaxy approaches on the Ge–Si system for photonics applications under particular consideration of possible growth mask materials. A gate spacer technology established in advanced silicon microelectronics is used to generate a periodic array of nanoscaled Si pillars. The spacing of these Si pillars is 360 nm; diameter and height are about 100 nm, which is still above the expected geometrical parameters to obtain a compliant behavior of the Si lattice in the pillars. Ge dots are deposited by reduced pressure chemical-vapor deposition on top of the Si pillars. The characterization is done by different x-ray diffraction methods and transmission electron microscopy. It is found that even 30 nm thick Ge dots are fully relaxed and they exhibit a clear network of misfit dislocations. Significantly thicker Ge dots generate additional structural defects, mainly microtwins. A strain partitioning between Si pillar and Ge dot was not observed. The main reason for this is not the geometry of pillars but the compressive in-plane strain inside the uncovered Si pillar caused by the surrounding SiO2 layer required as masking material to guaranty the selective growth of Ge on top of the pillars only. High temperature diffraction experiments show that a partial annealing of this strain is possible.

A kinetics model for the chemical vapor deposition growth of SiGe/Si heterojunction materials

Based on Grove model of CVD(chemical vapor deposition) and Fick’s first law, we propose and build the RPCVD(reduced pressure chemical vapor deposition) growth kinetics model of GeSi/Si heterojunction materials. Different from previous SiGe/Si kinetics model, which only considers surface reaction controlling mechanism, our model simultaneously considers two controlling mechanisms: surface reaction and vapor transport. We also consider the model at these two controlling mechanism limits. This model is suitable for charactering the growth of both strained GeSi/Si heterojunction materials at low temperatures and relaxed GeSi/Si heterojunction materials at high temperatures. The calculated value of the model is compared with experimental results. Whether for the growth of strained SiGe at low temperature of 625 ℃, or for the growth of relaxed SiGe at high temperature of 900 ℃, the model error are both lower than 10%, which is the subject technical target.

Accuracy of thickness measurement for Ge epilayers grown on SiGe/Ge/Si(100) heterostructure by x-ray diffraction and reflectivity

High-resolution x-ray diffraction rocking curve (RC), x-ray reflectivity (XRR), and transmission electron microscopy (TEM) were used to characterize strained Ge epilayers grown on relaxed SiGe/Ge/Si(100) virtual substrates by reduced pressure chemical vapor deposition. The investigation focused on the reliability and accuracy of thickness measurement by these different techniques. The authors found that both XRR and RC could give reliable values that agree well with TEM results over a wide range of Ge epilayer thicknesses. The best-fit thickness from both XRR and RC is within ±5% of the TEM measurement for a thickness in the range of 10–120 nm, with XRR producing more accurate values than RC. However, neither RC nor XRR could give reliable results for very thin Ge epilayers ( 122 nm) due to surface roughening caused by strain relaxation.

Highly strained Si epilayers grown on SiGe/Si(100) virtual substrate by reduced pressure chemical vapour deposition

AbstractBi‐axial tensile strained Si epilayers with extremely high lattice mismatch strain up to 2.13% were grown from a disilane (Si2H6) precursor on Si1‐xGex/Si(100) VSs by Reduced Pressure Chemical Vapour Deposition. We discuss the conditions under which fully strained Si epilayers of the required thickness can be grown. By demonstrating a fully strained 23 nm Si layer on a fully relaxed Si0.45Ge0.55(100) VS, this work indicates the potential for realizing high performance s‐Si n‐ and p‐MOSFETs on standard Si(100) substrates. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Double Si nanocrystal layers grown by RPCVD for non-volatile memory applications

We present in this paper a method to increase the density of nanocrystals (NCs) in a storage device having a discrete floating gate. The method consists of the growth, by reduced pressure chemical vapour deposition (RPCVD), of two superposed NC layers separated by a very thin deposited dielectric layer. The cross-sectional scanning electron microscopy and transmission electron microscopy observations will show that two stacked Si NC layers can be formed with approximately the same mean size and density by covering the bottom one with a few nanometres thick high thermal oxide layer and growing the top one on the dielectric layer. The write/erase characteristics of a memory device show that the use of two stacked Si NC layers improves the memory windows compared to devices with a single Si NC layer without introducing dispersions on the charging dynamics.

Silicon–germanium interdiffusion in strained Ge/SiGe multiple quantum well structures

A strain-symmetrized Ge/Si0.35Ge0.65 multiple quantum well (MQW) structure has been grown on a relaxed Si0.2Ge0.8 virtual substrate by reduced pressure chemical vapour deposition. The as-grown Ge/Si0.35Ge0.65 MQW structure with one period thickness of 25 nm (14 nm/11 nm) was annealed in nitrogen ambient at different temperatures from 550 to 750 °C. The thermal stability and interdiffusion properties were studied by high-resolution x-ray diffraction. No obvious interdiffusion or strain relaxation in the Ge/Si0.35Ge0.65 MQW structure was observed for annealing temperatures ⩽600 °C, while the onset of interdiffusion occurred as the temperature was increased to above 650 °C. The interdiffusion coefficient was obtained by analysing the decay rate of Ge/SiGe periodic satellites in the recorded intensity at temperatures 650–750 °C. The extracted activation energy was found to be 3.08 ± 0.1 eV for the strained Ge/Si0.35Ge0.65 MQW structure with an average Ge composition of 85 at%.

Control of epilayer thickness during epitaxial growth of high Ge content strained Ge/SiGe multilayers by RP-CVD

In this work, we have developed a reduced pressure chemical vapor deposition (RP-CVD) epitaxial process to grow strain-balanced Ge/Si0.4Ge0.6 multilayers on 200mm diameter Si(100) substrates, via an intermediate relaxed Si0.2Ge0.8/Ge buffer. The results obtained indicate that with proper selection of the epitaxial growth conditions, strain-balanced multilayered heterostructures can be produced with the precise Si0.4Ge0.6 alloy content and control of the strained epilayer thicknesses to within a few monolayers. XTEM analysis clearly resolved very abrupt Ge/Si0.4Ge0.6 heterointerfaces and the sample surfaces were seen, by AFM, to be very smooth with an RMS surface roughness below 1.5nm.

Optical Property of Si0.8Ge0.2/Si Multilayer Grown by Using RPCVD

We have investigated the characterization of Si0.8Ge0.2/Si multi-layer grown directly onto Si (001) substrates using reduced pressure chemical vapor deposition (RPCVD). The structural properties of the Si0.8Ge0.2/Si multi-layer were investigated using X-ray diffraction (XRD) and TEM. Three peaks are observed in Raman spectrum, which are located at about 514,404, and 303 cm-1, corresponding to the vibration of Si-Si, Si-Ge, and Ge-Ge phonons, respectively. The PL spectrum originates from the radiative recombinations both from the Si substrate and the Si0.8Ge0.2/Si multi-layer. For Si0.8Ge0.2/Si multi-layer, the transition peaks related to the QW region observed in the photocurrent spectrum were preliminarily assigned to electron-heavy hole (e-hh) and electron-light hole (e-lh) fundamental excitonic transitions.

Phosphorus Atomic Layer Doping in Si Using PH3

Atomic layer doping of P (P-ALD) in Si is investigated using reduced pressure chemical vapor deposition (RPCVD). For P-ALD, PH3 exposure on Si (100) surface followed by Si cap layer deposition using SiH4 or Si2H6 is performed. P adsorption is suppressed by hydrogen-termination of the Si surface. On the hydrogen-free Si surface, the P adsorption is increasing with increasing PH3 exposure temperature saturating at temperatures above 600oC. P adsorption is also increasing with increasing PH3 exposure time. It tends to saturate at long exposure time indicating a self-limitation of the process. By Si deposition using Si2H6, higher P peak concentration and higher P doping level in the Si cap layer is observed compared to those with SiH4 based Si deposition. For both SiH4 and Si2H6 based capping process lower P segregation is observed by lowering the growth temperature.

Kinetic Model of SiGe Selective Epitaxial Growth Using RPCVD Technique

Recently, selective epitaxial growth (SEG) of B-doped SiGe layers has been used in recessed source/drain (S/D) of pMOSFETs. The uniaxial induced strain enhances the carrier mobility in the channel. In this work, a detailed model for SEG of SiGe has been developed to predict the growth rate and Ge content of layers in dichlorosilane(DCS)-based epitaxy using a reduced-pressure CVD reactor. The model considers each gas precursor contributions from the gas-phase and the surface. The gas flow and temperature distribution were simulated in the CVD reactor and the results were exerted as input parameters for Maxwell energy distribution. The diffusion of molecules from the gas boundaries was calculated by Fick's law and Langmuir isotherm theory (in non-equilibrium case) was applied to analyze the surface. The pattern dependency of the selective growth was also modeled through an interaction theory between different subdivisions of the chips. Overall, a good agreement between the kinetic model and the experimental data were obtained.

Effect of growth rate on the threading dislocation density in relaxed SiGe buffers grown by reduced pressure chemical vapour deposition at high temperature

Fully relaxed, strain-tuning Si1−xGex buffers have been grown at very high temperatures of 950–1080 °C by reduced-pressure chemical vapour deposition (RP-CVD) as platforms for high quality strained Si layers. It is critical that these buffers have a low threading dislocation density (TDD) to maximize carrier mobility and minimize leakage currents in high performance electronic devices. The influence of the Si1−xGex growth rate on TDD has been investigated for buffers with Ge content x ⩽ 0.5. In contrast to the established understanding, the TDD, in this growth regime, exhibits almost no dependence upon the Si1−xGex growth rate. We suggest that at these high temperatures the gliding arms associated with dislocations have a sufficiently high velocity for the layers to relax even at the highest growth rates. Hence, no benefit is gained from reducing the growth rate, as required at lower growth temperatures to allow the threading arms to glide. The relaxed buffers produced at these high growth rates, nevertheless, have state-of-the-art TDD values of ∼6 × 104 cm−2 and ∼1 × 105 cm−2 for Si0.8Ge0.2 and Si0.5Ge0.5 buffers, respectively.

Low temperature Si homo-epitaxy by reduced pressure chemical vapor deposition using dichlorosilane, silane and trisilane

Dichlorosilane (DCS), silane and trisilane have been investigated as Si precursors for low temperature (<700 °C) Si reduced pressure chemical vapor deposition. DCS and silane are limited to growth temperatures higher than 600–650 and 500 °C, respectively. At lower temperatures, absence of either Cl or H desorption from the surface impedes Si growth with acceptable growth rate (>5 Å/min). Trisilane permits the growth of Si at lower temperatures below 350 °C due to a specific growth mechanism enhancing H desorption. Layers grown at temperatures lower than 500 °C are defective, irrespective of the carrier gas, pressure and precursor flow used.

Influence of Carbon in In-situ Carbon-Doped SiGe Films on Si(001) Substrates on Epitaxial Growth Characteristics

Carbon doped SiGe (SiGe:C)/Si(001) heterostructure were grown by reduced pressure chemical vapor deposition using silane, germane and methylsilane as a source of Si, Ge, and C, respectively. We performed a systematic experiment of growth of SiGe:C and carried out measurements to determine the surface roughness and occupation sites of carbon atoms as functions of C source flow, Ge concentration, growth temperature and growth rate. Ge concentration range was from 0 to 23.0%. Growth temperature was 575 to 625 °C. The range of Growth rate was between 1.5 and 4.3 Å/s. These SiGe:C analyzed by atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), high-resolution X-ray diffraction (HR-XRD) and cross-sectional transmission electron microscopy (TEM). Total C compositions did not depend on growth temperature with the constant Ge concentration and with SiH3CH3 flow ratio. Surface roughness of SiGe:C with high Ge concentration increased with the increase of C source gas flow. Interstitial C concentration in SiGe:C films with rough surface increased with the increase of C source gas flow. The roughness of SiGe:C layer grown constant C gas source flow ratio decreased for low growth temperature and/or faster growth rate. From these results, we revealed that the mechanism of defect formation with localized C as the cause of rough. The excess migration can suppress surface roughness.

Reverse graded SiGe/Ge/Si buffers for high-composition virtual substrates

The effect of compositional grading rate on reverse linear graded silicon germanium virtual substrates, grown by reduced pressure chemical vapor deposition, is investigated. For a Si(001)/Ge/RLG/Si0.22Ge0.78 buffer of 2.4 μm total thickness the threading dislocation density (TDD) within the top, fully relaxed, Si0.22Ge0.78 layer is 4×106 cm−2, with a surface roughness of 3 nm. For a thicker buffer, where the grading rate is reduced, a lower TDD of 3×106 cm−2 and a surface roughness of 2 nm can be achieved. The characteristics of reverse graded Si0.22Ge0.78 virtual substrates are shown to be comparable to, or exceed, conventional buffer techniques, leading to thinner high-quality high Ge composition SiGe virtual substrates.

High Quality Strained Ge Epilayers on a Si[sub 0.2]Ge[sub 0.8]/Ge/Si(100) Global Strain-Tuning Platform

High structural quality, compressively strained Ge surface epilayers have been grown on Si(100) substrates of up to 200 mm diameter. The epitaxial growth by industrially compatible reduced pressure chemical vapor deposition proceeded uninterruptedly via an intermediate relaxed Si0.2Ge0.8/Ge buffer. In-depth characterization of the epilayers revealed a relatively smooth surface and a low threading dislocation density. The Ge layers were demonstrated to remain fully strained for thicknesses of more than 100 nm. The high quality of the material and flexibility to choose the Ge layer thickness over a wide range make these heterostructures very attractive for fabricating various electronic and photonic devices. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3482159] All rights reserved.

Investigation of the Thermal Stability of Strained Ge Layers Grown at Low Temperature by Reduced-pressure Chemical Vapour Deposition on Si0.2Ge0.8 Relaxed Buffers

AbstractHigh quality strained Ge (s-Ge) epitaxial layers are a promising candidate to achieve high mobility channel MOSFETs suitable for the 22 nm technology node and beyond, due to the intrinsically higher mobility of Ge compared to Si, and the additional performance enhancements from strain [1]. In order to achieve an s-Ge channel more than a few monolayers thick it is necessary to engineer a relaxed Si1-xGex buffer with a high Ge content (x &gt; 0.5). We have recently reported high quality s-Ge layers grown by RP-CVD at low temperature (T ≤ 450 °C), on a fully relaxed Si0.2Ge0.8 buffer [2]. By using a reverse-grading approach, we achieved a high Ge composition in the buffer, with a smooth surface (rms surface roughness of ~2 nm), low threading dislocations density (~ 4 x 106 cm-2) and much thinner (~ 2.1 μm) than can be achieved with conventional linear grading [3].In this work, the thermal stability of s-Ge epilayers (up to 80 nm thick) grown on relaxed Si0.2Ge0.8 buffers has been investigated by in-situ annealing in H2 ambient at temperatures up to 650 °C. These temperatures are similar to those currently used during fabrication of advanced CMOS devices. All s-Ge layers were grown at 400 °C using GeH4 gaseous precursor. The relaxation of the annealed layers has been studied using high-resolution XRD reciprocal space maps (RSMs), and was found to depend strongly on both annealing temperature and thickness of the Ge epilayer. Strained Ge layers up to 50 nm thick remained fully strained after annealing at 450 °C, whereas after annealing at 550 °C s-Ge layers thicker than 20 nm were on the onset of relaxation; after annealing at 650 °C all s-Ge layers showed significant relaxation with defects clearly visible at the Si0.2Ge0.8/Ge interface. All annealed s-Ge layers exhibited higher surface roughness than s-Ge control samples without annealing (rms ~ 2 nm). Annealing at 450 °C resulted in only a slight increase in surface roughness (rms ~ 3 nm), almost independent of s-Ge thickness. However, annealing at 550 °C and 650 °C resulted in significant surface roughening (with maximum rms values of 5 nm and 35 nm, respectively) due to the formation of Ge islands, which were observed by AFM. At these higher temperatures, the surface roughness of the s-Ge layers was found to be thickness dependent, with a Ge smoothing effect observed for layers greater than 50 nm.These results are particularly important for the fabrication of s-Ge MOSFETs, for which the surface passivation prior to gate stack formation is critical to the performance of the device. Based on the results presented here, the thermal budget should be kept below 550 °C to avoid relaxation and roughening of the s-Ge epilayer, which could degrade the device performance.

Influence of Si precursor on Ge segregation during ultrathin Si reduced pressure chemical vapor deposition on Ge

This letter reports on the Ge segregation mechanism occurring during ultrathin (few monolayers) Si cap growth on Ge substrates by reduced pressure chemical vapor deposition. Thanks to extremely low energy secondary ion mass spectroscopy, we have highlighted that Ge segregation in Si-covered Ge does not depend on the growth temperature (in the 350–500 °C range) or on the carrier gas (H2,N2) used during Si growth. Solely the Si precursor used, i.e., the Si incorporation mechanism, impacts the Ge segregation rate. A multi-Ge segregation model is proposed, considering probabilities of sites exchanges in between all Si–Ge stacked atoms within the first nanometer of the layers.

Effect of isochronal hydrogen annealing on surface roughness and threading dislocation density of epitaxial Ge films grown on Si

We report the effect of hydrogen annealing on the surface roughness and threading dislocation density (TDD) of germanium (Ge) films grown on silicon (Si) substrates by reduced-pressure chemical vapor deposition (RPCVD). The surface roughness initially decreased with an increase in the annealing temperature. At annealing temperatures greater than 650 °C the film thickness varied owing to surface undulations, leading to an increase in the surface roughness. Although high-temperature annealing at 850 °C is effective for reducing TDD, the surface roughness of a 150-nm-thick Ge film annealed at 650 °C reaches a minimum value (~ 0.7 nm).

B atomic layer doping of Ge

B Atomic layer doping (B-ALD) of Ge is investigated at temperatures between 100 °C and 400 °C using a single wafer reduced pressure CVD system. Hydrogen-terminated and hydrogen-free Ge (100) surfaces are exposed to B 2H 6 at different H 2 partial pressures. B atoms are adsorbed on hydrogen-free Ge surface by B 2H 6 exposure even at 100 °C. Very steep B profiles (< 1 nm/dec.), which is the resolution limit of SIMS, have been achieved. On the hydrogen-free Ge surface at 200–400 °C, B adsorption is increasing with increasing B 2H 6 exposure time and no saturation behavior is observed. On the other hand, in the case of 100 °C, B adsorption is increasing with increasing B 2H 6 exposure time and tends to saturate, indicating that B 2H 6 is adsorbed at Ge surface site mainly. The level of the saturation is increasing with increasing B 2H 6 partial pressure. By decreasing the H 2 partial pressure, the level of the saturation is increasing and the saturation becomes less pronounced. For the B 2H 6 exposure without H 2, the saturation is not observed. This result indicates that H 2 has to be taken into consideration for the adsorption mechanism of B. These results demonstrate the possibility of dopant dose and location control at 100 °C.