Low temperature selective epitaxial growth of SiCP on Si(110) oriented surfaces

We demonstrate growth of SiCP film on Si(110) substrates with excellent structural quality, based on X-Ray Diffraction, Cross-sectional Transmission Electron Microscopy and Secondary Ion Mass Spectrometry analysis. This (110) surface orientation is very important since it represents the sidewall of recessed Source/Drain (S/D) areas when the film is used as an embedded stressor to induce uniaxial tensile strain in a planar transistor. An optimized (110) SiCP growth process can also be used to thicken the S/D regions of non-planar multi-gate device structures (e.g. Fin Field Effect Transistors, Tri-gate FETs) with a highly doped epitaxial film in order to enable good electrical contacts and/or induce strain. The films have been grown using Si₃H₈, SiH₃CH₃ and PH₃ for growth and Cl₂ as the etchant gas, all in inert carrier gas. H₂ has been eliminated, preventing Cl₂ from reacting with H₂ yielding HCl, since Cl₂ is needed to establish selectivity. We present trends on temperature, total pressure, SiH₃CH₃, PH₃ and Cl₂ etch flow. We studied selective epitaxial growth (SEG) in the 525-575 °C range. Thanks to the use of Si₃H₈ we can obtain high SEG rates even at 525 °C in conjunction with a high deposition pressure of 20 kPa (~ 150 Torr). It is observed that the growth rate, carbon concentration, phosphorous concentration and etch rate of SiCP on Si (110) differs greatly from that on Si (100). A process optimized specifically for Si(100) surfaces may yield no growth on Si(110) surfaces. However, optimizing a process on Si(110) is assured to result in growth on Si(100). Comparing one process optimized on Si(110) with the results on Si(100), we found a substantially lower SEG rate, higher [P] incorporation and lower [C] incorporation on Si(110). One key criterion for growth on patterned substrates with Si(110) sidewalls is that the SEG rate on the sidewall must be ≥ 0; otherwise the vertical sidewall will be etched and undercut of the spacer will occur, degrading the structural quality of the transistor and potentially impacting the electrical performance of the device.     

Growth studies and characterization of silicon nitride thin films deposited by alternating exposures to Si2Cl6 and NH3

We deposited silicon nitride films by alternating exposures to Si₂Cl₆ and NH₃ in a cold-wall reactor, and the growth rate and characteristics were studied with varying process temperature and reactant exposures. The physical and electrical properties of the films were also investigated in comparison with other silicon nitride films. The deposition reaction was self-limiting at process temperature of 515 and 557 °C, and the growth rates were 0.24 and 0.28 nm/cycle with Si₂Cl₆ exposure over 2 × 10⁸ L. These growth rates with Si₂Cl₆ are higher than that with SiH₂Cl₂, and are obtained with reactant exposures lower than those of the SiH₂Cl₂ case. At process temperature of 573 °C where the wafer temperature during Si₂Cl₆ pulse is 513 °C, the growth rate increased with Si₂Cl₆ exposure owing to thermal deposition of Si₂Cl₆. The deposited films are nonstoichiometric SiN, and were easily oxidized by air exposure to contain 7-8 at.% of oxygen in the bulk film. The deposition by using Si₂Cl₆ exhibited a higher deposition rate with lower reactant exposures as compared with the deposition by using SiH₂Cl₂, and exhibited good physical and electrical properties that were equivalent or superior to those of the film deposited by using SiH₂Cl₂.     

Effect of filament temperature and deposition time on the formation of tungsten silicide with silane

The effect of filament temperature and deposition time on the formation of tungsten silicide upon exposure to the SiH₄ gas in a hot wire chemical vapor deposition process was studied using the techniques of cross-sectional scanning electron microscopy and Auger electron spectroscopy. At a relatively low temperature of 1500 °C, the decomposition of WSi₂ phase and the diffusion of Si towards the silicide/W interface produce a thick W₅Si₃ layer. The diffusional nature leads to a parabolic rate law for silicide growth. An exponential decrease of silicide thickness with temperature between 1600 and 2000 °C illustrates the dominance of Si evaporation at higher temperatures (T ≥ 1600 °C) over the silicide formation.     

Influences of deposition and crystallization kinetics on the properties of silicon films deposited by low-pressure chemical vapour deposition from silane and disilane

The paper deals with the properties of silicon films obtained by low-pressure chemical vapour deposition (LPCVD). Two gaseous sources characterized by different deposition temperatures, i.e. disilane Si₂H₆ (420-520 °C) and silane SiH₄ (520-750 °C), was studied in order to understand the influences of deposition and crystallization kinetics on silicon film properties. Thus, the deposition of amorphous, semi-crystallized and polycrystalline silicon films was related to “volume random” and “surface columnar” crystallization phenomena, highlighting a linear relationship between the refractive index and the polysilicon volume fraction and, showing complex residual stress dependency with process conditions. Finally, by introducing the ratio V_d/V_c between the deposition and crystallization rates as a major parameter, different deposition behaviours and related semi-empirical relationships were defined in order to characterize fully the various properties of LPCVD silicon films (microstructure, polysilicon volume fraction, refractive index and residual stress) according to the chosen gaseous source, silane or disilane.     

Hot-wire chemical vapor deposition of silicon nanoparticles on fused silica

Silicon nanoparticles on fused silica have potential as recombination centers in infrared detectors due quantum confinement effects that result in a size dependent band gap. Growth on fused silica was realized by etching in HF, annealing under vacuum at 700-750 °C, and cooling to ambient temperature before ramping to the growth temperature of 600 °C. Silicon particles could not be grown in a thermal chemical vapor deposition (CVD) process with adequate size uniformity and density. Seeding fused silica with Si adatoms in a hot-wire chemical vapor deposition (HWCVD) process at a disilane pressure of 1.1 × 10^− 5 Pa followed by thermal CVD at a disilane pressure of 1.3 × 10^− 2 Pa, or direct HWCVD at a disilane pressure of 2.1 × 10^− 5 Pa led to acceptable size uniformity and density. Dangling bonds at the surface of the as-grown nanoparticle were passivated using atomic H formed by cracking H₂ over the HWCVD filament.     

Growth of 3C-SiC on 150-mm Si(100) substrates by alternating supply epitaxy at 1000 °C

To lower deposition temperature and reduce thermal mismatch induced stress, heteroepitaxial growth of single-crystalline 3C-SiC on 150 mm Si wafers was investigated at 1000 °C using alternating supply epitaxy. The growth was performed in a hot-wall low-pressure chemical vapor deposition reactor, with silane and acetylene being employed as precursors. To avoid contamination of Si substrate, the reactor was filled in with oxygen to grow silicon dioxide, and then this thin oxide layer was etched away by silane, followed by a carbonization step performed at 750 °C before the temperature was ramped up to 1000 °C to start the growth of SiC. Microstructure analyses demonstrated that single-crystalline 3C-SiC is epitaxially grown on Si substrate and the film quality is improved as thickness increases. The growth rate varied from 0.44 to 0.76 ± 0.02 nm/cycle by adjusting the supply volume of SiH₄ and C₂H₂. The thickness nonuniformity across wafer was controlled with ± 1%. For a prime grade 150 mm virgin Si(100) wafer, the bow increased from 2.1 to 3.1 μm after 960 nm SiC film was deposited. The SiC films are naturally n type conductivity as characterized by the hot-probe technique.     

Modelling boron diffusion in heavily implanted low-pressure chemical vapor deposited silicon thin films during thermal post-implantation annealing

We have investigated and modelled boron (B) diffusion in heavily implanted silicon (Si) thin films deposited from disilane (Si₂H₆) by low pressure chemical vapor deposition (LPCVD) at low temperatures. A comprehensive one-dimensional two-stream diffusion model adapted to the particular structure of deposited Si films and to the effects of high B concentrations has been developed. This model includes B clustering in grains as well as in grain boundaries. In addition, the effects of Si-films crystallization, during thermal post-implantation annealing, on B diffusion as well as on B clusters formation and dissolution were considered. The effects of clustering, growth of grains, dopant-enhanced grains growth and the driving force for grains growth were coupled with the dopant diffusion coefficients and the process temperature based on thermodynamic concepts. To investigate complex B diffusion in heavily implanted Si films deposited by LPCVD, we have used experimental profiles obtained by secondary ion mass spectroscopy (SIMS) for B implantation with doses of 1 × 10¹⁵ at./cm², 4 × 10¹⁵ at./cm² and 5 × 10¹⁵ at./cm² at an energy of 15 keV. Thermal post-implantation anneals were carried out at relatively low-temperatures (700 °C and 850 °C) for various short-times of 1 min to 15 min. The good adjustment of the simulated profiles with the experimental SIMS profiles allowed the validation of this model. It was found that the simulation well reproduces the experimental SIMS profiles when the growth of grains and immobile B clusters are considered.     

Characterization of 4H-SiC grown on AlN/Si(100) by CVD

By using chemical vapor deposition method, 4H-SiC films have been grown on AlN/Si(100) complex substrates at the temperature below 1100 °C. Substitutional Al and N are found in the SiC film. Photoluminescence (PL) peaks, related to Al acceptor and N shallow donor, respectively, have been observed at the room-temperature. The higher partial pressure ratio of SiH₄ and C₂H₄ (P_C2H4 / P_SiH4 ≧ 1.62) results in more Si-vacancy (V_Si) in the film. The PL peak related to the V_Si acceptor level is also observed.     

Mass spectrometric study of gas-phase chemistry in the hot-wire CVD processes of SiH4/NH3 mixtures

The gas-phase reaction products of SiH₄, NH₃ and their mixtures from a hot-wire CVD chamber were investigated using laser ionization time-of-flight mass spectrometry. Both vacuum ultraviolet laser single photon ionization and laser-induced electron impact ionization were used. The main products observed from a 50% NH₃/He sample were H₂ and N₂. The study of an NH₃/SiH₄ mixture (P_NH3:P_SiH4 = 100:1) has shown that the NH₃ dissociation on the filament was suppressed by the presence of SiH₄ in the system. Signals from Si(NH₂)₄ and Si(NH₂)₃ species were identified as products from the 100:1 NH₃/SiH₄ mixture. The spectrum for a 1:1 NH₃/SiH₄ mixture was dominated by mass peaks characteristic of SiH₄ chemistry in the reactor, i.e. H₂, Si₂H₆, and Si₃H₈, at low temperatures. The extent to which the decomposition of NH₃ is suppressed is enhanced with more SiH₄ molecules in the system.     

Behavior of N atoms after thermal nitridation of Si1 − xGex surface

Behavior of N atoms after thermal nitridation of Si_1 − xGe_x (100) surface in NH₃ atmosphere at 400 °C was investigated. X-ray photoelectron spectroscopy (XPS) results show that N atomic amount after nitridation tends to increase with increasing Ge fraction, and amount of N atoms bonded with Ge atoms decreases by heat treatment in H₂ at 400 °C. For nitrided Si_0.3Ge_0.7(100), the bonding between N and Si atoms forms Si₃N₄ structure whose amount is larger than that for nitrided Si(100). Angle-resolved XPS measurements show that there are N atoms not only at the outermost surface but also beneath surface especially in a deeper region around a few atomic layers for the nitrided Si(100), Si_0.3Ge_0.7(100) and Ge(100). From these results, it is suggested that penetration of N atoms through around a few atomic layers for Si, Si_0.3Ge_0.7 and Ge occurs during nitridation, and the N atoms for the nitrided Si_0.3Ge_0.7(100) dominantly form a Si₃N₄ structure which stably remains even during heat treatment in H₂ at 400 °C.     

Deposition of polycrystalline SiGe by surface wave excited plasma

With application to underlayer of strained Si film in mind, polycrystalline SiGe films were deposited by plasma chemical vapor deposition (PCVD) using a high-density surface wave-excited plasma in SiH₄/GeH₄/H₂ gas. The atomic ratio of Si/Ge in the film was controlled by adjusting the gas flow rate ratio of SiH₄/GeH₄. The lattice spacing of the film was also controlled by the gas flow rate ratio. Polycrystalline SiGe film with large grain size of ∼ 200 nm and high crystallinity was successfully deposited by surface wave-excited plasma.     

Epitaxial growth mode and silicon/silicon-germanium heterointerfaces

Silicon-germanium/silicon (Si_{1 – x} Ge _x /Si, x < 0.50) multiple quantum wells (MQWs) have been grown on (001) Si substrates by gas source molecular beam epitaxy (GSMBE) using disilane (Si₂H₆) and germane (GeH₄) as source gases. Their structural properties have been evaluated by X-ray diffraction (XRD), rocking curve techniques and transmission electron microscopy (TEM). For the substrate temperatures used in this work (450 C to 520 C) the Si growth rate is limited by hydrogen desorption kinetics, whereas the growth of SiGe is limited primarily by the arrival rate of the source gases onto the Si substrates. XRD analysis of the structures indicates a significant well plus barrier period variation of approximately 5–10%, attributed to fluctuations in the substrate temperature during growth, since these cause significant variations in the growth rate of the Si barriers. For x < 0.30 we find nearly ideal Si/SiGe interfaces as determined from a comparison of the XRD data with dynamical simulations of the 004 X-ray reflectivity, although TEM micrographs indicate that the x = 0.30 samples exhibit undulations in the first SiGe/Si interface of the structures. For x = 0.50 such undulations occur throughout the MQW structure; the undulation amplitude decreases with decreasing growth temperature but the period remains unchanged. The observed improvement in the SiGe/Si interface planarity at lower growth temperatures is attributed to a reduction in the surface diffusion of Si and Ge with decreasing growth temperature.     

Effect of rf power on the growth of silicon nanowires by hot-wire assisted plasma enhanced chemical vapor deposition (HW-PECVD) technique

Silicon nanowires (SiNWs) were synthesized by simultaneous evaporation of Au and Si deposition using H₂ diluted SiH₄. The deposition techniques combined hot-wire (HW) and plasma enhanced chemical vapor deposition (PECVD). Au wires were placed on the filament and heated simultaneously with the activation of the rf plasma for the dissociation of SiH₄ and H₂ gases. Five set of samples were deposited on ITO-coated glass substrate at different rf power varied from 20 to 100 W in an interval of 20 W, keeping other deposition parameters constant. High yield of SiNWs with diameter ranging from 60 to 400 nm and length about 10 μm were grown at rf power of 80 W (power density ~ 1018 mW cm⁻²). Rf power of 100 W (power density ~ 1273 mW cm⁻²) suppressed the growth of these SiNWs. The growth mechanisms of SiNWs are tentatively proposed. The nanocrystalline structure of SiNWs is confirmed by Raman spectra and HRTEM measurement.     

The effect of Si additions on the sintering and sintered microstructure and mechanical properties of Ti-3Ni alloy

Thermodynamic predictions suggest that silicon has the potential to be a potent sintering aid for Ti-Ni alloys because small additions of Si lower the solidus of Ti-Ni alloys appreciably (>200 °C by 1 wt.% Si). A systematic study has been made of the effect of Si on the sintering of a Ti-3Ni alloy at 1300 °C. The sintered density increased from 91.8% theoretical density (TD) to 99.2%TD with increasing Si from 0% to 2%. Microstructural examination reveals that coarse particles and/or continuous networks of Ti₅Si₃ form along grain boundaries when the addition of Si exceeds 1%. The grain boundary Ti₅Si₃ phase leads to predominantly intergranular fracture and therefore a sharp decrease in ductility concomitant with increased tensile strengths. The optimum addition of Si is proposed to be ≤1%. Dilatometry experiments reveal different shrinkage behaviours with respect to different Si contents. Interrupted differential scanning calorimetry (DSC) experiments and corresponding X-ray diffraction (XRD) analyses clarify the sequence of phase formation during heating. The results provide a useful basis for powder metallurgy (PM) Ti alloy design with Si.     

Solid-phase epitaxy of undoped amorphous silicon by in-situ postannealing

The solid phase epitaxy (SPE) of undoped amorphous Si (a-Si) deposited on SiO₂ patterned Si(001) wafers by reduced pressure chemical vapor deposition (RPCVD) using a H₂-Si₂H₆ gas system was investigated. The SPE was performed by applying in-situ postannealing directly after deposition process. By transmission electron microscopy (TEM) and scanning electron microscopy, we studied the lateral SPE (L-SPE) length on sidewall and mask for various postannealing times, temperatures and a-Si thicknesses. We observed an increase in L-SPE growth for longer postannealing times, temperatures and larger Si thicknesses on mask. TEM defect studies revealed that by SPE crystallized epi-Si exhibits a higher defect density on the mask than at the inside of the mask window. By introducing SiO₂-cap on the sample with 180 nm Si thickness following postannealing at 570 °C for 5 h, the crystallization of up to 450 nm epi-Si from a-Si is achieved. We demonstrated the possibility to use this technique for SiGe:C heterojunction bipolar transistor (HBT) base layer stack to crystallize Si-buffer layer to widen the monocrystalline region around the bipolar window and to improve base link resistivity of the HBT.     

Growth of 3C-SiC on Si(111) using the four-step non-cooling process

A modified four-step method was applied to grow a 3C-SiC thin film of high quality on the off-axis 1.5° Si(111) substrate in a mixed gas of C₃H₈, SiH₄ and H₂ using low pressure chemical vapor deposition. The modified four-step method adds a diffusion step after the carburization step and removes the cooling from the traditional three-step method (clean, carburization, and growth). The X-ray intensity of the 3C-SiC(111) peak is enhanced from 5 × 10⁴ counts/s (the modified three steps) to 1.1 × 10⁵ counts/s (the modified four steps). The better crystal quality of 3C-SiC is confirmed by the X-ray rocking curves of 3C-SiC(111). 3C-SiC is epitaxially grown on Si(111) supported by the selected area electron diffraction patterns taken at the 3C-SiC/Si(111) interface. Some {111} stacking faults and twins appear inside the 3C-SiC, which may result from the stress induced in the 3C-SiC thin film due to lattice mismatch. The diffusion step plays roles in enhancing the formation of Si-C bonds and in reducing the void density at the 3C-SiC/Si(111) interface.     

Growth of silicon carbide thin films by hot-wire chemical vapor deposition from SiH4/CH4/H2

Silicon carbide (SiC) thin films were prepared by hot-wire chemical vapor deposition from SiH₄/CH₄/H₂ and their structural properties were investigated by X-ray diffraction, Fourier transform infrared absorption and Raman scattering spectroscopies. At 2 Torr, Si-crystallite-embedded amorphous SiC (a-Si_1 − xC_x:H) grew at filament temperatures (T_f) below 1600 °C and nanocrystalline cubic SiC (nc-3C-SiC:H) grew above T_f = 1700 °C. On the other hand, At 4 Torr, a-Si_1 − xC_x:H grew at T_f = 1400 °C and nc-3C-SiC grew above T_f = 1600 °C. When the intakes of Si and C atoms into the film per unit time are almost the same and H radicals with a high density are generated, which takes place at high T_f, nc-3C-SiC grows. On the other hand, at low T_f the intake of Si atoms is larger than that of C atoms and, consequently, Si-rich a-Si_1 − xC_x:H or Si-crystallite-embedded a-Si_1 − xC_x:H grow.     

Low temperature Si:C co-flow and hybrid process using Si3H8/Cl2

In this paper we demonstrate a Si₃H₈/SiH₃CH₃/PH₃/Cl₂ based co-flow process and a “hybrid” co-flow process with interruptions of the deposition. The motivation for the work stems from the desire to improve manufacturability through higher growth rates and higher etch rates commensurate with the drive to lower thermal budgets of integration of Complementary Metal Oxide Semiconductor and memory platforms. For high volume manufacturing, high selective epitaxial growth rates are necessary for enhanced throughput and low cost of ownership. Both high growth rate and low temperatures enable sufficiently high substitutional carbon levels [C]_sub in dilute Si:C alloys. The hydride deposition gases Si₃H₈, SiH₃CH₃ and PH₃ and the etch gas Cl₂ were kept separate in the pressurized gas supply lines and injected separately into the reaction chamber thus avoiding premature chemical reactions. The importance and the role of a suitable inert carrier gas are emphasized.     

Growth of homogeneous polycrystalline Si1-xGex and Mg2Si1-xGex for thermoelectric application

Homogeneous polycrystalline Si_1-xGe_x were grown using a Si(seed)/Ge/Si(feed) sandwich structure under the low temperature gradient less than 0.4 °C/mm. It was found that the composition of the Si_1-xGe_x was controlled by the growth temperature. The homogeneous Mg₂Si_1-xGe_x was synthesized by heat treatment of the homogeneous Si_1-xGe_x powders under Mg vapor. The Mg₂Si_1-xGe_x sample with the relative density of 95% was synthesized by spark plasma sintering technique. The resistivity and the Seebeck coefficient of the Si, Ge, Si_1-xGe_x and Mg₂Si_1-xGe_x samples were evaluated as a function of temperature. It indicated that Seebeck coefficients of the Si_1-xGe_x and Mg₂Si_1-xGe_x samples were higher than those of Si and Ge. Moreover, the Seebeck coefficient of Mg₂Si_0.7Ge_0.3 sample was higher than that of Mg₂Si_0.5Ge_0.5 and Si_0.5Ge_0.5 samples.     

Effect of N2O/SiH4 flow ratios on properties of amorphous silicon oxide thin films deposited by inductively-coupled plasma chemical vapor deposition with application to silicon surface passivation

Silicon oxide (SiO_x) thin films have been deposited at a substrate temperature of 300 °C by inductively-coupled plasma chemical vapor deposition (ICP-CVD) using N₂O/SiH₄ plasma. The effect of N₂O/SiH₄ flow ratios on SiO_x film properties and silicon surface passivation were investigated. Initially, the deposition rate increased up to the N₂O/SiH₄ flow ratio of 2/1, and then decreased with the further increase in N₂O/SiH₄ flow ratio. Silicon oxide films with refractive indices of 1.47-2.64 and high optical band-gap values (>3.3 eV) were obtained by varying the nitrous oxide to silane gas ratios. The measured density of the interface states for films was found to have minimum value of 4.3 × 10¹¹ eV⁻¹ cm⁻². The simultaneous highest τ_eff and lowest density of interface states indicated that the formation of hydrogen bonds at the SiO_x/c-Si interface played an important role in surface passivation of p-type silicon.