Epitaxial Growth Rate Research Articles

Breakdown physics of low-temperature silicon epitaxy grown from silane radicals

We grow epitaxial silicon films on (100) Si wafers at low temperature $(l400\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$, from silane radicals, to understand the mechanisms of sudden epitaxy breakdown and simultaneous growth of amorphous and crystalline silicon phases. Surface roughness is below $0.7\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ before breakdown and below $1\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in epitaxial regions persisting after breakdown, in contrast to the roughness-induced breakdown observed in molecular beam epitaxy from atomic Si. Spherical caps of hydrogenated amorphous Si (a-Si:H) breakdown cones protrude above the crystal surface, with each sphere centered on its cone apex. This means that the a-Si:H grows isotropically from impinging radicals with low surface mobility and that the a-Si:H growth rate is higher than the epitaxial growth rate. Similar physical mechanisms likely apply to nanocrystalline silicon film growth.

Epitaxial Layers Grown with HCl Addition: A Comparison with the Standard Process

The growth rate of 4H-SiC epi layers has been increased by a factor 3 (up to 18μm/h) with respect to the standard process with the introduction of HCl in the deposition chamber. The epitaxial layers grown with the addition of HCl have been characterized by electrical, optical and structural characterization methods. An optimized process without the addition of HCl is reported for comparison. The Schottky diodes, manufactured on the epitaxial layer grown with the addition of HCl at 1600 °C, have electrical characteristics comparable with the standard epitaxial process with the advantage of an epitaxial growth rate three times higher.

Sexithiophene films on cleaved KBr(1 0 0) towards well-ordered semiconducting films

The morphology and possible molecular orientation of sexithiophene thin films on cleaved KBr(1 0 0) under different epitaxial growth rate are investigated by atomic force microscopy. It is found that both the surface morphology and the molecular orientation are strongly related to the epitaxial growth rate; the controlled domains exist as flat-topped domains and grow at a three-dimensional growth mode. The maximum domain size of 30 μm × 30 μm flat-topped domain is obtained; the surface cracks significantly decreases with the decrease of epitaxial growth rate.

Systematic Characterization of Pseudomorphic (110) Intrinsic SiGe Epitaxial Films for Hybrid Orientation Technology with Embedded SiGe Source/Drain

AbstractPFET devices fabricated using embedded SiGe source/drain on (110) silicon substrates have shown significant performance improvement compared to PFETs with embedded SiGe on (100) SOI substrates. In this paper, we report a systematic material characterization on the epitaxial SiGe films, both on blanket and patterned substrates, and corresponding PFET performance data. The SiGe films were deposited in an RTCVD system. The epitaxial growth rate on (110) substrates was 30% lower than on (100), and 30% higher on patterned device wafers compared to blanket wafers. Films were characterized using an array of methods such as High Resolution XRD (for Ge composition, strain and thickness), Auger (for Ge composition), UV Raman microprobe (for strain), AFM (for surface morphology), and TEM (for epi quality). The Ge compositions determined by XRD and Auger are in excellent agreement (15~16%). The amount of strain extracted from the Raman measurements is also consistent with the amount determined by XRD, which is 0.60%, corresponding to a fully strained Si0.85Ge0.15 film. AFM showed much higher RMS and Rmax for the SiGe films on (110) substrates compared to those on (100) substrates. XTEM showed high crystalline quality with very low defect count in the SiGe source/drain and Si channel regions. PFETs with an embedded Si0.85Ge0.15 source/drain on hybrid orientation (HOT) substrates provided a 30% advantage in drive current and a 23% enhancement in ring oscillator speed compared to control devices on (100) SOI wafer.

Structural analysis and reduction of in-grown stacking faults in 4H–SiC epilayers

We investigated the structure of in-grown stacking faults in the 4H–SiC(0001) epilayers. The in-grown stacking faults nucleate near the substrate/epilayer interface and expand the area with increasing epilayer thickness in a triangular shape. From transmission electron microscope observation, the formation of 1c of 8H polytype was confirmed in the in-grown stacking fault area. We also investigated the dependence of in-grown stacking fault density on the epitaxial growth rate, growth temperature, and substrate surface preparation.

Combined ab initio quantum chemistry and computational fluid dynamics calculations for prediction of gallium nitride growth

Computational fluid dynamics (CFD) is used in the semiconductor industry for the analysis and design of chemical vapor deposition reactors. One critical input needed for prediction of epitaxial thin film growth rates and uniformity is the chemistry occurring in the gas phase and at the surface. Traditionally, simplified chemistry derived from experimental observations has been used for this purpose. With the advent of modern high-speed computational techniques, it is now possible to formulate detailed reaction mechanisms using ab initio methods. Such detailed reaction mechanisms, comprising mostly of elementary reactions, have the advantage that they require little or no calibration. This paper presents a methodology in which the density functional theory, in combination with rate theories, was used to determine the reaction pathways and rates in the gas phase as well as at the surface for gallium nitride growth from tri-methyl gallium and ammonia. The reaction mechanisms were then used as input to a multi-dimensional CFD code enabling accurate prediction of growth rates. Validation studies were performed for four different laboratory-scale reactors, and one commercial reactor. In each case, the predictions agreed reasonably well with the experimental data indicating the universality of the reaction mechanisms.

Simple Model for Calculation of SiC Epitaxial Layers Growth Rate in Vacuum

Within the frame of a simple model, based on Hertz-Knudsen equation with account of temperature dependant sticking coefficient, temperature dependence of silicon carbide epitaxial layers growth rate in vacuum has been calculated. Calculation results are in a good agreement with the experimental data.

Effects of atomic hydrogen on the selective area growth of Si and Si1−xGex thin films on Si and SiO2 surfaces: Inhibition, nucleation, and growth

Supersonic molecular beam techniques have been used to study the nucleation of Si and Si1−xGex thin films on Si and SiO2 surfaces, where Si2H6 and GeH4 have been used as sources. A particular emphasis of this study has been an examination of the effects of a coincident flux of atomic hydrogen. The time associated with formation of stable islands of Si or Si1−xGex on SiO2 surfaces—the incubation time—has been found to depend strongly on the kinetic energy of the incident molecular precursors (Si2H6 and GeH4) and the substrate temperature. After coalescence, thin film morphology has been found to depend primarily on substrate temperature, with smoother films being grown at substrate temperatures below 600 °C. Introduction of a coincident flux of atomic hydrogen has a large effect on the nucleation and growth process. First, the incubation time in the presence of atomic hydrogen has been found to increase, especially at substrate temperatures below 630 °C, suggesting that hydrogen atoms adsorbed on Si-like sites on SiO2 can effectively block nucleation of Si. Unfortunately, in terms of promoting selective area growth, coincident atomic hydrogen also decreases the rate of epitaxial growth rate, essentially offsetting any increase in the incubation time for growth on SiO2. Concerning Si1−xGex growth, the introduction of GeH4 produces substantial changes in both thin film morphology and the rate nucleation of poly-Si1−xGex on SiO2. Briefly, the addition of Ge increases the incubation time, while it lessens the effect of coincident hydrogen on the incubation time. Finally, a comparison of the maximum island density, the time to reach this density, and the steady-state polycrystalline growth rate strongly suggests that all thin films [Si, Si1−xGex, both with and without H(g)] nucleate at special sites on the SiO2 surface, and grow primarily via direct deposition of adatoms on pre-existing islands.

Low temperature, high growth rate epitaxial silicon and silicon germanium alloy films

Epitaxial growth of silicon and silicon germanium alloy films on Si(1 0 0) substrates in an ASM Epsilon ® single wafer reactor system using trisilane and germane has been investigated. The results obtained reveal that it is possible to achieve epitaxial silicon and silicon germanium growth rates at 630 °C and below that are substantially higher than those possible using silane, while maintaining high quality crystalline structure. The films grown were characterized using Rutherford backscattering spectroscopy (RBS), high resolution X-Ray diffraction (HR-XRD), atomic force microscopy (AFM) and high resolution cross-sectional transmission electron microscopy (X-TEM).

Mathematical model for predicting molecular-beam epitaxy growth rates for wafer production

An analytical mathematical model for predicting molecular-beam epitaxy (MBE) growth rates is reported. The mathematical model solves the mass-conservation equation for liquid sources in conical crucibles and predicts the growth rate by taking into account the effect of growth source depletion on the growth rate. Assumptions made for deducing the analytical model are discussed. The model derived contains only one unknown parameter, the value of which can be determined by using data readily available to MBE growers. Procedures are outlined for implementing the model in MBE production of III–V compound semiconductor device wafers. Results from use of the model to obtain targeted layer compositions and thickness of InP-based heterojunction bipolar transistor wafers are presented.

Surface-oxidation studies of cube-textured, pure nickel to form NiO as a potential YBa2Cu3O7−x-coated conductor buffer layer

The growth of nickel oxide (NiO) on {100}〈001〉 cube textured, rolling-assisted biaxially textured substrates (RABiTS) of pure nickel was studied. Single-phase (100) NiO formed only in a narrow temperature range at 1250 ± 5 °C. At lower or higher temperatures, other orientations, namely (111), (311), and (220), also formed. At 1250 °C, practically single phase (100) NiO was observed for short oxidation times t of 0.2–10 min (oxide thickness < 10 μm). For 10 < t < 120 min, small quantities of (111) NiO formed in addition to (100), but near-single-phase (100) NiO formed once again after oxidation for >150 min (thickness > 35 μm). The ratio of (100) to (111) textures with oxidation time is explained in terms of epitaxial constraints, growth rates, and oxygen absorption on the (100) and (111) grains. The optimum oxidation conditions are oxidation for approximately 0.5 min at 1250 °C in flowing oxygen, yielding (100) NiO, a few microns in thickness, and root-mean-square roughness of approximately 40 nm on the length-scale of the grain size.

Low energy plasma enhanced chemical vapor deposition

We present a state-of-the-art growth technique, introduced recently for SiGe heteroepitaxy. At present, its most important application is the fast fabrication of high-quality relaxed SiGe buffer layers. The process is based on chemical vapor deposition (CVD), enhanced by a high intensity, low energy plasma, which is why we call it ‘low energy plasma enhanced CVD’ (LEPECVD). The key features of the process are a wide range of epitaxial growth rates (<1 Å s −1 up to at least 10 nm s −1), independent of the substrate temperature in the range of 500–750 °C and easy control of film composition, governed solely by the mixture of the precursor gases (SiH 4 and GeH 4). Possible applications of LEPECVD include electronic devices, such as modulation doped SiGe FETs (SiGe-MODFETs) or strained-layer SiGe MOSFETs, all based on relaxed buffer layers and targeting the fast-growing RF device market. Another field of applications is high-performance SiGe solar cells. For economic production, all these devices rely on fast, high-quality epitaxy, which is the strength of LEPECVD. The process, developed on the experimental system for 4-inch wafers, is now being transferred to a 300-mm single wafer reactor for production.

Flatness Deterioration of Silicon Epitaxial Film Formed Using Horizontal Single-Wafer Epitaxial Reactor

This study theoretically clarifies, for the first time, the mechanism of the flatness deterioration of a silicon epitaxial film which is formed on a rotating silicon substrate in a SiHCl3–H2 system at atmospheric pressure using an industrially used horizontal single-wafer epitaxial reactor. The plate of the multi-inlet in the reactor generates the narrow region having a small SiHCl3 gas concentration, because this plate locally weakens the cold finger effect due to various changes in transport phenomena in the reactor. This nonuniform distribution of SiHCl3 gas concentration generated above the silicon substrate results in a nonuniform epitaxial growth rate distribution on the silicon substrate. The substrate rotation then results in a silicon epitaxial film having a concentrically reduced thickness profile, the radius of which corresponds to the position of the plate of the multi-inlet. Due to this mechanism, the multi-inlet design leads to the flatness deterioration of the silicon epitaxial wafer.

Time-resolved measurements of stress effects on solid-phase epitaxy of intrinsic and doped Si

The effect of externally applied in-phase stresses on the solid-phase epitaxial growth rate of both intrinsic and B-doped Si has been measured using time-resolved reflectivity. The data are described phenomenologically by a product of a function of concentration, an Arrhenius function of temperature, and a Boltzmann factor in the product of the stress and the activation strain V*, with V11*=(+0.14±0.04) and (+0.17±0.02) times the atomic volume, in intrinsic and B-doped material, respectively.

Hot-wall and cold-wall environments for silicon epitaxial film growth

From the viewpoint of a systematic designing method for a chemical vapor deposition (CVD) reactor, double-wafer hot-wall and single-wafer cold-wall environments for silicon epitaxial film growth are studied, for the first time, by means of numerical calculations using the transport and epitaxy model which is effective for the SiHCl 3–H 2 system at atmospheric pressure. The distribution of the silicon epitaxial film growth rate and the profile of the silicon epitaxial film thickness are discussed in relation to the temperature and the gas velocity in the gas phase. The difference in the distribution of the epitaxial growth rate between the two types of reactors is discussed based on the transport phenomena of SiHCl 3 gas in the gas phase. Furthermore, in order to design future operations, the effect of the rotation direction of each substrate on the distribution of the silicon epitaxial growth rate is additionally discussed using the horizontal double-wafer hot-wall reactor.

The effect of coincident atomic hydrogen on the gas-source molecular beam epitaxial growth of silicon from disilane

The interaction of atomic hydrogen with both the clean Si(1 0 0) surface, and this same surface under conditions leading to steady-state epitaxial growth of Si from the reaction of disilane, Si 2H 6, has been examined. Reflectance anisotropy spectroscopy has been employed to measure the hydrogen adatom coverage on vicinal Si(1 0 0) surfaces as a function of atomic hydrogen exposure at differing substrate temperatures and differing atomic hydrogen fluxes. This set of experimental data can be fit well by a “hot-precursor” model that includes the elementary steps of adsorption, abstraction, migration, and desorption of atomic hydrogen, and where we account explicitly for adsorption site occupancy. Reflection high-energy electron diffraction has been used to quantify the effect of atomic hydrogen on the gas-source molecular beam epitaxial growth of Si from Si 2H 6. We observe suppression of the epitaxial growth rate by atomic hydrogen under a variety of reaction conditions. This set of data are described well by a model that combines rate expressions for the dissociative adsorption of Si 2H 6, the adsorption of atomic hydrogen, and the recombinative desorption of molecular hydrogen from the Si(1 0 0) surface.

Deuterium channeling analysis for He +-implanted 6H–SiC

Deuterium ion channeling is applied to study accumulated disorder on Si and C sublattices in 6H–SiC crystals irradiated with 50 keV He + ions at 100 and 300 K. The relative disorder on both sublattices follows sigmoidal dependence on dose. Carbon disorder is higher at low doses, suggesting a smaller C displacement energy. Above an ion fluence of 1.0×10 16 He +/ cm 2 , more C defects can be recovered during irradiation, indicating a lower activation energy for C migration and recombination. Isochronal annealing data show that the recovery behavior on the Si and C sublattices is similar. Annealing of a buried amorphous SiC layer, produced at 100 K (2.5×10 16 He +/ cm 2) , exhibits an epitaxial growth rate of ∼0.154 nm/K in the temperature range 370–870 K.

Thin Single Crystal Silicon on Oxide by Lateral Solid Phase Epitaxy of Amorphous Silicon and Silicon Germanium

ABSTRACTThe fabrication of 250 Å thick, undoped, single crystal silicon on insulator by lateral solid phase epitaxial growth from amorphous silicon on oxide patterned (001) silicon substrates is reported. Amorphous silicon was grown by low pressure chemical vapor deposition at 525°C using disilane. Annealing at temperatures between 540 and 570°C is used to accomplish the lateral epitaxial growth. The process makes use of a Si/Si1-xGex/Si stacked structure and selective etching. The thin Si1-xGex etch stop layer (x=0.2) is deposited in the amorphous phase and crystallized simultaneously with the Si layers. The lateral growth distance of the epitaxial region was 2.5 μm from the substrate seed window. This represents a final lateral to vertical aspect ratio of 100:1 for the single crystal silicon over oxide regions after selective etching of the top sacrificial Si layer. The effects of Ge incorporation on the lateral epitaxial growth process are also discussed. The lateral epitaxial growth rate of 20% Ge alloys is enhanced by roughly a factor of three compared to the rate of Si films at an anneal temperature of 555°C. Increased random nucleation rates associated with Ge alloy films are shown to be an important consideration when employing Si1-xGex to enhance lateral growth or as an etch stop layer.

Chemical process of silicon epitaxial growth in a SiHCl 3–H 2 system

The chemical process of silicon epitaxial growth in a SiHCl 3–H 2 system at atmospheric pressure is studied experimentally using a horizontal cold-wall single-wafer reactor and a quadrupole mass spectra analyzer. The dominant chlorosilane species in the gas phase and the dominant overall chemical reaction are experimentally determined to be SiHCl 3 gas and SiHCl 3+H 2→Si+3HCl, respectively. Since the amount of HCl gas produced in the reactor is proportional to the silicon epitaxial growth rate, it is concluded that the dominant chemical process of silicon epitaxial growth in a SiHCl 3–H 2 system occurs on the silicon substrate surface. The concentrations of SiCl 2, SiH 2Cl 2, SiHCl and SiCl 4 gases produced in the gas phase are too low to play a significant role in silicon epitaxial growth.

Facet‐Free Selective Silicon Epitaxy by Reduced‐Pressure Chemical Vapor Deposition Process Evaluation and Impact on Shallow Trench Isolation

A facet‐free, selective epitaxy process has been identified using the chemistry in single‐wafer reduced‐pressure chemical vapor deposition. The process window has been explored with respect to shallow trench isolation, simultaneous polycrystalline silicon (polysilicon) deposition, facet formation, and electrical parameters of polysilicon sheet resistance and junction leakage current. The isolation structure can be severely degraded by aggressive pre‐epitaxy bakes through volatile SiO formation; however, the impact is minimized when the prebake is limited to 900°C, 60 s. Concurrent deposition of polysilicon and silicon epitaxy can result in significantly different deposition rates. Low process pressures result in greater relative epitaxy growth rates and high pressures result in lower relative epitaxy deposition rates. The facet‐free process depends heavily on both the gate sidewall structure and the process conditions, where the combination of an undercut into the pad oxide and the nitride sidewall with the process pressure yield a reliably facet‐free process. Electrical results demonstrate that standard Ti or Co self‐aligned silicidation can be extended into a 0.1 μm gate length regime. © 1999 The Electrochemical Society. All rights reserved.