Off-axis Si Research Articles

Mg segregation in a (1 1¯ 0 1) GaN grown on a 7° off-axis (0 0 1) Si substrate by MOVPE

Redistribution behavior of magnesium (Mg) in the N-terminated (1 1¯ 0 1) gallium nitride (GaN) has been investigated. A nominally undoped GaN layer was grown on a heavily Mg-doped GaN template by metalorganic vapor-phase epitaxy (MOVPE). Mg dopant profiles were measured by secondary ion mass spectrometry (SIMS) analysis. A slow decay of the Mg concentration was observed in the nominally undoped GaN layer due to the surface segregation. The calculated decay lengths of the (1 1¯ 0 1) GaN are ∼75–85 nm/decade. These values are shorter than the decay length determined in the sample grown on the Ga-terminated (0 0 0 1) GaN. This result indicates that Mg exhibited weak surface segregation in the (1 1¯ 0 1) GaN as compared to the (0 0 0 1) GaN. The weak surface segregation is in agreement with the high efficiency of Mg incorporation on the (1 1¯ 0 1) face. The high density of hydrogen was obtained in the (1 1¯ 0 1) GaN, which might enhance the Mg incorporation.

Structural and Morphological Investigation of Pendeo-Epitaxy 3C-SiC on Si Substrates

Successful pendeo-epitaxy growth of cubic silicon carbide (3C-SiC) on off-axis Si(001) substrates was achieved. The structural and morphological characteristics of pendeo-epitaxy 3C-SiC were strongly affected by underlying stripes and seed layer thickness. Stripes perpendicular to the Si substrate off-axis provide about three times faster lateral growth rate compared with parallel oriented stripes. Root-mean-square (RMS) measurements using atomic force microscope (AFM) indicate that the surface morphology of Pendeo-epitaxy 3C-SiC films remarkably improves with increasing seed layer thickness: from 9.8 nm for 3 μm thickness to 0.5 nm for 10 μm thickness. These effects on pendeo-epitaxy 3C-SiC are discussed with scanning electron microscopy (SEM) and AFM investigation.

Fast homoepitaxial growth of 4H-SiC with low basal-plane dislocation density and low trap concentration by hot-wall chemical vapor deposition

Fast homoepitaxial growth of 4H-SiC has been carried out on 8° off-axis (0 0 0 1) Si substrates by horizontal hot-wall chemical vapor deposition (CVD) at 1650 °C. Growth at low pressure, by which gas-phase Si condensation can be minimized, has made it possible to obtain mirror-like surface at high growth rate up to 50 μm/h. Epilayers grown on chemical mechanically polished (CMP) substrates show much better surface morphology than those on as-received substrates. The basal-plane dislocation (BPD) density can be decreased by fast epitaxy on CMP substrates, and the minimum BPD density obtained in this study is 22 cm −2. The concentration of Z 1/2 and EH 6/7 centers is in the low 10 12 cm −3 range even at high growth rate of 50 μm/h. In photoluminescence (PL), free exciton peaks are remarkably dominant, and impurity-related peaks and L 1 peak are hardly observed.

Influence of starting material on analog technology fabrication yield and device component performance

Choice of substrate used for analog complementary metal-oxide-semiconductor (CMOS) technologies impacts device performance and fabrication yields significantly. This study examines the impact of low-angle (<5°) off-axis Si(100) substrate rotated around ⟨110⟩ axis and 0° Si(100) on-axis starting material on inline process control, parametric device performance, and ultimately fabrication yields. The interaction of thermal processes and silicon epitaxial growth process variation on inline photoalignment and its influence on device design and performance is discussed for both types of substrates. The device components include 3 and 5V analog CMOS, lateral p-n-p bipolar transistor, junction field effect transistors, and drain extended transistors, DENMOS and DEPMOS, where the drain extensions are formed using well implants. The necessity to reintegrate silicon epitaxial growth, well photolithography and implants, Vt implants, and gate oxide process loop to accommodate substrate crystal orientation changes will be presented. A novel front-end-of-the-line integration scheme to improve interwafer and intrawafer electrical distributions with excellent transistor matching and 1∕f noise performance for aforementioned device components will also be discussed in this context.

Mg doping in (1 1¯ 0 1)GaN grown on a 7° off-axis (0 0 1)Si substrate by selective MOVPE

Mg doping was attempted in (1 1¯ 0 1)GaN grown on a patterned (0 0 1)Si by selective metal-organic vapor phase epitaxy (MOVPE). The source material for the Mg doping was EtCp 2Mg and the electrical properties were studied on samples with different doping levels. All samples showed p-type conduction. However, the hole concentration was decreased by the Mg doping at low doping levels followed by an increase at high doping levels. The activation energy was around 106–130 meV depending on the doping level, which was larger than that found in undoped or carbon-doped samples. The AFM images showed gradual change in the surface structure in accordance with the Mg-doping level. The variation of the optical spectra was discussed in relation to the Mg-doping levels.

Suppression Mechanism of Double Positioning Growth in 3C-SiC(111) Crystal by Using an Off-Axis Si(110) Substrate

Hetero-epitaxial CVD growth of 3C-SiC on a Si(110) substrate gives a (111) crystal with low defects density. However, double positioning growth often disturbs growth of a single crystal. The growth on an off-axis Si(110) substrate suppressed propagation of the double positioning defects in the grown layer effectively. Cross-sectional transmission electron microscopy revealed the details of the suppression process on the off-axis substrate. The suppression mechanism and the origin of the defects formation at double positioning boundaries were interpreted by the growth model based on an anisotropic growth rate on (111) plane of 3C-SiC.

Optical and electrical properties of (1-101)GaN grown on a 7° off-axis (001)Si substrate

Uniform growth of (1-101)GaN was performed on coalesced stripes of GaN which had been prepared by selective metalorganic vapor phase epitaxy on a 7° off-axis (001)Si substrate via an AlN intermediate layer. The cathodoluminescence spectra at 4 K exhibited a donor bound excitonic emission at 358 nm followed by defect-related emission peaks at 363, 371, and 376 nm. The 363 and 376 emission bands are observed upon the coalescence region. The Hall measurements exhibited p-type conduction at 80–300 K (the hole carrier density 6.3×1012 cm−2 and hole mobility 278 cm2/V s at 100 K). The activation energy of the acceptor was estimated to be 60 meV. The possible origin of the p-type conduction is discussed in relation to the unintentionally doped carbon.

Preparation of Epitaxial Templates for Molecular Beam Epitaxy of III‐Nitrides on Silicon Substrates

In this paper, three different methods of composite substrate preparation for epitaxial growth of III-nitride epilayers are described. Firstly, molecular beam epitaxy (MBE) of thin 2H-AlN layers grown on off-axis Si(001) has been investigated. 2H-AlN was deposited at relatively low temperatures (730–830 °C) allowing a full coverage of the substrate to be quickly achieved. The growth of thin 3C-SiC layers on Si surface has been performed by chemical vapor deposition and MBE carbonization. The following types of SiC/Si composite substrates have been studied: (i) SiC/Si templates grown by rapid thermal carbonization of the Si surface, (ii) SiC/Si templates formed by MBE carbonization of the Si surface.

N-channel 3C-SiC MOSFETs on silicon substrate

Inversion-mode, n-channel 3C-SiC MOSFETs have been fabricated in a 3C-SiC epilayer grown on a 2°-off-axis Si(001) substrate with optimized SiC processing techniques. Phosphorus implantations are employed for source/drain formation and a sheet resistance of 70 Ω per square is obtained after annealing at 1250°C for 30 min in argon. Both drain characteristics and subthreshold characteristics show typical transistor behavior with an effective channel mobility of 165 cm2/Vs. The breakdown field of the gate oxide is about 3.5 MV/cm.

Influence of buffer layer and 6H-SiC substrate polarity on the nucleation of AlN grown by the sublimation sandwich technique

The initial nucleation stage of AlN crystal grown by the sublimation method on on-axis (0 0 0 1) Si and (0 0 0 1) C 6H-SiC as well as 3.5° off-axis (0 0 0 1) Si 6H-SiC substrates was investigated. Sublimation growth from a pure sintered AlN source was carried out in a resistively heated furnace with a source temperature of about 1800°C at a nitrogen pressure of 500 Torr. Direct growth on Si-terminated as-received SiC substrates was discontinuous, marked by sparse nucleation and slow lateral growth of nuclei. Several hexagonal sub-grains were usually obtained on the substrates after a long growth time (more than 3 h) due to the incomplete coalescence of the nuclei. In contrast, no sublimation growth occurred on the as-received C-terminated substrates. To enhance two-dimensional (2D) growth, an AlN epitaxial layer was first deposited on the substrates by MOCVD before sublimation growth. Continuous films could then be grown on all the substrates with AlN MOCVD buffer layers. The tensile stress of the AlN layer due to thermal expansion coefficient mismatch between SiC and AlN caused cracking across the AlN/SiC interface into the SiC substrates during the cooling process limiting the maximum of the thickness and lateral size of the AlN crystals.

Hexagonal AlN films grown on nominal and off-axis Si(0 0 1) substrates

Nucleation and growth of wurtzite AlN layers on nominal and off-axis Si(0 0 1) substrates by plasma-assisted molecular beam epitaxy is reported. The nucleation and the growth dynamics have been studied in situ by reflection high-energy electron diffraction. For the films grown on the nominal Si(0 0 1) surface, cross-sectional transmission electron microscopy and X-ray diffraction investigations revealed a two-domain film structure (AlN 1 and AlN 2) with an epitaxial orientation relationship of [0 0 0 1] AlN || [0 0 1] Si and 〈0 1 1 ̄ 0〉 AlN 1 || 〈 2 ̄ 1 1 0〉 AlN 2 || [1 1 0] Si. The epitaxial growth of single crystalline wurtzite AlN thin films has been achieved on off-axis Si(0 0 1) substrates with an epitaxial orientation relationship of [0 0 0 1] AlN parallel to the surface normal and 〈0 1 1 0〉 AlN || [1 1 0] Si.

Investigation of the Structure of 2H-AlN Films on Si(001) Substrates

By conventional transmission electron microscopy (CTEM) investigations on 2H-AlN films grown by plasma-assisted molecular beam epitaxy (MBE) on Si(001) the influence of the offaxis angle of the substrate surface on the film structure was studied. Three types of Si(001) substrates were used: on-axis, ~1°, and ~5° off-axis Si(001) substrates. The AlN layer on an exact oriented Si(001) substrates consists of 3 AlN film domains: two main film domains, AlN1 and AlN2, and a small domain AlN3 at substrate surface defects. Their c-axis orientations are parallel to the caxis of the substrate: [0001]AlN1,2,3||[001]Si. The a-axes of AlN1 and AlN2 rotated by 30° to each other: [11 2 0]AlN1||[01 1 0]AlN2||[1 1 0]Si [3]. The a-axis orientation of AlN3 is [01 1 0]AlN3||[100]Si. In 2H-AlN films grown on off-axis Si(001) substrates (~1° and ~5°) the ratio between the AlN1 and AlN2 film domains changes dramatically as far as a single domain film structure consisting of only AlN1 is reached. The AlN c-axes of all domains on the off-axis substrates are not parallel to the Si c-axis but tilted by the off-axis angle of the Si(001) substrate (~1° respectively ~5°), i.e. [0001]AlN is parallel to the Si(001) substrate surface orientation.

Single domain structure of 2H-AlN films on Si(001) substrates

ABSTRACTAluminum nitride (2H-AlN) films were grown by plasma-assisted molecular beam epitaxy (MBE) on Si(001). By conventional (CTEM) and high resolution transmission electron microscopy (HRTEM) investigations the influence of the off-axis angle of the substrate surface on the film structure was studied. Three types of Si(001) substrates were used: on-axis, ∼1°, and ∼5° off-axis. The 2H-AlN layer on an exact oriented Si(001) substrates consists of 3 AlN film domains: two main film domains, AlNI and AlNII, and a small domain AlNIII at substrate surface defects. Their c-axis orientations are parallel to the c-axis of the substrate: [0001]AlNI,II,III ∥ [001]Si. The a-axes of AlNI and AlNII rotated by 30° to each other: [11 20]AlNII∥[01 10]AlNII ∥ [1 1 0]Si. The orientation of AlNIII is [01 10]AlNIII ∥ [100]Si. In 2H-AlN films grown on off-axis Si(001) substrates (∼1° and ∼5°) the ratio between the AlNI and AlNII film domains changes dramatically as far as a single domain film structure consisting of mainly AlNI is reached. The AlN c-axes of all domains on the off-axis substrates are not parallel to the Si c-axis but tilted by the off-axis angle of the Si(001) substrate (∼1° respectively ∼5°), i.e. [0001]AlN is parallel to the Si(001) substrate surface orientation. Determination of the AlNI domain / Si(001) interface structure by HRTEM illuminates the origin of the preference of this domain in the 2H-AlN film by using off-axis Si(001) substrates. On the on-axis substrate a regular array of misfit dislocations causes a 5:4 fit between the (1 1 00)AlN and ( 1 1 0)Si lattice planes. The off-axis Si(001) leads to a rotation of the AlN lattice in respect of the Si lattice. An array of misfit dislocations with a 4:3 fit between (1 1 01)AlN and ( 1 1 1)Si lattice planes decreases the residual lattice misfit from -1.6% to -0.8%.

The growth of CoSi 2 through an oxide layer: dependence on Si(100) surface structure

The growth of Co–silicide on two different kinds of Si(100) substrates covered with a chemical oxide was investigated. The off-axis Si(100), which was cut 4° off to the (100) plane towards the [110] direction, and the on-axis Si(100), which was cut with less than 0.5°, were prepared. The atomic scale microsteps of the two different Si(100) substrates were observed by high resolution transmission electron microscope. These Si substrates were chemically oxidized by submerging the Si wafers into a hydrogen peroxide (H 2O 2) solution for 10 min and loaded into an ultrahigh vacuum evaporation system. The 10-nm cobalt thin films were deposited on both kinds of substrates in this system and subsequently in-situ annealed for 10 min at temperatures between 400 and 700°C with 100°C increments. After this treatment, the Co–silicide is formed and analyzed by an X-ray diffractometer, scanning electron microscope, transmission electron microscope and Auger electron spectroscopy to verify the phase formation, surface and interface morphologies, and chemical composition. The Co 2Si phase was found to be the first silicide formed during in-situ annealing. The formation temperature of CoSi 2 on the 4° off-axis Si(100) and on-axis Si(100) were 600 and 700°C, respectively. This difference in formation temperature of the CoSi 2 phase was considered to be related to the atomic scale microsteps of the Si surface.

The Growth of Co-Silicide Using a Chemical Oxide on Off-Axis Si(100) Substrates

The Growth of Co-Silicide Using a Chemical Oxide on Off-Axis Si(100) Substrates

Growth of CVD heteroepitaxial diamond on silicon (001) and its electronic properties

Abstract Microwave CVD heteroepitaxial diamond film on a 4° off-axis Si(100) substrate is obtained by two stages. The first one is to grow oriented 3c-SiC layers on Si(100) using a non-toxic and non-inflammable (CH3)6Si2NH organic compound carried by hydrogen. The following stage is to grow oriented diamond films on them under the atmosphere of CH4 and H2. In each stage there are bias and growth processions. The micro-Raman and micro-Auger analyses prove that there is a perfect orientation relationship between the film and substrate as following: diamond 〈001〉//3c-SiC〈001〉//Si〈001〉. The Hall effect indicates that the film is a P type, whose resistivity is 9.4×10−3 Ω cm, the Hall coefficient is 2.9 cm3/Q, the hole mobility is 309 cm2/V s and the carrier concentration reaches 2.2×1018 cm−3.

Epitaxial growth of AlN films on Si substrates by ECR plasma assisted MOCVD under controlled plasma conditions in afterglow region

Wurtzite-type aluminum nitride (h-AlN) films were epitaxially grown on off-axis Si (111) substrates by electron–cyclotron–resonance plasma-enhanced metalorganic chemical vapor deposition (ECRMOCVD) using trimethylalminum (TMA) and ammonia (NH 3) as source gases. Plasma space potential in the growth chamber was lowered by setting the magnetic field distribution as a mirror field. For the growth of h-AlN with excellent crystallinity on Si substrates, nitridation of the substrate surface, growth of a low-temperature (LT) buffer layer, and epitaxial growth of AlN films were performed under a mirror field condition in a growth chamber. Thermal nitridation at 1050°C prior to the epitaxial growth appreciably improved the crystallinity of AlN films. The growth of buffer layer at temperatures below 650°C was not so effective for the improvement of the crystallinity and crystal orientation of AlN epitaxial layer. The proportion of domain including stacking faults and that whose c-axis was parallel to the substrate surface was very small ( I (0002)/( I (10–10)+ I (10–11))>700), irrespective of the gas feed ratio of N source to Al source (NH 3/TMA) during the epitaxial growth process. Under a small gas feed ratio (NH 3/TMA<200), however, the diffraction peak intensities from the non-epitaxial domains became large.

Amorphous Titanium Silicide Phase Formation by Surface Microroughness on Si(100)

The formation of amorphous Ti-silicide phase on two different kinds of Si(100) substrates was investigated. Two different substrates, the off-axis Si(100) which was cut with 4° to the (100) plane and the on-axis Si(100) which was cut with less than 0.5° were prepared. The Si(100) substrates were examined with atomic force microscope (AFM) to verify the atomic scale microroughnesses of the initial Si substrates after HF clean removing the native oxide. The on-axis Si(100) substrate exhibited much rougher surface morphology than that of the off-axis Si(100). The atomic scale microroughness of two different Si(100) substrates such as atomic steps and pits were investegated by high resolution transmission electron microscopy (HRTEM). Ti thin films were deposited in an e-beam evaporator after HF clean and the amorphous Ti-silicide layers were formed by annealing. The amorphous layer thicknesses on the on axis Si(100) exhbited thicker than those of the off-axis Si(100) and this difference of amorphous Ti-silicide layer thicknesses was considered to be related with atomic scale microroughnesses of Si surface.

Amorphous Phase Formation of Titanium Silicide on The 4° off-Axis and on-Axis Si(100) Substrates

AbstractTwo different Si(100) substrates, the 4°off-axis and the on-axis Si(100), were prepared. Ti thin films were deposited in an e-beam evaporation system and the amorphous layers of Ti-silicide were formed at different annealing temperatures. The Si(100) substrates before Ti film deposition were examined with AFM to verify the atomic scale roughness of the initial Si substrates. The amorphous layer was observed by HRTEM and TEM. And the chemical analysis and phase identification were examined by AES and XRD. The Si(100) substrate after HF clean shows the atomic scale microroughness such as atomic steps and pits on the Si surface. The on-axis Si(100) substrate exhibits much rougher surface morphologies than those of the off-axis Si(100). These differences of atomic scale roughnesses of Si substrates result in the difference of the thicknesses of amorphous Ti-silicide layers. The amorphous layer thicknesses on the on-axis exhibit thicker than those of the off-axis Si(100) and these differences inamorphous layer thicknesses became decreased as annealing temperatures increased. These indicate that the role of the atomic scale roughness on the amorphous layer thickness is much significant at low temperatures. In this study, the correlation between the atomic scale roughness and the amorphous layer thickness is discussed in terms of the atomic steps and pits based on the observation with using analysis tools such as AFM, TEM and HRTEM.

Surface electronic structure of a single-domain Si(111)4 × 1-In surface: a synchrotron radiation photoemission study

The electronic structure of a Si(111)4 × 1-In surface has been studied by angle-resolved photoelectron spectroscopy (ARPES). Using a 1.1° off-axis Si(111) wafer as substrate, a single-domain Si(111)4 × 1-In surface has been prepared in order to determine the dispersion of surface state (SS) without the obscurity arising from multi-oriented 4 × 1 domains. Three SSs that cross the Fermi level have been found. Thus, the Si(111)4 × 1-In surface is concluded to be metallic. The dispersions of the metallic SS appeared to be almost one-dimensional, suggesting one-dimensional metallic bonds among In atoms. Completely occupied SSs have been also found. The characteristics of SSs are discussed in relation to the existing structural models for the Si(111)4 × 1-In surface.