Epitaxial Lateral Overgrowth Technique Research Articles

Multiple layers of silicon-on-insulator islands fabrication by selective epitaxial growth

This paper presents for the first time, multiple layers of silicon-on-insulator (MLSOI) device islands fabricated using selective epitaxial growth (SEG) and epitaxial lateral overgrowth (ELO) techniques. MLSOI has the potential for ultra dense device integration. SOI device islands as small as 150 nm×150 nm, with thickness down to 40 nm have been fabricated. SOI device islands (5 μm×500 μm) in the second layer have shown no stacking faults in the 1290 islands inspected. To demonstrate the device quality material, fully depleted SOI (FD-SOI) P-MOSFET's were fabricated in the first layer SOI islands with gate lengths down to less than 170 nm. Typically they had low subthreshold leakage, below 0.2 pA/μm, and a subthreshold swing of 76 mV/dec was measured.

Porous SiC Substrate Materials for High-Quality Epitaxial and Bulk Growth

AbstractThe main unsolved problem in SiC technology is a high density of defects in substrate materials (micropipes and dislocations) propagating into device structures and causing device failure. Recently, significant progress in defect density reduction in semiconductor materials has been achieved using epitaxial lateral overgrowth techniques. In this paper, we describe a novel technique, which shows a high potential for defect reduction in epitaxial and bulk SiC. This technique is based on nano-scale epitaxial lateral overgrowth (NELOG) method, which employs porous substrate materials. Usually, the pores are from 50 to 500 nm in size and epitaxial material overgrowing these pores, forms continues high-quality layer. It is important that the NELOG method does not require any mask. This technique may be easily scaled for large area substrates.In this work, SiC layers were grown on porous SiC by sublimation method, which is widely used for both epitaxial and bulk SiC growth. Porous SiC substrates were formed by surface anodization of SiC commercial wafers. It was shown that SiC layers grown on porous SiC substrates have smooth surface and high crystal quality. The surface of overgrown material was uniform and flat without any traces of porous structure. X-ray topography indicated significant defect density and stress reduction in SiC grown on porous material. Photoluminescence measurements showed a reduction of deep level recombination in SiC.

Synchrotron x-ray topography analysis of GaAs layers grown on GaAssubstrates by liquid phase epitaxial lateral overgrowth

Synchrotron x-ray topography techniques in section and back-reflection geometries have been applied to silicon and tin doped GaAs layers grown by the liquid phase epitaxial lateral overgrowth (ELO) technique on (100) GaAs substrates. Back-reflection topographs show that the laterally grown parts of the ELO layers are nearly dislocation free in spite of a large density of defects in the substrate. Section topographs reveal novel and unique features which are attributed to the bending of the ELO layers induced by their interaction with the SiO2 mask.

Fabrication of GaN with Buried Tungsten (W) Structures Using Epitaxial Lateral Overgrowth (ELO) via LP-MOVPE

AbstractA buried tungsten (W) mask structure with GaN is successfully obtained by epitaxial lateral overgrowth (ELO) technique via low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). The selectivity of GaN growth on the window region vs. the mask region is good. An underlying GaN with a striped W metal mask is easily decomposed above 500 °C by the W catalytic effect, by which radical hydrogen is reacted with GaN. It is difficult to bury the W mask because severe damage occurs in the GaN epilayer under the mask. It is found that an underlying AlGaN/GaN layer with a narrow W stripe mask width (mask/window = 2/2 νm) leads the ELO GaN layer to be free from damage, resulting in an excellent W-buried structure.

GaN and AlN Layers Grown by Nano Epitaxial Lateral Overgrowth Technique on Porous Substrates

AbstractDefect density and stress reduction in heteroepitaxial GaN and AlN materials is one of the main issues in group III nitride technology. Recently, significant progress in defect density reduction in GaN layers has been achieved using lateral overgrowth technique. In this paper, we describe a novel technique based on nano-scale epitaxial lateral overgrowth.GaN layers were overgrown by hydride vapour phase epitaxy (HVPE) on porous GaN. Porous GaN was formed by anodization of GaN layers grown previously on SiC ŝubstrates. Pore's size was in nano-scale range.Thickness of overgrown layers ranged from 2 to 120 microns. It was shown that GaN layers overgrown on porous GaN have good surface morphology and high crystalline quality. The surface of overgrown GaN material was uniform and flat without any traces of porous structure. Raman spectroscopy measurements indicated that the stress in the layers grown on porous GaN was reduced down to 0.1 - 0.2 GPa, while the stress in the layers grown directly on 6H-SiC substrates remains at its usual level of about 1.3 GPa.Preliminary experiments were done on HVPE growth of AlN layer on porous substrates. Improvement of surface morphology and crack density reduction has been observed.

GaN epitaxial lateral overgrowth and optical characterization

We demonstrate the epitaxial lateral overgrowth (ELO) of GaN from narrow stripes with triangular cross sections by atmospheric pressure metal organic chemical vapor deposition, and characterize the optical properties of these stripes at each stage of the growth using spatially resolved cathodoluminescence spectroscopy, wavelength imaging, and line scans. An improvement of the optical quality of the GaN materials grown by the ELO technique is clearly shown by the appearance of a free exciton peak, the enhancement of bandedge emission, and the weakening of the yellow emission.

Transmission electron microscopy of defects in GaN films formed by epitaxial lateral overgrowth

We have investigated by transmission electron microscopy (TEM) defect morphology and structure in GaN films formed using an epitaxial lateral overgrowth (ELO) technique on SiO2-mask/window-stripe-patterned GaN layers in hydride vapor-phase epitaxy. In this experiment, the regions overgrown on the SiO2 masks were thoroughly examined. Cross-sectional TEM clearly revealed characteristic defects along the [0001] direction in the overgrown region, which consisted of arrays of dislocations running along the mask stripe direction. These defects caused crystallographic tilting in that region near the mask with respect to the other region grown from the window area. We also observed, at the coalesced site on the mask, vertical repropagation of dislocations that had propagated laterally during ELO. The origin of the observed defects and their influence on the residual dislocation distribution near the film surface are discussed.

Kinetic Modelling Of The Selective Epitaxy Of GaAs On Patterned Substrates By Hvpe. Application to the Conformal Growth Of Low Defect Density GaAs Layers On Silicon

AbstractThe selective growth of GaAs by HVPE was studied on (001), (110), (111)Ga and (111)As, GaAs patterned substrates by varying the I1I/V ratio. A kinetic modelling of the growth was developed, based upon the SEM observations of the growth morphologies as well as on experimental curve synthesis. The growth rate is written as a function of the diffusion fluxes of the adsorbed AsGa and AsGaCI molecules and takes into account the chlorine desorption by H2. 1.5 μm thick GaAs films were then fabricated on Si (001) by a confined epitaxial lateral overgrowth technique. These conformal films exhibit intense and uniform luminescence signals, showing that the dislocation densities of GaAs are lower than 105 cm−2. SEM analyses reveal that conformal growth fronts consist in (110) and (111)As A planes under the III/V ratios (superior to 1) which were tested.

Substrate Defects Filtration During Epitaxial Lateral Overgrowth of GaAs

Results on the growth of GaAs on (001) GaAs substrates by the epitaxial lateral overgrowth technique are reported. We show that the ratio of normal to lateral growth rates in the epitaxial lateral overgrowth process can be controlled by the crystallographic orlentation of the seeds and by Si adding to the melt. Experimental data showing that the dislocations threading from the substrate are efficiently filtered and cannot propagate to the epitaxial lateral overgrowth layers are presented. These findings prove that the epitaxial 1ateral overgrowth process is the powerful method to grow epilayers with low dislocation density on high dislocation density substrates. PACS numbers: 68.55.Ln There is a continuous effort to reduce the defect denSity in heteroepitaxial structures grown on lattice mismatched substrates. Very sophisticated techniques of buffer layers and of defects filtration by superlattices have been elaborated to improve the quality of epitaxial layers thicker than the critical thickness. Unfor- tunately, very often the number of defects is still unacceptably high. Therefore, the growth of dislocation free epitaxial layers remains one of the most important goals in heteroepitaxy. The very promising way to reduce the dislocation den- sity in heteroepitaxy is the epitaxial lateral overgrowth (ELO) technique when combined with liquid phase epitaxy (LPE) growth method. However, controversy exists about the growth mechanism and the defect structure in layers grown by ELO. In this work we report the results on the growth of GaAs epilayers on (001) GaAs substrates using the ELO method. The growth mechanism and the effect of substrate defects filtration during the ELO procedure are discussed. The principle of the epitaxial lateral overgrowth technique is shown schemat- ically in Fig. 1. The substrate was covered by a 0.1 μm thick SiO2 film and pat- terned by a conventional photolithography to form on its whole area a grating of 10 μm wide oxide-free seeding windows. Then, an epitaxial layer was deposited on such substrate by the LPE technique. In our experiments the growth was initiated by covering the substrate with the saturated Ga-As solution at the temperature of 7500C while cooling the system. GaAs nucleated on the line seeds and the growth proceeded in the direction normal to the substrate. Then, the growth in lateral

High quality InP on Si by conformal growth

Conformal growth is a confined epitaxial lateral overgrowth technique previously used to achieve low dislocation density GaAs films on Si. Conformal growth was used here to obtain high quality InP films on silicon, starting from GaAs seeds. Detailed characterization of the InP films (chemical etching of dislocations, photoluminescence at 300 K, cross-section transmission electron microscopy) proved the high defect filtering power of this technique. Dislocations initially present in the GaAs seeds and dislocations generated at the InP/GaAs interface were blocked and did not propagate through the growing films. Dislocations densities below 5×105 cm−2 have been obtained in submicrometer-thick conformal InP films on Si.

Liquid-phase epitaxial lateral overgrowth of GaAs on 0.3 °-misoriented epitaxial Si substrates

A liquid-phase epitaxial lateral overgrowth (LPELO) technique combining molecular beam epitaxy (MBE) and liquid-phase epitaxy (LPE) is employed to obtain high-quality GaAs-on-Si material structure that can be used for opto-electronic applications. In this technique, first a GaAs coating layer is grown on an epitaxial Si substrate by MBE. Then, GaAs LPELO layer is grown by LPE under these conditions that the growth takes place only in the open regions formed in SiO 2 film deposited on MBE-grown GaAs. It is shown that defect-free epitaxial regions can be obtained by the LPELO technique. Up to now, although some investigations on LPELO have been carried out, there has been no systematic study of the influence of underlying MBE GaAs-on-Si on the LPELO growth. In the present study, the factors that affect the ELO growth were investigated systematically. In particular, the correlation between MBE substrate and LPELO was analyzed in detail.

Crystal silicon Fabry-Perot cavities deposited with dichlorosilane in a reduced pressure chemical vapour deposition reactor for thermal sensing

A surface-normal Fabry-Perot (FP) thermal sensor with embedded multiple QW dielectric mirrors, was fabricated and evaluated using a single crystal merged silicon epitaxial lateral overgrowth (MELO) technique. The sensitivity of the sensor has been improved owing to the higher finesse.

50‐nm‐Thick Silicon‐on‐Insulator Fabrication by Advanced Epitaxial Lateral Overgrowth: Tunnel Epitaxy

An advanced epitaxial lateral overgrowth (ELO) technique, called tunnel epitaxy is presented, in which the lateral epitaxy is grown in a small gap between the upper and lower layers of . Therefore, the fabricated silicon on insulator (SOI) thickness can be controlled precisely by the gap height. Thin SOI films with thicknesses of 50–150 nm are fabricated successfully using this technique. The fabricated SOI areas were 5–10 μm in length and 10–750 μm in width. Due to gas heating through a narrow tunnel, the optimal growth conditions for the tunnel epitaxy using ultrahigh vacuum chemical vapor deposition (UHV/CVD) depends on the tunnel length, distance between the gas injection window and the seed. A defect‐free area within 2–3 μm from the seed was obtained. An n‐channel metal oxide semiconductor field effect transistor (MOSFET) fabricated in this area shows good characteristics. Possible mechanisms for defect generation after 2–3 μm growth are discussed.

Detailed Characterisations of GaAs Films on Si Obtained by Conformal Growth.

ABSTRACTConformal growth is a confined epitaxial lateral overgrowth technique capable of yielding low dislocation density GaAs films on Si. This technique makes extensive use of selective epitaxy and crystal growth is confined by a dielectric cap as well as by the self-passivated Si surface itself.In this paper, we have performed a detailed characterisation of the state of stress of the GaAs films in various configurations (after conformal growth and removal of the seed regions, and after the regrowth of an MBE layer) by photoluminescence measurements at 5K and X-ray diffraction experiments. Although the as-grown conformal films are found in the same state of stress than reference MOCVD GaAs epilayers on Si, we report a significant decrease of this stress after MBE regrowth on conformal films.

Epitaxial lateral overgrowth of Si on non-planar substrate

We have studied epitaxial lateral overgrowth (ELO) by liquid phase epitaxy (LPE) on non-planar Si(111) substrates and found that the ELO layer has always a planar top surface irrespective of the shape of the substrates. Two types of substrates, one with a smoothly curved non-planar surface and another with a sharply changing non-planar surface were prepared. The former was prepared by selective chemical etching. The latter was fabricated by ELO on a planar substrate. It is confirmed from SEM micrographs that the ELO layer has a planar top surface independent of the shape of the substrate. When the smoothly curved non-planar substrates were used, no voids were observed between the ELO layers and the non-planar substrates. In contrast, when the sharply changing non-planar substrate was used, voids were created between the ELO layer and the non-planar substrates. However, both types of non-planar substrates have planar top surfaces due to the formation of a (111) facet. It was concluded that the flat top surfaces can be realized on any type of non-planar Si(111) substrates by employing the present ELO technique.

LPE Lateral Overgrowth of GaP

Epitaxial lateral overgrowth (ELO) of GaP on SiO2-coated (111)B or (111)A GaP substrates was carried out successfully by LPE. It was found that the ELO of GaP showed dependency on seed orientation similar to that of GaAs. However, a pronounced asymmetry of lateral growth in [2̄11] and [21̄1̄] orientations was found. Monomolecular growth steps on the ELO layer have been observed by a Nomarski differential interference contrast microscope equipped with an image processor without decoration. Nitrogen doping was performed, and its nonuniform distribution was investigated by a fluorescence microscope and spatially resolved photoluminescence. From the nonuniformity, an understanding of the ELO mechanism was derived. It was found that the epilayer had a much lower dislocation density than that in a substrate. It was concluded that wide and extremely flat GaP epilayers with high quality can be obtained by the ELO technique.

Issues and Problems Involved in Selective Epitaxial Growth of Silicon for SOI Fabrication

In the epitaxial lateral overgrowth (ELO) technique an SOI layer is formed by overgrowing oxide with CVD silicon seeded at the edges of an oxide island on single‐crystal silicon. In the ELO technique conventional epitaxial reactors are used for the production of epitaxial silicon. SOI films have low defect density (compared to other SOI approaches) and wafers supporting the ELO silicon are not warped. Electrical characteristics, such as mobility and lifetime of SOI/ELO films, are similar to homoepitaxial layer grown in the same reactor. In this paper the problems related to ELO and selective epitaxial growth (SEG) are discussed. Our present knowledge will be reviewed on the topics of: defect structure, dependence of the growth rate on pattern geometry, and overgrowth ratio. We will also discuss the electrical characteristics of ELO/ SEG films, with a special emphasis on the interfacial properties (formed by CVD overgrowth). The process used to obtain SOI wafers with a continuous oxide layer underneath a silicon film will be described. The potential and the problems faced in preparing these layers will be discussed.

MONO/POLY technology for fabricating low-capacitance CMOS integrated circuits

A process for the fabrication of CMOS transistors with oxide-isolated source-drain regions that are coplanar with the device channel region is described. The process uses the epitaxial lateral overgrowth technique to selectively grow single-crystal silicon from seed regions that will become the transistor channel regions. The source-drain regions are polycrystalline silicon and are deposited following the selective growth. n- and p-channel device characteristics are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fabrication of SOI CMOS over large-area continuous-oxide films formed using epitaxial lateral overgrowth techniques

The authors have developed techniques for producing thin, monocrystalline silicon films over large area continuous oxides using the epitaxial lateral overgrowth (ELO) approach and have investigated the electrical characteristics of CMOS devices fabricated in these films. A conventional ELO process using a growth-etchback technique to eliminate spurious nucleation was used to overgrow single-crystal silicon from seed regions over the oxide stripes. Silicon nitride was deposited and patterned with a mask which had an identical pattern to the first mask. After nitride etch, the original seed region was exposed. A partial silicon etch was performed and the wafers were then reoxidized. During this step an oxide was grown over the exposed seed region which subsequently coalesced with the initial oxide stripes, forming a continuous insulating region covered by stripes of single-crystal silicon. These formed the seed for a second ELO step that resulted in a continuous single-crystal silicon film over the underlying oxide. The transistors, fabricated in ELO material, exhibited electrical characteristics comparable to both SOS controls and to devices fabricated on SIMOX (silicon implanted with oxygen) wafers in the laboratory using an identical process. >

Selective epitaxial growth for the fabrication of CMOS integrated circuits

A process is described for the fabrication of CMOS integrated circuits which combines the epitaxial lateral overgrowth (ELO) technique with the concept of selective epitaxy. The resulting epitaxial material is shown to have a low defect density. Transistors fabricated in the selective epitaxy are shown to have characteristics which are a function of the epitaxial deposition conditions, the substrate orientation and dopant concentration, and the epitaxial layer thickness. Minimum device leakage currents were 250 pA/µm of channel width for n-channel devices fabricated in a p-well and 1.0 pA/µm for devices fabricated on p-substrates. The higher leakage currents for devices fabricated in a well are believed to be a result of the narrow vertical spacing (0.3-0.5 µm) between the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> source-drain regions and the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> substrate.