Defect Etching Research Articles

A Refined Model For Threading Dislocation Filtering In InxGa1−xAs/GaSAs Epitaxial Layers

AbstractA model is presented for the filtering of threading dislocations in InxGa1−xAs/GaAs epitaxial single layers by accurate control of the layer thickness. The model developed differs from previous models since the InxGa1−xAs growth is restricted to less than ten times the Matthews and Blakeslee critical thickness (hc) where the asymmetry in the [110] and [110] dislocation densities is the greatest. Beyond this thickness it is shown that the removal or annihilation of threading dislocations (TDs) in the epilayer is more than offset by the introduction of new TDs from spiral and Frank-Read type sources. Results from strain sensitive etching with CrO3 aqueous solutions show that the TD density can be reduced by up to a factor of ten below that found in the substrate. Atomic force microscopy shows that these thin layers maintain a high level of surface quality with an absence of striations. Evidence is also shown that this type of defect etching is suitable for revealing large scale dislocation blocking in samples that have been grown significantly beyond 10hc.

Morphological effects and the diffusion of iodine in CdTe

The morphology of undiffused and iodine-diffused CdTe slices and its effect on iodine concentration profiles is discussed. Such CdTe slices were analysed using defect etching, scanning electron microscopy (SEM), infrared microscopy and secondary ion mass spectrometry (SIMS). The results suggest that during diffusion a layer of an iodine compound forms in the surface region of the CdTe while, over a limited range further into the material, clusters of either this or a similar compound form at defect sites causing a high degree of crystal distortion.

Room Temperature Defect Etching of III-V Compounds and Alloys Grown on Si Substate Using Hydrogen Fluoride and Nitric Acid

Room Temperature Defect Etching of III-V Compounds and Alloys Grown on Si Substate Using Hydrogen Fluoride and Nitric Acid

Chemical Free Room Temperature Wafer To Wafer Direct Bonding

A limitation to the use of direct wafer bonding methods for micromachining and thin film device manufacturing has been the necessity for high temperature anneals to strengthen the bonded interface. Obviously, strong interface strength is needed to withstand backthinning processes and the rigors of device fabrication. Unfortunately, the elevated temperature exposure has a detrimental effect on implanted or diffused etch stop layers via diffusive broadening. Additionally, for many micromachined applications wafer bonding could be used as a final assembly step, replacing epoxies. However, the sensitive components of the device must be protected from thermal effects. This paper describes the use of oxygen plasmas to develop chemical free, room temperature, wafer to wafer bonding methods. The bond developed between plasma‐activated silicon wafers is virtually at full strength upon contact bonding and does not require further thermal strengthening. The results for silicon dioxide bonding show that full strength material is achieved with anneals below 300°C. This process has been applied to a number of wafer materials including sapphire, silicon dioxide, silicon nitride, and gallium arsenide. The data presented are the results of strength tests, interfacial defect etching, transmission electron microscopy analysis, initial interface reaction kinetics, and mechanisms studies. We also show preliminary results from a suggested model to explain the observed increases in kinetics compared to conventional aqueous solution processing of samples.

Thermal etching defect structures on Si(001): a comparative study with high-resolution low-energy electron diffraction and scanning tunnelling microscopy

Defect structures formed on Si(001) surfaces heated to different temperatures were studied comparatively with a high-resolution spot profile analysis low-energy electron diffraction (LEED) system and with a scanning tunnelling microscope. Using scanning tunnelling microscopy (STM) we observed tetragonal pyramids after annealing the surface to 1400 K which are formed by a thermal etching process that removes silicon from the surface. With increasing slope of the pyramid planes we observe a transformation from monatomic to DB double steps. For the latter, dimer rows of the (2*1) reconstruction extend perpendicular to the step edges. Pyramid planes with DB double steps that are rotated by 90 degrees transform into each other by the formation of single-stepped planes. For annealing temperatures of 1600 K, very flat surfaces with only monatomic steps are formed. A profile analysis of the specular and half-order beams of the two-domain Si(001) (2*1) LEED pattern was performed after the same preparation procedures were applied to the samples. This analysis leads to step structures that are identical with the results from the real-space STM studies.

Molecular-beam epitaxial growth of CdTe(112) on Si(112) substrates

High crystalline quality epitaxial CdTe(112)B/ZnTe films were deposited by molecular-beam epitaxy directly onto vicinal Si(112) substrates, without use of GaAs interfacial layers. The films were characterized with x-ray diffraction, optical microscopy, and wet chemical defect etching. Single crystal, twin-free CdTe(112)B films exhibit structural quality exceeding that previously reported for CdTe(112)B heteroepitaxy on GaAs/Si(112) or GaAs(112)B substrates. X-ray rocking curve full width at half-maximum of 72 arcsec for CdTe(224) reflection and near-surface etch pit densities (EPD) of 2×106 cm−2 have been observed for 8-μm-thick CdTe films. EPD depth profiles indicate that the threading dislocation density decreases with increasing II–VI epilayer thickness up to approximately 5 μm thickness and saturates at 2×106 cm−2 for thickness exceeding 5 μm. The CdTe epilayer orientation was observed to tilt 2° away from the Si(112) substrate orientation toward the [001] direction.

Comparison of the electrical properties of simultaneously deposited homoepitaxial and polycrystalline diamond films

The electrical transport properties of simultaneously deposited, B-doped homoepitaxial and polycrystalline diamond thin films have been evaluated by Hall-effect and resistivity measurements over a temperature range of 80–600 K. The same films were later characterized by scanning electron microscopy, secondary-ion-mass spectroscopy, and an oxidation defect etch. The study involved four sets of chemical-vapor-deposited diamond films with individual B concentrations ranging from 1.5×1017 to 1.5×1020 cm−3. In each of the four cases the mobility of the polycrystalline film was lower than that of the homoepitaxial film by 1–2 orders of magnitude over the entire temperature range. Polycrystalline films also incorporated 2–4 times more B, had 3–5 times higher compensation ratios, and displayed activation energies that were 0.05–0.09 eV lower than in the homoepitaxial films. Hopping conduction was observed in both types of films at low temperatures, but was enhanced in polycrystalline films as evident by higher transition temperatures. Preliminary efforts have been made to evaluate these results by considering the possible effects of crystal structure, compensation, impurity segregation, grain-boundary trapping, and impurity conduction.

Reciprocal Space Analysis of the Initial Stages of Strain Relaxation in SiGe Epilayers

ABSTRACTMetastable SiGe films were grown by MBE on Si (001) substrates and annealed to promote varying degrees of partial relaxation. X-ray diffraction reciprocal-space analysis was then used to monitor the structural evolution of the displacement fields of the dislocation array with increasing misfit density. The diffuse-x-ray-scattering patterns of the dislocated heterolayers were compared with lineal-misfit densities determined by defect etching, leading us to develop a geometric model which provides a framework for understanding the early-stage evolution of the displacement fields of the dislocation array, and which also explicitly links diffuse x-ray intensity to misfit density. At low misfit density, the diffuse intensity arises from two-dimensional displacement fields associated with single-nonoverlapping dislocations. As misfit density increases, the displacement fields of individual dislocations increasingly overlap producing three-dimensional displacements. The evolving diffuse intensity reflects the transition from 2-D to 3-D displacement fields. Finally, it is demonstrated that the diffuse x-ray intensity of the strained epilayer can be used to accurately measure lineal misfit-dislocation densities from 400 to 20,000 lines/cm.

Defect-Engineered Graded GexSi1-x Buffers on Si (001) with Extreme Low Threading Dislocation Density

AbstractStepwise equilibrated graded GexSii-x (x≤0.2) buffers with threading dislocation densities between 102 and 103 cm−2 on the whole area of 4 inch silicon wafers were grown and studied by transmission electron microscopy, defect etching, atomic force microscopy and photoluminescence spectroscopy.

Vibrational characterization and electronic properties of long range-ordered, ideally hydrogen-terminated Si(111)

The use of a well defined, long range ordered surface is of fundamental interest for the determination of surface-specific intrinsic physical parameters. Ideally hydrogen terminated Si(111) surfaces are prepared by wet chemical treatment in basic HF solutions. The mechanism of formation is based on preferential etching of defects, leading to an ideal hydrogen terminaison of the (111) plane, without any reconstruction and with a high degree of perfection. Infrared spectroscopy is used to probe the quality of the surfaces by quantifying the extent of the perfect domains. High resolution photoemission spectroscopy of such highly homogeneous surfaces shows exceptional narrow features in both the valence band and the core level regions. The valence band levels and their dispersion are well described by first-principles calculations using a quasi particle self-energy approach within the Heidin's GW approximation. Two surfaces core level states are evidenced, arising from the silicon surface atoms and the backbonds. A crystal field effect splits the surface Si 2 p 3 2 component. Their position and relative intensity find a satisfactory agreement with recent calculations using first principles perturbation theory.

Epitaxial Si-Ge etch stop layers with ethylene diamine pyrocatechol for bonded and etchback silicon-on-lnsulator

The etch rate in ethylene diamine pyrocatechol of Si1-xGe1-x (0.2 ≤ x< - 0.3) etch stops grown by molecular beam epitaxy was determined using Rutherford backscattering spectrometry. Etch rate selectivities as high as 390 were measured. Such etch stops allow for higher bonding temperatures than those possible with currently used boron-based etch stops. Defect etching was used to determine the maximal thickness of dislocation-free layers.

Etch defects in YBa 2Cu 3O 7−δ single crystals grown from flux

The crystallographic defects in (001), (100)/(010) and (011) faces of YBa 2Cu 3O 7−δ (YBCO) single crystals, revealed by chemical etching with acetic acid, as well as mixed solutions of acetic acid, nitric acid and methanol, have been studied. We have found clear evidence for growth hillocks and steps on these etched faces. Three types of etch pits are observed: Type I is a square pyramid with growth steps along the 〈100〉 and 〈010〉 directions; type II is an octagonal pattern of the above square truncated along the 〈110〉 direction; and type III is a shallow ellipse with long and short axes in the 〈100〉/〈010〉 and 〈001〉 direction, respectively. Due to their spiral growth features types I and II are designated screw dislocation etch pits and type III is thought to be of Hopper-like morphology, on the basis of the growth mechnism. Clustering and tangling of dislocation etch pits have also been observed. The etching rate is anisotropic with different speeds in the four principal directions being V a〈110〉> V a〈100〉/〈010〉> V c〈001〉> V i〈111〉. The density of the dislocation etch pits is of the order of 10 6 cm −2 (001) and 10 5 cm −2 in the (100)/(010) surfaces.

Hg 0.8Cd 0.2Te grown by liquid phase epitaxy using Cd 0.94Zn 0.06Te buffer layer

Buffered structures of Hg 0.8Cd 0.2Te/Cd 0.94Zn 0.06Te/Cd 0.97Zn 0.03Te were grown by a slider LPE technique and their material properties were compared with those of Hg 0.8Cd 0.2Te/Cd 0.97Zn 0.03Te structures which have no buffer layer. Photoluminescence spectroscopy (PL) was used to determine the compositions of the buffer layers and the substrates and analyse the impurities in the buffer layers. Auger electron spectroscopy (AES) was used to analyse impurities. Either sodium or lithium related donor-acceptor pair (DAP) peaks were observed in the substrate, but not in the Cd 0.94Zn 0.06Te buffer layer. AES analysis revealed that the substrate contained some impurities such as Si, Al, O, K, Fe, and Mg. In the Cd 0.94Zn 0.06Te buffer layer, the above impurities were not detected. The distribution of dislocations in the epi-layers were analysed by defect etching as well as double crystal X-ray diffraction. For the buffered structure, most misfit etch-pits were located just above the interface between the Hg 0.8Cd 0.2Te and Cd 0.94Zn 0.06Te buffer, and their density was much lower than that in the unbuffered structure, in which etch-pits were distributed rather broadly in the epi-layer. Electrical properties of the Hg 0.8Cd 0.2Te epi-layers, which were Hg-annealed at 250°C, were analysed by Hall measurement at 77 K. The buffered structure showed the carrier concentrations of 7 × 10 13 to 1 × 10 14 cm -3 and Hall mobilities of 2 to 5 × 10 5 cm 2/V · s.

Crystallographic defect studies in SIMOX material thinned by sacrificial oxidation

Crystallographic defects present in thermal oxidised SIMOX materials have been studied by means of plan view transmission electron microscopy (TEM) and chemical defect etching. It is observed that the presence of small stacking fault tetrahedra near the top Si/SiO 2 interface influence the formation of oxidation induced stacking faults (OISF). An explanation for this behaviour is given based on the assumption that these small Crystallographic defects contribute to the recombination of silicon interstitials emitted during thermal oxidation.

Dislocation Distributions in Cd1-xHgxTe/CdTe and Cd1-xHgxTe/Cd1-yZnyTe Grown by Liquid Phase Epitaxy

Epilayers of LPE Cdo.24Hgo.76Te grown on (111)B CdTe and Cdi-xZnxTe substrates have been examined by defect etching and triple axis x-ray diffraction. Defect etching of bevelled layers has shown the threading dislocation density to fall with increasing distance from the heterointerface, for distances &lt;6μm. In thicker regions however a constant ‘background’ dislocation density is observed. Background dislocation densities of ∼ 3 x 105cm-2 and 9 x 104cm-2 have been measured for layers grown on CdTe and Cdo.96Zn0.04Te respectively, this is compared with a substrate dislocation density of ∼ 3 x 104cm-2 measured in both types of substrates. The increase in the dislocation density within the epilayers compared with the corresponding substrate is discussed. An explanation is also given for the displacement of the peak dislocation density, from the interface to within the layer, observed in the Cd0.76Hg0.24Te / Cd0.96Zn0.04Te system.

The Effects of Process‐Induced Defects on the Chemical Selectivity of Highly Doped Boron Etch Stops in Silicon

Chemical etch selectivity using and water was determined for solid‐source diffused, ion implanted, and in situ, epitaxially‐grown boron‐doped etch stops formed in single‐crystal, polycrystalline, and low‐percentage germanium‐alloyed silicon. Defects in the etch stops were investigated using defect etching and Nomarski optical interference microscopy, scanning electron microscopy with energy dispersive x‐ray, and transmission electron microscopy. Defect density and type were found for all samples. Experimental results show that etch selectivity is not only a function of boron concentration but is also a function of the defect density, and to a lesser degree, defect type. Etch selectivity degrades approximately proportional to a one‐fourth power relationship with defect density.

Thin film photodetectors grown epitaxially on silicon

Abstract Epitaxial germanium films of thickness d≈4 μ m , grown on silicon (001) by a low-temperature MBE process, constituted the base material of a silicon-integrated infrared detector. Characterization of the fully relaxed films was performed mainly by ex situ techniques, such as X-ray diffraction, Rutherford backscattering spectrometry and channeling, room temperature Hall effect and defect etching. Mesa diodes, fabricated from the originally p-type Ge films after pn-junction formation by thermal diffusion of antimony (Sb), showed quantum yields above 40% at wavelengths between 1200 nm and 1500 nm without an antireflection coating. The rise time of the photodiode signal in response to a picosecond laser pulse ( τ = 300 ps ) at wavelength of 1300 nm was 530 ps. Forward current-voltage characteristics of the devices were described by an ideality factor n = 1.25 , while excess current under reverse bias was attributed to leakage caused by threading dislocations in the active layers.

A photoluminescence study of CF4 reactive-ion-etched silicon: Various process conditions and magnetically enhanced etching

The impact of reactive-ion-etching (RIE) on the near-surface crystal quality of Czochralski silicon has been studied by photoluminescence spectroscopy. The presence of carbon-related defects is investigated as a function of the pressure during CF4 RIE. The effects of adding hydrogen to the plasma as well as the time of treatment are studied and discussed in terms of defect formation and etch rate. Photoluminescence spectra of samples recorded after a magnetically enhanced reactive-ion-etching process are also presented. The introduction of defects depending on the self-bias voltage and the etch rate are investigated for different magnetic fields.

ChemInform Abstract: Novel Approach to Defect Etching in Thin Film Silicon‐on‐Insulator.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Chemical equilibration of plasma-deposited amorphous silicon with thermally generated atomic hydrogen.

Hydrogenated amorphous silicon (a-Si:H) thin films prepared by plasma-enhanced chemical vapor deposition (PECVD) from ${\mathrm{SiH}}_{4}$ have been further hydrogenated in situ by exposure to atomic H generated by a filament heated in ${\mathrm{H}}_{2}$ gas. Upon equilibration of the network with gas-phase H, as many as \ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}${10}^{21}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ additional Si-H bonds form within the top 200 \AA{} of the film without significant etching, surface roughening, or coordination defect generation. Real-time spectroscopic ellipsometry is applied to study the kinetics of near-surface Si-H bond formation at 250 \ifmmode^\circ\else\textdegree\fi{}C in order to improve our understanding of the effects of excess atomic H in the a-Si:H growth environment. Atomic H entering the film surface exhibits an effective diffusion coefficient &gt;3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}15}$ ${\mathrm{cm}}^{2}$/s and is trapped within the top 200 \AA{} of the film at a rate of \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. Most of this H is trapped irreversibly on the time scale of deposition with emission rates 2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. We also find that monolayer levels of surface oxide are an effective diffusion barrier to H, preventing chemical equilibration between the gas and solid phases.