Etch Hillocks Research Articles

Dissolution of diamond crystals in a heterogeneous (metal–sulfide–silicate) medium at 4 GPa and 1400 °C

As a result of artificial dissolution of diamonds at 4 GPa and 1400 °C in a heterogeneous solvent (Fe–S melt with the addition of natural kimberlite in an amount of 5 wt%), it is established that, in the dissolution process the diamond crystals of octahedron form with flat faces and sharp edges are transformed into rounded octahedroids. The role of silicate additives is to local screen the surface of diamonds with the formation of etch hillocks, which gives crystals a visually complex external morphology. Thus morphologically complex natural diamonds with irregular shapes may form by dissolution by heterogeneous solvents in the mantle. Metal–sulfide–silicate melts consisting of immiscible components with different carbon solubility are the most likely candidates for such solvents.

Silicon wet etching: Hillock formation mechanisms and dynamic scaling properties

Surface roughening due to anisotropic wet etching of silicon was studied experimentally and modeled using the Monte Carlo method. Simulations were used to determine the consequences of site-dependent detachment probabilities on surface morphology for a one- and two-dimensional substrate models, focusing on the formation mechanisms of etch hillocks. Dynamic scaling properties of the 1D model were also studied. Resorting to the height–height correlation function and the structure factor, it is shown that the model presents conventional and anomalous scaling (faceted) depending on the stability of the hillocks tops. We also found that there is an intermediate regime that cannot be described by the Family–Vicsek or anomalous scaling ansatz.

市川新松と市川鉱物研究室

Mr. Shinmatsu Ichikawa was a prominent mineralogist, although he was an ordinary citizen and not in government service. He lived from the late Meiji Period to the early Showa Period. He taught in elementary school and teacher training school despite not having a regular university education. He was self-taught in mineralogy and foreign language, and became a pioneer in the field of crystal morphology. His contributions include observations of the etched surfaces of natural minerals and of artificial etched quartz crystals and quartz spheres. He observed the etch pits, etch hillocks, growth hillocks and striations on the surfaces of several minerals found in Japan, engraved their positions, shapes and distributions on metal plates, and discussed his observations. He built the Ichikawa Mineral Laboratory in his house in 1918 to store his collection of minerals, rocks and fossils (more than 7000 specimens in all). His collection includes big quartz crystals twinned after Japan law from the Otome mine, twisted quartz from the Naegi region, amethyst crystals from Mt. Ametsuka and the Yusenji mine, natural etched minerals from various parts of Japan, and many minerals from the North America. The Laboratory is a historic cultural site in his hometown. Its preservation and enlightenment activities are cooperatively carried out by the local government and a neighborhood self-governing body.

Implications of alkaline solutions-induced etching on optical and minority carrier lifetime features of monocrystalline silicon

In this work, we search to optimize the surface textures of monocrystalline silicon (c-Si) intended to be used in silicon solar cells. For this purpose, we studied the morphology of formed etch hillocks during anisotropic etching of silicon using alkaline solutions based on sodium hydroxide (NaOH), potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH). Such treatments lead to the formation of various pyramids-like textures that can be well optimized to improve the photocurrent of c-Si-based solar cells. The produced textures were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–visible optical reflectivity and minority carrier lifetime measurements. These investigations allow evaluating the size and density of the formed pyramidal textures; the apex angles vary between 75° and 82°, while the heights and bases of the pyramids range from a few hundred nanometers to several micrometers. A minimum reflectivity value of about 6% was obtained at specific conditions using NaOH, whereas it was found that the apparent effective minority carrier lifetime (τeff) is sensitive to the injection level (Δn), which shows an apparent increase from 1.2μs to 2.4μs for a minority carrier density of about Δn=21014cm−3.

Characterization of directed ammonium malate single crystals grown by Sankaranarayanan–Ramasamy method

Ammonium malate, an organic nonlinear optical single crystal, has been grown to a dimension of 50 mm length and 20 mm diameter by uniaxial solution-crystallization method of Sankaranarayanan–Ramasamy (SR). The growth conditions and experimental details of the grown crystals have been presented. The crystalline perfection of the grown crystals has been evaluated by high-resolution X-ray diffraction technique and the results reveal that the crystal quality of SR grown crystal is better than the conventional method grown crystal. The growth features in SR grown crystal have been analyzed by chemical etching technique and well-defined triangular etch hillocks have been observed. The mechanical property of the grown crystal has been analyzed by Vickers microhardness method and it reveals that the grown crystal is moderately harder material. Ammonium malate crystal possesses lower cut off wavelength at 230 nm. It enables good optical transmission of the second harmonic generation of Nd:YAG laser and other applications in the blue-violet region. The second harmonic generation of the grown crystal has been confirmed by the Kurtz powder technique.

Influence of interface formation on the structural quality of AlN single crystals grown by sublimation method

AbstractAlN single crystals with 25 mm diameter and 3 mm thickness were grown on on‐axis, Si‐terminated, (001) 6H‐SiC substrates with a growth rate of 20‐25 μm/h by the sublimation method. The growth conditions were optimised and the grown crystals exhibit good crystalline quality as analysed by double‐crystal x‐ray diffraction measurements. The FWHM value of the rocking curves in ω‐scan is about 100 arcsec for 3 mm thick crystals. The kind of AlN/SiC interface formation influences the structural quality of the grown crystals by forming low‐angle grain boundaries. Optical and scanning electron microscopic analyses performed on cross‐cut samples demonstrate the existence of an array of hillocks and voids between them at the bottom of the grown AlN layer. These hillocks are confirmed by electron probe micro analysis as SiC etch hillocks and their origin was investigated. The possible mechanism for the formation of low‐angle grain boundaries is discussed and a simple physical model is proposed. Optimisation of the growth conditions was carried out in order to obtain crystals with low silicon carbide incorporation. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Origin of Etch Hillocks Formed on On-Axis SiC(0001) Surfaces by Molten KOH Etching

Molten KOH etching of 6H- and 4H-SiC0001 on-axis substrates was investigated. After molten KOH etching, etch pits originating from threading dislocations (TDs) and basal-plane dislocations (BPDs) were observed on (0001) surfaces. On the other hand, large and small hillocks were observed on (0001) surfaces. The etch hillocks consist of SiC, indicating slower etching at TDs. By comparing the (0001) side and (0001) side of the same substrate, it was found that large hillocks correspond to edge-type TDs, while small hillocks correspond to screw-type TDs.

Origin of Etch Hillocks Formed on On-Axis SiC(0001) Surfaces by Molten KOH Etching

Origin of Etch Hillocks Formed on On-Axis SiC(0001) Surfaces by Molten KOH Etching

Growth and Etching Studies of MgO-Doped LiNbO<sub>3</sub> Single Crystal

LiNbO3 (Mg:LN) crystal is an important electro-optical material and MgO-doped LiNbO3 was expected to improve its optical damage resistance. In the present work, we reported the Bridgman growth of MgO-doped LiNbO3 crystal. The growth parameters were discussed and the defects were investigated by the chemical etching method. The etch hillocks and etch pits were observed on the negative Z surface while only etch pits on the positive Z surface by the optical microscope and EPMA. The etching morphology was discussed considering the domain structure.

Basic mechanisms for hillock formation during etching

The formation of etch hillocks was explored in the framework of a site-dependent detachment probabilities model. Monte Carlo simulations were carried out for a one-dimensional substrate within a restricted solid-on-solid model in which only first neighbour interactions are considered. We specifically focus on describing the dynamics that lead to hillock-and-valley patterns. The mechanisms responsible for the steady state morphologies were related to apex creation and annihilation, together with valley and hillock etching, but pattern formation reflects two feedback loops that interrelate these mechanisms.

Dynamics of hillocks formation during wet etching

Etch hillocks formation was studied experimentally and modeled using the Monte Carlo method. Simulations were used to explore the consequences of site-dependent detachment probabilities on surface morphology for a one- and two-dimensional substrate models. Comparison with pyramidal etch hillocks that are regularly observed in anisotropic etching of Si(1 0 0) are presented. The steady-state morphologies are analyzed and the hillock size distributions determined. The mechanisms responsible for the steady-state morphologies are described.

Production of Highly Homogeneous Si(100) Surfaces by H2O Etching: Surface Morphology and the Role of Strain

The etching of Si(100) surfaces in ultrapure water was studied with a combination of infrared spectroscopy (FTIR) and scanning tunneling microscopy (STM). While the FTIR results show that the initially rough H/Si(100) surface becomes highly homogeneous during etching, a phenomenon generally associated with surface smoothing, STM images reveal that the homogeneity is associated with the formation of well-defined etch hillocks. After many hours of etching, the resulting H-terminated surface is composed of stripes of atomically flat Si(100) terminated by etch hillocks bounded by {111}- and {110}-oriented microfacets. Polarization analysis of the Si-H stretching modes provides strong evidence for uniform dihydride-termination of the flat regions, with the narrow (approximately 25 A) width of these stripes allowing for relaxation of steric strain between neighboring dihydrides. The unusual hill-and-valley etch morphology is attributed to the effects of steric strain on the reactivity of sites on the etched surface.

Wet Etching of Bulk AlN Crystals

ABSTRACTAlN bulk crystals of different crystallographic orientations were etched in aqueous KOH solution (general etchant) and molten KOH/NaOH eutectic alloy (defect selective etchant). In the general etchant, the aluminum polar surface (0001) was found to be stable while the nitrogen polar (0001) surface and non-polar m-plane (1010) surfaces showed significant etching. Etch patterns on nitrogen polar surfaces consisted of complete coverage of hexagonal pyramids while the m-plane surfaces were etched in a layer-by-layer mode. TEM studies revealed that the observed etch hillocks on nitrogen polar surfaces were not associated with extended structural defects. When etched in a defect-selective etchant, the aluminum polar surface showed well-defined hexagonal etch pits, with an etch pit density (EPD) of 2×104 cm−2. The nitrogen polar surfaces and m-plane surfaces showed etch features similar to the one obtained during general etching, however, the etch feature density was significantly lower. The etch mechanisms, etch kinetics, as well as the correlation between the observed etch features and structural defects in bulk crystals will be discussed.

Formation of pyramidal etch hillocks in a Kossel crystal

Surface roughening due to anisotropic etching was studied experimentally and modeled using the Monte Carlo method for a Kossel crystal. Simulations were used to explore a possible formation mechanism for the appearance of etch hillocks in two and three dimensions. Similarities with pyramidal etch hillocks that are regularly observed in anisotropic etching of Si(1 0 0) are discussed.

Development of Silicon Micro Multi-edged Tool Using Anisotropic Etching (1st Report)

This paper proposes a micro multi-edged tool made of silicon as a new tool in the micro/nano-cutting and the decision system of fabricating conditions to the tool. This new tool is expected to machine a softer material, like aluminum alloy, glass and so on, than iron because silicon is as hard as alloy tool steel and high speed tool steel. On this new tool, the pyramidal etch hillocks on Si(100) surfaces etched in aqueous KOH solution function as cutting edges because the shape and distribution of the hillocks are resemble to those of the cutting edges on grinding wheel surfaces. The multi-edged tool can be fabricated at the desire of user by only adjusting the etching conditions suitably because the topography of hillocks depends on them. Therefore, we have developed the decision system of the etching conditions corresponding to a specified tool. In this system, the genetic algorithms and the neural network model are applied and the suitable etching conditions; - temperature, concentration and time - are output corresponding to the inputs of average height and number of the hillocks. In this paper, the system is proved fit for practical use as the result of experiments.

Etch rates and morphology of silicon ( h k l) surfaces etched in KOH and KOH saturated with isopropanol solutions

Silicon wafers with (1 1 0), (3 3 1), (3 1 1) and (2 1 1) crystallographic orientations etched in KOH and KOH saturated with isopropyl alcohol solutions have been studied. Etch rates of selected ( h k l ) planes were estimated by direct etch depth measurements. The effects of IPA additive on etch rates, hillocks formation and surface roughness of considered planes were analysed. It was shown that IPA affects the planes of ( h h l )-type, causing both their etch rate reduction and surface quality improvement. IPA addition to KOH solution does not reduce etch rates of ( h l l )-type planes but results in bulky hillocks formation on the whole etched area. The type of IPA interaction with different crystallographic planes probably depends on bond configuration on a particular plane.

Characterization of GaN single crystals by defect‐selective etching

In this communication it is shown that both “orthodox” etching in molten KOH–NaOH eutectic (E etch and its modification) and photo-etching in aqueous KOH solution (PEC method) permit quick assessment of density, distribution and, after appropriate calibration, type of defects in GaN single crystals and epitaxial layers. Characteristic features of both etching methods are briefly discussed. It is shown that dislocations and micro-defects can be revealed in the form of etch pits (in “orthodox” E etch) and as etch hillocks (PEC method) on both Ga- and N-polar surfaces. The reliability of both methods has been confirmed by direct TEM calibration and by using indentation method. Very low dislocation density (EPD ≤ 2 × 102 cm–2) in the undoped GaN single crystals and MOCVD-grown epitaxial layers has been confirmed by this study.

An AFM study of the processing of hydrogen passivated silicon(1 1 1) of a low miscut angle

We present atomic force microscopy (AFM) measurements from a passivated silicon crystal miscut by 0.1° and show the etching regime to be significantly different from surfaces with a larger miscut angle. A simple kinetic model is developed to explain the results and is used to derive the optimal etching conditions for nominally flat Si(1 1 1)–(1×1)H. We show that small changes in miscut angle can alter the kinetic steady state and promote the formation of deep etch pits, even on the least stable, 〈 1 ̄ 1 ̄ 2〉 miscut surface. Collisions of steps with these pits result in arrays of stable, self-aligned `etch hillocks' over micron dimensions. Following preparation, we use AFM to observe the initial growth of native oxide on the Si(1 1 1)–(1×1)H surface, and demonstrate that AFM is a sensitive probe to surface oxidation in the sub-monolayer regime.

Formation and stabilization of pyramidal etch hillocks on silicon {100} in anisotropic etchants: Experiments and Monte Carlo simulation

On Si{100} surfaces etched in anisotropic etchants such as aqueous solutions KOH and TMAH, pyramidal etch hillocks are frequently found. Besides these hillocks, we have investigated hillocks that have partially disappeared using scanning electron microscopy (SEM). During re-etching numerous additional pyramidal etch hillocks are formed on the exact spots where SEM pictures were made earlier. These observations suggest that semipermeable particles adhering to the surface are responsible for the development of the pyramidal etch hillocks. In order to investigate the influence of such nanometer scale particles on the etch rate and the surface morphology, Monte Carlo simulations were performed of etching of Si{100} surfaces on which small semimasks are present. The presence of the microscopic semimasks is shown to cause the formation of macroscopic hillocks, which closely resemble experimentally observed hillocks. Removal of the semimask on top of a hillock leads to a vanishing pyramidal etch hillock. In the Monte Carlo model, however, the etch rate as a function of surface orientation has a maximum for {100}, while in reality {100} corresponds to a local minimum. This implies that for typical experimental conditions an etch hillock should not be stable despite a semipermeable particle on top, because of underetching starting from 〈110〉 ridges of the hillock. This paradox can be resolved by assuming that the ridges act as sinks of tiny particles. This gives a reduction in etch rate of the ridges, next to the top, which is necessary for the hillock to remain stable. The exact nature of these masking particles is unknown, but silicate particles are a likely candidate.

Cross-Sectional Transmission Electron Microscopic Observation of Etch Hillocks and Etch Pits in LiTaO3 Single Crystal

Cross sections of etch hillocks and etch pits in LiTaO3 single crystal have been observed by transmission electron microscopy. The cross-sectional samples were prepared at their exact positions by the focused ion beam microfabrication method. Inverted polarized domains were observed both at the top of etch hillocks and at the bottom of etch pits, indicating that the etching figures originate in the inverted domain formed on the surface. Furthermore, some inverted domains that were pinned by lattice defects were also observed at the inner part of the crystal.