Etching In Hydrofluoric Acid Solution Research Articles

Repairing slight damages on monocrystalline silicon surface by thermal annealing

The damages on silicon substrate, usually caused by machining and polishing processes, inevitably degrade the mechanical and electrical properties of the devices involved. Defect-free silicon substrates are essential with the miniaturization of integrated circuits to tens of nanometers, and repairing the damages is significant for manufacturing excellent devices. In this study, the slight damages, i.e. protrusive hillocks resulting from nanoscratching on monocrystalline silicon surface, was thermally annealed in vacuum for repairing, and groove-shaped scratches were also annealed for comparative study. In-situ topographies of the hillocks before and after the annealing were detected with an atomic force microscope (AFM), and then compared for finding the optimum annealing temperature. It is shown that the protrusive hillocks can be well repaired than the groove-shaped scratches. The repairing with annealing process was further verified by conductive AFM detection and selective etching in hydrofluoric acid solution. Raman spectroscopy detection was employed to clarify the annealing-dependent recovering mechanism of the damages on silicon surface, and it is suggested that structural transformation plays an important role in the repairing. In addition, the annealing of the hillocks on single-crystal quartz surface confirmed the structural recovery rather than the oxidation during annealing.

Erratum to: Effect of Conductivity Type and Doping Level of Silicon Crystals on the Size of Formed Pore Channels during Anodic Etching in Hydrofluoric Acid Solutions

Erratum to: Effect of Conductivity Type and Doping Level of Silicon Crystals on the Size of Formed Pore Channels during Anodic Etching in Hydrofluoric Acid Solutions

A Decisive Role of Si and Ge Energy Levels in the Process of Pore Formation during Electrochemical Etching in Hydrofluoric Acid Solutions

It has been shown that the difference in the structure of electronic orbitals of silicon and germanium atoms is a decisive factor responsible for the formation of porous layers during their electrochemical etching in solutions of hydrofluoric acid.

Effect of Conductivity Type and Doping Level of Silicon Crystals on the Size of Formed Pore Channels during Anodic Etching in Hydrofluoric Acid Solutions

In this paper, we discuss causes of the multidirectional effect of changes in the concentrations of free charge carriers in silicon crystals of p- and n-type conductivity on the transverse dimensions of pores formed as a result of anodic etching in hydrofluoric acid solutions, as well as the effect of anodic current density on pore size. The observed dependences are explained based on the concepts of electrochemical pore formation in semiconductor crystals as self-organizing cooperative processes accompanied by the injection of electrons from the chemical reaction region at the pore advancement front. Differences in the size of pores forming at the same current density in crystals differing in type and concentration of free charge carriers are associated with the effective temperature of the front of the cooperative chemical reaction at the bottom of germinating pores. This temperature, in turn, correlates with the power density of thermal energy released in the near-surface region of the etching crystal, either due to recombination processes for a p-type semiconductor or direct or indirect energy transfer from hot electrons to lattice vibrations in the case of a n-type semiconductor. The characteristic relaxation times of injected nonequilibrium electrons were calculated depending on the concentrations of the majority charge carriers in silicon crystals of both types of conductivity and the corresponding thicknesses of the regions of relaxation energy release. The revealed patterns of concentration changes in the power density of heat release in the near-frontal region of etching silicon crystals of p- and n-type conductivity are in good agreement with observed changes in the size of germinating pores.

Влияние типа проводимости и уровня легирования кристаллов кремния на размеры каналов пор, формирующихся в них при анодном травлении в растворах плавиковой кислоты

AbstractIn this paper, we discuss causes of the multidirectional effect of changes in the concentrations of free charge carriers in silicon crystals of p - and n -type conductivity on the transverse dimensions of pores formed as a result of anodic etching in hydrofluoric acid solutions, as well as the effect of anodic current density on pore size. The observed dependences are explained based on the concepts of electrochemical pore formation in semiconductor crystals as self-organizing cooperative processes accompanied by the injection of electrons from the chemical reaction region at the pore advancement front. Differences in the size of pores forming at the same current density in crystals differing in type and concentration of free charge carriers are associated with the effective temperature of the front of the cooperative chemical reaction at the bottom of germinating pores. This temperature, in turn, correlates with the power density of thermal energy released in the near-surface region of the etching crystal, either due to recombination processes for a p -type semiconductor or direct or indirect energy transfer from hot electrons to lattice vibrations in the case of a n -type semiconductor. The characteristic relaxation times of injected nonequilibrium electrons were calculated depending on the concentrations of the majority charge carriers in silicon crystals of both types of conductivity and the corresponding thicknesses of the regions of relaxation energy release. The revealed patterns of concentration changes in the power density of heat release in the near-frontal region of etching silicon crystals of p - and n -type conductivity are in good agreement with observed changes in the size of germinating pores.

Influence of the Crystallographic Orientation of a Substrate on the Nucleation, Shape, and Evolution of Silicon Pores during its Electrochemical Etching in Hydrofluoric-Acid Solutions

It is established that the crystallographic orientation of a single-crystal silicon substrate affects the nucleation, shape, and evolution of silicon pores during its electrochemical etching. The shape, spatial orientation, and initiation of silicon pores is demonstrated to depend on both the etchant-solution properties caused by an etching-ion structure and the Si lattice symmetry.

EFFECT OF ETCHING AS PRE-TREATMENT FOR ELECTROLESS COPPER PLATING ON SILICON WAFER

Metallic coatings, such as copper films can be easily deposited on semiconductor materials like silicon wafer without prior surface pre-treatment using the electroless process. However, the adhesion of the copper film can be very weak and can easily peels off. In this study, the effect of etching in hydrofluoric acid solution as a surface pre-treatment prior to electroless plating on silicon wafer was studied. The etching time in hydrofluoric acid was varied at 1, 3 and 5 minutes in order to investigate the adhesion behaviour of the coating layer. The surface morphology of the electroless plated samples was observed using a field emission scanning electron microscope (FESEM) and the coating thickness was measured using cross sectional analysis. The results showed that longer etching time (5 minutes) produced thicker Cu deposits (8.5μm) than 1 minute etching time (5μm). In addition, by increasing the etching time, the mechanical bonding between the copper film and the substrate is improved.

Control of Sidewall Profile in Dry Plasma Etching of Polyimide

Spin-on polyimide is an organic thin film often used as a sacrificial layer for surface micromachining due to its high thermal stability, ease of removal, and compatibility with many materials and processes used in the realization of microelectromechanical systems (MEMS). The incorporation of sloped sidewalls in polyimide for fabricating pedestal structures is crucial in order to provide strong anchors in free-standing MEMS devices, especially in cases having a high aspect ratio and/or where structural materials have limited deposition conformality. This paper demonstrates a reliable reactive ion etching (RIE) methodology for tuning the polyimide sidewall angle, ranging from a vertical sidewall up to an angle of about 25° from the vertical. The key modifications to the process parameter space include changes to the process temperature and chamber pressure. This paper also presents a novel lift-off process, which is based on the use of an interfacial polymer layer to facilitate removal of an overlying silicon oxide hard mask. This procedure allows polyimide sacrificial layers employing a silicon oxide hard mask to be used on samples that have exposed silicon oxide layers elsewhere on the chip that are required to remain intact during hard mask removal. Therefore, this lift-off process is applicable in situations where the silicon oxide hard mask removal cannot be accomplished by wet etching in hydrofluoric acid solutions.

Morphology of pores produced in n-Si {100} by etching in hydrofluoric acid solutions

Variations in the contours of pores produced in n-type silicon by electrochemical etching in hydrofluoric acid solutions are interpreted in terms of the mechanism underlying the chemical interaction of the etchant with silicon and the anisotropy of the etchant–silicon system. Mathematical expressions are proposed which describe the contours and limiting radial sizes of pores forming at the very beginning of the etching process (~10–15 s).

A model of the mechanism of the chemical interaction of the etchant ion (HF2)– with silicon during its electrochemical etching in hydrofluoric acid solutions

A model was proposed for the mechanism of the chemical interaction of the etchant ion (HF2)– with silicon during its electrochemical etching, which explains the possibility of porous silicon etching in the dark and the formation of hydride and hydroxyl groups on the silicon surface.

The role of the etchant ion in the formation and growth of pores in silicon during its etching in hydrofluoric acid solutions

The role of the etchant ion (HF2)– in the formation of pores in silicon during its etching in hydrofluoric acid solutions has been elucidated. The pore shape, size, and orientation in (100) and (111) silicon substrates have been explained by specific features of the etchant ion (HF2)–.

The effect of the hydrofluoric acid etchant–silicon system anisotropy on the shape of pores formed upon electrochemical etching of silicon

The shape of nanopores formed in silicon upon electrochemical etching in hydrofluoric acid solutions has been explained by the effect of anisotropy of the components involved in etching. A semiempirical formula that allows one to characterize, with a certain accuracy, the degree of anisotropy of the etchant–silicon system and describe the shape of the resulting pores has been suggested.

Nanopore formation during electrolytic etching of silicon in hydrofluoric acid solutions

A stepwise scheme has been proposed for gaining insight into the nanopore formation process in silicon during electrolytic etching in hydrofluoric acid solutions. We have studied the influence of the concentration and nature of dopants (phosphorus, arsenic, and antimony) in silicon, current density, electric field strength, and etching time on the axial and radial pore sizes and the pore distribution density. The dopants have been shown to play a predominant role in the nanopore formation process. The shape and spatial orientation of nanopores in Si substrates with the (100) and (111) crystallographic orientations have been interpreted in terms of specific features of the electrochemical etching of silicon in hydrofluoric acid solutions, related to the action of the etching ion (HF2)−. The observed discrepancy between the experimentally determined and calculated radial nanopore sizes has been accounted for by the low probability ( 6.25%) of simultaneous interaction of the fluorine atoms of an (HF2)− ion with the corresponding silicon atoms located at vertices of a cube of the crystal lattice.

Control of the dimension of nanopores and the structure of layers of nanoporous silicon during its electrolytic etching in hydrofluoric acid solutions

Control of the dimension of nanopores and the structure of layers of nanoporous silicon during its electrolytic etching in hydrofluoric acid solutions

In situ preparation and characterization of polyimide/silica composite hemispheres by inverse aqueous emulsion technique and sol-gel method

In this paper, micron-scale polyimide/nano-silica (PI/nano-SiO2) composite hemispheres were fabricated by employing inverse aqueous emulsion technique and sol-gel method. Homogeneous inverse emulsion was obtained through using the precursor solution as dispersed phase which contained poly(amic acid) ammonium salt (PAAS), tetraethyl orthosilicate (TEOS) and deionized water, liquid paraffin (LP) as continuous phase, and Span80 as surfactant. The PI/SiO2 hybrid hemispheres could be got by adding excess dehydrating agent into the emulsion. The Fourier transform infrared (FT-IR) results demonstrated that PAAS had been converted to polyimide (PI) after adding the dehydrating agent into the emulsion and that the success of the reaction between TEOS molecules. The research showed that the morphologies of PI/SiO2 hybrid hemispheres, compared with the pure PI hemispheres, were still hemispherical and did not change with the varied silica contents. The surfaces of these samples were without clear interface between the SiO2 particles and the polymer matrix. And, the SEM images of the hybrid hemispheres after hydrofluoric acid (HF) etching or high temperature calcination showed that the SiO2 particles were well dispersed in the organic component, and the diameter of silica particles was nano-scale. The EDX results of the spheres which were after etching in hydrofluoric acid solution or after calcination showed that some 99.98 % of the silica particles were removed and the success of the removal of the organic component, respectively. Furthermore, thermal gravimetric analysis (TGA) results showed that the thermal stability of PI hemispheres could be improved by incorporating the inorganic component.

Optical properties of silicon nanowire arrays formed by metal-assisted chemical etching: evidences for light localization effect

We study the structure and optical properties of arrays of silicon nanowires (SiNWs) with a mean diameter of approximately 100 nm and length of about 1–25 μm formed on crystalline silicon (c-Si) substrates by using metal-assisted chemical etching in hydrofluoric acid solutions. In the middle infrared spectral region, the reflectance and transmittance of the formed SiNW arrays can be described in the framework of an effective medium with the effective refractive index of about 1.3 (porosity, approximately 75%), while a strong light scattering for wavelength of 0.3 ÷ 1 μm results in a decrease of the total reflectance of 1%-5%, which cannot be described in the effective medium approximation. The Raman scattering intensity under excitation at approximately 1 μm increases strongly in the sample with SiNWs in comparison with that in c-Si substrate. This effect is related to an increase of the light-matter interaction time due to the strong scattering of the excitation light in SiNW array. The prepared SiNWs are discussed as a kind of ‘black silicon’, which can be formed in a large scale and can be used for photonic applications as well as in molecular sensing.

Efficient visible luminescence of nanocrystalline silicon prepared from amorphous silicon films by thermal annealing and stain etching

Films of nanocrystalline silicon (nc-Si) were prepared from hydrogenated amorphous silicon (a-Si:H) by using rapid thermal annealing. The formed nc-Si films were subjected to stain etching in hydrofluoric acid solutions in order to passivate surfaces of nc-Si. The optical reflectance spectroscopy revealed the nc-Si formation as well as the high optical quality of the formed films. The Raman scattering spectroscopy was used to estimate the mean size and volume fraction of nc-Si in the annealed films, which were about 4 to 8 nm and 44 to 90%, respectively, depending on the annealing regime. In contrast to as-deposited a-Si:H films, the nc-Si films after stain etching exhibited efficient photoluminescence in the spectral range of 600 to 950 nm at room temperature. The photoluminescence intensity and lifetimes of the stain etched nc-Si films were similar to those for conventional porous Si formed by electrochemical etching. The obtained results indicate new possibilities to prepare luminescent thin films for Si-based optoelectronics.

Influence of Glass Coating Thickness on Magnetoimpedance Ratio in Co-Based Amorphous Microwires

The effect of glass coating thickness on the magnetoimpedance in Co-based amorphous microwires was studied. The microwires with different thickness of the glass layer were obtained by means of etching in hydrofluoric acid solution. It was observed that the value of the external mag¬netic field corresponding to the maximum of the impedance decreased with the thickness of the glass layer, whereas the magnetoimpedance ratio did not change significantly. The experimental results are interpreted in terms of changes in the radial distribution of the easy magnetization axes.

Self-organized and high-density filamentous nanodomain patterns fabricated in lithium niobate by discharge poling

We report on spontaneous formation of nanoscale surface domains obtained in lithium niobate substrates by electric field discharge poling. A constant high voltage was applied at room temperature to virgin and unpatterned crystals in air, by using metal tip-shaped electrodes. An enhancement of the electric field in correspondence of the electrode tips was expected due to the fringing field effect, and electric discharge was observed during the process. The standard wet etching in hydrofluoric acid solution revealed the formation of nanoscale domain structures that exhibit filamentous self-organized geometries. Topographic measurements of the fabricated structures were performed by an atomic force microscope, and the corresponding results are presented and discussed. The investigation provides remarkable information about the shortest domain size possibly obtainable by electric field poling.

Structural property of nanoporous silicon: evidence of near ultraviolet photoluminescence

The structure of porous Si samples prepared by conventional photoexcited electrochemical etching in hydrofluoric acid solution is presented. Strain enhanced cracking was evidenced at the surface of the sample, which was synthesized at higher incidence angle of light. Combined modes of carbon-fluorine and/or oxygen related impurities, and silicon-oxides are revealed from Fourier transform infrared investigation. A resonant feature at ∼467 nm, originating from a strong coupling of localized excitons at the Si/SiO2 interfacial states and Si–O vibrational modes, is examined during photoluminescence measurements for an excitation wavelength of 320 nm. Furthermore, the appearance of luminescence bands in the range 378–412 nm is discussed in the light of a quantum confinement assisted radiative recombination of electrons and holes at impurity related defects or at the vacancies of neutral oxygen.