Laser-induced Etching Process Research Articles

Dynamic correction of optical aberrations for height-independent selective laser induced etching processing strategies.

Optical aberrations are a critical issue for tight focusing and high precision manufacturing with ultrashort pulsed laser radiation in transparent media. Controlling the wave front of ultrashort laser pulses enable the correction of low order phase front distortion and significantly enhances the simplification of laser-based manufacturing of 3D-parts in glass. The influence of system-inherent, dominating aberrations such as spherical and astigmatic aberrations affect the focal area, the beam caustic and therefore the focus intensity distribution. We correct these aberrations by means of a spatial light modulator (SLM) for various processing depths in glass thickness of up to 12 mm. This flexible aberration correction significantly simplifies the process control and scanning strategies for the selective laser induced etching process. The influence on the selectivity is investigated by comparing the three different focus conditions of the intrinsic microscope objective aberration corrected, the aberrated and the SLM aberration corrected beam profile. The previously necessary pulse energy adjustment for different z positions in the glass volume is compensated via SLM aberration correction in the end. Furthermore, the spatial extend of the modified and etched area is investigated. In consequence, a simplified scan strategy and depth-independent processing parameters can be achieved for the selective laser induced etching process.

Improvement Silicon Nanostructured Surface by Laser Induced Etching Process

Surface reconstruction of silicon using lasers could be utilized to produce silicon nanostructures of various features. Electrochemical and photoelectrochemical etching processes of silicon were employed to synthesize nanostructured surface. Effects of current densities 5, 10 and 20 mA/cm2 on the surface features were examined. It is found that the surface porosity and layer thickness increase with the current density. Moreover, large surface area of 410 m2/cm3 can be achieved when laser power density 0f 0.6 W/cm2 was used during the etching process. Optimum operating conditions were found to achieve better silicon nanostructured surface features. The surface roughness can be reduced to 8.3 nm using laser beam of 650 nm irradiated the silicon surface during the photoelectrochemical etching process. The surface morphology of the nanostructured silicon surface using SEM and AFM could give rich details about the surface. Silver nanoparticles of 10 – 20 nm was embedded at the nanostructured silicon surface by LIFT process to reduce the surface resistance and maintain the large surface area. This technique enables silicon nanostructures to be efficiently used in many optoelectronic applications.

Zero-dead-volume interfaces for two-dimensional electrophoretic separations.

We present the study on the sample transfer characteristics of two different microfluidic interfaces for 2D-CE . These interfaces were manufactured using two different microfabrication technologies: one was obtained via the classical photolithography-wet etching-anodic-bonding process; and the other was obtained via the selective laser-induced etching process. The comparison of the two interfaces, and an intact capillary as a reference, was made via the CE separation of amino acids (arginine and lysine) under different bulk flow conditions, with and without applying bias potential to the secondary channels. The influence on peak shapes, migration times, and repeatabiliy were evaluated.

New Optical Properties of Porosity Layer Controlled by Laser-Induced Etching

Three different power densities and fixed irradiation times have been used to prepare porous silicon using laserinduced etching process to control the size and shape of nanostructure. There are new optical properties of porous silicon. Scanning electron microscopy was used to study surface morphology after the etching process. Porous silicon was characterized using spectroscopic studies. There is shift in Raman peak position as a result of the increase of power densities. The photoluminescence spectra (PL) tend to blue shift in peak position due to etching conditions. Raman and PL data were explained using appropriate dimensional confinement of size and size distributions of nanocrystallites. There has been an agreement between the results of Raman and PL spectroscopic studies of the PS samples. Keywords: Nanostructure, porous silicon, spectroscopic, raman, PL, LIE.

Effect of Laser-Induced Etching Process on Porous Structures

Various features of Silicon micro and nanostructures have been produced by lasers. Laser micromachining of silicon wafer has been conducted to fabricate devices for microelectronic circuits. The laser beam initiates a chemical reaction between the silicon and HF acid to synthesize porous layers by a laser-induced etching process. It is found that the etching rate increases for longer laser wavelengths when CW lasers are used and could also be used to drill micro holes in the silicon wafer when higher laser power densities are used. While Q-switched Nd:YAG laser could be employed to produce ordered nanostructures. It is found that laser parameters are adequate to produce and control the micro/nanostructure characteristics. The surface morphology investigation reveals formation of porous layers of various structures and different laser parameters were affected differently on the surface morphology. Moreover, the SEM statistics imply that high pore density of smaller average pores diameters of 3μm are obtained when the HF concentration diluted to 30%. Furthermore, gratings of submicrons scale can be made when proper processing parameters are selected precisely. Experimental analysis has been carried out to characterize the microstructured surface using computer software.

The effect of sub-band gap photon illumination on the properties of GaN layers grown on Si(111) by MBE

Nanostructured GaN layers are fabricated by laser-induced etching processes based on heterostructure of n-type GaN/AlN/Si grown on n-type Si(111) substrate. The effect of varying laser power density on the morphology of GaN nanostructure layer is observed. The formation of pores over the structure varies in size and shape. The etched samples exhibit dramatic increase in photoluminescence intensity compared to the as-grown samples. The Raman spectra also display strong band at 522 cm−1 for the Si(111) substrate and a small band at 301 cm−1 because of the acoustic phonons of Si. Two Raman active optical phonons are assigned h-GaN at 139 and 568 cm−1 due to E2 (low) and E2 (high), respectively. Surface morphology and structural properties of nanostructures are characterized using scanning electron microscopy and X-ray diffraction. Photoluminance measurement is also taken at room temperature by using He–Cd laser (λ = 325 nm). Raman scattering is investigated using Ar+ Laser (λ = 514 nm).

Blue light emission from a glass/liquid interface for real-time monitoring of a laser-induced etching process

An organic dye, Oil-Red-O, dissolved in p-xylene was used for laser-induced backside wet etching using a visible laser (visible-LIBWE) for the first time. Blue light (360–500 nm) emission from the glass/liquid interface was observed during the etching of borosilicate glass using a nanosecond Q-switched green laser. The emission was confirmed to accompany the etching process. The UV–visible spectrum consists of characteristic peaks of metals, which are the components of the glass. The maximal emission intensity occurs when the laser focusing is at the glass/liquid interface. The etching threshold measured by observing the blue light emission is comparable to that determined by the traditional method. We concluded that the emission is the plasma emission of the etched glass. By measuring the plasma emission, the occurrence of the etching and the crack formation in the glass can be monitored in real time.

Porous silicon nanowires fabricated by electrochemical and laser-induced etching

Electrochemical and laser-induced etching processes were simultaneously used to synthesize the nanowires structure of porous silicon (PS). Surface morphology and structural properties of nanostructured silicon were characterized by using scanning electron microscopy (SEM) and atomic forces microscopy (AFM) images. Nanowires with dimensions of few nanometers were formed on the whole etched surface. The optical properties of silicon nanostructures were studied. Raman spectra were shifted and broadened relatively to 519.9 cm−1 of PS prepared by electrochemical etching, and shifted to 517.2 cm−1 for laser-induced etching process and to 508.9 cm−1 for electrochemical and laser etching simultaneously. Blue shift luminescence was observed at 649.6 nm for PS produced by electrochemical etching, and at 629.5 nm for laser-induced etching. PS produced a blue shift at 626.5 nm using both etching procedures simultaneously. X-Ray diffraction (XRD) was used to investigate the crystallites size of the PS as well as to provide an estimate of the degree of crystallinty of the etched sample.

High photoluminescence of silicon nanostructures synthesized by laser‐induced etching

PurposeThe purpose of this paper is to synthesize Si (porous silicon (PS)) by laser‐induced etching (LIE) technique. The LIE process has the added advantage of a controlling size and optical properties without using of electrodes. The LIE process is a promising technique for fabricating many optoelectronic devices including: light‐emitting devices, detectors, sensors and large‐scale integrated circuits.Design/methodology/approachPS has been fabricated by LIE technique. Surface morphology and structural properties of nanostructures are characterized by using scanning electron microscopy and X‐ray diffraction (XRD). Photoluminescence (PL) measurement is also performed at room temperature by using He‐Cd laser (λ=325 nm) and Raman scattering has been investigated using Ar+ laser (λ=514 nm).FindingsSurface morphology indicated that chemical reaction has been initiated with laser power density of 12 W/cm2, resulting in irregular structure. Micro‐columns are structured on surface with laser power density of 25 W/cm2. The pores structures are confined to smaller size, and the walls between the pore become extremely thin and shorter at 64 W/cm2 power density and 120 min irradiation time. PL spectra at room temperature for PS prepared at power density of 64 W/cm2 and irradiation time of 120 min shows the blue shift of PL at 400 nm and the full‐width and half maximum is about 60 nm. The broadening of the band gap energy occurs with a decrease of the crystallite size. The average diameter of nanosize Si crystallites is about 6‐10 nm. XRD indicated that the broadening in spectrum is due to the small size crystallites.Originality/valueLIE processes have been used to produce high‐luminescent nanocrystallites with small size and size distribution, which is due to the quantum confinement effect.

Surface morphology and formation of GaAs nanocrystals by laser-induced etching: SEM, PL and Raman studies

GaAs nanostructures were prepared by a laser-induced etching process using a Nd:YAG ( λ=1.06 μm) laser. Scanning electron microscope (SEM) was used to monitor changes in surface morphology produced on etching. The etched samples were subjected to photoluminescence (PL) and Raman spectroscopic investigations using an argon-ion laser of excitation energies of 2.54 and 2.71 eV. PL spectra from etched GaAs shows two broad luminescence bands along with a red shift in comparison to a sharp band in the unetched GaAs. Raman measurements exhibit enhancement of first-order LO mode peak intensity in the etched sample along with line-shape asymmetry and shifting of mode towards lower frequency with increasing laser excitation energy. Both Raman and photoluminescence results were explained using quantum confinement models involving Gaussian size distribution of nanocrystallites constituting of GaAs nanostructures. There is reasonable agreement between the results obtained from photoluminescence and Raman spectroscopic investigations of the etched GaAs samples.

Excimer laser induced chlorine etching of Si patterns for microelectronics

The laser-induced etching process of Si(100) and Si(111) surfaces in static chlorine atmosphere (10 −6–10 mbar) has been investigated using an excimer laser at 248 nm varying the energy fluence Φ from 0.1 to 1 J/cm 2. According to energy fluence the etching behaviour can be divided into three regions: At Φ > 0.65 J/cm 2 the etch rate increases linearly with Cl 2 pressure and saturates at about 0.55 Å/pulse. For 0.4–0.65 J/cm 2 the etching process is only detectable at chlorine pressures above 0.1 mbar with an etch rate R ∼ p 2(Cl 2). Below 0.4 J/cm 2 etching only occurs for chlorine pressures above 10 mbar. The etching mechanism in all regions can be described by laser-induced thermal desorption of chlorinated species. Based on our investigation of surface morphology and process induced defects, the parameters laser fluence and Cl 2 pressure can be optimised for an application in microelectronics technology.

Laser-induced desorption and etching processes on chlorinated Cu and solid CuCl surfaces

Time-resolved mass spectrometry is used to study the desorbed species due to laser-induced etching of a solid CuCl and a chlorinated Cu surface. The observed desorption threshold, mass distribution and kinetic energies of the desorbed atoms and molecules at 355 and 532 nm radiation show that the laser-induced etching process is not simply thermal evaporation. It is suggested that competing nonthermal mechanisms due to electronic excitations may be very important in laser-induced desorption and etching. These processes are different for a solid CuCl and a chlorinated Cu surface. For laser-induced etching of Cu surfaces, chlorination of Cu is essential; however, formation of stoichiometric CuCl is not necessary. Excess Cu in the surface layer is responsible for the observed different etching behavior of a chlorinated Cu and a solid CuCl surface. The effect of laser radiation on these surfaces and possible etching mechanisms are discussed based on the experimental observations.