A. Grigonis

Nanoparticle formation after nanosecond-laser irradiation of thin gold films

Evolution in nanoparticle formation was observed after nanosecond-laser irradiation of thin gold films on a silicon substrate and physical phenomena leading to the formation of nanoparticles were studied. Gold films of different thickness (3, 5, 10, 15, 20, and 25 nm) were evaporated on the silicon (110) substrate and irradiated with the pulsed nanosecond laser using different pulse energies and the number of pulses in a burst. Experimentally morphological changes appeared in the films only when the pulse energy was high enough to initiate the phase transition. The threshold energy density for phase transitions in the films was estimated from the thermal model of the laser beam and sample interaction. With the pulse energy just above the threshold, it was possible to observe evolution of nanoparticle formation from a plane metal film by changing the number of pulses applied, as duration of the pulse burst represented the time how long the liquid phase existed. The final size of nanoparticles was a functio...

Real dimensional simulation of anisotropic etching of silicon in CF4+O2 plasma

Abstract The reactive ion etching (RIE) of silicon in CF 4 +O 2 plasma is considered. The profiles of etched grooves are calculated as a function of mask dimensions, fluxes of chemically active and non-active plasma components and parameters of ion bombardment. To achieve this goal the chemical composition of CF 4 +O 2 plasma is calculated and the one-dimensional plasmochemical etching (PCE) of Si in this plasma is considered. The values of phenomenological constants are found by extrapolation from experimental results. Using values of phenomenological constants, found by analysis of chemical composition of plasma and one-dimensional etching, the etched groove profiles at real dimensions are calculated. Special attention is given to the etching anisotropy and lateral etching. The influence of oxygen addition to fluorocarbon plasma on etched groove profile is considered. The conditions under which anisotropic etching prevails are found.

Modification of the amorphous carbon films by the ns-laser irradiation

The effect of a nanosecond laser irradiation of thin (60 and 145 nm) amorphous, diamond-like carbon films deposited on Si substrate by an ion beam deposition (IBD) from pure acetylene and acetylene/hydrogen (1:2) gas mixture was analyzed in this work. The films were irradiated with the infrared (IR) and ultraviolet (UV) radiation of the nanosecond Nd:YAG lasers working at the first (1.16 eV) and the third (3.48 eV) harmonics, using a multi-shot regime. The IR laser irradiation stimulated a minor increase in the fraction of sp2 bonds, causing a slight decrease in the hardness of the films and initiated SiC formation. Irradiation with the UV laser caused the formation of carbides and increased hydrogenization of the Si substrate and the fraction of sp2 sites. Spalliation and ablation were observed at a higher energy density and with a large number of laser pulses per spot.

Formation of polymeric layers using halogen–carbon plasmas

Abstract This paper considers the state of the inhibitor layer formed on a single-crystal silicon surface after reactive ion etching (RIE) in CF4, CF4+H2, CF4+O2, CF3Cl, CF2Cl2 plasmas. The composition of the altered layer was subsequently analyzed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Analysis of XPS F 1s photoelectron spectra has shown that the maximum of the fluorine peak moves to larger energies when the etching duration in the CF4, CF4+H2 plasma increases. The shift of the fundamental peak shows that (CFx)n polymeric compounds were intensively formed on the surface. Fluorine and chlorine were removed with etching products during silicon treatment with CF4−xClx plasma. Part of the surface carbon was bonding to silicon because of the low Si–C bond enthalpy and high dissociation energy. Some carbon is free and can act as center for halogen recombination or formation of C–CF bonds. Etching duration is an important factor not only for concentration of impurities (especially for carbon and fluorine), but also for determining the bond type between atoms when the energy of the bombarding ion increases.

Optical and electron paramagnetic resonance studies of hydrogenated amorphous carbon (a-C:H) thin films formed by direct ion beam deposition method

The diamond-like carbon films, deposited by direct ion beam deposition method using mixture of C6H14 and H2 with and without silicon presence, have been investigated by Raman spectroscopy, X-ray photoelectron spectroscopy, ellipsometry, IR-visible-UV transmission, and electron paramagnetic resonance techniques. The D and G line widths and peak positions, integrated intensity ratio (ID/IG) in Raman spectra indicate these films being amorphous, mixture of sp2 and sp3 bonds. It has been found that a-C:H films formed while increasing substrate temperature and deposition ion energy tend to be graphite-like. Increasing of hydrogen content in gas mixture made these films more polymer-like with low content of dangling bonds. Traces of silicon increase sp3/sp2 ratio. The DLC films on silicon are able to greatly reduce IR reflection.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Simulation of silicon dry etching through a mask in low pressure fluorine-based plasma

The ion beam assisted etching of silicon through a mask in a low pressure fluorocarbon plasma is considered. The two-dimensional profiles of etched grooves are calculated using a proposed model involving a function of mask size, the fluxes of incident chemically active and non-active species from the plasma and bombarding ions. The model also includes the processes of adsorption, heterogeneous reactions, desorption, physical sputtering, activation of surface atoms and stochastic mixing between monolayers. Special attention is given to the etching anisotropy, lateral etching and elemental composition at the surface of a groove. It is shown, that formation of an inhibiting film on the sidewall of groove increases the etching anisotropy, however, the process of stochastic mixing leads to the formation of the altered layer in the near surface region. The thickness of altered layer and elemental composition at different surface regions of etched groove is considered.

The oxidation of surface layers during reactive ion etching of GaAs in CF2Cl2+O2 and O2 plasmas

Abstract The RF plasma was created in a plasmatron system with accelerating potential of 20–700 V, discharge power of 0.5–5.0 W/cm2 and at pressure of 10−4–10−2 Torr. The thickness and composition of formed oxide layer is considered experimentally at various etching parameters: ion current density, plasma composition, substrate temperature. The experimental curves were modeled by proposed phenomenological model. The model includes the main processes taking place during reactive ion etching: sputtering, adsorption, heterogeneous chemical reactions, desorption of volatile compounds and radiation enhanced diffusion. The model gives the kinetics of elemental composition on the surface and the composition of the altered layer.

The surface composition of GaAs affected by reactive plasma

The results of reactive ion etching of GaAs in Freon-12 plasma and its mixtures with oxygen are presented. The dependencies of etching rate on target temperature, plasma pressure and composition of etching gas mixture are considered. The influence of ion bombardment on the process of etching is studied. The elemental composition of the surface was measured using Auger electron spectroscopy and X-ray photoelectron spectroscopy. It is shown that the film with a complicated composition is grown on the surface during etching, but it does not stop the etching process. At a lower concentration of oxygen in the etching gas mixture, the formed oxide layer on the surface becomes non-homogeneous, having a high concentration of impurities.

Formation of carbon coatings employing plasma torch from argon-acetylene gas mixture

Amorphous carbon films were formed on Si (111) wafers from argon-acetylene gas mixture at atmospheric pressure by direct current (DC) plasma torch discharge. The Ar/C2H2 gas volume ratio varied from 12 to 100, and the distance between plasma torch nozzle exit and the samples was 0.005, 0.01 and 0.02 m. SEM revealed carbon coatings thickness in the range of 20-270 &mgr;m, and variation of the growth rate from 0.067 &mgr;m/s to 1.5 &mgr;m/s. Growth rate of the coatings increases decreasing Ar/C2H2 gas ratio and the distance. The Raman spectra of carbon films indicate the upward shift of the D (~1360 cm-1) and G (~1600 cm-1) peaks, compared to typical diamond-like carbon (DLC). a-C:H coatings deposited at higher Ar/C2H2 gas ratio (60 and 100) and distance d greater than or equal to 0.01 m contain high sp3 bond fraction and are attributed to DLC films. However Raman spectra shape and ID/IG ratio demonstrate existence of diamond phase mixed with glassy carbon phase. Films produced at lower Ar/C2H2 ratios are graphite-like carbon (GLC). The Fourier transform infrared (FTIR) spectroscopy has shown that film transparency increases decreasing acetylene gas content. Reflectance of the films depends on Ar/C2H2 gas ratio and distance, and varies from 60% up to 90%. The IR spectra showed clear evidence of C=C and C=O bonds in GLC films and presence of sp3 CH2 symmetric (2850 cm-1) and antisymmetric (2920 cm-1) modes in DLC coatings.

The altered layer formation during the reactive ion etching of GaAs in CF2Cl2+O2 plasma

Abstract The reactive ion etching of GaAs (100) in CF2Cl2+O2 plasma is reported. The RF plasma was excited in a diode asymmetrical system with accelerating potential of 300–1500 V, discharge power of 0.5–5.0 W\cm2 and pressure of 10−2–10 Pa. The experimental measurements have shown that with the increase of discharge power in plasma the surface becomes depleted by arsenic and enriched by gallium oxide. The experimental curves were modeled by proposed phenomenological model. The model includes the main processes taking place during reactive ion etching : sputtering, adsorption, heterogeneous chemical reactions, desorption of volatile compounds and radiation enhanced diffusion. As the balance equations are written for each component in each monolayer the model gives the kinetics of elemental composition on the surface and the composition of the altered layer.