Silicon etching in Cl2 environment

The ion-beam-assisted etching of silicon in Cl₂ environment is considered. The theoretically calculated dependences of silicon etching rate on the flux of Cl₂ molecules at different ion current densities are compared with experimentally measured. The composition of the adsorbed layer is determined. It is found that SiCl₂ molecules prevail in the adsorbed layer. The reciprocal of relative concentration of SiCl₂ molecules in the adsorbed layer linearly depends on the ion-to-neutral flux ratio.     

Comparison of the interaction of Cl2 and Br2 with Cu(100)

The adsorption, reaction and etching of Cu(100) by Cl₂ was studied using temperature programmed desorption (TPD) and low energy electron diffraction (LEED), and the results were compared with recent results for Br₂. Although the general etching mechanism was the same for both gases (adsorption rate limited Cu halide formation followed by halide sublimation), significant differences between the behavior of Cl₂ and Br₂ were observed. The desorption of CuCl was characterized by a single zero order sublimation peak, independent of CuCl coverage, while limiting the CuBr coverage resulted in a desorption peak at temperatures lower than a prediction based on vapor pressure data of all known phases of CuBr. In addition, Cl₂ was found to be at least an order of magnitude less reactive than Br₂ towards halide formation. For both Cl₂ and Br₂, the halide formation rate reversibly decreased with increasing reaction temperature. However, for Br₂, but not Cl₂, annealing a chemisorbed halogen layer prior to further reaction irreversibly increased the halide formation rate. Structural differences between CuCl and CuBr on Cu(100) were also observed. For CuCl, LEED data suggested that highly faceted crystallites form at 325 K and remain stable until desorption, while LEED data for CuBr reveal a compressed epitaxial (111) layer that disorders below 400 K and then desorbs. The implications of these differences on etching and oxidation processes are discussed.     

Realization of an ultra-flat silica surface with angstrom-scale average roughness using nonadiabatic optical near-field etching

We propose a new method of optical near-field etching where a nonadiabatic process is applied to a synthetic silica substrate using a continuum wave laser (λ=532 nm) with a Cl₂ gas source. Because the absorption band edge energy of Cl₂ is higher than the photon energy of the light source, we preclude the conventional adiabatic photochemical reaction. An optical near field, generated on the nanometrically rough substrate, induces the nonadiabatic chemical reaction to the Cl₂ molecules and thereby selectively etches away the roughness, leaving an ultra-flat synthetic silica surface with a minimum average surface roughness R _a of 1.37 Å.     

低能Cl原子刻蚀Si(100)表面的分子动力学模拟

使用分子动力学模拟方法研究了不同能量(0.3—10 eV)的Cl原子对表面温度为300 K的Si(100)表面的刻蚀过程.模拟中采用了Tersoff-Brenner势能函数来描述Cl-Si体系的相互作用.模拟结果显示,随着入射Cl原子在表面的吸附达到饱和,Si表面形成一层富Cl反应层.这和实验结果是一致的.反应层厚度随入射能量增加而增加.反应层中主要化合物类型为SiCl,且主要分布于反应层底部.模拟结果发现随初始入射能量的增加,Si的刻蚀率增大.在入射能量为0.3,1和5 eV时,主要的Si刻蚀产物为Si 关键词： 分子动力学 Cl刻蚀Si 分子动力学模拟 微电子机械系统     

Desorption of dimethylformamide from Zn4O(C8H4O4)3 framework

Both dimethylformamide (DMF) and diethylformamide (DEF) are important solvents for the synthesis of Zn₄O(C₈H₄O₄)₃ framework (MOF-5). It is generally recognized that DMF molecules can be completely displaced by CH₂Cl₂ during the synthesis of MOF-5. Herein, however, it was found that the DMF molecules inside the pores of the MOF-5 framework cannot be displaced by CH₂Cl₂. The desorption of the DMF molecules from the pores, which requires a temperature of 100 °C or above, is the first order with activation energy of 56.38 kJ/mol. In contrast, DEF molecules can be completely displaced by CH₂Cl₂ during the synthesis of MOF-5, because DEF molecules cannot penetrate into the pores of the MOF-5 paste.     

X-ray initiated molecular photochemistry of Cl-containing adsorbates on a Si(1 0 0) surface using synchrotron radiation

X-ray initiated molecular photochemistry for SiCl₄ and CCl₄ adsorbed on Si(1 0 0) at ∼90 K following Cl 2p core-level excitation is investigated by photon stimulated ion desorption and ion kinetic energy distribution measurements. The Cl excitation of solid SiCl₄ induces the significant enhancement (∼900%) of the Cl⁺ yield, while the Cl excitation of condensed CCl₄ leads to a moderate enhancement (∼500%) of the Cl⁺ yield. The enhancement of Cl⁺ yield at the specific core-excited states is strongly correlated to the ion escaped energy. Upon X-ray exposure for CCl₄ adsorbed on Si(1 0 0) (20-L exposure), the Cl⁺ yields at resonances decrease and new structures at higher photon energies are observed. Cl⁺ yields at these new resonances are significantly enhanced compared to those at other resonances. These changes are the results of desorption and surface reaction of the CCl₄-Si surface complex due to X-ray irradiation. We have demonstrated that state-specific enhancement of ion desorption can be successfully applied to characterize the reaction dynamics of adsorbates adsorbed on surfaces by X-ray irradiation.     

Fluorine etching on the Si(111)-7×7 surfaces using fluorinated fullerene

Fluorine etching on the Si(1 1 1)-7×7 surfaces using fluorinated fullerene molecules as a fluorine source has been investigated. At room temperature, adsorbed fluorinated fullerene molecules reacted with the Si(1 1 1)-7×7 surface to create a localized distribution of fluorine on the surface. Nanoscale etch pits were created by annealing at 300 °C, due to the adsorption of the fluorine localized around the C₆₀F_x molecules. Annealing at 400 °C resulted in the delocalized fluorine distribution on the surface and healing of the etch pits, due to the enhancement of the diffusion of both the fluorine and silicon atoms. Subsequent annealing at 500 °C led to desorption of SiF₂ reactants formed on the surface. The fluorine diffusion process was found to be an elemental process in the etching because the diffusion of adsorbed fluorines is a key for the formation of the SiF₂ species and their subsequent desorption.     

High-density plasma etching of indium-zinc oxide films in Ar/Cl2 and Ar/CH4/H2 chemistries

The dry etching characteristics of transparent and conductive indium-zinc oxide (IZO) films have been investigated using an inductively coupled high-density plasma. While the Cl₂-based plasma mixture showed little enhancement over physical sputtering in a pure argon atmosphere, the CH₄/H₂/Ar chemistry produced an increase of the IZO etch rate. On the other hand, the surface morphology of IZO films after etching in Ar and Ar/Cl₂ discharges is smooth, whereas that after etching in CH₄/H₂/Ar presents particle-like features resulting from the preferential desorption of In- and O-containing products. Etching in CH₄/H₂/Ar also produces formation of a Zn-rich surface layer, whose thickness (∼40 nm) is well-above the expected range of incident ions in the material (∼1 nm). Such alteration of the IZO layer after etching in CH₄/H₂/Ar plasmas is expected to have a significant impact on the transparent electrode properties in optoelectronic device fabrication.     

Photodissociation of the molecules SiCl3I and SiF3I

The parameters of lasing based on the transition of atomic iodine and occurring upon photodissociation of the molecules SiCl₃I and SiF₃I are experimentally investigated. The light source employed was a coaxial xenon-filled flash lamp of original construction. The main chemical reactions that accompany the photolysis of the molecules SiCl₃l and SiF₃I and determine the energy characteristics of the f~enerated radiation are analyzed.     

Mass spectrometry study of the kinetics of CdTe molecular-beam epitaxy: Part II. Cd, Te2, Te, and CdTe

The results of an in situ mass-spectrometric study of surface processes occurring during CdTe molecular beam epitaxy are presented. The measurements of kinetic parameters are performed with modulated Cd and Te₂ molecular beams with an intensity of 0.1–5.0 ML/s at a crystal temperature of 550–730 K. The experimental results are treated using a model in which condensation and evaporation proceed through adsorption and desorption steps. The desorption rates are 2–15 and 150 s^?1 for Te₂ and Cd, respectively. The activation energy of CdTe “evaporation” is found to be 1.2 eV; the desorption energies are E _d(Cd) = 1.0 eV and E _d(Te₂) = 0.3 eV. The adsobate coverage with cadmium atoms and tellurium molecules is estimated to be n(Cd) < 0.01, n(Te₂) = 0.02–0.20, and n(Te) = 0.2–1.0.     

Adsorption of nitrogen on platinum

The adsorption and desorption of nitrogen on a platinum filament have been studied by thermal desorption techniques. Nitrogen adsorption becomes significant only after any carbon contamination is removed from the surface by heating the platinum filament in oxygen, and after the CO content in the background gas is reduced substantially. At room temperature nitrogen populates an atomic tightly bound β-state, E^≠ = 19 kcal mole^?1. The saturation coverage of the (3-state is 4.5 × 10¹⁴ atoms cm^?2. Formation of the (β-state is a zero order process in the pressure range studied. At 90 K two additional α₁- and α₂-desorption peaks are observed. The activation energy for desorption for the α₂-state is 7.4 kcal mole^?1 at low coverage decreasing to 3 kcal mole^?1 at saturation of this state, 6 × 10 molecules cm^?2. The maximum total coverage in the α-states was 1.2 × 10¹⁵ molecules cm^?2. A replacement process between the β- and α-states has been observed where each atom in the (β-state excludes two molecules from the α-state.     

A study of the kinetics of isothermal nicotine desorption from silicon dioxide

The isothermal kinetics of nicotine desorption from silicon dioxide (SiO₂) was investigated. The isothermal thermogravimetric curves of nicotine at temperatures of 115 °C, 130 °C and 152 °C were recorded. The kinetic parameters (E_a, ln A) of desorption of nicotine were calculated using various methods (stationary point, model constants and differential isoconversion method). By applying the “model-fitting” method, it was found that the kinetic model of nicotine desorption from silicon dioxide was a phase boundary controlled reaction (contracting volume). The values of the kinetic parameters, E_a,α and ln A_α, complexly change with changing degree of desorption and a compensation effect exists. A new mechanism of activation for the desorption of the absorbed molecules of nicotine was suggested in agreement with model of selective energy transfer.     

Projection-patterned etching of silicon in chlorine atmosphere with a KrF excimer laser

The formation of relief features in silicon by a one-step process that avoids resist patterning has been achieved by laser-projection-patterned etching in a chlorine atmosphere. Etching is performed with a pulsed KrF excimer laser (λ=248 nm, τ=15 ns) and deep UV projection optics having an optical resolution of 2 μm. Etching takes place in two steps. Between laser pulses, the silicon surface is covered with a monolayer of chemisorbed chlorine atoms (one Cl per Si). During the laser pulse, surface transient heating at temperatures in excess of 1250 K results in the desorption of the reaction products (mainly SiCl₂). At laser energy densities that induce surface melting, this desorption results in a saturated etch. rate of 0.06 nm per pulse, corresponding to the removal of about 0.5 Si monolayer per pulse. At densities below the melting threshold, reduced thermal and possibly a small amount of photochemical etching result in lower etch rates. Projection of a resolution test photomask onto the silicon surface shows that the size of etched features differs from the size of the projected features and strongly depends on the laser energy density. As a result of the heat spread in silicon and of the highly nonlinear character of the etching reaction, etched features smaller than the irradiated area are obtained at all fluences in the range 350–700 mJ/cm². Etched lines having a width down to about 1.3 μm were produced. Proximity effects due to heat spread were also evidenced for small projected features (<4 μm). The characteristics of the etched patterns are compared with those obtained for GaAs etching in chlorinated gases with the same experimental set-up. Significant differences in pattern resolution for Si and GaAs etching are observed. This variation in resolution is believed to result from the fact that Si has a greater thermal diffusivity than GaAs.     

Features of ion-beam etching of quartz in a chlorine-containing gas medium

The processes of CCl₄ and SiCl₄ decomposition are simulated by determining the thermodynamic characteristics of reactions between a material subjected to etching and a gas medium. The features of ion-beam etching of quartz are investigated for different working media, including chlorine-containing gases (CCl₄ and SiCl₄) and their mixtures with oxygen. The optimal regimes have been revealed, in which the high rates of quartz etching were attained with the use of a Radical M-100 ion-beam source.     

Self-oscillatory heterogeneous recombination of hydrogen atoms and nonequilibrium desorption of molecules from the surface (Teflon)

The channel of the accommodation of the energy of a heterogeneous chemical reaction (recombination of hydrogen atoms) related to vibrational V-V exchange between excited chemical reaction products and adsorption layer molecules (H₂O, HDO, D₂O, and H₂) was studied by the method of modulated molecular beams. The chemical reaction was found to proceed in an oscillatory mode caused by the nonequilibrium character of its elementary steps. The participation of adsorbed molecules in accommodation was studied by analyzing nonequilibrium desorption of these molecules. An isotope effect was observed in nonequilibrium desorption. The kinetic mechanism of the reaction and the micromechanism of elementary reaction events, which determine the “physical” mechanism of catalysis in the system under study, are discussed.     

248 nm laser etching of GaAs in chlorine and ozone gas environments

KrF laser etching of GaAs in Cl₂ and O₃ gas ambients by direct laser illumination is reported. The etch depth per pulse in Cl₂ was found to be linear versus the laser fluence on the sample in the 0.2–1.1 J/cm² range. It increased as a function of the Cl₂ pressure up to 6 Torr and slightly decreased for pressures above this value. It also decreased as a function of the laser repetition rate. Very smoothly etched surfaces were obtained after irradiation using the Cl₂ and O₃ etching gases. Auger analysis of the etched GaAs surfaces shows almost no traces of chlorine after etching in Cl₂, whereas a thick oxide layer of about 1500 Å thickness was found after etching in ozone.     

Electron-induced interaction of condensed chlorine with Si(100)

We have studied electron-induced interaction of molecular chlorine with Si(100) surface under ultra-high vacuum conditions. Without electron beam irradiation, chlorine was found to be adsorbed both dissociatively (first step) and molecularly (second step) at 100 K. Illumination of molecular chlorine-covered surface at 100K with electron beam (1–3 keV) led to the formation of silicon tetrachloride on the Si(100) surface. We established that the surface reaction, that is responsible for the SiCl₄ formation, is initiated by Cl₂ dissociation and appearance of the active chlorine radicals. Importance of the such effect is also discussed in a view of their possible applications for selective etching of semiconductor surfaces.     

Selenium adsorption on Cs-covered Si(100) 2×1 surfaces

This report involves the study of Se adsorption on caesiated Si(100) 2×1 surfaces in ultra high vacuum (UHV) using low energy electron diffraction, Auger electron spectroscopy, thermal desorption spectroscopy and work function measurements. Selenium atoms on Cs/Si(100) 2×1 surface adsorb initially on uncaesiated portions of Si and subsequently on the Cs overlayer. The presence of Se increases the binding energy of Cs on Si(100). For Cs and Se coverages above 0.5 ml CsSe and Cs_xSe_ySi_z, compound formation was observed. The coadsorption of Se and Cs induces a high degree of surface disorder, while desorption most probably causes surface etching. The presence of Cs on Si(100) 2×1 surfaces prevents the diffusion of Se into the Si substrate and greatly suppresses the formation of SiSe₂ and SiSe₃, detected when Se is adsorbed on clean Si(100) 2×1 surfaces.     

Photochemical etching of GaAs with Cl2 induced by synchrotron radiation

The quality and efficiency of etching at room temperature is determined in the wavelength range from 105 nm to 300 nm by replicating a mask on a GaAs(100) wafer and by wavelength selection of synchrotron radiation with filters and a monochromator. A good anisotropy and selectivity is found for Cl₂ pressures from 10^–2 mbar up to 1.5 mbar, but above 3 mbar the selectivity is lost. Efficiencies for stimulation of the chlorination reaction and for desorption are separated and an optimal efficiency for stimulation of about 100 removed Ga and As atoms per photon is obtained around a wavelength of 122 nm at 1.5 mbar. Growth of reaction products on the surface occurs for short wavelengths and transport processes through layers up to a thickness of 350 nm are relevant. The efficiency and quality of etching can be improved by additional desorption with long wavelengths especially with lasers.     

Isotope effects in the kinetics of simultaneous H and D thermal desorption from Pd

The kinetics of simultaneous hydrogen and deuterium thermal desorption from PdH_xD_y has been investigated. A novel experimental approach for the study of the transition state (TS) characteristics of the surface recombination reaction is proposed based on the analysis of the H and D partitioning into H₂, HD and D₂ molecules. It has been found that the hydrogen molecular isotopes distribution is determined by the energy differences of the corresponding TS of the atom-atom recombination reactions. On the other hand, the mechanisms and activation energies of the desorption process have been obtained. At 420 K, the desorption reaction changes from a surface recombination limiting mechanism during desorption from β-PdH_xD_y to a reaction limited by the rate of β to α phase transformation during the two phase coexistence. Surface recombination reaction becomes again rate limiting above 480 K, due to a change in the catalytic properties of the Pd surface. TS energies obtained from the kinetic analysis of the thermal desorption spectra are in good accordance with those obtained from the analysis of the H₂, HD and D₂ distributions. Anomalous TS energies have been observed for the H-D recombination reaction, which may be related to the heteronuclear character of this molecule.