Electropolishing Silicon in Hydrofluoric Acid Solutions

Turner, Dennis R.

doi:10.1149/1.2428873

Cited by 650 publications

(315 citation statements)

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“…Porous silicon, first produced in the 1950's by Uhlir [32] and Turner [33], has been shown to be a high surface area (180-225 m 2 /cm 3 ) network of channels (20 A to 100 A wide) with crystalline and amorphous regions [34,35]. Such surfaces make excellent substrates for obtaining transmission FTIR spectra from surface species adsorbed on silicon.…”

Section: Methodsmentioning

confidence: 99%

Reaction of methanol with porous silicon

1995

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Section: Methodsmentioning

confidence: 99%

Reaction of methanol with porous silicon

1995

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“…PL spectra corresponding to samples prepared in each solution with the same anodization conditions, current density (56.5 mA cm -2 ), anodization time (10 min) and resistivity [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] cm, are shown in Figure 3. PL spectrum for sample produced from HF-MeCN solution presented a blue shift peak that may depend on the pore depth and diameter.…”

Section: Resultsmentioning

confidence: 99%

“…These processes cause hydrogen gas evolution, and highly branched microporous structures. 12,13 Also, for the resultant PS layer the structure is highly dependent on the experimental parameters, such as concentration of the HF acid, current density, anodization time, and also, the doping type associated to the carrier concentrations of the silicon wafer. 5,6,8,12 In addition, another parameter that affects the properties of the PS formed layer that has received little attention are the electrolyte additives.…”

Section: Introductionmentioning

confidence: 99%

Morphological and optical characteristics of porous silicon produced by anodization process in HF-acetonitrile and HF-ethanol solutions

Miranda¹,

Baldan²,

Beloto³

et al. 2008

J. Braz. Chem. Soc.

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Amostras de silício poroso (PS) foram obtidas pelo processo de anodização em lâminas de Si tipo n, dopadas com fósforo. A oxidação eletroquímica do PS foi obtida utilizando-se solução de ácido fluorídrico (HF) contendo aditivos como etanol e acetonitrila (MeCN). A formação dos poros foi estudada com a variação da resistividade das laminas de Si e parâmetros de processo como: concentração do ácido, densidade de corrente e tempo de anodização. As técnicas de Microscopia Eletrônica de Varredura (MEV) e Espectroscopia de Espalhamento Raman foram utilizadas para a investigação da morfologia e fotoluminescência, respectivamente. A camada de PS formada com o uso da solução de HF-MeCN mostrou maior uniformidade e homogeneidade na distribuição dos macroporos com diferentes tipos e tamanhos. Esse comportamento pode ser explicado devido a tensão superficial da MeCN ser maior que a do etanol. Consequentemente, as moléculas de MeCN podem passivar a superfície do silício durante o processo de anodização.Porous silicon (PS) samples were obtained by anodization etching process of n-type silicon wafer phosphorus-doped. Electrochemical oxidation of PS was investigated in aqueous hydrofluoric acid (HF) containing additive such as ethanol or acetonitrile. Pore formation was studied with the variation of type and resistivity of the silicon wafer, taking into account the most important anodization process parameters such as: acid concentration, current density and anodization time. Scanning Electron Microscopy (SEM) and Raman Scattering Spectroscopy measurements were used to characterize the macropore morphology changes and sample photoluminescense responses, respectively. PS layer formed in HF-acetonitrile solution showed more uniform and homogeneous macropore distributions with different shapes and sizes. Behavior may be explained because acetonitrile surface tension is greater than that of ethanol. Therefore, acetonitrile molecules might passivate the silicon surface dissolved during the anodization process. Keywords: porous silicon, HF-acetonitrile, HF-ethanol IntroductionSince the discovery of its visible photoluminescence (PL) at room temperature, porous silicon (PS) has been intensively studied. Nowadays, PS is considered a very attractive material for the sensing layer in a chemical sensor, sacrificial layer in micromachining, and light emitting diode (LED) in optoelectronic devices. [1][2][3][4] Porous Si might be formed by electrochemical etching of single monocrystalline Si in HF solutions containing additives as ethanol or acetonitrile (MeCN). However, the anodization process was firstly studied by Bomchil et al., 5 in 1983, using HF and ethanol solution and they reported that ethanol improved the homogeneity of PS layer. Consequently, HF-ethanol has been used by most research groups as the standard electrolyte for PS formation process. After that, Propst et al. 6 have reported the electrochemical oxidation of p-and n-type silicon in nonaqueous electrolyte of HF-MeCN and discussed their singular and large porous structure...

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“…A current is passed through the cell to result in the formation of an anodic film on the surface of the crystal. 17 The layer that is formed on the surface of the crystal is slightly soluble in the electrolytic solution, and therefore slowly dissolves over time to expose new layers of atoms. Using anodic polishing, the researchers at Bell Labs were successful in the preparation of atomically smooth p-type Si surfaces in concentrated solutions of HF if a threshold current density of 0.01 -0.1 A/cm 2 was exceeded on the surface of the crystal.…”

Section: Technological Developments Leading To Photoluminescent Siliconmentioning

confidence: 99%

“…Further studies into the etching mechanism of n-type Si suggested that below a threshold current density, the process was actually causing a thin mesoporous film to form on the crystal surface. 17 At the time, it was determined by electron and X-ray diffraction that the surface was amorphous, and that the outermost layer was made up of divalent Si atoms. It was further concluded that strong UV-illumination would be required in order to polish n-type Si, rather than etch the surface.…”

Section: Technological Developments Leading To Photoluminescent Siliconmentioning

confidence: 99%

Investigation into Effects of Instability and Reactivity of Hydride-Passivated Silicon Nanoparticles on Interband Photoluminescence

Radlinger¹

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While silicon has long been utilized for its electronic properties, its use as an optical material has largely been limited due to the poor efficiency of interband transitions. However, discovery of visible photoluminescence (PL) from nanocrystalline silicon in 1990 triggered many ensuing research efforts to optimize PL from nanocrystalline silicon for optical applications. Currently, use of photoluminescent silicon nanoparticles (Si NPs) is commercially limited by: 1) the instability of the energy and intensity of the PL, and 2) the low quantum yield of interband PL from Si NPs.Herein, red-emitting, hydrogen-passivated silicon nanoparticles (H-Si NPs) were synthesized by thermally-induced disproportionation of a HSiCl 3 -derived (HSiO 1.5 )n polymer. The H-Si NPs produced by this method were then subjected to various chemical and physical environments to assess the long-term stability of the optical properties as a function of changing surface composition. This dissertation is intended to elucidate correlations between the reported PL instability and the observed changes in the Si NP surface chemistry over time and as a function of environment.First, the stability of the H-Si NP surface at slightly elevated temperatures towards reactivity with a simple alkane was probed. The H-Si NPs were observed by FT-IR spectroscopy to undergo partial hydrosilylation upon heating in refluxing hexane, in addition to varying degrees of surface oxidation. The unexpected reactivity of the Si surface in n-hexane supports the unstable nature of the H-Si NP surface, and furthermore implicates the presence of highly-reactive Si radicals on the surfaces of the Si NPs. We propose that reaction of alkene impurities with the Si surface radicals is largely responsible for the observed surface alkylation. However, we also present an alternate ii mechanism by which Si surface radicals could react with alkanes to result in alkylation of the surface.Next, the energy and intensity stability of the interband PL from H-Si NPs in the presence of a radical trap was probed. Upon addition of (2,2,6,6,-tetramethyl-piperidin-1-yl)oxyl (TEMPO), the energy and intensity of the interband transition was observed to change over time, dependent on the reaction conditions. First, when the reaction occurred at 4ºC with minimal light exposure, the interband transition exhibited a gradual hypsochromic shift to between 595 nm and 655 nm, versus the λ max of the original low energy emission peak at 700 nm, depending on the amount of TEMPO in the sample.Second, when the reaction proceeded at room temperature with frequent exposure to 360 nm irradiation, the original interband transition at 660 nm was quenched while a new peak at 575 nm developed. Based on all the data collected and analyzed, we assign the 595 -655 nm transition as due to interband exciton recombination from Si NPs with reduced diameters relative to the original Si NPs. We furthermore assign the 575 nm transition as due to an oxide-related defect state resulting from rapid oxidation of pho...

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Electropolishing Silicon in Hydrofluoric Acid Solutions

Cited by 650 publications

References 0 publications

Reaction of methanol with porous silicon

Reaction of methanol with porous silicon

Morphological and optical characteristics of porous silicon produced by anodization process in HF-acetonitrile and HF-ethanol solutions

Investigation into Effects of Instability and Reactivity of Hydride-Passivated Silicon Nanoparticles on Interband Photoluminescence

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