RU2547016C2 - Method of producing nanosize silicon structures - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of pure nanostructured silicon and can be used in different semiconductor engineering fields. Nanostructured silicon structures are obtained by thermal decomposition of monosilane, which is carried out by adiabatic compression of a mixture of 10 vol % monosilane in argon with initial pressure of 0.095 MPa and temperature of 130°C.

EFFECT: invention enables to obtain solar-grade silicon nanostructures with size of 30-100 nm in amorphous and crystalline form.

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Description

The invention relates to methods for producing pure nanostructured silicon and can be used in the production technologies of new nanoscale materials for hydrogen energy, micro-, opto- and power electronics and other fields of semiconductor technology.

Known plasma-chemical methods for producing silicon powders based on the evaporation of solid silicon in a plasma stream [1. Gusev A.I. Nanomaterials, nanostructures, nanotechnology. - M .: Fizmatlit, 2005 .-- 416 p .; 2. Patent RU 2359906, IPC СВВ 33/02, 08/31/2007, Method for producing nanocrystalline silicon powders], laser ablation [3. Umezu I., Takata M., Sugimura A / Surface hydrogeneration of silicon nanocrystals during pulsed laser ablation of silicon target in hydrogen background gas // J. Appl. Phys. 2008. V.103. P.114309.] Or evaporation by electric discharge [4. LiuM., Lu G., Chen J. Synthesis, assambly and characterization of Si nanocrystals and Si-nanocrystal-carbon nanotube hybrid structures // Nanotechnology. 2008. V.19. P.265705.] The surface of solid silicon followed by condensation of silicon vapor.

The main disadvantages of such methods are high energy consumption, a wide distribution of particle sizes (from tens to thousands of nm) and a high content of impurities in the resulting product.

Another group of methods is based on the decomposition of volatile silicon compounds. Known methods for producing silicon powders by decomposition of monosilane in a gas discharge plasma [1. Gusev A.I. Nanomaterials, nanostructures, nanotechnology. - M .: Fizmatlit, 2005 .-- 416 p .; 5. Demin V.N., Vashchenko S.P., Saprykin A.I., Pozdnyakov B.A. Obtaining polycrystalline silicon by decomposition of silane in the plasma of an electric arc plasma torch // Meeting on the growth of crystals, films and defects in the structure of silicon. "Silicon 2002". Abstracts of reports. M .: 2002. P.184; 6. Bylinkina N.N., Mushtakova S.P., Oleinik V.A. et al. // Letters in ZhTF. 1996.V.22. AT 6. S.43-47] with the deposition of silicon particles on a substrate or filters. This also includes the laser-induced method of dissociation of monosilane [7. Vladimirov A., Korovin S., Surkov A., Kelm E., Pustovoy V. Synthesis of Luminescent Si Nanoparticles Using the Laser-Induced Pyrolysis // Laser Physics / 2011. V.21, No. 4. P.830; 8. Sublemontier O., Lacour F., Leconte Y., Herlin-Boime N., Reynaud C.CO ₂ laser-driven pyrolysis synthesis of silicon nanocrystals and applications // J. of Alloys and Compounds. 2009. V.483. P.499; 9. LT Cancham, 1990, Appl. Phys. Lett, 57, 1046]. Laser heating of a mixture of monosilane and argon provides the decomposition of monosilane with the subsequent formation of silicon particles. High-purity amorphous silicon is also obtained in devices of the rod type or in devices with a fluidized bed of germinal silicon particles [10. O. Gadalova, A. Kotenko, A. Kravchenko, H. Mirkurbanov, V. Odinokov. Establishment of production of polycrystalline silicon of electronic quality from monosilane, Nanoindustry 1/2010; 11. Patent RU 2329196, IPC СВВ 33/04 (2006.01) СВВ 33/029, 10/06/2006 A method for producing monosilane and high-purity polycrystalline silicon].

Gas-phase synthesis makes it possible to obtain the purest powders [10], however, it requires large expenditures of energy, the use of sophisticated equipment, but does not ensure the monodispersity of the target product.

The known method [12. Wiggers H., Starke R., Roth P. Silicon Particle Formation by Pyrolysis of Silane in a Hot Wall Gasphase Reactor // Chem. Eng. Technol. 2001. V.24, No. 3. H.261], selected as a prototype, in which nanosized silicon structures are obtained by thermal decomposition of monosilane. The technical implementation of the method [12] is the simplest. A gas mixture consisting of argon and monosilane is blown through a tubular reactor heated to a temperature of 1000 ° C. The residence time of the gas mixture in the hot zone (~ 1000 mm long) was ~ 3 s. Silicon particles formed during the thermal decomposition of monosilane were passed through a metal filter mounted at the outlet of the reactor and periodically collected in a receiving device. The product is a mixture of fractal crystalline (formed in Chemical Vapor Deposition or CVD process) and amorphous (formed in Chemical Vapor Synthesis or CVS process) agglomerates with sizes up to 500 nm, consisting of particles with characteristic sizes up to 25 nm. The different morphology of the resulting particles is a consequence of the heterogeneity of the conditions of their formation, which is a disadvantage of this method. Another drawback is the inability to control particle sizes.

The objective of the invention is to provide a method for producing nanosized powders of pure silicon, consisting of monodisperse particles with a given morphology.

The solution of the problem of the invention is achieved by using the adiabatic compression method of a mixture of monosilane and argon to initiate the process of dissociation of monosilane and the formation of silicon powders.

The adiabatic compression method is known and used in chemical technologies [13. Pulse compression of gases in chemistry and technology, M., 1982. Yu.A. Kolbanovsky] and is practically used, for example, for the pyrolysis of hydrocarbons [14. Patent RU 2299175, IPC С01В 3/34, F02B 43/12, F02B 47/02, 02/12/2006, Method for producing synthesis gas and installation for its implementation; 15. Patent RU 2317250, IPC С01В 3/34, F02B 43/12, 07/12/2006, Method for the production of synthesis gas]. However, no publications were found in the literature on the application of this method for the synthesis of solid particles and powders.

The distinctive features of the invention, providing a positive effect, are the possibility of obtaining monodisperse nanopowders due to the volumetric homogeneity of the reaction conditions in the entire reactor volume and controlling the properties of the target products by adjusting the chemical process conditions. In addition, the uniformity of conditions inside the adiabatic compression reactor, unlike all known methods, allows its size to be scaled.

The method is implemented on a mock device for adiabatic gas compression (Fig. 1). The installation is based on a pipe (1) placed inside a tubular ohmic heater (2). The pipe is divided by a movable piston (3) into two chambers. The reaction chamber (4) is located between the piston (3) and the flange (8) having a channel for filling the reaction volume with gaseous precursors (10) and a chromel-alumel thermocouple (9) for measuring the temperature in the reaction zone during compression. The chamber (5) is designed for injection of pushing gas, located between the pushing piston and the flange (6) having a channel (11) for connection to a cylinder with compressed gas.

The method of adiabatic compression of the reaction mixture is as follows. At the beginning, the reaction volume (4) is pumped out, then it is filled with a mixture of argon and monosilane and heated to the initial temperature (T ₀ ). Preheating the mixture reduces the degree of compression at which the target reaction is initiated and, if necessary, vaporize the liquid precursors. After that, the chamber (5) is filled with pushing gas from the cylinder. The piston is attached to the flange of the compression chamber (6) with a metal cable (7). The pressure of the pushing gas (P _t ) rises until the cable breaks. After that, the piston begins to move, compressing the reaction mixture. The temperature in the reactor increases rapidly, reaching a temperature (T _max ) at which decomposition of monosilane and the formation of silicon nanoparticles occur. The rise time of the temperature to T _max is about 20 ms. The time during which the temperature remains stable is approximately 1 s. The monosilane decomposition reaction product formed inside the chamber in the form of a “cotton wool” consisting of associates of silicon nanoparticles is recovered from the reactor.

The technical result is to simplify the hardware implementation of the method for the synthesis of nanosized particles of amorphous and crystalline silicon, increase the uniformity of the sizes of nanoparticles, gain the ability to control the properties of the target product (particle size and morphology) by changing the composition of the mixture of precursors and the operating parameters of the used adiabatic compression device.

The proposed method provides a reduction in energy consumption for the production of monodispersed pure nanostructured silicon in comparison with the prototype, since the process proceeds at a relatively low reactor temperature and does not require further product separation. In FIG. 2 shows a view of the silicon powder obtained by the proposed method.

The following examples show the possibility of obtaining both crystalline and amorphous nanostructured silicon powder.

To determine the chemical composition of silicon nanopowders and silicon carbide, atomic emission spectrometry with excitation of spectra in a direct current arc (DCT) and a PGS-2 spectrometer (Karl Zeiss, Germany) were used. For the structural analysis of silicon nanopowders and silicon carbide, an X-ray phase analysis method was used in the geometry of a sliding beam (a Shimadzu XRD-600 diffractometer using CuK _α radiation). To determine the shape and size of the particles, scanning and transmission electron microscopy (scanning electron microscopes: LEO-1430 (Leica Ltd, USA), Zeiss EVO ΜΑ 15 (Karl Zeiss, Germany) and transmission electron microscope TITAN 80-300CS (FEI, Netherlands) were used To determine the particle size distribution, the method of photon correlation spectrometry (90Plus refractometer, Brookhaven, USA) was used.

Example 1. An experiment from 01/06/2013 on adiabatic compression of a mixture of SiH ₄ (10%) + Ar (90%).

The initial parameters of the mixture: pressure P ₀ = 0.095 MPa, temperature Τ ₀ = 130 ° C.

The compression ratio is n = 9.3.

The image (Fig. 3a) obtained using a scanning electron microscope (CEM image) shows that the product consists of entangled nanoscale filaments. The image (Fig. 3b) obtained using a transmission electron microscope (PEM image) shows that the particles are close in size. The diffraction pattern shown in FIG. 3d shows the presence of amorphous and crystalline phases of silicon. The crystalline phase S of silicon is represented by three diffraction lines 111, 220, and 311. The PEM image of silicon particles having a characteristic size of 40 nm (Fig. 3c) shows that they consist of silicon nanocrystals and are coated with a thin layer of the amorphous phase.

Example 2. An experiment from 02/08/2013 on adiabatic compression of a mixture of SiH ₄ (10%) + Ar (90%).

The initial parameters of the mixture: pressure P ₀ = 0.095 MPa, temperature Τ ₀ = 130 ° C.

The compression ratio is n = 4.0.

The CEM image (Fig. 4a) shows that the morphology of the product is similar to that of Example 1. The PEM image (Fig. 4b) shows that the particles have almost the same size. The diffractogram (Fig. 4d) and the PEM image (Fig. 4c) show the presence of an exclusively amorphous phase of silicon. Silicon nanoparticles are oval or spherical in shape.

Examples 3, 4, 5 are similar to example 1, but the compression ratio is n = 5.7; n = 6.7; n = 7.5, respectively.

Diffraction patterns of silicon nanopowders obtained at compression ratios of 5.7; 6.7; and 7.5 are presented in figure 5. It is seen that with an increase in the degree of compression, the fraction of the crystalline phase of silicon increases.

According to atomic emission spectral analysis, the purity of nanosilicon obtained by adiabatic compression is 99.90 wt. %, which corresponds to solar-grade silicon. The main impurities are: Fe - 0.03%; Al - 0.03%; Cu - 0.02%; Ti and Zn are 0.001.

Thus, the proposed method allows the selection of certain adiabatic compression modes to obtain solar-grade silicon nanoparticles with sizes from 30 to 100 nm in amorphous and crystalline form. The method can be quite simply implemented in production lines, as it does not require sophisticated equipment and highly qualified staff.

Claims (1)

A method of producing silicon nanosized structures by thermal decomposition of monosilane, characterized in that the decomposition of monosilane is carried out by adiabatic compression of a mixture of 10 vol.% Monosilane in argon at an initial pressure of 0.095 MPa and a temperature of 130 ° C.

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