RU2526066C1 - Method of obtaining thread-like nanocrystals of semiconductors - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes the preparation of a silicon wafer by the application of nanodisperse catalyst particles on its surface with further placement into the growth furnace, heating and precipitation of the crystallised substance from the gas phase by scheme vapour→drop liquid→crystal, with the silicon wafer before the application of the catalyst particles and placement of a substrate into the growth furnace being doped with phosphorus to a specific resistance of 0.008-0.018 Ohm·cm and subjected to anodic treatment for not longer than 5 min with illumination of halogen lamp in a mixture of a 48% solution of HF and C₂H₅OH (96%) in a ratio of 1:1, with a density of anodisation current being supported at the level not lower than 10 mA/cm², and the catalyst nanoparticles being applied by electron-beam sputtering of not more than 2 nm thick metal film.

EFFECT: possibility of obtaining fine semiconductor thread-like nanocrystals with a diameter less than 10 nm, evenly distributed on the surface of the substrate and having high surface density.

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Description

The invention relates to a technology for producing semiconductor nanostructured materials intended for growing on silicon substrates according to the scheme steam → droplet liquid → crystal (PLC) thin whisker nanocrystals uniformly distributed over the surface of the substrate and having a high surface density.

Currently, there is a known method of creating regularly ordered systems of nanoscale whiskers (NCs), using in its basis the principle of setting the same particle size of the metal catalyst. In [1], during the pyrolysis of monosilane (SiH ₄ + 10% He) with a small variation in diameters, silicon nanowires were grown using colloidal gold particles on the surface of Si-SiO ₂ . For this, gold nanodrobes with a diameter of 8.4 ± 0.9 nm were deposited from a solution of colloidal gold on a smooth Si-SiO ₂ substrate. Then, a substrate with deposited gold particles was placed in a furnace. The transverse dimensions of the nanocrystals were: 6.4 ± 1.2 nm; 12.3 ± 2.5 nm; 20.0 ± 2.3 nm and 31.1 ± 2.7 nm. The disadvantages of the method [1] is the large variation in the diameter of the grown crystals (5-30%), the uneven distribution of crystals on the surface of the substrate and the inability to ensure the identical size of the droplets of colloidal gold.

DESCRIPTION OF THE INVENTION

A known method of growing regular silicon NC systems is described in patent No. 2117081 [2], in which the surface of a smooth silicon wafer is masked by photoresist photolithography, and the metal catalyst is deposited by electrochemical deposition of islands from an electrolyte solution. The disadvantage of this method is the unsuitability for creating nanoscale nanowires with diameters substantially less than 1000 nm due to the physical limits of the applied photolithographic methods, since it is not possible to form cylindrical holes with diameters substantially less than 250 nm using the photolithography methods used in photoresist. And the creation of holes in the photoresist with transverse dimensions much less than 250 nm is the main necessary condition for the formation of nanoparticles of the metal-catalyst of the FFA-growth of nanosized whiskers of the same size.

The closest technical solution that we have chosen as a prototype is a method of growing regular silicon nanocrystal systems, proposed in patent No. 2336224 [3]. The difference of this method is that cylindrical holes in the photoresist are created by imprint lithography with a diameter of less than 250 nm, metal islands of thickness less than 12.5 nm are deposited from the electrolyte solution, and then the photoresist in a 5% hydrofluoric acid solution is removed. The disadvantage of this method is its unsuitability for creating thin and ultrathin (units and tenths of a nanometer) NC semiconductor materials due to restrictions on the design standards of elements formed by imprint lithography (the achieved resolution of elements in imprint lithography for industrial products is 20-25 nm, for laboratory samples - 5-6 nm, and the distance between structural elements is 20-30 nm).

The invention is directed to the controlled manufacture of surface structures of thin and ultrathin whisker nanocrystals of semiconductor materials.

This is achieved by the fact that before applying the catalyst particles and placing the substrate in a growth furnace, the silicon wafer is doped with phosphorus to a specific resistance of 0.008-0.018 Ohm · cm and anodized for no more than 5 min in a mixture of a 48% solution of HF and C ₂ H ₅ OH ( 96%) in a 1: 1 ratio, whereby the anodization current density is maintained at a level of at least 10 mA / cm ² , and the catalyst nanoparticles are deposited by electron beam sputtering of a metal film with a thickness of not more than 2 nm.

A method of growing thin and ultra-thin whisker nanocrystals of semiconductor materials having a diameter of the order of nanometer units or less is as follows. The surface of a silicon wafer with a crystallographic orientation of (111) or (100) is heavily doped with phosphorus. Then, at a certain current density, process time and a given electrolyte composition, electrochemical etching of a silicon wafer heavily phosphorus-doped with phosphorus is carried out, which is the anode of the electrochemical cell. Thus, in the plate itself, pores or wells with uniform diameters of the order of a few or tenths of a nanometer are uniformly distributed over its surface. Subsequently, a thin film of the catalyst metal is sprayed onto the porous surface of the silicon wafer. Then the substrate is placed in a quartz reactor, purged with hydrogen, is heated to the temperature of the growth of nanocrystals. Within a few minutes, a thin film of the metal catalyst is divided into small nanoparticles localized in the pores in hydrogen and the metal nanoparticles are fused with the substrate. Then, the feeding material is fed into the gas phase and ultrafine whisker nanocrystals are grown.

Doping with phosphorus is determined by the fact that the phosphorus atoms embedded in silicon are activators of the formation of nanopores during subsequent electrochemical etching, and the smooth surface layer of the silicon substrate is coated with a uniform porous layer with pore sizes (radii) of 3 nm or less.

The value of the specific electrical resistance (0.008-0.018 Ohm · cm) of silicon is determined by the fact that, at the specified values of the specific resistance, the corresponding concentration of phosphorus atoms in silicon provides nanopores with sizes of 3 nm or less, allowing the formation of metal catalyst nanoparticles in their volume, which contribute to the production thin and ultrathin NK. To obtain a nanocrystal of a given diameter, it is necessary to set a 2.5 times larger diameter of the base of the nanocrystal. Nanopores with radii of 3 nm make it possible to obtain nanowires with diameters of the order of 2.4 nm.

The duration of the anodization of the silicon surface is not more than 5 min due to the need to minimize the bulk size of nanopores for the subsequent formation of the catalyst nanoparticles of the required volumes and the growth of thin and ultrathin nanocrystals, since the diameter and depth of the pores increase with anodization time.

High surface quality during anodic dissolution of silicon is provided in an anhydrous electrolyte, which is a solution of hydrofluoric acid (HF) in ethanol. The electrolyte composition (a mixture of a 48% solution of HF and C ₂ H ₅ OH (96%) in a 1: 1 ratio) is determined by the need for the presence of a solvent in the etching solution (hydrofluoric acid) to dissolve silicon oxide.

The anode current density of 10 mA / cm ² due to its optimal value to obtain the necessary results of etching silicon. A lower current density only leads to etching of silicon and is insufficient for the formation of pores. A large anodization current density causes microscopic erosion of the silicon surface.

The thickness of the metal film of not more than 2 nm is determined by the fact that for the formation of a single drop of metal catalyst in the pore volume with radii of 3 nm, it is necessary to ensure a ratio of film thickness to pore diameter of 0.33.

Using the proposed method can significantly facilitate the solution of the problem of creating nanoelectronic devices based on ultrathin whisker nanocrystals (solar cells based on photovoltaic photovoltaic structures of solar cells modified by nanowires, multichannel field-effect transistors with a shell gate, random access memory devices of high-density information computers, etc.).

Examples of the method

Example 1

The initial KDB (100) silicon wafers were doped with phosphorus in an SD.OM-3/100 single-zone diffusion furnace to a specific electric resistance of 0.018 Ohm · cm. Phosphorus trichloride (os.h) was used as a diffusant. Then, an electrochemical anodization of the silicon surface was carried out for 5 min in a Teflon electrolytic cell, where a silicon wafer and a platinum cathode were located. A mixture of hydrofluoric acid (HF, 48%) and ethanol (C ₂ H ₅ OH, 96%) in a 1: 1 ratio was used as the electrolyte. A halogen lamp was used to illuminate the back of the plate. After anodizing, a thin nickel film 2 nm thick was sprayed on the wafer surface on a VAK-501 electron-beam installation. Prepared substrates were cut and placed in a growth furnace. Within 2-10 minutes, at a temperature of 900-1100 ° C, nickel was fused with silicon and nanodroplets of Ni-Si melt were formed. Then, silicon tetrachloride was _introduced into the gas phase at a molar ratio M _SiCl4 / M _H2 = 0.008, and silicon _{nanocrystals were} grown. The growing time was (2-10) minutes, depending on the required length of the nanocrystals. Silicon crystals had a diameter of 2.4 ± 0.2 nm and a length of ~ 25 nm.

Example 2

The cultivation of ultrafine whisker nanocrystals was carried out analogously to example 1, but electrolytic copper was used as a metal catalyst for FFA growth. The thickness of the thin film of copper was 2 nm. The grown NCs had a diameter of 2.2 ± 0.2 nm and a length of ~ 30 nm.

Example 3

The invention was carried out analogously to example 1, but the silicon wafers were doped with phosphorus to a specific resistance of 0.008 Ohm · cm. The results obtained were consistent with the results of example 1.

Example 4

The implementation of the invention was carried out analogously to example 1, but the thickness of the sprayed film of Nickel was 1.5 nm. The results obtained were consistent with the results of example 1, but the diameters of the grown nanocrystals were 1.6 ± 0.2 nm.

Example 5

The cultivation of ultrafine whisker nanocrystals was carried out analogously to example 1, but tin was used as a metal catalyst for FFA growth. The thickness of the thin tin film was 2 nm. The grown NCs had a diameter of 1.4 ± 0.2 nm and a length of ~ 15 nm.

Example 6

The implementation of the invention was carried out analogously to example 1, but silicon tetrachloride (SiCl ₄ ) and germanium tetrachloride (GeCl ₄ ) were fed into the gas phase and the nanocrystals of the Si _x Ge _1-x solid solution were grown. The ratio of volume concentrations of SiCl ₄ and GeCl ₄ was 1: 1. The crystals of the solid solution Si _x Ge _1-x had a diameter of 2.6 ± 0.2 nm and a length of ~ 20 nm.

Example 7

The invention was carried out analogously to example 1, but germanium tetrachloride (GeCl ₄ ) was introduced into the gas phase at a molar ratio M _GeCl4 / M _H2 = 0.008 and a temperature of 700-800 ° C and germanium _{nanocrystals were} grown. The ratio of volume concentrations of SiCl ₄ and GeCl ₄ was 1: 1. Germanium crystals had a diameter of 1.9 ± 0.2 nm and a length of ~ 28 nm.

List of sources used

1. Gudiksen M.S., Lieber S.M. Diameter-selective synthesis of semiconductor nanowires // J. Am. Chem. Soc; (Communication); 2000; 122 (36); pp. 8801-8802.

2. RF patent No. 2117081, IPC ⁶ C30B 029/62, 025/02 / A.A. Schetinin, V. A. Nebolsin, A. I. Dunaev, E. E. Popova, P. Yu. Boldyrev.

3. RF patent No. 2336224, IPC ⁶ C30B 029/62, 025/00 / V.A. Nebolsin, A. A. Schetinin, A. I. Dunaev, M. A. Zavalishin.

Claims (1)

A method for producing whisker nanocrystals of semiconductor materials, comprising preparing a silicon wafer by depositing nanosized catalyst particles on its surface, followed by placement in a growth furnace, heating and precipitating a crystallizable substance from the gas phase according to the vapor → droplet → crystal scheme, characterized in that the silicon wafer is doped phosphorus to a specific resistance of 0.008-0.018 Ohm · cm and anodize for a duration of not more than 5 minutes in a mixture of 48% solution of HF and C ₂ H ₅ OH (96%) in a ratio of 1: 1, and the raft The anodization current is maintained at 10 mA / cm ² , and the catalyst nanoparticles are deposited by electron beam sputtering of a metal film with a thickness of not more than 2 nm.