RU2336224C1 - Method of production of regular systems of nano-size silicon whiskers - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: method of production of regular systems of nano-size silicon whiskers includes preparation of silicon plate by masking of its surface with photoresist, making holes in it, electrochemical deposition of metal islets into photoresist holes from electrolyte solution, and installation of prepared plate into growth furnace with further growing of silicon whiskers on it, at that cylindrical openings in photoresist are created with diameter of less than 250 nm by means of imprint-lithography, metal islets are deposited with thickness of less than 12.5 nm, after that photoresist is removed in 5% solution of hydrofluoric acid.

EFFECT: method makes it possible to considerably facilitate creation of nano-technological instruments on nano-crystals.

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Description

The invention relates to a technology for producing semiconductor nanostructured materials, is intended for growing regular systems of whisker silicon nanocrystals by gas transport chemical reactions in an open flow system.

Currently, there is a known method of creating regularly ordered systems of nanoscale whiskers (NCs), using at its core the principle of setting the same particle size of the activator metal. In [1], silicon nanowires were grown using colloidal Au particles on the surface of Si-SiO ₂ with a very small diameter difference during the pyrolysis of monosilane (SiH ₄ + 10% He). For this purpose, “nanogrob” of gold with a diameter of 8.4 ± 0.9 nm was deposited _{on a} SiO ₂ substrate from a solution of colloidal gold. Then, a Si-SiO ₂ 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 disadvantage of this method [1] is the large variation in the diameters of the grown crystals (5–30%) and the inability to ensure the identical size of the droplets of colloidal gold.

The closest technical solution that we have chosen as a prototype is the method of growing regular silicon nanocrystals, proposed in patent No. 2117081 [2]. The difference of this method is that the surface of a silicon wafer is masked by photoresist photolithography, and the activator metal is deposited by electrochemical deposition of metal islands from an electrolyte solution. The disadvantage of this method is its unsuitability for creating regular systems of nanoscale nanowires with diameters less than 100 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 photolistography methods used in the photoresistor. 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 activating metal of the pancreas with the same size of growth of nanoscale whiskers.

The invention is directed to the controlled manufacture of periodic surface structures of whiskers of nanometer diameters.

This is achieved by the fact that before placing the silicon wafer in the growth furnace and growing whiskers on it, the surface of the silicon wafer is masked with a photoresist, after which cylindrical holes with a diameter of less than 250 nm are created using imprint lithography with the subsequent deposition of metal islands with a thickness of less than 12 , 5 nm from the electrolyte solution and the removal of the photoresist in a 5% hydrofluoric acid solution.

A method of growing regular whisker silicon nanocrystals having a diameter of less than 100 nm is as follows. A photoresist layer is applied to the surface of a single-crystal silicon wafer by centrifugation. Then, holes (“windows”) of the required size are engraved in the photoresist using imprint lithography. In the “windows”, the metal of the initiating impurity is electrochemically deposited. Thus, on a silicon plate, which is an electrode, metal columns (islands) are grown with a given ratio of height to diameter to form a single nanodrople in each “window” during fusion. Then the substrate is placed in a quartz reactor, purged with hydrogen, is heated to a growth temperature. Within a few minutes, the metal nanoparticles are fused to a substrate in hydrogen. Then, the feeding material is fed into the gas phase and the nanocrystals are grown.

The use of the imprint lithography method is determined by the fact that the photolithography methods existing today do not make it possible to ensure element sizes less than 0.3 microns. The effectiveness of imprint lithography in our case is also achieved by the fact that only one lithography process is required to create a nanostructure, which eliminates the difficulties in combining stamps to form different layers of structures, which are the main limitations in the application of the imprint lithographic method.

The diameter of the hole in the photoresist (250 nm or less) is determined by the fact that the ratio of the diameter of the melting hole of the activator metal at the base of the whisker to the diameter of the crystal in the cylindrical portion of the single crystal silicon rod is 2.5. Thus, in order to obtain a nanometer (100 nm or less) across the crystal, it is necessary to set a 2.5 times larger diameter of the base of the NC.

The thickness of the layer of electrolytic precipitate in the holes of the photoresist (12.5 nm or less) is determined by the fact that for the formation of a single drop of metal-silicon solution-melt in the "window" it is necessary to provide a thickness-diameter ratio for a metal island of 0.02-0.05 ( depending on the type of metal).

The removal of photoresist residues in a weak aqueous solution of hydrofluoric acid after electrochemical deposition of the metal is due to the fact that in HF, simultaneously with the removal of the photoresist, the layer of silicon dioxide and other impurities are etched, which can appear on the plate during previous technological operations. Thus, along with the removal of the photoresist, the silicon wafer is cleaned of contaminants.

Using the proposed method can significantly facilitate the solution of the problem of creating high-density integrated devices on nanowires (random-access memory devices of computers), creating unheated cathodes of emission devices, high density of electron emission, manufacturing of light-emitting devices, etc.

Examples of the method.

Example 1

A single-crystal silicon wafer with a crystallographic orientation of {111} and a diameter of 300 mm was coated with ultraviolet radiation sensitive photoresistive organic material covering the surface of the crystal. Then, using imprint lithography, a system of nano-holes or “nano-windows” was formed using imprint lithography using known imprinting techniques. The diameter of each hole was 80 nm, and the distance between the centers of the holes was 70 nm.

In a solution of phosphate electrolyte gilding, an electrochemical layer of gold 3 nm thick was deposited on open areas of a silicon wafer open in "windows". In this case, the plate served as a conducting cathode distributing potential over the entire area of the plate. Since the photoresist is a dielectric, the electrolytic precipitate covered only open areas. In order for gold not to stand out on the non-front side of the plate, it was covered with a protective dielectric varnish.

After electrodeposition, the photoresist was removed in an aqueous 5% hydrofluoric acid solution. Regularly located islands of the activator metal of the same size formed on the silicon wafer.

Prepared substrates were cut and placed in a growth furnace. Within 2-10 minutes at a temperature of 900-1100 ° C, gold was fused with silicon and nanodroplets of Au-Si melt were formed. Then, silicon tetrachloride was _introduced into the gas phase at a molar ratio M _SiCl4 / M _H2 = 0.008, and whisker nanocrystals were grown. The growing time was (2-10) min, depending on the required height of the nanocrystals. The crystals had a diameter of 32 ± 1 nm and a length of ~ 200 nm.

Example 2

The growth of whisker nanocrystals was carried out analogously to example 1, but electrolytic nickel was used as a metal activator of pancreatic growth. The thickness of the sediment layer was 5 nm. Precipitation of the metal was carried out from a solution of nickel chloride. The grown nanocrystals had a diameter of 30 ± 1 nm and a length of ~ 150 nm.

Example 3

The implementation of the invention was carried out analogously to example 1, but the time of removal of the photoresist layer in a 5% solution of hydrofluoric acid was increased 5 times. 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 layer of sediment was 10 nm, and the temperature of the cultivation was 100 degrees lower. The results obtained were consistent with the results of example 1, but the diameters of the nanocrystals were 35 ± 1 nm.

List of sources used

1. Gudiksen, M.S., Lieber C.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.

Claims (1)

A method of obtaining regular systems of nanoscale whiskers of silicon, including preparing a silicon wafer by masking its surface with a photoresist, creating holes in it, electrochemical deposition of metal islands from an electrolyte solution into the holes of a photoresist, and placing the prepared wafer in a growth furnace, followed by growing whiskers on it characterized in that the cylindrical holes in the photoresist create a diameter of less than 250 nm by imprint lithography, metal islands deposited ayut thickness of less than 12.5 nm, after which the photoresist is removed in a 5% hydrofluoric acid solution.