RU2597801C1 - Diffraction periodic microstructure based on porous silicon - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to diffraction periodic microstructures for visible range, based on porous silicon. In diffraction periodic microstructure based on porous silicon, comprising a substrate, made of monocrystalline silicon with a diffraction periodic microstructure, formed diffraction periodic microstructure based on porous silicon comprises ion-synthesised metal-containing nanoparticles, dispersed in surface region of substrate at layer thickness from 10 to 200 nm with metal concentration of 2.5·10²⁰-6.5·10²³ atoms/cm³.

EFFECT: technical effect consists in creation of a diffraction periodic microstructure based on porous silicon with different metal-containing nanoparticles.

1 cl, 20 dwg

Description

The invention relates to optics [1], and in particular to devices for periodic diffraction microstructures (diffraction gratings, photonic crystals, etc.) for the visible range, made on the basis of porous silicon. In practice, periodic structures and gratings based on various semiconductors are used:

- in the elements of optical communication for introducing laser radiation into the thin-film waveguides or filtering the optical signal in the waveguide (periodic structures — Bragg gratings);

- for focusing singular vortex laser beams for sealing channels of information transmission;

- as test objects for calibrating magnification using a transmission electron microscope;

- to convert non-radiation plasmon-polariton modes into radiation ones;

- as resonators with distributed feedback in waveguide lasers, diffraction elements used to control light [1], etc.

A device is known, selected as an analog, made in the form of a diffraction grating, made on the surface of a single-crystal silicon substrate in the form of a periodic microstructure - alternating regions of single-crystal and amorphized silicon (Fattakhov Y.V., Galyautdinov M.F., Lvova T.N., Khaibullin IB A method for producing holograms on silicon (RF Patent No. 2120653, published October 20, 1998).

A disadvantage of the analogue is that such a diffraction grating on silicon does not contain periodic regions of porous silicon with metal-containing nanoparticles, and therefore these periodic structures do not have the properties of a metal-porous silicon composite material. In addition, the periodic diffraction microstructure described in the analogue is only a strip diffraction grating, in which the possibility of creating a periodic diffraction microstructure with the elements of its components of various shapes (square, triangular, etc.) is not realized.

It is known [2] a device made in the form of an optical diffraction grating based on a semiconductor - silicon, in which the formation of a given periodic microstructure (regions of silicon alternating with regions of porous silicon with gold nanoparticles) is carried out by a single-stage method for the simultaneous creation of porous silicon and the deposition of gold from it from gold a solution (etchant) containing hydrochloric acid and hydrofluoric acid. A periodic diffraction microstructure is formed when an acid solution - silicon interface is inhomogeneous over the illumination surface during etching. Illumination nonuniform in area means an interference field formed by two coherent linearly polarized light beams incident on the surface of the sample. As a result of the photochemical reaction, stable periodic spatial structures (diffraction grating) are formed, formed from silicon regions (unlit regions), alternating with local regions consisting of porous silicon with gold nanoparticles (illuminated regions). Hydrochloric acid is used for photoreduction of gold nanoparticles.

This periodic diffraction microstructure of the diffraction grating [2] based on porous silicon is the closest to the claimed method and is therefore selected as a prototype.

The disadvantages of the prototype:

- the periodic diffraction microstructure described in the prototype [2] is only a strip diffraction grating, in which the possibility of creating a periodic diffraction microstructure with the elements of its components of various shapes (square, triangular, etc.) is not realized;

- a diffractive periodic structure based on porous silicon, described in the prototype [2], can only be formed using a special oxidizing etching solution with noble metal ions. This reduces the available set of types of metals from which nanoparticles are formed, and thereby limit the set of composite materials based on porous silicon with metal nanoparticles for the construction of various diffraction devices and periodic structures.

The technical problem to be solved in the proposed application is to create a periodic diffraction microstructure based on porous silicon with various metal-containing nanoparticles.

The problem in the proposed technical solution in a periodic diffraction microstructure based on porous silicon, containing a substrate made of single crystal silicon with a diffraction periodic microstructure, is achieved by the fact that the formed diffractive periodic microstructure based on porous silicon contains ion-synthesized metal-containing nanoparticles dispersed in the surface region substrate at a layer thickness of from 10 to 200 nm at a metal concentration of 2.5 10 ²⁰ -6.5 × 10 ²³ but ohms / cm ^3.

In FIG. 1. An isometric drawing of a fragment of a periodic diffraction structure (diffraction grating — product) is shown, comprising: 1 — a substrate of single-crystal silicon; 2 - implanted cells of porous silicon; 3 - unirradiated partitions of single-crystal silicon between cells.

In FIG. 2. The calculated depth distribution of implanted silver in silicon is shown at an irradiation energy of 30 keV.

In FIG. 3. Image shown on a scanning electron microscope (SEM) at low magnification of the surface of a layer of porous silicon formed by implantation of single-crystal silicon with silver ions.

In FIG. 4. The image obtained by SEM at high magnification of the surface of a layer of porous silicon formed by the implantation of single-crystal silicon by silver ions is shown.

In FIG. 5. An SEM image of the surface of unimplanted silicon is shown.

In FIG. 6. A histogram of the pore size distribution in the structure of porous silicon (Fig. 2), formed by the implantation of single-crystal silicon by silver ions, is shown.

In FIG. 7. The optical reflection spectra of unirradiated silicon (1) and porous silicon with ion-synthesized silver nanoparticles (2) are shown.

In FIG. 8. An AFM image of the surface of a layer of porous silicon formed by the implantation of single-crystal silicon by silver ions is shown.

In FIG. 9. A cross-section profile of individual pores is shown, measured in the direction indicated in the fragment of FIG. 8.

In FIG. 10. The AFM image of the surface of microstructured single-crystal silicon (a fragment of the diffraction grating) implanted by silver ions through a surface mask is shown.

In FIG. 11. An optical microscope image of microstructured single-crystal silicon (a fragment of the diffraction grating) implanted by silver ions through a surface mask is shown. The cell size is 20 microns. The light illuminating the grill is directed from the lower right corner.

In FIG. 12. The image of the diffraction scattering pattern shown on the screen when reflecting the probe radiation of a helium-neon laser at a wavelength of 632.8 nm of light from microstructured silicon with periodic regions of porous silicon formed by implantation of silver ions is shown.

In FIG. 13. An SEM image of the surface of a layer of porous silicon obtained after implantation by single-crystal silicon ions of Ag ⁺ at a substrate temperature during irradiation of 200 ° C is shown.

In FIG. 14. The image obtained on an optical microscope shows microstructured single-crystal silicon (a fragment of a periodic microstructure) implanted with silver ions through a surface mask - a metal grid in the form of stripes. The distance between the strip structures is 40 μm.

In FIG. 15. The SEM image shown on a microscope at low magnification of the surface of a layer of porous silicon formed by the implantation of single-crystal silicon by cobalt ions is shown.

In FIG. 16. The SEM image obtained on a microscope at high magnification of the surface of a layer of porous silicon formed by implantation of single-crystal silicon by cobalt ions is shown.

In FIG. 17. An SEM image of the surface of microstructured single-crystal silicon (a fragment of the diffraction grating) implanted by cobalt ions through a surface mask is shown.

In FIG. 18. The image obtained using an optical microscope shows microstructured single-crystal silicon (a fragment of the diffraction grating) implanted with cobalt ions through a surface mask. The cell size is 20 microns.

In FIG. 19. An SEM image of the surface of a layer of porous silicon formed by implantation of single-crystal silicon by copper ions is shown.

In FIG. 20. An SEM image of the surface of microstructured single-crystal silicon (a fragment of the diffraction grating) implanted by copper ions through a surface mask is shown.

Consider a method of manufacturing a diffractive periodic microstructure based on porous silicon using specific examples. The condition for manufacturing a periodic diffraction microstructure based on porous silicon includes the formation of a predetermined microstructure of porous silicon on the surface of the initial single-crystal silicon substrate. The formation of a given periodic diffraction microstructure is carried out by implantation with noble or transition metal ions through a surface mask, with an energy of 5-100 keV, an irradiation dose that provides a concentration of introduced metal atoms in the irradiated silicon substrate of 2.5 · 10 ²⁰ -6.5 · 10 ²³ atoms / cm ³ , the ion beam current density of 2 · 10 ¹² -1 · 10 ¹⁴ ion / cm ² s at a substrate temperature during irradiation of 15-450 ° C.

In FIG. 1 is an isometric drawing of a porous silicon diffraction grating (product) containing a substrate 1 (made of single crystal silicon material) with a diffraction periodic microstructure on its surface, the elements of which are regions subjected to ion irradiation — implanted cells 2 (regions of porous silicon) and characterized by a different dielectric constant relative to the substrate material 1. The periodic diffraction microstructure of the implanted cells 2 contains ion synthesis metal nanoparticles dispersed in the near-surface region of the substrate 1 at a layer thickness of 10 to 200 nm at a metal atom concentration of 2.5 · 10 ²⁰ -6.5 · 10 ²³ atoms / cm ³ . Unirradiated partitions 3 located between the implanted cells 2 have the same dielectric constant as the silicon substrate 1.

Example 1. The diffraction grating is made on the basis of porous silicon, its manufacturing method involves the formation of a predetermined periodic diffraction microstructure based on porous silicon, while the formation of a given periodic diffraction microstructure was carried out by implantation on an ILU-3 accelerator with noble metal ions Ag ⁺ through a surface mask - a metal grid with a mesh size of 20 microns, with the energy E = 30 keV, a dose of D = 1.5 · October ¹⁷ ion / cm ^2, providing a metal concentration of the introduced atoms and 6.0 · October ²² atoms / cm ³ in the irradiated silicon substrate, the ion beam current density J = 3 10 ¹³ ions / cm ² at room temperature of the substrate during exposure.

Modeling the concentration profiles of the distribution of implanted silver with an energy of 30 keV into silicon in depth using the SRIM-2013 computer algorithm [3] (Fig. 2) showed that silver atoms accumulate in the near-surface implanted silicon layer, leading to the nucleation and growth of metal nanoparticles . The total thickness of the implanted layer with silver nanoparticles, and, consequently, the thickness of the active layer of the formed diffraction grating in silicon, for these implantation conditions, does not exceed 60 nm.

In FIG. Figures 3 and 4 show, at various scales, images of the surface of silicon implanted with silver ions, observed with a Merlin Zeiss scanning electron microscope (SEM). As follows from the presented SEM images, the morphology of irradiated silicon, in contrast to the initial polished substrate of single-crystal silicon (Fig. 5), is characterized by the presence of a pronounced porous silicon structure. Moreover, the porous silicon layer formed by implantation looks uniform over a large area of the sample of tens of microns (Fig. 3), which is an important characteristic for technological applications (scalability) [4].

The increase in the surface fragment (Fig. 4) allows us to estimate the average diameter of the pore openings (black areas): ~ 150-180 nm, as follows from the histogram of pore size distribution (Fig. 6), and the pore wall thickness (light gray areas): ~ 30-60 nm.

It should be noted that the formation of a layer of porous silicon occurs immediately or simultaneously with the nucleation and growth of metal nanoparticles from implanted impurity ions. In the case of Example 1, simultaneously with the growth of silicon pores during the implantation of single-crystal silicon, silver nanoparticles are formed. In FIG. 4 silver nanoparticles are clearly visible in the form of bright spots on the walls of silicon pores. The average nanoparticle size is estimated to be of the order of 5-15 nm.

In FIG. 7. The experimental linear optical reflection spectra are shown for the initial silicon, as well as for the porous silicon obtained by implantation with silver ions, measured on an Avantes-2014 spectrometer. Unlike the original silicon matrix of FIG. 7 (1), the implanted sample of FIG. 7 (2) is characterized by the presence in the visible region of the spectrum of a selective absorption band with a maximum of ~ 850 nm. This band indicates the formation of silver nanoparticles in the silicon matrix, and it is due to the manifestation of the surface plasmon resonance effect in metal nanoparticles [7].

Additional information confirming the formation of a layer of porous silicon upon implantation on the surface of single-crystal silicon implanted with silver ions was observed with an atomic force microscope (ACM) Innova Bruker. In FIG. Figure 8 shows AFM images of a fragment of the surface of porous silicon, which look typical of porous silicon structures synthesized by electrochemical methods [3]. In FIG. 9 shows a sectional profile of individual pores measured in the direction indicated in FIG. 8, allowing to evaluate the pore depth: ~ 100 nm. Thus, it can also be concluded from AFM that a layer of porous silicon is formed as a result of silicon implantation with silver ions.

Surface microstructures implanted with silver ions through a silicon mask were observed on a FastScan Brucker AFM microscope (Fig. 10) and on a Micromed POLAR-1 optical microscope (Fig. 11). It can be seen in the above images that the surface of the sample is an ordered lattice with cells 20 microns in size, which are formed upon implantation of silicon with silver ions in a given mode. In this case, the square cell represents the structure of porous silicon with silver nanoparticles, shown in FIG. 4. The walls between the cells of the lattice consist of unirradiated single-crystal silicon.

The resulting diffraction grating shown in FIG. 10 and 11, corresponds to the drawing shown in FIG. one.

Since it is known that implantation of metal ions in dielectrics and semiconductors leads to an increase in its refractive index by ~ 0.2–0.4 for the visible spectral region (especially at the plasmon resonance frequencies of metal nanoparticles) [6], it is obvious that silicon implantation through the mask forms a microstructure with a periodically variable distribution of the optical constants of the material, i.e. between the lattice cells and its walls (n _Si = 3.4).

Thus, the microstructure formed by implantation with a periodically variable refractive index is a periodic diffraction structure — a lattice. In FIG. Figure 12 shows a diffraction image recorded during the probing of the formed lattice by a helium-neon laser at a wavelength of 632.8 nm light.

Example 2. As the substrate using a plate of single-crystal silicon. The implantation is carried out on the ILU-3 accelerator by singly charged ions of the noble metal Ag ⁺ through a surface mask — a metal grid in the form of strips, the distance between which is 40 μm, with an energy of E = 30 keV, an irradiation dose of D = 1.0 · 10 ¹⁷ ion / cm ² , providing a concentration of introduced metal atoms in the irradiated substrate 2.0 · 10 ²² atoms / cm ³ , ion current density J = 3 · 10 ¹³ ion / cm ² s, at a substrate temperature during irradiation of 200 ° C.

A SEM image of the surface of a modified material obtained after implantation with single crystal silicon ions by Ag ⁺ ions at a substrate temperature during irradiation of 200 ° C is shown in FIG. 13. As can be seen from FIG. 13, similarly to implantation by silver ions into an unheated silicon substrate (Figs. 3 and 4), the morphology of the surface obtained by implantation of heated silicon is also characterized by a developed structure of porous silicon.

Surface microstructures implanted with silver ions through a silicon mask were observed on an optical microscope (Fig. 14). The image shows that the sample is an ordered periodic strip, the distance between which is 40 μm, which are formed during the implantation of silicon by silver ions in a given mode. In this case, the dark bands are areas of unimplanted single-crystal silicon, masked during implantation, and the light areas correspond to porous silicon (Fig. 14).

Example 3. As the substrate using a plate of single-crystal silicon. The implantation is carried out on the ILU-3 accelerator by single-charged Co ⁺ transition metal ions through a surface mask - a metal mesh with a mesh size of 20 μm, with an energy of E = 40 keV, an irradiation dose of D = 1.5 · 10 ¹⁷ ion / cm ² , which ensures the concentration of introduced metal atoms in the irradiated substrate, 10 ²³ atoms / cm ³ , the current density of the ion beam J = 3 · 10 ¹³ ion / cm ² s and room temperature of the substrate during irradiation.

Modeling the concentration profiles of the distribution of implanted cobalt with an energy of 40 keV into silicon in depth using the computer algorithm SRIM-2013 [3] showed that cobalt atoms accumulate in the near-surface implanted silicon layer, and the total thickness of the implanted near-surface layer will not exceed ~ 80 nm .

SEM images at various scales of the surface of single-crystal silicon implanted with Co ⁺ ions are shown in FIG. 15 and 16. Like implantation with silver ions (Fig. 3 and 4), the morphology of the implanted smooth smooth surface of silicon (Fig. 5) is transformed into a developed porous silicon structure. Also, the porous silicon layer formed by implantation looks rather uniform and scalable over a large area of the sample of tens of microns (Fig. 15). The porous surface of silicon at an enlarged scale (Fig. 16). It is known that when silicon is implanted with cobalt ions, metal-containing nanoparticles — cobalt silicide [7] —are formed, which, respectively, are in the structure of porous silicon (Figs. 15 and 16) formed under the indicated implantation conditions of Example 3.

Surface microstructures implanted with cobalt ions through a silicon mask were observed on a SEM microscope (Fig. 17) and on an optical microscope (Fig. 18). It can be seen in the above images that the surface of the sample is an ordered lattice with cells of 20 μm in size, which are formed upon implantation of silicon with cobalt ions in a given mode. In this case, the square cell represents the structure of porous silicon shown in FIG. 15 and 16. The walls between the square cells of the lattice consist of unirradiated single-crystal silicon.

Example 4. As the substrate using a plate of single-crystal silicon. The implantation is carried out on the ILU-3 accelerator with singly charged transition metal ions Cu ⁺ through a surface mask - a metal mesh with a mesh size of 20 μm, with an energy of E = 40 keV, an irradiation dose of D = 1.5 · 10 ¹⁷ ion / cm ² , which ensures the concentration of introduced metal atoms in the irradiated substrate, 10 ²³ atoms / cm ³ , the ion beam current density J = 3 · 10 ¹³ ion / cm ² s at room temperature of the substrate during irradiation.

Modeling the concentration profiles of the distribution of implanted copper with an energy of 40 keV into silicon in depth using the SRIM-2013 computer algorithm [3] showed that copper atoms accumulate in the near-surface implanted silicon layer, and the total thickness of the implanted near-surface layer will not exceed ~ 80 nm

SEM images of the surface of single-crystal silicon implanted with Cu ⁺ ions are shown in FIG. 19. Similarly to implantation with silver ions (Figs. 3 and 4), the morphology of the implanted smooth smooth silicon surface (Fig. 5) is transformed into a developed porous silicon structure.

Surface microstructures implanted with copper ions through a silicon mask were observed on an SEM microscope (Fig. 17) and an optical microscope (Fig. 20). It can be seen in the above images that the surface of the sample is an ordered lattice with cells 20 microns in size, which are formed upon implantation of silicon with copper ions in a given mode. In this case, the square cell represents the structure of porous silicon shown in FIG. 15 and 16. The walls between the square cells of the lattice consist of unirradiated single-crystal silicon.

In the manufacture of a periodic diffraction microstructure based on porous silicon, the ion implantation regimes according to the parameters have the following limitations, E = 5-100 keV, D - should provide the concentration of introduced metal atoms in the irradiated silicon substrate 2.5 · 10 ²⁰ -6.5 · 10 ²³ atoms / cm ³ , the current density of the ion beam J = 2 · 10 ¹² -1 · 10 ¹⁴ ion / cm ² s and the temperature of the substrate during irradiation T = 15-450 ° C. Beyond the boundaries of these regimes, the necessary technical result is not achieved, and the quality of the fabricated periodic diffraction microstructures based on porous silicon will not meet the necessary requirements.

The radiation dose is determined by the number of atoms of the metal substance necessary for the formation of metal-containing nanoparticles, the formation of which in the irradiated matrix causes pore formation of silicon. This condition, according to our studies of the dependence of the appearance of pores on the surface of the irradiated silicon on the implantation dose, is fulfilled at metal atom concentrations in the volume of the irradiated material of the order of 2.5 · 10 ²⁰ atoms / cm ³ . In this case, the amount of introduced impurity should not exceed the dose at which the adhesion of growing metal-containing nanoparticles begins, leading to the formation of a continuous metal-containing film, and according to our estimates, does not exceed 6.5 × 10 ²³ atoms / cm ³ .

The current density in the ion beam J determines, on the one hand, the time of implantation dose set, and on the other hand, the heating rate of the irradiated material. It was experimentally established that when the ion current density is exceeded J = 1 · 10 ¹⁴ ion / cm ² s, heating of the local surface silicon layer, leading to its melting, occurs so quickly that pore formation does not occur. Irradiation with a low ion current density does not expediently increase the implantation time. Therefore, the minimum ion current density is limited to J = 2 · 10 ¹² ion / cm ² s.

The energy of the ion E determines the value of its average projection range, which determines the depth of the implanted ion, and, consequently, the thickness of the modified layer and the diffraction periodic microstructure. From above, the ion acceleration energy is limited to E = 100 keV, since with an increase in this energy the implanted metal ions penetrate so deeply that the nucleation of the porous layer will occur not on the surface, but in the depth of the irradiated substrate. The lower limit for E = 5 keV is due to the fact that with a further decrease in E, it is not possible to obtain sufficiently large elements of the silicon structure to characterize them as pores, but only sputtering of its surface layer is observed [7].

The temperature of the irradiated substrate T determines the efficiency of heterogenization (collection) of the implanted ions of transition and noble metals into metal-containing nanoparticles. At temperatures below T = 20 ° C, the diffusion rate of embedded metal ions is so low that the formation of metal-containing nanoparticles does not occur. On the other hand, the diffusion rate of an ionic metal impurity at a temperature above T = 450 ° C is so high that a transient outflow of the impurity from the implanted surface layer of irradiated silicon deep into the sample occurs, which inevitably leads to a decrease in the concentration of the impurity, not reaching its solubility limit and, as a result , the impossibility of nucleation and growth of metal-containing nanoparticles.

Compared with the prototype, the proposed method allows to produce periodic diffraction microstructures based on porous silicon in a non-chemical way and using various types of metals.

List of references

1. Diffraction optics and nanophotonics. Ed. Soifer V.A. M .: Fizmatlid, 2014.

2. Vanstein Yu.S., Goryachev D.N., Ken O.S., Sreseli O.M. Surface plasmon polaritons in a porous silicon-gold composite system. FTP. 2015.V. 49, Issue. 4.P. 453-458.

3. Ziegel J.F., Biersak J.P., Littmark U. The stopping and range of ions in solids. N.Y .: Pergamon, 1996.

4. Ischenko A.A., Fetisov GV, Aslanov L.A .: Nanosilicon: properties, preparation, application, research and control methods. M .: Fizmatlit, 2011.573 s.

5. Kreibig U., Vollmer M. Optical properties of metal clusters. Berlin: Springer. 1995.

6. Townsend P.D., Chandler P.J., Zhang L. Optical effects of ion implantation. Cambridge: Univ. Press 1994.

7. Gerasimenko H., Parkhomenko Yu. Silicon - material for nanoelectronics. M .: Technosphere, 2007.276 s.

Claims (1)

A porous silicon-based periodic diffraction microstructure containing a substrate made of single crystal silicon with a diffraction periodic microstructure, characterized in that the porous silicon-based diffraction periodic microstructure contains ion-synthesized metal-containing nanoparticles dispersed in the surface region of the substrate to 10 from a layer thickness 200 nm at a metal concentration of 2.5 · 10 ²⁰ -6.5 · 10 ²³ atoms / cm ³ .

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