FABRICATION OF NANOSTRUCTURES IN AND ON ORGANIC AND INORGANIC SUBSTRATES USING MEDIATING LAYERS

Abstract

The present invention relates to a method for creating nanostructures in and on organic or inorganic substrates comprising at least the following steps: a) providing a primary substrate having a predetermined refractive index; b) coating the primary substrate with one or more mediating layers each having a predetermined refractive index different from that of the primary substrate, wherein the sequence of the layers is arranged so that a predetermined gradient of the refractive index is generated between the primary substrate and the uppermost layer of the one or more mediating layers; c) optionally coating the uppermost layer of the one or more mediating layers with an additional top layer; d) depositing a nanostructured etching mask onto the uppermost layer of the composite substrate obtained after steps a)-b) or a)-c); e) generating protruding structures, in particular conical or pillar structures, or recessed structures, in particular holes, in at least the uppermost layer of the composite substrate by means of reactive ion etching. A further aspect of the invention relates to a composite substrate with a nanostructured surface obtainable by said method.

Claims

1. A method for producing nanostructures in and on organic or inorganic substrates comprising at least the following steps: a) providing a primary substrate having a predetermined refractive index; b) coating the primary substrate with one or more mediating layers each having a predetermined refractive index different from that of the primary substrate, wherein a sequence of the layers is arranged so that a predetermined gradient of the refractive index is generated between the primary substrate and an uppermost layer of the one or more mediating layers; c) optionally coating the uppermost layer of the one or more mediating layers with an additional top layer; d) depositing a nanostructured etching mask onto the uppermost layer of a composite substrate obtained after steps a)-b) or a)-c); and e) generating protruding structures, or recessed structures in at least the uppermost layer of the composite substrate by reactive ion etching.

2. The method according to claim 1, wherein the nanostructured etching mask comprises an ordered array of nanoparticles or statistically distributed nanoparticles in which spatial frequencies of a statistical distribution shows only contributions which are larger than an inverse of the wavelength of light.

3. The method according to claim 2, wherein the ordered array of nanoparticles forming the etching mask is provided by micellar diblock or multiblock copolymer nanolithography.

4. The method according to claim 1, wherein the primary substrate comprises a material selected from the group consisting of quartz glasses and glasses.

5. The method according to claim 1, wherein the one or more mediating layers comprises a material selected from the group consisting of glass and quartz glass.

6. The method according to claim 1, wherein the additional top layer comprises a quartz glass material.

7. The method according to claim 1, wherein the refractive index of the primary substrate is in a range from 1.46 to 2.01 and the refractive index of the uppermost layer of the composite substrate is in a range from 1.3 to 1.6.

8. The method according to claim 1, wherein the etching comprises at least one treatment with an etchant which is selected from the group consisting of chlorine, gaseous chlorine compounds, fluorinated hydrocarbons, fluorocarbons, oxygen, argon, SF.sub.6 and mixtures thereof.

9. The method according to claim 8, wherein the etching comprises at least one treatment with a mixture of Ar/SF.sub.6/O.sub.2 or Ar/SF6 as the etchant and at least one treatment with a mixture of Ar/CHF.sub.3 as the etchant.

10. The method according to claim 1, wherein each etching treatment is carried out for a period in a range of 10 s to 10 min.

11. The method according to claim 1 which further comprises a mechanical treatment of the protruding structures generated.

12. The method according to claim 1 which comprises a further etching treatment by means of reactive ion beam etching (RIBE), chemically assisted ion beam etching (CAIBE), reactive ion etching (RIE) or inductive coupled plasma (RIE-ICP), wherein the structures generated in the top layer and/or the one or more mediating layers of the composite substrate are used as an etching mask and protruding structures corresponding to the protruding structures of layer(s) above are generated in the primary substrate and layer(s) above the primary substrate are removed in part or completely.

13. The method according to claim 1, wherein the composite substrate is an optical element and the structures generated form an anti-reflective surface structure on the optical element.

14. A composite substrate with a nanostructured surface comprising a primary substrate having a defined refractive index; one or more mediating layers having a predetermined refractive index different from that of the primary substrate wherein a sequence of the layers is arranged so that a defined gradient of the refractive index is provided between the primary substrate and an uppermost layer of the one or more mediating layers; optionally an additional top layer; and nanostructures on the surface of the composite substrate, which nanostructures are composed of a material of the additional top layer of the composite substrate and/or a material of the one or more mediating layers.

15. The composite substrate according to claim 14, wherein the nanostructures comprise protruding structures further comprising material of the primary substrate.

16. The composite substrate according to claim 15 which is an optical element and wherein the protruding structures form an anti-reflective surface structure on the optical element.

17. The composite substrate according to claim 15, wherein the protruding structures have a predetermined two-dimensional geometric arrangement, or are statistically distributed such that spatial frequencies of a statistical distribution show only contributions which are larger than an inverse of a wavelength of light.

18. The composite substrate according to claim 15, wherein the primary substrate comprises a material selected from the group consisting of quartz glasses and glasses.

19. The composite substrate according to claim 15, wherein the one or more mediating layers comprises a glass material.

20. The composite substrate according to claim 18, wherein the top layer comprises a quartz glass material.

21. The composite substrate according to claim 15, configured for use in fields selected from the group consisting of semi-conductor technology, optics, sensor technology and photo-voltaics.

22. The composite substrate according to claim 21 configured for use in a member selected from the group consisting of optical devices, sensors, and solar cells.

23. The method according to claim 1, wherein the protruding structures are conical or pillar structures, and the recessed structures are holes.

24. The method according to claim 2, wherein the light is in a range from 30 nm to 300 nm.

25. The method according to claim 4, wherein the material of the primary substrate is a member selected from the group consisting of: 1) B.sub.2O.sub.3La.sub.2O.sub.3M.sub.mO.sub.n (m being an integer from 1 to 2 and n being an integer from 2 to 5); 2) (B.sub.2O.sub.3, SiO.sub.2)La.sub.2O.sub.3MO; 3) SiO.sub.2PbOM.sub.2O; the PbO content in glasses of the system SiO.sub.2PbOM.sub.2O being partially or completely replaceable by TiO.sub.2; 4) SiO.sub.2B.sub.2O.sub.3BaO; 5) (SiO.sub.2, B.sub.2O.sub.3)BaOPbO; 6) SiO.sub.2M.sub.2OTiO.sub.2; 7) P.sub.2O.sub.5Al.sub.2O.sub.3MOB.sub.2O.sub.3; and 8) SiO.sub.2BaOM.sub.2O, where M is a metal.

26. The method according to claim 4, wherein the material of the primary substrate is a member selected from the group consisting of: 1) B.sub.2O.sub.3La.sub.2O.sub.3M.sub.mO.sub.n, where m is an integer from 1 to 2, n is an integer from 2 to 5, and M.sub.mO.sub.nis a member selected from the group consisting of ZrO.sub.2, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, Gd.sub.2O.sub.3, Y.sub.2O.sub.3, TiO.sub.2 and WO.sub.3; 2) (B.sub.2O.sub.3, SiO.sub.2)La.sub.2O.sub.3MO, where MO is a metal oxide selected from the group consisting of MgO, CaO, SrO, BaO and ZnO; 3) SiO.sub.2PbOM.sub.2O, where M.sub.2O is a member selected from the group consisting of Li.sub.2O, Na.sub.2O, K.sub.2O and Ca.sub.2O; the PbO content in glasses of the system SiO.sub.2PbOM.sub.2O being partially or completely replaceable by TiO.sub.2; 4) SiO.sub.2B.sub.2O.sub.3BaO; 5) (SiO.sub.2, B.sub.2O.sub.3)BaOPbO; 6) SiO.sub.2M.sub.2OTiO.sub.2, comprising additional molecules, atoms, or ions of fluorine and/or oxygen, where M.sub.2O is a metal oxide selected from the group consisting of Li.sub.2O, Na.sub.2O, K.sub.2O and Ca.sub.2O; 7) P.sub.2O.sub.5Al.sub.2O.sub.3MOB.sub.2O.sub.3, where MO is a member selected from the group consisting of MgO, CaO, SrO, BaO and ZnO; and 8) SiO.sub.2BaOM.sub.2O, where M.sub.2O is a member selected from the group consisting of Li.sub.2O, Na.sub.2O, K.sub.2O and Ca.sub.2O.

27. The method according to claim 5, wherein the material of the one or more mediating layers is selected from the group consisting of SiOx, where 1<x<2 and SiOxNy, where y/y+x is in a range from 0 to 0.5 and N/(N+O) is from 0% to 50%.

28. The method according to claim 6, wherein the quartz glass material of the additional top layer is a member selected from the group consisting of SiO.sub.2 and SiOxNy, where x and y are 1<x<2, y/y+x is in a range from 0 to 0.5 and N/(N+O) is from 0% to 50%.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0063] FIG. 1 schematically shows the main steps of the method according to the invention for preparing a nanostructured composite substrate or primary substrate.

[0064] FIG. 2 schematically shows the gradient of the refractive index formed by the primary substrate and the overlaid mediating layers.

[0065] FIG. 3 shows the data of transmission measurements performed on a plain SF10 substrate, a GRIN-coated SF10 substrate and a SF10 substrate coated with GRIN and an additional layer of MOES. The optical characterisation of plain, GRIN and MOES+GRIN substrates shows that the transmission of MOES+GRIN structured substrates is superior compared to the transmission of GRIN-structured surfaces alone.

[0066] The following examples are used for more in depth explanation of the present invention, without limiting the same thereto, however. It will be evident for the person skilled in the art that variations of these conditions in dependence of the specific materials used may be required and can be determined without difficulty by means of routine experiments.

EXAMPLE 1

Creation of Nanostructures on a Composite Substrate

1. Providing a Composite Substrate

[0067] A primary substrate of SF10 glass is coated with several intermediate layers of amorphous Si.sub.xO.sub.yN.sub.z forming a gradient of refractive indices (GRIN). The indices x, y and z of each intermediate layer are selected to provide a desired refractive index difference to the underlying layer. The GRIN layers are deposited by reactive pulse sputtering using a magnetron system from a silicon target. Argon was used as inert gas and a mixture of oxygen and nitrogen as reactive gas.

[0068] The layered structure of the GRIN-layer is formed by continuously adapting the ratio of the mixture of oxygen and nitrogen. The deposition of the GRIN profile is starting from the refractive index of the base substrate (SF10) and is decreased down to that of the covering SiO.sub.2 layer, forming the composite substrate consisting of SF10 (base), GRIN layer and a top SiO.sub.2 layer.

2. Providing an Array of Nanoparticles on the Substrate Surface

[0069] The surface of the uppermost layer of the composite substrate was coated with gold nanoparticles in a defined arrangement by means of micellar nanolithography. In this step, one of the protocols described in EP 1 027 157 B1, DE 197 47 815 A1 or DE 10 2007 017 032 A1 can be followed. The method involves the deposition of a micellar solution of a block copolymer (e.g. polystyrene(n)-b-poly(2-vinylpyridine(m)) in toluene) onto the substrate, e.g. by means of dip or spin coating, as a result of which an ordered film structure of polymer domains is formed on the surface. The micelles in the solution are loaded with a gold salt, preferably HAuCl.sub.4, which, following deposition with the polymer film, can be reduced to the gold nanoparticles.

[0070] The reduction can take place chemically, e.g. with hydrazine, or by means of energy-rich radiation, such as electron radiation or light. Optionally, after or at the same time as the reduction, the polymer film can be removed (e.g. by means of plasma etching with Ar-, H- or O-ions) . Thereafter, the substrate surface is covered with an arrangement of gold nanoparticles.

3. First Etching

[0071] Subsequently, the etching of the substrate surface covered with gold nanoparticles took place in a desired depth. A reactive ion etcher from Oxford Plasma, device: PlasmaLab 80 plus was used to this end. Other devices known in the prior art are likewise fundamentally suitable, however. The etching consisted of two treatment steps with various etchants which were carried out several times one after the other.

[0072] The following protocol was used to create conical nanostructures:

Step 1;

[0073] A mixture of Ar/SF.sub.6/O.sub.2 in the ratio 10:40:8 (sccm) was used as etchant (process gas). [0074] Pressure: 50 mTorr [0075] RF power: 120 W [0076] ICP power: 0 W [0077] Time: 60 s

Step 2:

[0078] Etchant: Ar/CHF.sub.3:40:40 [0079] Pressure: 50 mTorr [0080] RF power: 120 W [0081] ICP power: 20 W [0082] Time: 20 s

[0083] These 2 steps were carried out alternately 8 times.

[0084] Alternatively, the following protocol was used to create pillar-shaped nanostructures:

Step 1:

[0085] A mixture of Ar/SF.sub.6 in the ratio 40:40 (sccm) was used as etchant (process gas). [0086] Pressure: 50 mTorr [0087] RF power: 120 W [0088] ICP power: 0 W [0089] Time: 60 s

Step 2:

[0090] Etchant: Ar/CHF.sub.3:40:40 [0091] Pressure: 50 mTorr [0092] RF power: 120 W [0093] ICP power: 20 W [0094] Time: 20 s

[0095] These 2 steps were carried out alternately 8 times.

[0096] The total duration of the etching treatment varied depending on the desired depth of the etching within about 1-15 minutes. As a result, column-like or conical nanostructures were obtained, which still can show gold nanoparticles on their upper side.

4. Second Etching

[0097] The nanostructures created in the mediating layers according to step 3 above can further be used as an etching mask for transferring said nanostructures into the primary substrate layer by means of reactive ion beam etching (RIBE). Compared to the previous RIE process, the RIBE process is less selective and can etch substrates, which cannot be etched using RIE.

[0098] Reactive ion beam etching (RIBE) uses an energetic, broad beam collimated and highly directional ion source to physically mill material from a substrate mounted on a rotating fixture with adjustable tilt angle. In contrast to ion beaming (IBE), in the RIBE process reactive ions are incorporated in whole or in part in the etching ion beam.

[0099] The ion sources used are gridded ion sources, e.g. of the Kaufman type or microwave electron cyclotron resonance (ECR). The etching process involves the control of the ion incident angle and a separate control of the ion flux and ion energy. Typical reactive and inert gases used for RIBE are Ar, N.sub.2, O.sub.2, CHF.sub.3 CF.sub.4 and SF.sub.6.

[0100] The RIBE process directly transferred the nanostructure of the mediating layer into the base substrate.

EXAMPLE 2

Characterization of Nanostructured Composite or Primary Substrates

[0101] To illustrate the superior optical properties of the MOES+GRIN substrates, a plain SF10 surface, a GRIN coated SF10 surface and a single-sided MOES+GRIN coated surface were optically characterized using a spectrometer.

[0102] Compared to the plain SF10 substrate, the MOES+GRIN substrate shows a notably improved transmission, which covers a wide rage of wavelengths, as typical for MOES structures (see FIG. 3).