Multilayer material and method of preparing same
The invention relates to a multilayer material deposited by ALD. A multi-layer structure of a high refractive index material is deposited on a substrate using ALD at a temperature below about 450° C. Advantageous results are obtained when a high refractive index material A is coated with another material B after a certain thickness of material A has been achieved. Thus, the B barrier layer stops the tendency for material A to crystallize. The amorphous structure gives rise to less optical loss. Further, the different stress nature of materials A and B may be utilized to achieve a final optical material with minimal stress. The thickness of each material B layer is less than that of the adjacent A layer(s). The total effective refractive index of the high refractive index material A+B being shall be greater than 2.20 at a wavelength of 600 nm. Titanium oxide and aluminium oxide are preferred A and B materials. The structure is useful for optical coatings.
1. An Atomic Layer Deposition (ALD) method of manufacturing a material, said material comprising at least one layer of a first material (A), and at least one layer of a second material (B), materials A and B having at least one common interface, comprising carrying out the following at a deposition temperature of more than 150° C. and less than 450° C.:
a) depositing by ALD a layer of material A comprising titanium oxide to a thickness of 2 to about 8 nm,
b) depositing by ALD a layer of material B, selected from the group consisting of aluminium oxide, silicon oxide, and mixtures of these, to a thickness of 0.1 to 1.5 nm, using precursors selected from the group consisting of aluminium chloride, tris(tert-butoxy)silanol and tetra-butoxy silane, and
c) repeating a) and b) at least once until a material of desired total thickness is obtained,
to produce a material, the total effective refractive index of which is greater than 2.20 at a wavelength of 600 nm.
2. A method according to claim 1 , wherein titanium chloride is used as a precursor of material A.
3. A method according to claim 1 , wherein titanium ethoxide alone or in combination with titanium chloride is used as a precursor of material A.
4. A method according to claim 1 , wherein material B is aluminium oxide.
5. A method according to claim 1 , wherein material B is silicon oxide.
6. A method according to claim 1 , further comprising the step of depositing one or more layers of a material C, the refractive index of which is less than the refractive index of A+B.
7. A method according to claim 6 , wherein material C is selected from at least one of silicon oxide, aluminium oxide, or combinations of these.
8. A method according to claim 7 , further comprising depositing on top of a B layer a layer C comprising aluminium oxide using aluminium chloride as a precursor.
9. A method according to claim 7 , further comprising depositing on top of a B layer a layer C comprising aluminium oxide using trimethylaluminium as a precursor.
10. A method according to claim 7 , further comprising depositing on top of a B layer a layer C comprising silicon oxide using tris(tert-butoxy)silanol as a precursor.
11. A method according to claim 7 , further comprising depositing on top of a B layer a layer C comprising silicon oxide using tetrabutoxysilane as a precursor.
12. A method according to claim 1 , wherein a batch ALD process is utilized.
13. A method according to claim 12 , wherein the batch is placed with a distance between substrates of not more than about 8 mm, and the substrates are coated on at least two sides.
14. A method according to claim 12 , wherein the batch is placed with a distance between substrates of not more than about 8 mm, and the substrates are placed back to back.
15. A method according to claim 12 , wherein the substrates are placed on shelves having openings of less than the size of the substrates.
16. The method according to claim 1 , wherein the deposition temperature is from about 200° C. to about 450° C.