Planar optical devices and methods for their manufacture

• US 20020033330A1
• Filed: 07/10/2001
• Published: 03/21/2002
• Est. Priority Date: 08/07/2000
• Status: Active Grant

• Current Assignee: Demaray LLC
• Original Assignee: Symmorphix, Inc. (Demaray LLC)
• Inventors: Zhang, Hongmei, Demaray, Richard E., Pethe, Rajiv, Wang, Kai-An, Mullapudi, Ravi B., Stadtler, Douglas P.
• Granted Patent: US 6,506,289 B2
• Time in Patent Office: Days
• US Class Current: 204/192.26
• CPC Class Codes: C23C 14/345 using substrate bias
• CPC Class Codes: C23C 14/35 by application of a magnetic field, e.g. magnetron sputtering C23C14/3457 takes precedence
• CPC Class Codes: G02B 2006/12097 Ridge, rib or the like
• CPC Class Codes: G02B 2006/12147 Coupler
• CPC Class Codes: G02B 2006/1215 Splitter
• CPC Class Codes: G02B 6/132 by deposition of thin films
• CPC Class Codes: G02B 6/136 by etching
• CPC Class Codes: Y10T 156/10 Methods of surface bonding and/or assembly therefor

Abstract

Physical vapor deposition processes provide optical materials with controlled and uniform refractive index that meet the requirements for active and passive planar optical devices. All processes use radio frequency (RF) sputtering with a wide area target, larger in area than the substrate on which material is deposited, and uniform plasma conditions which provide uniform target erosion. In addition, a second RF frequency can be applied to the sputtering target and RF power can be applied to the substrate producing substrate bias. Multiple approaches for controlling refractive index are provided. The present RF sputtering methods for material deposition and refractive index control are combined with processes commonly used in semiconductor fabrication to produce planar optical devices such surface ridge devices, buried ridge devices and buried trench devices. A method for forming composite wide area targets from multiple tiles is also provided.

Claims

1. A method of making a material layer used in forming planar optical devices, the method comprising:

positioning a substrate opposite a planar target, the target having an area larger than the area of the substrate; and

applying radiofrequency power at a first frequency to the target in the presence of a gas, under a condition wherein a central portion of the target overlying the substrate is exposed to a uniform plasma condition, whereby a material layer is formed on the substrate.

2. The method of claim 1 wherein the uniform plasma condition is created by applying a time-averaged uniform magnetic field.

3. The method of claim 2 wherein the uniform magnetic field is applied by moving a magnet positioned proximate to the target across the target in a plane parallel to the plane of the target.

4. The method of claim 3 wherein moving a magnet across the target is moving a magnet in a first direction, the magnet extending beyond the target, in a second direction perpendicular to the first direction.

5. The method of claim 1 wherein the area of the planar target is at least 1.5 times greater than the area of the substrate.

6. The method of claim 5 wherein the material layer deposited on the substrate has a thickness nonuniformity of less than 5 percent.

7. The method of claim 6 wherein the material layer deposited on the substrate has a nonuniformity in an optical property that is smaller than a nonuniformity in thickness.

8. The method of claim 1 further comprising applying radiofrequency power at a second frequency to the target wherein the second frequency is lower than the first frequency.

9. The method of claim 1 further comprising applying radiofrequency power to the substrate.

10. The method of claim 8 further comprising applying radiofrequency power to the substrate.

11. The method of claim 1 wherein the uniform plasma condition is created without use of a magnet and further comprising applying radiofrequency power to the substrate.

12. The method of claim 1 wherein the target comprises refractory oxides.

13. The method of claim 12 wherein the target comprises oxides of silicon.

14. The method of claim 13 wherein the target comprises silicon monoxide.

15. The method of claim 12 wherein the target further comprises compounds of rare earths.

16. The method of claim 8 wherein the refractive index of a first material layer deposited with the radiofrequency power at the second frequency at a first power level is higher than the refractive index of a second material layer deposited with the radiofrequency power at the second frequency at a second power level, wherein the first power level is higher than the second power level and wherein the sum of the power levels of the first frequency and the second frequency are the same during deposition of the first material layer and the second material layer.

17. The method of claim 1 wherein the refractive index of a first material layer deposited with the substrate held at a first temperature is higher than the refractive index of a second material layer deposited with the substrate held at a second temperature wherein the first temperature is higher than the second temperature.

18. The method of claim 1 wherein the refractive index of a first material layer deposited at a first radiofrequency power is higher than the refractive index of a second material layer deposited at a second radiofrequency power wherein the first power is higher than the second power.

19. The method of claim 1 wherein the gas comprises an inert gas.

20. The method of claim 1 wherein the gas further comprises a reactive gas whereby the refractive index of the material layer is modified compared with the refractive index of a material layer formed in the absence of the reactive gas.

21. The method of claim 20 wherein the reactive gas is a reducing gas and wherein the refractive index of the material layer is greater than the refractive index of a material layer formed in the absence of the reducing gas.

22. The method of claim 20 wherein the reactive gas is an oxidizing gas and wherein the refractive index of the material layer is smaller than the refractive index of a material layer formed in the absence of the oxidizing gas.

23. The method of claim 1 wherein the target comprises a plurality of tiles.

24. The method of claim 23 wherein the tiles comprise an alloy material.

26. The method of claim 25 further comprising:

depositing a second layer of cladding material on the layer of core material by physical vapor deposition wherein radiofrequency power is applied to the planar source of cladding material positioned opposite the second structure under a condition wherein a central portion of the source overlying the second structure is exposed to a uniform plasma condition; and

etching regions of the second layer of the cladding material and a portion of the thickness of the layer of core material to produce a ridge structure in the second layer of cladding material and in a portion of the layer of core material.

27. The method of claim 25 further comprising;

etching regions of the layer of core material to produce a ridge structure in the layer of core material, forming a third structure; and

depositing a second layer of cladding material over the ridge structure by physical vapor deposition wherein

radiofrequency power is applied to the planar source of cladding material positioned opposite the third structure, under a condition wherein the central portion of the source of cladding material overlying the third structure is exposed to a uniform plasma condition, and

radiofrequency power is applied to the third structure.

28. The method of claim 27 wherein depositing the first layer of cladding material further comprises applying radiofrequency power to the substrate.

29. The method of claim 28 wherein depositing the layer of core material further comprises applying radiofrequency power to the second structure.

25. A method of making a planar optical device, the method comprising:

depositing a first layer of cladding material having a first refractive index on a substrate by physical vapor deposition to form a first structure, wherein radiofrequency power is applied to a planar source of cladding material positioned opposite the substrate, the source having an area greater than the area of the substrate, the power applied in the presence of a gas and under a condition wherein a central portion of the source overlying the substrate is exposed to a uniform plasma condition; and

depositing a layer of core material on the cladding material to form a second structure, the core material having a second refractive index greater than the first refractive index, the core material deposited by physical vapor deposition, wherein radiofrequency power is applied to a planar source of core material positioned opposite the first structure, the source of core material having an area greater than the area of the first structure, the power applied in the presence of a gas and under a condition wherein a central portion of the source of core material overlying the first structure is exposed to a uniform plasma condition;

30. A method of making a planar optical device, the method comprising:

depositing a first layer of cladding material having a first refractive index on a substrate by physical vapor deposition, wherein radiofrequency power is applied to a planar source of cladding material positioned opposite the substrate, the source having an area greater than the area of the substrate, the power applied in the presence of a gas and under a condition wherein a central portion of the source overlying the substrate is exposed to a uniform plasma condition;

forming a trench in the first layer of cladding material to form a first structure;

depositing a layer of core material on the cladding material completely filling the trench, the core material having a second refractive index greater than the first refractive index, the core material deposited by physical vapor deposition, wherein radiofrequency power is applied to the first structure and radiofrequency power is applied to a planar source of core material positioned opposite the first structure, the source of core material having an area greater than the area of the substrate, the power applied in the presence of a gas and under a condition wherein a central portion of the source of core material overlying the first structure is exposed to a uniform plasma condition;

removing core material overlying the first layer of cladding material exposing the cladding material except in the area of the trench to provide a cladding layer with filled trench; and

depositing a layer of cladding material on the cladding layer with filled trench by physical vapor deposition wherein radiofrequency power is applied to the planar source of cladding material positioned opposite the cladding material with filled trench.

31. The method of claim 30 wherein depositing a first layer of cladding material further comprises applying radiofrequency power to the substrate, and wherein depositing a layer of cladding material on the cladding layer with filled trench further comprises applying radiofrequency power to the cladding layer with filled trench.

32. A method of making a composite sputtering target comprising a plurality of tiles, the target used for physical vapor deposition of material, the method comprising:

sputter coating a side of each of the plurality of tiles with a wetting layer material to within an offset of the edge of each tile;

providing a backing plate composed of a metal with thermal expansion coefficient similar to the thermal expansion coefficient of the plurality of tiles;

plasma spray coating the backing plate with a ceramic material so as to cover the regions of the backing plate exposed during physical vapor deposition;

sputter coating regions of the backing plate corresponding in placement to the wetted regions of the tiles with a wetting layer;

wetting the sputtered regions of the plurality of tiles and of the backing plate with solder material; and

assembling the plurality of tiles on the backing plate so as to form a solder bonded non contacting array of uniformly spaced tiles.

33. The method of claim 32 wherein the plurality of tiles comprise an alloy material.

34. The method of claim 32 wherein the wetting layer material comprises chrome or nickel or mixtures thereof.

35. The method of claim 32 wherein the ceramic material comprises alumina or silica.

36. The method of claim 32 wherein the solder material is indium.