Thick optical waveguide and method of fabrication

Abstract

A thick optical waveguide and method of its fabrication. There is a first oxide layer on a substrate, with a first optical waveguide layer, such as a SiN layer, on the first oxide optical waveguide layer. A second oxide layer is deposited on the first optical waveguide layer and the top surface of each waveguide polished. A second optical waveguide layer is deposited on the top surface of the second oxide layer and top surfaces of each of the spaced waveguides, and then portions of the second optical waveguide layer are removed to expose a top portion of each of the spaced waveguides. A third oxide layer is then deposited over the second optical waveguide layer to cover the top portion of each of the spaced waveguides. The optical waveguide layers can be annealed one or more times during fabrication.

Description

THICK OPTICAL WAVEGUIDE AND METHOD OF FABRICATIONCROSS-REFERENCE TO RELATED APPLICATION

[0001] This invention claims the benefit of US Provisional Patent Application No. 63 / 553,385, filed on February 14, 2024, the entirety of which is hereby incorporated herein by this reference.BACKGROUND OF THE INVENTION

[0002] 1 . Field of the Invention

[0003] The present invention generally relates to semiconductors and methods of their fabrication. More particularly, the present invention relates to an optical waveguide for use in photonics applications.

[0004] 2. Description of the Related Art

[0005] A SiN photonic waveguide is a device guides light within optical modes in a SiN waveguide, which can be clad with a suitable material such as silica (Sit ).

[0006] In a silicon nitride photonic platform, a combination of (stoichiometric) silicon nitride (SiN) SisN4 as waveguide layers, filled by and encapsulated with silica (SiCh) as cladding layers on a silicon wafer. Silicon nitride (SiN) waveguides have a number of advantages over alternative technologies, including low propagation loss, wide range of transparency from visible to the mid-infrared, low cost, good reliability for high power and industrial operating conditions, as well as good coupling to standard single-mode fiber.

[0007] A silicon nitride waveguide has a high nonlinear refractive index and a low- loss property which makes them advantageous for a variety of applications. They can transmit Watts of optical power, are CMOS compatible, and are excellent material for photonics. The technology can be used in a wide range of applications, including quantum computing, MEMS, LIDAR, and CMOS-compatible chips.

[0008] The top layer of silicon nitride is crucial for coupling efficiency. This layer should be thin enough to allow good fabrication tolerance yet still have excellent dimensional stability. In such configuration, the SiN waveguide is a good choice for use high-power lasers. In fabrication, a high-quality silicon nitride is used to build the waveguides is a blend of silicon nitride and silicon dioxide. The nitride material is thinner than silica, which makes it more suitable for high-power applications.

[0009] Several problems occur in the fabrication of SiN waveguides. For example, “subtractive” manufacturing is the traditional method for creating integrated circuits(ICs) on a wafer by etching away unnecessary areas of the layer to leave behind the functional circuit components of semiconductors. This typically occurs through a chemical etching process, essentially "subtracting" material to form the desired circuit design. With SiN waveguides, a problem occurs in fabrication of high- confinement waveguides with heights larger than 0.5 pm. Semiconductor structures defined by a subtractive process often require a dielectric backfill for cladding, planarity, or layer separation purposes. During the backfill process, closely spaced waveguide devices will develop voids or keyholes which negatively impact performance. Overall, there can also be bow and warp problems with the wafer itself from the manufacturing process.

[0010] A “damascene" fabrication process in semiconductor manufacturing is a technique used to create intricate metal interconnects on a substrate by first etching trenches and vias into a dielectric layer. Filling those features with metal (typically copper) through an electroplating process, then planarizing the surface with chemical mechanical polishing (CMP), creates a structure by "inlaying" the metal into the dielectric layer. However, it is difficult to use a damascene process to produce a SiN waveguide as it is very difficult to control the height of waveguide. Furthermore, smaller lines of the waveguide are difficult to optimally fill. The damascene process also has wafer bow / warp challenges just like subtractive fabrication processes of a SiN waveguide.BRIEF SUMMARY OF THE INVENTION

[0011] Briefly described, the invention includes a thick optical waveguide and method of its fabrication. In one embodiment, the invention can provide a SiN waveguide with “coupling gap” control to minimize keyhole defects that are common in the prior art. The present invention allows for aggressive lines and spaces in the fabrication of waveguides. It allows for gap-filling for thick waveguides and avoids several problems with the existing methods of fabrication. The present invention can be applied to an integrated waveguide of any material and can be repeated multiple times to get thick optical layers, greater than 1 pm in thickness. The optical layers can be made from one or more of: SiN, SiCk, Si, SisN4, LiNbOs, GaAs, and InP. Additionally, the present invention can be used to make waveguides of various and differing materials within their core and cladding such as a graded index, gain incorporation, etc.

[0012] The preferred use of annealing the optical layer after each definition is important to achieving ultra low-losses (ULL), dB / m regime. To do this within the melting temperatures of typically CMOS stacks, the deposit / anneal allows a thinner layer to be annealed to a higher degree of purity than a thick layer, which enables the use of ULL waveguide for integrated photonics. By breaking the deposition and anneal steps up, this also allows wafer bow to be improved by employing different cheesing patterns in each deposit / anneal layer.

[0013] In one embodiment, the invention provides a thick optical waveguide having a substrate, a first oxide layer on the substrate, a first optical layer on the first oxide layer, and a series of spaced waveguides formed in the first optical layer by removal of portions of the first optical layer, with each spaced waveguide having a top surface thereof. There is a second oxide layer deposited on the first optical layer and the top surface of each of the waveguides, with the second oxide layer having a planarized top surface polished to expose the top surfaces of each of the spaced waveguides. There is a second optical layer deposited on the top surface of the second oxide layer and the top surfaces of each of the spaced waveguides, the second optical layer removed to expose a top portion of each of the spaced waveguides. The third oxide layer deposited over the second optical layer, the third oxide layer covering the top portion of each of the spaced waveguides, and the third oxide layer having a planarized top surface.

[0014] In an embodiment, the third oxide layer is polished to expose a top surface of each of the spaced waveguides, and a third optical layer is deposited on the third oxide layer, with the third optical layer is removed such that a top portion of each of the spaced waveguides is exposed. A fourth oxide layer is deposited on the third optical layer, with the fourth oxide layer having a planarized top surface.

[0015] The waveguide can be embodied with the first optical layer is annealed prior to removing portions of the first optical layer, the second optical layer is annealed prior to removing portions of the second optical layer, and the third optical layer is annealed prior to removing portions of the third optical layer. Each of the optical waveguides can have a thickness of greater than 1 pm, and the first optical layer and second optical layer can each be thicker than 0.5 pm. The series of waveguides can be spaced apart from each other at less than 0.5 pm. Ideally, the first oxide layer,second oxide layer and third oxide layer can be fabricated such that they are substantially void-free.

[0016] In an embodiment, the invention provides a method of fabricating a thick optical waveguide by depositing a first oxide layer on a substrate, depositing a first optical layer on the first oxide layer, and removing portions of the first optical layer to form a series of spaced waveguides, with each spaced waveguide having a top surface thereof. The method continues depositing a second oxide layer on the first optical layer and the top surface of each of the waveguides, planarizing a top surface of the second oxide layer, polishing the top surface of the second oxide layer to expose the top surfaces of each of the spaced waveguides, and depositing a second optical layer on the top surface of the second oxide layer and top surfaces of each of the spaced waveguides. Then the method continues with removing the second optical layer to expose a top portion of each of the spaced waveguides, depositing a third oxide layer over the second optical layer, the third oxide layer covering the top portion of each of the spaced waveguides, and planarizing a top surface of the third oxide layer.

[0017] The method can include polishing the top surface of the third oxide layer to expose a top surface of the each of the spaced waveguides, depositing a third optical layer on the third oxide layer, removing portions of the third optical layer such that a top portion of each of the spaced waveguides is exposed, then depositing a fourth oxide layer on the third optical layer, and planarizing a top surface of the fourth oxide layer. The method preferably includes annealing the first optical layer prior to removing portions of the first optical layer, annealing the second optical layer prior to removing portions of the second optical layer, and annealing the third Optical layer prior to removing portions of the third Optical layer.

[0018] In an embodiment, the invention includes a thick optical waveguide produced by the above process.

[0019] The present invention therefore provides an advantage in thick optical waveguides that limit the problems that occur with current methods of fabrication. The invention also has industrial application in the area of semiconductors and photonics. Other objects, advantages, and features of the present invention will be apparent to one of skill in the art after review of the present patent application.BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Fig. 1 A is a cross-sectional diagram of a substrate with a prior art subtractive method of fabricating a waveguide.

[0021] Fig. 1 B is a cross-sectional diagram of a substrate with the prior art subtractive method of fabricating a waveguide continuing from Fig. 1A.

[0022] Fig. 1C is a cross-sectional diagram of a substrate with the prior art subtractive method of fabricating a waveguide continuing from Fig. 1 B.

[0023] Fig. 1 D is a cross-sectional diagram of a substrate with the prior art subtractive method of fabricating a waveguide continuing from Fig. 1C.

[0024] Fig. 1 E is a cross-sectional diagram of a substrate with the prior art subtractive method of fabricating a waveguide continuing from Fig. 1 D.

[0025] Fig. 2 is a diagram illustrating the gap-to-height ratio between waveguide features that affect keyhole formations.

[0026] Fig. 3A is a cross-sectional diagram of a substrate with a prior art damascene method of fabricating a waveguide.

[0027] Fig. 3B is a cross-sectional diagram of a substrate with the prior art damascene method of fabricating a waveguide continuing from Fig. 3A.

[0028] Fig. 3C is a cross-sectional diagram of a substrate with the prior art damascene method of fabricating a waveguide continuing from Fig. 3B.

[0029] Fig. 3D is a cross-sectional diagram of a substrate with the prior art damascene method of fabricating a waveguide continuing from Fig. 3C.

[0030] Fig. 4A is a cross-sectional diagram of a substrate with an embodiment of the present inventive method of fabricating a waveguide with a series of deposit / anneals of the optical waveguide layer prior to removal.

[0031] Fig. 4B is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4A.

[0032] Fig. 4C is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4B.

[0033] Fig. 4D is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4C.

[0034] Fig. 4E is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4D.

[0035] Fig. 4F is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4E.

[0036] Fig. 4G is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4F.

[0037] Fig. 4H is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4G.

[0038] Fig. 41 is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4H.

[0039] Fig. 4J is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 41.

[0040] Fig. 4K is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4J.

[0041] Fig. 4L is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4K.

[0042] Fig. 4M is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4L.

[0043] Fig. 4N is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4M.DETAILED DESCRIPTION OF THE INVENTION

[0044] With reference to the figures in which like numerals represent like elements throughout the several views, Fig.1 A-1 E illustrate a prior art subtractive method of making and optical waveguide. Optical waveguides are structures that guide light from one point to another, typically using the principle of mode propagation.Waveguides are used in various devices like fiber optic cables and integrated optical circuits. The choice of substrate, e.g. substrate 60, Figs. 4A-4N, used for fabrication of optical waveguides largely depends on the required properties such as optical transparency, refractive index, and mechanical and thermal stability.

[0045] Various materials have been used to fabricate optical waveguides and can be used as to make the present invention, including: (1) Silica (SiO?) is one of the most common materials used for making fiber optic cables, which are a form of optical waveguide. Silica is preferred for its low loss at telecom wavelengths, high thermal stability, and robust mechanical properties; (2) Silicon (Si) is often used as the substrate in silicon-on-insulator (SOI) waveguides. The high refractive index contrast allows for tight bending radii, which is important for miniaturization in photonic integrated circuits; (3) Silicon Nitride (SixNy) is another commonly usedmaterial for fabricating waveguides, particularly for applications that require lower optical losses and broader wavelength operation than is typically achievable with silico; (4) Polymers such as PMMA (poly(methyl methacrylate)) or Ormocers can be used for the fabrication of optical waveguides, particularly for short distance communications, due to their ease of processing and ability to be directly written on; (5) Certain types of glass, such as phosphate and chalcogenide glasses, can be used to fabricate waveguides. They are often chosen for their unique optical properties such as high nonlinearity or broad transmission windows; (6) Lithium Niobate (LiNbOs) is a popular substrate for waveguides, particularly in applications that require high electro-optic coefficients, such as in modulators; and (7) lll-V Semiconductors, such as Gallium Arsenide (GaAs) and Indium Phosphide (InP) are used when active devices, such as lasers or amplifiers, need to be integrated into the waveguide. In addition to these, other materials such as diamond, aluminum oxide (AhOS), and various types of crystal materials (e.g., potassium titanyl phosphate (KTP), potassium dihydrogen phosphate (KDP), etc.) are used in specific applications. Other compounds can include Ta2O5, AIN, LiTaO3, SixNy, GaP, GaN, AIGaN,

[0046] A prior art process of fabricating an optical waveguide is illustrated in Figs. 1A-1 E. Fig. 1A is a cross-sectional diagram of a substrate 10 with a prior art subtractive method of fabricating a waveguide. A bottom oxide layer 12 is deposited on the substrate 10. Fig. 1 B is a cross-sectional diagram of a substrate 10 with the prior art subtractive method of fabricating a waveguide continuing from Fig. 1 A. A deposition of an optical waveguide layer 14, which here is SiN, is made unto the bottom oxide layer 12. The deposition is typically at a thickness of 50-300 nm. Fig. 1C is a cross-sectional diagram of the substrate 10 with the prior art subtractive method of fabricating a waveguide continuing from Fig. 1 B. In Fig. 1 C, portions of the SiN layer 14 is etched into waveguide features 16. The removal of the SiN can occur from etching or lithography.

[0047] Fig. 1 D is a cross-sectional diagram of the substrate 10 with the prior art subtractive method of fabricating a waveguide continuing from Fig. 1C. In Fig. 1 D, an second oxide layer 20 has been deposited over the SiN layer 14 and waveguide features 16. Note that voids 18 have formed between the waveguide features 16, which is also shown in the SEM image of Fig. 2. These voids 18 can adverselyaffect the fidelity of optical signals carried across the waveguide features 16, with significant dB loss over distance. Also note the ridges 22 formed over the waveguide features 16 in the second oxide layer 20. These ridges 22 will be planarized as shown in Fig. 1 E. Fig. 1 E is a cross-sectional diagram of the substrate 10 with the prior art subtractive method of fabricating a waveguide continuing from Fig. 1 D. The top surface 24 of the second oxide layer 20 is now planar, but voids 18 still remain in the second oxide layer 20.

[0048] Fig. 2 is a diagram illustrating the gap-to-height ratio between waveguide features 32 on a substrate 30 that affect keyhole formations. Due to the isotropic nature of the backfill deposition, both trench 34 and sidewalls 36 will have uniform growth during the deposition. Keyholes (holes 18) form when the gap-to-height ration is less than 2: 1 . For example, a waveguide feature’s height A of 1 pm would require a gap width B of 2 pm to avoid significant keyhole formation. The present invention accordingly allows the minimization or elimination of keyholes with waveguide features 32 below the 2:1 gap-to-width ratio.

[0049] Figs. 3A-3D is a prior art method of fabricating a thick optical waveguide with a damascene method. The optical waveguide 48 is about 1 pm in thickness. Fig. 3A is a cross-sectional diagram of a substrate 40 with a prior art damascene method of fabricating an optical waveguide 48. A bottom oxide layer 42 is deposited on the substrate 40. Fig. 3B is a cross-sectional diagram of the substrate 40 with the prior art damascene method of fabricating a waveguide continuing from Fig. 3A. The bottom oxide layer 42 is then etched into waveguide channels 46. The creation of the waveguide channel 46 can be accomplished via lithography.

[0050] Fig. 3C is a cross-sectional diagram of a substrate 40 with the prior art damascene method of fabricating a waveguide continuing from Fig. 3B. Fig. 3C shows the deposition of Si N as an optical waveguide layer 44 that also fills into the waveguide channel 46 to create the optical waveguide 48 features. One problem occurs with a depression 50 or other indentation forming in the optical waveguide layer 44 from the material filling into the waveguide channel 46. Then the optical waveguide layer 44 is planarized as shown in Fig. 3D. Fig. 3D is a cross-sectional diagram of a substrate 40 with the prior art damascene method of fabricating a waveguide continuing from Fig. 3C. A planar surface 52 has been created that also exposes the top surfaces 54 of the optical waveguide features 48. A second oxidelayer can then be deposited over the planar surface 52 and top surfaces 54 of the waveguide features 48 as cladding.

[0051] The damascene method shown in Figs. 3A-3D has several problems. As shown in Fig. 3D, it is ultimately difficult to control height of the waveguide features 48 as the planarization can be inexact. Furthermore, the method can have small gaps like depression 50 that are difficult to fill with the optical waveguide material. The larger wafer can still have wafer bow / warp challenges through the stages of fabrication.

[0052] In one embodiment shown in Figs. 4A-4N, a thick optical waveguide can be fabricated on a substrate 60. Fig. 4A is a cross-sectional diagram of a substrate 60 with an embodiment of the present inventive method of fabricating a waveguide with a series of deposit / anneals of the optical waveguide layer 64 prior to removal. As shown in Fig. 4B, there is a first oxide layer 62 on the substrate 60 and there is a first optical layer 64 deposited on the first oxide layer 62. Here, the optical layer 64 is SiN, but is not limited to that material. Fig. 4B is a cross-sectional diagram of the substrate 60 with the method of fabricating a waveguide continuing from Fig. 4A.

[0053] Fig. 4C is a cross-sectional diagram of a substrate 60 with the method of fabricating a waveguide continuing from Fig. 4B and illustrates a series of spaced optical waveguides 66 formed in the first optical layer 64 by removal of portions of the first optical layer 64, each spaced waveguide having a top surface 68 thereof. Fig. 4D is a cross-sectional diagram of the substrate 60 with the method of fabricating a waveguide continuing from Fig. 4C, with a second oxide layer 70 deposited on the first optical layer 64 and the top surface 68 of each of the optical waveguides 66. The bumps 72 over the waveguide features 66 are shown here as is known to occur in the prior art fabrication methods.

[0054] Fig. 4E is a cross-sectional diagram of the substrate 60 with the method of fabricating a waveguide continuing from Fig. 4D. The with the second oxide layer 70 is planarized to create a planarized top surface 72, and is then polished to expose the top surfaces 68 of each of the spaced waveguides 66, as shown in Fig. 4F. Fig. 4F is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4E

[0055] As shown in Fig. 4G, which is a cross-sectional diagram of a substrate 60 with the method of fabricating a waveguide continuing from Fig. 4F. There is asecond optical layer 76 deposited on the top surface 74 of the remnants of second oxide layer 68, the bottom oxide layer 62 and the top surfaces 68 of each of the spaced waveguides 66. As shown in Fig. 4H, which is a cross-sectional diagram of a substrate 60 with the method of fabricating a waveguide continuing from Fig. 4G, the second optical layer 76 has portions removed to expose a top portion 78 of each of the spaced waveguides 66. Then as shown in Fig. 41, which is a cross-sectional diagram of the substrate 60 with the method of fabricating a waveguide continuing from Fig. 4H, there is a third oxide layer 80 deposited over the second optical layer 76, the third oxide layer 80 covering the top portion 78 of each of the spaced waveguides 66. As shown in Fig. 4 J, which is a cross-sectional diagram of the substrate 60 with the method of fabricating a waveguide continuing from Fig. 41, the third oxide layer 80 can also cause bumps 82 or other surface irregularities that require planarizing. Accordingly, the third oxide layer 80 can be planarized to create a planar top surface 84

[0056] Fig. 4K is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4J. In this embodiment, the third oxide layer 80 is polished to expose a top surface 86 of each of the spaced waveguides 66. As shown in Fig. 4L, which is a cross-sectional diagram of the substrate 60 with the method of fabricating a waveguide continuing from Fig. 4K, a third optical layer 88 is deposited on the third oxide layer 80, or its remnants and over the top surfaces 86 of the waveguide features 66 with portions of the third optical layer 88 is removed such that a top portion of each of the spaced waveguides features 66 is exposed (similar to Fig. 4H.

[0057] Fig. 4M is a cross-sectional diagram of the substrate 60 with the method of fabricating a waveguide continuing from Fig. 4L. There is a fourth oxide layer 90 deposited on the third optical layer 88, with the fourth oxide layer 90 once again creating bumps 92 or surface anomalies that require planarization. Fig. 4N is a cross-sectional diagram of a substrate with the method of fabricating a waveguide continuing from Fig. 4M, wherein planarization has occurred such that the fourth oxide layer 90 has a planarized top surface 94.

[0058] The waveguide can be embodied with the first optical layer 64 is annealed prior to removing portions of the first optical layer 64, as shown in Fig. 4C. The second optical layer 76 can also be annealed prior to removing portions of thesecond optical layer 76 (Fig. 4H), and the third optical layer 88 is annealed prior to removing portions of the third optical layer. Each of the optical waveguides can have a thickness of greater than 1 pm, and the first optical layer 64 and second optical layer 76 can each be thicker than 0.5 pm. The series of waveguides can be spaced apart from each other at less than 0.5 pm. Ideally, the first oxide layer 64, second oxide layer 76 and third oxide layer 88 can be fabricated such that they are substantially void (keyhole)-free.

[0059] It can thus be seen that the invention provides a method shown in Figs. 4A- 4M of fabricating a thick optical waveguide, such as an SiN waveguide, by depositing a first oxide layer 62 on a substrate 60, depositing a first optical layer 64 on the first oxide layer 62 and removing portions of the first optical layer 64 to form a series of spaced waveguides 66 (Fig. 4C), with each spaced waveguide having a top surface 68 thereof. The method continues by depositing a second oxide layer 70 on the first optical layer 64 and the top surface 68 of each of the waveguides 66, planarizing a top surface 72 of the second oxide layer, polishing the top surface of the second oxide layer to expose the top surfaces of each of the spaced waveguides, and depositing a second optical layer on the top surface of the second oxide layer 70 and top surfaces 68 of each of the spaced waveguides 66. Then the method continues with removing the second optical layer 76 to expose a top portion of each of the spaced waveguides 66 (Fig. 4H), depositing a third oxide layer 80 over the second optical layer 76, the third oxide layer 80 covering the top portion 78 of each of the spaced waveguides 66, and planarizing a top planar surface 84 of the third oxide layer 80 (Fig. 4J).

[0060] The method can include polishing the top surface of the third oxide layer to expose a top surface 86 of the each of the spaced waveguides 66 (Fig. 4K), depositing a third optical layer 88 on the third oxide layer 80, removing portions of the third optical layer 88 such that a top portion of each of the spaced waveguides is exposed, then depositing a fourth oxide layer 90 on the third optical layer 88 (Fig. 4M) and planarizing a top planar surface 94 of the fourth oxide layer 90. The method preferably includes annealing the first optical layer 64 prior to removing portions of the first optical layer 64 (Fig. 4C), annealing the second optical layer 76 prior to removing portions of the second optical layer (Fig. 4H), and annealing the third optical layer 88 prior to removing portions of the third optical layer 88.

[0061] The steps for annealing can accordingly vary. Annealing can occur after each etching step, but before oxide backfill (anneal of each layer). Annealing can also occur after a complete and full deposition / etching / backfill process. Further, there can be one final annealing of the total completed waveguide stack, such as shown in Fig. 4N.

[0062] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below, if any, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention.

Claims

CLAIMSWhat is claimed is:1 . A thick optical waveguide, comprising: a substrate; a first oxide layer on the substrate; a first optical layer on the first oxide layer; a series of spaced waveguides formed in the first optical layer by removal of portions of the first optical layer, each spaced waveguide having a top surface thereof; a second oxide layer deposited on the first optical layer and the top surface of each of the waveguides, the second oxide layer having a planarized top surface polished to expose the top surfaces of each of the spaced waveguides; a second optical Layer deposited on the top surface of the second oxide layer and top surfaces of each of the spaced waveguides, the second optical layer removed to expose a top portion of each of the spaced waveguides; and a third oxide layer deposited over the second optical layer, the third oxide layer covering the top portion of each of the spaced waveguides, and the third oxide layer having a planarized top surface.

2. The waveguide of claim 1 , wherein: the third oxide layer is polished to expose a top surface of the each of the spaced waveguides; wherein a third optical layer is deposited on the third oxide layer, the third optical layer is removed such that a top portion of each of the spaced waveguides is exposed; and wherein a fourth oxide layer is deposited on the third optical layer, the fourth oxide layer having a planarized top surface.

3. The waveguide of claim 1 , wherein: the first optical layer is annealed prior to removing portions of the first optical layer; andthe second optical layer is annealed prior to removing portions of the second optical layer.

4. The waveguide of claim 2, wherein: each of the spaced waveguides have a height thereof; there is at least one gap between the spaced waveguides; there is a gap-to-height ratio for spacing between the spaced waveguides; and the gap-to-height ratio is less than 2:1 .

5. The waveguide of claim 1 , wherein each of the optical waveguides has a thickness of greater than 1 pm.

6. The waveguide of claim 1 , wherein the first optical layer and second optical layer are each thicker than 0.5 pm.

7. The waveguide of claim 1 , wherein the series of waveguides are spaced apart from each other at less than 0.5 pm.

8. The waveguide of claim 1 , wherein the first optical layer, second optical layer are made of one or more of: SixNy, SiOs, Si, LiNbOs, LiTaOs, TaxOy, GaAs, and InP.

9. A method of fabricating a thick optical waveguide, comprising: depositing a first oxide layer on a substrate; depositing a first optical layer on the first oxide layer; removing portions of the first optical layer to form a series of spaced waveguides, each spaced waveguide having a top surface thereof; depositing a second oxide layer on the first optical layer and the top surface of each of the waveguides; planarizing a top surface of the second oxide layer; polishing the top surface of the second oxide layer to expose the top surfaces of each of the spaced waveguides;depositing a second optical layer on the top surface of the second oxide layer and top surfaces of each of the spaced waveguides; removing the second optical layer to expose a top portion of each of the spaced waveguides; depositing a third oxide layer over the second optical layer, the third oxide layer covering the top portion of each of the spaced waveguides; and planarizing a top surface of the third oxide layer.

10. The method of claim 9, further comprising: polishing the top surface of the third oxide layer to expose a top surface of the each of the spaced waveguides; depositing a third optical layer on the third oxide layer; removing portions of the third optical layer such that a top portion of each of the spaced waveguides is exposed; depositing a fourth oxide layer on the third optical layer; and planarizing a top surface of the fourth oxide layer.11 . The method of claim 9, further comprising: annealing the first optical layer prior to removing portions of the first optical layer; and annealing the second optical layer prior to removing portions of the second optical layer.

12. The method of claim 10, wherein: each of the spaced waveguides have a height thereof, and there is at least one gap between the spaced waveguides; and further comprising spacing the spaced waveguides at a gap-to-height ratio less than 2:1 .

13. The method of claim 9, further forming each of the optical waveguides in a thickness of greater than 150 nm.

14. The method of claim 13, further forming each of the optical waveguides in a thickness of greater than 1 pm.

15. The method of claim 9, wherein depositing the first optical layer and second Optical layer are each deposited in a layer thicker than 0.5 pm.

16. The method of claim 9, wherein removing portions of the first optical layer forms a series of spaced waveguides are spaced apart from each other at less than 0.5 pm.

17. The method of claim 9, wherein removing portions of the first optical layer forms a series of spaced waveguides are spaced apart from each other in a range of 0.25 pm to 0.5 pm.

18. The method of claim 9, forming the first optical layer and second optical layer are forming each layer from of one or more of: SixNy, SiC>2, Si, SisN4, LiNbC , GaAs, and InP.

19. A thick optical waveguide produced by the process of: depositing a first oxide layer on a substrate; depositing a first optical layer on the first oxide layer; removing portions of the first optical layer to form a series of spaced waveguides, each spaced waveguide having a top surface thereof; depositing a second oxide layer on the first optical layer and the top surface of each of the waveguides; planarizing a top surface of the second oxide layer; polishing the top surface of the second oxide layer to expose the top surfaces of each of the spaced waveguides; depositing a second optical Layer on the top surface of the second oxide layer and top surfaces of each of the spaced waveguides; removing the second optical layer to expose a top portion of each of the spaced waveguides; depositing a third oxide layer over the second optical layer, the third oxide layer covering the top portion of each of the spaced waveguides; planarizing a top surface of the third oxide layer.

20. The waveguide produced by the process of claiml 9, further produced by the process of: polishing a top surface of the third oxide layer to expose a top surface of the each of the spaced waveguides; depositing a third optical layer on the third oxide layer; removing portions of the third optical layer such that a top portion of each of the spaced waveguides is exposed; depositing a fourth oxide layer on the third optical layer; and planarizing a top surface of the fourth oxide layer.

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