TWI844342B - Optical structure and method for forming the same - Google Patents

Abstract

The present disclosure provides a method for forming an optical structure, including: providing a substrate, wherein the substrate includes a lower cladding layer and an optical channel material layer disposed on the lower cladding layer; performing a local oxidation process on the optical channel material layer to form multiple oxidized parts embedded in the optical channel material layer; and performing a patterning process to pattern the optical channel material layer into an optical channel layer, with a curved surface on a top portion of the optical channel layer, wherein a dielectric constant of the lower cladding layer is lower than a dielectric constant of the optical channel layer.

Description

Optical structure and method for forming the same

The present invention relates to an optical structure and a method for forming the same, and in particular to an optical structure having a curved surface on the top of a light channel layer.

In photonic applications, photonic components such as waveguides, modulators, detectors, demodulators, resonators, taps, splitters, amplifiers, gratings, couplers, or other photonic components have been successfully integrated onto an integrated circuit substrate. Typically, a photonic device has a core for guiding light and a cladding structure surrounding the core to confine the light to the core. The material of the core may include, for example, silicon, and the cladding structure may include, for example, silicon oxide. In general, typical silicon-containing semiconductor structures can be fabricated using processes using complementary metal oxide semiconductor (CMOS) technology.

CMOS technology is a process used to make integrated circuits. CMOS processes are usually performed in CMOS factories to make integrated circuits in silicon wafers or substrates. During a typical CMOS process, various metal, semiconductor and dielectric material layers can be selectively deposited, etched, and doped on a single substrate, and even the substrate itself can be etched and doped to form a large number of field effect transistors and other electronic devices. Once the processing is completed, the substrate is cut into individual chips, and these chips can be packaged for use in electronic devices.

However, the formation of photonic components (such as gratings, ridge waveguides, etc.) requires accurate control of the thickness of the optical channel material layer used to form the core. For example, the etching process needs to be adjusted so that the thickness of the optical channel material layer is controlled within an accuracy of, for example, 2 nm. Although the shallow trench isolation (STI) process in the known CMOS technology has been widely used in the formation of photonic components, the etching depth of the STI process has an error range of at least about 30 nm for the optical channel material (such as silicon) of the photonic component, and is therefore not suitable for the manufacture of photonic components. In addition, in the CMOS technology process, since the optical channel material layer is etched by plasma, the core of the formed photonic component has a rougher surface. Therefore, a photonic device formed by a conventional etching method will have poor total reflection between the core and the cladding layer, which affects the performance of the formed photonic device.

A method for forming an optical structure includes: providing a substrate, wherein the substrate includes a lower cladding layer and an optical channel material layer disposed on the lower cladding layer; performing at least one local oxidation process on the optical channel material layer to form a plurality of oxidized components embedded in the optical channel material layer; and performing a patterning process to pattern the optical channel material layer into an optical channel layer having a curved surface at the top of the optical channel layer, wherein the dielectric constant of the lower cladding layer is less than the dielectric constant of the optical channel layer.

An optical structure includes: a lower cladding layer; and an optical channel layer disposed on the lower cladding layer and having a curved surface at the top of the optical channel layer, wherein the dielectric constant of the lower cladding layer is smaller than the dielectric constant of the optical channel layer.

The following disclosure provides many different embodiments or examples to show different components of the embodiments of the present invention. The following will disclose specific examples of the components of this specification and their arrangement to simplify the disclosure. Of course, these specific examples are not used to limit the disclosure. For example, if the following invention content of this specification describes forming a first component on or above a second component, it means that it includes an embodiment in which the first and second components formed are in direct contact, and also includes an embodiment in which an additional component can be formed between the above-mentioned first and second components, and the first and second components are not in direct contact. In addition, the various examples in the disclosure may use repeated reference symbols and/or words. The purpose of these repeated symbols or words is to simplify and clarify, and is not used to limit the relationship between the various embodiments and/or the configurations.

Furthermore, to facilitate description of the relationship between one element or component and another element or component in the drawings, spatially relative terms may be used, such as "under," "below," "lower," "above," "upper," and the like. In addition to the orientation depicted in the drawings, spatially relative terms also cover different orientations of the device in use or operation. When the device is turned to a different orientation (for example, rotated 90 degrees or other orientations), the spatially relative adjectives used therein will also be interpreted based on the orientation after the rotation.

Here, the terms "about", "approximately", and "generally" generally mean within 20% of a given value or range, preferably within 10%, and more preferably within 5%, or within 3%, or within 2%, or within 1%, or within 0.5%. It should be noted that the quantities provided in the specification are approximate quantities, that is, in the absence of specific description of "about", "approximately", and "generally", the meaning of "about", "approximately", and "generally" can still be implied.

Some embodiments of the present invention are described below, and additional steps may be provided before, during, and/or after the various stages described in these embodiments. Some of the stages may be replaced or deleted in different embodiments. Additional components may be added to the semiconductor device structure. Some of the components may be replaced or deleted in different embodiments. Although some of the embodiments discussed are performed in a specific order of steps, these steps may still be performed in another logical order.

As used herein, the term "substantially" means that a given amount of value may vary based on a particular technology node associated with the target semiconductor device. In some embodiments, based on a particular technology node, the term "substantially" may mean that a given amount of value is within a range of, for example, ±5% of a target (or desired) value.

The present disclosure provides an optical structure and a method for forming the same. After forming an oxidation component by a local oxidation process, a patterning process is performed on an optical channel material to form an optical structure in which the optical channel layer has a curved surface at the top. The depth to which the oxidation component is embedded in the optical channel material layer can be precisely controlled by adjusting the duration and temperature of the oxidation step. In this way, compared to the etching process of the known shallow trench isolation structure, the method for forming the optical structure disclosed in the present disclosure can precisely control the thickness of the optical channel layer, which is the core of the optical structure. For example, the difference between the local thickness of the optical channel layer and its ideal thickness can be controlled within a smaller range (e.g., about ≤2nm), making the optical structure more suitable for photonic applications. Furthermore, since the structure characteristics of the optical channel layer are changed by partially oxidizing the optical channel material, the optical channel layer in the present disclosure can have a surface with lower roughness compared to the optical channel layer formed by the conventional etching process. Therefore, when light is transmitted in the optical channel layer, it can have better total reflection properties between the optical channel layer and the materials around the optical channel layer, thereby improving the performance of the optical structure in photonic applications.

FIGS. 1A to 1H are cross-sectional views showing various stages in the manufacturing process of an optical structure according to some embodiments of the present disclosure.

Referring to FIG. 1A , a substrate 10 is provided. The substrate 10 may include a lower cladding layer 100 and an optical channel material layer 102 disposed on the lower cladding layer 100 . In some embodiments, the substrate 10 is a semiconductor-on-insulator (SOI) substrate. The substrate 10 may further include a base 104 disposed under the lower cladding layer 100 .

The lower cladding layer 100 may include a buried dielectric material, such as buried oxide (BOX), buried nitride, other suitable materials, or a combination thereof. By providing the lower cladding layer 100, the optical channel layer 112 can be surrounded by low dielectric materials. The optical channel material layer 102 may include silicon, germanium, silicon germanium, silicon nitride, gallium arsenide, indium phosphide, other suitable materials, or a combination thereof. In a specific embodiment, the lower cladding layer 100 includes silicon oxide, and the optical channel material layer 102 includes silicon. In addition, the dielectric constant of the lower cladding layer 100 is less than the dielectric constant of the optical channel material layer 102. For example, the dielectric constant of the lower cladding layer 100 may be in the range of 1.0 to 12.0, and the dielectric constant of the optical channel material layer 102 may be in the range of 3.0 to 20.0. In this way, light can be totally reflected at the interface between the lower cladding layer 100 and the optical channel layer formed subsequently. The substrate 104 may include a silicon substrate, a germanium substrate, a silicon germanium substrate, a silicon carbide substrate, an aluminum nitride substrate, a gallium nitride substrate, other suitable substrates, or a combination thereof.

In FIGS. 1A to 1H, a separator 11 is shown that separates the substrate 10 and the optical structure to be formed subsequently into a first region 10A and a second region 10B. It should be understood that the first region 10A and the second region 10B on both sides of the separator 11 may be adjacent regions or separated regions of the substrate 10 and the optical structure to be formed subsequently. In addition, although the first region 10A and the second region 10B are shown simultaneously in FIGS. 1A to 1H, the cross-sectional views of the first region 10A and the second region 10B shown in these figures may be cross-sectional views from different directions, such as directions perpendicular to each other.

Next, referring to FIGS. 1B to 1D, at least one local oxidation process is performed on the optical channel material layer 102 to form a plurality of oxidation components embedded in the optical channel material layer 102, such as a first oxidation component 108A and a second oxidation component 108B. Referring to FIGS. 1B to 1C and 1D, respectively, the at least one local oxidation process may include a first local oxidation process for forming a plurality of first oxidation components 108A and a second local oxidation process for forming a plurality of second oxidation components 108B, and the thickness of the first oxidation component 108A is greater than the thickness of the second oxidation component 108B. It should be understood that the present disclosure does not limit the formation order of the first local oxidation process and the second local oxidation process, and a person skilled in the art may select the formation order of the first oxidation component 108A and the second oxidation component 108B according to the design of the process. In the embodiments shown in the following figures, the second partial oxidation process is performed after the first partial oxidation process. That is, the following figures are described by first forming a thicker first oxidation component 108A and then forming a thinner second oxidation component 108B.

The following describes a first local oxidation process for forming a first oxidation component 108A. In order to form the first oxidation component 108A, as shown in FIG. 1B , a mask layer 106 may be formed on the optical channel material layer 102, and the mask layer 106 may have a plurality of openings O1 exposing the optical channel material layer 102 in the first region 10A. In some embodiments, these openings O1 are a plurality of striped openings. The mask layer 106 may include a photoresist, such as a positive photoresist or a negative photoresist. In some embodiments, the mask layer 106 may include a hard mask and may be formed of silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, silicon nitride carbide, similar materials, or a combination thereof. The mask layer 106 may be a single-layer or multi-layer structure. The method of forming the mask layer 106 may include a deposition process, a lithography process, etc. The deposition process may include, for example, a physical vapor deposition process, a chemical vapor deposition process, an atomic layer deposition process, or any suitable deposition process. The lithography process may include, for example, steps such as photoresist coating, soft baking, exposure, post-exposure baking, development, and hard baking.

Next, referring to FIG. 1C , multiple portions of the optical channel material layer 102 are oxidized to form oxidized components 108A. In some embodiments, the oxidized components 108A are formed by heating the portion of the optical channel material layer 102 exposed from the opening O1. More specifically, by performing a heat treatment, the material on the surface of the optical channel material layer 102 can be oxidized to form the oxidized components 108A including oxides.

The following describes a second local oxidation process for forming a second oxidation component 108B. Referring to FIG. 1D , a process similar to the process described above for forming the oxidation component 108A is performed to form the oxidation component 108B. More specifically, the formation of the oxidation component 108B may include forming a mask layer 106 on the optical channel material layer 102, and the mask layer 106 has a plurality of openings O2 exposing the optical channel material layer 102. Next, the formation of the oxidation component 108B may further include oxidizing a plurality of portions of the optical channel material layer 102 to form the oxidation component 108B. In some embodiments, the oxidation component 108A passes through the optical channel material layer 102 and contacts the lower cladding layer 100. On the other hand, the optical channel material layer 102 may extend laterally below the oxidation component 108B. In some other embodiments, the light channel material layer 102 also extends laterally below the oxidized component 108A, and the portion of the light channel material layer 102 extending laterally below the oxidized component 108A is substantially thinner than the portion extending laterally below the oxidized component 108B. A person skilled in the art can precisely control the depth of the oxidized components 108A and 108B embedded in the light channel material layer 102 by adjusting the duration and temperature of the above-mentioned oxidation step. In addition, the oxidation step in the second partial oxidation process is similar to that described in the first partial oxidation process, and its detailed description is omitted here for simplicity.

In addition, the mask layer 106 used in the first and second partial oxidation processes can be the same mask layer or different mask layers formed in separate processes. For example, in an embodiment using the same mask layer, a mask member (not shown) disposed on the mask layer 106 in the first region 10A is used to mask the first oxidized member 108A formed during the second partial oxidation process to prevent the first oxidized member 108A from further expanding during the second partial oxidation process.

In such an embodiment, the second partial oxidation process can be performed first to form the second oxidized component 108B with a smaller thickness, and then the first partial oxidation process can be performed to form the first oxidized component 108A with a larger thickness. That is, during the first partial oxidation process, a mask component (not shown) disposed on the mask layer 106 in the second region 10B is used to mask the formed second oxidized component 108B to prevent the second oxidized component 108B from further expanding during the first partial oxidation process. Therefore, by using a mask component (not shown) and the same mask layer 106 in the first and second partial oxidation processes, the order of forming the first oxidized component 108A and the second oxidized component 108B is not limited.

In some other embodiments, the mask layer 106 formed in the first local oxidation process is removed before the second local oxidation process. The removal of the mask layer 106 is performed using an etching process, such as a dry or wet etching process or a combination thereof. In some embodiments, the removal is performed using a wet etching process, and the etchant used includes hydrofluoric acid (HF), nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), phosphoric acid (H ₃ PO ₄ ), hydrochloric acid (HCl), ammonia (NH ₃ ), other suitable etchants, or a combination thereof. Then, another mask layer 106 can be formed on the optical channel material layer 102, and the mask layer 106 has a plurality of openings O2 that expose the optical channel material layer 102 in the second region 10B. In some embodiments, the openings O2 are a plurality of stripe-shaped openings. Since the another mask layer 106 covers the formed first oxidized component 108A, the first oxidized component 108A can be prevented from further expanding during the second partial oxidation process. The material and formation method of the another mask layer 106 are the same as those of the mask layer 106 used in the first partial oxidation process, and the detailed description thereof is omitted for simplicity.

In such an embodiment, the second partial oxidation process can be performed first to form the second oxidation component 108B with a smaller thickness, and then the first partial oxidation process can be performed to form the first oxidation component 108A with a larger thickness. That is, the mask layer 106 formed during the first partial oxidation process can cover the second oxidation component 108B that has been formed, and the second oxidation component 108B can be prevented from further expanding during the first partial oxidation process. Therefore, by using different mask layers 106 formed in the first and second partial oxidation processes in the respective processes, the formation order of the first oxidation component 108A and the second oxidation component 108B is not limited.

As discussed above, each local oxidation process may include forming a mask layer 106 having a plurality of openings exposing the light channel material layer 102 on the light channel material layer 102, and may include oxidizing a plurality of portions of the light channel material layer 102 to form an oxidized feature.

As shown in FIGS. 1C and 1D, in some embodiments, since the volume of the above-mentioned portion of the optical channel material layer 102 expands after being oxidized into the oxidized parts 108A and 108B, the top surfaces of the oxidized parts 108A and 108B are higher than the top surface of the optical channel material layer 102. After the above-mentioned local oxidation process, the top of the formed optical channel material layer 102 (and the optical channel layer 112 formed subsequently) has a curved surface. In addition, as shown in FIG. 1D, each oxidized part 108A and 108B may include a protrusion 108P, and there is a curved concave surface between the side wall of each oxidized part 108A and 108B and the protrusion 108P. The arc-shaped concave surface corresponds to the arc surface of the top of the optical channel material layer 102, and also corresponds to the arc surface of the top of the subsequently formed optical channel layer 112. In addition, as shown in FIG. 1D, the protrusion 108P can extend laterally on the top surface of the optical channel material layer 102.

The oxidized components 108A and 108B may include an element common to the light channel material layer 102. For example, the oxidized components 108A and 108B may include silicon oxide, germanium oxide, gallium oxide, indium oxide, other suitable materials, or a combination thereof. In addition, in some embodiments, the dielectric constant of the oxidized components 108A and 108B is less than the dielectric constant of the light channel material layer 102.

After forming the oxidized components 108A and 108B, referring to FIG. 1E , the mask layer 106 may be removed to expose the optical channel material layer 102. Then, referring to FIGS. 1F and 1G , a patterning process may be performed to pattern the optical channel material layer 102 into an optical channel layer 112, and the top of the optical channel layer 112 has a curved surface. Specifically, the patterning process may include forming a patterned mask 110 on the optical channel material layer 102 to cover the oxidized components 108A and 108B, and may further include etching the portion of the optical channel material layer 102 exposed by the patterned mask 110. In some embodiments, the patterning process includes etching the optical channel material layer 102 until the lower cladding layer 100 is exposed, as shown in FIG. 1G . The material of the patterned mask 110 may include silicon nitride, silicon oxynitride, silicon carbide, silicon carbide nitride, photoresist, similar materials, or a combination thereof. The etching process may be performed by a dry etching process, such as a reactive ion etching process.

After the patterning process, the patterned mask 110 may be removed. The removal of the patterned mask 110 is performed using an etching process, such as a dry or wet etching process, or a combination thereof. In some embodiments, the removal is performed using a wet etching process, and the etchant used includes hydrofluoric acid (HF), nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), phosphoric acid (H ₃ PO ₄ ), hydrochloric acid (HCl), ammonia (NH ₃ ), other suitable etchants, or a combination thereof.

The optical channel layer 112 may have different cross-sectional shapes in different regions of the formed optical structure. For example, as shown in FIG. 1G, the optical channel layer 112 may be formed into a stripe shape in the first region 10A and have a vertical side wall adjacent to the curved surface. On the other hand, as shown in FIG. 1G, the optical channel layer 112 may be formed into a ridge shape in the second region 10B and have a lateral extension portion 112H extending outward from the vertical side wall of the optical channel layer 112 adjacent to the curved surface. The lateral extension portion 112H may extend to align with the edge of the oxidized component 108B shown in FIG. 1F. In some embodiments, the lateral extension portion 112H is aligned with the protrusion 108P of the oxidized component 108B.

It should be understood that, since the light channel material layer 102 is partially oxidized to change the structural features of the formed light channel layer 112 in the present disclosure, compared with the light channel layer formed by the known etching process, the light channel layer 112 in the present disclosure can have a surface with lower roughness, such as the sidewall, the top surface of the lateral extension portion 112H, etc. Therefore, when light is transmitted in the light channel layer 112, it can have better total reflection properties between the light channel layer 112 and the materials around the light channel layer 112, thereby improving the performance of the optical structure in photonic applications.

In some embodiments, after the patterning process is performed to form the optical channel layer 112, the oxidized components 108A, 108B are removed. For example, the oxidized components 108A, 108B can be removed by a dry or wet etching process or a combination thereof. However, the oxidized components 108A, 108B can also be retained on the optical channel layer 112, and each oxidized component 108A, 108B can have a concave surface corresponding to the curved surface of the optical channel layer 112. In the case where the oxidized components 108A, 108B are retained, multiple top surfaces of the oxidized components 108A, 108B are higher than the top surface of the optical channel layer 112.

In some embodiments, as shown in FIG. 1H , an upper cladding layer 114 is formed on the optical channel layer 112, and the dielectric constant of the upper cladding layer 114 is smaller than that of the optical channel layer 112. In addition, since the dielectric constant of the lower cladding layer 100 is also smaller than that of the optical channel layer 112, light can be totally reflected at the interface between the cladding structure (e.g., the lower cladding layer 100 or the upper cladding layer 114) and the optical channel layer 112. The material of the upper cladding layer 114 can be the same as or similar to that of the lower cladding layer 100, and its detailed description is omitted here for simplicity. The method of forming the upper cladding layer 114 can include physical vapor deposition, chemical vapor deposition, atomic layer deposition, or other suitable methods, or a combination of the foregoing. In embodiments where the oxidized components 108A, 108B are retained on the light channel layer 112, an upper cladding layer 114 may be disposed on top of the light channel layer 112 and the oxidized components 108A, 108B. In some embodiments, the upper cladding layer 114 comprises the same or similar material as the oxidized components 108A, 108B.

FIG. 2A is a three-dimensional schematic diagram of an optical structure 1 according to some embodiments of the present disclosure. FIG. 2B is a cross-sectional view corresponding to the section line X-X' of FIG. 2A according to some embodiments of the present disclosure. FIG. 2C is a cross-sectional view corresponding to the section line Y-Y' of FIG. 2A according to some embodiments of the present disclosure. The optical structure 1 includes an optical channel layer 112 disposed on the lower cladding layer 100, and the top of the optical channel layer 112 has a curved surface as shown in FIGS. 2B and 2C (not shown in FIG. 2A).

In some embodiments, the formation of the optical structure 1 may include forming a waveguide 112A and/or a grating 112B of the optical channel layer 112. Specifically, in some embodiments, the first local oxidation process and the second local oxidation process are respectively used to form the waveguide 112A and the grating 112B of the optical channel layer 112. A thicker oxidation component may be used in the first local oxidation process to form the waveguide 112A with a curved surface, and a thinner oxidation component may be used in the second local oxidation process to form the grating 112B with a curved surface.

Referring to FIG. 2A , the waveguide 112A extends in a first direction (hereinafter, the y direction will be described as the first direction) parallel to the top surface of the lower cladding layer 100. In some embodiments, as shown in FIG. 2 , the waveguide 112A has a width that varies in a second direction (hereinafter, the x direction will be described as the second direction) perpendicular to the first direction to converge the light in the optical channel layer 112. The waveguide 112A shown in FIG. 2A is a striped waveguide, and as shown in FIG. 2B , it does not have a transverse extension portion in the cross section corresponding to the section line X-X’. However, a person skilled in the art may also, according to design requirements, make the optical channel layer 112 include a transverse extension portion similar to the transverse extension portion 112H shown in FIG. 1H , and the transverse extension portion may extend from multiple side walls of the waveguide 112A in a second direction perpendicular to the first direction. In some embodiments, by controlling the thickness of the transverse extension portion, it is possible to ensure that the light transmitted in the optical channel layer 112 does not enter the transverse extension portion, thereby reducing light leakage. The present disclosure does not limit the thickness of the transverse extension portion extending from the side wall of the waveguide 112A. For example, in a specific embodiment, the thickness of the waveguide 112A is in the range of 100nm to 1000nm, such as 220nm, and the thickness of the transverse extension portion is in the range of 20nm to 700nm, such as 90nm.

2A and 2C, the grating 112B of the optical channel layer 112 may include a plurality of stripe portions 112S each having a curved surface (not shown in FIG. 2A) and extending in a second direction (x direction) parallel to the top surface of the lower cladding layer 100. The grating 112B may further include a transverse connecting portion 112C extending between the stripe portion 112S and the lower cladding layer 100 in a first direction (y direction) perpendicular to the second direction. The grating 112B may be formed by forming a large number of oxidized components extending in the second direction in a local oxidation process. The present disclosure does not limit the thickness of the stripe portion 112S and the transverse connecting portion 112C of the grating 112B. For example, in a specific embodiment, the thickness of the stripe portion 112S is in the range of 100 nm to 1000 nm, such as 220 nm, and the thickness of the transverse connection portion 112C is in the range of 0 nm to 700 nm, such as 150 nm. In some embodiments, the thickness of the transverse connection portion 112C of the grating 112B is greater than the thickness of the transverse extension portion of the waveguide 112A.

Compared to the conventional etching process of the shallow trench isolation structure, the method for forming the optical structure disclosed herein can accurately control the thickness of the optical channel layer 112 as the core of the optical structure 1. For example, the difference between the local thickness of the waveguide 112A and the grating 112B and their ideal thickness can be controlled within a relatively small range (e.g., about ≤2 nm), making the optical structure 1 more suitable for photonic applications.

The operation principle of the optical structure 1 is explained below with reference to FIG. 2A. For example, light with a specific wavelength distribution λ ₀ from the light source 2 can be irradiated to the grating 112B with a period Λ at an incident angle θ, and then the light can be transmitted to the waveguide 112A in the optical channel layer 112. The period Λ of the grating 112B can be determined according to the wavelength of the light used corresponding to the optical structure 1. For example, when the wavelength distribution λ ₀ of the light is in the range of 100nm~2000nm, the period Λ can be in the range of 20nm~1000nm. It should be understood that, for the sake of simplicity, the upper cladding layer covering the optical channel layer 112 or the oxidized components that have not been removed on the optical channel layer 112 are not shown in FIG. 2A. Light can be totally reflected at the interface between the light channel layer 112 and the surrounding material.

In summary, the present disclosure provides an optical structure and a method for forming the same. After forming an oxidation component by a local oxidation process, a patterning process is performed on the optical channel material to form an optical structure in which the optical channel layer has a curved surface at the top. The depth to which the oxidation component is embedded in the optical channel material layer can be precisely controlled by adjusting the duration and temperature of the oxidation step. In this way, compared to the known etching process of the shallow trench isolation structure, the method for forming the optical structure disclosed in the present disclosure can precisely control the thickness of the optical channel layer, which is the core of the optical structure. For example, the difference between the local thickness of the optical channel layer and its ideal thickness can be controlled within a smaller range (e.g., about ≤2nm), making the optical structure more suitable for photonic applications. Furthermore, since the structure characteristics of the optical channel layer are changed by partially oxidizing the optical channel material, the optical channel layer in the present disclosure can have a surface with lower roughness compared to the optical channel layer formed by the conventional etching process. Therefore, when light is transmitted in the optical channel layer, it can have better total reflection properties between the optical channel layer and the materials around the optical channel layer, thereby improving the performance of the optical structure in photonic applications.

The features of several embodiments are summarized above so that those with ordinary knowledge in the art to which the present invention belongs can more easily understand the viewpoints of the embodiments of the present invention. Those with ordinary knowledge in the art to which the present invention belongs should understand that other processes and structures can be easily designed or modified based on the embodiments of the present invention to achieve the same purpose and/or advantages as the embodiments introduced herein. Those with ordinary knowledge in the art to which the present invention belongs should also understand that such equivalent processes and structures do not violate the spirit and scope of the present invention, and various changes, substitutions and replacements can be made without violating the spirit and scope of the present invention.

1: Optical structure

2: Light source

10: Substrate

10A: Area 1

10B: Second Area

11: Separator

100: Lower coating layer

102: Optical channel material layer

104: Base

106: Mask layer

108A, 108B: Oxidized parts

108P: Prominent

110: Patterned Mask

112: Optical channel layer

112A: Waveguide

112B: Grating

112C: Horizontal connection

112H: Horizontal extension

112S: Stripe

114: Upper coating

X-X’, Y-Y’: Section Line

x,y,z: direction

O1,O2: Open

λ: wavelength distribution

θ: angle of incidence

Λ: Cycle

The following will be described in detail with the accompanying drawings. It should be noted that, according to standard practices in the industry, various features are not drawn to scale and are only used for illustration. In fact, the size of the components can be arbitrarily enlarged or reduced to clearly show the features of the embodiments of the present invention. Figures 1A to 1H are cross-sectional views of various stages in the manufacturing process of the optical structure according to some embodiments of the present disclosure. Figure 2A is a three-dimensional schematic diagram of the optical structure according to some embodiments of the present disclosure. Figure 2B is a cross-sectional view corresponding to the section line X-X' of Figure 2A according to some embodiments of the present disclosure. Figure 2C is a cross-sectional view corresponding to the section line Y-Y' of Figure 2A according to some embodiments of the present disclosure.

10A: First Area

10B: Second area

11: Separator

100: Lower coating layer

104: Base

112: Optical channel layer

112H: Horizontal extension

114: Upper covering layer

Claims (23)

A method for forming an optical structure, comprising: Providing a substrate, wherein the substrate comprises a lower cladding layer and an optical channel material layer disposed on the lower cladding layer; Performing at least one local oxidation process on the optical channel material layer to form a plurality of oxidized components embedded in the optical channel material layer; and Performing a patterning process to pattern the optical channel material layer into an optical channel layer, and having a curved surface at the top of the optical channel layer; Wherein a dielectric constant of the lower cladding layer is less than a dielectric constant of the optical channel layer. A method for forming an optical structure as claimed in claim 1, wherein multiple top surfaces of the oxidized components are higher than a top surface of the optical channel material layer. A method for forming an optical structure as claimed in claim 1, wherein each of the oxidized components includes a protrusion, and an arc-shaped concave surface corresponding to the arc surface is provided between a side wall of each of the oxidized components and the protrusion. A method for forming an optical structure as claimed in claim 3, wherein the protrusion extends laterally on the top surface of the light channel material layer. A method for forming an optical structure as claimed in claim 1, wherein the dielectric constant of the oxidized components is smaller than the dielectric constant of the optical channel material layer. A method for forming an optical structure as claimed in claim 1, wherein a portion of the oxidized components pass through the light channel material layer and contact the lower cladding layer. A method for forming an optical structure as claimed in claim 1, wherein the light channel material layer extends laterally below a portion of the oxidized components. A method for forming an optical structure as claimed in claim 1, wherein the at least one local oxidation process comprises: a first local oxidation process to form a plurality of first oxidation components; and a second local oxidation process to form a plurality of second oxidation components; wherein the thickness of the first oxidation components is greater than the thickness of the second oxidation components. A method for forming an optical structure as claimed in claim 8, wherein the second local oxidation process is performed after some oxidation processes in the first local area. A method for forming an optical structure as claimed in claim 8, wherein the first local oxidation process and the second local oxidation process are used to form a waveguide and a grating of the optical channel layer, respectively. A method for forming an optical structure as claimed in claim 1, wherein each of the local oxidation processes comprises: forming a mask layer on the light channel material layer, and the mask layer has a plurality of openings exposing the light channel material layer; and oxidizing a plurality of portions of the light channel material layer to form the oxidation components. A method for forming an optical structure as claimed in claim 11, wherein the at least one local oxidation process includes a first local oxidation process and a second local oxidation process formed in sequence, and the mask layer formed in the first local oxidation process is removed before the second local oxidation process. A method for forming an optical structure as claimed in claim 11, wherein the openings are multiple striped openings. A method for forming an optical structure as claimed in claim 1, wherein the patterning process comprises: forming a patterned mask covering the oxidized components on the light channel material layer; and etching the portion of the light channel material layer exposed by the patterned mask. A method for forming an optical structure as claimed in claim 1, wherein the patterning process includes etching the optical channel material layer until the lower cladding layer is exposed. The method for forming an optical structure as claimed in claim 1 further includes removing the oxidized components. The method for forming an optical structure as claimed in claim 1 further includes forming an upper cladding layer on the optical channel layer, and a dielectric constant of the upper cladding layer is smaller than the dielectric constant of the optical channel layer. An optical structure includes: a lower cladding layer; an optical channel layer formed of a single material and disposed on the lower cladding layer, and having a curved surface at the top of the optical channel layer; wherein a dielectric constant of the lower cladding layer is smaller than a dielectric constant of the optical channel layer. An optical structure as claimed in claim 18, wherein the light channel layer includes a waveguide having the curved surface, and the waveguide extends in a first direction parallel to the top surface of the lower cladding layer. An optical structure as claimed in claim 19, wherein the light channel layer further includes a lateral extension portion, wherein the lateral extension portion extends from multiple side walls of the waveguide in a second direction perpendicular to the first direction. The optical structure of claim 18, wherein the light channel layer includes a grating, wherein the grating includes: a plurality of stripe portions, each having the arc surface and extending in a second direction parallel to the top surface of the lower cladding layer; and a transverse connecting portion extending between the stripe portions and the lower cladding layer in a first direction perpendicular to the second direction. The optical structure of claim 18 further includes an upper cladding layer covering the optical channel layer, and a dielectric constant of the upper cladding layer is smaller than the dielectric constant of the optical channel layer. An optical structure as in claim 22, wherein the upper cladding layer and the lower cladding layer comprise the same material.

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