Optical module structure and method for forming the same

Abstract

An optical module structure and its forming method are disclosed. The structure includes: a substrate comprising adjacent first and second regions; a photoelectric conversion structure located on the second region; and a first waveguide located on the first region, wherein the projected area of ​​the first waveguide onto the surface of the photoelectric conversion structure is greater than zero, and the distance from the first waveguide to the photoelectric conversion structure is less than the coupling distance. This structure reduces transmission loss and return loss, improves the performance of the optical module structure, and reduces limitations on manufacturing processes, facilitating the acquisition of a high-performance first waveguide.

Description

Technical Field

[0001] This invention relates to the field of optical device technology, and in particular to an optical module structure and its formation method. Background Technology

[0002] In recent years, photonic integration based on silicon-on-insulator (SOI) has developed rapidly. Silicon photonic integration has the advantages of large-area substrates, mature CMOS compatibility, and monolithic integration. However, various losses, crosstalk, and conventional silicon photonic fabrication platforms limit the development of silicon photonics.

[0003] In contrast, silicon nitride, a silicon-based material, can be fabricated using processes compatible with commercial semiconductor manufacturing. It boasts a broad transmission spectrum from visible to mid-infrared light, and its refractive index differs from that of the cladding layer by approximately 0.5, smaller than that of silicon on insulators. This allows for waveguide sizes on the micrometer scale, relatively reducing fabrication complexity. Simultaneously, its refractive index difference is larger than that of high-refractive-index glass planar waveguides, resulting in relatively smaller device sizes. This moderate refractive index and device size make silicon nitride waveguides a highly promising material.

[0004] Silicon nitride waveguide integrated optical modules based on silicon-on-insulator substrates have unique advantages in the field of data transmission. In terms of stacking, silicon nitride waveguides are widely used in the field of optical modules due to their superior low transmission loss characteristics.

[0005] Silicon-based photodetectors, which convert optical signals into electrical signals, play a crucial role as a key component in optoelectronics. Germanium photodetectors have garnered significant attention due to their low cost, compatibility with CMOS processes, and ease of optoelectronic integration. However, since germanium materials can only be epitaxially grown on silicon, and current detection requires silicon as a conductive medium, current methods typically involve coupling light from a silicon nitride waveguide into the silicon waveguide before coupling it into the germanium photodetector to obtain the signal.

[0006] However, the way optical signals enter the germanium photodetector from the silicon nitride waveguide needs further improvement. Summary of the Invention

[0007] The technical problem solved by this invention is to provide an optical module structure and its formation method to improve optical signal transmission performance.

[0008] To address the aforementioned technical problems, the present invention provides an optical module structure, comprising: a substrate, the substrate including an adjacent first region and a second region; a photoelectric conversion structure located on the second region; and a first waveguide located on the first region, wherein the projected area of ​​the first waveguide onto the surface of the photoelectric conversion structure is greater than zero, and the distance from the first waveguide to the photoelectric conversion structure is less than the coupling distance.

[0009] Optionally, the coupling distance is 800 nanometers.

[0010] Optionally, the substrate is a silicon-on-insulator substrate.

[0011] Optionally, the substrate further includes a third region adjacent to the first region, the third region having a second waveguide.

[0012] Optionally, it may also include: an optical splitting waveguide, which is used to transmit the optical signal from the first waveguide to the second waveguide.

[0013] Optionally, the material of the second waveguide includes silicon.

[0014] Optionally, it may also include: a device coupled to the second waveguide; the device may include one or more of a modulator, an optical attenuator, and a heater device.

[0015] Optionally, the first waveguide is used to transmit optical signals to the photoelectric converter via evanescent wave coupling.

[0016] Optionally, the material of the first waveguide may include silicon nitride; and the material of the photoelectric conversion structure may include germanium.

[0017] Accordingly, the present invention also provides a method for forming the above-mentioned semiconductor structure, comprising: providing a substrate, the substrate including an adjacent first region and a second region; forming a first dielectric material layer on the substrate; after forming the first dielectric material layer, forming a first waveguide on a portion of the surface of the first dielectric material layer or within the first dielectric material layer on the first region; after forming the first waveguide, forming a second dielectric material layer on the surface of the first dielectric material layer and the first waveguide; after forming the second dielectric material layer, etching the first dielectric material layer and the second dielectric material layer until a portion of the surface of the second region is exposed, forming an opening within the first dielectric material layer and the second dielectric material layer; forming a photoelectric conversion structure within the opening, wherein the projected area of ​​the first waveguide onto the surface of the photoelectric conversion structure is greater than zero, and the distance from the first waveguide to the photoelectric conversion structure is less than the coupling distance.

[0018] Optionally, the formation process of the first waveguide layer includes a low-pressure chemical vapor deposition process.

[0019] Optionally, the material of the first waveguide includes silicon nitride; the material of the photoelectric conversion structure includes germanium.

[0020] Compared with the prior art, the technical solution of the embodiments of the present invention has the following beneficial effects:

[0021] In the optical module structure provided by the present invention, on the one hand, the projected area of ​​the first waveguide onto the surface of the photoelectric conversion structure is greater than zero, and the distance from the first waveguide to the photoelectric conversion structure is less than the coupling distance. This allows the optical signal to directly enter the photoelectric conversion structure from the first waveguide via evanescent wave coupling, reducing the adverse effects of the optical signal being transmitted through an intermediate waveguide, reducing transmission damage and return loss, and improving the performance of the optical module structure. On the other hand, the photoelectric conversion structure and the first waveguide are located in different regions. Therefore, in the manufacturing process, the order in which the first waveguide and the photoelectric conversion structure are formed does not need to be restricted. The first waveguide can be fabricated first, followed by the photoelectric conversion structure, so that the formation process of the first waveguide (such as process temperature) does not affect the performance of the photoelectric conversion structure.

[0022] In the optical module structure formation method provided by the technical solution of the present invention, a first waveguide is formed first, and then a photoelectric conversion structure is formed. This ensures that the formation process of the first waveguide (such as process temperature) does not affect the performance of the photoelectric conversion structure, and facilitates the selection of material deposition processes that are beneficial to the performance of the first waveguide, thereby improving the performance of the first waveguide.

[0023] Furthermore, the formation process of the first waveguide layer includes a low-pressure chemical vapor deposition process. The low-pressure chemical vapor deposition process is conducive to forming a compact and dense structure, making the surface of the first waveguide smoother, and reducing the transmission loss to a very small value. The formed silicon nitride waveguide can achieve a transmission loss of 0.1 dB / cm. Attached Figure Description

[0024] Figure 1 This is a structural diagram of an optical module.

[0025] Figures 2 to 5 This is a cross-sectional structural diagram of each step in the optical module structure formation method of this invention. Detailed Implementation

[0026] It should be noted that the terms "surface" and "on" in this specification are used to describe the relative spatial position and are not limited to whether there is direct contact.

[0027] As described in the background section, the method by which optical signals enter the germanium photodetector from the silicon nitride waveguide needs further improvement, and its performance urgently needs to be enhanced. This paper will now illustrate and analyze this method using an optical module structure.

[0028] Figure 1 This is a schematic diagram of an optical module structure.

[0029] Please refer to Figure 1The optical module structure includes: a substrate, the substrate including a silicon substrate and an oxide layer on the silicon substrate, the substrate including a first region, a second region and a third region arranged along a first direction, the second region being adjacent to the first region and the third region on both sides respectively; a silicon waveguide located on the second region and the third region, the silicon waveguide extending parallel to the surface of the substrate and along the first direction; a germanium detector located on the surface of the silicon waveguide on the third region; and a silicon nitride waveguide located on the first region and the second region, the silicon nitride waveguide extending parallel to the surface of the substrate and along the first direction, the silicon nitride waveguide on the second region being located above the silicon waveguide.

[0030] In the aforementioned optical module structure, the silicon nitride waveguide 103 and the silicon waveguide are separated by a distance m. When the value of m is small enough, the optical signal in the silicon nitride waveguide 103 can enter the silicon waveguide 101 via evanescent wave coupling. After entering the silicon waveguide 101, the optical signal is transmitted within it and can then enter the germanium detector 102 via butt coupling or evanescent wave coupling.

[0031] On the one hand, evanescent wave coupling generates significant transmission loss, which is detrimental to optical modules. Severe transmission loss can distort the signal, thereby reducing the product's bandwidth. On the other hand, reflection occurs during the coupling of the optical signal into the silicon waveguide, resulting in return loss. This return loss reflects back to the laser source, causing instability in the light source output, affecting the signal amplitude, and inducing chirp. In short, the current method of optical signal entry into the silicon waveguide in silicon-on-insulator devices degrades the performance of optical modules and needs further improvement.

[0032] To address the aforementioned issues, this invention provides an optical module structure and its formation method. On one hand, the projected area of ​​the first waveguide onto the surface of the photoelectric conversion structure is greater than zero, and the distance from the first waveguide to the photoelectric conversion structure is less than the coupling distance. This allows the optical signal to directly enter the photoelectric conversion structure from the first waveguide via evanescent wave coupling, reducing the adverse effects of the optical signal being transmitted through an intermediate waveguide, minimizing transmission damage and return loss, and improving the performance of the optical module structure. On the other hand, the photoelectric conversion structure and the first waveguide are located in different regions. Therefore, in the manufacturing process, the order in which the first waveguide and the photoelectric conversion structure are formed does not need to be restricted. The first waveguide can be fabricated first, followed by the photoelectric conversion structure, ensuring that the formation process of the first waveguide (e.g., process temperature) does not affect the performance of the photoelectric conversion structure.

[0033] To make the above-mentioned objectives, features and beneficial effects of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] Figures 2 to 5 This is a cross-sectional structural diagram of each step in the optical module structure formation method of this invention.

[0035] Please refer to Figure 2 A substrate 201 is provided, the substrate 201 including adjacent first region I and second region II.

[0036] In this embodiment, the substrate 201 is a silicon-on-insulator (SOI) substrate. In other embodiments, the material of the substrate 201 includes silicon, silicon carbide, silicon germanium, a multi-element semiconductor material composed of group III-V elements, or germanium-on-insulator (GOI). The multi-element semiconductor material composed of group III-V elements includes InP, GaAs, GaP, InAs, InSb, InGaAs, or InGaAsP.

[0037] Subsequently, a first waveguide is formed on the first region I, and a photoelectric conversion structure is formed on the second region II.

[0038] In other embodiments, the substrate 201 further includes a third region adjacent to the first region I, and subsequently, a second waveguide is formed on the third region.

[0039] Please refer to Figure 3 A first dielectric material layer 202 is formed on the substrate 201; after the first dielectric material layer 202 is formed, a first waveguide 203 is formed on a portion of the surface of the first dielectric material layer 202 or within the first dielectric material layer 202 in the first region I.

[0040] The first dielectric material layer 202 is made of silicon oxide. In this embodiment, the first dielectric material layer 202 is made of silicon oxide. The first dielectric material layer 202 serves as a partial cladding layer for the first waveguide 203.

[0041] The first waveguide 203 is made of silicon nitride. In this embodiment, the first waveguide 203 is made of silicon nitride. Silicon nitride has a broad transmission spectrum from visible light to mid-infrared light, and its refractive index differs from that of the cladding layer by about 0.5, which is smaller than the refractive index difference of silicon on an insulator, giving it a significant advantage as an optical waveguide.

[0042] In this embodiment, the first waveguide 203 is located on the surface of the first dielectric material layer 202.

[0043] In this embodiment, the method for forming the first waveguide 203 includes: forming a first waveguide material layer (not shown in the figure) on the surface of the first dielectric material layer 202; and patterning the first waveguide material layer to form the first waveguide 203.

[0044] In another embodiment, the first waveguide is located within the first dielectric material layer.

[0045] In another embodiment, the method of forming the first waveguide includes: forming a groove in the first dielectric material layer; forming a first waveguide material layer on the surface of the groove and the first dielectric material layer; and etching back the first waveguide material layer until the surface of the first dielectric material layer is exposed to form the first waveguide.

[0046] In this embodiment, the formation process of the first waveguide layer 203 includes a low-pressure chemical vapor deposition (LPD) process. Specifically, the formation process of the first waveguide material layer is a LPD process.

[0047] The low-pressure chemical vapor deposition process facilitates the formation of a compact and dense structure, making the surface of the first waveguide smoother and reducing transmission loss to a very small value. The resulting silicon nitride waveguide can achieve a transmission loss of 0.1 dB / cm.

[0048] The process parameters of the low-pressure chemical vapor deposition process include a process temperature range of 600℃ to 1000℃. Under the conditions of the low-pressure chemical vapor deposition process, Si3N4 with a standard stoichiometric ratio is produced, which has the characteristics of high purity, high density, and relatively fixed refractive index (about 2.01), and the corresponding optical device module performance is relatively stable.

[0049] Although the low-pressure chemical vapor deposition process is above 600°C, the method of first preparing the first waveguide and then preparing the photoelectric conversion structure ensures that the formation process of the first waveguide 203 does not affect the performance of the photoelectric conversion structure.

[0050] In this embodiment, after forming the first waveguide 203, the process further includes annealing the first waveguide 203 at a temperature range of 1000°C to 1200°C. The annealing process reduces the hydrogen atom content within the first waveguide 203, thereby reducing the intrinsic absorption loss in the infrared band when the optical signal propagates through the first waveguide 203.

[0051] Please refer to Figure 4 After the first waveguide 203 is formed, a second dielectric material layer 204 is formed on the surface of the first dielectric material layer 202 and the first waveguide 203.

[0052] The material of the second dielectric material layer 204 includes silicon oxide. In this embodiment, the material of the second dielectric material layer 204 includes silicon oxide.

[0053] The refractive indices of the first dielectric material layer 202 and the second dielectric material layer 204 are lower than the refractive index of the first waveguide 203. The first dielectric material layer 202 and the second dielectric material layer 204 are used to confine the optical signal within the first waveguide 203.

[0054] Please refer to Figure 5 After forming the second dielectric material layer 204, the first dielectric material layer 202 and the second dielectric material layer 204 are etched until a portion of the surface of the second region II is exposed, and an opening (not shown in the figure) is formed in the first dielectric material layer 202 and the second dielectric material layer 204; a photoelectric conversion structure 205 is formed in the opening, the projection area of ​​the first waveguide 203 onto the surface of the photoelectric conversion structure 205 is greater than zero, and the distance from the first waveguide 203 to the photoelectric conversion structure 205 is less than the coupling distance.

[0055] The projected area of ​​the first waveguide 203 onto the surface of the photoelectric conversion structure 205 is greater than zero, and the distance from the first waveguide 203 to the photoelectric conversion structure 205 is less than the coupling distance. This allows the optical signal to directly enter the photoelectric conversion structure 205 from the first waveguide 203 via evanescent wave coupling, reducing the adverse effects of the optical signal being transmitted through an intermediate waveguide, reducing transmission damage and return loss, and improving the performance of the optical module structure.

[0056] In this embodiment, the coupling distance is 800 nanometers.

[0057] The photoelectric conversion structure 205 is made of germanium. The photoelectric conversion structure 205 is a germanium photodetector.

[0058] In this embodiment, after the photoelectric conversion structure 205 is formed, a third dielectric material layer 206 is also formed inside the opening.

[0059] The material of the third dielectric material layer 206 includes silicon oxide. In this embodiment, the material of the third dielectric material layer 206 includes silicon oxide.

[0060] In another embodiment, the method further includes: forming a second waveguide on the third region; forming a device coupled to the second waveguide, the device including one or more of a modulator, an optical attenuator, and a heater device; and forming a beam splitter waveguide. The beam splitter waveguide is used to transmit optical signals from the first waveguide to the second waveguide. Here, the method of forming the second waveguide and the device is not limited.

[0061] Accordingly, this invention also provides a semiconductor structure formed using the above method. Please refer to [link / reference needed]. Figure 5 The device includes: a substrate 201, which includes an adjacent first region I and a second region II; a photoelectric conversion structure 205 located on the second region II; and a first waveguide 203 located on the first region I, wherein the projected area of ​​the first waveguide 203 onto the surface of the photoelectric conversion structure 205 is greater than zero, and the distance from the first waveguide 203 to the photoelectric conversion structure 205 is less than the coupling distance.

[0062] The projected area of ​​the first waveguide 203 onto the surface of the photoelectric conversion structure 205 is greater than zero, and the distance from the first waveguide 203 to the photoelectric conversion structure 205 is less than the coupling distance. This allows the optical signal to directly enter the photoelectric conversion structure 205 from the first waveguide 203 via evanescent wave coupling, reducing the adverse effects of the optical signal being transmitted through an intermediate waveguide, reducing transmission damage and return loss, and improving the performance of the optical module structure. On the other hand, the photoelectric conversion structure and the first waveguide are located in different regions. Therefore, in the manufacturing process, the order in which the first waveguide and the photoelectric conversion structure are formed does not need to be restricted. The first waveguide can be fabricated first, followed by the photoelectric conversion structure, so that the formation process of the first waveguide (such as process temperature) does not affect the performance of the photoelectric conversion structure.

[0063] In this embodiment, the coupling distance is 800 nanometers.

[0064] In this embodiment, the substrate 201 is a silicon-on-insulator (SOI) substrate. In other embodiments, the material of the substrate 201 includes silicon, silicon carbide, silicon germanium, a multi-element semiconductor material composed of group III-V elements, or germanium-on-insulator (GOI). The multi-element semiconductor material composed of group III-V elements includes InP, GaAs, GaP, InAs, InSb, InGaAs, or InGaAsP.

[0065] In another embodiment, the substrate further includes a third region adjacent to the first region, the third region having a second waveguide.

[0066] In another embodiment, it further includes: a beam splitter waveguide, which is used to transmit the optical signal from the first waveguide to the second waveguide.

[0067] In another embodiment, the material of the second waveguide includes silicon.

[0068] In another embodiment, it further includes: a device coupled to the second waveguide; the device includes one or more of a modulator, an optical attenuator, and a heater device.

[0069] The first waveguide 203 is used to transmit optical signals to the photoelectric converter via evanescent wave coupling.

[0070] The first waveguide 203 is made of silicon nitride; the photoelectric conversion structure is made of germanium.

[0071] When the optical module structure is in operation, the optical signal enters the photoelectric conversion structure 205 directly from the first waveguide 203 via evanescent wave coupling. The optical signal can also be transmitted from the first waveguide 203 to the second waveguide via the beam splitter waveguide. The second waveguide is coupled to several devices (such as modulators, optical attenuators, and heaters), allowing the optical signal to enter these devices and achieve functions such as signal modulation.

[0072] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. An optical module structure, characterized in that, include: A substrate, the substrate comprising an adjacent first region and a second region, the first region and the second region being arranged along a first direction; A first dielectric material layer located on the substrate; A first waveguide located on a portion of the surface of the first dielectric material layer or within the first dielectric material layer in the first region, the first waveguide extending along the first direction; A second dielectric material layer located between the first dielectric material layer and the surface of the first waveguide; The photoelectric conversion structure is located on the surface of the second region and within the first dielectric material layer and the second dielectric material layer. The first waveguide and the photoelectric conversion structure are separate from each other. The projected area of ​​the first waveguide onto the surface of the photoelectric conversion structure is greater than zero, and the distance from the first waveguide to the photoelectric conversion structure is less than the coupling distance.

2. The optical module structure as described in claim 1, characterized in that, The coupling distance is 800 nanometers.

3. The optical module structure as described in claim 1, characterized in that, The substrate is a silicon-on-insulator substrate.

4. The optical module structure as described in claim 3, characterized in that, The substrate further includes a third region adjacent to the first region, and the third region has a second waveguide.

5. The optical module structure as described in claim 4, characterized in that, Also includes: The optical waveguide is used to transmit the optical signal from the first waveguide to the second waveguide.

6. The optical module structure as described in claim 4, characterized in that, The material of the second waveguide includes silicon.

7. The optical module structure as described in claim 5, characterized in that, Also includes: Devices coupled to the second waveguide; the devices include one or more of a modulator, an optical attenuator, and a heater.

8. The optical module structure as described in claim 1, characterized in that, The first waveguide is used to transmit optical signals to the photoelectric converter via evanescent wave coupling.

9. The optical module structure as described in claim 1, characterized in that, include: The first waveguide is made of silicon nitride; the photoelectric conversion structure is made of germanium.

10. A method for forming an optical module structure, characterized in that, A substrate is provided, the substrate comprising an adjacent first region and a second region, the first region and the second region being arranged along a first direction; A first dielectric material layer is formed on the substrate; After the first dielectric material layer is formed, a first waveguide is formed on a portion of the surface of the first dielectric material layer or within the first dielectric material layer in the first region, and the first waveguide extends along the first direction. After the first waveguide is formed, a second dielectric material layer is formed on the first dielectric material layer and the surface of the first waveguide; After the second dielectric material layer is formed, the first dielectric material layer and the second dielectric material layer are etched until a portion of the second region surface is exposed, forming an opening in the first dielectric material layer and the second dielectric material layer; A photoelectric conversion structure is formed within the opening. The first waveguide and the photoelectric conversion structure are separate from each other. The projected area of ​​the first waveguide onto the surface of the photoelectric conversion structure is greater than zero, and the distance from the first waveguide to the photoelectric conversion structure is less than the coupling distance.

11. The method for forming the optical module structure as described in claim 10, characterized in that, The formation process of the first waveguide layer includes low-pressure chemical vapor deposition.

12. The method for forming the optical module structure as described in claim 10, characterized in that, The first waveguide is made of silicon nitride; the photoelectric conversion structure is made of germanium.

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