Semiconductor structure, forming method thereof and silicon optical device

Abstract

The invention discloses a semiconductor structure, a forming method thereof and a silicon optical device. The dielectric layer is located on the substrate; the optical waveguide lamination layer is buried in the dielectric layer, the optical waveguide lamination layer comprises a first optical waveguide layer and a second optical waveguide layer located at the top of the first optical waveguide layer, the second optical waveguide layer and the first optical waveguide layer are isolated in the longitudinal direction, and the length of the second optical waveguide layer is smaller than that of the first optical waveguide layer. According to the invention, through the arrangement of the optical waveguide lamination layer with the lamination structure, the light entering the second optical waveguide layer is finally coupled to the first optical waveguide layer through the evanescent wave, so that the probability that an optical signal is coupled to the substrate and the dielectric layer is reduced, more light is coupled to the first optical waveguide layer, and the light emitting efficiency is improved. Therefore, the loss of optical signals is reduced, and the coupling efficiency is improved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of semiconductor manufacturing, and in particular to a semiconductor structure and a method for forming the same, and a silicon optical device. Background Art

[0002] With the demand for optical communication, network data transmission and processing, silicon photonics technology has become one of the important technical solutions in the field of communication. Silicon photonic devices are compatible with existing CMOS (Complementary Metal Oxide Semiconductor) standard processes and can be integrated with microelectronic circuits in integrated circuits. They have attracted widespread attention due to their small size, low cost, and excellent performance.

[0003] Silicon photonic chips are used in silicon photonic communications, laser radar and other fields. One of the important indicators of silicon photonic chips is optical loss. At present, edge coupling is a common way to couple optical signals in optical fibers to chip waveguides in silicon photonic chips. However, the loss of optical signals during propagation is too large, resulting in reduced coupling efficiency. Therefore, the performance of semiconductor structures still needs to be improved. Summary of the invention

[0004] The problem solved by the embodiments of the present invention is to provide a semiconductor structure and a method for forming the same, and a silicon optical device, so as to improve the light coupling efficiency, thereby improving the performance of the semiconductor structure.

[0005] To solve the above problems, an embodiment of the present invention provides a semiconductor structure, comprising: a substrate; a dielectric layer located on the substrate; an optical waveguide stack buried in the dielectric layer, wherein the optical waveguide stack comprises a first optical waveguide layer and a second optical waveguide layer located on top of the first optical waveguide layer, wherein the second optical waveguide layer and the first optical waveguide layer are isolated from each other in a longitudinal direction, and the length of the second optical waveguide layer is less than the length of the first optical waveguide layer.

[0006] Correspondingly, an embodiment of the present invention further provides a method for forming a semiconductor structure, comprising: providing a substrate; forming a dielectric layer and an optical waveguide stack buried in the dielectric layer on the substrate, the optical waveguide stack comprising a first optical waveguide layer and a second optical waveguide layer located on top of the first optical waveguide layer, the second optical waveguide layer and the first optical waveguide layer being isolated from each other in a longitudinal direction, and the length of the second optical waveguide layer being less than the length of the first optical waveguide layer.

[0007] Correspondingly, an embodiment of the present invention further provides a silicon optical device, comprising the semiconductor structure of an embodiment of the present invention; an optical fiber, which is arranged on one side of the optical waveguide stack along its extension direction, and the extension line of the core center of the optical fiber is located between the first optical waveguide layer and the second optical waveguide layer.

[0008] Compared with the prior art, the technical solution of the embodiment of the present invention has the following advantages:

[0009] The semiconductor structure provided by the embodiment of the present invention has an optical waveguide stack, wherein the optical waveguide stack includes a first optical waveguide layer and a second optical waveguide layer located on the top of the first optical waveguide layer, wherein the second optical waveguide layer and the first optical waveguide layer are isolated from each other in the longitudinal direction, and the length of the second optical waveguide layer is less than that of the first optical waveguide layer; by providing the optical waveguide stack with a stacked structure, it is easy to couple light into the first optical waveguide layer and the second optical waveguide layer, so that the distribution of light in the first optical waveguide layer and the second optical waveguide layer is relatively strong; at the same time, since the length of the second optical waveguide layer is less than that of the first optical waveguide layer, the light injected into the second optical waveguide layer is finally coupled into the first optical waveguide layer through an evanescent wave, thereby reducing the probability of the optical signal being coupled into the substrate and the dielectric layer, so that more light is coupled into the first optical waveguide layer, so as to reduce the loss of the optical signal, thereby improving the coupling efficiency.

[0010] The silicon optical device provided by the embodiment of the present invention includes the semiconductor structure and the optical fiber of the embodiment of the present invention. The optical fiber is arranged on one side of the optical waveguide stack along the extension direction thereof, and the extension line of the core center of the optical fiber is located between the first optical waveguide layer and the second optical waveguide layer, so that the coupling center of the optical fiber is raised, and it is easy to couple the light into the first optical waveguide layer and the second optical waveguide layer, and the distribution of the light in the first optical waveguide layer and the second optical waveguide layer is strong, so that it is easy for the light injected into the second optical waveguide layer to finally couple into the first optical waveguide layer through the evanescent wave, thereby improving the coupling efficiency, and thus improving the performance of the silicon optical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of a semiconductor structure;

[0012] Figures 2 to 4 A schematic diagram showing an embodiment of a semiconductor structure of the present invention is shown;

[0013] Figure 5 A schematic diagram showing an embodiment of a silicon optical device of the present invention is shown;

[0014] Figures 6 to 10 is a schematic structural diagram corresponding to each step in an embodiment of a method for forming a semiconductor structure of the present invention;

[0015] Fig.11 It is a simulation diagram of the optical waveguide stack coupling light field distribution of the semiconductor structure of the present invention. DETAILED DESCRIPTION

[0016] At present, the performance of semiconductor structures still needs to be improved. The reasons why the performance needs to be improved are analyzed in combination with a semiconductor structure.

[0017] Figure 1 It is a structural diagram of a semiconductor structure.

[0018] refer to Figure 1 The semiconductor structure includes: a substrate 10; a dielectric layer 11 located on the substrate 10; and an optical waveguide layer 12 buried in the dielectric layer 11.

[0019] Generally, the refractive index of the substrate 10 is greater than the refractive index of the optical waveguide layer 12, so it is difficult for the light injected into the substrate 10 to be coupled into the optical waveguide layer 12; moreover, the diameter of the optical fiber is generally greater than the thickness of the optical waveguide layer 12 (for example, the diameter of the optical fiber is generally at the micrometer level, while the thickness of the optical waveguide layer 12 is at the nanometer level), so compared with the optical fiber, the thickness of the optical waveguide layer 12 is relatively thin, and the light is more easily injected into the substrate 10. At the same time, part of the light injected into the dielectric layer 11 will eventually be coupled into the substrate 10. It can be seen that there will be a lot of losses in the optical signal during the coupling process, thereby reducing the coupling efficiency.

[0020] In order to solve the technical problem, an embodiment of the present invention provides a semiconductor structure, comprising: a substrate; a dielectric layer located on the substrate; an optical waveguide stack buried in the dielectric layer, the optical waveguide stack comprising a first optical waveguide layer and a second optical waveguide layer located on top of the first optical waveguide layer, the second optical waveguide layer and the first optical waveguide layer are isolated from each other in a longitudinal direction, and the length of the second optical waveguide layer is less than the length of the first optical waveguide layer.

[0021] The semiconductor structure provided by the embodiment of the present invention has an optical waveguide stack, wherein the optical waveguide stack includes a first optical waveguide layer and a second optical waveguide layer located on the top of the first optical waveguide layer, wherein the second optical waveguide layer and the first optical waveguide layer are isolated from each other in the longitudinal direction, and the length of the second optical waveguide layer is less than that of the first optical waveguide layer; by providing the optical waveguide stack with a stacked structure, it is easy to couple light into the first optical waveguide layer and the second optical waveguide layer, so that the distribution of light in the first optical waveguide layer and the second optical waveguide layer is relatively strong; at the same time, since the length of the second optical waveguide layer is less than that of the first optical waveguide layer, the light injected into the second optical waveguide layer is finally coupled into the first optical waveguide layer through an evanescent wave, thereby reducing the probability of the optical signal being coupled into the substrate and the dielectric layer, so that more light is coupled into the first optical waveguide layer, so as to reduce the loss of the optical signal, thereby improving the coupling efficiency.

[0022] In order to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and understandable, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0023] Figures 2 to 4FIG. 1 is a schematic diagram showing an embodiment of a semiconductor structure of the present invention. Figure 2 is a top view, Figure 3 for Figure 2 The cross-sectional view at position AA1, Figure 4 for Figure 2 Cross-sectional view at position BB1.

[0024] It should be noted that in order to clearly display the semiconductor structure, Figure 2 The metal interconnect stack, active devices, passive devices and substrate are omitted.

[0025] In this embodiment, the semiconductor structure includes: a substrate 100; a dielectric layer 110, which is located on the substrate 100; and an optical waveguide stack 120, which is buried in the dielectric layer 110. The optical waveguide stack 120 includes a first optical waveguide layer 121 and a second optical waveguide layer 122 located on top of the first optical waveguide layer 121. The second optical waveguide layer 122 is isolated from the first optical waveguide layer 121 in the longitudinal direction, and the length of the second optical waveguide layer 122 is less than the length of the first optical waveguide layer 121.

[0026] The substrate 100 is used to provide a process basis for forming a semiconductor structure.

[0027] The material of the substrate 100 can be silicon, germanium, silicon germanium, silicon carbide, gallium arsenide, indium gallium, or other materials. The substrate can also be a silicon-on-insulator (SOI) substrate or a germanium-on-insulator (GOI) substrate or other types of substrates.

[0028] In this embodiment, the substrate 100 is a silicon-on-insulator substrate.

[0029] Specifically, the substrate includes a bottom substrate layer 101, an insulating material layer 102, and a patterned top substrate layer (not shown) stacked in sequence from bottom to top. The material of the bottom substrate layer 101 is silicon, the material of the top substrate layer is undoped silicon or doped silicon, and the insulating material layer 102 is a buried oxide layer (BOX), and the material of the buried oxide layer can be silicon dioxide.

[0030] In other embodiments, the material of the bottom substrate layer may also be germanium or a mixture of germanium and silicon, and the material of the top substrate layer may also be undoped germanium or doped germanium.

[0031] In this embodiment, the substrate 100 includes a first region i and a second region ii.

[0032] The first region i provides a process platform for forming the optical waveguide stack 120 .

[0033] The second region ii provides a process platform for forming a metal interconnect stack.

[0034] In this embodiment, the semiconductor structure further includes an active device 104 located on the insulating material layer 102 in the second region ii, and a passive device 105 located on the insulating material layer 502 in the first region i.

[0035] Specifically, both the active device 104 and the passive device 105 include a patterned top substrate layer.

[0036] The dielectric layer 110 is used to achieve electrical isolation between various devices or conductive components, and is also used to protect various components located therein.

[0037] As an example, the material of the dielectric layer 110 is a dielectric material, such as silicon oxide, silicon nitride, or silicon oxynitride.

[0038] In this embodiment, the dielectric layer 110 includes a first dielectric layer 111 covering the first optical waveguide layer 121 , and a second dielectric layer 112 covering the second optical waveguide layer 122 .

[0039] Generally, the first optical waveguide layer 121, the first dielectric layer 111, the second optical waveguide layer 122 and the second dielectric layer 112 are sequentially stacked on the substrate 100, and the first dielectric layer 111 covers the first optical waveguide layer 121, and the second dielectric layer 112 covers the second optical waveguide layer 122, which is conducive to reducing the difficulty of forming the optical waveguide stack 120, and correspondingly, it is also easy to isolate the second optical waveguide layer 122 from the first optical waveguide layer 121 in the longitudinal direction.

[0040] As an example, the first dielectric layer 111 and the second dielectric layer 112 are made of the same material. In other embodiments, the first dielectric layer and the second dielectric layer may also be made of different materials.

[0041] The optical waveguide stack 120 is used for coupling and transmitting optical signals.

[0042] The optical waveguide stack 120 includes a first optical waveguide layer 121 and a second optical waveguide layer 122 located on top of the first optical waveguide layer 121. The second optical waveguide layer 122 and the first optical waveguide layer 121 are separated in the longitudinal direction. The length of the second optical waveguide layer 122 is less than the length of the first optical waveguide layer 121. By providing the optical waveguide stack 120 with a stacked structure, it is easy to couple light into the first optical waveguide layer 121 and the second optical waveguide layer 122, so that light is coupled into the first optical waveguide layer 121 and the second optical waveguide layer 122. Meanwhile, since the length of the second optical waveguide layer 122 is shorter than that of the first optical waveguide layer 121, the light injected into the second optical waveguide layer 122 is finally coupled to the first optical waveguide layer 121 through the evanescent wave, thereby reducing the probability of the optical signal being coupled to the substrate 100 and the dielectric layer 110, and coupling more light to the first optical waveguide layer 121, so as to reduce the loss of the optical signal and thus improve the coupling efficiency.

[0043] For example, the incident position of light may be set within the height range covered by the optical waveguide stack 120 so that light is coupled into the first optical waveguide layer 121 and the second optical waveguide layer 122 .

[0044] Here, the longitudinal direction refers to a direction perpendicular to the transmission direction of the first optical waveguide layer 121 (i.e., Figure 6 The area between the first optical waveguide layer 121 and the second optical waveguide layer 122 is a light-incoming area.

[0045] In this embodiment, the material of the optical waveguide stack 120 includes silicon nitride.

[0046] Compared with silicon waveguides, silicon nitride waveguides have higher optical power tolerance and lower transmission loss, are temperature-insensitive, and produce less optical loss. Therefore, the use of silicon nitride materials is beneficial to improving the performance of silicon optical devices.

[0047] In other embodiments, the material of the optical waveguide stack 120 may further include silicon.

[0048] In this embodiment, along the extension direction of the optical waveguide stack 120 (i.e. Figure 3 In the x' direction), the light receiving surfaces 123 of the first light waveguide layer 121 and the second light waveguide layer 122 are flush with each other.

[0049] The light receiving surfaces 123 of the first optical waveguide layer 121 and the second optical waveguide layer 122 are flush, which is conducive to the simultaneous coupling of light into the two waveguide layers, so that the light injected into the second optical waveguide layer 122 is finally coupled into the first optical waveguide layer 121 through the evanescent wave.

[0050] It should be noted that the difference in length between the second optical waveguide layer 122 and the first optical waveguide layer 121 should not be too small. If the difference in length between the second optical waveguide layer 122 and the first optical waveguide layer 121 is too small, the effect of light incident into the second optical waveguide layer 122 being finally coupled to the first optical waveguide layer 121 through the evanescent wave is likely to be poor, thereby easily leading to poor effect of increasing light coupling into the first optical waveguide layer 121, and correspondingly leading to unsatisfactory effect of reducing optical signal loss; therefore, in this embodiment, the difference in length between the second optical waveguide layer 122 and the first optical waveguide layer 121 is greater than 100 microns.

[0051] Here, the length direction of the first optical waveguide layer 121 is the same as the transmission direction of light in the first optical waveguide layer 121 (ie Figure 3 The direction of the length of the second optical waveguide layer 122 is the same as the transmission direction of the light in the second optical waveguide layer 122 (ie Figure 3 x' direction in the head).

[0052] It should be noted that the length of the second optical waveguide layer 122 should not be too small or too large along the extension direction of the second optical waveguide layer 122. If the length of the second optical waveguide layer 122 is too small, it is easy to increase the difficulty of forming the second optical waveguide layer 122, and the quality of the second optical waveguide layer 122 is poor, so that the effect of the light injected into the second optical waveguide layer 122 being finally coupled to the first optical waveguide layer 121 through the evanescent wave is not good, and the effect of reducing the optical signal loss is not ideal; if the length of the second optical waveguide layer 122 is too large, the length of the first optical waveguide layer 121 is also too large, which is easy to increase the area of ​​the silicon photonic chip, or, when the length of the first optical waveguide layer 121 remains unchanged, the difference between the lengths of the second optical waveguide layer 122 and the first optical waveguide layer 121 is too small. Therefore, in this embodiment, along the extension direction of the second optical waveguide layer 122, the length of the second optical waveguide layer 122 is 50 microns to 200 microns.

[0053] As an example, the length of the first optical waveguide layer 121 is greater than 500 micrometers. In other embodiments, the length of the first optical waveguide layer can also be determined according to actual needs.

[0054] In this embodiment, along the transmission direction of light in the second optical waveguide layer 122 , the line width of the second optical waveguide layer 122 gradually decreases.

[0055] Along the transmission direction of light in the second optical waveguide layer 122, the line width of the second optical waveguide layer 122 gradually decreases, which is conducive to allowing more light injected into the second optical waveguide layer 122 to be finally coupled to the first optical waveguide layer 121 through evanescent waves, thereby further reducing the loss of optical signals and improving coupling efficiency. In other embodiments, along the transmission direction of light in the second optical waveguide layer, the line width of the second optical waveguide layer gradually decreases, and along the normal direction of the top surface of the substrate, the thickness of the second optical waveguide layer also gradually decreases.

[0056] Here, the line width of the second optical waveguide layer 122 refers to the line width in a direction parallel to the surface of the second optical waveguide layer 122 and perpendicular to the extending direction of the second optical waveguide layer 122 .

[0057] It should be noted that the line width of the second optical waveguide layer 122 in the direction parallel to the surface of the second optical waveguide layer 122 and perpendicular to the extension direction of the second optical waveguide layer 122 should not be too small or too large. If the line width of the second optical waveguide layer 122 is too small, it is easy to increase the difficulty of forming the second optical waveguide layer 122; if the line width of the second optical waveguide layer 122 is too large, it is easy to make the light injected into the second optical waveguide layer 122 finally coupled to the first optical waveguide layer 121 through the evanescent wave poor, and accordingly make the effect of reducing the optical signal loss unsatisfactory. Therefore, in this embodiment, along the direction parallel to the surface of the second optical waveguide layer 122 and perpendicular to the extension direction of the second optical waveguide layer 122, the line width of the second optical waveguide layer 122 ranges from 500 nanometers to 1500 nanometers.

[0058] It can be understood that the line width of the second optical waveguide layer 122 being in the range of 500 nanometers to 1500 nanometers means that the line width at each position of the second optical waveguide layer 122 is in the range of 500 nanometers to 1500 nanometers.

[0059] For example, along the transmission direction of light in the second optical waveguide layer 122, the line width of the second optical waveguide layer 122 gradually decreases, and the line width at the minimum line width position of the second optical waveguide layer 122 is 500 nanometers, and the line width at the maximum line width position of the second optical waveguide layer 122 is 1500 nanometers.

[0060] It should be noted that the vertical distance h between the second optical waveguide layer 122 and the first optical waveguide layer 121 along the normal direction of the top surface of the substrate 100 should not be too small or too large. If the vertical distance h between the second optical waveguide layer 122 and the first optical waveguide layer 121 is too small, the vertical distance between the second optical waveguide layer 122 and the substrate 100 is too small, which may lead to a poor effect of reducing the coupling of the optical signal into the substrate 100. If the vertical distance h between the second optical waveguide layer 122 and the first optical waveguide layer 121 is too large, the light incident into the second optical waveguide layer 122 may be poorly coupled into the first optical waveguide layer 121. Therefore, in the present embodiment, the vertical distance h between the second optical waveguide layer 122 and the first optical waveguide layer 121 along the normal direction of the top surface of the substrate 100 is in the range of 1 micrometer to 3 micrometers.

[0061] In this embodiment, the transmission loss of the first optical waveguide layer 121 is lower than the transmission loss of the second optical waveguide layer 122 .

[0062] The transmission loss of the first optical waveguide layer 121 is lower than the transmission loss of the second optical waveguide layer 122, which is beneficial to achieve a better effect of reducing the loss of the optical signal, thereby achieving a better effect of improving the coupling efficiency; moreover, in this embodiment, the second optical waveguide layer 122 is formed in the back-end of line (BEOL) process, so the process temperature for forming the second optical waveguide layer 122 is usually lower than the process temperature for forming the first optical waveguide layer 121, so that the transmission loss of the second optical waveguide layer 122 is easily greater than the transmission loss of the first optical waveguide layer 121.

[0063] Specifically, the transmission loss of the first optical waveguide layer 121 is 0.08 dB / cm to 0.15 dB / cm; and the transmission loss of the second optical waveguide layer 122 is 0.3 dB / cm to 0.4 dB / cm.

[0064] It should be noted that the transmission loss of the first optical waveguide layer 121 should not be too small or too large. If the transmission loss of the first optical waveguide layer 121 is too small, it is easy to increase the difficulty of forming the first optical waveguide layer 121; if the transmission loss of the first optical waveguide layer 121 is too large, it is easy to reduce the loss of the optical signal and improve the coupling efficiency. Therefore, in this embodiment, the transmission loss of the first optical waveguide layer 121 is 0.08 dB / cm to 0.15 dB / cm

[0065] It should also be noted that the transmission loss of the second optical waveguide layer 122 should not be too small or too large. If the transmission loss of the second optical waveguide layer 122 is too small, it is easy to increase the difficulty of forming the second optical waveguide layer 122; if the transmission loss of the second optical waveguide layer 122 is too large, it is easy to make the light injected into the second optical waveguide layer 122 finally coupled to the first optical waveguide layer 121 through the evanescent wave poor, and correspondingly make the effect of reducing the loss of the optical signal and improving the coupling efficiency poor. Therefore, in this embodiment, the transmission loss of the second optical waveguide layer 122 is 0.3 dB / cm to 0.4 dB / cm.

[0066] In this embodiment, the material of the first optical waveguide layer 121 includes silicon nitride, and the material of the second optical waveguide layer 122 also includes silicon nitride. In other embodiments, the material of the first optical waveguide layer may also include silicon, and the material of the second optical waveguide layer may also include silicon.

[0067] refer to Figure 4 , Figure 4 for Figure 2 In the cross-sectional view at the position BB1, in this embodiment, the semiconductor structure further includes: a metal interconnection stack 140, buried in the dielectric layer 110 on the side of the optical waveguide stack 120, and the metal interconnection stack 140 includes a plurality of metal interconnection layers 141; the first optical waveguide layer 121 is located in the dielectric layer 110 below the bottom metal interconnection layer 141, and the second optical waveguide layer 122 is located in the dielectric layer 110 in the thickness region between any two adjacent metal interconnection layers 141.

[0068] The metal interconnect stack 140 is an interconnect structure formed by a back-end process, and the metal interconnect stack 140 is used to electrically connect to the active device 104, thereby leading out the electrical properties of each device or realizing electrical connection between devices. As an example, the metal interconnect stack 140 is electrically connected to the active device 104 through the plug 106.

[0069] The metal interconnect stack 140 is located on the side of the optical waveguide stack 120 , which makes it easy to have a gap between the metal interconnect stack 140 and the optical waveguide stack 120 , thereby facilitating avoiding mutual interference between the metal interconnect stack 540 and the optical waveguide stack 120 .

[0070] Specifically, the metal interconnection stack 140 includes a plurality of metal interconnection layers 141 and a via interconnection structure (Via) 142 that electrically connects adjacent layers of the metal interconnection layers 141 .

[0071] As an example, the material of the metal interconnection stack 140 is copper. In other embodiments, the material of the interconnection structure may also be other conductive materials, such as aluminum.

[0072] It should be noted that the dielectric layer 110 includes an interlayer dielectric layer (ILD) 113 located below the bottom metal interconnect layer 141, and a multi-layer stacked metal interlayer dielectric layer (IMD) 114 located between adjacent metal interconnect layers 141. It is understood that the interlayer dielectric layer 114 is located above the interlayer dielectric layer 113.

[0073] The interlayer dielectric layer 113 is used to isolate and realize electrical isolation between various devices or conductive components, such as electrical isolation between the active device 104 and the passive device 105 , or electrical isolation between the active device 104 and the metal interconnect stack 140 .

[0074] The intermetallic dielectric layer 114 is used to achieve electrical isolation between adjacent metal interconnection layers 141 .

[0075] It should also be noted that the first optical waveguide layer 121 is located in the dielectric layer 110 below the bottom metal interconnection layer 141, that is, the first optical waveguide layer 121 is located in the interlayer dielectric layer 113 below the bottom metal interconnection layer 141. The second optical waveguide layer 122 is located in the dielectric layer 110 in the thickness region between any two adjacent metal interconnection layers 141, that is, the second optical waveguide layer 122 is located in the intermetallic dielectric layer 114.

[0076] It can be understood that the dielectric layer 110 includes a first dielectric layer 111 covering the first optical waveguide layer 121 and a second dielectric layer 112 covering the second optical waveguide layer 122. Therefore, the first dielectric layer 111 includes an interlayer dielectric layer 113 and a portion of the metal interlayer dielectric layers 114, and the second dielectric layer 112 is the remaining number of metal interlayer dielectric layers 114.

[0077] It should be noted that the first optical waveguide layer 121 is located in the interlayer dielectric layer 113, and the second optical waveguide layer 122 is located in the metal interlayer dielectric layer 114, which is beneficial for combining the process of forming the dielectric layer 110 with the existing process of forming the interlayer dielectric layer 113 and the process of forming the metal interlayer dielectric layer 114, thereby improving process integration and process compatibility.

[0078] Moreover, the first optical waveguide layer 121 is located in the interlayer dielectric layer 113, and the second optical waveguide layer 122 is located in the metal interlayer dielectric layer 114, which makes it easy to isolate the second optical waveguide layer 122 and the first optical waveguide layer 121 in the longitudinal direction, thereby reducing the difficulty of forming the second optical waveguide layer 122 and the first optical waveguide layer 121.

[0079] In other embodiments, the first optical waveguide layer may also be located in a dielectric layer in a thickness region between any two adjacent metal interconnection layers, and correspondingly, the second optical waveguide layer is located in a dielectric layer in a thickness region between any two adjacent metal interconnection layers above the first optical waveguide layer.

[0080] The second optical waveguide layer 122 is located in the dielectric layer 110 in the thickness region between any two adjacent metal interconnection layers 141. Generally, after forming the first optical waveguide layer 121, a plurality of stacked metal interlayer dielectric layers 114 are formed on the substrate 100, and after each layer of the metal interlayer dielectric layer 114 is formed, a corresponding metal interconnection layer 141 is formed in the metal interlayer dielectric layer 114 of the current layer, which is conducive to reducing the process difficulty of forming the multi-layer stacked metal interlayer dielectric layer 114, and is also conducive to the metal interlayer dielectric layer 114 electrically isolating the metal interconnection layer 141 of the adjacent layer.

[0081] The second optical waveguide layer 122 is located in the dielectric layer 110 in the thickness region between any two adjacent metal interconnection layers 141, that is, after forming the nth metal interconnection layer 141 and before forming the n+1th metal interlayer dielectric layer 114, the second optical waveguide layer 122 is formed on the metal interlayer dielectric layer 114 at the side of the nth metal interconnection layer 141, so that the n+1th metal interlayer dielectric layer 114 can easily bury the second optical waveguide layer 122, that is, the second optical waveguide layer 122 can be easily located in the metal interlayer dielectric layer 114 between the adjacent metal interconnection layers 141, thereby facilitating the reduction of the difficulty of forming the second optical waveguide layer 122, and correspondingly facilitating the control of the position accuracy and size accuracy of the second optical waveguide layer 122, thereby further improving the quality of the second optical waveguide layer 122; wherein n is a natural number.

[0082] In this embodiment, the second optical waveguide layer 122 is located in the dielectric layer 110 in the thickness region between the second metal interconnection layer 1412 and the third metal interconnection layer 1413 .

[0083] The second optical waveguide layer 122 is located in the dielectric layer 110 in the thickness region between the second metal interconnection layer 1412 and the third metal interconnection layer 1413, that is, the second optical waveguide layer 122 is located in the second metal interlayer dielectric layer 1142, and the first optical waveguide layer 121 is located in the interlayer dielectric layer 113, which is beneficial to control the longitudinal distance between the second optical waveguide layer 122 and the first optical waveguide layer 121.

[0084] Moreover, according to the simulation results, the second optical waveguide layer 122 is located between the second metal interconnection layer 1412 and the third metal interconnection layer 1413, which is beneficial to achieve a better effect of improving the coupling efficiency.

[0085] In this embodiment, the semiconductor structure further includes a passivation layer 150 located on the dielectric layer 110 .

[0086] The passivation layer 150 is used to protect the formed semiconductor device and reduce the probability of damage thereof in subsequent process steps.

[0087] Specifically, the material of the passivation layer 150 is a dielectric material, such as silicon oxide, silicon nitride, silicon oxynitride, etc.

[0088] In this embodiment, the semiconductor structure further includes an opening 155 , wherein the opening 155 exposes the topmost metal interconnection layer 141 .

[0089] The opening 155 is used to realize electrical connection between the metal interconnect stack 140 and an external circuit.

[0090] refer to Fig.11 , Fig.11 It is a simulation diagram of the optical waveguide stack coupling light field distribution of the semiconductor structure of this embodiment.

[0091] Among them, the horizontal axis x represents different positions along the length direction of the optical waveguide layer (unit: 10^-6m), the vertical axis z on the left represents different positions along the normal direction of the top surface of the optical waveguide layer (unit: 10^-6m), and the color comparison chart on the right represents the corresponding relationship between light field intensity and color. The smaller the value of the light field intensity in the color comparison chart, the closer the color is to blue and the darker the color is, which corresponds to a smaller light field intensity; the larger the value of the light field intensity in the color comparison chart, the closer the color is to red and the darker the color is, which corresponds to a larger light field intensity.

[0092] Depend on Fig.11 It can be seen that by providing the optical waveguide stack 120 with a stacked structure, it is easy to couple light into the first optical waveguide layer 121 and the second optical waveguide layer 122, so that the distribution of light in the first optical waveguide layer 121 and the second optical waveguide layer 122 is relatively strong. At the same time, since the length of the second optical waveguide layer 122 is shorter than that of the first optical waveguide layer 121, the light injected into the second optical waveguide layer 122 is finally coupled to the first optical waveguide layer 121 through the evanescent wave.

[0093] Correspondingly, the present invention also provides a silicon optical device.

[0094] Figure 5 A schematic diagram of an embodiment of a silicon optical device of the present invention is shown.

[0095] The silicon optical device includes: the semiconductor structure of the above embodiment; an optical fiber 2 arranged on one side of the optical waveguide stack 220 along its extension direction, and the extension line of the core center of the optical fiber 2 is located between the first optical waveguide layer 221 and the second optical waveguide layer 222.

[0096] The silicon optical device includes a semiconductor structure according to an embodiment of the present invention and an optical fiber 2. The optical fiber 2 is arranged on one side of the optical waveguide stack 220 along its extension direction, and the extension line of the core center of the optical fiber is located between the first optical waveguide layer 221 and the second optical waveguide layer 222, so that the coupling center of the optical fiber 2 is raised, and it is easy to couple the light into the first optical waveguide layer 221 and the second optical waveguide layer 222, and the distribution of the light in the first optical waveguide layer 221 and the second optical waveguide layer 222 is strong, so that it is easy for the light injected into the second optical waveguide layer 222 to be finally coupled to the first optical waveguide layer 221 through the evanescent wave, thereby improving the coupling efficiency, and thus improving the performance of the silicon optical device.

[0097] As an example, the vertical distances from the extension line of the core center of the optical fiber 2 to the first optical waveguide layer 221 and the second optical waveguide layer 222 are the same, so that light can be uniformly injected into the first optical waveguide layer 221 and the second optical waveguide layer 222 .

[0098] Accordingly, the present invention also provides a method for forming a semiconductor structure. Figures 6 to 10 It is a schematic structural diagram corresponding to each step in an embodiment of a method for forming a semiconductor structure of the present invention.

[0099] refer to Figure 6 to Figure 7 , Figure 6 is a top view, Figure 7 for Figure 5 In a cross-sectional view at position AA1, a substrate 500 is provided.

[0100] The substrate 500 is used to provide a process basis for subsequent processes.

[0101] The material of the substrate 500 may be silicon, germanium, silicon germanium, silicon carbide, gallium arsenide, indium gallium, or other materials. The substrate may also be other types of substrates such as a silicon on insulator substrate or a germanium on insulator substrate.

[0102] In this embodiment, the substrate 500 is a silicon-on-insulator substrate.

[0103] Specifically, the substrate 500 includes a bottom substrate layer 501, an insulating material layer 502, and a top substrate layer 503 stacked sequentially from bottom to top. The material of the bottom substrate layer 501 is silicon, the material of the top substrate layer 503 is undoped silicon or doped silicon, the insulating material layer 502 is an oxide buried layer, and the material of the oxide buried layer can be silicon dioxide.

[0104] In other embodiments, the material of the bottom substrate layer may also be germanium or a mixture of germanium and silicon, and the material of the top substrate layer may also be undoped germanium or doped germanium.

[0105] In this embodiment, the substrate 500 includes a first region I and a second region II. The first region I provides a process platform for the subsequent formation of an optical waveguide stack. The second region II provides a process platform for the subsequent formation of a metal interconnect stack.

[0106] In this embodiment, after providing the substrate 500 and before forming the dielectric layer and the optical waveguide stack, the formation method also includes: patterning the top substrate layer 503 of the second region II and the top substrate layer 503 of the first region I, forming an active device (not shown) on the insulating material layer 502 of the second region II, and forming a passive device 505 on the insulating material layer 502 of the first region I.

[0107] refer to Figures 8 to 9 A dielectric layer 510 and an optical waveguide stack 520 buried in the dielectric layer 510 are formed on a substrate 500, wherein the optical waveguide stack 520 includes a first optical waveguide layer 521 and a second optical waveguide layer 522 located on top of the first optical waveguide layer 521, wherein the second optical waveguide layer 522 and the first optical waveguide layer 521 are separated in a longitudinal direction, and a length of the second optical waveguide layer 522 is less than a length of the first optical waveguide layer 521.

[0108] in, Figure 8 This is a top view of the dielectric layer and optical waveguide stack. Fig. 9 for Figure 8 Cross-sectional view at position AA1.

[0109] It should be noted that in order to clearly display the semiconductor structure, Figure 8 The metal interconnect stack, active devices, passive devices and substrate are omitted.

[0110] The dielectric layer 510 is used to achieve electrical isolation between various devices or conductive components, and is also used to protect various components located therein.

[0111] As an example, the material of the dielectric layer 510 is a dielectric material, such as silicon oxide, silicon nitride, or silicon oxynitride. In other embodiments, the material of the dielectric layer may also be a resin material.

[0112] In this embodiment, the steps of forming a dielectric layer 510 on a substrate 500 and an optical waveguide stack 520 buried in the dielectric layer 510 include: forming a first optical waveguide layer 521 on the substrate 500; forming a first dielectric layer 511 covering the first optical waveguide layer 521; forming a second optical waveguide layer 522 on the first dielectric layer 511; forming a second dielectric layer 512 covering the second optical waveguide layer 522; the dielectric layer 510 includes the first dielectric layer 511 and the second dielectric layer 512.

[0113] The first optical waveguide layer 521, the first dielectric layer 511, the second optical waveguide layer 522 and the second dielectric layer 512 are stacked on the substrate 500 in sequence, and the first dielectric layer 511 covers the first optical waveguide layer 521, and the second dielectric layer 512 covers the second optical waveguide layer 522, which is conducive to reducing the difficulty of forming the optical waveguide stack 520, and correspondingly, it is also easy to isolate the second optical waveguide layer 522 and the first optical waveguide layer 521 in the longitudinal direction.

[0114] As an example, the materials of the first dielectric layer 511 and the second dielectric layer 512 are the same. In other embodiments, the materials of the first dielectric layer and the second dielectric layer may also be different.

[0115] The optical waveguide stack 520 is used for coupling and transmitting optical signals.

[0116] The optical waveguide stack 520 includes a first optical waveguide layer 521 and a second optical waveguide layer 522 located on top of the first optical waveguide layer 521. The second optical waveguide layer 522 and the first optical waveguide layer 521 are separated in the longitudinal direction. The length of the second optical waveguide layer 522 is shorter than that of the first optical waveguide layer 521. By providing the optical waveguide stack 520 with a stacked structure, it is easy to couple light into the first optical waveguide layer 521 and the second optical waveguide layer 522, so that light is coupled into the first optical waveguide layer 521 and the second optical waveguide layer 522. At the same time, since the length of the second optical waveguide layer 522 is less than that of the first optical waveguide layer 521, the light injected into the second optical waveguide layer 522 is finally coupled to the first optical waveguide layer 521 through the evanescent wave, thereby reducing the probability of the optical signal being coupled to the substrate 500 and the dielectric layer 510, so that more light is coupled to the first optical waveguide layer 521, so as to reduce the loss of the optical signal and thus improve the coupling efficiency.

[0117] For example, the incident position of light can be set within the height range covered by the optical waveguide stack 520 , thereby making it easy for light to be coupled into the first optical waveguide layer 521 and the second optical waveguide layer 522 .

[0118] Here, the longitudinal direction refers to the direction perpendicular to the transmission direction of the first optical waveguide layer 521 (i.e., the direction perpendicular to the transmission direction of the first optical waveguide layer 521). Figure 8 The area between the first optical waveguide layer 521 and the second optical waveguide layer 522 is a light-incoming area.

[0119] In this embodiment, the material of the optical waveguide stack 520 includes silicon nitride. Compared with silicon waveguides, silicon nitride waveguides have higher optical power tolerance and lower transmission loss, and are temperature insensitive, and produce less optical loss. Therefore, the use of silicon nitride material is conducive to improving the performance of silicon optical devices. In other embodiments, the material of the optical waveguide stack may also include silicon.

[0120] In this embodiment, in the step of forming the optical waveguide stack 520 , along the extending direction of the optical waveguide stack, the light receiving surfaces 523 of the first optical waveguide layer 521 and the second optical waveguide layer 522 are flush.

[0121] The light receiving surfaces 523 of the first optical waveguide layer 521 and the second optical waveguide layer 522 are flush, which is conducive to the simultaneous coupling of light into the two waveguide layers, thereby facilitating the light injected into the second optical waveguide layer 522 to be finally coupled into the first optical waveguide layer 521 through the evanescent wave.

[0122] It should be noted that the difference in length between the second optical waveguide layer 522 and the first optical waveguide layer 521 should not be too small. If the difference in length between the second optical waveguide layer 522 and the first optical waveguide layer 521 is too small, the effect of light incident into the second optical waveguide layer 522 being finally coupled to the first optical waveguide layer 521 through the evanescent wave is likely to be poor, thereby easily leading to poor effect of increasing light coupling into the first optical waveguide layer 521, and correspondingly leading to unsatisfactory effect of reducing optical signal loss. Therefore, in this embodiment, the difference in length between the second optical waveguide layer 522 and the first optical waveguide layer 521 is greater than 100 microns.

[0123] Here, the length direction of the first optical waveguide layer 521 is the same as the transmission direction of light in the first optical waveguide layer 521 (ie Figure 8 The direction of the length of the second optical waveguide layer 522 is the same as the transmission direction of the light in the second optical waveguide layer 522 (ie Figure 8 X' head direction in the figure).

[0124] It should be noted that the length of the second optical waveguide layer 522 should not be too small or too large along the extension direction of the second optical waveguide layer 522. If the length of the second optical waveguide layer 522 is too small, it is easy to increase the difficulty of forming the second optical waveguide layer 522, and the quality of the second optical waveguide layer 522 is poor, so that the effect of the light injected into the second optical waveguide layer 522 being finally coupled to the first optical waveguide layer 521 through the evanescent wave is not good, and the effect of reducing the loss of the optical signal is not ideal; if the length of the second optical waveguide layer 522 is too large, the length of the first optical waveguide layer 521 is also too large, which is easy to increase the area of ​​the silicon photonic chip, or, when the length of the first optical waveguide layer 521 remains unchanged, the difference between the lengths of the second optical waveguide layer 522 and the first optical waveguide layer 521 is too small. Therefore, in this embodiment, along the extension direction of the second optical waveguide layer 522, the length of the second optical waveguide layer 522 is 50 microns to 200 microns.

[0125] As an example, the length of the first optical waveguide layer 521 is greater than 500 micrometers. In other embodiments, the length of the first optical waveguide layer can also be determined according to actual needs.

[0126] In this embodiment, in the step of forming the optical waveguide stack, along the transmission direction of light in the second optical waveguide layer 522 , the line width of the second optical waveguide layer 522 gradually decreases.

[0127] Along the transmission direction of light in the second optical waveguide layer 522, the line width of the second optical waveguide layer 522 gradually decreases, which is conducive to allowing more light injected into the second optical waveguide layer 522 to be finally coupled to the first optical waveguide layer 521 through evanescent waves, thereby further reducing the loss of optical signals and improving coupling efficiency. In other embodiments, along the transmission direction of light in the second optical waveguide layer, the line width of the second optical waveguide layer gradually decreases, and along the normal direction of the top surface of the substrate, the thickness of the second optical waveguide layer also gradually decreases.

[0128] Here, the line width of the second optical waveguide layer 522 refers to the line width in a direction parallel to the surface of the second optical waveguide layer 522 and perpendicular to the extending direction of the second optical waveguide layer 522 .

[0129] It should be noted that the line width of the second optical waveguide layer 522 in the direction parallel to the surface of the second optical waveguide layer 522 and perpendicular to the extension direction of the second optical waveguide layer 522 should not be too small or too large. If the line width of the second optical waveguide layer 522 is too small, it is easy to increase the difficulty of forming the second optical waveguide layer 522; if the line width of the second optical waveguide layer 522 is too large, it is easy to make the light injected into the second optical waveguide layer 522 finally coupled to the first optical waveguide layer 521 through the evanescent wave poor, and accordingly make the effect of reducing the optical signal loss unsatisfactory. Therefore, in this embodiment, along the direction parallel to the surface of the second optical waveguide layer 522 and perpendicular to the extension direction of the second optical waveguide layer 522, the line width of the second optical waveguide layer 522 ranges from 500 nanometers to 1500 nanometers.

[0130] It can be understood that the line width of the second optical waveguide layer 522 being in the range of 500 nanometers to 1500 nanometers means that the line width at each position of the second optical waveguide layer 1522 is in the range of 500 nanometers to 1500 nanometers.

[0131] For example, along the transmission direction of light in the second optical waveguide layer 522, the line width of the second optical waveguide layer 522 gradually decreases, and the line width at the minimum line width position of the second optical waveguide layer 522 is 500 nanometers, and the line width at the maximum line width position of the second optical waveguide layer 522 is 1500 nanometers.

[0132] It should be noted that the vertical distance H between the second optical waveguide layer 522 and the first optical waveguide layer 521 along the normal direction of the top surface of the substrate 500 should not be too small or too large. If the vertical distance H between the second optical waveguide layer 522 and the first optical waveguide layer 521 is too small, the vertical distance between the second optical waveguide layer 522 and the substrate 500 is too small, which may lead to a poor effect of reducing the coupling of the optical signal into the substrate 500. If the vertical distance H between the second optical waveguide layer 522 and the first optical waveguide layer 521 is too large, the light incident into the second optical waveguide layer 522 may be coupled to the first optical waveguide layer 521 gradually as the second optical waveguide layer 522 is coupled. Therefore, in this embodiment, along the normal direction of the top surface of the substrate 500, the vertical distance H between the second optical waveguide layer 522 and the first optical waveguide layer 521 is in the range of 1 micrometer to 3 micrometers.

[0133] In this embodiment, the transmission loss of the first optical waveguide layer 521 is lower than the transmission loss of the second optical waveguide layer 522 .

[0134] The transmission loss of the first optical waveguide layer 521 is lower than the transmission loss of the second optical waveguide layer 522, which is beneficial to achieve a better effect of reducing the loss of the optical signal, thereby achieving a better effect of improving the coupling efficiency; moreover, in this embodiment, the second optical waveguide layer 522 is formed in the back-end process, so the process temperature for forming the second optical waveguide layer 522 is usually lower than the process temperature for forming the first optical waveguide layer 521, so that the transmission loss of the second optical waveguide layer 522 is easily greater than the transmission loss of the first optical waveguide layer 521.

[0135] Specifically, the transmission loss of the first optical waveguide layer 521 is 0.08 dB / cm to 0.15 dB / cm; and the transmission loss of the second optical waveguide layer 522 is 0.3 dB / cm to 0.4 dB / cm.

[0136] It should be noted that the transmission loss of the first optical waveguide layer 521 should not be too small or too large. If the transmission loss of the first optical waveguide layer 521 is too small, it is easy to increase the difficulty of forming the first optical waveguide layer 521; if the transmission loss of the first optical waveguide layer 521 is too large, it is easy to reduce the loss of the optical signal and improve the coupling efficiency. Therefore, in this embodiment, the transmission loss of the first optical waveguide layer 521 is 0.08 dB / cm to 0.15 dB / cm.

[0137] It should also be noted that the transmission loss of the second optical waveguide layer 522 should not be too small or too large. If the transmission loss of the second optical waveguide layer 522 is too small, it is easy to increase the difficulty of forming the second optical waveguide layer 522; if the transmission loss of the second optical waveguide layer 522 is too large, it is easy to make the light injected into the second optical waveguide layer 522 finally coupled to the first optical waveguide layer 521 through the evanescent wave poor, and correspondingly make the effect of reducing the loss of the optical signal and improving the coupling efficiency poor. Therefore, in this embodiment, the transmission loss of the second optical waveguide layer 522 is 0.3 dB / cm to 0.4 dB / cm.

[0138] In this embodiment, the material of the first optical waveguide layer 521 includes silicon nitride, and the material of the second optical waveguide layer 522 also includes silicon nitride. In other embodiments, the material of the first optical waveguide layer may also include silicon, and the material of the second optical waveguide layer may also include silicon.

[0139] In this embodiment, the deposition process used to form the first optical waveguide layer 521 includes a low pressure chemical vapor deposition (LPCVD) process. The LPCVD process can easily make the quality of the first optical waveguide layer 521 better, and the LPCVD process uses less gas and has low power consumption, which is conducive to reducing process costs. Moreover, compared with silicon nitride deposited by a plasma enhanced chemical vapor deposition (PECVD) process, silicon nitride deposited by a low pressure chemical vapor deposition process provides less material absorption loss in the communication band.

[0140] In other embodiments, other suitable deposition processes may also be used to form the first optical waveguide layer.

[0141] In this embodiment, the deposition process used to form the second optical waveguide layer 522 includes a plasma enhanced chemical vapor deposition process.

[0142] The plasma enhanced chemical vapor deposition process has the characteristic of a lower deposition temperature, which is beneficial to reduce the impact on the formed devices.

[0143] In addition, in this embodiment, the second optical waveguide layer 522 is formed in the back-end process, and the plasma enhanced chemical vapor deposition process has the characteristic of low deposition temperature, which is conducive to reducing the impact on the metal interconnect stack formed in the back-end process. For example, when the temperature is too high, it is easy to cause the metal interconnect stack to melt.

[0144] Thirdly, the plasma enhanced chemical vapor deposition process is used to improve the film adhesion of the second optical waveguide layer 522 in the dielectric layer 510 .

[0145] In other embodiments, other deposition processes with lower deposition temperature and stronger film adhesion may also be used to form the second optical waveguide layer.

[0146] It should be noted that the process temperature for forming the second optical waveguide layer 522 should not be too low or too high. If the process temperature for forming the second optical waveguide layer 522 is too low, the quality of the second optical waveguide layer 522 is likely to be poor, so that the effect of the light injected into the second optical waveguide layer 522 being finally coupled to the first optical waveguide layer 521 through the evanescent wave is poor; if the process temperature for forming the second optical waveguide layer 522 is too high, the probability of adverse effects on the formed device is likely to increase, and the possibility of melting of the metal interconnect stack is also likely to increase. Therefore, in this embodiment, the process temperature for forming the second optical waveguide layer 522 is 100 degrees Celsius to 400 degrees Celsius.

[0147] refer to Fig.10 , Fig.10 for Figure 8 In the cross-sectional view at the position of BB1, in this embodiment, the formation method further includes: forming a metal interconnection stack 540 buried in the dielectric layer 510, the metal interconnection stack 540 includes a plurality of metal interconnection layers 541, and the metal interconnection stack 540 is located on the side of the optical waveguide stack 520.

[0148] The metal interconnect stack 540 is an interconnect structure formed by a back-end process, and the metal interconnect stack 540 is used to electrically connect to the active device 504, thereby leading out the electrical properties of each device or realizing electrical connection between devices. As an example, the metal interconnect stack 540 is electrically connected to the active device 504 through the plug 506.

[0149] The metal interconnect stack 540 is located on the side of the optical waveguide stack 520 , which makes it easy to have a gap between the metal interconnect stack 540 and the optical waveguide stack 520 , thereby facilitating avoiding mutual interference between the metal interconnect stack 540 and the optical waveguide stack 520 .

[0150] Specifically, the metal interconnect stack 540 includes a plurality of metal interconnect layers 541 and a through-hole interconnect structure 542 that electrically connects adjacent metal interconnect layers 541. As an example, the material of the metal interconnect stack 540 is copper. In other embodiments, the material of the interconnect structure can also be other conductive materials, such as aluminum.

[0151] It should be noted that the dielectric layer 510 includes an interlayer dielectric layer 513 located below the bottom metal interconnect layer 541 and a multi-layer stacked metal interlayer dielectric layer 514 located between adjacent metal interconnect layers 541. It is understood that the metal interlayer dielectric layer 514 is located above the interlayer dielectric layer 513.

[0152] The interlayer dielectric layer 513 is used to isolate and realize electrical isolation between various devices or conductive components, such as electrical isolation between the active device 504 and the passive device 505 , or electrical isolation between the active device 504 and the metal interconnect stack 540 .

[0153] The intermetallic dielectric layer 514 is used to achieve electrical isolation between adjacent metal interconnection layers 541 .

[0154] Accordingly, in the present embodiment, in the step of forming the optical waveguide stack buried in the dielectric layer 510, the first optical waveguide layer 521 is located in the dielectric layer 510 below the bottom metal interconnect layer 541, and the second optical waveguide layer 522 is located in the dielectric layer 510 in the thickness region between any two adjacent metal interconnect layers 541.

[0155] It should be noted that the first optical waveguide layer 521 is located in the dielectric layer 510 below the bottom metal interconnection layer 541, that is, the first optical waveguide layer 521 is located in the interlayer dielectric layer 513 below the bottom metal interconnection layer 541. The second optical waveguide layer 522 is located in the dielectric layer 510 in the thickness region between any two adjacent metal interconnection layers 541, that is, the second optical waveguide layer 522 is located in the intermetallic dielectric layer 514.

[0156] It can be understood that the dielectric layer 510 includes a first dielectric layer 511 covering the first optical waveguide layer 521 and a second dielectric layer 512 covering the second optical waveguide layer 522. Therefore, the first dielectric layer 511 includes an interlayer dielectric layer 513 and a portion of the metal interlayer dielectric layers 514, and the second dielectric layer 512 is the remaining number of metal interlayer dielectric layers 514.

[0157] It should be noted that the first optical waveguide layer 521 is located in the interlayer dielectric layer 513, and the second optical waveguide layer 522 is located in the metal interlayer dielectric layer 514, which is beneficial for combining the process of forming the dielectric layer 510 with the existing process of forming the interlayer dielectric layer 513 and the process of forming the metal interlayer dielectric layer 514, thereby improving process integration and process compatibility.

[0158] Moreover, the first optical waveguide layer 521 is located in the interlayer dielectric layer 513, and the second optical waveguide layer 522 is located in the metal interlayer dielectric layer 514, which makes it easy to isolate the second optical waveguide layer 522 and the first optical waveguide layer 521 in the longitudinal direction, thereby reducing the difficulty of forming the second optical waveguide layer 522 and the first optical waveguide layer 521.

[0159] In other embodiments, the first optical waveguide layer may also be located in a dielectric layer in a thickness region between any two adjacent metal interconnection layers, and correspondingly, the second optical waveguide layer is located in a dielectric layer in a thickness region between any two adjacent metal interconnection layers above the first optical waveguide layer.

[0160] In this embodiment, after forming the first optical waveguide layer 521, a plurality of stacked metal interlayer dielectric layers 514 are formed on the substrate 500, and after each metal interlayer dielectric layer 514 is formed, a corresponding metal interconnection layer 541 is formed in the metal interlayer dielectric layer 514 of the current layer; wherein, after forming the n-th metal interconnection layer 541 and before forming the n+1-th metal interlayer dielectric layer 514, a second optical waveguide layer 522 is formed on the metal interlayer dielectric layer 514 on the side of the n-th metal interconnection layer 541, where n is a natural number.

[0161] After each layer of intermetallic dielectric layer 514 is formed, a corresponding metal interconnection layer 541 is formed in the current layer of intermetallic dielectric layer 514, which is beneficial to reducing the process difficulty of forming a multi-layer stack of intermetallic dielectric layers 514, and is also beneficial for the intermetallic dielectric layer 514 to electrically isolate the metal interconnection layer 541 of the adjacent layer.

[0162] After forming the n-th metal interconnection layer 541 and before forming the n+1-th metal interlayer dielectric layer 514, the second optical waveguide layer 522 is formed on the metal interlayer dielectric layer 514 at the side of the n-th metal interconnection layer 541, so that the n+1-th metal interlayer dielectric layer 514 can easily bury the second optical waveguide layer 522, that is, the second optical waveguide layer 522 can be easily located in the metal interlayer dielectric layer 514 between the adjacent metal interconnection layers 541, thereby reducing the difficulty of forming the second optical waveguide layer 522, and correspondingly facilitating the control of the position accuracy and size accuracy of the second optical waveguide layer 522, thereby further improving the quality of the second optical waveguide layer 522.

[0163] Specifically, after forming the second metal interconnection layer 5412 in the second intermetal dielectric layer 5142 , and before forming the third intermetal dielectric layer 5143 , the second optical waveguide layer 522 is formed on the second intermetal dielectric layer 5142 .

[0164] It can be understood that the second optical waveguide layer 522 is located between the second metal interconnection layer 5412 and the third metal interconnection layer 5413, and the first optical waveguide layer 521 is located in the interlayer dielectric layer 513, which is beneficial to control the longitudinal spacing between the second optical waveguide layer 522 and the first optical waveguide layer 521.

[0165] Moreover, according to the simulation results, the second optical waveguide layer 522 is located between the second metal interconnection layer 5412 and the third metal interconnection layer 5413, which is beneficial to achieve a better effect of improving the coupling efficiency.

[0166] In this embodiment, after forming the n-th metal interconnection layer 541 and before forming the n+1-th metal interlayer dielectric layer 514, the second optical waveguide layer 522 is formed on the metal interlayer dielectric layer 514 at the side of the n-th metal interconnection layer 541; accordingly, in the step of forming the n+1-th metal interlayer dielectric layer 514, the n+1-th metal interlayer dielectric layer 514 buries the second optical waveguide layer 522 therein.

[0167] In this embodiment, after forming the dielectric layer, the optical waveguide stack, and the metal interconnect stack, the formation method further includes: forming a passivation layer 550 on the dielectric layer 510. The passivation layer 550 is used to protect the formed semiconductor device and reduce the probability of damage in the subsequent process. Specifically, the material of the passivation layer 550 is a dielectric material, such as silicon oxide, silicon nitride, silicon oxynitride, etc.

[0168] In this embodiment, after forming the passivation layer 550, the forming method further includes: forming an opening 555 to expose the topmost metal interconnection layer 541. The opening 555 is used to realize the electrical connection between the metal interconnection stack 540 and the external circuit.

[0169] It should be noted that the semiconductor structure can be formed by the formation method described in the above embodiment, or by other formation methods. For the specific description of the semiconductor structure described in this embodiment, reference can be made to the corresponding description in the above embodiment, and this embodiment will not be repeated here.

[0170] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A semiconductor structure, characterized in that: include: substrate; a dielectric layer, located on the substrate; An optical waveguide stack is buried in the dielectric layer, the optical waveguide stack comprises a first optical waveguide layer and a second optical waveguide layer located on top of the first optical waveguide layer, the second optical waveguide layer is isolated from the first optical waveguide layer in a longitudinal direction, and the length of the second optical waveguide layer is shorter than the length of the first optical waveguide layer.

2. The semiconductor structure according to claim 1, wherein: Along the transmission direction of light in the second optical waveguide layer, the line width of the second optical waveguide layer gradually decreases.

3. The semiconductor structure according to claim 1, wherein: The material of the first optical waveguide layer includes silicon nitride; the material of the second optical waveguide layer includes silicon nitride.

4. The semiconductor structure according to claim 1, wherein: Along the extending direction of the optical waveguide stack, the light receiving surfaces of the first optical waveguide layer and the second optical waveguide layer are flush with each other.

5. The semiconductor structure according to claim 1, wherein: The difference between the lengths of the second optical waveguide layer and the first optical waveguide layer is greater than 100 micrometers.

6. The semiconductor structure according to claim 1, wherein: Along the extension direction of the second optical waveguide layer, the length of the second optical waveguide layer is 50 micrometers to 200 micrometers.

7. The semiconductor structure according to claim 1, wherein: Along a direction parallel to a surface of the second optical waveguide layer and perpendicular to an extending direction of the second optical waveguide layer, a line width of the second optical waveguide layer ranges from 500 nanometers to 1500 nanometers.

8. The semiconductor structure according to claim 1, wherein: Along the normal direction of the top surface of the substrate, a vertical distance between the second optical waveguide layer and the first optical waveguide layer ranges from 1 micrometer to 3 micrometers.

9. The semiconductor structure according to claim 1, wherein: The transmission loss of the first optical waveguide layer is lower than the transmission loss of the second optical waveguide layer ； The transmission loss of the first optical waveguide layer is 0.08 dB / cm to 0.15 dB / cm; the transmission loss of the second optical waveguide layer is 0.3 dB / cm to 0.4 dB / cm.

10. The semiconductor structure according to claim 1, wherein: The semiconductor structure further comprises: a metal interconnect stack buried in the dielectric layer at the side of the optical waveguide stack, the metal interconnect stack comprising a plurality of metal interconnect layers; The first optical waveguide layer is located in a dielectric layer below the bottom metal interconnection layer, and the second optical waveguide layer is located in a dielectric layer in a thickness region between any two adjacent metal interconnection layers.

11. The semiconductor structure according to claim 10, characterized in that The second optical waveguide layer is located in the dielectric layer in a thickness region between the second metal interconnect layer and the third metal interconnect layer.

12. A method for forming a semiconductor structure, characterized in that: include: providing a substrate; A dielectric layer and an optical waveguide stack buried in the dielectric layer are formed on the substrate, the optical waveguide stack comprising a first optical waveguide layer and a second optical waveguide layer located on top of the first optical waveguide layer, the second optical waveguide layer and the first optical waveguide layer are separated in a longitudinal direction, and the length of the second optical waveguide layer is shorter than that of the first optical waveguide layer.

13. The method for forming a semiconductor structure according to claim 12, wherein: In the step of forming the optical waveguide stack, a line width of the second optical waveguide layer gradually decreases along a propagation direction of light in the second optical waveguide layer.

14. The method for forming a semiconductor structure according to claim 12, wherein: The step of forming a dielectric layer on the substrate and an optical waveguide stack buried in the dielectric layer comprises: forming a first optical waveguide layer on the substrate; forming a first dielectric layer covering the first optical waveguide layer; forming a second optical waveguide layer on the first dielectric layer; forming a second dielectric layer covering the second optical waveguide layer; The dielectric layer includes the first dielectric layer and a second dielectric layer.

15. The method for forming a semiconductor structure according to claim 12, wherein: The forming method further comprises: forming a metal interconnect stack buried in the dielectric layer, the metal interconnect stack comprising a plurality of metal interconnect layers, the metal interconnect stack being located on a side of the optical waveguide stack; In the step of forming an optical waveguide stack buried in the dielectric layer, the first optical waveguide layer is located in the dielectric layer below the lowest metal interconnect layer, and the second optical waveguide layer is located in the dielectric layer in the thickness region between any two adjacent metal interconnect layers.

16. The method for forming a semiconductor structure according to claim 15, wherein: After forming the first optical waveguide layer, forming a plurality of stacked metal interlayer dielectric layers on the substrate, and after forming each metal interlayer dielectric layer, forming a corresponding metal interconnect layer in the metal interlayer dielectric layer of the current layer; wherein, after forming the nth metal interconnection layer and before forming the n+1th metal interlayer dielectric layer, the second optical waveguide layer is formed on the metal interlayer dielectric layer at the side of the nth metal interconnection layer, where n is a natural number; In the step of forming the n+1th intermetallic dielectric layer, the n+1th intermetallic dielectric layer buries the second optical waveguide layer therein.

17. The method for forming a semiconductor structure according to claim 16, wherein: After forming a second metal interconnection layer in the second intermetal dielectric layer, and before forming a third intermetal dielectric layer, the second optical waveguide layer is formed on the second intermetal dielectric layer.

18. The method for forming a semiconductor structure according to claim 12 or 15, characterized in that: The deposition process used to form the first optical waveguide layer includes a low pressure chemical vapor deposition process; the deposition process used to form the second optical waveguide layer includes a plasma enhanced chemical vapor deposition process.

19. The method for forming a semiconductor structure according to claim 12 or 15, characterized in that: The process temperature for forming the second optical waveguide layer is 100 degrees Celsius to 400 degrees Celsius.

20. A silicon optical device, characterized in that: include: The semiconductor structure according to any one of claims 1 to 11; The optical fiber is arranged on one side of the optical waveguide stack along its extending direction, and the extension line of the core center of the optical fiber is located between the first optical waveguide layer and the second optical waveguide layer.

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