Grating coupling device and preparation method thereof

Abstract

The invention discloses a grating coupling device and a preparation method thereof. The grating coupling device comprises a dielectric layer arranged on the surface of a substrate; the functional layer is arranged in the dielectric layer and is provided with a first grating and a waveguide which are adjacent to each other; the second grating is arranged in the dielectric layer and located on the side, away from the surface of the substrate, of the first grating, the grating constant of the second grating corresponds to the grating constant of the first grating, and the second grating is aligned to the first grating; and the material refractive index of the second grating is greater than that of the first grating. The overall coupling efficiency of the device can be obviously improved, and the coupling loss is reduced.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor integrated circuit process technology, and in particular to a grating coupling device and a preparation method thereof. Background Art

[0002] Integrated photonic technology is one of the development directions to continue Moore's Law. It uses light instead of electricity to transmit and control information, which can improve signal transmission efficiency and has become a research hotspot in recent years.

[0003] Grating couplers have the advantages of large spatial freedom, simple manufacturing process, and convenient wafer-level testing. The research on grating couplers based on silicon on insulating substrate (SOI) platform is relatively mature. Through reasonable design of grating structure and adding reflective layer and other technologies, the coupling loss between SOI platform grating and single-mode optical fiber can be reduced to less than 1dB. In recent years, the silicon nitride photonic material platform, which is fully compatible with CMOS process, has the advantages of lower nonlinearity, lower loss and greater energy input, making silicon nitride passive waveguides more advantageous in achieving extremely low loss on chip. However, due to the small relative refractive index difference of silicon nitride platform, it is difficult to further reduce the coupling loss of grating couplers on silicon nitride platform, making it difficult to manufacture silicon nitride grating couplers with high coupling efficiency.

[0004] The prior art can effectively improve the coupling efficiency of silicon nitride grating couplers by increasing the thickness of the silicon nitride layer grating, apodizing the grating amplitude and phase, and making a metal mirror or a Bragg reflector (DBR) structure under the silicon nitride grating coupler. However, increasing the thickness of the silicon nitride layer grating requires setting up a complex and fragile mode conversion structure with poor stability. Making a metal mirror under the silicon nitride grating coupler will cause the problem of incompatibility with CMOS process. As for the schemes of reducing the coupling loss of silicon nitride grating couplers by apodizing the grating amplitude and phase, and making a Bragg reflector structure under the silicon nitride grating coupler, they all put forward higher requirements on the preparation process, making these methods difficult to apply to the grating preparation of silicon nitride integrated photonic platforms. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects in the prior art and to provide a grating coupling device and a preparation method thereof.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] The present invention provides a grating coupling device, comprising:

[0008] A dielectric layer disposed on the surface of the substrate;

[0009] A functional layer disposed in the dielectric layer, the functional layer being provided with adjacent first gratings and waveguides;

[0010] a second grating disposed in the dielectric layer, the second grating being located on a side of the first grating away from the substrate surface, the grating constant of the second grating corresponding to the grating constant of the first grating, and the second grating being aligned with the first grating;

[0011] The refractive index of a material of the second grating is greater than the refractive index of a material of the first grating.

[0012] Furthermore, it also includes: a light reflection structure arranged in the dielectric layer, and the light reflection structure is located on a side of the first grating close to the substrate surface.

[0013] Furthermore, the light reflection structure comprises a third grating, the third grating is arranged opposite to the first grating, and the grating constant of the third grating is smaller than the grating constant of the first grating.

[0014] Further, the first grating and the second grating form a composite grating as a diffraction grating, and the composite grating and the third grating as a reflection grating form a combined grating.

[0015] Further, the functional layer material includes a first semiconductor compound, and / or the second grating material includes a second semiconductor, and / or the third grating material includes a first semiconductor.

[0016] Further, the first semiconductor compound includes silicon nitride, and / or the second semiconductor includes amorphous silicon, polycrystalline silicon or germanium, and / or the first semiconductor includes single crystal silicon.

[0017] The present invention also provides a method for preparing a grating coupling device, comprising:

[0018] providing a substrate;

[0019] forming a dielectric layer on the surface of the substrate;

[0020] A functional layer is formed in the dielectric layer, a first grating and a waveguide are formed in the functional layer, a second grating located in the dielectric layer is formed on the first grating, a grating constant of the second grating corresponds to a grating constant of the first grating, the second grating is aligned with the first grating, and a material refractive index of the second grating is greater than a material refractive index of the first grating.

[0021] Furthermore, before forming the functional layer, it also includes: first forming a third grating in the dielectric layer, then forming the functional layer in the dielectric layer above the third grating, and forming the first grating opposite to the third grating in the functional layer, and making the grating constant of the first grating greater than the grating constant of the third grating.

[0022] Further, forming the third grating, the first grating and the second grating specifically includes:

[0023] forming a first dielectric layer and a first semiconductor layer in sequence on the surface of the substrate;

[0024] Patterning the first semiconductor layer to form a first semiconductor third grating;

[0025] forming a second dielectric layer on the exposed surface of the first dielectric layer to cover the third grating;

[0026] sequentially forming a first semiconductor compound functional layer and a second semiconductor layer on the surface of the second dielectric layer;

[0027] Patterning the second semiconductor layer and the functional layer to form a second semiconductor second grating and a first semiconductor compound first grating aligned and located below the second grating, and a first semiconductor compound waveguide adjacent to one side of the first grating;

[0028] A third dielectric layer is formed on the exposed surface of the second dielectric layer to cover the functional layer and the second grating.

[0029] Furthermore, after forming the third dielectric layer, annealing is performed.

[0030] It can be seen from the above technical scheme that the present invention can improve the directivity of grating coupling by further aligning a second grating of different materials (such as a grating of amorphous silicon, polycrystalline silicon or germanium material) on the first grating (such as silicon nitride grating) used for optical coupling with the waveguide, and can increase the refractive index contrast between the bars and grooves of the first grating by utilizing the higher refractive index of the second grating material. In addition, by further forming a third grating with high reflectivity (such as a single crystal silicon grating) between the first grating and the substrate, a structure having a reflector function and compatible with CMOS technology can be formed. When input light enters the grating coupling device of the present invention, the high refractive index material on the second grating can improve the directivity of the input light, so that the silicon nitride first grating can couple most of the input light into the silicon nitride waveguide, and the transmitted light that passes through the silicon nitride first grating toward the substrate will be effectively reflected back to the silicon nitride first grating by the silicon third grating with high reflectivity, and coupled into the silicon nitride waveguide by the silicon nitride first grating. Therefore, the present invention forms a composite grating as a diffraction grating through the first grating and the second grating, and forms a combined grating with the third grating as a reflection grating, which significantly improves the overall coupling efficiency of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The figure is a schematic structural diagram of a grating coupling device according to a preferred embodiment of the present invention.

[0032] Figure 2-Figure 8 The figure is a schematic diagram of the process steps of a method for preparing a grating coupling device according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be understood by people with general skills in the field to which the present invention belongs. "Including" and similar words used in this article mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0034] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0035] refer to Figure 1A grating coupling device of the present invention comprises a dielectric layer 18 disposed on the upper surface of a substrate 10, and a functional layer 12 disposed in the dielectric layer 18. The functional layer 12 is provided with adjacent first gratings 19 and waveguides 14.

[0036] A second grating 13 is also provided in the dielectric layer 18. The second grating 13 is located on the upper surface of the first grating 19. The grating constant of the second grating 13 corresponds to the grating constant of the first grating 19, and the second grating 13 is aligned with the first grating 19. At the same time, the material refractive index of the second grating 13 is greater than the material refractive index of the first grating 19. Thus, the first grating 19 and the second grating 13 form a composite grating.

[0037] refer to Figure 1 In some embodiments, a light reflecting structure 11 is further provided in the dielectric layer 18 . The light reflecting structure 11 is located between the bottom of the first grating 19 and the upper surface of the substrate 10 .

[0038] In some embodiments, the light reflecting structure 11 includes a third grating 20 . The third grating 20 is disposed opposite to the first grating 19 , and a grating constant of the third grating 20 is smaller than a grating constant of the first grating 19 .

[0039] The first grating 19 is connected to the second grating 13 . The first grating 19 and the third grating 20 are isolated from each other and are disposed in the dielectric layer 18 . The third grating 20 and the substrate 10 are also isolated from each other by the dielectric layer 18 .

[0040] The projection area of ​​third grating 20 on substrate 10 at least completely surrounds the projection area of ​​first grating 19 on substrate 10 .

[0041] In some embodiments, the first grating 19 and the second grating 13 form a composite grating as a diffraction grating. In addition, the first grating 19 and the second grating 13 further form a combined grating with the third grating 20 as a reflection grating.

[0042] In some embodiments, the material of the functional layer 12 includes a first semiconductor compound, such as silicon nitride, thereby forming a silicon nitride first grating 19 and a silicon nitride waveguide 14 .

[0043] The material of the second grating 13 includes a second semiconductor, such as amorphous silicon, polycrystalline silicon or germanium, and the refractive index of these materials is greater than that of silicon nitride, thereby forming the second grating 13 of amorphous silicon, polycrystalline silicon or germanium.

[0044] The material of the third grating 20 includes a first semiconductor, for example, the first semiconductor includes single crystal silicon, thereby forming the third grating 20 of single crystal silicon.

[0045] refer to Figure 1In some embodiments, the substrate 10 includes a silicon substrate 10. The dielectric layer 18 includes a first dielectric layer 17, a second dielectric layer 16, and a third dielectric layer 15 which are sequentially arranged on the upper surface of the substrate 10. The third grating 20 is arranged on the upper surface of the first dielectric layer 17 and is located in the second dielectric layer 16, and the second dielectric layer 16 material is filled in the gate groove of the third grating 20, and is connected to the upper surface of the first dielectric layer 17 below the gate groove. The functional layer 12 is arranged on the upper surface of the second dielectric layer 16 and is located in the third dielectric layer 15, and the third dielectric layer 15 material is filled in the gate groove of the second grating 13 and the gate groove of the first grating 19, and is connected to the upper surface of the second dielectric layer 16 below the gate groove.

[0046] The material of dielectric layer 18 includes silicon dioxide.

[0047] A method for preparing a grating coupling device of the present invention is further described in detail below through specific implementation modes and in conjunction with the accompanying drawings.

[0048] refer to Figure 2-Figure 8 The method for preparing a grating coupling device of the present invention can be used to prepare the above-mentioned Figure 1 A grating coupling device of the present invention may include the following steps:

[0049] Step S1: providing a substrate 10 .

[0050] like Figure 2 As shown, a silicon semiconductor first substrate 10 is used to prepare a grating coupling device of the present invention.

[0051] Step S2 : forming a first dielectric layer 17 on the surface of the substrate 10 , and forming a third grating 20 on the surface of the first dielectric layer 17 .

[0052] like Figure 2As shown, a silicon dioxide layer of a certain thickness is grown on the surface of the first substrate 10 by a thermal oxidation process. In addition, a silicon dioxide layer of a certain thickness is also grown on the surface of another silicon semiconductor second substrate by a thermal oxidation process. Then, the surface of the second substrate with the silicon dioxide layer is aligned with the surface of the first substrate 10 with the silicon dioxide layer for bonding, and after bonding, the second substrate is thinned to a desired thickness by back etching. Thus, a first dielectric layer 17 formed by a silicon dioxide layer is formed between the first substrate 10 and the second substrate by the bonding back etching technology, and a SOI substrate (Bond and Etch-back SOI, BESOI) is formed by the silicon first substrate 10, the silicon dioxide first dielectric layer 17 and the silicon second substrate. Among them, the thinned silicon second substrate is used as the first semiconductor layer 21 for the subsequent preparation of the third grating 20. In this way, the silicon dioxide first dielectric layer 17 and the silicon first semiconductor layer 21 are sequentially formed on the surface of the silicon substrate (first substrate) 10.

[0053] Alternatively, a first dielectric layer of silicon dioxide may be formed in a silicon substrate by using a separation by implanted oxygen (SIMOX) technique, so as to form an SOI substrate through the silicon substrate. The silicon layer of the substrate located below the first dielectric layer is used as the silicon substrate, and the silicon layer of the substrate located above the first dielectric layer is used as the first silicon semiconductor layer, and is used to prepare the third grating later. Alternatively, the SOI substrate may be formed by using a technique such as Smart-Cut.

[0054] like Figure 3 As shown, the first silicon semiconductor layer 21 on the surface of the SOI substrate is completely etched by reactive ion etching (RIE) to form a third silicon grating 20. The third silicon grating 20 formed by etching includes a plurality of silicon bars arranged in parallel and at intervals.

[0055] Step S3 : forming a second dielectric layer 16 on the surface of the first dielectric layer 17 to cover the third grating 20 .

[0056] like Figure 4 As shown, a silicon dioxide second dielectric layer 16 is formed on the exposed surface of the first dielectric layer 17 after the silicon third grating 20 is formed by a low pressure chemical vapor deposition process (LPCVD) or a plasma enhanced chemical vapor deposition process (PECVD) to cover the third grating 20. The surface of the second dielectric layer 16 is polished by a chemical mechanical polishing process (CMP) to obtain a flat surface (after polishing, the second dielectric layer 16 still needs to cover the third grating 20).

[0057] Step S4 : forming the first grating 19 and the waveguide 14 on the surface of the second dielectric layer 16 , and forming the second grating 13 on the surface of the first grating 19 .

[0058] like Figure 5 As shown, a silicon nitride (first semiconductor compound) functional layer 12 is formed on the surface of the second dielectric layer 16 by a low-pressure chemical vapor deposition process. Then, a high refractive index material layer is formed on the surface of the silicon nitride functional layer 12 by a sputtering deposition process or a low-pressure chemical vapor deposition process or a reduced-pressure chemical vapor deposition process, as a second semiconductor layer 22. The second semiconductor layer 22 is formed by a semiconductor material such as amorphous silicon, polycrystalline silicon or germanium having a higher refractive index than silicon nitride. For example, the second semiconductor layer 22 can be made of amorphous silicon.

[0059] like Figure 6 As shown, a photoresist layer is formed on the surface of the second semiconductor layer 22. Then, a photoresist pattern 23 for preparing the second grating 13, the first grating 19 and the waveguide 14 is formed on the surface of the second semiconductor layer 22 by using a photolithography process.

[0060] like Figure 7 As shown, then, the amorphous silicon second semiconductor layer 22 and the silicon nitride functional layer 12 are etched by using an etching process and through a photoresist pattern 23, and an amorphous silicon second grating 13 and a silicon nitride first grating 19 aligned below the second grating 13, as well as a silicon nitride waveguide 14 adjacent to one side of the first grating 19 are formed on the surface of the second dielectric layer 16. Thus, the silicon nitride first grating 19 and the silicon nitride waveguide 14 located in the functional layer 12, and the amorphous silicon second grating 13 aligned on the surface of the first grating 19 are formed on the surface of the second dielectric layer 16, so that the second grating 13 and the first grating 19 form a composite grating structure.

[0061] In this embodiment, the silicon nitride first grating 19 formed by complete etching includes a plurality of parallel and spaced silicon nitride grating strips, and the grating constant of the first grating 19 (the second grating 13) is greater than the grating constant of the third grating 20. The third grating 20 is formed into a silicon reflection grating having a reflector effect. Furthermore, through the above process, the grating constant of the second grating 13 corresponds to the grating constant of the first grating 19, the second grating 13 is aligned with the first grating 19, and the material refractive index of the second grating 13 is greater than the material refractive index of the first grating 19.

[0062] The silicon nitride waveguide 14 can be configured as a tapered waveguide 14. The width of the tapered waveguide 14 adjacent to the first grating 19 is equal to or close to the width of the first grating 19 (along the drawing direction) to improve the coupling efficiency between the silicon nitride waveguide 14 and the silicon nitride first grating 19; the width of the tapered waveguide 14 at one end away from the first grating 19 is reduced to be equal to or close to the width of the front end waveguide (not shown) to be coupled to improve the coupling efficiency of the light output from the silicon nitride waveguide 14.

[0063] Afterwards, the unnecessary amorphous silicon second semiconductor layer 22 material and the residual photoresist at the position of the functional layer 12 other than the first grating 19 can be removed.

[0064] Step S5: forming a third dielectric layer 15 on the surface of the second dielectric layer 16 to cover the second grating 13, the first grating 19 and the waveguide 14, and performing annealing.

[0065] like Figure 8 As shown, a silicon dioxide third dielectric layer 15 is formed on the surface of the second dielectric layer 16 exposed after the second grating 13, the first grating 19 and the waveguide 14 are prepared by a low-pressure chemical vapor deposition process or a plasma enhanced chemical vapor deposition process, and the functional layer 12 including the second grating 13, the first grating 19 and the waveguide 14 is covered. The surface of the third dielectric layer 15 is polished by a chemical mechanical polishing process to obtain a flat surface (after polishing, the third dielectric layer 15 still needs to cover the second grating 13, the first grating 19 and the waveguide 14).

[0066] The first dielectric layer 17 to the third dielectric layer 15 together constitute, for example Figure 1 Thus, a silicon third grating 20 located in the dielectric layer 18 is formed on the substrate 10, a silicon nitride first grating 19 and a silicon nitride waveguide 14 adjacent to the first grating 19 are formed in the dielectric layer 18 above the third grating 20, and an amorphous silicon second grating 13 located in the dielectric layer 18 is formed on the first grating 19, so that the first grating 19 to the third grating 20 together form a combined grating structure.

[0067] After polishing the third dielectric layer 15, a high temperature annealing step is finally performed. For example, annealing can be performed at a high temperature of 1000° C. for 3 hours to obtain the final grating coupling device structure.

[0068] Normally, under the conditions of making standard silicon nitride gratings, the directivity of light is only 10% to 20%, and the coupling loss can be as high as 12dB. However, after the high refractive index material is deposited on the surface of the silicon nitride first grating 19 (forming the second grating 13), the directivity of light can reach 50% to 60%, that is, it can be improved by 3 to 4 times. At the same time, by selecting appropriate structural parameters for the silicon third grating 20 located at the bottom, a high reflectivity of more than 90% can be obtained, so that at a wavelength of 1550nm, the coupling efficiency of unidirectional transmission can reach more than 80%, and the grating with a uniform structure can theoretically achieve a low coupling loss of 1.47dB.

[0069] In summary, the present invention further forms a second grating 13 of a different material, such as amorphous silicon, on the silicon nitride first grating 19 for optical coupling with the waveguide 14, and can utilize the higher refractive index of the second grating 13 material to increase the refractive index contrast between the bars and grooves of the first grating 19, so as to improve the directivity during grating coupling. In addition, by further forming a single crystal silicon third grating 20 with high reflectivity between the first grating 19 and the substrate 10, a structure having a reflector function and being compatible with CMOS technology can be formed. When input light enters the grating coupling device of the present invention, the high refractive index material on the second grating 13 can improve the directivity of the input light, so that the silicon nitride first grating 19 can couple most of the input light into the silicon nitride waveguide 14, and the transmitted light that passes through the silicon nitride first grating 19 toward the substrate 10 will be effectively reflected back to the silicon nitride first grating 19 by the silicon third grating 20 with high reflectivity, and coupled into the silicon nitride waveguide 14 by the silicon nitride first grating 19. Therefore, the present invention can prepare a grating coupling device with low coupling loss on a silicon nitride integrated photonic platform by a method compatible with CMOS process, and improve the coupling efficiency and 1dB bandwidth of the grating coupling device.

[0070] Although the embodiments of the present invention are described in detail above, it is obvious to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as described in the claims. Moreover, the present invention described herein may have other embodiments and may be implemented or realized in a variety of ways.

Claims

1. A grating coupling device, characterized in that: include: A dielectric layer disposed on the surface of the substrate; A functional layer disposed in the dielectric layer, the functional layer being provided with adjacent first gratings and waveguides; a second grating disposed in the dielectric layer, the second grating being located on a side of the first grating away from the substrate surface, the grating constant of the second grating corresponding to the grating constant of the first grating, and the second grating being aligned with the first grating; The refractive index of a material of the second grating is greater than the refractive index of a material of the first grating.

2. The grating coupling device according to claim 1, characterized in that: Also includes: A light reflecting structure is arranged in the dielectric layer, and the light reflecting structure is located on a side of the first grating close to the substrate surface.

3. The grating coupling device according to claim 2, characterized in that: The light reflection structure comprises a third grating, the third grating is arranged opposite to the first grating, and the grating constant of the third grating is smaller than the grating constant of the first grating.

4. The grating coupling device according to claim 3, characterized in that: The first grating and the second grating form a composite grating as a diffraction grating, and the composite grating and the third grating as a reflection grating form a combined grating.

5. The grating coupling device according to claim 3, characterized in that: The functional layer material includes a first semiconductor compound, and / or the second grating material includes a second semiconductor, and / or the third grating material includes a first semiconductor.

6. The grating coupling device according to claim 5, characterized in that: The first semiconductor compound includes silicon nitride, and / or the second semiconductor includes amorphous silicon, polycrystalline silicon or germanium, and / or the first semiconductor includes single crystal silicon.

7. A method for preparing a grating coupling device, characterized in that: include: providing a substrate; forming a dielectric layer on the surface of the substrate; A functional layer is formed in the dielectric layer, a first grating and a waveguide are formed in the functional layer, a second grating located in the dielectric layer is formed on the first grating, a grating constant of the second grating corresponds to a grating constant of the first grating, the second grating is aligned with the first grating, and a material refractive index of the second grating is greater than a material refractive index of the first grating.

8. The method for preparing a grating coupling device according to claim 7, characterized in that: Before forming the functional layer, the method further includes: first forming a third grating in the dielectric layer, then forming the functional layer in the dielectric layer above the third grating, and forming the first grating opposite to the third grating in the functional layer, and making the grating constant of the first grating greater than the grating constant of the third grating.

9. The method for preparing a grating coupling device according to claim 8, characterized in that: Forming the third grating, the first grating and the second grating specifically includes: forming a first dielectric layer and a first semiconductor layer in sequence on the surface of the substrate; Patterning the first semiconductor layer to form a first semiconductor third grating; forming a second dielectric layer on the exposed surface of the first dielectric layer to cover the third grating; sequentially forming a first semiconductor compound functional layer and a second semiconductor layer on the surface of the second dielectric layer; Patterning the second semiconductor layer and the functional layer to form a second semiconductor second grating and a first semiconductor compound first grating aligned and located below the second grating, and a first semiconductor compound waveguide adjacent to one side of the first grating; A third dielectric layer is formed on the exposed surface of the second dielectric layer to cover the functional layer and the second grating.

10. The method for preparing a grating coupling device according to claim 9, characterized in that: After forming the third dielectric layer, annealing is performed.

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