Lithium niobate-silicon nitride heterogeneous integrated electro-optical modulator and preparation method thereof

Abstract

The invention relates to the technical field of semiconductors, and provides a lithium niobate-silicon nitride heterogeneous integrated electro-optical modulator and a preparation method thereof, and the electro-optical modulator comprises a substrate, a lower cladding, a silicon-rich silicon nitride waveguide core, a lithium niobate-silicon nitride composite waveguide core and an electrode. At least two grooves are formed in the lower cladding layer, and the grooves comprise a middle equal-width groove and end part gradually-shrinking grooves which are located at the two ends of the middle equal-width groove and have gradually-shrinking widths. The silicon-rich silicon nitride waveguide core is positioned in the groove; the lithium niobate-silicon nitride composite waveguide core comprises a silicon nitride waveguide core and a lithium niobate film; the electrodes are located on the two sides of the silicon-rich silicon nitride waveguide core and arranged on the bonding dielectric layer or the lithium niobate film. According to the electro-optical modulator, an optical field can perform interlayer coupling transition between the silicon nitride waveguide core and the lithium niobate-silicon nitride composite waveguide core through the silicon-rich silicon nitride waveguide core, the thickness of a film layer can be reduced, and meanwhile, the uniformity of interlayer coupling is ensured.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator and a preparation method thereof. Background Art

[0002] Thin-film lithium niobate is heterogeneously integrated on a silicon nitride (Si3N4) waveguide core prepared by low-pressure chemical vapor deposition (LPCVD) through a bonding process. This process has a wide range of applications in the field of integrated optical devices. The heterogeneous integration of thin-film lithium niobate gives the silicon nitride photonics platform high modulation efficiency, high modulation speed and low power consumption electro-optical modulation capabilities, with the advantages of low light propagation loss and a wide spectral transparency range. At the same time, it can also avoid the reduction of CMOS process compatibility caused by patterning lithium niobate.

[0003] At present, one of the problems faced by the heterogeneous integration of lithium niobate and silicon nitride photonics platforms is the low-loss transition of the propagating light field between the silicon nitride waveguide and the silicon nitride-lithium niobate composite waveguide. The traditional methods for achieving low-loss transition of the light field between the silicon nitride waveguide and the silicon nitride-lithium niobate composite waveguide include the following:

[0004] (1) A two-dimensional conical structure is formed on both sides of the lithium niobate along the silicon nitride waveguide core, and interlayer coupling is performed with the silicon nitride waveguide core to achieve optical field transition. During the preparation process, when the lithium niobate is integrated into the silicon nitride platform through the micro-transfer process, the lithium niobate two-dimensional conical structure and the silicon nitride optical waveguide core need to have a high alignment accuracy to achieve low transition loss, which greatly increases the difficulty of the process.

[0005] (2) Multiple steps are formed on both sides of the lithium niobate along the silicon nitride waveguide core to achieve light field transition. This method requires forming multiple steps on the lithium niobate, which means that the lithium niobate needs to be dry-etched multiple times. However, lithium niobate etching is relatively difficult and is incompatible with CMOS process equipment.

[0006] (3) Using silicon-rich silicon nitride waveguide cores with a higher refractive index than lithium niobate for interlayer coupling to achieve optical field transition. This method can achieve compatibility between the silicon-rich silicon nitride waveguide core preparation process and the CMOS process. However, the silicon-rich silicon nitride waveguide core is used as a transition structure, and a silicon dioxide layer is usually provided between the silicon-rich silicon nitride waveguide core and the silicon nitride waveguide core, which will increase the thickness of the film layer and require chemical mechanical polishing to control the thickness of the silicon dioxide layer to ensure the uniformity of the interlayer coupling, which has high process requirements. Summary of the invention

[0007] In order to solve the technical problems such as increased process difficulty, process incompatibility and increased film thickness caused by reducing transition loss in the heterogeneous integration design of lithium niobate and silicon nitride photonics platform.

[0008] The present invention discloses a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator, comprising:

[0009] A substrate, a lower cladding layer is formed on the substrate, and at least two grooves are formed on the lower cladding layer, wherein the grooves include a middle groove of equal width and end tapered grooves located at both ends of the middle groove of equal width and having tapered widths;

[0010] A silicon-rich silicon nitride waveguide core, wherein the silicon-rich silicon nitride waveguide core is located in the groove;

[0011] A lithium niobate-silicon nitride composite waveguide core, the lithium niobate-silicon nitride composite waveguide core comprising a silicon nitride waveguide core and a lithium niobate film, the silicon nitride waveguide core being arranged on the lower cladding at the periphery of the silicon-rich silicon nitride waveguide core and covering the silicon-rich silicon nitride waveguide core; the lithium niobate film being arranged on the silicon nitride waveguide core via a bonding dielectric layer, wherein the lithium niobate film at least covers a portion of equal-width portions and the entirety of a tapered portion of two silicon-rich silicon nitride waveguide cores;

[0012] Two electrodes, which are located at two sides of the silicon-rich silicon nitride waveguide core in horizontal projection, and are arranged on the bonding medium layer or the lithium niobate film.

[0013] Furthermore, the silicon nitride waveguide core includes a silicon nitride waveguide core outside the groove and a silicon nitride waveguide core inside the groove. The silicon nitride waveguide core outside the groove is located between two adjacent grooves and includes a stacked first silicon nitride waveguide core, an intermediate layer and a second silicon nitride waveguide core; the silicon nitride waveguide core inside the groove includes the intermediate layer.

[0014] Furthermore, the silicon nitride waveguide core in the groove includes a first silicon nitride waveguide core in the groove and a second silicon nitride waveguide core in the groove, the first silicon nitride waveguide core in the groove is located at the middle equal-width groove position, the second silicon nitride waveguide core in the groove is located at the end tapered groove position, and the second silicon nitride waveguide core in the groove also includes the second silicon nitride waveguide core located above the intermediate layer.

[0015] Furthermore, the first silicon nitride waveguide core is also formed on the bottom wall and side walls of the groove.

[0016] Furthermore, the end tapered groove takes the end of the middle equal-width groove as a starting point and gradually reduces the groove width in a linear or nonlinear manner.

[0017] Furthermore, the refractive index of silicon-rich silicon nitride is greater than the refractive index of lithium niobate.

[0018] The present invention also discloses a method for preparing a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator, the method comprising the following steps:

[0019] Step 1, forming a lower cladding layer on a substrate, forming at least two middle equal-width grooves on the lower cladding layer, and forming end tapered grooves with tapered widths at both ends of each of the middle equal-width grooves to obtain a groove;

[0020] Step 2, sequentially forming a first silicon nitride layer and a silicon-rich silicon nitride layer on the lower cladding layer, and removing a portion of the silicon-rich silicon nitride layer outside the groove by chemical mechanical polishing to form a silicon-rich silicon nitride waveguide core;

[0021] Step 3, sequentially covering the first silicon nitride layer and the silicon-rich silicon nitride waveguide core with an intermediate layer and a second silicon nitride layer, and performing a patterning process to obtain a silicon nitride waveguide core;

[0022] Step 4, covering the lower cladding and the silicon nitride waveguide core with a bonding dielectric layer, and bonding a lithium niobate film on the surface of the bonding dielectric layer, wherein the lithium niobate film at least covers a portion of the middle equal-width groove and the entirety of one end tapered groove of each groove, to form a lithium niobate-silicon nitride composite waveguide core;

[0023] Step 5: forming an electrode on the bonding dielectric layer or the lithium niobate film to obtain the above-mentioned lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator.

[0024] Furthermore, in step 2, a first silicon nitride layer and a silicon-rich silicon nitride layer are sequentially formed on the lower cladding layer, comprising:

[0025] Step 211, forming a first silicon nitride layer on the lower cladding layer outside the groove;

[0026] Step 212: forming a silicon-rich silicon nitride layer in the groove and on the first silicon nitride layer, wherein an upper surface of the silicon-rich silicon nitride layer in the groove is higher than an upper surface of the first silicon nitride layer.

[0027] Furthermore, in step 2, a first silicon nitride layer and a silicon-rich silicon nitride layer are sequentially formed on the lower cladding layer, comprising:

[0028] Step 221, forming a first silicon nitride layer on the bottom wall and side walls of the groove and the lower cladding layer outside the groove;

[0029] Step 222 : forming a silicon-rich silicon nitride layer on the first silicon nitride layer, wherein an upper surface of the silicon-rich silicon nitride layer located in the groove is higher than an upper surface of the first silicon nitride layer located outside the groove.

[0030] Furthermore, in step 3, the intermediate layer and the second silicon nitride layer are sequentially covered on the first silicon nitride layer and the silicon-rich silicon nitride waveguide core, and a patterning process is performed to obtain the silicon nitride waveguide core, including:

[0031] Step 311, covering the first silicon nitride layer and the silicon-rich silicon nitride waveguide core with an intermediate layer, and covering the intermediate layer with a second silicon nitride layer;

[0032] Step 312: synchronously patterning the second silicon nitride layer, the intermediate layer and the first silicon nitride layer to obtain the silicon nitride waveguide core whose projection at least completely covers the two silicon-rich silicon nitride waveguide cores, wherein the silicon nitride waveguide core includes an integrated silicon nitride waveguide core outside the groove and a silicon nitride waveguide core inside the groove;

[0033] Step 313: Each position of the silicon nitride waveguide core outside the groove and the silicon nitride waveguide core inside the groove includes a stacked first silicon nitride waveguide core, the middle layer, and a second silicon nitride waveguide core, and the first silicon nitride waveguide core, the middle layer, and the second silicon nitride waveguide core have the same width.

[0034] Furthermore, in step 3, the intermediate layer and the second silicon nitride layer are sequentially covered on the first silicon nitride layer and the silicon-rich silicon nitride waveguide core, and a patterning process is performed to obtain the silicon nitride waveguide core, including:

[0035] Step 321, covering the first silicon nitride layer and the silicon-rich silicon nitride waveguide core with an intermediate layer, and covering the intermediate layer with a second silicon nitride layer;

[0036] Step 322, patterning the second silicon nitride layer to obtain a second silicon nitride waveguide core, wherein the second silicon nitride waveguide core comprises a second sub-silicon nitride waveguide core with equal width in the middle portion between the two grooves and tapered at both ends, wherein the tapered portions at both ends of each of the second sub-silicon nitride waveguide cores are invertedly superimposed on the tapered portion of the silicon-rich silicon nitride waveguide core;

[0037] Step 323: synchronously patterning the intermediate layer and the first silicon nitride layer to obtain a first silicon nitride waveguide core.

[0038] The lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator designed by the present invention forms a groove on the lower cladding, designs the groove into a groove with equal width in the middle and a groove with tapered ends at both ends, and fills the groove with silicon-rich silicon nitride to form a silicon-rich silicon nitride waveguide core, so that the light field can pass through the silicon-rich silicon nitride waveguide core to perform interlayer coupling transition between the silicon nitride waveguide core and the lithium niobate-silicon nitride composite waveguide core, which can reduce the thickness of the film layer and ensure the uniformity of the interlayer coupling. Compared with the prior art, the beneficial effects that can be achieved by at least one of the above technical solutions adopted in the embodiments of this specification include at least:

[0039] 1. Compared with the technical solution of forming multiple steps on both sides of lithium niobate along the silicon nitride waveguide core to achieve light field transition, the present invention does not need to etch lithium niobate, and the manufacturing process is more compatible with CMOS technology;

[0040] 2. Compared with the solution of forming a two-dimensional cone structure on both sides of the lithium niobate along the silicon nitride waveguide core to realize the light field transition, the waveguide core alignment of the present invention is realized by a photolithography process, which has higher alignment accuracy, lower process difficulty, and smaller transition loss caused by alignment deviation;

[0041] 3. Compared with using a silicon-rich silicon nitride waveguide core with a higher refractive index than lithium niobate for interlayer coupling to achieve light field transition, the present invention uses a first silicon nitride layer as a polishing stop layer of the silicon-rich silicon nitride waveguide core. The first silicon nitride layer is flush with the upper surface of the silicon-rich silicon nitride waveguide core, which can reduce the increase in film thickness caused by the introduction of the silicon-rich silicon nitride waveguide core. At the same time, the thickness of the silicon dioxide intermediate layer located between the silicon-rich silicon nitride waveguide core and the silicon nitride waveguide core and participating in the light field transition can be controlled by a deposition process rather than a chemical mechanical polishing process. Therefore, its thickness uniformity is better, the uniformity of interlayer coupling is better, and the process difficulty is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 It is a schematic diagram of the groove on the lower cladding disclosed in the present invention;

[0044] Figure 2 for Figure 1 Cross-sectional view at AA in the middle;

[0045] Figure 3 It is a cross-sectional view of forming a silicon-rich silicon nitride layer on the first silicon nitride layer disclosed in the present invention;

[0046] Figure 4 A top view of the silicon-rich silicon nitride waveguide core obtained after polishing disclosed in the present invention;

[0047] Figure 5 for Figure 4 Cross-sectional view at AA in the middle;

[0048] Figure 6 It is a cross-sectional view of forming an intermediate layer and a second silicon nitride layer on the silicon-rich silicon nitride waveguide core disclosed in the present invention;

[0049] Figure 7 for Figure 6A top view after being graphed in ;

[0050] Figure 8 for Figure 7 Cross-sectional view at AA in the middle;

[0051] Fig. 9 for Figure 7 Cross-section at the middle BB;

[0052] Fig.10 exist Figure 6 A top view of a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator formed on the structure shown;

[0053] Fig.11 for Fig.10 Cross-sectional view at AA in the middle;

[0054] Fig.12 for Fig.10 Cross-section at the middle BB;

[0055] Fig.13 Another cross-sectional schematic diagram of forming a first silicon nitride layer on a lower cladding layer disclosed in the present invention;

[0056] Fig.14 For Fig.13 A schematic diagram of forming a silicon-rich silicon nitride waveguide layer on the first silicon nitride layer;

[0057] Fig.15 For Fig.14 A cross-sectional view of a silicon-rich silicon nitride waveguide core obtained after polishing the structure shown;

[0058] Fig.16 for Fig.13 A cross-sectional view of a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator formed on the structure shown at the groove position;

[0059] Fig.17 A top view of another structure of the second silicon nitride waveguide core and the silicon-rich silicon nitride waveguide core disclosed in the present invention;

[0060] Fig.18 for Fig.17 Cross-sectional view at AA in the middle;

[0061] Fig.19 for Fig.17 Cross-section at the middle BB;

[0062] Fig. 20 for Fig.17 Cross-section at CC;

[0063] Fig.21 For Fig.17 A top view of a structure shown in FIG. 1 and FIG. 2 is a diagram showing a first silicon nitride waveguide core being patterned on the structure shown in FIG. 1 ;

[0064] Fig. 22 for Fig.21 Cross-sectional view at AA in the middle;

[0065] Fig.23 for Fig.21 Cross-section at the middle BB;

[0066] Fig.24 for Fig.21 Cross-section at CC;

[0067] Fig.25 For Fig.21 A top view of a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator formed on the structure shown;

[0068] Fig.26 for Fig.25 Cross-sectional view at AA in the middle;

[0069] Fig. 27 for Fig.25 Cross-section at the middle BB;

[0070] Fig.28 for Fig.25 Cross-section at CC;

[0071] Fig.29 For Fig.15 and Fig.17 The structure shown in the top view is Fig.25 A cross-sectional view of the lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator at AA is shown;

[0072] Fig.30 For Fig.15 and Fig.17 The structure shown in the top view is Fig.25 A cross-sectional view at BB of a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator is shown;

[0073] Fig.31 It is a flow chart of the preparation method of the lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator disclosed in the present invention;

[0074] Among them, 1. substrate; 2. lower cladding; 3. groove; 31. middle equal-width groove; 32. end tapered groove; 4. silicon-rich silicon nitride waveguide core; 5. first silicon nitride waveguide core; 6. middle layer; 7. second silicon nitride waveguide core; 8. bonding dielectric layer; 9. lithium niobate film; 10. electrode; 101. first silicon nitride layer; 102. silicon-rich silicon nitride layer; 103. second silicon nitride layer. DETAILED DESCRIPTION

[0075] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0076] The following describes the implementation methods of the present application through specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and the features of the embodiments can be combined with each other in the absence of conflict. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0077] The embodiment of the present invention discloses a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator, see Fig.10 and Fig.25 As shown, the electro-optic modulator includes a substrate 1 , a silicon-rich silicon nitride waveguide core 4 , a lithium niobate-silicon nitride composite waveguide core and an electrode 10 .

[0078] Among them, see Figure 1 and Figure 2 As shown, a lower cladding layer 2 is formed on a substrate 1, and at least two grooves 3 are formed on the lower cladding layer 2, wherein the grooves 3 include a middle equal-width groove 31 and end tapered grooves 32 located at both ends of the middle equal-width groove 31 and tapered in width. Figures 4 to 6 , Figure 8 , Fig.11 , Fig.15 , Fig.16 , Fig.18 , Fig.19 , Fig. 22 , Fig.23 , Fig.26 , Fig. 27 , Fig.29 and Fig.30 As shown, the silicon-rich silicon nitride waveguide core 4 is located in the groove 3 .

[0079] See also Fig.10 , Fig.12 , Fig.25 , Fig. 27 , Fig.28 and Fig.30 As shown, the lithium niobate-silicon nitride composite waveguide core includes a silicon nitride waveguide core and a lithium niobate film 9, wherein the silicon nitride waveguide core is arranged on the lower cladding 2 at the periphery of the silicon-rich silicon nitride waveguide core 4 and covers the silicon-rich silicon nitride waveguide core 4; the lithium niobate film 9 is arranged on the silicon nitride waveguide core via a bonding medium layer 8, wherein the lithium niobate film 9 at least covers a part of the equal-width parts of the two silicon-rich silicon nitride waveguide cores 4 and the entirety of one tapered part.

[0080] See also Fig.10 , Fig.12 , Fig.25 and Fig.28 As shown, there are two electrodes 10 , and in horizontal projection, the two electrodes 10 are located on both sides of the silicon-rich silicon nitride waveguide core 4 , and are arranged on the bonding medium layer 8 or the lithium niobate film 9 .

[0081] The lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator of the present invention forms a groove 3 on the lower cladding 2, designs the groove 3 into a groove 31 with equal width in the middle and grooves 32 with tapered ends at both ends, and fills the groove with silicon-rich silicon nitride to form a silicon-rich silicon nitride waveguide core 4. The light field can pass through the silicon-rich silicon nitride waveguide core 4 to perform interlayer coupling transition between the silicon nitride waveguide core and the lithium niobate-silicon nitride composite waveguide core, thereby reducing the thickness of the film layer and ensuring the uniformity of the interlayer coupling.

[0082] In an optional embodiment, the silicon nitride waveguide core includes a silicon nitride waveguide core outside the groove and a silicon nitride waveguide core inside the groove, see Figure 8 , Fig.11 , Fig.16 , Fig. 22 , Fig.23 , Fig.26 , Fig. 27 , Fig.29 and Fig.30 As shown, the silicon nitride waveguide core in the groove includes a stacked first silicon nitride waveguide core 5, an intermediate layer 6 and a second silicon nitride waveguide core 7. Fig. 9 , Fig.12 , Fig.24 and Fig.28 As shown, the silicon nitride waveguide core outside the groove is located between two adjacent grooves 3 and includes a stacked first silicon nitride waveguide core 5 , an intermediate layer 6 and a second silicon nitride waveguide core 7 .

[0083] Further, see Fig.21 As shown, the silicon nitride waveguide core in the groove includes a first silicon nitride waveguide core in the groove and a second silicon nitride waveguide core in the groove, the first silicon nitride waveguide core in the groove is located at the middle equal-width groove 31, the second silicon nitride waveguide core in the groove is located at the end tapered groove 32, and the second silicon nitride waveguide core in the groove also includes the second silicon nitride waveguide core 7 located above the intermediate layer 6. The cross-sectional view of the first silicon nitride waveguide core in the groove is as shown in FIG. Fig. 22 As shown, the cross-sectional view of the second silicon nitride waveguide core in the groove is as follows Fig.23 shown.

[0084] Further, see Figure 8 , Fig.11 , Fig. 22, Fig.23 , Fig.26 and Fig. 27 As shown, the first silicon nitride waveguide core 5 is also formed on the bottom wall and side walls of the groove 3.

[0085] Further, see Figure 1 and Figure 2 As shown, the end tapered groove 32 takes the end of the middle equal-width groove 31 as a starting point and gradually reduces the groove width in a linear or nonlinear manner.

[0086] The present invention also discloses a method for preparing a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator, see Fig.31 As shown, the method comprises the following steps:

[0087] Step 1: forming a lower cladding layer 2 on a substrate 1, forming at least two middle equal-width grooves 31 on the lower cladding layer 2, and forming end tapered grooves 32 with tapered width at both ends of each middle equal-width groove 31 to obtain a groove 3.

[0088] Step 2, sequentially forming a first silicon nitride layer 101 and a silicon-rich silicon nitride layer 102 on the lower cladding layer 2, and removing a portion of the silicon-rich silicon nitride layer 102 outside the groove 3 by chemical mechanical polishing to form a silicon-rich silicon nitride waveguide core 4;

[0089] Step 3, sequentially covering the intermediate layer 6 and the second silicon nitride layer 103 on the first silicon nitride layer 101 and the silicon-rich silicon nitride waveguide core 4, and performing patterning to obtain a silicon nitride waveguide core;

[0090] Step 4, covering the lower cladding 2 and the silicon nitride waveguide core with a bonding dielectric layer 8, and bonding a lithium niobate film 9 on the surface of the bonding dielectric layer 8, wherein the lithium niobate film 9 covers at least a portion of the middle equal-width groove 31 of each groove 3 and the entirety of one end tapered groove 32, to form a lithium niobate-silicon nitride composite waveguide core;

[0091] Step 5: forming an electrode 10 on the bonding dielectric layer 8 or the lithium niobate film 9 to obtain the above-mentioned lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator.

[0092] The present invention illustrates the preparation process of the lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator through the following examples 1 to 4:

[0093] Example 1 and Example 2:

[0094] (1) In Example 1 and Example 2, Figure 1 and Figure 2As shown, a lower cladding layer 2 can be formed on a substrate 1, and at least two grooves 3 can be formed on the lower cladding layer 2. The groove 3 includes an equal width portion and a width gradient portion. The width gradient portion is located at both ends of the equal width portion, and the width of the width gradient portion gradually decreases from the width of the equal width portion to both ends of the groove 3 in a linear or nonlinear manner. Among them, the material of the substrate 1 can be selected to be silicon; the material of the lower cladding layer 2 can be selected to be silicon dioxide, and the thickness of the lower cladding layer 2 is 2 to 20um; the depth of the groove 3 can be selected to be processed to 0.2 to 0.8um, and the width of the equal width portion of the groove 3 can be set to 0.5 to 2um.

[0095] (2.1) In Example 1, the first silicon nitride layer 101 and the silicon-rich silicon nitride layer 102 are sequentially formed on the lower cladding layer 2, specifically including the following steps:

[0096] Step 211: forming a Fig.13 The first silicon nitride layer 101 is shown;

[0097] Step 212: forming a Fig.14 The silicon-rich silicon nitride layer 102 shown, wherein the upper surface of the silicon-rich silicon nitride layer 102 located in the groove 3 is higher than the upper surface of the first silicon nitride layer 101 .

[0098] Specifically, in step 211, the first silicon nitride layer 101 can be formed on the lower cladding layer 2, and the first silicon nitride layer 101 and the lower cladding layer 2 can be patterned simultaneously to obtain at least two grooves 3. At this time, after the patterning process, there is no first silicon nitride layer 101 (that is, the first silicon nitride waveguide core 5) in the groove 3, and its structure is as follows: Fig.13 , Fig.15 and Fig.16 shown.

[0099] In step 212, see Fig.14 As shown, a silicon-rich silicon nitride layer 102 may be first formed on the first silicon nitride layer 101 , and the lowest point of the upper surface of the silicon-rich silicon nitride layer 102 is higher than the highest point of the surface of the first silicon nitride layer 101 (ie, the silicon-rich silicon nitride layer 102 fills and exceeds the groove 3 ).

[0100] (2.2) The difference between Example 2 and Example 1 is that the first silicon nitride layer 101 is formed on the bottom wall and the side wall of the groove 3 in Example 2. The first silicon nitride layer 101 and the silicon-rich silicon nitride layer 102 are sequentially formed on the lower cladding layer 2, such as Figure 3 As shown, the specific steps include:

[0101] Step 221 : forming a first silicon nitride layer 101 on the bottom wall and the side wall of the groove 3 and the lower cladding layer 2 located outside the groove 3 .

[0102] Step 222 , forming a silicon-rich silicon nitride layer 102 on the first silicon nitride layer 101 , wherein an upper surface of the silicon-rich silicon nitride layer 102 located in the groove 3 is higher than an upper surface of the first silicon nitride layer 101 located outside the groove 3 .

[0103] In step 212 of example 1 and step 222 of example 2, the thickness of the silicon-rich silicon nitride layer 102 in the groove 3 needs to be greater than the depth of the groove 3 to ensure that the silicon-rich silicon nitride layer 102 can fill the groove 3. At the same time, the refractive index of the silicon-rich silicon nitride needs to be greater than the refractive index of the lithium niobate of the lithium niobate film 9 described below.

[0104] The structure after the silicon-rich silicon nitride layer 102 is formed is processed, and the silicon-rich silicon nitride layer 102 outside the groove 3 is removed by chemical mechanical polishing, so that the silicon-rich silicon nitride layer 102 in the groove 3 is parallel to the first silicon nitride layer 101 outside the groove. At this time, the structure formed in the groove 3 can be obtained. Figure 4 , Figure 5 and Fig.15 The silicon-rich silicon nitride waveguide core 4 shown has a uniform width in the middle and tapered widths at both ends. When chemical mechanical polishing is performed, the first silicon nitride layer 101 is used as a stop layer for polishing the silicon-rich silicon nitride layer 102 .

[0105] It should also be noted that in step 1 and step 2, the groove 3 can be formed directly in the lower cladding layer 2, or the first silicon nitride layer 101 can be first formed on the lower cladding layer 2, and then the first silicon nitride layer 101 and the lower cladding layer 2 are synchronously patterned to form the groove 3.

[0106] (3) Figure 6 As shown, the intermediate layer 6 and the second silicon nitride layer 103 are sequentially covered on the first silicon nitride layer 101 and the silicon-rich silicon nitride waveguide core 4, and a patterning process is performed to obtain a silicon nitride waveguide core, which specifically includes the following steps:

[0107] Step 311, covering the first silicon nitride layer 101 and the silicon-rich silicon nitride waveguide core 4 with an intermediate layer 6, and covering the intermediate layer 6 with a second silicon nitride layer 103;

[0108] Step 312: synchronously pattern the second silicon nitride layer 103, the intermediate layer 6 and the first silicon nitride layer 101 to obtain Figure 7 The projection shown at least completely covers the silicon nitride waveguide cores of the two silicon-rich silicon nitride waveguide cores 4. Figures 7 to 9 As shown, the silicon nitride waveguide core includes an integrated silicon nitride waveguide core outside the groove and a silicon nitride waveguide core inside the groove, and the silicon nitride waveguide core outside the groove is located between two adjacent silicon nitride waveguide cores inside the groove.

[0109] like Figure 8 , Fig. 9 , Fig.11 , Fig.12 and Fig.16 As shown, each position of the silicon nitride waveguide core outside the groove and the silicon nitride waveguide core inside the groove includes a stacked first silicon nitride waveguide core 5, the intermediate layer 6 and the second silicon nitride waveguide core 7, and the first silicon nitride waveguide core 5, the intermediate layer 6 and the second silicon nitride waveguide core 7 have the same width.

[0110] Specifically, after the silicon-rich silicon nitride waveguide core 4 is formed by step 2, Figure 6 As shown, an intermediate layer 6 and a second silicon nitride layer 103 are sequentially formed on the surface of the first silicon nitride layer 101 outside the groove 3 and the silicon-rich silicon nitride waveguide core 4; the second silicon nitride layer 103, the intermediate layer 6 and the first silicon nitride layer 101 are synchronously patterned so that the projections of the second silicon nitride layer 103, the intermediate layer 6 and the first silicon nitride layer 101 on the plane where the silicon-rich silicon nitride waveguide core 4 is located at least completely cover a pair of silicon-rich silicon nitride waveguide cores 4.

[0111] After the synchronous patterning operation, the in-groove silicon nitride waveguide core of the laminated structure formed by the intermediate layer 6 and the second silicon nitride waveguide core 7 of Example 1 can be obtained, or the in-groove silicon nitride waveguide core of the laminated structure formed by the first silicon nitride waveguide core 5, the intermediate layer 6 and the second silicon nitride waveguide core 7 of Example 2 can be obtained. The laminated structure includes a plurality of equal-width parts and width gradient parts, and each equal-width part of the laminate can have a different width, and the width gradient part of the laminate can partially or not overlap with the width gradient part of the silicon-rich silicon nitride waveguide core in horizontal projection. It is also possible to obtain the following as shown in Examples 1 and 2: Fig. 9 , Fig.12 The silicon nitride waveguide core outside the groove is a laminated structure formed by the first silicon nitride waveguide core 5, the intermediate layer 6 and the second silicon nitride waveguide core 7. At this time, the silicon nitride waveguide core outside the groove and the silicon nitride waveguide core inside the groove are a whole, and finally a top view is obtained as shown in FIG. Figure 7 The integrated silicon nitride waveguide core is shown.

[0112] (4) When implementing steps 4 and 5 in the above method, first, refer to Fig.11 , Fig.16 , Fig.26 and Fig.29 As shown, the bonding dielectric layer 8 covers the lower cladding layer 2, the surface of the second silicon nitride waveguide core 7 and the intermediate layer 6, and the side surfaces of the second silicon nitride waveguide core 7, the intermediate layer 6 and the first silicon nitride waveguide core 5; secondly, referring to Fig.10 , Fig.12 , Fig.25 , Fig. 27 , Fig.28 and Fig.30As shown, a lithium niobate film 9 is bonded to the surface of the bonding dielectric layer, and in horizontal projection, the lithium niobate film 9 covers a portion of the equal-width portion and the entirety of a width gradient portion of each of at least two silicon-rich silicon nitride waveguide cores 4; finally, as shown Fig.10 , Fig.12 , Fig.25 and Fig.28 Electrodes 10 are formed on the lithium niobate film 9 and / or the bonding dielectric layer 8 on both sides of the lower stack.

[0113] Among them, the bonding dielectric layer can be silicon dioxide, aluminum oxide, a bonding adhesive film or a combination thereof, and the thickness of the bonding dielectric layer located above the second silicon nitride waveguide core 7 can be set to 10 to 300 nm; the thickness of the lithium niobate film 9 can be set to 100 to 500 nm; the material of the electrode 10 can be selected from Au, Al, Cu, etc., the spacing between the electrodes 10 is 4 to 10 um, and the thickness of the electrode 10 can be set to 0.5 to 2 um.

[0114] It should also be noted that, depending on the thickness of the intermediate layer 6, when the thickness of the intermediate layer 6 is relatively thick, the silicon nitride waveguide core is the second silicon nitride waveguide core 7, and when the thickness of the intermediate layer 6 is relatively thin, the silicon nitride waveguide core is formed by laminating the second silicon nitride waveguide core 4, the intermediate layer 6, and the first silicon nitride waveguide core 5. That is, the lithium niobate-silicon nitride composite waveguide core finally formed can be composed of the lithium niobate film 9 and the second silicon nitride waveguide core 7, or can be composed of the lithium niobate film 9, the second silicon nitride waveguide core 7, the intermediate layer 6, and the first silicon nitride waveguide core 5.

[0115] Example 3 and Example 4:

[0116] The difference between Examples 3 and 4 and Examples 1 and 2 is that the patterning method of step (3) is different. The intermediate layer 6 and the second silicon nitride layer 103 are sequentially covered on the first silicon nitride layer 101 and the silicon-rich silicon nitride waveguide core 4, and the patterning is performed to obtain the silicon nitride waveguide core, which specifically includes the following steps:

[0117] Step 321, covering the first silicon nitride layer 101 and the silicon-rich silicon nitride waveguide core 4 with an intermediate layer 6, and covering the intermediate layer 6 with a second silicon nitride layer 103;

[0118] Step 322: Pattern the second silicon nitride layer 103 to obtain a second silicon nitride waveguide core 7, wherein: Fig.17 , Fig.19 , Fig.21 and Fig.30As shown in the figure, the second silicon nitride waveguide core 7 comprises a second sub-silicon nitride waveguide core with equal width in the middle part and tapered at both ends, which is located between the two grooves 3. The tapered parts at both ends of each of the second sub-silicon nitride waveguide cores are inverted and superimposed on the tapered parts of the silicon-rich silicon nitride waveguide core 4.

[0119] Step 323: synchronously pattern the intermediate layer 6 and the first silicon nitride layer 101 to obtain Fig.21 The first silicon nitride waveguide core 5 shown (located below the intermediate layer 6 and having the same width as the intermediate layer 6) Fig.21 The cross-section diagram at CC is as follows Fig.23 shown.

[0120] Specifically, in step 322, the second silicon nitride layer 103 is patterned so that the second silicon nitride layer 103 is formed as follows: Fig.17 As shown, several second sub-silicon nitride waveguide cores have an equal-width portion in the middle and a width-gradient portion at both ends. A width-gradient portion of a second sub-silicon nitride waveguide core and a width-gradient portion of a silicon-rich silicon nitride waveguide core connected to it (i.e., the silicon-rich silicon nitride waveguide core 4 at the position of the end tapered groove 32) are inverted (one gradually becomes narrower in width and the other gradually becomes wider in width) and superimposed (the horizontal projections partially overlap).

[0121] In step 323, the intermediate layer 6 and the first silicon nitride layer 101 are patterned simultaneously to form the first silicon nitride waveguide core 5. Fig.23 , Fig. 27 and Fig.30 As shown in FIG. 1 , the second silicon nitride waveguide core 7 and the silicon-rich silicon nitride waveguide core 4 are completely located within the horizontal projection range of the first silicon nitride waveguide core 5 ;

[0122] The material of the intermediate layer 6 can be silicon dioxide, and the thickness of the intermediate layer 6 can be set to 50-500 nm; the thickness of the second silicon nitride layer 103 can be set to 200-400 nm.

[0123] The lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator designed by the present invention forms a groove on the lower cladding, designs the groove into a groove with equal width in the middle and a groove with tapered ends at both ends, and fills the groove with silicon-rich silicon nitride to form a silicon-rich silicon nitride waveguide core, so that the light field can pass through the silicon-rich silicon nitride waveguide core to perform interlayer coupling transition between the silicon nitride waveguide core and the lithium niobate-silicon nitride composite waveguide core, which can reduce the thickness of the film layer and ensure the uniformity of the interlayer coupling. Compared with the prior art, the beneficial effects that can be achieved by at least one of the above technical solutions adopted in the embodiments of this specification include at least:

[0124] 1. Compared with the technical solution of forming multiple steps on both sides of lithium niobate along the silicon nitride waveguide core to achieve light field transition, the present invention does not need to etch lithium niobate, and the manufacturing process is more compatible with CMOS technology;

[0125] 2. Compared with the solution of forming a two-dimensional cone structure on both sides of the lithium niobate along the silicon nitride waveguide core to realize the light field transition, the waveguide core alignment of the present invention is realized by a photolithography process, which has higher alignment accuracy, lower process difficulty, and smaller transition loss caused by alignment deviation;

[0126] 3. Compared with using a silicon-rich silicon nitride waveguide core with a higher refractive index than lithium niobate for interlayer coupling to achieve light field transition, the present invention uses a first silicon nitride layer as a polishing stop layer of the silicon-rich silicon nitride waveguide core. The first silicon nitride layer is flush with the upper surface of the silicon-rich silicon nitride waveguide core, which can reduce the increase in film thickness caused by the introduction of the silicon-rich silicon nitride waveguide core. At the same time, the thickness of the silicon dioxide intermediate layer located between the silicon-rich silicon nitride waveguide core and the silicon nitride waveguide core and participating in the light field transition can be controlled by a deposition process rather than a chemical mechanical polishing process. Therefore, its thickness uniformity is better, the uniformity of interlayer coupling is better, and the process difficulty is reduced.

[0127] Specifically, those skilled in the art should understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the embodiments of the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator, characterized in that: include: A substrate (1), a lower cladding layer (2) formed on the substrate (1), at least two grooves (3) formed on the lower cladding layer (2), the grooves (3) comprising a middle equal-width groove (31) and end tapered grooves (32) located at both ends of the middle equal-width groove (31) and having gradually tapered widths; A silicon-rich silicon nitride waveguide core (4), wherein the silicon-rich silicon nitride waveguide core (4) is located in the groove (3); A lithium niobate-silicon nitride composite waveguide core, the lithium niobate-silicon nitride composite waveguide core comprising a silicon nitride waveguide core and a lithium niobate film (9), the silicon nitride waveguide core being arranged on the lower cladding (2) at the periphery of the silicon-rich silicon nitride waveguide core (4) and covering the silicon-rich silicon nitride waveguide core (4); the lithium niobate film (9) being arranged on the silicon nitride waveguide core via a bonding medium layer (8), wherein the lithium niobate film (9) at least covers a portion of equal-width portions and the entirety of a tapered portion of two silicon-rich silicon nitride waveguide cores (4); Two electrodes (10), the two electrodes (10) are located on both sides of the silicon-rich silicon nitride waveguide core (4) in horizontal projection, and are arranged on the bonding medium layer (8) or the lithium niobate film (9).

2. The lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator according to claim 1, characterized in that: The silicon nitride waveguide core comprises a silicon nitride waveguide core outside the groove and a silicon nitride waveguide core inside the groove; the silicon nitride waveguide core outside the groove is located between two adjacent grooves (3) and comprises a stacked first silicon nitride waveguide core (5), an intermediate layer (6) and a second silicon nitride waveguide core (7); and the silicon nitride waveguide core inside the groove comprises the intermediate layer (6).

3. The lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator according to claim 2, characterized in that: The silicon nitride waveguide core in the groove comprises a first silicon nitride waveguide core in the groove and a second silicon nitride waveguide core in the groove, wherein the first silicon nitride waveguide core in the groove is located at the middle equal-width groove (31), the second silicon nitride waveguide core in the groove is located at the end tapered groove (32), and the second silicon nitride waveguide core in the groove further comprises the second silicon nitride waveguide core (7) located above the intermediate layer (6).

4. The lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator according to claim 2 or 3, characterized in that: The first silicon nitride waveguide core (5) is also formed on the bottom wall and the side wall of the groove (3).

5. The lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator according to claim 1, characterized in that: The end tapered groove (32) takes the end of the middle equal-width groove (31) as a starting point and gradually reduces the groove width in a linear or nonlinear manner.

6. The lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator according to claim 1, characterized in that: The refractive index of silicon-rich silicon nitride is greater than that of lithium niobate.

7. A method for preparing a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator according to any one of claims 1 to 6, characterized in that: The preparation method comprises: A lower cladding layer (2) is formed on a substrate (1), at least two middle equal-width grooves (31) are formed on the lower cladding layer (2), and end tapered grooves (32) with tapered widths are formed at both ends of each middle equal-width groove (31) to obtain a groove (3); forming a first silicon nitride layer and a silicon-rich silicon nitride layer on the lower cladding layer (2) in sequence, and removing the portion of the silicon-rich silicon nitride layer located outside the groove (3) by chemical mechanical polishing to form a silicon-rich silicon nitride waveguide core (4); An intermediate layer (6) and a second silicon nitride layer are sequentially covered on the first silicon nitride layer and the silicon-rich silicon nitride waveguide core (4), and a patterning process is performed to obtain a silicon nitride waveguide core; A bonding dielectric layer (8) is covered on the lower cladding (2) and the silicon nitride waveguide core, and a lithium niobate film (9) is bonded on the surface of the bonding dielectric layer (8), wherein the lithium niobate film (9) at least covers a portion of the middle equal-width groove (31) and the entirety of one end tapered groove (32) of each groove (3), so as to form a lithium niobate-silicon nitride composite waveguide core; An electrode (10) is formed on the bonding medium layer (8) or the lithium niobate film (9) to obtain a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator.

8. The method for preparing the lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator according to claim 7, characterized in that: A first silicon nitride layer and a silicon-rich silicon nitride layer are sequentially formed on the lower cladding layer (2), comprising: forming a first silicon nitride layer on the lower cladding layer (2) located outside the groove (3); A silicon-rich silicon nitride layer is formed in the groove (3) and on the first silicon nitride layer, wherein the upper surface of the silicon-rich silicon nitride layer in the groove (3) is higher than the upper surface of the first silicon nitride layer.

9. The method for preparing a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator according to claim 7, characterized in that: A first silicon nitride layer and a silicon-rich silicon nitride layer are sequentially formed on the lower cladding layer (2), comprising: A first silicon nitride layer is formed on the bottom wall and the side wall of the groove (3) and the lower cladding layer (2) located outside the groove (3); A silicon-rich silicon nitride layer is formed on the first silicon nitride layer, wherein the upper surface of the silicon-rich silicon nitride layer located in the groove (3) is higher than the upper surface of the first silicon nitride layer located outside the groove (3).

10. The method for preparing a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator according to any one of claims 7 to 9, characterized in that: An intermediate layer (6) and a second silicon nitride layer are sequentially covered on the first silicon nitride layer and the silicon-rich silicon nitride waveguide core (4), and a patterning process is performed to obtain a silicon nitride waveguide core, comprising: An intermediate layer (6) is covered on the first silicon nitride layer and the silicon-rich silicon nitride waveguide core (4), and a second silicon nitride layer is covered on the intermediate layer (6); Synchronously patterning the second silicon nitride layer, the intermediate layer (6) and the first silicon nitride layer to obtain the silicon nitride waveguide core whose projection at least completely covers the two silicon-rich silicon nitride waveguide cores (4), wherein the silicon nitride waveguide core comprises an integrated silicon nitride waveguide core outside the groove and a silicon nitride waveguide core inside the groove; Each position of the silicon nitride waveguide core outside the groove and the silicon nitride waveguide core inside the groove comprises a stacked first silicon nitride waveguide core (5), the intermediate layer (6) and the second silicon nitride waveguide core (7); the first silicon nitride waveguide core (5), the intermediate layer (6) and the second silicon nitride waveguide core (7) have the same width.

11. The method for preparing a lithium niobate-silicon nitride heterogeneous integrated electro-optic modulator according to any one of claims 7 to 9, characterized in that: An intermediate layer (6) and a second silicon nitride layer are sequentially covered on the first silicon nitride layer and the silicon-rich silicon nitride waveguide core (4), and a patterning process is performed to obtain a silicon nitride waveguide core, comprising: An intermediate layer (6) is covered on the first silicon nitride layer and the silicon-rich silicon nitride waveguide core (4), and a second silicon nitride layer is covered on the intermediate layer (6); The second silicon nitride layer is patterned to obtain a second silicon nitride waveguide core (7), wherein the second silicon nitride waveguide core (7) comprises a second sub-silicon nitride waveguide core with an equal width in the middle and tapered at both ends, located between the two grooves (3), wherein the tapered portions at both ends of each second sub-silicon nitride waveguide core are inverted and superimposed on the tapered portion of the silicon-rich silicon nitride waveguide core (4); The intermediate layer (6) and the first silicon nitride layer are patterned simultaneously to obtain a first silicon nitride waveguide core (5).

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