A lithium niobate-silicon nitride heterogeneous integrated electro-optical modulator and its preparation method

Abstract

The present invention relates to the field of semiconductor technology and provides a lithium niobate-silicon nitride heterogeneous integrated electro-optical modulator and a preparation method thereof. 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 on the lower cladding, the grooves comprising a central groove of equal width and end tapered grooves with tapered widths at both ends of the central groove of equal width. The silicon-rich silicon nitride waveguide core is located 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 both sides of the silicon-rich silicon nitride waveguide core and are arranged on a bonding dielectric layer or a lithium niobate film. The electro-optical modulator of the present invention can enable the light field to 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, thereby reducing the thickness of the film layer while ensuring the uniformity of the interlayer coupling.

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-optical modulator and a preparation method thereof. Background Art

[0002] Heterogeneous integration of thin-film lithium niobate onto a silicon nitride (Si3N4) waveguide core fabricated by low-pressure chemical vapor deposition (LPCVD) via a bonding process has broad applications in integrated optical devices. Heterogeneous integration of thin-film lithium niobate enables high modulation efficiency, high modulation speed, and low-power electro-optical modulation capabilities in silicon nitride photonics platforms, offering advantages such as low optical propagation loss and a wide spectral transparency range. This also avoids the reduced CMOS process compatibility associated with patterning the lithium niobate.

[0003] Currently, one of the challenges facing 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. 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 with the silicon nitride waveguide core is performed 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 two-dimensional conical structure of the lithium niobate and the silicon nitride optical waveguide core must 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 forms 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) A silicon-rich silicon nitride waveguide core with a higher refractive index than lithium niobate is used 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 lead to an increase in the film thickness. The thickness of the silicon dioxide layer needs to be controlled by chemical mechanical polishing 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-optical modulator, comprising:

[0009] A substrate, a lower cladding layer formed on the substrate, and at least two grooves 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 gradually 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, comprising a silicon nitride waveguide core and a lithium niobate film, wherein the silicon nitride waveguide core is disposed on the lower cladding layer surrounding the silicon-rich silicon nitride waveguide core and covers the silicon-rich silicon nitride waveguide core; the lithium niobate film is disposed on the silicon nitride waveguide core via a bonding dielectric layer, wherein the lithium niobate film covers at least a portion of the equal-width portions and the entirety of a tapered portion of two silicon-rich silicon nitride waveguide cores;

[0012] Two electrodes are located on both sides of the silicon-rich silicon nitride waveguide core in horizontal projection and are arranged on the bonding dielectric 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, and the second silicon nitride waveguide core in the groove is located at the end tapered groove position. 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 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 manner or a nonlinear manner.

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

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

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

[0020] Step 2: forming a first silicon nitride layer and a silicon-rich silicon nitride layer on the lower cladding layer in sequence, 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 patterning 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 covers at least a portion of the middle equal-width groove and the entirety of one end tapered groove of each groove, thereby forming a lithium niobate-silicon nitride composite waveguide core;

[0023] Step 5: forming an electrode on the bonding dielectric layer or the lithium niobate thin film to obtain the 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 sidewalls 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 within the groove is higher than an upper surface of the first silicon nitride layer located outside the groove.

[0030] Furthermore, in step 3, an intermediate layer and a 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 a 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] In 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 intermediate layer, and a second silicon nitride waveguide core, and the first silicon nitride waveguide core, the intermediate layer, and the second silicon nitride waveguide core have the same width.

[0034] Furthermore, in step 3, an intermediate layer and a 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 a silicon nitride waveguide core, including:

[0035] Step 321: Covering an intermediate layer on the first silicon nitride layer and the silicon-rich silicon nitride waveguide core, and covering a second silicon nitride layer on the intermediate 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 includes a second sub-silicon nitride waveguide core having an equal width in the middle portion and tapered at both ends, located between the two grooves. 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.

[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 tapered grooves at both ends, and fills the groove with silicon-rich silicon nitride to form a silicon-rich silicon nitride waveguide core. This allows the light field to pass through the silicon-rich silicon nitride waveguide core to achieve interlayer coupling transition between the silicon nitride waveguide core and the lithium niobate-silicon nitride composite waveguide core, thereby reducing the film thickness while ensuring the uniformity of the interlayer coupling. Compared with the existing technology, the beneficial effects achieved by at least one of the above technical solutions adopted in the embodiments of this specification include at least the following:

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

[0040] 2. Compared with the solution of forming a two-dimensional tapered structure along both sides of the silicon nitride waveguide core on lithium niobate to achieve light field transition, the waveguide core alignment of the present invention is achieved through 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 optical field transition, the present invention uses a first silicon nitride layer as a polishing stop layer for 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 optical 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 following briefly introduces the drawings required for use in the embodiments. 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 any creative work.

[0043] Figure 1 Schematic diagram of the groove on the lower cladding disclosed in the present invention;

[0044] Figure 2 for Figure 1 Cross-section at AA;

[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-section at AA;

[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 6The top view after being graphed in ;

[0050] Figure 8 for Figure 7 Cross-section at AA;

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

[0052] Figure 10 exist Figure 6 A top view of a lithium niobate-silicon nitride heterojunction electro-optical modulator formed on the structure shown;

[0053] Figure 11 for Figure 10 Cross-section at AA;

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

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

[0056] Figure 14 For Figure 13 Schematic diagram of forming a silicon-rich silicon nitride waveguide layer on the first silicon nitride layer;

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

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

[0059] Figure 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] Figure 18 for Figure 17 Cross-section at AA;

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

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

[0063] Figure 21 For Figure 17 A top view of a first silicon nitride waveguide core is formed by patterning the structure shown;

[0064] Figure 22 for Figure 21 Cross-section at AA;

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

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

[0067] Figure 25 For Figure 21 A top view of a lithium niobate-silicon nitride heterojunction electro-optical modulator formed on the structure shown;

[0068] Figure 26 for Figure 25 Cross-section at AA;

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

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

[0071] Figure 29 For Figure 15 and Figure 17 The structure shown in the top view is as shown Figure 25 A cross-sectional view at AA of the lithium niobate-silicon nitride heterojunction electro-optical modulator shown;

[0072] Figure 30 For Figure 15 and Figure 17 The structure shown in the top view is as shown Figure 25 A cross-sectional view at BB of the lithium niobate-silicon nitride heterojunction electro-optical modulator shown;

[0073] Figure 31 This is a flow chart of the method for preparing 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. intermediate 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 embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents 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 embodiments, 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, in the absence of conflict, the features of the following embodiments and embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application.

[0077] The embodiment of the present invention discloses a lithium niobate-silicon nitride heterogeneous integrated electro-optical modulator, see Figure 10 and Figure 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. The grooves 3 include a middle groove 31 of equal width and end tapered grooves 32 located at both ends of the middle groove 31 and having tapered widths. Figures 4 to 6 、 Figure 8 、 Figure 11 、 Figure 15 、 Figure 16 、 Figure 18 、 Figure 19 、 Figure 22 、 Figure 23 、 Figure 26 、 Figure 27 、 Figure 29 and Figure 30 As shown, the silicon-rich silicon nitride waveguide core 4 is located in the groove 3 .

[0079] See also Figure 10 、 Figure 12 、 Figure 25 、 Figure 27 、 Figure 28 and Figure 30 As shown, the lithium niobate-silicon nitride composite waveguide core includes a silicon nitride waveguide core and a lithium niobate film 9. The silicon nitride waveguide core is arranged on the lower cladding 2 outside 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 dielectric layer 8, wherein the lithium niobate film 9 covers at least a portion of the equal-width portions and the entirety of one tapered portion of the two silicon-rich silicon nitride waveguide cores 4.

[0080] See also Figure 10 、 Figure 12 、 Figure 25 and Figure 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 dielectric 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 of equal width in the middle and tapered grooves 32 at both ends, and fills the groove 3 with silicon-rich silicon nitride to form a silicon-rich silicon nitride waveguide core 4. This allows the light field to 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 film thickness while 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 、 Figure 11 、 Figure 16 、 Figure 22 、 Figure 23 、 Figure 26 、 Figure 27 、 Figure 29 and Figure 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. Figure 9 、 Figure 12 、 Figure 24 and Figure 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 Figure 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, and the second silicon nitride waveguide core in the groove is located at the end tapered groove 32. 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 shown in FIG. Figure 22 As shown, the cross-sectional view of the second silicon nitride waveguide core in the groove is as follows Figure 23 shown.

[0084] Further, see Figure 8 、 Figure 11 、 Figure 22、 Figure 23 、 Figure 26 and Figure 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-optical modulator, see Figure 31 As shown, the method includes 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: forming a first silicon nitride layer 101 and a silicon-rich silicon nitride layer 102 on the lower cladding layer 2 in sequence, and removing the 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 first silicon nitride layer 101 and the silicon-rich silicon nitride waveguide core 4 with the intermediate layer 6 and the second silicon nitride layer 103, 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 to the surface of the bonding dielectric layer 8, wherein the lithium niobate film 9 covers at least a portion of the middle uniform-width groove 31 and the entirety of one end tapered groove 32 of each groove 3, thereby forming 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 thin film 9 to obtain the 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-optical 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. At least two grooves 3 are formed on the lower cladding layer 2. The grooves 3 include a constant-width portion and a gradually decreasing-width portion. The gradually decreasing-width portions are located at both ends of the constant-width portion. The width of the gradually decreasing portions decreases linearly or nonlinearly from the constant-width portion toward the ends of the grooves 3. Silicon can be used as the material for the substrate 1; silicon dioxide can be used as the material for the lower cladding layer 2, and the thickness of the lower cladding layer 2 can be 2 to 20 μm. The depth of the grooves 3 can be machined to 0.2 to 0.8 μm, and the width of the constant-width portion of the grooves 3 can be set to 0.5 to 2 μm.

[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 comprising the following steps:

[0096] Step 211: forming a thin film on the lower cladding layer 2 outside the groove 3. Figure 13 The first silicon nitride layer 101 is shown;

[0097] Step 212: forming a silicon nitride layer in the groove 3 and on the first silicon nitride layer 101. Figure 14 The silicon-rich silicon nitride layer 102 is 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, a first silicon nitride layer 101 may be formed on the lower cladding layer 2, and the first silicon nitride layer 101 and the lower cladding layer 2 may 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 (i.e., the first silicon nitride waveguide core 5) in the groove 3. The structure is as follows: Figure 13 、 Figure 15 and Figure 16 shown.

[0099] In step 212, see Figure 14 As shown, a silicon-rich silicon nitride layer 102 can be formed on the first silicon nitride layer 101 first, 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 side wall of the groove 3 of 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, as shown in FIG. Figure 3 As shown, the specific steps include:

[0101] Step 221 : forming a first silicon nitride layer 101 on the bottom wall and side walls 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 completely fill the groove 3. Furthermore, 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 inside the groove 3 is parallel to the first silicon nitride layer 101 outside the groove. At this time, the structure can be formed in the groove 3 as shown in FIG. Figure 4 、 Figure 5 and Figure 15 The silicon-rich silicon nitride waveguide core 4 is shown to have a uniform width in the middle and tapered widths at both ends. During chemical mechanical polishing, 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 here that the groove 3 in step 1 and step 2 can be formed directly in the lower cladding layer 2, or the first silicon nitride layer 101 can be formed on the lower cladding layer 2 first, 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 the 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 completely covers at least two of the 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 、 Figure 9 、 Figure 11 、 Figure 12 and Figure 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 forming the silicon-rich silicon nitride waveguide core 4 in 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 and the silicon-rich silicon nitride waveguide core 4 outside the groove 3; the second silicon nitride layer 103, the intermediate layer 6 and the first silicon nitride layer 101 are patterned simultaneously 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 are located completely cover at least 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 several equal-width parts and width gradient parts. The equal-width parts of the laminate can have different widths. 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: Figure 9 、 Figure 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 integrated into a whole, and the top view is finally 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 Figure 11 、 Figure 16 、 Figure 26 and Figure 29 As shown, the bonding dielectric layer 8 is used to cover the surface of the lower cladding layer 2, the second silicon nitride waveguide core 7 and the intermediate layer 6, as well as the side surfaces of the second silicon nitride waveguide core 7, the intermediate layer 6 and the first silicon nitride waveguide core 5; secondly, see Figure 10 、 Figure 12 、 Figure 25 、 Figure 27 、 Figure 28 and Figure 30As shown, a lithium niobate film 9 is bonded to the surface of the bonding dielectric layer. In horizontal projection, the lithium niobate film 9 covers a portion of the equal-width portion and the entirety of the width-gradient portion of each of at least two silicon-rich silicon nitride waveguide cores 4. Finally, as shown Figure 10 、 Figure 12 、 Figure 25 and Figure 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. 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 μm, and the thickness of the electrode 10 can be set to 0.5 to 2 μm.

[0114] It should also be noted that depending on the thickness of the intermediate layer 6, when the intermediate layer 6 is thick, the silicon nitride waveguide core is the second silicon nitride waveguide core 7. When the intermediate layer 6 is thin, the silicon nitride waveguide core is formed by stacking the second silicon nitride waveguide core 4, the intermediate layer 6, and the first silicon nitride waveguide core 5. In other words, the final lithium niobate-silicon nitride composite waveguide core can be composed of a stack of the lithium niobate film 9 and the second silicon nitride waveguide core 7, or a stack 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 lies in the different patterning methods in step (3). 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 process is performed to obtain the silicon nitride waveguide core, specifically comprising 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: Figure 17 、 Figure 19 、 Figure 21 and Figure 30The second silicon nitride waveguide core 7 shown in the figure includes a second sub-silicon nitride waveguide core with equal width in the middle portion and tapered at both ends, located between the two grooves 3. 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.

[0119] Step 323: Synchronously pattern the intermediate layer 6 and the first silicon nitride layer 101 to obtain Figure 21 The first silicon nitride waveguide core 5 is shown (located below the intermediate layer 6 and having the same width as the intermediate layer 6), wherein Figure 21 The cross-section at CC is as follows Figure 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: Figure 17 As shown, several second sub-silicon nitride waveguide cores have a middle portion of equal width and portions of gradually varying width at both ends. A gradually varying width portion of a second sub-silicon nitride waveguide core and a gradually decreasing width portion of a connected silicon-rich silicon nitride waveguide core (i.e., the silicon-rich silicon nitride waveguide core 4 at the end tapered groove 32) are inverted (one gradually becomes narrower in width and the other gradually becomes wider in width) and superimposed (horizontally projected portions 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. Figure 23 、 Figure 27 and Figure 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 tapered grooves at both ends, and fills the groove with silicon-rich silicon nitride to form a silicon-rich silicon nitride waveguide core. This allows the light field to pass through the silicon-rich silicon nitride waveguide core to achieve interlayer coupling transition between the silicon nitride waveguide core and the lithium niobate-silicon nitride composite waveguide core, thereby reducing the film thickness while ensuring the uniformity of the interlayer coupling. Compared with the existing technology, the beneficial effects achieved by at least one of the above technical solutions adopted in the embodiments of this specification include at least the following:

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

[0125] 2. Compared with the solution of forming a two-dimensional tapered structure along both sides of the silicon nitride waveguide core on lithium niobate to achieve light field transition, the waveguide core alignment of the present invention is achieved through 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 optical field transition, the present invention uses a first silicon nitride layer as a polishing stop layer for 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 optical 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 merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will appreciate that various modifications and variations are possible in the embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection 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), and 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 (3) and includes a stacked first silicon nitride waveguide core (5), an intermediate layer (6), and a second silicon nitride waveguide core (7); the silicon nitride waveguide core inside the groove includes the intermediate layer (6), a first silicon nitride waveguide core inside the groove, and a second silicon nitride waveguide core inside the groove. The first silicon nitride waveguide core inside the groove is located at the position of the middle equal-width groove (31), and the second silicon nitride waveguide core inside the groove is located at the position of the end tapered groove (32), including the second silicon nitride waveguide core (7) located above the intermediate layer (6); 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) outside 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 dielectric layer (8), wherein the lithium niobate film (9) at least covers a portion of equal-width portions and the entirety of one 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 first silicon nitride waveguide core (5) is also formed on the bottom wall and side walls of the groove (3).

3. 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.

4. 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.

5. A method for preparing a lithium niobate-silicon nitride heterogeneous integrated electro-optical modulator according to any one of claims 1 to 4, 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 in sequence on the lower cladding layer (2), and removing a portion of the silicon-rich silicon nitride layer 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 to 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) and the entirety of one end tapered groove (32) of each groove (3), thereby forming 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-optical modulator.

6. The method for preparing a lithium niobate-silicon nitride heterogeneous integrated electro-optical modulator according to claim 5, 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.

7. The method for preparing a lithium niobate-silicon nitride heterogeneous integrated electro-optical modulator according to claim 5, 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 bottom wall and side walls of the groove (3) and on 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).

8. The method for preparing a lithium niobate-silicon nitride heterogeneous integrated electro-optical modulator according to any one of claims 5 to 7, 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 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.

9. The method for preparing a lithium niobate-silicon nitride heterogeneous integrated electro-optical modulator according to any one of claims 5 to 7, 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 a middle portion having an equal width 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 and the tapered portion of the silicon-rich silicon nitride waveguide core (4) are inverted and superimposed on each other; 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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