Heterogeneous integrated electro-optical modulator and preparation method thereof

Abstract

The invention provides a heterogeneous integrated electro-optical modulator and a preparation method thereof. The method comprises the following steps: sequentially forming a lower cladding and a waveguide core layer on a substrate, patterning the waveguide core layer to form a waveguide core, forming a first bonding dielectric layer, and covering the waveguide core and the lower cladding; forming grooves in two sides of the waveguide core, forming a metal layer, covering the grooves and the first bonding dielectric layer, and forming a patterned first photoresist layer in the formed metal groove; the first photoresist layer is ashed, the ashed first photoresist layer serves as a mask, the patterned metal layer is etched through a dry method, then the first photoresist layer is removed, and an electrode is formed; a patterned second photoresist layer is formed on the electrode, the residual metal layer in the groove is removed through wet etching, and then the second photoresist layer is removed; and filling a second bonding dielectric layer in the groove, and forming electro-optical material layers on the surfaces of the first bonding dielectric layer and the second bonding dielectric layer. According to the invention, both low light propagation loss and high CMOS process compatibility can be considered.

Description

Technical Field

[0001] The present invention relates to the technical field of electro-optic modulators, and in particular to a heterogeneous integrated electro-optic modulation device and a preparation method thereof. Background Art

[0002] Stoichiometric silicon nitride (Si) prepared by low pressure chemical vapor deposition (LPCVD) 3 N 4 The electro-optical modulator device formed by heterogeneous integration of the waveguide core and thin-film lithium niobate fully combines the advantages of the two materials, and has the advantages of low light propagation loss, high-speed and low-power electro-optical modulation, and a wide spectral transparency range, and has therefore attracted widespread attention. Due to the large difference in thermal expansion coefficients between lithium niobate and silicon, as well as the difficulty in etching and the potential risk of contamination to CMOS devices, improving the structure and manufacturing process of silicon nitride-lithium niobate electro-optical modulator devices and improving CMOS process compatibility has become one of the research directions.

[0003] Thin-film lithium niobate is usually bonded to a silicon nitride waveguide core to form a composite waveguide and an electro-optical modulation device. Existing technical solutions include: (1) Thin-film lithium niobate is bonded to a silicon nitride waveguide core, and then the electrode of the electro-optical modulation device is formed on the thin-film lithium niobate. In this solution, the electrode is formed after the thin-film lithium niobate is bonded, which reduces the CMOS process compatibility of the silicon nitride-lithium niobate electro-optical modulation device manufacturing process; (2) The electrode of the electro-optical modulation device is located below the thin-film lithium niobate. Due to the limitation that the electrode is not resistant to high temperature, the silicon nitride waveguide core is manufactured by the PECVD process. The silicon nitride waveguide core manufactured by the PECVD process in this solution has significantly improved optical propagation loss compared to the silicon nitride waveguide core manufactured by the LPCVD process; in addition, the distance from the electrode to the silicon nitride-lithium niobate composite waveguide optical field increases, and the electro-optical modulation efficiency is reduced. Summary of the invention

[0004] In view of this, an embodiment of the present application provides a heterogeneous integrated electro-optical modulation device and a method for preparing the same. The embodiment of the present application adopts a method of first dry etching to form an electrode, then protecting the electrode with a photoresist, and then wet etching to remove metal residues. Electrodes are formed in the bonding dielectric layer on both sides of the waveguide core and in the grooves in the cladding, and then a thin film of lithium niobate is bonded to achieve the purpose of achieving both low light propagation loss and high CMOS process compatibility.

[0005] The present application provides the following technical solution: a method for preparing a heterogeneous integrated electro-optical modulation device, comprising:

[0006] forming a lower cladding layer and a waveguide core layer on the substrate in sequence, patterning the waveguide core layer to form a waveguide core, and forming a first bonding dielectric layer to cover the waveguide core and the lower cladding layer through the first bonding dielectric layer;

[0007] Grooves are formed on both sides of the waveguide core, respectively, and the bottom of the grooves extends from the first bonding medium layer to the lower cladding layer;

[0008] Forming a metal layer to cover the surface of the groove and the surface of the first bonding dielectric layer through the metal layer, and forming a metal groove after the metal layer covers the surface of the groove, and forming a patterned first photoresist layer in the metal groove;

[0009] Performing an ashing process on the first photoresist layer to reduce the width of the first photoresist layer;

[0010] Using the ashed first photoresist layer as a mask, patterning the metal layer by dry etching, and then removing the first photoresist layer to form an electrode in the groove;

[0011] Forming a patterned second photoresist layer on the electrode to cover the electrode with the second photoresist layer, removing the residual metal layer at the inner side wall of the groove by wet etching, and then removing the second photoresist layer;

[0012] A second bonding medium layer is deposited and filled in the groove, and a surface formed by the second bonding medium layer and the first bonding medium layer is made flat, and an electro-optical material layer is formed on the surfaces of the first bonding medium layer and the second bonding medium layer.

[0013] According to an embodiment of the present application, the spacing between the waveguide core and the side walls of the groove that are close to each other is 0.5-2 um.

[0014] According to an embodiment of the present application, the thickness of the metal layer is 50-500 nm smaller than the depth of the groove; the thickness of the first photoresist layer is 0.2-2 um larger than the depth of the metal groove.

[0015] According to an embodiment of the present application, the distance between the first photoresist layer and the side walls of the metal groove that are close to each other is 0.5-1um.

[0016] According to an embodiment of the present application, after the first photoresist layer is ashed, the width of the first photoresist layer is reduced by 0.2-2 um.

[0017] According to an embodiment of the present application, the spacing between the side walls of adjacent electrodes that are close to each other is 5-10 um.

[0018] According to an embodiment of the present application, the thickness of the second photoresist layer is greater than the height of the electrode, the width of the second photoresist layer is greater than the width of the electrode, and is smaller than the spacing between the residual metals on the two opposite side walls in the groove.

[0019] According to one embodiment of the present application, a second bonding medium layer is deposited and filled in the groove so that the surface of the second bonding medium layer is higher than the surface of the groove, and the surface formed by the second bonding medium layer and the first bonding medium layer is flattened by a CMP process, and the thickness of the first bonding medium layer located above the waveguide core is 10-300nm.

[0020] According to an embodiment of the present application, the electro-optical material layer is made of any one of lithium niobate, barium titanate, and lithium tantalate, and the thickness of the electro-optical material layer is 100-500nm.

[0021] The present application also provides a heterogeneous integrated electro-optical modulation device prepared by the above method.

[0022] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above-mentioned technical solutions adopted in the embodiments of this specification include at least the following: the embodiments of the present invention can accurately identify and extract the vehicle identification code through depth information, thereby improving the recognition accuracy of the vehicle identification code and solving the problem of low recognition rate caused by reflection and color in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] 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.

[0024] Figure 1 is a first structural schematic diagram of a process for preparing a heterogeneous integrated electro-optical modulation device according to an embodiment of the present invention;

[0025] Figure 2 is a second structural schematic diagram of a process for preparing a heterogeneous integrated electro-optical modulation device according to an embodiment of the present invention;

[0026] Figure 3 is a third structural schematic diagram of the process of preparing the heterogeneous integrated electro-optical modulation device according to an embodiment of the present invention;

[0027] Figure 4 is a fourth structural schematic diagram of a process for preparing a heterogeneous integrated electro-optical modulation device according to an embodiment of the present invention;

[0028] Figure 5 is a fifth structural schematic diagram of a process for preparing a heterogeneous integrated electro-optical modulation device according to an embodiment of the present invention;

[0029] Figure 6is a sixth structural schematic diagram of a process for preparing a heterogeneous integrated electro-optical modulation device according to an embodiment of the present invention;

[0030] Figure 7 is a seventh structural schematic diagram of a process for preparing a heterogeneous integrated electro-optical modulation device according to an embodiment of the present invention;

[0031] Figure 8 is a schematic structural diagram of a heterogeneous integrated electro-optical modulation device after preparation according to an embodiment of the present invention;

[0032] Among them, 1-substrate, 2-lower cladding, 3-waveguide core, 4-first bonding medium layer, 5-metal layer, 6-first photoresist layer, 7-electrode, 8-second photoresist layer, 9-second bonding medium layer, 10-electro-optical material layer. DETAILED DESCRIPTION

[0033] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0034] The following describes the implementation methods 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 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, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. 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.

[0035] In an embodiment of the present invention, a method for preparing a silicon nitride-lithium niobate electro-optical modulation device structure that can take into account both low light propagation loss and high CMOS process compatibility is adopted, that is, electrodes are formed in the grooves of the cladding on both sides of the silicon nitride waveguide core made by the LPCVD process, and then a thin film of lithium niobate is bonded. However, when forming electrodes in the grooves and patterning the metal film, if dry etching is used, metal residues will be formed on the side walls of the grooves, which will sharply increase the light propagation loss of the composite waveguide; if wet etching is used, the drilling etching caused by wet etching will increase the electrode spacing, reducing the electro-optical modulation efficiency. Therefore, on this basis, an embodiment of the present invention proposes a method for preparing a silicon nitride-lithium niobate electro-optical modulation device by first dry etching to form electrodes, then protecting the electrodes with photoresist, and then wet etching to remove the metal residues on the side walls of the grooves. The specific process is as follows.

[0036] like Figure 1-Figure 8As shown, an embodiment of the present invention provides a method for preparing a heterogeneous integrated electro-optical modulation device, comprising:

[0037] A lower cladding layer 2 and a waveguide core layer are sequentially formed on a substrate 1, the waveguide core layer is patterned to form a waveguide core 3, and a first bonding dielectric layer 4 is formed to cover the waveguide core 3 and the lower cladding layer 2 through the first bonding dielectric layer 4;

[0038] Grooves are formed on both sides of the waveguide core 3, respectively, and the bottom of the grooves extends from the first bonding medium layer 4 to the lower cladding layer 2;

[0039] Forming a metal layer 5, so that the surface of the groove and the surface of the first bonding medium layer 4 are covered by the metal layer 5, and a metal groove is formed after the metal layer 5 covers the surface of the groove, and a patterned first photoresist layer 6 is formed in the metal groove;

[0040] Performing an ashing process on the first photoresist layer 6 to reduce the width of the first photoresist layer 6, and the width of the first photoresist layer 6 after ashing is smaller than the thickness of the first photoresist layer 6;

[0041] Using the first photoresist layer 6 after ashing as a mask, patterning the metal layer 5 by dry etching, and then removing the first photoresist layer 6 to form an electrode 7 in the groove;

[0042] forming a patterned second photoresist layer 8 on the electrode 7 to cover the electrode 7 with the second photoresist layer 8, removing the residual metal layer 5 at the inner sidewall of the groove by wet etching, and then removing the second photoresist layer 8;

[0043] A second bonding medium layer 9 is deposited and filled in the groove, and the surface formed by the second bonding medium layer 9 and the first bonding medium layer 4 is made flat, and an electro-optical material layer 10 is formed on the surfaces of the first bonding medium layer 4 and the second bonding medium layer 9 .

[0044] In some embodiments of the present invention, Figure 1 As shown, first, a lower cladding layer 2 and a waveguide core layer are formed in sequence on a substrate 1, the waveguide core layer is patterned to form a waveguide core 3, and then a first bonding medium layer 4 is formed to cover the lower cladding layer 2 and the waveguide core 3; the surface of the first bonding medium layer 4 is flattened by a CMP process.

[0045] In specific implementation, the substrate 1 can be made of silicon; the lower cladding 2 can be made of silicon dioxide with a thickness of 2-20um; the refractive index of the waveguide core layer is higher than the refractive index of the lower cladding 2, and can be made of silicon nitride, silicon and other materials, and can be a single layer or a laminated structure with an intermediate layer of low refractive index material. The thickness of the waveguide core 3 is preferably 0.1-0.5um, and the width is preferably 0.1-2um; the first bonding medium layer 4 can be made of silicon oxide, aluminum oxide, BCB and other materials or their laminates, and the thickness of the first bonding medium layer 4 above the waveguide core 3 is 100-500nm.

[0046] In some embodiments of the present invention, Figure 2 As shown, a groove is formed in the first bonding dielectric layer 4 and the lower cladding layer 2 on both sides of the waveguide core 3 respectively; wherein, the spacing between the side walls of the waveguide core 3 and the groove that are close to each other is 0.5-2um. The purpose of setting this spacing is: i. protecting the waveguide core 3 from being etched when forming the groove; ii. the first bonding dielectric layer 4 and the lower cladding layer 2 around the waveguide core 3 usually cause less propagation loss than the second bonding dielectric layer 9 formed subsequently, so retaining more first bonding dielectric layer 4 and the lower cladding layer 2 around the waveguide core 3 is conducive to reducing propagation loss; iii. leaving enough space for subsequent processes, according to the spacing requirements of the electrodes 7 in the subsequent steps, the spacing between adjacent electrodes 7 includes: the distance between the edge of the electrode 7 and the metal residue on the side wall of the groove × 2 (the spacing required for forming the electrode by dry etching), the thickness of the metal residue on the side wall of the groove × 2 (related to the thickness of the metal layer 5), the distance between the side wall of the groove and the side wall of the waveguide core 3 × 2, and the width of the waveguide core 3.

[0047] In some embodiments of the present invention, Figure 3 As shown, a metal layer 5 is formed to cover the first bonding medium layer 4 and the groove. Due to conformality, the metal layer 5 forms a metal groove in the groove. A patterned first photoresist layer 6 is formed on the metal layer 5 in the metal groove through a photolithography process.

[0048] In specific implementation, the metal layer 5 can be made of materials such as Al and Cu, and the thickness of the metal layer 5 needs to be less than the groove depth of 50-500nm, the reason for which is to prevent the electrode from being higher than the first bonding dielectric layer 4 in the subsequent step, and thus being unable to perform the CMP process or bonding the electro-optical material layer 10. Preferably, the thickness of the first photoresist layer 6 is greater than the groove depth by 0.2-2um to ensure that the coated photoresist completely fills the metal groove, and at the same time is greater than the thickness of the metal layer 5 (electrode) to ensure that the electrode 7 can be covered when the photoresist of the same size is formed in the subsequent step, that is, the first photoresist layer 6 is higher than the surface of the metal layer 5 outside the groove; the spacing between the first photoresist layer 6 and the side walls of the metal groove close to each other is 0.5-1um, the purpose of which is to leave space for etching the metal layer 5 at the bottom of the groove to form the electrode 7.

[0049] In some embodiments of the present invention, Figure 4 As shown, the first photoresist layer 6 is subjected to an ashing process to make the first photoresist layer 6 narrower.

[0050] In specific implementation, the pattern of the first photoresist layer 6 after ashing becomes narrower by 0.2-2um (0.1-1um on one side) than before ashing. The purpose is to enable the subsequent step to form a photoresist of the same size as the previous step to cover the electrode 7. There is a sufficiently thick photoresist on the top and both sides of the electrode 7. Half of the narrowed width of the first photoresist layer 6 after ashing (i.e. the narrowed width on one side) is less than the thickness of the first photoresist layer 6. The purpose is to ensure that there is still a sufficiently thick photoresist after ashing to provide a mask for etching the metal layer 5 to form the electrode 7.

[0051] In some embodiments of the present invention, Figure 5 As shown, the metal layer 5 is patterned by dry etching using the ashed first photoresist layer 6 as a mask, and the first photoresist layer 6 is removed to form an electrode 7 in the groove, and metal residue is formed at the side wall of the groove. The spacing between the side walls of adjacent electrodes 7 is 5-10um, so as to obtain the maximum electro-optical modulation efficiency and set the optimal electrode spacing.

[0052] In some embodiments of the present invention, Figure 6 As shown, a second photoresist layer 8 is formed. The second photoresist layer 8 is a photoresist pattern covering the electrode 7 formed in the groove by a photolithography process.

[0053] In a specific implementation, the thickness of the second photoresist layer 8 is greater than the height of the electrode 7, and the width of the second photoresist layer 8 is greater than the width of the electrode 7, and is less than the spacing between the residual metals on the two opposite side walls in the groove. Preferably, the same mask and photoresist thickness in the previous steps are used to obtain the patterned second photoresist layer 8, which can completely cover the electrode 7 without adding a new mask, thereby simplifying the process.

[0054] In some embodiments of the present invention, Figure 7 As shown, the residual metal at the side wall of the groove of the first bonding dielectric layer 4 / lower cladding layer is removed by wet etching, and the second photoresist layer 8 is removed; wherein the electrode 7 is covered and protected by the second photoresist layer 8 from wet etching.

[0055] In some embodiments of the present invention, Figure 8 As shown, a second bonding medium layer 9 is deposited and filled in the groove, so that the surface of the second bonding medium layer 9 is higher than the surface of the groove, and the surface formed by the second bonding medium layer 9 and the first bonding medium layer 4 is flattened by a CMP process, and the thickness of the first bonding medium layer 4 located above the waveguide core 3 is 10-300nm.

[0056] In a specific implementation, the electro-optic material layer 10 can be lithium niobate, barium titanate, lithium tantalate, etc., with a thickness of 100-500 nm. The parameter range of the thickness of the first bonding medium layer 4 above the waveguide core 3 and the parameter range of the electro-optic material layer 10 are intended to enable the waveguide core 3 and the electro-optic material layer 10 to form a composite waveguide core, so that the optical signal propagates along the composite waveguide core and phase modulates the propagated optical signal when the electrode 7 applies an electrical signal.

[0057] The embodiment of the present invention first forms a photoresist pattern on the surface of the metal layer in the groove by a photolithography process, and then ashes the photoresist to make it narrower; then dry-etches the metal layer to form an electrode, and removes the photoresist; applies photoresist again, and uses the same photoresist thickness, mask and photolithography process in the previous step to form a photoresist pattern covering the electrode; then wet-etches to remove the metal residue on the side wall of the groove, and removes the photoresist. The embodiment of the present invention adopts a method of first dry-etching to form an electrode, then protecting the electrode with photoresist, and then wet-etching to remove the metal residue, forming electrodes in the bonding dielectric layer and the groove in the cladding on both sides of the waveguide core, and then bonding a thin film of lithium niobate to form a silicon nitride-lithium niobate electro-optical modulation device structure and preparation method that can take into account low light propagation loss and high CMOS process compatibility.

[0058] Specifically, compared with the prior art solution in which the electrode is formed after the thin film lithium niobate is bonded, the electrode of the embodiment of the present invention is formed before the thin film lithium niobate is bonded, and has higher CMOS process compatibility. In the prior art solution, in order to achieve higher CMOS process compatibility, the metal electrode cannot withstand the high temperature process of LPCVD, and the silicon nitride waveguide core is made by PECVD process, and the distance from the electrode to the silicon nitride-lithium niobate composite waveguide light field increases, and the electro-optical modulation efficiency is reduced; compared with this, the embodiment of the present invention first forms the waveguide core and then makes the electrode, which can take into account low light propagation loss, CMOS process compatibility and higher electro-optical modulation efficiency. In addition, the solution of the embodiment of the present invention forms the electrode by dry etching, protects the electrode with photoresist, and removes the metal residue on the side wall of the groove by wet etching, thereby avoiding the significant light propagation loss caused by the metal residue close to the waveguide core, and ensuring the controllable electrode morphology, spacing and higher modulation efficiency of the electro-optical modulation device.

[0059] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A method for preparing a heterogeneous integrated electro-optical modulation device, characterized in that: include: forming a lower cladding layer and a waveguide core layer on the substrate in sequence, patterning the waveguide core layer to form a waveguide core, and forming a first bonding dielectric layer to cover the waveguide core and the lower cladding layer through the first bonding dielectric layer; Grooves are formed on both sides of the waveguide core, respectively, and the bottom of the grooves extends from the first bonding medium layer to the lower cladding layer; Forming a metal layer to cover the surface of the groove and the surface of the first bonding dielectric layer through the metal layer, and forming a metal groove after the metal layer covers the surface of the groove, and forming a patterned first photoresist layer in the metal groove; Performing an ashing process on the first photoresist layer to reduce the width of the first photoresist layer; Using the ashed first photoresist layer as a mask, patterning the metal layer by dry etching, and then removing the first photoresist layer to form an electrode in the groove; Forming a patterned second photoresist layer on the electrode to cover the electrode with the second photoresist layer, removing the residual metal layer at the inner side wall of the groove by wet etching, and then removing the second photoresist layer; A second bonding medium layer is deposited and filled in the groove, and a surface formed by the second bonding medium layer and the first bonding medium layer is made flat, and an electro-optical material layer is formed on the surfaces of the first bonding medium layer and the second bonding medium layer.

2. The method for preparing a heterogeneous integrated electro-optical modulation device according to claim 1, characterized in that: The distance between the waveguide core and the side walls of the groove that are close to each other is 0.5-2um.

3. The method for preparing a heterogeneous integrated electro-optical modulation device according to claim 1, characterized in that: The thickness of the metal layer is 50-500 nm smaller than the depth of the groove; the thickness of the first photoresist layer is 0.2-2 um larger than the depth of the metal groove.

4. The method for preparing a heterogeneous integrated electro-optical modulation device according to claim 1, characterized in that: The distance between the first photoresist layer and the side walls of the metal groove that are close to each other is 0.5-1 um.

5. The method for preparing a heterogeneous integrated electro-optical modulation device according to claim 1, characterized in that: After the first photoresist layer is ashed, the width of the first photoresist layer is reduced by 0.2-2 um.

6. The method for preparing a heterogeneous integrated electro-optical modulation device according to claim 1, characterized in that: The spacing between the side walls of adjacent electrodes that are close to each other is 5-10 um.

7. The method for preparing a heterogeneous integrated electro-optical modulation device according to claim 1, characterized in that: The thickness of the second photoresist layer is greater than the height of the electrode, the width of the second photoresist layer is greater than the width of the electrode, and is smaller than the spacing between the residual metals on the two opposite side walls in the groove.

8. The method for preparing a heterogeneous integrated electro-optical modulation device according to claim 1, characterized in that: Also includes: A second bonding medium layer is deposited and filled in the groove so that the surface of the second bonding medium layer is higher than the surface of the groove. The surface formed by the second bonding medium layer and the first bonding medium layer is flattened by a CMP process, and the thickness of the first bonding medium layer located above the waveguide core is 10-300 nm.

9. The method for preparing a heterogeneous integrated electro-optical modulation device according to claim 1, characterized in that: The electro-optic material layer is made of any one of lithium niobate, barium titanate and lithium tantalate, and the thickness of the electro-optic material layer is 100-500nm.

10. A heterogeneous integrated electro-optical modulation device prepared by the method according to any one of claims 1 to 9.

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