CN114217459A

CN114217459A - Micro-ring modulator and preparation method thereof

Info

Publication number: CN114217459A
Application number: CN202111546738.4A
Authority: CN
Inventors: 张宇光; 肖希; 王磊; 胡晓; 陈代高
Original assignee: Wuhan Optical Valley Information Optoelectronic Innovation Center Co Ltd
Current assignee: Wuhan Optical Valley Information Optoelectronic Innovation Center Co Ltd
Priority date: 2021-12-16
Filing date: 2021-12-16
Publication date: 2022-03-22

Abstract

The embodiment of the invention provides a micro-ring modulator and a preparation method thereof, wherein the method comprises the following steps: providing a substrate layer; forming a coupling waveguide and a micro-ring resonance structure which are arranged in parallel on the substrate layer, wherein the micro-ring resonance structure comprises a first doping structure and a second doping structure which are sequentially stacked along the thickness direction of the substrate layer, and the doping types of the first doping structure and the second doping structure are opposite; and forming an electrode electrically connected to the micro-ring resonator structure.

Description

Micro-ring modulator and preparation method thereof

Technical Field

The invention relates to the technical field of semiconductors, in particular to a micro-ring modulator and a preparation method thereof.

Background

In view of the development route of large-scale integrated circuits, research is being conducted at home and abroad to integrate active devices (e.g., modulators, detectors, etc.) and optical waveguide devices (e.g., splitters/condensers, etc.) onto one substrate to realize photonic integrated chips having advantages similar to those of large-scale integrated circuits. The photonic integrated chip has the characteristics of low cost, small size, low power consumption, flexible expansion, high reliability and the like. In optical fiber communication, the intensity of light can be controlled by an electro-optical modulator, and thus the electro-optical modulator plays an important role in an optical fiber communication system. Meanwhile, the electro-optical modulator is also one of important photoelectric devices in the photonic integrated chip solution.

In recent years, silicon-based electro-Optical modulators are an important research direction in electro-Optical modulators, and have a significant role in Optical Cross-connects (OXCs) and Optical differential multiplexing (OADMs) in the field of Optical communications. The silicon-based electro-optic modulator mainly comprises two types, one type is an electro-refractive index electro-optic modulator, the phase to intensity change is realized through an interferometer or a resonance device, and the modulation of an optical signal is finally realized; the other is an electro-absorption electro-optical modulator, the imaginary part of the refractive index is changed through an external electric field, so that the intensity change of the optical wave in the electro-optical modulator is directly changed, and finally the modulation of the optical signal is realized.

At present, various silicon-based electro-optical modulators are successfully designed and manufactured, various technical indexes are gradually improved, but the comprehensive performance of the silicon-based electro-optical modulator is different from that of a mature lithium niobate electro-optical modulator, and the future development requirements of optical interconnection and optical communication cannot be met. Specifically, since the photoelectric effect of the silicon material itself is very weak compared with other materials, the change of the refractive index of the silicon material is relatively small due to the change of the external electric field, and the size of the electro-optical modulator needs to be increased to achieve a good modulation effect in order to overcome the defect. In order to achieve small-scale integration, researchers have studied many novel architectures, of which the micro-ring modulator is the most effective. In the related art, it is necessary to further improve the modulation efficiency of the micro-ring modulator while reducing the size of the micro-ring modulator, so as to improve the integration level of the photonic integrated chip and reduce the manufacturing cost.

Disclosure of Invention

In view of the above, embodiments of the present invention are directed to a micro-ring modulator and a method for manufacturing the same.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

the preparation method of the micro-ring modulator provided by the embodiment of the invention comprises the following steps:

providing a substrate layer;

forming a coupling waveguide and a micro-ring resonance structure which are arranged in parallel on the substrate layer, wherein the micro-ring resonance structure comprises a first doping structure and a second doping structure which are sequentially stacked along the thickness direction of the substrate layer, and the doping types of the first doping structure and the second doping structure are opposite; and

and forming an electrode electrically connected with the micro-ring resonance structure.

In the above solution, the forming of the coupling waveguide and the micro-ring resonance structure arranged in parallel on the substrate layer includes:

forming a first material layer on the substrate layer;

removing part of the first material layer to form a coupling waveguide and a first doping structure material layer;

carrying out first doping on the first doping structure material layer to form the first doping structure;

forming a second material layer on the first doped structure;

removing part of the second material layer to form a second doping structure material layer;

and carrying out second doping on the second doping structure material layer to form the second doping structure.

In the foregoing aspect, the removing the portion of the first material layer includes:

performing first etching on the first material layer to form the coupling waveguide and a first sub-material layer; the projection of the first sub-material layer on a preset plane is circular; the first etch stops on a top surface of the substrate layer; the preset plane is perpendicular to the thickness direction of the substrate layer;

performing second etching on the first sub-material layer to form the first doping structure material layer with a groove; the projection of the part of the first sub-material layer removed by the second etching on the preset plane is circular; the second etch stops in the first sub-material layer.

In the foregoing scheme, the performing the first doping on the first doped structure material layer to form the first doped structure includes:

carrying out first sub-doping on the middle area of the bottom of the groove in the first doping structure material layer to obtain a first doping area;

performing second sub-doping on the remaining region of the first doping structure material layer, wherein the second sub-doping type is the same as the first sub-doping type, so as to obtain a second doping region; wherein the content of the first and second substances,

the first doped region and the second doped region together form the first doped structure.

In the above scheme, the projection of the second doped structure material layer on the preset plane is annular; the side edge of the second doping structure material layer is flush with the side edge of the first doping structure material layer;

the second doping structure material layer to form the second doping structure includes:

carrying out third sub-doping on the middle annular region of the second doping structure material layer to obtain a third doping region;

performing fourth sub-doping on the remaining region of the second doping structure material layer, wherein the fourth sub-doping type is the same as the third sub-doping type, so as to obtain a fourth doping region; wherein the content of the first and second substances,

the third doped region and the fourth doped region together form the second doped structure.

In the above scheme, the first doping includes P-type doping, and the second doping includes N-type doping.

In the above scheme, the method further comprises:

and forming a covering layer covering the coupling waveguide and the micro-ring resonance structure, wherein the refractive index of the covering layer is smaller than that of the coupling waveguide and the micro-ring resonance structure.

In the above scheme, the electrodes include a first electrode and a second electrode; the forming of the electrode electrically connected to the micro-ring resonator structure includes:

performing third etching on the covering layer to form a first electrode contact hole, wherein the third etching is stopped on the first doping structure; filling a conductive material in the first electrode contact hole to form the first electrode;

performing fourth etching on the covering layer to form a second electrode contact hole, wherein the fourth etching is stopped on the second doping structure; and filling a conductive material in the second electrode contact hole to form the second electrode.

An embodiment of the present invention further provides a micro-ring modulator, including:

a substrate layer;

the micro-ring resonant structure comprises a first doping structure and a second doping structure which are sequentially stacked along the thickness direction of the substrate layer, and the doping types of the first doping structure and the second doping structure are opposite; and

and the electrode is electrically connected with the micro-ring resonance structure.

In the above scheme, the first doping structure includes a first doping region and a second doping region that is the same as the doping type of the first doping region and surrounds the first doping region;

the second doping structure comprises a third doping area and a fourth doping area which is the same as the third doping area in doping type and surrounds the third doping area;

wherein the first doped structure and the second doped structure are physically connected with the fourth doped region through the second doped region; the first doped region is not in physical contact with the third doped region.

The embodiment of the invention provides a micro-ring modulator and a preparation method thereof, wherein the method comprises the following steps: providing a substrate layer; forming a coupling waveguide and a micro-ring resonance structure which are arranged in parallel on the substrate layer, wherein the micro-ring resonance structure comprises a first doping structure and a second doping structure which are sequentially stacked along the thickness direction of the substrate layer, and the doping types of the first doping structure and the second doping structure are opposite; and forming an electrode electrically connected to the micro-ring resonator structure. In the embodiment of the invention, the first doping structure and the second doping structure are sequentially stacked along the thickness direction of the substrate layer, and the vertical (the direction indicated by the vertical direction is parallel to the thickness direction of the substrate layer) PN junction electrical modulation structure is formed at the junction of the first doping structure and the second doping structure, so that the vertical PN junction electrical modulation structure can increase the overlapping area between a PN junction depletion region and an optical mode field, improve the interaction between optical waves and current carriers, and further improve the modulation efficiency; meanwhile, the vertical PN junction electrical modulation structure can reduce the size occupied by the modulation structure, thereby reducing the size of the micro-ring modulator, further improving the integration level of the photonic integrated chip and reducing the preparation cost. In addition, the coupling waveguide and the micro-ring resonance structure are directly formed on the substrate layer, and compared with a micro-ring modulator with the coupling waveguide and the micro-ring resonance structure formed in the flat waveguide layer, the micro-ring modulator avoids light loss caused by light leakage through the flat waveguide layer, further improves the modulation efficiency of the micro-ring modulator, and further reduces the size of the micro-ring modulator.

Drawings

Fig. 1 is a schematic flow chart illustrating an implementation of a method for manufacturing a micro-ring modulator according to an embodiment of the present invention;

fig. 2 a-fig. 2m are schematic cross-sectional views illustrating implementation steps of a method for manufacturing a micro-ring modulator according to an embodiment of the present invention;

FIG. 3 is a schematic cross-sectional view taken along A-A of FIG. 2 m;

FIG. 4 is a schematic cross-sectional view taken along line B-B of FIG. 2 m;

fig. 5 is a schematic cross-sectional view along the direction C-C in fig. 2 m.

Detailed Description

The technical solution of the present invention is further described in detail with reference to the drawings and the specific embodiments of the specification.

In the description of the present invention, it is to be understood that the terms "length", "width", "depth", "up", "down", "outer", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention.

In embodiments of the present invention, the term "substrate" refers to a material on which subsequent layers of material are added. The substrate itself may be patterned. The material added on top of the substrate may be patterned or may remain unpatterned. In addition, the substrate may include a variety of semiconductor materials, such as silicon, germanium, arsenic, indium phosphide, and the like. Alternatively, the substrate may be made of a non-conductive material, such as glass, plastic, or sapphire wafers.

In embodiments of the present invention, the term "layer" refers to a portion of material that includes a region having a thickness. A layer may extend over the entirety of the underlying or overlying structure or may have an extent that is less than the extent of the underlying or overlying structure. Furthermore, a layer may be a region of a homogeneous or heterogeneous continuous structure having a thickness less than the thickness of the continuous structure. For example, a layer may be located between the top and bottom surfaces of the continuous structure, or a layer may be between any horizontal pair at the top and bottom surfaces of the continuous structure. The layers may extend horizontally, vertically and/or along inclined surfaces. The layer may comprise a plurality of sub-layers. For example, the interconnect layer may include one or more conductors and contact sub-layers (in which interconnect lines and/or via contacts are formed), and one or more dielectric sub-layers.

In the embodiments of the present invention, the terms "first", "second", and the like are used for distinguishing similar objects, and are not necessarily used for describing a particular order or sequence.

The technical means described in the embodiments of the present invention may be arbitrarily combined without conflict.

In optical communication systems, an electro-optic modulator is a key device. There are generally three types of electro-optic modulators in commercial use today: lithium niobate-based electro-optic modulators, group iii-v material-based electro-optic modulators, and silicon-based electro-optic modulators. However, the traditional lithium niobate modulator has low modulation efficiency and large modulator size; the cost of manufacturing electro-optic modulators based on group iii-v materials is high. The silicon-based modulator can be compatible with the mature Complementary Metal Oxide Semiconductor (CMOS) process, so that the silicon-based modulator can be processed and prepared on a large scale, and the preparation cost of the electro-optical modulator is reduced.

Due to the central symmetrical structure of the silicon material, there is no Pockels (Pockels) effect, while the Kerr (Kerr) and Franz-keldis (Franz-keldis) effects of the silicon material are also extremely weak; even if applied 10⁵The change of refractive index generated by the electric field of V/cm is still less than 10^-5It is not practical to use the Kerr effect and the Franz-keldis effect to achieve electro-optic modulation effects. Therefore, in silicon materials, the most effective electro-optic effect is the Plasma Dispersion (Plasma Dispersion) effect. This effect can be expressed as: the refractive index of the material decreases with increasing carrier concentration in the material, and the absorption coefficient of the material for the optical field increases with increasing carrier concentration. By utilizing the effect, the carrier concentration in the silicon waveguide is changed through an external voltage signal, the transmission characteristic of light in the waveguide can be changed, and the electro-optic modulation purpose can be achieved through a certain optical structure, such as a Micro-Ring resonant cavity (MR). Since the plasma dispersion effect is quite remarkable in the electro-optical modulator, the silicon-based electro-optical modulator is mainly realized by the plasma dispersion effect of free carriers in the silicon material at present.

In the related art, considering that the modulation efficiency of the plasma dispersion modulator is low, in order to achieve an ideal modulation depth, the modulator needs to be designed to be very long, and the length is generally several millimeters, so that the size of the modulator is very large, the integration level is difficult to further improve, and the manufacturing cost is further increased. The size of the modulator can be greatly reduced by using a resonant structure such as a micro-ring resonator, a micro-disk resonator, or a photonic crystal resonator. Compared with the traditional optical resonant cavity, such as a Fabry-Perot (FP) resonant cavity, a butterfly resonant cavity and the like, the micro-ring resonant cavity does not need a cavity surface or a grating to provide feedback, so that the manufacturing process is simple. The micro-ring resonant cavity structure is combined with a waveguide with a small section and a high refractive index, so that the volume of the modulator can be reduced, the loss of the bent waveguide is reduced, and the electro-optic modulation rate is improved. Modulators based on micro-rings have the advantages of small size, high sensitivity and easy integration, and are always concerned by researchers in the industry.

In the related art, it is considered that the micro-ring modulator generally includes a P-type doped region and an N-type doped region juxtaposed in a horizontal direction (parallel to a surface of a substrate layer), and the P-type doped region and the N-type doped region constitute a lateral PN junction. Since the lateral PN junction is easier to fabricate, the micro-ring modulator generally employs the lateral PN junction. However, the lateral PN junction has small interaction with the optical field, which results in low modulation efficiency of the micro-ring modulator, thereby affecting the size of the micro-ring modulator.

Based on this, the embodiment of the invention aims to provide a subminiature micro-ring modulator and a preparation method thereof. According to the embodiment of the invention, the first doping structure and the second doping structure are sequentially stacked along the thickness direction of the substrate layer, and the vertical PN junction electrical modulation structure is formed at the junction of the first doping structure and the second doping structure, so that the vertical PN junction electrical modulation structure can increase the overlapping area between a PN junction depletion region and an optical wave mode field, and the interaction between optical waves and current carriers is improved, thereby improving the modulation efficiency; meanwhile, the vertical PN junction electrical modulation structure can reduce the size occupied by the modulation structure, thereby reducing the size of the micro-ring modulator, further improving the integration level of the photonic integrated chip and reducing the preparation cost. In addition, the coupling waveguide and the micro-ring resonance structure are directly formed on the substrate layer, and compared with a micro-ring modulator with the coupling waveguide and the micro-ring resonance structure formed in the flat waveguide layer, the micro-ring modulator avoids light loss caused by light leakage through the flat waveguide layer, further improves the modulation efficiency of the micro-ring modulator, and further reduces the size of the micro-ring modulator.

The embodiment of the invention provides a method for manufacturing a micro-ring modulator, wherein fig. 1 is a schematic flow chart illustrating the implementation of the method for manufacturing the micro-ring modulator according to the embodiment of the invention. As shown in fig. 1, the method comprises the steps of:

step 101, providing a substrate layer;

102, forming a coupling waveguide and a micro-ring resonance structure which are arranged in parallel on the substrate layer, wherein the micro-ring resonance structure comprises a first doping structure and a second doping structure which are sequentially stacked along the thickness direction of the substrate layer, and the doping types of the first doping structure and the second doping structure are opposite;

and 103, forming an electrode electrically connected with the micro-ring resonance structure.

Fig. 2a to fig. 2m are schematic cross-sectional views illustrating implementation steps of a method for manufacturing a micro-ring modulator according to an embodiment of the present invention. It should be understood that the operations shown in fig. 1 are not exclusive, and other operations may be performed before, after, or between any of the operations shown. The method for manufacturing the micro-ring modulator of the present embodiment is described below with reference to fig. 1 and fig. 2a to 2 m.

A step 101 is performed, as shown in fig. 2a, providing a substrate layer 10. In practice, the material of the substrate layer 10 may include, but is not limited to, silicon dioxide.

Next, step 102 is executed, a coupling waveguide 30 and a micro-ring resonant structure 40 are formed on the substrate layer 10, where the coupling waveguide 30 and the micro-ring resonant structure 40 are arranged in parallel, the micro-ring resonant structure 40 includes a first doping structure 41 and a second doping structure 42 that are sequentially stacked in a thickness direction of the substrate layer 10, and doping types of the first doping structure 41 and the second doping structure 42 are opposite.

Here, the micro-ring resonator structure 40 is configured to modulate light input from one end of the coupling waveguide 30 and coupled into the micro-ring resonator structure 40 under the action of the voltage supplied from the electrode 50, and the modulated light is output from the other end of the coupling waveguide 30. Specifically, the doping type of the first doping structure 41 is opposite to that of the second doping structure 42, so that a vertical PN junction electrical modulation structure is formed at the physical boundary of the first doping structure 41 and the second doping structure 42. According to the diffusion and drift effects of free carriers in the PN junction, when a forward bias is applied to the PN junction in the micro-ring resonance structure 40, a current is injected into a PN junction depletion region under the action of an external electric field, so that the concentration of the free carriers in the PN junction depletion region is increased sharply; when a reverse bias is applied to the PN junction in the micro-ring resonator structure 40, free carriers distributed in the PN junction are pumped away. Meanwhile, according to the plasma dispersion effect of the silicon material, when the concentration of free carriers in the silicon material changes, the refractive index of the silicon material changes. Thus, a change in the free carrier concentration in the PN junction will result in a change in the refractive index of the PN junction section waveguide material. When an external voltage is applied to the micro-ring resonant structure 40, the concentration of free carriers in the PN junction changes, so that the refractive index of the silicon material changes, the wavelength of the optical signal transmitted in the optical waveguide shifts, and the modulation effect on the optical signal is achieved.

In practical applications, the first doped structure 41 may include a ridge waveguide micro-ring, and the second doped structure 42 may include a polysilicon micro-ring. The ridge waveguide micro-ring and the polysilicon micro-ring covering the ridge waveguide micro-ring form a micro-ring resonant cavity.

In practical applications, the coupling waveguide 30 is located at a short distance (typically several hundred nanometers) from the micro-ring resonator structure 40, and light input at one end of the coupling waveguide 30 can be coupled into the micro-ring resonator structure 40 by evanescent waves. That is, the optical mode field in the coupling waveguide 30 couples with the waveguide in the micro-ring resonator structure 40, and a part of the light penetrates into the micro-ring resonator. When the light penetrating into the micro-ring resonant cavity meets a certain condition, resonance can occur in the micro-ring resonant cavity and is continuously enhanced due to the positive feedback effect, and meanwhile, part of the light can also be coupled out of the micro-ring and enter the coupling waveguide 30; if a certain condition is not met, the light in the micro-ring resonant cavity can be weakened continuously. Another portion of the light that is not coupled into the micro-ring resonator is output from the other end of the coupling waveguide 30. In practical application, when the wavelength of the transmitted light and the parameters of the radius of the micro-ring, the effective refractive index of the transmitted light in the micro-ring and the like satisfy a specific relationship, the light can resonate in the micro-ring and is continuously strengthened due to the action of positive feedback.

In the embodiment of the present invention, the micro-ring resonant structure 40 is specially designed, that is, a vertical PN junction electrical modulation structure is formed at a physical boundary between the first doping structure 41 and the second doping structure 42 by sequentially stacking the first doping structure 41 and the second doping structure 42 along the thickness direction of the substrate layer 10. It can be understood that, in the micro-ring resonant structure 40 provided by the present invention, the vertical PN junction electrical modulation structure can increase the overlapping area between the PN junction depletion region and the optical mode field, and improve the interaction between the optical wave and the carrier, thereby improving the modulation efficiency; meanwhile, the vertical PN junction electrical modulation structure can reduce the size occupied by the modulation structure, thereby reducing the size of the micro-ring modulator, further improving the integration level of the photonic integrated chip and reducing the preparation cost. In addition, the coupling waveguide 30 and the micro-ring resonator 40 are directly formed on the substrate layer 10, and compared with a micro-ring modulator in which the coupling waveguide 30 and the micro-ring resonator 40 are formed in a slab waveguide layer, light loss caused by light leakage through the slab waveguide layer is avoided, the modulation efficiency of the micro-ring modulator is further improved, and the size of the micro-ring modulator is further reduced.

In an embodiment, as shown in fig. 2b, a first material layer 20 is formed on the substrate layer 20. In practice, the refractive index of the first material layer 20 is smaller than that of the substrate layer 20. Here, the first material layer 20 may include, but is not limited to, single crystal silicon.

Next, a portion of the first material layer 20 is removed to form the coupling waveguide 30 and the first doped structure material layer 412. Here, the coupling waveguide 30 serves to receive incident light and output outgoing light. In practice, the material of the coupling waveguide 30 may include monocrystalline silicon. The projection of the coupling waveguide 30 on the predetermined plane comprises a long strip. Here, the predetermined plane is perpendicular to the thickness direction of the substrate layer 10.

It should be noted that, in the embodiments of the present invention, the specific structure of the coupling waveguide 30 is not limited. Specifically, the coupling waveguide 30 of the micro-ring modulator in the embodiment of the present invention may include a strip waveguide or an L-shaped waveguide, or other equivalent waveguide structures.

In practical application, as shown in fig. 2c, a first etching is performed on the first material layer 20 to form the coupling waveguide 30 and the first sub-material layer 411; the projection of the first sub-material layer 411 on a preset plane is circular; the first etch stops on the top surface of the substrate layer 20; the predetermined plane is perpendicular to the thickness direction of the substrate layer 20.

In practical application, as shown in fig. 2d, performing a second etching on the first sub-material layer 411 to form the first doped structure material layer 412 with a groove; the projection of the second etched and removed part of the first sub-material layer 411 on the preset plane is circular; the second etching is stopped in the first sub-material layer 411. Here, the projection of the side wall of the groove on the preset plane is annular, and the side wall of the groove and the bottom wall of the groove form the ridge waveguide micro-ring.

In practical applications, the first etching and the second etching may include, but are not limited to, Inductively Coupled Plasma (ICP) deep silicon etching.

In practice, the first etch stops on the top surface of the substrate layer 20, as shown in fig. 2 c. That is, the first material layer 20 around the coupling waveguide 30 and the first doped structure 41 is completely removed by the first etching, so that light loss caused by light leakage through the coupling waveguide 30 and the first material layer 20 around the first doped structure 41 is avoided, interaction between light waves and carriers is improved, and modulation efficiency of the micro-ring modulator is improved.

Next, the first doping structure material layer 412 is first doped to form the first doping structure 41.

In practical application, as shown in fig. 2e, a first sub-doping is performed on a middle region of the bottom of the groove in the first doping structure material layer 412 to obtain a first doping region 41A; performing second sub-doping on the remaining region of the first doped structure material layer 412, wherein the second sub-doping type is the same as the first sub-doping type, so as to obtain a second doped region 41B; wherein the first doped region 41A and the second doped region 41B together form the first doped structure 41. Here, the middle region of the bottom of the trench in the first layer 412 of doped structure material includes the region at and around the center of the bottom of the trench. In an embodiment, the middle region of the groove bottom comprises an area evenly distributed along the geometrical centre line of the groove bottom. The remaining regions of the first doped structure material layer 412 include regions other than the middle region of the trench bottom, specifically, the remaining regions include trench sidewalls and a trench bottom region other than the middle region.

Next, a second material layer 421 is formed on the first doping structure 41. In practical applications, the second material layer 421 includes polysilicon.

In one embodiment, the first material layer 20 and the second material layer 421 can be formed using one or more thin film deposition processes; specifically, the formation process of each Layer structure includes, but is not limited to, a Chemical Vapor Deposition (CVD) process, a Physical Vapor Deposition (PVD) process, an Atomic Layer Deposition (ALD) process, or a combination thereof.

In practical applications, before forming the second material layer 421 on the first doped structure 41, as shown in fig. 2f, a covering material layer 111 is further formed on the coupling waveguide 30 and the first doped structure 41. As shown in fig. 2g, a portion of the covering material layer 111 is removed to expose the top surfaces of the coupling waveguide 30 and the first doped structure 41. In practical applications, the manner of removing the portion of the cover material layer 111 includes, but is not limited to, Chemical Mechanical Polishing (CMP).

Next, as shown in fig. 2h, a second material layer 421 is formed on the first doping structure 41.

Next, as shown in fig. 2i, a portion of the second material layer 421 is removed to form a second doped structure material layer 422.

In practical applications, the projection of the second doped structure material layer 422 on the preset plane is annular; the sides of the second layer of doped structural material 422 are flush with the sides of the first layer of doped structural material 412. That is to say, along the stacking direction of the first doped structure material layer 412 and the second doped structure material layer 422, the outer side surfaces of the first doped structure material layer 412 and the second doped structure material layer 422 are located in the same plane, so that the exposed surface areas of the first doped structure 41 and the second doped structure 42 formed in the subsequent process can be reduced, further, the light scattering caused by surface roughness is reduced, the light loss in the first doped structure 41 and the second doped structure 42 is reduced, the interaction between the light wave and the carrier is improved, and the modulation efficiency of the micro-ring modulator is improved.

Next, the second doping structure material layer 422 is second doped to form the second doping structure 42.

In practical applications, as shown in fig. 2j, a third sub-doping is performed on the middle annular region of the second doping structure material layer 422, so as to obtain a third doping region 42A; performing fourth sub-doping on the remaining region of the second doping structure material layer 422, wherein the fourth sub-doping type is the same as the third sub-doping type, so as to obtain a fourth doping region 42B; wherein the third doped region 42A and the fourth doped region 42B together form the second doped structure 42.

In practical applications, the first doping may include either P-type doping or N-type doping; correspondingly, the second doping may include either N-type doping or P-type doping.

In one embodiment, the first doping comprises a P-type doping and the second doping comprises an N-type doping. That is, the first doped region 41A and the second doped region 41B include P-type doping, and the third doped region 42A and the fourth doped region 42B include N-type doping. The first doped region 41A is a P-type heavily doped region, and the second doped region 41B is a P-type lightly doped region; the third doped region 42A is an N-type heavily doped region, and the fourth doped region 42B is an N-type lightly doped region. Here, compared to the case where the second doping region 41B includes N-type doping and the fourth doping region 42B includes P-type doping, carriers in the P-type doping region are holes at the same voltage, so that more refractive index change can be generated and the loss is lower. Therefore, the modulation efficiency of the micro-ring modulator is higher when the second doped region 41B near the coupling waveguide 30 includes P-type doping.

In practical applications, the second doping region 41B (P-type lightly doped region) and the fourth doping region 42B (N-type lightly doped region) are in physical contact to form a vertical PN junction, and a carrier type in a depletion region near the P-type lightly doped region in the vertical PN junction is an electron. When a reverse bias is applied to the electrode 50, carriers distributed in the PN junction are extracted. In the above embodiment, since the P-type lightly doped region, i.e., the second doped region 41B, is closer to the coupling waveguide 30, the interaction between the carriers and the light waves in the second doped region 41B is stronger, and meanwhile, since the mobility of electrons is much greater than that of holes, when an external voltage is applied to the PN junction, the carriers near the P-type lightly doped region are more quickly pumped away, i.e., the carrier concentration in the second doped region 41B changes more quickly. Therefore, the modulation speed is faster as the rate of change of the carrier concentration in the second doped region 41B near the coupling waveguide 30 is faster. That is, when the second doped region 41B near the coupling waveguide 30 is a P-type lightly doped region, the modulation speed of the micro-ring modulator is faster.

In practical application, the first doped region 41A is a lightly doped region, and the second doped region 41B is a heavily doped region; the third doped region 42A is a lightly doped region, and the fourth doped region 42B is a heavily doped region. The first doped region 41A is in direct contact with the second doped region 41B to form a first doped structure 41 including a ridge waveguide microring; the third doped region 42A is in direct contact with the fourth doped region 42B to form a second doped structure 42 comprising a polysilicon microring. The ridge waveguide micro-ring and the polysilicon micro-ring covering the ridge waveguide micro-ring form a micro-ring resonant cavity. The micro-ring resonant cavity can limit light waves within a small range, and the size of the electro-optical modulator is greatly reduced.

In practical applications, the doping concentration of the first doping region 41A is higher than that of the second doping region 41B, and the doping concentration of the third doping region 42A is higher than that of the fourth doping region 42B, so as to reduce the contact resistance between the electrode and the doping region, and further improve the efficiency of the micro-ring modulator.

Next, step 103 is performed to form an electrode 50 electrically connected to the micro-ring resonant junction 40. In practice, an applied voltage is applied to the micro-ring resonator structure 40 through the electrodes 50. The electrodes 50 include a first electrode 51 and a second electrode 52. The first electrode 51 and the second electrode 52 are positive and negative electrodes, respectively, and are connected with the micro-ring resonant structure 40 to form a loop.

In practical applications, before forming the electrode 50, as shown in fig. 2k, a covering layer 11 covering the coupling waveguide 30 and the micro-ring resonator structure 40 is formed, and a refractive index of the covering layer 11 is smaller than that of the coupling waveguide 30 and the micro-ring resonator structure 40. Here, the material of the capping layer 11 may include, but is not limited to, silicon dioxide.

In practical applications, as shown in fig. 2l, a third etching is performed on the capping layer 11 to form a first electrode contact hole 510, where the third etching is stopped on the first doped structure 41; and performing fourth etching on the covering layer 11 to form a second electrode contact hole 520, wherein the fourth etching is stopped on the second doping structure 42.

In practical applications, the third etching and the fourth etching may include, but are not limited to, dry etching.

Next, as shown in fig. 2m, a conductive material is filled in the first electrode contact hole 510 to form the first electrode 51; the second electrode contact hole 520 is filled with a conductive material to form the second electrode 52. In practical applications, the top surface of the first electrode 51 and the top surface of the second electrode 52 may be higher than the top surface of the cover layer 11. Here, the conductive material may include, for example, gold, copper, aluminum, silver, and/or other suitable metal materials. In practical application, as shown in fig. 4, the projection of the first electrode 51 on the preset plane is circular; as shown in fig. 5, the projection of the second electrode 52 on the predetermined plane is annular. That is, the shape of the first electrode 51 may include a cylindrical shape; the shape of the second electrode 52 may include a circular ring shape. The first electrode 51 and the second electrode 52 may have other shapes.

It should be noted that although an exemplary method of forming a micro-ring modulator is described herein, it is understood that one or more steps may be omitted from the formation of such a micro-ring modulator.

Based on the preparation method of the micro-ring modulator, the embodiment of the invention also provides the micro-ring modulator. FIG. 3 is a schematic cross-sectional view taken along A-A of FIG. 2 m; FIG. 4 is a schematic cross-sectional view taken along line B-B of FIG. 2 m; fig. 5 is a schematic cross-sectional view along the direction C-C in fig. 2 m. As shown in fig. 2m, 3, 4 and 5, the micro-ring modulator includes: a substrate layer 10; the coupling waveguide 30 and the micro-ring resonant structure 40 are arranged on the substrate layer 10 in parallel, the micro-ring resonant structure 40 includes a first doping structure 41 and a second doping structure 42 which are sequentially stacked along the thickness direction of the substrate layer 10, and the doping types of the first doping structure 41 and the second doping structure 42 are opposite; and an electrode 50 electrically connected to the micro-ring resonator structure 40.

It should be noted that the micro-ring modulators shown in fig. 2m, fig. 3, fig. 4, and fig. 5 are only exemplary descriptions of the micro-ring modulators provided in the embodiments of the present invention, and should not be construed as limiting the micro-ring modulators.

In the above embodiment, the micro-ring resonant structure 40 is specially designed, that is, the first doping structure 41 and the second doping structure 42 are sequentially stacked along the thickness direction of the substrate layer 10, so that a vertical PN junction electrical modulation structure is formed at the physical boundary of the first doping structure 41 and the second doping structure 42. It can be understood that, in the micro-ring resonant structure 40 provided by the present invention, the vertical PN junction electrical modulation structure can increase the overlapping area between the PN junction depletion region and the optical mode field, and improve the interaction between the optical wave and the carrier, thereby improving the modulation efficiency; meanwhile, the vertical PN junction electrical modulation structure can reduce the size occupied by the modulation structure, thereby reducing the size of the micro-ring modulator, further improving the integration level of the photonic integrated chip and reducing the preparation cost. In addition, the coupling waveguide and the micro-ring resonance structure are directly formed on the substrate layer, and compared with a micro-ring modulator with the coupling waveguide and the micro-ring resonance structure formed in the flat waveguide layer, the micro-ring modulator avoids light loss caused by light leakage through the flat waveguide layer, further improves the modulation efficiency of the micro-ring modulator, and further reduces the size of the micro-ring modulator.

In an embodiment, the first doping structure 41 includes a first doping region 41A and a second doping region 41B which is the same doping type as the first doping region 41A and surrounds the first doping region 41A; the second doping structure 42 comprises a third doping region 42A and a fourth doping region 42B which is of the same doping type as the third doping region 42A and surrounds the third doping region 42A; wherein the first doped structure 41 and the second doped structure 42 are physically connected with the fourth doped region 42B through the second doped region 41B; the first doped region 41A is not in physical contact with the third doped region 42A.

In practical applications, the first doped region 41 and the second doped region 42 are physically connected to the fourth doped region 42B through the second doped region 41B to form a vertical PN junction; the change in carrier concentration in the vertical PN junction results in a change in the refractive index of the waveguide material in the PN junction region.

In one embodiment, the top surface of the coupling waveguide 30 is flush with the top surface of the second doped region 41B. On one hand, the top surface of the coupling waveguide 30 is flush with the top surface of the second doped region 41B, so that the coupling effect can be enhanced, and the interaction between the optical mode field and the carriers can be improved; on the other hand, the coupling waveguide 30 and the second doped region 41B may be completed in the same process, thereby simplifying the process.

In one embodiment, the projection of the coupling waveguide 30 on the predetermined plane is a long strip; the projection of the first doped region 41A on the preset plane is circular, and the projections of the second doped region 41B, the third doped region 42A and the fourth doped region 42B on the preset plane are all annular. That is, the micro-ring resonator structure 40 includes a ring-shaped modulation region, and the ring-shaped modulation region changes the concentration of carriers by an applied voltage, thereby changing the effective refractive index of the modulation region, and realizing the constructive and destructive of light. The annular modulation area realizes large influence of small refractive index change on transmission special effect through resonance effect, and realizes low power consumption and high modulation rate.

In an embodiment, the width of the physical contact between the second doped region 41B and the fourth doped region 42B is: 300 to 500 nanometers.

In practical application, in order to improve the efficiency of the micro-ring modulator, the width of the PN junction should cover the range of the optical mode field in the micro-ring as much as possible, but the width of the PN junction cannot be too large, otherwise the bandwidth of the micro-ring modulator is reduced, and generally the width of the PN is selected to be between 300 nanometers and 500 nanometers. In the above embodiments, a vertical PN junction is formed at the physical contact position between the second doped region 41B and the fourth doped region 42B, and the width of the PN junction is the diameter width of the physical contact position between the second doped region 41B and the fourth doped region 42B.

In practical applications, as shown in fig. 2m, the micro-ring modulator includes a coupling waveguide 30 having a straight waveguide and a micro-ring resonator structure 40 having a ring waveguide coupled thereto, in which case the micro-ring modulator is a single-ring single-waveguide structure. In some embodiments, the micro-ring resonator structure 40 includes a track-shaped waveguide, that is, the projection of the micro-ring resonator on the predetermined plane includes a track shape composed of two identical straight lines and two identical semi-circles. Of course, the embodiment provided by the present invention can also be extended to a multi-ring single waveguide structure, that is, the micro-ring modulator includes a coupling waveguide and a plurality of micro-ring resonant structures coupled thereto. In some embodiments, a coupling waveguide is arranged in parallel with a plurality of micro-ring resonant structures, and the plurality of micro-ring resonant structures are arranged along a direction in which the coupling waveguide extends. It should be noted that the "plurality of ring waveguides" herein refers to two or more ring waveguides. For both single and multiple rings, the resonance condition of the micro-ring modulator needs to be satisfied, that is, when the signal wavelength and the perimeter of the micro-ring resonator satisfy a certain condition, the optical signal is coupled into the micro-ring resonator.

It should be noted that the solution provided by the embodiments of the present invention is applicable to silicon-based micro-ring modulators, and also applicable to micro-ring modulators based on iii-v materials such as gallium arsenide (GaAs), indium phosphide (InP), P-type doped gallium nitride (GaN), and the like.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims

1. A method of making a micro-ring modulator, comprising:

providing a substrate layer;

2. The method for manufacturing a micro-ring modulator according to claim 1, wherein the forming of the coupling waveguide and the micro-ring resonator structure on the substrate layer in parallel comprises:

forming a first material layer on the substrate layer;

forming a second material layer on the first doped structure;

3. The method of claim 2, wherein the removing the portion of the first material layer comprises:

4. The method of claim 3, wherein the first doping the first doped structure material layer to form the first doped structure comprises:

5. The method of claim 3, wherein the projection of the second doped structure material layer on the predetermined plane is annular; the side edge of the second doping structure material layer is flush with the side edge of the first doping structure material layer;

6. The method of manufacturing a micro-ring modulator according to claim 2,

the first doping comprises P-type doping and the second doping comprises N-type doping.

7. The method of making a micro-ring modulator according to claim 1, further comprising:

8. The method of manufacturing a micro-ring modulator according to claim 7, wherein the electrodes comprise a first electrode and a second electrode; the forming of the electrode electrically connected to the micro-ring resonator structure includes:

9. A micro-ring modulator, comprising:

a substrate layer;

10. The micro-ring modulator of claim 9,

the first doping structure comprises a first doping region and a second doping region which is the same as the doping type of the first doping region and surrounds the first doping region;