Optical splitter based on silicon nitride photonic crystal and preparation method thereof

Abstract

The present invention provides an optical splitter based on silicon nitride photonic crystal and a preparation method thereof, the optical splitter comprising: a silicon layer, a silicon oxide layer and a silicon nitride waveguide layer arranged in sequence from bottom to top; a two-dimensional silicon nitride photonic crystal waveguide is formed in the middle part of the silicon nitride waveguide layer, and grating emitters are formed at both ends; the two-dimensional silicon nitride photonic crystal waveguide comprises a row of circular grooves arranged periodically along the length direction of the silicon nitride waveguide layer and a silicon nitride waveguide layer in the middle part; the grating emitter is a semicircular concentric surrounding grating and has two semicircular hollow holes. The applicable bandwidth of silicon nitride material is large, and the silicon nitride grating designed with two semicircular hollow holes has low optical loss and high light emission efficiency; in addition, the optical beam splitter can realize the collection of off-chip light waves while transmitting and splitting light waves to form off-chip emitted light; finally, the preparation method is well compatible with CMOS technology, the process is simple, and it is easy to mass produce.

Description

Technical Field

[0001] The invention belongs to the field of semiconductors and optoelectronic integration, and in particular relates to an optical splitter based on silicon nitride photonic crystals and a preparation method thereof. Background Art

[0002] With the rise of smart devices and the popularity of social networks, the volume of communication business has exploded. Traditional electrical interconnection technology faces the problems of excessive power consumption and high latency due to the increase in the number of transistors and the exponential growth in chip throughput. The power consumed by global computing centers alone currently accounts for 0.8% of the world's total power generation. The development of silicon photonics technology provides an effective way to solve these problems. In the past few decades, silicon photonics technology on the silicon-on-insulator (SOI) platform has made great progress due to its compact footprint, high integration, low power consumption, and compatibility with complementary metal oxide semiconductor (CMOS) processes.

[0003] Silicon nitride (SiN) material is also the main material for expanding optical interconnection applications, and there are many studies on optical transmission. Based on the good optical properties of silicon nitride (SiN) near 700nm ~ 800nm, it is currently mostly used in grating coupling devices. Since different light sources and SiN structure designs will have different coupling efficiencies, it is possible to consider designing a new type of optical splitter based on silicon nitride photonic crystals. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide an optical splitter based on silicon nitride photonic crystals and a preparation method thereof, so as to apply the silicon nitride photonic crystal design to the optical splitter structure to expand the transmission wavelength of the existing optical splitter.

[0005] To achieve the above-mentioned object and other related objects, the present invention provides an optical splitter based on silicon nitride photonic crystal, the optical splitter comprising:

[0006] A silicon layer, a silicon oxide layer and a silicon nitride waveguide layer are sequentially arranged from bottom to top;

[0007] A two-dimensional silicon nitride photonic crystal waveguide is formed in the middle portion of the silicon nitride waveguide layer, and grating emitters are formed at both ends of the silicon nitride waveguide layer;

[0008] The two-dimensional silicon nitride photonic crystal waveguide comprises a row of circular grooves periodically arranged along the length direction of the silicon nitride waveguide layer and the middle portion of the silicon nitride waveguide layer, wherein the circular grooves extend from the surface of the silicon nitride waveguide layer to the inside of the silicon nitride waveguide layer;

[0009] The grating emitter is a semicircular concentric surrounding grating and has two semicircular hollow holes. The hollow holes extend from the surface of the silicon nitride waveguide layer to the silicon oxide layer.

[0010] Optionally, the thickness of the silicon oxide layer is between 900 nm and 1100 nm, and the thickness of the silicon nitride waveguide layer is between 280 nm and 320 nm.

[0011] Optionally, the extension depth of the annular hollow hole in the silicon oxide layer is between 750 nm and 850 nm.

[0012] Optionally, the width of the annular hollow hole is between 260nm and 360nm.

[0013] Optionally, a middle portion of the silicon nitride waveguide layer and two ends thereof are connected as waveguides.

[0014] Optionally, the width of the connecting waveguide is the same as that of the two-dimensional silicon nitride photonic crystal waveguide.

[0015] Optionally, the circular grooves in the two-dimensional silicon nitride photonic crystal waveguide have the same size and etching depth.

[0016] The present invention also provides a method for preparing an optical splitter based on silicon nitride photonic crystal, the preparation method comprising the following steps:

[0017] Providing a silicon nitride-on-insulator substrate, wherein the silicon nitride-on-insulator substrate comprises, from bottom to top, a silicon layer, a silicon oxide layer and a silicon nitride layer;

[0018] Etching the silicon nitride layer to form a silicon nitride waveguide layer;

[0019] Etching the middle portion of the silicon nitride waveguide layer to form a row of circular grooves periodically arranged along the length direction of the silicon nitride waveguide layer, so that the middle portion of the silicon nitride waveguide layer is formed into a two-dimensional silicon nitride photonic crystal waveguide;

[0020] The two ends of the silicon nitride waveguide layer are etched to form grating emitters at the two ends respectively. The grating emitters are semicircular concentric surrounding gratings and have two semicircular hollow holes. The hollow holes extend from the surface of the silicon nitride waveguide layer to the silicon oxide layer.

[0021] Optionally, before the step of forming the silicon nitride waveguide layer, the method further includes: a step of preparing an alignment mark on the silicon nitride layer.

[0022] Optionally, before the step of forming the grating emitter, the method further includes: forming a protective layer on the surface of the silicon nitride waveguide layer.

[0023] As described above, the optical splitter based on silicon nitride photonic crystal and the preparation method thereof of the present invention have a large applicable bandwidth using silicon nitride material, and the silicon nitride grating designed with two semicircular hollow holes has low optical loss and high light emission efficiency; in addition, the optical beam splitter can realize the collection of off-chip light waves while transmitting and splitting the light waves to form off-chip output light, that is, the optical beam splitter as a whole realizes off-chip splitting of the off-chip light waves after passing through the optical beam splitter of this embodiment. The function of the optical beam splitter lays the foundation for the interconnection between light wave layers in the future, and has important application value; finally, the preparation method is well compatible with the complementary metal oxide semiconductor (CMOS) process, the process is simple, and it is easy to mass produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Shown is a schematic diagram of the top view of the structure of the optical splitter based on silicon nitride photonic crystal of the present invention.

[0025] Figure 2 The optical splitter based on silicon nitride photonic crystal of the present invention is shown along Figure 1 Schematic diagram of the cross-sectional structure at the AA position.

[0026] Figure 3 Shown is the light field diagram of the grating emitter in the optical splitter based on silicon nitride photonic crystal of the present invention.

[0027] Figure 4 Shown is the far-field diagram of the grating emitter in the optical splitter based on silicon nitride photonic crystal of the present invention.

[0028] Figure 5 Shown is a process flow chart of a method for preparing an optical splitter based on silicon nitride photonic crystal according to the present invention.

[0029] Figures 6 to 11 The schematic diagram of the cross-sectional structure of each step in the method for preparing an optical splitter based on silicon nitride photonic crystal of the present invention is shown, and the cross-sectional cutting position of each step is Figure 1 AA position in.

[0030] Component number description

[0031] 10 Silicon Nitride on Insulator Substrate

[0032] 101 Silicon Layer

[0033] 102 Silicon oxide layer

[0034] 103 Silicon nitride layer

[0035] 104 Silicon nitride waveguide layer

[0036] 11 The middle part of the silicon nitride waveguide layer

[0037] 12 Two-dimensional silicon nitride photonic crystal waveguide

[0038] 121 Circular groove

[0039] 13 End of silicon nitride waveguide layer

[0040] 14 Grating Transmitter

[0041] 141 Concentric surround grating

[0042] 142 Annular Hole

[0043] 15 Connection Zone

[0044] 151 Connecting waveguide

[0045] 16 Alignment mark

[0046] 17 Alignment mark protection layer

[0047] Steps S1 to S4 DETAILED DESCRIPTION

[0048] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention 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 invention.

[0049] See also Figures 1 to 11 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0050] Example 1

[0051] like Figure 1 and Figure 2 As shown, this embodiment provides an optical splitter based on silicon nitride photonic crystal, and the optical splitter includes:

[0052] A silicon layer 101, a silicon oxide layer 102 and a silicon nitride waveguide layer 104 are sequentially arranged from bottom to top;

[0053] A two-dimensional silicon nitride photonic crystal waveguide 12 is formed in the middle portion 11 of the silicon nitride waveguide layer, and grating emitters 14 are formed at both ends of the silicon nitride waveguide layer 104;

[0054] The two-dimensional silicon nitride photonic crystal waveguide 12 comprises a row of circular grooves 121 arranged periodically along the length direction of the silicon nitride waveguide layer 104 and the silicon nitride waveguide layer 104 in the middle part, wherein the circular grooves 121 extend from the surface of the silicon nitride waveguide layer 104 to the inside of the silicon nitride waveguide layer 104;

[0055] The grating emitter 14 is a semicircular concentric surrounding grating 141 and has two semicircular hollow holes 142 . The hollow holes 142 extend from the surface of the silicon nitride waveguide layer 104 to the silicon oxide layer 102 .

[0056] The working principle of the optical splitter is as follows: a point light source polarized in the z direction (polarized in the direction perpendicular to the paper surface Ez) is placed on the upper end face of the two-dimensional silicon nitride photonic crystal waveguide 12, and the Ez polarized light emitted by the point light source enters the two-dimensional silicon nitride photonic crystal waveguide 12, and the light wave is transmitted through the two-dimensional silicon nitride photonic crystal waveguide 12, wherein the wavelength band of the transmitted light wave is between 750nm and 800nm, including the end values; the light wave is transmitted along the two-dimensional silicon nitride photonic crystal waveguide 12 to the grating emitter 14 at both ends of the silicon nitride waveguide layer 104, and is emitted by the concentric surrounding grating 141 with two semicircular ring hollow holes 142, so as to obtain two beams of completely identical output light, thereby realizing two-port light splitting. The silicon nitride material used in this embodiment has a large applicable bandwidth, and the silicon nitride grating designed with two semicircular hollow holes has low optical loss and high light emission efficiency. In addition, the optical beam splitter of this embodiment can realize the collection of off-chip light waves and simultaneously transmit and split the light waves to form off-chip emitted light, that is, the optical beam splitter as a whole realizes off-chip splitting of the off-chip light waves after passing them through the optical beam splitter of this embodiment. The function of the optical beam splitter lays the foundation for the subsequent interconnection between light wave layers and has important application value.

[0057] like Figure 6 As shown, as an example, the thickness H1 of the silicon oxide layer is between 900nm and 1100nm, including the end value, and the thickness H2 of the silicon nitride waveguide layer is between 280nm and 320nm, including the end value. Fig.11 As shown, as a preferred example, the extension depth H3 of the annular hollow hole 142 in the silicon oxide layer 102 is between 750nm and 850nm, including the end value. As another preferred example, the width of the annular hollow hole 142 is between 260nm and 360nm, including the end value.

[0058] like Figure 2 As shown, as an example, the middle part 11 of the silicon nitride waveguide layer and the end 13 of the silicon nitride waveguide layer are connected to each other in a connection area 15, and the silicon nitride waveguide layer of the connection area 15 is a connection waveguide 151. This embodiment does not limit the shape of the connection waveguide 151, and its shape can be designed according to the splitting direction requirements of the optical splitter, for example, it can be a shape with a gradually decreasing width from one end of the two-dimensional silicon nitride photonic crystal waveguide 12 to one end of the grating emitter 14, or it can be a shape with a uniform width, which is not limited here. In this embodiment, the width of the connection waveguide 151 is selected to be the same as that of the two-dimensional silicon nitride photonic crystal waveguide 12.

[0059] like Figure 2 As shown, as an example, the circular grooves 121 in the two-dimensional silicon nitride photonic crystal waveguide 12 have the same size and etching depth.

[0060] like Figure 3 and Figure 4 As shown, the optical splitter of this embodiment adopts the parameters that the thickness H1 of the silicon oxide layer is 1000nm, the thickness H2 of the silicon nitride waveguide layer is 300nm, the extension depth H3 of the annular hollow hole 142 in the silicon oxide layer is 800nm, the width of the annular hollow hole 142 is 300nm to form an optical splitter structure, and the transmission of light waves in the optical splitter when the Ez point light source is placed at a position about 5nm from the upper end surface of the two-dimensional silicon nitride photonic crystal waveguide 12. Figure 3 is the light field diagram of the grating emitter. The light incident from outside the chip is collected by the two-dimensional silicon nitride photonic crystal waveguide 12, and is transmitted to the grating emitters 14 at both ends along the waveguide, and is emitted by the hollow grating emitter 14 to obtain two identical outgoing off-chip lights. Figure 3 The efficiencies of the grating emitters 14 at both ends obtained are 32% respectively; Figure 4 This is a far-field image of the grating emitter 14. It can be clearly seen that the light is collected at a particularly small angle, which is conducive to later collection and utilization.

[0061] Example 2

[0062] This embodiment provides a method for preparing an optical splitter based on silicon nitride photonic crystals. The preparation method can be used to prepare the optical splitter based on silicon nitride photonic crystals described in Example 1. The beneficial effects that can be obtained by this method can be found in Example 1 and will not be described in detail here.

[0063] like Figure 5 As shown, the preparation method comprises the following steps:

[0064] like Figure 5 and Figure 6As shown, step S1 is first performed to provide a silicon nitride-on-insulator substrate 10 , wherein the silicon nitride-on-insulator substrate 10 includes a silicon layer 101 , a silicon oxide layer 102 , and a silicon nitride layer 103 in order from bottom to top.

[0065] As an example, the thickness of the silicon oxide layer 102 is between 900 nm and 1100 nm, including the endpoint values, and the thickness of the silicon nitride layer 103 is between 280 nm and 320 nm, including the endpoint values.

[0066] like Figure 5 and Fig. 9 As shown, step S2 is then performed to etch the silicon nitride layer 103 to form a silicon nitride waveguide layer 104 .

[0067] The parameters such as the shape and size of the silicon nitride waveguide layer 104 are not limited here, and are specifically designed according to the shape and size of the optical splitter to be formed subsequently.

[0068] like Figure 7 As shown, as an example, before the step of forming the silicon nitride waveguide layer 104, an alignment mark 16 is first prepared on the silicon nitride layer 103. The shape and size of the alignment mark 16 are not limited here, as long as the alignment function for the subsequent process can be achieved. Figure 8 As shown, preferably, after forming the alignment mark 16, an alignment mark protection layer 17 may be formed thereon to prevent damage to the alignment mark during a subsequent etching process. Preferably, the material of the alignment mark protection layer 17 is gold material.

[0069] As an example, the method of etching the silicon nitride layer 103 to form the silicon nitride waveguide layer 104 includes: coating a photoresist layer on the silicon nitride layer 103; then using electron beam etching (EBL for short) to etch the photoresist layer to form a patterned photoresist layer; then using ICP (inductively coupled plasma etching) to etch the silicon nitride layer 103 to form the silicon nitride waveguide layer 104; and finally removing the photoresist layer.

[0070] like Figure 5 , Figure 2 and Fig.10 As shown, step S3 is then performed to etch the middle portion 11 of the silicon nitride waveguide layer 104 to form a row of circular grooves 121 periodically arranged along the length direction of the silicon nitride waveguide layer 104, so that the middle portion of the silicon nitride waveguide layer 104 is formed into a two-dimensional silicon nitride photonic crystal waveguide 12.

[0071] As an example, the method of etching to form the two-dimensional silicon nitride photonic crystal waveguide 12 includes: coating a photoresist layer on the silicon nitride waveguide layer 104; then etching the photoresist layer using EBL to form a patterned photoresist layer; then etching the middle portion 11 of the silicon nitride waveguide layer 104 using ICP to form the circular groove 121, and the etching depth, diameter, period and other parameters of the circular groove 121 can be set according to actual needs and are not limited here; finally, removing the photoresist layer.

[0072] like Figure 5 and Fig.11 As shown, step S4 is finally performed to etch the two ends of the silicon nitride waveguide layer 104 to form grating emitters 14 at the two ends respectively. The grating emitter 14 is a semicircular concentric surrounding grating 141 and has two semicircular hollow holes 142. The hollow holes 142 extend from the surface of the silicon nitride waveguide layer 104 to the silicon oxide layer 102.

[0073] As an example, before forming the grating emitter 14, a protective layer, such as an aluminum-plated protective layer, is electroplated on the surface of the structure except for the area where the grating emitter 14 is located. The protective layer is equivalent to a mask plate. Since the etching depth of the annular hollow hole 142 is deep, the protective layer can effectively prevent damage to the device surface during the subsequent etching of the annular hollow hole 142.

[0074] As an example, the method of etching to form the grating emitter 14 includes: coating a photoresist layer on the silicon nitride waveguide layer 104; then etching the photoresist layer using EBL to form a patterned photoresist layer; then etching the end 13 of the silicon nitride waveguide layer 104 using ICP to form two semicircular hollow holes 142; and finally removing the photoresist layer.

[0075] The method for preparing the optical splitter based on silicon nitride photonic crystal in this embodiment is well compatible with the complementary metal oxide semiconductor (CMOS) process, has a simple process, and is easy to mass produce.

[0076] In summary, the present invention provides an optical splitter based on silicon nitride photonic crystal and a preparation method thereof. The applicable bandwidth of silicon nitride material is large, and the optical loss of the silicon nitride grating designed with two semicircular ring hollow holes is small, and the light emission efficiency is high; In addition, the optical beam splitter can realize the collection of off-chip light waves while transmitting and splitting the light waves to form off-chip emitted light, that is, the optical beam splitter as a whole realizes off-chip light splitting after the off-chip light waves pass through the optical beam splitter of this embodiment. The function of the optical beam splitter lays the foundation for the interconnection between light wave layers in the future, and has important application value; Finally, the preparation method is well compatible with the complementary metal oxide semiconductor (CMOS) process, the process is simple, and it is easy to mass produce. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0077] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. An optical splitter based on silicon nitride photonic crystal, characterized in that: The optical splitter comprises: A silicon layer, a silicon oxide layer and a silicon nitride waveguide layer are sequentially arranged from bottom to top; A two-dimensional silicon nitride photonic crystal waveguide is formed in the middle portion of the silicon nitride waveguide layer, and grating emitters are formed at both ends of the silicon nitride waveguide layer; The two-dimensional silicon nitride photonic crystal waveguide comprises a row of circular grooves periodically arranged along the length direction of the silicon nitride waveguide layer and the middle portion of the silicon nitride waveguide layer, wherein the circular grooves extend from the surface of the silicon nitride waveguide layer to the inside of the silicon nitride waveguide layer; The grating emitter is a semicircular concentric surrounding grating and has two semicircular hollow holes. The hollow holes extend from the surface of the silicon nitride waveguide layer to the silicon oxide layer.

2. The optical splitter based on silicon nitride photonic crystal according to claim 1, characterized in that: The thickness of the silicon oxide layer is between 900nm and 1100nm, and the thickness of the silicon nitride waveguide layer is between 280nm and 320nm.

3. The optical splitter based on silicon nitride photonic crystal according to claim 2, characterized in that: The extension depth of the annular hollow hole in the silicon oxide layer is between 750nm and 850nm.

4. The optical splitter based on silicon nitride photonic crystal according to claim 2, characterized in that: The width of the annular hollow hole is between 260nm and 360nm.

5. The optical splitter based on silicon nitride photonic crystal according to claim 1, characterized in that: The middle part of the silicon nitride waveguide layer and the two ends thereof are connected waveguides.

6. The optical splitter based on silicon nitride photonic crystal according to claim 5, characterized in that: The width of the connecting waveguide is the same as that of the two-dimensional silicon nitride photonic crystal waveguide.

7. The optical splitter based on silicon nitride photonic crystal according to claim 1, characterized in that: The circular grooves in the two-dimensional silicon nitride photonic crystal waveguide have the same size and etching depth.

8. A method for preparing an optical splitter based on silicon nitride photonic crystal, characterized in that: The preparation method comprises the following steps: Providing a silicon nitride-on-insulator substrate, wherein the silicon nitride-on-insulator substrate comprises, from bottom to top, a silicon layer, a silicon oxide layer and a silicon nitride layer; Etching the silicon nitride layer to form a silicon nitride waveguide layer; Etching the middle portion of the silicon nitride waveguide layer to form a row of circular grooves periodically arranged along the length direction of the silicon nitride waveguide layer, so that the middle portion of the silicon nitride waveguide layer is formed into a two-dimensional silicon nitride photonic crystal waveguide; The two ends of the silicon nitride waveguide layer are etched to form grating emitters at the two ends respectively. The grating emitters are semicircular concentric surrounding gratings and have two semicircular hollow holes. The hollow holes extend from the surface of the silicon nitride waveguide layer to the silicon oxide layer.

9. The method for preparing an optical splitter based on silicon nitride photonic crystal according to claim 8, characterized in that: Before the step of forming the silicon nitride waveguide layer, the method further includes: a step of preparing an alignment mark on the silicon nitride layer.

10. The method for preparing an optical splitter based on silicon nitride photonic crystal according to claim 8, characterized in that: Before the step of forming the grating emitter, the method further includes: forming a protective layer on the surface of the silicon nitride waveguide layer.

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