CN116953850B - Lithium niobate thin film waveguide device and preparation method thereof - Google Patents

Abstract

The invention is applicable to the technical field of micro-nano processing of optical communication devices, and in particular relates to a lithium niobate thin film waveguide device and a preparation method thereof. The method includes: providing a lithium niobate thin film wafer; coating the lithium niobate thin film wafer with an electron beam photoresist, where the electron beam photoresist includes a positive resist; and passing the lithium niobate thin film wafer coated with the electron beam photoresist through Electron beam exposure, development, coating, and stripping processes are used to obtain marks and waveguide structure hard masks; the coating process includes metal plating, and the marks and waveguide structure hard masks are all made of metal materials; after the mark is protected, the waveguide structure hard mask is used, The lithium niobate film is etched through an etching process, and after cleaning, a marked lithium niobate film waveguide structure is obtained; a lithium niobate film waveguide device is obtained through the marked lithium niobate film waveguide structure. The invention improves the resolution and overlay precision and reduces overlay errors.

Description

A lithium niobate thin film waveguide device and its preparation method

Technical field

The invention is applicable to the technical field of micro-nano processing of optical communication devices, and in particular relates to a lithium niobate thin film waveguide device and a preparation method thereof.

Background technique

Since the 1960s, lithium niobate (LiNbO ₃ , LN) has become the most versatile and attractive due to its excellent electrical, nonlinear and acousto-optical properties, as well as its wide transparent window and relatively high refractive index. One of the photonic materials. Although LN has great potential, it generally lags behind other integrated photonic platforms due to the huge difficulties in material integration and processing.

With the rise, development, commercialization and breakthroughs in manufacturing technology of lithium niobate single crystal thin film (LNOI) technology, ultra-low loss, high refractive index contrast LN waveguides have now been realized. In the past few years, a complete set of integrated optical components has been developed on the LNOI platform, such as: compact and ultra-high performance modulators, broadband frequency comb sources, frequency conversion devices, and photon pair sources, etc. The platform can host a wide variety of devices, including various optical and optical microcavities, tunable filters, electro-optic modulators, acousto-optic modulators, microwave-optical transducers, nonlinear frequency converters, frequency combs, Non-classical light sources, detectors and quantum memories, etc. With such a rich set of component tools, the LNOI platform is expected to become a material platform for multifunctional, high-performance integrated optical circuits that enable classical and quantum applications.

In order to obtain the best measurement error, it is necessary to overlay the mark on the wafer. Some experts pointed out that using the LNOI platform to produce electro-optical modulators prepared by EBL high-precision alignment requires a two-step overlay method: first expose to make the mark (mark), and then For waveguide production, expensive HSQ electron beam exposure glue is required, which is not only cumbersome but also expensive. Although some people in the prior art have proposed a one-step overlaying solution for marks and waveguides at the same time, for example: the Chinese invention patent application document with application publication number CN 113985526 A, which discloses a lithium niobate thin film waveguide microring based on overlaying The preparation method, however, uses ultraviolet lithography, which results in uneven waveguide line widths, large sidewall roughness, large scattering effects, and high losses. It is not suitable for the preparation of lithium niobate film waveguides with a thickness less than 1000 nm.

At the same time, some people have proposed a one-step overlay technology solution based on electron beam lithography. For example, the Chinese invention patent application document with publication number CN111564363 A discloses a HSQ-based electron beam lithography preparation of overlay marks. The method is as follows: spin-coating HSQ photoresist on the wafer, pre-baking and then performing electron beam exposure. It utilizes the characteristics of HSQ as a negative photoresist to draw a mark exposure layout, and use the coordinate system established by the exposure layout to perform layout overlay. To reduce process steps, negative photoresist HSQ can be used to prepare overlay marks. Although this method can also achieve one-step overlaying to prepare lithium niobate thin film waveguide devices, HSQ electron beam exposure glue is expensive (200,000 yuan/L), and the production cost is too high, and HSQ glue exposure is based on the electron beam exposure system. The developed mark has poor conductivity and poor contrast, resulting in low resolution and large errors during overlay engraving.

Contents of the invention

In view of this, embodiments of the present invention provide a lithium niobate thin film waveguide device and a preparation method thereof to solve the problems of low overlay resolution and large errors during the preparation of existing lithium niobate thin film waveguide devices.

This application provides a method for preparing a lithium niobate thin film waveguide device, which includes the following steps:

Provide lithium niobate thin film wafers;

Coating an electron beam photoresist on the lithium niobate thin film wafer, the electron beam photoresist includes a positive photoresist;

The lithium niobate thin film wafer coated with electron beam photoresist is subjected to electron beam exposure, development, coating, and stripping processes to obtain the mark and waveguide structure hard mask; the coating process includes metal plating, and the mark and waveguide structure hard mask are metallic material;

After the mark protection treatment, the waveguide structure hard mask is used to etch the lithium niobate film through an etching process, and after cleaning, a marked lithium niobate film waveguide structure is obtained;

A lithium niobate thin film waveguide device is obtained through a labeled lithium niobate thin film waveguide structure.

In addition, this application also proposes a lithium niobate thin film waveguide device, which is prepared according to the above-mentioned preparation method of the lithium niobate thin film waveguide device.

Compared with the prior art, the lithium niobate film waveguide device and its preparation method of the present invention have beneficial effects as follows: for thinner lithium niobate films, the present invention uses markers and masks once under electron beam exposure technology. The overlay technology improves the resolution and overlay accuracy, reduces the overlay error, and the one-step overlay process greatly reduces the process steps.

Furthermore, in the above-mentioned lithium niobate thin film waveguide device and its preparation method, the step of dehydrating and baking the lithium niobate thin film wafer is also included before coating the lithium niobate thin film wafer with electron beam photoresist.

Furthermore, in the above-mentioned lithium niobate thin film waveguide device and its preparation method, after applying electron beam photoresist on the lithium niobate thin film wafer, the steps of baking, applying conductive glue, and baking are sequentially included.

Further, in the above-mentioned lithium niobate thin film waveguide device and its preparation method, electron beam photoresist is coated on the lithium niobate thin film wafer by rotating.

Further, in the above lithium niobate film waveguide device and its preparation method, the thickness of the lithium niobate film in the lithium niobate film wafer is 300-1200 nm.

Further, in the above-mentioned lithium niobate thin film waveguide device and its preparation method, the waveguide structure hard mask includes straight waveguide, microring, Y waveguide, S waveguide, MMI, and/or PBS waveguide structure.

Further, in the above-mentioned lithium niobate thin film waveguide device and its preparation method, the metal material plated in the coating process is chromium.

Further, in the above-mentioned lithium niobate thin film waveguide device and its preparation method, the thickness of chromium is greater than 150 nm.

Further, in the above lithium niobate thin film waveguide device and its preparation method, the electron beam photoresist includes PMMA.

Description of the drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings in the following description are only illustrative of the present invention. For some embodiments, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is a process flow chart of the preparation method of the lithium niobate thin film waveguide device of the present invention;

Figure 2 is a flow chart of the preparation method of the lithium niobate thin film waveguide device of the present invention;

Figure 3 is an optical microscope rendering of the present invention after PMMA exposure and development;

Figure 4 is an optical microscope rendering of the metal chromium Cr mask of the present invention after cleaning;

Figure 5a is a morphology diagram of the waveguide of the present invention after PMMA exposure, development, and metal chromium Cr mask cleaning;

Figure 5b is a waveguide morphology diagram of the prior art after HSQ (FOX16) exposure, development, and metal chromium Cr mask cleaning;

Figure 6a is a morphology diagram of the upper surface of the waveguide after PMMA exposure, development, and metal chromium Cr mask cleaning according to the present invention;

Figure 6b is a morphology diagram of the upper surface of the waveguide after HSQ (FOX16) exposure, development, and metal chromium Cr mask cleaning in the prior art;

Figure 7a is a morphological view of the side wall of the waveguide after PMMA exposure, development and metal chromium Cr mask cleaning according to the present invention;

Figure 7b is a morphological view of the waveguide sidewall after HSQ (FOX16) exposure, development, and metal chromium Cr mask cleaning in the prior art;

In the figure, 1. Silicon; 2. Silicon dioxide; 3. Lithium niobate film; 4. Electron beam photoresist; 5. Conductive glue; 6. Marker; 7. Waveguide structure hard mask; 8. Protective glue; 9. Metallic gold.

Detailed ways

As used in the description of the present invention and the appended claims, the term "if" may be interpreted as "when" or "once" or "in response to determining" or "in response to detecting" depending on the context. . Similarly, the phrase "if determined" or "if [the described condition or event] is detected" may be interpreted, depending on the context, to mean "once determined" or "in response to a determination" or "once the [described condition or event] is detected ]" or "in response to detection of [the described condition or event]".

In addition, in the description of the present specification and appended claims, the terms "first", "second", "third", etc. are only used to distinguish the description and shall not be understood as indicating or implying relative importance.

Reference in the specification of the invention to "one embodiment" or "some embodiments" or the like means that a particular feature, structure or characteristic described in connection with the embodiment is included in one or more embodiments of the invention. Therefore, the phrases "in one embodiment", "in some embodiments", "in other embodiments", "in other embodiments", etc. appearing in different places in this specification are not necessarily References are made to the same embodiment, but rather to "one or more but not all embodiments" unless specifically stated otherwise. The terms “including,” “includes,” “having,” and variations thereof all mean “including but not limited to,” unless otherwise specifically emphasized.

It should be understood that the sequence number of each step in the following embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

In order to illustrate the technical solution of the present invention, specific examples will be described below.

This embodiment proposes a method for preparing a lithium niobate thin film waveguide device, as shown in Figures 1 and 2, including the following steps:

S101. Provide lithium niobate thin film wafers and bake the lithium niobate thin film wafers.

In this step, the lithium niobate film wafer is shown in Figure 1, including silicon 1 (Si), silicon dioxide 2 (SiO ₂ ), and lithium niobate film 3 from bottom to top. The lithium niobate film 3 The thickness range is 300-1200nm. In this embodiment, the thickness of the lithium niobate film 3 is 600nm, and the lithium acid film wafer is an X-cut 600nm lithium niobate film wafer.

The specific baking steps are to place the X-cut 600nm lithium niobate film wafer on a 150°C hot plate for dehydration and baking for 2 minutes.

S102. Coat electron beam photoresist 4 on the lithium niobate thin film wafer and bake it.

In this step, the electron beam photoresist 4 coated on the lithium niobate thin film wafer includes a positive resist, such as PMMA. This type of electron beam photoresist 4 has high resolution, high contrast, is easy to peel off, and has low cost.

The electron beam photoresist 4 is coated on the lithium niobate thin film wafer in a rotating manner. In this embodiment, the rotation speed is 3000 r/min, and in order to enhance the stability and strength of the electron beam photoresist 4, the electron beam After the photoresist 4 is applied, place it on a 150°C hot plate for 5 minutes of baking.

The coating method of the electron beam photoresist can be replaced by other mature coating methods in the prior art, and the present invention is not limited to this.

S103. Then apply conductive adhesive 5 and bake.

In this step, the conductive adhesive 5 is also applied in a rotating manner, and after application, it is placed on an 80°C hot plate for baking for 1.5 minutes.

S104. Electronic exposure (EBL) and development process.

In this step, MIBK solution is used for development. The specific optical microscope effect after PMMA exposure and development is shown in Figure 3.

S105. Coating and lift off processes to obtain the mark 6 and the waveguide structure hard mask 7.

In this step, electron beam evaporation technology is used for coating, and the coating is metal plating. The mark 6 and the waveguide structure hard mask 7 are both made of metal materials, such as metal chromium Cr. The selectivity ratio of Cr to lithium niobate is high, so the selection is preferred. , In this embodiment, the thickness of the metal chromium is greater than 150nm, and NMP solution is used in the stripping process. Of course, as for the metal plating material, other materials with the same function can be used instead, and the present invention is not limited.

The waveguide structure hard mask 7 here includes different waveguide structures, specifically including straight waveguide, microring, Y waveguide, S waveguide, MMI, and/or PBS waveguide structure.

S106. Apply glue protection treatment to mark 6 and apply protective glue 8.

S107. Use the waveguide structure hard mask 7 to etch the lithium niobate film 3 through an etching process.

In this embodiment, the waveguide structure hard mask 7 is used to etch the lithium niobate film 3 through ICP (inductively coupled plasma).

S108. After cleaning, the lithium niobate thin film waveguide structure with mark 6 is obtained.

In this step, the waveguide structure hard mask 7 is etched away with a metal etching solution, the waveguide structure is cleaned with an RCA cleaning solution, and the protective glue 8 of the mark 6 is cleaned using an NMP solution. The optical microscope rendering after corrosion of the metal chromium Cr mask is shown in Figure 4.

S109. Obtain lithium niobate thin film waveguide device through the lithium niobate thin film waveguide structure with mark 6.

This step is a subsequent process for preparing the lithium niobate thin film waveguide device. It needs to be prepared according to the specific functions of the lithium niobate thin film waveguide device. The specific process includes the following steps:

a. Coat the lithium niobate thin film waveguide structure with the mark 6 obtained in step S108 with the electron beam photoresist 4 as required.

b. Electron beam exposure, development.

In this step, the pattern overlay is carried out according to the coordinate system established by the above-mentioned mark 6 exposure pattern, and the top electron beam photoresist 4 is developed.

c. After coating and peeling, a lithium niobate thin film waveguide device with mark 6 is obtained.

In this step, electron beam evaporation is used to evaporate 10 nm metal titanium (Ti) or 490 nm metal gold 9 (Au). At the same time, the stripping process can also be replaced by an etching process to remove the top electron beam photoresist 4 .

d. Plated protective film of silicon dioxide 2 (SiO ₂ ).

Step S109 is a subsequent step for preparing a lithium niobate thin film waveguide device. The specific manufacturing process can be other relatively mature processes in the existing technology, and is not limited by the present invention.

In order to verify the effect of the preparation method of the present invention, the waveguide morphology after HSQ (FOX16) exposure, development, and metal chromium Cr mask cleaning, and the waveguide morphology after PMMA exposure, development, and metal chromium Cr mask cleaning were analyzed. Comparison, the comparison results are shown in Figure 5a, Figure 5b, Figure 6a, Figure 6b, Figure 7a, Figure 7b. In the comparison result figure, the x and y coordinate axes represent the length of the test in the x and y directions (y direction is the propagation direction), Ra is the roughness. It can be seen that the roughness of the upper surface and side wall of the ridge waveguide prepared by the method of the present invention is basically not increased compared to the ridge waveguide produced by the expensive HSQ and complex process, and the scattering is not significantly increased.

The preparation method of the lithium niobate thin film waveguide device of the present invention adopts the technology of one-time overlaying of the mark 6 and the mask plate for the thinner lithium niobate film 3, which improves the overlaying accuracy and reduces the overlaying error in one step. The overlay process greatly reduces the process steps. The cost savings lies in the reduction of metal evaporation and lift-off process steps. It also reduces the pollution of the wafer by lift-off and improves the yield.

At the same time, electron beam photoresist 4 uses positive resist, which is beneficial to cost savings. HSQ electron beam exposure resist is expensive, about 200,000 yuan/L, and PMMA is less than 10,000 yuan/L, so the cost is greatly reduced.

In addition, this embodiment proposes a lithium niobate thin film waveguide device. The lithium niobate thin film waveguide device is prepared according to the above-mentioned preparation method of the lithium niobate thin film waveguide device. Regarding the specific implementation process of the preparation method, in the above method embodiment It has been introduced and will not be repeated here.

The above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions of the foregoing embodiments. Modifications are made to the recorded technical solutions, or equivalent substitutions are made to some of the technical features; however, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of each embodiment of the present invention, and should all be included in the present invention. within the scope of protection.

Claims (10)

1. The preparation method of the lithium niobate thin film waveguide device is characterized by comprising the following steps:

providing a lithium niobate thin film wafer;

coating electron beam photoresist on a lithium niobate thin film wafer, wherein the electron beam photoresist comprises positive photoresist;

carrying out electron beam exposure, development, coating and stripping on a lithium niobate film wafer coated with electron beam photoresist to obtain a mark and a waveguide structure hard mask; obtaining a mark while obtaining a waveguide structure hard mask; the coating process comprises metal plating, wherein the marks and the waveguide structure hard mask are all made of metal materials;

after the mark protection treatment, etching the lithium niobate thin film by using a waveguide structure hard mask through an etching process, and cleaning to obtain a lithium niobate thin film waveguide structure with a mark;

and obtaining the lithium niobate thin film waveguide device through the lithium niobate thin film waveguide structure with the marks.

2. The method of fabricating a lithium niobate thin film waveguide device of claim 1, further comprising a step of dehydration baking the lithium niobate thin film wafer before coating the electron beam resist on the lithium niobate thin film wafer.

3. The method of manufacturing a lithium niobate thin film waveguide device according to claim 1, further comprising the steps of baking, applying a conductive paste, and baking sequentially after applying an electron beam resist to the lithium niobate thin film wafer.

4. The method of fabricating a lithium niobate thin film waveguide device according to claim 1, wherein the electron beam resist is applied to the lithium niobate thin film wafer by spin-coating.

5. The method of manufacturing a lithium niobate thin film waveguide device according to claim 1, wherein the thickness of the lithium niobate thin film in the lithium niobate thin film wafer is 300 to 1200nm.

6. The method of fabricating a lithium niobate thin film waveguide device of claim 1, wherein the waveguide structure hard mask comprises a straight waveguide, a micro-ring, a Y-waveguide, an S-waveguide, an MMI, and/or a PBS waveguide structure.

7. The method of manufacturing a lithium niobate thin film waveguide device according to claim 1, wherein the metal material plated in the plating process is chromium.

8. The method of fabricating a lithium niobate thin film waveguide device of claim 7, wherein the thickness of chromium is greater than 150nm.

9. The method of fabricating a lithium niobate thin film waveguide device of claim 1, wherein the electron beam resist comprises PMMA.

10. A lithium niobate thin film waveguide device, characterized by being produced according to the production method of a lithium niobate thin film waveguide device according to any one of claims 1 to 9.