Grating with phase shift and preparation method thereof

Abstract

The invention relates to the technical field of optical processing, in particular to a grating with phase shift and a preparation method thereof, masks with different thicknesses are prepared on the surface of a wafer, mask areas with different thicknesses are etched into a periodic uniform grating structure through a displacement Talbot effect grating photoetching technology, and then the grating with phase shift is prepared through an inclined etching mode. The masks with different thicknesses are utilized to shield different areas of the to-be-etched surface, then the grating with the phase shift can be obtained, the thickness difference of different mask areas and the inclined etching angle can be adjusted according to needs in actual production, and then the phase shift amount is accurately controlled. According to the invention, the limitation of a displacement Talbot effect grating photoetching technology in the aspect of introducing local phase shift is successfully broken through, the limitation that the displacement Talbot effect grating photoetching technology is only suitable for manufacturing a large-size and periodic grating structure is solved, and the application requirement of a current high-precision phase shift DFB laser can be met.

Description

Technical Field

[0001] The invention relates to the technical field of optical processing, and specifically provides a grating with a phase shift and a preparation method thereof. Background Art

[0002] With the rapid development of technologies such as big data, cloud computing, quantum communication, 5G communication, and lidar, the performance requirements for lasers, such as high power, narrow linewidth, tunability, high stability, high reliability, and high modulation rate, are constantly increasing. Semiconductor lasers with advantages such as small size, long working life, and high energy conversion efficiency are increasingly valued. Compared with FP semiconductor lasers with wide linewidth and multi-longitudinal mode lasing, distributed feedback Bragg (DFB) semiconductor lasers with narrow linewidth, single longitudinal mode lasing, and direct modulation are becoming the core of various active devices. Compared with ordinary FP cavity lasers, DFB lasers add a grating layer above or below the active region. The grating achieves resonance selection of a specific wavelength by periodically perturbing the physical parameters (refractive index or gain / loss) of the laser waveguide and active region. DFB lasers with uniform grating period are dual-mode lasing during operation, and their single-mode yield is low even if an end-face reflection film is introduced. Using phase-shift grating structure for mode selection is currently a popular solution.

[0003] At present, the commonly used technical means for preparing phase-shift gratings are: using holographic gratings plus phase-shift masks and electron beam lithography, but electron beam lithography requires expensive electron beam lithography machines, has high environmental requirements, and the speed of electron beam lithography is slow, and it takes a long time to fill a large-size epitaxial wafer; holographic lithography plus phase-shift masks to prepare phase-shift gratings can quickly obtain the corresponding structure, but it is difficult to obtain high uniformity and precision due to the limitations of holographic lithography itself.

[0004] In addition, the displacement Talbot effect grating preparation technology is a new type of lithography technology based on the laser Talbot self-imaging effect. This technology uses a phase mask to repeatedly move the substrate during lithography, thereby integrating the light field energy in the space in the photoresist, thereby obtaining a photoresist grating lithography pattern with steep and smooth side walls. The photoresist side walls have high precision in the subsequent transfer to the wafer. However, it is limited by its principle: using the movement of the chip to be prepared in the direction perpendicular to the photomask, the grating pattern prepared can only be a large-scale periodic uniform structure. For non-periodic grating structures with phase shifts, they cannot be prepared using the displacement Talbot effect grating preparation technology. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a grating with phase shift and a preparation method thereof. By preparing masks of different thicknesses and cooperating with an inclined etching method, different width areas of the etched surface are shielded by masks of different thicknesses, and grating phase shift is achieved at the junction of masks of different thicknesses, thereby solving the technical difficulty of introducing phase shift in local areas when preparing gratings using the displacement Talbot effect grating lithography technology.

[0006] To achieve the above object, the technical solution created by the present invention is implemented as follows: In one aspect, the present invention provides a method for preparing a grating with a phase shift, comprising: Prepare a first thickness mask area and a second thickness mask area on the surface to be etched of the substrate; etching the first thickness mask region and the second thickness mask region into a periodic grating structure; Using the periodic grating structure as a mask, the substrate is etched from a direction that is not perpendicular to the surface to be etched, and a grating with a phase shift is obtained after removing the first thickness mask area and the second thickness mask area.

[0007] Preferably, the substrate is a wafer Preferably, the first thickness mask region and the second thickness mask region are both made of dielectric materials.

[0008] Preferably, the preparation process of the first thickness mask area and the second thickness mask area is: Silicon dioxide is deposited on the surface to be etched of the substrate by PECVD equipment, and the silicon dioxide in some areas is thinned. The thinned area is the first thickness mask area, and the unthinned area is the second thickness mask area.

[0009] Preferably, the thickness of the first thickness mask region is half of the thickness of the second thickness mask region.

[0010] Preferably, before etching the first thickness mask area and the second thickness mask area into the periodic grating structure, the method further includes: The photoresist is spin-coated on the first thickness mask area and the second thickness mask area, and the upper surface of the photoresist is parallel to the surface to be etched of the substrate.

[0011] Preferably, the photoresist is exposed based on the shifted Talbot effect to obtain a photoresist with a periodic grating pattern; Using a photoresist with a periodic grating pattern as a mask, vertical etching is performed on the first thickness mask area and the second thickness mask area to obtain a periodic grating structure.

[0012] Preferably, after etching the first thickness mask area and the second thickness mask area into the periodic grating structure, the method further includes: removing the photoresist on the periodic grating structure and placing the substrate tilted relative to the horizontal plane.

[0013] Preferably, the requirement for the tilt angle of the substrate is that, in the vertical direction, the periodic grating structure of the first thickness mask area and the periodic grating structure of the second thickness mask area do not completely cover the surface of the substrate to be etched.

[0014] On the other hand, the present invention provides a grating with a phase shift, which is prepared by a method for preparing a grating with a phase shift.

[0015] Compared with the prior art, the invention can achieve the following beneficial effects: The present invention provides a grating preparation scheme capable of introducing phase shift locally in the process of preparing a grating using the displacement Talbot effect. By adopting a combination of masks of different thicknesses and the tilted etching technology, in the tilted etching process, since masks of different thicknesses block different areas of the etched surface, the widths of the grating lines obtained by etching will also be different, and the required phase shift effect will be generated at the intersection where the mask thickness changes. The method effectively overcomes the technical challenge of introducing local phase shift in the displacement Talbot effect grating lithography technology, solves the disadvantage that the displacement Talbot effect grating preparation technology can only be used to prepare large-size, periodic grating structures, and provides an innovative solution for accurately controlling the grating structure.

[0016] The present invention is mainly applied to the preparation technology of displacement Talbot effect grating, and has the advantages of displacement Talbot effect grating preparation technology, such as high etching accuracy, high preparation efficiency, low economic cost and the like in preparing the grating, and solves the problems of complex preparation process, low preparation efficiency, high economic cost and the like of traditional phase-shift grating.

[0017] In addition, the thickness difference of masks of different thicknesses and the angle of inclined etching in the present invention can be adjusted in actual production, thereby accurately controlling the magnitude of the grating phase shift, which can meet the application requirements of high-precision phase-shifted DFB lasers and is beneficial to improving the single-mode yield of DFB lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings: Figure 1 is a flow chart of a method for preparing a grating with phase shift provided in an embodiment of the present invention; Figure 2 is a process flow chart of preparing a grating with phase shift according to an embodiment of the present invention; Figure 3 is a schematic diagram of oblique etching provided according to an embodiment of the present invention.

[0019] Reference numerals include: Wafer 1, silicon dioxide layer 2, thin mask 21, etching blocking area 211 of thin mask 21, thick mask 22, etching blocking area 221 of thick mask 22, photoresist 3, phase shift area 4, stage 5. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the invention clearer, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the invention and do not constitute a limitation to the invention. Similar components in different embodiments use associated similar component numbers. In the following embodiments, many detailed descriptions are to enable the invention to be better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other components, materials, and methods. In some cases, some operations related to the invention are not shown or described in the specification, in order to avoid the core part of the invention being overwhelmed by too much description, and for those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0021] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment and are not meant to be a necessary sequence, unless otherwise specified that a certain sequence must be followed.

[0022] In the description of the invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0023] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0024] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0025] See also Figure 1 and Figure 2 In one embodiment of the present invention, a method for preparing a grating with a phase shift is provided, which mainly aims at realizing a phase shift in a specific area by using a displacement Talbot effect grating lithography technology, and solves the technical difficulty of introducing a phase shift in a local area during the preparation of a grating by using the displacement Talbot effect grating lithography technology. The specific preparation process is as follows: S1: First, a substrate to be prepared is provided, which is a wafer 1 in the embodiment of the present invention. A silicon dioxide layer 2 having a certain thickness is deposited on the surface to be etched of the wafer 1 by using PECVD (plasma enhanced chemical vapor deposition) equipment. The thickness of the silicon dioxide layer 2 is usually controlled in the range of 400 to 1200 nanometers, providing a basis for subsequent photolithography.

[0026] After the silicon dioxide layer 2 is prepared, a part of the silicon dioxide layer 2 is thinned by photolithography, etching and other techniques. The thinned silicon dioxide layer 2 area is called the first thickness mask area, and the unthinned silicon dioxide layer 2 area is called the second thickness mask area. In the embodiment of the present invention, both the first thickness mask area and the second thickness mask area are prepared by dielectric materials, specifically silicon dioxide materials. In addition, other dielectric materials such as silicon nitride, tantalum oxide, titanium oxide, etc. can also be used, and multiple dielectric materials can be used at the same time.

[0027] As a preferred embodiment, the silicon dioxide layer 2 can be subjected to multi-stage thinning treatment, that is, the silicon dioxide layer 2 is prepared into a mask area with multiple thickness gradient changes, correspondingly recorded as a first thickness mask area, a second thickness mask area, a third thickness mask area, ..., an Nth thickness mask area. The thickness difference of different mask areas can be designed according to actual preparation requirements.

[0028] In the embodiment of the present invention, only the first thickness mask area and the second thickness mask area are taken as examples for description. For the convenience of description, the first thickness mask area is simply referred to as thin mask 21, and the second thickness mask area is simply referred to as thick mask 22. The thickness of thin mask 21 should be half of the thickness of thick mask 22, that is, it should be controlled between 200 and 600 nanometers.

[0029] S2: After preparing a thin mask 21 and a thick mask 22 on the wafer 1, a layer of photoresist 3 is spin-coated on the surface of the thin mask 21 and the thick mask 22, so that the upper surface of the photoresist 3 is parallel to the surface to be etched of the wafer 1, to ensure the uniformity and flatness of the photoresist 3, and to facilitate the subsequent photolithography by the displacement Talbot effect grating lithography technology. After the photoresist 3 is spin-coated, the wafer 1 is placed in a baking device for pre-baking to avoid deformation and defects during the photolithography process. After baking, a periodic grating structure is etched on the thin mask 21 and the thick mask 22 by a large-area displacement Talbot effect grating lithography technology, that is, the baked wafer 1 is placed at the Talbot distance of the ultraviolet lithography machine for exposure, and a periodic light intensity distribution is formed on the surface of the photoresist 3 by using the displacement Talbot effect, and a periodic grating pattern is formed on the photoresist 3.

[0030] S3: Using the photoresist 3 with a periodic grating pattern as a mask, use the IPC equipment to vertically etch the thin mask 21 and the thick mask 22 on the surface to be etched of the wafer 1. The etching depth set by the IPC equipment is equal to the thickness of the thick mask 22. The etching gas in this step will hardly cause etching damage to the surface to be etched of the wafer 1, and will only etch the thin mask 21 and the thick mask 22 to form a periodic grating structure.

[0031] S4: The wafer 1 is immersed in a dissolving solution of the photoresist 3. Usually, the wafer 1 is first immersed in acetone, which is a strong organic solvent that can effectively dissolve the photoresist 3. After the acetone immersion is completed, the wafer 1 is then transferred to anhydrous ethanol for immersion. Anhydrous ethanol is a cleaning agent that can further remove residues on the sample surface, including acetone and photoresist 3 that has not been completely removed.

[0032] After the photoresist 3 is removed, the wafer 1 is rinsed and dried, and finally a periodic grating structure without the photoresist 3 is formed. A grating structure with a thickness of h1 is formed on the thin mask 21, and a grating structure with a thickness of h2 is formed on the thick mask 22. h1 and h2 are the thicknesses of the thin mask 21 and the thick mask 22, respectively, and the thicknesses of the two are different.

[0033] S5: Place the wafer 1 prepared in S4 with the surface to be etched facing upward on a Figure 3 On the inclined stage 5 shown, the inclined angle between the plane of the stage 5 and the horizontal plane is θ. The stage 5 with the wafer 1 is placed in the ICP device for inclined etching. In this process, the etching only acts on the wafer 1, and the thin mask 21 and the thick mask 22 are not etched. Since the surface to be etched and the etching direction are not perpendicular, the angle between the two is θ. The angle θ or the inclination angle θ of the stage 5 is required as follows: from the vertical direction, the periodic grating structure of the thin mask 21 and the periodic grating structure of the thick mask 22 do not completely cover the surface to be etched of the wafer 1, that is, the numerical projections of the periodic grating structures of the thin mask 21 and the thick mask 22 do not completely cover their corresponding surfaces to be etched. In the process of etching using the periodic grating structure of the thin mask 21 and the thick mask 22 as masks, since the thicknesses of the thin mask 21 and the thick mask 22 are different, the projection areas of the thin mask 21 and the thick mask 22 in the vertical direction will also be different, that is, the widths of the etching shielding area 211 of the thin mask 21 and the etching shielding area 221 of the thick mask 22 are different, and the corresponding etching widths are also different. Therefore, after etching, a plurality of etching shielding areas 211 of the thin mask 21 with a width of L1 will be formed on the surface to be etched of the wafer 1, and a plurality of etching shielding areas 221 of the thick mask 22 with a width of L2 will be formed on the surface to be etched of the wafer 1 where the thick mask 22 is located. The values ​​of L1 and L2 are different. Since the values ​​of the widths L1 and L2 of the etching shielding area 211 and the etching area 221 are different, the junction of the thin mask 21 and the thick mask 22 is the phase shift area 4.

[0034] S6: Using BOE (buffered oxide etchant) solution to remove the thin mask 21 and the thick mask 22 on the wafer 1 after the tilt etching, the preparation of the grating with phase shift is completed, which solves the problem that the displacement Talbot effect grating preparation technology can only be used to prepare large-size, periodic grating structures and cannot introduce phase shift locally. The grating prepared by the embodiment of the present invention has the advantages of high etching accuracy, high preparation efficiency, and low economic cost of the displacement Talbot effect grating preparation technology.

[0035] The grating with phase shift prepared by the method for preparing a grating with phase shift shown in an embodiment of the present invention is suitable for the application requirements of high-precision phase-shifted DFB lasers. Applying the grating in the DFB laser can improve the single-mode yield of the DFB laser and avoid the introduction of an end face reflection film in the DFB laser, which leads to problems such as single-mode yield.

[0036] In short, the above description is only a preferred embodiment of this specification and is not intended to limit the protection scope of this specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this specification shall be included in the protection scope of this specification.

[0037] The systems, devices, modules or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0038] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0039] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0040] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A method for preparing a grating with phase shift, characterized in that: include: Prepare a first thickness mask area and a second thickness mask area on the surface to be etched of the substrate; etching the first thickness mask region and the second thickness mask region into a periodic grating structure; The substrate is etched from a direction non-perpendicular to the surface to be etched using the periodic grating structure as a mask, and a grating with a phase shift is obtained after removing the first thickness mask area and the second thickness mask area.

2. The method for preparing a grating with phase shift according to claim 1, characterized in that: The substrate is a wafer.

3. The method for preparing a grating with phase shift according to claim 1, characterized in that: The first thickness mask region and the second thickness mask region are both made of dielectric materials.

4. The method for preparing a grating with phase shift according to claim 3, characterized in that: The preparation process of the first thickness mask area and the second thickness mask area is: Silicon dioxide is deposited on the surface to be etched of the substrate by PECVD equipment, and the silicon dioxide in a partial area is thinned. The thinned area is the first thickness mask area, and the unthinned area is the second thickness mask area.

5. The method for preparing a grating with phase shift according to claim 1, characterized in that: Before etching the first thickness mask area and the second thickness mask area into a periodic grating structure, the method further includes: A photoresist is spin-coated on the first thickness mask area and the second thickness mask area, wherein the upper surface of the photoresist is parallel to the surface to be etched of the substrate.

6. The method for preparing a grating with phase shift according to claim 5, characterized in that: Exposing the photoresist based on the displacement Talbot effect to obtain a photoresist with a periodic grating pattern; The first thickness mask area and the second thickness mask area are vertically etched using a photoresist with a periodic grating pattern as a mask to obtain the periodic grating structure.

7. The method for preparing a grating with phase shift according to claim 6, characterized in that: After etching the first thickness mask area and the second thickness mask area into a periodic grating structure, the method further includes: removing the photoresist on the periodic grating structure and placing the substrate tilted relative to a horizontal plane.

8. The method for preparing a grating with phase shift according to claim 7, characterized in that: The requirement for the tilt angle of the substrate is that, from a vertical direction, the periodic grating structure of the first thickness mask area and the periodic grating structure of the second thickness mask area do not completely cover the surface of the substrate to be etched.

9. A grating with phase shift, characterized in that: The grating is prepared by the method for preparing a phase-shifted grating as described in any one of claims 1 to 8.

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