MEMS micromirror structure fabrication method and MEMS micromirror structure
By employing glass substrate and silicon wafer thinning technology in MEMS micromirror structures, combined with photolithography, etching and bonding processes, the micromirror structure is formed stepwise through etching. This solves the problems of complex and high cost in the traditional MEMS micromirror structure fabrication process, and achieves higher integration and design flexibility.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- PEKING UNIV
- Filing Date
- 2026-02-27
- Publication Date
- 2026-05-26
AI Technical Summary
Traditional MEMS micromirror fabrication techniques are complex and costly, making them incompatible with other technologies. This limits the integration of MEMS micromirrors with other devices and results in insufficient design flexibility and product yield.
Using glass substrate and silicon wafer thinning technology, combined with photolithography, etching and bonding processes, a MEMS micromirror structure is formed through step-by-step etching. This includes forming a micromirror anchor layer and a comb layer on the back of the silicon wafer, and forming mirror electrodes through multiple etching processes. A protective layer is used to avoid the etching from affecting the substrate.
It reduces the complexity and cost of the manufacturing process, improves the process tolerance, product yield and design flexibility, enhances the integration with other devices, and reduces the adverse effects of deep etching on the comb tooth surface.
Smart Images
Figure CN121742115B_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of micro-electro-mechanical systems (MEMS) technology, and in particular to a method for fabricating a MEMS micromirror structure and the MEMS micromirror structure. Background Technology
[0002] With the development of the information society, high-speed, high-capacity, flexible, and reconfigurable optical communication networks have become an important means of communication. Core dynamic optical devices such as optical switches, tunable filters, and wavelength-selective switches are crucial components of modern optical communication systems. Traditional dynamic optical devices often face problems such as large size, high power consumption, limited switching speed, and high cost, making it difficult to meet the rapid development needs of modern optical communication equipment.
[0003] The rise of microelectromechanical systems (MEMS) technology has provided an important solution to the above problems. Traditional MEMS micromirror fabrication techniques are complex and costly, and are difficult to integrate with other technologies, thus limiting the integration of MEMS micromirrors with other devices. Summary of the Invention
[0004] According to various embodiments of this disclosure, a method for fabricating a MEMS micromirror structure and a MEMS micromirror structure are provided, which can at least reduce the complexity and cost of the fabrication process and improve the process tolerance, product yield, design flexibility and integration.
[0005] According to some embodiments, a first aspect of this disclosure provides a method for fabricating a MEMS micromirror structure, comprising:
[0006] Provide a substrate to form a protective layer covering the target surface of the substrate;
[0007] A silicon wafer is provided, the back side of which includes a first sacrificial layer for defining a micromirror anchor layer;
[0008] A first patterned photoresist layer is formed over the first sacrificial layer to define the back comb layer;
[0009] A back comb layer is formed within the silicon wafer based on the first patterned photoresist layer;
[0010] Based on the first sacrificial layer and the back comb layer, the silicon wafer is etched to obtain the protrusion located directly below the first sacrificial layer and the micromirror anchor layer surrounded by the protrusion.
[0011] After removing the first sacrificial layer, the top surface of the boss is bonded to the substrate so that the boss surrounds the protective layer;
[0012] After forming a mirror electrode on the front side of the thinned silicon wafer, a first patterned mask layer is formed to cover the mirror electrode;
[0013] The silicon wafer is etched at least twice based on the first patterned mask layer to form a MEMS micromirror structure.
[0014] The MEMS micromirror structure fabrication method in the above embodiments can use a glass substrate, and the thickness of the silicon wafer can be freely controlled by thinning, reducing the thickness and volume of the MEMS micromirror structure. A composite mask etching process forms a back comb layer, allowing for free control of the comb tooth height difference and improving the flexibility of the MEMS micromirror structure design. Based on the first sacrificial layer and the back comb layer, the silicon wafer is etched to obtain a protrusion located directly below the first sacrificial layer and a micromirror anchor layer surrounded by the protrusion. After removing the first sacrificial layer, the top surface of the protrusion is bonded to the substrate, so that the protrusion surrounds the protective layer. The silicon wafer is then etched at least twice using photolithography, etching, and other processes to form the MEMS micromirror structure. The protective layer not only prevents the etching process from adversely affecting the substrate but also reduces the complexity of subsequent bonding alignment. Since standard processes such as photolithography, etching, and bonding are used, the process compatibility is stronger, the process difficulty is lower, and there is no need to develop other supporting non-standard processes. Multiple etching processes to form the MEMS micromirror structure can reduce the adverse effects of deep etching on the comb tooth surface.
[0015] According to some embodiments, the target surface is used to define a MEMS micromirror structure; forming a protective layer covering the target surface of the substrate includes: forming a first patterned photoresist layer on the surface of the pretreated substrate, the first patterned photoresist layer defining the target surface; magnetron sputtering a metal layer, the metal layer covering the first patterned photoresist layer and the target surface; removing the metal layer and the first patterned photoresist layer outside the target surface, the metal layer remaining on the target surface constituting the protective layer. The protective layer can not only avoid adverse effects on the substrate from subsequent etching processes, but also reduce the complexity of subsequent bonding alignment. By first forming the first patterned photoresist layer that exposes the target surface, and then magnetron sputtering to form a metal layer covering the first patterned photoresist layer and the target surface, the metal layer directly above the first patterned photoresist layer can be removed simultaneously during the peeling and removal of the first patterned photoresist layer, reducing the complexity and cost of the fabrication process.
[0016] According to some embodiments, an acetone solution is used to remove the first patterned photoresist layer and the metal layer directly above it, avoiding corrosion of the metal layer directly above the target surface and reducing the complexity and cost of the fabrication process.
[0017] According to some embodiments, a silicon wafer is provided, comprising: forming a silicon dioxide layer on the surface of an initial silicon wafer after pre-processing; forming a second patterned photoresist layer on the top surface of the silicon dioxide layer; using the second patterned photoresist layer as a mask, etching the silicon dioxide layer to obtain a first sacrificial layer for defining a micromirror anchor layer. The first sacrificial layer is used to define the position, size, shape, and other features of the boss directly below it, facilitating further patterning of the silicon wafer inside the boss to obtain a micromirror anchor layer surrounded by the boss. Thus, after bonding the top surface of the boss to the substrate, the boss surrounds the back comb layer, allowing the use of a protective layer to prevent subsequent etching processes from adversely affecting the substrate, and also reducing the complexity of subsequent bonding alignment.
[0018] According to some embodiments, after forming the back comb layer, the first patterned photoresist layer is removed; using the first sacrificial layer and the back comb layer as a mask, the silicon wafer is etched a first target number of times to obtain a protrusion located directly below the first sacrificial layer and a micromirror anchor layer surrounded by the protrusion; the first target number of times is related to the etching depth of the micromirror anchor layer and the single etching depth. The anchor height is appropriately set according to the actual MEMS micromirror structure design. In this embodiment, the etching depth adopts a step-by-step etching method, dividing the etching depth of the micromirror anchor layer into multiple small etching depths for multiple etchings, reducing the impact of deep etching on the comb surface.
[0019] According to some embodiments, forming a mirror electrode on the front side of a thinned silicon wafer includes: after bonding the top surface of the boss to the substrate, wet etching and thinning the front side of the silicon wafer; forming a third patterned photoresist layer on the front side of the thinned silicon wafer; magnetron sputtering a metal material layer covering the third patterned photoresist layer; removing the third patterned photoresist layer and the metal material layer directly above it, with the remaining metal material layer used to form the mirror electrode. The mirror electrode can assist in alignment steps in subsequent process steps.
[0020] According to some embodiments, etching a silicon wafer at least twice based on a first patterned mask layer includes: forming a fourth patterned photoresist layer on the top surface of the first patterned mask layer; etching the first patterned mask layer using the fourth patterned photoresist layer as a mask to obtain a target mask layer; etching the silicon wafer at least twice using the fourth patterned photoresist layer as a mask to form a MEMS micromirror structure; and removing the fourth patterned photoresist layer and the target mask layer. In this embodiment, the etching depth for forming the MEMS micromirror structure is divided into multiple small etching depths for multiple etching operations to reduce the impact of deep etching on the comb tooth surface. The etching depth and the difference in comb tooth height can be appropriately set according to the actual MEMS micromirror structure design.
[0021] According to some embodiments, the silicon wafer is etched at least twice, including: etching the silicon wafer using a fourth patterned photoresist layer as a mask to form a front comb layer; and etching the front comb layer using the fourth patterned photoresist layer as a mask to form a MEMS micromirror structure. This reduces the impact of deep etching on the comb surface.
[0022] According to some embodiments, the metallic material layer includes Ti, Pt, Au, or combinations thereof.
[0023] According to some embodiments, a second aspect of this disclosure provides a MEMS micromirror structure, including: a semiconductor structure fabricated using any of the aforementioned MEMS micromirror structure fabrication methods.
[0024] The MEMS micromirror structure fabrication method and MEMS micromirror structure in the above embodiments have at least the following unexpected technical effects:
[0025] Using a glass substrate, the thickness of the silicon wafer can be freely controlled through thinning, reducing the thickness and volume of the MEMS micromirror structure. A composite mask etching process forms a back comb layer, allowing for free control of the comb tooth height difference and improving the flexibility of the MEMS micromirror structure design. Based on the first sacrificial layer and the back comb layer, the silicon wafer is etched to obtain a protrusion directly below the first sacrificial layer and a micromirror anchor layer surrounded by the protrusion. After removing the first sacrificial layer, the top surface of the protrusion is bonded to the substrate, so that the protrusion surrounds a protective layer. The silicon wafer is then etched at least twice more using photolithography and etching processes to form the MEMS micromirror structure. The protective layer not only prevents the etching process from adversely affecting the substrate but also reduces the complexity of subsequent bonding alignment. Since standard processes such as photolithography, etching, and bonding are used, the process compatibility is stronger, the process difficulty is lower, and there is no need to develop additional non-standard processes. Multiple etching processes to form the MEMS micromirror structure reduce the adverse effects of deep etching on the comb tooth surface. Attached Figure Description
[0026] To more clearly illustrate the technical solutions in the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0027] Figure 1 This is a schematic diagram of the MEMS micromirror structure fabrication method provided in one embodiment;
[0028] Figure 2 A schematic diagram of the cross-sectional structure of the resulting structure after providing the base;
[0029] Figure 3A schematic diagram of the cross-sectional structure of the structure after the metal layer is formed;
[0030] Figure 4 A schematic diagram of the cross-sectional structure of the resulting structure after the protective layer has been formed;
[0031] Figure 5 A schematic diagram of the cross-sectional structure of the structure obtained after forming the second patterned photoresist layer;
[0032] Figure 6 A schematic diagram of the cross-sectional structure of the structure obtained after forming the first patterned photoresist layer;
[0033] Figure 7 A schematic diagram of the cross-sectional structure of the structure obtained after forming the back comb layer;
[0034] Figure 8 A schematic diagram of the cross-sectional structure of the structure obtained after forming the back comb layer;
[0035] Figure 9 This is a schematic diagram of the cross-sectional structure of the structure obtained after bonding the silicon wafer to the substrate;
[0036] Figure 10 A schematic diagram of the cross-sectional structure of the structure obtained after forming the mirror electrode;
[0037] Figure 11 A schematic diagram of the cross-sectional structure of the resulting structure after the hard mask is formed;
[0038] Figure 12 A schematic diagram of the cross-sectional structure of the structure obtained after forming the first patterned mask layer;
[0039] Figure 13 A schematic diagram of the cross-sectional structure of the structure obtained after forming the fourth patterned photoresist layer;
[0040] Figure 14 A schematic diagram of the cross-sectional structure of the resulting structure after the target mask layer has been formed;
[0041] Figure 15 A schematic diagram of the cross-sectional structure of the structure obtained after forming the front comb layer;
[0042] Figure 16 A schematic diagram of the cross-sectional structure of the resulting MEMS micromirror structure;
[0043] Figure 17 This is a schematic diagram of the cross-sectional structure of the structure obtained after removing the target mask layer.
[0044] Explanation of reference numerals in the attached figures:
[0045] 100, Substrate; 10, Silicon Wafer; 30, First Sacrificial Layer; 40, First Patterned Photoresist Layer; 50, Back Comb Layer; 61, Protrusion; 62, Micromirror Anchor Layer; 70, Mirror Electrode; PR1, First Patterned Photoresist Layer; M11, Metal Layer; M1, Protective Layer; PR2, Second Patterned Photoresist Layer; PR3, Third Patterned Photoresist Layer; M21, Metal Material Layer; PR4, Fourth Patterned Photoresist Layer; Y11, First Patterned Mask Layer; Y10, Hard Mask; Y1, Target Mask Layer; 80, Front Comb Layer; 81, Lateral Protrusion; 90, MEMS Micromirror Structure. Detailed Implementation
[0046] To facilitate understanding of this disclosure, a more complete description will now be given with reference to the accompanying drawings, in which preferred embodiments of the present disclosure are shown. However, this disclosure may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure.
[0048] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, regions, layers, doping types, and / or portions, these elements, components, regions, layers, doping types, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, doping type, or portion from another element, component, region, layer, doping type, or portion. Therefore, without departing from the teachings of this invention, the first element, component, region, layer, doping type, or portion discussed below may be referred to as a second element, component, region, layer, or portion.
[0049] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, the element or feature described as “below,” “under,” or “below” will be oriented “above” the other element or feature. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. Furthermore, the device may also include other orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptive terms used herein will be interpreted accordingly.
[0050] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that when the terms “comprise” and / or “comprising” are used in this specification, the presence of the stated feature, integer, step, operation, element, and / or part is established, but the presence or addition of one or more other features, integers, steps, operations, elements, parts, and / or groups is not excluded. Meanwhile, when used herein, the term “and / or” includes any and all combinations of the associated listed items.
[0051] Embodiments of the invention are described herein with reference to cross-sectional views illustrating ideal embodiments (and intermediate structures) of the invention, thus allowing for the anticipation of variations in the shown shapes due to, for example, manufacturing techniques and / or tolerances. Therefore, embodiments of the invention should not be limited to the specific shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing techniques. The regions shown in the figures are substantially schematic, and their shapes do not represent the actual shapes of regions of the device, nor do they limit the scope of the invention.
[0052] MEMS technology utilizes mature semiconductor mass production processes, such as photolithography, etching, and thin film deposition, to mass-produce miniaturized and integrated mechanical structures on silicon wafers. MEMS micromirrors leverage this technology to reduce the size of traditional optical mirrors by several orders of magnitude, achieving millimeter-level miniaturization. This gives MEMS micromirrors advantages such as small size, low power consumption, and high response speed.
[0053] Currently, there are two main fabrication processes for MEMS vertical comb-driven micromirrors:
[0054] One method utilizes silicon-on-insulator (SOI) technology, bonding multiple SOI wafers together and using a silicon dioxide layer as an etch stop layer to create comb teeth of varying heights. Alternatively, movable and fixed comb teeth can be defined on two different SOI wafers, with bonding used to drive the micromirrors. This SOI wafer-based processing method is costly, and the fixed thickness of the SOI wafer itself limits design and fabrication flexibility. Furthermore, the release of the SOI bulk silicon structure layer often involves wet etching of the silicon oxide layer. Due to capillary forces, delicate structures (such as comb teeth, mirror surfaces, and substrate adhesion) are prone to adhesion failure, increasing process complexity and cost, and posing a high risk for small-sized structures. The photolithography of the front-side structure during the process uses double-sided alignment, further increasing process complexity and cost.
[0055] Another approach involves utilizing residual stress or applying external forces (such as electrostatic force or pressure) to post-process the etched structure, creating comb-like teeth of varying heights to fabricate MEMS micromirrors. Compared to SOI bulk silicon processes, this method effectively reduces the number of photolithography, etching, and bonding steps, thereby reducing process costs. However, in this method, process parameters significantly influence the residual stress of the MEMS micromirror, making it difficult to guarantee batch-to-batch consistency. Furthermore, the MEMS micromirrors fabricated using this method are no longer horizontal surfaces, making this process incompatible with other planar processes and limiting further integration of MEMS micromirrors with other devices.
[0056] Based on this, this application aims to provide a method for fabricating MEMS micromirror structures and a MEMS micromirror structure, which can at least reduce the complexity and cost of the fabrication process, and improve the process tolerance, product yield, design flexibility and integration.
[0057] Please see Figure 1 This disclosure provides a method for fabricating a MEMS micromirror structure, which includes the following steps:
[0058] Step S210: Provide a substrate and form a protective layer covering the target surface of the substrate;
[0059] Step S220: Provide a silicon wafer, the back side of which includes a first sacrificial layer for defining the micromirror anchor layer;
[0060] Step S230: Form a first patterned photoresist layer covering the first sacrificial layer to define the back comb layer;
[0061] Step S240: Based on the first patterned photoresist layer, a back comb layer is formed in the silicon wafer;
[0062] Step S250: Based on the first sacrificial layer and the back comb layer, the silicon wafer is etched to obtain the protrusion located directly below the first sacrificial layer and the micromirror anchor layer surrounded by the protrusion.
[0063] Step S260: After removing the first sacrificial layer, bond the top surface of the boss to the substrate so that the boss surrounds the protective layer;
[0064] Step S270: After forming a mirror electrode on the front side of the thinned silicon wafer, a first patterned mask layer covering the mirror electrode is formed;
[0065] Step S280: The silicon wafer is etched at least twice based on the first patterned mask layer to form a MEMS micromirror structure.
[0066] For example, please continue to refer to Figure 1 A glass substrate can be used, and the thickness of the silicon wafer can be freely controlled by thinning, reducing the thickness and volume of the MEMS micromirror structure. A composite mask etching process forms a back comb layer, allowing for free control of the comb tooth height difference and improving the flexibility of the MEMS micromirror structure design. Based on the first sacrificial layer and the back comb layer, the silicon wafer is etched to obtain a protrusion directly below the first sacrificial layer and a micromirror anchor layer surrounded by the protrusion. After removing the first sacrificial layer, the top surface of the protrusion is bonded to the substrate, so that the protrusion surrounds the protective layer. The silicon wafer is then etched at least twice more using photolithography and etching processes to form the MEMS micromirror structure. The protective layer not only prevents the etching process from adversely affecting the substrate but also reduces the complexity of subsequent bonding alignment. Since standard processes such as photolithography, etching, and bonding are used, the process compatibility is stronger, the process difficulty is lower, and there is no need to develop other supporting non-standard processes. Multiple etching processes to form the MEMS micromirror structure reduce the adverse effects of deep etching on the comb tooth surface.
[0067] Please refer to Figure 2 In some embodiments, the substrate 100 provided in step S210 can be glass. Forming a protective layer M1 covering the target surface of the substrate 100 includes: forming a first patterned photoresist layer PR1 on the surface of the substrate 100 after pretreatment, the first patterned photoresist layer PR1 defining the target surface; the target surface is used to define the MEMS micromirror structure.
[0068] Please continue to refer to this. Figure 2 In some embodiments, photoresist is spin-coated onto the surface of a pre-processed glass and photolithography is performed. The photoresist acts as a mask to etch the glass, resulting in... Figure 2The structure is shown. Before spin-coating the photoresist, the pre-processed glass can be organically cleaned with acetone and ethanol, followed by cleaning with deionized water and drying to ensure the glass surface is free of dust, grease, contaminants, water, and other pollutants, thus ensuring the spin-coating effect and quality of the photoresist and improving the lithography quality. Next, the glass is placed in a vacuum oven, where an adhesive, such as hexamethyldisilazane (HMDS), is deposited on the surface to enhance the adhesion of the photoresist. Then, the glass is spin-coated with photoresist on a spin coater, followed by a pre-baking treatment. Finally, photolithography is performed on the lithography machine, followed by a post-baking treatment to obtain the first patterned photoresist layer PR1 with strong corrosion resistance. A targeted glass etching solution is used for etching the glass.
[0069] Please refer to Figure 2 In some embodiments, the glass thickness and the type and thickness of the photoresist can be appropriately set according to actual needs, and the etching depth can be determined according to the thickness of the protective layer. In this embodiment, the glass thickness can be set to 295μm-305μm, such as 295μm, 300μm, or 305μm, etc.; the thickness of the first patterned photoresist layer PR1 is 1.95μm-2.05μm, such as 1.95μm, 2.00μm, or 2.05μm, etc.; the etching solution can be hydrofluoric acid buffered etching solution BHF; the etching depth can be set to 245nm-255nm, such as 245nm, 250nm, or 255nm, etc.
[0070] Please refer to Figure 3 In some embodiments, a metal layer M11 is magnetron sputtered, covering the first patterned photoresist layer PR1 and the target surface. The metal layer M11 may include Ti, Pt, Au, or a combination thereof. For example, the metal layer M11 may be a composite metal layer of Ti, Pt, and Au, with a Ti layer thickness of 30 nm, a Pt layer thickness of 40 nm, and an Au layer thickness of 220 nm. This configuration allows the metal thickness to be greater than the trench depth, facilitating metal stripping without affecting subsequent anodic bonding steps.
[0071] Please refer to Figure 4In some embodiments, the metal layer M11 outside the target surface and the first patterned photoresist layer PR1 are removed, and the metal layer M11 remaining on the target surface is used to form a protective layer M1. The protective layer M1 not only avoids adverse effects on the substrate 100 from subsequent etching processes, but also reduces the complexity of subsequent bonding alignment. By first forming the first patterned photoresist layer PR1 that exposes the target surface, and then forming the metal layer M11 covering the first patterned photoresist layer PR1 and the target surface by magnetron sputtering, the metal layer M11 directly above the first patterned photoresist layer PR1 is removed simultaneously during the stripping and removal of the first patterned photoresist layer PR1, reducing the complexity and cost of the fabrication process.
[0072] Please refer to Figure 4 In some embodiments, acetone solution can be used to remove the first patterned photoresist layer PR1 and the metal layer M11 directly above it, leaving the metal layer M11 in the etching groove, thus avoiding etching the metal layer M11 directly above the target surface and reducing the complexity and cost of the fabrication process.
[0073] Please refer to Figure 5 In some embodiments, step S220 includes providing a silicon wafer 10, comprising:
[0074] Step S221: A silicon dioxide layer is formed on the surface of the initial silicon wafer after pre-processing;
[0075] Step S222: Form a second patterned photoresist layer PR2 on the top surface of the silicon dioxide layer;
[0076] Step S223: Using the second patterned photoresist layer PR2 as a mask, etch the silicon dioxide layer to obtain the first sacrificial layer 30 used to define the micromirror anchor layer 62.
[0077] Please continue to refer to this. Figure 5 In some embodiments, in step S221, a silicon dioxide layer is formed on the surface of the initial silicon wafer after pre-processing. This can be achieved by first cleaning to remove any possible contaminants from the surface of the initial silicon wafer, followed by thermal oxidation of the initial silicon wafer to obtain a silicon wafer 10 with a silicon dioxide layer on its surface. In step S222, a second patterned photoresist layer PR2 is formed on the top surface of the silicon dioxide layer, and the second patterned photoresist layer PR2 is used as a mask to etch the silicon dioxide layer, resulting in... Figure 5The structure shown is followed by removal of the photoresist. The thickness of the second patterned photoresist layer PR2 is 1.95μm-2.05μm, for example, 1.95μm, 2.00μm, or 2.05μm, etc. In step S223, BOE solution can be used to etch the silicon dioxide layer. BOE solution has a slow etching rate, which allows for precise control of etching time, reduces lateral etching, and improves process accuracy. After obtaining the first sacrificial layer 30, which defines the position, size, and shape of the boss 61 directly below it, the second patterned photoresist layer PR2 is organically removed with acetone and ethanol, followed by dry photoresist removal in a dry photoresist remover to reduce photoresist residue. Unless otherwise specified, the photoresist removal process in this step is preferred in subsequent steps.
[0078] Please refer to Figure 6 In some embodiments, in step S230, a first patterned photoresist layer 40 for defining the back comb layer 50 is formed, covering the first sacrificial layer 30.
[0079] Please refer to Figure 7 In some embodiments, in step S240, a back comb layer 50 is formed within the silicon wafer 10 based on the first patterned photoresist layer 40. The height difference of the comb teeth can be designed according to the actual MEMS micromirror structure, thereby setting the etching depth in this embodiment. In this embodiment, the etching depth is 9.5μm-10.5μm, for example, 9.5μm, 10μm, or 10.5μm, etc.
[0080] Please refer to Figures 7-8 In some embodiments, in step S250, the silicon wafer 10 is etched based on the first sacrificial layer 30 and the back comb layer 50 to obtain a boss 61 located directly below the first sacrificial layer 30 and a micromirror anchor layer 62 surrounded by the boss 61.
[0081] Please continue to refer to this. Figures 7-8 In some embodiments, after forming the back comb layer 50, the first patterned photoresist layer 40 is removed; using the first sacrificial layer 30 and the back comb layer 50 as a mask, the silicon wafer 10 is etched a first target number of times to obtain a protrusion 61 located directly below the first sacrificial layer 30 and a micromirror anchor layer 62 surrounded by the protrusion 61. The anchor height is appropriately set according to the actual MEMS micromirror structure design; the first target number of times is related to the etching depth of the micromirror anchor layer 62 and the single etching depth. The anchor height is appropriately set according to the actual MEMS micromirror structure 90 design. In this embodiment, the etching depth adopts a step-by-step etching method, dividing the etching depth of the micromirror anchor layer 62 into multiple small etching depths for multiple etchings, reducing the impact of deep etching on the comb surface.
[0082] Please continue to refer to this. Figures 7-8In some embodiments, the etching depth of the micromirror anchor layer 62 is adopted by step etching, which is divided into multiple small etching depths for multiple etchings to reduce the impact of deep etching on the comb surface. In this embodiment, the etching depth of the micromirror anchor layer 62 can be set to 20μm. The total depth of 20μm can be divided into 5 etchings, each with an etching depth of 4μm.
[0083] Please refer to Figure 9 In some embodiments, in step S260, after removing the first sacrificial layer 30, the top surface of the boss 61 is bonded to the substrate 100, so that the boss 61 surrounds the protective layer M1. This facilitates further patterning of the silicon wafer 10 inside the boss 61, resulting in a micromirror anchor layer 62 surrounded by the boss 61. Thus, by using the top surface of the boss 61 to bond to the substrate 100, the boss 61 surrounds the back comb layer 50. The protective layer M1 can be used to avoid adverse effects on the substrate 100 by subsequent etching processes, and can also reduce the complexity of subsequent bonding alignment.
[0084] Please continue to refer to this. Figure 9 In some embodiments, the top surface of the boss 61 is anoly bonded to the substrate 100, followed by thinning of the silicon wafer 10. Of course, before anoly bonding, to ensure bonding success, the silicon wafer 10 and glass can be dry-cleaned and organically cleaned to reduce surface contamination. There are many options for thinning the silicon wafer 10 after bonding, such as using KOH solution to etch the silicon wafer 10 for thinning.
[0085] Please refer to Figure 10 In some embodiments, a mirror electrode 70 is formed on the front side of the thinned silicon wafer 10, including: after bonding the top surface of the protrusion 61 to the substrate 100, wet etching and thinning the front side of the silicon wafer 10; forming a third patterned photoresist layer PR3 (not shown) on the front side of the thinned silicon wafer 10; magnetron sputtering a metal material layer M21 (not shown), the metal material layer M21 covering the third patterned photoresist layer PR3; removing the third patterned photoresist layer PR3 and the metal material layer M21 directly above it, the remaining metal material layer M21 being used to form the mirror electrode 70. The mirror electrode 70 can assist in the alignment steps in subsequent process steps. The metal material layer M21 may include Ti, Pt, Au, or combinations thereof, for example, the metal material layer M21 may be a composite metal layer of Ti, Pt, and Au, with a Ti layer thickness of 30 nm, a Pt layer thickness of 40 nm, and an Au layer thickness of 100 nm.
[0086] Please refer to Figure 11In some embodiments, a hard mask Y10 is deposited on the front side of the silicon wafer 10, covering the mirror electrode 70. Silicon dioxide can be deposited using PECVD or aluminum can be deposited using magnetron sputtering as the hard mask Y10. In this embodiment, for example, silicon dioxide is deposited using PECVD as the hard mask Y10, and the thickness of the hard mask Y10 is 300 nm.
[0087] Please refer to Figure 12 In some embodiments, photoresist is spin-coated onto the top surface of the hard mask Y10, the hard mask Y10 is etched, and then the photoresist is removed to obtain a centrally symmetrical first patterned mask layer Y11. For example, BOE solution can be used to etch silicon dioxide to a depth of 300 nm.
[0088] Please refer to Figure 13 In some embodiments, a fourth patterned photoresist layer PR4 is formed on the top surface of the first patterned mask layer Y11; the fourth patterned photoresist layer PR4 is used to define the micromirror structure. The first patterned mask layer Y11 may include silicon dioxide. The thickness of the first patterned mask layer Y11 may be 250 μm-400 μm. For example, the thickness of the first patterned mask layer Y11 may be 250 μm, 300 μm, 350 μm, or 400 μm, etc.
[0089] Please refer to Figure 14 In some embodiments, the first patterned mask layer Y11 is etched using the fourth patterned photoresist layer PR4 as a mask to obtain the target mask layer Y1. This achieves self-alignment of the two-layer mask and reduces deviations caused by process errors.
[0090] Please refer to Figures 15-17 In some embodiments, the silicon wafer 10 is etched at least twice using the fourth patterned photoresist layer PR4 as a mask to form a centrally symmetrical MEMS micromirror structure 90; the fourth patterned photoresist layer PR4 and the target mask layer Y1 are then removed. In this embodiment, the etching depth to form the MEMS micromirror structure 90 is achieved through a step-by-step etching method, dividing the etching into multiple small etching depths for multiple etching operations to reduce the impact of deep etching on the comb tooth surface. The etching depth and the difference in comb tooth height can be appropriately set according to the actual design of the MEMS micromirror structure 90.
[0091] Please refer to Figure 15 In some embodiments, the silicon wafer 10 is etched at least twice, including etching the silicon wafer 10 using the fourth patterned photoresist layer PR4 as a mask to form the front comb layer 80. The etching depth is appropriately set according to the design requirements of the MEMS micromirror structure, for example, the etching depth is 20 μm.
[0092] Please refer to Figure 16In some embodiments, the front comb layer 80 is etched using the fourth patterned photoresist layer PR4 as a mask, removing at least the lateral protrusions 81 of the front comb layer 80 to form a centrally symmetrical MEMS micromirror structure 90, wherein the lateral direction is parallel to the flush surface of the silicon wafer. This etching process employs a step-by-step etching method to reduce the impact of deep etching on the comb surface. In this embodiment, a total etching depth of 10 μm is preferably achieved through two etching passes, each with a depth of 5 μm. The protective layer can be made of metal, which can adsorb etching ions, preventing them from damaging the comb morphology. Please refer to [reference needed]. Figure 17 In some embodiments, a wet process is used to etch away the target mask layer Y1.
[0093] Please refer to Figure 17 In some embodiments, a MEMS micromirror structure 90 is provided, comprising: a semiconductor structure fabricated using any of the aforementioned MEMS micromirror structure 90 fabrication methods.
[0094] Please continue to refer to this. Figures 1-17 The MEMS micromirror structure fabrication method and MEMS micromirror structure in the above embodiments have at least the following unexpected technical effects:
[0095] Using a glass substrate 100, the thickness of the silicon wafer 10 can be freely controlled by thinning, reducing the thickness and volume of the MEMS micromirror structure 90. A composite mask is used to etch a back comb layer 50, which allows for free control of the height difference of the comb teeth, improving the design flexibility of the MEMS micromirror structure 90. Based on the first sacrificial layer 30 and the back comb layer 50, the silicon wafer 10 is etched to obtain a protrusion 61 located directly below the first sacrificial layer 30 and a micromirror anchor layer 62 surrounded by the protrusion 61. After removing the first sacrificial layer 30, the top surface of the protrusion 61 is bonded to the substrate 100, so that the protrusion 61 surrounds the protective layer M1. The silicon wafer 10 is then etched at least twice through photolithography, etching, and other processes to form the MEMS micromirror structure 90. The protective layer M1 not only avoids the adverse effects of etching and other processes on the substrate 100, but also reduces the complexity of subsequent bonding alignment. Because standard processes such as photolithography, etching, and bonding are used, the process compatibility is stronger and the process difficulty is lower, and there is no need to develop other supporting non-standard processes. The silicon wafer 10 is etched multiple times to form the MEMS micromirror structure 90, which can reduce the adverse effects of deep etching on the comb surface.
[0096] Although Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the exact order indicated by the arrows. Unless otherwise specified in this document, there is no strict order in which these steps are executed, and they can be executed in other sequences. Moreover, although Figure 1At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution of these sub-steps or stages is not necessarily sequential, but can be performed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.
[0097] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features of the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0098] The embodiments described above are merely illustrative of several implementation methods of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these modifications and improvements all fall within the scope of protection of this disclosure.
Claims
1. A method for fabricating a MEMS micromirror structure, characterized in that, include: A glass substrate is provided, and a metal protective layer is formed covering the target surface of the substrate; the metal protective layer is used to reduce the alignment complexity of subsequent bonding steps; A silicon wafer is provided, the back side of which includes a first sacrificial layer for defining a micromirror anchor layer; the first sacrificial layer is at least used to define the position, size and shape of the boss directly beneath it. A first patterned photoresist layer is formed over the first sacrificial layer to define the back comb layer; the back comb layer is surrounded by bosses. Based on the first patterned photoresist layer, the back comb layer is formed within the silicon wafer; After removing the first patterned photoresist layer, the silicon wafer is etched a first target number of times based on the first sacrificial layer and the back comb layer to obtain a protrusion located directly below the first sacrificial layer and a micromirror anchor layer surrounded by the protrusion; the first target number of times is related to the etching depth and single etching depth of the micromirror anchor layer. After removing the first sacrificial layer, the top surface of the boss is bonded to the substrate, so that the boss surrounds the protective layer; A mirror electrode is formed on the front side of the thinned silicon wafer, and then a first patterned mask layer is formed to cover the mirror electrode. The silicon wafer is etched at least twice based on the first patterned mask layer to form the MEMS micromirror structure. The protective layer is also used to adsorb etching ions during the etching of the silicon wafer to avoid damage to the comb morphology.
2. The method for fabricating MEMS micromirror structures according to claim 1, characterized in that, The metal protective layer forming the target surface covering the substrate includes: A first patterned photoresist layer is formed on the pretreated substrate surface, the first patterned photoresist layer defining the target surface; A magnetron sputtered metal layer is formed, which covers the first patterned photoresist layer and the target surface; the metal layer and the first patterned photoresist layer outside the target surface are removed, and the metal layer remaining on the target surface is used to form the protective layer.
3. The method for fabricating MEMS micromirror structures according to claim 2, characterized in that, The first patterned photoresist layer and the metal layer directly above it were removed using an acetone solution.
4. The method for fabricating a MEMS micromirror structure according to claim 1, characterized in that, The silicon wafer provided includes: A silicon dioxide layer is formed on the surface of the pre-processed initial silicon wafer; A second patterned photoresist layer is formed on the top surface of the silicon dioxide layer; Using the second patterned photoresist layer as a mask, the silicon dioxide layer is etched to obtain a first sacrificial layer for defining the micromirror anchor layer.
5. The method for fabricating a MEMS micromirror structure according to claim 1, characterized in that, The process of forming a mirror electrode on the front side of the thinned silicon wafer includes: After bonding the top surface of the boss to the substrate, the front side of the silicon wafer is wet-etched and thinned. A third patterned photoresist layer is formed on the front side of the thinned silicon wafer; A magnetron sputtered metal material layer is used to cover the third patterned photoresist layer. The third patterned photoresist layer and the metal material layer directly above it are removed, and the remaining metal material layer is used to form the mirror electrode.
6. The method for fabricating a MEMS micromirror structure according to claim 1, characterized in that, The silicon wafer is etched at least twice based on the first patterned mask layer, including: A fourth patterned photoresist layer is formed on the top surface of the first patterned mask layer; The first patterned mask layer is etched using the fourth patterned photoresist layer as a mask to obtain the target mask layer; The silicon wafer is etched at least twice using the fourth patterned photoresist layer as a mask to form the MEMS micromirror structure; Remove the fourth patterned photoresist layer and the target mask layer.
7. The method for fabricating a MEMS micromirror structure according to claim 6, characterized in that, The silicon wafer is etched at least twice, including: The silicon wafer is etched using the fourth patterned photoresist layer as a mask to form a front comb layer; The front comb layer is etched using the fourth patterned photoresist layer as a mask to form the MEMS micromirror structure.
8. The method for fabricating a MEMS micromirror structure according to claim 5, characterized in that, The metallic material layer includes Ti, Pt, Au, or a combination thereof.
9. A MEMS micromirror structure, characterized in that, It is prepared by the MEMS micromirror structure preparation method according to any one of claims 1-8.