CN113031253B

CN113031253B - Wafer-level micromirror, optical window and manufacturing method thereof

Info

Publication number: CN113031253B
Application number: CN201911256483.0A
Authority: CN
Inventors: 马宏
Original assignee: Juexin Electronics Wuxi Co ltd
Current assignee: Juexin Electronics Wuxi Co ltd
Priority date: 2019-12-09
Filing date: 2019-12-09
Publication date: 2023-12-26
Anticipated expiration: 2039-12-09
Also published as: CN113031253A

Abstract

The invention provides a wafer-level micromirror, an optical window and a method for manufacturing the same. The micromirror includes: a micromirror body comprising one or more monocrystalline silicon device layers; an optical frame, one major face of the optical frame bonded to the device layer; the optical frame also comprises an optical window, wherein the optical window is of a convex window structure and is provided with a first inclined surface, and an included angle is formed between the first inclined surface and the main surface of the optical frame.

Description

Wafer-level micromirror, optical window and manufacturing method thereof

Technical Field

The invention relates to the technical field of micro-nano manufacturing and processing, in particular to a wafer-level micro-mirror, an optical window and a manufacturing method thereof.

Background

Since the first scanning type silicon mirror in 1980, microelectromechanical systems (MEMS) system, micro electro-mechanical systems, hereinafter referred to as MEMS, have been widely used in the field of optical scanning and a number of technologies and products have been developed. The field of optical scanning has become an important direction of MEMS research. As technology has evolved, the use of micro-projection technology and numerous medical imaging technologies has become the main direction of current MEMS optical scanning devices, especially laser scanning devices, development in the last decade. Development of micro projection technology has prompted the emergence of some new products, such as a micro laser projector with a mobile phone size or a smart phone with a laser projection function, a head-up display HUD which is placed in a car and can be used for displaying navigation information when the car is driven, and various wearable devices including a virtual reality technology VR, an augmented reality technology AR and the like for comparing fire and explosion in the last year.

MEMS systems rely on external electrical actuation to produce micro-displacement or micro-actuation forces, forming the critical actuation components of the overall system. The structural design of the MEMS itself and the packaging protection for the MEMS structure form an important factor affecting its performance and lifetime from the present point of view.

When the MEMS micro-mirror device is applied to the micro-projection technology, a light-transmitting material such as glass is required to encapsulate the MEMS structure, which is called a window, so that the light beam can enter the micro-mirror while protecting the MEMS structure, and is reflected by the micro-mirror to be led to a field of view. However, in practical applications, when the light beam passes through the window structure, very little light is reflected by the window structure and directed toward the field of view. The reflected light of the window structure is projected onto the imaging surface together with the scanning beam for imaging, but the reflected light of the window structure is always projected onto a point, unlike the scanning beam for imaging. Therefore, in the integration time of human eyes, the light reflected by the extremely weak energy window can form an obvious bright spot on the imaging surface, and the imaging quality is affected.

In addition, in the conventional MEMS micro-mirror manufacturing process, it is necessary to invert the wafer on which the device layer structure has been formed, and form the back cavity by an etching process, and release the movable structure of the device layer. Before the wafer inversion, a protective layer is formed on the surface of the device layer of the wafer by spin coating or PECVD, and the material of the protective layer is usually photoresist. However, since the MEMS structure is already formed on the surface of the device layer and has a large aspect ratio when the protective layer is formed, it is quite difficult to perform both the filling operation when the protective layer is formed and the subsequent removal operation of the protective layer.

Disclosure of Invention

In order to solve the above technical problems, the present invention provides a wafer level micromirror, an optical window and a method for manufacturing the same.

In a first aspect of the present invention, a micromirror is provided, the micromirror comprising: a micromirror body (110) comprising one or more single crystal silicon device layers (111); a substrate (120); -an optical frame (130), one main face of the optical frame (130) being bonded to the device layer (111); the optical window (140) is of a convex window structure and is provided with a first inclined surface, and an included angle is formed between the first inclined surface and the main surface of the optical frame (130).

In a second aspect of the invention, a micromirror body comprises one or more single crystal silicon device layers; an optical frame, one major face of the optical frame bonded to the device layer; the optical window is of a convex window structure and is provided with a first main surface and a second main surface which are parallel to each other, and the first main surface and the second main surface form a first included angle alpha with a first frame main surface of the optical frame; the optical window has a third main face and a fourth main face parallel to each other, and the third main face and the fourth main face form a second included angle beta with the first frame main face of the optical frame.

In a third aspect of the present invention, a method of manufacturing an optical window, the method comprising: pretreating a first main surface and a second main surface of a glass wafer, and spin-coating a protective layer on the first main surface; spin-coating photoresist on the second main surface of the glass wafer, and pre-baking the photoresist; after the pre-baking is finished, stamping a cavity with an inclined plane on the photoresist layer by adopting a mould pressing process, and forming a graph layer with the inclined plane; transferring the pattern of the pattern layer to a glass wafer through an etching process to form a cavity structure with an inclined plane; and plating an anti-reflection layer on the surface of the cavity structure with the inclined surface. In a fourth aspect of the present invention, a method for manufacturing a micromirror, the method comprising: forming a micromirror body on a first wafer; forming an optical frame on a second wafer and bonding a first main surface of the micromirror body and the optical frame; forming an optical window on a third wafer, and bonding the optical window with the optical frame to complete half-packaging of the micromirror body; photoetching and etching the first wafer to release the movable part of the micro-mirror body; bonding the second major face of the micromirror body with a substrate to form a full package for the micromirror body; photoetching and etching the bonded third wafer to finish a final optical window; dicing the whole formed by the bonded first wafer, second wafer and third wafer to separate the independent and complete MEMS micro-mirror devices from each other. The invention has the following beneficial effects:

1. When the MEMS structure is coupled with the substrate, an additional protective layer is not required to be provided for protecting the processed device layer structure through the traditional process, and the problems that the filling of the early-stage protective material is difficult and the removal of the later-stage protective material is difficult when the traditional process is adopted are avoided.

2. The packaging technology belongs to the wafer level, and has high production efficiency and low cost.

3. The package belongs to vertical package, has compact structure, and the obtained unit device belongs to millimeter level, has small volume and high integration degree.

4. An optical frame structure is added in the packaging process, so that a larger deflection space is provided for the packaged MEMS micro mirror, and air damping is reduced.

5. The wafer level package is suitable for the MEMS micro-mirror device, is used for eliminating the influence of window reflected light generated by the reflection of an optical window, and can obviously improve the anti-interference capability and the service life of the system in long-term use after sealing and packaging.

6. Compared with the traditional optical window with similar functions, the optical window structure has smaller thickness and size and better effect of eliminating the reflected light of the window.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 (a) is a schematic diagram of a MEMS micro-mirror device with comb structure according to an embodiment of the present invention;

FIG. 1 (b) is a schematic diagram of a MEMS micro-mirror device packaged at a wafer level according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a wafer level packaged MEMS micro-mirror device according to an embodiment of the present invention;

fig. 3 (a), fig. 3 (b), fig. 3 (c), fig. 3 (d), fig. 3 (e), fig. 3 (f), fig. 3 (g), fig. 3 (h), fig. 3 (i), fig. 3 (j), fig. 3 (k), fig. 3 (l), and fig. 3 (m) are schematic process flow diagrams of a wafer level packaged MEMS micro-mirror device according to an embodiment of the present invention;

fig. 4 (a), fig. 4 (b), fig. 4 (c 1), fig. 4 (c 2), fig. 4 (d), fig. 4 (e) and fig. 4 (f) are flowcharts of an optical window processing process according to an embodiment of the present invention;

FIG. 5 (a) is a top view of a wafer level MEMS micromirror before packaging according to an embodiment of the present invention;

FIG. 5 (b) is a top view of a packaged wafer level MEMS micromirror provided by an embodiment of the present invention;

fig. 6 (a) -6 (f) are schematic diagrams illustrating an optical window forming process according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic may be included in at least one implementation of the invention. In the description of the present invention, it should be understood that the directions or positional relationships indicated by the terms "upper", "lower", "top", "bottom", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of description and simplification of the description, and do not indicate or imply that the apparatus or element in question must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may include one or more of the feature, either explicitly or implicitly. Moreover, the terms "first," "second," and the like, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein.

Embodiment one:

in one possible embodiment, as shown in fig. 1 (a), a MEMS micro-mirror device having a comb structure is proposed. The structure includes a micromirror structure and a comb structure for driving the micromirror structure. However, moisture in the air or the like affects the driving of the MEMS micro-mirror device, and thus the MEMS micro-mirror device needs to be packaged. A common packaging process at this stage is wafer level packaging, i.e., packaging using a glass wafer directly at the wafer level during semiconductor processing of SOI wafers to fabricate MEMS micro-mirror devices. After packaging is completed, the MEMS micro-mirror devices of each unit on the wafer are separated through a cutting process. Currently, when performing wafer level packaging, the main surface of a commonly used optical window is parallel to the optical window of the coupled MEMS micro-mirror device, and both main surfaces of the optical window are plated with an antireflection film, so that the light beam transmittance reaches 99%.

When the laser beam passes through the optical window, a part of the beam is reflected to the view field direction by the two main surfaces of the optical window, and a light spot is generated at a fixed position of the projection surface. Although the light beam reflected by the optical window has only a small energy, the light spot generated by the reflection of the optical window is still not negligible due to the principle of laser display and the integral effect of human eye imaging, and has a negative effect on the laser projection display.

Accordingly, the present invention is directed to an innovative wafer level packaging process for MEMS micro-mirror devices and an optical window for wafer level packaging that can be applied in wafer level packaging of optical MEMS micro-mirror devices. The MEMS micro-mirror device packaged at the wafer level can be further integrated in a laser display module system and can be used for eliminating light spots generated by reflection of an optical window during laser projection display.

The wafer level packaging process disclosed by the invention is innovative on the basis of the traditional process flow, and an additional protection device is not needed to protect the processed device layer structure.

In one possible embodiment, as shown in fig. 1 (b), a schematic diagram of a wafer level packaged MEMS micro-mirror device is shown.

The wafer level packaged MEMS micro-mirror device 100 comprises the following structure: MEMS micro-mirror structure 110 is fabricated by a semiconductor processing process from an SOI wafer comprised of one or more single crystal silicon device layers 111, one or more buried layers 112 of silicon dioxide, and a bottom single crystal silicon substrate layer 113.

In an alternative embodiment, the monocrystalline silicon device layer 111 is between 10 and 100 μm thick, the buried silicon dioxide layer 112 is between 0.1 and 3 μm thick, and the monocrystalline silicon substrate layer 113 is between 100 μm and 1mm thick. Meanwhile, a metal layer is deposited on a specific area of the upper surface of the device layer 111 of the MEMS micro-mirror structure 110, to form a mirror surface 114 and a bonding pad 115 of the MEMS micro-mirror structure 110 as shown. The metal layer material is typically gold, with a thickness between 50 and 500 nm.

MEMS micro-mirror structure 110 comprises a comb structure, in addition to the horizontal comb shown in fig. 1, in other embodiments MEMS micro-mirror structure 110 may comprise a vertical comb structure, or both. The comb structure, torsion shaft, spring, etc. of the MEMS micromirror has various shapes, arrangements, etc. and is not limited to the structures described or shown herein.

The embodiment shown in fig. 1 (b) is an electrostatically actuated MEMS micromirror. The mirror surface can deflect and translate in at least one dimension through movable components such as a comb tooth structure, a torsion shaft, a spring and the like under the driving of electrostatic force. The specific movement mode depends on the comb tooth type of the MEMS micro-mirror and the like. Depending on the type of comb, the mirror can be moved in a periodic resonance or quasi-static motion. In addition, the wafer-level packaged MEMS micro-mirror device described herein may be applied to various types of MEMS micro-mirrors including pyroelectric, piezoelectric, electromagnetic, etc., in addition to the electrostatic MEMS micro-mirrors shown in fig. 1.

The substrate 120 of the micromirror device 100 is made of a semiconductor wafer (typically monocrystalline silicon). After the MEMS micro-mirror structure 110 is fabricated on the SOI wafer by the conventional semiconductor processing technology, the SOI wafer containing the MEMS structure is bonded to the single crystal silicon wafer serving as the substrate 120 at a wafer level, and the bottom single crystal silicon substrate layer 113 of the SOI wafer is bonded and coupled to the substrate 120 by eutectic bonding, glass paste bonding, or the like. The substrate is composed of a variety of encapsulation materials, and in particular, the encapsulation materials may be selected from monocrystalline silicon, ceramics, plastics, and the like.

The material of the optical frame 130 of the micromirror device 100 is monocrystalline silicon or insulating material such as glass, plastic, etc., and in this embodiment, the material of the optical frame 130 is a semiconductor wafer (monocrystalline silicon). After the optical frame 130 is manufactured by the semiconductor processing process, the second main surface (bottom surface) thereof is bonded to the device layer 111 of the MEMS micro-mirror structure by electrically insulating glass paste bonding. For a single MEMS micromirror structure, the optical frame 130 bonded thereto contains one larger-sized optical window structure exposing the movable structures (including the immovable comb structures, etc.) of the MEMS micromirror and several smaller-sized perforated structures, increasing the active space of the micromirror after packaging, and exposing the bonding pads on the MEMS micromirror for later wire bonding. The remaining structures of the MEMS micro-mirror, such as the electrical isolation trenches, etc., are completely encapsulated by the optical frame 130. The optical frame 130 increases the spatial dimensions of the package, providing more deflection space for the MEMS micro-mirrors, helping to reduce air damping.

The optical window 140 of the wafer level package has a major face at an angle α to the frame. The optical window 140 is made of glass wafer and is manufactured by etching technology. The fabrication methods of the optical window 140 are various and are not limited to the fabrication processes described herein. The glass wafer containing the optical window 140 is also provided with a plurality of perforations. The size and the position of the through holes are in one-to-one correspondence with the through holes on the optical frame bonded at the bottom. After the wafer level optical window 140 is fabricated, it is coupled to the first main surface of the optical frame 130 by anodic bonding or the like, as shown in fig. 1. The optical window (glass wafer), the optical frame (monocrystalline silicon wafer) and the substrate (monocrystalline silicon wafer) together form a package for the MEMS micro-mirror, and meanwhile, the through holes corresponding to the optical window and the frame only expose the bonding pad structure on the surface of the MEMS micro-mirror device, so that the subsequent wire bonding is facilitated. The transverse dimension of the perforated structure is w, the overall depth (comprising two layers of the optical window and the optical frame) is d, and the depth-to-width ratio is d/w. In order to facilitate wire bonding, a certain depth-to-width ratio d/w is required to be met during design. In addition, during manufacture, the first main surface and the second main surface of the optical window are plated with an antireflection film, so that the light beam transmittance reaches 99%.

As shown in fig. 1 (b), in operation, the MEMS micro-mirror is rotated or translated in at least one dimension under the control of a drive system. Meanwhile, the MEMS micro-mirror can perform resonance motion or quasi-static motion according to different comb structures. The light beam is incident on the wafer level packaged MEMS micro-mirror device 100 of the present invention at an angle θ. First, when the light beam passes through the wafer-level optical window 140, a part of the light beam is reflected by both principal surfaces of the optical window, respectively, and becomes window reflected light. Since the two main faces of the optical window are at an angle α to the optical frame, window reflected light generated by the main faces is reflected to a direction different from the field of view and is absorbed by a light absorbing material (not shown) that may be contained in the module. After passing through the wafer level optical window 140, the beam is incident on the MEMS micro-mirror and is reflected by the moving mirror surface to form a scanning beam, which is directed in the direction of the field of view.

Embodiment two:

in one possible embodiment, as shown in fig. 2, a schematic diagram of a wafer level packaged MEMS micro-mirror device is provided.

The wafer level packaged MEMS micro-mirror device 200 has a wafer level optical window with a different structure than the wafer level packaged MEMS micro-mirror device 100 described in embodiment one, and the "substrate-MEMS micro-mirror-optical frame-optical window" basic structure of the micro-mirror device is the same. MEMS micro-mirror device 200 has an optical window 240, optical window 240 having 10 major faces, wherein first window major face 241 and second window major face 242 are parallel and parallel to the mirror surface of the MEMS micro-mirror device when resting.

The third window major surface 243 and the fourth window major surface 244 are parallel to each other and are at an angle α to the first frame major surface 231 of the optical frame 230.

The fifth window major face 245 and the sixth window major face 246 are parallel and at an angle β to the first frame major face 231 of the optical frame. The main surfaces of the other windows are parallel to the optical frame, and the main surfaces of the windows are plated with antireflection films, so that the light beam transmittance reaches 99%.

Meanwhile, similar to the embodiment shown in fig. 1, the optical window and frame structure of the embodiment shown in fig. 2 also includes a plurality of through holes with a size w, and the through holes are arranged directly above the bonding pads of the MEMS structure one by one, and the overall thickness of the through holes of 2 layers is d, so that the requirement on the depth-to-width ratio d/w is the same as that of the embodiment shown in fig. 1.

As shown in fig. 2, when a light beam is incident, the light beam is incident on the wafer-level packaged MEMS micro-mirror device 200 at an angle θ. First, when the light beam passes through the wafer-level optical window 240, a part of the light beam is reflected by the third window main surface 243 and the fourth window main surface 244 of the optical window, respectively, and becomes window reflected light. Since the third 243 and fourth 244 window major faces of the optical window are at an angle β to the first frame major face 231 of the optical frame, window reflected light generated by the major faces is reflected in a direction different from the field of view. In an alternative embodiment, a light absorbing material may also be arranged in the module to absorb light reflected by the window. The MEMS micro-mirrors are rotated or translated in at least one dimension under the control of a drive system. Meanwhile, the MEMS micro-mirror can perform resonance motion or quasi-static motion according to different comb structures. After passing through the optical window 240, the beam is incident on the MEMS micro-mirror and reflected by the moving mirror to form a scanning beam, which is directed in the direction of the field of view. Since the window reflected light is not in the view field direction of the scanning beam, the window reflected light is not affected at all during scanning imaging. In some possible embodiments, the optical window 240 is directly bonded to the device layer of the MEMS micro-mirror 210. Compared with the structure shown in fig. 1, when the lateral dimensions of the optical window are the same and the capability of eliminating the light reflected by the window is the same, the unique shape of the optical window 240 enables the optical window to provide enough movable space for the packaged micromirror with smaller height dimension h, and the manufacturing process is the same but the process and the processing difficulty are slightly increased. The ability of the window to cancel reflected light depends on the angle between the main face of the optical window through which the incident light passes and the optical frame, i.e., α in fig. 1 and β in fig. 2, where α is an acute angle and β is an obtuse angle.

In summary, by using the wafer-level optical window structure provided in this embodiment, the optical window function can be realized, and meanwhile, the height h of the optical window can be reduced, so as to realize miniaturization of the whole device.

Embodiment III:

in one embodiment of the present invention, as shown in fig. 3 (a) -3 (m), a schematic process flow diagram of one embodiment of the fabrication of the wafer level packaged MEMS micro-mirror device of the present invention is presented.

An SOI wafer for use in fabricating a MEMS micro-mirror structure is shown in fig. 3 (a). The SOI wafer used is composed of one or more monocrystalline silicon device layers 301, one or more buried layers 302 of silicon dioxide and a bottom monocrystalline silicon substrate layer 303.

In an alternative embodiment, wherein the thickness of the monocrystalline silicon device layer 301 is between 10-100 μm, the thickness of the silicon dioxide buried layer 302 is between 0.1-3 μm, and the thickness of the monocrystalline silicon substrate layer 303 is between 100 μm-1 mm.

As shown in fig. 3 (b), when the MEMS micro-mirror structure is fabricated, the range of the main structure of the micro-mirror is defined on the surface of the wafer device layer 301 by shallow etching, and the main structure includes a mirror surface, a comb structure, and the like. Then, a metal layer is deposited on the surface of the SOI wafer in a range defined by the vapor deposition and lift-off process, so as to form the mirror reflection layer 304 and the bonding pad 305 of the MEMS micromirror.

In an alternative embodiment, the evaporated metal is gold, with a thickness between 50-500 nm.

As shown in fig. 3 (c), when the MEMS micro-mirror structure is fabricated, the main structure of the MEMS micro-mirror, including the mirror surface, the comb structure, the torsion shaft, the electrical isolation groove, etc., is etched in the device layer 301 of the wafer by a deep etching process.

Fig. 3 (d) is a schematic view showing a portion of the arrangement of each MEMS structure on an SOI wafer, and fig. 3 (d) contains 2 complete MEMS structures.

As shown in fig. 3 (e), after the device layer 301 of the wafer has been etched to form the primary structure of the MEMS micro-mirror, the second major surface 332 of the pre-fabricated optical frame 330 is coupled to the device layer 301 of the wafer by glass paste bonding. The optical frame 330 material is a semiconductor wafer (monocrystalline silicon) fabricated by a semiconductor processing process. Optionally, the optical frame 330 may be made of an electrically insulating material such as glass, plastic, or the like.

As shown in fig. 3 (f), after the glass wafer is processed, the obtained optical window blank is coupled to the first main surface 331 of the optical frame 330 by anodic bonding or the like. The pretreatment comprises grinding, polishing, single-sided dry etching in a specific range and the like. After the dry etching is completed, an antireflection layer is further required to be deposited on the main surface 342 formed after the etching. The processing of the glass wafer is specifically illustrated in fig. 4.

As shown in fig. 3 (g), after bonding is completed, the upper surface of the glass wafer is ground and polished, and photoresist or Polyimide (PI) is spin-coated on the upper surface of the glass wafer, and a protective layer 350 is formed after curing to protect the upper surface of the glass wafer in the following process.

Optionally, the lapping and polishing of the upper surface of the glass wafer and the formation of the protective layer 350 may also be performed during the pretreatment of the glass wafer. That is, when the glass wafer is pretreated, the first main surface is polished and polished, and the photoresist or PI is spin-coated on the main surface, and then the protective layer is formed after curing. And then grinding, polishing, dry etching and evaporating an antireflection film on the second main surface of the optical window blank. Through the process, damage to the bonding structure, even the MEMS structure, caused by polishing after bonding can be avoided.

As shown in fig. 3 (h), after the optical window, the optical frame and the SOI wafer are coupled together, the substrate layer 303 of the SOI wafer is subjected to photolithography and etching, and a back cavity is formed within a defined range, exposing the buried layer 302 within the back cavity.

As shown in fig. 3 (i), the exposed buried layer 302 within the back cavity is etched by a dry etching process, releasing the movable structure of the galvanometer. And manufacturing the MEMS micro-mirror structure. During dry etching, the etching time needs to be precisely controlled so as not to influence the optical window by over etching. The dry etching process comprises a dry etching process commonly used in the current stage such as reactive ion etching.

As shown in fig. 3 (j), the fabricated MEMS micro-mirror structure is coupled to the first main surface 321 of the pre-prepared substrate 320 by eutectic bonding or glass paste bonding, thereby completing the wafer level package of the MEMS micro-mirror device. The substrate 320 is a semiconductor wafer, and the material is monocrystalline silicon, and in other embodiments, the substrate may be made of plastic, ceramic, or the like.

As shown in fig. 3 (k), after the wafer substrate is coupled, the passivation layer 350 on the top surface of the optical window blank is removed.

After removing the protective layer 350, a second dry etch is performed on the optical window blank to form a complete optical window 340, as shown in fig. 3 (l).

As shown in fig. 3 (m), after the optical window of the MEMS micro-mirror device packaged at the wafer level is completed, an antireflection film is deposited on the upper surface. After all the above steps are completed, the packaged MEMS micro-mirror device of the present invention at the wafer level can be obtained. Next, it is further required to divide the MEMS micro-mirror device into several independent MEMS micro-mirror devices through conventional semiconductor processing processes such as dicing.

Fig. 3 (m) shows 2 individual, complete wafer-level packaged MEMS micro-mirror devices arranged adjacently on a complete wafer. The "complete wafer" includes 4 layers of wafers, in order from top to bottom, a glass wafer, a single crystal silicon wafer (optical frame), an SOI wafer (MEMS micro-mirror structure), and a single crystal silicon wafer (substrate). In total, 2 cuts are required, with cut lines 361 and 362 for the 2 cuts, respectively. The first dicing is performed along dicing line 361, and after the glass wafer layer 6 is completely diced, dicing is stopped, and the region of the device layer where the bonding pads are integrated is exposed. And cutting along the cutting line 362 for the second time, and stopping cutting after the 4-layer wafer is completely cut, so that the independent and complete MEMS micro-mirror devices packaged at the wafer level are mutually separated. The dicing line 361 is an outer side surface of the optical frame of each MEMS micro-mirror device (error range 0 to +100 μm, first dicing does not allow dicing of the optical frame structure).

Fig. 3 (a) -3 (m) depict the general steps of fabricating a wafer-level packaged MEMS micro-mirror device of the present invention, and the results shown in the embodiment of fig. 2 can be fabricated by the above process flows without loss of generality.

In summary, by applying the process shown in fig. 3, the MEMS structure can be protected by the optical window blank during the back cavity etching, so as to avoid direct contact between the SOI wafer and the vapor deposition metal layer and the etching equipment. Meanwhile, the upper surface (the first main surface) of the optical window blank is not etched, and is still a flat glass wafer surface, so that the optical window blank is beneficial to processing such as coupling and back cavity etching by using the existing process equipment in the actual production and processing process.

In addition, because the optical window and the optical frame structure are bonded in advance, when back cavity etching and movable structure release are carried out, a protective layer is not required to be formed on the surface of a device layer with an MEMS structure through spin coating or PECVD and other processes, and the problems that in the traditional process, the protective layer is difficult to fill, and the protective layer is difficult and incomplete to remove later are directly avoided.

Embodiment four:

in the process flow shown in fig. 3, a semi-processed optical window needs to be prefabricated, and the schematic process flow is shown in fig. 4 (a) -4 (f).

As shown in fig. 4 (a), after polishing and polishing the first main surface 401 of the glass wafer 400, photoresist or Polyimide (PI) is spin-coated on the first main surface, and the protective layer 410 is formed after curing. The inverted glass wafer is flipped over and the second major surface 402 of the glass wafer 400 is polished, lapped, and the like.

As shown in fig. 4 (b), a photoresist layer 420 having a certain thickness d is formed by spin-coating a photoresist on the second main surface 402 of the glass wafer 400 (positive photoresist is exemplified in the following embodiments) after polishing, and pre-baking is performed to promote the solvent in the photoresist film to be sufficiently volatilized, thereby enhancing the adhesion and uniformity of the photoresist on the substrate and preventing the photoresist from contaminating the mask. The pretreatment comprises the basic processes of substrate cleaning, drying, priming and the like in the photoetching process. After the photoresist is coated, the edge photoresist is also removed to prevent the influence on the rest of the pattern caused by photoresist stripping.

After the pre-baking is completed, as shown in fig. 4 (c 1), a plurality of cavities having inclined surfaces are stamped in the photoresist layer 420 using a pre-prepared light-transmitting (quartz) stamp 440 by a molding process. After imprinting is completed, a pattern layer 430 having an inclined surface is formed through a series of processes of exposure, post baking, development (photoresist stripping), and hardening. The hardening can adopt a hard baking process, so that the adhesive film is compact and firm, and the phenomena of undercutting and pinholes during etching are reduced. The optical window has larger size, low requirement on the precision of the inclined plane and the error requirement range of about 1 mu m, so that the optical window is prepared by adopting a simple hard baking process.

The stamp 440 may also be made of a material (nickel) that is opaque or low in light transmittance, and if such a stamp is used, the photoresist layer 420 is heated to a temperature higher than the glass transition temperature of the photoresist used by a hot-melt process, and the photoresist layer is stamped at a certain pressure at the temperature. The application of the hot melt process does not require an exposure operation.

Instead of the stamp 440 used in the embossing process, a gray-scale lithography technique may be used, and a pattern layer may be formed by controlling the light transmittance at the time of exposure using a gray-scale mask 450 prepared in advance, as shown in fig. 4 (c 2).

As shown in fig. 4 (d), the inclined surface of the pattern layer 430 has a thickness t1 and an inclination angle γ. The pattern of the pattern layer 430 is transferred to the glass wafer 400 by a dry etching process. After etching, the thickness of the inclined surface on the glass wafer is t2, and the inclination angle is alpha. the ratio of t2 to t1 approximates the etch selectivity between the glass wafer and the photoresist. In this embodiment, under the same etching conditions, the etching rates of the photoresist and the glass wafer (typically quartz) are different, i.e., the etching selectivity of the two materials is different.

In an alternative embodiment, the reactive ion beam etching is performed with the working gas being trifluoromethane, the ion energy being 500eV, the beam current being 250mA, the accelerating voltage being 200V, and the etching selectivity being about 2.0-3.0. In other embodiments, the etch selectivity of the two materials is the same. Common dry etching processes include reactive ion etching and the like. The specific etching selection ratio and etching process can be selected according to actual requirements, and are not limited to the invention.

In order to obtain a glass wafer having an inclined surface with an inclination angle of a design value α, the thickness t1 of the inclined surface of the pattern layer 430 is designed according to the dry etching process and specific etching conditions (assuming that the lateral dimensions of the optical window are constant, the width is 3 to 4mm, and the length is 5 to 6 mm). Thus, for a process flow employing a stamping process, the pattern size of the stamp 410 used is designed; for a process flow employing a gray scale lithography process, the transmittance of each position in the gray scale mask needs to be designed.

As shown in fig. 4 (e), after the glass wafer is dry etched, a plurality of cavity structures with inclined surfaces are formed. The cavity structure is arranged on the surface of the glass wafer at a position corresponding to the optical frame structure coupled later. And removing the residual photoresist on the surface 401 of the glass wafer to obtain an optical window blank 405.

As shown in fig. 4 (f), an anti-reflection layer 406 is deposited on the upper surface of the obtained optical window blank 405, and all the pretreatment work on the glass wafer described herein is completed, thereby obtaining the wafer-level optical window blank described herein.

The optical window of the structure shown in fig. 2 can also be formed into a blank by a similar process flow.

In addition to the etching process-based process flow shown in fig. 4, the optical window and the embryonic form can be fabricated by a conventional simple hot-melt process.

Fifth embodiment:

in an alternative embodiment, shown in fig. 5 (a) -5 (b), a top view of the wafer level MEMS micro-mirrors before and after packaging is provided, for ease of illustration, fig. 5 (a) is two independent unpackaged MEMS micro-mirrors arranged on the same wafer, and fig. 5 (b) is a schematic view after packaging of fig. 5 (a). Fig. 5 (a) shows two identical packaged MEMS micro-mirror devices arranged adjacent to each other on the same wafer.

As shown in fig. 5 (a), two identical unpackaged MEMS micro-mirror devices are adjacently arranged on an SOI wafer. The MEMS micro-mirror device is fabricated by the process flow shown in fig. 3, and the movable structure of the MEMS micro-mirror device is not released before packaging. As shown in fig. 5 (a), the MEMS micro-mirror device has a mirror structure, a comb structure, a torsion shaft, an anchor point, an electrical isolation groove, and an immovable base, wherein the anchor point and the immovable base are isolated by the electrical isolation groove, and a pad structure is integrated on the surface.

As shown in fig. 5 (b), after the encapsulation is completed, only the pads 520 directly under the through holes are exposed to the air by the through holes penetrating the wafer of each layer. To reduce the process accuracy, the size of the via is slightly larger than the corresponding pad, so that a small amount of SOI wafer (device layer) 511 around the pad is also exposed to air. The remaining structures in the MEMS device, such as the electrical isolation trenches, are encapsulated and not exposed to air. The area 501 is covered with a direct bond optical frame and glass wafer together, for a total of 2 wafers. Only the optical window 1 layer wafer on the region 502 is an inclined surface structure protruding on the glass wafer, and the glass wafer (optical window) in the region is not in direct contact with the SOI wafer (MEMS structure).

Fig. 5 (b) better illustrates the bonding of the optical frame to the SOI wafer. As shown in fig. 5 (b), when the optical frame is bonded to the SOI wafer, the movable structures such as the mirror surface, the comb teeth, and the torsion shaft of the MEMS structure do not participate in the bonding. Only the immovable stage of the MEMS (not including the comb structure), the anchor point of the torsion shaft, and the like are directly bonded to the optical frame. The range 503 of MEMS structures that are not coupled to the optical frame is at or slightly smaller than the range 502 of the corresponding optical window.

Example six:

in combination with the above embodiments, the present embodiment provides a wafer level packaging process suitable for a MEMS micro-mirror device. By applying the process, when back cavity etching is performed, the direct contact between the SOI wafer and the vapor deposition metal layer and etching equipment is avoided through the optical window embryonic form, and the MEMS structure is protected. Meanwhile, the upper surface (the first main surface) of the optical window blank is not etched, and is still a flat glass wafer surface, so that the optical window blank is beneficial to processing such as coupling and back cavity etching by using the existing process equipment in the actual production and processing process. The wafer level packaging process at least comprises the following characteristics:

the optical window of the wafer level packaged MEMS micro-mirror device and the MEMS micro-mirror, when coupled, do not independently complete the entire fabrication process. That is, the glass wafer and the SOI wafer are first separately semi-processed to obtain the blank of the optical window and the MEMS micro mirror. Half-processing of a glass wafer means that only one of the flat main faces of the glass wafer is subjected to single-sided etching, forming a part of one of the main faces of the optical window. The other flat major surface of the glass wafer is not operative. The half processing of the SOI wafer means that the device layer processing is only carried out on the SOI wafer, and comprises shallow etching definition range, metal reflecting layer evaporation, comb structure etching and the like.

After the semi-processing of the SOI wafer is completed, the obtained MEMS micro-mirror blank is coupled with the prefabricated optical frame in a eutectic bonding mode or a glass paste bonding mode.

After finishing the semi-processing of the glass wafer, the obtained optical window blank is coupled with the optical frame-MEMS micro-mirror structure which is coupled in advance, and the coupling mode is anodic bonding and the like.

And when back cavity etching is performed, the coupled optical window embryonic form is used for avoiding direct contact between the SOI wafer device layer and etching equipment and protecting the MEMS structure. Meanwhile, the upper surface (the first main surface) of the optical window blank is not etched, and is still a flat glass wafer surface, so that the optical window blank is beneficial to processing such as coupling and back cavity etching by using the existing process equipment in the actual production and processing process.

And when the movable structure of the MEMS micro-mirror device is released, etching the buried layer of the SOI wafer by using a dry etching process. The etching time of the dry etching process is precisely controlled to prevent over etching.

After the release process is completed, the wafer substrate prepared in advance is coupled with the substrate layer of the SOI wafer, and the wafer level packaging of the MEMS device is completed. The coupling mode is eutectic bonding or glass paste bonding, etc.

MEMS micromirrors that are adapted for use in various actuation schemes include, but are not limited to, electrostatic actuation, electromagnetic actuation, thermoelectric actuation, piezoelectric actuation, and the like.

Example seven

In combination with the foregoing embodiments, the present embodiment also provides an optical window structure, which is suitable for a wafer level package of a MEMS micro-mirror device, and is used for eliminating the influence of window reflected light generated by the reflection of the optical window itself. The optical window structure has the advantages of smaller thickness dimension and better effect. Meanwhile, the optical window reserves the manufacturing process of the optical window adopted by the traditional wafer level packaging, can be manufactured in a mass production mode with low cost, high yield and high process controllability through the existing technical equipment, and is subjected to wafer level packaging through coupling.

The inventive optical window structure for wafer level packaging has at least one of the following features:

the wafer level fabrication is performed from a glass wafer by an etching process. The optical window has at least 6 main faces in addition to the main faces for coupling. Of the 6 main faces, 3 pairs of parallel main faces are total, and 2 main faces parallel to each other are not parallel to the remaining 4 main faces.

Of the 6 main faces, a pair of parallel main faces are at an angle alpha to the coupled optical frame, a pair of parallel main faces are at an angle beta to the coupled optical frame, and a pair of parallel main faces are parallel to the coupled optical frame. The optical frame defines a datum for the packaged micromirror device as a whole.

The 6 main surfaces are plated with antireflection films, so that the transmittance of incident light reaches 99%.

The wafer level optical window can be manufactured by various processing techniques, and mature process techniques such as etching, mould pressing and the like are preferably selected. After the optical window is etched for at least one single side, the optical window is coupled with the optical frame, the MEMS micro mirror and other structures which are coupled in advance. The coupling mode comprises eutectic bonding, anodic bonding, glass paste bonding and the like.

Example eight:

the micro mirror provided by the embodiment of the invention can be used in laser projection equipment or projection equipment carried by a mobile terminal.

Example nine:

the optical window and the blank according to the foregoing embodiments may also be manufactured by a simple thermal fusion process, as shown in fig. 6 (a) -6 (f).

As shown in fig. 6 (a), a glass wafer is first processed, and both main surfaces of the glass wafer 400 are pretreated, and then the first main surface is coupled to a carrier substrate 700. After the second major surface is aligned with the mold 600, the glass wafer 400 is heated to be thermally melted, and a certain pressure is applied to the mold, so that the glass wafer 400 is formed into the shape of the optical window blank and then cooled. The mold 600 is made from a single crystal silicon wafer by an etching process.

As shown in fig. 6 (b), after the carrier substrate is removed, the exposed first main surface is polished, and then a protective layer is formed after curing by spin coating photoresist or PI.

As shown in fig. 6 (c), the single crystal silicon mold 600 is removed by an etching process to obtain the optical window preform.

Alternatively to the above method, the optical window preform may be fabricated and bonded to the MEMS micro-mirror by a step.

As shown in fig. 6 (d). The two major faces of the glass wafer 400 are pre-treated and aligned with the two molds 610, 620. The glass wafer 400 is heated to be thermally melted, and a certain pressure is applied to the mold, so that the glass wafer 400 is cooled after forming the shape of the optical window. The molds 610, 620 are each made from a single crystal silicon wafer by an etching process. The entirety of the mold and glass wafer shown may be referred to as an optical window blank.

In use, as shown in fig. 6 (e), the monocrystalline silicon mold 610 in contact with the first major surface of the glass wafer is removed by an etching process to expose the first major surface of the optical window. Then, an antireflection film is deposited on the inclined surface of the first main surface of the optical window by an evaporation process.

After bonding the first major surface of the optical window to the optical frame (not shown), the monocrystalline silicon mold 620 on the second major surface of the glass wafer is removed by an etching process, exposing the second major surface of the optical window, as shown in fig. 6 (f). Then, an antireflection film is evaporated on the inclined surface of the first main surface of the optical window through an evaporation process, and the optical window is completed.

The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.

Claims

1. A method of manufacturing an optical window, the method comprising:

pretreating a first main surface and a second main surface of a glass wafer (400), and spin-coating a protective layer on the first main surface;

spin-coating photoresist on the second main surface of the glass wafer, and pre-baking the photoresist;

after the pre-baking is completed, stamping a cavity with an inclined plane on the photoresist layer by adopting a mould pressing process, and forming a graph layer (430) with the inclined plane;

transferring the pattern of the pattern layer (430) to the glass wafer (400) by an etching process to form a cavity structure with an inclined surface;

plating an anti-reflection layer on the surface of the cavity structure with the inclined surface to obtain a wafer-level optical window prototype;

coupling the obtained optical window prototype with an optical frame which is coupled in advance;

and after the micromirror body is fully packaged, photoetching and etching the coupled optical window blank to finish a final optical window.

2. A method for fabricating a micromirror, the method comprising:

forming a micromirror body on a first wafer;

forming an optical frame on a second wafer and bonding a first main surface of the micromirror body and the optical frame;

forming a preset part structure of an optical window on a third wafer, and bonding the optical window with the optical frame to complete half-packaging of the micro-mirror body, wherein the optical window is manufactured by the method as claimed in claim 1;

photoetching and etching the first wafer to release the movable part of the micro-mirror body;

bonding the second major face of the micromirror body with a substrate to form a full package for the micromirror body;

photoetching and etching the bonded third wafer to finish a final optical window;

dicing the whole formed by the bonded first wafer, second wafer and third wafer to separate the independent and complete MEMS micro-mirror devices from each other.

3. The method of claim 2, wherein dicing the bonded wafer ensemble to separate individual, complete MEMS micro-mirror devices from each other comprises:

Cutting for the first time along a first cutting line (361), stopping cutting after cutting the third round layer, and exposing a region of the device layer, which is integrated with the bonding pad;

and cutting along a second cutting line (362) for the second time, and sequentially cutting the four layers of structures consisting of the third wafer, the second wafer, the first wafer and the substrate from top to bottom to separate the MEMS micro-mirror devices of the independent complete wafer level package from each other.

4. A method according to claim 2 or 3, characterized in that the prefabricating of the optical window is done by:

pre-treating a first main surface and a second main surface of the third wafer, spin-coating a protective layer on the first main surface, coupling the first main surface with a bearing substrate, and aligning the second main surface with a monocrystalline silicon die; heating the third wafer to be hot-melted, applying a certain pressure to the die, forming the third wafer into the shape of an optical window blank, and then cooling;

and etching to remove the monocrystalline silicon mould, and evaporating an antireflection film on the second main surface with the inclined surface to obtain the optical window blank.

5. A method according to claim 2 or 3, wherein the optical window is completed by:

The first main surface and the second main surface of the third wafer are aligned with the first die and the second die after being pretreated, the third wafer is heated, and pressure is applied to the first die and the second die, so that the third wafer is in the shape of an optical window;

removing the monocrystalline silicon mold in contact with the second major face to expose the second major face of the optical window; evaporating an antireflection film on the inclined plane of the second main surface of the optical window;

bonding the second major surface of the optical window to the optical frame, removing the monocrystalline silicon die on the first major surface of the third wafer to expose the first major surface of the optical window;

an antireflection film is deposited on the inclined surface of the first main surface of the optical window.

6. A micromirror manufactured by the method of any one of claims 2 to 5 or an optical window of the micromirror manufactured by the method of claim 1, the micromirror comprising:

a micromirror body (110) comprising one or more single crystal silicon device layers (111);

a substrate (120);

-an optical frame (130), one main face of the optical frame (130) being bonded to the device layer (111);

the optical window (140) is of a convex window structure and is provided with a first inclined surface, and an included angle is formed between the first inclined surface and the main surface of the optical frame (130).

7. The micromirror according to claim 6, wherein the optical frame (130) has a first perforated structure

And, the optical window (140) has a second perforated structure corresponding to the first perforated structure.

8. The micromirror according to claim 6 or 7, characterized in that,

the optical frame (130) is bonded with the device layer (111) to increase the movable space after the micromirror packaging;

the optical frame (130) is made of an electric insulating material, or the optical frame (130) is made of an electric conducting material;

the optical window (140) covers and encapsulates the micromirror body;

and/or, the first and second perforated structures expose a pad structure (115) of the micromirror.

9. The micromirror according to claim 6, wherein the micromirror body (110) comprises, in addition to the one or more single crystal silicon device layers (111):

one or more buried layers of silicon dioxide (112);

a bottom monocrystalline silicon substrate layer (113).

10. A micromirror manufactured by the method of any one of claims 2 to 5 or an optical window of the micromirror manufactured by the method of claim 1, the micromirror comprising:

A micromirror body comprising one or more monocrystalline silicon device layers;

an optical frame, one major face of the optical frame bonded to the device layer;

the optical window is of a convex window structure and is provided with a first main surface and a second main surface which are parallel to each other, and a first included angle (alpha) is formed between the first main surface and the second main surface and between the first main surface and the first main surface of the optical frame;

the optical window has a third main face and a fourth main face parallel to each other, the third main face and the fourth main face being at a second angle (beta) to the first frame main face of the optical frame.