CN113031253A

CN113031253A - Wafer level micro mirror, optical window and manufacturing method thereof

Info

Publication number: CN113031253A
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: 2021-06-25
Anticipated expiration: 2039-12-09
Also published as: CN113031253B

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 layers of single crystalline silicon device layers; an optical frame having one major face bonded to the device layer; the optical frame further comprises an optical window, 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 micro mirror, 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 type of scanning silicon mirror was released in 1980, micro-electro-mechanical systems (MEMS), which is hereinafter referred to as MEMS, has been widely used in the field of optical scanning, and a large number of technologies and products have been developed. The field of optical scanning has become an important direction of MEMS research. With the development of technology, in the past decade, the application of micro-projection technology and numerous medical imaging technologies has become the main direction for the development of current MEMS optical scanning devices, especially laser scanning devices. The development of the miniature projection technology promotes the appearance of some novel products, such as a miniature laser projector with the size of a mobile phone or a smart phone with a laser projection function, a head-up display HUD which is placed in a vehicle and can be used for displaying navigation information when the vehicle is driven, and various wearable devices including a virtual reality technology VR and an augmented reality technology AR which are relatively explosive in the last year.

MEMS systems rely on external electrical actuation to generate micro-displacements or micro-actuation forces, forming critical actuation components of the overall system. From the present point of view, the structural design of the MEMS itself, as well as the package protection for the MEMS structure, form important factors that affect its performance and lifetime.

When the MEMS micro-mirror device is applied to micro-projection technology, the MEMS structure needs to be packaged with a transparent material such as glass, which is called a window, so as to protect the MEMS structure and simultaneously enable a light beam to enter the micro-mirror and be reflected by the micro-mirror to be directed to a field of view. However, in practical applications, when the light beam passes through the window structure, a very small amount of light will be reflected by the window structure and directed in the direction of the field of view. The reflected light of the window structure is projected onto the image forming surface together with the scanning beam for image formation, but the reflected light of the window structure is projected onto one point at all times unlike the scanning beam for image formation. Therefore, in the integration time of human eyes, the window reflected light with extremely weak energy can form an obvious bright spot on the imaging surface, and the imaging quality is influenced.

In addition, in the conventional MEMS micro-mirror manufacturing process, a wafer on which a device layer structure is formed needs to be inverted, and a back cavity is formed and a movable structure of the device layer is released through an etching process. Before inversion of a wafer, a protective layer is formed on the surface of a device layer of the wafer by spin coating or PECVD, and the protective layer is usually made of photoresist. However, since the MEMS structure is formed on the surface of the device layer when the protection layer is formed, and the device layer has a large aspect ratio, it is difficult to perform the filling operation during the formation of the protection layer or the subsequent removal operation of the protection layer.

Disclosure of Invention

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 micro mirror is provided, which includes: a micromirror body (110) comprising one or more layers of single crystalline silicon device layers (111); a substrate (120); an optical frame (130), one major 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 layers of single crystalline silicon devices; an optical frame having one major face 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 first main surface as well as between the second main surface and the first frame main surface of the optical frame; the optical window is provided with a third main surface and a fourth main surface which are parallel to each other, and the third main surface and the fourth main surface form a second included angle beta with the first frame main surface 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 a 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 surface on the photoresist layer by adopting a mould pressing process, and forming a pattern layer with an inclined surface; transferring the pattern of the pattern layer to a glass wafer through an etching process to form a cavity structure with an inclined surface; 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 of fabricating a micromirror comprises: forming a micromirror body on a first wafer; forming an optical frame on a second wafer and bonding the first major surface of the micromirror body with the optical frame; forming an optical window on a third wafer and bonding the optical window to the optical frame to complete half-packaging of the micromirror body; photoetching and etching the first wafer to release the movable part of the micromirror body; bonding the second main surface of the micro mirror body with a substrate to form a full package of the micro mirror body; photoetching and etching the bonded third wafer to complete a final optical window; and cutting the whole formed by the bonded first wafer, the bonded second wafer and the bonded third wafer to separate the independent and complete MEMS micro-mirror devices from each other. The invention has the following beneficial effects:

when the MEMS structure and the substrate are coupled, an extra protective layer is not needed to be prepared through the traditional process to protect the processed device layer structure, and the problems that the early-stage protective material is difficult to fill and the later-stage protective material is difficult to remove when the traditional process is adopted are avoided.

And secondly, the packaging process belongs to the wafer level, the production efficiency is high, and the cost is low.

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

And fourthly, an optical frame structure is newly added in the packaging process, a larger deflection space is provided for the packaged MEMS micro-mirror, and the reduction of air damping is facilitated.

And fifthly, the optical window is suitable for wafer-level packaging of the MEMS micro-mirror device, is used for eliminating the influence of window reflected light generated by reflection of the optical window, and can remarkably improve the anti-interference capability and prolong the service life of the system after being sealed and packaged for a long time.

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

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1(a) is a schematic structural 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 wafer-level packaged MEMS micro-mirror device 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), fig. 3(m) are schematic process flow diagrams of the wafer-level packaged MEMS micro-mirror device according to the embodiment of the present invention;

fig. 4(a), fig. 4(b), fig. 4(c1), fig. 4(c2), fig. 4(d), fig. 4(e) fig. 4(f) are flow charts of optical window processing processes provided by the embodiments of the present invention;

FIG. 5(a) is a top view of a wafer-level MEMS micro-mirror provided by an embodiment of the present invention before packaging;

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

fig. 6(a) -6(f) are schematic diagrams of the optical window forming process provided by the embodiment of the invention.

Detailed Description

The technical solution 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 is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present 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 is to be understood that the terms "upper", "lower", "top", "bottom", and the like, as used herein, refer to an orientation or positional relationship based on that shown in the drawings, which is for convenience and simplicity of description, and does not indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," and the like are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein.

The first embodiment is as follows:

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 or the like in the air affects the driving of the MEMS micro-mirror device, and thus the MEMS micro-mirror device needs to be packaged. A commonly used packaging process at the present stage is wafer level packaging, that is, in the process of manufacturing the MEMS micromirror device by semiconductor processing on the SOI wafer, the glass wafer is directly used for packaging on the wafer level. After the packaging is finished, all the unit MEMS micro-mirror devices on the wafer are separated out through a cutting process. At present, when wafer level packaging is performed, a main surface of a commonly used optical window is parallel to an optical window of a coupled MEMS micro-mirror device, and both main surfaces of the optical window are plated with antireflection films, so that a light beam transmittance reaches 99%.

And when the laser beam penetrates through the optical window, part of the beam is reflected to the field of view 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 and has a negative effect on the laser projection display due to the principle of laser display and the integration effect of human eye imaging.

Accordingly, the present invention is directed to a novel wafer level packaging process for MEMS micro-mirror devices and an optical window for wafer level packaging, which can be applied in wafer level packaging of optical MEMS micro-mirror devices. The wafer-level packaged MEMS micro-mirror device 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 is innovated on the basis of the traditional process flow, and does not need to use an additional protection device to protect the processed device layer structure.

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

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

In an alternative embodiment, the thickness of the monocrystalline silicon device layer 111 is between 10 and 100 μm, the thickness of the buried silicon dioxide layer 112 is between 0.1 and 3 μm, and the thickness of the monocrystalline silicon substrate layer 113 is between 100 μm and 1 mm. Meanwhile, a metal layer is evaporated on a specific area 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. The metal layer is usually made of gold and has a thickness of 50-500 nm.

The MEMS micro-mirror structure 110 includes a comb structure, and in addition to the horizontal comb shown in fig. 1, in other embodiments, the MEMS micro-mirror structure 110 may include a vertical comb structure, or both comb structures. The comb structure, torsion axis and spring of the MEMS micromirror have various shapes and arrangements, and are not limited to the structures described or shown herein.

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

The substrate 120 of the micro mirror device 100 is a semiconductor wafer (typically single crystal silicon). After the MEMS micro-mirror structure 110 is fabricated on the SOI wafer by a conventional semiconductor processing process, the SOI wafer containing the MEMS structure is wafer-level bonded to the single-crystal silicon wafer as the substrate 120, and the single-crystal silicon substrate layer 113 at the bottom of the SOI wafer is bonded and coupled to the substrate 120 by eutectic bonding or glass paste bonding. The substrate is made of various packaging materials, and particularly, the packaging materials can be monocrystalline silicon, ceramics, plastics and the like.

The optical frame 130 of the micromirror device 100 is made of single crystal silicon or an insulating material such as glass, plastic, etc., and in this embodiment, the optical frame 130 is made of a semiconductor wafer (single crystal silicon). After the optical frame 130 is manufactured by a semiconductor process, the second main surface (bottom surface) thereof is bonded to the device layer 111 of the MEMS micro-mirror structure by means of electrically insulating glass paste bonding. For a single MEMS micro-mirror structure, the optical frame 130 bonded to the single MEMS micro-mirror structure includes an optical window structure with a larger size and a plurality of through-hole structures with a smaller size, the former exposes the movable structure (including the immovable comb structure, etc.) of the MEMS micro-mirror and increases the moving space of the packaged micro-mirror, and the latter exposes the bonding pad on the MEMS micro-mirror for later wire bonding. The remaining structures of the MEMS micromirror, such as the electrically isolated trenches, etc., are completely encapsulated by the optical frame 130. The optical frame 130 increases the spatial size of the packaged device, provides more deflection space for the MEMS micro-mirrors, and helps to reduce air damping.

The optical window 140 of the wafer level package has a main surface forming an angle alpha with the frame. The optical window 140 is made of a glass wafer by etching. The method of manufacturing the optical window 140 is various and is not limited to the manufacturing process described herein. The glass wafer containing the optical window 140 is also lined with a number of through holes. The size and the position of the through holes correspond to those of the optical frames which are bonded at the bottom in a one-to-one mode. After fabrication of the wafer-level optical window 140, it is coupled to the first major 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) jointly form the package of the MEMS micromirror, 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 micromirror device, so that subsequent wire bonding is facilitated. The transverse dimension of the perforation structure is w, the overall depth (including two layers of the optical window and the optical frame) is d, and the aspect ratio is d/w. In order to facilitate wire bonding, the design needs to satisfy a certain aspect ratio d/w. In addition, during manufacturing, the first main surface and the second main surface of the optical window are coated with antireflection films, so that the light beam transmittance reaches 99%.

In operation, the MEMS micromirror rotates or translates in at least one dimension under the control of a drive system, as shown in fig. 1 (b). Meanwhile, the MEMS micro-mirror can perform resonant motion or quasi-static motion according to different comb tooth structures. The light beam is incident on the wafer-level packaged MEMS micro-mirror device 100 according to the present invention at an angle θ. First, when a light beam passes through the wafer-level optical window 140, a part of the light beam is reflected by both main 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, the window reflection light generated by the main faces is reflected into a direction different from the field of view and is absorbed by the light absorbing material (not shown in the figures) that may be contained in the module. After passing through the wafer level optical window 140, the light beam enters the MEMS micro-mirror and is reflected by the moving mirror, forming a scanning beam, and is directed in the field of view.

Example two:

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

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

The third window main surface 243 and the fourth window main surface 244 are parallel to each other and form an angle α with the first frame main 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 other main surfaces of the 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 one by one right above the bonding pads of the MEMS structure, and the overall thickness of the 2 layers of through holes is d, and the requirement on the aspect 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 window major surface 243 and the fourth window major surface 244 of the optical window are at an angle β with the first frame major surface 231 of the optical frame, the window reflected light generated by the major surfaces is reflected into 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 the window reflected light. The MEMS micromirror rotates or translates in at least one dimension under the control of a drive system. Meanwhile, the MEMS micro-mirror can perform resonant motion or quasi-static motion according to different comb tooth structures. After passing through the optical window 240, the light beam enters the MEMS micro-mirror and is reflected by the moving mirror, forming a scanning light beam, and is directed to the field of view. Since the window reflected light is not in the field of view direction of the scanning beam, the scanning imaging is not affected by the window reflected light at all. In some possible embodiments, the optical window 240 is bonded directly to the device layer of the MEMS micro-mirror 210. Compared to the structure shown in fig. 1, when the lateral dimensions of the optical windows are the same and the capability of eliminating the reflected light of the windows is the same, the unique shape of the optical window 240 enables it to provide enough space for the packaged micromirror with a smaller height dimension h, and the process is the same but the process flow and the processing difficulty are slightly increased. The ability of the window to reflect light is dependent on the angle between the major surface 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, with the wafer level optical window structure provided in this embodiment, the height h of the optical window can be reduced while the optical window function is realized, so as to achieve the miniaturization of the entire device.

Example three:

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

Fig. 3(a) shows an SOI wafer used for fabricating MEMS micro-mirror structures. The SOI wafer used is comprised of one or more layers of single crystal silicon device layers 301, one or more buried layers of silicon dioxide 302 and a bottom single crystal silicon substrate layer 303.

In an alternative embodiment, where the single crystal silicon device layer 301 is between 10-100 μm thick, the buried silicon dioxide layer 302 is between 0.1-3 μm thick, and the single crystal silicon substrate layer 303 is between 100 μm-1mm thick.

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 layer of metal is evaporated in the range defined by the surface of the SOI wafer through evaporation and stripping processes to form the mirror reflection layer 304 and the bonding pad 305 of the MEMS micro-mirror.

In an alternative embodiment, the evaporated metal is gold and has a thickness of 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 axis, and the electrical isolation groove, is etched on the device layer 301 of the wafer by the deep etching process.

Fig. 3(d) is a partial schematic diagram showing the arrangement of the MEMS structures on the SOI wafer, and fig. 3(d) contains 2 complete MEMS structures.

As shown in fig. 3(e), after the main structure of the MEMS micromirror is etched on the device layer 301 of the wafer, the second main surface 332 of the prefabricated optical frame 330 is coupled with the device layer 301 of the wafer by means of glass paste bonding. The optical frame 330 is made of a semiconductor wafer (monocrystalline silicon) and is manufactured through a semiconductor processing technology. Alternatively, the optical frame 330 may be made of an electrically insulating material such as glass, plastic, etc.

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-side dry etching in a specific range and the like. After the dry etching is completed, an anti-reflection layer is evaporated on the main surface 342 formed after the etching. The processing of the glass wafer is described in detail in fig. 4.

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

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

After the optical window, optical frame and SOI wafer are integrally coupled, the substrate layer 303 of the SOI wafer is then etched and etched to define a back cavity exposing the buried layer 302 within the back cavity, as shown in fig. 3 (h).

As shown in fig. 3(i), the movable structure of the galvanometer is released by etching the buried layer 302 exposed in the back cavity area by a dry etching process. And finishing the manufacturing of the MEMS micro-mirror structure. During dry etching, the etching time needs to be precisely controlled so as to avoid the influence of over-etching on the optical window. 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 substrate 320 prepared in advance by eutectic bonding or glass paste bonding, and the wafer-level package of the MEMS micro-mirror device is completed. The substrate 320 is a semiconductor wafer made of 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 coupling of the wafer substrate is completed, the protection layer 350 on the upper surface of the optical window blank is removed.

As shown in fig. 3(l), after the protective layer 350 is removed, the optical window prototype is subjected to a second dry etching process to form a complete optical window 340.

As shown in fig. 3(m), after the optical window of the wafer-level packaged MEMS micro-mirror device is completed, an antireflection film is deposited on the upper surface. After all the above processes are completed, the packaged MEMS micro-mirror device of the present invention can be obtained at a wafer level. Next, the MEMS micromirror device is further divided into several independent MEMS micromirror devices by conventional semiconductor processing techniques 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, which are, 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). A total of 2 cuts were needed, with the cut lines for the 2 cuts being 361 and 362, respectively. And cutting for the first time along a cutting line 361, stopping cutting after the glass wafer layer 6 is completely cut, and exposing the region of the device layer integrated with the bonding pad. And a second cutting is performed along the cutting line 362, the 4-layer wafer is completely cut, and then the cutting is stopped, so that the independent and complete wafer-level packaged MEMS micro-mirror devices are separated from each other. The cutting line 361 is the outer side of the optical frame of each MEMS micro-mirror device (error range 0- +100 μm, the first cutting does not allow cutting the optical frame structure).

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

In summary, by applying the process shown in fig. 3, when the back cavity etching is performed, the direct contact between the SOI wafer and the vapor-deposited metal layer and the etching apparatus can be avoided through the optical window prototype, so as to protect the MEMS structure. Meanwhile, the upper surface (the first main surface) of the optical window prototype is not etched and is still a flat glass wafer surface, so that the existing process equipment is favorable for processing such as coupling, back cavity etching and the like in the actual production and processing process.

In addition, because the optical window and the optical frame structure are bonded in advance, a protective layer does not need to be formed on the surface of the device layer with the MEMS structure by processes such as spin coating or PECVD (plasma enhanced chemical vapor deposition) when back cavity etching and movable structure release are carried out, and the problems that the protective layer is difficult to fill and the protective layer is difficult to remove and incomplete in the traditional process are directly avoided.

Example four:

in the process flow shown in fig. 3, a semi-finished optical window needs to be manufactured in advance, and the process flow schematic diagrams thereof are shown in fig. 4(a) -4 (f).

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

As shown in fig. 4(b), a photoresist (positive photoresist is taken as an example in the following embodiment) is spin-coated on the second main surface 402 of the glass wafer 400 which is polished, a photoresist layer 420 with a certain thickness d is formed, and a 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 simultaneously preventing the photoresist from staining the mask. The pretreatment comprises basic processes of substrate cleaning, drying, priming and the like in the photoetching process. After the photoresist is coated, the edge photoresist is also required to be removed so as to prevent the influence on the pattern of the rest part caused by the stripping of the photoresist.

After the pre-bake is completed, a number of cavities with tilted surfaces are imprinted in the photoresist layer 420 using a pre-prepared transparent (quartz) stamp 440 using an embossing process, as shown in fig. 4(c 1). After the imprinting is completed, the pattern layer 430 having the inclined surface is formed through a series of processes of exposure, post-baking, development (resist stripping), and hardening. The hard baking process can be adopted for hardening the film, so that the glue film is compact and firm, and the phenomena of undercutting and pinholes during etching are reduced. The optical window has larger size, the requirement on the precision of the inclined plane is not high, and the error requirement range is about 1 mu m, so the optical window can be prepared by adopting a simple hard baking process.

The stamp 440 may also be made of a material (nickel) with no or low 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 melting process, and the photoresist layer is imprinted at the temperature under a certain pressure. The application of the hot melt process eliminates the need for an exposure operation.

Instead of the stamp 440 used in the embossing process, a gray scale lithography technique may be used instead of the embossing process using a gray scale mask 450 prepared in advance to form a pattern layer by controlling the transmittance of light upon exposure, 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, the etching rates of the photoresist and the glass wafer (usually quartz) are different under the same etching condition, i.e. the etching selectivity ratio of the two materials is different.

In an optional embodiment, trifluoromethane is used as a working gas, the ion energy is 500eV, the beam current is 250mA, the acceleration voltage is 200V, reactive ion beam etching is carried out, and the etching selectivity is 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 the etching process can be selected according to actual requirements, and are not limited in the invention.

In order to obtain a glass wafer with an inclined surface and a designed inclination angle α, the thickness t1 of the inclined surface of the pattern layer 430 needs to be designed according to the dry etching process and the specific etching conditions (assuming that the lateral dimensions of the optical window are all constant, the width is 3-4 mm, and the length is 5-6 mm). Therefore, for the process flow of the molding process, the pattern size of the used stamp 410 needs to be designed; for a process flow using a gray scale photolithography process, transmittance at each position in a 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 prototype 405.

As shown in fig. 4(f), an anti-reflection layer 406 is evaporated on the upper surface of the obtained optical window prototype 405, and all pretreatment operations on the glass wafer described herein are completed, so as to obtain the wafer-level optical window prototype described herein.

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

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

Example five:

in an alternative embodiment, as shown in fig. 5(a) -5(b), top views of wafer-level MEMS micromirrors before and after packaging are provided, and for convenience of illustration, fig. 5(a) is two independent unpackaged MEMS micromirrors arranged on the same wafer, and fig. 5(b) is a schematic diagram of fig. 5(a) after packaging. Two identical packaged MEMS micro-mirror devices arranged adjacent to each other on the same wafer in fig. 5 (a).

As shown in fig. 5(a), two identical unpackaged MEMS micro-mirror devices are arranged adjacent to each other on an SOI wafer. The MEMS micro-mirror device is manufactured 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 includes a mirror structure, a comb structure, a torsion axis, an anchor point, an electrical isolation groove, and an immovable base platform, wherein the anchor point and the immovable base platform are isolated by the electrical isolation groove, and a pad structure is integrated on a surface of the anchor point and the immovable base platform.

After the packaging is completed, only the pads 520 directly under the through holes are exposed to the air through the through holes penetrating the wafers of the respective layers, as shown in fig. 5 (b). To reduce the process accuracy, the size of the through-hole is slightly larger than the corresponding pad, so that a little SOI wafer (device layer) 511 around the pad is also exposed to the air. The remaining structures in the MEMS device, such as the electrically isolated trenches, are encapsulated and not exposed to air. The area 501 is covered with a directly bonded optical frame and glass wafer, which are 2 layers of wafers. The region 502 has only the optical window 1 wafer, which is a raised inclined plane structure on the glass wafer, and the glass wafer (optical window) in the region does not directly 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, no movable structures such as the mirror surface, comb teeth, and torsion axis of the MEMS structure participate in the bonding. Only the immovable platform (not including the comb structure) of the MEMS and the anchor point of the torsion axis, etc. are directly bonded to the optical frame. The extent 503 of the MEMS structure that is not coupled to the optical frame is at or slightly less than the extent 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 MEMS micromirror devices. By applying the process, when back cavity etching is carried out, direct contact between the SOI wafer and the vapor plating metal layer and etching equipment is avoided through the optical window prototype, and the MEMS structure is protected. Meanwhile, the upper surface (the first main surface) of the optical window prototype is not etched and is still a flat glass wafer surface, so that the existing process equipment is favorable for processing such as coupling, back cavity etching and the like in the actual production and processing process. The wafer level packaging process at least comprises the following characteristics and steps:

when the optical window and the MEMS micromirror of the wafer-level packaged MEMS micromirror device are coupled, not all the manufacturing processes are completed independently. Namely, the glass wafer and the SOI wafer are respectively subjected to independent half-processing to obtain the rudiment of the optical window and the MEMS micro-mirror. The semi-processing of the glass wafer means that only one flat main surface of the glass wafer is subjected to single-side etching to form a part of the main surface of the optical window. The other flat main surface of the glass wafer is not manipulated. The semi-processing of the SOI wafer refers to the processing of a device layer only on the SOI wafer, and comprises shallow etching definition range, metal reflecting layer evaporation, comb tooth structure etching and the like.

After the SOI wafer is half-processed, the obtained MEMS micro-mirror prototype is coupled with the optical frame which is manufactured in advance, and the coupling mode is eutectic bonding or glass slurry bonding and the like.

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

When back cavity etching is carried out, direct contact between an SOI wafer device layer and etching equipment is avoided through the coupled optical window prototype, and the MEMS structure is protected. Meanwhile, the upper surface (the first main surface) of the optical window prototype is not etched and is still a flat glass wafer surface, so that the existing process equipment is favorable for processing such as coupling, back cavity etching and the like 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.

And after the release process is finished, coupling the wafer substrate prepared in advance with the substrate layer of the SOI wafer to finish wafer-level packaging of the MEMS device. The coupling method is eutectic bonding or glass paste bonding.

The MEMS micro-mirror is suitable for various driving modes, including but not limited to electrostatic driving, electromagnetic driving, thermoelectric driving, piezoelectric driving and the like.

EXAMPLE seven

In combination with the foregoing embodiments, the present embodiment further provides an optical window structure suitable for wafer-level packaging of MEMS micro-mirror devices, for eliminating the effect of window reflected light generated by reflection of the optical window itself. The optical window structure has the advantages of smaller thickness and better effect. Meanwhile, the optical window reserves the manufacturing process of the optical window adopted by the traditional wafer level packaging, can be produced and manufactured in a large batch manner in a low-cost, high-yield and high-process controllability mode through the existing technical equipment, and is coupled to carry out wafer level packaging.

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

and carrying out wafer-level manufacturing on the glass wafer through an etching process. The optical window has at least 6 main faces in addition to the main face for coupling. Of the 6 main surfaces, there are 3 pairs of parallel main surfaces in total, and 2 main surfaces parallel to each other are not parallel to the remaining 4 main surfaces.

Of the 6 major faces, a pair of parallel major faces makes an angle α with the coupled optical frame, a pair of parallel major faces makes an angle β with the coupled optical frame, and a pair of parallel major faces is parallel with the coupled optical frame. The optical frame defines a reference plane for the packaged micromirror device as a whole.

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

The wafer-level optical window can be manufactured by various processing technologies, and mature process technologies such as etching, die pressing and the like are preferably selected. After the optical window is subjected to at least one-sided etching, the optical window is coupled with the optical frame, the MEMS micro-mirror and other structures which are coupled in advance. The coupling method includes 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 preform in the foregoing embodiments can also be manufactured by a simple hot-melt process, as shown in fig. 6(a) -6 (f).

As shown in fig. 6(a), the glass wafer is first processed, and after both main surfaces of the glass wafer 400 are pretreated, the first main surface is coupled to the carrier substrate 700. After the second main surface is aligned with the mold 600, the glass wafer 400 is heated to be hot-melted, and a certain pressure is applied to the mold to form the glass wafer 400 into the shape of the optical window blank, followed by cooling. 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 photoresist or PI is applied by spin coating, and a protective layer is formed after curing.

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

Alternatively to the above method, the optical window preform can be fabricated and bonded to the MEMS micro-mirror in the following steps.

As shown in fig. 6 (d). The two major faces of the glass wafer 400 are pre-treated and then aligned with the two

molds

610, 620. The glass wafer 400 is heated to be hot-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. Both

molds

610, 620 are made from a single crystal silicon wafer by an etching process. The entirety of the mold shown with the glass wafer may be referred to as an optical window blank.

In use, as shown in fig. 6(e), the single crystal silicon mold 610 in contact with the first main surface of the glass wafer is removed by an etching process to expose the first main surface of the optical window. And then, evaporating a layer of antireflection film on the inclined plane of the first main surface of the optical window through an evaporation process.

After bonding the first main surface of the optical window to the optical frame (not shown), the single crystal silicon mold 620 on the second main surface of the glass wafer is removed by an etching process to expose the second main surface of the optical window, as shown in fig. 6 (f). And then, evaporating a layer of antireflection film on the inclined plane of the first main surface of the optical window through an evaporation process, and finishing the optical window.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A micro mirror, comprising:

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

a substrate (120);

an optical frame (130), one major 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).

2. The micromirror of claim 1, 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.

3. The micro mirror according to claim 1 or 2,

the optical frame (130) is bonded with the device layer (111) to increase the movable space after the micro mirror is packaged;

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

the optical window (140) is covered and packaged with the micromirror body;

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

4. The micromirror of claim 1, wherein the micromirror body (110) comprises, in addition to the one or more single crystalline silicon device layers (111):

one or more buried layers of silica (112);

a bottom monocrystalline silicon substrate layer (113).

5. A micro mirror, comprising:

a micromirror body comprising one or more layers of single crystalline silicon device layers;

an optical frame having one major face 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, the third main face and the fourth main face forming a second angle (β) with the first frame main face of the optical frame.

6. 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 coating a protective layer on the first main surface in a spinning mode;

spin-coating a 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 surface on the photoresist layer by adopting a mould pressing process, and forming a pattern layer (430) with an inclined surface;

transferring the pattern of the pattern layer (430) to the glass wafer (400) through an etching process to form a cavity structure (450) with an inclined surface;

and plating an anti-reflection layer on the surface of the cavity structure with the inclined surface.

7. A method of fabricating a micromirror, the method comprising:

forming a micromirror body on a first wafer;

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

forming an optical window on a third wafer and bonding the optical window to the optical frame to complete half-packaging of the micromirror body;

photoetching and etching the first wafer to release the movable part of the micromirror body;

bonding the second main surface of the micro mirror body with a substrate to form a full package of the micro mirror body;

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

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

8. The method of claim 7, wherein the step of dicing the bonded wafer assembly to separate the individual and complete MEMS micro-mirror devices from each other comprises:

cutting for the first time, wherein cutting is carried out along a first cutting line (361), and cutting is stopped after the third round layer is cut, so that the region of the device layer integrated with the bonding pad is exposed;

and a second cutting step, wherein the cutting step is carried out along a second cutting line (362), and a four-layer structure consisting of a third wafer, a second wafer (optical frame), a first wafer and a substrate is sequentially cut from top to bottom, so that the independent and complete wafer-level packaged MEMS micro-mirror devices are mutually separated.

9. The method of claim 7 or 8, wherein the pre-fabricating optical window is accomplished by:

pretreating the first main surface and the second main surface of the third wafer, coating a protective layer on the first main surface in a spinning mode, then 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 certain pressure to the die, and cooling the third wafer after the third wafer is formed into the shape of the optical window prototype;

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

10. The method of making a micromirror according to claims 7 and 8, wherein the optical window is completed by the following steps:

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

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

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

and evaporating a layer of antireflection film on the inclined surface of the first main surface of the optical window.