CN113031254A

CN113031254A - Micro-mirror device, micro-mirror wafer level packaging method and optical window prototype manufacturing method

Info

Publication number: CN113031254A
Application number: CN201911256879.5A
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

Abstract

The invention provides a wafer-level packaging method for a micromirror, which comprises the following steps of preparing a first wafer, wherein the first wafer comprises a device layer, a buried layer and a substrate layer; defining the outline of the micro-mirror on the surface of the device layer, and forming at least one mirror reflection layer and a plurality of bonding pads in a vapor deposition mode in a specific range of the surface of the device layer; exposing a micro-mirror structure defined on the surface of the device layer; coupling a pre-fabricated optical window blank with the device layer; back cavity etching is carried out on the substrate layer within a defined range until the buried layer is formed; etching the buried layer exposed in the range of the back cavity to release the movable part of the micromirror; the substrate layer is coupled with a third wafer to package the micro-mirror structure; and etching the surface of the optical window prototype far away from the first wafer to form a convex window structure. According to the micromirror wafer level packaging method, before the etching of the first wafer back cavity is carried out, the optical window prototype is coupled in advance, so that the working procedures are reduced, the cost is reduced, and the production and processing efficiency is increased.

Description

Micro-mirror device, micro-mirror wafer level packaging method and optical window prototype manufacturing method

Technical Field

The invention relates to the field of optical systems, in particular to a micromirror device, a micromirror wafer-level packaging method and an optical window prototype manufacturing method.

Background

Since the first release of scanning silicon mirrors, Micro Electro Mechanical Systems (MEMS), hereinafter, are widely used in the field of optical scanning, and a large number of technologies and products are 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.

For the MEMS micromirror device with comb structure, the driving of the MEMS micromirror device is affected by the moisture in the air, and the like, so the MEMS micromirror device needs to be sealed and packaged to improve the anti-interference ability and the service life of the system when used for a long time. The common packaging process at present stage is wafer level packaging

In wafer level packaging, the main surface of the optical window is typically parallel to the optical window of the coupled MEMS micro-mirror device. 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.

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 problem, a first aspect of the present invention discloses a micromirror device, comprising:

an optical window having a bay window structure;

a micromirror structure layer having a movable micromirror;

a base layer;

the optical window, the micromirror structure layer and the substrate layer are sequentially connected.

Further, the micromirror structure layer is manufactured by a first wafer through a semiconductor processing technology, and the first wafer comprises a device layer, a buried layer and a substrate layer;

the optical window is coupled to the device layer and the base layer is coupled to the substrate layer.

Furthermore, the optical window comprises a substrate, and the substrate forms the convex window structure towards the recess on the side far away from the micromirror structure layer.

Furthermore, a plurality of contact parts are arranged on the device layer, and the contact parts are bonding pads;

the substrate is further provided with a plurality of through holes distributed on the periphery of the convex window structure, and the through holes correspond to the contact parts, so that the contact parts are exposed.

Further, the bay window structure has at least one inclined plane.

Preferably, the bay window structure is a triangular bay window or a trapezoidal bay window.

Furthermore, at least one groove is formed in one side, facing the micromirror structure layer, of the convex window structure, and the optical window, the micromirror structure and the substrate layer seal the groove to form a closed cavity.

In a second aspect of the present invention, a wafer level packaging method for micro mirrors is provided, which includes the following steps:

preparing a first wafer, wherein the first wafer comprises a device layer, a buried layer and a substrate layer;

defining the outline of the micro-mirror on the surface of the device layer, and forming at least one mirror reflection layer and a plurality of bonding pads in a vapor deposition mode in a specific range of the surface of the device layer;

performing deep etching on the surface of the device layer to form a defined micro-mirror structure;

coupling a pre-fabricated optical window blank with the device layer;

back cavity etching is carried out on the substrate layer within a defined range until the buried layer is formed;

etching the buried layer exposed in the range of the back cavity to release the movable part of the micromirror;

the substrate layer is coupled with a third wafer to package the micro-mirror structure;

and etching the surface of the optical window prototype far away from the first wafer to form a convex window structure.

Further, before the step of back cavity etching the substrate layer to the buried layer within the defined range, the method further includes the steps of: and coating a protective layer on the surface of the optical window prototype far away from the first wafer.

Optionally, the protective layer may also be applied and cured during the preparation of the optical window preform.

Further, the optical window prototype is a second wafer in a semi-finished state, the optical window prototype is provided with a first base surface and a second base surface which are opposite to each other, at least one first groove and at least one second groove are formed in the first base surface, the first grooves and the second grooves are arranged at intervals, and the first grooves are provided with at least one inclined surface.

Further, after the step of etching the surface of the optical window prototype far away from the first wafer to form a convex window structure, the method further comprises the steps of: and cutting the second wafer to expose the bonding pad.

In a third aspect of the present invention, a method for manufacturing an optical window prototype is provided, which includes the following steps:

step one, coating a photoresist layer on one side surface of the pretreated second wafer, and optionally coating and curing the photoresist layer on the other side surface of the pretreated second wafer to form a protective layer;

step two, preparing a pattern layer on the photoresist layer;

step three, transferring the graph of the graph layer to the second wafer;

step four, removing the residual photoresist layer on the surface of the second wafer;

and fifthly, evaporating an antireflection film on the surface of the second wafer with the pattern to complete the manufacturing of the optical window prototype.

Further, the pattern layer is provided with at least one third groove and at least one fourth groove, the third groove is provided with at least one inclined surface, and the volume of the fourth groove is smaller than that of the third groove.

Further, the pattern layer can be prepared by a molding process or gray scale lithography.

By adopting the technical scheme, the technical scheme of the invention has the following beneficial effects:

1) the micro-mirror device belongs to vertical packaging, has a compact structure, and the obtained unit device belongs to millimeter level, has small volume and high integration degree;

2) according to the micromirror wafer level packaging method, before etching of the first wafer back cavity, the optical window prototype is coupled in advance, so that the first wafer and the evaporated metal layer are prevented from being in direct contact with etching equipment, the structure of a finished device layer including an MEMS is protected, an MEMS protective layer does not need to be prepared through the traditional process, the working procedures are reduced, the cost is reduced, the production and processing efficiency is increased, 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 also avoided;

3) the wafer-level packaging method for the micro mirror can be realized by using the existing equipment, and has considerable practicability;

4) the wafer level packaging method of the micro-mirror can be used for producing various wafer level packaged MEMS micro-mirror devices, and the micro-mirror devices can be integrated in various module systems.

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 is a schematic view of a micro-mirror device according to embodiment 1 of the present invention;

FIG. 2 is a schematic view of a micro-mirror device according to embodiment 2 of the present invention;

fig. 3(a) -3 (l) are process flow diagrams of a micromirror wafer level packaging method according to embodiment 3 of the invention;

FIG. 3(m) is a top view of FIG. 3(c 2);

FIG. 3(n) is a top view of a completed wafer level packaged micromirror device of example 3,

FIG. 4(a) -FIG. 4(g) are process flow diagrams of the method for manufacturing the optical window prototype according to embodiment 4 of the present invention;

the following is a supplementary description of the drawings:

110-an optical window; 111-bay window configuration; 112-a substrate; 113-a first major face; 114-a second major face; 115-through holes; 116-an antireflection film; 120-micromirror structure layer; 121-device layer; 122-buried layer; 123-a substrate layer; 124-micro mirror; 125-a reflective layer; 126-contact; 130-a base layer;

210-an optical window; 211-bay window structure; 212-a substrate; 213-a first window; 2131-a first major face; 2132-a second major face; 214-a second window; 2141-a third major face; 2142-a fourth major face; 215-a third window; 2151-fifth major face; 2152-sixth major face; 216-a via hole; 217-antireflection film; 220-a micromirror structure layer; 221-a device layer; 222-a buried layer; 223-a substrate layer; 224-micro mirror; 225-a reflective layer; 226-a contact portion; 230-a base layer;

310-a first wafer; 311-device layer; 312 — a buried layer; 313-a substrate layer; 314-specular reflective layer; 315-pad; 3161-mirror surface; 3162-comb structure; 3163-torsion axis; 3164-electrically isolated trenches; 317-a first area; 318-a second region; 320-a second wafer; 321-a first base surface; 322-a second base surface; 323-a first groove; 324-a second groove; 325-protective layer; 326-bay window configuration; 327-first cut line; 328-a second cut line; 329-antireflection film; 330-third wafer;

401-a second wafer; 4011-a first base surface; 4012-a second base surface; 402-a photoresist layer; 403-graphics layer; 404-a third groove; 405-a fourth groove; 406 — a first groove; 407-a second groove; 408-an antireflection film; 409-a protective layer; 410-a seal; 420-grayscale mask.

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, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are only for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, 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.

Example 1:

as shown in fig. 1, a micromirror device comprises an optical window 110, a micromirror structure layer 120 and a substrate layer 130 sequentially connected from top to bottom in a vertical direction;

the optical window 110 has a bay window structure 111;

the micromirror structure layer 120 has movable micromirrors 124.

The micromirror structure layer 120 is manufactured from a first wafer through a semiconductor process. The first wafer is an SOI wafer that includes a device layer 121, a buried layer 122, and a substrate layer 123. Specifically, the device layer 121 and the substrate layer 123 are composed of one or more layers of single crystal silicon, and the buried layer 122 is composed of one or more layers of silicon dioxide. Preferably, the device layer 121 is between 10 μm-100 μm thick.

The optical window 110 is coupled to the device layer 121. Specifically, the optical window 110 and the device layer 121 are coupled by anodic bonding or the like.

The optical window 110 includes a substrate 112, and the substrate 112 forms the convex window structure 111 towards the recess on the side far away from the micromirror structure layer 120. The louver structure 111 is a triangular louver having opposing first 113 and second 114 major faces, the first 113 and second 114 major faces being parallel. The first main surface 113 and the device layer 121 form a first preset included angle α. The first main surface 113 and the second main surface 114 are both coated with an antireflection film 116, so that the light beam transmittance is 99%. Preferably, the triangular bay window is a right triangle, and the first major surface 113 and the second major surface 114 are inclined surfaces.

The micromirror structure layer 120 includes a fixed part and a movable part, the movable part includes a micromirror 124 and a reflective layer 125, and the reflective layer 125 forms a mirror surface of the micromirror structure layer 120 by vapor-depositing metal on the top surface of the micromirror.

A groove is formed in one side, facing the micromirror structure layer 120, of the bay window structure 111, the optical window 110, the micromirror structure and the substrate layer 130 seal the groove to form a sealed cavity, and the movable part is located in the sealed cavity.

The base layer 130 is coupled to the micromirror structure layer 120. Specifically, after the micromirror structure layer 120 is manufactured by a semiconductor process, the substrate layer 123 and the substrate layer 130 are coupled and connected by eutectic bonding or glass paste bonding. The base layer 130 is a semiconductor wafer, and the material of the base layer 130 is monocrystalline silicon, ceramic, plastic, glass, or the like.

The optical window 110 is made of a glass wafer by an etching technique. In some possible embodiments, the manufacturing method of the optical window 110 is various and is not limited to the manufacturing process mentioned in this embodiment.

A plurality of contact portions 126 are disposed on the device layer 121, and the contact portions 126 are pads.

The substrate 112 is further provided with a plurality of peripheral through holes 115 distributed on the louver structure 111, and the through holes 115 correspond to the contact portions 126, so that the contact portions 126 are exposed. The through hole 115 penetrates the top and bottom surfaces of the substrate 112. The through hole 115 has a depth of d, a width of w, and an aspect ratio of d/w. The through holes 115 need to meet a certain aspect ratio to meet the wire bonding requirements. Except for the bonding pads. The main structures such as the electrical isolation grooves on the device layer 121 are always covered by the optical window 110, so as to realize packaging.

The micromirror structure layer 120 contains comb-tooth structures, and in addition to the horizontal comb-teeth shown in fig. 1, in some possible embodiments, the micromirror structure layer 120 can also contain vertical comb-tooth structures, or both comb-tooth structures. The comb structure, torsion axis, and spring of the micromirror structure layer 120 have various shapes and arrangements, and are not limited to the structure described or shown in this embodiment.

As shown in fig. 1, the present embodiment is an electrostatic 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, besides the electrostatic MEMS micro-mirror shown in fig. 1, the wafer-level packaged MEMS micro-mirror device of the present embodiment can also be applied to various MEMS micro-mirrors including a thermoelectric type, a piezoelectric type, an electromagnetic type, and the like.

In operation, as shown in FIG. 1, a light beam is incident on the micromirror device of the wafer level package of the present invention at an angle θ. First, when the light beam passes through the optical window 110, a part of the light beam is reflected by the first main surface 113 and the second main surface 114 of the optical window 110 as window reflected light, and is reflected to a direction different from the field of view, and is absorbed by a light absorption material (not shown in the figure) which may be contained in the module. The micromirrors rotate or translate in at least one dimension under the control of a drive system. Meanwhile, the micro mirror can perform resonant motion or quasi-static motion according to different comb tooth structures. After passing through the optical window 110, the light beam is incident on the micromirror and reflected by the moving mirror, forming a scanning light beam, and is directed to the field of view. The window reflected light generated by the invention does not influence the imaging effect because the window reflected light is not reflected to the field of view direction.

Example 2:

as shown in fig. 2, a micromirror device comprises an optical window 210, a micromirror structure layer 220 and a substrate layer 230 sequentially connected from top to bottom;

the optical window 210 has a bay window structure 211;

the micromirror structure layer 220 has movable micromirrors 224.

The micromirror structure layer 220 is manufactured from a first wafer through a semiconductor process. The first wafer is an SOI wafer, and the first wafer includes a device layer 221, a buried layer 222, and a substrate layer 223, specifically, the device layer 221 and the substrate layer 223 are composed of one or more layers of monocrystalline silicon, and the buried layer 222 is composed of one or more layers of silicon dioxide. Preferably, the device layer 221 is between 10 μm-100 μm thick.

The optical window 210 is coupled to the device layer 221. Specifically, the optical window 210 and the device layer 221 are coupled by anodic bonding or the like.

The substrate layer 230 is coupled to the micromirror structure layer 220. Specifically, after the micromirror structure layer 220 is manufactured by a semiconductor process, the substrate layer 223 and the substrate layer 230 are coupled and connected by eutectic bonding or glass paste bonding. The base layer 230 is a semiconductor wafer, and the material of the base layer 230 is monocrystalline silicon, plastic, ceramic, or glass.

The optical window 210 includes a substrate 212, and the substrate 212 is recessed away from the micromirror structure layer 220 to form the convex window structure 211.

The bay window structure 211 is a trapezoidal bay window, which includes a first window 213, a second window 214, and a third window 215 connected in sequence,

the first window 213 has a first major face 2131 and a second major face 2132 opposite to each other, the first major face 2131 and the second major face 2132 are parallel, and the first major face 2131 forms a first preset included angle α with the device layer 221;

the second window 214 has opposite third and fourth

main faces

2141, 2142, the third and fourth

main faces

2141, 2142 being parallel, preferably the third main face 2141 being parallel to the device layer 221;

the third window 215 has a fifth and a sixth opposing main faces 2151, 2512, the fifth and sixth main faces 2151, 2512 being parallel, the fifth main face 2151 being at a second predetermined angle β with the device layer 221;

the first major surface 2131, the second major surface 2132, the third major surface 2141, the fourth major surface 2142, the fifth major surface 2151, and the sixth major surface 2512 are each coated with an antireflection film 217 so that the light beam transmittance is 99%. Preferably, the triangular convex window is an isosceles trapezoid, and the first window 213 and the third window 215 are symmetrical with respect to the second window 214.

The micromirror structure layer 220 includes a fixed part and a movable part, the movable part includes a micromirror 224 and a reflective layer 225, the reflective layer 225 forms a mirror surface of the micromirror structure layer 220 by evaporating metal on the top surface of the micromirror 224.

A groove is formed in one side, facing the micromirror structure layer 220, of the convex window structure 211, the optical window 210, the micromirror structure and the substrate layer 230 seal the groove to form a closed cavity, and the movable part is located in the closed cavity.

The optical window 210 is made of a glass wafer by an etching technique. In some possible embodiments, the manufacturing method of the optical window 210 is various and is not limited to the manufacturing process mentioned in this embodiment.

A plurality of contact portions 226 are disposed on the device layer 221, and the contact portions 226 are pads.

The substrate 212 further has a plurality of through holes 216 distributed on the periphery of the louver structure 211, and the through holes 216 correspond to the contact portions 226, so that the contact portions 226 are exposed. The through-hole 216 penetrates the top and bottom surfaces of the substrate 212. The through hole 216 has a depth of d, a width of w, and an aspect ratio of d/w. The via 216 needs to meet a certain aspect ratio to meet the wire bonding requirement. Except for the bonding pads. The main structures such as the electrical isolation grooves on the device layer 221 are always covered by the optical window 210, so as to realize packaging.

The micromirror structure layer 220 contains comb-tooth structures, and in addition to the horizontal comb-teeth shown in fig. 2, in some possible embodiments, the micromirror structure layer 220 can also contain vertical comb-tooth structures, or both comb-tooth structures. The comb structure, torsion axis and spring of the micromirror structure layer 220 have various shapes and arrangements, and are not limited to the structure described or shown in this embodiment.

In operation, as shown in FIG. 2, a light beam is incident on the micromirror device of the wafer level package of the present invention at an angle θ. First, when the light beam passes through the optical window 210, a part of the light beam is reflected by the first main surface 2131 and the second main surface 2132 of the optical window 210 as window reflected light, and since the first main surface 2131 and the second main surface 2132 form a certain angle α with the device layer 221, the window reflected light generated from the main surfaces is reflected in a direction different from the field of view, and is absorbed by a light absorbing material (not shown) that may be included in the module. The micromirrors rotate or translate in at least one dimension under the control of a drive system. Meanwhile, the micro mirror can perform resonant motion or quasi-static motion according to different comb tooth structures. After passing through the optical window 210, the light beam is incident on the micromirror and reflected by the moving mirror, forming a scanning light beam, and is directed to the field of view.

Compared with the structure of embodiment 1, the optical window 210 in this embodiment can provide a larger active space for the micromirror with a smaller height dimension h, i.e. the height h of the structure of embodiment 2 is smaller under the condition of the same active space. The process is the same but the flow and processing difficulty are slightly increased.

Example 3:

a wafer level packaging method of a micromirror comprises the following steps:

first, a first wafer 310 is prepared, wherein the first wafer 310 includes a device layer 311, a buried layer 312 and a substrate layer 313, as shown in fig. 3 (a).

Specifically, in the first step, the first wafer 310 is an SOI wafer, the device layer 311 and the substrate layer 313 are composed of one or more layers of monocrystalline silicon, and the buried layer 312 is composed of one or more layers of silicon dioxide.

Preferably, the device layer 311 is between 10 μm-100 μm thick, the buried layer 312 is between 0.1 μm-3 μm thick, and the substrate layer 313 is between 100 μm-1mm thick.

Step two, defining the outline of the micro-mirror on the surface of the device layer 311, and forming at least one mirror reflection layer 314 and a plurality of bonding pads 315 in a specific range of the surface of the device layer 311 by evaporation;

specifically, in the second step, as shown in fig. 3(b), when the micro-mirror structure is fabricated, the range of the main structure of the micro-mirror is defined on the surface of the device layer 311 by shallow etching, and the main structure includes a mirror surface, a comb structure, and the like; then, one or more layers of metal are evaporated in a specific range on the surface of the device layer 311 by evaporation and lift-off processes to form the specular reflection layer 314 and the pads 315 of the micromirror.

Preferably, the evaporated metal is gold and has a thickness of 0-500 nm.

Exposing the micro-mirror structure defined on the surface of the device layer 311;

specifically, in the third step, as shown in fig. 3(c1), when the micro mirror structure is manufactured, main structures of the micro mirror, including a mirror surface, a comb structure, a torsion axis, an electrical isolation groove, and the like, are etched on the device layer 311 by a deep etching process. Preferably, as shown in fig. 3(c2), two identical micromirror structures are arranged on the same first wafer 310. In some possible embodiments, more micromirror structures, the same or different, can be arranged on the same first wafer 310 to be prepared together.

Step four, coupling a pre-prepared optical window prototype with the device layer 311;

specifically, in the fourth step, as shown in fig. 3(d), after the main structure of the micromirror is etched on the device layer 311, the optical window prototype prepared in advance is coupled with the device layer 311 of the first wafer 310, and preferably, the coupling manner adopts anodic bonding. The optical window preform and the first wafer 310 can also be connected in other ways in some possible embodiments.

Specifically, in the fourth step, the optical window prototype is the second wafer 320 in the half-finished state, the optical window prototype has a first base surface 321 and a second base surface 322 which are opposite to each other, at least one first groove 323 and at least one second groove 324 are formed on the first base surface 321, and the first groove 323 and the second groove 324 are alternately arranged. Preferably, the second wafer 320 is a glass wafer. The semi-processed second wafer 320 is formed by performing dry etching on only one side of the second wafer 320 to form glass wafer main faces alternately arranged by first grooves 323 and second grooves 324; meanwhile, the other base surface of the second wafer 320 is not dry-etched, but only polished, and a protective layer is formed by photoresist or PI curing.

The first groove 323 has at least one inclined surface, and the volume of the second groove 324 is smaller than that of the first groove 323. Preferably, the second groove 324 has no inclined surface and has a smaller depth than the first groove 323. Specifically, the first groove 323 corresponds to the louver structure 326 of embodiment 1, and the second groove 324 corresponds to the through hole for bare bonding pad of embodiment 1.

Preferably, before coupling, the first base surface 321 of the optical window blank is vapor-plated with an antireflection film 329. The antireflection film 329 is evaporated by an evaporation process. Preferably, the antireflection film 329 may be evaporated only on the inclined surface of the first groove. Further, the specific process flow of the optical window prototype is not elaborated again, and is specifically described in embodiment 4.

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.

Step five, coating a protective layer 325 on the surface of the optical window prototype far away from the first wafer 310;

specifically, in the fifth step, as shown in fig. 3(e), after the optical window blank is coupled with the first wafer 310 into a whole, the second base surface 322 of the optical window blank is polished, and then the protective layer 325 is formed after curing by spin-coating a photoresist or PI, so as to protect the second base surface 322 of the second wafer 320 from being damaged by contact with equipment.

Alternatively, in other embodiments, the above operations may be performed on the second base surface 322 of the second wafer 320 when processing the optical window preform.

Sixthly, back cavity etching is carried out on the substrate layer 313 within a definition range until the buried layer 312 is obtained;

specifically, in the sixth step, as shown in fig. 3(f), the substrate layer 313 is subjected to photolithography and etching, and back cavity etching is performed within a defined range, so as to expose the buried layer 312 within the back cavity. Preferably, the bonded integrated optical window precursor and micromirror structure are inverted for ease of processing.

Step seven, etching the buried layer 312 exposed in the range of the back cavity to release the movable part 326 of the micromirror;

specifically, in the seventh step, as shown in fig. 3(g), the buried layer 312 exposed in the back cavity area is etched by a dry etching process, the movable portion 326 of the micromirror of the galvanometer is released, and the micromirror structure is completed. During dry etching, the etching time needs to be precisely controlled so as to avoid the influence of over-etching on the prototype of the optical window.

Step eight, coupling the substrate layer 313 and the third wafer 330 to package the micro-mirror structure;

specifically, in the eighth step, as shown in fig. 3(h), the completed micromirror structure is coupled to a third wafer 330 prepared in advance by eutectic bonding or glass paste bonding, so as to complete the wafer-level packaging of the micromirror device. The third wafer 330 is the base layer in embodiment 1, the third wafer 330 is a semiconductor wafer, and the material of the third wafer 330 is monocrystalline silicon.

Step nine, removing the protection layer 325, and etching the surface of the optical window prototype far away from the first wafer 310 to form a convex window structure 326;

specifically, in the ninth step, after the third wafer 330 is coupled to the substrate layer 313, the protection layer 325 protecting the second wafer 320 is removed, as shown in fig. 3 (i). Then, a photoresist is spin-coated, and after the processes of exposure, development, hardening and the like, the second base surface 322 of the second wafer 320 is dry-etched to form the protrusion window structure 326, as shown in fig. 3 (j). The second base surface 322 after the etching is characterized in that: first, the second base plane 322 has an inclined plane corresponding to the first base plane 321, and together form an optical window structure of a wafer level package; secondly, by controlling the etching depth, it is ensured that the second base plane 322 forms a thin layer right above the first groove 323 without etching through the second glass wafer. After the window structure 326 is formed, an antireflection film 329 is vapor-deposited on the second base surface 322, as shown in fig. 3 (k).

Step ten, cutting the second wafer 320 to expose the bonding pad 315;

specifically, in the tenth step, as shown in fig. 3(l), after the wafer level package is completed, a thin layer of the second wafer 320 is cut along a first cutting line 327 by a laser cutting process, so that the pad 315 is exposed to the air. Further, the packaged micromirror devices are separated from the whole body into individual wafer-level packaged micromirror devices by cutting along the second cutting line 328. Fig. 3(m) is a top view of the first wafer 310 before being coupled to the second wafer 320, i.e., the top view of fig. 3(c 2). As shown in fig. 3(m), the main structures of the micromirror, including the mirror surface 3161, the comb structure 3162, the torsion axis 3163, the electrical isolation groove 3164, etc., have been etched on the device layer 311 by a deep etching process. Meanwhile, a plurality of bonding pads 315 are evaporated on the surface of the device layer 311. Fig. 3(m) is a schematic diagram, and the number, size, distribution, etc. of the bonding pads 315 can be designed according to actual needs.

Fig. 3(n) is a top view of the completed wafer-level packaged micromirror device, which is divided into two schematic diagrams 3(n1) and 3(n2) for convenience of description. As shown in fig. 3(n1), the first wafer 310 containing micro mirror structures is almost completely covered by the second wafer 320 containing the window structures 326. When the second wafer 320 is coupled to the first wafer 310, the range of the window structure 326 is larger than the ranges of the mirror 3161 and the comb structures 3162, and the coupling positions of the two layers of wafers have a certain distance from the frames of the comb structures and the mirror 3161.

Preferably, as shown in fig. 3(n1), the first wafer 310 is in direct contact with the second wafer 320 in the second region 318, and is not in direct contact with the second wafer 320 in the first region 317 corresponding to the bay window structure 326. As shown in fig. 3(n2), the glass wafer has a plurality of through holes penetrating the entire glass wafer, exposing the pads 315 integrated on the first wafer 310 directly below, and leaving a few portions of the first wafer 310 reserved for reducing the process accuracy. The main structures of the electrical isolation grooves 3164 and the like on the first wafer 310 are not exposed to the air except for the bonding pads 315.

The above process flow is mainly for the production of the product of example 1, and the same method is also used for the production of the product of example 2, with the difference only in the bay window structure 326.

The wafer level packaging process of the embodiment is suitable for MEMS micro-mirrors with driving modes, including but not limited to electrostatic driving, electromagnetic driving, thermoelectric driving, piezoelectric driving, and the like. The wafer level packaging process described in this embodiment is applicable to optical windows of various shapes, and is not limited to the optical windows shown in embodiments 1 and 2.

Example 4:

a method for manufacturing an optical window prototype comprises the following steps:

step one, coating a photoresist layer 402 on one side surface of a pretreated second wafer 401;

in the first step, the second wafer 401 has a first base surface and a second base surface opposite to each other, as shown in fig. 4(a1), a photoresist (positive photoresist is taken as an example in the following embodiment) is spin-coated on the first base surface of the second wafer 401 after the pretreatment, a photoresist layer 402 with a certain thickness is formed, and a pre-bake is performed to promote the solvent in the photoresist film to be sufficiently volatilized, so that the adhesion and uniformity of the photoresist on the substrate are enhanced, and the photoresist is prevented from contaminating 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 needs to be removed, so that the influence on the pattern of the rest part caused by the stripping of the photoresist in the photoetching process is avoided. The pretreatment also comprises the working procedures of grinding, polishing and the like.

Step two, preparing a pattern layer 403 on the photoresist layer 402;

in the second step, the patterned layer 403 has at least one third groove 404 and at least one fourth groove 405, the third groove 404 has at least one inclined surface, and the volume of the fourth groove 405 is smaller than that of the third groove 404. Preferably, the fourth groove 405 has no inclined surface and has a smaller depth than the third groove 404. The third grooves 404 and the fourth grooves 405 are arranged at intervals.

The pattern layer 403 can be prepared by a molding process or gray scale lithography.

After the pre-baking is completed, a third groove 404 having an inclined surface and a fourth groove 405 having no inclined surface and a shallow depth are stamped on the photoresist layer 402 by using a stamp 410 prepared in advance through a stamping process, as shown in fig. 4 (b). After the imprinting is completed, the pattern layer 403 having the third groove 404 and the fourth groove 405 is formed through a series of processes of exposure, post-baking, development (resist stripping), and hardening, as shown in fig. 4 (d). The stamp 410 is made of a transparent quartz material. In some embodiments, the stamp 410 can also be made of opaque or low-transmittance material (e.g. nickel), and if such a stamp 410 is used, the photoresist layer 402 is heated to a temperature higher than the glass transition temperature of the photoresist used by a hot melting process, and the photoresist layer 402 is subjected to imprint molding at the temperature and with a certain pressure without subsequent exposure and other operations.

In some embodiments, instead of the stamp 410 used in the embossing process, a gray scale lithography technique may be used, as shown in FIG. 4(c), in addition to the patterning layer 403 produced by the embossing process, using a pre-prepared gray scale mask 420. 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 of the invention has larger size and low requirement on the precision of the inclined plane, and the error requirement range is about 1 μm. Therefore, a simple hard-baking process is adopted here. Deep ultraviolet hard film processes or other processes may also be employed in further embodiments.

Step three, transferring the pattern of the pattern layer 403 to the second wafer 401;

in the third step, specifically, as shown in fig. 4(d), the depth of the third groove 404 structure of the pattern layer 403 is t1, and the inclination angle is γ. The pattern of the pattern layer 403 is transferred to the second wafer 401 by a dry etching process. The third groove 404 is correspondingly transferred to the second wafer 401 to form a first groove 406; the fourth notch 405 is transferred to the second wafer 401 to form a second notch 407. After etching, the depth of the corresponding first groove 406 on the second wafer 401 is t2, and the inclination angle is α. the ratio of t2 to t1 approximates the etch selectivity between the glass wafer and the photoresist. In this embodiment, under the same etching condition, the etching rates of the photoresist and the second wafer 401 are different, that is, the etching selection ratios of the two materials are different. For example, using trifluoromethane as working gas, ion energy is 500eV, beam current is 250mA, acceleration voltage is 200V, and reactive ion beam etching is carried out, wherein the etching selectivity is about 2.30. The material of the second wafer 401 is usually quartz. In some possible embodiments, the etch selectivity of the two materials is the same. Common dry etching processes include plasma reactive ion etching and the like.

In order to obtain the second wafer 401 having an inclined surface and a designed inclination angle α, the depth t1 of the first groove 406 of the pattern layer 403 needs to be designed according to the dry etching process and the specific etching conditions (etching selection ratio), and it is assumed that the lateral dimensions of the optical window are constant, the width is 3-4mm, and the length is 5-6 mm. Therefore, for the process flow of the molding process, the pattern size of the stamp 410 to be used needs to be designed; for a process flow using a gray scale photolithography process, the transmittance at each position in the gray scale mask 420 needs to be designed.

And fourthly, removing the residual photoresist layer 402 on the surface of the second wafer 401 to finish the manufacturing of the optical window prototype.

In the fourth step, specifically, as shown in fig. 4(e), after the etching is completed, the residual photoresist on the surface of the second wafer 401 is removed, so that the designed optical window prototype subjected to single-sided etching can be obtained. Further, as shown in fig. 4(f), an antireflection film 408 is evaporated on one side surface (the first base surface) of the optical window blank having the first groove 406.

In addition, in the first step of this embodiment, the pre-treatment of the second wafer 401 may further include polishing the second base surface, and then forming a protective layer 409 after curing by spin-coating a photoresist or PI, as shown in fig. 4 (g).

The above process flow is mainly directed to the fabrication of the optical window prototype corresponding to the product of example 1, and the method is also applied to the fabrication of the product of example 2, and the difference is only the structure of the first groove 406. The optical window of the structure shown in example 2 can also be made into a prototype by a similar process flow.

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 device, characterized by: the method comprises the following steps:

an optical window having a bay window structure;

a micromirror structure layer having a movable micromirror;

a base layer;

2. The micro-mirror device of claim 1,

the micro-mirror structure layer is manufactured by a first wafer through a semiconductor processing technology, and the first wafer comprises a device layer, a buried layer and a substrate layer;

the optical window is coupled with the device layer and comprises a substrate, and the substrate forms the convex window structure towards the recess on one side far away from the micromirror structure layer.

3. The micro-mirror device of claim 2, wherein the device layer has a plurality of contacts thereon, the contacts being pads;

4. The micro mirror device of claim 2, wherein the bay window structure has at least one inclined surface.

5. A wafer level packaging method for micro mirrors is characterized by comprising the following steps:

deeply etching to form a micro-mirror structure defined on the surface of the device layer;

coupling a pre-fabricated optical window blank with the device layer;

6. The micromirror wafer level packaging method of claim 5, wherein before the step back cavity etching the substrate layer to the buried layer within a defined range, further comprising the steps of: and coating a protective layer on the surface of the optical window prototype far away from the first wafer.

7. The micromirror wafer level packaging method of claim 5, wherein the optical window blank is a second wafer in a semi-processed state, the optical window blank has a first base surface and a second base surface opposite to each other, the first base surface is provided with at least one first groove and at least one second groove, the first grooves and the second grooves are arranged alternately, and the first grooves have at least one inclined surface.

8. The micromirror wafer level packaging method of claim 7, wherein after the step of etching the surface of the rudimentary optical window away from the first wafer to form a bay window structure, further comprising the steps of: and cutting the second wafer to expose the bonding pad.

9. A method for manufacturing an optical window prototype is characterized by comprising the following steps:

step one, coating a photoresist layer on the surface of one side of the second wafer after pretreatment;

step two, preparing a pattern layer on the photoresist layer;

step three, transferring the graph of the graph layer to the second wafer;

10. The method of claim 9, wherein the pattern layer has at least one third groove and at least one fourth groove, and the third groove has at least one inclined surface.

11. The method for manufacturing the optical window blank as claimed in claim 9 or 10, wherein the step one further comprises spin coating and curing a protective layer on the other side surface of the second wafer after the pretreatment.