DE102017222404A1 - SECONDARY MIRROR - Google Patents

Abstract

A mirror (150) includes a mirror front side (151) that includes a reflective layer. The mirror (150) also includes a mirror backside (152). The mirror backside (152) comprises a frame structure (157) with ribs (158) and cavities (159). The mirror front side (151) and the mirror back side (152) are not formed in one piece.

Description

TECHNICAL AREA

Various embodiments of the invention relate to techniques for producing a mirror, e.g. for a scanning module suitable for resonant scanning of light, e.g. for use by a LIDAR system. Various examples of the invention relate specifically to a two-part production process in which a mirror front side and a mirror back side are separately produced and subsequently coupled.

BACKGROUND

Mirrors for scanning light (scanning mirrors) are required in various applications. An exemplary use case is distance measurement using light (light detection and ranging; LIDAR). Pulsed or continuous laser light is transmitted and detected after reflection on an object. To provide lateral resolution, the light may be scanned using a scanning mirror.

Techniques for producing scanning mirrors are for example US 7,078,778 B2 known. Such techniques typically employ microelectromechanical systems (MEMSs). Here, the mirror is defined by a wafer, such as a silicon wafer. The wafer is processed using one or more of the following techniques: lithography; dry; wet etching; Take off; etc.

Conventional techniques for fabricating a scanning mirror using MEMS techniques are faced with certain limitations and disadvantages. For example, in some scenarios, it may be desirable to make a mirror with a comparatively large diameter of the respective reflective layer. In particular, this can facilitate the implementation of large emitter apertures and / or detector apertures for the particular optics. Then, when using MEMS techniques, it is typically necessary to remove a substantial amount of wafer material using etching. A typical MEMS technique relies on deep reactive ion beam etching (DRIE). An exemplary DRIE process is accomplished US 5,501,893 A described. However, when such a DRIE process is used to remove large quantities of material - as is typically found in the manufacture of large diameter mirrors - certain technical limitations are encountered: for example, process gas / etching gas may not readily operate at the required high rates be supplied. This can lead to concentration gradients over the wafer; This leads to inhomogeneous etch rates over the wafer. Inhomogeneous etching is highly undesirable because structures positioned at different positions over the wafer are then processed differently. This makes it hard to implement a process. A second disadvantage of conventional DRIE processes used in conjunction with MEMS techniques is that heat introduced into the system increases with the increase in volume of removed material. Then, when producing mirrors with a large diameter, the cooling capacity - for example, of backside cooling - may not be sufficient to limit the temperature rise. Furthermore, temperature gradients can be observed across the wafer, again resulting in inhomogeneous processing. Conventional DRIE processes have limitations in terms of making large mirrors that are relatively lightweight.

SUMMARY

Therefore, there exists a need for advanced techniques for producing mirrors using MEMS techniques. In particular, there is a need for advanced techniques for fabricating MEMS mirrors having a comparatively large diameter of the respective reflective material.

This need is met by the features of the independent claims. The features of the dependent claims define embodiments.

A method of manufacturing a mirror includes forming a mirror front surface and forming a mirror back surface. The mirror back comprises a frame structure. The frame structure includes ribs and cavities. The method also includes coupling the mirror front and the mirror back to obtain the mirror.

MEMS techniques can be used to make the mirror. The mirror front and mirror back can be defined by one or more wafers. For example, a glass MEMS technique can be used.

For example, the frame structure may implement a track structure. For example, an area of the frame structure may cover not less than 50% of the area of the front of the mirror, optionally not less than 80%, further optionally not less than 95%. This can be a Structural rigidity of the mirror front side are provided by the frame structure.

A mirror includes a mirror front and a mirror back. The mirror front comprises a reflective layer. The mirror back comprises a frame structure. The frame structure includes ribs and cavities. The mirror front and the mirror back are not formed in one piece.

The mirror front and the mirror back can thus be two parts that are coupled together.

The method may further comprise isolating the mirrors of surrounding wafer material after coupling. The mirror front side and the mirror back side can be made from at least one wafer including the surrounding wafer material.

The method may further comprise isolating the mirror from surrounding wafer material after coupling. In other examples, the method may include insulating the mirror front side from surrounding wafer material and insulating the mirror backside from surrounding wafer material prior to coupling.

A mirror includes a mirror front and a mirror back. The mirror front comprises a reflective layer. The mirror back comprises a frame structure. The frame structure includes ribs and cavities. At least one rib of the ribs extends beyond an outer periphery of the mirror front side.

In particular, it would be possible for the at least one rib to extend beyond an outer circumference of the reflective layer.

The mirror can be a mesoscopic mirror. The mirror may have a diameter not smaller than 4 millimeters, optionally not smaller than 6 millimeters, further optionally not smaller than 8 millimeters.

A scanning unit includes the mirror and an elastic mount. The scanning unit may further include an actuator configured to resonantly scan the mirror by exciting a self-mode of the resilient mount. For example, a torsion eigenmode of the elastic mount may be resonantly excited.

A LIDAR system comprises such a scanning unit. The LIDAR system may be configured to determine the distance to a target object, for example, by implementing the time of light measurements of laser light.

It is understood that the above-mentioned features and those to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without departing from the scope of the invention.

list of figures

• 1 schematically illustrates a scanning unit that includes a mirror and an elastic mount according to various examples.
• 2 FIG. 12 is a perspective view of a scanner unit according to various examples. FIG.
• 3 is another perspective view of the scanning unit according to 2 ,
• 4 is another perspective view of the scanning unit according to 2 ,
• 5 FIG. 10 is a flowchart of a method of manufacturing a mirror and resilient mount of a scanner unit according to various examples. FIG.
• 6 FIG. 12 illustrates a process step of producing a mirror back according to various examples. FIG.
• 7 schematically illustrates a process step for producing the mirror back, the process step of 6 follows.
• 8th schematically illustrates a process step for producing the mirror back, the process step of 7 follows.
• 9 schematically illustrates a process step for making the mirror back, the process step of 8th follows.
• 10 FIG. 12 illustrates an array of wafer-level mirror backs according to various examples. FIG.
• 11 schematically illustrates a process step for producing a mirror front according to various examples.
• 12 schematically illustrates a process step for producing the mirror front, the process step according to 11 follows.
• 13 schematically illustrates a process step for producing the mirror front, the process step according to 12 follows.
• 14 schematically illustrates a process step for producing the mirror front, the process step according to 13 follows.
• 15 schematically illustrates a process step for producing a mirror by coupling a mirror front side and a mirror back, wherein the process step according to 15 according to the process steps 9 and 14 follows.
• 16 schematically illustrates a process step for producing the mirror, the process step according to 15 follows.
• 17 schematically illustrates the mirror obtained from the process step according to 16 is obtained.
• 18 schematically illustrates a process step for producing a mirror, wherein the process step according to 18 according to the process steps 9 and 11 follows.
• 19 schematically illustrates a process step for producing the mirror, wherein the process step according to 19 according to the process step 18 follows.
• 20 schematically illustrates a process step for producing the mirror, the process step of 19 follows.
• 21 schematically illustrates a process step for producing the mirror, the process step according to 20 follows.
• 22 schematically illustrates a process step for producing the mirror, the process step according to 21 follows.
• 23 schematically illustrates a mirror derived from the process step according to 22 is obtained.
• 24 schematically illustrates a process step for producing a mirror back according to various examples.
• 25 schematically illustrates a process step for producing the mirror back, the process step of 24 follows.
• 26 schematically illustrates a process step for producing the mirror back, the process step of 25 follows.
• 27 schematically illustrates a process step for producing the mirror back, the process step of 26 follows.
• 28 schematically illustrates a process step for producing the mirror back, the process step of 27 follows.
• 29 schematically illustrates a process step for producing a mirror front according to various examples.
• 30 schematically illustrates a process step for producing the mirror front, the process step of 29 follows.
• 31 schematically illustrates a process step for producing a mirror, the process steps of 28 and 30 follows.
• 32 schematically illustrates a process step for producing the mirror, the process step of 31 follows.
• 33 schematically illustrates a process step for producing the mirror, the process step of 32 follows.
• 34 schematically illustrates a process step for producing the mirror, the process step of 33 follows.
• 35 schematically illustrates a process step for producing the mirror, the process step of 34 follows.
• 36 schematically illustrates a process step for producing the mirror, the process step of 35 follows.
• 37 schematically illustrates a process step for producing the mirror, the process step of 36 follows.
• 38 schematically illustrates the mirror derived from the process step of 37 is obtained.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings. It should be understood that the following description of embodiments is not to be taken in a limiting sense. The scope of the invention is not intended to be limited by the embodiments described hereinafter or by the drawings, which are to be considered as illustrative only.

The drawings are to be considered as schematic representations and elements illustrated in the drawings are not necessarily to scale. Instead, the various elements are presented in such a way that their function and general purpose will become apparent to a person skilled in the art. Any connection or coupling between functional blocks, devices, components or other physical or functional units shown in the drawings or described herein may also be implemented by indirect connection or coupling. A coupling between components can also be established via a wireless connection. Function blocks can be implemented in hardware, firmware, software or a combination thereof.

Hereinafter, techniques related to mirrors will be described. The mirrors can be used to deflect light, such as laser light. The mirrors can be moved, for example, by an elastic holder. This allows the light to be scanned. Thus, the techniques described herein may refer to scanning mirrors.

The mirrors described herein may find application in a variety of applications. Example cases include, but are not limited to: LIDAR with lateral resolution; Spectrometer; projectors; endoscopes; etc.

The techniques described herein may facilitate the production of mesoscopic mirrors, i. mirrors having a diameter of the respective reflective surface located at a transition regime between micromirrors (typically of sub-millimeter diameter diameter) and macroscopic mirrors (typically of the centimeter regime of each reflective layer, for example for multi-faceted polygon mirrors).

The techniques described herein can facilitate the production of large mirrors that are relatively lightweight. Specifically, the techniques described herein help to provide mirrors with a web-like framing structure of low fill factor, thus creating structural rigidity, which provides a lightweight structure.

Such mesoscopic mirrors may have certain advantages: first, they may be made sufficiently lightweight, particularly in comparison with a macroscopic mirror, to be resonantly actuated using an elastic mirror mount. This facilitates resonant sampling at comparatively high frequencies, for example above 100 Hz up to kHz. Resonant strain detection by elastic deformation is smooth, and therefore, respective sensing devices typically have a higher mean time between failure (MTBF) as compared to sensing devices using pivot bearings, etc. Second, mesoscopic mirrors may be small enough to be fabricated using MEMS processes on one or more wafers. For example, such mesoscopic mirrors may be made of silicon using standard MEMS processes. Specifically, this helps to facilitate automated production and reduce production costs compared to macroscopic mirrors. Third, mesoscopic mirrors can support comparatively large emitter apertures and / or detector apertures of the corresponding optics. This may help to implement a high measurement signal level, for example, by collecting a large number of photons reflected from a target object when used in a LIDAR use case. This applies in particular in comparison with micromirrors application.

According to some examples, techniques for producing mirrors, more specifically mesoscopic mirrors, are described. According to examples, a two-stage production process is provided. Here, a mirror front and a mirror back can be individually, e.g. on different wafers. Then, the mirror front side and the mirror back side are coupled to obtain the mirror. Such a two-step process can provide certain advantages over a one-step process in which the mirror front and the mirror back are created in-situ. For example, in such a two-stage production process, the amount of material that needs to be removed can be reduced by dry etching, such as DRIE. This can be achieved by combining dry etching with release processes rather than by etching the material. Frequently, insitu production processes do not offer the possibility to implement release processes.

In particular, the two-stage production process helps to provide the mirror with a mirror back with a frame structure. The frame structure includes ribs - sometimes referred to as webs - and corresponding cavities between the ribs. Specifically, the frame structure can be created at a comparatively low fill factor: the fill factor defines the area of the ribs with respect to the total area covered by the frame structure. At low fill factors, the ribs occupy only a small area of the frame structure.

The mirror produced by the techniques described herein may have a frame structure fill factor not greater than 20%, optionally not greater than 5%, and optionally not greater than 2%. This may not be less than 4 mm, optionally not less than 6 mm, further optionally not less than 8 mm, for a mirror reflecting layer diameter which is typically completely or predominantly covered by the frame structure. This makes provision for a large aperture of the corresponding optics.

The frame structure provided by the mirror back surface supports the mirror front surface and the reflective material. This allows the mirror to be accelerated rapidly, as is typically the case for resonant scanning, with the mirror in between Stop positions oscillates and therefore has a periodic acceleration. More specifically, the frame structure can impart rigidity to the mirror front surface, thereby reducing the deformation of the mirror front reflective layer during acceleration. This gives the corresponding optics stability; unwanted deflection or divergence of the light is avoided. At the same time, where the fill factor of the frame structure is limited, the mass moment of inertia of the mirror backside is limited. This facilitates that the high resonance of the eigenmodes of the mirror is resonantly driven. Depending on the eigenmodes used for scanning, different motion patterns of the mirror can be implemented. Thus, the techniques described herein may facilitate one-dimensional or two-dimensional scanning. The scanning may refer to the repeated transmission of light at different emitter angles.

In various examples, laser light can be scanned. For example, coherent or incoherent laser light can be used. Polarized or unpolarized laser light can be used. Pulsed laser light can be used. Laser pulses of full width at half maximum in the range of femtoseconds or picoseconds or nanoseconds can be used. For example, a pulse duration in the range of 0.5-3 nanoseconds can be used. The laser light can have a wavelength in the range of 700 - 1800 Nanometers, for example 1550 Nanometer or 950 Have nanometer. For the sake of simplicity, laser light will be primarily referred to hereinafter; the various techniques described herein could also be used for light derived from other light sources, eg, broadband light sources or RGB light sources. RGB light sources can refer to light sources in the visible spectrum, whereby the color space is covered by superposition of different colors - eg red, green or blue.

In the various examples described herein, light may be scanned using a mirror mounted on an elastic mount. The elastic holder may comprise one or more spring elements. The one or more spring elements can provide shape-induced and / or material-induced elasticity and therefore can not be rigidly implemented. Therefore, the one or more spring elements may also be referred to as support elements. The mirror may be coupled to a moveable end of at least one of the one or more spring members. Twist and / or transverse movement of the one or more spring elements may include rotation and / or inclination, i. generally distraction, trigger the mirror. As a result, different scanning angles can be implemented. Resonant motion, i. oscillating movement of the one or more spring elements is possible.

It is possible that the one or more spring elements have a length in the range of 2 millimeters - 8 millimeters, e.g. ranging from 3 millimeters to 6 millimeters. The one or more spring elements may be of linear shape in a rest position. The one or more spring elements may have a diameter of e.g. 50-250 microns. The one or more spring elements may be made of silicon.

In various examples, it would be possible for the one or more spring elements to be produced by MEMS techniques. Thus, lithography and / or etching may be applied to a wafer to produce the one or more spring elements. For example, a DRIE process may be used. Silicon on insulator wafers (SOI wafers) can be used to define stops for etching.

In the various examples described herein, the one or more spring elements may extend from the mirror back. Thus, the one or more spring elements may have a significant angle with a reflecting layer on the front of the mirror, e.g. in the range of 30 ° - 90 °, optionally 45 °. In other examples, it would also be possible for the one or more spring elements to be disposed in the plane defined by the reflective layer from the front of the mirror.

When used in conjunction with a LIDAR technique, a particular scanning device may include a mirror that can be used both to emit laser light and to detect reflected laser light. Consequently, the detector aperture can be defined by the mirror. Such techniques are sometimes referred to as spatial filtering: by means of spatial filtering, a particularly large signal-to-noise ratio can be achieved because light is selectively detected for the particular direction in which laser light was emitted. This suppresses background noise from other areas. By means of the large signal-to-noise ratio, long range measurements become possible.

1 illustrates aspects related to a scanner 100 , The scanning unit 100 includes a base 141 , The base 141 defines a reference coordinate system. For example, the base could 141 and a light source for light 180 (in 1 not illustrated) at fixed positions in the Reference coordinate system can be arranged. The scanning unit 100 also includes a spring element 111 , The spring element 111 can be used for resonant scanning of a mirror 150 be deformed. The spring element 111 provides elasticity. The spring element 111 is with the mirror 150 via an interface 142 coupled. The base 141 , the spring element 111 and the interface 142 implement an elastic mount 119 , By deformation of the spring element 111 becomes the mirror 150 moved to thereby different deflection angle 181 of the light 180 to implement.

For example, the elastic holder 119 be configured to turn the mirror 150 opposite the base 141 or the reference coordinate system and, for example, along a central axis of the elastic holder 119 to facilitate. This is done by torsion of the spring element 111 reached. For example, the torsional mode of the elastic holder 119 resonantly excited. Alternatively or additionally, the torsion could be implemented stepwise, ie non-resonant. The torsion turns the light 180 around a changing angle 181 distracted.

1 also illustrates an actuator 172 , The actuator 172 is configured to control the movement of the spring element 111 to stimulate. For example, a self-mode of the elastic holder 119 be stimulated. As a general rule, different types and types of actuators 172 be used in the various techniques described herein, for example, the torsion of the spring element 111 to press. For example, piezoelectric actuators can be used. For example, piezoelectric bending actuators can be used. Alternatively or additionally, it would be possible to use a magnetic actuator that is configured to generate a magnetic field in the region of a magnet that is attached to the elastic mount. An AC component of the magnetic field acting on the resonance curve of the torsion mode of the elastic mount 119 is tuned, facilitates resonant scanning of light at high repetition rates, eg in the range of 100 Hz - 2 kHz.

A control unit 171 is configured to control the operation of the actuator 172 to control. A closed-loop control of the movement of the mirror 150 can by means of the control unit 171 be implemented.

2 illustrates aspects related to the scanner 100 , 2 FIG. 12 is a perspective view of an exemplary structural implementation of the scanner unit. FIG 100 , The scanning unit 100 can be made of silicon, eg using MEMS techniques.

In the example of 2 includes the scanning unit 100 a mirror 150 , The mirror 150 includes a reflective layer on a mirror front side (the viewing of the mirror front and the reflective layer is in the perspective of 2 blocked). The mirror 150 also includes a mirror back 152 , The mirror back 152 is located opposite the mirror front. As in 2 illustrated, the mirror back comprises a frame structure comprising ribs and cavities. As a result, the moment of inertia of the mirror 150 be tailored by suitable geometric implementation of the frame structure. Thereby, the natural frequency of the torsion own mode of the elastic holder 119 be matched. The frame structure also provides rigidity against deformation of the mirror-front reflective layer due to acceleration during resonant scanning.

In the example of 2 extends a total of four spring elements 111 - 1 . 111 - 2 . 111 - 3 . 111 - 4 between the interface element 142 and the base 141 , In the example of 2 becomes an intermediate coupling 155 provided, which is optional. The spring elements 111 - 1 . 111 - 2 . 111 - 3 . 111 - 4 extend from the mirror back 152 path. the interface 142 includes an end stop 153 to avoid excessive distraction of the mirror 140 by engaging with a corresponding end stop (in 2 not shown).

The base 141 , the interface element 142 and the spring elements 111 - 1 . 111 - 2 . 111 - 3 . 111 - 4 can be formed in one piece. They can be produced by a single wafer.

2 also illustrates a surface normal 151A the reflective layer of the mirror 150 , From 2 it can be seen that the surface normal 151A an angle of about 45 ° with a central axis 119A the elastic holder 119 encloses, by the spring elements 111 - 1 . 111 - 2 . 111 - 3 . 111 - 4 is formed. This will produce a periscope-like scan of light 180 by torsion of the elastic holder 190 relieved when light is on the reflective layer parallel to the central axis 119A meets.

The angle between the surface normal 151A and the spring elements 111 - 1 . 111 - 2 . 111 - 3 . 111 - 4 can be defined by laterally structuring the wafer, which is the elastic mount 119 Are defined.

2 also illustrates aspects related to the dynamics of the elastic mount 119 , Illustrated in detail 2 Aspects with Regarding the torsion of the elastic holder 119 , In the lower part of the 2 A sectional view along the axis A - A is illustrated. From the sectional view it can be seen that the spring elements 111 - 1 - 111 - 4 with a fourfold rotational symmetry with respect to the central axis 119A are arranged, ie in particular at the edges of a notional square, which is arranged in the plane of the sectional view. Such an arrangement mitigates nonlinear effects. A twist 501 is illustrated in the sectional view. Here, the solid lines illustrate the rest position of the spring elements 111 - 1 - 111 - 4 and the dashed lines illustrate the actuated position of the spring elements 111 - 1 - 111 - 4 passing through a torsion angle 502 is marked.

Here, if torsion on the elastic mount 119 is applied, the torsion angle 502 the spring elements 111 - 1 - 111 - 4 be approximately equal to the scan angle to the deflection angle 181 changed to the rest position.

From 2 it can be seen that the spring elements 111 - 1 . 111 - 2 in a plane 988 are arranged in the rest position. The spring elements 111 - 3 . 111 - 4 are in a distant plane 989 arranged.

The total length 119B the elastic holder 119 can be in the range of 2 millimeters - 10 millimeters, ie approximately equal to the diameter of the mirror 150 his.

3 - 4 are further prospective views of the scanning unit 100 according to the example of 2 ,

3 illustrates the mirror front 151 with a reflective layer deposited thereon 151A ,

The outer circumference 151B the reflective layer 151A is in 4 illustrated.

4 illustrates aspects related to the frame structure 157 the mirror back 152 , As in 4 , The frame structure includes 157 ribs 158 and cavities 159 between adjacent ribs 158 are formed.

As in 4 illustrates implements the frame structure 157 a web-like structure. The frame structure 147 covers in the example of 4 essentially the entire area of the mirror front 151 from.

In the 4 illustrated specific embodiment of the frame structure 157 is just an example. As a general rule, however, it is possible for the frame structure 157 according to the example of the embodiment of 4 both radial ribs 158 extending from a center of the frame structure at the back of the mirror 152 away, as well as circumferential ribs 158 , which are around the middle of the frame structure 157 and the mirror back 152 extend at a fixed radius includes. The elastic holder 119 is at the mirror 150 in the middle of the mirror back 152 attached.

Furthermore, they extend from the multiple ribs 158 the frame structure 157 Ribs 151 - 1 . 158 - 2 . 158 - 3 . 158 - 4 over the outer circumference 151B the reflective layer 151A the mirror front 151 out. This has certain advantages in connection with the method for the production of the mirror 150 on. Specifically, it is through these extended ribs 151 - 1 . 158 - 2 . 158 - 3 possible, the mirror 150 expediently to isolate from the surrounding wafer material in a MEMS technique for production. These and other techniques will be discussed in conjunction with the following FIGURES.

5 FIG. 10 is a flowchart of a method of manufacturing a mirror according to various examples. FIG. For example, the method according to 5 used to the mirror 150 according to one of 1 - 4 manufacture. The method according to 5 can use MEMS techniques. The mirror may be made of one or more wafers, eg a monocrystalline wafer or a polycrystalline wafer. For example, more than a single wafer may be used in conjunction with the production process of 5 to be used. One or more wafers associated with the production process of 5 can be made of silicon, SOI or other semiconductor material, eg gallium arsenide, etc., glass wafers, eg a pyrex wafer, borofloate wafers or the like.

Typical silicon wafers used in the processes may be 500 μm thick and 200 mm or 300 mm in lateral diameter.

5 is a two-stage production process. In detail, at block 1001 a mirror front and at block 1002 generates a mirror back. For example, the mirror front side can be defined by a first wafer and the mirror back side by a different second wafer.

Next will be at block 1003 the mirror front and the mirror back coupled together. This defines the mirror.

Specifically, the mirror front side may have a reflective layer to thereby be configured to deflect light. on the other hand For example, the mirror back may have a frame structure with ribs and cavities to provide structural rigidity to the mirror front, which aids in resonantly scanning the mirror in an oscillatory motion.

In block 1001 For example, one or more of the following MEMS techniques may be used: etching; dry; ion beam etching; reactive ion beam etching; DRIE; wet etching; Lithograph; Photoresist exposure using a mask; Take off; Material deposition; Grind; Attaching to a glass wafer; and / or polishing.

Similarly, one or more such MEMS techniques may be used in the block 1002 to be used.

In block 1001 and / or block 1002 Release processes can be used. Release processes help to reduce the amount of material that must be removed by etching. Instead of using large area etching of the material - which introduces heat and requires significant amounts of etching gas - trenches are etched. Trenches can be deeper than further. For example, a width of a trench may not be greater than 20% of a trench depth. Material within a closed loop formed by a trench may then be released from the surrounding wafer material because it is not connected in any way by the surrounding wafer material. This corresponds to implementing a release of the wafer material. For example, the loop closed by a trench can be aligned with a circumference of a cavity of the frame structure. Thus, the frame structure can be generated using the release process.

As a general rule, various options are available to implement the release. This is due to the high flexibility that is obtained from the two-stage production process. In one scenario, the release is implemented using recesses in a glass wafer on which the wafer defining the mirror front and / or mirror back is supported. In another scenario, the release is implemented using wafer loops. Grinding, as used herein, may involve thinning and / or polishing.

Typically, at block 1001 and / or at block 1002 a large number of mirror front sides and / or mirror backs produced by parallel processing of a wafer. Thus, an array of mirror front side structures may be processed at the first wafer and / or an array of mirror back side structures may be processed at the second wafer. By implementing large wafer diameters, such as 150 millimeters or 300 millimeters, the production throughput can be increased. Finally, individual mirror front sides and individual mirror backs must be isolated from the respective wafer. Such isolation, which marks the transition from wafer level processing to device level processing, may generally occur before or after the mirror front and mirror backside coupling at block 1003 occur. Specifically, it would be possible for the coupling of the mirror front and mirror back to block 1003 implemented at the wafer level. Then, isolating the multiple mirrors after running block 1003 occur.

As a general rule, wafer level processing may generally correspond to any process step performed starting from a scenario where multiple devices on a wafer, e.g. in an arrangement, are arranged. There is a tendency that the wafer-level processing utilizes parallel processing of the plurality of devices. In various ways, the device level processing may correspond to a single processing of individual devices, i. starting from a scenario where multiple devices are not located on a wafer. There is a tendency that device level processing relies on serial processing of the multiple devices. The transition from wafer level processing to device level processing is typically marked by isolating a device from surrounding wafer material.

Isolating the wafer-level mirror after coupling the mirror front side and the mirror back side has the advantage that the coupling of the mirror front side and the mirror back side can be efficiently implemented in parallel for a large number of mirrors, and by utilizing positioning marks at a large distance With respect to each other, a highly accurate alignment of the mirror front with the mirror back side is possible.

In general, different techniques for coupling at block 1003 to be used. Examples include the use of an epoxy adhesive and silicon-silicon wafer bonding or general wafer bonding. Direct wafer bonding can be used.

For example, direct wafer bonding may be assisted by using one or more glass wafers on which the wafers which support the wafer Mirror front and / or define the mirror back, are attached.

The use of epoxy adhesive has the advantage of not having to rely on high processing temperatures, which generally helps to protect the integrity of, for example, a reflective layer of the mirror. The epoxy adhesive may be placed on certain contact surfaces of the mirror front and back of the mirror.

One or more of the mirror front and the mirror back may be on a handling wafer to perform the coupling at block 1003 to be placed.

To make the scanning unit, at block 1004 the mirror mount optionally manufactured. Again, the mirror mount can be created using a MEMS technique, as above in connection with blocks 1001 and 1002 explained. The mirror mount may include one or more spring elements, such as in conjunction with the mirror mount 119 and the preceding figures. The mirror mount may be generated from a different wafer compared to the one or more wafers used, the mirror front and the mirror back at blocks 1001 and 1002 manufacture.

Finally, at an optional block 1005 the one from the block 1003 obtained mirrors and those from the block 1004 obtained mirror holder coupled together. Typically, the coupling of the mirror and mirror mount at block 1005 be executed at the device level, but it would also be possible to block 1005 at the wafer level. For example, it would be possible to couple the elastic mirror mount to the mirror using one or more contiguous concavity features provided on the respective contact surfaces of the resilient mount and mirror back. For example, a center portion of the mirror back may include one or more notches or recesses to receive corresponding protrusions of the resilient mount.

With reference to the following FIGURES, example implementations of the method for producing a mirror will be described.

6 - 10 illustrate aspects related to block 1002 ie the production of the mirror back 152 ,

6 illustrates the etching of a respective wafer 701 , Illustrated in detail 6 the etching (illustrated by the arrows) of the wafer 701 , In 6 For example, trenches are etched using a DRIE or other dry etch process. The trenches 785 are with the contours of the cavities 159 the frame structure 157 aligned. For example, the trenches 785 the contours of the cavities 159 like a closed circle enclose.

In detail, left in 6 on the left a scheme of the frame structure 157 illustrated. In 6 will be left material 781 which is intended to remain to thereby form the ribs of the frame structure 157 to build; and further illustrates material 782 which is to be removed. As right in 6 is illustrated by selectively etching the trenches along the contour of the cavities 159 not all material 782 away. material 782 remains in the cavities, which is not etched. This remaining material 782 will be removed later by a release process.

Such etching of the trenches helps to confine the material that needs to be removed by etching. This, in turn, limits the required etching gas flow rate, with an inhomogeneous distribution of the etching gas along different lateral positions of the wafer 701 is avoided. Furthermore, the heat input is limited. This is especially true for large scale frame structures 157 with a low filling fraction application, as is typically encountered for mesoscopic mirrors. The processing time is also reduced.

In 6 For the sake of simplicity, no lithographic mask is illustrated which is used to laterally limit the etching to the trenches 785 is used.

7 illustrates a next process step for making the mirror backside 152 which is the process step of 6 follows. In detail, in 7 the wafer 701 - after etching the trenches 785 on a handling wafer 709 attached.

8th illustrates the process step involved in the process step of 7 follows. Here is the page 705 of the wafer 701 - opposite the page 704 of which the etching in the process step of 6 is carried out - subjected to grinding. Here, large areas of the material are removed by using a grinding fluid and a grinding tool. This can also be called wafer thinning. For example, the thickness of the material removed by grinding 782 between 20 microns and 100 microns. In different ways, the depth of the trenches 785 eg greater than 200 Micrometer or about 400 microns. Because the trenches 785 have a laterally restricted width, the entire amount of material removed by etching 782 however, less than 10% of the total amount of material removed by grinding 782 his.

9 illustrates a process step corresponding to the process step of 8th follows. In 9 becomes the wafer 701 from the handling wafer 709 separated. This will result in remaining material 782 and the wafer side 704 between adjacent trenches 785 released from the surrounding material. Only the material 781 remains, see 9 Left.

As in 9 illustrated, the frame structure 157 not yet isolated from the surrounding wafer material, using instead the material 781 the frame structure 157 in a frame structure of the surrounding wafer material 781 over the extended radial ribs 158 - 1 - 158 - 4 is embedded. Consequently, these ribs represent 158 - 1 - 158 - 4 a fixation of the material 781 ready, that the frame structure 157 defined within the surrounding wafer material.

10 illustrates the corresponding wafer 701 after the material 782 was removed and the material 781 that the frame structure 157 defined remains. The isolation of the individual frame structures 157 did not take place yet. The individual frame structures 157 are with the surrounding wafer material over the extended ribs 158 - 1 - 158 - 4 coupled.

11 - 14 illustrate aspects of making a mirror back eg as per block 1002 from 5 , In general, the process of producing the mirror front side may correspond to the process of manufacturing the mirror back.

11 illustrates etching - eg, dry etching, such as DRIE etching - of a wafer 711 , As in 11 illustrates, it is possible the entire material 782 on the side 714 of the wafer 711 so that subsequently no release process is required. A lithography mask for laterally limiting the etching is shown in FIG 11 not illustrated again for the sake of simplicity.

Next will be in 12 a reflective layer 770 on the website 714 of the wafer 711 deposited. For example, a gold or aluminum layer can be deposited. Evaporation or electron heating can be used.

13 illustrates the process step involved in the process step of 12 follows. In the process step of 13 becomes the wafer 711 now with the reflective layer 770 coated on a handling wafer 709 attached. In particular, the handling wafer 709 on the side 714 of the wafer 711 attached, which also through the reflective layer 770 is coated.

14 illustrates the process step involved in the process step of 13 follows. In the process step of 14 Grinding is used to remove the remaining material 782 on the side 715 of the wafer 711 to remove. Then no material remains 782 , please refer 14 Left. As in 14 illustrated on the left is the material 781 , the mirror front 151 defined, not with the surrounding wafer material 781 laterally coupled (and thus, if the handling wafer 709 was removed, the mirror front 151 from the wafer 711 released). As explained hereinbelow, this facilitates easy and reliable isolation of the mirror 150 at the wafer level.

15 - 17 illustrate examples relating to the coupling of the mirror front 151 and the mirror back 152 to the mirror 150 to obtain. The process step of 15 is the process step that is the process step of 14 follows. In detail, in the process step of 15 the wafer 711 , the mirror front 151 defined on the handling wafer 709 attached. Then the wafer 711 on the side 715 with the wafer 701 brought into contact. That's what the ribs are made of 158 the frame structure 157 with reference to the center of the mirror front 151 aligned.

As mentioned above, the wafers can 701 and 711 using an adhesive, such as an epoxy adhesive, or wafer bonding.

As can be seen from the above, the coupling can, as by the process step of 15 illustrated, implemented at the wafer level.

16 illustrates the process step involved in the process step of 15 follows. 16 illustrates aspects related to the isolation of the mirror 150 , Illustrated in detail 16 cutting blade 790 , Cutting is often referred to as slicing or dicing the wafer that is in 16 as a scenario is illustrated, wherein the cutting blades 790 Ribs 158 - 1 - 158 - 4 cut at a position from the outer circumference 151B the mirror front 151 is offset. Then the mirror becomes 150 , as in 17 illustrated by the surrounding wafer material 781 the wafer 701 . 711 isolated. As can be seen from the above description, because the extended ribs extend 158 - 1 - 158 - 4 on one of the outer circumference 151B staggered position to be cut, these ribs 158 - 1 - 158 - 4 over the outer circumference 151B out, as soon as the mirror 150 was isolated (cf. 4 ).

In general, it is not necessary, all radial ribs 158 as extended ribs 158 - 1 - 158 - 4 to implement; instead, the number of ribs can be extended 158 - 1 - 158 - 4 be adjusted to provide structural stability before insulating the mirrors 150 from the wafers 701 . 711 provide. For example, it may be sufficient, as in connection with the example of 4 illustrates extended ribs 158 - 1 - 158 - 4 towards the north, south, east and west of the mirror 150 to use.

In the examples of 11 - 17 becomes the reflective layer 770 before coupling the mirror front 151 and the mirror back 152 deposited (cf. 12 and 15 ). Furthermore, the reflective layer becomes 770 on the website 714 of the wafer 711 deposited on the side 715 opposite, which is ground (see. 12 and 14 ). Other scenarios are conceivable, as explained in connection with the following FIGURES.

18 - 21 illustrate another example. 18 illustrates a process step corresponding to the process step of 12 follows. 18 illustrates aspects related to the coupling of the wafer 701 who the mirror back 152 defined, and the wafer 711 , the mirror front 151 Are defined. In the example of 18 become the mirror front 151 and the mirror back 152 before the wafer tears the wafer 711 coupled to the mirror front 151 Are defined. Furthermore, the mirror front 151 and the mirror back 152 before applying the reflective layer 770 coupled.

Specifically, in the example of 18 direct wafer wafer bonding can be used for the coupling.

19 schematically illustrates the process step, the process step of 18 follows. In 19 is a handling wafer 709 on the wafer 701 opposite to the wafer 711 coupled side attached.

20 illustrates the process step involved in the process step of 19 follows. In 20 will make a wafer thinning on the wafer 711 by grinding the page 715 of the wafer 711 applied. As such, the process step of 20 generally the process step of 14 ; although in the scenario of 20 the sanding of the page 715 of the wafer 711 before depositing the reflective layer 770 and after coupling the mirror front 151 with the mirror back 152 is carried out.

21 illustrates the process step involved in the process step of 20 follows. In 21 becomes the reflective layer 770 on the website 715 of the wafer 711 deposited. Around a level reflective layer 770 To facilitate, the grinding in the process step of 20 be followed by polishing. Like 21 it can be seen, the reflective layer 770 after coupling the mirror front 151 with the mirror back 152 deposited. The grinding is also performed after the coupling. The reflective layer 770 will be on the sanded side 715 deposited.

22 illustrates the process step involved in the process step of 21 follows. 22 illustrates aspects related to cutting 790 the wafer 701 . 711 to isolate the mirror 150 , As such, the process of 22 in general, the process of 16 , Around the reflective layer 770 in the process step of 22 To protect, a protective layer can be applied (in 22 not illustrated).

23 illustrates the isolated mirror 150 that of cutting at the process step of 22 is obtained.

24 - 38 illustrate yet another MEMS process that can be used to mirror 150 manufacture.

In 24 becomes a glass wafer 708 provided. Next, in the process step of 25 recesses 708A etched in the glass wafer. This can be achieved using wet etching, eg using hydrofluoric acid. The special shape of the recesses 708A is not crucial because the recesses 708A merely to implement a release of material of the wafer 701 to be used, the mirror back 152 Are defined.

26 illustrates the process step involved in the process step of 25 follows. In 26 became the wafer 701 on the glass wafer 708 attached. This can be achieved by anodic wafer bonding with SOG (silicon-on-glass).

The wafer 701 is on the side of the glass wafer 708 fastened in the the recesses 708A were etched to facilitate the release later.

27 illustrates the process step involved in the process step of 26 follows. The process step of 27 corresponds essentially to the process step of 6 , The trenches 785 be completely in the recesses 708A etched. This will be the material 782 released the cavities 159 defined, see 28 ,

In 27 and 28 Again, for simplicity, no mask will be used to etch the trenches 785 illustrated.

29 illustrates the generation of the mirror front 151 , Here is the respective wafer 711 on a corresponding glass wafer 707 attached using anodic wafer bonding with SOG or another process.

30 illustrates the process step involved in the process step of 29 follows. Here is the page 715 of the wafer 711 eg made thinner using loops and / or polishing.

31 illustrates a process step for coupling the wafer 711 , the mirror front 151 defined, and the wafer 701 who the mirror back 152 Are defined. The process step of 31 follows the process steps of 28 and 30 ,

In 31 become the wafer 701 and the wafer 711 coupled using direct wafer bonding. The coupling becomes the wafer 711 on the glass wafer 707 and the wafer 701 on the glass wafer 708 attached, thereby facilitating handling.

32 illustrates the coupled wafers 701 . 711 , The wafer 711 gets over the thinner side 715 coupled.

33 illustrates a process step corresponding to the process step of 32 follows. In 33 becomes the glass wafer 707 away. This can be achieved using wet etching, eg using hydrofluoric acid. To the removal of the glass wafer 708 To avoid a protective mask can be applied.

34 illustrates a process step corresponding to the process step of 33 follows. In 34 Trenches are etched to the mirror front 151 define. As such, the process step of 34 essentially the process step of 11 , For example, DRIE etching may be used. In the example of 34 becomes different from the example of 11 - the etching of the mirror front 151 after coupling the wafer 111 and the wafer 101 implemented.

35 illustrates a process step corresponding to the process step of 34 follows. In the process step of 35 becomes the reflective layer 770 on the website 714 of the wafer 711 deposited. As a result, the reflective layer becomes 770 on the website 714 deposited on the side 715 opposed in the process step of 30 thinner and over the wafer 711 with the wafer 701 is coupled. As can be seen, the reflective layer becomes 770 on the website 714 after coupling the mirror front 151 and the mirror back 152 deposited.

36 illustrates a process step corresponding to the process step of 35 follows. The wafer 711 will be on the side 714 - now with the reflective layer 770 covered - with a handling wafer 709 attached.

37 illustrates a process step corresponding to the process step of 36 follows. Here is the glass wafer 708 removed by wet etching, for example. Further, the cutting of the wafer 701 along the cutting lines 790 implemented. As such, the process step of 37 generally the process step of 22 and the process step of 16 ,

However, as from the left side of 37 it is not necessary to see the extended ribs 158 - 1 - 158-4 provide. In detail, the mirror back 152 at any time during the process of 26 - 37 either through the glass wafer 708 or by the handling wafer 709 carried. Consequently, there is no need for the extended ribs 158 - 1 - 158 - 4 or any other supporting structure. Therefore, the for etching at 27 used mask from that for etching 16 used mask differ.

38 Illustrates the mirror 150 that of the process step of 37 is obtained (in the scenario of 24 - 38 become the cavities 159 the frame structure 157 for the sake of simplicity, in a simplified manner).

Although the invention has been shown and described with respect to certain preferred embodiments, equivalents and modifications will occur to others skilled in the art upon reading and understanding the specification. The present invention includes all such equivalents and modifications, and is limited only by the scope of the appended claims.

By way of illustration, various examples have been described in which one or more extended ribs extend beyond the outer periphery of the mirror front. However, this is generally optional. In other examples, there may be no elongated ribs. For example, dedicated load-bearing structures may be provided to secure the mirror or portions thereof Mirror to connect with the surrounding wafer material until the mirror or the respective mirror parts are isolated from the surrounding wafer material by cutting the supporting structures. The carrying structures may be different from the extended ribs.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 7078778 B2 [0003]
• US 5501893 A [0004]

Claims (23)

A method of making a mirror (150) comprising: Producing a mirror front side (151), - Producing a mirror back (152) comprising a frame structure (157) with ribs (158) and cavities (159), and Coupling the mirror front side (151) and the mirror back side (152) to obtain the mirror (150). Method according to Claim 1 wherein forming the mirror backside (152) comprises: - etching trenches (785) along a contour of the cavities (159) of the frame structure (157), the etching starting from a first side (704) from a first wafer (701) wherein the first side (704) defines the mirror front side (151), and - implementing a release of wafer material from the cavities (159) of the frame structure (157) by means of the trenches (785). Method according to Claim 2 wherein the release is implemented using recesses in a glass wafer. Method according to Claim 2 wherein the release is implemented using wafer loops on a second side (705) opposite the first side (704). The method of any one of the preceding claims, wherein the coupling of the mirror front side (151) and the mirror back side (152) is implemented at the wafer level. The method of any one of the preceding claims, wherein coupling the mirror front side (151) and the mirror back side (152) using direct wafer bonding comprises a first wafer defining the mirror front side (151) and a second wafer defining the mirror back side (152) , is implemented. Method according to Claim 6 wherein the first wafer is coupled to a first glass wafer when coupled, and the second wafer is coupled to a second glass wafer when coupled. Method according to one of the preceding claims, further comprising: Isolating the mirror (150) from surrounding wafer material by cutting at least one of the ribs (158-1, 158-2, 158-3, 158-4) of the frame structure (157) at a position starting from an outer periphery of the mirror front side (15) 151) is offset. Method according to Claim 8 wherein when insulating the mirror (150), the mirror front side (151) is not laterally coupled to a surrounding wafer material. Method according to one of the preceding claims, wherein the mirror front side (151) and the mirror back side (152) are coupled by aligning the ribs (158) of the frame structure (157) with respect to a center of the mirror front side (151), and wherein, after coupling, at least one rib (158-1, 158-2, 158-3, 158-4) of the ribs (158) of the frame structure (157) extends beyond an outer periphery of the mirror front side (151). Method according to one of the preceding claims, wherein the mirror front side (151) is coupled to the mirror backside (152) via a first side (714, 715) of a second wafer (711) defining the mirror front side (151), the method further comprising: Depositing a reflective layer on a second side (714, 715) of the second wafer (711), the second side (714, 715) of the second wafer (711) facing the first side (714, 715) of the second wafer (711 ), wherein the reflective layer is deposited before or after coupling the mirror front side (151) and the mirror back side (152). Method according to Claim 11 , further comprising: - grinding the second side (714, 715) of the second wafer (711). Method according to Claim 12 wherein the grinding of the second side of the second wafer is performed after coupling the mirror front side (151) and the mirror back side (152). Method according to Claim 13 , further comprising: - grinding the first side (714, 715) of the second wafer (711). The method of any one of the preceding claims, wherein the mirror front side (151) and the mirror back side (152) are coupled using at least one of an epoxy adhesive and / or a silicon-silicon wafer bonding. Method according to one of the preceding claims, further comprising: - Creating an elastic holder, and - Coupling of the mirror (150) and the elastic holder. Method according to Claim 16 wherein the resilient mount is coupled to the mirror (150) using one or more contiguous indentation features provided on respective contact surfaces of the resilient mount and the mirror back (152). Mirror (150) comprising: a mirror front side (151) comprising a reflective layer, - A mirror back (152) comprising a frame structure (157) with ribs (158) and cavities (159), wherein the mirror front side (151) and the mirror back side (152) are not formed in one piece. Mirror (150) comprising: a mirror front side (151) comprising a reflective layer, and - A mirror back (152) comprising a frame structure (157) with ribs (158) and cavities, wherein at least one rib (158-1, 158-2, 158-3, 158-4) of the ribs (158) via an outer periphery (151B) of the mirror front side (151). Mirror (150) according to Claim 18 or 19 wherein a diameter of the reflective layer of the mirror (150) is not smaller than 4 mm, optionally not smaller than 6 mm, further optionally not smaller than 8 mm. Mirror (150) according to one of Claims 18 to 20 wherein a fill factor of the frame structure (157) is not greater than 20%, optionally not greater than 5%, further optionally not greater than 2%. Mirror (150) according to one of Claims 18 to 21 wherein the mirror (150) is formed by a method according to any one of Claims 1 to 17 is produced. A scanning device (100) comprising: - the mirror (150) according to any one of Claims 18 to 22 - an elastic mount (119) coupled to the mirror (150), and - an actuator (172), the actuator (172) configured to resonantly scan the mirror (150).

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