METHOD FOR PRODUCING AT LEAST ONE FIRST AND ONE SECOND MICROMIRROR DEVICE

Description

[0001] The invention relates to a method for producing at least a first and a second micromirror device. Furthermore, the invention relates to a first and / or second micromirror device produced by the method, and to a first and / or second micromirror device, in particular produced by a method according to any one of claims 1 to 13, having a first and / or second mirror plate, each comprising a polysilicon layer. State of the art

[0002] Document WO 2014 / 064606 A1 discloses a method for producing micromirrors. This method involves using a silicon oxide wafer, which is first separated along a separation plane by wet etching in one process step. In a further, separate process step, the mirror plates of the micromirrors are separated.

[0003] From the document US 2005 / 136663 A1, a method for producing micromirrors is also known, in which two etching steps, one from the front side and one from the back side of a substrate carrying thin film layers, are applied one after the other to form a micromirror.

[0004] Based on this prior art, it is the object of the present invention to produce a simplified method for producing micromirror devices. Disclosure of the invention

[0005] A method according to the invention is defined in claim 1.

[0006] To achieve this object, a method for producing at least a first and a second micromirror device is proposed. A micromirror device here refers in particular to a mechanical micromirror, i.e., a micromirror that is not yet connected to the drive unit of the micromirror. In one method step, a silicon wafer, in particular a plate-shaped one, having a front side and a back side is provided. The front side of the silicon wafer refers in particular to the side that, in the finished micromirror device, is oriented toward the surface of the micromirror device that reflects incident light rays. In a further method step, a silicon oxide layer is thermally applied to at least the front side of the silicon wafer, in particular with a silicon oxide layer thickness in a range from 1 µm to 3 µm.In particular, the silicon oxide layer is applied with a layer thickness of 2 µm. In a subsequent method step, the silicon oxide layer is removed, in particular down to an outer surface of the silicon wafer, in such a way that at least a first separation region and at least a second separation region of the silicon oxide layer are created. The first and second separation regions of the silicon oxide layer are spatially separated from one another along a separation plane. Accordingly, there is no longer any material cohesion between the first and second separation regions of the silicon oxide layer. The separation plane is in particular a plane that is arranged substantially perpendicular to an outer surface of the silicon wafer.In a further method step, a silicon layer, in particular a polysilicon layer with a layer thickness in a range from 5 µm to 50 µm, is applied to the front side of the silicon wafer and to the silicon oxide layer, in particular to the first and second separation regions of the silicon oxide layer. The silicon layer is therefore in direct contact with the front side of the silicon wafer, in particular with an outer surface of the front side of the silicon wafer, and with the silicon oxide layer, in particular with an outer surface of the silicon oxide layer. Furthermore, an etching mask is applied to the back side of the silicon wafer, wherein the etching mask has a first opening along the separation plane of the first and second separation regions of the silicon oxide layer. The etching mask is in particular a hard mask or a resist mask.In particular, a further silicon oxide layer is applied to the backside of the silicon wafer as an etching mask. In a further method step, the silicon layer, in particular a portion of the silicon layer, and the silicon wafer, in particular a portion of the silicon wafer, are then removed using an etching process depending on the etching mask on the backside of the silicon wafer and depending on the silicon oxide layer of the silicon wafer, in particular the first and second separation regions of the silicon oxide layer, so that at least a first and a second micromirror device are produced. The etching mask, as well as the silicon oxide layer, serve as layers that stop the etching (etch stop layers).The use of the pre-structured silicon oxide wafer within the method described here makes it possible to carry out the last-described method step, in which the micromirror devices are separated from one another, in a single method step. Preferably, by removing the silicon layer, in particular part of the silicon layer, by means of the etching method, at least one first separation region and one second separation region of the silicon layer are created. The first and second separation regions of the silicon layer are spatially separated from one another along the separation plane and thus form a first mirror plate of the first micromirror device, comprising the first separation region of the silicon layer, and a second mirror plate of the second micromirror device, comprising the second separation region of the silicon layer.The reflective surfaces of such mirror plates later serve in a micromirror to deflect incident light rays, for example, for projecting an image. Such mirror plates have, for example, a reflective surface of 50 mm 2 to 200 mm 2 . The mirror plates have, for example, a round, oval, or rectangular shape. In this context, the first and second separation regions of the silicon oxide layer are preferably created depending on a desired respective size and a respective shape, in particular a circular and / or oval and / or rectangular shape, of the first mirror plate of the first micromirror device and the second mirror plate of the second micromirror device. Furthermore, at least one first separation region and one second separation region of the silicon wafer are preferably created by removing the silicon wafer, in particular the part of the silicon wafer, by means of the etching process.The first and second separation regions of the silicon wafer are spatially separated from one another along the separation plane. This creates a first stiffening structure of the first micromirror device, comprising the first separation region of the silicon wafer and the first separation region of the silicon oxide layer, and a second stiffening structure of the second micromirror device, comprising the second separation region of the silicon wafer and the second separation region of the silicon oxide layer. Such a stiffening structure serves to connect the mirror plate to the subsequent drive unit of the micromirror. The stiffening structure should be as lightweight as possible to enable high mobility of the micromirror, and the stiffening structure must also provide the necessary stability to the mirror plate.In this context, the etching mask preferably further comprises at least one second opening, in particular for separating the first stiffening structure into a first separation region of the first stiffening structure and a second separation region of the first stiffening structure. The respective stiffening structure can thus be constructed as at least two stiffening struts running parallel to one another.

[0007] A plasma etching process, in particular the DRIE etching process, is preferably used as the etching process. Alternatively, an ion beam etching process is used. The mirror plate, as well as the stiffening structure of a micromirror device, can thus be produced in a single process step.

[0008] Preferably, the silicon wafer is provided as a raw wafer at the beginning of the process with a thickness of substantially 300 to 400 µm. In this case, the raw wafer already has a thickness at the beginning of the process which the stiffening structure in the finished micromirror device should have as the target thickness in order to meet the requirements with regard to weight and stability. Alternatively, the silicon wafer is provided as a raw wafer at the beginning of the process with a thickness of substantially 725 µm. In this case, preferably in a further process step which follows the application of the silicon layer, in particular the polysilicon layer, to the front side of the silicon wafer and to the silicon oxide layer, the back side of the silicon wafer is ground down, in particular until a target thickness of the silicon wafer is reached. The target thickness corresponds in particular to a layer thickness in a range of 300 µm to 400 µm.

[0009] Preferably, the silicon oxide layer is additionally thermally applied to the backside of the silicon wafer. In this case, the silicon oxide layer can be used, for example, as an etching mask on the backside if the silicon wafer is provided as a raw wafer at the beginning of the process with a thickness of essentially 300 to 400 µm.

[0010] Preferably, in a further method step, a first metal layer, in particular a first gold layer or a first aluminum layer, is applied to the silicon layer, in particular to an outer surface of the first separation region of the silicon layer. Furthermore, a second metal layer, in particular a second gold layer or a second aluminum layer, is applied to the silicon layer, in particular to an outer surface of the second separation region of the silicon layer. This increases the reflectance of the mirror plate of the respective micromirror device. Preferably, at least two markings are applied to the silicon layer for aligning the first metal layer relative to the first separation region of the silicon oxide layer and for aligning the second metal layer relative to the at least second separation region of the silicon oxide layer.The at least two markings are etched, in particular, into an outer surface of the silicon layer. To apply the markings in the correct position on the silicon layer, an infrared measuring device is used, in particular, by means of which the structure of the first separation region and the at least second separation region of the silicon oxide layer, buried within the layer stack, can be detected. The at least two markings are then applied, in particular, to an edge region of the layer stack. Thus, the metal layers on the front side of the silicon wafer can be aligned with the structure of the first separation region and the at least second separation region of the silicon oxide layer, buried within the layer structure.

[0011] Preferably, the silicon layer, in particular an outer surface of the first separation region of the silicon layer and an outer surface of the second separation region of the silicon layer, are further bonded directly or indirectly with an adhesive tape, in particular a single-sided adhesive tape. The adhesive tape, which can be designed in particular as a bluetape, serves, on the one hand, to transport the finished first and second micromirror devices to the respective drive unit of the micromirror and, on the other hand, to stop the etching process in which part of the silicon layer and the silicon wafer is removed.

[0012] Preferably, the etching mask is removed in a further process step. If the etching mask is a resist mask, the etching mask is removed, for example, using plasma stripping. If a hard mask is used as the etching mask, the etching mask can be removed using an oxide etching process. If an oxide etching process is used, the exposed parts of the silicon oxide layer on the front side of the silicon wafer are also etched away. This allows the pressure of the stiffening structure on the mirror plate to be reduced.

[0013] Preferably, the silicon layer is applied in the form of a deposition of silicon, in particular polysilicon, on the front side of the silicon wafer and on the silicon oxide layer, in particular on the first and second separation region of the silicon oxide layer, followed by a polishing step. Description of the drawings

[0014] Figures 1a.1-1a.3schematically show the method steps of a first embodiment of a method for producing at least a first and a second micromirror device. Figures 1b.1-1b.4 schematically show the method steps of a second embodiment of a method for producing at least a first and a second micromirror device. Figure 2 shows a first micromirror device with a first and / or second mirror plate, each comprising a polysilicon layer. Embodiments of the invention

[0015] Figure 1a.1 to 1a.3schematically show the method steps of a first embodiment of a method for producing at least a first and a second micromirror device. In a first method step 10, a silicon wafer 100, in particular a plate-shaped one, having a front side 110 and a back side 120 is provided. In a subsequent method step 20, a silicon oxide layer 130 is applied to the front side 110 of the silicon wafer 100, in particular with a layer thickness 135 of the silicon oxide layer 130 of essentially 2 µm. In a subsequent method step 30, the silicon oxide layer 130 is removed, in particular up to an outer surface 111 of the silicon wafer 100, such that a first separation region 131 and a second separation region 132 of the silicon oxide layer 130 are produced.The first 131 and the second separation region 132 of the silicon oxide layer 130 are spatially separated from one another along a separation plane 140. In a subsequent method step 40, a silicon layer 150, in particular with a layer thickness 116 of substantially 20 µm, is deposited on the front side 110 of the silicon wafer 100 and on the first 131 and second separation region 132 of the silicon oxide layer 130. In this case, the silicon layer 150 is a polysilicon layer. In a subsequent method step 70, an etching mask 180 is applied to the back side 120 of the silicon wafer 100. The etching mask 180 has a first opening 190 along the separation plane 140. In this case, the etching mask 180 is a hard mask formed from a further silicon oxide layer 181 and applied to the back side 120 of the silicon wafer.In a subsequent method step 80, the silicon layer 150, in particular a portion of the silicon layer 150, and the silicon wafer 100, in particular a portion of the silicon wafer 100, are then removed by means of an etching process depending on the etching mask 180 on the rear side 120 of the silicon wafer 100 and depending on the first 131 and second separation regions 132 of the silicon oxide layer 130, so that at least one first 205 and one second micromirror device 206 are produced. The first 131 and second separation regions 132 of the silicon oxide layer 130 are formed as etch stop layers.

[0016] In the illustrated embodiment, at least a first separation region 200 and a second separation region 201 of the silicon layer 150 are created by removing the silicon layer 150 by means of the etching process in method step 80. The first separation region 200 and the second separation region 201 of the silicon layer 150 are also arranged spatially separated from one another along the separation plane 140. Thus, a first mirror plate 211 of the first micromirror device 205, comprising the first separation region 200 of the silicon layer 150, and a second mirror plate 212 of the second micromirror device 206, comprising the second separation region 201 of the silicon layer 150, are created.

[0017] Furthermore, in the illustrated embodiment, a first separation region and a second separation region of the silicon wafer 100 are created by removing the silicon wafer 100 by means of the etching process in method step 80. The first and second separation regions of the silicon wafer 100 are spatially separated from one another along the separation plane 140. Thus, a first stiffening structure 195 of the first micromirror device 205, comprising the first separation region of the silicon wafer 100 and the first separation region 131 of the silicon oxide layer 130, and a second stiffening structure 196 of the second micromirror device 206, comprising the second separation region of the silicon wafer 100 and the second separation region 132 of the silicon oxide layer 130, are created.

[0018] Furthermore, in the illustrated embodiment, the etching mask 180 has a second opening 221, a third opening 222, a fourth opening 223, and a fifth opening 224. These openings are designed to separate the first and second stiffening structures 195 and 196 into further separation regions, which in this embodiment are formed as first stiffening struts 231, 232, 233, 234, 235, and 236.

[0019] In the illustrated first embodiment of the method, a plasma etching method, in particular the DRIE etching method, is used as the etching method in method step 80.

[0020] In the illustrated first embodiment of the method, the silicon wafer 100 with a thickness 119 of substantially 300 to 400 µm is provided in method step 10.

[0021] In a further method step 60, in this first embodiment of the method, a first metal layer 170 is applied to an outer surface 151 of the silicon layer 150. In this case, the first metal layer is formed as a gold layer, and this gold layer is applied to a region of the silicon layer 150 that later corresponds to the first separation region 200 of the silicon layer 150. Furthermore, a second metal layer 171 is applied to an outer surface 151 of the silicon layer 150. In this case, too, the second metal layer 171 is formed as a gold layer, and this gold layer is applied to a region of the silicon layer 150 that later corresponds to the second separation region 201 of the silicon layer 150. Furthermore, in a method step 50 following method step 40, two markings 160 and 161 are applied to the silicon layer 150.The two markings 160 and 161 are etched into an outer surface 151 of the silicon layer 150. These markings 160 and 161 serve to align the first metal layer 17 relative to the first separation region 131 of the silicon oxide layer 130 and to align the second metal layer 17 relative to the at least second separation region 132 of the silicon oxide layer. In order to apply the markings 160 and 161 in the correct position on the silicon layer 150, an infrared measuring device (not shown here) is used, by means of which the first separation region 131 and second separation region 132 of the silicon oxide layer 130, buried within the layer stack comprising the silicon wafer 100 and the silicon layer, can be detected. The two markings 131 and 132 are then applied in particular to an edge region of the layer stack.

[0022] Furthermore, an outer surface 152 of the first separation region 200 of the silicon layer 150 and an outer surface 153 of the second separation region 201 of the silicon layer are indirectly connected to an adhesive tape 220. In the illustrated case, the first 170 and second metal layer 171 are directly bonded to the adhesive tape 220. In the illustrated embodiment, the adhesive tape 220 serves, on the one hand, as an etch stop layer during the etching process in method step 80. On the other hand, the adhesive tape 220, which is designed in particular as a single-sided adhesive tape, serves to transport the finished first and second micromirror devices to the respective drive unit (not shown here), in particular the piezoelectric drive unit, of the micromirror.

[0023] In a further method step 90, the etching mask 180, which is embodied as a hard mask, is removed using an oxide etching process. In this process, the exposed regions 241 of the first separation region 131 of the silicon oxide layer 130 and the exposed regions 242 of the second separation region 132 of the silicon oxide layer 130 are also etched away.

[0024] Au f Figures 1b.1 to 1b.4The method steps of a second embodiment of a method for producing at least a first and a second micromirror device are shown schematically. In contrast to the first embodiment, in method step 11, a silicon wafer 101 with a thickness 126 of substantially 725 µm is provided. Furthermore, in the following method step 20, a silicon oxide layer 130 is applied not only to the front side 110 of the silicon wafer 101, but also additionally to the back side 120 of the silicon wafer 101. Furthermore, in contrast to the first embodiment of the method, in a method step 65, which follows method step 60, the back side 120 of the silicon wafer 101 is ground down until a target thickness 145 of the silicon wafer 101 is reached. The target thickness 145 corresponds to a thickness of the silicon wafer 101 of substantially 300 µm to 400 µm.

[0025] Figure 2shows a first micromirror device 300, which in particular by means of one of the Figures 1a.1-1a.3 or Figures 1b.1-1b.4The micromirror device 300 has a stiffening structure 310, which is divided into a first 311, second 312 and third stiffening strut 313. Each stiffening strut 311, 312 and 313 has a part of a first separation region 325 of a silicon wafer and a part of a first separation region 330 of a silicon oxide layer. The stiffening struts 311, 312 and 313 can also be connected to one another via cross struts (not shown here). Furthermore, the first micromirror device 300 has a first mirror plate 320. This mirror plate 320 has a first separation region 345 of a silicon layer 350. The silicon layer 350 is formed as a polysilicon layer. In the case shown, the polysilicon layer has a layer thickness 360 of essentially 20 µm.

Claims

1. Process for producing at least a first (205, 300) and a second micromirror device (206), wherein the process comprises the following process steps: - providing (10, 11) a silicon wafer (100, 101), in particular plate-shaped, having a front (110) and a rear (120), and - applying (20) a silicon oxide layer (130) to at least the front (110) of the silicon wafer (100, 101), in particular with a layer thickness (135) of the silicon oxide layer (130) in a range from 1 µm to 3 µm, and - removing (30) the silicon oxide layer (130), in particular up to an outer surface (111) of the silicon wafer (100, 101), such that at least one first separation region (131) and at least a second separation region (132) of the silicon oxide layer (130) are produced, wherein the first (131) and the second separation region (132) of the silicon oxide layer (130) are arranged separately from each other spatially, along a separation plane (140), and - applying (40) a silicon layer (150, 350), in particular a polysilicon layer having a layer thickness (116) in a range from 5 µm to 50 µm, to the front (110) of the silicon wafer (100, 101) and to the silicon oxide layer (130), in particular to the first (131) and second (132) separation regions of the silicon oxide layer (130), and - applying (70) an etching mask (180) to the rear (120) of the silicon wafer (100), wherein the etching mask (180) has a first opening (190) along the separation plane (140) of the first (131) and second (132) separation regions of the silicon oxide layer (130), and - removing (80) the silicon layer (150, 350) and the silicon wafer (100, 101) by means of an etching process in one process step depending on the etching mask (180) on the rear (120) of the silicon wafer (100, 101) and depending on the silicon oxide layer (130) of the silicon wafer (100, 101), in particular the first (131) and second (132) separation regions of the silicon oxide layer (130), so that at least a first (205, 300) and a second micromirror device (206) are produced.

2. Process according to Claim 1, characterized in that by removing (80) the silicon layer (150, 350) by means of the etching process, at least a first separation region (200, 345) and a second separation region (201) of the silicon layer (150, 350) are produced, wherein the first (200) and the second (201) separation regions of the silicon layer (150, 350) are arranged separately from each other spatially, along the separation plane (140), so that a first mirror plate (211, 320) of the first micromirror device (205, 300), comprising the first separation region (200, 345) of the silicon layer (150, 350), and a second mirror plate (212) of the second micromirror device (206), comprising the second separation region (201) of the silicon layer (150, 350), are produced.

3. Process according to either of Claims 1 or 2, characterized in that by removing (80) the silicon wafer (100, 101) by means of the etching process, at least a first separation region and a second separation region of the silicon wafer (100, 101) are produced, wherein the first and the second separation regions of the silicon wafer (100, 101) are arranged separately from each other spatially, along the separation plane, so that a first stiffening structure (195, 310) of the first micromirror device (205, 300), comprising the first separation region of the silicon wafer (100, 101) and the first separation region (131) of the silicon oxide layer (130), and a second stiffening structure (196) of the second micromirror device (206), comprising the second separation region of the silicon wafer (100, 101) and the second separation region of the silicon oxide layer (100, 101), are produced.

4. Process according to Claim 3, characterized in that the etching mask (180) has at least a second opening (221), in particular for separating the first stiffening structure (195, 310) into a first separation region, in particular a first stiffening strut (231, 311) of the first stiffening structure (195, 310) and a second separation region, in particular a second stiffening strut (232, 312) of the first stiffening structure (195, 310).

5. Process according to any of Claims 1 to 4, characterized in that the etching process used is a plasma etching process, in particular the DRIE etching process.

6. Process according to any of Claims 1 to 5, characterized in that the silicon wafer (100) provided (10) has a thickness (119) of substantially 300 to 400 µm.

7. Process according to any of Claims 1 to 5, characterized in that the silicon wafer (101) provided (11) has a thickness (126) of substantially 725 µm.

8. Process according to Claim 7, characterized in that, in a further process step, in particular subsequent to the application (60) of the silicon layer (150, 350), in particular the polysilicon layer, to the front (110) of the silicon wafer (100, 101) and to the silicon oxide layer (130), the rear (120) of the silicon wafer (100, 101) is abraded (65), in particular until a target thickness (145) of the silicon wafer (100, 101) is reached.

9. Process according to any of Claims 1 to 8, characterized in that the silicon oxide layer (130) is additionally applied (20) to the rear (120) of the silicon wafer (100, 101).

10. Process according to any of Claims 1 to 9, characterized in that in a further process step, a first metal layer (170), in particular a first gold layer or a first aluminium layer, is applied to the silicon layer (150, 350), in particular to an outer surface (152) of the first separation region (200, 345) of the silicon layer (150, 350), and a second metal layer (171), in particular a second gold layer or a second aluminium layer, is applied (60) to the silicon layer (150, 350), in particular to an outer surface (153) of the second separation region (201) of the silicon layer (150, 350).

11. Process according to Claim 10, characterized in that process according to any of Claims 1 to 9, characterized in that for the orientation of the first metal layer (170) relative to the first separation region (131) of the silicon oxide layer (130) and for the orientation of the second metal layer (171) relative to the at least second separation region (132) of the silicon oxide layer (130), at least two marks (160, 161) are applied on the silicon layer (150, 350).

12. Process according to any of Claims 1 to 11, characterized in that the silicon layer (150, 350), in particular the outer surface (152) of the first separation region (200, 345) of the silicon layer (150, 350) and the outer surface (153) of the second separation region (201) of the silicon layer (150, 350), is connected directly or indirectly with an adhesive tape (220), in particular a single-sided adhesive tape.

13. Process according to any of Claims 1 to 12, characterized in that in a further process step, the etching mask (180) is removed (90).

14. Process according to any of Claims 1 to 13, characterized in that the silicon layer (150, 350) is applied in the form of a deposition of silicon, in particular polysilicon, on the front (110) of the silicon wafer (100, 101) and on the silicon oxide layer (130), in particular on the first (131) and second (132) separation regions of the silicon oxide layer (130), and a polishing step, in particular of the deposited silicon.