Method for closing an opening in a flexible membrane of a MEMS element

Abstract

The invention relates to a method for closing an opening in a flexible membrane of a MEMS element, the method comprising the steps of: - providing at least one opening in the flexible membrane, - arranging a closing material in the area of the at least one opening, - at least melting the closing material applied in the area of the at least one opening and subsequently cooling the melted material for closing the at least one opening.

Description

Technical Field

[0001] The invention relates to a method for closing an opening in a flexible membrane of a MEMS element.

[0002] The invention further relates to a MEMS component having a flexible membrane with at least one opening.

[0003] Although the invention is generally applicable to any MEMS component having a flexible diaphragm, the invention is explained with reference to a MEMS sensor in the form of a MEMS microphone or a MEMS pressure sensor having a defined internal pressure between an upper diaphragm and a lower diaphragm.

[0004] Known MEMS sensors, such as MEMS pressure sensors or MEMS microphones, have at least one cavity covered by at least one flexible diaphragm. Pressure-dependent, in particular sound-pressure-dependent, deflection changes of the flexible diaphragm are detected via capacitance changes, which are generated, for example, by electrodes between the flexible diaphragm and a fixed electrode surface and can be read. During the manufacture of the MEMS pressure sensor, in order to expose the diaphragm, inlet openings must be etched into the diaphragm to allow the entire diaphragm to be exposed. These openings, in turn, must be sealed to maintain a defined internal pressure. Background Art

[0005] DE 10 2015 224 520 A1 discloses a method for producing a micromechanical component comprising a substrate and a cover connected to the substrate and enclosing a first cavity together with the substrate, wherein an inlet opening is substantially completely filled between a first plane and a second plane by a material region of the substrate or the cover which transitions to a liquid aggregate state in a method step, the first plane extending substantially parallel to a main extension plane of the substrate and being arranged on a side of a region of the inlet opening constructed substantially perpendicularly to the main extension plane facing away from the first cavity, and the second plane extending substantially parallel to the main extension plane of the substrate and being arranged on a side of a region of the inlet opening constructed substantially perpendicularly to the main extension plane facing toward the first cavity.

[0006] DE 10 2015 224 506 A1 discloses a method for producing a micromechanical component having a substrate and a cap connected to the substrate and enclosing a first chamber with the substrate, wherein a first pressure prevails in the first chamber and a first gas mixture having a first chemical composition is enclosed, wherein:

[0007] In a first method step, an access opening connecting the first chamber to the environment of the micromechanical component is formed in the substrate or the cap, wherein:

[0008] - in a second method step, a first pressure and / or a first chemical composition is set in the first chamber, wherein

[0009] - in a third method step, the entry opening is closed by means of a laser by introducing energy or heat into the absorbing portion of the substrate or the cover, wherein the getter introduced into the first chamber prior to the third method step is at least partially activated during the third method step by means of laser radiation generated by the laser. SUMMARY

[0010] The application provides in an embodiment a method for closing an opening in a flexible membrane of a MEMS element, the method comprising the following steps:

[0011] - providing at least one opening in the flexible membrane,

[0012] - arranging a closing material in the region of the at least one opening,

[0013] - at least melting the closing material applied in the region of the at least one opening and subsequently cooling the melted material to close the at least one opening.

[0014] The application provides in a further embodiment a MEMS element having a flexible membrane with at least one opening, which is closed by means of melting of a closing material applied in the region of the at least one opening and subsequent cooling of the melted closing material.

[0015] One advantage achieved thereby is that a closing of a flexible membrane of a MEMS element with a defined internal pressure can be achieved thereby. A further advantage is that the opening is less limited in its geometric configuration and can be reliably closed even so. A further advantage is that fewer particles can be brought into a chamber possibly defined by the flexible membrane when closing the opening. Furthermore, the opening can be reliably and cost-advantageously closed in a flexible manner.

[0016] Further features, advantages and further embodiments of the application are described below or can be derived therefrom:

[0017] According to an advantageous extension, the application of the closing material is achieved in particular in the region of the at least one opening by means of centrifugal coating and / or by means of a spray method and / or by means of bonding of a wafer. One advantage achieved thereby is that a laser-sensitive material, such as silicon dioxide, a metal, a polymer or the like in the form of a paste, an emulsion, emulsion drops or the like, can be applied in a flexible manner thereby.

[0018] According to a further advantageous embodiment, the melting is carried out by means of a laser beam. This has the advantage that the melting can be locally limited in a simple and at the same time very reliably manner and thus the at least one opening can be reliably closed.

[0019] According to a further advantageous embodiment, in addition to melting the applied sealing material, the material of the flexible membrane is also melted in the region of the at least one opening. This has the advantage that a particularly reliable connection of the sealing material and the membrane material in the region of the at least one opening can be achieved.

[0020] According to another advantageous embodiment, the sealing material is moved into the area of ​​the at least one opening by means of a laser beam. Thus, the sealing material can also be initially arranged outside the immediate area of ​​the opening and then moved toward the opening by means of the laser beam to seal it. This eliminates the need for complex and precise placement of the sealing material directly in the area of ​​the at least one opening.

[0021] According to another advantageous embodiment, the sealing material is provided at least partially in the form of a membrane material. This has the advantage that no further material types need to be applied as sealing material. In this way, a particularly reliable sealing is achieved using a single material.

[0022] According to another advantageous embodiment, the sealing material is provided by peeling off the film material of the flexible film. In this case, the flexible film can already be dimensioned, in particular thicker, in preparation for the peeling off, so that the desired (target) layer thickness of the flexible film is subsequently achieved by the corresponding peeling off. Thus, the sealing and the appropriate dimensioning of the flexible film are essentially carried out in one step.

[0023] According to another advantageous embodiment, the laser beam is provided in the form of a hollow ring or hollow ellipse by means of an optical device. This allows for particularly precise and reliable melting of the sealing material and sealing of the at least one opening by shaping the laser beam, in particular its cross-section. For example, the hollow ring allows for targeted irradiation of the transition area between the sealing material and the opening without introducing high energy into the center of the sealing material or the opening. This allows the sealing material to be melted only in the edge region, avoiding complete melting of the sealing material.

[0024] According to a further advantageous embodiment, a laser beam is provided which is regularly varied in its power and / or in at least one diameter. This increases flexibility, since the laser beam can be flexibly adapted to different materials and openings of different sizes.

[0025] According to another advantageous embodiment, the planes of the laser beam and the flexible membrane are arranged obliquely relative to one another. This has the advantage that, for example, a larger spot size of the laser beam can be achieved at a smaller penetration depth into the flexible membrane, which optimizes the energy input by the laser beam into the desired shallow material depth of the flexible membrane and simultaneously increases the melting area.

[0026] According to another advantageous embodiment, the cavity is formed at least partially by means of a flexible diaphragm, the at least one opening is designed as an inlet to the cavity, and a defined pressure is enclosed in the cavity by closing the at least one opening in the flexible diaphragm. This has the advantage of providing a precise and reliable MEMS element for pressure applications.

[0027] According to another advantageous embodiment of the MEMS element, an anti-adhesion material is arranged below the flexible membrane, in particular on the inner surface of the cavity. This has the advantage that permanent adhesion of parts inside the cavity is reduced.

[0028] Further important features and advantages of the invention are apparent from the dependent claims, the drawings and from the corresponding description of the figures with reference to the drawings.

[0029] Of course, the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination, but also in other combinations or alone without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Preferred embodiments and implementations of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals relate to identical or functionally identical components or elements.

[0031] Figure 1 A MEMS pressure sensor according to an embodiment of the present invention is shown schematically in cross section before the opening is closed.

[0032] Figure 2 Schematic cross section showing the closing of the opening according to Figure 1 MEMS pressure sensor.

[0033] Figure 3 A schematic cross-section of a device for sealing an embodiment of the present invention is shown. Figure 1 Steps of a method for opening a MEMS pressure sensor.

[0034] Figure 4 The steps of a method for closing an opening of a MEMS pressure sensor according to an embodiment of the present invention are shown.

[0035] Figure 5a-d shows different forms of the laser beam for sealing the opening of the MEMS pressure sensor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] Figure 1 A MEMS pressure sensor according to an embodiment of the present invention is shown schematically in cross section before the opening is closed.

[0037] exist Figure 1 . The MEMS pressure sensor 1 comprises a substrate 4, on which a lower diaphragm 3 is arranged, which is partially exposed or can be exposed from the substrate 4 on its lower side. A support structure 5 is arranged on the upper side of the lower diaphragm 4, which supports the upper diaphragm 2 relative to the lower diaphragm 3. The upper diaphragm 2 and the lower diaphragm 3 are arranged essentially horizontally and parallel to each other. In this case, a plurality of cavities 10 are formed by the lower and upper diaphragms 2, 3 and the support structure 5. Electrodes 7 are arranged on the upper side of the lower diaphragm 3 and on the lower side of the upper diaphragm 2, respectively, which electrodes are subjected to a change in capacitance between these electrodes when the diaphragms 2, 3 move. However, this capacitance change can be read accordingly by means of a reading method and, for example, the pressure acting on the diaphragms 2, 3 can be acquired.

[0038] To produce the MEMS layer structure for MEMS pressure sensor 1, an etching access 6 in the form of an opening is arranged in upper diaphragm 2. This opening 6 must in turn be sealed in order to achieve, for example, a defined internal pressure of 1 to 10 mbar in cavity 10 between the two diaphragms 2, 3.

[0039] Figure 2 Schematic cross section showing the closing of the opening according to Figure 1 MEMS pressure sensor.

[0040] exist Figure 2 Basically, it is shown that Figure 1 MEMS pressure sensor 1. Different from the Figure 1 The MEMS microphone 1, in accordance with Figure 2 In the MEMS microphone 1, sealing material 8 is only partially disposed in or on opening 6. Sealing material 8 is selectively melted onto or into the opening using a laser beam 9, thereby sealing the cover opening after cooling. Sealing material 8 is, for example, a correspondingly adapted laser-sensitive material, such as silicon dioxide, metal, polymer, or the like, in the form of a paste, emulsion, emulsion drops, or the like. This laser-sensitive material can be applied, for example, by spin coating or in a targeted manner using a spraying method. Alternatively, an additional wafer, which is also bonded, can be used as sealing material 8.

[0041] Figure 3A schematic cross-section of a device for sealing an embodiment of the present invention is shown. Figure 1 Steps of a method for opening a MEMS pressure sensor.

[0042] exist Figure 3 Basically, it is shown that Figure 1 MEMS pressure sensor 1. Different from the Figure 1 The MEMS pressure sensor 1, in accordance with Figure 3 In the MEMS pressure sensor 1, the sealing material 8 is not arranged directly in or on the opening 6, but is accordingly arranged next to the right side of the opening. By means of an obliquely incident laser beam 9, the sealing material 8 is moved onto the opening 6 (reference numeral 20) by the laser beam 9, so that finally according to Figure 2 A sealing material 8 is arranged on or in the opening 6. This sealing material is then heated again by means of a laser beam 9, whereby it melts and seals the opening 6 after cooling.

[0043] Figure 4 The steps of a method for closing an opening of a MEMS microphone according to an embodiment of the present invention are shown.

[0044] exist Figure 4 Basically, it is shown that Figure 1 MEMS pressure sensor 1. Different from the Figure 1 The MEMS pressure sensor 1, in accordance with Figure 4 In the MEMS pressure sensor 1 of FIG. 1 , the upper diaphragm 2 is designed to be thicker. The thickness of the upper diaphragm 2 , measured perpendicularly to the distance between the two diaphragms 2 , 3 , is determined so that a material front can be generated from the melted diaphragm material as sealing material 8 using the laser beam 9 , without damaging the diaphragm 2 . The laser beam 9 is directed onto the upper diaphragm 2 such that the material front moves in direction 21 , i.e., the melted material moves in the direction of the opening 6 . The laser beam 9 scans the diaphragm surface of the upper diaphragm 2 . In other words, the thickness of the upper diaphragm 2 is determined so that the desired target thickness of the upper diaphragm 2 is achieved or provided after the material removal and sealing of the opening 6 using the laser beam 9 .

[0045] Figure 5a -d shows different forms of the laser beam for sealing the opening of the MEMS pressure sensor according to an embodiment of the present invention.

[0046] exist Figure 5a -d show variations of the form of the laser beam 9. Figure 5a In FIG, the laser beam 9 has a point-shaped laser spot 9 or a circular form. Figure 5bIn the embodiment, a laser beam 9 is provided in the form of a hollow ring 9b in its cross section by means of corresponding optical means. Figure 5c Basically provide the basis Figure 5b However, according to Figure 5c The diameter 30 of the hollow ring 9b' in this case varies, for example, periodically, randomly or similarly, around an average diameter. In this case, the average diameter in particular corresponds essentially to the diameter of the circular opening 6 of the upper diaphragm 2. Finally, in Figure 5d , a hollow ellipse 9c is shown, the diameter 30 of which along the axis of the hollow ellipse varies or changes regularly. It is also possible to change the diameter of another axis accordingly, alternatively or additionally.

[0047] With the help of Figure 5b The embodiment of -d can, for example, result in a locally better melt distribution of the sealing material 8 .

[0048] In other embodiments, the laser beam 9 can be incident on the surface of the MEMS element, in particular the upper flexible membrane 2, at a corresponding angle relative to the surface in order to achieve a larger spot size, in other words, a larger area exposed by the laser beam 9, while penetrating less deeply into the membrane 2. This makes it possible to optimize the energy introduction to the desired shallow material depth and increase the melting area.

[0049] The MEMS element can be used in particular as a MEMS pressure sensor, a MEMS inertial sensor, a combination of a MEMS inertial sensor and a MEMS pressure sensor, a MEMS microphone, a MEMS loudspeaker and / or a MEMS gas sensor with a reference gas enclosed in a cavity, such as in the form of a NOx sensor, a Lambda sensor or the like.

[0050] The sensor element with the flexible membrane has, for example, a thickness in the range of approximately several hundred nanometers to several micrometers. As a sealing material, for example, a silicon-rich nitride Si having a thickness in the range of approximately several hundred nanometers to several micrometers can be used. x N y or stoichiometric silicon nitride Si3N4. As already explained in detail, silicon dioxide in spin-on-glass or a metal paste with dissolved tungsten oxide can also be used as the sealing material, wherein the solvent is subsequently evaporated and the silicon dioxide or metal is used as the sealing material 8. If the sealing material 8 can be applied by means of a spraying method, aluminum or copper can be applied therefrom, for example. The sealing material 8 can also be applied to the diaphragm 2 by means of LIFT (laser induced forward transfer). Chromium, aluminum, copper, selenium dioxide, or graphite can be used as the sealing material, for example.

[0051] In summary, at least one embodiment of the present invention has at least one of the following advantages:

[0052] When closing an opening in a membrane, fewer particles are introduced into the region of the underside of the same membrane.

[0053] • Freer geometrical choice in openings, especially etched inlets.

[0054] The possibility of subsequently coating the cavity below the membrane with an anti-adhesive material, for example, and subsequently sealing it with a defined internal pressure.

[0055] Contain multiple internal pressures in different cavity areas formed by the diaphragm.

[0056] High flexibility.

[0057] High reliability.

[0058] Although the present invention has been described with reference to preferred embodiments, it is not limited thereto but can be modified in various ways.

Claims

1. A method for closing an opening (6) in a flexible membrane (2) of a MEMS element (1), the method comprising the following steps: - providing at least one opening (6) in said flexible membrane (2), - arranging a sealing material (8) in the region of the at least one opening (6), - melting at least the sealing material (8) applied in the region of the at least one opening (6) and subsequently cooling the melted material (8) in order to seal the at least one opening (6), wherein the sealing material (8) is moved into the region of the at least one opening (6) by means of a laser beam (9, 9a, 9b, 9b', 9c), in that the planes of the laser beam (9, 9a, 9b, 9b', 9c) and the flexible membrane (2) are arranged obliquely relative to one another, the sealing material (8) arranged next to the at least one opening (6) is moved onto the at least one opening (6) by means of the obliquely incident laser beam (9, 9a, 9b, 9b', 9c), and then the sealing material (8) is heated by means of the laser beam (9, 9a, 9b, 9b', 9c), whereby the sealing material (8) is melted and, after cooling, seals the at least one opening (6).

2. The method according to claim 1, wherein The sealing material (8) is applied in the region of the at least one opening (6) by means of spin coating and / or by means of a spraying method and / or by means of wafer bonding.

3. The method according to claim 1 or 2, wherein: In addition to the melting of the applied sealing material (8), the material of the flexible membrane (2) is melted in the region of the at least one opening (6).

4. The method according to claim 1 or 2, wherein: The closing material (8) is provided at least partially in the form of a membrane material.

5. The method according to claim 4, wherein The closing material (8) is provided by peeling off the membrane material of the flexible membrane.

6. The method according to claim 1 or 2, wherein: The laser beam (9, 9a, 9b, 9b', 9c) is provided in the form of a hollow ring (9b, 9b') or a hollow ellipse (9c) by means of an optical device.

7. The method according to claim 1 or 2, wherein: The laser beam (9, 9a, 9b, 9b', 9c) is provided so as to vary regularly in terms of its power and / or in terms of at least one diameter (30).

8. The method according to claim 1 or 2, wherein: A cavity is formed at least partially by means of the flexible membrane, and the at least one opening (6) is configured as an inlet to the cavity (10), and a defined pressure is enclosed in the cavity (10) by closing the at least one opening (6).

9. MEMS element (1) having a flexible membrane (2) with at least one opening (6) which is closed by melting a sealing material (8) applied in the region of the at least one opening (6) and subsequent cooling of the melted sealing material (8), wherein: The sealing material (8) is moved into the area of ​​the at least one opening (6) by means of a laser beam (9, 9a, 9b, 9b', 9c), in that the planes of the laser beam (9, 9a, 9b, 9b', 9c) and the flexible membrane (2) are arranged obliquely relative to each other, the sealing material (8) arranged next to the at least one opening (6) is moved onto the at least one opening (6) by means of the obliquely incident laser beam (9, 9a, 9b, 9b', 9c), and the sealing material (8) is then heated by means of the laser beam (9, 9a, 9b, 9b', 9c), whereby the sealing material (8) is melted and, after cooling, seals the at least one opening (6).

10. The MEMS element according to claim 9, wherein: An anti-adhesion material is arranged below the flexible membrane (2).

11. The MEMS element according to claim 10, wherein: The anti-adhesion material is arranged on the inner surface of the cavity (10).

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