Method for producing a layer structure for a MEMS device, and MEMS device comprising such a layer structure

Abstract

The invention relates to a method for producing a layer structure for a MEMS device, to a layer structure which is produced using the method, and to a MEMS device 200 (300, 400, 500) which comprises said layer structure. For the layer structure, a high-temperature annealing step is provided during the production process after the functional layer (3) is structured for example. The structured regions and trenches of the functional layer (3) and in particular the spring structure which is formed in the functional layer (3) have lateral walls which are smoothed in regions (3a) and / or rounded corners after the annealing step such that the breaking point thereof can be increased and premature breaks of the functional layer (3) during the operation of the MEMS device 200 (300, 400, 500) can be advantageously prevented.

Description

[0001] Method for producing a layered structure for a MEMS device and MEMS device having such a layered structure

[0002] Description

[0003] The present disclosure relates to a method for manufacturing a layer structure for a MEMS device, a layer structure manufactured by the method, and a MEMS device comprising the layer structure.

[0004] background

[0005] A generic method for producing a layer structure for a MEMS device and a generic MEMS device comprising the layer structure are known, for example, from US 2009 / 0185253 A1.

[0006] In the prior art, the structuring of a mechanically active functional layer (often referred to as the device layer) of the MEMS (Micro-Electro-Mechanical System) layer structure typically involves the use of high-rate etching or deep reactive ion etching (DRIE for short). This is used to create deep trenches in the functional layer, particularly, for example, to create or carve out the moving or oscillating bodies and the corresponding spring structure that holds the moving or oscillating bodies in the functional layer. In the field of MEMS device manufacturing, this is sometimes referred to as the so-called Bosch process, as it is based on a process developed by Bosch in the 1990s.

[0007] When using such dry etching processes to pattern the moving or oscillating bodies and the spring structure that holds the moving or oscillating bodies, process-related damage or unevenness occurs in the functional layer on the etched sidewalls in the structured areas of the functional layer, particularly so-called scallops (e.g., surface undulations, surface nose structures, etc.). Furthermore, the mask used for patterning causes direct transfer into the material of the functional layer (usually silicon), and therefore the resulting structures usually have right-angled corners.

[0008] At the locations of surface damage (e.g. so-called scallops, notches, sidewall penetrations and atomic defects, etc.) on the sidewalls of the trenches of the structured functional layer and at the formed right-angled corners, high stresses occur in the MEMS structure during the resonant oscillations, which can adversely lead to premature fractures in the structures of the functional layer.

[0009] In view of the disadvantages described above, it is an object of the present disclosure, based on the prior art described above, to provide an improved method for producing a layer structure for a MEMS device, in particular in order to be able to provide MEMS devices comprising the layer structure with higher mechanical fracture limits of the mechanically acting components of the layer structure or with lower susceptibility to fracture.

[0010] Summary

[0011] The present disclosure relates to a method for producing a layer structure for a MEMS device, a layer structure produced by the method, and a MEMS device comprising the layer structure, in particular a vacuum-packed MEMS mirror device.

[0012] In particular, to achieve the above-mentioned object, a method for producing a layer structure for a MEMS device and a layer structure produced by the method are proposed according to the independent claims, as well as a MEMS device comprising the layer structure, in particular a vacuum-packed MEMS mirror device. The dependent claims relate to some exemplary preferred embodiments.

[0013] According to a first aspect, in some embodiments, a method for producing a layer structure for a MEMS device, in particular a MEMS mirror device or a vacuum-packed MEMS mirror device, is proposed, comprising: providing a layer structure comprising a substrate layer and / or a functional layer; applying a piezoelectric layer, e.g. on and / or above the functional layer, in particular on a side of the functional layer opposite the substrate layer, ie particularly preferably on a side of the functional layer opposite the substrate layer; and / or structuring the piezoelectric layer, in particular to form structured regions of the piezoelectric layer.

[0014] In some embodiments, an electrode layer (bottom electrode layer) can be provided between the functional layer and the piezoelectric layer, which can form a bottom electrode, e.g. made of metal (e.g. molybdenum), that electrically contacts the piezoelectric layer from below. In such embodiments, the method can also comprise applying an electrode layer to the functional layer before applying the piezoelectric layer, wherein the piezoelectric layer can be applied to the electrode layer. In further embodiments, the functional layer can be at least partially electrically conductive (e.g. in doped regions), so that the functional layer can at least partially provide a bottom electrode for the piezoelectric layer.

[0015] In some preferred embodiments, the method may comprise structuring the functional layer, particularly preferably for forming structured regions and / or trenches (i.e., trenches surrounding the structured regions) in the functional layer, particularly preferably optionally by means of high-rate etching or deep reactive ion etching (DRIE for short).

[0016] In some preferred embodiments, the method may preferably further comprise annealing structured regions of the functional layer or trenches in the structured regions (e.g., particularly preferably for at least partially smoothing sidewalls of the trenches in the functional layer and / or for rounding corners of the trenches in the functional layer), preferably at temperatures substantially greater than or equal to 700°C.

[0017] In some preferred embodiments, the annealing of structured regions of the functional layer may be carried out to at least partially smooth sidewalls of the trenches in the functional layer and / or to round corners of the trenches in the functional layer.

[0018] Smoothing the sidewalls of the trenches in the structured regions of the functional layer is understood in particular to mean that the unevenness and / or surface effects or defects that arise on the sidewalls during the structuring of the functional layer due to the process are reduced, so that, relative to the state of the sidewall surfaces after structuring of the functional layer, smoother sidewall surfaces are present after annealing, up to and including a possibly completely smooth and / or crystal-defect-free sidewall. Preferably, the sidewall surfaces after annealing can have a roughness substantially less than or equal to 50 nm, preferably in particular a roughness substantially less than or equal to 30 nm, and particularly preferably in particular a roughness substantially less than or equal to 10 nm.

[0019] In some preferred embodiments, the annealing of structured regions of the functional layer can preferably be carried out at temperatures substantially greater than or equal to 800°C. In some preferred embodiments, the annealing of structured regions of the functional layer can be carried out at temperatures substantially less than or equal to 1400°C, particularly preferably at temperatures substantially less than or equal to 1350°C, particularly preferably at temperatures substantially less than or equal to 1250°C or substantially less than or equal to 1200°C.

[0020] Preferably, in some embodiments, the temperatures in the annealing step or preferably in the entire manufacturing process should not exceed 1400°C, particularly preferably 1350°C, since the melting point of silicon is approximately 1410°C, since the substrate layer and / or the functional layer can typically comprise silicon.

[0021] In this case, the integration of a high-temperature annealing step according to embodiments (e.g. by hydrogen annealing and / or by sacrificial oxidation according to embodiments) successfully and advantageously enables any structured or possibly deep-etched side walls of the structured functional layer to be at least partially smoothed in order to smooth out any defects and roughnesses (e.g. superficial scallops, superficial nose structures, superficial corrugations, side wall breakthroughs and atomic defects, etc.) on the surface of the side walls that have arisen during the etching process (e.g. DRIE) and / or to round off any right-angled corners that have arisen during the etching.

[0022] According to embodiments, this advantageously leads to a significantly increased stability or fracture stability of the movable elements of the layer structure and / or of the MEMS device comprising such a layer structure, with higher fracture limits and in particular of the spring structure formed from the functional layer with increased fracture limits, whereby premature fractures can be avoided overall. In comparison to methods in the prior art without a healing step, according to embodiments with a healing step, the fracture limits of the movable or oscillating parts of the functional layer or in particular of the spring structure formed in the functional layer can be at least doubled, or even fivefold or tenfold. In comparison to the prior art, ie when components without healed side walls (ieIf components are manufactured without smooth side walls and / or without rounded corners), in which fractures can occur particularly already at smaller deflection angles or deflection amplitudes, the occurrence of fractures in the deflection structures or the spring structure can advantageously be significantly reduced and in particular larger deflection angles or deflection amplitudes can also be made possible, at which fractures in the deflection structures or the spring structure would already occur in components manufactured according to the state of the art.

[0023] In some preferred embodiments, the annealing of structured regions of the functional layer may preferably comprise hydrogen annealing, in particular preferably at temperatures of substantially greater than or equal to 900°C and / or substantially less than or equal to 1350°C, in particular preferably at temperatures of substantially greater than or equal to 1000°C and / or substantially less than or equal to 1250°C (or, by way of example, substantially less than or equal to 1200°C).

[0024] In some preferred embodiments, the annealing of structured regions of the functional layer may preferably comprise oxidizing sidewalls of the trenches in the functional layer, preferably at temperatures of substantially greater than or equal to 700°C, in particular substantially greater than or equal to 800°C, and / or substantially less than or equal to 1250°C (or, by way of example, substantially less than or equal to 1200°C).

[0025] In some preferred embodiments, the annealing of structured regions of the functional layer may preferably further comprise removing an oxidation layer formed on sidewalls of the trenches in the functional layer, e.g., in particular removing an oxidation layer formed on sidewalls of the trenches in the functional layer, particularly preferably by etching (e.g., etching back the sacrificial oxidation layer).

[0026] In some preferred embodiments, the method may preferably further comprise: applying an electrode layer, preferably after the annealing of structured regions of the functional layer, to form an electrode structure for the structured regions of the piezoelectric layer and / or to form a mirror and / or a mirror layer on one or more structured regions of the functional layer.

[0027] In some embodiments, the electrode layer can serve as the top electrode of the piezoelectric layer. In further embodiments, the electrode layer can also be used as a routing layer and / or as a bonding pad (e.g., for electrical connection to a bottom electrode).

[0028] In some preferred embodiments, the method may preferably comprise: applying a high-temperature stable electrode layer, preferably before the annealing of structured regions of the functional layer, to form an electrode structure for the structured regions of the piezoelectric layer.

[0029] In some embodiments, the high-temperature-stable electrode layer can serve as the top electrode of the piezoelectric layer. In further embodiments, the high-temperature-stable electrode layer can also be used as a routing layer and / or as a bonding pad (e.g., for electrical connection to a bottom electrode).

[0030] In some preferred embodiments, the material of the electrode layer or the high-temperature stable electrode layer may comprise an electrically conductive doped silicon, in particular doped polycrystalline silicon.

[0031] In some preferred embodiments, the material of the electrode layer or high-temperature-stable electrode layer can comprise a high-temperature-stable metal, a high-temperature-stable metal alloy or metal compound, particularly preferably a high-melting metal, particularly preferably platinum, molybdenum (melting point at approximately 2623°C) and / or a high-temperature-stable molybdenum alloy and / or molybdenum compound, tungsten (melting point at approximately 3422°C) and / or a high-temperature-stable tungsten alloy and / or tungsten compound, in particular tungsten titanium and / or tungsten carbide.

[0032] In some preferred embodiments, the method may preferably further comprise: applying a further layer, preferably after the annealing of structured regions of the functional layer, to form a mirror and / or a mirror layer on one or more structured regions of the functional layer. In some preferred embodiments, the method may preferably further comprise: applying a dielectric layer, in particular at least on the structured regions of the piezoelectric layer. In some preferred embodiments, the application of the dielectric layer may take place after the application and / or structuring of the piezoelectric layer. In such embodiments, the application of the dielectric layer may preferably take place before the annealing of structured regions of the functional layer.In further embodiments, the dielectric layer can also be applied after the annealing of structured regions of the functional layer.

[0033] In some preferred embodiments, the structured regions of the piezoelectric layer can preferably be encapsulated between the functional layer and the dielectric layer applied to the structured regions of the piezoelectric layer, particularly preferably if the dielectric layer is applied before the annealing of structured regions of the functional layer.

[0034] It was advantageously recognized here that the provision of a layer structure according to embodiments with structured regions of the piezoelectric layer encapsulated under a high-temperature stable layer (e.g. under a dielectric layer) can improve the integration of one or more high-temperature annealing steps (such as hydrogen annealing of deeply etched surfaces (e.g. at approx. 1000°C-1250°C) and / or sacrificial oxidation, e.g. at approx. 800°C-1250°C, with etching back of the sacrificial oxide layer), in particular also with less high-temperature stable piezoelectric materials and in particular also with less chemically resistant piezoelectric materials which can be protected by the encapsulation of aggressive media, such as oxygen (e.g. in an annealing step with sacrificial oxidation) and / or hydrogen (e.g. in an annealing step with hydrogen annealing).

[0035] In some preferred embodiments, the method may therefore preferably further comprise: applying a dielectric layer at least on the structured regions of the piezoelectric layer, before the annealing of structured regions of the functional layer and particularly preferably before applying an electrode layer, preferably in such a way that the structured regions of the piezoelectric layer are encapsulated between the functional layer and the dielectric layer applied to the structured regions of the piezoelectric layer.

[0036] Alternatively or additionally, in some embodiments, the piezoelectric layer can also be protected by encapsulation under the electrode layer made of high-temperature stable material or high-temperature stable metal (see embodiments with exemplary high-temperature stable electrode layer).

[0037] In some preferred embodiments, the structured regions of the piezoelectric layer can preferably be encapsulated between the functional layer and the high-temperature-stable electrode layer applied to the structured regions of the piezoelectric layer (optionally with a dielectric layer lying therebetween or in some regions therebetween), particularly preferably if the high-temperature-stable electrode layer is applied before the annealing of structured regions of the functional layer.

[0038] In some preferred embodiments, the method may therefore preferably further comprise: applying and / or structuring the high-temperature stable electrode layer, particularly preferably before the annealing of structured regions of the functional layer, preferably such that the structured regions of the piezoelectric layer are encapsulated between the functional layer and the applied high-temperature stable electrode layer (optionally with a dielectric layer lying therebetween or in some regions therebetween).

[0039] In some preferred embodiments, the method may preferably further comprise: structuring and / or opening regions of the dielectric layer, preferably during or before structuring the functional layer, in particular preferably such that the structured regions of the piezoelectric layer remain encapsulated between the functional layer and the dielectric layer applied to the structured regions of the piezoelectric layer.

[0040] In embodiments in which the piezoelectric layer is encapsulated, the material of the piezoelectric layer may comprise a ferro- and / or piezoelectric material, particularly preferably aluminum nitride (AIN), aluminum scandium nitride (AlScN), lead zirconate titanate (PZT) and / or niobium-doped PZT (PZT-Nb).

[0041] In some other preferred embodiments, the method may preferably further comprise: applying a dielectric layer at least on the structured regions of the piezoelectric layer after annealing structured regions of the functional layer. In some preferred embodiments, the method may preferably further comprise: structuring and / or opening regions of the dielectric layer.

[0042] In such embodiments, the material of the piezoelectric layer may comprise a high-temperature stable ferro- and / or piezoelectric material, particularly preferably aluminum nitride (AIN) and / or aluminum scandium nitride (AlScN).

[0043] In some preferred embodiments, the structured regions of the functional layer may comprise one or more movable elements, which are preferably formed in the functional layer, and / or a spring structure, which is preferably formed in the functional layer, wherein the spring structure can particularly preferably hold the one or more movable elements.

[0044] In some preferred embodiments, the one or more movable elements of the structured regions of the functional layer may comprise a mirror support element, wherein the mirror may preferably be arranged on the mirror support element.

[0045] In some preferred embodiments, the spring structure of the structured regions of the functional layer can hold the mirror support element with the mirror. The spring structure in the functional layer can preferably be designed such that the mirror support element with the mirror is held so that it can swing around one or two axes, in particular oscillation and / or torsion axes, particularly preferably for a two-dimensional Lissajous scanning movement of the mirror support element with the mirror.

[0046] In some embodiments, the spring structure may comprise springs, particularly preferably bending and / or torsion springs, which are preferably designed to hold the mirror support element in such a way that the mirror support element can perform an oscillating rotational movement about the respective oscillation and / or torsion axis about the corresponding axis (e.g. torsional oscillations).

[0047] In some preferred embodiments, the structuring of the functional layer may comprise high-rate etching and / or reactive ion deep etching. According to a second aspect, some embodiments further propose a layer structure produced by the method according to at least one of the preceding embodiments.

[0048] In some preferred embodiments, the layer structure may comprise: a substrate layer, a structured functional layer, a structured piezoelectric layer, preferably on a side of the functional layer opposite the substrate layer, i.e., in particular, on a side of the functional layer opposite the substrate layer, and / or a dielectric layer, preferably at least on the structured regions of the piezoelectric layer. In some preferred embodiments, the structured regions of the piezoelectric layer may preferably be encapsulated between the functional layer and the dielectric layer, which is preferably applied to the structured regions of the piezoelectric layer.

[0049] In some embodiments, an electrode layer may be provided between the functional layer and the piezoelectric layer, which may form a bottom electrode, e.g. made of metal (e.g. molybdenum), that electrically contacts the piezoelectric layer from below.

[0050] In some preferred embodiments, trenches in the functional layer may preferably be healed in structured regions of the functional layer, in particular on side walls of the trenches and in particular preferably have smoothed side walls and / or rounded corners.

[0051] In some preferred embodiments, trenches in the functional layer in structured regions of the functional layer may preferably have smoothed sidewalls and / or rounded corners and / or the sidewalls and / or structured regions of the functional layer may have rounded corners.

[0052] In some preferred embodiments, a surface roughness of side walls of the trenches in the functional layer in structured regions of the functional layer may be substantially less than or equal to 50 nm, in particular substantially less than or equal to 30 nm, particularly preferably less than or equal to 10 nm

[0053] According to a third aspect, some embodiments further propose a MEMS device, in particular a MEMS mirror device or a vacuum-packed MEMS mirror device, comprising a layer structure produced by the method according to at least one of the preceding embodiments. Further aspects and embodiments, as well as advantages and more specific implementation options of the aspects and features described above, can be further inferred from the following descriptions and explanations of the attached figures, which are not to be construed as limiting in any way.

[0054] Short description of the characters

[0055] Fig. 1 shows an exemplary flowchart of a method for manufacturing a layer structure for a MEMS device according to a background example,

[0056] Figs. 2A-2C show exemplary sectional views of the layer structure during the manufacturing process according to an exemplary manufacturing sequence based on the method according to Fig. 1,

[0057] Fig. 3 shows an exemplary flowchart of a method for manufacturing a layer structure for a MEMS device according to embodiments of the present disclosure,

[0058] Figs. 4A-4B show exemplary sectional views of the layer structure during the manufacturing process according to an exemplary manufacturing sequence based on the method according to Fig. 3,

[0059] Fig. 5 shows an exemplary sectional view of a MEMS device manufactured according to the exemplary manufacturing sequence of Figs.4A-4B,

[0060] Figs. 6A-6B show exemplary sectional views of the layer structure during the manufacturing process according to another exemplary manufacturing sequence based on the method according to Fig. 3,

[0061] Fig. 7 shows an exemplary sectional view of a MEMS device manufactured according to the exemplary manufacturing sequence of Figs. 6A-6B,

[0062] Fig. 8 shows an exemplary flowchart of a method for manufacturing a layer structure for a MEMS device according to further embodiments of the present disclosure,

[0063] Figs. 9A-9B show exemplary sectional views of the layer structure during the manufacturing process according to an exemplary manufacturing sequence based on the method according to Fig. 8, Fig. 10 shows an exemplary sectional view of a MEMS device manufactured according to the exemplary manufacturing sequence of Figs. 9A-9B,

[0064] Fig. 11 shows an exemplary flowchart of a method for manufacturing a layer structure for a MEMS device according to further embodiments of the present disclosure,

[0065] Figs. 12A-12B show exemplary sectional views of the layer structure during the manufacturing process according to an exemplary manufacturing sequence based on the method according to Fig. 11, and

[0066] Fig. 13 shows an exemplary cross-sectional view of a MEMS device manufactured according to the exemplary manufacturing sequence of Figs. 12A-12C.

[0067] Detailed description of the figures and preferred embodiments

[0068] Examples and embodiments of the present disclosure are described in detail below with reference to the accompanying figures. Identical or similar elements in the figures may be designated by the same reference numerals, although sometimes different reference numerals may be used.

[0069] It should be emphasized, however, that the subject matter of the present disclosure is in no way limited or restricted to the exemplary embodiments and their embodiment features described below, but further comprises modifications of the exemplary embodiments, in particular those which are encompassed by modifications of the features of the described examples or by combination of one or more of the features of the described examples within the scope of protection of the independent claims.

[0070] With regard to the terminology used in this disclosure, it should be noted that in the following, reference is sometimes made to "high-temperature-stable" materials or to a material property of "high-temperature stability". For the purposes of the present disclosure, the term "high-temperature-stable" material or the material property of "high-temperature stability" is intended to express that such materials can withstand temperatures greater than or equal to substantially 1200°C, particularly preferably greater than or equal to substantially 1250°C or substantially greater than 1250°C, and in particular have a melting point greater than or equal to substantially 1200°C, particularly greater than or equal to substantially 1250°C or substantially greater than 1250°C, particularly preferably greater than or equal to substantially 1400°C.

[0071] First, a background example is described below with reference to Figs. 1 and 2A-2C, which is intended to facilitate understanding of the embodiments and advantages described below. However, the method underlying Figs. 1 and 2A-2C is not actually publicly known prior art. A generic prior art method can be found, for example, in US 2009 / 0185253 A1.

[0072] Even if the following description with reference to Figs. 1 and 2A-2C refers to a background example, any technical details and / or features described of the method, the manufacturing sequence, the layer structure and in particular of individual steps and / or layers of the layer structure and / or of their possible materials may also relate to corresponding details and / or features of the embodiments described below, unless a difference is explicitly pointed out.

[0073] In particular, it should be noted that steps S101 to S104 of Fig. 1 as well as the manufacturing sequence (i) to (iv) of Fig. 2A and their description are always to be used for the embodiments of Figs. 3 to 10 and steps S101 to S103 of Fig. 1 as well as the manufacturing sequence (i) to (iii) of Fig. 2A and their description are also to be used for the embodiments of Figs. 11 to 13.

[0074] Fig. 1 shows an exemplary flowchart of a method for manufacturing a layer structure for a MEMS device according to a background example, and Figs. 2A-2C show exemplary cross-sectional views of the layer structure during the manufacturing process according to an exemplary manufacturing sequence based on the method of Fig. 1.

[0075] Referring to Fig. 1, in an exemplary step S101, a layer structure is provided which comprises a substrate layer 1 and a functional layer 3 (often referred to as a device layer). A corresponding exemplary layer structure also forms the basis of the layer structure shown in Fig. 2A (i). The layer structure according to Fig. 2A (i) comprises, for example, an intermediate layer 2 (e.g. a passivation layer), which is arranged, for example, between the substrate layer 1 and the functional layer 3, wherein the functional layer 3 is formed, for example, on the intermediate layer 2. In an exemplary step S102 of the method according to Fig. 1, a piezoelectric layer 4 is applied to the functional layer 3. The layer structure according to Fig.2A (i) thus comprises, by way of example, according to steps S101 and S102, a piezoelectric layer 4 which is formed on the functional layer 3, wherein the piezoelectric layer 4 is applied, by way of example, in step S102 according to Fig. 1 to the layer structure above the functional layer 3.

[0076] In a further exemplary step S103 of the method according to Fig. 1, the piezoelectric layer 4, which is applied on or above the functional layer 3, is structured; see also Fig. 2A (ii).

[0077] In a further exemplary step S104 of the method according to Fig. 1, a dielectric layer 5 is applied, for example; see also Fig. 2A (iii). The dielectric layer 5 is applied, for example, according to Fig. 2A (iii), to regions of the piezoelectric layer 4 and is further applied, for example, to regions of the functional layer 3 that are open after structuring the piezoelectric layer 4.

[0078] In some embodiments, the applied dielectric layer 5 can be opened in selected regions. According to Fig. 2A (iv), for example, in region 5b, the dielectric layer 5 is opened toward the functional layer 3, in particular before applying an electrode layer (see below), in order to provide a region 5b intended for a later bond pad.

[0079] It should be noted that the above aspects and features of the background example also analogously relate to the initial manufacturing steps of the embodiments described later. In particular, all embodiments of the manufacturing sequences according to Figs. 4A, 6A, and 9A described later already begin with an exemplary step (iv), which may be preceded by one or more of the steps (i) to (iv) according to Fig. 2A.

[0080] Referring again to Fig. 1, in a further exemplary step S105 of the method, an electrode layer 6 is applied to the dielectric layer 5, which may optionally have been previously opened in regions (e.g., opened region 5b for a later bond pad); see also Fig. 2A (v). During the application of the electrode layer 6, the region 5b previously opened in the dielectric layer 5 is also filled with the material of the electrode layer 6, for example, to form a bond pad. In a further exemplary step S106 of the method according to Fig. 1, the electrode layer 6, which is applied on or above the dielectric layer 5, is structured, for example; see also Fig. 2A (vi).In this case, for example, in the region 5b that was opened in the dielectric layer 5, a bonding pad 6b is formed with the material of the electrode layer 6, which provides an electrical contact to the upper side of the functional layer 3 (and / or in embodiments to a bottom electrode that can be electrically connected to the underside of the structured regions of the piezoelectric layer 4).

[0081] In the exemplary step S106 of structuring the electrode layer 6, the desired structure of the upper electrode (top electrode) for the upper electrical contacting of the piezoelectric layer 4 is formed. Furthermore, in the exemplary step S106 of structuring the electrode layer 6, a mirror 6a (mirror layer with a reflective surface) is formed in the center of the layer structure according to Fig. 2A (vi) using the material of the electrode layer 6.

[0082] In such examples, for example, the electrode layer can comprise metal, in particular aluminum, so that the surface of the electrode layer 6 already has a reflective surface and is suitable for forming the mirror 6a. In further examples, it is possible to provide a non-reflective or non-metallic electrode layer (e.g., doped polycrystalline silicon), in which case a further, for example metallic mirror layer (e.g., as a thin metal film, e.g., with a layer thickness of substantially greater than or equal to 100 nm and / or substantially less than or equal to 2000 nm) can then be applied in the region of the layer 6a.

[0083] In a further exemplary step S107 of the method according to Fig. 1, the dielectric layer 5 is opened in regions 5a toward the functional layer 3, see also Fig. 2B (vii). These are, in particular, regions 5a of the dielectric layer 5 to be opened, in which the underlying functional layer 3 is structured to form the mechanically active structures of the MEMS device.

[0084] In relation to a MEMS, "mechanically effective" is to be understood in particular to mean that the mechanically effective layer or the at least one mechanically effective functional layer (device layer) of the MEMS layer structure preferably forms the layer which, according to its structuring, is designed or configured to execute an oscillatory movement, in particular a one-dimensional or two-dimensional oscillatory movement, or in such a way that one or more structures or bodies formed in the mechanically effective layer or mechanically effective functional layer can execute an oscillatory movement, in particular a one-dimensional or two-dimensional oscillatory movement (e.g., about an oscillation / torsion axis or about two oscillation / torsion axes which are preferably transverse or, in particular, perpendicular to one another, in particular, for example, for Lissajous scanning movements).

[0085] For this purpose, the holding and / or spring structure for the movable structures or bodies of the mechanically active layer or mechanically active functional layer can preferably also be formed in this mechanically active layer or mechanically active functional layer. In some embodiments, the spring structure can comprise springs, particularly preferably bending and / or torsion springs, which are preferably designed to hold the mirror support element in such a way that the mirror support element can execute an oscillating rotational movement about the respective oscillation and / or torsion axis around the corresponding axis (e.g., torsional oscillations).

[0086] Furthermore, the formation of the mechanically active layer or mechanically active functional layer can preferably determine the resonance frequency or resonance frequencies of the MEMS, the deflection amplitudes and / or any dynamic deformations (e.g. in a holding and / or spring structure formed in the mechanically active layer or mechanically active functional layer).

[0087] In a further exemplary step S108 of the method according to Fig. 1, the functional layer 3 is structured in regions 3a, see also Fig. 2B (viii). In particular, the mechanically active structures of the MEMS device are formed in the functional layer. This includes, for example, the formation or exposure of a mirror support element (here, for example, the region of the functional layer 3 below the mirror layer 6a), which is formed, for example, from central regions of the functional layer 3, as well as any retaining webs formed from the functional layer 3, wherein the retaining webs act, for example, as a spring structure and can hold the mirror support element so that it can vibrate about one, two, or more oscillation or torsion axes.

[0088] In the prior art methods, so-called high-rate etching or deep reactive ion etching (DRIE for short) is typically used for structuring the functional layer 3 in step S108 to form the deep trenches in the functional layer 3 (e.g., regions 3a in Fig. 2B (viii)). In the field of MEMS device manufacturing, this is sometimes referred to as the so-called Bosch process, as it is based on a process developed by Bosch in the 1990s.

[0089] When applying such dry etching processes to pattern the oscillating bodies and the supporting spring structure in functional layer 3, process-related damage or unevenness occurs on the etched sidewalls in the patterned areas of the functional layer, in particular so-called scallops (e.g., surface undulations, surface nose structures, etc.; see, for example, the unevenness indicated by black dots in areas 3a in Fig. 2B (ix)) or, for example, possible sidewall perforations and / or atomic defects. Furthermore, the mask used for patterning causes direct transfer into the material of functional layer 3 (usually silicon), and therefore the resulting structures usually have right-angled corners.

[0090] At the points of surface damage (such as so-called scallops, sidewall penetrations and atomic defects) on the sidewalls of the trenches of the structured functional layer 3 and at the formed right-angled corners, high stresses arise during the resonant oscillations, which can disadvantageously lead to premature fractures in the structures of the functional layer 3. These disadvantages can advantageously be avoided in the exemplary embodiments described further below. In comparison to the prior art, i.e. when components are manufactured without healed sidewalls (i.e. in particular without smoothed sidewalls and / or without rounded corners), in which fractures can occur in particular even at smaller deflection angles or deflection amplitudes, the occurrence of fractures in the deflection structures or the spring structure can advantageously be significantly reduced and in particular even larger deflection angles orDeflection amplitudes are made possible at which fractures of the deflection structures or the spring structure would already occur in components manufactured according to the state of the art.

[0091] In a further exemplary step S109 of the method according to Fig. 1, the layer structure is opened on the back in order to expose the functional layer 3 on the side opposite the piezoelectric layer 4; see also Fig. 2B (ix), in which, for example, the substrate layer 1 is opened on the back towards the intermediate layer 2, and Fig. 2B (x), in which, for example, the intermediate layer 2 is opened on the back towards the functional layer 3. In a further exemplary step S110 of the method according to Fig. 1, the produced layer structure is provided, for example, in a vacuum-packed MEMS device 100 according to Fig. 2B (xi). Here, for example, the layer structure was hermetically sealed from above with a light-transmitting dome element 7 (e.g., a glass dome) and from below with a base body element 8 under a vacuum atmosphere.

[0092] Thus, a vacuum-packed MEMS mirror device 100 (e.g., a MEMS mirror scanner) comprising the fabricated layer structure can be provided with piezoelectrically deflectable or controllable mirrors 6a, see, for example, Fig. 2B (xi).

[0093] Various exemplary embodiments are described below. Any details or exemplary features from the above examples, in particular regarding individual process steps and materials, may also apply analogously to the exemplary embodiments below, unless differences are explicitly pointed out. Furthermore, descriptions of details or exemplary features from the following exemplary embodiments, in particular regarding individual process steps and materials, may also apply analogously to other exemplary embodiments, unless differences are explicitly pointed out.

[0094] In contrast to the above embodiment, embodiments preferably provide a healing step, in particular for healing structured regions of the functional layer, at temperatures substantially greater than or equal to 700°C.

[0095] In some preferred embodiments, the annealing of structured regions of the functional layer can be carried out to at least partially smooth the sidewalls of the trenches in the functional layer and / or to round the corners of the trenches in the functional layer. Smoothing the sidewalls of the trenches in the structured regions of the functional layer is understood in particular to mean that the unevenness and / or surface effects or defects that arise on the sidewalls during the structuring of the functional layer due to the process are reduced, so that, relative to the state of the sidewall surfaces after the structuring of the functional layer, smoother sidewall surfaces are present after annealing, up to and including a possibly completely smooth and / or crystal defect-free sidewall.Preferably, the sidewall surfaces after annealing can have a roughness substantially less than or equal to 50 nm, preferably in particular substantially less than or equal to 30 nm and particularly preferably in particular substantially less than or equal to 10 nm.

[0096] In some preferred embodiments, the annealing of structured regions of the functional layer can preferably be carried out at temperatures substantially greater than or equal to 800°C. In some preferred embodiments, the annealing of structured regions of the functional layer can be carried out at temperatures substantially less than or equal to 1400°C, particularly preferably at temperatures substantially less than or equal to 1350°C. Preferably, in some embodiments, the temperatures in the annealing step or preferably in the entire manufacturing process should not exceed 1400°C, particularly preferably 1350°C, since the melting point of silicon is approximately 1410°C, since the substrate layer and / or the functional layer can typically comprise silicon.

[0097] Fig. 3 shows an exemplary flowchart of a method for manufacturing a layer structure for a MEMS device according to embodiments of the present disclosure.

[0098] The first steps of the method according to Fig. 3 correspond, for example, to steps S101 to S104 of the method according to Fig. 1 or the exemplary manufacturing sequence (i) to (v) according to Fig. 2A. Following Fig. 2A (v), the following Figs. 4A-4B show exemplary sectional views of the layer structure during the manufacturing process according to an exemplary manufacturing sequence based on the method according to Fig. 3.

[0099] Referring to Fig. 3 and Fig. 2A (i) to (v), in an exemplary step S301 (e.g., analogous to S101 in Fig. 1), a layer structure comprising the substrate layer 1 and the functional layer 3 is provided. In an exemplary step S302 (e.g., analogous to S102 in Fig. 1), the piezoelectric layer 4 is applied to the functional layer 3.

[0100] In exemplary embodiments, the substrate layer 1 can, for example, be formed from silicon or comprise silicon. In expedient exemplary embodiments, the substrate layer 1 can, for example, be provided as an SCS wafer (SCS, English: single-crystal silicon), i.e., for example, as a crystalline bulk silicon substrate. Furthermore, the substrate layer can also be provided by means of an SOI wafer, which can already comprise the substrate layer 1 and, for example, also the functional layer 3 and / or the intermediate layer(s) 2. SOI wafers can comprise a handling wafer, which can, for example, consist of a crystalline bulk silicon substrate, followed, for example, by an intermediate layer (typically, for example, a silicon oxide with a thickness of approximately 100 - 2000 nm), but can also consist of other preferably dielectric layers, such as, for example, silicon nitride, silicon oxynitride, or aluminum oxide.In particular, different intermediate layers can consist of different materials.

[0101] The intermediate layer 2 can thus, in exemplary embodiments, be present as silicon oxide, in particular silicon dioxide, or at least comprise silicon oxide, in particular silicon dioxide. The intermediate layer 2 can then be produced, for example, by wet and / or dry oxidation. In further exemplary embodiments, the intermediate layer 2 can also additionally or alternatively comprise silicon nitride (e.g., Si3N4), aluminum oxide (e.g., Al2O3), and / or silicon oxide nitride (e.g., SiON).

[0102] The functional layer 3 (device layer) can be formed, for example, from silicon or comprise silicon. In some embodiments, the functional layer 3 can have a layer thickness of substantially 5-300 μm. In some embodiments, the functional layer 3 can be present as a pure crystalline substrate, particularly preferably as a single crystal (e.g., SCS), or in further embodiments, can be applied by means of epitaxial deposition processes, particularly in polycrystalline form (polycrystal).

[0103] In some embodiments, an electrode layer can be provided between the functional layer 3 and the piezoelectric layer 4, which can form a bottom electrode, e.g. made of metal (e.g. molybdenum), that electrically contacts the piezoelectric layer from below.

[0104] Such an exemplary bottom electrode layer beneath the piezoelectric layer 4 can, in preferred embodiments, be designed to be highly temperature-stable, e.g., as doped polycrystalline silicon. In further embodiments, the functional layer 3 can itself comprise doped polycrystalline silicon, at least in the regions of the later-structured piezoelectric layer 4, or can be formed from doped polycrystalline silicon. In such embodiments, the functional layer 3 can, on the one hand, form the mechanically active elements (e.g., mirror support element and / or holding and spring structure) and, on the other hand, serve as a high-temperature-stable bottom electrode for the piezoelectric layer 4. The piezoelectric layer 4 can preferably comprise piezoelectric material or be formed from piezoelectric material that preferably has high piezoelectric, pyroelectric, and / or ferroelectric constants.

[0105] In some preferred embodiments, the piezoelectric layer 4 may comprise, for example, aluminum nitride (AlN), aluminum scandium nitride (AlScN), lead zirconate titanate (PZT), and / or niobium-doped PZT (PZT-Nb). The piezoelectric layer 4 may also comprise semi-crystalline polymer materials such as PVDF (polyvinylidene fluoride (CF2-CH2)n).

[0106] In the further exemplary step S303 (e.g. analogous to S103 in Fig. 1), the piezoelectric layer 4, which is applied on or above the functional layer 3, is structured, particularly preferably by means of a wet and / or dry etching process.

[0107] In embodiments, the remaining regions of the piezoelectric layer 4 define the piezoelectric elements and / or drive and / or detection elements (e.g. actuator and / or sensor surfaces) for generating, driving, controlling and / or detecting the movements or vibrations of the movably held components or elements of the MEMS in the later MEMS structure.

[0108] In the further exemplary step S304 (e.g., analogous to S104 in Fig. 1), the dielectric layer 5 is applied, for example. The dielectric layer 5 is applied, for example, to regions of the piezoelectric layer 4 and is further applied, for example, to regions of the functional layer 3 that are exposed after structuring the piezoelectric layer 4.

[0109] The dielectric layer 5 can, for example, comprise silicon oxide, in particular SiO2, or be formed from silicon oxide, in particular SiO2. In further embodiments, the dielectric layer 5 can comprise silicon nitride (e.g., Si3N4) and / or aluminum oxide (Al2O3), oxynitride and / or SiLi um-oxynitride (e.g., SiON) or be formed from it.

[0110] In some embodiments, the applied dielectric layer 5 can be opened in selected regions, e.g., by wet and / or dry etching, for example, to provide a region 5b that can be provided for a later bond pad. In some embodiments, the applied dielectric layer 5 can also be opened or partially opened over the structured regions of the piezoelectric layer 4. In contrast to the sequence of the background example according to Fig. 1, in the method according to Fig. 3, the application of the electrode layer is not yet carried out, for example, before the structuring of the functional layer 3, in order to preferably carry out an annealing step, which can follow the structuring of the functional layer 3, at high temperatures above approximately 700°C (i.e., at temperatures substantially greater than or equal to 700°C) up to possibly approximately 1250°C (i.e.,at temperatures substantially less than or equal to 1250°C), which an already conventionally applied electrode layer, e.g. made of aluminum (melting point at approx. 660°C), could not withstand.

[0111] In the further exemplary step S305 of the method according to Fig. 3 (e.g., analogous to step S107 in Fig. 1), the dielectric layer 5 is opened in regions 5a toward the functional layer 3. These are, in particular, regions 5a of the dielectric layer 5 to be opened, in which the underlying functional layer 3 is structured to form the mechanically active structures of the MEMS device.

[0112] In some particularly expedient embodiments, it can be provided, for example, that the remaining regions of the piezoelectric layer 4 remain completely encapsulated by the dielectric layer 5 (see, for example, Fig. 4A (v) and also Fig. 6A (v)), ie the remaining regions of the piezoelectric layer 4 are or remain, particularly preferably, completely encapsulated between the functional layer 3 and the dielectric layer 5.

[0113] This has the advantage that the layer structure can still be subjected to high-temperature processes (e.g., at temperatures above approximately 700°C to 1250°C) without adversely affecting the encapsulated regions of the piezoelectric layer 4. This advantageously enables, for example, further embodiments with one or more annealing steps at high temperatures greater than or equal to 700°C, such as the sacrificial oxidation processes described further below, for example, at approximately 800°C to 1250°C (see, for example, the exemplary manufacturing sequence according to Figs. 4A-4B) and / or hydrogen annealing, for example, at approximately 1000°C to 1250°C (see, for example, the exemplary manufacturing sequence according to Figs. 6A-6B).

[0114] For example, it has been recognized that this encapsulation of the structured regions of the piezoelectric layer 4, e.g., by means of the dielectric layer, advantageously protects the structured regions of the piezoelectric layer 4 despite the high temperatures in the annealing step and despite the chemically aggressive media (e.g., oxygen or hydrogen), so that even piezoelectric materials that are not highly stable or not so chemically resistant, such as PZT, can still be used as piezoelectric material (encapsulated in the annealing step). In embodiments using highly stable and / or chemically resistant piezoelectric materials, it is not necessary to encapsulate the structured regions of the piezoelectric layer 4.

[0115] In the further exemplary step S306 of the method according to Fig. 3 (e.g., analogous to step S108 in Fig. 1), the functional layer 3 is structured in regions 3a, see also Fig. 4A (v). In particular, the mechanically active structures of the MEMS device are formed in the functional layer 3, preferably by high-rate etching or deep reactive ion etching (DRIE for short).

[0116] The structuring of the functional layer 3 comprises, for example, the formation or exposure of the mirror support element formed from the functional layer 3 (under the later applied mirror layer 6a, see e.g. Fig. 5) as well as the holding webs (spring structure) which are formed from the functional layer 3 and act as a holding spring structure, and which can hold the mirror support element so that it can swing about one, two or more oscillation and / or torsion axes. In some embodiments, the spring structure can comprise springs, particularly preferably bending and / or torsion springs, which are preferably designed to hold the mirror support element in such a way that the mirror support element can execute an oscillating rotational movement about the respective oscillation and / or torsion axis around the corresponding axis (e.g. torsional oscillations).

[0117] In some embodiments, the reactive ion deep etching for structuring the functional layer 3 can be carried out, for example, using a photolithography mask.

[0118] The partial opening of the dielectric layer 5 can be performed separately beforehand or in the same step using the same photolithography mask. The photolithography mask can then be removed, for example, using a plasma or a wet-chemical process.

[0119] In general, all patterning steps of the present disclosure can be performed using photolithography masks that can be removed by a plasma or a wet chemical process.

[0120] In the further exemplary step S307 of the method according to Fig. 3, an annealing step is carried out at high temperatures substantially greater than or equal to 700°C in order to smooth the side walls of the regions 3a of the functional layer 3, which were deep etched in step S306, and to round off corners of the regions 3a of the functional layer 3.

[0121] The annealing step S307 may, in some embodiments, comprise a step in which the surface of the regions 3a of the functional layer 3 is oxidized at oxidation temperatures (e.g., temperatures of substantially greater than or equal to 700°C, in particular substantially greater than or equal to 800°C or more, optionally preferably substantially less than or equal to 1250°C); see, for example, the oxidation layer 11 shown by way of example in Fig. 4A (vi).

[0122] By way of example, in the manufacturing sequence according to Figs. 4A and 4B, following the structuring S306 of the functional layer 3, a sacrificial oxidation is carried out as a healing step according to S307 (see, for example, Fig. 4A (vi)).

[0123] By means of this oxidation or sacrificial oxidation in such embodiments of the annealing step S307, the surface effects or surface defects created during etching (e.g., irregularities such as formed noses, waves, so-called scallops, as well as any further surface defects such as, for example, crystal defects, etchings, sidewall breakthroughs and atomic defects, etc.) on the sidewalls of the deep-etched sidewalls of the regions 3a of the functional layer 3 can be oxidized.

[0124] After the sacrificial oxidation, the sacrificial oxidation layer 11 can preferably be selectively removed in embodiments of the annealing step S307, and in such embodiments of the annealing step S307, advantageously smoothed sidewalls of the regions 3a of the functional layer 3 remain after selective removal of the sacrificial oxidation layer 11, with reduced unevenness of the sidewalls and rounded corners; see, for example, Fig. 4A (vii).

[0125] In particular, any etch scallops and any other surface defects (e.g., crystal defects, initial etching, sidewall penetrations, and atomic defects, etc.) can be reduced or eliminated, resulting in smoothed sidewalls, even transforming them into a completely smooth and / or defect-free sidewall. Furthermore, the rectangular structural corners created during the structuring of the functional layer can be rounded (rounded or rounded structural corners).

[0126] The corresponding layer structure or the MEMS device comprising the layer structure advantageously has, after the corresponding annealing step S307, smoothed side walls with reduced unevenness or even smooth and / or crystal defect-free (e.g. completely smoothed) side walls and rounded corners on the structured regions and trenches of the functional layer, so that the fracture limits of the movable or oscillating parts of the functional layer or in particular the spring structure formed in the functional layer can be significantly increased and the occurrence of premature fractures of the spring structure can be successfully reduced. In comparison to the prior art, ie when components are manufactured without annealed side walls (ie in particular without smoothed side walls and / or without rounded corners), in which fractures already occur in particular at smaller deflection angles orDeflection amplitudes can occur, the occurrence of fractures in the deflection structures or the spring structure can be advantageously significantly reduced and, in particular, larger deflection angles or deflection amplitudes can also be made possible, at which fractures in the deflection structures or the spring structure would already occur in components manufactured according to the state of the art.

[0127] In a further exemplary step S308 of the method according to Fig. 3, the electrode layer 6 is applied, for example, after the annealing step S307; see also Fig. 4A (viii). Here, for example, the region 5b, which was previously opened in the dielectric layer 5, is also filled with the material of the electrode layer, in particular to form a bond pad.

[0128] In some preferred embodiments, a top electrode layer 6 can be deposited over the entire surface, e.g., made of metal, in particular, for example, aluminum. In further embodiments, high-temperature-stable materials, in particular, for example, high-temperature-stable metals, can also be used for the electrode layer. In such embodiments, the annealing step can also take place after the application and / or structuring of the electrode layer and optionally after the rear opening of the layer structure, which preferably comprises high-temperature-stable and chemically resistant materials; see, for example, the embodiments described below according to Figs. 8 to 10.

[0129] In a further exemplary step S309 of the method according to Fig. 3, the electrode layer 6, which is applied on or above the dielectric layer 5, is structured; see also Fig. 4B (ix). Furthermore, in the region 5b in which the dielectric layer 5 was opened, a bonding pad 6b can be formed with the material of the electrode layer 6, which provides electrical contact to the top side of the functional layer 3 (and / or, in exemplary embodiments, to a bottom electrode, which can be electrically connected to the underside of the structured regions of the piezoelectric layer 4).

[0130] In the exemplary step S309 of structuring the electrode layer 6, the desired structure of the upper electrode (top electrode) for the upper electrical contacting of the piezoelectric layer 4 is formed. Furthermore, in step S309 of structuring the electrode layer 6, a mirror 6a (mirror layer with a reflective surface) is formed, for example, in the center of the layer structure according to Fig. 4B (iv) using the material of the electrode layer 6.

[0131] In such embodiments, for example, the electrode layer can comprise metal, in particular aluminum, so that the surface of the electrode layer 6 already has a reflective surface and is suitable for forming the mirror 6a. In some preferred embodiments, a top electrode layer deposited over the entire area, e.g. made of metal, in particular aluminum, for example, can be structured using wet and / or dry chemical photolithographic steps, e.g. using spray-coat lithography or alternatively using a lift-off process in which the lithography takes place before the metal deposition. In some embodiments, the electrode layer can also be applied using shadow mask deposition.

[0132] In further embodiments, it is possible to provide a non-reflective or non-metallic electrode layer (e.g., doped polycrystalline silicon), wherein a further, for example, metallic mirror layer (e.g., as a thin metal film, e.g., with a layer thickness of substantially greater than or equal to 100 nm and / or substantially less than or equal to 2000 nm) can then be applied in the region of layer 6a. In some preferred embodiments, the material of the metallic mirror layer can be selected depending on the desired application for the respective wavelength range, in particular with very good reflection behavior in the wavelength range of the desired application, for example, aluminum or silver for visible light (e.g., substantially at wavelengths of 400-700 nm) or gold for infrared light or infrared radiation (e.g., substantially at wavelengths of 850-2000 nm).

[0133] In a further exemplary step S310 of the method according to Fig. 3 (e.g. analogous to S109 in Fig. 1), the layer structure is opened on the back side in order to expose the functional layer 3 on the side opposite the piezoelectric layer 4; see also Fig. 4B (x), in which the substrate layer 1 is shown as an example for the intermediate layer - TI -

[0134] 2 is opened at the back (e.g. by high-rate etching or reactive ion deep etching), and Fig. 4B (xi), in which, for example, the intermediate layer 2 is opened at the back towards the functional layer 3.

[0135] In a further exemplary step S311 of the method according to Fig. 3 (e.g., analogous to S110 in Fig. 1), the produced layer structure is provided, by way of example, in a vacuum-packed MEMS device 200 according to Fig. 5. Here, by way of example, the layer structure was hermetically sealed from above with a translucent cover element 7 (e.g., a translucent dome element or a glass dome) and from below with a base body element 8 under a vacuum atmosphere (e.g., vacuum encapsulation). In further exemplary embodiments, differently shaped cover elements or 3D-shaped cover elements are also possible (e.g., square or planar). The material of the cover elements is preferably translucent, e.g., glass or other optically transparent materials (e.g., approx. 400-2500 nm), such as, for example, borosilicate glass (e.g., Borofloat® BF33 from SCHOTT).

[0136] Fig. 5 shows an exemplary sectional view of a MEMS device 200 manufactured according to the exemplary manufacturing sequence of Figs. 4A-4B. Consequently, a vacuum-packed MEMS mirror device 200 (e.g., a MEMS mirror scanner) comprising the manufactured layer structure can be provided with piezoelectrically deflectable or controllable mirrors 6a, wherein the corresponding layer structure or the MEMS device 200 comprising the layer structure advantageously has smooth and / or crystal defect-free side walls and rounded corners at the structured regions and trenches of the functional layer, so that the fracture limits of the movable or oscillating parts of the functional layer or, in particular, of the spring structure formed in the functional layer, can be significantly increased and the occurrence of premature fractures of the spring structure can be successfully reduced. Compared to the prior art, i.e.If components are manufactured without healed side walls (i.e., in particular, without smoothed side walls and / or without rounded corners), in which fractures can occur, in particular, even at smaller deflection angles or deflection amplitudes, the occurrence of fractures in the deflection structures or the spring structure can advantageously be significantly reduced, and in particular, larger deflection angles or deflection amplitudes can also be enabled, at which fractures in the deflection structures or the spring structure would already occur in components manufactured according to the prior art. Figs. 6A-6B show exemplary sectional views of the layer structure during the manufacturing process according to a further exemplary manufacturing sequence based on the method according to Fig. 3. Consequently, the exemplary sequence according to Figs. 6A-6B is a further exemplary embodiment of the method according to Fig. 3.

[0137] The first steps of the method according to Fig. 3 again correspond, by way of example, to steps S101 to S104 of the method according to Fig. 1 or the exemplary manufacturing sequence (i) to (v) according to Fig. 2A. Following Fig. 2A (v), Figs. 6A-6B illustrate the exemplary manufacturing sequence based on further embodiments of the method according to Fig. 3.

[0138] Here too, in contrast to the sequence of the background example according to Fig. 1, in the method according to Fig. 3 in conjunction with Figs. 6A-6B, the application of the electrode layer is not carried out, for example, before the structuring of the functional layer 3, in order to preferably enable an annealing step following the structuring of the functional layer 3 at high temperatures of substantially greater than or equal to 700°C, which an already conventionally applied electrode layer, e.g. made of aluminum, could not withstand.

[0139] In the exemplary step S306 of the method according to Fig. 3 (e.g. analogous to step S108 in Fig. 1), the functional layer 3 is also structured in regions 3a in the manufacturing sequence according to Figs. 6A-6B, see Fig. 6A (v).

[0140] Here, again, the mechanically active structures of the MEMS device are formed in the functional layer, preferably by high-rate etching or deep reactive ion etching (DRIE). Structuring the functional layer 3 includes, for example, forming or exposing the mirror support element beneath the mirror layer 6a, wherein the mirror support element is formed from the functional layer 3, as well as the retaining webs (spring structure), which can be formed from the functional layer 3 and can act as a spring system, and which can keep the mirror support element oscillatable about one, two, or more oscillation and / or torsion axes.In some embodiments, the spring structure may comprise springs, particularly preferably bending and / or torsion springs, which are preferably designed to hold the mirror support element in such a way that the mirror support element can perform an oscillating rotational movement about the respective oscillation and / or torsion axis (e.g., torsional oscillations). Furthermore, all descriptions of steps S301 to S306 above are also applicable to the manufacturing sequence according to Figs. 6A-6B.

[0141] In the further exemplary step S307 of the method according to Fig. 3, an annealing step at high temperatures above substantially greater than or equal to 700°C is also carried out in the manufacturing sequence according to Figs. 6A-6B, for example, in order to smooth the side walls of the regions 3a of the functional layer 3, which were deeply etched in step S306, and to round off corners of the regions 3a of the functional layer 3.

[0142] In some embodiments, the annealing step S307 may comprise a step in which the surface of the regions 3a of the functional layer 3 is subjected to a hydrogen annealing step at temperatures of substantially greater than or equal to 1000°C and preferably substantially less than or equal to 1250°C (alternatively or in addition to the sacrificial oxidation described above).

[0143] By way of example, in the production sequence according to Figs. 6A and 6B, following the structuring S306 of the functional layer 3 as an annealing step according to S307, the surface of the regions 3a of the functional layer 3 is subjected to a hydrogen annealing step at temperatures of substantially greater than or equal to 900°C, in particular substantially greater than or equal to 1000°C, and preferably substantially less than or equal to 1350°C, in particular substantially less than or equal to 1250°C (see, for example, Fig. 6A (vi)).

[0144] After hydrogen annealing in such embodiments of the annealing step S307, advantageously smoothed sidewalls of the regions 3a of the functional layer 3 with rounded corners remain; see, for example, Fig. 6A (vi).

[0145] As a result of the hydrogen annealing or the annealing step, smoothed or smooth sidewalls and rounded corners form on the surface of the regions 3a of the functional layer 3. In particular, any etching scallops as well as any other surface defects (e.g., crystal defects, initial etching, sidewall breakthroughs, and atomic defects, etc.) can be reduced or eliminated, so that smoothed sidewalls are formed, up to and including complete transformation into a completely smooth and / or crystal-defect-free sidewall. In addition, the rectangular structural corners that arose during the structuring of the functional layer can be rounded off (round or rounded structural corners). The corresponding layer structure or the MEMS device comprising the layer structure advantageously has smoothed orsmooth and / or crystal defect-free side walls and rounded corners in the structured regions and trenches of the functional layer, so that the fracture limits of the movable or oscillating parts of the functional layer or in particular of the spring structure formed in the functional layer can be significantly increased and the occurrence of premature fractures in the spring structure can be successfully reduced. In comparison to the prior art, i.e. when components are manufactured without healed side walls (i.e. in particular without smoothed side walls and / or without rounded corners), in which fractures can occur in particular even at smaller deflection angles or deflection amplitudes, the occurrence of fractures in the deflection structures or the spring structure can advantageously be significantly reduced and in particular even larger deflection angles orDeflection amplitudes are made possible at which fractures of the deflection structures or the spring structure would already occur in components manufactured according to the state of the art.

[0146] In the exemplary step S308 of the method according to Fig. 3, the electrode layer 6 is applied, for example, after the annealing step S307; see also Fig. 6A (vii). Here, the region 5b previously opened in the dielectric layer 5 is also filled with the material of the electrode layer, in particular, for example, to form a bond pad.

[0147] In some preferred embodiments, an electrode layer 6 (top electrode layer) can be deposited over the entire surface, e.g., made of metal, in particular, for example, aluminum. In further embodiments, high-temperature-stable materials, in particular, for example, high-temperature-stable metals, can also be used for the electrode layer. In such embodiments, the annealing step can also take place after the application and / or structuring of the electrode layer and optionally also after the rear opening of the layer structure, which preferably comprises high-temperature-stable and chemically resistant materials; see, for example, the embodiments described below according to Figs. 8 to 10.

[0148] In the further exemplary step S309 of the method according to Fig. 3, the electrode layer 6, which is applied on or above the dielectric layer 5, is structured; see also Fig. 6B (viii). Here, a bond pad 6b is formed, for example, in the region 5b that is open in the dielectric layer 5, using the material of the electrode layer, which can provide electrical contact to the upper side of the functional layer 3.

[0149] In the further exemplary step S310 of the method according to Fig. 3 (e.g., analogous to S109 in Fig. 1), the layer structure is opened on the back side, for example, to expose the functional layer 3 on the side opposite the piezoelectric layer 4; see also Fig. 6B (ix), in which, for example, the substrate layer 1 is opened on the back toward the intermediate layer 2, and Fig. 6B (x), in which, for example, the intermediate layer 2 is opened on the back toward the functional layer 3.

[0150] In a further exemplary step S311 of the method according to Fig. 3 (e.g., analogous to S110 in Fig. 1), the produced layer structure is provided, by way of example, in a vacuum-packed MEMS device 300 according to Fig. 6. Here, by way of example, the layer structure was hermetically sealed from above with a translucent cover element 7 (e.g., a translucent dome element or a glass dome) (see, for example, Fig. 6B (xi)) and hermetically sealed from below with a base body element 8 under a vacuum atmosphere (e.g., vacuum encapsulation). In further exemplary embodiments, differently shaped cover elements or 3D-shaped cover elements are also possible (e.g., square or planar). The material of the cover elements is preferably translucent, e.g., glass or other optically transparent materials (e.g., approx. 400-2500 nm), such as, for example, borosilicate glass (e.g., Borofloat® BF33 from SCHOTT).

[0151] Furthermore, all descriptions of steps S308 to S311 above are also applicable to the manufacturing sequence according to Figs. 6A-6B.

[0152] Fig. 7 shows an exemplary sectional view of a MEMS device 300, which can be manufactured according to the exemplary manufacturing sequence of Figs. 6A-6B. Consequently, a vacuum-packed MEMS mirror device 300 (e.g., a MEMS mirror scanner) comprising the manufactured layer structure can be provided with piezoelectrically deflectable or controllable mirrors 6a, wherein the corresponding layer structure or the MEMS device 300 comprising the layer structure advantageously has smooth and / or crystal defect-free sidewalls and rounded corners at the structured regions and trenches of the functional layer, so that the fracture limits of the movable or oscillating parts of the functional layer or, in particular, of the spring structure formed in the functional layer, can be significantly increased and the occurrence of premature fractures of the spring structure can be successfully reduced. Compared to the prior art, i.e.If components are manufactured without healed side walls (i.e. in particular without smoothed side walls and / or without rounded corners), in which fractures can occur particularly already at smaller deflection angles or deflection amplitudes, the occurrence of fractures in the deflection structures or the spring structure can be advantageously significantly reduced and in particular larger deflection angles or deflection amplitudes can also be made possible, at which fractures in the deflection structures or the spring structure would already occur in components manufactured according to the state of the art.

[0153] Fig. 8 shows an exemplary flowchart of a method for manufacturing a layer structure for a MEMS device according to further embodiments of the present disclosure. Figs. 9A-9B show exemplary cross-sectional views of the layer structure during the manufacturing process according to an exemplary manufacturing sequence based on the method of Fig. 8.

[0154] However, the first steps of the method according to Fig. 8 initially correspond, by way of example, again to steps S101 to S104 of the method according to Fig. 1 or the exemplary manufacturing sequence (i) to (v) according to Fig. 2A. Following Fig. 2A (v), the following Figs. 9A-9B show exemplary sectional views of the layer structure during the manufacturing process according to an exemplary manufacturing sequence based on the method according to Fig. 8.

[0155] Referring to Fig. 8 and Fig. 2A (i) to (v), in an exemplary step S801 (e.g., analogous to S101 in Fig. 1), a layer structure is provided which, by way of example, already comprises the substrate layer 1 and the functional layer 3. In the exemplary step S802 (e.g., analogous to S102 in Fig. 1), the piezoelectric layer 4 is applied to the functional layer 3. In the further exemplary step S803 (e.g., analogous to S103 in Fig. 1), the piezoelectric layer 4, which is applied on or above the functional layer 3, is structured, by way of example.

[0156] In the further exemplary step S804 (e.g., analogous to S104 in Fig. 1), the dielectric layer 5 is applied, for example. The dielectric layer 5 is applied, for example, to regions of the piezoelectric layer 4 and is further applied, for example, to regions of the functional layer 3 that are open after structuring the piezoelectric layer 4. In some embodiments, the applied dielectric layer 5 can be opened in selected regions, for example, to provide a region 5b intended for a later bond pad. In some embodiments, the applied dielectric layer 5 can also be opened or partially opened over the structured regions of the piezoelectric layer 4.

[0157] Furthermore, all descriptions of steps S301 to S304 above are also applicable, by way of example, to the manufacturing sequence according to Figs. 9A-9B in connection with steps S801 to S804 according to Fig. 8.

[0158] In a further exemplary step S805 of the method according to Fig. 1, an electrode layer 9 is applied to the dielectric layer 5, which can optionally be opened in regions beforehand; see also Fig. 9A (v).

[0159] In contrast to the sequence of the background example according to Fig. 1, in step S805, a high-temperature-stable, electrically conductive material is used when applying the electrode layer 9. In preferred embodiments (instead of, for example, aluminum of the electrode layer 6 in Figs. 2A to 2C), a high-temperature-stable material can be used that can withstand temperatures substantially greater than or equal to 700°C, in further embodiments preferably substantially greater than or equal to 800°C and preferably greater than or equal to 1000°C, and in further embodiments particularly preferably substantially greater than or equal to 1250°C.

[0160] In particularly preferred embodiments, for example, a conductive silicon layer can be used as the high-temperature-stable material of the high-temperature-stable electrode layer 9 (e.g., deposited by physical vapor deposition (PVD), by chemical vapor deposition (CVD), or by plasma-enhanced chemical vapor deposition (PECVD), etc.). Particularly preferred is the use of a doped polysilicon as the (non-metallic) high-temperature-stable material of the high-temperature-stable electrode layer 9.

[0161] In further preferred embodiments, alternatively or additionally, for example, a high-temperature-stable metal can be used as the material of the high-temperature-stable electrode layer 9 (e.g., molybdenum, platinum, tungsten, tungsten titanium or WTi, tungsten carbide or WC, etc.). Such high-temperature-stable materials for use as the material of the high-temperature-stable electrode layer 9 enable the layer structure to continue to be compatible with a high-temperature-stable process sequence at temperatures substantially greater than or equal to 700°C or substantially greater than or equal to 800°C, wherein, in particular, the already applied electrode layer 9 can also withstand a subsequent annealing step (e.g., sacrificial oxidation and / or hydrogen annealing according to the above embodiments) at temperatures substantially greater than or equal to 700°C, in particular between substantially 700°C and 1250°C.

[0162] In a further exemplary step S806 of the method according to Fig. 8 (e.g., analogous to S106 in Fig. 1), the electrode layer 9, which is applied on or above the dielectric layer 5, is structured; see also Fig. 9A (vi). In the exemplary step S806 of structuring the electrode layer 9, the desired structure of the upper electrode (top electrode) for controlling the piezoelectric layer 4 can be formed.

[0163] In a further exemplary step S807 of the method according to Fig. 8 (e.g., analogous to S107 in Fig. 1), the dielectric layer 5 is opened in regions 5a toward the functional layer 3, see also Fig. 9A (vii). These are, in particular, regions 5a of the dielectric layer 5 to be opened, in which the underlying functional layer 3 is structured to form the mechanically active structures (e.g., the spring structure) of the MEMS device.

[0164] Here too, in some embodiments it is provided that the remaining regions of the piezoelectric layer 4 remain completely encapsulated by the dielectric layer 5 (see e.g. Fig. 9A (vii)), i.e. the remaining regions of the piezoelectric layer 4 are or remain, particularly preferably, completely encapsulated between the functional layer 3 and the dielectric layer 5. This has the advantage that the layer structure can still be subjected to high-temperature processes at temperatures substantially greater than or equal to 700°C, e.g. at more than approx. 700°C to 1250°C, without impairing the encapsulated regions of the piezoelectric layer 4. This enables, for example, further annealing steps such as the processes of sacrificial oxidation (at e.g. approx. 800°C-1250°C) and / or hydrogen annealing (at e.g. approx.1000°C-1250°C), even if less high-temperature stable and / or less chemically resistant materials are used under the encapsulation (e.g. for a possible bottom electrode and / or for the piezoelectric layer).

[0165] This encapsulation of the structured regions of the piezoelectric layer 4, e.g., by means of the dielectric layer, is able to advantageously protect the structured regions of the piezoelectric layer 4 despite the high temperatures in the annealing step and despite the chemically aggressive media (e.g., oxygen or hydrogen), so that even piezoelectric materials that are not highly stable or not so chemically resistant, such as PZT, can still be used as piezoelectric materials (encapsulated in the annealing step). In embodiments using highly stable and / or chemically resistant piezoelectric materials, it is not necessary to encapsulate the structured regions of the piezoelectric layer 4.

[0166] In addition or as an alternative to encapsulating the piezoelectric layer 4, e.g., by means of the dielectric layer or with encapsulating regions of the dielectric layer, the high-temperature-stable electrode layer 9 can also be used to encapsulate the structured regions of the piezoelectric layer 4. For this purpose, it can be provided in some exemplary embodiments that the remaining regions of the piezoelectric layer 4 are or remain completely encapsulated by the high-temperature-stable electrode layer 9, i.e., the remaining regions of the piezoelectric layer 4 are or remain, particularly preferably, completely encapsulated between the functional layer 3 and the high-temperature-stable electrode layer 9 (optionally with a dielectric layer 5 lying therebetween or lying therebetween in some regions).

[0167] This also has the advantage that the layer structure can still be subjected to high-temperature processes at substantially greater than or equal to 700°C, e.g. at over approximately 700°C to 1250°C, without impairing the encapsulated areas of the piezoelectric layer 4, wherein in particular any less chemically resistant piezoelectric materials can be protected by the encapsulation of aggressive media, such as oxygen (e.g. in an annealing step with sacrificial oxidation) and / or hydrogen (e.g. in an annealing step with hydrogen annealing).

[0168] This allows, for example, further annealing steps such as the sacrificial oxidation processes (at e.g. approx. 800°C-1250°C) and / or hydrogen annealing (at e.g. approx. 1000°C-1250°C) described below, even if less high-temperature stable and / or less chemically resistant materials are used under the encapsulation (e.g. for a possible bottom electrode and / or for the piezoelectric layer).

[0169] In a further exemplary step S808 of the method according to Fig. 8 (e.g. analogous to S108 in Fig. 1), the functional layer 3 is structured in areas 3a, see also Fig. 9A (viii).

[0170] Here, the mechanically active structures of the MEMS device are again formed in the functional layer, preferably by high-rate etching or deep reactive ion etching (DRIE). Structuring the functional layer 3 includes, for example, forming or exposing the mirror support element, which is formed from the functional layer 3, as well as the retaining webs (spring structure), which are formed from the functional layer 3 and act as a spring system, and which can keep the mirror support element oscillatable about one, two, or more oscillation and / or torsion axes.In some embodiments, the spring structure may comprise springs, particularly preferably bending and / or torsion springs, which are preferably designed to hold the mirror support element in such a way that the mirror support element can perform an oscillating rotational movement about the respective oscillation and / or torsion axis about the corresponding axis (e.g. torsional oscillations).

[0171] In the further exemplary step S809 of the method according to Fig. 8 (e.g. analogous to S307 in Fig. 3), an annealing step at high temperatures substantially greater than or equal to 700°C is also carried out in the production sequence according to Figs. 6A-6B, in particular in order to smooth the side walls of the regions 3a of the functional layer 3 deeply etched in step S808 and to round off corners of the regions 3a of the functional layer 3.

[0172] In some embodiments, the annealing step S809 may comprise a step in which the surface of the regions 3a of the functional layer 3 is oxidized at temperatures substantially greater than or equal to 700°C, preferably at temperatures substantially greater than or equal to 800°C (e.g., at approximately 800°C-1250°C). For example, after the structuring S808 of the functional layer 3, a sacrificial oxidation may be carried out as a annealing step according to S809. This oxidation can oxidize the surface effects created during etching (e.g., irregularities such as formed noses, waves, so-called scallops, as well as any other surface defects such as, for example, crystal defects, etching, sidewall penetrations, and atomic defects, etc.) on the sidewalls of the deeply etched sidewalls of the regions 3a of the functional layer 3.

[0173] After the sacrificial oxidation, the sacrificial oxidation layer 11 can preferably be selectively removed and, in particular, any etching scallops as well as any surface defects (e.g., crystal defects, etchings, sidewall penetrations and atomic defects, etc.) can be reduced or eliminated, so that smoothed sidewalls are formed, up to the complete transformation into a completely smooth and / or crystal defect-free sidewall.

[0174] In addition, the rectangular structural corners created during the structuring of the functional layer can be rounded (round or rounded structural corners). In such embodiments of the annealing step S809, advantageously smoothed sidewalls and rounded structural corners of the sidewalls of the regions 3a of the functional layer 3 remain after selective removal of the sacrificial oxidation layer 11; see, for example, Fig. 9B (ix).

[0175] In some embodiments, the annealing step S809 may (alternatively or in addition to the surface oxidation) also comprise a step in which the surface of the regions 3a of the functional layer 3 is subjected to a hydrogen annealing step, e.g., at temperatures substantially greater than or equal to 1000°C, e.g., from approximately 1000°C to 1250°C. Thus, for example, after the structuring S808 of the functional layer 3, as an annealing step according to S809, the surface of the regions 3a of the functional layer 3 may be subjected to a hydrogen annealing step at temperatures substantially greater than or equal to 1000°C, e.g., from approximately 1000°C to 1250°C.

[0176] Through hydrogen annealing or the annealing step, smooth sidewalls and rounded corners form on the surface of regions 3a of functional layer 3. In particular, any etching scallops as well as any surface defects (e.g., crystal defects, initial etching, sidewall penetrations, and atomic defects, etc.) can be reduced or eliminated, resulting in smoothed sidewalls, up to and including complete transformation into a completely smooth and / or crystal-defect-free sidewall; see, for example, Fig.

[0177] 9B (ix).

[0178] By annealing by means of oxidation or sacrificial oxidation and / or by means of hydrogen annealing, in such embodiments of the annealing step S809, the surface effects or surface defects (e.g., formed noses, waves, so-called scallops, etc.) on the side walls of the deep-etched side walls of the regions 3a of the functional layer 3 that were created during etching can be smoothed (analogous to S307 according to Fig. 3).

[0179] In particular, any etching scallops as well as any other surface defects (e.g., crystal defects, initial etching, sidewall penetrations, and atomic defects, etc.) can be reduced or eliminated, resulting in smoothed sidewalls, up to and including complete transformation into a completely smooth and / or crystal-defect-free sidewall. Furthermore, the rectangular structural corners created during the structuring of the functional layer can be rounded (round or rounded structural corners). Consequently, after the annealing step S809, advantageously smoothed sidewalls of the regions 3a of the functional layer 3 remain with rounded corners; see, for example, Fig. 9A (ix).

[0180] The corresponding layer structure or the MEMS device comprising the layer structure advantageously has, after the corresponding annealing step S809, smooth and / or crystal defect-free side walls and rounded corners in the structured regions and trenches of the functional layer, so that the fracture limits of the movable or oscillating parts of the functional layer or in particular of the spring structure formed in the functional layer can be significantly increased and the occurrence of premature fractures in the spring structure can be successfully reduced. In comparison to the prior art, i.e. when components are manufactured without annealed side walls (i.e. in particular without smoothed side walls and / or without rounded corners), in which fractures can occur in particular already at smaller deflection angles or deflection amplitudes, the occurrence of fractures in the deflection structures orthe spring structure can advantageously be significantly reduced and in particular larger deflection angles or deflection amplitudes can also be made possible, at which fractures of the deflection structures or the spring structure would already occur in components manufactured according to the prior art. Furthermore, it can be expedient, in particular if an electrically conductive silicon-based electrode layer 9 was applied in step S806, that a mirror layer is formed on the mirror carrier element of the functional layer 3, which is formed in step S806, following the annealing step S809.

[0181] In some embodiments, the method according to Fig. 8 may therefore, for example, comprise a further step S810 of applying a mirror layer 10 for forming the mirror 10a on the mirror carrier element of the functional layer 3; see, for example, also Fig. 9B (x).

[0182] Here, a simple metal, such as aluminum, can also be used. In some preferred embodiments, the material of the metallic mirror layer can be selected depending on the desired application for the respective wavelength range, in particular with very good reflection behavior in the wavelength range of the desired application, for example aluminum or silver for visible light (e.g., essentially at wavelengths of 400-700 nm) or gold for infrared light or infrared radiation (e.g., essentially at wavelengths of 850-2000 nm). If a conductive material is used, this can also be used, for example, to form the bond pad 10b; see, for example, also Fig. 9B (x).

[0183] In the further exemplary step S811 of the method according to Fig. 8 (e.g., analogous to S109 in Fig. 1), the layer structure is opened on the back, in particular to expose the functional layer 3 on the side opposite the piezoelectric layer 4; see also Fig. 9B (xi), in which, for example, the substrate layer 1 and the intermediate layer 2 are opened on the back toward the functional layer 3.

[0184] In a further exemplary step S812 of the method according to Fig. 8 (e.g., analogous to S110 in Fig. 1), the produced layer structure is provided, by way of example, in a vacuum-packed MEMS device 400 according to Fig. 10. Here, by way of example, the layer structure was hermetically sealed from above with a translucent cover element 7 (e.g., a translucent dome element or a glass dome) and hermetically sealed from below with a base body element 8 under a vacuum atmosphere (e.g., vacuum encapsulation).

[0185] In further embodiments, differently shaped cover elements or 3D-shaped cover elements are also possible (e.g., square or planar). The material of the cover elements is preferably translucent, e.g., glass or other optically transparent materials (e.g., approximately 400-2500 nm), such as borosilicate glass (e.g., Borofloat® BF33 from SCHOTT).

[0186] Fig. 10 shows an exemplary sectional view of a MEMS device 400 manufactured according to the exemplary manufacturing sequence of Figs. 9A-9B. Consequently, a vacuum-packed MEMS mirror device 400 (e.g., a MEMS mirror scanner) can be provided, which comprises the manufactured layer structure, e.g., with piezoelectrically deflectable or controllable mirror 10a, wherein the corresponding layer structure or the MEMS device 400 comprising the layer structure advantageously has smoothed or smooth and / or crystal defect-free sidewalls and rounded corners at the structured regions and trenches of the functional layer, so that fracture limits of the movable or oscillating parts of the functional layer or, in particular, of the spring structure formed in the functional layer, can be significantly increased and the occurrence of premature fractures of the spring structure can be successfully reduced.In comparison to prior art methods without a healing step, according to embodiments with a healing step, the fracture limits of the movable or oscillating parts of the functional layer or in particular of the spring structure formed in the functional layer can be at least doubled, or even fivefold or tenfold increased. In comparison to the prior art, i.e. when components are manufactured without healed side walls (i.e. in particular without smoothed side walls and / or without rounded corners), in which fractures can occur in particular already at smaller deflection angles or deflection amplitudes, the occurrence of fractures in the deflection structures or the spring structure can advantageously be significantly reduced and in particular even larger deflection angles or deflection amplitudes can be enabled, at which fractures in the deflection structures or the spring structure would already occur in components manufactured according to the prior art.

[0187] Fig. 11 shows an exemplary flowchart of a method for manufacturing a layer structure for a MEMS device according to further embodiments of the present disclosure.

[0188] However, the first steps of the method according to Fig. 11 initially correspond again, by way of example, to steps S101 to S103 of the method according to Fig. 1. Figs. 12A-12B show exemplary sectional views of the layer structure during the manufacturing process according to an exemplary manufacturing sequence based on the method according to Fig. 11.

[0189] Referring to Fig. 11 and Fig. 12A (i) to (iii), in an exemplary step S1101 (e.g., analogous to S101 in Fig. 1), the layer structure is provided, which comprises, for example, the substrate layer 1 and the functional layer 3. In an exemplary step S1102 (e.g., analogous to S102 in Fig. 1), the piezoelectric layer 4 is applied to the functional layer 3. In the further exemplary step S1103 (e.g., analogous to S103 in Fig. 1), the piezoelectric layer 4, which is applied on or above the functional layer 3, is structured, for example.

[0190] Furthermore, all descriptions of steps S301 to S303 above are also applicable, by way of example, to the manufacturing sequence according to Figs. 12A-12C in connection with steps S1101 to S1104 according to Fig. 11.

[0191] In contrast to the embodiments described above, according to some embodiments according to Fig. 11, the functional layer 3 is now structured directly before the dielectric layer 5 is applied (step S1104 of Fig. 11) and then, for example, the annealing step S1105 takes place in a state of the layer structure in which structured regions of the piezoelectric layer 4 are open at the top.

[0192] Accordingly, in such embodiments, a piezoelectric layer 4 made of a high-temperature stable and / or chemically resistant piezoelectric material can preferably be applied in step S1102. In some preferred embodiments, the high-temperature stable and / or chemically resistant piezoelectric layer 4 can comprise, for example, aluminum nitride (AlN) and / or aluminum scandium nitride (AlScN).

[0193] In the further exemplary step S1104 of the method according to Fig. 11 (e.g., analogous to step S108 in Fig. 1), the functional layer 3 is structured in regions 3a, see also Fig. 12A (iii). In particular, the mechanically active structures of the MEMS device are formed in the functional layer, preferably by high-rate etching or deep reactive ion etching (DRIE for short).

[0194] The structuring of the functional layer 3 comprises, for example, the formation or exposure of the mirror support element (under the later applied mirror layer 6a, see e.g. Fig. 13), which is formed by way of example from the functional layer 3, as well as the holding webs (spring structure), which are formed by way of example from the functional layer 3 and can act as a holding spring structure, and which can hold the mirror support element so that it can swing about one, two or more oscillation and / or torsion axes. In some embodiments, the spring structure can comprise springs, particularly preferably bending and / or torsion springs, which are preferably designed to hold the mirror support element in such a way that the mirror support element can execute an oscillating rotational movement about the respective oscillation and / or torsion axis around the corresponding axis (e.g. torsional oscillations).

[0195] In some embodiments, the reactive ion deep etching for structuring the functional layer 3 can be carried out, for example, using a photolithography mask.

[0196] In the further exemplary step S1105 of the method according to Fig.11 (e.g. analogous to S307 in Fig. 3), an annealing step at high temperatures substantially greater than or equal to 700°C is also carried out in the production sequence according to Figs. 12A-12C, in particular in order to smooth the side walls of the regions 3a of the functional layer 3 which were deeply etched in step S1104 and to round off corners of the regions 3a of the functional layer 3.

[0197] In some embodiments, the annealing step S1105 may comprise a step in which the surface of the regions 3a of the functional layer 3 is oxidized at temperatures substantially greater than or equal to 700°C, preferably at temperatures substantially greater than or equal to 800°C (e.g., at approximately 800°C to 1250°C). For example, after the structuring S1104 of the functional layer 3, a sacrificial oxidation may be performed as an annealing step according to S1105.

[0198] Through this oxidation, the surface effects created during etching (e.g., irregularities such as formed noses, waves, so-called scallops, as well as any other surface defects such as crystal defects, initial etching, sidewall penetrations, and atomic defects, etc.) on the sidewalls of the deep-etched sidewalls of the regions 3a of the functional layer 3 can be oxidized. After the sacrificial oxidation, the sacrificial oxidation layer can preferably be selectively removed, and in particular, any etching scallops as well as any surface defects (e.g., crystal defects, initial etching, sidewall penetrations, and atomic defects, etc.) can be reduced or eliminated, so that smoothed sidewalls are formed, up to and including complete transformation into a completely smooth and / or crystal-defect-free sidewall. In addition, the rectangular structural corners created during the structuring of the functional layer can be rounded (round or rounded structural corners).In such embodiments of the annealing step S1105, after selective removal of the sacrificial oxidation layer 11, advantageously smoothed sidewalls and rounded structural corners of the sidewalls of the regions 3a of the functional layer 3 remain; see, for example, Fig. 12A (iv).

[0199] The annealing step S1105 may, in some embodiments (alternatively or in addition to the surface oxidation), also comprise a step in which the surface of the regions 3a of the functional layer 3 is subjected to a hydrogen annealing step, e.g., at temperatures substantially greater than or equal to 1000°C, e.g., from approximately 1000°C to 1250°C. Thus, for example, after structuring

[0200] 51104 of the functional layer 3 as a healing step according to S1105 the surface of the regions 3a of the functional layer 3, e.g. at temperatures substantially greater than or equal to 1000°C, e.g. from approximately 1000°C to 1250°C, is subjected to a hydrogen annealing step.

[0201] Through hydrogen annealing or the annealing step, smooth sidewalls and rounded corners form on the surface of regions 3a of functional layer 3. In particular, any etching scallops as well as any surface defects (e.g., crystal defects, initial etching, sidewall penetrations, and atomic defects, etc.) can be reduced or eliminated, resulting in smoothed sidewalls, up to and including complete transformation into a completely smooth and / or crystal-defect-free sidewall; see, for example, Fig. 12A (iv).

[0202] By annealing by means of oxidation or sacrificial oxidation and / or by means of hydrogen annealing, in such embodiments of the annealing step

[0203] 51105 the surface effects or surface defects (e.g., sidewall perforations and atomic defects, or also formed noses, waves, so-called scallops, etc.) on the sidewalls of the deep-etched sidewalls of the regions 3a of the functional layer 3 resulting from etching are smoothed (analogous to S307 according to Fig. 3). After the annealing step S1105, advantageously smoothed sidewalls of the regions 3a of the functional layer 3 remain with rounded corners; see, for example, Fig. 12A (iv).

[0204] The corresponding layer structure or the MEMS device comprising the layer structure, after the corresponding annealing step S1105, advantageously has smoothed or smooth and / or crystal defect-free side walls and rounded corners on the structured regions and trenches of the functional layer, so that the fracture limits of the movable or oscillating parts of the functional layer or in particular of the spring structure formed in the functional layer can be significantly increased and the occurrence of premature fractures of the spring structure can be successfully reduced. Compared to prior art methods without an annealing step, according to embodiments with an annealing step, the fracture limits of the movable or oscillating parts of the functional layer or in particular of the spring structure formed in the functional layer can be at least doubled, or even increased fivefold or tenfold. Compared to the prior art, i.e.If components are manufactured without healed side walls (i.e. in particular without smoothed side walls and / or without rounded corners), in which fractures can occur particularly already at smaller deflection angles or deflection amplitudes, the occurrence of fractures in the deflection structures or the spring structure can be advantageously significantly reduced and in particular larger deflection angles or deflection amplitudes can also be made possible, at which fractures in the deflection structures or the spring structure would already occur in components manufactured according to the state of the art.

[0205] In a further exemplary step S1106 of the method according to Fig. 11, a dielectric layer 5 is applied, for example; see also Fig. 12B (v). The dielectric layer 5 is applied, for example, according to Fig. 12B (v), to regions of the piezoelectric layer 4 and, furthermore, to regions of the functional layer 3 that are exposed after structuring the piezoelectric layer 4.

[0206] In some embodiments, the applied dielectric layer 5 can be opened in selected regions (step S1107 of Fig. 11). According to Fig. 12B (vi), for example, in region 5b, the dielectric layer 5 is opened toward the functional layer 3 to provide a region 5b that can be provided for a later bond pad. In some embodiments, the applied dielectric layer 5 can also be opened or partially opened over the structured regions of the piezoelectric layer 4.

[0207] In a further exemplary step S1108 of the method, an electrode layer 6 is applied to the dielectric layer 5, which has optionally been previously opened in regions; see also Fig. 12B (vii). Here, the region 5b, which was previously opened in the dielectric layer 5, in particular to form a bond pad, and the opened regions 3a of the trenches of the functional layer 3 are also at least partially filled with the material of the electrode layer 6.

[0208] In a further exemplary step S1109 of the method according to Fig. 11, the electrode layer 6, which is applied on or above the dielectric layer 5, is structured; see also Fig. 12B (viii). In this case, a bonding pad 6b is formed with the material of the electrode layer in the region 5b that is open in the dielectric layer 5, which provides electrical contact to the top side of the functional layer 3. In addition, any material of the electrode layer 6 can be removed again from the open regions 3a of the trenches of the functional layer 3.

[0209] In the exemplary step S1109 of structuring the electrode layer 6, the desired structure of the upper electrode (top electrode) for the upper electrical contacting of the piezoelectric layer 4 is formed. Furthermore, in step S1109 of structuring the electrode layer 6, a mirror 6a (mirror layer with a reflective surface) is formed, for example, in the center of the layer structure, according to Fig. 12B (viii) using the material of the electrode layer 6.

[0210] In such examples, for example, the electrode layer can comprise metal, in particular aluminum, so that the surface of the electrode layer 6 already has a reflective surface and is suitable for forming the mirror 6a. In further examples, it is possible to provide a non-reflective or non-metallic electrode layer (e.g., doped polycrystalline silicon), in which case a further, for example metallic mirror layer (e.g., as a thin metal film, e.g., with a layer thickness of substantially greater than or equal to 100 nm and / or substantially less than or equal to 2000 nm) can then be applied in the region of the layer 6a.

[0211] In some preferred embodiments, the material of the metallic mirror layer can be selected depending on the desired application for the respective wavelength range, in particular with very good reflection behavior in the wavelength range of the desired application, for example aluminum or silver for visible light (e.g. essentially at wavelengths of 400-700nm) or gold for infrared light or infrared radiation (e.g. essentially at wavelengths of 850-2000nm).

[0212] In a further exemplary step S1110 of the method according to Fig. 11, the layer structure is opened on the back, in particular to expose the functional layer 3 on the side opposite the piezoelectric layer 4; see also Fig. 12C (ix), in which, for example, the substrate layer 1 is opened on the back toward the intermediate layer 2, and Fig. 12C (x), in which, for example, the intermediate layer 2 is opened on the back toward the functional layer 3.

[0213] In a further exemplary step S111 of the method according to Fig. 11, the produced layer structure is provided in a vacuum-packed MEMS device 500 according to Fig. 13. Here, by way of example, the layer structure was hermetically sealed from above with a translucent cover element 7 (e.g., a translucent dome element or a glass dome) and from below with a base body element 8 under a vacuum atmosphere (e.g., vacuum encapsulation). In further exemplary embodiments, differently shaped cover elements or 3D-shaped cover elements are also possible (e.g., square or planar). The material of the cover elements is preferably translucent, e.g., glass or other optically transparent materials (e.g., approx. 400-2500 nm), such as, for example, borosilicate glass (e.g., Borofloat® BF33 from SCHOTT).

[0214] In the above embodiments, in particular, steps S1106 and S1107 can be executed analogously to steps S304 and S305, and corresponding descriptions of Fig. 3 and the associated exemplary manufacturing sequences can be applied by way of example. Furthermore, in particular, steps S1108 to S1110 can be executed analogously to steps S308 to S311, and corresponding descriptions of Fig. 3 and the associated exemplary manufacturing sequences can be applied by way of example.

[0215] Fig. 13 shows an exemplary sectional view of a MEMS device 500 manufactured according to the exemplary manufacturing sequence of Figs. 12A-12C. Consequently, a vacuum-packed MEMS mirror device 500 (e.g., a MEMS mirror scanner) comprising the manufactured layer structure, in particular with piezoelectrically deflectable or controllable mirror 6a, can be provided, wherein the corresponding layer structure or the MEMS device 500 comprising the layer structure advantageously has smoothed or smooth and / or crystal defect-free sidewalls and rounded corners at the structured regions and trenches of the functional layer, so that fracture limits of the movable or oscillating parts of the functional layer or, in particular, of the spring structure formed in the functional layer, can be significantly increased and the occurrence of premature fractures of the spring structure can be successfully reduced.In comparison to prior art methods without a healing step, according to embodiments with a healing step, the fracture limits of the movable or oscillating parts of the functional layer or in particular of the spring structure formed in the functional layer can be at least doubled, or even fivefold or tenfold increased. In comparison to the prior art, i.e. when components are manufactured without healed side walls (i.e. in particular without smoothed side walls and / or without rounded corners), in which fractures can occur in particular already at smaller deflection angles or deflection amplitudes, the occurrence of fractures in the deflection structures or the spring structure can advantageously be significantly reduced and in particular even larger deflection angles or deflection amplitudes can be enabled, at which fractures in the deflection structures or the spring structure would already occur in components manufactured according to the prior art.

[0216] Embodiments have been described above which, based on the prior art, are able to provide improved methods for producing a layer structure for a MEMS device, in particular in order to be able to provide the MEMS device comprising the layer structure with higher mechanical fracture limits of the mechanically acting components of the layer structure or with lower susceptibility to fracture.

[0217] Particularly advantageously, the provision of a layer structure according to embodiments with structured regions of the piezoelectric layer encapsulated under a high-temperature stable layer (e.g. under a dielectric layer) enables the integration of one or more high-temperature annealing steps (such as hydrogen annealing of deeply etched surfaces, e.g. at approximately 1000°C-1250°C, and / or sacrificial oxidation, e.g. at approximately 800°C-1250°C, with etching back of the sacrificial oxide layer), even if less high-temperature stable and / or less chemically resistant materials are used under the encapsulation (e.g. for a possible bottom electrode and / or for the piezoelectric layer, e.g. PZT).In further embodiments, high-temperature stable and / or chemically more resistant materials can also be used for the bottom electrode and / or for the piezoelectric layer, so that such annealing steps can also be carried out without encapsulation.

[0218] In particular, it was found that the integration of a high-temperature annealing step according to embodiments (e.g. by hydrogen annealing and / or by sacrificial oxidation according to embodiments) successfully and advantageously enables the deep-etched sidewalls of the structured functional layer to be smoothed in order to smooth out the defects and roughnesses (e.g. scallops, sidewall penetrations and atomic defects, etc.) on the surface that arose during the etching process (e.g. DRIE) and also to round off right-angled corners that arose during the etching.

[0219] In particular, it was found that roughness values ​​of up to 200 nm and generally over 50 nm usually occur on the deep-etched side walls of the structured functional layer, which could be significantly smoothed to roughness values ​​below approximately 50 nm (in particular less than or equal to 50 nm) by annealing according to the above embodiments (e.g. by hydrogen annealing and / or by sacrificial oxidation according to embodiments), in particular to roughness values ​​less than or equal to 30 nm, in particular less than or equal to 10 nm down to approximately less than or equal to 2-3 nm. In addition, the 90° corners on the deep-etched side walls of the structured functional layer could be rounded (finite corner radius).

[0220] According to embodiments, this advantageously leads to a significantly increased stability or fracture stability of the movable elements of the MEMS device and in particular of the spring structure formed from the functional layer, with increased fracture limits, whereby premature fractures of the spring structure or fractures of the spring structure at small deflection angles can be avoided.

[0221] In comparison to prior art methods without a healing step, according to embodiments with a healing step, the fracture limits of the movable or oscillating parts of the functional layer or in particular of the spring structure formed in the functional layer can be at least doubled, or even fivefold or tenfold increased. In comparison to the prior art, i.e. when components are manufactured without healed side walls (i.e. in particular without smoothed side walls and / or without rounded corners), in which fractures can occur in particular already at smaller deflection angles or deflection amplitudes, the occurrence of fractures in the deflection structures or the spring structure can advantageously be significantly reduced and in particular even larger deflection angles or deflection amplitudes can be enabled, at which fractures in the deflection structures or the spring structure would already occur in components manufactured according to the prior art.

[0222] In particular, it has the advantage that the layered structure according to embodiments with advantageously smoothed side walls of the regions 3a of the functional layer 3 with rounded corners has increased load-bearing capacity and stability or fracture resistance. It has been demonstrated that the layers of the layered structure, including the functional layer 3 with advantageously smoothed side walls and rounded corners, result in the functional layer having improved fracture limits.

[0223] In particular, by smoothing / healing the sidewalls or by healing the sidewall damage and rounding the corners, the original fracture behavior, e.g., of silicon, can be restored. This means, for example, that fracture strengths can be significantly increased compared to the state of the art without annealing. In particular, it has been demonstrated that fracture strengths can be increased from approximately 0.5-1.5 GPa to over 3 GPa and even more than 5 GPa.

[0224] In embodiments in which a vacuum-packed MEMS device is provided, higher quality factors of at least greater than 1000, greater than 10000, or greater than 20000 can be achieved by resonant oscillation operation in vacuum (e.g., <1 mbar) (at least a factor of 5 or 10 greater than when operating under room atmosphere (~ 1 bar)).

[0225] It should also be noted that the higher mechanical fracture limits enabled by the layer structure of the MEMS device according to embodiments advantageously further enable larger deflection amplitudes of the movable elements (e.g., scan amplitudes of the oscillating mirror surface) to be increased. According to embodiments, this in turn has the advantage that the MEMS devices according to embodiments can be dimensioned differently or smaller, i.e., with a more compact design, which in turn enables significant cost savings. Due to the higher fracture limit, higher stress values ​​can advantageously be permitted in the springs, which advantageously enables the use of shortened springs according to further embodiments.This means, for example, that while maintaining the same chip size, more space is available for the mirror plate, allowing for larger mirror plates, thus providing higher optical resolutions.

[0226] Embodiments of layered structures with layers have been described above. It should be noted that such embodiments should not be construed as limiting the possibility of no further intermediate layers being present in further embodiments. On the contrary, further layers and / or intermediate layers may be provided in further embodiments and / or described layers may be omitted.

[0227] It should be noted that only examples or exemplary embodiments of the present disclosure, as well as technical advantages, have been described in detail above with reference to the accompanying figures. However, the present disclosure is in no way limited or restricted to the exemplary embodiments described above and their design features or the described combinations thereof, but further encompasses modifications of the exemplary embodiments, in particular those encompassed by modifications of the features of the described examples or by combinations or partial combinations of individual or several of the features of the described examples within the scope of the independent claims.

[0228] List of reference symbols

[0229] 1 substrate layer

[0230] 2 Intermediate layer

[0231] 3 Functional layer (device layer)

[0232] 3a Trenches or structured areas of the functional layer

[0233] 4 piezoelectric layer

[0234] 5 dielectric layer

[0235] 5a opened area of ​​the dielectric layer

[0236] 6 Electrode layer

[0237] 6a Mirror

[0238] 6b Bond pad

[0239] 7 Cover element

[0240] 8 Floor element or base body element

[0241] 9 Electrode layer (high temperature stable)

[0242] 11 Sacrificial oxide layer

[0243] 10 Electrode layer or mirror layer

[0244] 10a Mirror

[0245] 10b Bond pad

[0246] 100 MEMS device

[0247] 200 MEMS device

[0248] 300 MEMS device

[0249] 400 MEMS device

[0250] 500 MEMS device

Claims

Patent claims 1. A method for producing a layer structure for a MEMS device, in particular a vacuum-packed MEMS mirror device, comprising: - providing (S301; S801; S1101) a layer structure comprising a substrate layer (1) and a functional layer (3), - applying (S302; S802; S1102) a piezoelectric layer (4), in particular on a side of the functional layer (3) opposite the substrate layer (1), - Structuring (S303; S803; S1103) the piezoelectric layer (4) to form structured regions of the piezoelectric layer (4), - Structuring (S306; S805; S1104) the functional layer (3) to form structured regions in the functional layer (3), and - annealing (S307; S809; S1105) trenches in the structured regions of the functional layer (3) at temperatures substantially greater than or equal to 700°C.

2. The method according to claim 1, characterized in that the annealing (S307; S809; S1105) of structured regions of the functional layer (3) is carried out to at least partially smooth side walls of the trenches in the functional layer (3) and / or to round corners of the trenches in the functional layer (3).

3. Method according to claim 1 or 2, characterized in that the annealing (S307; S809; S1105) of structured regions of the functional layer (3) is carried out at temperatures substantially greater than or equal to 800°C.

4. Method according to at least one of the preceding claims, characterized in that the annealing (S307; S809; S1105) of structured regions of the functional layer (3) is carried out at temperatures substantially less than or equal to 1400°C, in particular at temperatures substantially less than or equal to 1350°C.

5. Method according to at least one of the preceding claims, characterized in that the annealing (S307; S809; S1105) of structured regions of the functional layer (3) comprises hydrogen annealing.

6. The method according to claim 5, characterized in that the hydrogen annealing is carried out at temperatures substantially greater than or equal to 900°C and / or substantially less than or equal to 1350°C, in particular at temperatures substantially greater than or equal to 1000°C and / or substantially less than or equal to 1250°C.

7. The method according to at least one of the preceding claims, characterized in that the annealing (S307; S809; S1105) of structured regions of the functional layer (3) comprises oxidizing side walls of the trenches in the functional layer (3).

8. The method according to claim 7, characterized in that the oxidation of side walls of the trenches in the functional layer (3) is carried out at temperatures of substantially greater than or equal to 700°C, in particular at substantially greater than or equal to 800°C, and / or at substantially less than or equal to 1250°C.

9. The method according to claim 7 or 8, characterized in that the annealing (S307; S809; S1105) of structured regions of the functional layer (3) further comprises removing an oxidation layer (11) formed on side walls of the trenches in the functional layer (3), in particular by etching.

10. Method according to at least one of the preceding claims, characterized by - applying (S308; S1108) an electrode layer (6) after the annealing (S307; S1105) of structured regions of the functional layer (3) for forming an electrode structure for the structured regions of the piezoelectric layer (4) and / or for forming a mirror and / or a mirror layer (6a) on one or more structured regions of the functional layer (3).

11. Method according to at least one of claims 1 to 9, characterized by - Applying (S805) a high-temperature stable electrode layer (9) before annealing (S809) structured regions of the functional layer (3) to form an electrode structure for the structured regions of the piezoelectric layer (4).

12. The method according to claim 11, characterized in that the material of the high-temperature stable electrode layer (9) comprises an electrically conductive doped silicon, in particular doped polycrystalline silicon.

13. The method according to claim 11 or 12, characterized in that the material of the high-temperature stable electrode layer (9) comprises a high-temperature stable metal, a high-temperature stable metal alloy and / or a high-temperature stable metal compound.

14. The method according to claim 13, characterized in that the material of the high-temperature-stable electrode layer (9) comprises platinum, molybdenum and / or a high-temperature-stable molybdenum alloy or molybdenum compound, tungsten or a high-temperature-stable tungsten alloy or tungsten compound, in particular tungsten titanium and / or tungsten carbide.

15. Method according to at least one of claims 11 to 14, characterized in that the high-temperature stable electrode layer (9) is applied and / or structured in such a way that the structured regions of the piezoelectric layer (4) are encapsulated between the functional layer (3) and the high-temperature stable electrode layer (9) with an optional dielectric layer (5) lying therebetween or in regions therebetween.

16. Method according to at least one of the preceding claims, characterized by - applying (S810) a further layer after the annealing (S809) of structured regions of the functional layer (3) to form a mirror and / or a mirror layer (10a) on one or more structured regions of the functional layer (3).

17. Method according to at least one of the preceding claims, characterized by - applying (S304; S804) a dielectric layer (5) at least on the structured regions of the piezoelectric layer (4) before the annealing (S307; S809) of structured regions of the functional layer (3) and in particular before applying an electrode layer (6; 9).

18. The method according to claim 17, characterized in that the dielectric layer (5) is applied in such a way that the structured regions of the piezoelectric layer (4) are encapsulated between the functional layer (3) and the dielectric layer (5) applied to the structured regions of the piezoelectric layer (4).

19. Method according to claim 17 or 18, characterized by - Structuring and / or opening (S305; S807) regions of the dielectric layer (5) during or before structuring (S306; S805) the functional layer (3).

20. The method according to claim 19, characterized in that the dielectric layer (5) is structured and / or opened in such a way that the structured regions of the piezoelectric layer (4) remain encapsulated between the functional layer (3) and the dielectric layer (5) applied to the structured regions of the piezoelectric layer (4).

21. Method according to at least one of the preceding claims, characterized in that the material of the piezoelectric layer (4) comprises a ferro- and / or piezoelectric material, in particular aluminum nitride (AIN), aluminum scandium nitride (AlScN), lead zirconate titanate (PZT) and / or niobium-doped PZT (PZT-Nb).

22. Method according to at least one of claims 1 to 16, characterized by - applying (S1106) a dielectric layer (5) at least on the structured regions of the piezoelectric layer (4) after the annealing (S1105) of structured regions of the functional layer (3), wherein the material of the piezoelectric layer (4) comprises a high-temperature stable ferro- and / or piezoelectric material, in particular aluminum nitride (AIN) and / or aluminum scandium nitride (AlScN).

23. Method according to at least one of the preceding claims, characterized in that the structured regions of the functional layer (3) comprise one or more movable elements formed in the functional layer (3) and / or a spring structure formed in the functional layer (3), wherein the spring structure in particular holds the one or more movable elements.

24. Method according to claim 23, characterized in that the one or more movable elements of the structured regions of the functional layer (3) comprise a mirror carrier element, wherein the mirror (6a; 10a) is arranged on the mirror carrier element.

25. The method according to claim 24, characterized in that the spring structure of the structured regions of the functional layer (3) holds the mirror support element with mirror (6a; 10a) and the spring structure in the functional layer (3) is formed such that the mirror support element with mirror (6a; 10a) is held so as to be oscillatable about one or two axes, in particular oscillation and / or torsion axes, particularly preferably for a two-dimensional Lissajous scanning movement of the mirror support element with mirror (6a; 10a).

26. Method according to at least one of the preceding claims, characterized in that the structuring (S306; S805; S1104) of the functional layer (3) comprises high-rate etching and / or reactive ion deep etching.

27. A layer structure produced by the method according to at least one of the preceding claims, comprising: - a substrate layer (1), - a structured functional layer (3), and - a structured piezoelectric layer (4) on one side of the functional layer (3) which is opposite to the substrate layer (1), wherein trenches in the functional layer (3) are formed in structured areas of the Functional layer (3) have been healed, and in particular have smoothed and / or crystal defect-free side walls and / or rounded corners.

28. Layer structure according to claim 27, characterized in that a surface roughness of side walls of the trenches in the functional layer (3) in structured regions of the functional layer (3) is substantially less than or equal to 50 nm, in particular substantially less than or equal to 30 nm, particularly preferably less than or equal to 10 nm.

29. MEMS device, in particular MEMS mirror device (200; 300; 400; 500), comprising a layer structure according to claim 27 or 28.

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