Method for creating a micromechanical layer structure and the resulting structure

Abstract

Title: Method for creating a micromechanical layered structure and resulting structure. A method for creating a micromechanical structure (10) consists of structuring a first protective layer (3) with an access point (100) filled with sacrificial material. A structure (4, 4') comprising a functional layer (4) is applied, and a first access point (101) is created in it, leading to an access point (100) in the first layer (3). The width of this access point in one of the layers (4, 4') is greater than or equal to that of an access point (100) in the first layer (3). A second protective layer (5) is applied over the structure (4, 4') to fill the first access point (101) with material from the second layer (5). The second layer (5) and the first access (101) are structured with a second access (102) to the first layer (3). This access (102) has a width equal to or less than that of the first access (101). The walls of the second access (102) are formed by the material of the second layer (5).The sacrificial layer is removed from the access (100) of the first protective layer (3) and from the protective layer of the second access (102). Figure 1g.

Description

Title of the invention: "Method for creating a micromechanical structure of layers and resulting structure" FIELD OF THE INVENTION

[0001] The present invention relates to a method for creating a micromechanical structure of layers. The invention also relates to such a micromechanical structure of layers.

[0002] Although the present invention can be applied, in general, to any micromechanical layer structures, it is described with reference to micromechanical layer structures in the form of resonators having piezoresistive functional layers. STATE OF THE ART

[0003] Micromechanical resonators are used, for example, as clock generators for watches or in high-frequency electronic communication devices, for example, in the fields of Wi-Fi, Bluetooth, NFC, or similar technologies. To create such resonators, micromechanical structures of layers are fabricated, in particular by giving them a specific structure and applying sacrificial layers that will be subsequently removed. Gas etching processes are frequently used to remove the sacrificial layers.

[0004] The quality of the micromechanical resonator depends on the electrical resistance of its RC element; this quality influences the accuracy and power consumption of the micromechanical resonator. The lower the power consumption, the better the quality of the resonator. The electrical resistance of the RC element depends on the electrodes and the power supply lines; for example, tungsten electrodes are used to achieve the lowest electrical resistance, which allows for low power consumption and ensures high resonator quality.

[0005] DESCRIPTION AND ADVANTAGES OF THE INVENTION

[0006] The invention relates to a method for producing a layered micromechanical structure comprising the following steps: providing a first protective layer, this first protective layer being structured with at least one access point filled with sacrificial layer material; applying a functional layer-layer structure comprising at least one functional layer onto the first protective layer; and creating a first access point in the functional layer-layer structure to at least one access point in the first protective layer such that the width of the first access point in the functional layer-layer structure in at least one of the layers of the functional layer-layer structure is greater than or equal to the width of at least one access of the first protective layer, apply a second protective layer on the functional layer-layer structure so that the first access is filled with the material of the second protective layer, structure the second protective layer and the first access filled with a second access to the first protective layer, this second access having a width equal to or less than that of the first access so that in the case of a smaller width of the second access, the walls of the second access are formed by the material of the second protective layer, remove the material of the sacrificial layer at least in the access of the first protective layer and remove the material of the protective layer at least of the second access.

[0007] According to another development, the invention relates to a micromechanical layer structure obtained according to the process developed above and comprising a first protective layer having in particular silicon, a functional layer-layer structure on the first protective layer and having at least one functional layer, in particular a piezoelectric layer, a second protective layer on the functional layer-layer structure comprising in particular silicon, with at least one access extending in the vertical direction through the functional layer-layer structure and the protective layers to expose a part of the micromechanical layer structure.

[0008] The term "protective layer" in this description describes a layer whose material is insensitive to an etching process, in particular a gas-phase etching process. The protective layer may be made of silicon and serve as an electrode layer for contact with a functional layer; in other words, the term "protective layer" also refers to the electrode, the conductive path, or similar elements.

[0009] The term "access" in this description refers to a structure in the form of an orifice, groove, vertical channel, slot, opening or interruption with similar shapes in the respective layer which allows fluidic communication between one or more other layers located below and / or accesses.

[0010] One of the resulting advantages is that the protective layers shield the functional layer from the negative effects of other aggressive process steps, particularly gas etching with hydrofluoric acid. Another advantage is that the process equipment is protected from impurities by the functional layer material for carrying out other manufacturing steps. For example, epitactic silicon deposition is performed at approximately 1000°C, while polycrystalline silicon and silicon oxide deposition is performed at approximately 600-800°C, so the high temperatures cause the material to outgas. The protective layers of the functional layer can pollute the installation used for the process. Applying these protective layers eliminates the need for polluting proprietary processes, thus avoiding considerable additional costs. Similarly, the costly cleaning and recalibration of the installation using such processes is avoided. Another advantage is that if the protective layer is made of silicon, it can simultaneously serve as an electrode or power supply line to the electrical contact of the functional layer. A further benefit is the production of improved resonators—higher-quality resonators that allow the use of piezoelectric materials, including those containing metals.

[0011] Examples of materials for the functional layers include, for example,

[0012] Aluminium nitride,

[0013] Lead zirconate titanate and / or

[0014] Scandium-doped aluminium nitride.

[0015] As materials for the electrode layers / conductive paths, materials at least partly made of metal or with a metallic combination can be used, for example,

[0016] Tungsten,

[0017] Tungsten silicide,

[0018] Titanium,

[0019] Titanium nitride,

[0020] Titanium silicide,

[0021] Platinum,

[0022] Palladium,

[0023] Copper,

[0024] Tantalus,

[0025] Molybdenum,

[0026] Tantalum silicide

[0027] According to an advantageous development, the material of the protective layer is removed laterally through access points in at least one of the protective layers. This results in the advantage of allowing a defined clearance. Furthermore, flexibility is increased because the functional layers of this layer-functional layer structure can be accessed over different widths, so that the previously applied protective layer can be removed not only in the vertical direction, but also in the lateral direction.

[0028] According to another advantageous development, the removal of material from the sacrificial layer and / or the material from the protective layer is carried out by gas-phase etching. The advantage is, in particular, that it is possible to use known and reliable processes for removing sacrificial layers.

[0029] According to another advantageous development, the sacrificial layer material is removed with hydrofluoric acid and / or the protective layer material is removed with a halogenated fluoride. This results in the advantage of being able to remove the sacrificial layer material and / or the protective layer material in a targeted, i.e., selective, manner with different etching materials without unintentionally removing other material.

[0030] According to another advantageous development, the application of the functional layer-layer structure includes the steps of: applying a functional layer on the first protective layer, applying an electrode layer on the applied functional layer which comprises at least partly a metal and / or a metal combination, in particular a metal nitride and / or metal silicide combination.

[0031] For the electrode layer, a highly conductive metal is used. The advantage is twofold: firstly, it increases overall flexibility because several layers can be used in the functional layer structure; and secondly, it provides better, low-ohmic contact between the functional layer and the electrode layer, which contains at least some of a metal and / or a metal compound, for example, a metal, a metal nitride, or a metal silicide compound. The functional layer can be connected both by an electrode layer that is at least partially made of metal and / or a metal compound, and also by a protective silicon layer. Overall, this reduces the contact resistance between the functional layer and both the electrodes and the power supply lines.

[0032] According to another development, the first access point in the electrode layer is made with a width greater than or equal to that of the first access point in the functional layer below. This allows for the simple application of a protective layer in the region of the electrode layer, in the lateral direction, during the subsequent manufacturing process, this protective layer then protecting the electrode layer in the lateral direction.

[0033] According to another advantageous development, an intermediate protective layer is applied to the functional layer before applying the electrode layer. This prevents, for example, the materials of the two layers—the functional layer on the one hand and the electrode layer on the other, which comprises at least part a metal and / or a metal combination—from interacting with each other in the vertical direction. An example is a functional layer made of aluminum nitride and an electrode layer made of tungsten.

[0034] According to another advantageous development, the material from the protective layer is completely removed in the first access to the electrode layer in the area The upper access point is accessible, while only partially removed from the lower zone, in the lateral direction. This results in the advantage of preventing a reaction between the materials of the layers, on the one hand the functional layer and on the other hand the electrode layer, in an even more effective manner.

[0035] According to another advantageous development, access points are made in the different layers above the first protective layer with different widths, in particular the width of the first access point which decreases from layer to layer from top to bottom. This allows, for example, the remaining lateral protective layers from top to bottom in the respective layers, which are then protected for subsequent operations, for example, the removal of the sacrificial layer.

[0036] According to another advantageous development, the sacrificial layer material is deposited to close the first access point before applying the second protective layer and / or to close the second access point after the second protective layer has been structured. After the application of the sacrificial layer material, it can be further structured. This advantageously allows for a simple implementation of the micromechanical structure of the layers. Similarly, the sacrificial layer material can be deposited beforehand under the first protective layer onto a substrate or similar element.

[0037] According to another advantageous development of the micromechanical structure of the layers, access in a protective layer below and / or above the functional layer is wider than in the functional layer itself. This allows for the greatest possible clearance, for example, of a resonator formed by the clearance of the functional layer.

[0038] According to another advantageous development, an electrode layer is applied above the functional layer, which comprises at least part of a metal and / or a metal combination. This allows for simple and reliable contact with low electrical resistance.

[0039] According to another advantageous development, the width of the access in the electrode layer is greater than or equal to the width of the access in the functional layer. This makes it possible, for example, to equip the electrode layer with protective layer material in the lateral direction within the electrode layer even more simply, without the minimum width of all accesses in the layers above the first protective layer preventing this overall.

[0040] According to another advantageous development, an intermediate protective layer is provided between the functional layer and the electrode layer, and access to the area of ​​the intermediate protective layer is wider than to at least one of the two adjacent layers. The intermediate protective layer allows for constructive separation of the two layers and prevents the materials of the two layers from reacting. adjacent during the manufacturing process of the micromechanical structure of the layers.

[0041] According to another advantageous development, at least one of the protective layers is partially provided in an access point of at least one of the functional layers; in particular, this protective layer is provided only in the lower area of ​​the access point of the respective functional layer. This results in the advantage that the electrode layer is not only vertically separated from the functional layer but also partially separated laterally from a protective layer, thus enabling a particularly robust realization of the exposed area of ​​the layer-functional layer structure. Brief description of the drawings

[0042] The present invention will be described below in more detail with reference to the accompanying drawings in which:

[0043] [Fig. la]

[0044] [Fig.lb]

[0045] [Fig. le]

[0046] [Fig.ld]

[0047] [Fig. le]

[0048] [Fig.lf]

[0049] [Fig. 1g] show the steps of a process according to one embodiment of the invention,

[0050] [Fig.2] shows part of a micromechanical structure of layers according to a mode of the realization of the present invention, with a cross-sectional representation,

[0051] [Fig.3a]

[0052] [Fig.3b]

[0053] [Fig.3c] respectively show a section of micromechanical structures of layers according to another embodiment of the invention,

[0054] [Fig.3d]

[0055] [Fig.3e] show a section of micromechanical structures of layers according to the steps of a process corresponding to one embodiment of the invention,

[0056] [Fig.4a]

[0057] [Fig.4b] show in section micromechanical structures of layers according to the steps of a process corresponding to an embodiment of the invention,

[0058] [Fig.5] shows a cross-sectional view of a micromechanical layer structure corresponding to one embodiment of the invention.

[0059] DESCRIPTION OF EMBODIMENT METHODS OF THE INVENTION

[0060] Figures la-lg show in cross-section the steps of a method for implementing the present invention.

[0061] Fig. 1a is a cross-sectional view of a micromechanical structure of layers 10 which comprises, from bottom to top, first a substrate 1. The substrate 1 is covered with a sacrificial layer 2, for example, of silicon oxide. The sacrificial layer 2 receives a first electrode layer 3, for example, of silicon; this layer is structured with two accesses 100 to the sacrificial layer 2, and these accesses are filled with sacrificial layer material. The top of the lower electrode layer 3 receives a piezoelectric layer 4, for example, of aluminum nitride, which is structured with two accesses 101 wider than the width of the accesses 100 of the lower electrode layer 3. However, this width may also be equal. The piezoelectric layer 4 receives a top electrode layer 5, for example, made of silicon, the material of which also arrives in the accesses 101 of the piezoelectric layer 4.Access points 101 are located above the respective access points 100 of the lower electrode layer 3. Access points 100 and 101 are designed to allow the release of part of the micromechanical structure of the layers to form a micromechanical element which is here a resonator 200.

[0062] Figure [Fig. 1b] shows a micromechanical structure of layers 10 which essentially corresponds to Figure [Fig. 1a]. Unlike the micromechanical structure of layers 10 in Figure [Fig. 1a], the micromechanical structure of layers 10 according to Figure [Fig. 1b] now has two accesses 102 through the piezoelectric layer 4 and the upper electrode layer 5 to reach accesses 100, 101. The accesses 100 are filled with sacrificial layer material. The diameter of the second accesses 102 is narrower than the width of the accesses 101 in the piezoelectric layer 4 below, so that the piezoelectric layer 4 is completely surrounded above and laterally in the region of access 101 by material from the upper electrode layer 5.

[0063] [Fig. 1e] shows a micromechanical structure of layers 10 which corresponds essentially to that of [Fig. 1b]. Unlike the micromechanical structure of layers 10 according to [Fig. 1b], the micromechanical structure of layers 10 according to [Fig. 1e] comprises a sacrificial layer 6 applied to the upper electrode layer 5; this sacrificial layer 6 is, on the one hand, structured (reference 6a) and, on the other hand, due to the application of the sacrificial layer 6, the material of the sacrificial layer 6 is found in the second accesses 102 in the region of the upper electrode layer 5 and the piezoelectric layer 4.

[0064] Fig. 1d shows a micromechanical structure of layers 10 which essentially corresponds to that of Fig. 1e. Unlike the micromechanical structure of layers 10 in Fig. 1e, in the micromechanical structure of layers 10 according to Fig. 1d, the sacrificial layer 6 is covered by a covering layer 7, for example, of silicon. The material of the covering layer 7 has also arrived in structures 6a of sacrificial layer 6, structured.

[0065] [Fig. 1e] shows a micromechanical structure of layers 10 which corresponds essentially to that of [Fig. 1d]. Unlike the micromechanical structure of layers 10 of [Fig. 1d], the micromechanical structure of layers 10 according to [Fig. 1e] now includes accesses 7a in the cover layer 7 to access the sacrificial layer 6.

[0066] [Fig. 11] shows a micromechanical structure of layers 10 which corresponds, essentially, to that of [Fig. 11]. Unlike the micromechanical structure of layers 10 according to [Fig. 11], in the case of the micromechanical structure of layers 10 according to [Fig. 11], a gas-phase etching process acting on silicon oxide, for example, hydrofluoric acid 50, was used to remove material from the sacrificial layer in the accesses 100, 101, 102 as well as partly in the sacrificial layers 2, 6. The applied material of the upper protective layer 5, which is also found in the accesses 101 of the piezoelectric layer 4, protects these accesses in the lateral direction, i.e. in the area of ​​the accesses 100, 101, 102, against a reaction with the etching gas.

[0067] Fig. lg shows a micromechanical structure of layers 10 which corresponds, essentially, to that of Fig. lf. Unlike the micromechanical structure of layers 10 according to Fig. lf, in the case of the micromechanical structure of layers 10 according to Fig. lg, using a gas-phase etching process acting on the material of the protective layer, for example, a process based on halogenated fluoride 51, silicon has been partially removed from the material of the protective layer in the accesses 100, 101, 102 and in the accesses 7a so that the piezoelectric layer 4 is no longer laterally protected by the material of the protective layer. For a certain duration of action, a small part of the lower and upper protective layers 3,5 will also be removed in the lateral direction so that a part of the functional layer 4 of the resonator 200 thus produced exceeds the two protective layers 3, 5 in the lateral direction.In other words, the piezoelectric layer 4 of the resonator 200 has a greater width than the lower and upper protective layers 3, 5 that have been exposed. The two protective layers, 3, 5, serve to bring the functional layer 4 into contact and are electrically conductive.

[0068] Layer 2 shows in section a part of a micromechanical structure of layers according to an embodiment of the present invention.

[0069] Figure 2 shows a micromechanical structure of 10 layers which corresponds mainly to that of Figure 11. Unlike the micromechanical structure of 10 layers according to Figure 11, in the case of the micromechanical structure of 10 layers according to Figure 2, there is an electrode layer 4', for example, made of metal or a metallic silicide. Between the two layers 4 and 4' is the protective layer 5. The electrode layer 4' has access ports 103 corresponding to the access ports 101 of the first functional layer 4. The same applies to the upper protective layer 5. This layer has access ports 102 corresponding to the two layers 4 and 4'. All access ports 100, 101, 102, and 103 have the same width and are filled with material from the sacrificial layer 2 or the sacrificial layer 6. Thus, the protective layer 5 prevents a reaction between the electrode layers or functional layers 4 and 4'. Furthermore, processes suitable for high temperatures largely prevent outgassing through the protective layer 5.

[0070] Figures 3a-3c each show in section, a micromechanical structure of layers according to other embodiments of the invention.

[0071] Fig. 3a shows a micromechanical structure of layers 10 which corresponds mainly to Fig. 1f. Unlike the micromechanical structure of layers 10 according to Fig. 1f, in the case of the micromechanical structure of layers 10 according to Fig. 3a, instead of the functional layer 4, there is the functional layer 4 and an electrode layer 4' which directly covers it; the second protective layer 5 is applied over the electrode layer 4'. The electrode layer 4' is made of metal. Furthermore, in Fig. 3a there is no lateral protective layer in the access points 101, 103. The protective layer 5 nevertheless also serves as a vertical protective layer; It prevents the piezoelectric layer 4 from being attacked in the vertical direction during gas etching when the material is removed from the sacrificial layer by a gas phase etching process 50 acting on the material of the sacrificial layer.

[0072] Fig. 3b shows a micromechanical structure of layers 10 practically according to Fig. 3a. Unlike the micromechanical layer of structure 10 of Fig. 3a, the micromechanical structure of layers 10 according to Fig. 3b has accesses 102 in the electrode layer 4' which are larger than the accesses 101 in the functional layer 4. In the accesses 102 of the electrode layer 4' and on the electrode layer 4' there is the material of the protective layer.

[0073] [Fig. 3c] shows a micromechanical structure of layers 10 corresponding practically to that of [Fig. 3b]. Unlike the micromechanical structure of layers 10 according to [Fig. 3b], in the case of the micromechanical structure of layers 10 according to [Fig. 3c], the width of the accesses 102 in the electrode layer 4' is equal to that of the accesses 101 in the functional layer 4. The accesses 101, 102 in both layers 4, 4' are wider than the access 100 of the lower protective layer 3, so that both layers 4, 4' are protected in all directions in the region of the resonator 200 to be made, when the material of the sacrificial layer is removed.

[0074] Figures 3d, 3e show micromechanical structures of layers according to the steps of the process corresponding to one embodiment of the invention, according to a cross-sectional representation.

[0075] Figure 3d shows a micromechanical structure of 10 layers which essentially corresponds to that of Figure 3c. Unlike the micromechanical structure of 10 layers according to Figure 3c, in the case of the micromechanical structure of 10 layers according to Figure 3d, there is a protective layer 5' between the functional layer and the electrode layer 4, 4'. Overall, the two layers 4, 4' are thus completely surrounded respectively by the material of the protective layer in the region of the resonator 200 to be fabricated, when the material of the sacrificial layer is removed.

[0076] Figure 3e shows the micromechanical structure of layers 10, which corresponds practically to that of Figure 3d, after application of a gas etching process to remove material from the protective layer. The functional layer and the electrode layer 4, 4' are thus practically exposed laterally, and the electrode layer 4' is also freed from the protective layer material on its upper surface.

[0077] Figures 4a-4b show a micromechanical structure section of layers after the steps of a process according to an embodiment of the present invention.

[0078] Figure 4a shows a micromechanical structure of layers 10 that is practically identical to that of Figure 3b. Unlike the micromechanical structure of layers 10 according to Figure 3b, in the case of the micromechanical structure of layers 10 according to Figure 4a, there is a protective layer 5 between the functional layer and the electrode layer 4, 4', such that the electrode layer 4' is not covered by a protective layer. The width of the access points 103 in the upper electrode layer 4' is greater than that of the corresponding access points 101 in the functional layer 4. Furthermore, removing material from the protective layer in the access points 103 of the electrode layer 4' does not remove this material from the lower area of ​​the access points 103 in this lateral direction. In section, [Fig.4a] thus has a clear area for the electrode layer 4' which is U-shaped in the region of resonator 200, surrounded by the material of the protective layer.On the side opposite that of resonator 200, the electrode layer 4' is surrounded by the protective layer material practically in an L shape in the protective layer 5 with a respective vertical extension in the accesses 103.

[0079] Figure 4b shows a micromechanical structure of layers 10 practically identical to that of Figure 3e. Unlike the micromechanical structure of layers 10 according to Figure 3e, in the case of the micromechanical structure of layers 10 according to Figure 4b, there is another protective layer 5' between the electrode layer 4' and the sacrificial layer 6. The material of the sacrificial layer 6 is removed only in the lateral direction in the region of accesses 102, 104. In other words, according to Figure 4b, the other protective layer 5' is made or constituted so as to cor- respond to the protective layer 5.

[0080] Figure 5 shows another embodiment of a micromechanical layer structure according to the present invention.

[0081] Figure 5 shows a micromechanical structure of 10 layers, terminated, and its resonator 200. The resonator 200 is electrically connected along the electrical path 90 by the metal electrode 8, which runs horizontally from right to left and then extends in the vertical direction (reference 8a) and joins the upper protective layer 5. The electrical resistance is low in the region of the conductive metal paths 30. The electrical path 90 passes through the protective layer 5 and then, with high electrical resistance 31, reaches the resonator 200. As shown, for example, in Figure 4a, the contact of the functional layer 4 can be improved by a layer of metal electrode 4' in the horizontal direction.Although the protective layer 5 is also conductive, it contributes only slightly to the overall resistance of the contact with the resonator 200, despite its relatively high resistance compared to that of the metallic electrode.

[0082] In summary, one of the embodiments has at least the following advantages: protection of the functional layers against the aggressive influence of subsequent treatments such as gas etching, heating processes, etc.; avoiding a reaction or diffusion between the different layers, in particular between the piezoelectric layers and the electrode layers, metallic or metallic silicides, protection of the installations implementing the process for the following process steps against impurities by the materials of the piezoresistive layers, metals or metallic silicides.

[0083] NOMENCLATURE OF MAIN ELEMENTS

[0084] Substrate

[0085] Sacrificial layer

[0086] Electrode layer / protective layer

[0087] Piezoelectric layer

[0088] 4' Electrode layer

[0089] Protective layer

[0090] 6 Sacrificial layer

[0091] 7 Cover layer

[0092] 7a Access

[0093] 8

[0094] 0 Micromechanical structure of layers

[0095] 5 Metallic electrode

[0096] 10 Hydrofluoric acid

[0097] 90 Electric path

[0098] 100 Access

[0099] 101 Access

[0100] 102 Access

[0101] 103 Access

[0102] 200 Resonator

Claims

Claims

1. A method for producing a layered micromechanical structure (10) comprising the following steps: - providing a first protective layer (3), this first protective layer (3) being structured with at least one access (100) filled with sacrificial layer material, - applying a functional layer-layer structure (4, 4') comprising at least one functional layer (4) to the first protective layer (3), - producing a first access (101) in the functional layer-layer structure (4, 4') to at least one access (100) of the first protective layer (3) such that the width of the first access (101) in the functional layer-layer structure (4, 4') in at least one of the layers (4, 4') of the functional layer-layer structure is greater than or equal to the width of at least one access (100) of the first protective layer (3),- applying a second protective layer (5) to the functional layer-layer structure (4, 4') so that the first access (101) is filled with the material of the second protective layer (5), - structuring the second protective layer (5) and the filled first access (101) with a second access (102) to the first protective layer (3), this second access (102) having a width equal to or smaller than that of the first access (101) so that in the case of a smaller width of the second access (102), the walls of the second access (102) are formed by the material of the second protective layer (5), - removing the material of the sacrificial layer at least in the access (100) of the first protective layer (3) and - removing the material of the protective layer at least from the second access (102).,

2. Method according to claim 1, according to which in the accesses (100, 101, 102) in at least one of the protective layers (3, 5) the material of the protective layer is removed in the lateral direction.

3. Method according to one of claims 1 and 2, according to which the material of the sacrificial layer and / or the material of the protective layer is removed by gas phase etching.

4. A method according to claim 3, wherein the material of the sacrificial layer is removed with hydrofluoric acid and / or the protective layer material with halogenated fluoride.

5. Method according to one of claims 1 to 4, according to which the application of the functional layer-layer structure (4, 4') comprises the steps of: applying a functional layer (4) on the first protective layer (3), applying an electrode layer (4') on the applied functional layer (4) which at least partly comprises a metal and / or a metal combination, in particular a metal nitride and / or metal silicide combination.

6. Method according to claim 5, according to which the first access (103) in the electrode layer (4') is made with a width greater than or equal to the width of the first access (101) of the functional layer (4) located below.

7. A method according to claim 6, wherein an intermediate layer (5, 5') is applied to the functional layer (4) before applying the electrode layer (4').

8. Method according to claim 7, wherein the material of the protective layer in the first access (103) of the electrode layer (4') is removed completely laterally in the upper area of the access and only partially in the lateral direction in the lower area.

9. Method according to one of claims 5 to 8, according to which the accesses (101, 103) are made in different layers (4, 4') above the first protective layer (3) with different widths, in particular the width of the first access (101, 102, 103) decreases in layers from top to bottom.

10. Method according to one of claims 1 to 9, according to which the material of the sacrificial layer is deposited to close the first access (101) before applying the second protective layer (5) and / or to close the second access (102) after the structure of the second protective layer (5).

11. Micromechanical layer structure (10) produced with a method according to one of claims 1 to 10, comprising: - a first protective layer (3) having silicon, a functional layer-layer structure (4, 4') on the first protective layer (3) and having at least one functional layer, in particular a piezoelectric layer, a second protective layer (5) on the functional layer-layer structure (4, 4') comprising silicon, with at least one access (100, 101, 102, 103, 104) passing through in the direction vertical the functional layer-layer structure (4, 4') and the protective layers (3, 5) to expose a part (200) of the micromechanical layer structure (10), the access in a protective layer (3, 5, 5') under and / or above the functional layer (4, 4') is wider than in the functional layer (4, 4') the electrode layer (4') above the functional layer (4) in the functional layer-layer structure (4, 4') comprises at least partly a metal and / or a metal combination, Structure in which the width of the access (103) in the electrode layer (4') is greater than or equal to the width of the access (101) in the material of the functional layer (4).

12. A micromechanical layer structure according to claim 11, wherein an intermediate protective layer (5, 5') is provided between the functional layer (4) and the electrode layer (4') and the access (104) in the area of the intermediate protective layer (5, 5') has a greater width than at least one of the two functional layers (4, 4').

13. Micromechanical layer structure according to one of claims 11 to 152, wherein at least one of the protective layers (3, 5, 5') in an access (101, 103) is provided at least partly in one of the layers (4, 4') of the functional layer-layer structure (4, 4'), in particular it is provided at least only in the lower region of the access (101, 103) in the respective layer of the functional layer-layer structure (4, 4').

Images