Method for producing a micromechanical layer structure

Abstract

The invention relates to a method for producing a micromechanical layer structure, having the steps of: - providing a first protective layer, said first protective layer being structured with at least one access which is filled with a sacrificial layer material, - applying a functional-layer layer structure, comprising at least one functional layer, onto the first protective layer, - producing a first access in the functional- layer layer structure in order to form at least one access of the first protective layer such that the width of the first access 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 the at least one access of the first protective layer, - applying a second protective layer onto the functional-layer layer structure such that the first access is filled with material of the second protective layer, - structuring the second protective layer and the filled first access with a second access to the first protective layer, wherein the second access has the same or a smaller width than the first access such that if the second access has a smaller width, the walls of the second access are produced by the material of the second protective layer, - removing sacrificial layer material at least in the access of the first protective layer, and - removing protective layer material at least in the second access.

Description

Method for producing a micromechanical layer structure Technical Area The invention relates to a method for producing a micromechanical layer structure. The invention furthermore relates to a micromechanical layer structure. Although the present invention is generally applicable to arbitrary micromechanical layer structures, the present invention is described with reference to micromechanical layer structures in the form of resonators having piezoresistive functional layers. Prior Art Micromechanical resonators are used, for example, as clock generators in clocks or also in high-speed electronic communication devices, for example, for Wi-Fi, Bluetooth, NFC, or the like. To produce such resonators, micromechanical layer structures are produced, these are structured in particular, and sacrificial layers are applied, which are removed again later. Gas phase etching methods are frequently used for removing the sacrificial layers. A quality of a micromechanical resonator is determined by the electrical resistance of the corresponding RC element. The quality influences the precision and the power consumption of the micromechanical resonator in this case. The lower the power consumption, the higher the quality of the resonator. The electrical resistance of the RC element consists in this case of electrodes and feed lines, wherein tungsten is used for the electrodes, for example, to achieve a lower electrical resistance, which enables a low power consumption and a high quality of the resonator. Disclosure of the Invention In one embodiment, the invention provides a method for producing a micromechanical layer structure, comprising the following steps - providing a first protective layer, wherein the first protective layer is structured using at least one access, which is filled with sacrificial layer material, - applying a functional layer layer structure, comprising at least one functional layer, to the first protective layer, - producing a first access in the functional layer layer structure to the at least one access of the first protective layer, so that a width of the first access 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 the at least one access of the first protective layer, - applying a second protective layer to the functional layer layer structure in such a way that the first access is filled with material of the second protective layer, - structuring the second protective layer and the filled first access using a second access to the first protective layer, wherein the second access has the same or a lesser width than the first access, so that in the case of a lesser width of the second access, the walls of the second access are formed by material of the second protective layer, - removing sacrificial layer material at least in the access of the first protective layer, and - removing protective layer material at least in the second access. In a further embodiment, the invention provides a micromechanical structure, produced using a method according to the present disclosure, comprising a first protective layer, in particular comprising silicon, a functional layer layer structure arranged on the first protective layer, comprising at least one functional layer, in particular a piezoelectric layer, a second protective layer arranged on the functional layer layer structure, in particular comprising silicon, wherein at least one access is arranged, which extends in the vertical direction through the functional layer layer structure and the protective layers to expose a part of the micromechanical layer structure. The term "protective layer" is to be understood in particular in the description, preferably in the claims, as a layer, the material of which is insensitive with respect to at least one etching method, in particular a gas phase etching method. A protective layer can be produced in this case from silicon and can be used as an electrode layer for contacting a functional layer. In other words, the term "protective layer" is also to be understood as an electrode, a conductor track, or the like. The term "access" is to be understood in particular in the description, preferably in the claims, as a structuring in the form of a hole, a trench, a vertical channel, a gap, an opening, or an interruption of the like in the respective layer, which enables a fluidic connection to one or more underlying layers and / or accesses. One of the advantages thus achieved is that the functional layer is protected from negative effects due to aggressive further processing steps, in particular gas phase etching using hydrogen fluoride, by the protective layers. A further advantage is that processing plants for carrying out later production steps are protected from contamination by material of the functional layer. For example, a deposition of epitactic silicon is performed at approximately 1000°C, or a deposition of polycrystalline silicon and silicon oxide is performed at approximately 600 - 800°, so that outgassing of material of the functional layer takes place here due to the high temperatures, which contaminates the processing plant. Due to the application of the protective layers, an exclusive processing plant for this contaminating process is no longer required, so that significant additional costs are avoided. A complex costly cleaning and recalibration of the processing plant is also dispensed with. A further advantage, if the respective protective layer is produced from silicon, is that this layer can be used simultaneously as an electrode or as an electrical feed line for electrically contacting the functional layer. A further advantage is that better resonators, i.e. resonators having higher quality, can be produced, if in particular metal-containing piezoelectric materials can be used. For example, - aluminum nitride, lead zirconium titanate, and / or - scandium-doped aluminum nitride can be used as materials for the functional layers. For example: - tungsten, - tungsten silicide, - titanium, - titanium nitride, - titanium silicide, - platinum, - palladium, - copper, - tantalum, - molybdenum, - tantalum silicide, or the like can be used as materials for the electrode layers / conductor tracks, comprising or at least partially produced from metal or a metal compound. Further features, advantages, and further embodiments of the invention are described hereinafter or are thus obvious. According to one advantageous refinement, protective layer material is removed in the lateral direction in the accesses in at least one of the protective layers. The advantage thereof is that a defined exposure is enabled. In addition, the flexibility is increased, since functional layers in the functional layer layer structure can also be exposed having different widths by means of the accesses, and the previously applied protective layer can thus be removed not only vertically, but rather also laterally. According to a further advantageous refinement, the removal of the sacrificial layer material and / or the protective layer material is performed by means of gas phase etching. The advantage thereof is that in particular reliable and known methods for removing sacrificial layers can be used. According to a further advantageous refinement, the removal of the sacrificial layer material is carried out based on hydrogen fluoride and / or the removal of the protective layer material is carried out based on a halogen fluoride. The advantage thereof is that sacrificial layer material and / or protective layer material can be removed intentionally and / or selectively by means of different etching materials, without undesired erosion of the respective other material taking place. According to a further advantageous refinement, the application of the functional layer layer structure comprises the following steps: - applying a functional layer to the first protective layer, - applying an electrode layer to the applied functional layer, which at least partially comprises a metal and / or a metal compound, in particular a metal nitride and / or a metal silicide compound. In particular a metal having high conductivity is used for this electrode layer. The advantage thereof is that, on the one hand, the flexibility is thus generally increased, since multiple layers can be arranged in the functional layer layer structure, on the other hand, an improved, i.e. lower-resistance contacting of the functional layer by means of the electrode layer, which at least partially comprises a metal and / or a metal compound, for example produced from a metal, metal nitride, or a metal silicide compound, can be enabled. The contacting of the functional layer can take place here both via an electrode layer, which at least partially comprises a metal and / or a metal compound, and also via a protective layer made of silicon. Overall, the resistance for the contacting of the functional layer sinks both in the electrodes and also in the feed lines. According to a further advantageous refinement, the first access in the electrode layer is produced having a width which is greater than or equal to the width of the first access of the underlying functional layer. A protective layer, which then protects the electrode layer in the lateral direction, can thus be applied in a simple manner in the region of the electrode layer in the lateral direction in the further course of the production method. According to a further advantageous refinement, an intermediate protective layer is applied to the functional layer before applying the electrode layer. In this way, for example, it is possible to prevent the materials of the two layers, functional layer on the one hand and electrode layer on the other hand, which at least partially comprise a metal and / or a metal compound, from reacting with one another in the vertical direction. One example of this is a functional layer produced from aluminum nitride and an electrode layer produced from tungsten. According to a further advantageous refinement, the protective layer material is completely removed in the first access in the electrode layer in the upper region of the access, but is only partially removed in the lower region in the lateral direction. One of the advantages thus achieved is that a reaction of materials of the layers, functional layer on the one hand and electrode layer on the other hand, can thus be prevented even better. According to a further advantageous refinement, the accesses in different layers above the first protective layer are produced having different widths, in particular wherein the width of the first access decreases layer by layer from top to bottom. In this manner, for example, lateral protective layers can remain in the respective layer from top to bottom, so that they are protected during corresponding following processes, for example the removal of a sacrificial layer. According to a further advantageous refinement, sacrificial layer material is deposited to close the first access before the application of the second protective layer and / or to close the second access after the structuring of the second protective layer. After the application of the sacrificial layer material, it can still be structured in particular. The advantage thereof is that a simple production of the micromechanical layer structure is enabled. Sacrificial layer material can also be deposited on a substrate or the like beforehand below the first protective layer. According to an advantageous refinement of the micromechanical structure, the access in a protective layer has a greater width below and / or above the functional layer than in the functional layer. In this manner, the largest possible exposure is enabled, for example, by a resonator formed by the exposure of the functional layer. According to a further advantageous refinement, an electrode layer is arranged above the functional layer, which at least partially comprises a metal and / or a metal compound. Simple and reliable contacting with low electrical resistance is thus enabled. According to a further advantageous refinement, the width of the access in the electrode layer is greater than or equal to the width of the access in the functional layer. In this manner, for example, the electrode layer can be provided in a still simpler manner with protective layer material in the lateral direction within the electrode layer, without the minimal width of all accesses in the layers above the first protective layer thus being reduced overall. According to a further advantageous refinement, an intermediate protective layer is arranged between functional layer and electrode layer and the access in the region of the intermediate protective layer has a greater width than at least one of the two adjacent layers. An intermediate protective layer enables the structural separation of the two layers and prevents a reaction of the materials of the two adjacent layers with one another during the production process of the micromechanical layer structure. According to a further advantageous refinement, at least one of the protective layers is partially arranged in an access in at least one of the functional layers, in particular wherein it is solely arranged in the lower region of the access in the respective functional layer. The advantage thereof is that the electrode layer, in addition to its vertical separation from the functional layer, is also partially provided in the lateral direction with a protective layer, which enables a particularly robust formation of the exposed region of the functional layer layer structure. Further important features and advantages of the invention result from the dependent claims, from the drawings, and from the associated description of the figures on the basis of the drawings. It is obvious that the above-mentioned features and the features to be explained hereinafter are usable not only in the respective specified combination, but rather also in other combinations or alone, without leaving the scope of the present invention. Preferred designs and embodiments of the invention are illustrated in the drawings and will be explained in greater detail in the following description, wherein identical reference signs refer to identical or similar or functionally identical components or elements. Brief Description of the Drawings Figures 1a-g show steps of a method according to one embodiment of the present invention. Figure 2 shows a part of a micromechanical layer structure according to one embodiment of the present invention in cross section. Figures 3a-c each show a micromechanical layer structure according to a further embodiment of the invention in cross section. Figures 3d-e show micromechanical layer structures after steps of a method according to one embodiment of the present invention in cross section. Figures 4a-4b show micromechanical layer structures after steps of a method according to one embodiment of the present invention in cross section. Figure 5 shows a micromechanical layer structure according to one embodiment of the present invention in cross section. Embodiments of the Invention Figures 1a-1g show steps of a method according to one embodiment of the present invention in cross section. A micromechanical layer structure 10 is shown in cross section in Figure 1a, which from bottom to top firstly comprises a substrate 1. A sacrificial layer 2, for example made of silicon oxide, is applied to the substrate 1. A lower electrode layer 3, for example made of silicon, is applied to the sacrificial layer 2, and is structured with two accesses 100 to the sacrificial layer 2 which are filled with sacrificial layer material. A piezoelectric layer 4, for example made of aluminum nitride, is arranged on the upper side of the lower electrode layer 3, and is structured with two accesses 101, the width of which is greater than the width of the accesses 100 of the lower electrode layer 3. However, the width can also be equal. An upper electrode layer 5, for example made of silicon, is arranged on the piezoelectric layer 4, and the material thereof is also arranged in the accesses 101 of the piezoelectric layer 4. The accesses 101 are arranged above the respective accesses 100 of the lower electrode layer 3. The accesses 100, 101 are applied here so that an exposure of a part of the micromechanical layer structure is performed to form a micromechanical element, a resonator 200 here. Figure 1b essentially shows a micromechanical layer structure 10 according to Figure 1a. In contrast to the micromechanical layer structure 10 according to Figure 1a, in the micromechanical layer structure 10 according to Figure 1b, two second accesses 102 are now produced through the piezoelectric layer 4 and the upper electrode layer 5 for access to the accesses 100, 101, wherein the accesses 100 are filled with sacrificial layer material. However, the diameter of the second accesses 102 has a width which is less than the width of the underlying accesses 101 of the piezoelectric layer 4, so that the piezoelectric layer 4 is enclosed completely above and laterally by the material of the upper electrode layer 5 in the region of the access 101. Figure 1c essentially shows a micromechanical layer structure 10 according to Figure 1b. In contrast to the micromechanical layer structure 10 according to Figure 1b, in the micromechanical layer structure 10 according to Figure 1c a sacrificial layer 6 is now applied to the upper electrode layer 5, which is structured on one side (reference sign 6a), on the other side material of the sacrificial layer 6 is located in the second accesses 102 in the region of the upper electrode layer 5 and the piezoelectric layer 4 due to the application of the sacrificial layer 6. Figure 1d essentially shows a micromechanical layer structure 10 according to Figure 1c. In contrast to the micromechanical layer structure 10 according to Figure 1c, in the micromechanical layer structure 10 according to Figure 1d a closure cap layer 7, which consists of silicon for example, is now arranged on the sacrificial layer 6. The material of the closure cap layer 7 is also arranged in the structures 6a of the structured sacrificial layer 6. Figure 1e essentially shows a micromechanical layer structure 10 according to Figure 1d. In contrast to the micromechanical layer structure 10 according to Figure 1d, in the micromechanical layer structure 10 according to Figure 1e accesses 7a are now arranged in the closure cap layer 7 for access to the sacrificial layer 6. Figure 1f essentially shows a micromechanical layer structure 10 according to Figure 1e. In contrast to the micromechanical layer structure 10 according to Figure 1e, in the micromechanical layer structure 10 according to Figure 1f the sacrificial layer material was removed in the accesses 100, 101 and 102 and also partially in the sacrificial layers 2, 6 themselves by means of a gas phase etching method sensitive for silicon oxide, for example by means of hydrogen fluoride 50. By means of the applied material of the upper protective layer 5, which is also arranged in the accesses 101 of the piezoelectric layer 4, they are protected from a reaction with the etching gas in the lateral direction, i.e. in the region of the accesses 100, 101, 102. Figure 1g essentially shows a micromechanical layer structure 10 according to Figure 1f. In contrast to the micromechanical layer structure 10 according to Figure 1f, in the micromechanical layer structure 10 according to Figure 1g the protective layer material has partially been removed in the accesses 100, 101, 102 and in the accesses 7a by means of a gas phase etching method sensitive for the protective layer material, for example based on a halogen fluoride 51 for removing silicon, so that now the piezoelectric layer 4 is no longer laterally protected by the protective layer material. With correspondingly long action duration, a small part is also removed in the lateral direction from the lower and upper protective layers 3, 5, so that a part of the functional layer 4 of the produced resonator 200 protrudes beyond 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 exposed lower and upper protective layer 3, 5 thereof. The two protective layers 3, 5 are used here for contacting the functional layer 4 and are electrically conductive. Figure 2 shows a part of a micromechanical layer structure according to one embodiment of the present invention in cross section. Figure 2 essentially shows a micromechanical layer structure 10 according to Figure 1d. In contrast to the micromechanical layer structure 10 according to Figure 1d, in the micromechanical layer structure 10 according to Figure 2 an electrode layer 4' is now arranged, for example produced from metal or a metal silicide. The protective layer 5 is now arranged between the two layers 4, 4'. Furthermore, the electrode layer 4' is provided with accesses 103 corresponding to the accesses 101 of the first functional layer 4. This also applies accordingly to the upper protective layer 5. It comprises accesses 102 corresponding to the two layers 4, 4'. All accesses 100, 101, 102 and 103 have the same width here and are filled with sacrificial layer material of the sacrificial layer 2 or the sacrificial layer 6, respectively. In this manner, a reaction can be prevented between electrode layer and functional layer 4, 4' by the protective layer 5. Furthermore, outgassing due to corresponding processes at high temperatures is also accordingly prevented to a large extent by protective layer 5. Figures 3a-c each show a micromechanical layer structure according to further embodiments of the invention in cross section. Figure 3a essentially shows a micromechanical layer structure 10 according to Figure 1f. In contrast to the micromechanical layer structure 10 according to Figure 1f, in the micromechanical layer structure 10 according to Figure 3a, instead of only one functional layer 4, the functional layer 4 and an electrode layer 4' are now arranged directly one over another, wherein the second protective layer 5 is applied to the electrode layer 4'. The electrode layer 4' is produced from metal. In addition, the lateral protective layer in the accesses 101, 103 is absent in Figure 3a. The protective layer 5 is also used, however, as a vertical protective layer and prevents, upon removal of sacrificial layer material by means of a gas phase etching method 50 sensitive to sacrificial layer material, the piezoelectric layer 4 from being attacked in the vertical direction during the gas phase etching method. Figure 3b essentially shows a micromechanical layer structure 10 according to Figure 3a. In contrast to the micromechanical layer structure 10 according to Figure 3a, in the micromechanical layer structure 10 according to Figure 3b the width of the accesses 102 in the electrode layer 4' is greater than the accesses 101 in the functional layer 4. Protective layer material is arranged in the accesses 102 of the electrode layer 4' and also on the electrode layer 4'. Figure 3c essentially shows a micromechanical layer structure 10 according to Figure 3b. In contrast to the micromechanical layer structure 10 according to Figure 3b, in the micromechanical layer structure 10 according to Figure 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 the two layers 4, 4' have a greater width than the access 100 of the lower protective layer 3, so that the two layers 4, 4' in the region of the resonator 200 to be produced, are protected during the removal of sacrificial layer material in relation thereto in all directions. Figures 3d and 3e show micromechanical layer structures after steps of a method according to one embodiment of the present invention in cross section. Figure 3d essentially shows a micromechanical layer structure 10 according to Figure 3c. In contrast to the micromechanical layer structure 10 according to Figure 3c, in the micromechanical layer structure 10 according to Figure 3d a protective layer 5' is now arranged between functional layer and electrode layer 4, 4'. Overall, the two layers 4, 4' are thus each completely enclosed by protective layer material in the region of the resonator 200 to be produced upon the removal of sacrificial layer material. Figure 3e essentially shows the micromechanical layer structure 10 according to Figure 3d after application of a gas phase etching method for removing protective layer material. Functional layer and electrode layer 4, 4' are essentially now freed in a lateral aspect and the electrode layer 4' is also freed on its upper side from protective layer material. Figures 4a to 4b show micromechanical layer structures in cross section after steps of a method according to one embodiment of the present invention. Figure 4a essentially shows a micromechanical layer structure 10 according to Figure 3b. In contrast to the micromechanical layer structure 10 according to Figure 3b, in the micromechanical layer structure 10 according to Figure 4a, on the one hand, the protective layer 5 is now arranged between functional layer and electrode layer 4, 4', so that the electrode layer 4' does not have a protective layer arranged above it. On the other hand, the width of the accesses 103 in the upper electrode layer 4' is embodied to be larger than the corresponding accesses 101 in the functional layer 4. Additionally, during the removal of protective layer material in the accesses 103 of the electrode layer 4', it was not removed in the lateral direction in the lower region of the accesses 103. The exposed region of the electrode layer 4' is thus enclosed by protective layer material in a U shape in the region of the resonator 200 in the cross section in Figure 4a. On the side facing away from the resonator 200, the electrode layer 4' is enclosed essentially in an L shape by protective layer material in the form of the protective layer 5 and a respective vertical extension in the accesses 103. Figure 4b essentially shows a micromechanical layer structure 10 according to Figure 3e. In contrast to the micromechanical layer structure 10 according to Figure 3e, in the micromechanical layer structure 10 according to Figure 4b a further protective layer 5' is now arranged between the electrode layer 4' and sacrificial layer 6. Upon removal of protective layer material, it is only removed in the region of the accesses 102, 104 in the lateral direction. In other words, in Figure 4b, the further protective layer 5' is formed and / or arranged corresponding to the protective layer 5. Figure 5 shows a micromechanical layer structure according to one embodiment of the present invention. A completely produced micromechanical layer structure 10 having a resonator 200 is shown in Figure 5. The resonator 200 is electrically contacted here via a metal electrode 8, which first extends horizontally from right to left along the electrical path 90, and then continues further in the vertical direction (reference sign 8a) and is connected to the upper protective layer 5. The electrical resistance is low in the region of the metal conductor tracks 30. The electrical path 90 then extends inside the protective layer 5 with high electrical resistance 31 up to the resonator 200. As shown in Figure 4a for example, the contacting of the functional layer 4 can be improved by means of an electrode layer 4' made of metal in the horizontal direction. If the protective layer 5 is then also formed to be conductive, it only hardly still contributes to the overall resistance of the contacting of the resonator 200 - in spite of its higher resistance in comparison to the metal electrode. In summary, at least one of the embodiments comprises at least one of the following advantages: - Protecting functional layers from the aggressive influence of posttreatments, for example gas phase etching, heating processes, etc. - Preventing a reaction or diffusion between various layers, in particular between piezoelectric layers and metallic electrode layers or electrode layers produced from metal silicide. - Protecting the processing plants for later processing steps from contamination by materials of piezoresistive layers, metals or metal silicides. Although the present invention was described with the aid of preferred exemplary embodiments, it is not restricted thereto, but rather is modifiable in manifold ways.

Claims

1. A method for manufacturing a micromechanical layer structure, comprising the following steps: providing a first protective layer, the first protective layer being patterned to include at least one opening that is filled with sacrificial layer material; depositing a functional-layer layer structure on the first protective layer, the functional-layer layer structure including at least one functional layer; producing a first opening in the functional-layer layer structure to the at least one opening of the first protective layer, so that in at least one of the at least one layer of the functional-layer layer structure, a width of the first opening in the functional-layer layer structure is greater than or equal to a width of the at least one opening of the first protective layer; depositing a second protective layer on the functional- layer layer structure in such a manner that the first opening is filled with material of the second protective layer; patterning the second protective layer and the filled, first opening to have a second opening to the first protective layer, the second opening having the same or a lesser width than the first opening, so that in the case of the lesser width of the second opening, walls of the second opening are formed by material of the second protective layer; and removing the sacrificial layer material at least in the opening of the first protective layer; and removing protective layer material at least in the second opening.

2. The method as claimed in claim 1, wherein in the first opening and / or the second opening, protective layer material is removed in a lateral direction.

3. The method as claimed in either one of claims 1 − 2 1-2 , wherein the sacrificial layer material and / or the protective layer material is removed using gas-phase etching.

4. The method as claimed in claim 3, wherein the sacrificial layer material is removed using hydrogen fluoride, and / or the protective layer material is removed using a halogen fluoride.

5. The method as claimed in any one of claims 1 − 4 1-4 , wherein the depositing of the functional-layer layer structure includes the following steps: depositing the at least one functional layer on the first protective layer; and depositing an electrode layer on the deposited at least one functional layer, the electrode layer at least partially containing a metal and / or a metallic compound.

6. The method as recited in claim 5, wherein the electrode layer at least partially contains a metallic nitride compound and / or a metallic silicide compound.

7. The method as claimed in claim 5, wherein the first opening in the electrode layer is produced to have a width which is greater than or equal to a width of the first opening of the at least one functional layer.

8. The method as claimed in claim 7, wherein an intermediate protective layer is deposited on the at least one functional layer prior to the depositing of the electrode layer.

9. The method as claimed in claim 8, wherein in the first opening in the electrode layer, the protective layer material is removed laterally completely in an upper region of the first opening, and removed only partially in the lateral direction in a lower region of the first opening.

10. The method as claimed in any one of claims 6-9, wherein openings having different widths are produced in different layers above the first protective layer.

11. The method as recited in claim 10, wherein a width of the first opening decreases layer-by-layer from top to bottom.

12. The method as claimed in any one of claims 1-11, wherein sacrificial layer material is deposited to close the first opening prior to the depositing of the second protective layer, and / or to close the second opening after the patterning of the second protective layer.

13. A micromechanical layer structure, comprising: a first protective layer including silicon; a functional-layer layer structure situated on the first protective layer, the functional-layer layer structure including at least one functional layer, the at least one functional layer including a piezoelectric layer; and a second protective layer situated on the functional- layer layer structure, the second protective layer including silicon, at least one opening, which extends in a vertical direction through the functional-layer layer structure, the first protective layer, and the second protective layer, being positioned to expose a part of the micromechanical layer structure, wherein the opening in the first and / or second protective layer has a greater width below and / or above the at least one functional layer than a width of the opening in the at least one functional layer.

14. The micromechanical layer structure as claimed in claim 13, wherein an electrode layer, which at least partially comprises a metal and / or a metallic compound, is situated above the functional layer in the functional-layer layer structure.

15. A micromechanical layer structure, comprising: a first protective layer including silicon; a functional-layer layer structure situated on the first protective layer, the functional-layer layer structure including at least one functional layer, the at least one functional layer including a piezoelectric layer; and a second protective layer situated on the functional- layer layer structure, the second protective layer including silicon, at least one opening being positioned, which extends in a vertical direction through the functional-layer layer structure, the first protective layer, and the second protective layer, to release a part of the micromechanical layer structure, wherein an electrode layer, which at least partially contains a metal and / or a metallic compound, is situated above the at least one functional layer in the functional-layer layer structure, wherein at least one of: the width of the opening in the electrode layer is greater than or equal to the width of the opening in the material of the at least one functional layer; or an intermediate protective layer is situated between the at least one functional layer and the electrode layer, and the opening has a greater width in a region of the intermediate protective layer than in at least one of the at least one functional layer.

16. A micromechanical layer structure, comprising: a first protective layer including silicon; a functional-layer layer structure situated on the first protective layer, the functional-layer layer structure including at least one functional layer, the at least one functional layer including a piezoelectric layer; and a second protective layer situated on the functional- layer layer structure, the second protective layer including silicon, at least one opening being positioned, which extends in a vertical direction through the functional-layer layer structure, the first protective layer, and the second protective layer, to release a part of the micromechanical layer structure, wherein at least one of: at least one of the first and second protective layers is situated partially in an opening in at least one of the at least one layer of the functional-layer layer structure; or at least one of the first and second protective layers is situated only in a lower region of the opening in the at least one functional layer of the functional- layer layer structure.