Stress-decoupled micromechanical pressure sensor and method for producing pressure sensor

Abstract

The invention relates to a micromechanical pressure sensor (100), comprising a substrate (110) having a layer system (120) arranged thereon. The micromechanical pressure sensor (100) further comprises a sensor structure (200) fixed to the layer system (120) in a self-supporting manner by means of at least one suspension structure (140), the sensor structure has a first membrane structure (210), a second membrane structure (220) and a cavity region (240) which is arranged between the two membrane structures (210, 220) and which is closed by a side wall (230) extending in an edge region (212, 222) of the two membrane structures (210, 220). In this case, the sensor structure (200) comprises an effective capacitor (250), which is arranged in the cavity region (240) between the two diaphragm structures (210, 220), the active capacitor has a first electrode (251) fixed to the first membrane structure (210) and a second electrode (253) arranged between the first electrode (251) and the second membrane structure (220) and fixed to the second membrane structure (220).

Description

TECHNICAL FIELD

[0001] The invention relates to a stress-decoupled micromechanical pressure sensor in the form of a self-supporting double-diaphragm structure. The invention also relates to a manufacturing method for such a stress-decoupled micromechanical pressure sensor. BACKGROUND

[0002] Micromechanical pressure sensors are used for different applications. In addition, capacitive pressure sensors are known, in which an intermediate electrode is arranged between two diaphragms, wherein this arrangement on at least one spring structure / anchor structure is fixed self-supportingly on a silicon substrate. If such an arrangement is loaded with pressure, the diaphragms bend simultaneously or synchronously in the direction of the intermediate electrode. A measurable change in the capacitance is thereby caused, on the basis of which a measurement or determination of the applied pressure can be carried out. In this arrangement there is an active electrode of the capacitive measuring system consisting of the two diaphragms themselves. A non-linear capacitive sensor signal is produced by the cambering of the diaphragms on pressure loading. As a result, the pressure can only be measured linearly and with a relatively high resolution in a small pressure range.

[0003] Furthermore, it is required for the manufacture of such a diaphragm arrangement that a sacrificial layer between the diaphragms and the intermediate electrode is removed through a hole in the uppermost diaphragm structure, which hole must then be closed again. Since a certain layer thickness of the closing material is required for this, the diaphragm thickness cannot be implemented thinner than the layer thickness of the closing material and / or the closing material at least locally changes the bending strength of the diaphragm structure. SUMMARY

[0004] The task on which the invention is based can thus be to provide the possibility of implementing a stress-decoupled capacitive pressure sensor with high sensitivity, a linear pressure sensor signal and an optional reference capacitance, which can advantageously be arranged in the cavity region with a space-saving. The task is solved by the respective subject matter of the independent claims. Advantageous configurations of the invention are the subject matter of the respective dependent claims.

[0005] According to the application a micromechanical pressure sensor is provided, which comprises a substrate and a sensor structure, the substrate having a layer system arranged thereon, and the sensor structure being fixed self-supportingly on the layer system by means of at least one suspension structure and having a first diaphragm structure, a second diaphragm structure and a cavity region arranged between the two diaphragm structures and enclosed by side walls extending in the edge regions of the two diaphragm structures. Here, the sensor structure comprises an effective capacitor structure arranged in the cavity region, the effective capacitor structure having a first electrode, which is preferably fixed on / in a central region of the first diaphragm structure, and a second electrode, which is arranged between the first electrode and the second diaphragm structure and is preferably fixed on a central region of the second diaphragm structure.

[0006] By the configuration of the sensor structure in the form of a double diaphragm structure in self-supporting construction, a stress decoupling with respect to the surrounding layer system and the silicon substrate is achieved. It is thus achieved that mechanical bowing of the sensor structure, for example caused by thermal expansion, no longer has an influence on the resulting sensor signal. Furthermore, by the self-supporting structure, an applied external pressure can deform not only the first diaphragm structure but also the second diaphragm structure. Here, for example the first and second active configurations and the electrodes fixed / anchored on the first and second diaphragm structures move towards one another. It is thus possible to achieve that the amount of change in the spacing between the active electrodes upon a change in pressure is twice as large in the case of a sensor structure having only one active implemented electrode (in the case of identical implementation of the diaphragm structures). In this way it is thus possible to achieve an increase in the measurement sensitivity in addition to the stress decoupling. In the case of a sensor structure having only one active diaphragm, for the same measurement sensitivity it is necessary to use a larger and / or thinner diaphragm or at least two smaller diaphragm structures must be electrically connected in a Wheatstone half-bridge configuration, whereas in the case of a self-supporting double diaphragm structure the same measurement sensitivity can be achieved on a significantly smaller area. This has the advantage that the diaphragm structure can be implemented more robustly for a defined pressure range and is thus mechanically more robust with respect to an applied overpressure. This can be further supported by specific stop structures, which are fixed on the diaphragm structure and can prevent an excessively strong local deformation of the diaphragm structure.

[0007] By means of the proposed pressure measurement structure or pressure measurement device it is possible to achieve the same comparable measurement sensitivity or measurement accuracy on a significantly smaller area. Since the chip area represents a significant proportion of the overall cost of the sensor element, it is possible in this way to achieve a cost reduction of the sensor structure or to use a smaller space requirement for this purpose, at least with the same performance, in order to provide two pressure measurement structures / pressure measurement devices on the original area, which are able to achieve a measurement of two pressure measurement ranges or a measurement of a larger pressure measurement range. A further advantage of the electrodes of the sensor structure which are only partially suspended on the membrane is that a substantially linear pressure measurement signal is achieved in this respect upon pressure loading. This is not the case in the case of a membrane structure of the sensor structure which has electrodes which are used simultaneously as measurement capacitances.

[0008] Since the proposed pressure sensor requires a significantly smaller area for the same measurement sensitivity, it is also possible to provide two pressure sensors with a double membrane structure on the area required for a comparable pressure sensor with only one membrane structure. The two pressure sensors can be of identical construction and are electrically connected, for example, in a Wheatstone half-bridge configuration, whereby a fourfold measurement sensitivity can be achieved in relation to two identically connected membrane structures each with only one active electrode structure. It is further possible to exploit the area advantage achieved by means of the double membrane structure to provide a further double membrane structure in addition to the already existing double membrane structure, which is designed, for example, for a second pressure range. In this way, the area required for the detection / measurement of a pressure range by means of one membrane structure or by means of two membrane structures arranged side by side can be used for the detection of a second or larger pressure range.

[0009] In one embodiment it is provided that the electrodes are each fixed on the corresponding membrane structure in the inner region of the respective membrane structure by means of at least one fixing structure. A particularly linear measurement behavior of the pressure sensor can thus be achieved.

[0010] In one embodiment it is provided that at least one reference capacitor with two opposite fixed electrodes is also provided in the edge region of the cavity region, wherein each fixed electrode is arranged between the corresponding other fixed electrode and one of the membrane structures. This particular construction of the sensor structure makes it possible to provide integrated reference capacitors which can advantageously be arranged in the cavity region between the deformable membrane structures in a space-saving manner.

[0011] In another embodiment provision is made for the at least one reference capacitor to be anchored at least partially or locally in or on the side wall and to be arranged self-supportingly and parallel to the diaphragm structure between the diaphragm structures. The reference capacitor is thus mechanically decoupled from the diaphragm structures to such an extent that the bowing of the diaphragm structures due to an applied external pressure has no significant influence on the reference measurement.

[0012] In another embodiment provision is made for a silicon dioxide layer composed of the material of the third silicon dioxide layer to be arranged between the fixed electrodes of the reference capacitor. The capacitance of the reference capacitor can thus be increased or, at the same capacitance, the reference capacitor structure can be made smaller in area, and thus the active electrode structure of the effective capacitor can be implemented larger in area again.

[0013] In another embodiment provision is made for at least one etching access opening to the cavity region to be configured in the layer system, wherein the etching access opening has a closure which is formed by at least one material deposited on the surface of the layer system and / or introduced into the etching access opening and / or by at least one material of the layer system which is locally melted and solidified again.

[0014] In another embodiment provision is made for at least one etching access opening to the cavity region to be configured in the layer system outside the deflectable sensing surface of the second diaphragm structure. Here, the etching access opening has a closure which is formed by at least one material deposited on the surface of the layer system and / or introduced into the etching access opening or by a material of the layer system which is locally melted and solidified again. The arrangement of the etching access opening outside the deflectable sensing surface enables precise setting of the layer thickness and / or mechanical properties of the diaphragm structure in the region of the deflectable sensing surface. A higher measurement accuracy of the pressure sensor can thus be achieved.

[0015] In another embodiment provision is made for the etching access opening to be arranged outside the sensor structure and to be connected to the cavity region by means of an etching channel which extends through at least one suspension structure. This arrangement enables a particularly large effective area of the pressure sensor.

[0016] In another embodiment provision is made for the etching access opening to be arranged inside the suspension structure. This arrangement enables a very small space requirement of the pressure sensor.

[0017] In another embodiment provision is made for the etching access opening to be arranged in an edge region of the sensor structure. This arrangement of the etching access opening or of the etching access openings enables better or faster etching of the sacrificial layer inside the cavity.

[0018] In another embodiment provision is made that the sensor structure has an additional anchoring structure for fixing the diaphragm structure, wherein the at least one etching opening is arranged between the surrounding side wall and the additional anchoring structure. The stability of the double diaphragm structure can thus be improved and the influence of the closing structure / layer closing the at least one etching opening on the measuring signal or measuring behavior can be reduced or avoided.

[0019] In another embodiment provision is made that the surrounding side wall is formed by the outer anchoring structure, the inner anchoring structure and the remaining silicon dioxide material of the silicon dioxide layer of the layer system between the outer anchoring structure and the inner anchoring structure. The stability of the side wall is improved by the additional silicon dioxide material.

[0020] In another embodiment provision is made that in the cavity region at least one mechanical stop structure is also fixed on the at least one diaphragm structure, which mechanical stop structure limits the relative movement between the two diaphragm structures starting from a predefined pressure value. Such a stop structure prevents an excessive strong local deformation of the diaphragm structures. The sensor is thus protected against mechanical overload.

[0021] According to another aspect a method for manufacturing the above-mentioned micromechanical pressure sensor is also proposed, in which method a semiconductor substrate is provided and a layer structure is produced on the semiconductor substrate by depositing and structuring some layers. Here, in a functional region of the layer structure a sensor structure is produced which is connected to the remaining layer structure via a suspension structure, which sensor structure comprises a first diaphragm structure, a second diaphragm structure and a cavity region, the first diaphragm structure is composed of a first polysilicon layer which is structured, the second diaphragm structure is composed of a fourth polysilicon layer which is structured, and the cavity region is bounded by a side wall which extends in the edge region of the diaphragm structures. Here, in addition an effective capacitor is produced in the cavity region, which effective capacitor has a first electrode which is structured from a second polysilicon layer and is fixed on the first diaphragm structure and a second electrode which is structured from a third polysilicon layer and is fixed on the second diaphragm structure. Subsequently, the silicon dioxide layers arranged between the polysilicon layers in the cavity region are removed via at least one etching opening in the fourth polysilicon layer by means of an etching method. Afterwards, the first silicon dioxide layer arranged between the first diaphragm structure and the surface of the semiconductor substrate is removed by means of an etching method. The advantages already mentioned in connection with the micromechanical pressure sensor apply for the method.

[0022] In another embodiment provision is made that the etching opening is closed by depositing at least one material on the surface of the layer system in the region of the etching opening and / or by melting at least one material of the upper layer of the layer system.

[0023] In another embodiment provision is made that the removal of the silicon dioxide layer in the cavity region and the removal of the first silicon dioxide layer under the first diaphragm structure are carried out in a common etching process. The manufacturing method can thus be simplified.

[0024] In another embodiment provision is made that a trench structure is produced in the surface of the semiconductor substrate under the sensor structure, which trench structure is not completely filled when the first silicon dioxide layer is deposited. The trench structure here causes a rapid distribution of the etching medium under the first silicon dioxide layer during the etching of the first silicon dioxide layer under the first diaphragm structure. The removal of the sacrificial layer under the sensor structure can thus be improved or accelerated. BRIEF DESCRIPTION OF DRAWINGS

[0025] The application is explained further below on the basis of the drawings. Shown here are: Figure 1 : Schematic representation of a cross section through a micromechanical pressure sensor according to the first embodiment, which has a self-supportingly suspended double-diaphragm sensor structure and an etching inlet arranged outside the sensor structure; Figure 2 : Schematic representation of a top view of a micromechanical pressure sensor according to the first embodiment; Figure 1 : Schematic representation of a cross section through a micromechanical pressure sensor according to the second embodiment, which has a self-supportingly suspended double-diaphragm sensor structure and an etching inlet arranged in the edge region of the sensor structure; Figures 3 to 7 : Schematic representation of different stages of a manufacturing method for a micromechanical pressure sensor according to the first embodiment; Figure 1 Figure 8 : Schematic representation of an alternative embodiment of a micromechanical pressure sensor, in which the reference capacitor is filled with a dielectric; Figure 9 : Schematic representation of an alternative embodiment of an unfinished pressure sensor, in which a special trench structure for supporting the undercut of the sensor structure is provided on the substrate.

[0026] Figure 10 : Schematic representation of a cross section through a micromechanical pressure sensor according to the second embodiment, which has a self-supportingly suspended double-diaphragm sensor structure and an etching inlet arranged in the edge region of the sensor structure;

[0027] Figure 11 : Schematic representation of a cross section through an unfinished micromechanical pressure sensor according to the first embodiment before the sensor structure is etched from below, Figure 10 Figure 12 : Schematic representation of a top view of a micromechanical pressure sensor according to the second embodiment, Figure 10 Figure 13 : Schematic representation of a cross section through an unfinished micromechanical pressure sensor according to the second embodiment before the sensor structure is etched from below, Figure 10 ​​​an alternative embodiment of a micromechanical pressure sensor with reinforced side walls, and Figure 14 a flow chart of a manufacturing method simplified. DETAILED DESCRIPTION

[0028] The sensor concept further explained below is based on a sensing area / sensor structure which is self-supportingly suspended above a silicon substrate on at least one spring structure or anchor structure, but in which no intermediate electrode is provided between the two deformable diaphragms in the sensing area, but rather locally suspended electrode structures are provided on the diaphragm structure, which electrode structures move towards one another upon deformation of the diaphragms and which themselves do not bow or bend here.

[0029] Figure 1 An exemplary micromechanical pressure sensor 100 is shown which has a sensor structure 200 which is self-supportingly suspended by at least one spring structure or suspension structure 140. The sensor structure 200 is produced here in a layer system 120 which is arranged on a semiconductor substrate 110 and is separated from the remaining area of the layer system 110 by one or more separation regions 161 which extend along its periphery. The separation regions are separated from the surrounding area of the layer structure 120 by etch stop structures 286 which are additionally formed in the present example by vertical regions of the layers 131, 124, 132, 133. The sensor structure 200, also referred to below as sensing area, is a two-diaphragm structure with a first diaphragm and a second diaphragm 210, 220 and a cavity region 240 arranged between the two diaphragms 210, 220. The cavity region 240 is hermetically closed here with respect to the surrounding environment 300 via a side wall 230 which is arranged between the diaphragm structures 210, 220 and which extends along the periphery of the sensor structure 200. The side wall 230 is formed here by etch stop structures which also serve as anchor structures for the diaphragms 210, 220 and the fixed electrodes 261, 262 in the present example.

[0030] In the center region 241 of the cavity region 240, an effective capacitance 250 is arranged, which comprises two movable electrodes 251, 253 arranged opposite to each other at a defined spacing and fixed on one of the two diaphragm structures 210, 220, respectively, wherein the first electrode 251 is arranged between the second electrode 253 and the first diaphragm structure 210 and the second electrode 253 is arranged between the first electrode 251 and the second diaphragm structure 220. Here, the first electrode 251 is fixed on / in the inner region 211, e.g. the center region, of the first diaphragm structure 210 by means of at least one first fixing structure 252, while the second electrode 251 is preferably fixed on / in the inner or center region 221 of the second diaphragm structure 220 by means of at least one second fixing structure 254. In the embodiment shown here, each electrode 251, 253 is fixed in the center of the corresponding diaphragm structure 210, 220 by means of one fixing structure 252, 254, instead of which the fixing of the electrodes 210, 220 on the diaphragm structures 210, 220 can also be carried out by means of a plurality of fixing structures, which can also be arranged in an inner region other than the exact center of the diaphragm structures 210, 220, depending on the embodiment.

[0031] For example by Figure 1 It can also be seen that in the cavity region 240 there is also a mechanical stop structure 290, which limits the maximum deflection of the diaphragm structures 210, 220 starting from a predefinable / definable pressure value.

[0032] The stop structure 290 in the present example is of two-part construction, wherein the two complementary parts are fixed on the diaphragm structures 210, 220 by means of their own anchoring structures 291, 292, respectively.

[0033] Depending on the application, in addition at least one reference capacitance 260 can also be placed in the cavity region 240, which is preferably located in an outer region of the cavity region 240. Such a reference capacitance 260 is preferably produced in the same layer plane as the effective capacitance 250 and comprises a first fixed electrode 261 and a second fixed electrode 262 spaced apart from the first fixed electrode at a predefined spacing, respectively, wherein the first fixed electrode 261 is arranged between the second fixed electrode 262 and the first polysilicon layer 210 forming the first diaphragm structure 210 and the second fixed electrode 262 is arranged between the first fixed electrode 261 and the fourth polysilicon layer forming the second diaphragm structure 220. The two fixed electrodes 261, 262 can be connected to each other and / or to other layers of the sensing region 200 via separation and anchoring structures 287, 289, which can also function or be used as lateral etching stop structures, electrically conductively and / or electrically insulating.

[0034] For example byFigure 1 It can also be seen that the pressure sensor 100 has at least one etching inlet 150 arranged outside the sensor element 200, which is connected to the cavity region 240 via at least one etching channel 153 extending within the suspension structure 140. The at least one etching inlet 150 is sealingly blocked or closed with respect to the ambient medium by a closure 151, such that a gas volume with a defined pressure and a defined composition is present in the cavity region 240. In principle, the etching channels can also be provided between the second and third polysilicon layers or planes and / or between the third and fourth polysilicon layers or planes.

[0035] In the operation of the pressure sensor, the two diaphragm structures 210, 220 bow inwards or outwards depending on the pressure prevailing in the ambient 300. This results in a reduction or increase in the spacing between the two active electrodes 251, 253 of the effective capacitor 150 from one another, which is measured as a corresponding linear change in the capacitance of the effective capacitor 250. By virtue of the decoupling of the bending regions of the diaphragm structures 210, 220 from the fixed electrodes 261, 262, no relevant change in the capacitance occurs in the reference capacitor 260 in the opposite direction.

[0036] Figure 2 A top view of an exemplary pressure sensor 100 is shown, which has a sensing region 200 which is stress-decoupled via a suspension structure 140 and is suspended spaced apart from the semiconductor substrate 110. In the present example, the sensing region 200 is configured circularly and is connected to the region of the surrounding layer system for anchoring via only one suspension structure. In principle, however, the sensing region 200 can also be configured differently, for example quadrangularly. Furthermore, there can be more than one suspension structure 140 for suspending the sensing region 200. Furthermore, the at least one suspension structure 140 can assume or have any shape and any geometric dimensions.

[0037] According to the following Figures 3 to 9 , exemplary possible alternative embodiments of the pressure sensor are explained in addition to the explanation of the method for manufacturing the respective pressure sensor. Here, a basic configuration of the underlying concept is illustrated Figure 3A method phase is shown in which a layer system 120 has already been arranged on a semiconductor substrate 110 (silicon substrate). In order to manufacture the layer system 120, a first silicon dioxide layer (SiO2 layer) 121 is first produced on the semiconductor substrate 110 and is then structured. Subsequently, the first SiO2 layer 121 is at least partially removed in order to produce a stress decoupling and self-supporting sensing region. Subsequently, a first layer 131, which is electrically insulating and etch-resistant with respect to a later SiO2 sacrificial layer etching process, for example a first SiRiN layer (silicon-rich nitride), is deposited on the first SiO2 layer 121 and structured. Here, the previously produced SiO2-free regions in the first SiO2 layer 121 are at least partially filled with the first SiRiN layer 131. The filled regions can later serve, for example, as electrically insulating etch stop boundaries in the sacrificial layer etching process. A further structuring of the first SiO2 layer 121 and / or the first SiRiN layer 131 can optionally be carried out after the structuring of the first SiRiN layer 131. Contact hole structures are produced here, which can later be used for electrical contacting of the silicon substrate 110.

[0038] After the optional second structuring of the first SiO2 layer 121 and / or the first SiRiN layer 131, a deposition and structuring of a first polysilicon layer 122 is carried out. By means of the first polysilicon layer 122, a first diaphragm structure 210 is later formed. Further structures, for example at least one electrical substrate contact or at least one conductive track structure, can also be realized by means of the first polysilicon layer 122. Subsequently, a second SiO2 layer 123 is produced and structured on the first polysilicon layer 122. The SiO2 layer 123 additionally serves as a sacrificial layer in the cavity region 240 and is then removed again in the cavity region. Subsequently, a deposition and structuring of a second polysilicon layer 124 is carried out. Here, the SiO2-free regions in the second SiO2 layer 123 are at least partially filled with the material of the second polysilicon layer 124. The thus filled regions in the second SiO2 layer 123 can here be used for realizing an electrically conductive connection between the first and second polysilicon layer / surface 122, 124, a lateral etch boundary structure, a partial region of a subsequent stop structure, a partial region of an anchoring structure of the first and second diaphragm structure 210, 220, a partial region of the sidewall 230 surrounding the cavity region 240, a partial region of the outer etch stop structure 286, and / or for realizing an anchoring structure of the first fixed electrode 261 of the first electrode structure 251, which is later freely movable, and / or of the integrated reference capacitor structure 260. The structuring of the second polysilicon layer 124 serves for the manufacture of at least one subsequent movable first electrode structure 251. Here, a first conductive track structure (not shown here) and / or the first fixed electrode 261 of the reference capacitor structure 260 can also be produced at the same time.

[0039] Alternatively thereto, at least one further structuring of the second SiO2layer 123 can be carried out prior to the deposition of the second polysilicon layer 124 and a further SiRiN layer 134 can be deposited and structured which is at least partially covered by the second polysilicon layer 124 or embedded therein (see Figure 4 ). In this way, the anchoring of the stop structure 292 in the cavity region 240 and / or the lateral etching limit structure provided between the first and second polysilicon layer / surface 122, 124 and / or the anchoring structure of the subsequently active first electrode structure 210 and / or the fixed first electrode 261 of the reference capacitor structure 260 and / or the anchoring structure of the first and second diaphragm structure 210, 220 and / or the partial region of the sidewall 230 surrounding the cavity region 240 and / or the partial region of the outer etching stop structure 286 are implemented electrically insulating.

[0040] A third SiO2layer 125 is deposited and structured on the structured second polysilicon layer 124. This SiO2layer 125 essentially defines the spacing between the two subsequently active implemented electrode structures 251, 253 of the effective capacitor 250 and also between the fixed electrodes 261, 262 of the one or more optional reference capacitor 260. As mentioned above, the fixed electrodes 261, 262 can at least partially be in the cavity region and / or alternatively thereto also outside the cavity region 240. Alternatively, the third SiO2layer can be implemented locally / regionally with different thicknesses by means of an etching process and / or by depositing and structuring at least two SiO2layers for manufacturing different spacings between the active implemented electrode structures 251, 253 of the effective capacitor 250 and between the fixed electrodes 261, 262 of the one or more optional reference capacitor 260.

[0041] The structured third SiO2layer 125 can be structured in such a way that it is not completely removed in the region of the cavity region 240 in which the particle portion or the vertical stop structure 290 should be provided. By means of the residual remaining thickness of the third SiO2layer 125, the maximum deflection of the diaphragm structure 210, 220 due to the pressure loading can be set, i.e. how far the diaphragm structure 210, 220 can subsequently move towards each other when a pressure measurement is carried out.

[0042] After structuring the third SiO2 layer 125, the second SiRiN layer 132 is deposited. Here, the SiO2-free regions or previously produced recesses in the third SiO2 layer 125 are at least partially filled in order to be able to produce a part region of the etch stop structure, which is implemented electrically insulating, and / or of the vertical stop structure 290, and / or of the anchoring structure of the fixed first and second electrodes 261, 262 of the reference capacitor structure 260, and / or of a part region of the anchoring structure of the first and second membrane structures 210, 220, and / or of a part region of the sidewall 230 surrounding the cavity region 240, and / or of a part region of the outer etch stop structure 286.

[0043] Subsequently, after a further optional structuring of the second SiRiN layer 132 and / or of the third SiO2 layer 125, the second SiRiN layer 132 is structured in order to produce the contact hole structures. After this process step, the third polysilicon layer 126 is deposited and structured. This third polysilicon layer 126 is used to produce the second active electrode structure 253 of the effective capacitor 250 and the second electrode 262 of the optional reference capacitor structure 260. Furthermore, an electrically conductive connection between the second and third polysilicon layer / surface 124, 126 and / or at least one electrically conductive track structure can be realized by depositing the material of the third polysilicon layer 126 in the respective contact hole structures of the third SiO2 layer 125.

[0044] Alternatively, after structuring the second SiRiN layer 132 and / or the third SiO2 layer 125, the structures exposed here by the second SiRiN layer 132 and / or the third SiO2 layer 125 can be at least partially filled with the material of the third polysilicon layer / surface 124, 126 in order to be able to electrically conductively configure an electrical connection, a lateral etch stop structure, a part region of a subsequent stop structure, a part region of the anchoring structure of the first and second membrane structures 210, 220, a part region of the sidewall 230 surrounding the cavity region 240, and / or the outer etch stop structure 286 between the second and third polysilicon layer / surface 124, 126.

[0045] In order to be able to avoid an etching action on the third SiO2 layer 125 when structuring the second SiRiN layer 132, a further polysilicon layer can be deposited on the third SiO2 layer 125 before depositing the second SiRiN layer 132 and structured together with the third SiO2 layer 125. The etching process stops on / in this further polysilicon layer when subsequently structuring the second SiRiN layer 132 and the third SiO2 layer 125 can be avoided from being etched. This is particularly advantageous since the third SiO2 layer 125 serves to define the electrode spacing and its thickness thus determines the capacitance of the effective capacitor 250 and thus also indirectly the measurement sensitivity and the measurement range of the pressure sensor 100. Subsequently, here, depositing and structuring the third polysilicon layer 126 can also be carried out together with the further polysilicon layer which serves or is used as an etching stop.

[0046] After jointly structuring the third polysilicon layer 126 and the further polysilicon layer, a fourth SiO2 layer 127 is deposited and structured, followed by depositing a third SiRiN layer 133. Here, the previously produced SiO2-free regions in the fourth SiO2 layer 127 are at least partially filled with the third SiRiN layer 133. The filled regions can then serve as etching stop boundaries which are electrically insulating, for example, in a sacrificial layer etching process. After structuring the third SiRiN layer 133, a further structuring of the fourth SiO2 layer 127 and / or the third SiRiN layer 133 can optionally be carried out. Here, contact hole structures, partial regions of subsequent stop structures and / or anchoring structures are produced which can then be used for electrical contacting between the third polysilicon layer / surface and the fourth polysilicon layer / surface 126, 128, for mechanical suspension of the active electrode on the second diaphragm structure, as lateral etching stop structures, as partial regions of anchoring structures of the first diaphragm structure and the second diaphragm structure 210, 220, as partial regions of the sidewalls 230 surrounding the cavity region 240 and / or as partial regions of the outer etching stop structure 286.

[0047] After manufacturing the structures, a fourth polysilicon layer 128 is deposited and structured. Here, the SiO2-free regions in the fourth SiO2 layer 127 are at least partially filled and the structures previously described composed of the material of the fourth polysilicon layer 128 are produced. In addition, the fourth polysilicon layer 128 is also used to realize the second diaphragm structure 220 and for manufacturing at least one conductive track structure (not shown here). When structuring the fourth polysilicon layer 128, insulating trenches can be produced, for example, in addition to the insulating trenches 129 shown in Figure 3 and used for electrically insulating the second diaphragm structure 220. Further layer depositions can then still be carried out, which are not shown in detail here in Figure 3Further layers deposition are shown in detail. These layers deposition can for example be used for manufacturing pad structures, conductive tracks and electrically insulating termination structures for the conductive tracks and / or for manufacturing diffusion barriers, for example used as a moisture barrier.

[0048] Alternatively, after deposition of the fourth SiO2 layer 127 and deposition of the third SiRiN layer 133, the structured fourth SiO2 layer 127 and the third SiRiN layer 133 are structured such that the previously described structures are composed of the material of the fourth polysilicon layer 128. In this case, the elements / structures configured between the third polysilicon layer / surface and the fourth polysilicon layer / surface 126, 128 are preferably configured electrically conductive.

[0049] As shown in Figure 5 The SiO2 material present in the cavity region 240 in the sacrificial layer etching process can be removed by providing at least one etching inlet 150 outside the anchoring region of the diaphragms 210, 220 and by providing at least one etching channel 153 between the etching inlet 150 and the cavity region 240. In this case, the SiO2 material of the second, third and fourth SiO2 layers 123, 125, 127 is removed between the first and second diaphragm structures 210, 220, between the first and second active electrodes 251, 253 of the effective capacitor structure 250, between the corresponding stop structures and, if necessary, also between the first and second fixed electrodes 261, 262 of the reference capacitor structure 260.

[0050] As shown for example also in Figure 6 The at least one etching inlet 150 can subsequently be closed again by means of at least one layer deposition and / or by locally melting at least one portion of the layer system 120, for example by means of a laser. Here, a defined pressure and / or a defined gas or gas mixture can be set in the cavity region 240.

[0051] After closing the etching inlet 150, the layer system 120 can be removed at least partially around the first and second diaphragm structures 210, 220 and their anchoring regions up to the first SiO2 layer 121 by means of known structuring methods, in order to achieve a self-supporting sensing region 200 with two active diaphragms 210, 220 after subsequent removal of the first SiO2 layer 121 between the first diaphragm structure 210, its anchoring region, the at least one suspension structure 140 and the silicon substrate 110. One such self-supporting sensor structure 200 is shown in Figure 7The suspension of the self-supporting region 200 by the at least one suspension structure 140 can be arbitrarily configured in terms of shape and / or geometry. In this case, a conductive track (not shown here) extends through the at least one suspension structure 140 to connect the electrodes of the active capacitors 250 with one or more reference capacitors 260. In particular, the conductive layers of the layer stack forming the corresponding suspension structure 140 can be used as conductive tracks in this case. For example, the conductive tracks can be produced by means of a known structuring method, for example by means of a photolithographic method. Figure 7 It can be seen that the at least one etching channel 153 also extends through the at least one suspension structure 140, which connects the cavity region 240 with the at least one etching inlet and through which the SiO2sacrificial oxide layer is removed from the cavity region.

[0052] It is also possible in principle to remove the sacrificial oxide layer in the cavity region 240 and under the first diaphragm structure 210 in a common etching process. It is possible in this case to first remove the layer system 120 at least partially (for example around the first and second diaphragm structures 210, 220 and their anchoring regions) up to the first SiO2layer 121 by means of a known structuring method and subsequently to produce the at least one etching inlet 150 to remove the sacrificial oxide layer 123, 125, 127 in the cavity region 240. In this variant, it is thus possible to remove the sacrificial oxide from the cavity region 240 and the first SiO2layer 121 between the first diaphragm structure 210, its anchoring region, the at least one suspension structure 140 and the silicon substrate 110 at the same time. Subsequently, the at least one etching inlet 150 can be closed.

[0053] If at least one etching inlet 150 is provided in the anchoring region and / or in the second diaphragm structure 220, through which the sacrificial oxide layer in the cavity region 240 can be removed and which is subsequently closed again by a medium-tight seal, it is possible to dispense with the provision of an etching inlet 150 outside the anchoring region of the diaphragm and with the provision of the at least one etching channel 153 connecting the etching inlet 150 with the cavity region 240 between the diaphragm structures 210, 220.

[0054] As is also exemplarily shown in Figure 7 It is also possible, as is also exemplarily shown in

[0055] As is also exemplarily shown in Figure 8It is shown that instead of the previously described embodiments it is also possible to not remove the third SiO2 layer 125 between the fixed electrodes 261, 262 of the at least one reference capacitor 260. Thus, the capacitance of the reference capacitor structure 260 can be increased, or, at the same capacitance, the reference capacitor structure 260 can be reduced in area, whereby the active electrode structure 251, 253 of the effective capacitor 250 can be implemented again larger in area.

[0056] Figure 9 Another embodiment of the manufacturing process is described. For example, it can be seen here that a special structure 162 can also be introduced into the surface 115 of the silicon substrate 110 at least in the region of the sensor structure 200 below the layer system 120, which is not completely filled with the first SiO2 layer 121. The structure 162, which is exemplarily configured in the form of a trench or channel, is preferably used to distribute the etching medium for removing the first SiO2 layer 121 as quickly as possible in this area. In this way, the complete removal of the first SiO2 layer 121 under the first membrane structure 210 can be carried out in significantly shorter time. In Figure 9 Such a structure 162 is exemplarily shown in the form of a regular trench structure in the above-mentioned embodiment.

[0057] Alternatively, a channel-like SiO2-free structure can be provided within the first SiO2 layer 121 for the removal of the first SiO2 layer 121 and, optionally, for example, within the second SiO2 layer 123 for the removal of the sacrificial oxide layers 123, 125, 127 in the cavity region 240 in order to quickly distribute the etching medium planarly.

[0058] In the above-described embodiments, an external etching inlet 150 for removing the SiO2 sacrificial layers in the cavity region 240 is described, which is outside the stress-decoupled sensing region 200, which etching inlet extends at least through the fourth polysilicon layer 128 and which etching inlet extends via an etching channel 153 extending in the suspended structure 140 for stress decoupling up to the cavity region 240.

[0059] However, it is also possible in principle that at least one etching inlet 150 is provided through the at least fourth polysilicon layer 128 on the sensor structure 200 after stress decoupling, via which the SiO2 sacrificial layers 123, 125, 127 in the cavity region 240 can be removed and which etching inlet can be closed after removal of the SiO2 sacrificial layers by means of at least one layer deposition and / or laser resealing process. Figure 10A pressure sensor 100 with a correspondingly configured sensing region 200 is exemplarily shown for this. As can be seen here, the etching inlets 150 are in this case arranged as far as possible on the edge of the sensing region 200 in the region between the outer and inner anchoring structures 288, 289, in order not to change or influence the properties of the second diaphragm structure 220 anchored on the inner anchoring structure 289. Here, the number, size and distribution of the etching inlets 150 can vary depending on the application.

[0060] As can be seen in Figure 11 , between the inner etching inlets 150 and the center of the diaphragm structures 210, 220, between the respective polysilicon layers 124, 126, 128, further anchoring structures 289 for the first and second diaphragm structures 210, 220 can be provided at least partially / locally, which are composed of polysilicon and / or of SiRiN. Here, the anchoring structures 289 can be centered on one another or partially deviate from the center alignment. The advantage of this optional anchoring structure 289 is that the closed area of the at least one etching inlet 150 can be placed between the diaphragm anchoring of the second diaphragm structure 220 and the lateral etching stop structure 288 composed of polysilicon and / or SiRiN provided at least on the periphery of the stress-decoupled sensing region, and thus a negative influence of the closed area on the diaphragm properties of the second diaphragm 220 can be avoided.

[0061] Figure 12 A top view of a pressure sensor 100 is shown, which is configured according to the embodiments shown in Figure 10 and 11 . The pressure sensor 100 exemplarily shown here has a circularly configured sensing region 200, which is stress-decoupled by a suspension structure 140. As exemplarily shown here, there are a total of four etching inlets 150 arranged in the edge region of the sensing region 200, which are distributed along the circumference of the sensing region 200 and arranged between the outer and inner anchoring structures 288, 289.

[0062] In principle, the circumferential contour of the stress-decoupled sensor structure / sensing region 200 can be arbitrary and need not correspond to the shape / contour of the first and / or second diaphragm face 210, 220 fixed by the further anchoring structures 289.

[0063] Figure 13Another possible embodiment is shown, in which by providing further lateral etch stop structures 231 of polysilicon and / or SiRiN between the individual polysilicon layers 124, 126, 128 within the sensing region 200 a defined edge region 232 can be created in which the SiO2sacrificial layer is not removed. These edge regions 232 filled with SiO2may for example be used to reinforce or make the surrounding edge 230 of the sensor structure 200 formed by the outer etch stop structure more robust.

[0064] Here, the lateral etch stop structures of SiRiN can be provided not only between the polysilicon layers, but also at least partially / local or completely through the polysilicon layers.

[0065] In Figure 14 A simplified flow chart of the manufacturing method 400 is shown in Fig. 4. Here, in a first step 410 a semiconductor substrate 110 is first provided. In a step 420 a layer system 120 is created on the semiconductor substrate 110 by depositing and structuring suitable materials such as silicon dioxide, polysilicon and SiRiN (English: silicon rich nitride) etc. By structuring these layers a dual diaphragm structure 210, 220 with a cavity region 240 is created in the functional region 111 of the layer system 120. In a further step 430 the SiO2material present in the cavity region 240 is removed via the previously created etch opening 150. In a step 440 the etch opening 150 is closed by depositing material or by means of a laser resealing process. Finally in a step 450 a self-supporting sensor structure 200 is created by etching the SiO2material present under the dual diaphragm structure 210, 220.

[0066] In the foregoing description and in the drawings the structure of the pressure sensor is not completely described. Rather, the manufacturing method can comprise further steps which are apparent to the person skilled in the art. Thus, for example after closing at least one etch opening for removing the sacrificial oxide layer in the cavity region, further process steps can still be carried out, for example to provide or implement pad structures, conductive tracks and wiring layers, electrically insulating structures and insulation layers, diffusion barriers and diffusion barrier layers and similar structures. Furthermore, after each deposition optionally a planarization of the deposited layer surface can be carried out, for example by means of a CMP process (English: chemical mechanical polishing), in order to achieve a planar surface. In order to improve the electrical conductivity, the deposited polysilicon layers can also optionally be doped at least partially or locally by means of known methods, and optionally additional structures can be provided within the first silicon dioxide layer 121, for example planarized regions and / or at least one conductive track of polysilicon. Since here known methods are involved, a detailed description is omitted.

[0067] Although the present application has been further shown and described with respect to preferred embodiments, the application is not to be limited to the examples disclosed. Rather, other variations which will become apparent to those skilled in the art, can be made thereto without departing from the scope of the application.

Claims

1. Micromechanical pressure sensor (100), comprising: - a substrate (110) with a layer system (120) arranged thereon, - a sensor structure (200) self-supportingly fixed on the layer system (120) by means of at least one suspension structure (140), the sensor structure having a first diaphragm structure (210), a second diaphragm structure (220) and a cavity region (240) arranged between the two diaphragm structures (210, 220) and enclosed by side walls (230) extending in edge regions (212, 222) of the two diaphragm structures (210, 220), wherein the sensor structure (200) comprises an effective capacitor (250) arranged in the cavity region (240) between the two diaphragm structures (210, 220), the effective capacitor having a first electrode (251) fixed on the first diaphragm structure (210) and a second electrode (253) arranged between the first electrode (251) and the second diaphragm structure (220) and fixed on the second diaphragm structure (220).

2. Micromechanical pressure sensor (100) according to claim 1, wherein the electrodes (251, 253) being fixed on the respectively belonging diaphragm structure (210, 220) in an inner region (211, 221) of the respectively belonging diaphragm structure (210, 220) by means of at least one fixing structure (252, 254), respectively.

3. Micromechanical pressure sensor (100) according to claim 1 or 2, wherein in an edge region (242) of the cavity region (240) at least one reference capacitor (260) is further provided, the reference capacitor having two oppositely arranged fixed electrodes (261, 262), wherein each of the fixed electrodes is arranged between the respectively other fixed electrode and one of the diaphragm structures.

4. Micromechanical pressure sensor (100) according to claim 3, wherein the reference capacitor (260) being at least partially or locally anchored in the side walls (230) and arranged self-supportingly and parallel to the diaphragm structures (210, 220).

5. Micromechanical pressure sensor (100) according to claim 4, wherein between the fixed electrodes (261, 262) of the reference capacitor (260) a silicon dioxide layer consisting of the material of a third silicon dioxide layer (125) is arranged.

6. Micromechanical pressure sensor (100) according to any of the preceding claims, wherein in the layer system (120) at least one etching inlet (150) to the cavity region (240) is configured outside the deflectable sensing face (201) of the second diaphragm structure (220), and wherein the etching inlet (150) has a closure (151) which is formed by at least one material deposited on the surface of the layer system (120) and / or introduced into the etching inlet (150) and / or by at least one locally melted and again solidified material of the layer system (120).

7. The micromechanical pressure sensor (100) according to claim 6, wherein the etching inlet (150) is arranged outside the sensor structure (200) and is connected to the cavity region (240) by means of an etching channel (153) extending through the suspension structure (140).

8. The micromechanical pressure sensor (100) according to claim 6, wherein the at least one etching inlet (150) is arranged within the at least one suspension structure (140).

9. The micromechanical pressure sensor (100) according to claim 6, wherein, the at least one etching inlet (150) is arranged in an edge region (242) of the sensor structure (200).

10. The micromechanical pressure sensor (100) according to claim 9, wherein, the sensor structure (200) has an additional anchor structure (289) for fixing the diaphragm structure (210, 220), and wherein the etching inlet (150) is arranged between a surrounding side wall (230) and the additional anchor structure (289).

11. The micromechanical pressure sensor (100) according to any one of the preceding claims, wherein the surrounding side wall (230) is formed by an outer anchor structure (288), an inner anchor structure (289) and a residual silicon dioxide material of the silicon dioxide layers (123, 125, 127) of the layer system (120) between the outer anchor structure and the inner anchor structure (288, 289).

12. The micromechanical pressure sensor (100) according to any one of the preceding claims, wherein, in the cavity region (240) at least one mechanical stop structure (290) is also fixed on at least one diaphragm structure (210, 220), which limits the relative movement between the two diaphragm structures (210, 220) starting from a predefined pressure value.

13. Method for manufacturing a micromechanical pressure sensor (100), which is configured according to any one of claims 1 to 12, wherein providing a semiconductor substrate (110), wherein a layer structure (120) is produced on the semiconductor substrate (110) by depositing and structuring some layers (121-128), wherein, in the functional region (111) of the layer structure (120), a sensor structure (200) is produced which is connected to the remaining layer structure (120) via a suspension structure (140), the sensor structure comprising a first diaphragm structure (210) which is composed of a first polysilicon layer (121) which is structured, a second diaphragm structure (220) which is composed of a fourth polysilicon layer (128) which is structured, and a cavity region (240) which is delimited by a side wall (230) which extends in the edge region (212, 222) of the diaphragm structures (210, 220), wherein, in the cavity region (240), an effective capacitor (250) is produced which has a first electrode (251) which is structured from a second polysilicon layer (124) and is fixed on the first diaphragm structure (210) and a second electrode (253) which is structured from a third polysilicon layer (126) and is fixed on the second diaphragm structure (220), wherein, subsequently, the silicon dioxide layers (123, 125, 127) which are arranged between the polysilicon layers (122, 124, 126, 128), respectively, are removed in the cavity region (240) by means of an etching method via at least one etching inlet (150) which has an opening (152) in the fourth polysilicon layer (128), wherein, furthermore, the first silicon dioxide layer (121) which is arranged between the first diaphragm structure (210) and the surface (115) of the semiconductor substrate (110) is removed by means of an etching method.

14. The method according to claim 13, wherein the etching inlet (150) is closed by depositing at least one material on the surface of the layer system (120) in the region of the etching inlet (150) and / or by locally melting at least one material of the upper layers of the layer system (120).

15. The method according to claim 13 or 14, wherein, the removal of the silicon dioxide layers (123, 125, 127) in the cavity region (240) and the removal of the first silicon dioxide layer (121) under the first diaphragm structure (210) are carried out in a common etching process.

16. The method according to any one of claims 13 to 15, wherein a trench structure (162) is produced in the surface (115) of the sensor substrate (110) under the sensor structure (200), which trench structure is not completely filled when the first silicon dioxide layer (121) is deposited, and wherein the trench structure (162) causes or facilitates the distribution of the etching medium under the first silicon dioxide layer (121) during the etching of the first silicon dioxide layer (121) under the first diaphragm structure (210).

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