TW201739687A - Micromechanical sensor device and related manufacturing method - Google Patents

Abstract

The present invention provides a micromechanical sensor device and a related method of manufacture. The micromechanical sensor device is equipped with a sensor substrate (MC) having a front side (VS) and a rear side (RS) and a rear side cavity (K); one of the substantially closed diaphragms a region (M) formed on the front side (VS), the diaphragm region being disposed above the back side cavity (K) of the sensor substrate (MC); a sensor region (SB) disposed on the a membrane region (M) or above the membrane region (M); and a heating device (HE) for heating the sensor region (SB), the heating device being disposed in the membrane region (M) Or above the membrane zone (M); wherein the membrane zone (M) has one or more pressure equalization holes (L1 to L6; L1 to L4) for pressure equalization of the rear cavity (K) ).

Description

Micromechanical sensor device and related manufacturing method

The present invention relates to a micromechanical sensor device and a related manufacturing method by means of a heating device.

While any micromechanical assembly having a heating device is also applicable, the invention and the problems addressed by the present invention will be explained with reference to components having a gas sensor based on a crucible and a heating device (heating plate).

Miniature heating plates are important components of micromechanical sensors. These micro-hotplates are used for functional principles in situations where a high temperature sensor principle is required. A gas sensor in the case of a chemical transducer principle can be mentioned here mainly: the desired chemical reaction has not yet been carried out at room temperature, but a certain activation energy is required and therefore a higher operating temperature is required. Conventional sensors of this type are, for example, metal oxide gas sensors that typically must operate between 250 °C and 400 °C.

In addition to chemical sensors, the heating plate is also used in sensors with physical transducer principles, such as thermal conductivity sensors, Pirani components (vacuum sensors) or mass flow rate Detector.

According to the prior art, the micro heating plate acts as a closed diaphragm or by means of a suspension Membranes are produced as described by Isolde Simon et al., Micromachined metal oxide gas sensors: opportunities to improve sensor performance, pages 1 to 26 of Sensors and Actuators B 73 (2001).

Such sensor elements having miniature heating plates according to the prior art typically have a lateral dimension greater than 1 mm x 1 mm. In order to meet the requirements of consumer electronic devices such as those presented in, for example, smart phones, miniaturization of lateral dimensions of less than about 1 mm x 1 mm is currently sought, and at the same time a reduction in power requirements is required. In addition to the challenges associated with special heater designs, the areas available for wafer adhesive bonding are becoming smaller and smaller, and the challenges for construction and joining techniques suitable for manufacturing are increasing.

Suspended separators (such as, for example, produced by surface micromachining techniques) have advantages with respect to "wafer handling" and adhesive bonding because the wafer can be adhesively bonded over the entire area on the back side in this condition, and The possible adhesive bonding areas are therefore much larger than in the case of a diaphragm exposed from the rear by means of wet chemical exposure (using, for example, KOH) or dry etching (using, for example, DRIE). However, closing the membrane (typically a membrane under tensile stress) has advantages with respect to stability and compatibility with various coating methods such that it will retain its right to exist even in the case of extremely miniaturized systems, Although the adhesive joint area is small.

A surface micromachining technique is used to suspend a membrane on a web, such as a property in which a central carrier structure is sensitive to mechanical loads, such as vibration or shock, as compared to a closed membrane using integral micromachining. Moreover, its mechanical stability is insufficient relative to a particular coating method, such as time pressure dispensing. In the case of a closed diaphragm using surface micromachining techniques, the cavity is closed to appear at the wafer surface by means of a production control tube. Here, the pressure between atmospheric pressure and several megabars is set depending on the closing method. If the closing is performed under atmospheric pressure, the enclosing gas is heated during operation and deformation of the diaphragm occurs. This in turn causes impedance changes on the diaphragm and effects on the performance of the sensor. If the closure is performed in the millibar range, the diaphragm is deflected by the ambient atmospheric pressure. However, this deflection has an adverse effect on the production process because, for example, the diaphragm is not positioned in the same focal plane as the wafer surface, and imaging aberrations therefore occur in the lithography process. In both cases, it is necessary to pay special attention to the method of applying the gas sensing material in order to reliably avoid mechanical damage to the diaphragm.

As a result, the choice of possible methods for coating is limited. A method that only subjects the structure to only low mechanical loads is therefore appropriate. It is generally possible to deposit only the film-like layer, for example by means of CVD, PCD or inkjet processes; to exclude often desirable coatings by paste or liquid materials, for example by means of spraying, by means of time-pressure printing, or by rotation Printing or impression method.

Likewise, for example, a larger layer thickness having a greater weight should be considered important in the case of a micromachined membrane suspended from the surface of the web, as it may be specifically established after the vibration. Damage to the contents.

3 is a schematic cross-sectional view of a micromechanical sensor device for illustrating the problem solved by the present invention.

In FIG. 3, reference numeral 1 denotes a carrier substrate such as a ceramic carrier substrate or a printed circuit board. The MEMS sensor substrate MC having the front side VS and the back side RS is adhesively bonded to the carrier substrate 1 at the back side RS of the substrate MC by means of the adhesive layer KL.

The MEMS sensor substrate MC has a side cavity K extending from the rear side RS toward the front side VS. The side wall S' of the rear side cavity K has a slanted flank originating from a wet chemical etch (e.g., KOH) during the production process.

On the front side VS, the closed diaphragm region M is formed by a functional layer FS on the front side VS of the MEMS sensor substrate MC, which is disposed above the rear side cavity K. The functional layer FS and thus the membrane region M can be constructed from individual layers (for example yttria, tantalum nitride or tantalum carbide) or by layer sequences (for example from yttria and tantalum nitride layers) in which additional metal conductor tracks are positioned And/or on the layers, the additional metal conductor track may have the function of a heater and/or an electrode.

The heating device HE is integrated in its center into the diaphragm region M by means of which the diaphragm region M can be heated to a predetermined temperature. The sensor region SB is disposed above the heating device HE in the diaphragm region M, and the sensor region includes, for example, a metal oxide-based thick film or a metal oxide-based film and an electrode embedded in the sensor region. Therefore in order to implement, for example, a gas sensor device.

The adhesive joint of the adhesive layer KL is not peripheral (for example, a dot or a strip), that is, does not cover the entire back side RS, so that the gas volume can be in the rear side cavity K during the heating operation of the heating device HE Expansion, that is, gas exchange with the environment can occur. This prevents the diaphragm region M from undergoing a continuous pressure change that can cause wear of the diaphragm region M during sensor operation.

The present invention provides a micromechanical sensor device as claimed in claim 1 and a related method of manufacturing a micromechanical sensor device as claimed in claim 11.

The respective subsidiary claims are a preferred development in relation to the present invention.

Advantages of the invention

The concept underlying the invention is that the diaphragm region has one or more pressure equalization holes for pressure equalization of the rear side cavity.

The present invention thus makes it possible to provide a full or substantially annular perimeter adhesive bond and achieve sufficient gas exchange in the presence of a miniaturized sensor substrate, regardless of the annular adhesive bond. It is thus possible to avoid a situation in which the sensor substrate is tilted during the necessary baking step during construction and joining techniques due to gas expansion, and a subsequent wire bonding process is therefore not possible. Furthermore, pressure changes during the heating operation of the heating device can be avoided or compensated.

Other advantages are one of the further processing steps high manufacturing reliability. The pressure equalization holes can be positioned/sized to maintain the advantageous properties of a clamp closed diaphragm compared to one of the membranes suspended from the web. A hole having a diameter in the range of a few [mu]m will suffice for adequate ventilation.

A robust adhesive bonding process can be achieved regardless of a small adhesive bond area (typically having a typical sensor element size of less than or equal to 1 mm x 1 mm).

This gas exchange is particularly advantageous for vacuum and thermal conductivity sensors because the measurement principle here is based on the fact that the heat dissipation of a heating element varies with the thermal conductivity of the surrounding gas. In the absence of ventilation, only the gas above the diaphragm can contribute to the measurement; in the case of ventilation, the gas under the diaphragm can also contribute to the measurement signal.

According to a preferred development, the (equal) pressure equalization holes are provided in varying sizes. An optimization of one of the mechanical stability can thus be achieved.

According to a preferred development, the (equal) pressure equalization aperture is disposed in the outer edge region of one of the diaphragm regions outside the sensor region and the heating device. These pressure equalization holes therefore do not affect the sensor function. In order to be able to ensure the highest possible mechanical stability of the membrane, the pores are ideally introduced into the zone of the membrane having a minimum of stress or positioned adjacent thereto.

According to another preferred development, the side wall of the rear side cavity extends substantially perpendicular to the front side. This achieves another miniaturization.

According to another preferred development, the rear side is adhesively bonded to a carrier substrate by means of an adhesive region in such a manner that the rear side cavity is hermetically sealed at the rear side. This improves stability in the case of increased miniaturization.

According to another preferred development, the rear side is adhesively bonded to a carrier substrate by means of an adhesive region, wherein pressure equalization is provided for pressure equalization of the rear side cavity in the sensor substrate aisle. This further improves the pressure equalization without degrading stability.

According to another preferred development, the back side is adhesively bonded to a carrier substrate by means of an adhesive region, wherein a pressure equalization channel for pressure equalization of the back side cavity in the carrier substrate is provided. This even further improves the pressure equalization without reducing stability.

According to another preferred development, the heating device is introduced into the membrane zone and the sensor zone is provided above the heating device on the membrane zone. This ensures an efficient heating function.

According to another preferred development, the sensor region comprises a gas sensor region or a thermal conductivity sensor region or an infrared sensor region or a mass flow rate sensor region.

According to another preferred development, the (equal) pressure equalization holes have a diameter of from 1 μm to 50 μm, preferably from 1 μm to 10 μm. This reduces the mechanical impact of the pressure equalization holes and is sufficient for the desired pressure equalization function. The pressure equalization holes are preferably positioned in regions of the diaphragm region that have low mechanical stress, and/or the pressure equalization holes are positioned in the region of the heating device and the sensor region.

1‧‧‧ Carrier substrate

AK‧‧‧pressure equalization channel

FS‧‧‧ functional layer

HE‧‧‧heating unit

K‧‧‧back side cavity

KL‧‧·adhesive area/adhesive layer

L1‧‧‧pressure equalization hole

L2‧‧‧pressure equalization hole

L3‧‧‧pressure equalization hole

L4‧‧‧pressure equalization hole

L5‧‧‧pressure equalization hole

L6‧‧‧pressure equalization hole

M‧‧‧ diaphragm area

MC‧‧‧Sensor Substrate

RS‧‧‧ back side

S‧‧‧ side wall

S'‧‧‧ side wall

SB‧‧‧Sensor Zone

VS‧‧‧ front side

1a), 1b) show a schematic illustration for illustrating a micromechanical sensor device according to a first embodiment of the invention, in particular Fig. 1a) is shown in plan view in cross section and Fig. 1b); 2a), FIG. 2b) shows a schematic illustration for illustrating a micromechanical sensor device according to a second embodiment of the invention, in particular FIG. 2a) in a plan view and in FIG. 2b) in a side view; 3 shows a schematic cross-sectional view of a micromechanical sensor device for illustrating the problem solved by the present invention.

In the drawings, the same reference symbols designate the same or functionally identical elements.

1a) and 1b) are used to illustrate a schematic illustration of a micromechanical sensor device according to a first embodiment of the invention, in particular Fig. 1a) in cross section and Fig. 1b) in plan view.

In Figures 1a), 1b), reference numeral 1 indicates a carrier substrate, such as a ceramic carrier substrate or a printed circuit board. The MEMS sensor substrate MC having the front side VS and the back side RS is adhesively bonded to the carrier substrate 1 at the back side RS of the substrate MC by means of the adhesive layer KL. The adhesive bond of the adhesive layer KL is peripheral, and this stability is supported in the case of miniaturization in advance.

The MEMS sensor substrate MC has a side cavity K extending from the rear side RS toward the front side VS. The side wall S of the rear side cavity K has a vertical flank originating from an anisotropic etch during the production process compared to the back side cavity described above with respect to FIG. This support is miniaturized. By means of the side wall S, a straight vertical form is used and is substantially perpendicular to the diaphragm zone M or the front side VS The fact that it is extended can produce the smallest possible sensor device under the predetermined size of the diaphragm area. A particularly preferred possibility for this purpose is the use of dry etching processes (DRIE).

On the front side VS, the closed diaphragm region M is formed by a functional layer FS on the front side VS of the MEMS sensor substrate MC, which is disposed above the rear side cavity K. The functional layer FS and thus the membrane region M can be constructed from individual layers (for example yttria, tantalum nitride or tantalum carbide) or by layer sequences (for example from yttria and tantalum nitride layers) in which additional metal conductor tracks are positioned And/or on the layers, the additional metal conductor track may have the function of a heater and/or an electrode.

The heating device HE is integrated in its center into the diaphragm region M by means of which the diaphragm region M can be heated to a predetermined temperature. The sensor region SB is disposed above the heating device HE in the diaphragm region M, the sensor region comprising, for example, a metal oxide-based thick film or a metal oxide-based film on the electrode structure, so as to achieve, for example, gas sensing Equipment.

Compared to the MEMS sensor device explained above in connection with FIG. 3, the diaphragm region M has pressure equalization holes L1, L2, L3, L4, L5, L6 under the condition of the first specific example, and the pressure equalization The holes are disposed in the edge region of the diaphragm region M outside the heating device HE and the sensor region SB disposed above it.

The diameter of the pressure equalization holes is preferably between 1 μm and 50 μm , preferably between 1 μm and 10 μm . The pressure equalization holes L1 to L6 are preferably disposed in a region of the diaphragm region M having low mechanical stress. In addition to the pressure equalization effect, the pressure equalization hole can also improve the thermal insulation of the diaphragm region M.

2a) and 2b) are used to illustrate a schematic illustration of a micromechanical sensor device according to a second embodiment of the invention, in particular Fig. 2a) in plan view and Fig. 2b) in side view.

In the case of the second embodiment, the pressure equalization channel AK is additionally disposed in the sensor substrate MC, and the pressure equalization channel is positioned to be adhered in a state of being adhesively bonded to the carrier substrate 1 (not shown here). In the free zone of layer KL, additional pressure equalization is made possible by means of pressure equalization of the channel AK. Therefore, only four pressure equalization holes L1, L3, L4, L6 are provided in the second specific example. Depending on the configuration of the pressure equalization channel AK, it is also possible to dispense with the pressure equalization holes L1, L3, L4, L6.

Otherwise, the second specific example is equivalent to the first specific example.

In another embodiment (not illustrated), in addition or as an alternative to the pressure equalization channel AK in the sensor substrate MC, it is possible to provide a pressure equalization channel in the carrier substrate 1 below the back side cavity K.

During production of the MEMS sensor device according to the first and second embodiments, respectively, the hole may be equalized by an etching process (e.g., a dry etching process) or by a laser process.

Since the method for producing the diaphragm region M involves an exposure etching process from the back side of the wafer RS (removing the germanium layer under the diaphragm region M by means of the DRIE etching process in the exposure etching process), in the previous process It has been advantageous in the case where the pressure equalization holes L1 to L6 or L1 to L4 have been introduced into the functional layer FS and thus introduced into the diaphragm region M. During the exposure of the diaphragm region M, the pressure equalization holes are opened, and the pressure equalization between the front side and the rear side of the diaphragm region M in the latter sensor element is made possible.

Although the invention has been described based on preferred exemplary embodiments, the invention is not limited thereto. In particular, the materials and topologies mentioned are merely examples and are not limited to the examples explained.

In addition to the positions of the pressure equalization holes as illustrated in the first and second specific examples, other implementations are also contemplated, such as a different number of holes/hole shapes or trough shape embodiments or the like.

A particularly preferred application of the MEMS sensor device according to the invention is generally all sensor devices comprising a membrane and comprising a heating device, for example in addition to a chemical gas sensor, such as a metal oxide gas sensor , thermal conductivity sensor, picophone element, mass flow rate sensor, such as air mass flow measuring device, lambda probe on micromechanical diaphragm, infrared sensor device, and the like.

1‧‧‧ Carrier substrate

FS‧‧‧ functional layer

HE‧‧‧heating unit

K‧‧‧back side cavity

KL‧‧·adhesive zone

L2‧‧‧pressure equalization hole

L5‧‧‧pressure equalization hole

M‧‧‧ diaphragm area

MC‧‧‧Sensor Substrate

RS‧‧‧ back side

S‧‧‧ side wall

SB‧‧‧Sensor Zone

VS‧‧‧ front side

Claims (15)

A micromechanical sensor device comprising: a sensor substrate (MC) having a front side (VS) and a back side (RS) and a back side cavity (K); one of which is substantially closed a diaphragm region (M) formed on the front side (VS), the diaphragm region (M) being disposed above the rear side cavity (K) of the sensor substrate (MC); a sensor region (SB), It is disposed in the diaphragm region (M) or on the diaphragm region (M); and a heating device (HE) for heating the sensor region (SB), the heating device (HE) is disposed on the diaphragm In the zone (M) or on the membrane zone (M); wherein the membrane zone (M) has one or more pressure equalization holes (L1 to L6) for pressure equalization of the rear cavity (K); L1 to L4). The micromechanical sensor device of claim 1, wherein the one or more pressure equalization holes (L1 to L6; L1 to L4) are provided in varying sizes. The micromechanical sensor device of claim 1 or 2, wherein the one or more pressure equalization holes (L1 to L6; L1 to L4) are in the sensor region (SB) and the heating The device (HE) is externally disposed in one of the outer edge regions of the diaphragm region (M). A micromechanical sensor device according to claim 1, 2 or 3, wherein the side wall (S) of the rear side cavity (K) extends substantially perpendicular to the front side (VS). The micromechanical sensor device of any one of claims 1 to 4, wherein the rear side (RS) is by means of an adhesive region (KL) such that the rear side cavity (K) is The rear side (RS) is adhesively bonded to a carrier substrate (1) in a hermetic seal. The micromechanical sensor device according to any one of claims 1 to 5, wherein the rear side (RS) is adhesively bonded to a carrier substrate (1) by means of an adhesive region (KL) And wherein one of the pressure equalization channels (AK) for the pressure equalization of the back side cavity (K) in the sensor substrate (MC) is provided. The micromechanical sensor device according to any one of claims 1 to 5, wherein the rear side (RS) is adhesively bonded to a carrier substrate (1) by means of an adhesive region (KL) And wherein one of the pressure equalization channels (AK) for the pressure equalization of the back side cavity (K) in the carrier substrate (1) is provided. The micromechanical sensor device of any one of clauses 1 to 7, wherein the heating device (HE) is introduced into the diaphragm region (M), and the sensor region (SB) Provided above the heating device (HE) on the diaphragm region (M). The micromechanical sensor device of any one of claims 1 to 8, wherein the sensor region (SB) comprises a gas sensor region or a thermal conductivity sensor region or an infrared A sensor zone or a mass flow rate sensor zone. The micromechanical sensor device according to any one of claims 1 to 9, wherein the one or more pressure equalization holes (L1 to L6; L1 to L4) have a diameter of 1 μm to 50 μm. Preferably, it is from 1 μm to 10 μm, and is preferably positioned in a region of the diaphragm region (M) having low mechanical stress, and/or the pressure equalization holes are positioned in the heating device (HE) and the sensor In the district of District (SB). A method for fabricating a micromechanical sensor device, the method comprising the steps of: forming a sensor substrate (MC) having a front side (VS) and a back side (RS) and a back side cavity (K), wherein a substantially closed diaphragm region (M) is formed on the front side (VS) Upper, the diaphragm region (M) is disposed above the rear side cavity (K) of the sensor substrate (MC); forming a feeling disposed in the diaphragm region (M) or the diaphragm region (M) a detector zone (SB); forming a heating device (HE) for heating the sensor zone (SB), the heating device (HE) being disposed in the diaphragm zone (M) or on the diaphragm zone (M) Forming the diaphragm region in such a manner that the diaphragm region (M) has one or more pressure equalization holes (L1 to L6; L1 to L4) for equalizing the pressure of the rear side cavity (K) M). The method of claim 11, wherein the one or more pressure equalization holes (L1 to L6; L1 to L4) are formed by an etching process. The method of claim 11 or 12, wherein the sidewall (S) of the backside cavity (K) extends substantially perpendicular to the front side (VS) in a trench etching process The rear side cavity (K) is formed. The method of claim 12, wherein the one or more pressure equalization holes (L1 to L6; L1 to L4) are formed by a plasma etching process, a wet chemical etching process or a laser process. The method of any one of clauses 11 to 14, wherein the membrane region (M) is formed by an exposure etching process, and the film is removed under the membrane region (M) during the exposure etching process. a sacrificial layer, wherein the one or more pressure equalization holes (L1 to L6; L1 to L4) are formed by a plasma etching process, a wet chemical etching process or a laser process before performing the exposure etching process .