WO2017148715A1

WO2017148715A1 - Micromechanical sensor device and corresponding production method

Info

Publication number: WO2017148715A1
Application number: PCT/EP2017/053656
Authority: WO
Inventors: Heribert Weber; Isolde Simon; Tobias Sebastian Frey; Melissa Delheusy; Michael Knauss
Original assignee: Robert Bosch Gmbh
Priority date: 2016-02-29
Filing date: 2017-02-17
Publication date: 2017-09-08
Also published as: TWI698392B; TW201739687A; KR20180116357A; DE102016203239A1; KR102642272B1

Abstract

The invention relates to a micromechanical sensor device and to a corresponding production method. The micromechanical sensor device is equipped with a sensor substrate (MC), having a front side (VS) and a back side (RS) and a back side cavity (K); wherein a substantially closed membrane region (M) is formed on the front side (VS), which membrane region is arranged above the back side cavity (K) of the sensor substrate (MC); a sensor region (SB) arranged in or on the membrane region (M); and a heating device (HE) arranged in or on the membrane region (M) for heating the sensor region (SB); wherein the membrane region (M) has one or more pressure equalization holes (L1-L6; L1-L4) for pressure equalization of the back side cavity (K).

Description

Description title

Micromechanical sensor device and corresponding manufacturing method

The invention relates to a micromechanical sensor device and to a corresponding production method with a heating device.

State of the art

Although any micromechanical components with a heater are applicable, the present invention and its underlying problem will be explained with reference to components with gas sensors based on silicon with a heater (hotplate).

Micro hotplates are an important component for micromechanical sensors. They are used in sensor principles that provide an elevated temperature for the

Need functional principle. Gas sensors with a chemical transducer principle should be mentioned here in the first place: The desired chemical reaction does not yet take place at room temperature, but requires a certain activation energy and thus an increased operating temperature. Classic sensors of this type are e.g. Metal oxide gas sensors, which typically need to be operated between 250 ° C and 400 ° C.

In addition to chemical sensors, hotplates are also used for sensors with physical transducer principle, such as such as thermal conductivity sensors, Pirani elements (vacuum sensors) or mass flow sensors. Micro hotplates are known in the art as either closed

Membranes or via suspended membranes, as described for example in Micromachined metal oxide sensors: opportunities to improve sensor Performance, Simon Simon et al., Sensors and Actuators B 73 (2001), pp 1 - 26 described. Such sensor elements with micro hotplates according to the prior art typically have lateral dimensions of greater than 1 mm × 1 mm. To the Demands of the consumer electronics, such as existing in smartphones to meet, is currently being pursued a miniaturization of the lateral dimensions of less than ~ 1 mm x 1 mm and at the same time required a reduction in power requirements. In addition to the challenges posed by special heater designs, the area available for chip bonding is becoming smaller and smaller, and so are the challenges for production-ready assembly and connection technology.

Suspended membranes, e.g. are produced with the help of the OMM technology, have advantages in terms of "chip handling" and bonding, as chips can be glued here on the back of the entire surface and thus the possible adhesive surface is much larger than a membrane that has a wet-chemical release Closed membranes - typically they are under tensile stress - but have advantages in terms of robustness and compatibility with different coating methods, so that they despite the lower adhesive surface even in highly miniaturized

Systems continue to maintain their right to exist.

A web-suspended membrane in OMM technique has e.g. to a closed membrane in bulk micromechanics the property that the support structure in the middle is sensitive to mechanical stress such as e.g. Vibrations or shock reacts. Also, their mechanical stability with respect to certain

Coating methods, such as e.g. the time-pressure dispensing, not enough. With closed diaphragms in OMM technology it comes to manufacturing reasons

closed caverns on the wafer surface. Depending on the sealing method, pressures between atmospheric pressure and a few millibars are set here. If the closure is at atmospheric pressure, the trapped gas heats up during operation and deformation of the membrane occurs. This in turn leads to a change of resistances on the membrane and to an influence on the sensor performance. If the closure is in the millibar range, the membrane is deflected by the surrounding atmospheric pressure. However, this deflection has a negative effect on the manufacturing process, as e.g. the membrane is not located in the same focal plane as the wafer surface and thus imaging errors occur in the lithographic process. In both cases, special attention must be paid to the application process of the gas-sensitive material to mechanical

Damage to the membranes can be safely avoided. This limits the choice of possible methods for the coating. In question, therefore, only methods that mechanically burden the structure only slightly. In most cases, only thin-layer-based layers, for example by means of CVD, PCD or inkjet processes, can be deposited, an often desirable coating with a pasty or liquid material, for example by a spray method

Printing processes via time-pressure or transfer or stamping processes are ruled out.

Likewise, e.g. larger layer thicknesses with greater weight, with at webs

Suspended OMM membranes, to be regarded as critical, since damage to suspensions may occur especially in vibration.

Fig. 3 is a schematic cross-sectional view of a micromechanical

Sensor device for explaining the problem underlying the present invention.

In FIG. 3, reference numeral 1 designates a carrier substrate, for example a ceramic carrier substrate or a printed circuit board. A MEMS sensor substrate MC, which has a front side VS and a rear side RS, is glued to the carrier substrate 1 with an adhesive layer KL on its rear side RS

The MEMS sensor substrate MC has a backside cavern K which extends from the rear side RS to the front side VS. The side wall S 'of

Backside cavern K has sloping edges resulting from wet chemical etching (e.g., KOH) in the manufacturing process.

On the front side VS, a closed membrane region M, which is arranged above the rear cavern K, is formed from a functional layer FS on the front side VS of the MEMS sensor substrate MC. The functional layer FS and thus the membrane region M can be composed of a single layer, for example silicon oxide, silicon nitride or silicon carbide or of a layer sequence, for example of silicon oxide and silicon nitride layers, in or on which additional metal conductor tracks are located, which have the functions of Heater or electrodes may have. Integrated in the membrane region M is in the center of a heater HE, through which the membrane region M can be heated to a predetermined temperature. Above the heating device HE, a sensor region SB is arranged in the membrane region M, which has, for example, a metal-oxide-based thick film or metal oxide-based thin film and electrodes embedded therein, thus realizing, for example, a gas sensor device.

The adhesion of the adhesive layer KL is not circumferential (for example, punctiform or strip-shaped), d. H. does not cover the entire rear side RS, so that the gas volume inside the rear cavern K can expand during the heating operation of the heating device HE, that is, it can be created in gas exchange with the environment. This avoids that the membrane region M is subjected to constant pressure changes during sensor operation, which could cause wear of the membrane region M. Disclosure of the invention

The invention provides a micromechanical sensor device according to claim 1 and a corresponding manufacturing method according to claim 11. Preferred developments are the subject of the respective subclaims.

Advantages of the invention

The idea underlying the present invention is that the

Membrane area one or more pressure equalization holes for a pressure compensation of the back cavern.

The present invention thus makes it possible to provide a completely or essentially annular peripheral bond in the case of a miniaturized sensor substrate and to realize a sufficient gas exchange despite such an annular bond. It can thus be avoided that the sensor substrate is tilted during necessary annealing steps in the assembly and connection technique due to gas expansions and thus a subsequent Drahtbondprozess is not possible. Furthermore, the pressure changes during heating operation of the heater can be avoided or

be compensated. Further advantages are high manufacturing reliability for further processing steps. The pressure compensation holes can be dimensioned in such a way that the advantageous properties of a clamped closed membrane over a membrane suspended from webs are maintained. For a sufficient ventilation already holes in the range of a few μηη diameter.

A sturdy gluing process can be carried out despite a small adhesive surface (typical

Sensor element dimension laterally less than or equal to 1 mm x 1 mm) can be achieved. Gas exchange is of particular advantage for vacuum and thermal conductivity sensors, since the measuring principle is based on the fact that the heat dissipation of a

Heating element varies with the thermal conductivity of the surrounding gas. Without ventilation, only the gas above the membrane can contribute to the measurement, with ventilation also the gas below contributes to the measurement signal.

According to a preferred embodiment, the one or more pressure equalization holes are provided in different sizes. Thus, an optimization in terms of mechanical stability can be achieved. According to a preferred embodiment, the pressure equalization holes or the pressure compensation holes are arranged in an outer edge region of the membrane region outside the sensor region and the heating device. Thus, the pressure equalization holes do not affect the sensor function. In order to be able to ensure the highest possible mechanical stability of the membrane, the holes are ideally introduced into regions of the membrane which have a stress minimum or are located in the vicinity thereof.

According to a further preferred development, the side wall of the

Rear cavern essentially perpendicular to the front. This allows for further miniaturization.

According to a further preferred development, the rear side is by means of a

Adhesive area glued on a support substrate such that the backside cavern is hermetically sealed at the back. This increases the stability with increasing miniaturization. According to a further preferred refinement, the rear side is adhesively bonded to a carrier substrate by means of an adhesive region, wherein a pressure compensation channel is provided for pressure equalization of the rear cavern in the sensor substrate. This further improves pressure equalization without reducing stability.

According to a further preferred development, the rear side is adhesively bonded to a carrier substrate by means of an adhesive region, a pressure equalization channel being provided for pressure equalization of the rear cavern in the carrier substrate. This further improves pressure balance without reducing stability.

According to a further preferred development, the heating device is in

Membrane area introduced and provided the sensor area above the heater on the membrane area. So is granted an efficient heating function. According to a further preferred development, the sensor region comprises a gas sensor region or a heat conductivity sensor region or a

Infrared sensor area or a mass flow sensor area.

According to a further preferred development, the one or more

Pressure equalization holes have a diameter of 1 to 50 μηη, preferably 1 to 10 μηη on. This reduces the mechanical influence of the pressure equalization holes and is sufficient for the desired pressure compensation function. Preferably, the are

Pressure equalization holes in areas of the membrane area with low mechanical stress and / or are the pressure equalization holes in the area of the heater and the sensor area.

Brief description of the drawings

Further features and advantages of the present invention will be explained below with reference to embodiments with reference to the figures.

Show it:

Fig. 1 a), b) are schematic representations for explaining a micromechanical

Sensor device according to a first embodiment of the present invention

Invention, namely Fig. 1 a) in cross-section and Figure 1 b) in plan view. Fig. 2a), b) are schematic representations for explaining a micromechanical

Sensor device according to a second embodiment of the present invention, namely Fig. 2a) in plan view and Fig. 2b) in side view; and

Fig. 3 is a schematic cross-sectional view of a micromechanical

Sensor device for explaining the problem underlying the present invention. Embodiments of the invention

In the figures, like reference numerals designate the same or functionally identical

Elements. Fig. 1 a), b) are schematic representations for explaining a micromechanical sensor device according to a first embodiment of the present invention, namely Fig. 1 a) in cross section and Fig. 1 b) in plan view.

In Fig. 1 a), b) reference numeral 1 denotes a carrier substrate, for example a

Ceramic carrier substrate or a printed circuit board. A MEMS sensor substrate MC, which has a front side VS and a rear side RS, is glued to the carrier substrate 1 with an adhesive layer KL on its rear side RS. The adhesion of the adhesive layer KL is circumferential, which promotes stability with advancing miniaturization. The MEMS sensor substrate MC has a backside cavern K which extends from the rear side RS to the front side VS. The side wall S of

Backside cavern K, in contrast to the backside cavern described above with respect to FIG. 3, has vertical flanks, which originate from an anisotropic etching in the production process. This supports the miniaturization. As a result of the fact that the side wall S assumes a straight vertical shape and runs essentially perpendicular to the plane of the membrane region M or the front side VS, the smallest possible sensor device can be produced for a given size of the membrane region. A particularly preferred option for this is the application of a

Dry etching process (DRIE). On the front side VS, a closed membrane region M, which is arranged above the rear cavern K, is formed from a functional layer FS on the front side VS of the MEMS sensor substrate MC. The functional layer FS and thus the membrane region M may consist of a single layer, for example silicon oxide, silicon nitride or silicon carbide or of a layer sequence, for example

Silicon oxide and Siliziumnitridschichten be constructed, in or on the additional metal tracks are located, which may have the functions of a heater or of electrodes. Integrated in the membrane region M is in the center of a heater HE, through which the membrane region M can be heated to a predetermined temperature. Above the heating device HE, a sensor region SB is arranged in the membrane region M, which has, for example, a metal-oxide-based thick film or metal oxide-based thin film on electrode structures, in order thus

For example, to realize a gas sensor device.

In contrast to the MEMS sensor device, which was explained in connection with FIG. 3 above, the membrane region M in the first embodiment has pressure equalization holes L1, L2, L3, L4, L5, L6 which are located in the edge region of the

Membrane region M outside of the heater HE and arranged above the sensor area SB are arranged.

These pressure equalization holes preferably have a diameter between 1 and 50 μm, preferably between 1 and 10 μm. Preferably, the pressure equalization holes L1 - L6 are arranged in regions of the membrane region M, which have low mechanical stress. In addition to the pressure compensation effect, the pressure compensation holes can also improve the thermal insulation of the membrane region M.

Fig. 2a), b) are schematic representations for explaining a micromechanical sensor device according to a second embodiment of the present invention, namely Fig. 2a) in plan view and Fig. 2b) in side view.

In the second embodiment, in addition, in the sensor substrate MC

Pressure equalization channel AK provided, which is in the adhered to the carrier substrate 1 state (not shown here) in a free region of the adhesive layer KL, so that through the pressure equalization channel AK an additional pressure compensation is possible. In the second embodiment, therefore, only four pressure equalizing holes L1, L3, L4, L6 are provided. Depending on the design of the pressure compensation channel AK can also be dispensed with the pressure equalization holes L1, L3, L4, L6. Otherwise, the second embodiment is identical to the first embodiment.

In a further embodiment (not shown), in addition to or as an alternative to the pressure compensation channel AK in the sensor substrate MC, a pressure compensation channel in

Carrier substrate 1 are provided below the Rückseitenkaverne K.

In manufacturing the MEMS sensor device according to the first or second embodiment, the pressure equalizing holes may be manufactured either by an etching process, for example, a dry etching process, or by a laser process.

Since the described production method of the membrane region M is an excretion etching process from the wafer back RS, in which a silicon layer underlying the membrane region M is removed by means of a DRIE etching process, it is advantageous if in a process step before the pressure equalization holes L1 - L6 , or L1 - L4 have already been introduced into the functional layer FS and thus into the membrane region M. In the course of the exemption of the membrane area M, these are opened and a pressure equalization between the front and back of the membrane area M in the later sensor element is made possible. Although the present invention has been described in terms of preferred embodiments, it is not limited thereto. In particular, the materials and topologies mentioned are only examples and not limited to the illustrated examples.

In addition to the positions of the pressure equalization holes shown in the first and second embodiments, other embodiments are conceivable, for. B. a different number of holes / hole shapes or a slot-shaped training o.ä.

Particularly preferred applications for the MEMS sensor device according to the invention are generally all sensor devices which have a membrane and have a heating device, for example in addition to chemical gas sensors, such as metal oxide gas sensors, thermal conductivity sensors, Pirani elements, Mass flow sensors, such as air mass meters, lambda probes on micromechanical membrane, infrared sensor devices, etc.

Claims

claims

1 . A micromechanical sensor device comprising: a sensor substrate (MC) having a front surface (VS) and a back surface (RS) and a backside cavern (K); wherein on the front side (VS) a substantially closed membrane region (M) is formed, which is arranged above the rear cavern (K) of the sensor substrate (MC); a sensor region (SB) arranged in or on the membrane region (M); and a heating device (HE) arranged in or on the membrane region (M) for heating the sensor region (SB); wherein the membrane region (M) has one or more pressure equalization holes (L1 - L6; L1 - L4) for pressure compensation of the backside cavern (K).

2. A micromechanical sensor device according to claim 1, wherein the or

Pressure equalization holes (L1 - L6; L1 - L4) are provided in different sizes.

3. A micromechanical sensor device according to claim 1 or 2, wherein the or the pressure equalization holes (L1 - L6; L1 - L4) in an outer edge region of the

Membrane region (M) outside the sensor area (SB) and the heater (HE) are arranged.

4. A micromechanical sensor device according to claim 1, 2 or 3, wherein the

Side wall (S) of the rear cavern (K) is substantially perpendicular to the front (VS).

5. Micromechanical sensor device according to one of the preceding claims, wherein the back (RS) by means of an adhesive region (KL) on such a

Carrier substrate (1) is glued, that the rear cavern (K) is hermetically sealed at the back.

6. Micromechanical sensor device according to one of claims 1 to 5, wherein the back (RS) by means of an adhesive region (KL) is glued to a carrier substrate (1) and wherein a pressure compensation channel (AK) for pressure equalization of

Rear cavern (K) in the sensor substrate (MC) is provided.

7. Micromechanical sensor device according to one of claims 1 to 5, wherein the back side (RS) by means of an adhesive region (KL) on a carrier substrate (1) is glued and wherein a pressure equalization channel (AK) for pressure equalization of

Rear cavern (K) in the carrier substrate (1) is provided.

8. Micromechanical sensor device according to one of the preceding claims, wherein the heating device (HE) in the membrane region (M) is introduced and the

Sensor area (SB) above the heater (HE) on the membrane area (M) is provided.

9. Micromechanical sensor device according to one of the preceding claims, wherein the sensor region (SB) a gas sensor region or a

Wärmeleitfähigkeitssensorbereich or an infrared sensor range or a

Includes mass flow sensor area.

10. Micromechanical sensor device according to one of the preceding claims, wherein the one or more pressure equalization holes (L1 - L6; L1 - L4) have a diameter of 1 to 50 μηη, preferably 1 to 10 μηη, and preferably in areas of the membrane area (M) with low mechanical stress and / or the pressure equalization holes in the area of the heater (HE) and the sensor area (SB) are located.

1 1. Method for producing a micromechanical sensor device with the steps:

Forming a sensor substrate (MC) having a front side (VS) and a rear side (RS) and a rear side cavern (K), wherein on the front side (VS) an in

Substantially closed diaphragm region (M) is formed, which is arranged above the rear cavern (K) of the sensor substrate (MC); Forming a sensor region (SB) arranged in or on the membrane region (M);

Forming a heating device (HE) arranged in or on the membrane region (M) for heating the sensor region (SB); wherein the membrane portion (M) is formed to have one or more pressure equalizing holes (L1-L6; L1-L4) for pressure equalization of the rear cavern (K).

12. The method of claim 1 1, wherein the one or more pressure equalization holes (L1 - L6; L1

- L4) are formed by an etching process.

13. The method of claim 1 1 or 12, wherein the rear cavern (K) is formed in a Trenchatzprozess such that the side wall (S) of the Rückseitenkaverne

(K) is substantially perpendicular to the front (VS).

14. A method according to claim 12, wherein the one or more pressure equalizing holes (L1-L6; L1

L4) are formed by a plasma etching process, a wet chemical etching process or a laser process.

15. The method according to claim 1, wherein the membrane region is formed by a release set process in which a sacrificial layer located below the membrane region is removed, the pressure compensation orifice (s) (L1-L6; L4) by a plasma etching process, a wet chemical etching process or

Laser process are formed before the Exemption etching process is performed.