WO2018054470A1

WO2018054470A1 - Micromechanical component

Info

Publication number: WO2018054470A1
Application number: PCT/EP2016/072575
Authority: WO
Inventors: Markus Ulm; Johannes Classen
Original assignee: Robert Bosch Gmbh
Priority date: 2016-09-22
Filing date: 2016-09-22
Publication date: 2018-03-29

Abstract

The invention relates to a method for the production of a micromechanical component (100), comprising the steps of: - providing a MEMS wafer (10); - providing an ASIC wafer (20); - forming at least two at least partially overlapping stationary or movable structures (14,15) in the MEMS wafer (10); - joining the MEMS wafer (10) and the ASIC wafer (20); - forming electrically conductive connecting elements in the MEMS wafer (10), the connecting elements penetrating the at least two stationary or movable structures (14,15) in the MEMS wafer (10) and being formed to extend to the ASIC wafer (20); and − applying a cap wafer (30) onto the interconnected wafers (10, 20).

Description

Description title

Micromechanical component

The invention relates to a micromechanical component and to a method for producing a micromechanical component.

State of the art

Micromechanical sensors for measuring, for example, acceleration, rate of rotation, magnetic field and pressure are known and are mass-produced for various applications in the automotive and consumer sectors.

DE 10 2009 000 167 A1 discloses an inertial sensor with two micromechanical planes. This can be used to realize sensor topologies that significantly increase performance, for example with respect to a

Allow offset stability of acceleration sensors. In this case, a z-acceleration sensor is realized in which the movable mass of two micromechanical layers (first and second MEMS functional layer) is formed and in which both below and above the movable structure capacitive evaluation electrodes are arranged, namely in

Wiring layer on the substrate wafer and in the second MEMS functional layer.

With this so-called fully differential electrode arrangement on the one hand a capacitance (capacitance / area) can be increased and on the other hand also a good robustness with respect to substrate deformations (for example caused by assembly stress) can be achieved. The former aspect leads to a improved signal-to-noise ratio, the second among other things to an improved offset stability of the sensor.

Furthermore, approaches are known in which a MEMS and an evaluation ASIC wafer are joined together mechanically and electrically via wafer bonding processes, which is referred to as "vertical integration" or "hybrid integration" or "3D integration" and, for example, from US Pat 250 353 B2, US Pat. No. 7,442,570 B2, whereby sensor topologies for inertial sensors with movements perpendicular to the chip plane can be realized A movable MEMS structure is arranged on an evaluation ASIC, preferably a CMOS wafer, wherein the uppermost metal layer of the ASIC as a solid

Counter electrode acts.

An extension of the aforementioned technology provides that, in addition to evaluation electrodes in the CMOS wafer, evaluation electrodes are provided in the MEMS wafer, as is known, for example, from DE 10 2012 208 032 A1. As a result, an integration density, in this case a capacitance per area of the components can be increased, which can lead to reduced noise and / or a smaller area requirement for the components.

DE 10 2012 208 032 A1 also discloses an arrangement having two micromechanical layers, which are linked to a vertical integration process. The MEMS wafer is produced surface micromechanically and is mechanically and electrically connected to an ASIC by means of a wafer bonding process. In addition to the substrate, the MEMS wafer has three polycrystalline silicon layers (one wiring level and two micromechanical layers), which can be structured largely independently of one another. As a result, the MEMS wafer thereby comprises two micromechanical functional layers and one interconnect plane. The two micromechanical functional layers are connected to one another and form a one-piece or integral mass element. By means of through-holes (through silicon, TSV), which are formed in the ASIC wafer, an electrical connection with wiring levels of the ASIC wafer can be realized externally. DE 10 2009 029 202 A1 discloses a stacked arrangement of micromechanical components comprising a plurality of MEMS layers, in which a first MEMS structure in a functional layer and at least one further MEMS structure are arranged at least partially in at least one further functional layer. Such structures, in which also the integration view is increased, can be realized by means of a process which is known from DE 10 2009 000 167 A1.

Also known are vertically integrated components, in which two

Waferstapel be bonded together, wherein both wafer composites are formed by a MEMS wafer and a CMOS wafer, such as

For example, from DE 10 2012 206 875 A1 is known, wherein the MEMS wafer is first applied to the CMOS wafer via a wafer bonding process and thus a total of a quadruple wafer stack is formed. Even with this arrangement, an integration density of the components can be increased. The arrangement may be advantageous if the area required for MEMS functional structures and the electronic evaluation circuit are approximately equal.

DE 10 2012 208 053 A1 discloses a hybrid integrated component and a

Process for its preparation. In this case, a support is provided, in particular in the form of an ASIC, a MEMS and a cap. The MEMS device is mounted on the carrier via a standoff structure, wherein the cap is disposed over the micromechanical structure of the MEMS device.

Disclosure of the invention

It is an object of the present invention to provide an improved micromechanical device and a method of manufacturing the same.

According to a first aspect, the object is achieved with a method for producing a micromechanical device, comprising the steps:

Providing a MEMS wafer;

Providing an ASIC wafer; Forming at least two fixed or movable structures arranged one above the other at least in sections in the MEMS wafer; - connecting the MEMS wafer to the ASIC wafer;

Forming electrically conductive connection elements in the MEMS wafer, wherein the connection elements penetrate the at least two fixed or movable structures in the MEMS wafer and are formed as far as the ASIC wafer; and

Applying a cap wafer to the interconnected wafers. In this way two MEMS structures can be arranged one above the other

MEMS functional layers are provided, which are either electrically and mechanically connected to each other or only mechanically interconnected. This provides the advantageous option of selectively electrically activating the movable structures of the MEMS layers as electrodes.

According to a second aspect, the object is achieved with a

Micromechanical component, comprising:

a MEMS wafer having at least two solid or movable MEMS structures arranged one above another at least in sections, an ASIC wafer, wherein

the MEMS wafer is functionally connected to the ASIC wafer, wherein at least one electrically conductive connection element penetrating the two MEMS structures is formed as far as the ASIC wafer, the wafers being capped by means of a cap wafer.

Preferred embodiments of the method and of the micromechanical component are the subject of dependent claims. A preferred embodiment of the method provides that the formation of the electrical connection elements is carried out by means of introducing at least one layer of conductive material into contact holes.

In this way, an electrical contact within the MEMS layers can be made very variable. Another preferred embodiment of the method is characterized in that tungsten is used as the conductive material. This results in favorable material and processing properties.

Further preferred embodiment of the method provide that is formed as a contacting element for electrically contacting the micromechanical device, a wire bonding element, or that a

Through-hole is formed in the ASIC wafer. As a result, different possibilities for electrically contacting the component are advantageously provided.

A further preferred embodiment of the method provides that a bonding of the ASIC wafer to the MEMS wafer is carried out after the at least partial structuring of the MEMS wafer. As a result, advantageously, the MEMS wafer can first be completely surface micromechanically structured. This allows structuring of bonding steps

be performed separately from each other, whereby a manufacturing process can be optimized.

The invention will be described below with further features and advantages with reference to several figures in detail. In this case, all disclosed features, regardless of their relationship in the claims and regardless of their representation in the description and in the figures form the subject of the present invention. Same or functionally identical

Components have the same reference numerals. The figures are particularly intended to illustrate the principles essential to the invention and are not necessarily drawn to scale.

In the figures shows:

1 shows a conventional micromechanical sensor topology;

FIG. 2 shows another conventional micromechanical sensor topology; FIG. 3-24 results of individual process steps for producing the micromechanical component according to the invention;

Fig. 25-31 results of individual process steps of others

Embodiments of the micromechanical device according to the invention; and

32 shows a basic sequence of an embodiment of the

inventive method.

Description of embodiments

Fig. 1 shows a result of a conventional standard process for

Production of a micromechanical device 100, e.g. in the form of an inertial sensor (acceleration, angular acceleration, yaw rate sensor). In this case, a movable MEMS structure 14 is formed in a monocrystalline MEMS functional layer of a MEMS wafer. It will be appreciated that the moveable MEMS structure 14 is disposed on oxide material stand-off elements on an ASIC wafer 20. A cap wafer 30 seals the arrangement of the MEMS structure 14 on the ASIC wafer 20.

2 shows a cross section through a further conventional micromechanical component 100 with a MEMS wafer 10 and an ASIC wafer 20. Movable micromechanical MEMS structures 14, 15 are formed in the MEMS wafer 10. By means of a plated-through hole 60 with an additional rewiring in the form of a distribution layer (redistribution layer, RDL), electrical contacting of circuit elements of the ASIC wafer 20 can be realized in combination with contacting elements 50 in the form of solder balls.

The following FIGS. 3 to 25 show results of process steps for producing embodiments of the micromechanical component 10 according to the invention.

FIG. 3 shows a simplified cross section through a CMOS wafer, which represents an initial state for an ASIC wafer 20. Recognizable are one Substrate layer 21, a circuit layer 22 and a transistor layer 23. On the ASIC wafer 20, a passivation layer 24 is arranged, for example in the form of a nitride passivation.

FIG. 4 shows the cross-section of FIG. 3, wherein the passivation layer 24 has been opened or structured.

In FIG. 5 it can be seen that an oxide material 40 for spacers has been deposited on the structured passivation layer 24.

FIG. 6 shows a structuring of the oxide material 40 in the form of a formation of spacer elements which serve as contact surfaces for subsequent wafer-direct bonding.

FIG. 7 shows a cross section through a MEMS wafer 10 with a first substrate layer 11 (preferably a silicon substrate), an insulation layer 12 (preferably an oxide material) disposed thereon and one on the

Insulation layer 12 arranged second substrate layer 13 (preferably silicon substrate). The MEMS wafer 10 is thus formed in its basic structure by an SOI wafer.

FIG. 8 shows a cross section through the arrangement of FIG. 7, wherein now a first trench of the second substrate layer 13 has been carried out.

It can be seen from FIG. 9 that material of the insulating layer 12 was etched out below the structure of the second substrate layer 13 by means of a gas phase etching step.

Fig. 10 indicates that a filling of the opened access holes with a conductive material 16, preferably poly-silicon was performed. Alternatively conceivable is also a metallic backfilling, for example with tungsten. In this way, the first substrate layer 11 can be electrically conductively connected to the second substrate layer 13 in a locally limited manner. FIG. 1 1 indicates that a smooth surface of the second substrate layer 13 is provided for a subsequent wafer bonding by means of a CMP process step (English: chemical mechanical polishing). From the cross-sectional view of FIG. 12, it can be seen that a second trench of the second substrate layer 13 has been implemented, whereby a structure in the first substrate layer 13 has been realized.

FIG. 13 shows a cross section of the MEMS wafer 10 after a second gas phase etching step of the insulation layer 12, whereby the insulation layer 12 has been locally released. The second gas phase etching step is preferably timed.

FIG. 14 shows the MEMS wafer 10 of FIG. 13 rotated by 180 ° before a wafer bonding with the ASIC wafer 20.

FIG. 15 shows a result of wafer bonding of the MEMS wafer 10 to the ASIC wafer 20, preferably in the form of a plasma-activated direct bonding process.

FIG. 16 shows a result of loopback and possibly a CMP step of the first substrate layer 11 to target thickness, preferably to about 5 μm to about 100 μm. FIG. 17 shows a result of a first trenching of the first substrate layer 11 for applying contact holes 17 in the first substrate layer 11.

It can be seen from the cross-sectional view of FIG. 18 that the contact holes 17 have been filled with an electrically conductive material 18, preferably with tungsten. The filling of the contact holes 17 can, as shown in Fig. 18, completely done. Alternatively, only side walls of the contact holes 17 can be covered with the conductive material 18 (not shown). FIG. 19 shows a patterning of the conductive material 18, as a result of which electrically conductive connections ("conductive posts") through the two

Substrate layers 1 1, 13 and an electrically conductive connection to structures of the ASIC wafer 20 are provided.

FIG. 20 shows a cross-section through the arrangement of FIG. 19 after trenching of the first substrate layer 11 for a final definition and release of the MEMS structures 14, 15. In this case, also accessible partial regions of the second substrate layer 13 are trimmed.

Fig. 21 indicates that MEMS regions are made movable. In particular, the figure serves to illustrate that, similar to FIG. 2, movable MEMS structures 14, 15 with a fully differential electrode arrangement, with an upper fixed electrode in the first substrate layer 11 and a lower fixed electrode in an uppermost metallization plane of the ASIC Wafers 20 can be realized.

FIG. 22 shows a finished micromechanical component 100, wherein a bonding of a cap wafer 30 to the ASIC wafer 20 is performed. Subsequently, the cap wafer 30 is opened in a bonding pad area and a wire bonding to an external contacting of the micromechanical

Device 100 performed. Visible is an external contacting element 50 in the form of a bonding wire.

FIG. 23 shows an alternative form of a micromechanical device 100, in which case the cap wafer 30 is bonded to the MEMS wafer 10.

Fig. 24 shows a further embodiment of the micromechanical

Component 100 with an alternative external electrical contacting by means of plated-through holes 60 in ASIC wafer 20. Also conceivable (not shown) is external electrical contacting via plated-through holes 60 in cap wafer 30. In this case, by means of plated-through holes 60 with additional redistribution in the form of a distribution plane (FIG. Engl, redistribution layer, RDL) together with contacting elements 50 in the form of solder balls an electrical contacting of circuit elements of the ASIC wafer 20 can be realized.

FIGS. 25 to 31 show an alternative realization of the MEMS wafer 10, in which a surface micromechanical process is carried out for its production. The starting point is a first substrate layer 11, to which an insulation layer 12, preferably an oxide layer, is preferably applied via thermal oxidation. In this case, standard methods of surface micromechanics are used, which methods are simpler and less expensive due to the lower price of the raw material. The grown second micromechanical layer is predominantly polycrystalline in this case.

The layer thickness ratios of the first and second substrate layers 11, 13 shown in the figures are to be regarded as exemplary only. With the proposed method, without fundamental changes in the process flow, both layer thicknesses may be the same or the second layer thicker than the first layer. Fig. 26 shows an opened insulation layer 12 for forming contact holes.

Fig. 27 shows a deposition of a second substrate layer 13 on the

Insulation layer 12, either as polycrystalline silicon or epitaxial growth (with a polycrystalline starting layer on the

Oxide layer 12, not shown). In the region of the contact hole, a strong topography of the surface of the second substrate layer 13 is formed. This can optionally be minimized by means of a multiplicity of small contact holes, in which a trench width is smaller than the layer thickness of the second substrate layer 13.

Fig. 28 shows a result of a CMP step of the second substrate layer 13 for preparation of a subsequent wafer bonding. The state of the MEMS wafer 10 now substantially corresponds to that of FIG. 11, but here large areas of the second substrate layer 13 are polycrystalline educated. The further process sequence proceeds analogously to FIGS. 12 to 22.

FIG. 29 shows a process stage similar to FIG. 20, ie after the second trenching of the first substrate layer 13, in which case the conductive material 18 is structured differently than in the arrangement of FIG. 20. In this case, a completely different design of the micromechanical device 100 is realized, namely a capacitive pressure sensor with fully differential

Electrode assembly.

FIG. 30 shows that, in addition to the process steps of FIGS. 3 to 20, a gas phase etching step with gaseous HF (hydrogen fluoride) is also carried out. As a result, a pressure sensor membrane realized in the second substrate layer 13 and a solid detection electrode arranged above it and realized in the first substrate layer 11 are simultaneously realized. In addition, the uppermost metal layer of the ASIC wafer 20 may be used as a counter electrode so that a differential evaluation of the movement of the pressure sensor membrane becomes possible. Preferably, the distances of the membrane to the upper and lower electrodes are identical (not shown in FIG. 30).

It can also be seen from FIG. 30 that a "stamp" made of conductive material 18 is made electrically conductive with that in the second substrate layer 13

Pressure sensor diaphragm is formed.

Fig. 31 shows qualitatively a state of the pressure sensor membrane in the deflected state.

FIG. 32 shows a basic sequence of a method for producing a micromechanical component 100.

In a step 200, a MEMS wafer 10 is provided.

In step 210, an ASIC wafer 20 is provided. In a step 220, formation of at least two fixed or movable structures 14, 15, which are arranged one above the other at least in sections, is carried out in the MEMS wafer 10.

In a step 230, a connection of the MEMS wafer 10 to the ASIC wafer 20 is performed.

In a step 240, formation of electrically conductive

Connecting elements performed in the MEMS wafer 10, wherein the

Connecting elements which penetrate at least two fixed or movable structures 14,15 in the MEMS wafer 10 and are formed up to the ASIC wafer 20.

Finally, in a step 250, a cap wafer 30 is applied to the interconnected wafers 10, 20.

In summary, the present invention proposes a micromechanical component and a method for its production. The micromechanical component can be used particularly advantageously in order to realize fully differential capacitive electrode arrangements for MEMS elements that can be deflected perpendicular to the chip plane. In this case, a fixed bottom electrode is formed by the (preferred) uppermost metal level of the ASIC wafer 20, wherein a solid top electrode is formed in the first substrate layer 11. The movable electrode then lies between the bottom and top electrodes and is formed from regions of the second substrate layer.

Advantageously, the MEMS layers can be formed from monocrystalline material using an SOI wafer. As a result, smaller intrinsic stresses are possible, with inhomogeneities in the crystal structure of polycrystalline silicon can lead to intrinsic stresses. This can disadvantageously be noticeable, for example, in slight forward deflections of the sensor structures that are the case in acceleration sensors

lead to unwanted offset signals. The layer thicknesses of the MEMS structures are easily scalable, whereby the thicknesses of the first and second substrate layer can be increased more easily than in the case of surface micromechanical methods.

It is also easy to represent movable MEMS structures with mechanically connected, but electrically separated areas, which is feasible only with increased effort in a surface micromechanical approach. This option may be advantageous to reduce the crosstalk between functional elements of a sensor (eg drive and detection circuit of a rotation rate sensor), or to use so-called fully differential evaluation methods for acceleration sensors, in which a common sensor mass is divided into two electrically separate segments, which are counteracted by an ASIC and evaluated differentially. Parasitic signals, for example due to EMV or PSSR disturbances (Engl., Power supply rejection ratio), which have a common-mode effect, can thus be effectively suppressed.

Particularly advantageous is the micromechanical device for a

micromechanical inertial sensor, e.g. usable for an acceleration sensor and / or a rotation rate sensor.

Although the invention has been described above with reference to concrete application examples, the person skilled in the art can realize previously not or only partially disclosed embodiments, without departing from the essence of

Deviate from the invention.

Claims

claims

1 . A method of manufacturing a micromechanical device (100), comprising the steps of:

- providing a MEMS wafer (10);

- providing an ASIC wafer (20);

Forming at least two fixed or movable structures (14, 15, 15) arranged one above another at least in sections in the MEMS wafer (10);

- connecting the MEMS wafer (10) to the ASIC wafer (20);

Forming electrically conductive connection elements in the MEMS wafer (10), wherein the connection elements penetrate the at least two fixed or movable structures (14, 15) in the MEMS wafer (10) and are formed as far as the ASIC wafer (20); and

Applying a cap wafer (30) to the interconnected wafers (10, 20).

2. The method of claim 1, wherein forming the electrical

Connecting elements by means of introducing at least one layer of conductive material (18) in contact holes (17) is performed.

3. The method of claim 2, wherein tungsten is used as the conductive material.

4. The method according to any one of the preceding claims, wherein as a

Contacting element (50) for electrically contacting the

micromechanical device (100) a wire bonding element is formed.

5. The method according to any one of claims 1 to 3, wherein for electrically contacting the micromechanical device (100) a

Via (60) is formed in the ASIC wafer (20).

6. The method according to any one of the preceding claims, wherein a bonding of the ASIC wafer (20) with the MEMS wafer (10) after the at least partial structuring of the MEMS wafer (10) is performed.

7. The method according to any one of the preceding claims, wherein the base material for the MEMS wafer (10) is an arrangement of a first

Substrate layer (1 1), one on the first substrate layer (1 1) arranged insulating layer (12) and one on the insulating layer (12) arranged second substrate layer (13) is used.

8. A micromechanical device (100), comprising:

a MEMS wafer (10) having at least two fixed or movable MEMS structures (14, 15) arranged one above the other at least in sections,

- An ASIC wafer (20), wherein

- The MEMS wafer (10) is operatively connected to the ASIC wafer (20), wherein at least one of the two MEMS structures (14,15)

penetrating electrically conductive connecting element to the ASIC wafer (20) is formed, wherein the wafer (10,20) by means of a

Cap wafer (30) are capped.

9. micromechanical device (100) according to claim 8, characterized

characterized in that at least one structure (14) of the MEMS wafer (10) consists of monocrystalline silicon.

10. Micromechanical component (100) according to claim 8 or 9, characterized in that the two MEMS structures (14, 15) are electrically conductively connected to each other or electrically isolated from each other.

1 1. Micromechanical component (100) according to one of claims 8 to 10, characterized in that a contacting element (50) for electrically contacting the component (100) on the ASIC wafer (20). is formed and / or has a via (60) of the ASIC wafer (20).

12. A micromechanical component (100) according to any one of claims 8 to 1 1, characterized in that the micromechanical device (100) a

Inertialsensor or a pressure sensor or a combination of inertial and pressure sensor is.