DE102004058880A1 - Integrated microsensor and method of manufacture - Google Patents

Abstract

It is proposed to form a microsensor on a substrate as a micro-electro-mechanical system (MEMS) with sensor function. For this purpose, at least the uppermost layer on the substrate (SUB) of the micro-electro-mechanical system is set in an electrically conductive manner and connected to electrical contacts of a carrier plate (TP) with the aid of an electrically conductive wafer bonding compound (WBC). An integrated circuit (IC) for processing the sensor signals can be integrated in the carrier plate.

Description

The The invention relates to a microsensor according to the preamble of the claim 1.

Such a microsensor is for example off DE 100 27 234 A1 known. Here, a microsensor is described with a circuit integrated in a carrier plate and a micromechanical sensor element mounted thereon. The sensor element is mechanically and electrically connected by a circumferential solder seam to the integrated circuit.

It are also microsensors known by means of bonding wire connections with the contacts of a carrier plate are connected. However, this creates a high production cost and requires a packaging, in which also or the bonding wires with protected or at least taken into account Need to become. This concludes the availability of particularly cost-effective packaging methods out.

at a direct solder joint between sensor element and carrier plate There is a risk that the connection is under the influence deformed mechanical stresses. Also an aging of the solder joint can lead to a change of position Lead sensor element relative to the integrated circuit, so that electrical properties of the sensor can change. These Danger is caused by a temperature increase, as for example when soldering of the microsensor can occur on a printed circuit board, clearly elevated.

moreover requires the manufacture of a plurality of microsensors with solder joints in the Waferverbund a high technical effort, as many solder surfaces simultaneously with high precision soldered together Need to become.

It For example, microsensors are known for measuring moments of inertia or inertial forces, such as in the automotive industry as acceleration sensors for navigation and security systems are used. For this have been wire bonding techniques or connections used in flip chip technology.

Of the Invention is based on the object, a microsensor of the above mentioned type with an improved connection between a sensor element and the contacts on the carrier plate create. Preferably, the microsensor is to be manufactured in the wafer composite can be.

These The object is achieved by a microsensor having the features of claim 1 solved. advantageous Further developments of the invention and a method for producing the microsensor are the subject of further claims.

The The invention provides a microsensor in which, in a substrate, that on the surface has a crystalline silicon layer, a microelectromechanical System, a so-called MEMS device is designed with sensor function. The microsensor is also on a carrier plate arranged and fixed, which has electrical contacts. The Silicon layer is set electrically conductive and with the electrical conductive contacts connected to a wafer bond, which is the electrical and mechanical Represent connection between sensor and carrier plate.

Of the inventive structure of the microsensor thus includes an integrated contact, the solely by structuring the silicon layer and its electrical Connection to the carrier plate by means Waferbondens is realized. That means no extra Effort for making electrical contacts of the sensor with the outside world is required. The sensor therefore has no sensitive bonding wires, which would require special protection in the packaging of the component. As well has the sensor according to the invention no solder joints on, which are also mechanically and thermally sensitive and affect the function of the sensor can. The contacts having carrier plate can provide electrical interconnections and functions. It is also integrated and can be manufactured independently of the sensor.

Of the Microsensor according to the invention As mentioned, has a MEMS structure on, thus has electrical and mechanical functions and is in particular produced by microstructuring techniques. The electrical and mechanical components of a MEMS sector can by Working out of a compact substrate and in particular from Silicon are produced. Is possible it too, the ingredients over to produce a structured layer structure, the processes layer deposition, Structuring and optionally extracting low lying "trapped" sacrificial layers can.

The MEMS sensor may include freely movable or even only flexible parts which are fixed on at least one end but can fulfill a mechanical function with another end or a surface area and are therefore at least partially movable. A MEMS sensor has a sensor function, wherein preferably the capacitance of the sensor is changed by the movement of the movable sensor part and that of the measured variable-dependent measurement signal supplies.

One such sensor may be for example an acceleration sensor, the one opposite the Slow down acceleration Part has, for example, a bending beam. Another preferred application, a sensor according to the invention as a rotation rate sensor find that uses the effect of the Coriolis force. The sensor can also be a Magnetic sensor and in particular a Hall sensor be sensitive across from the angle of incidence and the strength of a magnetic field. Possible It is also a MEMS sensor form as a pressure sensor or as chemical sensor that over chemical-physical interaction is a mechanical change generated at the sensor, which in turn read out as an electrical measurement signal can be.

The Substrate on which or in which the MEMS sensor system is formed is, has at least one mechanical carrier function, and exists therefore of a mechanically stable, solid and in particular structurable Material. The substrate provides the basic material for the construction of the sensor system available and therefore comprises at least partially electrically conductive layers or layer areas. The substrate may be a unitary material be. The microsensor can also be structured out of a layer structure which comprises at least two layers or by wafer bonding at least two wafers that are processed separately can, is composed. Possible it is also the substrate by a combination of said methods or to use such a substrate for the MEMS system. Preferably, the substrate is a silicon wafer, or an SOI substrate (Silicon on insulator) or any other layer structure on a mechanically stable carrier substrate. Advantageously, a substrate is used, which is a monocrystalline silicon layer which preferably has a defined thickness and over one Layer of a dielectric is arranged. Such substrates can by Wafer bonding, wherein a first wafer with the dielectric layer is connected to a silicon wafer. Especially stress-free is a construction in which both wafers are made of crystalline silicon (SOI wafer).

Under Waferbond compound according to the invention all compounds understood performed at the wafer level can be. Preferably, the wafer bonding compounds include those in which a mechanically stable structure arises between the surfaces to be joined, in particular by reaction of the interfaces. The invention is limited on electrically conductive Wafer bond compounds used for the sensor supplied by the measurement signal are permeable, or the Measurement signal oppose not too high electrical resistance. Well suited as wafer bonding compounds are for example eutectic compounds, which are produced by eutectic wafer bonding. It will be two layers of material are brought into contact with each other, which together a homogeneous phase with a lower melting point than the starting materials form. Eutectic wafer bonding compounds can be relatively moderate Temperatures of less than 400 degrees are produced. You create both mechanically and thermally stable compounds and are electrically conductive. Waferbond compounds can also be virtually stress-free be generated.

preferred Eutectic is silicon-gold eutectic, which has a melting point of about 363 degrees Celsius and at maximum temperatures up to 410 degrees Celsius are formed under appropriate contact pressure can. It has the necessary electric conductivity is mechanically strong and thermally stable.

Is possible However, it also, other eutectic use, especially those with silicon. For example, silver-silicon and silicon-aluminum eutectic are known.

In A preferred embodiment of the invention is the silicon layer the substrate is structured so that they have a micro-electro-mechanical system enclosing and thus forms a closed framework. This silicon frame is with an appropriately trained, also frame-shaped closed Wafer bond with the backing plate connected so that a gas-tight closure of the microelectromechanical System arises. This has the advantage of being integrated in this way and without procedural overhead and without additional costs a gas- and moisture-proof encapsulation of the microsensor be performed can. The wafer bonding provides protection to the MEMS system Environmental influences, in particular Protection against mechanical or chemical action, moisture or too fast a change in these environmental conditions. Due to the secure encapsulation is a stable electrical and ensures mechanical function of the sensor, whereby the aging stability is increased. By including an atmosphere fixed composition, the sensor function is stabilized.

It is also possible to include a vacuum inside the silicon frame to obtain a microsensor with further improved electrical and mechanical functions. A vacuum-operated MEMS system has no interference with an enclosed atmosphere, which in particular leads to noise of the sensor signal due to Brownian motion can. In this way, the sensor sensitivity is improved.

The support plate has electrical contacts, including an electrical connection is made with the electrically active parts of the MEMS system. About that In addition, the carrier plate contacts on, to the outside connection serve the microsensor. Between the contacts and the external connection An integrated circuit can be arranged.

Preferably is the carrier plate however, formed as an IC device, in particular as a CMOS device. This IC device can have different functions, for example, the sensor with the necessary Tension or the necessary Supply electricity. The IC device can drive the sensor, especially at certain time intervals or even permanently pick up the sensor signal. In the IC component can also be supplied by the sensor Measuring signals are processed and usable output signals be implemented. Possible it is, for example, from the measurement signal, a voltage as an output signal to generate. Furthermore, the IC device may include an amplifier, which amplifies the possibly weak measuring signal of the sensor. Also Is it possible, an optionally non-linear dependence of the sensor supplied Measuring signal from the size to be measured in a linear output signal implement, so that a linear dependence of the output signal is obtained from the physical quantity to be measured. Furthermore can be incorporated in the IC device, a logic circuit, the additional control functions in dependence from the supplied output signal triggers or makes.

in the IC device or in the integrated circuit, which is in the carrier plate integrated, can Furthermore built with the sensor interacting electrical structures be. For example, it is possible to provide in the integrated circuit an electrode, which in capacitive interaction occurs with a sensor component and so that is part of the sensor system. This capacitive electrode For example, with a movable sensor component, for Example of a bending beam in an inertial sensor one of a Acceleration dependent measure capacitive change.

in the Below, the invention will be explained in more detail with reference to embodiments and associated figures. The Figures are merely illustrative of the invention and are therefore leads only schematically and not true to scale. Same or equivalent parts are designated by the same reference numerals.

1 shows a known sensor arrangement in schematic cross section,

2 shows a sensor according to the invention in a schematic cross section,

3 shows the sensor fragmentary in schematic cross-section before producing the wafer bonding compound,

4 shows a section of a wafer bond in schematic cross section.

1 shows a known sensor arrangement with a microsensor. In this case, a microsensor MS, which is arranged as a MEMS system on a substrate SUB and the IC component IC separate components, which are electrically connected to one another via a bonding wire BW. The arrangement in turn is connected to a leadframe LF, which is part of a housing in which the sensor arrangement is tightly encapsulated against environmental influences. The microsensor MS is, for example, an inertial sensor which receives accelerations along a main axis (indicated by the double arrow) and generates a sensor signal which is passed to the IC component IC where it is processed and / or evaluated.

2 shows a microsensor according to the invention, which may be similar in terms of the micromechanical system and have the same function as a known and eg in 1 illustrated microsensor. The sensor components are indicated only schematically and comprise in the present case, in which the microsensor is designed as an inertial sensor, at least one sensor tongue ST which is attached at one end, while the other end due to the flexibility of the material used and its inertia when acting on an acceleration, performs a deflection, for example, in the plane of the double arrows drawn or even vertically thereto. Furthermore, the sensor comprises vertical connection structures VS1 and VS2, which consist of electrically conductive material, and via which the electrical connection of the sensor takes place. Further, in the figure, a sealing frame SF is shown, which encloses the MEMS system as a ring-shaped closed.

All parts of the sensor plane SE are preferably formed of the same material, in particular of conductively adjusted and therefore correspondingly doped silicon. In preferably capacitive sensors are not too high demands on the conductivity of the silicon in order to guarantee a good functioning of the sensor. For example, a conductivity of approx. 1 ohm centimeter is sufficient.

This Silicon forms the surface a substrate SUB. Preferably, the substrate comprises a carrier substrate, which on the surface an insulator layer IS, on which an epitaxial silicon layer in a desired Thickness is applied. The insulator layer can be used as etch stop layer for structuring the components of the sensor plane SE from the bottom serve. Part of the structures of the sensor plane SE can also be used by the back be structured forth, so from the side facing the substrate SUB the sensor level. For this purpose, the substrate in a conventional manner open and the structures exposed or structuring Processing be generated. In the present case, the structure designed so that it by structuring in a conventional manner from the front (in the figure, the bottom) made can be.

From The structures of the sensor plane are at least the undersides the sealing frame SF and the vertical connection structures VS in a plane, allowing a simple connection of these structures with the carrier plate TP possible by wafer bonding is. By contrast, the sensor tongue ST is at a distance both from the substrate SUB as well as to the carrier plate arranged to ensure freedom of movement. The distance can also by depressions in carrier plate guaranteed become.

The support plate TP is made of a mechanically stable material with bonding structures on its surface are arranged. Part of the bond structures is connected to electrical Conductors LB in contact with the surface or in the carrier plate TP integrated run and as electrical contacts EK the electrical Enable connection of the microsensor. These bonding structures are the parts intended for connection the sensor plane SE, in particular the lower sides of the sealing cream SF and the vertical connection structures VS set up and means connected to a wafer bonding process. Through the wafer bonding process be electrically conductive connections between the vertical Connection structures VS and the tracks LB generated.

Next the conductor tracks LB may be the carrier plate TP still comprise at least one integrated circuit. The electric Connection of the sensor element with the outside world via another electrical contact AK, for example, also on the surface of the support plate is arranged in addition to the sensor arrangement and with the conductor track LB is in electrical connection.

Preferably are at least two electrical connections for the sensor element and accordingly also for the carrier plate intended. about further connections For example, the power supply, for example, the admission done with a predetermined operating voltage.

The support plate TP may also be an IC device on the surface of which corresponding bond structures for connection to the elements of Sensor level SE are applied. The wafer bonding connections to the gasket frame Although SF are also electrically conductive, but usually have no connection to the tracks LB and thus to possible integrated circuits within the carrier plate TP. The sealing frame but can can also be used for shielding and are then at substrate potential.

The Vertical interconnect structures VS1, VS2 may be of limited cross-section be and have any cross-sectional shape. Preferably is the cross section in dependence from the conductivity of the material of the sensor plane SE sufficient to the sensor signal safe to the IC or generally to the interconnection of the carrier plate TP guide.

Of the On the other hand, sealing frame SF circulates the entire area of the sensor plane and encloses the micro-electromechanical System. It concludes the sealing frame SF not only with the carrier plate TP but also with the substrate SUB circumferentially tight, so enclosed within the sealing frame between substrate SUB and carrier plate TP creates a sealed cavity, for example, a vacuum maintains. The interface for example, exists between the sealing frame SF and the substrate SUB in its uppermost insulating layer IS, applied over the entire surface or structured according to the sensor level SE no.

3 shows the arrangement shortly before the preparation of the wafer bonding compound on the basis of a section in schematic cross section. The carrier plate TP comprises at least one isolation region IG, which consists of a dielectric, and in which at least one conductor track LB and optionally an integrated circuit IC is embedded. The insulated region IG can be applied to a baseplate GP or represent the cover layer of an integrated semiconductor component. On the surface of the support plate TP structures HS, KS, MS are pre-formed, which are seen for electrical and mechanical connection with the parts of the MEMS structure before. These comprise at least one metal layer MS. Between the surface of the support plate TP or the insulating region IG and In the case of the metal layer MS, additional auxiliary layers such as an adhesion layer HS and a contact layer KS can be provided. For example, an adhesion layer of titanium and a contact layer of copper are well suited. The metal layer consists of the metal which is to form the later eutectic compound with silicon, in particular of gold. The bonding structure, which is provided for connection to the vertical connection structures VS, is connected to the conductor LB via a through-connection DK, for example, and represents the electrical contact EK.

The Sensor level SE of the micro-electro-mechanical system is, for example formed of electrically conductive adjusted monocrystalline silicon. Between substrate and silicon layer is still an insulation layer arranged from a dielectric.

On the underside of the provided for connection to the carrier plate parts of the silicon layer, in particular the sealing frame SF and the vertical connection structures VS a polysilicon layer SS is applied. Between polysilicon layer SS and silicon layer may still be arranged a dielectric layer DS. This defines the amount of silicon intended for the formation of the eutectic and achieves the formation of the eutectic exclusively in the desired plane. In the dielectric layer DS on the underside of the vertical connection structures, an opening is provided which forms at least one electrical connection between polysilicon layer SS and silicon layer. In addition, all structures of the sensor level SE as in 2 to 4 shown on its underside have a stage STU. This is structured, for example, together with the freely movable sensor tongue ST. This makes it possible to set the distance between the bonding structures or the elec- trically conductive Waferbondverbindungen each other to an appropriate value.

The Thickness of the polysilicon layer SS and the metal layer MS are so coordinated, that the corresponding volume ranges the mass fraction revealed that the respective material has in the later eutectic. For example, to make a gold-silicon eutectic (with the same area) a layer thickness ratio Gold to polysilicon of 100 to 52 advantageous, which in the eutectic corresponds to a weight fraction of 94 percent gold.

to Production of the eutectic and thus the Waferbondverbindung is the substrate with the MEMS sensor assembly fits the contact structures on the carrier plate TP attached. Under a contact pressure and increasing the Temperature at the formation temperature of the eutectic (390 degrees Celsius for Gold-silicon eutectic), the metal of the metal layer reacts with the polysilicon to form a eutectic.

4 shows the arrangement with ready made Wafferbondverbindung WBC. While the wafer-bonding compound is seated in the region of the sealing frame SF or its adhesive and contact layer on the insulating region IG, in the region of the in 4 illustrated vertical connection structure VS an electrically conductive contact via the silicon of the connection structure VS, the wafer bonding WBC and the adhesive and contact layer HS, KS made to the feedthrough DK, wherein the electrical connection of the micro-electro-mechanical sensor element to the support plate and thus via the external terminals AK is guaranteed to the outside world.

The Invention was based on the embodiments explained only by way of example, but of course not limited to this. In particular, the type and exact configuration of the sensor element, or its micromechanical part is not relevant to the invention, so that the invention also encompasses other sensor types. The invention is also not limited to the eutectic wafer bonding compound and can be replaced by other electrically conductive wafer bonding compounds become. The sealing frame SF is not a mandatory component the invention, however, an advantageous embodiment.

Also the exact configuration of the substrate and the carrier plate are variable and not central to the invention. Not either limited is the choice of materials for the sensor level SE, which is not must consist of uniform material, but by generation a suitable layer structure also other materials and in particular Insulators may include. This can be especially in conjunction with Other sensor types may be required or advantageous.

MS

microsensor

MEMS

Microelectromechanical system

SUB

substratum

BW

bonding wire

LF

leadframe

IC

integrated circuit

SF

sealing frame

ST

sensor tongue

WBC

Wafer bond

LB

conductor path

TP

support plate

VS

vertical connecting structure

SE

sensor level

HS

adhesive layer

KS

contact layer

IG

insulating region

DK

via

IS

insulating

SS

silicon layer

MS

metal layer

DS

dielectric layer

GP

baseplate

AK

electrical external connection

EK

electrical Contact

Claims (13)

Microsensor having a microelectromechanical system, comprising - a substrate (SUB) having on the surface a crystalline silicon layer in which the microelectromechanical system (MEMS) is formed, having a carrier plate (TP) having electrical contacts (EK), on which the microsensor is arranged, - with an electrical connection (WBC) between the electromechanical system and the contacts, characterized in that - the silicon layer is set electrically conductive and connected to the carrier plate via a wafer bond (WBC), and - Wafer bond represents the said electrical connection between the electromechanical system and the contacts. A microsensor according to claim 1, wherein the wafer bonding compound (WBC) includes a eutectic. Microsensor according to claim 1 or 2, wherein the substrate (SUB) formed with the silicon layer of an SOI substrate is. Microsensor according to one of claims 1 to 3, wherein the micro-electromechanical System (MEMS) as inertial sensor is trained. Microsensor according to one of claims 1 to 4, wherein in the Silicon layer a microelectromechanical system (MEMS) enclosing frame (SF) is formed, with a corresponding frame-shaped closed ge Wafer bond (WBC) with the support plate (TP) so connected is that a gas-tight closure of the system is formed. Microsensor according to one of claims 1 to 5, wherein the carrier plate (TP) comprises an integrated circuit. Microsensor according to claim 6, wherein the carrier plate (TP) is an IC device that has an integrated circuit (IC) for operation of the sensor. Microsensor according to one of claims 5 to 7, wherein the micro-electromechanical System (MEMS) in a between support plate (TP), silicon layer and substrate (SUB) formed, gas-tight cavity is arranged, is maintained in the vacuum. A microsensor according to any one of claims 1 to 8, wherein the wafer bonding compound (WBC) a gold-silicon eutectic is. Method of making an integrated microsensor with the steps - on a substrate (SUB) becomes an electrically conductive crystalline silicon layer intended, - in the silicon layer becomes micro-electromechanical through microstructuring System (MEMS) designed with a sensor function, - in the Microstructuring becomes vertical connection structures (VS) formed with electrically functional components of the Systems are connected, - it becomes a carrier plate (TP) into which an electrical connection (LB, IC, DK) is integrated, arranged on the surface bondable contact surfaces are, - the Substrate (SUB) is coated with the silicon layer using a wafer bonding process on the carrier plate (TP) Bonded, using a bonding method is used, with an electric conductive connection between the connection structures (VS) and the corresponding contact surfaces made on the carrier plate becomes. Method according to claim 10, - in which the crystalline silicon layer by Waferbonden on an insulating surface the substrate (SUB) is applied, - In which the silicon layer is structured so that the micro-electromechanical system (MEMS) enclosing Frame (SF) is formed, During the wafer bonding process also the frame over its entire circumference is connected to the carrier plate (TP). Method according to claim 10 or 11, - in which on all for the Waferbondverbindung (WBC) provided areas of the support plate (TP) a gold layer is applied, which is in electrical and pure structured mechanical connection points, - in which while the wafer bonding process and under contact pressure and elevated temperature a eutectic of the gold layer and surface areas of the silicon layer is trained. A method according to claim 11 or 12, wherein the bonding of silicon layer and carrier plate (TP) a gas-tight closed cavity is formed, in which the micro-electromechanical System (MEMS) is arranged and wherein the bonding process under vacuum is carried out, so that a vacuum remains in the cavity.