FR2738705A1 - ELECTROMECHANICAL SENSOR DEVICE AND METHOD FOR MANUFACTURING SUCH A DEVICE - Google Patents

Abstract

The electromechanical sensor device comprises an electrical connection plate (10) carrying electrical interconnection tracks and an active plate (12). In the active wafer is cut a mechanical sensor comprising a metallized level (30) of interconnection. The tracks and the metallized level are then secured by punctual contact balls and possibly a bead of an electrically conductive solder material. Such a device can constitute a gyrometer or an accelerometer.

Description

ELECTROMECHANICAL SENSOR DEVICE AND METHOD

FOR MANUFACTURING SUCH A DEVICE

  The present invention relates to measuring devices

  including an electromechanical sensor, generally mini-

  ture, cut from a wafer provided with interconnection tracks

  electrical connection intended to convey the intervention signals

  in measure. It is applicable to devices for measuring physical parameters capable of creating stresses or deformations of an active part of the

  sensor. Mention may in particular be made of pressure devices

  sion, acceleration and rotational speed, such as

those used on vehicles.

  There are already known sensor devices comprising on the one hand an active plate in which is cut a mechanical sensor and on the other hand on which are deposited interconnection tracks and a plate carrying electrical connections and connection pads with the exterior, which can be described as "passive". The electrical connections between the wafers and the joining of the wafers to each other (in particular when the space between the wafers must be sealed) are produced during separate operations, by techniques which give rise to

at a high scrap rate.

  The present invention aims to provide a device

  miniaturizable sensor, responding better than those previous-

  known to the requirements of the practice, in particular in that it is achievable in a simple manner and with yields

high manufacturing.

  To this end, the invention proposes in particular an electromechanical sensor device comprising: - an electrical connection plate carrying electrical interconnection tracks, - an active plate, in which the mechanical sensor is cut, comprising an interconnection level by making facing the electrical connection plate, and - means for electrical connection and securing the two plates, comprising punctual contact balls and, if necessary, a cord surrounding the mechanical sensor and the balls, the balls and the cord being in one

  electrically conductive solder material.

  In general, the electrical interconnection tracks of the electrical connection plate comprise, on a substrate, a first interconnection level forming output pads and a second interconnection level separated from the first by a dielectric interlayer. The first interconnection level can thus be separated from the cord by the dielectric interlayer and makes it possible to form the output pads on a part of the electrical connection plate.

  protruding from the active wafer.

  Often, the cord will be provided to form a sealing barrier between a volume containing the mechanical sensor itself and the outside. In other cases, such as that of a pressure measuring device, a passage will be made on the contrary in the bead or one of the plates. The sensor device can be completed by a protective cover against the external environment, attached to the

  active board, for example using an adhesive.

  The electrical connection substrate can be made of various materials, for example monocrystalline silicon,

  ceramic, glass resistant to building temperature

  tution of the means of solidarity. The wafer can even be constituted by an integrated application circuit

specific, or ASIC.

  The present invention also aims to provide a method of manufacturing a sensor device enabling collective production of a large number of devices on the same wafer of substrate, with subsequent cutting of

separation of devices.

  To this end, the invention proposes in particular a method for manufacturing an electromechanical sensor, according to which: - electrical interconnection tracks are formed on a first wafer in the form of at least one level - we place on the wafer of electrical connection, drops and a solder bead at locations intended to be connected to the active wafer, - the wafers are connected to each other by heating, by vacuum remelting or in an inert or reducing atmosphere, by heating and cooling, so as to create electrical and connection connections between the plates, and of interconnection, - finally an active plate is formed by cutting

  of a mechanical sensor and deposition of an intercon-

  nexion. The above features as well as others

  will appear better on reading the description which follows

  particular embodiments of the invention, given

  by way of nonlimiting examples. Description refers

  in the accompanying drawings, in which: - Figure 1 is a section showing the basic construction of a device according to a particular mode of

  realization of the invention, which may constitute an accelerator

  metre; - Figure 2, similar to Figure 1, shows a fraction of a device which can constitute a pressure sensor; - Figure 3 is a top view, with parts broken away

  partial of the active wafer, of an accelerometer consisting

  killing a particular embodiment;

  - Figure 4, similar to Figure 3, shows schematically

  only a device constituting a vibrating gyrometer.

  The sensor device, the basic structure of which is shown in FIG. 1, comprises an electrical connection plate 10 and an active plate 12 covered by a protective cover 14. The electrical connection plate

  represented comprises a substrate 16. In the case of a -

  miniaturized device, this substrate will generally be monocrystalline silicon. However, other materials can be used. In particular, it is possible to use a substrate made of quartz, of temperature-resistant glass.

  necessary for soldering, or even ceramic. For consti-

  kill a miniature device, we will usually use a

  monocrystalline silicon substrate 500 to 600 ium thick-

  sor, having on the surface an insulating oxide film.

  The electrical connection plate 10 of the

  embodiment of FIG. 1 has two levels of metalli-

  station. The first level 18 which can be produced by one of the usual techniques at present, for example by photolithography, comprises the output pads 20 making it possible to connect an external circuit. He has some

thick pine.

  On the first level 18, a thin layer of dielectric 22 is deposited or formed, which may consist of an oxide or a nitride or, more frequently, a resin

  dielectric, such as a polyimide. In the dielect layer

  plate 22 are then formed, by an etching process which may be conventional, openings intended for interconnection with the second level of metallization or with the electrical connection means which will be described

further.

  The second metallization level 24 can have a constitution similar to that of the first. This level 24 has

  a few thick pine. To allow subsequent fixing

  it has a composite structure. It can in particular comprise successive deposits of titanium, nickel and gold

  a few thick. This constitution may also

  be the first. The deposit can be made by

  example, by sputtering.

  After optional masking with a resin, a layer of brazing material is locally formed which will then form the electrical and mechanical connection means. One can in particular use a masking resin playing a role of sparing varnish to delimit the zones where the solder must be deposited. The solder composition can be a tin-lead commonly adopted and having a melting point of the order of 200 ° C. to 300 ° C. (tin-lead alloy 60/40 or / 5). This composition can be deposited by deposit

electrolytic.

  The balls 26 and the cord 28 subsequently intended for

  ensuring the connections are constituted by reflow and re-

  brazing of the solder under vacuum, in an inert atmosphere or in a slightly reducing atmosphere (for example in a nitrogen or N2H2 atmosphere). The surface tension during cooling ensures the shape of a ball or bead. The thickness of the deposit and the size of the base of the studs and of the bead are chosen so that the balls have a diameter of 10 to 100 lum in diameter and that the bead has 20

to 30iim thick.

  The second plate 12, represented by

  felt in Figure 1 in the state it is in after

  machining. This plate is made up, like the previous-

  te, from a substrate, the nature of which will be different depending on the type of effect that we want to implement

  (in particular piezoresistive, piezoelectric or capacitive effect

  citive). A level of metallization is deposited on the substrate.

  tion 30, by a process which can be the same as that

used for plate 10.

  The two plates 10 and 12 are then fixed one

  to the other, in alignment. To do this, we process

  prior surface treatment, for example by sputtering. Then the two wafers are brought into contact and the seals made by heating to the melting temperature of the solder and cooling, under vacuum, in an inert atmosphere or in a slightly reducing atmosphere. In the case illustrated in FIG. 1, portions 32 are shown in overhang, the anchoring of which is achieved by one or more lines of balls. The cutting can be done by litho-photography processes and then

  anisotropic etching, such as reactive ion etching.

  As an example of feasible structures, mention may be made of those described in French patent applications.

  Nos 92 02782 and 95 08447 to which we can refer.

  One advantage of the constitution which has just been described is that it is possible to collectively produce a large number of devices from substrate wafers, for example silicon. The machining of the active wafer can be carried out after the joining which gives rise to a robust assembly (for example by running in up to a few tens of μm thick, then chemical etching of the face

  and / or reactive ion etching).

  As shown in FIG. 1 in dashed lines, the metallization and isolation patterns are then reproduced at regular intervals on the wafers, before mounting and

final cutting, with a saw.

  In this case, protection of the devices by a cover 14 may be necessary. Indeed, the sealed slices are cut one on the other with sprinkling with deionized water. The distances between the moving parts and the fixed parts being small, the capillary forces

  may cause, during subsequent drying, the destruction

tion of active parts.

  This risk is avoided by providing a plate

  killing all of the covers 14 glued, using an adhesive film 34, on each of the zones of the plate intended to give rise to the plate 12. The cutting can then be carried out in two phases. During the first phase, a partial cut along the direction

  arrow fl allows to clear the contact pads 20.

  A second cut along f2, through the cover and the

  two slices, used to separate the devices.

  Figure 2, o the elements corresponding to Figure 1 are designated by the same reference number, shows a fraction of plates 10 and 12 of a device intended for

constitute a pressure sensor.

  In this case, the active wafer 12 is locally thinned to form a deformable membrane 36. In this case, before etching, the wafer (or the entire wafer in the case of collective production) is subjected to mechanical lapping and polishing. Polishing on both sides will often be necessary, in the case of collective manufacturing, to allow engraving of alignment marks allowing

  subsequently a precise relative positioning of the pads-

before sealing.

  The thin membrane 36 can be produced, once the thickness of the wafer 12 has been reduced to a few tens of pim, by chemical etching of the upper part or by

reactive ion etching.

  The fixing of the two plates one on the other is carried out as indicated above. However, the sealing bead 28 leaves a gap to allow access to the reference pressure, as indicated by the arrow P. The measurement of the deformations of the membrane 36 can

  be carried out by one of the methods known at present.

  One can in particular use a capacitive measurement, piezo

  resistive or even piezoelectric.

  In the figure, only the sealing bead and a fixing ball have been shown. Other connections will be provided between the active element and the output ranges

  , on the part of the plate 10 which projects laterally-

ment of the plate 12.

  Platelets will generally be made of the same

  material or materials having coefficients of dilation-

  substantially equal, to avoid constraints

of thermal origin.

  The sensor device shown schematically in Figure 3 is intended to measure the accelerations occurring in the direction of the arrows F. In this figure, the elements corresponding to those of Figure 1 are still

  designated by the same reference number.

  The electrical connection plate 10 has the constitution previously described. Before mounting the active wafer, it receives the metallization levels, the balls of solder material 26 and the bead 28. The active wafer may be formed from a silicon wafer

  monocrystalline having the standard thickness of 500 or 600 tim.

  This plate can be lapped and polished after fixing to the interconnection plate, to reduce its thickness up to 10 to 30 μm. The cutting intended to constitute the seismic mass and its link arms can be carried out by methods already used for micro-machining of silicon throughout its thickness, for example by wet etching or by anisotropic dry etching, which makes it possible to obtain sides perpendicular to the faces. If parts of the

  active wafer are separated from the rest, they are now

naked by the balls 26.

  In the case illustrated in FIG. 3, the accelerometer comprises a central seismic mass 38 connected to two lateral parts forming a base by flexible arms, obtained by cutting. Such a constitution will not

  described in detail, as it is one of the usual-

  used to form miniature accelerometers

  res. The sensor device shown diagrammatically in FIG. 4 constitutes a vibrating gyrometer. The active plate has a central fixing pad 40, fixed to the interconnection plate by balls 26, connected by cut arms constituting suspension springs 42 to a cylindrical seismic mass 44. Additional balls 26 placed at the periphery ensure the connection between the outputs 20 and fixed electrodes 46 for detection and excitation. In the illustrated case, nine output pads 20

  are provided. Eight pads correspond to the circumferential electrodes

  ferential. The ninth corresponds to the electrode connected to the

stud 40.

  It can be seen that the invention allows arrangements to be made

  sensors with a plate in which is micro-

  machined a deformable structure in the plane of the wafer or perpendicular to this plane, for example in the form of a beam or a membrane. The structure is mechanically anchored and electrically connected to a second plate forming an interconnection substrate and it can be entirely protected from the external environment, this while preserving

  directly accessible electrical contact pads.

Claims (11)

  1. Electromechanical sensor device comprising: - an electrical connection plate (10) and of structure carrying electrical interconnection tracks; - an active plate (12) in which is cut a mechanical sensor, comprising a metallized level (30) of interconnection, opposite the electrical connection plate (10); electrical connection and connection means   of the two plates, comprising sanding contact balls   tuel (26) and possibly a cord (28) surrounding the   mechanical sensor and balls, balls and possible-   the cord being made of an electrically brazed material only conductive.   2. Sensor device according to claim 1, character-   risé in that the active plate (12) has dimensions smaller than those of the electrical connection plate (10) to allow access to electrical output pads   (20) provided on said electrical connection plate.   3. Sensor device according to claim 1 or 2, characterized in that the wafers comprise a monocrystalline silicon, quartz, glass or ceramic substrate, the electrical connection wafer possibly being a circuit   integrated specific application.   4. Device according to claim 1, 2 or 3, character-   risé in that the electrical interconnection tracks of the electrical connection plate (10) comprises) on a substrate (16), a first interconnection level forming   output pads (20) and a second level of interconnection   connection separated from the first by a dielectric interlayer (22).   5. Device according to any one of the claims   1 to 4, characterized in that the cord (28) constitutes a sealing barrier between a volume containing the sensor   metallic proper and the exterior.   6. Sensor device according to any one of   Claims 1 to 5, characterized in that it comprises a   cover (14) for protection against the external environment, attached to the active board (10) using an adhesive (34).   7. Device according to any one of the claims   previous, characterized in that the active wafer is cut so as to constitute an accelerometer or a gyrometer measuring by capacitive, piezoelectric or piezoresistive effect. 8. Method of manufacturing an electromechanical sensor device, according to which: - electrical interconnection tracks are formed on a first substrate (16) in the form of at least one interconnection level to form a connection plate electrical (10), - an active wafer (12) is prepared in a second substrate and by depositing an interconnection level (30), - balls and a solder bead are deposited on the electrical connection wafer at locations intended to be connected to the active wafer, the wafers are connected to one another by heating and cooling, by vacuum reflow or in an inert or reducing atmosphere, so as to create electrical and bonding connections between the boards, the active board (12) is machined to complete the production of the mechanical sensor.   9. Method according to claim 8, characterized in that the active plate (12) is rode and polished, after fixing the active plate (12) to the plate. link (10).   10. Method according to claim 8 or 9, characterized   in that we collectively constitute several provisions   tifs by simultaneously forming the electrical interconnection tracks of connection plates on a first wafer, in that the balls and the solder cords intended for all the devices are deposited on said first wafer, in that the the interconnection level of the corresponding active wafers is constituted on a second wafer and in that the   active plates before slicing.   11. Method according to claim 10, characterized in that, before separation of the devices, an additional section is fixed, intended to constitute covers (14), on the first two sections already fixed to each other, in that that we cut the stack thus formed without attacking the first section, and in that we then finish separation of devices.