Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B3/00—Devices comprising flexible or deformable elements, e.g. comprising elastic tongues or membranes
  • B81B3/0035—Constitution or structural means for controlling the movement of the flexible or deformable elements
  • B81B3/0051—For defining the movement, i.e. structures that guide or limit the movement of an element
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
  • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
  • B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
  • B81C1/00134—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems comprising flexible or deformable structures
  • B81C1/00182—Arrangements of deformable or non-deformable structures, e.g. membrane and cavity for use in a transducer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
  • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
  • B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
  • B81C1/00261—Processes for packaging MEMS devices
  • B81C1/00333—Aspects relating to packaging of MEMS devices, not covered by groups B81C1/00269 - B81C1/00325
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
  • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
  • G01L9/0042—Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
  • B81C2201/00—Manufacture or treatment of microstructural devices or systems
  • B81C2201/01—Manufacture or treatment of microstructural devices or systems in or on a substrate
  • B81C2201/0174—Manufacture or treatment of microstructural devices or systems in or on a substrate for making multi-layered devices, film deposition or growing
  • B81C2201/0191—Transfer of a layer from a carrier wafer to a device wafer
  • B81C2201/0194—Transfer of a layer from a carrier wafer to a device wafer the layer being structured
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
  • B81C2203/00—Forming microstructural systems
  • B81C2203/05—Aligning components to be assembled
  • B81C2203/051—Active alignment, e.g. using internal or external actuators, magnets, sensors, marks or marks detectors

Definitions

• the invention relates to the field of electromechanical systems formed of elements of micrometric dimensions also called MEMS (acronym for "Micro-Electromechanical System”) and / or elements of nanometric dimensions also called NEMS (acronym for Nano-Electromechanical System » ).
• MEMS micrometric dimensions
• NEMS nanometric dimensions
• the invention relates more particularly to a method of manufacturing such a system.
• M & NEMS Micro- and Nano-ElectroMechanical Systems
• force sensors such as accelerometers, gyrometers and magnetometers.
• force sensors are typically in the form of devices comprising a movable mass mechanically held by deformable elements such as springs.
• the mobile mass is also mechanically coupled to deformable structures such as measurement beams used to measure the movements of the mass.
• measurement beams may for example be strain gages or resonators.
• the mass and beam assembly is held in suspension over a cavity.
• an inertial force is applied to the moving mass and induces a stress on the measuring beam.
• the stress applied by the mass induces a variation of the frequency of the resonator
• the stress applied by the mass induces a variation of the electrical resistance.
• the acceleration is deduced from these variations. It is therefore understood that it is advantageous to combine a moving mass of micrometric thickness and a measurement beam of nanometric thickness.
• a large mass of the movable element makes it possible to maximize the inertial force and thus to induce a sufficient stress on the measurement beam.
• by favoring a thin beam it maximizes the stress applied by the mass on this beam.
• Such an arrangement therefore also has the advantage of increasing the sensitivity of the force sensor.
• EP 1 840 582 discloses such a force sensor, namely a sensor in which the moving mass has a thickness greater than that of the beam, and furthermore proposes a method of manufacturing such a sensor based on SOI technology. ("Silicon On Insulator" in English).
• the strain gauge is first etched in a surface layer of an SOI substrate, then covered with a protection. Silicon epitaxy is then performed on this surface layer so as to obtain a layer of thickness desired for producing the test body.
• the epitaxial growth technique is cumbersome and expensive to implement, and does not make it possible to obtain very large thicknesses of silicon layer. Because of this limitation, it is difficult to obtain an optimal dimensioning of the test body, and therefore of its mass, to maximize the stress applied to the gauge.
• the moving mass is first etched in an SOI substrate.
• a polycrystalline silicon layer of nanometric thickness is then deposited for the formation of the strain gauge.
• the small thickness of the polycrystalline silicon layers is still difficult to control, and its mechanical and electrical properties are lower than those of a monocrystalline silicon layer.
• the deposition of such a thin layer may be subject to constraints, such as deformations, which may affect the performance of the gauge. It is therefore difficult, by this method, to obtain a gauge having mechanical and electrical characteristics that optimize the sensitivity of the sensor.
• Another solution may be to use two separate SOI substrates to separately form the moving mass and the gauge, and then seal the two substrates together.
• a misalignment of the various elements, especially between the moving mass, the gauge and the cavity is likely to occur during sealing, increasing the risk of altering the overall sensitivity of the sensor.
• the present invention aims in particular to provide a solution for the manufacture of electromechanical devices free from the limitations mentioned above.
• the invention thus relates to a method of manufacturing an electromechanical device comprising at least one micromechanical structure (or active body) of predetermined thickness suspended above a cavity of predetermined depth.
• the manufacturing method comprises sealing a first face of a first substrate with a second substrate.
• the first substrate is only formed of a solid layer
• the second substrate is formed of at least one solid layer and an insulating layer.
• the seal is made so that the insulating layer of the second substrate is interposed between the first substrate and the solid layer of the second substrate.
• This sealing of the two substrates is followed by the formation of the cavity having said predetermined depth in the first substrate.
• the formation of this cavity is obtained in particular by etching a second face of the first substrate, this second face being opposite to the first face of the first substrate.
• the thickness of the remaining portion of the first substrate which is opposite the cavity is substantially equal to said predetermined thickness.
• the final depth of the cavity and the final thickness of the micromechanical structure are defined by this etching.
• the cavity is then closed by sealing the second face of the first substrate with a third substrate.
• This third substrate is formed of a solid layer and an insulating layer.
• the insulating layer of this third substrate is brought into direct contact with the second face of the first substrate for closing the cavity, which can be obtained by another sealing.
• the solid layer and the insulating layer of the second substrate are then removed.
• the opening of the cavity and the formation of the micromechanical structure are obtained via a single etching of the second face of the first substrate.
• micro-mechanical structure is meant a structure whose thickness is of micro-metric dimensions.
• the predetermined depth of the cavity is also preferably of micrometric dimensions.
• the manufacturing method of the invention is a simple and inexpensive solution that overcomes the alignment problem mentioned above, since the opening of the cavity and the formation of the micro-metric structure are obtained simultaneously with using a single step of burning.
• This unique etching is made possible in particular by the successive formation of the future cavity and the future micromechanical structure in the same monolayer substrate, commonly called bulk.
• This is made possible by the use of two other distinct substrates, one serving as substrate support for delimiting the bottom of the cavity, the other serving as a handling substrate ("handle substrate”) or temporary support (" carriers).
• Another advantage provided by this manufacturing method is that the bottom of the cavity of the electromechanical device thus obtained is covered with an insulating layer, usually an oxide layer.
• This insulating layer has the particular advantage of preventing the occurrence of irregularities resulting from the chemical process used in particular to release the cavity.
• the bottom of the cavity will not be attacked during the etching process used to release the cavity.
• the resulting device is thus cleaner, that is to say containing less dust likely to block the active body or interfere with measurements.
• the risk of degassing of the internal surfaces of the cavity is reduced, which ensures a stable pressure over time in the housing in which the device is encapsulated.
• the manufacturing method may further comprise, prior to sealing the first substrate with the second substrate, the production of alignment marks on the first face of the first substrate.
• these alignment marks serve as indicators to ensure correct positioning of the masks used in the etching processes used for the realization of the cavity and the micromechanical structure.
• These alignment marks can in particular be in the form of predefined structures (verniers, squares, barcodes, etc.) and can be obtained conventionally, for example by an etching technique.
• the method may also comprise, prior to the production of the cavity, the release of the alignment marks on the second face of the first substrate.
• these alignment marks are covered during the step of sealing the first substrate with the second substrate, and then released prior to the etching step of the cavity so as to make them visible on the side of the second face of the first substrate.
• the recovery of these alignment marks can be obtained by lithography and etching of the second face of the first substrate.
• the manufacturing method may further comprise, prior to the production of the cavity, the thinning of the first substrate.
• the massive layer of the first substrate used may typically have an initial thickness of several hundred micrometers, for example 450 ⁇ .
• the useful thickness of the solid layer for producing the cavity and the micromechanical structure is, for example, less than a hundred micrometers, for example 50 ⁇ m.
• This thinning thus makes it possible to obtain a residual thickness of the first substrate that is substantially equal to the predetermined thickness of the micro-mechanical structure added to the predetermined depth of the cavity.
• This residual thickness typically corresponds to said useful thickness.
• this thinning can be obtained by grinding or chemical etching, mechanical-chemical etching or dry etching.
• the manufacturing method may further comprise, simultaneously with the production of the cavity, the formation of at least one abutment within the cavity, the abutment extending from the first substrate towards the third substrate .
• the realization of the cavity and the stop (or stopper) can be obtained by:
• the depth of this first etching is therefore substantially equal to the desired distance (for example ⁇ ⁇ ) between the free end of the stop and the insulating layer of the third substrate delimiting the bottom of the cavity;
• the stop is secured, not with the bottom of the cavity, but is secured to the active body and in particular to the MEMS structure.
• the manufacturing method may further comprise, prior to sealing the first substrate with the second substrate, the production of at least one predefined depth recess on the first face of the first substrate.
• the bottom of this hollow is in particular covered by a dielectric layer.
• the embodiment of the cavity further comprises the production of a through hole connecting the cavity to the hollow.
• the hollow serves in particular to mark the location of the future nanomechanical structure.
• nanomechanical structure is meant a structure whose thickness is of nanometric dimensions.
• the recess may be in the form of a recess and is made prior to the realization of alignment marks. This marking can be obtained by a double lithogravure of the first face of the first substrate for:
• each hole defining the location of a future nanomechanical structure to be produced
• the second substrate is formed of an insulating layer interposed between a solid layer and a thin layer relative to the solid layer.
• the first face of the first substrate is preferably brought into direct contact with the thin layer of the second substrate.
• the second substrate is therefore formed of an insulating layer, for example an oxide layer, interposed between a solid layer of micrometric thickness and typically intended for handling the device in formation, and a thin layer called a layer active, typically silicon, of nanometric thickness.
• the step of sealing the first substrate with the second substrate is reflected in particular by the direct sealing of the nanometric active layer of the second substrate with the micrometric solid layer of the first substrate.
• the realization of the single etching for the opening of the cavity and the formation of the micromechanical structure also comprises the formation of the nanomechanical structure in the thin layer of the second substrate, this nanomechanical structure facing the through hole .
• the nanomechanical structure is formed in the thin layer of the second substrate.
• the etching step implemented to simultaneously open the cavity and to form the micromechanical structure can also be used to form the nanomechanical structure.
• the cavity and the micro- and nano-mechanical structures are obtained via a single etching.
• the doping of the thin layer can be obtained by different doping techniques, such as for example by diffusion, or ion implantation by plasma immersion or by ion beam.
• the subject of the invention is also an electromechanical device comprising:
• the electromechanical device may further comprise at least one stop within the cavity, the stop extending from the micromechanical structure in the direction of the insulating layer.
• the solid layer comprises the micromechanical structure interposed between the insulating layer and a thin layer relative to the solid layer.
• the device may further comprise a nano-mechanical structure formed in the thin layer and a through hole connecting the nanomechanical structure to the cavity.
• the nanomechanical structure may be a deformable measuring element such as a strain gauge, a deformable membrane, or a nano-mechanical resonator;
• the micromechanical structure may be formed of a mobile mass coupled to deformable elements such as springs, a membrane, or nanomechanical structures;
• the nanomechanical structure may have a thickness of less than 1 ⁇ ;
• the micromechanical structure may have a thickness less than ⁇ and greater than 5 ⁇ ;
• the thickness ratio of the micromechanical and nanomechanical structures is of the order of 100;
• the solid layers and the thin layer are preferably made of silicon and the insulating layers are preferably made of oxide.
• FIGS. 1A to 1J are schematic views illustrating the steps of the method of manufacturing an electromechanical device incorporating an active structure of micro dimensions, according to one embodiment of the invention.
• FIGS. 2A to 2K are schematic views illustrating the steps of the method of manufacturing an electromechanical device incorporating an active structure of micrometric dimensions and an active structure of nanometric dimensions, according to another embodiment of the invention. Detailed presentation of particular embodiments
• FIG. 1J illustrates the various steps of a method of manufacturing an electromechanical device according to one embodiment.
• the electromechanical device that one wishes to obtain is illustrated in FIG. 1J and integrates in particular a micromechanical structure 60, 61 of predetermined thickness, for example 20 ⁇ m, in suspension over a cavity 4 of predetermined depth, for example 5 ⁇ .
• the micromechanical structure 60, 61 is an active body formed for example of a moving mass 60 coupled to springs 61.
• the electromechanical device may further comprise a stop 5 which extends from the micromechanical structure 60, 61 towards the bottom of the cavity 4.
• the spacing between the free end of the abutment 5 and the bottom of the cavity 4 is substantially equal to ⁇ ⁇ .
• the cavity and the micromechanical structure are produced, by etching, in a single monolayer substrate corresponding to the first substrate 1 illustrated in FIG. 1A.
• This first substrate 1, commonly called “bulk”, is therefore formed solely of a solid layer 10, for example a silicon layer 450 ⁇ thick, and has two opposite faces, namely a first face 11 and a second face 12.
• alignment marks 13 are made (FIG. 1B) on the first face 11 of this first substrate 1.
• a second substrate 2 is sealed to this first substrate 1 ( Figure 1C).
• This second substrate 2 is formed of a solid layer 20, for example a silicon layer 450 ⁇ thick, and an insulating layer 21, for example an oxide layer ⁇ thick.
• the insulating layer 21 of the second substrate is brought into direct contact with the first face 11 of the first substrate 1.
• the alignment marks 13 previously made are therefore covered by this second substrate 2.
• a thinning of this first substrate 1 is first performed ( Figure 1D). More precisely, the thinning is such that the residual thickness of this first substrate 1 corresponds substantially to the predetermined thickness of the micromechanical structure 60, 61 added to the predetermined depth of the cavity 4. In such a way that Classically, this thinning may for example be obtained by grinding or chemical etching.
• the alignment marks 13 are then released (FIG. 1E) by lithography and etching of the second face 12 of the first substrate 1. These alignment marks 13 are thus made visible on the side of the second face 12 of the first substrate 1.
• lithography and then partial etching are carried out (FIG. 1F) in order to initiate the etching of the cavity 4 in the first thinned substrate 1 and in order to define the height of the abutment 5.
• the depth of the partial etching is substantially equal to the desired spacing between the free end of the abutment 5 and the bottom of the cavity 4.
• the partial etching step may be omitted.
• a simple lithogravure (Figure 1G) is then made to form the abutment 5 and to define the depth of the cavity 4 in the first substrate 1 thinned.
• the dimensions of the cavity 4 and the abutment 5 already correspond to the desired final dimensions.
• the thickness of the remaining portion of the first substrate facing the cavity 4 is substantially equal to the desired final thickness of the micromechanical structure 60, 61.
• the cavity 4, the abutment 5 and the thickness of the the micromechanical structure 60, 61 are defined by this single etching.
• the next step is to seal a third substrate 3 with the first substrate 1 to close the cavity 4 thus formed (Figure 1H).
• This third substrate is also formed of a solid layer 30, for example a silicon layer with a thickness greater than 300 ⁇ , and an insulating layer 31, for example an oxide layer of ⁇ thick.
• this sealing is such that the insulating layer 31 of this third substrate 3 is brought into direct contact with the second face 12 of the first substrate 1.
• the second substrate 2 is then removed (FIG. II), and a single etching (FIG. 1J) of the first substrate 1 is performed to simultaneously open the cavity 4 and form the micromechanical structure 60, 61.
• the electromechanical device thus obtained (FIG. 1J) thus comprises a stack formed of an insulating layer 31 interposed between two solid layers 10, 30.
• the cavity 4 and the micromechanical structure 60, 61 are made in one of the 10 two massive layers of the stack, and the insulating layer 31 forms the bottom of the cavity 4.
• the electromechanical device illustrated in FIG. 2K that it is desired to obtain integrates, in addition to the micromechanical structure 60, 61, the cavity 4 and the abutment 5 described above, a nanometric structure 7 of thickness predetermined, for example 250nm, also in suspension above the cavity 4.
• This nanomechanical structure 7 is for example a strain gauge. The method of manufacturing such a device is illustrated in FIGS. 2A to 2K.
• the cavity 4, the abutment 5 and the micromechanical structure 60, 61 are made in the same monolayer substrate (FIG. 2A) identical to that used previously.
• a hollow 14 is formed (Figure 2B) on the first face 11 of the first substrate 1, for example by lithography.
• This predetermined depth of hollow generally less than ⁇ ⁇ , has a bottom covered by a dielectric layer 15, for example an oxide layer.
• a second substrate 2 is sealed to this first substrate 1 ( Figure 2D).
• This second substrate 2 is formed of an insulating layer 21, for example an oxide layer of thickness ⁇ , interposed between a solid layer 20, for example a silicon layer 450 ⁇ thick, and a thin layer 22 relative to the solid layer 20.
• the thin layer 22 is in particular a so-called "active" layer, typically a silicon layer of nanometric thickness, for example 250 nm.
• the thin layer 22 of the second substrate 2 is brought into direct contact with the first face 11 of the first substrate 1.
• the alignment marks 13 and the hollow 14 are covered by this second substrate 2.
• the first substrate 1 is thinned (FIG. 2E) so that the residual thickness of this first substrate 1 also corresponds substantially to the predetermined thickness of the micromechanical structure 60, 61 added to the predetermined depth of the cavity 4.
• the alignment marks 13 are also released (FIG. 2F) by lithography and etching of the second face 12 of the first substrate 1.
• a lithography and then a partial etching are then performed in order to initiate the etching of the cavity 4 in the first thinned substrate 1 and to define the spacing between the bottom of the cavity 4 and the free end of the stop 5.
• the partial etching step can be omitted.
• a simple lithogravure (FIG. 2H) is then produced in order to form the abutment 5, to define the depth of the cavity 4 in the first thinned substrate 1, and to make a through-hole 16 for connecting the cavity 4 to the recess 14.
• the dielectric layer 15 placed at the bottom of the recess 14 protects the thin layer 22 of the second substrate during this bed etching, and is eliminated.
• a third substrate 3 identical to the third substrate used previously, is then sealed with the first substrate to close the cavity 4 thus formed ( Figure 21). This sealing is such that the insulating layer 31 of this third substrate 3 is brought into direct contact with the second face 12 of the first substrate 1.
• the following step consists in eliminating the solid layer 20 and the insulating layer 21 of the second substrate (FIG. 2J) to leave only the thin layer 22, and to make a single etching (Figure 2K) to simultaneously open the cavity 4 and form the micromechanical structures 60, 61 and nanomechanics 7. In particular, the nanomechanical structure 7 is performed opposite the through hole
• the electromechanical device thus obtained (FIG. 2K) thus comprises the cavity 4, the micromechanical structure 60, 61 and the abutment 5 formed in the same solid layer 10, as well as the nanomechanical structure 7 formed in the thin layer 22 disposed on the massive layer. 10.
• the insulating layer 31 forms the bottom of the cavity 4.
• the manufacturing processes presented are therefore simple and globally inexpensive although three substrates are used. They make it possible in particular to obtain electromechanical devices of the MEMS or M & NEMS type which are less bulky and more efficient, wherein at least the cavity and the micromechanical structure are made in a single monolayer substrate. Moreover, the life of such a device is increased thanks to the insulating layer at the bottom of the cavity which prevents the appearance of irregularities in the bottom of the cavity during etching. Finally, the proposed solution also offers the possibility of adapting the thickness of the micrometric structure by simple adjustment of the engraving equipment.

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• Physics & Mathematics (AREA)
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• Pressure Sensors (AREA)

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• 2014
  • 2014-11-10 FR FR1460871A patent/FR3028257A1/fr not_active Withdrawn
• 2015
  • 2015-11-09 KR KR1020177011711A patent/KR101847793B1/ko active IP Right Grant
  • 2015-11-09 JP JP2017522962A patent/JP6305647B2/ja not_active Expired - Fee Related
  • 2015-11-09 US US15/520,618 patent/US9944512B2/en not_active Expired - Fee Related
  • 2015-11-09 WO PCT/EP2015/076110 patent/WO2016075098A1/fr active Application Filing
  • 2015-11-09 EP EP15791617.2A patent/EP3218302A1/fr not_active Withdrawn
  • 2015-11-09 CN CN201580056216.2A patent/CN107074531A/zh active Pending

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