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WO2015042701A1 - Dispositif mems comprenant un anneau protecteur d'électrode et procédé de fabrication associé - Google Patents

Dispositif mems comprenant un anneau protecteur d'électrode et procédé de fabrication associé Download PDF

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Publication number
WO2015042701A1
WO2015042701A1 PCT/CA2014/050904 CA2014050904W WO2015042701A1 WO 2015042701 A1 WO2015042701 A1 WO 2015042701A1 CA 2014050904 W CA2014050904 W CA 2014050904W WO 2015042701 A1 WO2015042701 A1 WO 2015042701A1
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WO
WIPO (PCT)
Prior art keywords
electrode
mems
top cap
wafer
cap wafer
Prior art date
Application number
PCT/CA2014/050904
Other languages
English (en)
Inventor
Robert Mark Boysel
Original Assignee
Motion Engine Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motion Engine Inc. filed Critical Motion Engine Inc.
Publication of WO2015042701A1 publication Critical patent/WO2015042701A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • G01P15/125—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by capacitive pick-up
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
    • B81B7/0032—Packages or encapsulation
    • B81B7/0064—Packages or encapsulation for protecting against electromagnetic or electrostatic interferences
    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • G01P15/0802—Details
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B2201/00—Specific applications of microelectromechanical systems
    • B81B2201/02—Sensors
    • B81B2201/0228—Inertial sensors
    • B81B2201/0235—Accelerometers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B2201/00—Specific applications of microelectromechanical systems
    • B81B2201/02—Sensors
    • B81B2201/0264—Pressure sensors

Definitions

  • the general technical field relates to micro-electro-mechanical systems (MEMS), and more particularly, to a MEMS device including a guard ring surrounding an electrode, and to a method of manufacturing such a MEMS device.
  • MEMS micro-electro-mechanical systems
  • MEMS Micro-electro-mechanical systems
  • ICs integrated circuits
  • MEMS devices are manufactured using high-volume silicon wafer fabrication techniques developed over the last fifty years for the microelectronics industry. Their resulting small size and low cost make them attractive for use in an increasing number of applications in consumer, automotive, medical, aerospace, defense, green energy, industrial, and other markets.
  • MEMS devices use capacitive sensing as a transduction method.
  • a conventional MEMS pressure sensor can include a fixed electrode and a flexible membrane electrode that moves in response to variations in external pressure. Monitoring the capacitance between the two electrodes can provide a direct measurement of the pressure variations.
  • MEMS motion sensors also generally rely on capacitive measurements.
  • Existing capacitive-based MEMS devices can involve the detection of capacitance variations of the order of femtofarads (fF) or even attofarads (aF). The measurement of such small capacitance variations can become quite sensitive to parasitic capacitance effects between the sensing electrodes and their surroundings.
  • MEMS micro-electro-mechanical system
  • the electrode structure including an electrode and a guard ring laterally surrounding and electrically insulated from the electrode, the electrode and the guard ring each extending through the entire thickness of the top cap wafer;
  • step b) includes the substep of: - forming an inner insulation channel extending through the entire thickness of the top cap wafer, the inner insulation channel laterally bordering a first region of the top cap wafer corresponding to the electrode;
  • step b) includes the substeps of:
  • the trench having inner and outer sidewalls, the trench extending from the first side partially into the top cap wafer and laterally bordering a volume of the top cap wafer corresponding to the electrode to be formed;
  • the electrically conductive material includes one of a metal and polysilicon.
  • step b) includes the substeps of: - forming spaced-apart inner and outer closed-loop trenches each extending from the first side partially into the top cap wafer, the inner trench laterally bordering a first volume of the top cap wafer corresponding to the electrode to be formed, the inner and outer trenches together laterally bordering a second volume of the top cap wafer corresponding to the guard ring to be formed;
  • the electrically insulating material includes silicon dioxide.
  • removing top cap wafer material from the second side of the top cap wafer includes at least one of grinding, polishing and etching.
  • the method includes, after step b), the substeps of:
  • the method includes, after step b), the substeps of:
  • the method includes the step of
  • the electrically conductive semiconductor material includes a silicon-based semiconductor.
  • step a) includes forming the MEMS structure as a pendulous proof mass, and wherein the electrical connection is a capacitive electrical connection.
  • MEMS micro-electro- mechanical system
  • MEMS wafer including a MEMS structure, the MEMS wafer having opposed top and bottom sides;
  • top cap wafer having opposed first and second sides and a thickness extending therebetween, the first side being bonded to the top side of the MEMS wafer, the MEMS wafer and the top cap wafer being made of an electrically conductive semiconductor material;
  • the electrode structure including an electrode establishing an electrical connection with the MEMS structure and a guard ring laterally surrounding and electrically insulated from the electrode, the electrode and the guard ring each extending through the entire thickness of the top cap wafer.
  • the electrode structure includes: - an inner insulation channel extending through the entire thickness of the top cap wafer, the inner insulation channel laterally bordering a first region of the top cap wafer corresponding to the electrode; and
  • the inner and outer insulation channels are each made of an electrically insulating material including silicon dioxide.
  • the MEMS device includes:
  • a cap insulating layer formed on the second side of the top cap wafer and defining a guard ring contact opening over at least a portion of the guard ring;
  • the cap insulating layer further defines an electrode contact opening over at least a portion of the electrode, the MEMS device including a second electrical connection providing electrical contact to the electrode through the electrode contact opening.
  • the electrically conductive semiconductor material includes a silicon-based semiconductor.
  • the guard ring is made of an electrically conductive material including one of metal, silicon and polysilicon.
  • the MEMS device includes a bottom cap wafer bonded to the bottom side of the MEMS wafer.
  • the MEMS structure includes a pendulous proof mass, and wherein the electrical connection is a capacitive electrical connection.
  • Figs 1 A and 1 B illustrate two configurations of a measurement setup in which a coaxial cable including a central conductor surrounded by a shield is connected between a capacitor whose capacitance is to be measured and a measurement amplifier.
  • the shield In Fig 1A the shield is grounded and the central conductor is unguarded, while in Fig 1 B the shield is held at the same potential as the central conductor and acts as a guard surrounding the central conductor.
  • Fig 2A is a schematic perspective view of a MEMS device, in accordance with an exemplary embodiment.
  • Fig 2B is a schematic cross-sectional view of the MEMS device of Fig 2A.
  • Fig 2C is another schematic cross-sectional view of the MEMS device of Fig 2A, illustrating sources of parasitic capacitances that may affect the sensitivity and reliability of measurements obtained by the MEM device.
  • Figs 3A to 3G schematically illustrate steps of a method for manufacturing a MEMS device, in accordance with an exemplary embodiment.
  • Figs 4A to 4H schematically illustrate steps of a method for manufacturing a MEMS device, in accordance with another exemplary embodiment.
  • Fig 5 is an enlarged view of a portion of Fig 3F, illustrating a guard ring bordered by inner and outer trenches filled with an electrically insulating material.
  • Fig 6 is an enlarged view of a portion of Fig 4G, illustrating a guard ring bordered by electrically insulating material lined on the inner and outer sidewalls of a trench.
  • Fig 7 is a schematic cross-sectional view of a MEMS device, in accordance with another exemplary embodiment, wherein a guard ring is provided around a conductive electrical lead. It should be noted that the appended drawings illustrate only exemplary embodiments of the invention, and are therefore not to be construed as limiting of its scope, for the invention may admit to other equally effective embodiments.
  • the present description generally relates to a MEMS device provided with an electrode guard ring.
  • the present description also generally relates to a method of manufacturing a MEMS device provided with an electrode guard ring.
  • the term "MEMS device” is meant to encompass any suitable device such as, but not limited to, motion sensors, pressure sensors, magnetometers, actuators, micro-fluidic devices, micro-optic devices, and any other MEMS device where it may be relevant to apply the techniques and principles described herein.
  • motion sensors have seen their use grow steadily over the past decades.
  • MEMS motion sensors are used to sense changes in the state of motion of an object, including changes in position, velocity, acceleration or orientation, and encompass devices such as accelerometers, gyroscopes, vibrometers and inclinometers.
  • MEMS device described below is implemented as a motion sensor, this embodiment is presented only as a non-limiting example of applying the techniques and principles described herein to a MEMS device.
  • the embodiments of the MEMS device include a MEMS wafer having opposed top and bottom sides, a top cap wafer having opposed first and second sides and a thickness extending therebetween, and an electrode structure. The first side of the top cap wafer is bonded to the top side of the MEMS wafer.
  • Both the MEMS and top cap wafers are made of an electrically conductive semiconductor material.
  • the MEMS wafer is provided with a MEMS structure which can include or be embodied by any sensing and/or control element or combination of sensing and/or control elements such as, but not limited to, membranes, diaphragms, proof masses, comb sensors, actuators, transducers, micro-valves, micro-pumps, and the like.
  • the electrode structure is formed into the top cap wafer and includes an electrode establishing an electrical connection with the MEMS structure, as well as a guard ring laterally surrounding and electrically insulated from the electrode. Each of the electrode and guard ring extends through the entire thickness of the top cap wafer.
  • guard ring refers to an electrically conducting element of the MEMS device, which is electrically insulated from and laterally surrounds the electrode of the MEMS device. The guard ring forms a closed electrical loop within the top cap wafer.
  • electrode is intended to refer to an electrically conducting element of the MEMS device that is used to establish an electrical connection with the MEMS structure of the MEMS device in view of transmitting signals (e.g., electrical signals such as charges, voltages or currents) to and/or from the MEMS structure.
  • the electrode can be capacitive (e.g., a drive or sense capacitor), conductive, (e.g., a resistive electrical element, an inductive electrical element or a lead), or a combination thereof.
  • the electrical connection established between the electrode and the MEMS structure can involve a resistive electrical connection, a capacitive electrical connection, an inductive electrical connection, or a combination thereof.
  • guard ring is not limited to circular or oval ring-shaped structures in a strict geometric sense, but may admit a variety of shapes, including rectangular, polygonal, and other more complex shapes.
  • Figs 1 A and 1 B illustrate two configurations of a charging-rate measurement setup in which a coaxial cable 100 including a central conductor 102 surrounded by a shield 104 is connected between a capacitor whose capacitance C x is to be determined and a measurement amplifier 106.
  • the shield 104 is grounded and the central conductor 102 is unguarded.
  • the shield and the low side of C x are at the same ground potential, so that measuring the current / charges not only the capacitor of capacitance Cx, but also the capacitor of capacitance C c established between the central conductor 102 and the grounded shield 104 of the coaxial cable 100. Additionally, leakage current can flow between the central conductor and the shield since it is at a different potential. Meanwhile, in Fig 1 B, the shield 104 is connected to the output terminal of the measurement amplifier 106 (or a separate voltage supply at the same potential) so that the central conductor 102 and the shield 104 are held at the same potential. Thus no leakage current can flow between the conductor and the shield and no charge is generated across the capacitor formed by the conductor and shield since the capacitor electrodes are at the same potential.
  • the central conductor 102 is "guarded" by the shield 104, which contributes to eliminating or at least reducing parasitic cable capacitance C c and leakage current, and enables a more direct measurement of the unknown capacitor Cx.
  • a MEMS device including an electrode guard ring.
  • the MEMS device 10 consists of a multi- wafer stack implemented as a MEMS motion sensor. Other types of MEMS devices can be used in other embodiments, as mentioned above.
  • the MEMS device 10 includes a top cap wafer 12 having opposed first and second sides 121 , 122 and a thickness 123 extending therebetween; a MEMS wafer 16 having opposed top and bottom sides 161 , 162; and, optionally, a bottom cap wafer 14 having opposed first and second sides 141 , 142 and a thickness 143 extending therebetween.
  • top and bottom should be taken in the context of the figures and should not be considered as being limitative.
  • the terms “top” and “bottom” are used to facilitate reading of the description, and those skilled in the art of MEMS will readily recognize that, when in use, MEMS devices can be placed in different orientations such that the “top” and “bottom” cap wafers and the “top” and “bottom” sides of the MEMS wafer may be positioned upside down in certain configurations.
  • the MEMS wafer 16 can consist of a standard wafer, a silicon-on-insulator (SOI) wafer, or of multiple wafers.
  • the MEMS wafer 16 is an SOI wafer including a device layer 20, a handle layer 22 and an insulating layer 24 sandwiched between the device layer 20 and the handle layer 22.
  • the device layer 20 and the handle layer 22 of the MEMS wafer 16, as well as the top and bottom cap wafers 12, 14 can be made of an electrically conductive semiconductor material, for example a silicon-based semiconductor.
  • the MEMS wafer 16 is provided with a MEMS structure 17 which, in the illustrated embodiment, includes a pendulous proof mass 171 coupled to a peripheral region of the MEMS wafer 16 via flexible springs 27.
  • the term "proof mass” refers broadly to any predetermined inertial mass used in a MEMS motion sensor, such as an accelerometer or a gyroscope, whose displacement serves as a reference for the motion to be measured or monitored.
  • the flexible springs 27 join the proof mass 171 to the peripheral region of the MEMS wafer 16 for providing a restoring force to the proof mass 171. This restoring force enables the proof mass 171 to move relative to the peripheral region of the MEMS wafer 16 in response to a motion experienced by the MEMS device 10. This relative displacement of the proof mass 171 may be sensed by electrodes or other suitable transducing means.
  • the first side 121 of the top cap wafer 12 is bonded to the top side 161 of the MEMS wafer 16, and the first side 141 of the bottom cap wafer 14 is bonded to the bottom side 162 of the MEMS wafer 16.
  • the top cap wafer 12, the MEMS wafer 16 and the bottom cap wafer 14 are typically bonded with a conductive bond.
  • the top cap wafer 12 is bonded to and in electrical contact with the device layer 20, while the bottom cap wafer 14 is bonded to and in electrical contact with the handle layer 22.
  • the insulating layer 24 which typically consists of buried oxide, insulates the top half of the MEMS device 10 from the bottom half. SOI conducting shunts (not shown) can be provided that extend through the insulating layer 24 to electrically connect the device layer 20 and handle layer 22, in specific desired places.
  • the top cap wafer 12, the MEMS wafer 16 and the bottom cap wafer 14 together define a cavity 31 for receiving and housing the MEMS structure 17, as depicted in the cross-sectional view of Fig 2B.
  • at least part of the cavity 31 can be defined by a top recess 31 1 formed by removing top cap wafer material from a central region of the first side 121 of the top cap wafer 12 prior to bonding the first side 121 of the top cap wafer 12 to the MEMS wafer 16.
  • At least part of the cavity 31 can alternatively or additionally be defined by a bottom recess 312 formed by removing bottom cap wafer material from a central region of the first side 141 of the bottom cap wafer 14 prior to bonding the first side 141 of the bottom cap wafer 14 to the MEMS wafer 16.
  • a bottom recess 312 formed by removing bottom cap wafer material from a central region of the first side 141 of the bottom cap wafer 14 prior to bonding the first side 141 of the bottom cap wafer 14 to the MEMS wafer 16.
  • the MEMS device 10 of Figs 2A and 2B is a motion sensor capable of sensing the motion of a pendulous proof mass 171 to determine any of a number of parameters (e.g., acceleration, velocity, angular rate or orientation) indicative of a state of motion of an object or structure to which the MEMS device 10 is associated.
  • the motion of the proof mass is measured using capacitive sensing techniques.
  • the MEMS device 10 can be provided with a plurality of electrodes including top and bottom electrodes 13, 15 provided in the top and bottom cap wafers 12, 14, respectively, and forming capacitors with the proof mass 171 .
  • some of the top and bottom electrodes 13, 15 can be operated a driving electrodes and be connectable to driving means, while other ones of the top and bottom electrodes 13, 15 can be operated as sensing electrodes and be connectable to sensing means.
  • the top and bottom electrodes 13, 15 may alternatively be reconfigurably connectable to driving and sensing means, for switching between drive and sense modes.
  • the terms “driving means” and “sensing means” refer broadly to any electronic circuitry configured to deliver electrical signals to and receive electrical signals from the electrodes in order to drive and sense a response from the MEMS structure (e.g., a proof mass) of the MEMS device, respectively.
  • the plurality of electrodes includes five top electrodes 13 (one central driving electrodes and four peripheral sensing electrodes) and five bottom electrodes 15 (one central driving electrodes and four peripheral sensing electrodes), which extend through the entire thicknesses 123, 143 of the top and bottom cap wafers 12, 14, respectively.
  • the number, size, shape, position, arrangement and type (e.g., driving or sensing) of electrodes can vary depending on the application in which the MEMS device is to be used.
  • the architecture of the embodiment of the MEMS device 10 illustrated in Figs 2A and 2B can allow for the placement of electrodes and electrical leads above, below, and/or around the MEMS structure 17 (e.g., the proof mass 171 ) for measuring signals from the MEMS structure 17 (e.g., acceleration and/or angular rate).
  • This architecture can be referred to as a "three-dimensional through-chip-via" (3DTCV) architecture and can allow routing all the signals to one side of the chip where they can be accessed for signal processing.
  • 3DTCV three-dimensional through-chip-via
  • the signals detected by the top and bottom electrodes 13, 15 can be routed to electrical contacts connected to the top surface of the MEMS device 10, to which a CMOS chip can be connected for controlling and/or measuring the electrical signals to/from the MEMS device 10.
  • electrodes 13, but also leads, bond pads, guard rings and other structures can be defined in the top cap wafer 12 by insulating channels.
  • the insulating channels can be made using a through-silicon-via (TSV)-like fabrication process in which the vias are completely filled with an insulator, or by an insulator and conductor, as the insulating channels are used essentially to for isolation purposes, and not to carry electrical signals vertically through MEMS device 10.
  • TSV through-silicon-via
  • the capacitance of each capacitor formed between the proof mass 171 and the top or bottom electrodes 13, 15 can be monitored to determine the motion of the proof mass 171 in response to external forces.
  • the top and bottom electrodes 13 and 15 are used to measure very low electrical signals (e.g., charges, voltages or currents) associated with correspondingly small capacitance variations.
  • the value of the "undetected" capacitance can be of the order of 1 picofarad (pF), and the capacitance variations corresponding to proof mass motions of interest can be of the order of fF or even aF.
  • Fig 2C there are shown some parasitic capacitors 18 that may appear between the top electrodes 13 and other elements of the MEMS device 10 and that may affect the reliability of the measurement of the motion of the proof mass 171 (or, more generally, a response of interest of the MEMS structure 17).
  • the MEMS device 10 in order to eliminate or at least reduce the impact of parasitic and stray capacitance, current leakage, and other adverse electrical coupling effects, the MEMS device 10 according to embodiments of the invention includes one or more guard rings 54.
  • Each guard ring 54 forms a closed-loop electrical circuit that laterally surrounds and is electrically insulated from a corresponding electrode 13, 15 formed in the top and bottom cap wafers 12, 14.
  • the terms “lateral” and “laterally” refers to directions that lie in a plane perpendicular to the thickness of the top or the bottom cap wafer, that is, in plane perpendicular to the wafer stacking direction of the MEMS device.
  • each guard ring 54 forms a two-dimensional continuous or closed-loop conducting path or channel around its associated electrode 13, 15. Additionally, each guard ring 54 and its associated electrode 13, 15 extend through the entire thickness 123, 143 of the top or bottom cap wafer 12, 14 and define what is referred to as an "electrode structure" 19.
  • the guard ring 54 can laterally guard the sidewalls of the electrode 13, 15 from the rest of the cap wafer 12, 14 through the entire thickness of the electrode 13, 15 and not just at the surface.
  • the provision of a guard ring 54 around an electrode 13, 15 of the MEMS device 10 can shield or protect that electrode 13, 15 from parasitic capacitance, leakage current and other unwanted electrical coupling effects that could otherwise degrade the integrity of the electrode signals (e.g., electrical signals such as charges, voltages or currents) transmitted from and/or to the MEMS structure 17.
  • a guard ring 54 is provided around each of the four sensing electrodes 13 in the top cap wafer 12 and around each of the four sensing electrodes 15 in the bottom cap wafer 14.
  • the guard ring 54 is preferably made of an electrically conductive material 32 including one of metal (e.g., copper), silicon and polysilicon.
  • metal e.g., copper
  • the material, number, size, shape and position of the guard rings and the type of electrodes (e.g., driving and sensing) to which the guard ring paired can be varied in other embodiments.
  • electrodes of only one of the top and bottom cap wafers may be provided with guard rings without departing from the scope of the present invention.
  • an electrode structure 19 formed in the top cap wafer 12 can include an inner insulation channel 21 and an outer insulation channel 23 laterally spaced from the inner insulation channel 21 .
  • Each of the inner and outer insulation channels 21 , 23 extends through the entire thickness 123 of the top cap wafer 12 and is made of an electrically insulating material 30, preferably including silicon dioxide (S1O2).
  • the inner insulation channel 21 laterally borders a first region of the top cap wafer 12 that corresponds to the electrode 13 of the electrode structure 19. Meanwhile, the inner and outer insulations 21 , 23 together laterally border a second region of the top cap wafer 12 corresponding to the guard ring 54 of the electrode structure 19.
  • the inner and outer insulation channels 21 , 23 can have various configurations and structures, and be fabricated according to different techniques and processes.
  • the inner and outer insulation channels 21 , 23 can be embodied by spaced-apart inner and outer closed-loop trenches 28a, 28b formed into the top cap wafer 12 and filled with electrically insulating material 30 (see, e.g., Fig 3E).
  • a single closed-loop trench 28 having inner and outer sidewalls 31 a, 31 b can be formed in the top cap wafer 12, and the inner and outer insulating channels 21 , 23 can be formed respectively by lining the inner and outer sidewalls 31 a, 31 b of the trench 28 with an electrically insulating material 30.
  • An electrically conductive material 32 e.g., a metal such as copper, silicon, polysilicon or any suitable conductor
  • the use of a single trench 28 in which are formed the guard ring 54 and both the inner and outer insulation channels 21 , 23 can allow for the area occupied by the guard ring 54 to be reduced, and thus the area occupied by the electrode 13 to be increased.
  • the MEMS device 10 can include a cap insulating layer 40 formed on the second side 122 of the top cap wafer 12 and defining a guard ring contact opening 55 over at least a portion of each guard ring 54.
  • the MEMS device 10 can also include a first electrical connection or contact 42 providing an electrical connection to each guard ring 54 through the guard ring contact opening 55.
  • the cap insulating layer 40 can further define an electrode contact opening 57 over at least a portion of an electrode 13 in the top cap wafer 12, so that a second electrical connection or contact 43 can provide an electrical connection to the electrode 13 through the electrode contact opening 57.
  • the first and second electrical connections 42, 43 may be formed by depositing a metallic layer 41 , in some scenarios with an additional sticking or barrier layer, on the cap insulating layer 40 and by patterning the metallic layer 41 to form the first and second electrical connections 42, 43.
  • a passivating layer 45 may also be applied over the first and second electrical connections 42, 43. In some embodiments, the passivating layer 45 can extend over substantially the entire surface of the second side 122 of the top cap wafer 10. Finally, openings may be formed in the passivating layer 45 to expose at least partially the first and second electrical connections 42, 43.
  • the guard ring 54 can be held at the same or at a similar electrical potential as its associated electrode 13, thus contributing to reducing parasitic capacitance and other detrimental electrical coupling effects between the electrode 13 and its environment.
  • the cap insulating layer is not depicted in Fig 2A in order to show the electrodes 13 and the guard rings 54 formed in the top cap wafer 12.
  • a guard ring can be used not only to guard a capacitive electrode, as in Figs 2A to 2C, but also a conductive electrode or lead.
  • an additional guard ring 54 may be provided that surrounds a MEMS electrical lead 47 (e.g., a feedthrough or a conductive wafer plug) connecting a MEMS electrical connection 44 to the MEMS structure 17 via a spring 27.
  • the arrow 58 indicates the conducting path followed by the MEMS lead 47 between the MEMS electrical connection 44 and the MEMS structure d.
  • a method of manufacturing a MEMS device including an electrode guard ring.
  • the method for manufacturing the MEMS device will be described with reference to the diagrams of Figs 3A to 3G and Figs 4A to 4H, which schematically illustrate steps of a first and a second exemplary embodiment, respectively. It will be understood, however, that there is no intent to limit the invention to these two embodiments, for the method may admit to other equally effective embodiments. It will also be understood that the manufacturing method can, by way of example, be performed to fabricate a MEMS device like that described above with reference to Figs 2A to 2C, or any other suitable MEMS device provided with one or more electrode guard rings. First embodiment of the manufacturing method
  • FIGs 3A to 3G there are schematically illustrated fabrication steps of a first exemplary embodiment of the method for manufacturing a MEMS device.
  • the method first includes a step of providing a top cap wafer 12 and a MEMS wafer 16.
  • the top cap wafer 12 has opposed first and second sides 121 , 122 and a thickness 123 extending therebetween, and the MEMS wafer 16 has opposed top and bottom sides 161 , 162.
  • the top cap wafer 12 and the MEMS wafer 16 are each made of an electrically conductive semiconductor material 30 such as, for example a silicon-based semiconductor.
  • the MEMS wafer 16 can be provided as a standard wafer, an SOI wafer, or as multiple wafers.
  • the MEMS wafer 16 is an SOI wafer including a device layer 20, a handle layer 22 and an insulating layer 24 sandwiched between the device layer 20 and the handle layer 22, as described above.
  • the MEMS wafer 16 includes a MEMS structure 17 which, as also described above, can include or be embodied by any sensing element or combination of sensing elements such as, but not limited to, membranes, diaphragms, proof masses, comb sensors, actuators, transducers, micro-valves, micro-pumps, and the like.
  • the MEMS device is a MEMS motion sensor so that the step of providing the MEMS wafer 16 can include forming the MEMS structure 17 as a pendulous proof mass 171 coupled to a peripheral region of the MEMS wafer 16 via flexible springs 27.
  • the flexible springs 27 provide a restoring force to the proof mass 171 which enables the proof mass 171 to move relative to the peripheral region of the MEMS wafer 16 in response to external forces.
  • the step of providing the top cap wafer 12 can include a preliminary step of forming a recess 31 1 by removing top cap wafer material from a central region of the first side 121 of the top cap wafer 12.
  • the recess 31 1 may eventually form part of a cavity whose role is to house the MEMS structure once the top cap wafer 12 is bonded to the MEMS wafer 16, as described below.
  • the method next includes a step of forming one or more electrode structures from the first side into the top cap wafer, wherein each electrode structure include an electrode and a guard ring laterally surrounding and electrically insulated from the electrode.
  • each electrode structure include an electrode and a guard ring laterally surrounding and electrically insulated from the electrode.
  • the step of forming one such electrode structure may be conceptually described as including two substeps.
  • the first substep can involve forming an inner insulation channel extending through the entire thickness of the top cap wafer, wherein the inner insulation channel laterally borders a first region of the top cap wafer corresponding to the electrode to be formed.
  • the second substep can involve forming an outer insulation channel also extending through the entire thickness of the top cap wafer and spaced from the inner insulation channel, such that the inner and outer vertical insulation channels together lateral borders a second region of the top cap wafer corresponding to the guard ring to be formed.
  • forming the inner and outer insulation channels to define the electrode and the guard ring can involve different fabrication techniques and structural features, as will be appreciated by comparing the present embodiment of Figs 3A to 3G and the second exemplary embodiment described below with reference to Figs 4A to 4H.
  • the step of forming an electrode structure can include a first substep of forming spaced-apart inner and outer closed-loop trenches 28a, 28b each extending from the first side 121 partially into the top cap wafer 12.
  • Fig 3B is a schematic plan view of the top cap wafer 12 illustrating the two-dimensional closed-loop paths defined by the inner and outer trenches 28a, 28b.
  • the inner trench 28a laterally borders a first volume 29a of the top cap wafer 12, which corresponds to the electrode to be formed, and that the inner and outer trenches 28a, 28b together laterally border a second volume 29b of the top cap wafer 12, which corresponds to the guard ring to be formed.
  • the trenches 28a, 28b may be produced using a selective etching process. Selective etching processes for producing trenches in a wafer body are well known in the art and need not be described in further detail herein. Typically, a deep silicon reactive ion etch (DRIE) is used to etch high aspect ratio features with vertical sidewalls into silicon, but other etching processes may be used.
  • DRIE deep silicon reactive ion etch
  • the step of forming an electrode structure can include a second substep of depositing an electrically insulating material 30 into the inner and outer trenches 28a, 28b.
  • the electrically insulating material 30 may include silicon dioxide (Si0 2 ) or any other suitable material.
  • LPCVD low pressure chemical vapor deposition
  • PECVD plasma enhanced chemical vapor deposition
  • the substep of depositing an electrically insulating material into the inner and outer trenches may include forming an insulation layer one the sidewalls of each trench, followed by filling each trench with an electrically conductive material.
  • the step of forming an electrode structure 19 can include a third substep of removing top cap wafer material from the second side 122 of the top cap wafer 12 to expose the electrically insulating material 30 of the inner and outer trenches 28a, 28b.
  • the step of removing top cap wafer material from the second side 122 of the top cap wafer 12 can include at least one of grinding, polishing and etching.
  • the electrode 13 and the guard ring 54 are formed and are electrically insulated from each other by the electrically insulating material 30 deposited into the inner trench 28a.
  • the electrode 13 and the guard ring 54 each extends through the entire thickness 123 of the top cap wafer 12, and both the electrode 13 and the guard ring 54 are made of the same electrically conductive semiconductor material as the top cap wafer 12.
  • the exposed inner and outer trenches 28a, 28b filled with electrically insulating material 30 correspond respectively to the inner and outer insulating channels introduced above.
  • the method can include successive substeps of (i) forming a cap insulating layer 40, typically thermally or chemical vapor deposited silicon dioxide, on the second side 122 of the top cap wafer 12; (ii) partially removing the cap insulating layer 40, for example by selective etching, to expose at least a portion of the guard ring 54 and at least a portion of the electrode 13; and (iii) forming first and second electrical connections 42, 43 on the exposed portions of the guard ring 54 and the electrode 13, respectively.
  • a cap insulating layer 40 typically thermally or chemical vapor deposited silicon dioxide
  • the first and second electrical connections 42, 43 may be formed by depositing a metallic layer 41 (in some cases including an underlying sticking or barrier layer) on the cap insulating layer 40 and by patterning the metallic layer 41 to form the first and second electrical connections 42, 43.
  • the first and second electrical connections 42, 43 are formed so that they establish an electrical contact with the guard ring 54 and the electrode 13, respectively.
  • a passivating layer 45 may also be applied over the first and second electrical connections 42, 43. As mentioned above, the passivating layer 45 can extend over substantially the entire surface of the second side 122 of the top cap wafer 10. Finally, openings may be formed in the passivating layer 45 to expose at least partially the first and second electrical connections 42, 43.
  • the guard ring 54 can be held at the same or at a similar electrical potential as its associated electrode 13, thus contributing to reducing parasitic capacitance and other detrimental electrical coupling effects between the electrode 13 and its environment.
  • the method includes a step of bonding the first side 121 of the top cap wafer 12 to the top side 161 of the MEMS wafer 16 to form the MEMS device 10 in a manner such that an electrical connection is established between the electrode 13 and the MEMS structure 17.
  • the electrical connection between the electrode 13 and the MEMS structure 17 is a capacitive electrical connection, but a resistive or inductive electrical connection may be envisioned without departing from the scope of the present invention.
  • Bonding the first side 121 of the top cap wafer 12 to the top side 161 of the MEMS wafer 16 can made with a conductive bond.
  • a conductive bond For example, fusion bonding can be used but other alternatives can be considered, such as using a conducting material. Bonding can be made for example using gold thermocompression bonding, or gold- silicon eutectic bonding.
  • the method may also include a step of bonding a bottom cap wafer 14 to the bottom side of the MEMS wafer 16.
  • the bottom cap wafer 14 may, but need not, be provided with electrodes 15 surrounded by guard rings 54.
  • the number, size, shape and configuration of the electrodes 15 and guard rings 54 formed in the bottom cap wafer 14 may, but need not, be identical to the number, size, shape and configuration of the electrodes 13 and guard rings 54 formed in the top cap wafer 12.
  • the method steps illustrated in Fig 3G may be performed before the steps performed in Figs 3E and 3F, without departing from the scope of the present invention.
  • Those skilled in the art will recognize that, in some embodiments, it may be desirable or necessary that electrodes, guard rings and other structures formed into a cap wafer of a MEMS device satisfy certain criteria or requirements in terms of size.
  • the minimum width of the inner and outer insulating channels bordering a guard ring and its associated electrode is generally controlled by the resolution of the etching techniques used to defined trenches formed in the cap wafers. As the size of MEMS devices is reduced, so is the available surface area to that can be used to form electrodes. In turn, a smaller electrode is associated with lower capacitance and reduced sensitivity.
  • the maximum area that can be occupied by electrodes is further reduced by the presence of guard rings.
  • each of the inner and outer trenches 28a, 28b is typically between 5 and 50 micrometers ( m) wide.
  • the guard ring 54 generally has to be at least as wide as the trenches 28a, 28b.
  • FIGs 4A to 4H there are schematically illustrated fabrication steps of a second exemplary embodiment of the method for manufacturing a MEMS device.
  • this second exemplary embodiment can provides a reduction of the area occupied by guard rings, with a resulting increase in electrode area.
  • the second exemplary embodiment illustrated in Figs 4A to 4H share common steps with the first exemplary embodiment described above and illustrated in Figs 3A to 3G. Accordingly, the description of these common steps and of any features or variants thereof that were provided above will not be repeated in detail hereinbelow.
  • the method first includes a step of providing a top cap wafer 12 and a MEMS wafer 16.
  • the top cap wafer 12 has opposed first and second sides 121 , 122 and a thickness 123 extending therebetween, and the MEMS wafer 16 has opposed top and bottom sides 161 , 162.
  • the top cap wafer 12 and the MEMS wafer 16 are each made of an electrically conductive semiconductor material 30 such as, for example a silicon-based semiconductor.
  • the MEMS wafer 16 may be an SOI wafer including a device layer 20, a handle layer 22 and an insulating layer 24 sandwiched between the device layer 20 and the handle layer 22.
  • the MEMS wafer 16 includes a MEMS structure 17 which can include or be embodied by any sensing element or combination of sensing elements such as, but not limited to, membranes, diaphragms, proof masses, comb sensors, actuators, transducers, micro-valves, micro-pumps, and the like.
  • the MEMS device is a MEMS motion sensor including a pendulous proof mass 171
  • the method next includes a step of forming one or more electrode structures from the first side into the top cap wafer, wherein each electrode structure include an electrode and a guard ring laterally surrounding and electrically insulated from the electrode.
  • the step of forming an electrode structure can include a first substep of forming a single closed-loop trench 28 having inner and outer sidewalls 31 a, 31 b, rather than forming a pair of spaced-apart inner and outer electrodes as in the embodiment of Figs 3A to 3G.
  • the trench 28 extends from the first side 121 partially into the top cap wafer 12, and may be defined using a suitable etching process.
  • Fig 4B is a schematic plan view of the top cap wafer 12 illustrating the two-dimensional closed-loop path defined by the single trench 28. It can be seen that the trench 28 laterally borders a volume 29 of the top cap wafer 12 corresponding to the electrode 13 to be formed.
  • the step of forming an electrode structure can include a second substep of lining the inner and outer sidewalls 31 a, 31 b of the trench 28 with an electrically insulating material 30 to form an insulator-lined trench.
  • the electrically insulating material 30 may include silicon dioxide (S1O2) or any other suitable material.
  • Various deposition processes may be used to line the inner and outer sidewalls 31 a, 31 b of the trench 28 with the electrically insulating material 30.
  • the step of forming an electrode structure can include a third substep of depositing an electrically conductive material 32 into the insulator-lined trench, for example polysilicon or a metal such as copper.
  • the deposited electrically conductive material 32 corresponds to the guard ring to be formed.
  • the step of forming an electrode structure can include a fourth substep of removing top cap wafer material from the second side 122 of the top cap wafer 12 to expose the electrically conducting material 32, which can include at least one of grinding, polishing and etching.
  • the electrode 13 and the guard ring 54 are formed and are electrically insulated from each other by the electrically insulating material 30 lining the inner sidewall 31 a.
  • the electrode 13 and the guard ring 54 each extends through the entire thickness 123 of the top cap wafer 12.
  • the method can include successive substeps of (i) forming a cap insulating layer 40, typically thermally or chemical vapor deposited silicon dioxide, on the second side 122 of the top cap wafer 12; (ii) partially removing the cap insulating layer 40, for example by selective etching, to expose at least a portion of the guard ring 54 and at least a portion of the electrode 13; and (iii) forming first and second electrical connections 42, 43 on the exposed portions of the guard ring 54 and the electrode 13, respectively.
  • a cap insulating layer 40 typically thermally or chemical vapor deposited silicon dioxide
  • the first and second electrical connections 42, 43 may be formed by depositing a metallic layer 41 (in some cases including an underlying sticking or barrier layer) on the cap insulating layer 40 and by patterning the metallic layer 41 to form the first and second electrical connections 42, 43.
  • the first and second electrical connections 42, 43 are formed so that they establish an electrical contact with the guard ring 54 and the electrode 13, respectively.
  • a passivating layer 45 may also be applied over the first and second electrical connections 42, 43, and be etched to form openings exposing at least partially the first and second electrical connections 42, 43.
  • the method includes a step of bonding the first side 121 of the top cap wafer 12 to the top side 161 of the MEMS wafer 16 to form the MEMS device 10 in a manner such that an electrical connection is established between the electrode 13 and the MEMS structure 17.
  • a bottom cap wafer 14 may also be bonded to the bottom side of the MEMS wafer 16, which may or may not electrode guard rings 54.
  • the method steps illustrated in Fig 4H may be performed before the steps performed in Figs 4F and 4G, without departing from the scope of the present invention.
  • FIG 6 there is provided an enlarged view of a portion of Fig 4G, illustrating a guard ring 54 defined by electrically conducting material 32 filing a trench 28 whose inner and outer sidewalls 31 a, 31 b were previously lined with an electrically insulating material 30.
  • the minimum achievable width of the trench 28 typically ranges from 5 to 50 m, with the guard ring 54 being necessarily at least slightly narrower than the trench 28.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Electromagnetism (AREA)
  • Computer Hardware Design (AREA)
  • Micromachines (AREA)
  • Pressure Sensors (AREA)

Abstract

La présente invention concerne un dispositif MEMS, qui comprend un anneau protecteur qui entoure une électrode, et un procédé de fabrication d'un tel dispositif MEMS. Le procédé comprend la fourniture d'une tranche formant coiffe supérieure qui possède une épaisseur, et d'une tranche MEMS qui présente une structure MEMS, la tranche MEMS et la tranche formant coiffe supérieure étant constituées d'un matériau semi-conducteur électroconducteur. Le procédé comprend également la formation d'une structure d'électrode dans un premier côté de la tranche formant coiffe supérieure. La structure d'électrode comprend une électrode et un anneau protecteur qui entoure latéralement l'électrode et est électriquement isolé de cette dernière, l'électrode et l'anneau protecteur s'étendant chacun à travers l'épaisseur entière de la tranche formant coiffe supérieure. Le procédé comprend également la liaison du premier côté de la tranche formant coiffe supérieure à un côté supérieur de la tranche MEMS de sorte qu'une connexion électrique soit établie entre l'électrode et la structure MEMS.
PCT/CA2014/050904 2013-09-24 2014-09-19 Dispositif mems comprenant un anneau protecteur d'électrode et procédé de fabrication associé WO2015042701A1 (fr)

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Cited By (8)

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WO2016044932A1 (fr) * 2014-09-23 2016-03-31 Motion Engine Inc. Procédé de fabrication de capteur inertiel 3d
US10214414B2 (en) 2014-01-09 2019-02-26 Motion Engine, Inc. Integrated MEMS system
US10273147B2 (en) 2013-07-08 2019-04-30 Motion Engine Inc. MEMS components and method of wafer-level manufacturing thereof
US10407299B2 (en) 2015-01-15 2019-09-10 Motion Engine Inc. 3D MEMS device with hermetic cavity
US10768065B2 (en) 2014-04-10 2020-09-08 Mei Micro, Inc. MEMS pressure sensor
US11287486B2 (en) 2014-12-09 2022-03-29 Motion Engine, Inc. 3D MEMS magnetometer and associated methods
US11674803B2 (en) 2014-06-02 2023-06-13 Motion Engine, Inc. Multi-mass MEMS motion sensor
US11852481B2 (en) 2013-08-02 2023-12-26 Motion Engine Inc. MEMS motion sensor and method of manufacturing

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EP1802952B1 (fr) * 2004-10-18 2010-03-03 Silverbrook Research Pty. Ltd Capteur de pression micro électromécanique
US20130115729A1 (en) * 2004-10-18 2013-05-09 Precision Mechatronics Pty Ltd Lithographic fabrication process for a pressure sensor
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EP1802952B1 (fr) * 2004-10-18 2010-03-03 Silverbrook Research Pty. Ltd Capteur de pression micro électromécanique
US20130115729A1 (en) * 2004-10-18 2013-05-09 Precision Mechatronics Pty Ltd Lithographic fabrication process for a pressure sensor
JP2008114354A (ja) * 2006-11-08 2008-05-22 Seiko Epson Corp 電子装置及びその製造方法
JP2013164285A (ja) * 2012-02-09 2013-08-22 Seiko Epson Corp 電子デバイスおよびその製造方法、並びに電子機器

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10273147B2 (en) 2013-07-08 2019-04-30 Motion Engine Inc. MEMS components and method of wafer-level manufacturing thereof
US11852481B2 (en) 2013-08-02 2023-12-26 Motion Engine Inc. MEMS motion sensor and method of manufacturing
US10214414B2 (en) 2014-01-09 2019-02-26 Motion Engine, Inc. Integrated MEMS system
US10768065B2 (en) 2014-04-10 2020-09-08 Mei Micro, Inc. MEMS pressure sensor
US11579033B2 (en) 2014-04-10 2023-02-14 Mei Micro, Inc. MEMS pressure sensor
US11674803B2 (en) 2014-06-02 2023-06-13 Motion Engine, Inc. Multi-mass MEMS motion sensor
WO2016044932A1 (fr) * 2014-09-23 2016-03-31 Motion Engine Inc. Procédé de fabrication de capteur inertiel 3d
US11287486B2 (en) 2014-12-09 2022-03-29 Motion Engine, Inc. 3D MEMS magnetometer and associated methods
US10407299B2 (en) 2015-01-15 2019-09-10 Motion Engine Inc. 3D MEMS device with hermetic cavity

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