US20020022291A1 - Production method for integrated angular speed sensor device - Google Patents
Production method for integrated angular speed sensor device Download PDFInfo
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- US20020022291A1 US20020022291A1 US09/791,965 US79196501A US2002022291A1 US 20020022291 A1 US20020022291 A1 US 20020022291A1 US 79196501 A US79196501 A US 79196501A US 2002022291 A1 US2002022291 A1 US 2002022291A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
- G01C19/5719—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using planar vibrating masses driven in a translation vibration along an axis
- G01C19/5733—Structural details or topology
- G01C19/574—Structural details or topology the devices having two sensing masses in anti-phase motion
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
- G01C19/5719—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using planar vibrating masses driven in a translation vibration along an axis
- G01C19/5769—Manufacturing; Mounting; Housings
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- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/76—Making of isolation regions between components
- H01L21/762—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers
- H01L21/76202—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using a local oxidation of silicon, e.g. LOCOS, SWAMI, SILO
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/76—Making of isolation regions between components
- H01L21/764—Air gaps
Definitions
- the present invention relates to an integrated angular speed sensor device and the production method thereof.
- an angular speed sensor or gyroscope, or yaw sensor, is a device which can measure the variation of direction of the speed vector of a moving body.
- Angular sensors can be used in the car industry, for ABS, active suspensions, ASR, dynamic control of the vehicle and inertial navigation systems; in consumer goods, for image stabilization systems in cinecameras, in sports equipment, in three-dimensional “mice”; in industrial process control, for example in the control of industrial machines, in robotics; in the medical field; and in the military field, for new weapons systems.
- the first vibrating gyroscopes were thus produced: they measure the angular speed of the systems on which they are fitted, by detecting the effect of the Coriolis force on a mass which vibrates in the non-inertial rotating system. In these sensors it is essential for the sensing mass to be kept moving by means of an actuation mechanism.
- the first gyroscope produced in the 1950s used a magnetic field for excitation of the sensing mass and detection of the Coriolis force; subsequently in the 1960s, the piezoelectric effect, which is now the most commonly used type, was employed (see for example B. Johnson, “Vibrating Rotation Sensors”, Sensors and Actuators, 1995, SAE, SP-1066, pages 41-47).
- the present invention provides a motion-sensing device that is a vibrating-type, integrated angular speed sensor and a production method that results in a motion-sensing device at a low cost, and with a high level of performance and reliability.
- the integrated angular speed sensor device includes a mobile structure anchored to a semiconductor material body and having first mobile excitation electrodes which are intercalated with first fixed excitation electrodes.
- the first mobile and first fixed excitation electrodes have a first direction of extension.
- the speed sensor device also includes second mobile detection electrodes which are intercalated with second fixed detection electrodes.
- the second mobile and second fixed detection electrodes have a second direction of extension which is substantially perpendicular to said first direction.
- the present invention includes a method for production of an integrated angular speed sensor device.
- the method includes forming a mobile structure having first mobile excitation electrodes which are intercalated with first fixed excitation electrodes and which extend in a first direction of extension and forming second mobile detection electrodes which are intercalated with second fixed detection electrodes which extend in a second direction of extension which is substantially perpendicular to said first direction.
- FIG. 1 is a simplified plan view of part of an integrated circuit incorporating a motion-sensing device, in accordance with embodiments of the present invention
- FIG. 2 is an enlarged view of a portion of the integrated circuit of FIG. 1, in accordance with embodiments of the present invention
- FIG. 3 is a simplified isometric cross-section of a portion of the motion-sensing device of FIG. 1, in accordance with embodiments of the present invention
- FIG. 4 is a simplified cross-sectional view of the motion-sensing device, taken along the plane IV-IV of FIG. 3, in accordance with embodiments of the present invention
- FIGS. 5 - 12 are simplified cross-sectional views through a wafer of semiconductor material incorporating the motion-sensing device, in accordance with embodiments of the present invention.
- FIG. 13 is a simplified plan view of the motion-sensing device, showing the shape of buried regions which are formed in an intermediate step of the present method, in accordance with embodiments of the present invention.
- the present device includes a motion-sensing device 1 and related signal processing circuitry.
- the motion-sensing device 1 which is shown in detail in FIGS. 1 - 3 , has a structure which is symmetrical with respect to a horizontal central axis indicated at A in FIG. 1, in which, consequently, only approximately half of the motion-sensing device 1 is shown.
- the motion-sensing device 1 comprises two mobile masses 2 a and 2 b , which are connected to one another and are anchored to a bulk region 12 of N + -doped polycrystalline silicon by anchorage elements 3 and 4 .
- the mobile masses 2 a , 2 b have substantially the shape of two adjacent squares or rectangles which have first sides 10 a facing one another, second sides 10 b are parallel to the first sides, and third and fourth sides 10 c , 10 d perpendicular to the first and second sides 10 a , 10 b . From the first sides 10 a of the mobile masses 2 a , 2 b (which face one another) there extend the anchorage elements 4 .
- the mobile electrodes 6 a extend from the third and fourth sides 10 c , 10 d of each of the mobile masses 2 a , 2 b , perpendicularly to the sides 10 c , 10 d , and form mobile excitation electrodes
- the mobile electrodes 6 b extend from the second side 10 b of each mobile mass 2 a , 2 b , perpendicularly to the second side 10 b , and form mobile detection electrodes.
- the anchorage elements 3 extend from the comers of the mobile masses 2 a , 2 b between the third side 10 c , the second side 10 b and the fourth side 10 d of the mobile masses 2 a , 2 b .
- the anchorage elements 3 are L-shaped and comprise, starting from the mobile mass 2 a , 2 b , a first section 3 a which is parallel to the mobile electrodes 6 a , and a second section 3 b which is parallel to the mobile electrodes 6 b .
- the second section 3 b extends away from the mobile electrodes 6 a .
- the anchorage elements 4 extend from the center of the first sides 10 a of the mobile masses 2 a , 2 b .
- the anchorage elements 4 starting from the mobile masses 2 a , 2 b , comprise first sections 4 a which are parallel to the mobile electrodes 6 a ; second sections 4 b which are U-shaped, with concavities which face one another, and a third section 4 c which is common to the two anchorage elements 4 which face one another, thereby forming two forks 5 which face one another and extend between the two mobile masses 2 a , 2 b.
- the mobile electrodes 6 a , 6 b are intercalated or interdigitated (alternate) with fixed electrodes 7 a 1 , 7 a 2 and 7 b 1 , 7 b 2 , starting from respective fixed regions 8 a 1 , 8 a 2 and 8 b 1 , 8 b 2 .
- the fixed electrodes 7 a 1 and 7 a 2 are interdigitated with the mobile electrodes 6 a and are adjacent to one another.
- the fixed electrodes 7 a 1 are disposed in the vicinity of the anchorage elements 4 and the fixed electrodes 7 a 2 are disposed in the vicinity of the anchorage elements 3 .
- the fixed electrodes 7 b 1 and 7 b 2 are interdigitated with the mobile electrodes 6 b and are adjacent to one another.
- the fixed electrodes 7 b 1 are disposed on the left in FIG. 1, and the fixed electrodes 7 b 2 are disposed on the right.
- the fixed electrodes 7 a 2 are biased to a positive voltage with respect to the fixed electrodes 7 a 1 , as symbolized in the Figure by the voltages V + and V ⁇ .
- the voltage V + applied to the fixed electrodes 7 a 2 is a square wave, and is in counter-phase or phase opposition for the two mobile masses 2 a , 2 b , such as to generate a direct force alternately towards the top and towards the bottom of FIG. 1.
- the fixed electrodes 7 b 1 and 7 b 2 represent the electrodes for detection of the signal generated by the mobile masses 2 a , 2 b , as described hereinafter.
- each mobile electrode 6 a , 6 b and the two facing fixed electrodes 7 a 1 , 7 a 2 , 7 b 1 , 7 b 2 in the static condition (in the absence of vibrations) is not the same, as shown in the enlarged detail in FIG. 2 in which the mobile electrodes are simply indicated as 6 and the fixed electrodes as 7 .
- each mobile electrode 6 forms two capacitors which are parallel with one another, one of which (the one which is defined by the mobile electrode 6 and by the fixed electrode 7 at a shorter distance) constitutes the capacitor which determines vibration of the two mobile masses 2 a and 2 b or generation of the signal that is detected and processed to determine the angular speed of the device.
- the various regions which form the mobile masses 2 a , 2 b , the mobile electrodes 6 a , 6 b , the anchorage elements 3 , 4 , the fixed regions 8 a 1 , 8 a 2 , 8 b 1 , 8 b 2 and the fixed electrodes 7 a 1 , 7 a 2 , and 7 b 1 , 7 b 2 are separated from one another and from the bulk region 12 by a trench 13 , the overall shape of which is shown in FIG. 1.
- the bulk region 12 is surrounded by a first P-type polycrystalline epitaxial region 14 , which in turn is surrounded by a second P-type polycrystalline epitaxial region 17 .
- the two polycrystalline epitaxial regions 14 , 17 are separated from one another by a second trench 15 with a closed rectangular shape, which electrically insulates the motion-sensing device 1 from the remainder of the device.
- the fixed regions 8 a 1 , 8 a 2 , 8 b 1 , 8 b 2 and the bulk region 12 are biased by buried contacts, as shown in FIG. 3 for the regions 8 a 2 and 8 b 1 .
- the regions 8 a 2 and 8 b 1 extend above a P-type substrate 20 , and are electrically insulated therefrom by a nitride region 18 c , a nitride region 18 a , and thick oxide regions 21 a , 21 b , as shown in FIG. 13.
- the thick oxide regions 21 a , 21 b have in their center an aperture 23 , at which the fixed regions 8 a 2 and 8 b 1 are in electrical contact with respective N + buried contact regions 24 a , 24 b extending along the upper surface 30 of the substrate 20 .
- the buried contact regions 24 a , 24 b extend from the apertures 23 , below a series of insulating regions which include the nitride region 18 a , a thick oxide region 21 c and a nitride region 18 b , as shown near the sensor area for the buried contact region 24 a , which is also shown in FIG. 4.
- the buried contact regions 24 a , 24 b extend beyond the confines of the polycrystalline epitaxial region 17 , below a monocrystalline epitaxial region 37 ′′, where the buried contact regions are in electrical contact with corresponding deep contact or sinker regions, as shown in FIGS. 10 - 12 for the buried contact region 24 a , which is electrically connected to the sinker region 26 , extending from a surface 41 of the wafer.
- contact with the other fixed regions 8 a 1 , 8 a 2 , 8 b 2 and with the bulk region 12 (which is electrically coupled to the mobile masses 2 a , 2 b ) is obtained in a manner similar to that described for the fixed region 8 a 2 , and in particular the bulk region 12 is connected by a buried contact region (not shown) extending parallel to the region 24 a , along a plane parallel to that of the cross-sectional view shown in FIG. 3.
- the trench 13 extends from the surface 41 of the device as far as an air gap 16 in the area of the mobile masses 2 a , 2 b of the mobile electrodes 6 a , 6 b , of the fixed electrodes 7 a 1 , 7 a 2 , and 7 b 1 , 7 b 2 and of the anchorage elements 3 , 4 , and as far as the insulating nitride regions 18 a in the area of the fixed regions 8 a 1 , 8 a 2 and 8 b 1 , 8 b 2 .
- the trench 15 extends from the surface 41 of the device as far as the insulating nitride region 18 b.
- the presence of the two mobile masses 2 a , 2 b and of the anchorage forks 5 makes it possible to eliminate, by suitable signal processing, effects caused by apparent inertial forces to which the two mobile masses are subjected.
- the non-inertial system does not rotate, but is subject to linear acceleration A
- the two mobile masses 2 a , 2 b (which have the same mass m) are subjected to a force F a which is the same for both.
- the Coriolis force F c is dependent on the direction of the speed vector, and by subtracting the signals detected by the fixed electrodes 7 b 1 , 7 b 2 , it is possible to eliminate the common effect caused by the inertial force F a . If W is the angular speed of the non-inertial system, and A is its linear acceleration, the Coriolis force F c which acts on the mobile mass with a mass m moving with a speed V relative to the rotating system, is provided by the vector product:
- both excitation and detection are electrostatic.
- the pairs of electrodes 6 a , 7 a 1 , 7 2 make the mobile masses 2 a , 2 b oscillate along the axis Y at their resonance frequency, thus optimizing the conversion of the electrical energy into mechanical energy.
- the pairs of electrodes 6 b , 7 b 1 , 7 b 2 owing to the effect of the vibration (aforementioned force F a ) and of the rotation (Coriolis force F c ), which give rise to variation of the distance of the electrodes in the direction X, detect a variation of the capacitance associated with the pairs of electrodes 6 b , 7 b 1 , 7 b 2 , and generate a corresponding signal which can be processed by the associated circuitry.
- the motion-sensing device 1 is manufactured in the manner described hereinafter with reference to FIGS. 5 - 13 , in which the thicknesses of the various layers of material are not shown to scale, and some layers are not shown in all Figures, for clarity of representation and ease of understanding.
- a sensor area 32 and a circuitry area 34 are defined in the P-type monocrystalline silicon substrate 20 by conventional photomasking and ion implantation techniques.
- the N + buried contact regions are similarly formed (only the buried contact region 24 a is shown in FIG. 5).
- a pad oxide layer 31 is formed, for example thermally grown, on the surface 30 of the substrate 20 with a thickness of 200-900 ⁇ .
- a silicon nitride layer 18 is deposited, with a thickness of 700-3000 ⁇ , above the pad oxide layer 31 .
- the silicon nitride layer 18 is then photolithographically defined to have the shape shown in FIG. 13.
- the portions of the surface 30 of the substrate 20 which are not covered by the nitride layer 18 are then locally oxidized, with formation of thick oxide regions which comprise a sacrificial region 33 and the buried oxide regions 21 a , 21 b and 21 c (only the regions 33 , 21 a and 21 c are shown in FIG. 6), as well as similar regions for buried contact with the other electrodes.
- FIG. 13 showing the various nitride and oxide regions which are present in this step.
- plasma etching removes the portions of the layers 31 , 18 in the sensor area 32 where the buried contacts of the motion-sensing device 1 are to be formed (apertures 23 ), and removes the silicon nitride layer 18 in the circuitry area 34 .
- This provides the structure of FIG. 7, wherein the nitride regions 18 a , 18 b and 18 c can be seen, but the underlying pad oxide regions are not shown.
- a polycrystalline or amorphous silicon layer 35 is then deposited as shown in FIG. 8.
- the polycrystalline or amorphous silicon layer 35 is removed, with the exception of the sensor area 32 , forming a silicon region 35 ′ which represents the nucleus for a subsequent epitaxial growth step.
- the pad oxide layer 31 is removed where it is exposed, and epitaxial growth is carried out, with formation of a so-called pseudo-epitaxial P-type layer 37 .
- the pseudo-epitaxial P-type layer 37 has a polycrystalline structure in the sensor area 32 (polycrystalline region 37 ′), and has a monocrystalline structure elsewhere (monocrystalline region 37 ′′). Thereby a wafer 38 is obtained, which is shown in FIG. 9.
- the pseudo-epitaxial layer 37 is doped N-type by conventional ion implantation in order to produce sinker regions.
- a portion of the wafer 38 is shown which is slightly displaced to the left compared with FIGS. 5 - 9 .
- the sinker region 26 is formed in the monocrystalline region 37 ′′, and a N + well region 42 is formed in the polycrystalline region 37 ′, to accommodate the motion-sensing device 1 , and to form the mobile masses 2 a , 2 b , the mobile and fixed electrodes 6 , 7 , and the bulk region 12 .
- the well region 42 electrically contacts the buried contact region 24 a in the position of the aperture 23 in the buried oxide region 21 a.
- an N-type collector well 44 is formed extending from the surface 41 of the wafer 38 to the substrate 20 .
- An NPN transistor 45 is formed in the collector well 44 , having a N + collector contact region 46 , a P base region 47 , and a N + emitter region 48 .
- a dielectric layer 50 is then deposited for contact opening, for example of BPSG (Boron Phosphorous Silicon Glass). Then, by a masking and selective removal step, the contacts are opened in the circuitry area 34 and on the sinker region 26 , the dielectric layer 50 is removed from the sensor area 32 , and a metal layer is deposited and shaped, forming contacts 51 for the transistor 45 and for the motion-sensing device 1 .
- BPSG Bipolar Phosphorous Silicon Glass
- a passivation dielectric layer 52 is then deposited.
- the passivation dielectric layer 52 is removed in the area of the contact pads in order to permit electrical contacts to be made to the device, and in the sensor area 32 , resulting in the structure of FIG. 10.
- a layer of silicon carbide 53 and an oxide layer 54 are then deposited and defined, to form a mask for the subsequent step of excavating the polycrystalline region 37 ′.
- the oxide layer 54 is formed by conventional TEOS.
- the oxide layer 54 forms the masking layer for subsequent etching of the trenches, whereas the carbide layer 53 forms the masking layer during the step of removing the sacrificial regions.
- etching separates the fixed electrodes and the mobile electrodes, for separation of the fixed regions 8 a 1 , 8 a 2 and 8 b 1 , 8 b 2 from one another and from the remainder of the well 42 , in order to form the anchorage elements 3 , 4 for forming holes 56 (see FIGS. 1 and 3) inside the mobile masses 2 a and 2 b , and for insulation of regions which have different potential.
- the nitride regions 18 a , 18 b protect the substrate 20 and the buried contact region 24 a against etching.
- the holes 56 and the trenches 13 and 15 are formed, and the P-type polycrystalline epitaxial region 37 ′ is divided into the regions 14 and 17 . Therefore, the structure is obtained which is shown in cross-section in FIG. 11, taken along the same cross-sectional plane as in FIG. 3.
- the sacrificial region 33 is removed by wet etching with hydrofluoric acid or with hydrofluoric acid vapors, through the trenches 13 and 15 and the holes 56 , and the area which was previously occupied by the sacrificial region 33 forms the air gap 16 which separates the mobile masses 2 a , 2 b , the corresponding anchorage elements 3 and 4 , and the fixed electrodes 7 , from the underlying substrate 20 .
- the oxide layer 54 is also removed, whereas the silicon carbide layer 53 protects the polycrystalline silicon regions beneath, as well as the passivation dielectric layer 52 . Thereby, the structure of FIG. 12 is obtained.
- the silicon carbide layer 53 is removed from the entire wafer 38 , thus providing the structure shown in FIGS. 1 - 4 , which has previously been described.
Abstract
An angular speed sensor comprises a pair of mobile masses which are formed in an epitaxial layer and are anchored to one another and to the remainder of the device by anchorage elements. The mobile masses are symmetrical with one another, and have first mobile excitation electrodes which are intercalated with respective first fixed excitation electrodes and second mobile detection electrodes which are intercalated with second fixed detection electrodes. The first mobile and fixed excitation electrodes extend in a first direction and the second mobile and fixed detection electrodes extend in a second direction which is perpendicular to the first direction and is disposed on a single plane parallel to the surface of the device.
Description
- The present invention relates to an integrated angular speed sensor device and the production method thereof.
- As is known, an angular speed sensor, or gyroscope, or yaw sensor, is a device which can measure the variation of direction of the speed vector of a moving body.
- Angular sensors can be used in the car industry, for ABS, active suspensions, ASR, dynamic control of the vehicle and inertial navigation systems; in consumer goods, for image stabilization systems in cinecameras, in sports equipment, in three-dimensional “mice”; in industrial process control, for example in the control of industrial machines, in robotics; in the medical field; and in the military field, for new weapons systems.
- Conventional gyroscopes, which are based on conservation of the angular moment of a rotating mass, are too costly and bulky, and are insufficiently reliable for the new applications. In addition, although optical fiber and laser gyroscopes have excellent performance levels, they are too costly for the applications indicated.
- The increasing need for small, inexpensive gyroscopes has stimulated development activity in many industrial and academic research centers. In about the 1950s, the first vibrating gyroscopes were thus produced: they measure the angular speed of the systems on which they are fitted, by detecting the effect of the Coriolis force on a mass which vibrates in the non-inertial rotating system. In these sensors it is essential for the sensing mass to be kept moving by means of an actuation mechanism. The first gyroscope produced in the 1950s used a magnetic field for excitation of the sensing mass and detection of the Coriolis force; subsequently in the 1960s, the piezoelectric effect, which is now the most commonly used type, was employed (see for example B. Johnson, “Vibrating Rotation Sensors”, Sensors and Actuators, 1995, SAE, SP-1066, pages 41-47).
- At present, there is need for vibrating gyroscopes in which the motion-sensing device comprises a silicon microstructure. In fact, the possibility of using machinery and production processes which are typical of the microelectronics industry should make it possible to produce gyroscopes in large volumes and at a low cost, which are essential requirements for car industry and consumer goods applications.
- In one aspect, the present invention provides a motion-sensing device that is a vibrating-type, integrated angular speed sensor and a production method that results in a motion-sensing device at a low cost, and with a high level of performance and reliability.
- In one aspect, the integrated angular speed sensor device includes a mobile structure anchored to a semiconductor material body and having first mobile excitation electrodes which are intercalated with first fixed excitation electrodes. The first mobile and first fixed excitation electrodes have a first direction of extension. The speed sensor device also includes second mobile detection electrodes which are intercalated with second fixed detection electrodes. The second mobile and second fixed detection electrodes have a second direction of extension which is substantially perpendicular to said first direction.
- In another aspect, the present invention includes a method for production of an integrated angular speed sensor device. The method includes forming a mobile structure having first mobile excitation electrodes which are intercalated with first fixed excitation electrodes and which extend in a first direction of extension and forming second mobile detection electrodes which are intercalated with second fixed detection electrodes which extend in a second direction of extension which is substantially perpendicular to said first direction.
- For the understanding of the present invention, a preferred embodiment is now described, purely by way of non-limiting example, with reference to the attached drawings, in which:
- FIG. 1 is a simplified plan view of part of an integrated circuit incorporating a motion-sensing device, in accordance with embodiments of the present invention;
- FIG. 2 is an enlarged view of a portion of the integrated circuit of FIG. 1, in accordance with embodiments of the present invention;
- FIG. 3 is a simplified isometric cross-section of a portion of the motion-sensing device of FIG. 1, in accordance with embodiments of the present invention;
- FIG. 4 is a simplified cross-sectional view of the motion-sensing device, taken along the plane IV-IV of FIG. 3, in accordance with embodiments of the present invention;
- FIGS.5-12 are simplified cross-sectional views through a wafer of semiconductor material incorporating the motion-sensing device, in accordance with embodiments of the present invention; and
- FIG. 13 is a simplified plan view of the motion-sensing device, showing the shape of buried regions which are formed in an intermediate step of the present method, in accordance with embodiments of the present invention.
- In one embodiment, the present device includes a motion-
sensing device 1 and related signal processing circuitry. The motion-sensing device 1, which is shown in detail in FIGS. 1-3, has a structure which is symmetrical with respect to a horizontal central axis indicated at A in FIG. 1, in which, consequently, only approximately half of the motion-sensing device 1 is shown. The motion-sensing device 1 comprises twomobile masses bulk region 12 of N+-doped polycrystalline silicon byanchorage elements 3 and 4. - In detail, as viewed from above, the
mobile masses first sides 10 a facing one another,second sides 10 b are parallel to the first sides, and third andfourth sides second sides first sides 10 a of themobile masses fourth sides 10 b-10 d of each of themobile masses mobile electrodes 6 a, 6 b of the sensor, and specifically, themobile electrodes 6 a extend from the third andfourth sides mobile masses sides second side 10 b of eachmobile mass second side 10 b, and form mobile detection electrodes. - The
anchorage elements 3 extend from the comers of themobile masses third side 10 c, thesecond side 10 b and thefourth side 10 d of themobile masses anchorage elements 3 are L-shaped and comprise, starting from themobile mass first section 3 a which is parallel to themobile electrodes 6 a, and asecond section 3 b which is parallel to the mobile electrodes 6 b. Thesecond section 3 b extends away from themobile electrodes 6 a. On the other hand, the anchorage elements 4 extend from the center of thefirst sides 10 a of themobile masses mobile masses first sections 4 a which are parallel to themobile electrodes 6 a;second sections 4 b which are U-shaped, with concavities which face one another, and athird section 4 c which is common to the two anchorage elements 4 which face one another, thereby forming twoforks 5 which face one another and extend between the twomobile masses - The
mobile electrodes 6 a, 6 b are intercalated or interdigitated (alternate) with fixed electrodes 7 a 1, 7 a 2 and 7 b 1, 7 b 2, starting from respective fixed regions 8 a 1, 8 a 2 and 8 b 1, 8 b 2. In particular, the fixed electrodes 7 a 1 and 7 a 2 are interdigitated with themobile electrodes 6 a and are adjacent to one another. For both the third andfourth sides mobile masses anchorage elements 3. The fixed electrodes 7 b 1 and 7 b 2 are interdigitated with the mobile electrodes 6 b and are adjacent to one another. The fixed electrodes 7 b 1 are disposed on the left in FIG. 1, and the fixed electrodes 7 b 2 are disposed on the right. The fixed electrodes 7 a 2 are biased to a positive voltage with respect to the fixed electrodes 7 a 1, as symbolized in the Figure by the voltages V+ and V−. In one embodiment, the voltage V+ applied to the fixed electrodes 7 a 2 is a square wave, and is in counter-phase or phase opposition for the twomobile masses mobile masses mobile masses - The distance between each
mobile electrode 6 a, 6 b and the two facing fixed electrodes 7 a 1, 7 a 2, 7 b 1, 7 b 2 in the static condition (in the absence of vibrations) is not the same, as shown in the enlarged detail in FIG. 2 in which the mobile electrodes are simply indicated as 6 and the fixed electrodes as 7. Thereby, together with the twofixed electrodes 7 which faces it, eachmobile electrode 6 forms two capacitors which are parallel with one another, one of which (the one which is defined by themobile electrode 6 and by thefixed electrode 7 at a shorter distance) constitutes the capacitor which determines vibration of the twomobile masses - In one embodiment of the motion-
sensing device 1, the various regions which form themobile masses mobile electrodes 6 a, 6 b, theanchorage elements 3, 4, the fixed regions 8 a 1, 8 a 2, 8 b 1, 8 b 2 and the fixed electrodes 7 a 1, 7 a 2, and 7 b 1, 7 b 2 (which, in one embodiment, all comprise polycrystalline silicon of N+-type) are separated from one another and from thebulk region 12 by atrench 13, the overall shape of which is shown in FIG. 1. In one embodiment, thebulk region 12 is surrounded by a first P-type polycrystallineepitaxial region 14, which in turn is surrounded by a second P-type polycrystallineepitaxial region 17. The two polycrystallineepitaxial regions second trench 15 with a closed rectangular shape, which electrically insulates the motion-sensing device 1 from the remainder of the device. - The fixed regions8 a 1, 8 a 2, 8 b 1, 8 b 2 and the
bulk region 12 are biased by buried contacts, as shown in FIG. 3 for the regions 8 a 2 and 8 b 1. In one embodiment, the regions 8 a 2 and 8 b 1 extend above a P-type substrate 20, and are electrically insulated therefrom by anitride region 18 c, anitride region 18 a, andthick oxide regions thick oxide regions aperture 23, at which the fixed regions 8 a 2 and 8 b 1 are in electrical contact with respective N+ buriedcontact regions upper surface 30 of thesubstrate 20. In one embodiment, the buriedcontact regions apertures 23, below a series of insulating regions which include thenitride region 18 a, athick oxide region 21 c and anitride region 18 b, as shown near the sensor area for the buriedcontact region 24 a, which is also shown in FIG. 4. The buriedcontact regions epitaxial region 17, below a monocrystallineepitaxial region 37″, where the buried contact regions are in electrical contact with corresponding deep contact or sinker regions, as shown in FIGS. 10-12 for the buriedcontact region 24 a, which is electrically connected to thesinker region 26, extending from asurface 41 of the wafer. As shown, contact with the other fixed regions 8 a 1, 8 a 2, 8 b 2 and with the bulk region 12 (which is electrically coupled to themobile masses bulk region 12 is connected by a buried contact region (not shown) extending parallel to theregion 24 a, along a plane parallel to that of the cross-sectional view shown in FIG. 3. - As can be seen in FIG. 3, the
trench 13 extends from thesurface 41 of the device as far as anair gap 16 in the area of themobile masses mobile electrodes 6 a, 6 b, of the fixed electrodes 7 a 1, 7 a 2, and 7 b 1, 7 b 2 and of theanchorage elements 3, 4, and as far as theinsulating nitride regions 18 a in the area of the fixed regions 8 a 1, 8 a 2 and 8 b 1, 8 b 2. Thetrench 15 extends from thesurface 41 of the device as far as theinsulating nitride region 18 b. - In the above-described embodiment of the motion-
sensing device 1, the presence of the twomobile masses anchorage forks 5 makes it possible to eliminate, by suitable signal processing, effects caused by apparent inertial forces to which the two mobile masses are subjected. In fact, if the non-inertial system does not rotate, but is subject to linear acceleration A, the twomobile masses - F c=2m(W×V),
- whereas the inertial force Fa caused by the effect of the acceleration A is:
- F a =mA.
- Since the two
mobile masses - In the structure shown, both excitation and detection are electrostatic. The pairs of
electrodes mobile masses - In some embodiments, the motion-sensing
device 1 is manufactured in the manner described hereinafter with reference to FIGS. 5-13, in which the thicknesses of the various layers of material are not shown to scale, and some layers are not shown in all Figures, for clarity of representation and ease of understanding. - As shown in the embodiment of FIG. 5, a
sensor area 32 and acircuitry area 34 are defined in the P-typemonocrystalline silicon substrate 20 by conventional photomasking and ion implantation techniques. The N+ buried contact regions are similarly formed (only the buriedcontact region 24 a is shown in FIG. 5). Apad oxide layer 31 is formed, for example thermally grown, on thesurface 30 of thesubstrate 20 with a thickness of 200-900 Å. Asilicon nitride layer 18 is deposited, with a thickness of 700-3000 Å, above thepad oxide layer 31. Thesilicon nitride layer 18 is then photolithographically defined to have the shape shown in FIG. 13. The portions of thesurface 30 of thesubstrate 20 which are not covered by thenitride layer 18 are then locally oxidized, with formation of thick oxide regions which comprise asacrificial region 33 and the buriedoxide regions regions - Subsequently, after a photolithography step, plasma etching removes the portions of the
layers sensor area 32 where the buried contacts of the motion-sensingdevice 1 are to be formed (apertures 23), and removes thesilicon nitride layer 18 in thecircuitry area 34. This provides the structure of FIG. 7, wherein thenitride regions - A polycrystalline or
amorphous silicon layer 35 is then deposited as shown in FIG. 8. By a photolithography and plasma etching step, the polycrystalline oramorphous silicon layer 35 is removed, with the exception of thesensor area 32, forming asilicon region 35′ which represents the nucleus for a subsequent epitaxial growth step. Then, by an etching step, thepad oxide layer 31 is removed where it is exposed, and epitaxial growth is carried out, with formation of a so-called pseudo-epitaxial P-type layer 37. The pseudo-epitaxial P-type layer 37 has a polycrystalline structure in the sensor area 32 (polycrystalline region 37′), and has a monocrystalline structure elsewhere (monocrystalline region 37″). Thereby awafer 38 is obtained, which is shown in FIG. 9. - Subsequently, the
pseudo-epitaxial layer 37 is doped N-type by conventional ion implantation in order to produce sinker regions. In one embodiment, as shown in FIG. 10, a portion of thewafer 38 is shown which is slightly displaced to the left compared with FIGS. 5-9. Thesinker region 26 is formed in themonocrystalline region 37″, and a N+ well region 42 is formed in thepolycrystalline region 37′, to accommodate the motion-sensingdevice 1, and to form themobile masses electrodes bulk region 12. In particular, thewell region 42 electrically contacts the buriedcontact region 24 a in the position of theaperture 23 in the buriedoxide region 21 a. - Subsequently, the electronic elements of the circuitry are formed in the
circuitry area 34 by conventional processing steps. In the example shown, an N-type collector well 44 is formed extending from thesurface 41 of thewafer 38 to thesubstrate 20. AnNPN transistor 45 is formed in the collector well 44, having a N+collector contact region 46, aP base region 47, and a N+ emitter region 48. - On the
surface 41 of thewafer 38, adielectric layer 50 is then deposited for contact opening, for example of BPSG (Boron Phosphorous Silicon Glass). Then, by a masking and selective removal step, the contacts are opened in thecircuitry area 34 and on thesinker region 26, thedielectric layer 50 is removed from thesensor area 32, and a metal layer is deposited and shaped, formingcontacts 51 for thetransistor 45 and for the motion-sensingdevice 1. - A
passivation dielectric layer 52 is then deposited. Thepassivation dielectric layer 52 is removed in the area of the contact pads in order to permit electrical contacts to be made to the device, and in thesensor area 32, resulting in the structure of FIG. 10. - Then, a layer of
silicon carbide 53 and anoxide layer 54 are then deposited and defined, to form a mask for the subsequent step of excavating thepolycrystalline region 37′. In one embodiment, theoxide layer 54 is formed by conventional TEOS. In one embodiment, theoxide layer 54 forms the masking layer for subsequent etching of the trenches, whereas thecarbide layer 53 forms the masking layer during the step of removing the sacrificial regions. Then, etching separates the fixed electrodes and the mobile electrodes, for separation of the fixed regions 8 a 1, 8 a 2 and 8 b 1, 8 b 2 from one another and from the remainder of the well 42, in order to form theanchorage elements 3, 4 for forming holes 56 (see FIGS. 1 and 3) inside themobile masses nitride regions substrate 20 and the buriedcontact region 24 a against etching. Thereby, theholes 56 and thetrenches polycrystalline epitaxial region 37′ is divided into theregions - Finally, the
sacrificial region 33 is removed by wet etching with hydrofluoric acid or with hydrofluoric acid vapors, through thetrenches holes 56, and the area which was previously occupied by thesacrificial region 33 forms theair gap 16 which separates themobile masses anchorage elements 3 and 4, and the fixedelectrodes 7, from the underlyingsubstrate 20. In this step, theoxide layer 54 is also removed, whereas thesilicon carbide layer 53 protects the polycrystalline silicon regions beneath, as well as thepassivation dielectric layer 52. Thereby, the structure of FIG. 12 is obtained. By subsequent plasma etching, thesilicon carbide layer 53 is removed from theentire wafer 38, thus providing the structure shown in FIGS. 1-4, which has previously been described. - Some advantages of the described device and production method are as follows. The structure of the above-described sensor element, with detection electrodes extending perpendicularly to the excitation electrodes, make it possible to directly detect the signal generated by virtue of speed variations of the device. Additionally, it is compatible with the process steps for production of integrated circuits, permitting integration of the motion-sensing
device 1 and of the circuitry which processes the signal generated by the latter on a single integrated circuit. In this respect, it is particularly advantageous that an electrostatic solution is used both for excitation of the motion-sensingdevice 1, and for detection of the response. In the structure described, the connection of the twomobile masses forks 5 ensures matching of the respective resonance frequencies. In turn, this permits elimination in a simple manner of the inertial acceleration effect. - Production of the two
mobile masses - Finally, it will be appreciated that many modifications and variants can be made to the device and the method described here, all of which are within the context of the inventive concept, as defined in the attached claims. In particular, the types of doping of the various regions can be inverted with one another; the circuitry can comprise both bipolar and MOS devices, and the details can be replaced by others which are technically equivalent.
- From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.
Claims (10)
1. A method for production of an integrated angular speed sensor device, comprising:
forming a sacrificial region on a substrate of semiconductor material;
growing a pseudo-epitaxial layer including a polycrystalline epitaxial region in contact with the sacrificial region and a monocrystalline epitaxial region in contact with the substrate;
forming electronic elements in the monocrystalline epitaxial region;
removing selective portions of the polycrystalline epitaxial region thereby forming excitation electrodes that are intercalated with fixed excitation electrodes that extend in a first direction of extension; forming mobile detection electrodes that are intercalated with fixed detection electrodes that extend in a second direction of extension which is substantially perpendicular to the first direction; and forming a trench separating from one another the mobile and fixed excitation and detection electrodes; and
removing the sacrificial region through the trench.
2. A method according to claim 1 wherein removing the sacrificial region comprises removing a silicon oxide region.
3. A method according to claim 1 wherein the pseudo-epitaxial layer and the substrate have a first conductivity type, the method further comprising:
forming in the substrate buried contact regions with a second conductivity type before growing the pseudo-epitaxial layer;
forming regions of electrically isolating material extending above the buried contact regions and delimiting between one another selective contact portions of the buried contact regions;
forming a well region having the second conductivity type above the sacrificial region after growing the pseudo-epitaxial layer; and
forming sinker contact regions having the second conductivity type and extending from a surface of the pseudo-epitaxial layer as far as the buried contact regions thereby forming sinker contacts, after growing the pseudo-epitaxial layer.
4. A method according to claim 1 , further comprising:
forming a first mask of silicon carbide above the pseudo-epitaxial layer, the first mask protecting regions beneath during the step of removing the sacrificial region; and
forming a second mask of silicon oxide above the first mask, the second mask protecting the first mask during the step of formation of the trench.
5. A method for production of an integrated angular speed sensor device, the method comprising:
forming a mobile structure flexibly anchored to a semiconductor body, the mobile structure including mobile excitation electrodes and mobile detection electrodes;
forming on the semiconductor body fixed excitation electrodes alternating with the mobile excitation electrodes, the mobile and fixed excitation electrodes having a first direction of extension;
forming on the semiconductor body fixed detection electrodes alternating with the mobile detection electrodes, the mobile and fixed detection electrodes having a second direction of extension at an angle to the first direction, the mobile and fixed excitation and detection electrodes all being in the plane of the surface; and
forming in the semiconductor body, prior to forming the mobile and fixed excitation and detection electrodes, a buried contact region that is doped to provide a conductive path, wherein one of the fixed excitation and detection electrodes is formed in connection with the buried contact region.
6. The method of claim 5 wherein the semiconductor body is a monocrystalline substrate, the method further comprising:
growing a monocrystalline epitaxial region in contact with the substrate and the buried contact region; and
forming electronic elements in the monocrystalline epitaxial region.
7. The method of claim 6 , further comprising forming a conductive sinker contact region extending through the monocrystalline epitaxial region as far as the buried contact region, after growing the monocrystalline epitaxial region.
8. The method of claim 5 wherein forming the mobile structure and fixed excitation and detection electrodes includes:
forming a sacrificial region on the semiconductor body;
growing a polycrystalline epitaxial region in contact with the sacrificial region;
removing selective portions of the polycrystalline epitaxial region to form the mobile structure and fixed excitation and detection electrodes and a trench separating from one another the mobile and fixed excitation and detection electrodes; and
removing the sacrificial region through the trench to release the mobile structure from the semiconductor body.
9. A method according to claim 8 , further comprising:
forming a first mask of silicon carbide above the polycrystalline epitaxial region, the first mask protecting regions beneath the first mask during the step of removing the sacrificial region; and
forming a second mask of silicon oxide above the first mask, the second mask protecting the first mask during the step of formation of the trench.
10. The method of claim 8 wherein the semiconductor body is a monocrystalline substrate, the method further comprising:
growing a monocrystalline epitaxial region in contact with the substrate and the buried contact region; and
forming electronic elements in the monocrystalline epitaxial region.
Priority Applications (1)
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US09/791,965 US6387725B1 (en) | 1997-10-23 | 2001-02-22 | Production method for integrated angular speed sensor device |
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
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EP97830537A EP0911606A1 (en) | 1997-10-23 | 1997-10-23 | Integrated angular speed sensor device and production method thereof |
EP97830537.3 | 1997-10-23 | ||
EP97830537 | 1997-10-23 | ||
US09/178,285 US6209394B1 (en) | 1997-10-23 | 1998-10-23 | Integrated angular speed sensor device and production method thereof |
US09/791,965 US6387725B1 (en) | 1997-10-23 | 2001-02-22 | Production method for integrated angular speed sensor device |
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US09/178,285 Division US6209394B1 (en) | 1997-10-23 | 1998-10-23 | Integrated angular speed sensor device and production method thereof |
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US20020022291A1 true US20020022291A1 (en) | 2002-02-21 |
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US09/791,965 Expired - Lifetime US6387725B1 (en) | 1997-10-23 | 2001-02-22 | Production method for integrated angular speed sensor device |
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EP (1) | EP0911606A1 (en) |
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Cited By (3)
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US20210381833A1 (en) * | 2020-06-08 | 2021-12-09 | Analog Devices, Inc. | Drive and sense stress relief apparatus |
US20220057208A1 (en) * | 2020-08-24 | 2022-02-24 | Analog Devices, Inc. | Isotropic attenuated motion gyroscope |
US11686581B2 (en) | 2020-06-08 | 2023-06-27 | Analog Devices, Inc. | Stress-relief MEMS gyroscope |
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EP1039529B1 (en) | 1999-03-22 | 2006-12-13 | STMicroelectronics S.r.l. | Method for manufacturing a microintegrated structure with buried connections, in particular an integrated microactuator for a hard-disk drive unit |
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US6257059B1 (en) * | 1999-09-24 | 2001-07-10 | The Charles Stark Draper Laboratory, Inc. | Microfabricated tuning fork gyroscope and associated three-axis inertial measurement system to sense out-of-plane rotation |
DE10017976A1 (en) * | 2000-04-11 | 2001-10-18 | Bosch Gmbh Robert | Micromechanical component and corresponding manufacturing method |
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1998
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- 1998-10-23 JP JP10302417A patent/JPH11325916A/en active Pending
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2001
- 2001-02-22 US US09/791,965 patent/US6387725B1/en not_active Expired - Lifetime
Cited By (6)
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US20210381833A1 (en) * | 2020-06-08 | 2021-12-09 | Analog Devices, Inc. | Drive and sense stress relief apparatus |
US11686581B2 (en) | 2020-06-08 | 2023-06-27 | Analog Devices, Inc. | Stress-relief MEMS gyroscope |
US11692825B2 (en) * | 2020-06-08 | 2023-07-04 | Analog Devices, Inc. | Drive and sense stress relief apparatus |
US20220057208A1 (en) * | 2020-08-24 | 2022-02-24 | Analog Devices, Inc. | Isotropic attenuated motion gyroscope |
US11698257B2 (en) * | 2020-08-24 | 2023-07-11 | Analog Devices, Inc. | Isotropic attenuated motion gyroscope |
US11965740B2 (en) | 2020-08-24 | 2024-04-23 | Analog Devices, Inc. | Isotropic attenuated motion gyroscope |
Also Published As
Publication number | Publication date |
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US6387725B1 (en) | 2002-05-14 |
US6209394B1 (en) | 2001-04-03 |
EP0911606A1 (en) | 1999-04-28 |
JPH11325916A (en) | 1999-11-26 |
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