Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
  • H03H9/24—Constructional features of resonators of material which is not piezoelectric, electrostrictive, or magnetostrictive
  • H03H9/2405—Constructional features of resonators of material which is not piezoelectric, electrostrictive, or magnetostrictive of microelectro-mechanical resonators
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
  • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
  • H03H3/0072—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks of microelectro-mechanical resonators or networks
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
  • H03H9/02—Details
  • H03H9/02244—Details of microelectro-mechanical resonators
  • H03H2009/02488—Vibration modes
  • H03H2009/02496—Horizontal, i.e. parallel to the substrate plane

Definitions

• the present invention relates to a microresonator. Presentation of the prior art
• FIG. 1 is a perspective view of a known microresonator.
• This microresonator is described in patent WO-02/17482 entitled “Micromechanical resonator device and micro-mechanical device utilizing same”.
• This microresonator is formed above a substrate 1. It comprises a resonant element 2 in the form of a "mushroom” consisting of a cylindrical head placed on a foot fixed on the substrate. Two metal studs 3 and 4 are placed on each side of the resonant element 2. The vertical wall of each of the studs 3 and 4 facing the wall of the cylindrical head is curved and surrounds the cylindrical head. The distance between the resonant element 2 and the pads 3 and 4 is very small, of the order of a few tens of nanometers to a micrometer.
• the resonant element 2 When an alternating voltage is applied between the resonant element 2 and the studs 3 and 4, the resonant element 2 tends to deform by expanding or retracting. When the resonant element 2 comes into resonance, the resonant element expands and retracts at the resonant frequency.
• the studs 3 and 4 and the resonant element 2 are then equivalent to a conden ⁇ sateur whose capacitance varies with the resonant frequency.
• the microresonator described above can be used in various ways. An example of use in filter is described below.
• the resonant element 2 is connected to a bias voltage Vpol via a coil L and connected to a resonance detection circuit via a capacitor C.
• the detection circuit is represented by a load resistor Rc placed between the capacitor C and the ground.
• the pads 3 and 4 receive an input voltage ve.
• the voltage ve comprises a DC component and an alternating component varying at the resonance frequency
• a current is varying at the resonant frequency is supplied to the detection circuit.
• the voltage ve varies at a frequency different from the resonance frequency, the variation of the current is supplied to the detection circuit is substantially zero.
• a perforated insulating portion 11 consisting for example of silicon oxide is formed on a substrate 10.
• a mushroom shaped element 12 is formed comprising a foot placed in the hole of the insulating portion 11 and a cylindrical head placed on the insulating portion 11.
• a thin layer of silicon oxide 13 is formed around the resonant element 12 and on the free parts of the insulating portion 11. Subsequently, on the substrate 10, studs are formed. conductors 14 and 15 on each side of the element 12. The conductive pads are in contact with the silicon oxide layer 13.
• a fourth phase, illustrated in FIG. 2D the silicon oxide layer 13 and the insulating portion 11 are eliminated. A resonator as illustrated in FIG. 1 is then obtained.
• the method previously described has the following features: disadvantage of forming a resonant element having a polycrystalline structure. Indeed, the resonant element 12 is obtained by deposition of silicon on a silicon oxide layer which leads to form polycrystalline silicon.
• the polycrystalline structure of the resonant element is a disadvantage as this is at the origin of mechanical weaknesses.
• the resonance frequency of a polycrystalline silicon resonant element may vary from one resonant element to another.
• An object of the present invention is to provide a simple method of manufacturing a microresonator.
• Another object of the present invention is to provide a microresonator structure whose resonant element has good mechanical strength. Another object of the present invention is to provide such a microresonator which the resonant element has a fre quency ⁇ substantially constant resonance of a micro-resonator to another.
• Another object of the present invention is to provide such a microresonator whose lateral movements are accurately detected.
• the present invention provides a microresonator comprising a resonant element and at least one activation electrode placed in proximity to the resonant element, wherein the resonant element is placed in an opening of a semiconductor layer overlying a resonant element. substrate, the activation electrode being formed in the semiconductor layer ⁇ and flush at the opening, characterized in that the resonant element is monocrystalline silicon.
• the resonant element has a mushroom shape whose foot is fixed on the substrate.
• the microresonator further comprises a vertical detection transistor comprising a stack of three doped semiconductor regions formed in the semiconductor layer and flush at the opening, the semiconductor regions doped lower and upper region constituting source and drain zones of a first type of doping, the intermediate semiconductor zone constituting a "substrate" zone of a second type of doping, the resonant element constituting the gate of the transistor.
• the present invention also provides a method of forming a microresonator comprising the steps of forming a sacrificial portion over a substrate; forming a first semiconductor layer above the previously obtained structure; forming in the semi ⁇ conductive layer at least one electrode area placed against or above a peripheral portion of the sacrificial portion; forming an aperture in the first semiconductor layer above the first sacrificial portion, whereby said at least one electrode region is flush at the aperture; forming a sacrificial layer covering the bottom, the wall and the edges of the opening; forming a hole in the sacrificial layer at the bottom of the opening; forming a second semiconductor layer on the previously obtained structure; etching the second semiconductor layer so as to retain a portion constituting a resonant element placed in the opening and extending slightly at the edges of the OPEN ⁇ ture; and removing the sacrificial portion and layer, and wherein the sacrificial portion and layer are made of a material such as silicon-germanium that is
• the method further comprises, after the formation of the silicon-germanium sacrificial portion, the formation of an insulating portion above the sacrificial portion, the insulating portion serving as a dielectric layer. stopping when forming the aperture by etching the first semiconductor layer.
• the first and second semiconductor layers are epitaxially grown silicon layers, the resonant element being made of monocrystalline silicon.
• the sacrificial layer has a thickness of a few tens of nanometers.
• the method is intended to form a microresonator comprising a vertical detection transistor, and comprises prior to the formation of the opening a step of performing three successive implantations from the same mask offset litho ⁇ graphy to form three stepped doped zones, the lower doped zone being placed against or above the sacrificial portion and the upper doped zone being placed on the surface of the first semiconductor layer, the doped zones possibly being partially engraved during the formation of the opening in the first semiconductor ⁇ trice, which results in the three doped areas are flush at the opening.
• the insulating portion does not cover the entire portion sacrificed ⁇ cial three doped regions being formed above an open area of the sacrificial portion.
• FIG. 1 is a perspective view of a known microresonitor
• FIGS. 2A to 2D are sectional views, previously described, of structures obtained at the end of successive steps of a method for forming the microresonator of FIG. 1
• FIGS. 3A to 3H are sectional views of structures obtained at the end of successive steps of a method for manufacturing a microresonator according to the present invention
• FIGS. 4A and 4B are examples of views from above of a section of the structure obtained at the end of the last step illustrated in FIG. 3H
• FIGS. 5A to 5C are sectional views of structures obtained at the end of successive steps of a method for manufacturing a microresonator according to a variant of the method of the present invention.
• an insulating zone 101 surrounding an upper portion 102 of the substrate 100 is formed in the surface of a substrate 100.
• the substrate 100 is for example of monocrystalline silicon and the insulating zone 101 a trench filled with silicon oxide.
• a silicon-germanium portion 103 is grown above the substrate portion 102.
• This epitaxial growth is conventionally carried out according to a gas phase deposition process carried out at from a mixture of dichlorosilane and germane. The deposition process is selective so as not to grow silicon-germanium above the insulating zone 101.
• An insulating layer portion 104 is then formed on the silicon-germanium portion 103.
• the insulating portion 104 is narrower than the silicon-germanium portion 103 so as to discover one or more peripheral zones of the silicon-germanium portion 103.
• two open areas Z1 and Z2 are respectively located on the left and right of the silicon-germanium portion 103.
• the insulating portion 104 can be obtained in various ways. It is possible to deposit an insulating layer on the previously obtained structure, then to etch this insulating layer while retaining a portion over a portion of the silicon-germanium portion 103. It will also be possible to perform a thermal oxidation of the portion of silicon-germanium 103 and then etch the layer of silicon oxide thus formed in order to discover certain zones of the silicon-germanium portion 103.
• a layer of silicon 110 is grown by non-selective epitaxy above the previously obtained structure.
• the silicon portions placed above the insulating zone 101 and the insulating portion 104 are polycrystalline while the silicon portions placed above the Zl and Z2 discovered zones are monocrystalline.
• an ion implantation is carried out so as to form at least one electrode zone in the silicon layer 110 over a peripheral portion of the silicon-germanium portion 103 or optionally against the portion of silicon-germanium 103.
• two zones of electrodes 120 and 121 are formed. strongly doped N-type above the exposed zones Z1 and Z2 of the silicon-germanium portion 103.
• an opening 130 is formed by etching in the silicon layer 110 above the insulating portion 104.
• the opening 130 is formed between the electrode areas 120 and 121 so that they are flush with the opening 130.
• the etching process used is preferably anisotropic so that the wall of the opening is vertical.
• the insulating portion 104 is then eliminated, which therefore does not appear in FIG. 3D.
• the insulating portion 104 serves as a stop layer during etching of the silicon layer 110.
• the step of forming an insulating portion on the silicon-germanium portion 103 prior to the formation of the silicon layer 110 could be avoided insofar as there are etching methods for etching the silicon selectively with respect to silicon-germanium. In this case, it is the portion of silicon-germanium 103 that serves as a stop layer during etching of the silicon layer 110 to form the opening 130.
• the use of an insulating portion as a layer stopping allows better control of the depth of the opening 130, which allows ⁇ to define more precisely the thickness of the resonant element of the microresonator, as will appear below.
• a thin layer of silicon-germanium 140 is grown by non-selective epitaxy in order to cover the walls and the bottom of the opening 130 as well as the silicon layer 110. It will be noted that the silicon-germanium layer 140 is monocrystalline in and on the edges of the opening 130.
• a hole is formed through the portion 103 and the silicon germanium layer 140, substantially in the middle of the opening 130.
• a layer of non-selective epitaxy is then grown. silicon 150 above the silicon-germanium layer 140. This silicon layer will be monocrystalline at least above the locations where the underlying layer of silicon-germanium is monocrystalline.
• the silicon layer 150 is etched so as to preserve silicon in the opening 130. In practice, a small portion of silicon will be kept on the edges of the opening 130 to avoid etching the silicon placed against the walls of the opening 130. The remaining silicon portion constitutes a resonant element 160.
• FIGS. 4A and 4B are sectional views
• the opening 130 has a substantially rectangular shape as well as the resonant element 160 placed inside this opening.
• the electrode regions 120 and 121 have a substantially rectangular shape and are placed against two opposite walls of the opening 130.
• the opening 130 has a substantially circular shape as well as the resonant element. 160.
• the electrode zones 120 and 121 are curved and are placed opposite each other against the wall of the opening 130.
• the portion 103 and the layer 140 of silicon-germanium are sacrificial layers.
• a material other than silicon-germanium could to be used .
• the selected material must be selectively etchable ⁇ relative to the substrate 100, the silicon layer 110 and the resonant element 160, and must allow to deposit, or to grow by epitaxy, a semiconductor layer having a monocrystalline structure.
• An advantage of the process of the present invention is that it makes it possible to form a semiconductor resonant element having a monocrystalline structure.
• a material will be preferably used to obtain a very thin layer in order to finally have a small gap between the resonant element 160 and the electrode zones.
• the resonant frequency of such a microresonator can reach a few GHz, the frequency depending on the polarization conditions of the resonant element.
• a microresonator according to the present invention comprises a resonant element placed in an opening of a semiconductor layer covering a substrate.
• the semiconductor layer and the "support" substrate are made of the same material, it may be considered that the layer and the substrate constitute a single substrate, the resonant element then being placed in a cavity of this substrate.
• the resonant element is attached to the substrate by one or more "feet".
• the microresonator further comprises one or more electrode zones placed against the walls of the opening in which the resonant element is placed.
• the part of the resonant element placed in the opening has a substantially identical shape. the latter so that the distance between the resonant element and the wall of the opening is relatively small opposite the electrode zones.
• the resonant element is made of a semiconductor material having a monocrystalline structure.
• the transistor type of components may be formed in the surface silicon layer 110.
• a "bubble" may be placed above the micro ⁇ resonator, then one or more metal connections ⁇ lic levels can be formed above the semiconduc- trice layer 110 and the bubble.
• a metal contact may be placed above each of the electrode areas 120 and 121 to connect them to other circuit components via a metal line.
• a buried doped zone can be formed in the substrate 100.
• This buried doped zone for example of the N type if the substrate is of the P type, then connects the foot of the resonant element at a zone of the silicon layer 110 passing under the insulating zone 101.
• This buried doped zone can be connected to a metal connection line via a doped zone formed in the silicon layer 110.
• a microresonator according to the present invention can be used in various circuits, for example as a filter. It can be used in a manner similar to that described for the microresonator illustrated in FIG.
• movement detection of the resonant element is performed by means of a transistor verti cal ⁇ having to gate the resonant element.
• the source, drain and channel regions of this transistor are placed in the substrate against the wall of the opening in which the resonant element is placed.
• a layer of resin is deposited on top of the silicon layer 110 and this resin is insulated so as to keep, after development, the resin on the entire surface of the silicon layer except in an area lying above the Z2 discovery area.
• the resin used is a positive resin
• the lithography mask M used for insolating the resin is represented at position "a" above the structure represented in FIG. 5A.
• An implantation of doping elements of a first type, for example of the P type, is then performed to form a doped zone 122 above the exposed zone Z2.
• a second implantation is then carried out. To do this, the M lithography mask is shifted to the left in this example, so that the opening of the mask M is shifted towards the insulating portion 104, the mask being in position "b". A new layer of resin is then deposited, which is insulated according to the mask M and then developed. An implantation of doping elements of a second type, for example of the N type, is then carried out so as to form a doped zone.
• the doped zones 122 and 124 have a thickness of 40 nanometers, and the doped zone 123 a thickness of 300 nanometers.
• the sum of the thicknesses of the areas 122, 123 and 124, or 380 nanometers is equal to the thickness of the silicon layer 110.
• the offset between each of the mask implanted ⁇ tions is about 200 to 250 nanometers.
• One or more areas of electrodes are then formed.
• a single electrode 120 is formed above the Zl discovery zone.
• the electrode 121 has been replaced by the doped zones 122, 123 and 124.
• the zones 123 and 124 have been partially etched so that the three doped zones 122, 123, 124 are flush at the level of the ' opening .
• the microrésona ⁇ tor finally obtained includes a vertical MOS transistor placed in front of the resonant element 160.
• the doped areas 122 and 124 are source / drain regions.
• the doped zone 123 constitutes a "substrate” zone.
• the resonant element 160 constitutes the gate of the transistor.
• the gate capacitance of the tran sistor ⁇ varies.
• the gate and the source / drain regions of the transistor are biased so as to turn on the tran ⁇ sistor, a variation of the gate capacitance results in a variation of the current flowing through the transistor.
• the transistor thus makes it possible to detect the movements of the resonant element, especially when the latter comes into resonance.
• the present invention is susceptible of various variations and modifications which will be apparent to those skilled in the art.

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• 2005
  • 2005-01-31 FR FR0550276A patent/FR2881416B1/fr not_active Expired - Fee Related
• 2006
  • 2006-01-31 WO PCT/FR2006/050078 patent/WO2006079765A1/fr active Application Filing
  • 2006-01-31 EP EP06709462A patent/EP1843970A1/de not_active Withdrawn
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