Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B3/00—Devices comprising flexible or deformable elements, e.g. comprising elastic tongues or membranes
  • B81B3/0062—Devices moving in two or more dimensions, i.e. having special features which allow movement in more than one dimension
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
  • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
  • G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
  • G02B26/0841—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD the reflecting element being moved or deformed by electrostatic means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B2201/00—Specific applications of microelectromechanical systems
  • B81B2201/04—Optical MEMS
  • B81B2201/045—Optical switches
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B2203/00—Basic microelectromechanical structures
  • B81B2203/01—Suspended structures, i.e. structures allowing a movement
  • B81B2203/0181—See-saws
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B2203/00—Basic microelectromechanical structures
  • B81B2203/05—Type of movement
  • B81B2203/058—Rotation out of a plane parallel to the substrate

Definitions

• the invention relates to an optical pivot micro-mirror as well as a matrix of such micro-mirrors and its production method.
• This micro-mirror is suitable for being electrically controlled.
• Micro-mirrors are generally used in systems involving deflections of light beams and in particular in optical routing systems or in image projection systems.
• micro-mirrors most often using electrostatic, electro-magnetic, piezoelectric or thermoelastic forces
• They generally use hinge configurations allowing, depending on the complexity of the technological steps involved, to oscillate around an axis (single hinge) or two axes of rotation (double hinge) most often oriented orthogonally.
• FIG. 1a shows a view of such a micromirror with electrostatic controls allowing rotation along 2 perpendicular axes, used in optical routing systems.
• the fixed frame 2 of the micro-mirror and the moving parts 3 and 4 articulated respectively around the hinges 5 and 6 which allow the desired rotations around the 2 orthogonal axes.
• Each axis of rotation passes through a separate hinge.
• the movable part 4 is covered with a layer of material of high reflectivity.
• Figure 1b gives a very schematic sectional view of the various elements forming this type of micro-mirror (section along the axis of the hinge 5). This figure also shows the different control electrodes 7, 8, 9 and 10 of the micro-mirror.
• the opposite electrodes 7 and 8 make it possible to rotate the mobile part 3 around the hinge 5, while the opposite electrodes 9 and 10 make it possible to rotate the mobile part around the hinge 6.
• the movable part of the hinged micro-mirrors has limited degrees of freedom. Indeed, each hinge can only offer one axis of rotation to the movable part, this axis being in the plane of the movable part u and passing through the hinge. Also, to increase the degrees of freedom of the mobile part, it is necessary to divide the mobile part into independent patterns, located in the same plane and respectively articulated by a hinge, which complicates the structure without allowing it a large number of degrees of freedom. Currently, only micro-mirrors with double hinges have been produced. The references cited at the end of the description give examples of hinged micro-mirrors. Statement of the invention and brief description of the figures
• the present invention relates to an optical micromirror overcoming the drawbacks of the prior art and having a movable part having a large number of axes of rotation while proposing a method of manufacturing such a micro-mirror easy to implement .
• the micro-mirror of the invention comprises a fixed part, a mobile part comprising reflection means, the micro-mirror further comprising articulation means connecting the mobile part to the fixed part;
• this micro-mirror is characterized in that the articulation means are formed by a pivot located under the movable part between the latter and the fixed part and capable of allowing movement of the mobile part along axes of rotation contained in the part movable and passing through the axis of the pivot.
• a very large number of axes of rotation for the movable part is possible, since the latter can pivot around the pivot and describe in the case of a circular movable part, a cylinder.
• the axes of rotation of the movable part correspond to all the radii describing a center semicircle, the pivot.
• the pivot is centered under the movable part, but one can completely envisage in particular applications, an off-center pivot under the movable part and ⁇ or even a movable part of thickness. not homogeneous allowing to favor certain axes of rotations and ⁇ or certain directions of rotations.
• the micro-mirror of the invention also advantageously comprises means for electrically controlling the movement of the movable part along all or part of said axes of rotation.
• the electrical control means comprise a set of so-called lower electrodes arranged on the fixed part opposite the movable part and a set of so-called upper electrodes arranged on the movable part opposite the lower electrodes.
• the set of lower electrodes comprises at least 2.n electrodes arranged in sectors around the axis of the pivot, n being the number of axes of rotation which one chooses to have the movable part take and the set of upper electrodes comprises a single electrode arranged opposite at least in part of each of the 2.n lower electrodes.
• the set of upper electrodes comprises at least 2.n electrodes arranged in sectors around the axis of the pivot, n being the number of axes of rotation which one chooses to have the movable part take and the set of lower electrodes comprises a single electrode arranged opposite at least in part of each of the 2.n upper electrodes.
• the electrical control means also comprises connection lines and contact sockets at the ends of the lines to connect the lower and upper electrodes to control electronics.
• the connection lines and the contact points are advantageously made on the fixed part opposite the mobile part, the set of upper electrodes being connected to one or more of these lines via the pivot and one or more electrodes placed under the pivot, on the fixed part.
• the connection lines are produced by metallized holes through the fixed part, the set of upper electrodes being connected to one or more of these metallized holes by means of the pivot and one or more electrodes arranged under the pivot, on the fixed part; the contact points being located at the ends of these holes on the face of the fixed part, opposite to that carrying the lower electrodes.
• the invention can also use electrical control means using other forces than electrostatic forces and for example electromagnetic, or piezoelectric or thermoelastic forces.
• forces for example, the control of the mobile parts by magnetic forces (Laplace forces) then requires coils and magnets adapted to generate the necessary magnetic fields.
• the fixed part comprises at least one cavity facing at least one zone of one of the ends of the movable part, of geometric shape and dimensions such that they make it possible to separate the parameters of dimensions of the movable part and the total angular excursion ⁇ according to the different axis or axes of rotation.
• step a) consists on the mechanical support, to transfer the second layer, the support and ⁇ or the second layer comprising on their faces to transfer a sacrificial layer which will form after transfer the first layer.
• the second layer can be associated with an intermediate support by a connecting zone capable of allowing the withdrawal of the intermediate support after postponement or in certain specific cases before postponement.
• this bonding zone is a weakening zone obtained by ion implantation (see in particular the patents US-5,374,564 and US-6,020,252) and ⁇ or by creation of porosity in the second layer, the removal of the intermediate support is carried out according to this embrittlement zone by an appropriate treatment such as the application of mechanical forces, and ⁇ or the use of a heat treatment.
• this connection zone is a sacrificial layer which is attacked " chemically to allow removal of the intermediate support.
• the transfer technique used in this second mode allows the implementation of several plates and thus allows greater freedom for the realization of structures, which may have several mobile parts superposed.
• a localized etching of the layer or layers arranged above the support is carried out before step d), so as to form a via and an epitaxy is carried out through the via, the epitaxy material in the via forming all or part of the pivot of the articulation means.
• the pivot can be produced in several parts, in particular in the case of the second embodiment using the transfer of the second layer.
• a deposit such as an epitaxy
• a via comprising insulating meshes (each mesh corresponding to an opening bordered with insulator) so that these elements are isolated after production.
• one or more cavities are produced in the fixed part opposite the mobile part, advantageously by etching.
• a peripheral cavity is etched, facing a peripheral zone of the end of the movable part.
• the method of the invention applies particularly well to a collective production of micro-mirrors.
• FIGS. 5a to 5g schematically represent, in section, the different stages of a second method of manufacturing the movable part of a micro-mirror of the invention
• FIGS. 7a to 7g schematically represent, in section, the different stages of a third method of manufacturing the fixed part of a micro-mirror of the invention
• - Figures 8a to 8c show top views of different micro-mirrors of the invention showing in particular different geometries of electrodes allowing rotations around one (fig.8a), two (fig.8b) or four axes of rotation (fig. 8c), and
• FIGS. 2a, 2b and 2c an example of a pivoting micro-mirror according to the invention is shown in three different positions.
• FIG. 2a shows the mobile part arranged in a plane parallel to the plane of the support
• FIG. 2b illustrates the mobile part which has pivoted along an axis of rotation perpendicular to that of the pivot and perpendicular to the plane of the figure, one of the ends of the mobile part is located in the cavity 36
• FIG. 2c illustrates the mobile part which has pivoted around the same axis of rotation but at 180 °, the opposite end of the mobile part is in turn in the cavity 36.
• the following description sets out two methods for manufacturing a micro-mirror of the invention, knowing on the one hand that these methods allow collective production of micro-mirrors and on the other hand that numerous variants of these methods can be used without departing from the scope of the invention.
• the first process is carried out on a wafer while that the second process is carried out on two separate plates A and B then transferred.
• the thermal oxide layer is preferably produced by high temperature oxidation under a dry atmosphere (between 800 ° C and 1100 ° C under oxygen) or under a humid atmosphere (between 800 ° C and 1100 ° C under water vapor) and at atmospheric or high pressure.
• a monocrystalline silicon layer of surface 20 is then deposited by all the known deposition techniques and in particular those of the thin layer transfer.
• FIG. 3b shows the production of the electrodes of the electrical control means by the formation of different doped zones. 24, 24 'and 23 in the upper part of the undoped silicon support 21 and in the monocrystalline silicon layer of surface 20.
• FIG. 3c shows the formation of the location 25 of the future pivot by local etching of the layers 20 and 22 to form a via above the implanted area 24 '.
• the doping of the epitaxy material can be modified and for example chosen higher at the start of the process (corresponding to the formation of the pivot 27 which must be electrically 65186
• FIG. 3e shows a section of the device after the epitaxy and thinning step, for example by mechanical-chemical polishing necessary to erase the depression 28 and obtain a layer of monocrystalline silicon 26 of perfect flatness.
• Other thinning techniques can of course be used and in particular that described in US Pat. No. 5,374,564 or in US Pat. No. 6,020,252.
• Figure 3g illustrates the etching step of the future mobile part of the micro-mirror.
• This etching involves layers 29 and 26 and possibly the thermal silica layer 22.
• This etching is carried out for example by all types of etching adapted to the materials involved (ionic etching, reactive ionic etching and ⁇ or chemical etching).
• this etching is carried out through a mask (not shown) by a first reactive ion attack, for example with chlorinated gases to attack the aluminum, then by a second reactive ion attack using for example an SF 6 gas to attack the silicon.
• a first reactive ion attack for example with chlorinated gases to attack the aluminum
• a second reactive ion attack using for example an SF 6 gas to attack the silicon.
• This cavity can be easily produced by the rear face of the wafer, for example by preferential chemical etching as illustrated in FIG. 3i, and therefore it must pass through the thickness of the silicon support.
• FIGS. 4, 5 and 6 The second embodiment of the invention which carries out the steps of the method on two plates A and B then which transfers these plates is shown in FIGS. 4, 5 and 6.
• FIG. 4c illustrates a step of thermal oxidation of the support, intended to form a layer of thermal oxide 32 of perfectly controlled thickness and in general between 1 and 3 microns; during this step, generally carried out at high temperature, there is diffusion of dopants from the implanted zones and increase in the volume occupied by these zones.
• the steps shown in fig.4b 'and fig.4c can be reversed at the cost of increasing the implantation energies for producing the doped zones 33, 33 ′ (the implanted ions then having to pass through the layer of thermal silica).
• FIG. 4d shows the next step corresponding to the formation of the localized etching 34 of the thermal silica layer 32 above the doped zone 33 'to form a via.
• FIG. 4e illustrates an epitaxy step which makes it possible to grow monocrystalline silicon doped in via 34.
• the part of the articulation element 35 thus formed is of thickness generally very slightly greater than the thickness of the silica layer 32; this part of the element will constitute a part of the future pivot.
• FIG. 4f illustrates a mechanical-chemical polishing step intended to planarize the surface of the wafer A and "erase" the possible excess thickness of the articulation element 35.
• FIG. 4g represents a step of etching cavities 36 which make it possible to separate the dimensions of the mobile part and the maximum angular excursion ⁇ of said part.
• the dimensions (position relative to the axis of the future pivot, width and depth) of the openings 36 are determined from the dimensions of the mobile part and of the desired angular excursion ⁇ along the different axes of rotation.
• FIGS. 5 show the different stages of manufacturing the wafer B.
• a substrate 41 for example made of monocrystalline silicon, in which an electrode 43 is formed, for example by ion implantation (fig. 5b) whether or not followed by thermal annealing.
• a thermal oxide layer 42 (fig.5c) is formed in the same way as for layer 32.
• This layer 42 is then etched to form a via 44 (fig.5d) which extends to l 'electrode 43; this opening has dimensions very close to those of the opening 34 (fig.4d); an epitaxy step (fig.5e) from monocrystalline silicon then makes it possible to form in the opening 44 another part of the pivot which is made of doped monocrystalline silicon 45.
• a chemical mechanical polishing step (fig.5f) allows if necessary to obtain a perfect planarization of the surface of the wafer B.
• the step illustrated in FIG. 5g consists in creating a connection zone 46 in the wafer 41 such as a weakening zone created for example by implantation of ions.
• This zone delimits in the wafer a layer (previously called second layer) of thickness typically between 0.1 and 2 microns between the silica layer 42, and the rest of the wafer (which may be an intermediate support).
• This weakening zone makes it possible to separate the second layer, from the rest of the wafer, either before transfer but more generally after transfer (see in particular US Patents 5,374,564 and US 6,020,252).
• Assembly of plates A and B The first step illustrated in Figure 6a consists in assembling the two plates A and B with the oxidized side against the oxidized side. During this assembly, the positioning of the two plates is carried out so as to align the two parts of the pivot 35 and 45 and form the pivot 47.
• the sealing can favorably be carried out by known techniques of molecular adhesion.
• the upper part of the layer 41 of the wafer B is separated from the assembly A and B at the level of the weakened zone 46.
• This separation can favorably be made from a heat treatment. and ⁇ or mechanical. After this separation, there remains, see FIG. 6b, only a thin layer of monocrystalline silicon 41 ′ possibly comprising zones of different dopings.
• the method can also comprise (see FIG. 6 c) an epitaxy step intended to increase the thickness of the monocrystalline film 41 ′ in order to increase the mechanical rigidity of what will form the movable part of the mirrors, this step can be followed by a chemical mechanical polishing step to planarize the surface.
• the final thickness of this layer 41 ′ is for example from 5 to 60 ⁇ m.
• a layer 48 of high reflectivity at the optical working wavelengths, either metallic or multi-dielectric, is then deposited on the layer 41 '.
• FIG. 6d shows the next step of etching the layers 41 ′ and 48 according to the desired pattern for the mobile part of the future micro-mirror. This engraving is carried out through a mask not shown.
• FIG. 6e illustrates the step of releasing the movable part around the pivot 47 by removing the sacrificial layers of thermal silica by chemical attack, for example using an attack bath using hydrofluoric acid or a reactive ion attack based on fluorinated gases.
• the different manufacturing steps presented in the various Figures 3 to 6 can include many variants. In particular, the order of the different steps can in certain cases be reversed and some of the steps can be modified.
• connection lines and the contact points to control electronics can be produced in different ways and in particular by ion implantation followed or not by an appropriate thermal diffusion of the dopants. These lines are advantageously made on the front face of the support opposite the mobile part, the electrode of the mobile part being connected to some of these lines by means of the pivot when the latter is conductive and of the electrode 33 . These connection lines can also be produced by metallized holes through the support, the electrode of the movable part being connected to some of these metallized holes by means of the pivot when the latter is conductive and of the electrode 33 .
• FIG. 4g shows in dotted lines the embodiment through the support of metallized holes 70 connecting the electrodes 33 and 33 ′ to contact sockets 71.
• the micro-mirror When the micro-mirror must rotate around at least two perpendicular axes of rotation while retaining the advantage of separating the value of the angular excursion ⁇ , from the dimension L of the movable part, it is advantageously carried out in the support, cavities completely surrounding the pivot 47.
• the connection lines are made on the front face of the support, so as not to cut through the cavities, the electrical connection lines (shown by way of example in the figures 9 and designated by 62) supplying the various electrodes, the support is etched to forming a peripheral cavity before forming the doped zones 33 33 '.
• FIG. 7c embdiments of the doped zones
• FIG. 7d production of the thermal oxide
• FIG. 7e production of a via 34 in the oxide layer
• FIG. 7f epitaxy to produce a part of the pivot
• Figure 7g planarization of the structure
• the following is then transferred to the wafer obtained in FIG. 7g, for example the wafer obtained in FIG. 5g and the rest of the steps of the process are carried out as described with reference to FIGS.
• the micro-mirror obtained is for example that shown in FIGS. 2.
• FIG. 8a shows a top view of a geometry of lower electrodes 33 in the fixed part.
• the electrodes allowing the mobile part to oscillate in 2 positions around a single axis of rotation RI are 2 in number and are arranged symmetrically with respect to the axis of rotation RI which passes through the pivot 47, the electrode 33 'central only allows the electrical connection of the mobile part.
• FIG. 8b shows a geometry of lower electrodes 33 making it possible to obtain 4 positions around 2 perpendicular axes of rotation RI and R2 passing through the pivot; these electrodes 33 are 4 in number and are matched 2 to 2, each pair of electrodes being arranged symmetrically with respect to one of the axes; similarly, the central electrode 33 ′ only allows the electrical connection of the mobile part.
• FIG. 8c gives an example with 4 axes of rotation (RI, R2, R3, R4) at 45 ° from each other and 4 pairs of lower electrodes 33 arranged in sectors around the axis of the pivot.
• FIGS. 8a, 8b and 8c the various key elements of the micro-mirrors are shown in transparency. There is shown the sets of lower electrodes 33 (electrodes of the fixed part), and the upper electrode 43 (electrode of the mobile part); the lower electrode 33 'which is electrically connected to the upper electrode by the pivot 47 is drawn in dark gray while in FIG.
• the two sets of electrodes allowing the rotation control of the micro-mirror along each of the perpendicular axes of rotation are drawn with two shades of gray which are lighter but different.
• the reflecting surface 48 of the movable part and the traces 50 and 51 of the etched areas 36 allowing the separation of the dimensions variables of the micro-mirror and total angular excursion ⁇ are also shown.
• the axes of the pivots 47 and 77 are combined; these pivots are multi-element and allow the electrodes 73, 53 and 43 of the mobile parts 41 and 71 to be connected to control electronics, via connection lines 62 arranged on the fixed part.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Mechanical Light Control Or Optical Switches (AREA)
• Micromachines (AREA)

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• 2001
  • 2001-02-15 FR FR0102065A patent/FR2820833B1/fr not_active Expired - Fee Related
• 2002
  • 2002-02-13 US US10/468,060 patent/US20040061961A1/en not_active Abandoned
  • 2002-02-13 EP EP02704815A patent/EP1390793A2/de not_active Withdrawn
  • 2002-02-13 WO PCT/FR2002/000545 patent/WO2002065186A2/fr not_active Ceased
  • 2002-02-13 CA CA002437816A patent/CA2437816A1/fr not_active Abandoned
  • 2002-02-13 JP JP2002564645A patent/JP2004522996A/ja not_active Withdrawn

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