Patent Publication Number: US-2022227621-A1

Title: Mems mirror arrays with reduced crosstalk and methods of manufacture

Description:
CROSS-REFERENCE 
     This application claims the benefit of U.S. Provisional Application No. 63/139,516, filed Jan. 20, 2021, entitled MEMS MIRROR ARRAYS WITH REDUCED CROSSTALK AND METHODS OF MANUFACTURE which application is incorporated herein in its entirety by reference. 
    
    
     BACKGROUND 
     Microelectromechanical systems (MEMS) and arrays can include parallel-plate actuators designed with gaps that are significantly larger than a stroke range of an actuator. When a voltage is applied between two electrode plates, an attractive force is produced between the electrode plates that rotates plate. The maximum rotation is determined by the gap between the two electrode plates. The larger the separation between the plates, the larger the deflection. Thus, gap is typically much larger than absolutely necessary for the physical movement of electrode plates, because if the electrodes approach too closely to each other (e.g., less than about ⅓ of gap), a point of instability is reached where the electrodes may snap together. 
     The force produced by a parallel-plate actuator is proportional to (voltage/gap) 2 . Thus, as the gap increases, the voltage also increases with the square of the distance to achieve the same force. With the movement of the structure, electrode plates do not remain parallel to each other and gap between them decreases. Hence, the voltage required to move electrode plates a given distance is high, nonlinear, and constantly changing. The use of a large gap may result in crosstalk between adjacent actuators in an array. 
     Additionally, mirror arrays can suffer from crosstalk when one mirror is actuated and one or more adjacent mirrors also move. An example of crosstalk that can occur is shown in  FIG. 1  and discussed below. 
     What is needed are MEMS mirror arrays and methods of manufacturing the arrays that reduce crosstalk between adjacent mirrors in the arrays. 
     SUMMARY 
     Disclosed are MEMS mirror arrays and methods of manufacture that reduce crosstalk between adjacent mirrors in the arrays. Additionally, coupling between adjacent mirrors in the array is reduced without changing the normal operation of the mirrors. 
     An aspect of the disclosure is directed to MEMS arrays. MEMS arrays comprise: a first stage, a first frame pivotally coupled to the first stage, and a first stage reflective surface, wherein the first stage reflective surface has a first resonant frequency; a second stage, a second frame pivotally coupled to the second stage, and a second stage reflective surface, wherein the second stage reflective surface has a second resonant frequency; and a base wafer positioned below the first stage and the second stage, wherein the first stage is adjacent the second stage on the base wafer. The first stage can be operable to be pivotally coupled to the first frame with a pair of first stage flexures and the second stage is pivotally coupled to the second frame with a pair of second stage flexures. Additionally, the first stage flexures and the second stage flexures are can be operable to rotate about a single axis and substantially restrict rotation about other axes, the single axis residing along a length of one or more of the first stage flexures and the second stage flexures. The flexures can also comprise a plurality of torsion beams. Additionally, in some configurations, the plurality of torsion beams can be positioned substantially parallel to one another. In at least some configurations, the torsion beams have a torsion beam length and wherein the plurality of torsion beams are non-parallel along portion of the torsion beam lengths. The MEMS array can further comprise: a first set of one or more first stage blades coupled to the first stage, the first set of one or more first stage blades electrically connected to each other; and a second set of one or more first stage blades coupled to the first stage, the second set of one or more first stage blades electrically connected to each other; and a first set of one or more second stage blades coupled to the second stage, the first set of one or more second stage blades electrically connected to each other; and a second set of one or more second stage blades coupled to the second stage, the second set of one or more second stage blades electrically connected to each other. Additionally, the MEMS array can further comprise: a third stage, a third frame pivotally coupled to the third stage, and a third stage reflective surface, wherein the third stage reflective surface has a third resonant frequency, further wherein the third stage is positioned on the base wafer adjacent the first stage on a first side and the second stage on a second side perpendicular to the first side. In at least some configurations, the MEMS array, further comprises: a fourth stage, a fourth frame pivotally coupled to the fourth stage, and a fourth stage reflective surface, wherein the fourth stage reflective surface has a fourth resonant frequency, further wherein the fourth stage is positioned on the base wafer adjacent at least one of the first stage, the second stage and the third stage. A device wafer can also be provided that is secured to the base wafer by a bonding element. In some configurations, the base wafer further comprises a support anchor in contact with a support webbing, further wherein the contact between the support anchor and the support webbing is operable to dampen mechanical motion of the reflective surface. 
     Another aspect of the disclosure is directed to methods for fabricating a microelectromechanical (MEMS) array. The fabricating method comprises: forming a layer of dielectric material on a first side of a substrate; forming on the first side of the substrate vertical isolation trenches containing dielectric material; patterning a masking layer on a second side of the substrate that is opposite to the first side of the substrate; forming vias on the first side of the substrate; metallizing the first side of the substrate; depositing a second metal layer on the first side of the substrate to form a reflective surface; forming second trenches on the first side of the substrate to define structures; deeply etching the second side of the substrate to form narrow blades; bonding a base wafer to the second side of the substrate after forming the narrow blades; and etching through the second trenches on the first side of the substrate to release the structures and to provide electrical isolation, wherein the microelectromechanical array has a first stage, a first frame pivotally coupled to the first stage, and a first stage reflective surface, wherein the first stage reflective surface has a first resonant frequency, and a second stage, a second frame pivotally coupled to the second stage, and a second stage reflective surface, wherein the second stage reflective surface has a second resonant frequency. The substrate can comprises a silicon wafer. Additionally, the dielectric material can be silicon dioxide. Additionally the method can include one or more of forming a passivation dielectric layer on the first side of the substrate after metallizing the first side of the substrate and attaching a lid wafer to the first side of the substrate. The lid wafer can also be comprised of glass. 
     Yet another aspect of the disclosure is directed to a MEMS array, comprising: a first stage, a first frame pivotally coupled to the first stage, and a first stage reflective surface; and a base wafer positioned below the first stage, wherein the base wafer further comprises a support anchor in contact with a support webbing, further wherein the contact between the support anchor and the support webbing is operable to dampen mechanical motion of the reflective surface. In some configurations, the first stage is pivotally coupled to the first frame with a pair of first stage flexures. Additionally, the first stage flexures can be configured to rotate about a single axis and substantially restrict rotation about other axes, the single axis residing along a length of the flexures. The flexures can also comprise a plurality of torsion beams, including torsion beams that are substantially parallel to one another. Furthermore, each of the plurality of torsion beams has a torsion beam length and wherein the plurality of torsion beams are non-parallel along portion of the torsion beam lengths. A first set of one or more first stage blades can be provided that are coupled to the first stage, the first set of one or more first stage blades electrically connected to each other; and a second set of one or more first stage blades coupled to the first stage, the second set of one or more first stage blades electrically connected to each other. Additionally, a device wafer can be secured to the base wafer by a bonding element. 
     INCORPORATION BY REFERENCE 
     All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. 
     U.S. Pat. No. 3,493,820 A dated Feb. 3, 1970 by Rosvold; 
     U.S. Pat. No. 4,104,086 A dated Aug. 1, 1978 by Bondur et al.; 
     U.S. Pat. No. 4,421,381 A dated Dec. 20, 1983 by Ueda et al.; 
     U.S. Pat. No. 4,509,249 A dated Apr. 9, 1985 by Goto et al.; 
     U.S. Pat. No. 4,519,128 A dated May 28, 1985 by Chesebro et al.; 
     U.S. Pat. No. 4,553,436 A dated Nov. 19, 1985 by Hansson; 
     U.S. Pat. No. 4,571,819 A dated Feb. 25, 1986 by Rogers et al.; 
     U.S. Pat. No. 4,670,092 A dated Jun. 2, 1987 by Motamedi; 
     U.S. Pat. No. 4,688,069 A dated Aug. 18, 1987 by Joy et al.; 
     U.S. Pat. No. 4,706,374 A dated Nov. 17, 1987 by Murakami; 
     U.S. Pat. No. 4,784,720 A dated Nov. 15, 1988 by Douglas; 
     U.S. Pat. No. 4,855,017 A dated Aug. 8, 1989 by Douglas; 
     U.S. Pat. No. 4,876,217 A dated Oct. 24, 1989 by Zdebel; 
     U.S. Pat. No. 5,426,070 A dated Jun. 20, 1995 by Shaw et al.; 
     U.S. Pat. No. 5,536,988 A dated Jul. 16, 1996 by Zhang et al.; 
     U.S. Pat. No. 5,563,343 A dated Oct. 8, 1996 by Shaw et al.; 
     U.S. Pat. No. 5,610,335 A dated Mar. 11, 1997 by Shaw et al.; 
     U.S. Pat. No. 5,628,917 A dated May 13, 1997 by MacDonald et al.; 
     U.S. Pat. No. 5,719,073 A dated Feb. 17, 1998 by Shaw et al.; 
     U.S. Pat. No. 5,726,073 A dated Mar. 10, 1998 by Zhang et al.; 
     U.S. Pat. No. 5,770,465 A dated Jun. 23, 1998 by MacDonald et al.; 
     U.S. Pat. No. 5,846,849 A dated Dec. 8, 1998 by Shaw et al.; 
     U.S. Pat. No. 5,847,454 A dated Dec. 8, 1998 by Shaw et al.; 
     U.S. Pat. No. 5,068,203 A dated Nov. 26, 1991 by Logsdon et al.; 
     U.S. Pat. No. 5,083,857 A dated Jan. 28, 1992 by Hornbeck; 
     U.S. Pat. No. 5,097,354 A dated Mar. 17, 1992 by Goto; 
     U.S. Pat. No. 5,172,262 A dated Dec. 15, 1992 by Hornbeck; 
     U.S. Pat. No. 5,198,390 A dated Mar. 30, 1993 by MacDonald et al.; 
     U.S. Pat. No. 5,203,208 A dated Apr. 20, 1993 by Bernstein; 
     U.S. Pat. No. 5,226,321 A dated Jul. 13, 1993 by Varnham et al.; 
     U.S. Pat. No. 5,235,187 A dated Aug. 10, 1993 by Arney et al.; 
     U.S. Pat. No. 5,316,979 A dated May 31, 1994 by MacDonald et al.; 
     U.S. Pat. No. 5,393,375 A dated Feb. 28, 1995 by MacDonald et al.; 
     U.S. Pat. No. 5,397,904 A dated Mar. 14, 1995 by Arney et al.; 
     U.S. Pat. No. 5,399,415 A dated Mar. 21, 1995 by Chen et al.; 
     U.S. Pat. No. 5,427,975 A dated Jun. 27, 1995 by Sparks et al.; 
     U.S. Pat. No. 5,428,259 A dated Jun. 27, 1995 by Suzuki; 
     U.S. Pat. No. 5,449,903 A dated Sep. 12, 1995 by Arney et al.; 
     U.S. Pat. No. 5,454,906 A dated Oct. 3, 1995 by Baker et al.; 
     U.S. Pat. No. 5,488,862 A dated Feb. 6, 1996 by Neukermans et al.; 
     U.S. Pat. No. 5,501,893 A dated Mar. 26, 1996 by Laermer et al.; 
     U.S. Pat. No. 5,611,888 A dated Mar. 18, 1997 by Bosch et al.; 
     U.S. Pat. No. 5,611,940 A dated Mar. 18, 1997 by Zettler; 
     U.S. Pat. No. 5,629,790 A dated May 13, 1997 by Neukermans et al.; 
     U.S. Pat. No. 5,637,189 A dated Jun. 10, 1997 by Peeters et al.; 
     U.S. Pat. No. 5,645,684 A dated Jul. 8, 1997 by Keller; 
     U.S. Pat. No. 5,673,139 A dated Sep. 30, 1997 by Johnson; 
     U.S. Pat. No. 5,703,728 A dated Dec. 30, 1997 by Smith et al.; 
     U.S. Pat. No. 5,759,913 A dated Jun. 2, 1998 by Fulford Jr et al.; 
     U.S. Pat. No. 5,798,557 A dated Aug. 25, 1998 by Salatino et al.; 
     U.S. Pat. No. 5,804,084 A dated Sep. 8, 1998 by Nasby et al.; 
     U.S. Pat. No. 5,853,959 A dated Dec. 29, 1998 by Brand et al.; 
     U.S. Pat. No. 5,915,168 A dated Jun. 22, 1999 by Salatino et al.; 
     U.S. Pat. No. 5,920,417 A dated Jul. 6, 1999 by Johnson; 
     U.S. Pat. No. 5,933,746 A dated Aug. 3, 1999 by Begley et al.; 
     U.S. Pat. No. 5,969,848 A dated Oct. 19, 1999 by Lee et al.; 
     U.S. Pat. No. 5,998,816 A dated Dec. 7, 1999 by Nakaki et al.; 
     U.S. Pat. No. 5,998,906 A dated Dec. 7, 1999 by Jerman et al.; 
     U.S. Pat. No. 5,999,303 A dated Dec. 7, 1999 by Drake; 
     U.S. Pat. No. 6,000,280 A dated Dec. 14, 1999 by Miller et al.; 
     U.S. Pat. No. 6,020,272 A dated Feb. 1, 2000 by Fleming; 
     U.S. Pat. No. 6,044,705 A dated Apr. 4, 2000 by Neukermans et al.; 
     U.S. Pat. No. 6,072,617 A dated Jun. 6, 2000 by Henck; 
     U.S. Pat. No. 6,075,639 A dated Jun. 13, 2000 by Kino et al.; 
     U.S. Pat. No. 6,097,858 A dated Aug. 1, 2000 by Laor; 
     U.S. Pat. No. 6,097,859 A dated Aug. 1, 2000 by Solgaard et al.; 
     U.S. Pat. No. 6,097,860 A dated Aug. 1, 2000 by Laor; 
     U.S. Pat. No. 6,101,299 A dated Aug. 8, 2000 by Laor; 
     U.S. Pat. No. 6,121,552 A dated Sep. 19, 2000 by Brosnihan et al.; 
     U.S. Pat. No. 6,753,638 A dated Feb. 2, 2001 by Adams et al.; 
     U.S. Pat. No. 7,098,571 A dated Aug. 29, 2006 by Adams, et al.; 
     U.S. Pat. No. 7,261,826 B2 dated Aug. 28, 2007 by Adams et al.; 
     US 2008/190198 A1 dated Aug. 14, 2008 by Prandi et al.; 
     US 2008/284028 A1 dated Nov. 20, 2008 by Greywall; 
     US 2009/196623 A1 dated Aug. 6, 2009 by Detry; 
     US 2010/263998 A1 dated Oct. 21, 2010 by Anderson et al.; 
     US 2011/018095 A1 dated Jan. 27, 2011 by Booth Jr., et al.; 
     US 2011/140569 A1 dated Jun. 16, 2011 by Moidu; 
     US 2012/133023 A1 dated May 31, 2012 by Booth Jr., et al.; 
     US 2014/014480 A1 dated Jan. 16, 2014 by Anderson et al. 
     WO 2001/057902 A2 dated Aug. 9, 2001 by Adams et al.; 
     WO 1994/018697 A1 dated Aug. 18, 1994 by Shaw et al.; 
     WO 1997/004283 A2 dated Feb. 6, 1997 by Miller et al.; and 
     WO 1999/036941 A2 dated Jul. 22, 1999 by Adams et al. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
         FIG. 1  illustrates an actuation voltage ramping up on a mirror in a MEMS array and undesirable oscillations in an adjacent mirror, 
         FIG. 2  illustrates a portion of a mirror array; 
         FIG. 3  illustrates a cross-section of a prior art mirror array taken along the lines  3 - 3  in  FIG. 2 ; 
         FIG. 4  illustrates a cross-section of a fusion bonded mirror array with support anchors; 
         FIG. 5  illustrates a current frequency distribution in an array; 
         FIG. 6  illustrates a proposed frequency distribution in an array; 
         FIG. 7  illustrates a second proposed frequency distribution in an array; 
         FIG. 8A  illustrates an individual mirror with full loading and frequency (f 0 ); 
         FIG. 8B  illustrates an individual mirror with partial loading and frequency (f 1 ); 
         FIG. 8C  illustrates an individual mirror with partial loading and frequency (f 2 ); 
         FIG. 8D  illustrates an individual mirror with partial loading and frequency (f 3 ); 
         FIG. 9A  illustrates a cross-section of a silicon wafer; 
         FIG. 9B  illustrates a portion of a wafer with a masking layer, photo-resistant layer, and an opening to the silicon surface of the wafer; 
         FIG. 9C  illustrates an isolation trench formed in a silicon wafer; 
         FIG. 9D  illustrates a portion of a wafer with a dielectric layer on the top surface of the silicon wafer and on the sidewalls and bottom of the isolation trench: 
         FIG. 9E  illustrates a portion of a wafer after planarization of a dielectric layer; 
         FIG. 9F  illustrates isolation trenches on top of a wafer and a masking layer for blades on a bottom of the wafer: 
         FIG. 9G  illustrates metallization on the top of the wafer; 
         FIG. 9H  illustrates trenches on the top of the wafer; 
         FIG. 9I  illustrates blades that result from deep silicon etching; 
         FIG. 9J  illustrates a base wafer bonded to a wafer containing blades: 
         FIG. 9K  illustrates a wafer after a release etch separates portions of the structure and after attachment of a lid wafer; and 
         FIGS. 10A-C  illustrate another variation prior to bonding. 
     
    
    
     DETAILED DESCRIPTION 
     I. Microelectromechanical (MEMS) Arrays 
     Disclosed are microelectromechanical (MEMS) arrays. The MEMS arrays comprise: a first stage (e.g., stage  802 ), a first frame (e.g., frame  804 ) pivotally coupled to the first stage, and a first stage reflective surface (e.g. mirror), wherein the first stage reflective surface has a first resonant frequency (e.g., resonant frequency  502 ); a second stage, a second frame pivotally coupled to the second stage, and a second stage reflective surface, wherein the second stage reflective surface has a second resonant frequency (e.g., resonant frequency  604 ); and a base wafer (e.g., silicon wafer  910 ) positioned below the first stage and the second stage, wherein the first stage is adjacent the second stage on the base wafer. The first stage can be operable to be pivotally coupled to the first frame with a pair of first stage flexures (e.g., central stage flexures  832 ,  832 ′) and the second stage is pivotally coupled to the second frame with a pair of second stage flexures. Additionally, the first stage flexures and the second stage flexures are can be operable to rotate about a single axis and substantially restrict rotation about other axes, the single axis residing along a length of one or more of the first stage flexures and the second stage flexures. The flexures can also comprise a plurality of torsion beams. Additionally, in some configurations, the plurality of torsion beams can be positioned substantially parallel to one another. In at least some configurations, the torsion beams have a torsion beam length and wherein the plurality of torsion beams are non-parallel along portion of the torsion beam lengths. The MEMS array can further comprise: a first set of one or more first stage blades (e.g., blade  812 ) coupled to the first stage, the first set of one or more first stage blades electrically connected to each other; and a second set of one or more first stage blades coupled to the first stage, the second set of one or more first stage blades electrically connected to each other; and a first set of one or more second stage blades coupled to the second stage, the first set of one or more second stage blades electrically connected to each other; and a second set of one or more second stage blades coupled to the second stage, the second set of one or more second stage blades electrically connected to each other. Additionally, the MEMS array can further comprise: a third stage, a third frame pivotally coupled to the third stage, and a third stage reflective surface, wherein the third stage reflective surface has a third resonant frequency, further wherein the third stage is positioned on the base wafer adjacent the first stage on a first side and the second stage on a second side perpendicular to the first side. In at least some configurations, the MEMS array, further comprises: a fourth stage, a fourth frame pivotally coupled to the fourth stage, and a fourth stage reflective surface, wherein the fourth stage reflective surface has a fourth resonant frequency, further wherein the fourth stage is positioned on the base wafer adjacent at least one of the first stage, the second stage and the third stage. A device wafer can also be provided that is secured to the base wafer by a bonding element. In some configurations, the base wafer further comprises a support anchor in contact with a support webbing, further wherein the contact between the support anchor and the support webbing is operable to dampen mechanical motion of the reflective surface. 
     Another configuration of a MEMS array, comprises: a first stage, a first frame pivotally coupled to the first stage, and a first stage reflective surface, and a base wafer positioned below the first stage, wherein the base wafer further comprises a support anchor in contact with a support webbing, further wherein the contact between the support anchor and the support webbing is operable to dampen mechanical motion of the reflective surface. In some configurations, the first stage is pivotally coupled to the first frame with a pair of first stage flexures. Additionally, the first stage flexures can be configured to rotate about a single axis and substantially restrict rotation about other axes, the single axis residing along a length of the flexures. The flexures can also comprise a plurality of torsion beams, including torsion beams that are substantially parallel to one another. Furthermore, each of the plurality of torsion beams has a torsion beam length and wherein the plurality of torsion beams are non-parallel along portion of the torsion beam lengths. A first set of one or more first stage blades can be provided that are coupled to the first stage, the first set of one or more first stage blades electrically connected to each other; and a second set of one or more first stage blades coupled to the first stage, the second set of one or more first stage blades electrically connected to each other. Additionally, a device wafer can be secured to the base wafer by a bonding element. 
     Turning now to  FIG. 1 , an actuation voltage ramping up when an actuation voltage  110  is applied is shown. The actuation voltage  110  ramps-up overtime on a mirror in a MEMS array and undesirable oscillation  120  is detected in an adjacent mirror. One cause for the crosstalk between adjacent mirrors is the mechanical coupling of the supports for each mirror in the MEMS array. The voltage measurement  130  on an adjacent mirror is also illustrated. 
       FIG. 2  illustrates an upper layer view of a portion of a prior MEMS mirror array  200 . The MEMS mirror array  200  has a metal layer  210 , a mirror cavity  212 , and a support  220 . 
     As will be appreciated by those skilled in the art, a MEMS array  200  has multiple stage actuators. Each actuator in an array includes a central stage, a movable frame, and a stationary frame. The stationary frame can form a cavity in which central stage and movable frame are disposed. A reflective element (e.g., a mirror) may be coupled to central stage and suspended from movable frame by a first central stage flexure and a second central stage flexure. The reflective element may be used to redirect a light beam along an optical path different from the optical path of the received light beam. An actuator that includes a mirror on the central stage is also referred to as a mirror cell or a MEM actuator with a mirror. 
     The rotation of the central stage can be independent of the rotation of movable frame. An actuator thus can allow decoupled motion. For example, central stage can rotate with respect to stationary frame while movable frame remains parallel and stationary with respect to stationary frame. In addition, movable frame can rotate with respect to the stationary frame while central stage remains parallel (and stationary) with respect to the movable frame. The moveable frame couples to the stationary frame via a first stationary frame flexure and a second stationary frame flexure. Furthermore, the central stage and the movable frame can, for example, both rotate concurrently yet independently of each other. Thus, for example, the central stage, movable frame, and stationary frame can concurrently be non-parallel and decoupled with respect to each other during actuation. 
     The first central stage flexure and the second central stage flexure are coupled to the movable frame via a first end bar and a second end bar. The first end bar and the second end bar are, in turn, attached to the main body of movable frame using multiple support members. Support members are silicon dioxide beams providing a tensioning force. The support members provide a tensioning force by expanding a different amount than the material system used in moveable frame, central stage, first end bar, second end bar, and stationary frame. Material systems of differing expansion can be placed into the movable frame in order to put the first central flexure and the second central flexure into tension. In particular, the expansion provided by connection members acting against the moveable frame and the first and second end bars causes a tensioning force on each pair of the central stage flexure and the stationary frame flexure. Support members serve to apply a tension force in order to minimize the potential for positional distortions due to buckling of the flexures under compressive forces. Generally, if any of the flexures are under too great a compressive force, the flexures may buckle. As such, support members may be coupled between the main body of movable frame and first and second end bars at a non-perpendicular angle in order to pull on central stage flexures to place them in tension. Because stationary frame flexures are perpendicular to central stage flexures, the non-perpendicular angle of attachment of support members causes a pull on the main body of movable frame and, thereby, a pull on and a tensioning of stationary frame flexures. 
     Support members may be coupled between the main body of movable frame and the first and second end bars can be positioned at approximately a 45 degree angle. Alternatively, support members may be coupled between the main body of movable frame and the first and second end bars at an angle less than or greater than 45 degrees. 
     Central stage flexures allow the central stage to pivot. Central stage flexures also provide some torsional resistance proportional to the rotation angle, but substantially less resistance than all other directions. In other words, there is substantial resistance to undesired twisting movement of central stage in other directions (e.g., side-to-side, or around an axis perpendicular to the surface of central stage). Moreover, central stage flexures extend into a corresponding slot formed in the central stage in order to provide sufficient length to the flexures for appropriate flexibility and torsion resistance. The central stage flexures may have a length of approximately 100 microns, a height of approximately 10 microns, and a width of approximately 1 micron, resulting in a 10:1 aspect ratio. Such an aspect ratio may provide for greater compliance in the direction of desired motion and stiffness in the undesired directions. In an alternative embodiment, other lengths, heights, widths, and aspect ratios may be used. 
     Similarly, stationary frame flexures enable the movable frame to pivot while providing resistance to undesired twisting movement of movable frame in other directions (e.g., side-to-side, or around an axis perpendicular to the surface of movable frame). Stationary frame flexures extend into slots a pair of corresponding slots formed into movable frame and stationary frame in order to provide sufficient length to the flexures for appropriate flexibility and torsion resistance. 
     One or more of the central stage flexures and stationary frame flexures may comprise a pair of torsion beams. The torsion beams can have a length with a plurality of torsion beams that are non-parallel along the lengths. The use of multiple torsion beams may provide for increased resistance to undesired twisting movement of a frame or stage, as compared to a single beam flexure. A pair of torsion beams may have various configurations. Torsion beams may be non-parallel beams with ends near the movable frame are substantially parallel and spaced apart by a gap. The gap between torsion beams reduces along the length of the beams such that the ends of the beams near fixed frame are closer together than the ends of the beams near movable frame. The angling of torsion beams relative to each other may aid flexure to resist unstable twisting modes. In an alternative embodiment, torsion beams may be configured such that their ends near fixed frame are farther apart than their ends near movable frame. In yet another embodiment, torsion beams may be substantially parallel to each other such that gap is substantially uniform along the length of the beams. 
       FIG. 3  illustrates a partial cross-section of a prior MEMS mirror array  200  taken along the lines  3 - 3  in  FIG. 2  with a top side  10  and a bottom side  20  where each layer within the MEMS mirror array  200  has a layer top surface oriented towards top side  10  and a bottom surface oriented towards bottom side  20 . The array has a silicon wafer  310 , which is a base wafer for the array, and a lid wafer  350  which acts as a protective layer. The base wafer  310  has a first pair of bonding elements  312 ,  312 ′ which are a frit glass seal at either end of the base wafer layer which bonds the silicon wafer  310  to the device wafer  320 . The bonding elements  312 ,  312 ′ can provide a hermetic seal when bonded. The bonding elements  312 ,  312 ′ are located along the perimeter of the mirror array such that the entire mirror array is suspended above the silicon wafer  310 . A second pair of bonding elements  322 ,  322 ′ bond the device wafer  320  to the lid wafer  350 . 
     Structure release is accomplished at the upper surface (e.g., top side  10 ) of the device wafer  320  using dry etching, which punctures through a plurality of trenches  326  to suspend the movable elements of the mirror  336  and the frame  330 . Isolation joints  328  are also created by etching the front until the etch approaches or just reaches the bottom of the isolation joint  328 . In addition, the release etch promotes electrical isolation by separating, for example, the silicon of the frame  330  from the silicon of surrounding members  338 ,  338 ′. The vias  324  serve to connect the regions of silicon to the metal interconnects  340 . To completely seal the mirrors from the outside environment, a lid wafer  350  is bonded to the device wafer  320 , for example through the second pair of bonding elements  322 ,  322 ′ which are a frit glass seal. The lid wafer  350  is typically glass to allow incoming light to be transmitted with low loss in the mirror cavity  332 , reflect off of the upper surface of mirror  336 , and transmit out of the mirror cavity. 
       FIG. 4  illustrates a partial cross-section of a fusion bonded MEMS mirror array  400  with support anchors  430 . The MEMS mirror array  400  has a top side  10  and a bottom side  20  where each layer within the MEMS mirror array  400  has a layer top surface oriented towards top side  10  and a bottom surface oriented towards bottom side  20 . The use of support anchors  430  eliminates, or substantially eliminates, mirror crosstalk around each mirror. The support anchors  430 , or support pillars, are created by etching pillars or posts having a height of 10-100 um into the silicon wafer  310 . The silicon wafer  310  is bonded to the device wafer  320  using, for example, eutectic bonding, thermocompression bonding, fusion bonding or anodic bonding. During the boding process, the support anchors  430  contact the support webbing  334 . In some configurations, the support anchors  430  bond to the support webbing  334 . In other configurations, the support anchors  430  are in contact with the support webbing  334 . Bonding or contact between the support anchors  430  and the support webbing  334  dampens any coupled mechanical motion from the mirrors  336  through their common anchors. 
     The mirror cell (not shown) cuts across four blades and three suspended sections of the mirror cell. A bond and polish sequence is used to tune the depth of the blades to a value substantially less than the thickness of a normal wafer. Because thinner wafers are fragile and subject to significant handling loss, the base wafer is used early in the process to provide handling support. The moveable blades  424  are patterned and etched using deep silicon etching techniques into the device wafer  320  at the beginning of the process. The depth of the blade trench  426  is tunable and depends on design, swing, and actuator deflection requirements. The blade depth may be 200 um, for example. A silicon wafer  310  can then be fusion bonded to the device wafer  320  at a bonding interface of the masking layer  412 . The fusion bonding process directly bonds silicon to silicon or silicon oxide and requires a high temperature anneal to form a strong bond. A recess is etched into the silicon wafer  310  to provide space for the moveable blades  424  to rotate. 
       FIGS. 5-7  illustrate current frequency distributions in a portion of a prior MEMS mirror array  200 , and MEMS mirror array  400  having a plurality of mirrors  510 . Coupling between adjacent mirrors can be reduced by increasing the frequency separation between adjacent mirrors (detuning). MEMS mirror array  400  provide for all mirrors in an array to be identical which results in all mirrors resonating at the same frequency (f 0 )  502  as shown in  FIG. 5 . Motion of one mirror  502  at resonance can excite a resonant response in an adjacent mirror. 
     If adjacent mirrors had different resonant frequencies, such as the layouts in  FIGS. 6 and 7 , then mechanical coupling would be off-resonance and less efficient.  FIGS. 6-7  illustrate potential layouts where three or more resonant frequencies are used. In  FIG. 6  a first mirror with a resonant frequency (f 0 )  502  is adjacent a mirror with a resonant frequency (f 1 )  604  on one side another mirror with a resonant frequency (f 2 )  606  on the opposing side. In a first row, resonant frequency (f 2 )  606  is adjacent a mirror with a resonant frequency (f 1 )  604  which is followed by a mirror with a resonant frequency (f 0 )  502 . In a second row, below the first row, resonant frequency (f 0 )  502  is adjacent a mirror with a resonant frequency (f 2 )  606  which is followed by a mirror with a resonant frequency (f 1 )  604 . The sequence within a row and across the number of rows then repeats as many times as desired. 
     In  FIG. 7  the mirrors are organized in a first row alternating a mirror with a resonant frequency (f 3 )  708  adjacent a mirror with a resonant frequency (f 0 )  502 . These two resonant frequencies repeat in an alternating fashion across the row. A second row provides a mirror having a resonant frequency (f 1 )  604  adjacent a mirror having a resonant frequency (f 2 )  606 . A third row has resonant frequency (f 0 )  502  followed by a mirror with a resonant frequency (f 3 )  708 . These three rows with repeating pairs of alternating mirrors then repeats. The resulting organization achieves a similar result to the organization in  FIG. 6 , with a greater position distance between two resonant frequencies. 
     As will be appreciated by those skilled in the art, a given row does not necessarily need to start with a particular resonant frequency (e.g., as illustrated herein) and the examples herein are by way of illustration only. The resulting organization results in a configuration where any mirror adjacent any other individual mirror does not have the same resonant frequency. Moreover, additional rows and combinations of resonant frequencies can be employed without departing from the scope of the disclosure provided mirrors in the array are configured so that at least one neighboring mirror does not share the same resonant frequency. Since resonant frequency is proportional to stiffness and mass, mirror designs with different frequencies can be created by changing one or more of stiffness and/or mass. Keeping stiffness the same and changing only mass, actuation characteristics (angle moved vs. voltage applied) can remain consistent among all mirror designs in an array. 
       FIGS. 8A-8D  are individual MEMS mirrors with resonant frequencies used in the layouts illustrated in  FIGS. 5-7 .  FIG. 8A  can be considered an individual MEMS mirror with full loading and frequency (f 0 );  FIG. 8B  can be considered an individual MEMS mirror with partial loading and frequency (f 1 );  FIG. 8C  can be considered an individual MEMS mirror with partial loading and frequency (f 2 ); and  FIG. 8D  can be considered an individual MEMS mirror with partial loading and frequency (f 3 ). As will be appreciated by those skilled in the art, the assignment of frequency, e.g. (f 1 ), (f 2 ), and (f 3 ), is arbitrary. 
       FIG. 8A  illustrates a prior art individual MEMS mirror with full loading and frequency (f 0 ). At each end of a stage or frame, actuator  800  uses a single movable blade such as moveable blade  424  in  FIG. 4 , with two corresponding fixed blades as an actuation mechanism structure to enable rotation. Actuator  800  uses two such actuation mechanism structures per stage and two such actuation mechanism structures per frame. A plurality of blades are provided. A first blade  812  is coupled to central stage  802  and is flanked on either side by a pair of first flanking blades  814 ,  814 ′ which are coupled to moveable frame  804  on opposite ends of first blade  812 . Central stage  802  is pivotally coupled to moveable frame  804  such that first blade  812  is configured to move relative to first flanking blades  814 ,  814 ′. When a potential difference is applied between first blade  812  and one of the first flanking blades  814 ,  814 ′, an attraction is generated between the blades causing central stage  802  to pivot. For example, first blade  812  may be held at a ground potential while an active voltage is applied to either of the first flanking blades  814 ,  814 ′. The application of an active voltage to first flanking blade  814 , for example, will attract the first blade  812 , thereby causing central stage  802  to rotate in a corresponding direction. Similarly, the application of an active voltage to first flanking blade  814 ′ will attract first blade  812  and cause stage  802  to rotate in an opposite direction to that resulting from the attraction to first flanking blades  814 . 
     A second blade  816  is coupled on end of central stage  802  opposite the location of the first blade  812 , with a pair of second side flanking blades  818 ,  818 ′ coupled to moveable frame  804  on opposite ends of second blade  816 . Second blade  816  moves relative to second side flanking blades  818 ,  818 ′. In order to provide the desired motion of central stage  802  and to resist unwanted rotations, actuation voltages are applied concurrently with respect to first blade  812  and second blade  816 . When the potential difference is applied between the second blade  816  and one of second side flanking blades  818 ,  818 ′, an attraction is generated between the blades resulting in the rotation of central stage  802  in a manner similar to that discussed above with respect to the first blade. The use of actuation mechanisms in tandem on each end of central stage  802  minimizes undesired twisting of the central stage  802  to provide for more uniform rotation. 
     A similar actuation mechanism structure may be used for rotation of moveable frame  804 . For example, a first side blade  822  is coupled to moveable frame  804  and first side flanking blades  824 ,  824 ′ are coupled to stationary frame  840  on opposite ends of first side blade  822 . 
     Moveable frame  804  is pivotally coupled to stationary frame  840  such that first side blade  822  is configured to move relative to first side flanking blades  824 ,  824 ′. When a potential difference is applied between the first side blade  822  and one of the first side flanking blades  824 ,  824 ′, an attraction is generated between the blades causing the moveable frame  804  to pivot in a manner similar to that discussed above in relation to central stage  802 . 
     Second side blade  826  is coupled on the opposite end of moveable frame  804 , with second side flanking blades  828 ,  828 ′ coupled to stationary frame  840  on opposite ends of second side blade  826 . Second side blade  826  moves relative to second side flanking blades  828 ,  828 ′. When the potential difference is applied between second side blade  826  and one of second side flanking blades  828 ,  828 ′, an attraction is generated between the blades facilitating the rotation of moveable frame  804 . The use of actuation mechanisms in tandem on each end of moveable frame  804  minimizes undesired twisting of the frame to provide for more uniform rotation. 
     Alternatively, a central stage  802  or frame may only have an actuation mechanism structure on only a single end. For another embodiment, actuator  800  may have other actuation mechanism structures without departing from the scope of the disclosure. 
     For one embodiment, a plurality of elongated members  830  can be provided (e.g., elongated member  830 ) which are coupled to the undersurface of central stage  802  to stiffen the central stage  802  and minimize top surface distortions. In addition, elongated members  830  on central stage  802  may be used to remove etch depth variations across the device. Elongated member  830  may be constructed similar to that of blades discussed herein.  FIG. 8A  illustrates seven elongated members  830  where six of the elongated members have substantially the same length and are positioned off-center on the central stage  802 , and the seventh elongated member has a shorter length and is positioned centrally on the central stage  802 . 
     Because the actuation mechanism of actuator  800  is located entirely beneath the central stage  802  to be rotated, none of the top surface areas of central stage  802  need be taken up by the actuation mechanism. 
     For one embodiment, actuator  800  may be fabricated on a wafer level using semiconductor fabrication techniques, as discussed below. For such an embodiment, stationary frame  840  may be formed from a substrate, for example, constructed from silicon. Where all blades are directly driven by different control voltages, actuator  800  may use four voltages, plus a ground. With this arrangement, the number of conductive paths on a substrate quickly becomes very large as multiple actuators are combined to form an array. The low voltages required by the blade actuators discussed herein may allow for control circuitry to be fabricated into the substrate so that only control signals need be routed, rather than separate lines for each blade. This results in a significant reduction in lead count. Lower voltages may also reduce the necessity for spacing between leads to avoid arcing and crosstalk. 
     The central stage  802  for each actuator  800  in an array has a moveable frame  804 , and a stationary frame  840 . The stationary frame  840  can form a cavity in which central stage  802  and moveable frame  804  are disposed. A reflective element (e.g., a mirror) may be coupled to central stage  802  and suspended from moveable frame  804  by a first central stage flexure  832  and a second central stage flexure  832 ′. The reflective element may be used to redirect a light beam along an optical path different from the optical path of the received light beam. As noted above, an actuator  800  that includes a mirror on the central stage is also referred to as a mirror cell or a MEM actuator with a mirror. 
     The moveable frame  804  engages the stationary frame  840  via a first stationary frame flexure  834  and a second stationary frame flexure  834 ′. Furthermore, the central stage  802  and the moveable frame  804  can, for example, both rotate about a single axis concurrently yet independently of each other. Thus, for example, the central stage  802 , moveable frame  804 , and stationary frame  840  can concurrently be non-parallel and decoupled with respect to each other during actuation. 
     The first central stage flexure  832  and the second central stage flexure  832 ′ are coupled the moveable frame  804  via a first end bar and a second end bar. The first end bar and the second end bar are, in turn, attached to the main body of moveable frame  804  using multiple support members. Support members are silicon dioxide beams providing a tensioning force. The support members provide a tensioning force by expanding a different amount than the material system used in moveable frame  804 , central stage  802 , first end bar, second end bar, and stationary frame  840 . 
       FIG. 8B  illustrates an individual mirror (reflective surface) similar to  FIG. 8A  with partial loading and frequency (f 1 ).  FIG. 8B  illustrates four elongated members  830  each of which have substantially the same length and are positioned off-center on the central stage  802 , such that the elongated members are positioned in a corner of a square or rectangular space on the central stage  802 . The reflective surface is positioned on a stage (e.g., a first stage, a second stage, a third stage, etc.). 
       FIG. 8C  illustrates an individual mirror similar to  FIG. 8A  with partial loading and frequency (f 2 ).  FIG. 8C  illustrates three elongated members  830  two of which have substantially the same length and are positioned aligned off-center on the central stage  802 . The third elongated member has a length less than the other two elongated members and is positioned centrally or substantially centrally on the central stage  802 . 
       FIG. 8D  illustrates an individual mirror similar to  FIG. 8A  with partial loading and frequency (f 3 ).  FIG. 8D  has no elongated members  830  on the central stage  802 . 
     Turning back to  FIGS. 5-7 , the array in  FIG. 5  would be comprised of a plurality of rows featuring the actuator  800  of  FIG. 8A .  FIG. 6  would have a first row, for example, of actuator  800  of  FIG. 8C  followed by the actuator  800  of  FIG. 8B , and then actuator  800  of  FIG. 8A , with the sequence repeating across the row as often as desired. The second row would have actuator  800  of  FIG. 8A  followed by actuator  800  of  FIG. 8C , and then actuator  800  of  FIG. 8B , with the sequence repeating across the row as often as desired. The third row would then repeat the order of row one and row four would repeat the order of row two.  FIG. 7  would have a first row, for example, of actuator  800  of  FIG. 8D  followed by the actuator  800  of  FIG. 8A , with the sequence repeating across the row as often as desired. The second row would have actuator  800  of  FIG. 8B  followed by actuator  800  of  FIG. 8C , with the sequence repeating across the row as often as desired. The third row would have actuator  800  of  FIG. 8A  followed by actuator  800  of  FIG. 8D , with the sequence repeating across the row as often as desired. The remaining rows would repeat the sequence in rows one through three. 
     A number of techniques can be used to fabricate actuator  800  shown in  FIGS. 8A-D . The techniques discussed with respect to  FIGS. 9A-K  are associated with the view provided by cross-section line  9 - 9  in in  FIG. 8A . The fabrication methods of embodiments of the disclosure result in a mirror platform suspended by cantilevered silicon beams. Electrical isolation between sections of the mirror or between different blades is achieved through the use of integral isolation segments, which serve to mechanically connect but electrically isolate separate elements of the mirror. 
     A design parameter for the mirror actuator is the depth of the blades, measured perpendicular to the axis of rotation. Increasing the blade depth results in increased force, but requires more swing space to rotate through high angles. Shallower blades more easily accommodate higher deflections but usually require a greater number of blades in order to achieve the same force. Therefore, it is advantageous to have several blade depths available to the designer. Different blade depths require multiple approaches to the fabrication process, which are described herein. 
     II. Methods of Manufacture 
     The methods for fabricating a microelectromechanical (MEMS) array. The fabricating method comprises: forming a layer of dielectric material on a first side of a substrate; forming on the first side of the substrate vertical isolation trenches containing dielectric material; patterning a masking layer on a second side of the substrate that is opposite to the first side of the substrate; forming vias on the first side of the substrate; metallizing the first side of the substrate; depositing a second metal layer on the first side of the substrate to form a reflective surface; forming second trenches on the first side of the substrate to define structures; deeply etching the second side of the substrate to form narrow blades; bonding a base wafer to the second side of the substrate after forming the narrow blades; and etching through the second trenches on the first side of the substrate to release the structures and to provide electrical isolation, wherein the microelectromechanical array has a first stage, a first frame pivotally coupled to the first stage, and a first stage reflective surface, wherein the first stage reflective surface has a first resonant frequency, and a second stage, a second frame pivotally coupled to the second stage, and a second stage reflective surface, wherein the second stage reflective surface has a second resonant frequency. The substrate can comprises a silicon wafer. Additionally, the dielectric material can be silicon dioxide. Additionally the method can include one or more of forming a passivation dielectric layer on the first side of the substrate after metallizing the first side of the substrate and attaching a lid wafer to the first side of the substrate. The lid wafer can also be comprised of glass. 
     One embodiment of the invention uses a single device wafer and the associated method is set forth with reference to  FIGS. 9A-9K   
       FIG. 9A  illustrates a cross-section of a silicon on insulator (SOI) wafer  910  that is chosen to be in the thickness range of 300-600 micrometers (um). The silicon wafer  910  has a top side  10  (or device side or simply a top) and a backside or bottom side  20 . Each layer within the MEMS mirror array  900  formed from the silicon wafer  910  has a layer top surface oriented towards top side  10  and a bottom surface oriented towards bottom side  20 . The upper left hand portion  902  is marked. In the preferred embodiment, the buried oxide layer  912  is 0.5-1 um thick and located 10-50 um beneath the top side  10 . 
       FIGS. 9B-9E  illustrate the upper left hand portion  902  of the silicon wafer  910  in a MEMS mirror array  900  which illustrates fabrication techniques for of isolation trenches  920  on the top side  10  of silicon wafer  910 . The isolation trenches  920  are vertically positioned on the silicon wafer substrate and filled with a dielectric material, which for one embodiment is silicon dioxide. Once filled, the isolation trenches  920  provide electrical isolation between blades after the mirror is released. A layer  914  also remains on the surface of the silicon wafer  910  and is planarized after the isolation trench fill process to ease subsequent lithographic patterning and eliminate surface discontinuities. 
     Referring to  FIG. 9B , a silicon wafer  910  is provided with a masking layer  914 . The masking layer  914  can be silicon dioxide (e.g., an oxide layer). The silicon wafer  910  can be of arbitrary doping, resistivity, and crystal orientation, because the process depends only on reactive ion etching to carve and form the structures. The masking layer  914  serves the function of protecting the upper surface of the silicon wafer  910  during the isolation trench etching process, and thus represents a masking layer. This masking layer can be formed from any number of techniques, including thermal oxidation of silicon or chemical vapor deposition (CVD). The typical thickness of the masking layer  914  is 0.5-1.0 um. A photoresist layer  916  is then spun onto the silicon wafer  910  and exposed and developed using standard photolithography techniques to define the isolation trench pattern for the isolation trench  920 . Reactive ion etching is used to transfer the photoresist pattern to the masking layer  914 , exposing the top surface of the silicon wafer  910  (i.e., the bottom  922  of the isolation trench  920 ). Typically, the silicon dioxide mask is etched in Freon gas mixture, for example CHF 3  or CF 4 . High etch rates for silicon dioxide etching are achieved using a high density plasma reactor, such as an inductively coupled plasma (“ICP”) chamber. These ICP chambers use a high power RF source to sustain the high density plasma and a lower power RF bias on the wafer to achieve high etch rates at low ion energies. Oxide etch rates of 200 nm/min and selectivities to photoresist greater than 1:1 are common for this hardware configuration. 
     As illustrated in  FIG. 9C , an isolation trench  920  is formed in the silicon wafer  910  by deep reactive ion etching of silicon using high etch rate, high selectivity etching. The trench is commonly etched in a high-density plasma using a sulfur hexafluoride (SF 6 ) gas mixture as described in U.S. Pat. No. 5,501,893. Preferably, etching is controlled so that the isolation trench  920  profile is reentrant, or tapered, with the top  924  of the isolation trench  920  being narrower than the bottom  922  of the isolation trench  920 . Tapering of the isolation trench  920  ensures that good electrical isolation is achieved in subsequent processing. Profile tapering can be achieved in reactive ion etching by tuning the degree of passivation, or by varying the parameters (power, gas flows, pressure) of the discharge during the etching process. Because the isolation trench  920  is filled with dielectric material, the opening at the top  924  of the isolation trench  920  is typically less than 2 um in width. The isolation trench  920  depth is typically in the range 10-50 um. In the preferred embodiment, the isolation trench  920  etch stops at the buried oxide layer  912 . A common procedure for etching the isolation trench  920  is to alternate etch steps (SF 6  and argon mixture) with passivation steps (Freon with argon) in an ICP plasma to achieve etch rates in excess of 2 um/min at high selectively to photoresist (&gt;50:1) and oxide (&gt;100:1). The power and time of the etch cycles are increased as the trench deepens to achieve the tapered profile. Although the trench geometry is preferably reentrant, arbitrary trench profiles can be accommodated with adjustments in microstructure processing. Good isolation results can be achieved with any of a number of known trench etch chemistries. After the silicon trench is etched, the photoresist layer  916  is removed with wet chemistry or dry ashing techniques, and the masking layer  914  is removed with a reactive ion etch (“RIE”) or buffered hydrofluoric acid. 
     Referring to  FIG. 9D , the isolation trench  920  is then filled with an insulating dielectric material, typically silicon dioxide. The filling procedure results in the mostly solid isolation segment in the isolation trench  920 , and serves to deposit a layer of dielectric material on the top side  10  (top surface) of the silicon wafer  910  and dielectric layers on the sidewall  928  and bottom  922  of the isolation trench  920 . The thickness of the deposited layer is usually in excess of 1 um. This fill can be accomplished with chemical vapor deposition (“CVD”) techniques or preferably with oxidation of silicon at high temperatures. In thermal oxidation, the wafer is exposed to an oxygen rich environment at temperatures from 900-1150° C. This oxidation process consumes silicon surfaces to form silicon dioxide. The resulting volumetric expansion from this process causes the sidewalls of the trenches to encroach upon each other, eventually closing the trench opening. In a CVD fill, some dielectric is deposited on the walls but filling also occurs from deposition on the bottom of the trench. CVD dielectric fill of trenches has been demonstrated with TEOS or silane mixtures in plasma enhanced CVD chambers and low pressure CVD furnace tubes. 
     During the isolation trench  920  filling process, it is common for most isolation trench profiles to be incompletely filled, causing an interface  932  and a void  930  to be formed in the isolation trench  920 . A local concentration of stress in the void  930  can cause electrical and mechanical malfunction for some devices, but is generally unimportant for micromechanical devices due to the enclosed geometry of the isolation trench  920 . The interface  932  and void  930  can be eliminated by shaping the isolation trench  920  to be wider at the isolation trench opening located at the top  924  of the isolation trench  920  than the bottom  922  of the isolation trench  920 . However, good electrical isolation would then require additional tapering of the microstructure trench etch in the later steps. Another artifact of the isolation trench filling process is an indentation  926  that is created in the surface of the masking layer  914  centered over the isolation trench  920 . This indentation is unavoidable in most trench filling processes, and can be as deep as 0.5 um, depending on the thickness of the deposition. To remove the indentation  926 , the surface is planarized to form a flat, or substantially flat, surface, as illustrated in  FIG. 9E , for subsequent lithographic and deposition steps. Planarization is performed either by chemical-mechanical polishing (CMP) or by depositing a viscous material, which can be photoresist, spin-on glass, or polymide, and flowing the material to fill the indentation  926  to a smooth finish. During etchback of the viscous material, which is the second step of planarization, the surface is etched uniformly, including the filled indentation. Therefore, by removing part of the surface oxide layer, the indentation  926  is removed to create a uniform thickness layer. For example, if the masking layer  914  is originally 2 um in thickness, then planarization to remove the indentation  926  leaves a masking layer  914  having a final thickness of less than 1 um. The top side  10  (upper surface) of silicon wafer  910  is free from imperfection and is ready for further lithography and deposition. 
       FIG. 9F  shows silicon wafer  910  with masking layer  914  and isolation trenches  920 . After the isolation trenches  920  are fabricated, standard front-to-back alignment is used to lithographically pattern the masking layer for the blades on the bottom side  20  (backside) of the silicon wafer  910 . The blade pattern  972  is exposed and etched into a masking layer  914 . The masking layer  914  is typically a layer comprised of a combination of thermally grown silicon oxide and oxide deposited by chemical vapor deposition. It may also be comprised of a metal layer such as aluminum. The lithography pattern is transferred in the masking layer by reactive ion etching, yet the silicon blade etching is not completed until later in the process. Without the blades etched, the wafer is easily processed through the remaining device layers. The backside of the blade pattern  972  is typically aligned topside to the isolation trenches  920  to within several microns. 
     Metallization on the top side  10  of the silicon wafer  910  then proceeds as illustrated in  FIG. 9G . In order to make contact to the underlying silicon wafer  910  vias  952  are patterned and etched into the masking layer  914  using standard lithography and reactive ion etching. After the vias  952  are etched, metallization is deposited to form a metal layer  940  and patterned to form a metal interconnect  956  and a contact  954  to the silicon wafer  910  through the via  952 . For one embodiment, the metal is aluminum and is patterned using wet etching techniques. In mirror arrays with high interconnect densities, it is advantageous to pattern the metal using dry etching or evaporated metal lift-off techniques to achieve finer linewidths. The metal layer  940  is used to provide bond pads and interconnects, which connect electrical signals from control circuitry to each mirror to control mirror actuation. 
     Deposition of a second metal layer  960  provides a reflective mirror surface. This metal is tuned to provide high mirror reflectivities at the optical wavelengths of interest, and is typically evaporated and patterned using lift-off techniques to allow a broader choice of metallization techniques. For one embodiment, the metallization is comprised of 500 nm of aluminum. However, additional metal stacks such as Cr/Pt/Au may be used to increase reflectivities in the wavelength bands common to fiber optics. Because the metals are deposited under stress and will affect the eventual mirror flatness, it is advantageous to reduce the thickness of the masking layer  914  in the region of the mirror. This can be accomplished through the use of dry etching of the underlying dielectric prior to evaporation. 
     In  FIG. 9H , the topside processing is completed. First, a passivation dielectric layer (not shown) may be applied to protect the metallization during subsequent processing. The passivation dielectric layer is removed in the region of the bonding pads. Second, the mirror structure including frame, mirror, and supports are defined using multiple etches that define trenches  921  separating the structural elements. The etches are self-aligned and proceed through the various metal, dielectric, and silicon wafers  910 . A further blanket deposition is applied to the topside which passivates the sidewalls of the trenches  921  and prepares the topside for mechanical release. 
     As shown in  FIG. 9I , backside silicon etching transfers the blade pattern  972  into the silicon wafer  910  substrate to obtain the blades  970 . The etching is performed using deep silicon etching at high selectivity to oxide using the techniques disclosed in U.S. Pat. No. 5,501,893. The deep silicon etching achieves near vertical profiles in the blades  970 , which can be nominally 5-20 um wide and in excess of 300 um deep. The etch stops on the buried oxide layer  912  to provide a uniform depth across the wafer while not punching through the top side  10  surface of the silicon wafer  910 . Since the etch stops on the buried oxide layer  912 , there is no need for elongated members  830  on central stage  802  to be used to remove etch depth variations across the device. Therefore, the different patterns of  FIGS. 8B, 8C, and 8D  are possible. All blades  970  can be etched simultaneously across the mirror element and across the mirror array. Buried oxide layer  912  may be etched at this time. 
     Referring to  FIG. 9J , because the device wafer is now prepared for microstructure release, the device wafer  320  becomes more susceptible to yield loss due to handling shock or air currents. In order facilitate handling and aid in hermetically sealing the mirror array, a silicon wafer  310  is bonded to the device wafer  320  to protect the blades after release. For one embodiment, the bonding is accomplished through the use of a bonding element  322 , such as a frit glass material bonding element, that is heated to its flow temperature and then cooled. In this manner, a 400° C. temperature bonding elements  312  produces a hermetic seal to surround the entire mirror array. The separation between the device wafer  320  and the silicon wafer  310  using the bonding elements  322 , such as a frit glass material bonding element, allows the blades  970  to swing through high rotation angles without impedance. Typically, the standoff required is greater than 25 um. 
     Final structure release is accomplished on the wafer topside in  FIG. 9K . using a combination of dry etching of silicon dioxide and silicon, which punctures through the trenches  921  to suspend the movable elements of the mirror  336  and the frame  330 . In addition, the release etch promotes electrical isolation by separating, for example, the silicon of the frame  330  from the silicon of surrounding members  338 ,  338 ′ and device wafer  320 . The vias  952  serve to connect the regions of silicon to the metal interconnects  956  (shown in  FIG. 9G ). To completely seal the mirrors from the outside environment, a lid wafer  350  is bonded to the device wafer  320 , preferably through the bonding element  322  (e.g., frit glass seal). The lid wafer  350  is typically glass that allows incoming light to be transmitted with low loss in the mirror cavity  332 , reflect off of the upper surface of the mirror  336 , and transmit out of the mirror cavity  332 . 
     In another variation, prior to bonding with device wafer  320 , the silicon wafer  310  is coated with a masking layer  412  (shown in  FIG. 10A ). This masking layer may be comprised of a combination of thermally grown silicon oxide and oxide deposited by chemical vapor deposition. It may also be comprised of a metal layer such as aluminum, germanium, or gold such as may be used for a eutectic or thermo-compression bond. The masking layer  412  is patterned using standard lithography and reactive ion etching (as shown in  FIG. 10B ). Silicon etching transfers the pattern of the masking layer  412  into the silicon wafer  310  substrate to obtain the support anchors  430 . The etching is performed using deep silicon etching at high selectivity to oxide using the techniques disclosed in U.S. Pat. No. 5,501,893. The etch depth allows the blades  970  to swing through high rotation angles without impedance. Typically, the depth required is greater than 25 um. The silicon wafer  310  is bonded to the device wafer  320  using, for example, eutectic bonding, thermo-compression bonding, fusion bonding or anodic bonding. During the boding process, the support anchors  430  contact the support webbing  334  (as shown in  FIG. 4 ). In some configurations, the support anchors  430  bond to the support webbing  334 . In other configurations, the support anchors  430  are in contact with the support webbing  334 . Bonding or contact between the support anchors  430  and the support webbing  334  dampens any coupled mechanical motion from the mirrors  336  through their common anchors. 
     While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.