Patent Publication Number: US-6709886-B2

Title: Method of fabricating micromachined devices

Description:
This application claims priority under 35 U.S.C. §119(e) to the following U.S. provisional applications: Ser. No. 60/200,497 filed on Apr. 25, 2000, Ser. No. 60/218,550 filed on Jul. 13, 2000, and Ser. No. 60/231,124 filed on Sep. 8, 2000, the disclosures of which are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to methods of fabricating micromachine devices, and more specifically, to fabricating silicon micromachined optical attenuators and switches for a plurality of light beams propagating along a respective plurality of beam paths. 
     2. Description of the Related Art 
     Micro-electro-mechanical systems (MEMS) are physically small systems with both electrical and mechanical components, and with dimensions on the order of microns. To achieve the small dimensions of the various components, MEMS are typically fabricated using techniques which were developed in part for integrated circuit fabrication. MEMS-based devices are found in an increasing number of applications, such as inkjet-printer cartridges, accelerometers that deploy car airbags, and other sensors and actuators. MEMS has developed into a growth industry with an estimated yearly market of tens of billions of dollars. In addition, MEMS-based optical systems, such as optical attenuators and switches, are becoming increasingly important in the field of telecommunications and computer networks. 
     A variable optical attenuator (VOA) is a device which can adjust the optical signal power passing through an optical fiber transmission circuit, such as dense wavelength-division multiplexing (DWDM) systems. Because the amount of light passing through an optical fiber depends on the wavelength of the light, VOAs are often needed to ensure power equalization of the individual wavelengths by adjusting the intensity for each wavelength. VOAs used in fiber optic communications system may use absorptive or reflective techniques to controllably adjust the transmitted power. 
     An optical switch is a device which can selectively switch optical signals from one optical circuit to another, and are typically used in optical systems such as optical add/drop multiplexers (OADMs). Various technologies can be used in optical switches, including, but not limited to, physically shifting an optical fiber to drive one or more alternative fibers, physically moving a reflective element, electro-optic effects, or magneto-optic effects. 
     MEMS technology has been identified as being able to satisfy the requirements of optical systems in the telecommunications and computer networking fields. These requirements include multi-channel operation in a dense package, high reliability, sufficiently fast operation, and inexpensive fabrication techniques. 
     Typically, multiple MEMS devices are fabricated on the same wafer substrate to take advantage of economies of scale. To separate the MEMS devices from one another, the wafer substrate is diced and separated into chips, each of which comprises at least one of the MEMS devices. However, MEMS devices also typically contain various fragile components, such as the flaps, cantilevers. These MEMS components are often damaged by the standard processes of dicing and separating the wafer substrate into chips, thereby reducing the yield of MEMS devices obtained from a given wafer substrate. 
     Previous attempts to improve the yield of MEMS devices from diced and separated wafer substrates have included the addition of a photoresist layer to the wafer substrate, thereby covering the MEMS devices and providing structural support during the dicing and separating processes. However, the application of a photoresist layer includes a spin coating method, which induces forces and stresses which can also damage fragile MEMS devices. Spin coating also is inefficient for large area substrates and the use of photoresist materials leads to environmental, health, and safety issues. In addition, photoresist layers typically are not conformal and have poor step coverage, especially when applied to high aspect ratio structures. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a method of fabricating a module for at least partially intercepting a light beam propagating along a beam path comprises providing a single crystal silicon substrate with a first substrate surface and a second substrate surface. The method further comprises forming a reflector support layer on the first substrate surface. The method further comprises forming a support frame and at least one reflector by etching the substrate from the second substrate surface. The method further comprises forming at least one electrical conduit on the reflector support layer. The method further comprises forming a reflector support by etching the reflector support layer from the first substrate surface. The reflector support is mechanically coupled to the support frame and the reflector. The reflector support is movable such that the reflector is movable substantially perpendicularly to the first substrate surface. 
     According to another aspect of the present invention, a method of fabricating a module for at least partially intercepting a light beam propagating along a beam path comprises providing a substrate comprising single crystal silicon, a first substrate surface, a second substrate surface, and an etch stop layer below the first substrate surface. The method further comprises providing a reflector support layer comprising the etch stop layer. The method further comprises forming a support frame and at least one reflector by etching the substrate from the second substrate surface to the etch stop layer. The method further comprises forming at least one electrical conduit on the reflector support layer. The method further comprises forming a reflector support by etching the reflector support layer from the first substrate surface. The reflector support is mechanically coupled to the support frame and the reflector. The reflector support is movable such that the reflector is movable substantially perpendicularly to the first substrate surface. 
     According to another aspect of the present invention, a method of fabricating a device on a substrate, where the device comprises at least one fragile component, comprises providing the substrate and forming the device on the substrate. The method further comprises forming a conformal layer on the device by depositing a polymeric material in a vapor phase onto the substrate. The method further comprises dicing and separating the substrate into a plurality of chips. At least one chip contains the device, and the conformal layer provides structural support for the fragile component of the device. The method further comprises removing the conformal layer from the device subsequently to dicing the substrate into the plurality of chips. 
     According to another aspect of the present invention, a method of fabricating a module for at least partially intercepting a light beam propagating along a beam path comprises providing a single crystal silicon substrate with a first substrate surface and a second substrate surface. The method further comprises forming a reflector support layer on the first substrate surface. The method further comprises forming a support frame and at least one reflector by etching the substrate from the second substrate surface. The method further comprises forming at least one electrical conduit on the reflector support layer. The method further comprises forming a conformal layer by depositing a polymeric material in a vapor phase onto the substrate from the second substrate surface. The method further comprises forming a reflector support by etching the reflector support layer. The reflector support is mechanically coupled to the support frame and the reflector. The reflector support is movable such that the reflector is movable substantially perpendicularly to the first substrate surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 schematically illustrate an apparatus for at least partially intercepting a plurality of light beams propagating along a respective plurality of beam paths in accordance with an embodiment of the present invention. 
     FIGS. 3 and 4 schematically illustrate a module for at least partially intercepting a light beam propagating along a beam path in accordance with an embodiment of the present invention. 
     FIGS. 5A and 5B schematically illustrate an embodiment of the apparatus in which only attenuation, and not switching is warranted. 
     FIG. 6 schematically illustrates a module comprising a compensation structure. 
     FIG. 7A schematically illustrates a cantilever with a serpentine configuration which couples the flap to the substrate. 
     FIGS. 7B and 7C schematically illustrate two types of torsional springs which couples the flap to the substrate. 
     FIG. 8 schematically illustrates the movement of the reflector along a curved path lying substantially in the reflector plane. 
     FIG. 9 schematically illustrates a reflector driver comprising a magnetic actuator. 
     FIG. 10 schematically illustrates a reflector driver comprising a thermal actuator. 
     FIG. 11A schematically illustrates a thermal actuator comprising a first material and a second material. 
     FIG. 11B schematically illustrates the displacement of the thermal actuator upon heating where the first material has a lower thermal coefficient of expansion than that of the second material. 
     FIG. 11C schematically illustrates the displacement of the thermal actuator upon heating where the first material has a higher thermal coefficient of expansion than that of the second material. 
     FIG. 12 schematically illustrates one embodiment of the apparatus comprising a (5×5) array configured to switch at least one light beam from a beam path to a second beam path. 
     FIG. 13 schematically illustrates one embodiment of the apparatus which can be used as an optical add/drop multiplexer (OADM) with a maximum of five light beams. 
     FIG. 14 schematically illustrates an embodiment in which the reflector is configured to transmit a portion of the incoming light beam, thereby switching only the remaining portion of the light beam. 
     FIG. 15A schematically illustrates an embodiment which has modules which each comprise a compensation structure which comprises a second reflector surface. 
     FIG. 15B schematically illustrates an embodiment in which the second reflector surface comprises the surface of the reflector which is opposite the reflector surface. 
     FIG. 16 schematically illustrates an embodiment with modules which each comprise a second reflector surface to be utilized in conjunction with transmit/receive pairs. 
     FIG. 17 schematically illustrates an embodiment in which the light beam can be attenuated by applying a selected amount of electrical current to the reflector driver to place the reflector in a selected first position. 
     FIG. 18 is a flowchart corresponding to a method of fabricating a module for at least partially intercepting a light beam propagating along a beam path. 
     FIGS. 19A-19K schematically illustrate the formation of the module using one embodiment of the method. 
     FIG. 20 is a flowchart of one embodiment for the formation of the reflector support layer on the first substrate surface. 
     FIG. 21 is a flowchart of one embodiment for forming a substratum layer on the silicon dioxide layer. 
     FIG. 22 is a flowchart of one embodiment for forming the support frame and at least one reflector. 
     FIG. 23 is a flowchart of one embodiment for the formation of the electrical conduit on the reflector support layer. 
     FIG. 24 schematically illustrates an exemplary deposition system for forming a conformal layer in accordance with embodiments of the present invention. 
     FIG. 25 is a flowchart of one embodiment for the deposition of parylene onto the substrate. 
     FIG. 26A schematically illustrates one embodiment of the conformal layer formed after the formation of the support frame, reflector, and electrical conduit, but before the formation of the reflector support. 
     FIG. 26B schematically illustrates one embodiment of the conformal layer after the formation of the reflector support. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 schematically illustrate an apparatus  10  for at least partially intercepting a plurality of light beams  12  propagating along a respective plurality of beam paths  14  in accordance with an embodiment of the present invention. The apparatus  10  comprises a single crystal silicon substrate  20  comprising a substrate surface  22  with a surface normal direction  24 . The apparatus  10  further comprises an array  30  comprising a plurality of modules  32 . 
     Each of the modules  32 , schematically illustrated in FIGS. 3 and 4, comprises a reflector  40  comprising single crystal silicon and a reflector surface  42  lying in a reflector plane  44  substantially perpendicular to the substrate surface  22 . Each of the modules  32  further comprises a reflector support  50  which mounts the reflector  40  to move substantially within the reflector plane  44  with a displacement component  46  along the surface normal direction  24  of the substrate surface  22 . Each of the modules  32  further comprises a reflector driver  60  responsive to electrical current to selectively move the reflector  40  between a first position  62  in which the reflector  44  intercepts at least a portion of one of the beam paths  14  and a second position  64  in which the reflector  44  does not intercept the portion of one of the beam paths  14 . At least a portion of the reflector driver  60  is mounted to the reflector support  50  and is conductive to electrical current. The reflector  40  moves to the first position  62  when electrical current flows therethrough and moves to the second position  64  when electrical current flow ceases, whereby the movement of the reflectors  40  is individually addressable. 
     In certain embodiments, the wavelengths of the plurality of light beams  12  are in the visible portion of the electromagnetic spectrum, typically between approximately 400 nm and approximately 800 nm. In alternative embodiments, wavelengths of the plurality of light beams  12  are in the infrared portion of the electromagnetic spectrum, between approximately 1200 nm and approximately 1600 nm. In addition, in certain embodiments, the light beams  12  are polarized, while in certain other embodiments, the light beams  12  are unpolarized. Persons skilled in the art are able to select appropriate wavelengths and polarizations of the light beams  12  in accordance with embodiments of the present invention. 
     The plurality of light beams  12  propagate along a respective plurality of beam paths  14 . In the embodiment schematically illustrated in FIGS. 1 and 2, the beam paths  14  are substantially parallel to the substrate surface  22  and are substantially parallel to one another. Furthermore, the beam paths  14  are spaced from the substrate surface  22  in the direction of the surface normal  24  such that the light beam  12  is not occluded by the substrate  20 . The beam paths  14  are spaced from one another such that each module  32  is below only one of the beam paths  14 . The beam paths  14  are separated from one another by a distance of preferably between approximately 0.3 mm to approximately 10 mm, more preferably between approximately 0.75 mm to approximately 4 mm, and most preferably between approximately 1 mm to approximately 2 mm. In other embodiments, the beam paths  14  can be spaced from the substrate surface  22  in the direction opposite to the surface normal  24 . In such embodiments, the beam paths  14  can be within the substrate  20  or can be below the substrate  20 . Persons skilled in the art can configure the beam paths  14  in accordance with embodiments of the present invention. 
     In the embodiment schematically illustrated in FIGS. 1 and 2, which is configured for optical switching, the second beam paths  16  are also substantially parallel to the substrate surface  22 , and substantially parallel to one another. In addition, the second beam paths  16  intersect the beam paths  14  and are co-planar with the beam paths  14 . As described more fully below, in embodiments in which the reflector planes  44  are oriented at approximately 45° to the beam paths  14 , the second beam paths  16  are substantially perpendicular to the beam paths  14 . Furthermore, the second beam paths  16  are spaced from one another such that each module  32  is below only one of the second beam paths  16 . The second beam paths  16  are separated from one another by a distance of preferably between approximately 0.3 mm to approximately 10 mm, more preferably between approximately 0.75 mm to approximately 4 mm, and most preferably between approximately 1 mm to approximately 2 mm. 
     The single crystal silicon substrate  20  comprises a substrate surface  22  with a surface normal direction  24 . In certain embodiments, the single crystal silicon substrate  20  comprises a portion of a single crystal silicon wafer, the wafer having a thickness preferably between approximately 10 μm and approximately 1000 μm, more preferably between approximately 200 μm and approximately 800 μm, and most preferably between approximately 400 μm and approximately 600 μm. In certain embodiments, the substrate surface  22  has a {110} crystallographic orientation. In certain other embodiments, the substrate surface  22  has a {100} crystallographic orientation. More generally, in other embodiments, the substrate surface  22  comprises at least one plateau surface region, with each plateau surface region having a {110} or {100} crystallographic orientation. As used herein, the surface normal direction  24  is defined as the perpendicular direction away from the substrate surface  22 . In certain embodiments, the substrate  20  also has a second substrate surface  25  which is generally parallel to the substrate surface  22 . Persons skilled in the art are able to provide a single crystal silicon substrate  20  with a substrate surface  22  having a surface normal direction  24  in accordance with embodiments of the present invention. 
     The apparatus  10  of the embodiment schematically illustrated in FIGS. 1 and 2 has a (5×5) array  30  comprising twenty-five modules  32  to at least partially intercept five light beams  12  or channels. Each module  32  is positioned below the intersection of one of the beam paths  14  and one of the second beam paths  16 . The array  30  is oriented so that the rows and columns of modules  32  are positioned along the beam paths  14  and second beam paths  16 . This embodiment, which has five modules  32  for each light beam  12 , can switch at least a portion of the light beam  12  from the beam path  14  to five separate second beam paths  16 . More generally, similar configurations of (M×N) modules  32  can be utilized to switch light beams  12  from M beam paths  14  to N second beam paths  16 , where M and N are integers which, in various embodiments, range from 1 to 64. Furthermore as described more fully below, the reflector  40  of each module  32  of the embodiment schematically illustrated in FIGS. 1 and 2 is oriented at 45° with respect to the beam path  14 , which is particularly conducive to operating as an optical add/drop multiplexer (OADM). 
     Alternatively, in other embodiments in which only attenuation, and not switching is warranted, the apparatus  10  can comprise an array  30  with only one module  32  for each light beam  12 , as schematically illustrated in FIGS. 5A and 5B. For example, in embodiments in which there are five light beams  12  to be attenuated, there are five modules  32  with one module  32  positioned below each of the beam paths  14 . Furthermore as described more fully below, the reflector  40  of each module  32  of the embodiment schematically illustrated in FIGS. 5A and 5B is to be substantially perpendicular to the beam path  14 . In such an embodiment, each module  32  can intercept at least a portion of the corresponding light beam  12  from the beam path  14 . Persons skilled in the art can configure an array  30  with an appropriate number and configuration of modules  32  to at least partially intercept light beams  12  in accordance with embodiments of the present invention. 
     As schematically illustrated in FIGS. 3 and 4, each of the modules  32  comprises a reflector  40  comprising single crystal silicon and a reflector surface  42  lying in a reflector plane  44  substantially perpendicular to the substrate surface  22 . As used herein, the term “reflector” is used to denote a body which reflects a portion of the electromagnetic radiation incident on the body. As is described more fully below, in certain embodiments, the reflector  40  is fabricated from the single crystal silicon substrate  20 , so the reflector  40  comprises a portion of the single crystal silicon substrate  20 . In such embodiments, the reflector surface  42  has a {111} crystallographic orientation when the substrate surface  22  has a {110} crystallographic orientation. Also, in such embodiments, the reflector surface  42  has a {100} crystallographic orientation when the substrate surface  22  has a {100} crystallographic orientation. The {111} crystallographic orientation of the reflector surface  42  provides a mechanically robust, smooth, and low stress surface which is preferable over polycrystalline reflector surfaces which have a high degree of stress, often resulting in inherent curvature of the surface. 
     In certain embodiments, the reflector  40  further comprises a metal layer formed as part of the reflector surface  42 . Examples of materials for the metal layer include, but are not limited to, chromium, gold, titanium, aluminum, silver, platinum, or combinations of these materials. The thickness of the metal layer is preferably between approximately 10 Å to approximately 1000 Å, more preferably between approximately 100 Å to approximately 900 Å, and most preferably between approximately 200 Å to approximately 600 Å. In certain embodiments, the reflector surface  42  reflects substantially all of the incident light beam  12 . In other embodiments, the reflector surface  42  reflects a portion of the incident light beam  12  and transmits a second portion of the incident light beam  12 . As described more fully below, the thickness of the metal layer can be selected to provide a desired reflectivity and transmittance of the incoming optical power incident on the reflector  40 . 
     Due to the fabrication process described below and the crystallographic directions of the single crystal silicon substrate  20 , the reflector  40  schematically illustrated in FIGS. 3 and 4 has a generally rectangular shape. Furthermore, the height  43  of the reflector  40  in such embodiments is constrained to be less than or equal to the thickness  23  of the silicon substrate  20 , while there is no such constraint on the width  45  of the reflector  40 . The height  43  of the reflector  40  is preferably between approximately 10 μm and approximately 1000 μm, more preferably between approximately 200 μm and approximately 800 μm, and most preferably between approximately 400 μm and approximately 600 μm. Typically, the width  45  of the reflector  40  is approximately 700 μm, and the thickness  47  of the reflector  40  is typically between approximately 20 μm and approximately 30 μm. Other widths and thicknesses of the reflector  40  are also compatible with embodiments of the present invention. 
     The reflector support  50  mounts the reflector  40  to move substantially within the reflector plane  44  with a displacement component  46  along the surface normal direction  24  of the substrate surface  22 . In the embodiment schematically illustrated in FIGS. 3 and 4, the reflector support  50  comprises a flap  52  and at least one coupler  54  which mechanically couples the flap  52  to the substrate  20 . The flap  52  is generally flat and parallelogram-shaped, and can be positioned substantially parallel to the substrate surface  22  as schematically illustrated in FIG.  3 . In certain embodiments, the shape of the flap  52  is defined by the crystallography of the single crystal silicon substrate  20  and the fabrication process. The dimensions of the sides of the flap  52  are preferably between approximately 0.2 mm and approximately 10 mm, more preferably between approximately 0.5 mm and approximately 5 mm, and most preferably between approximately 1 mm and approximately 3 mm. The thickness of the flap  52  is typically between approximately 3 μm and approximately 50 μm, but other thicknesses are also compatible with embodiments of the present invention. 
     In certain embodiments, the flap  52  is at least partially fabricated from the single crystal silicon substrate  20 , so the flap  52  comprises single crystal silicon. In other embodiments, the flap  52  comprises other materials which can include, but are not limited to, polycrystalline silicon, amorphous silicon, silicon nitride, silicon carbide, metal, or a combination of these materials. Persons skilled in the art can select appropriate materials for the flap  52  in accordance with various embodiments of the present invention. 
     In certain embodiments, the module  32  further comprises a compensation structure  41  which comprises single crystal silicon, as schematically illustrated in FIG.  6 . In this embodiment, the compensation structure  41  is similar to the reflector  40  in that both the compensation structure  41  and the reflector  40  have the same general dimensions and comprise the same general materials. In addition, as is described more fully below, the compensation structure  41  is fabricated along with the reflector  40 . In certain embodiments, the compensation structure  41  can serve as a counterbalancing mass which balances the mass of the reflector  40  to provide more symmetric dynamics of the reflector support  50  and as a thermal mass to provide more symmetric response of the reflector support  50  to thermal fluctuations. In such embodiments, the compensation structure  41  and reflector  40  are positioned symmetrically with respect to an axis of symmetry of the reflector support  50 . In addition, in other embodiments, the compensation structure  41  comprises a second reflector surface which can be utilized to deflect a light beam  12 , as is described more fully below. 
     In the embodiment schematically illustrated in FIG. 3, the flap  52  is coupled to the substrate  20  by a pair of couplers  54 . The presence of more than one coupler  54  helps to ensure rigidity to keep the reflector surface  42  substantially perpendicular to the substrate surface  22 . In embodiments in which the couplers  54  are at least partially fabricated from the single crystal silicon substrate  20 , the couplers  54  comprise single crystal silicon. In other embodiments, the couplers  54  comprise other materials which can include, but are not limited to, polycrystalline silicon, amorphous silicon, silicon nitride, silicon carbide, metal, or a combination of these materials. 
     In the embodiment schematically illustrated in FIGS. 3 and 4, each coupler  54  comprises a cantilever  55  which couples the flap  52  to the substrate  20 . In such an embodiment, the flap  52  is movable relative to the substrate  20 , as schematically illustrated in FIG.  4 . As the flap  52  is moved away from its equilibrium position, the cantilevers  55  provide a restoring force in a direction to return the flap  52  to its equilibrium position. In the embodiment schematically illustrated in FIGS. 3 and 4, the cantilevers  55  are not bent when the flap  52  is in its equilibrium position. 
     Alternatively, as schematically illustrated in FIGS. 7A,  7 B, and  7 C, the coupler  54  can have other configurations. FIG. 7A schematically illustrates a cantilever  55  with a serpentine configuration which couples the flap  52  to the substrate  20 . FIGS. 7B and 7C schematically illustrate two types of torsional springs  56  which couples the flap  52  to the substrate  20 , a straight configuration (FIG.  7 B), and a serpentine configuration (FIG.  7 C). In each of these embodiments, as the flap  52  is moved away from its equilibrium position, the couplers  54  provides a restoring force in a direction to return the flap  52  to its equilibrium position. In the embodiments schematically illustrated in FIGS. 3,  4 ,  7 A,  7 B, and  7 C, the flap  52  is substantially parallel to the substrate surface  22  when in its equilibrium position. Alternatively, in other embodiments, the flap  52  is tilted at an angle relative to the substrate surface  22  when the flap  52  is in its equilibrium position. 
     As schematically illustrated in FIGS. 3 and 4, the reflector plane  44  is substantially perpendicular to the flap  52  and the flap  52  is coupled to the substrate  20  such that the flap  52  is rotatable about an axis of rotation which is parallel with the substrate surface  22  and perpendicular to the reflector plane  44 . In this way, the reflector  40  is mounted to the flap  52  of the reflector support  50  such that the reflector  40  moves substantially within the reflector plane  44 . The movement of the reflector  40  can be described as having a displacement vector, and this displacement vector has a displacement component  46  along the surface normal direction  24  of the substrate surface  22 . Besides the displacement vector, this movement of the reflector  40  also comprises a rotation of the reflector  40 , as schematically illustrated in FIG.  4 . 
     This movement of the reflector  40  can also be described as moving along a curved path  48  lying substantially in the reflector plane  44 , as schematically illustrated in FIG.  8 . By following this curved path  48 , the reflector  40  rotates about an axis substantially perpendicular to the reflector plane  44 . In certain other embodiments, the curved path  48  can also include a displacement of the reflector  40  which is dependent on the particular deflection experienced by the coupler  54 . 
     The reflector driver  60  is responsive to electrical current to selectively move the reflector  40  between a first position  62  and a second position  64 . The reflector driver  60  comprises a portion which is mounted to the reflector support  50  and is conductive to electrical current. In the embodiment schematically illustrated in FIG. 3, the reflector driver  60  comprises a magnetic actuator  70  which comprises a magnetic field  71  generated externally from the array  30  and an electrical conduit  72  mechanically coupled to the reflector support  50 . The magnetic field  71  is generated by a magnet (not shown) which can be a permanent magnet or an electromagnet. For example, the substrate  20  can be placed in the airgap between the poles of a magnetic yoke, with the pole shapes optimized to inprove the uniformity of the magnetic field. The magnetic field strength depends somewhat on the design and spring constants of the module  32 , and in certain embodiments, the magnetic field strength is approximately 5000 gauss. 
     In certain embodiments, the poles of the magnet are spaced from the substrate surface  22  such that the magnetic field  71  has a component perpendicular to the substrate surface  22  and substantially uniform in a region above the array  30 . The magnetic field  71  of such embodiments forms an angle  73  with the surface normal direction  24  of the substrate surface  22  and has a component parallel to the reflector surface  42 . In alternative embodiments, the substrate  20  can be placed in the airgap such that the magnetic field  71  is parallel to the substrate surface  22 . In still other embodiments, individual north-south pole pairs can be located under or above each flap  52  to generate a separate magnetic field  71  for each module  32 . 
     In the embodiment schematically illustrated in FIG. 3, the electrical conduit  72  is fabricated on the flap  52  and extends across the couplers  54 . In certain embodiments, such as the embodiment schematically illustrated in FIG. 3, the electrical conduit  72  has a generally spiral configuration and has two conductive layers on top of one another, separated by an insulating layer. Electrical current enters and flows through the spiralpatterned first conductive layer, and exits through the second conductive layer. The electrical current can be supplied from an off-substrate source by using standard electrical connections such as bond wires and bond pads located on the substrate  20 . Other embodiments can utilize electrical conduits  72  with other configurations. 
     By applying the magnetic field  71  and flowing an electrical current through the electrical conduit  72 , as schematically illustrated in FIG. 9, the magnetic actuator  70  generates a torque which moves the reflector  40  between the first position  62  and second position  64 . An electrical current flowing through the electrical conduit  72  interacts with the externally-applied magnetic field  71  to create forces on the electrical conduit  72  which are perpendicular to both the magnetic field  71  and the electrical conduit  72  at each point along the electrical conduit  72 . These forces are given by the equation: F=I×B, where I is the current vector through the electrical conduit  72  and B is the magnetic field vector  71  and I×B denotes the vector cross product of the current vector and the magnetic field vector. For the embodiment schematically illustrated in FIGS. 3 and 9, the sum of these forces on the electrical conduit  72  is substantially zero. However, the sum of the torques generated by these forces about the axis of rotation is non-zero because the forces are applied to the electrical conduit  72  at different distances from the axis of rotation. In this way, a non-zero torque is produced by the forces generated when electrical current flows through the electrical conduit  72 , thereby deflecting the flap  52  and reflector  40 . The forces produced by the electrical current will deflect the flap  52  either up or down, depending on the direction of the electrical current and the direction of the magnetic field  71 . The deflection reaches a position at which the torque produced by the restoring force of the couplers  54  equals the torque produced by the forces generated by the flow of electrical current. By adjusting the magnitude of the electrical current, and thereby adjusting the torque applied by the reflector driver  60 , the amount of deflection of the flap  52  and reflector  40  can be controlled. For certain embodiments of fiber optic switching applications, the deflection is determined by the beam size, typically between 5 μm and 600 μm, and power consumption is typically on the order of tens of milliwatts. 
     In other embodiments, the module  32  can comprise more than one electrical conduit  72  on the flap  52 . For example, the flap  52  can have two electrical conduits  72 . In such embodiments, each electrical conduit  72  can have a separate electrical current applied to it, thereby providing additional control on the forces applied to the flap  52  to more precisely control the movement of the flap  52  and reflector  40 . 
     In other embodiments, such as schematically illustrated in FIG. 10, the reflector driver  60  comprises a thermal actuator  80  which comprises a first material  81  and a second material  82  which expand by differing amounts in response to thermal energy generated by the electrical current. Expressed differently, the first material  81  has a different thermal coefficient of expansion than does the second material  82 . Examples of materials which can be utilized as the first material  81  and second material  82  include, but are not limited to, single crystal silicon, polycrystalline silicon, silicon nitride, metal, or a combination of these materials. 
     In the embodiment schematically illustrated in FIG. 10, the thermal actuator  80  comprises a pair of cantilevers  55 , such as described above in relation to the reflector support  50 , and at least one electrical conduit  83 . In such embodiments, the cantilevers  55  serve as part of both the reflector support  50  and the reflector driver  60 . Each cantilever  55  is configured to have a first portion  84  comprising the first material  81 , and a second portion  85  comprising the second material  82 . The first portion  84  and second portion  85  are configured in relation to one another to provide a displacement of the flap  52  as described herein. As schematically illustrated in FIGS. 11A-11C, in one embodiment, the first portion  84  is on top of the second portion  85 , and both the first portion  84  and second portion  85  are coupled to the substrate  20  and the flap  52 . Other configurations of the first portion  84  and second portion  85  are compatible with embodiments of the present invention. 
     The electrical conduit  83  is configured to generate thermal energy via joule heating upon flowing an electrical current flowing therethrough. Furthermore, the electrical conduit  83  is configured such that the the cantilevers  55  are exposed to the thermal energy generated by the electrical current. In certain embodiments, such as the embodiment schematically illustrated in FIGS. 11A-11C, the electrical conduit  83  comprises a metal layer on the flap  52  and the couplers  54 . Examples of materials for the electrical conduit  83  include, but are not limited to, chromium, gold, titanium, aluminum, copper, nickel, or combinations of these materials. Alternatively in other embodiments, the electrical conduit  83  comprises the cantilevers  55  which are electrically conductive. In such an embodiment, electrical current can flow through the cantilevers  55  themselves. The electrical current can be supplied from an off-substrate source by using standard electrical connections such as bond wires and bond pads located on the substrate  20 . 
     In embodiments in which the cantilevers  55  are initially straight when not heated, as schematically illustrated in FIG. 11A, heating the cantilevers  55  by applying electrical current to the electrical conduit  83  will curve the cantilevers  55  out of the plane of the substrate surface  22 , thereby raising (FIG. 11B) or lowering (FIG.  11 C) the flap  52  and reflector  40  from their original positions. In the embodiment schematically illustrated in FIG. 11B, the raising of the flap  52  is achieved by using a first material  81  which has a lower thermal coefficient of expansion than that of the second material  82 . In the embodiment schematically illustrated in FIG. 11C, the lowering of the flap  52  is achieved by using a first material  81  which has a higher thermal coefficient of expansion than that of the second material  82 . Similarly, for embodiments in which the cantilevers  55  are initially curved out of the plane of the substrate surface  22 , (e.g., due to intrinsic stresses in the cantilevers  55 ) applying electrical current to the electrical conduit  83  can straighten the cantilevers  55 . 
     By selectively applying electrical current to the reflector driver  60  of selected modules  32 , the movement of the reflectors  40  is individually addressable. The direction and magnitude of the displacement of the reflector  40  is dependent on the configuration of the first portion  84  and second portion  85  of the cantilevers  55  and on the difference of the thermal coefficients of expansion for the first material  81  and second material  82 . When the electrical current is removed and the cantilevers  55  are permitted to cool, the reflector  40  returns to its original position. By adjusting the magnitude of the electrical current, the amount of deflection of the flap  52  and reflector  40  can be controlled. For certain embodiments of fiber optic switching applications, the deflection is determined by the beam size, typically 5 μm to 600 μm, and power consumption is typically on the order of tens of milliwatts. 
     The reflector driver  60  of a given module  32  selectively moves the reflector  40  of the module  32  between a first position  62  and a second position  63 . When in the first position  62 , the reflector  40  intercepts at least a portion of one of the beam paths  14 . When in the second position  64 , the reflector  40  does not intercept the portion of one of the beam paths  14 . The reflector  40  moves to the first position  62  when electrical current flows through the conductive portion of the reflector driver  60 , whereby the movement of the reflectors  40  is individually addressable. The reflector  40  moves to the second position  64  when electrical current ceases to flow through the conductive portion of the reflector driver  60 . In certain embodiments, the reflector  40  in the first position  62  is deflected out of the substrate surface  22 , and the second position  64  is the equilibrium position of the reflector  40 , as schematically illustrated in FIG.  4 . 
     FIG. 12 schematically illustrates one embodiment in which the apparatus  10  comprises a (5×5) array  30  configured to switch at least one light beam  12  from a beam path  14  to a second beam path  16 . In the embodiment schematically illustrated in FIG. 12, the plurality of light beams  12  are propagating along the plurality of beam paths  14 , which are configured to be above and substantially parallel to the substrate surface  22 . By selectively addressing one of the five reflectors  40   aa - 40   ae  corresponding to the beam path  14   a  of the light beam  12   a , the light beam  12   a  can be deflected into one of five second beam paths  16   a - 16   e . For example, when the reflector  40   ab  is in the first position  62 , and reflectors  40   aa ,  40   ac - 40   ae  are each in the second position  64 , the reflector  40   ab  completely intercepts the beam path  14   a , and deflects the light beam  12   a  into the second beam path  16   b . Also, in certain embodiments, the size of the reflector  40  is larger than the spot size of the light beam  12 , thereby requiring less precision in the positioning of the reflector  40  to completely intercept the beam path  14 . 
     Similarly, one reflector  40  corresponding to each of the other light beams  12  can be moved into the first position  62  to completely intercept each beam path  14  and to deflect each of the light beams  12  into a unique second beam path  16 . More generally, at any given time, N reflectors  40  would be moved into the first position  62 , each with a unique column and row address, and the other N 2 -N reflectors  40  would be in the second position  64 . In this way, each of the five light beams  12   a - 12   e  propagating along the five beam paths  14   a - 14   e  can be selectively deflected utilizing the twenty-five reflectors  40   aa - 40   ee  into five unique second beam paths  16   a - 16   e.    
     Alternatively, the apparatus  10  can be used as an optical add/drop multiplexer (OADM) with a maximum of five light beams  12 , as schematically illustrated in FIG.  13 . In such an embodiment, one or more of the incoming light beams  12   a - 12   e  can be effectively “dropped” from the output of the apparatus  10  by not deflecting the dropped light beam  12  into one of the second beam paths  16   a - 16   e . In addition, an incoming “added” second light beam  90  can propagate along the second beam path  16 , effectively replacing the dropped light beam  12 . For example, in the embodiment schematically illustrated in FIG. 13, the light beam  12   b  is dropped and the second light beam  90  is added in its place. By not selectively addressing any of the reflectors  40  corresponding to the beam path  14   b , the dropped light beam  12   b  selected to be removed will continue to propagate along the beam path  14   b . In this way, the output from the apparatus  10  has four of the incoming light beams  12   a ,  12   c - 12   e  and the added second light beam  90 . This procedure of dropping an incoming light beam  12  and adding another second light beam  90  in its place is termed “optical add/drop multiplexing.” 
     Alternatively, in other embodiments, the reflector  40  is configured to transmit a portion of the incoming light beam  12 , thereby switching only the remaining portion of the light beam  12 . For example, as schematically illustrated in FIG. 14, one embodiment of the present invention can be used with infrared light beams  12 . Because silicon transmits infrared light, each reflector  40  of this embodiment has a metal layer  100  with a thickness which determines the transmittance of the reflector  40  to the infrared light beam  12 . The dependence of the reflectance and transmittance of metal layers as a function of layer thickness is described in pages 35.3-35.15 of “Handbook of Optics, Volume II: Devices, Measurements, and Properties,” second edition, edited by Michael Bass, published by McGraw-Hill, Inc., which is incorporated herein in its entirety by reference. The thickness of the metal layer  100  is selected to provide a reflector  40  with a selected transmittance and reflectance to the light beam  12 . While the reflected portion of the light beam  12  is switched to the second beam path  16 , the transmitted portion of the light beam  12  which continues to propagate along the beam path  14  can be sampled to monitor the performance of the apparatus  10 . 
     Other embodiments of the present invention utilize modules  32  which each comprise a second reflector surface  110 . Certain embodiments, such as schematically illustrated in FIG. 15A have modules  32  which comprise a compensation structure  41  which comprises a second reflector surface  110 . Alternatively as schematically illustrated in FIG. 15B, in other embodiments, the second reflector surface  110  can comprise the surface of the reflector  40  which is opposite the reflector surface  42 . 
     The second reflector surface  110  of each module  32  can be utilized in conjunction with transmit/receive pairs, as schematically illustrated in FIG.  16 . In such an embodiment, incoming light beams  12   a - 12   e  are initially propagating along beam paths  14   a - 14   e , and incoming second light beams  90   a - 90   e  are initially propagating along second beam paths  16   a - 16   e . When the module  32  corresponding to beam path  14   a  and second beam path  16   b  is activated, light beam  12   a  is reflected by the reflector surface  42  from beam path  12   a  to second beam path  16   b . At the same time, second light beam  90   b  is reflected by the second reflector surface  110  from the second beam path  16   b  into the beam path  12   a . Thus, the light beam  12   a  and second light beam  90   b  have been exchanged with each other. Similarly, other pairs of light beams  12  and second light beams  90  can be exchanged with one another. Using the embodiment schematically illustrated in FIG. 16, up to five pairs of light beams  12  and second light beams  90  can be exchanged with one another. 
     In other embodiments, the apparatus  10  can be used as an optical attenuator to reduce the amount of optical power propagating along one or more of the beam paths  14 . In one embodiment as schematically illustrated in FIG. 5, five light beams  12   a - 12   e  propagate into the apparatus  10  along their respective beam paths  14   a - 14   e , and each light beam  12  has a corresponding module  32  and reflector  40 . Each of the reflectors  40   a - 40   e  of the array  30  is individually addressable, so the five light beams  12   a - 12   e  can be individually attenuated. A reflector  40  in the first position  62  intercepts at least a portion of the respective beam path  14 , and a reflector  40  in the second position  64  does not intercept the portion of the respective beam path  14 . 
     In certain embodiments, the first position  62  of the reflector  40  is selectable, whereby the reflector  40  in the first position  62  intercepts a selected portion of the respective light beam  12 . As described above, the deflection of the reflector  40  is controllable by adjusting the electrical current applied to the reflector driver  60  of the module  32 . For example, as schematically illustrated in FIG. 17, the light beam  12  can be attenuated by applying a selected amount of electrical current to the reflector driver  60  to place the reflector  40  in a selected first position  62 . In the embodiment schematically illustrated in FIG. 17, the first position  62  is selected such that 50% of the incoming optical power of the light beam  12  continues to propagate along the beam path  14 . The remaining 50% of the incoming optical power of the light beam  12  is intercepted partially by the reflector  40  and partially by other components of the module  32 , such as the flap  52 . In certain other embodiments, the attenuation of light beams  12  can be combined with the switching of light beams. For example, rather than placing the reflector  40  in a first position  62  in which the reflector  40  completely intercepts the light beam  12 , the first position  62  can be selected to only intercept a portion of the light beam  12 , thereby switching the intercepted portion of the light beam  12  and transmitting the unintercepted portion of the light beam  12 . 
     FIG. 18 is a flowchart corresponding to a method  200  of fabricating a module  32  for at least partially intercepting a light beam  12  propagating along a beam path  14 . The method  200  comprises an operational block  210  for providing a single crystal silicon substrate  300  with a first substrate surface  310  and a second substrate surface  312 . The method  200  further comprises an operational block  220  for forming a reflector support layer  320  on the first substrate surface  310 . The method  200  further comprises an operational block  230  for forming a support frame  330  and at least one reflector  340  by etching the substrate  300  from the second substrate surface  312 . The method  200  further comprises an operational block  240  for forming at least one electrical conduit  350  on the reflector support layer  320 . The method  200  further comprises an operational block  250  for forming a reflector support  360  by etching the reflector support layer  320  from the first substrate surface  310 . The reflector support  360  is mechanically coupled to the support frame  330  and the reflector  340 . The reflector support  360  is movable such that the reflector  340  is movable substantially perpendicularly to the first substrate surface  310 . FIGS. 19A-19K schematically illustrate the formation of the module  32  using one embodiment of the method  200 . 
     A single crystal silicon substrate  300  with a first substrate surface  310  and a second substrate surface  312  is provided in the operational block  210 . In the embodiment schematically illustrated in FIG. 19A, the single crystal silicon substrate  300  comprises a single crystal silicon substrate wafer with the first substrate surface  310  and second substrate surface  312  each having a {110} crystallographic orientation. Typically, the single crystal silicon substrate wafer is generally circular with a diameter of four inches. In other embodiments, the first substrate surface  310  and second substrate surface  312  each having a {100} crystallographic orientation. More generally, in other embodiments, the first substrate surface  310  and second substrate surface  312  each comprise at least one plateau surface region, with each plateau surface region having a {110} or {100} crystallographic orientation. 
     A reflector support layer  320  is formed on the first substrate surface  310  in the operational block  220 . FIG. 20 is a flowchart of one embodiment of operational block  220  for the formation of the reflector support layer  320  on the first substrate surface  310 . In this embodiment, the operational block  220  comprises forming a silicon dioxide layer  321  on the first substrate surface  310  in an operational block  221 , and forming a substratum layer  322  on the silicon dioxide layer  321  in an operational block  222 . In certain embodiments, such as the embodiment illustrated in FIG. 20, the operational block  220  further comprises forming an insulating layer  323  on the substratum layer  322  in an operational block  223 . 
     In certain embodiments, formation of the silicon dioxide layer  321  is performed by forming low-temperature oxide (LTO) using low-pressure chemical vapor deposition (LPCVD). In such a process, the first substrate surface  310  is exposed to silane and oxygen at pressures of approximately 350 mtorr while being held at temperatures of approximately 450 C. In certain embodiments, the first substrate surface  310  is also exposed to other gases, such as phosphine, to form the silicon dioxide film. The LTO LPCVD process is used to deposit a smooth silicon dioxide layer  321  with a thickness of approximately 2 μm. The deposition rate is a function of temperature, pressure, and gas flows, with higher temperatures favoring higher deposition rates. In the embodiment corresponding to FIG. 19A, the second substrate surface  312  is also exposed to the silane and oxygen and held at approximately 450 C., so a silicon dioxide layer  324  is also formed on the second substrate surface  312 . As is described more fully below, this silicon dioxide layer  324  is utilized in later processing steps. 
     A substratum layer  322  is formed on the silicon dioxide layer  321  in the operational block  222 , one embodiment of which is shown in FIG.  21 . The operational block  222  comprises forming a protective layer  325  on the silicon dioxide layer  321  in an operational block  224 , and forming a polycrystalline silicon layer  326  on the protective layer  325  in an operational block  225 . In certain embodiments, the protective layer  325  comprises silicon nitride, which is deposited onto the silicon dioxide layer  321  by LPCVD using silicon-containing gases such as silane or dichlorosilane and nitrogen-containing gases such as ammonia. The thickness of the silicon nitride resulting from exposing the silicon dioxide layer  321  at approximately 820 C. for approximately 30 minutes is approximately 0.2 μm. Other embodiments can deposit the silicon nitride using other techniques, or can utilize other materials for the protective layer  325 . The polycrystalline silicon layer  326  is formed on the protective layer by LPCVD. Other embodiments can deposit the polycrystalline silicon layer  326  using other techniques. 
     An insulating layer  323  is formed on the substratum layer  322  in the operational block  223 . In certain embodiments, the insulating layer  323  comprises silicon nitride, which is deposited onto the substratum layer  322  using a LPCVD process similar to that used to form the protective layer  325 , as described above. The resulting thickness of the insulating layer  323  is approximately 0.2 μm. Other embodiments can deposit the silicon nitride using other techniques. 
     The process of forming the substratum layer  322  on the silicon dioxide layer  321  and the insulating layer  323  on the substratum layer  322  can also form similar layers  322 ′,  323 ′ on the second substrate surface  312 , as schematically illustrated in FIG.  19 A. Using a dry plasma etching process, these layers  322 ′,  323 ′ can be removed while leaving the silicon dioxide layer  324  on the second substrate surface  312 , resulting in the structure schematically illustrated in FIG.  19 B. Other embodiments can remove the layers  322 ′,  323 ′ using different techniques, or can avoid forming these layers  322 ′,  323 ′ during deposition. 
     A support frame  330  and at least one reflector  340  is formed by etching the substrate  300  from the second substrate surface  312  in the operational block  230 , and FIG. 22 is a flowchart of one embodiment of the operational block  230 . In this embodiment, the operational block  230  comprises forming an etch-resistant layer  331  on the second substrate surface  312  in an operational block  231 . The operational block  230  of this embodiment further comprises patterning the etch-resistant layer  331  on the second substrate surface  312  in an operational block  232  to selectively expose a first region  332  of the second substrate surface  312  and to maintain the etch-resistant layer  331  on a second region  333  of the second substrate surface  312 . The operational block  230  of this embodiment further comprises etching the substrate  300  from the first region  332  of the second substrate surface  312  to the reflector support layer  320  in an operational block  233 , thereby forming sidewalls  334  of the support frame  330  and at least one reflective surface  335  of the reflector  340 . The operational block  230  of this embodiment further comprises removing the etch-resistant layer  331  from the second region  333  of the second substrate surface  312  in an operational block  234 . 
     In certain embodiments, the etch-resistant layer  331  comprises silicon dioxide, and the etch-resistant layer  331  can be formed on the second substrate surface  312  while the silicon dioxide layer  321  is formed on the first substrate surface  310 , as described above. In such an embodiment, the etch-resistant layer  331  comprises the silicon dioxide layer  324  on the second substrate layer  312 , as schematically illustrated in FIG.  19 B. Alternatively, other embodiments can utilize different materials for the etch-resistant layer  331 , or can form the etch-resistant layer  331  in a separate step from the formation of the silicon dioxide layer  321  on the first substrate surface  310 . 
     In certain embodiments, the patterning of the etch-resistant layer  331  can be performed using photolithography. In such an embodiment, a photoresist layer of approximately 10 μm thickness is spin-coated onto the etch-resistant layer  331 , exposed to a pattern of light, and developed, thereby leaving a patterned photoresist layer on the etch-resistant layer  331 . Using a standard wet etching technique, portions of the etch-resistant layer  331  can be removed, thereby selectively exposing the first region  332  of the second substrate surface  312  while maintaining the etch-resistant layer  331  on the second region  333  of the second substrate surface  312 . FIG. 19C schematically illustrates a resulting structure corresponding to this embodiment. Persons skilled in the art can select appropriate photoresist layers and techniques in accordance with embodiments of the present invention. 
     In certain embodiments, the etching of the substrate  300  from first region  332  of the second substrate surface  312  is performed using a deep-reactive ion etching (DRIE) process. One example of an etching process compatible with embodiments of the present invention is the “Bosch” process for anisotropically plasma etching silicon to provide laterally defined recess structures. This process is described in U.S. Pat. No. 5,501,893, entitled “Method of Anisotropically Etching Silicon,” which issued to Laermer, et al., and which is incorporated in its entirety by reference herein. The Bosch process yields etched regions with long sidewalls. The etching of the substrate  300  continues until the reflector support layer  320  is reached, thereby forming the sidewalls  334  and the reflective surface  335 . FIG. 19D schematically illustrates a resulting structure corresponding to this embodiment. 
     As schematically illustrated in FIG. 19D, the sidewalls  334  and reflective surface  335  resulting from the DRIE process in certain embodiments do not have the desired crystallographic orientation, so the etching of the substrate  300  can also include an anisotropic wet etch process subsequent to the DRIE process. An example of an anisotropic wet etch process compatible with embodiments of the present invention includes exposing the substrate  300  to an aqueous solution of tetramethylammonia hydroxide (TMAH) (e.g., approximately 15% TMAH in H 2 O) while being held at approximately 90 C. for approximately 3-3.5 hours. In alternative embodiments, a KOH solution or an ethylene diamine/pyrocatecol (EDP) solution can be used in the wet etch process. Persons skilled in the art can select other etching processes to form the sidewalls  334  and reflective surface  335  in accordance with embodiments of the present invention. As schematically illustrated in FIG. 19E, the anisotropic wet etch process yields generally straight sidewalls  334  and reflective surface  335  which are generally perpendicular to the reflector support layer  320 . 
     The formation of the support frame  330  and the reflector  340  includes removing the etch-resistant layer  331  from the second region  333  of the second substrate surface  312 . In one embodiment, the removal of the etch-resistant layer  331  is performed by a wet etching process using a 5% HF aqueous solution. The wet etching process terminates at the protective layer  325  of the reflector support layer  320 . In this way, the protective layer  325  protects the other layers of the reflector support layer  320 . Besides removing the etch-resistant layer  331 , in embodiments in which the reflector support layer  320  comprises a silicon dioxide layer  321 , the silicon dioxide layer  321  of the reflector support layer  320  is also removed from a portion of the reflector support layer  320  corresponding to the first region  332  of the substrate  300 . In alternative embodiments, the silicon dioxide layer  321  is removed during a separate process from the removal of the etch-resistant layer  331 . The resulting structure is schematically illustrated in FIG.  19 F. 
     In certain embodiments, the formation of the support frame  330  and the reflector  340  further comprises forming a metal layer  336  on the reflective surface  335  of the reflector  340  in an operational block  235 , as illustrated in the flowchart of FIG.  22 . One example of such an embodiment includes deposition of aluminum onto the reflective surface  335 . Another example of such an embodiment includes thermal evaporation of an adhesion layer onto the reflective surface  335  from the second substrate surface  312 , followed by thermal evaporation of a gold layer onto the adhesion layer from the second substrate surface  312 . The adhesion layer can comprise various materials, examples of which include, but are not limited to chromium and titanium. In order to deposit the metal layer  336 , the substrate  300  is typically tilted with respect to the thermal evaporation direction by approximately 10°. These thermal evaporation processes are typically performed in a vacuum chamber with a vacuum pressure of approximately 10 −7  torr. As described above, the reflectivity and transmittance of the metal layer is a function of its thickness. In certain embodiments, the thickness of the chromium layer is approximately 150 Å and the thickness of the gold layer is approximately 0.2-0.5 μm. Examples of other materials for the metal layer  336  which are compatible with embodiments of the present invention include, but are not limited to, copper and aluminum. The resulting structure is schematically illustrated in FIG.  19 G. 
     One embodiment of the formation of the electrical conduit  350  on the reflector support layer  320  of the operational block  240  is illustrated in the flowchart of FIG.  23 . This embodiment comprises forming a first metallic layer  341  on the reflector support layer  320  in an operational block  241 . This embodiment further comprises patterning the first metallic layer  341 , thereby forming a first portion  342  of the electrical conduit  350 , in an operational block  242 . This embodiment further comprises forming an insulating layer  343  on the first portion  342  of the electrical conduit  350  in an operational block  243 , and patterning the insulating layer  343 , thereby forming at least one via hole  344  to the first portion  342  of the electrical conduit  350  in an operational block  244 . This embodiment further comprises forming a second metallic layer  345  on the insulating layer  343  in an operational block  245 , and patterning the second metallic layer  345 , thereby forming a second portion  346  of the electrical conduit  350  in an operational block  246 . The second portion  346  of the electrical conduit  350  is conductively coupled to the first portion  342  of the electrical conduit  350  through the via hole  344  of the insulating layer  343 . 
     In certain embodiments, the formation of the first metallic layer  341  on the reflector support layer  320  of the operational block  241  includes depositing a chromium layer on the reflector support layer  320  by thermal evaporation and depositing a gold layer on the chromium layer by thermal evaporation. The first metallic layer  341  then comprises a chromium layer and a gold layer. Typically, the thickness of the chromium layer is approximately 100 Å, and the thickness of the gold layer is approximately 1 μm. Using standard photolithographic processes, the first metallic layer  341  can be patterned to form the first portion  342  of the electrical conduit  350  in the operational block  242 . In certain embodiments, the patterning of the first metallic layer  341  can be followed by other processes, such as electroplating or electroless deposition, to increase the metal thickness and thereby decrease the resistance. Such processes can require selective masking of other metal portions of the module  32 . Persons skilled in the art are able to configure photolithographic or other processes to form the first portion  342  in accordance with embodiments of the present invention. In certain embodiments, the first portion  342  of the electrical conduit  350  has a generally spiral configuration. The resulting structure is schematically illustrated in FIG.  19 H. 
     In certain embodiments, the insulating layer  343  comprises silicon dioxide, and the insulating layer  343  is formed in the operational block  243  by a LPCVD process similar to that process which forms the silicon dioxide layer  321  of the reflector support layer  320  in the operational block  221 . The thickness of the insulating layer  343  is approximately 1 μm. Using standard photolithographic processes, the insulating layer  343  can be patterned to form the via hole  344  to the first portion  342  of the electrical conduit  350 . Persons skilled in the art are able to configure photolithographic processes in accordance with embodiments of the present invention. The resulting structure is schematically illustrated in FIG.  19 I. 
     In certain embodiments, the formation of the second metallic layer  345  on the insulating layer  343  of the operational block  245  includes depositing a chromium layer on the insulating layer  343  and a gold layer on the chromium layer by thermal evaporation as described above in relation to the deposition of the first metallic layer  341 . The second metallic layer  345  then comprises a chromium layer and a gold layer. Typically, the thickness of the chromium layer is approximately 100 Å, and the thickness of the gold layer is approximately 1.2 μm. Using standard photolithographic processes, the second metallic layer  345  can be patterned to form the second portion  346  of the electrical conduit  350  in the operational block  246 . In certain embodiments, the patterning of the second metallic layer  345  can be followed by other processes, such as electroplating or electroless deposition, to increase the metal thickness and thereby decrease the resistance. Such processes can require selective masking of other metal portions of the module  32 . Persons skilled in the art are able to configure photolithographic or other processes to form the second portion  346  in accordance with embodiments of the present invention. 
     In addition, the via hole  344  is filled with metallic material such that the second portion  346  of the electrical conduit  350  is conductively coupled to the first portion  342  of the electrical conduit  350 . In certain embodiments, the second portion  346  of the electrical conduit  350  has a generally spiral configuration. In such an embodiment in which the electrical conduit  350  is part of a magnetic actuator, the direction of current through the spiral of the first portion  342  and the spiral of the second portion  346  is configured so as not to generate forces which effectively cancel each other out. The resulting structure is schematically illustrated in FIG.  19 J. 
     In certain embodiments, the formation of the reflector support  360  of the operational block  250  is performed by etching the reflector support layer  320  from the first substrate surface  310 . Using standard photolithographic processes, a patterned photoresist layer can be formed on the reflector support layer  320 , the pattern defining the reflector support  360 , including any flaps  52  or couplers  54  which comprise the reflector support  360 . In embodiments in which the reflector support layer  320  comprises a silicon dioxide layer  321 , a protective layer  325  comprising silicon nitride, a polysilicon layer  326 , and an insulating layer  323 , a plasma etch process can be used. In addition, the portion of the metal layer  336  on the reflector support layer  320  between the sidewalls  334  and the reflective surface  335  can be removed by a wet etch process. Persons skilled in the art are able to configure photolithographic processes in accordance with embodiments of the present invention. The resulting structure is schematically illustrated in FIG. 19K, the structure comprising a reflector support  360  with a reflector  40 , a compensation structure  41 , and an electrical conduit  350 . 
     Various additional alternative embodiments are compatible with the present invention. For example, certain embodiments of the formation of the substratum layer  322  can omit the protective layer  325 , thereby forming the polycrystalline silicon layer  326  on the silicon dioxide layer  321 . In certain other embodiments, the reflector support layer  320  on the first substrate surface  310  is protected from being etched during the anisotropic wet etch process during the formation of the support frame  330  and reflector  340  of the operational block  230 . In such embodiments, the reflector support layer  320  can be first coated with a protective material, such as Cytop®, an amorphous fluorocarbon polymer which is produced by Asahi Glass Co. of Tokyo, Japan. After the anisotropic wet etch process is completed, the protective material is removed. 
     During the formation of modules  32  with a second reflector surface  110  in other alternative embodiments, the metal layer can also be formed on the opposite surfaces of the reflector  40  and/or the compensation structure  41  during the operational block  234 . Typically, this metal layer is also formed using standard metal evaporation techniques once the substrate  300  and evaporator are re-oriented to deposit metallic material onto the desired surfaces. 
     In alternative embodiments in which the formation of the insulating layer  343  also forms silicon dioxide residue on the sidewalls  334  or the reflective surfaces  335 , a wet etch process can be utilize to remove the silicon dioxide residue from these surfaces. The insulating layer  343  on the first portion  342  of the electrical conduit  350  is typically protected from the wet etch process by a layer of photoresist. Still other alternative embodiments of the method  200  include the formation of the metal layer  336  on the reflective surface  335  of the reflector  340  after the formation of the electrical conduits  350 , thereby avoiding the possibility of the silicon dioxide residue being formed on the metal layer  336  of the reflective surface  335 . 
     In still other alternative embodiments, the substrate  300  can be provided with an etch stop layer which comprises a portion of the reflector support layer  320 . For example, the substrate  300  can comprise a silicon-on-insulator wafer which comprises a silicon wafer with a subsurface silicon dioxide layer which serves as the etch stop layer. In another example, a boron diffusion layer in the substrate  300  can serve as the etch stop layer. In such embodiments, the reflector support layer  370  can further comprise an epitaxial silicon layer formed on the first substrate surface  310 . The support frame  330  and reflector  340  are formed by etching the substrate  300  from the second substrate surface  312  to the etch stop layer. The reflector support layer  320  of such embodiments can also comprise an insulating layer, such as silicon nitride, formed on the first substrate surface  310 . 
     In certain alternative embodiments, the reflector driver  60  receives and is responsive to an electrical signal to selectively move the reflector  40  of a module  32 . In such embodiments, the electrical signal can comprise a voltage which charges portions of a reflector driver  60  configured to utilize electrostatic forces to move the reflector  40 . In still other embodiments, the reflector  40  can move to the second position  64  when electrical current is applied to the reflector driver  60 , and can move to the first position  62  when electrical current is not applied to the reflector driver  60 . In such embodiments, the flap  52  can be given an initial displacement by depositing a magnetic material, such as permalloy, on the flap  52 . 
     Typically, multiple MEMS devices, such as the apparatus  10  described herein, are fabricated on the same wafer substrate to take advantage of economies of scale. To separate the MEMS devices from one another, the wafer substrate is diced and separated into chips, each of which comprises at least one of the MEMS devices. However, MEMS devices also typically contain various fragile components, such as the flaps  52 , cantilevers  55 , and reflectors  40  of the apparatus  10  described herein. These MEMS components are often damaged by the standard processes of dicing and separating the wafer substrate into chips, thereby reducing the yield of MEMS devices obtained from a given wafer substrate. 
     Previous attempts to improve the yield of MEMS devices from diced and separated wafer substrates have included the addition of a photoresist layer to the wafer substrate, thereby covering the MEMS devices and providing structural support during the dicing and separating processes. However, the application of a photoresist layer includes a spin coating method, which induces forces and stresses which can also damage fragile MEMS devices. Spin coating also is inefficient for large area substrates and the use of photoresist materials leads to environmental, health, and safety issues. In addition, photoresist layers typically are not conformal and have poor step coverage, especially when applied to high aspect ratio structures such as the reflectors  40  of the apparatus  10  described herein. 
     In certain embodiments of the present invention, the method  200  of fabricating the module  32  further comprises forming a conformal layer  370  by depositing a polymeric material in a vapor phase onto the substrate  300  from the second substrate surface  312  in an operational block  260 . One example of a polymeric material compatible with the present invention includes, but is not limited to, parylene. Parylene is the generic name for members of a unique family of thermoplastic polymers that are deposited by using the dimer of para-xylylene (di-para-xylylene, or DPXN). Parylene can be deposited under vacuum conditions from a vapor phase at room temperature. There are three types of commercially available parylene. The basic member of the series is poly-para-xylylene (also referred to as Parylene N), a linear and highly crystalline polymer which exhibits a low dissipation and high dielectric strength. A second type, Parylene C, has para-xylylene monomers which have a chlorine atom replacing one of the aromatic hydrogen atoms in Parylene N. Parylene C also has a low permeability to moisture and other corrosive gases. Parylene D, the third member of the series, also has para-xylylene monomers, but with two chlorine atoms replacing two aromatic hydrogen atoms in the monomer of Parylene N. Parylene D has similar properties to Parylene C, with the ability to withstand higher temperatures. The chemical structure of parylene, its physical properties, and various deposition and patterning techniques are provided in more detail in “Integrated Parylene Micro Electro Mechanical Systems (MEMS),” doctoral thesis of Xuan-Qi Wang from California Institute of Technology, Pasadena, Calif., 2000, which is incorporated in its entirety by reference herein. 
     FIG. 24 schematically illustrates an exemplary deposition system  400  for forming a conformal layer  370  by depositing a polymeric material in a vapor phase onto the substrate  300  in accordance with embodiments of the present invention. The deposition system schematically illustrated in FIG. 24 comprises a sublimator  410 , a pyrolysis chamber  420 , a deposition chamber  430 , a cold trap  440 , and a vacuum pump  450 . In certain embodiments, as illustrated in the flowchart of FIG. 25, the deposition of parylene onto the substrate  300  of the operational block  260  comprises a sublimation process of an operational block  261  in which the parylene sublimates from its solid dimer form into a vapor phase. The sublimation process of the operational block  261  is accomplished in the sublimator  410  by the application of heat to solid parylene while under vacuum conditions. The temperature range for sublimation of parylene is typically between approximately 140 C. and 170 C. The deposition of parylene of the operational block  260  further comprises a pyrolysis process of an operational block  262 , in which the gaseous form of the parylene dimer is cleaved into monomers. The pyrolysis process of the operational block  262  is typically performed in a pyrolysis chamber  420  which is heated to above approximately 650 C. The deposition of parylene of the operational block  260  further comprises a polymerization process of an operational block  263  in which the gaseous parylene monomers are deposited onto the substrate and polymerized, which typically occurs at approximately room temperature in the deposition chamber  430 . While the sublimation process of operational block  261  and pyrolysis process of operational block  262  are achieved by controlled temperatures, the final deposition rate during the polymerization process of operational block  263  is controlled by the pressure inside the deposition chamber. In certain embodiments, the cold trap  440  and vacuum pump  450  maintain the pressure inside the deposition chamber  430  during the polymerization process of operational block  263  between approximately 20 mtorr and 30 mtorr. 
     Parylene deposited in this manner yields thin films with a high degree of conformity; i.e., the parylene is deposited on the exposed surfaces at approximately the same rate. For all the types of parylene, the para-xylylene monomers are cross-linked into polymerized long-chain macromolecules to form a thin film which has anisotropic properties and high rigidity. Parylene is also inert, non-toxic, and non-hazardous. It emits no volatile organic compounds during storage, handling, or deposition. Parylene resists room temperature chemical attack and is insoluble in organic solvents up to approximately 150 C. Parylene films are also resistant to permeation by most solvents. 
     As schematically illustrated in FIG. 26A, in certain embodiments, the conformal layer  370  is formed on the substrate  300  after the formation of the support frame  330  and reflector  340  in the operational block  230 , after the formation of the electrical conduit  350  in the operational block  240 , but before the formation of the reflector support  360  in the operational block  250 . The conformal layer  370  deposited from the second substrate surface  312  substantially covers the sidewalls  334 , reflective surface  335 , metal layers  336 , and the reflector support layer  320 . FIG. 26B schematically illustrates the conformal layer  370  after the formation of the reflector support  360  in the operational block  250 . While the reflector support layer  320  has been etched away from the first substrate surface  310 , the conformal layer  370  remains substantially intact. Since the reflector support  360  is formed subsequently to forming the conformal layer  370 , the conformal layer  370  provides protection to the reflector  40  from the etching of the reflector support layer  320 . 
     The conformal layer  370  then provides structural support for the reflector support  360  during the dicing and separating of the substrate  300  into individual chips in the operational block  264 . The conformal layer  370  is then removed from the modules  32  in an operational block  265 , resulting in the structure schematically illustrated in FIG.  19 K. In certain embodiments, the conformal layer  370  is removed by a dry plasma etch process which utilizes an oxygen plasma applied to the conformal layer  370  from the second substrate surface  312  for approximately 200 minutes, and from the first substrate surface  310  for approximately 80 minutes. 
     Various embodiments of the present invention have been described above. Although this invention has been described with reference to these specific embodiments, the descriptions are intended to be illustrative of the invention and are not intended to be limiting. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims.