Abstract:
A method of manufacturing a conformal grating device, that includes the steps of: forming a spacer layer on a substrate; removing portions of the spacer layer to define an active region with at least two channels and at least one intermediate support; forming a sacrificial layer in the active region; forming conductive reflective ribbon elements over the active region, and removing the sacrificial layer from the active region.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This is a continuation-in-part of U.S. application Ser. No. 09/491,354, filed Jan. 26, 2000, entitled Spatial Light Modulator with Conformal Grating Elements, by Kowarz. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to the fabrication of a micromechanical device for spatially and temporally modulating an incident beam of light by diffraction. More particularly, this invention discloses a method for manufacturing an electromechanical device with a conformal grating structure.  
         BACKGROUND OF THE INVENTION  
         [0003]    Electromechanical spatial light modulators with a variety of designs have been used in applications such as display, optical processing, printing, optical data storage and spectroscopy. These modulators produce spatial variations in the phase and/or amplitude of an incident light beam using arrays of individually addressable devices.  
           [0004]    One class of electromechanical spatial light modulators has devices with a periodic sequence of reflective elements that form electromechanical phase gratings. In such devices, the incident light beam is selectively reflected or diffracted into a number of discrete orders. Depending on the application, one or more of these diffracted orders may be collected and used by the optical system. Electromechanical phase gratings can be formed in metallized elastomer gels; see U.S. Pat. No. 4,626,920, issued Dec. 2, 1986 to Glenn, and U.S. Pat. No. 4,857,978, issued Aug. 15, 1989 to Goldburt et al. The electrodes below the elastomer are patterned so that the application of a voltage deforms the elastomer producing a nearly sinusoidal phase grating. These types of devices have been successfully used in color projection displays.  
           [0005]    An electromechanical phase grating with a much faster response time can be made of suspended micromechanical ribbon elements, as described in U.S. Pat. No. 5,311,360, issued May 10, 1994, to Bloom et al. This device, also known as a grating light valve (GLV), can be fabricated with CMOS-like processes on silicon. Improvements in the device were later described by Bloom et al. that included: 1) patterned raised areas beneath the ribbons to minimize contact area to obviate stiction between the ribbons and the substrate, and 2) an alternative device design in which the spacing between ribbons was decreased and alternate ribbons were actuated to produce good contrast. See U.S. Pat. No. 5,459,610, issued Oct. 17, 1995. Bloom et al. also presented a method for fabricating the device; see U.S. Pat. No. 5,677,783, issued Oct. 14, 1997. Additional improvements in the design and fabrication of the GLV were described in U.S. Pat. No. 5,841,579, issued Nov. 24, 1998 to Bloom et al., and in U.S. Pat. No. 5,661,592, issued Aug. 26, 1997 to Bornstein et al.  
           [0006]    Previously mentioned linear GLV arrays have a diffraction direction that is not perpendicular to the array direction, and thus increases the complexity of the optical system required for separating the diffracted orders. Furthermore, the active region of the array is relatively narrow, hence requiring good alignment of line illumination over the entire length of the array, typically to within 10-30 microns over a few centimeters of length. The line illumination then also needs to be very straight over the entire linear array.  
           [0007]    There is a need, therefore, for a linear array of grating devices that has a large active region with the diffraction direction perpendicular to the array direction. Furthermore, the device must be able to diffract light efficiently at high speed into discrete orders and the device fabrication must be compatible with CMOS-like processes.  
         SUMMARY OF THE INVENTION  
         [0008]    The need is met according to the present invention by providing a method of manufacturing a conformal grating device, that includes the steps of: forming a spacer layer on a substrate; removing portions of the spacer layer to define an active region with at least two channels and at least one intermediate support; forming a sacrificial layer in the active region; forming conductive reflective ribbon elements over the active region; and removing the sacrificial layer from the active region. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a perspective, partially cut-away view of a spatial light modulator with electromechanical conformal grating devices, showing two devices in a linear array;  
         [0010]    [0010]FIG. 2 is a top view of a spatial light modulator with electromechanical conformal grating devices, showing four individually operable devices in a linear array;  
         [0011]    [0011]FIGS. 3 a  and  3   b  are cross-sectional views through line  3 - 3  in FIG. 2, showing the operation of an electromechanical conformal grating device in an unactuated state and an actuated state, respectively;  
         [0012]    [0012]FIG. 4 a  and  4   b  are cross-sectional views through line  4 - 4  in FIG. 2 showing the device in an unactuated state and an actuated state, respectively;  
         [0013]    [0013]FIG. 5 is a plot showing ribbon element position as a function of applied voltage;  
         [0014]    [0014]FIG. 6 is a diagram showing the device profile in response to two different actuation voltages;  
         [0015]    [0015]FIG. 7 a  is a cross-sectional view through line  3 - 3  in FIG. 2 illustrating the layer structure prior to any patterning;  
         [0016]    [0016]FIG. 7 b  is a cross-sectional view through line  3 - 3  in FIG. 2 illustrating patterning of the active region to form channels and intermediate supports;  
         [0017]    [0017]FIG. 7 c  is a cross-sectional view through line  3 - 3  in FIG. 2 illustrating deposition of a sacrificial layer;  
         [0018]    [0018]FIG. 7 d  is a cross-sectional view through line  3 - 3  in FIG. 2 illustrating patterning of the sacrificial layer;  
         [0019]    [0019]FIG. 7 e  is a cross-sectional view through line  3 - 3  in FIG. 2 illustrating planarizing of the sacrificial layer;  
         [0020]    [0020]FIG. 7 f  is a cross-sectional view through line  3 - 3  in FIG. 2 illustrating deposition of a ribbon layer and a reflective and conductive layer;  
         [0021]    [0021]FIG. 7 g  is a cross-sectional view through line  3 - 3  in FIG. 2 illustrating removal of the sacrificial layer after patterning elongated ribbon elements;  
         [0022]    [0022]FIG. 8 is a top view of an alternate embodiment of the spatial light modulator;  
         [0023]    [0023]FIG. 9 a  is a cross sectional view of an alternative embodiment of the conformal grating device in an unactuated state; and  
         [0024]    [0024]FIG. 9 b  is a cross sectional view of an alternative embodiment of the conformal grating device in an actuated state.  
         [0025]    [0025]FIG. 10 a - 10   f  illustrate the fabrication steps used to make an alternative embodiment of the conformal grating device. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    The conformal grating devices of the preferred embodiment of the present invention are illustrated in FIGS.  1 - 4 . FIG. 1 shows the structure of two side-by-side conformal grating devices  5   a  and  5   b  in an unactuated state. In this embodiment, the devices can be operated by the application of an electrostatic force. A substrate  10  made of glass, metal, plastic or semiconductor materials, is covered by a bottom conductive layer  12 . The grating devices  5   a  and  5   b  are formed on top of the bottom conductive layer  12  and the substrate  10 . The bottom conductive layer  12  acts as an electrode to actuate the devices. The bottom conductive layer  12  can be made of materials such as aluminum, titanium, gold, silver, tungsten, doped silicon or indium tin oxide. A dielectric protective layer  14  covers the bottom conductive layer  12 . Above the protective layer  14  a standoff layer  16  is formed which is followed by a spacer layer  18 . On top of the spacer layer  18 , a ribbon layer  20  is formed which is covered by a reflective layer  22 . In the present embodiment, the reflective layer  22  is also a conductor in order to provide electrodes for the actuation of the conformal grating devices  5   a  and  5   b . The reflective and conductive layer  22  is patterned to provide electrodes to the two conformal grating devices  5   a  and  5   b . The ribbon layer  20  preferably comprises a material with a sufficient tensile stress to provide a large restoring force. Examples of ribbon materials are silicon nitride, titanium aluminide, and titanium oxide. The thickness and tensile stress of the ribbon layer  20  are chosen to optimize performance by influencing the electrostatic force for actuation and the restoring force. These forces affect the voltage requirement, speed and resonance frequency of the conformal grating devices  5   a  and  5   b.    
         [0027]    Each of the two devices  5   a  and  5   b  has an associated elongated ribbon element  23   a  and  23   b , respectively, patterned from the reflective and conductive layer  22  and the ribbon layer  20 , and herein referred to as conductive reflective ribbon elements. The elongated-conductive reflective ribbon elements  23   a  and  23   b  are supported by end supports  24   a  and  24   b  formed from the spacer layer  18  and by one or more intermediate supports  27 . In FIG. 1, three intermediate supports  27  are shown formed from the spacer layer  18 . These intermediate supports  27  are uniformly separated in order to form four equal-width channels  25 . The conductive reflective ribbon elements  23   a  and  23   b  are secured to the end supports and to the intermediate supports  27 . The end supports  24   a  and  24   b  are not defined other than at their edges facing the channel  25 . A plurality of square standoffs  29  is patterned at the bottom of the channels  25  from the standoff layer  16 . These standoffs  29  reduce the possibility of the ribbon elements sticking when actuated. The standoffs may also be patterned in shapes other than square for example rectangular or round.  
         [0028]    A top view of a four-device linear array of conformal grating devices  5   a ,  5   b ,  5   c  and  5   d  is shown in FIG. 2. The conductive reflective ribbon elements are depicted partially removed over the portion of the diagram below the line  2 - 2  in order to show the underlying structure. For best optical performance and maximum contrast, the intermediate supports  27  must be completely hidden below the conductive reflective ribbon elements  23   a ,  23   b ,  23   c  and  23   d.  Therefore, when viewed from the top, the intermediate supports must not be visible in the gaps  28  between the conformal grating devices  5   a - 5   d . Here each of the conformal grating devices has three intermediate supports  27  with four equal-width channels  25 . The active region  8  is the portion of the device where the electromechanical actuation takes place and contains the channels  25 , the intermediate supports  27  and the end supports  24   a  and  24   b.  The active region  8  is completely covered by the ribbon layer  20  in the form of the elongated-conductive reflective ribbon elements  23   a ,  23   b ,  23   c,  and  23   d.    
         [0029]    The center-to-center separation A of the intermediate supports  27  defines the period of the conformal grating devices in the actuated state. The conductive reflective ribbon elements  23   a - 23   d  are mechanically and electrically isolated from one another, allowing independent operation of the four conformal grating devices  5   a - 5   d.  The bottom conductive layer  12  of FIG. 1 can be common to all of the devices.  
         [0030]    [0030]FIG. 3 a  is a side view, through line  3 - 3  of FIG. 2, of two channels  25  of the conformal grating device  5   b  in the unactuated state. FIG. 3 b  shows the same view of the actuated state. For operation of the device, an attractive electrostatic force is produced by applying a voltage difference between the bottom conductive layer  12  and the conducting layer  22  of the conductive reflective ribbon element  23   b . In the unactuated state (see FIG. 3 a ), with no voltage difference, the ribbon element  23   b  is suspended flat between the supports. In this state, an incident light beam  30  is primarily reflected  32  into the mirror direction. To obtain the actuated state, a voltage is applied to the conformal grating device  5   b , which deforms the conductive reflective ribbon element  23   b  and produces a partially conformal grating with period Λ. FIGS. 3 b  shows the device in the fully actuated state with the conductive reflective ribbon element  23   b  in contact with the standoffs  29 . The height difference between the bottom of element  23   b  and the top of the standoffs  29  is chosen to be approximately ¼ of the wavelength λ of the incident light. The optimum height depends on the specific shape of the actuated device. In the actuated state, the incident light beam  30  is primarily diffracted into the +1st order  35   a  and −1st order  35   b,  with additional light diffracted into the +2nd order  36   a  and −2nd order  36   b.  A small amount of light is diffracted into even higher orders and some is reflected. For light incident perpendicular to the surface of the device, the angle θm between the incident beam and the mth order diffracted beam is given by  
         sin θ m=mλΛ,   
         [0031]    where m is an integer. One or more of the diffracted orders can be collected and used by the optical system, depending on the application. When the applied voltage is removed, the forces due to the tensile stress and bending restores the ribbon element  23   b  to its original unactuated state.  
         [0032]    [0032]FIGS. 4 a  and  4   b  show a rotated side view through line  4 - 4  of FIG. 2 of the conformal grating device  5   b  in the unactuated and actuated states, respectively. The conductive reflective ribbon element  23   b  is suspended by the end support  24   b  and the adjacent intermediate support  27  (not shown in this perspective). The application of a voltage actuates the device as illustrated in FIG. 4 b.    
         [0033]    To understand the electromechanical and optical operation of the conformal grating device in more detail, it is helpful to examine the expected performance of a realistic design with the following materials and parameters:  
         [0034]    Substrate material: silicon  
         [0035]    Bottom conductive layer: doped silicon  
         [0036]    Protective layer: silicon dioxide, thickness=50 nm  
         [0037]    Spacer layer: silicon dioxide, thickness=150 nm  
         [0038]    Ribbon layer: silicon nitride, thickness=100 nm, tensile stress=600 Mpa  
         [0039]    Reflective and conductive layer: aluminum, thickness=50 nm  
         [0040]    Grating period Λ=20 μm  
         [0041]    Suspended length of conductive reflective ribbon element=16 μm  
         [0042]    Width of conductive reflective ribbon element w=30 μm  
         [0043]    Width of intermediate supports=4 μm  
         [0044]    This type of design allows for fabrication with CMOS methods and integration with CMOS circuitry. The resonant frequency of the ribbon elements in this particular design is approximately 11 MHz. Most practical designs have resonant frequencies between 2 MHz and 15 MHz. Because of this high resonance, the switching time of the device can be very short.  
         [0045]    [0045]FIGS. 5 and 6 show the modeled electromechanical operation of this particular device. FIG. 5 is a plot of the position of the conductive reflective ribbon element at the center of a channel as a function of applied voltage, illustrating the associated hysteresis. As the voltage is increased from 0 V, the center displacement increases in approximately a quadratic manner until the pull-down voltage of 20.1 V is reached. At this voltage, the electrostatic force overcomes the tensile restoring force and the ribbon slams into the substrate. Further increasing the applied voltage changes the shape of the deformed ribbon, but cannot change the center position. With the ribbon in contact with the substrate, the voltage can be reduced below the pull-down value while maintaining contact, until release at 10.8 V. This hysteresis can be exploited to improve the optical performance of the device. It can also be used as a switch in certain applications.  
         [0046]    [0046]FIG. 6 demonstrates how the grating profile may be modified by adjusting the applied voltage. The profile of two periods of the actuated device is shown at 12 V (dotted line) and at 22 V (solid line), with the ribbon and substrate in contact. To obtain this 12 V profile, contact must first be established by applying a value larger than the pull-down voltage of 20.1 V. Because 12 V is only slightly larger that the release voltage, only a small portion of the ribbon touches the substrate. This change in shape with voltage has an important impact on the diffraction efficiency of the device.  
         [0047]    The fabrication sequence for making a conformal grating device is illustrated in FIGS. 7 a - 7   g.  Referring now to FIG. 7 a,  which is a cross-sectional view along line  3 - 3  indicated in FIG. 2 to illustrate the layer built-up of one embodiment of the invention with standoffs  29  formed at the bottom of the channels  25 . The device is built upon a substrate  10 , covered by the bottom conductive layer  12 , and a dielectric protective layer  14  on top of the bottom conductive layer  12 . As mentioned above, the substrate  10  can be glass, plastic, metal or a semiconductor material. In a preferred embodiment the substrate  10  is silicon and the dielectric protective layer  14  is a thermal oxide. An epitaxial layer, doping by diffusion, or ion implantation can form the bottom conductive layer  12 . To form the standoffs  29  and channels  25 , a standoff layer  16  is deposited followed by a spacer layer  18 . The spacer layer  18  is selected from the group consisting of silicon oxide, silicon nitride polysilicon and polyimide. In a preferred embodiment the standoff layer  16  is silicon nitride deposited by chemical vapor deposition. The top surface of the standoff layer  16  will be used to define an actuation height resulting from operation. In a preferred embodiment the spacer layer  18  is silicon oxide deposited by chemical vapor deposition. The total height of the actuation of the elongated-conductive reflective ribbon elements  23   a - 23   d  is defined by the thickness of the spacer layer  18 .  
         [0048]    Referring now to FIG. 7 b , which is a cross-sectional view along line  3 - 3  indicated in FIG. 2 to illustrate etching of the channels  25  to form the intermediate supports  27 . The patterning of the spacer layer  18  is carried out using standard photolithographic processing and etching methods to define the active region  8  where the channels  25  and intermediate supports  27  are located. The etching of the oxide spacer layer uses chemistry designed to stop on the silicon nitride standoff layer  16 . The standoff layer  16  is then patterned using photolithographic processing and etching methods to produce the standoffs  29 , as illustrated in FIG. 7 b . The standoffs  29  act as mechanical stops for the actuation of the conformal grating device. The actuated elongated-conductive reflective ribbon elements  23   a - 23   d  come into contact with the surface standoffs  29 .  
         [0049]    Referring now to FIG. 7 c , which is a cross-sectional view along line  3 - 3  indicated in FIG. 2 to illustrate the deposition of a sacrificial layer  19 . To allow additional layers atop the existing structure, as shown in FIG. 7 c , a conformal sacrificial layer  19  is deposited to a thickness greater than the sum of the thickness of the standoff layer  16  and the spacer layer  18 . The material for the sacrificial layer  19  is different from the spacer layer  18  and is selected from the group consisting of silicon oxide, silicon nitride, polysilicon, doped-polysilicon, silicon-germanium alloys and polyimide. In a preferred embodiment the sacrificial layer  19  is polysilicon deposited by chemical vapor deposition.  
         [0050]    Referring now to FIG. 7 d , which is a cross-sectional view along line  3 - 3  indicated in FIG. 2 to illustrate the patterning of the sacrificial layer  19 . The patterning of the sacrificial layer  19  is carried out using standard photolithographic processing and a mask which is the reverse of the mask used to etch the spacer layer  18  defining the active region  8  where the channels  25  and intermediate supports  27  are located. The mask can be biased to account for misalignment. The sacrificial layer  19  is then completely removed from the intermediate supports  27  and the areas outside of the active region  8 . The removal of the sacrificial layer  19  outside of the active region  8  improves the uniformity of the planarization step described below. The removal of the sacrificial layer  19  may be done prior to providing the ribbon layer  20 . This removal process ensures good mechanical attachment of the elongated-conductive reflective ribbon elements  23   a - 23   d  to the intermediate supports  27  and the end supports  24   a  and  25   b  (not shown in FIG. 7 d ).  
         [0051]    Referring now to FIG. 7 e,  which is a cross-sectional view along line  3 - 3  indicated in FIG. 2, to illustrate the planarization of the sacrificial layer  19  to a level substantially near the top surface of the intermediate supports  27 . Chemical mechanical polishing methods are used to achieve the polished structure. The polished surface of sacrificial layer  19  filling the channels  25  is preferably polished to be optically coplanar with the top surface of the intermediate supports  27 . As is well known in the practice of optical engineering, this requires a surface planarity of less than about 200 Angstrom units at visible wavelengths.  
         [0052]    Referring now to FIG. 7 f,  which is a cross-sectional view along line  3 - 3  indicated in FIG. 2 to illustrate deposition of the ribbon layer  20  and of the reflective and conductive layer  22 . The ribbon layer  20  is provided on top of the optically-coplanar sacrificial layer  19  and intermediate supports  27 , thereby also covering the entire active region  8  of the device. Silicon nitride is a well-suited material for the ribbon layer  20  and can be patterned to provide the needed mechanical structure. Its material properties are well suited for the application because of the intrinsic tensile stress easily controlled by the deposition process. In a preferred alternative embodiment titanium aluminide is used as the ribbon layer  20  material. Its material properties are well suited for the application because its intrinsic tensile stress is easily controlled by sputter deposition and annealing. Titanium aluminide is also electrically conducting. The reflective and conductive layer  22  deposited atop the ribbon layer  20  needs to have good electric conducting properties. The light reflecting properties of the reflective and conductive layer  22  improve the efficiency of diffraction so as to maximize the diffracted light and minimize loss of light by absorption. The material for the reflective and conductive layer  22  is selected from the group consisting of aluminum, titanium, gold, silver, tungsten, silicon alloys and indium tin oxide.  
         [0053]    Electrical contact to the bottom conductive layer can be made from the back side through the substrate  10  if the substrate is electrically conductive. Alternatively electrical contact can be made on the front side by photolithographically patterning areas outside the active region (not shown) and etching through the spacer layer  18 , standoff layer  16  and dielectric protective layer  14 .  
         [0054]    The elongated-conductive reflective ribbon elements  23   a - 23   d  are now patterned from the ribbon layer  20  and the reflective and conductive layer  22  using photolithographic processing and etching. This etching process defines the top-view geometry of the elongated-conductive reflective ribbon elements  23   a - 23   d  shown in FIGS. 1 and 2.  
         [0055]    Referring now to FIG. 7 g , which is a cross-sectional view along line  3 - 3  indicated in FIG. 2 to illustrate the removal of the sacrificial layer  19  from within the active region  8  to form channels  25  and intermediate supports  27 . In a preferred embodiment the sacrificial layer  19  is polysilicon which can be selectively removed by dry etching methods using xenon difluoride to yield the cross-sectional view illustrated in FIG. 7 g.  The gas has access to the sacrificial layer  19  through the gaps  32  between the elongated-conductive reflective ribbon elements  23   a - 23   d . The removal of the sacrificial layer  19  is the final step needed to produce operational conformal grating devices  5   a - 5   d.  The devices can now be actuated to operate as described earlier. After removal of the sacrificial layer  19 , the elongated-conductive reflective ribbon elements  23   a - 23   d  remain optically coplanar providing the ribbon layer  20  is deposited with uniform thickness and uniform tensile stress.  
         [0056]    An alternate embodiment of conformal grating devices is shown in FIG. 8, which depicts a top view of a four-device linear array similar to FIG. 2. Each of the conformal grating devices  5   a ,  5   b ,  5   c  and  5   d  now has an associated pair of subdivided elongated-conductive reflective ribbon elements ( 51   a ,  52   a ), ( 51   b ,  52   b ), ( 51   c ,  52   c ) and ( 51   d ,  52   d ), respectively. This subdivision of each device permits fabrication of wider devices without significantly impacting optical performance. The preferred method of fabrication is to etch a sacrificial layer from the channel, thus releasing the ribbon elements. The subdivided gaps  55  between the elements allow the etchant to access this sacrificial layer. Increasing the number of subdivided gaps  55  can therefore improve the etching process. In practice, it may be necessary to further subdivide the conformal grating devices into more than two. The conductive reflective ribbon elements are depicted partially removed over the portion of the diagram below the line  2 - 2  in order to show the underlying structure. For best optical performance and maximum contrast, the intermediate supports  27  must be completely hidden below the conductive reflective ribbon elements  51   a ,  52   a ,  51   b ,  52   b ,  51   c ,  52   c ,  51   d  and  52   d . Therefore, when viewed from the top, the intermediate supports  27  must not penetrate into the subdivided gaps  55 . The ribbon elements within a single conformal grating device are mechanically isolated, but electrically coupled. They therefore operate in unison when a voltage is applied.  
         [0057]    The conformal grating devices described in the above embodiments have intermediate supports attached to the conductive reflective ribbon elements. To obtain very high contrast, these supports must be completely hidden when the devices are not actuated and the ribbon elements must be completely flat. However, in practice, the fabrication causes some nonuniformity in the profile of the ribbon element just above the intermediate supports. The nonuniformity produces a weak grating reducing the contrast of the device. FIGS. 9 a  and  9   b  show an alternate embodiment that reduces this problem. The side view is the same as in FIG. 3 a  and  3   b . FIG. 9 a  depicts the two channels  25  between the three intermediate supports  27  of the device in the unactuated state. FIG. 9 b  shows the same view of the actuated state. In the unactuated state, with no voltage applied to the device, the ribbon element  23   b  is suspended flat above the intermediate supports  27  by the two end supports  24   a  and  24   b  (see FIG. 2), leaving a small intermediate support gap  60  between the top of the intermediate supports  27  and the bottom of the ribbon element  23   b.  When a voltage is applied to actuate the device, the bottom of the ribbon element  23   b  makes contact with the top of the intermediate supports and a partially conforming grating is created. FIG. 9 b  shows the device in the fully actuated state with the conductive reflective ribbon element  23   b  also touching the standoffs  29 .  
         [0058]    [0058]FIGS. 10 a - 10   f  illustrate the fabrication sequence for making the conformal grating device with elongated-conductive reflective ribbon elements suspended above intermediate supports. These figures show the same view of the device as FIGS. 9 a  and  9   b . The first few steps are the same as the process of FIGS. 7 a  and  7   b . Referring to FIG. 10 a , the device is built upon a substrate  10 , covered by the bottom conductive layer  12 , and a dielectric protective layer  14  on top of the bottom conductive layer  12 . To form the standoffs  29  and channels  25 , a standoff layer  16  is deposited followed by a spacer layer  18 .  
         [0059]    [0059]FIG. 10 b  illustrates etching of the channels  25  to form the intermediate supports  27 . The patterning of the spacer layer  18  is carried out using standard photolithographic processing and etching methods to define the active region  8  where the channels  25  and intermediate supports  27  are located. The standoff layer  16  is then patterned using photolithographic processing and etching methods to produce the standoffs  29 , as illustrated in FIG. 10 b.    
         [0060]    In order to generate an intermediate support gap  60  with a desired height, the end supports  24   a  and  24   b  can be fabricated to be higher than the intermediate supports  27  (not shown in FIG. 10 b ). This step can be performed by depositing and patterning a support layer made, for example, of silicon nitride to increase the height of the end supports  24   a  and  24   b  relative to the intermediate supports.  
         [0061]    [0061]FIG. 10 c  illustrates deposition of a conformal sacrificial layer  19  on top of the structure from FIG. 10 b.  In order to ensure that the planarization step (FIG. 10 d ) leaves some sacrificial layer on top of the intermediate supports  27 , the thickness of the sacrificial layer must be substantially greater that the sum of the thickness of the standoff layer  16  and the thickness of the spacer layer  18 .  
         [0062]    [0062]FIG. 10 d  illustrates planarization of the sacrificial layer  19  to a level above the top surface of the intermediate supports  27 . The sacrificial layer  19  needs to be substantially flat after planarization with some sacrificial material left above the intermediate supports  27  to prevent attachment of the elongated-conductive reflective ribbon element  23   b  to the intermediate supports  27 . Furthermore, in practice to improve the uniformity of planarization and ensure good attachment of the elongated-conductive reflective ribbon element  23   b  to the end supports  24   a  and  24   b,  it is preferable to pattern and remove the sacrificial layer  19  outside of the active region  8  (not shown in FIG. 10 d ).  
         [0063]    [0063]FIG. 10 e  illustrates deposition of the ribbon layer  20  and of the reflective and conductive layer  22 . The ribbon layer  20  does not make contact with the top surface of the intermediate supports  27  because of the sacrificial material present in the intermediate support gap  60 . The elongated-conductive reflective ribbon elements  23   a - 23   d  are now patterned from the ribbon layer  20  and the reflective and conductive layer  22  using photolithographic processing and etching. This etching process defines the top-view geometry of the elongated-conductive reflective ribbon elements  23   a - 23   d  shown in FIG. 2.  
         [0064]    [0064]FIG. 10 f  illustrates removal of the sacrificial layer  19  from within the active region  8  to reveal channels  25  and intermediate supports  27 . This step also removes the sacrificial layer  19  from the intermediate support gap  60 , thereby suspending the elongated-conductive reflective ribbon element  27  above the top surface of the intermediate supports  27 . The elongated-conductive reflective ribbon element  23   b  is held in tension above the intermediate supports  27  by the two end supports  24   a  and  24   b  (not shown in FIG. 10 f ). The removal of the sacrificial layer  19  is the final step needed to produce operational devices.  
         [0065]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.  
       PARTS LIST  
       [0066]    [0066] 5   a  conformal grating device  
         [0067]    [0067] 5   b  conformal grating device  
         [0068]    [0068] 5   c  conformal grating device  
         [0069]    [0069] 5   d  conformal grating device  
         [0070]    [0070] 8  active region  
         [0071]    [0071] 10  substrate  
         [0072]    [0072] 12  bottom conductive layer  
         [0073]    [0073] 14  protective layer  
         [0074]    [0074] 16  standoff layer  
         [0075]    [0075] 18  spacer layer  
         [0076]    [0076] 19  sacrificial layer  
         [0077]    [0077] 20  ribbon layer  
         [0078]    [0078] 22  reflective and conductive layer  
         [0079]    [0079] 23   a  elongated-conductive reflective ribbon element  
         [0080]    [0080] 23   b  elongated-conductive reflective ribbon element  
         [0081]    [0081] 23   c  elongated-conductive reflective ribbon element  
         [0082]    [0082] 23   d  elongated-conductive reflective ribbon element  
         [0083]    [0083] 24   a  end support  
         [0084]    [0084] 24   b  end support  
         [0085]    [0085] 25  channel  
         [0086]    [0086] 27  intermediate support  
         [0087]    [0087] 28  gap  
         [0088]    [0088] 29  standoff  
         [0089]    [0089] 30  incident light beam  
         [0090]    [0090] 32  reflected light beam  
         [0091]    [0091] 35   a + 1 st  order beam  
         [0092]    [0092] 35   b − 1 st  order beam  
         [0093]    [0093] 36   a + 2 nd  order beam  
         [0094]    [0094] 36   b − 2 nd  order beam  
         [0095]    [0095] 51   a  subdivided elongated-conductive reflective ribbon element  
         [0096]    [0096] 51   b  elongated-conductive reflective ribbon element  
         [0097]    [0097] 51   c  subdivided elongated-conductive reflective ribbon element  
         [0098]    [0098] 51   d  subdivided elongated-conductive reflective ribbon element  
         [0099]    [0099] 52   a  subdivided elongated-conductive reflective ribbon element  
         [0100]    [0100] 52   b  subdivided elongated-conductive reflective ribbon element  
         [0101]    [0101] 52   c  subdivided elongated-conductive reflective ribbon element  
         [0102]    [0102] 52   d  subdivided elongated-conductive reflective ribbon element  
         [0103]    [0103] 55  subdivided gap  
         [0104]    [0104] 60  intermediate support gap