Abstract:
A method for producing co-planar surface areas is disclosed. At first a first layer with at least one recess is provided. Onto the first layer a second layer is deposited over the entire area of the first layer wherein the second layer has a thickness greater than the depth of the recess. The second layer is composed of material different to the material of the first layer. The next step removes the second layer completely beyond the area of at least one recess. The remaining portion of the second layer is removed until the second layer is coplanar with the first layer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to U.S. Ser. No. 09/216,374 filed concurrently, entitled An Electro-Mechanical Grating Device; and to U.S. Ser. No. 09/216,202, filed concurrently, entitled Process For Manufacturing An Electro-Mechanical Grating Device; and to U.S. Ser. No. 09/216,375, filed concurrently, entitled A Multilevel Electro-Mechanical Grating Device. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a method for producing co-planar surface structures. More particular, the invention relates to a method for producing co-planar surface structures which are used as a basis for the formation of additional structural elements having flat surfaces over a wide range. 
     BACKGROUND OF THE INVENTION 
     Advances in micromachining technology have given rise to a variety of Micro-electromechanical systems (MEMS) including light modulators for low cost display applications. Such modulators provide high-resolution, high operating speeds (kHz frame rates), multiple gray scale levels, color adaptability, high contrast ratio, and compatibility with VLSI technology. One such modulator has been disclosed in U.S. Pat. No. 5,311,360, issued May 10, 1994 to Bloom et al., entitled “Method and Apparatus for Modulating a Light Beam”. This modulator is a micromachined reflective phase grating. It consists of a plurality of equally spaced deformable elements in the form of beams suspended at both ends above a substrate thereby forming a grating. The deformable elements have a metallic layer that serves both as an electrode, and as reflective surface for incident light. The substrate is also reflective and contains a separate electrode. The disclosure in U.S. Pat. No. 5,311,360 is silent about the efficiency decrease of the device if not all the beams of the device do not have a completely flat surface and the same cross section. 
     As disclosed in U.S. Ser. No. 90/216,202, entitled “Process for Manufacturing an Electro-Mechanical Grating Device,” chemical mechanical planarization can be used to advantageously accomplish the requirements of such a device namely; all the beams to have an optically flat surface, the same cross-section and a well defined beam to substrate distance, elimination of surface topography resulting in higher photo and dry etch yields as well as removing step coverage concerns. 
     Chemical mechanical polishing (CMP) has become a key technology as currently practiced in the semiconductor art for the planarization of metals and dielectrics and as taught in numerous U.S. patents such as that by Chow et al., U.S. Pat. No. 4,789,648, Carr et al., U.S. Pat. No. 4,954,142, and Beyer et al., U.S. Pat. No. 4,944,836. CMP provides full wafer planarization without additional masking or coating steps. 
     The use of CMP is also disclosed in U.S. Pat. No. 5,804,084, issued Sep. 8, 1998 to Nasby et al., entitled “Use of Chemical Mechanical Polishing In Micromachining”. The process suggested therein is for removing topography effects during fabrication of micromachines. A sacrificial oxide layer is deposited over a level containing functional elements (driving gear, liquid pump, etc.) with etched valleys between the elements such that the sacrificial layer has sufficient thickness to fill the valleys and extend thickness upwards to an extent that the lowest point on the upper surface of the oxide layer is at least as high as the top surface of the functional elements in the covered level. The sacrificial oxide layer is then polished down and planarized by CMP. Another level of functional elements is formed upon the new planarized surface. The teaching of his document does not provide a technique or a method how to get coplanar surfaces with the a CMP method. U.S. Pat. No. 5,804,084 shows only a method which can bring a plurality of islands existing in one layer to a single level. There is no need to consider a dishing effect which happens during the production of two coplanar surfaces. 
     However many of the micromachined structures typically fall into the regime of wide (&gt;10 μm wide) recesses and sparsely populated structures. One of the difficulties encountered with CMP planarization is the “dishing” effect, which occurs in the planarization of wide recesses (i.e., usually &gt;10 μm wide). The “dishing” effect during planarization results in thinning of the overfill layer in wide recesses resulting in a non-planar surface. The polish rate is affected by the topology of the surrounding areas with dishing becoming worse in sparsely populated regions. Dishing problems therefore present a severe manufacturing constraint in micromachining. 
     The dishing phenomenon is illustrated by reference to the schematic cross-sectional diagrams of FIG. 1 a  and FIG. 1 b . Shown in FIG. 1 a  is a substrate  10  onto which a first layer  15  is deposited. A narrow recess  11  and the wide recess  12  are shown formed in the first layer  15 . The surface of the first layer will contain small areas  13  between recesses and large areas  14  between recesses. Deposited over the first layer  15  and into both the narrow recess  11  and the wide recess  12  is a blanket conformal fill layer  20 . Shown in FIG. 1 b  is the results of planarizing through a conventional CMP planarization method the blanket conformal fill layer  20  as illustrated in FIG. 1 a . As shown in FIG. 1 b , the surface of the planarized filled recess  22  is substantially dished in comparison with the surface of planarized filled recess  21 . There is also shown in FIG. 1 b  the presence of a fill residue layer  24  formed simultaneously over the small areas  13  and large areas  14  on the surface of the first layer  15  when the blanket conformal fill layer  20  is planarized through the CMP planarization method to form the planarized filled recesses  21  and  22 . As is understood by a person skilled in the art, when planarizing large areas of the blanket conformal fill layer  20 , generally of dimensions greater than about 1000 microns, the blanket conformal fill layer  20  will in addition to planarizing more rapidly over the wide recess  12  and forming a dish within the planarized filled recess  22  simultaneously also polish more slowly over the large area  14  on the surface of the first layer  15  and leave the fill residue layer  24  formed over the large area  14  on the first layer  15 . Attempts to remove the fill residue layer  24  by further planarization will cause increased dishing of the planarized filled recesses  21  and  22 . Fill residue layers such as the fill residue layer  24  are undesirable since they impede further device processing on the planarized surface. 
     A method to limit dishing is used in U.S. Pat. No. 5,721,172, issued Feb. 24, 1998, to Jang et al., entitled, “Self-Aligned Polish Stop Layer Hard Masking Method For Forming Planarized Aperture Fill Layers”. A conformal polish stop layer is formed on top of the conformal fill layer. The conformal polish stop layer and the conformal aperture fill layer are then planarized through a first CMP planarization method until there is reached the lower planar region of the conformal polish stop layer, while simultaneously forming a patterned polish stop layer and a partially CMP planarized aperture fill layer. The patterned polish stop layer is then employed as a etch mask to form an etched partially CMP planarized aperture fill layer with a protrusion over the aperture, where the height of the protrusion compensates for a dish which would otherwise form when the etched partially CMP planarized aperture fill layer is planarized through a second CMP method to form a planarized aperture fill layer within the aperture. The teaching of this document requires a complicated process involving the deposition of an extra layer and two separate CMP planarization steps. The method of CMP in this teaching also requires relatively low selectivity between the fill layer and the polish etch stop layer. Therefore the polish etch stop layer final thickness is not well controlled. 
     An Article by B. H. Roh et al. entitled “Easily Manufacturable Shallow Trench Isolation for Gigabit Dynamic Random Access Memory”, Jpn. J. Appl. Phys. Pt. 1,Vol.35 (1996), pp.1618-4623 describes a method to limit the dishing phenomenon in shallow trench isolation techniques. The oxide isolation layer is partially etched on a semiconductor active region prior to performing a planarization step. The result of this method is a planarized oxide surface. There is no need to create coplanar surfaces between a first layer and a second layer. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a coplanar surface between at least two different materials by minimizing the dishing effect while ensuring complete removal of the fill material outside of the critical areas. Furthermore, the coplanarity of the surface is necessary in order to allow the formation of additional structures which require the flatness of the surface on which they are grown or built. 
     The object is achieved by a method comprising the steps of: 
     a) providing a first layer with at least one recess wherein said recess has a depth defined by the thickness of the first layer; 
     b) depositing a second layer over the entire area of the first layer wherein the second layer has a thickness greater than the depth of the recess and is composed of a differing material to the first layer; 
     c) removing the second layer completely beyond the area of at least one recess; and 
     d) removing the remaining portion of the second layer until the second layer is coplanar with the first layer. 
     The object is also achieved by a method comprising the steps of: 
     a) providing a first layer with at least one recess wherein said recess has a depth defined by the thickness of the first layer; 
     b) depositing a second layer over the entire area of the first layer wherein the second layer has a thickness greater than the depth of the recess, thereby providing a conformed recess in the second layer defining a ground level, said second layer is composed of a differing material to the first layer; 
     c) removing partially the second layer beyond the area of at least one recess until a surface level defined by the partially removed second layer matches the ground level; and 
     d) removing the remaining portion of the second layer until the second layer is coplanar with the first layer. 
     An advantage of the inventive method is that the fill material outside the critical area is completely removed to ensure no residual fill material on that surface. The height differential between the pattern area and adjacent regions remains but the high points are a very small fraction of the total surface area being polished. The mechanical effect of the polish will be a more rapid removal of material from these non-critical areas. The total area affected by CMP is more uniform and the result in the pattern area is a more planar surface. The extent of coverage outside the pattern area may vary but need not extend much more than the alignment tolerance of the exposure unit used to pattern the fill layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The subject matter of the invention is described with reference to the embodiments shown in the drawing. 
     FIG. 1 a - 1   b  show the dishing phenomenon reference to the schematic cross-sectional views of multilayered structures; 
     FIG. 2 is a partial perspective description of the method for producing coplanar surfaces, wherein a first fill material is applied to the first layer; 
     FIG. 3 a  is a partial perspective description of the method for producing coplanar surfaces, wherein the fill material is partially etched; 
     FIG. 3 b  is a partial perspective description of another embodiment of the method for producing coplanar surfaces, wherein the fill material is partially etched but not removed completely from the area beyond the recess; 
     FIG. 4 is a partial perspective description showing the finished coplanar surfaces; 
     FIG. 5 is a partial perspective description of the method for producing coplanar surfaces, wherein a second fill material is applied to the first layer; 
     FIG. 6 is a partial perspective description of the method for producing coplanar surfaces, wherein the second fill material is partially etched; 
     FIG. 7 is a partial perspective description showing the finished coplanar surfaces; 
     FIG. 8 shows a profilometer trace after the etching of the second layer as disclosed in FIG. 3 a;    
     FIG. 9 shows a profilometer trace after the CPM process of the second layer as disclosed in FIG. 3 a;    
     FIG. 10 shows a profilometer trace after the CPM process without the patterning as disclosed in FIG. 3 a;    
     FIG. 11 perspective, partially cut-away view of the mechanical grating device which incorporates the invention of producing coplanar surfaces; 
     FIG. 12 is a cross-sectional view along a plane determined by the lines A—A and B—B as indicated in FIG. 11 to illustrate the layer built-up of one embodiment of the invention utilizing coplanar surfaces; 
     FIG. 13 is a cross-sectional view along a plane determined by the lines A—A and B—B as indicated in FIG. 11 to illustrate the plane A—A indicated in FIG. 3 to illustrate etching of a channel; 
     FIG. 14 is a cross-sectional view along a plane determined by the lines A—A and B—B as indicated in FIG. 11 to illustrate the deposition of a sacrificial layer; 
     FIG. 15 is a cross-sectional view along a plane determined by the lines A—A and B—B as indicated in FIG. 11 to illustrate the patterning of the sacrificial layer exceeding area of the channel; and 
     FIG. 16 is a cross-sectional view along a plane determined by the lines A—A and B—B as indicated in FIG. 11 to illustrate the coplanar surface according to the inventive method. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 2 through 7 which are perspective descriptions of the inventive method for producing at least one coplanar surface. The following description is limited to a device which has a limited number of recesses. It is clear for any skilled person that the inventive method is not limited to the embodiments disclosed in the specification. According to FIG. 2, a first layer  26  is provided on a substrate  28  which has a first and a second recess  30  and  32  formed therein. The recesses  30  and  32  have a width W and a height H which is determined by the thickness of the first layer  26 . The first and second recess  30  and  32  have a length which extends along the longitudinal axis of the substrate  28 . The longitudinal direction of the substrate  28  is marked by an arrow L—L. On top of the first layer  26  a second layer  34  conformed to the first layer  26  is provided. The thickness of the second layer  34  is at least of the height H of the first or second recess  30  or  32 . The applied second layer  34  defines a conformed recess  35  at the same location as the first and second recesses  30  and  32  in the first layer  26 . Each conformed recess  35  in the second layer  34  defines a ground level  35   a . The material used for the second layer  34  has to be different from the material of the first layer. FIG. 3 a  shows a first embodiment of the present invention. The second layer  34  is removed completely except for an area beyond at least one recess  30  or  32  (here recess  30 ). The selective removal of the second layer  34  is carried out by an appropriate patterning process which is, for example, followed by an etching step. The removal of the second layer  34  exposes a top surface  36  of the first layer  26 . How much material of a second remaining layer  34   a  extends beyond the recess  30  has to be adjusted to the setup parameters (pressure, slurry used, speed, etc.) of a CMP device (not shown). The width of the remaining second layer  34   a  has to have at least the width W of the recess  30 . As mentioned above the device (as shown in FIG. 3 a ) is then subjected to a removing process of the remaining second layer  34   a . The removing process used here is CMP. The removing process (see FIG. 4) lasts until only the first recess is filled with the material of the remaining second layer  34   a . The second remaining layer  34   a , filling the first recess  30 , defines a surface  36   a  which is coplanar with the surface  36  of the first layer  26 . In a second embodiment, a shown in FIG. 3 b , the second layer  34  is not removed completely from the area beyond at least one recess  30  or  32 . The second layer  34  is removed form the area beyond recess  30  to such an extent that still material of the second layer  34  covers the first layer  26 . The selective removal of the second layer  34  is carried out by an appropriate patterning process, which is, for example, followed by an etching step thereby defining a surface level  37   a . The removal of the second layer  34  is stopped when the surface level  37   a  is coplanar with ground level  35   a  of the recess  35  of the remaining second layer  34   a  after partial removal of the second layer  34 . As mentioned already with the first embodiment (FIG. 3 a ), the material used for the second layer  34  has to be different from the material of the first layer  26 . The pattern, as shown in FIG. 3 b , is then subjected to the CMP. The removing process lasts until only the first and the second recess  30  and  32  are filled with the material of the remaining second layer  34 . The following description of the process is limited to the first embodiment (see FIG. 3 b ). 
     Referring now to FIG. 5 an additional second layer  38  is applied on top of the first layer  24 , thereby covering the surface  36  of the first layer  24  and the surface  16   a  of the remaining second layer  34   a  in the first recess  30 . As mentioned above, the thickness of the additional second layer  38  is at least of the height H of the second recess  32 . The material used for the additional second layer  38  has to be different from the material of the first layer  26 . The material for the additional second layer  38  differs from the material of the remaining second layer  34   a . The next process step is similar to the process step as disclose in FIG. 3 a . Now in FIG. 6 the additional second layer  38  is removed. In the present embodiment the additional second layer  38  is not removed from the area beyond the second recess  32 . The selective removal of the additional second layer  38  is carried out by an appropriate patterning process which is, for example, followed by an etching step. The removal of the additional second layer  38  exposes again the top surface  36  of the first layer  26  and the top surface  36   a  of the remaining second layer  34   a  in the first recess  30 . How much material of a remaining additional layer  38   a  extends beyond the recess  32  has to be adjusted to the setup parameters (pressure, slurry used, speed, etc.) of a chemical mechanical planarizing device (not shown). The removing process of the remaining additional second layer  38   a  is done with CMP. The removing process (see FIG. 7) lasts until only the material of the remaining additional second layer  38   a  defines a surface  36   b  which is coplanar with the surface  36  of the first layer  26  and surface  36   a  of the remaining second layer  36   b  in the first recess  30 . 
     It is clear for a skilled person that the described method may be carried out with a plurality of recesses. Therefore, the embodiments described in the specification should not be regarded as a limitation of the scope of the invention. 
     FIGS. 8-10 show the improvement of surface quality achieved with the inventive method. The topography in FIGS. 8-10 is in arbitrary units. The layer structure, used for the topography results, is comparable to the structure as shown in FIG. 2 and 3 a . A first layer  26  of thermally grown silicon dioxide is applied to the substrate  28  and etched to define a 50 μm wide recess  30 . A second layer  34  consisting of polysilicon is then deposited. A Photoresist is patterned over the polysilicon to serve as an etch mask. The polysilicon is etched away defining a silicon dioxide surface  36  everywhere except in the recess  30  including  2  microns of remaining second layer  34   a  overlap between the polysilicon and silicon dioxide around the recess  30 . FIG. 8 shows a surface profilometer trace of such a feature after the photoresist etch mask is removed. 
     The substrates proceed through CMP, which reduces the polysilicon height to match that of the silicon dioxide first layer  26 . The removal rate of the polysilicon is much greater than the silicon dioxide removal rate, therefore, little oxide is lost; less than 50 Å. The removal rate of the polysilicon on the overlap regions is higher than in the recess regions resulting in a planar polysilicon surface that is coplanar with the silicon dioxide surface. Since the polysilicon was previously etched away in all other regions of the silicon dioxide, the purpose of the CMP process is limited to just planarizing the recess areas and not clearing the polysilicon off the silicon dioxide surface. FIG. 9 shows the surface topography around a 50 μm wide recess after CMP. Without patterning the polysilicon first, heavy dishing results as illustrated in FIG.  10 . The processing for both examples included Rodel SDE3000 slurry, Rodel IC1000 pad with a SubaIV subpad on a Strasbaugh 6DS-SP CMP tool. The CMP conditions included a table speed of 55 rpm, spindle speed of 50 rpm, down pressure of 3 PSI, and table temperature of 25° C. It is clear for a skilled person that variations and modifications of the CMP conditions be effected. 
     The following part of the specification shows the use of the inventive method to provide coplanar surfaces which are important for the construction of additional elements. The method should be further discussed with respect to a mechanical grating device  100 . 
     FIG. 11 is a perspective, partially cut-away view of the mechanical grating device  100  of the present invention. The mechanically deformable structures of the mechanical grating device  100  are formed on top of a base  50 . The present embodiment as shown in FIG. 7 discloses a mechanical grating device  100  which can be operated by the application of an electrostatic force. According to the fact that the actuation force of the mechanical gating device  100  is electrostatic, the base  50  comprises the several layers of different materials. The base  50  comprises a substrate  52 . The material of the substrate  52  is chosen from the materials glass, plastic, metal and semiconductor materials. The substrate is covered by a bottom conductive layer  56 . In this embodiment the thin bottom conductive layer  56  is necessary since it acts as an electrode for applying the voltage to actuate the mechanical grating device  100 . The thin bottom conductive layer  56  is covered by a protective layer  58 . The bottom conductive layer  56  is selected from the group consisting of aluminum, titanium, gold, silver, tungsten, silicon alloys, and indium tinoxide. Above the protective layer  58 , a standoff layer  60  is formed which is followed by a spacer layer  65 . On top of the spacer layer  65  a ribbon layer  70  is formed which is covered by a reflective layer  78 . In the present embodiment the reflective layer  78  has also to be conductive in order to provide electrodes for the actuation of the mechanical grating device  100 . The electrodes are patterned from the reflective and conductive layer  78 . 
     The spacer layer  65  has a longitudinal channel  67  formed therein. The longitudinal channel  67  comprises a first and second side wall  67   a  and  67   b  and a bottom  67   c . The channel  67  is open to the top and covered by a first and a second set of deformable ribbon elements  72   a  and  72   b . Each deformable ribbon element  72   a  and  72   b  spans the channel  67  and is secured to the surface of the spacer layer  65  on either side of the channel  67 . The bottom  67   c  of the channel  67  is covered by a protective layer  58 . As mentioned above, the ribbon layer  70  is covered by the reflective layer  78 . The reflective layer  78  (conductive) is patterned such that there is a first and a second conducting region  78   a  and  78   b . Both, the first and the second conductive region  78   a  and  78   b  have according to the patterning, a comb-like structure and are arranged at the surface of the mechanical grating  100  device in a inter-digitated manner. The first and second conductive region  78   a  and  78   b  are mechanically and electrically isolated from one another. According to the pattern of the reflective layer  78  the ribbon layer  70  is patterned in the same manner. As a result there are the first and the second set of deformable ribbon elements  72   a  and  72   b  spanning the channel  67  and in the direction of the channel  67  are arranged such that every other deformable ribbon element belongs to one set. Furthermore, the deformable ribbon elements  72   a  and  72   b  define a top surface  70   a  and a bottom surface  70   b . It is important for the efficiency of the mechanical grating device that the top surface  70   a  and the bottom surface  70   b  of all deformable ribbon elements are coplanar. 
     In the embodiment as shown in FIG. 111 a plurality of standoffs  61  are positioned on the bottom  67   c  of the channel  67 . The standoffs  61  are patterned from the standoff layer  60  such that a group of standoffs  61  is associated only with the deformable ribbon elements  72   a  and  72   b  of the first or the second set. In the embodiment shown here, the group of standoffs  61  is associated with the second set of deformable ribbon elements  72   b . The standoffs  61  may also be patterned in the form of a single bar. 
     Referring to FIG. 12, the mechanical grating device  100  (the following description is limited to an electromechanical device) is fabricated using standard microelectronic thin-film processing, the substrate  52  is a single crystal silicon wafer. Although the silicon is a conducting material, ion implantation can be used to increase the conductivity near a surface  53  defined by the base  50  confinement within the base  50 . The implantation results in a highly conducting thin region  56  designated as the ground plane of the electrical circuit (not shown) at the surface  53  of the base  50 . The protective layer  58  of thermal oxide is grown at the surface  53  of the base  50 . Next, a standoff layer  60  of silicon nitride is deposited. The standoff layer  60  defines an upper surface  54   a  which will be used to define an actuation height resulting from the operation of the mechanical device  100 . Next, a spacer layer  65  of silicon oxide deposited by chemical vapor deposition is added. The total height of the actuation is defined by the thickness of the spacer layer  65  having an upper surface level  64   a.    
     The next step is illustrated in FIG. 13, showing the pattering of the spacer layer  65  using standard photolithographic processing and etching methods to define the channel  67  where the active region of the mechanical device  100  will be located. The standoff layer  60  is then patterned using photolithographic processing and etching methods to produce silicon nitride standoffs  61 , as illustrated in FIG.  13 . Although not illustrated, these patterns can consist of pedestals or lines. The standoffs  61  act as mechanical stops for the actuation of the device and the upper surface of the standoffs  61  is surface  54   a.    
     To allow the additional layers atop the existing structure, a conformal sacrificial layer  66  of polycrystalline silicon is deposited to a thickness greater than the separation of surfaces  54   a  and  64   a  as illustrated in FIG.  14 . The deposited sacrificial layer  66  shows a conform recess  68   a  in the area of the channel  67  which is located beneath the deposited sacrificial layer  66 . 
     The next step, as illustrated in FIG. 15, is the removal of the sacrificial layer  66  from the device  100  completely except an area beyond the channel  67 . The selective removal of the sacrificial layer  12  is carried out by an appropriate patterning process, which is, for example, followed by an etching step. The removal of the sacrificial layer  66  exposes a top surface  64  of the spacer layer  65 . How much material of a remaining sacrificial layer  66   a  extends beyond the area of the channel  67  has to be adjusted to the setup parameters (pressure, slurry used, speed etc.) of a chemical mechanical polishing device (not shown). The width of the remaining sacrificial layer  66   a  has to have at least the width of the channel  67 . 
     FIG. 16 illustrates the planarization of the remaining sacrificial layer  66   a  to a level substantially near the surface  64   a  using chemical mechanical polishing methods. The removing process (see FIG. 16) lasts until only the channel  67  is filled with the material of the remaining sacrificial layer  66   a . The remaining sacrificial layer  66   a , filling the channel  67 , defines a surface  68   b  which is coplanar with the surface  64   a  of the spacer layer  65 . The coplanar surface allows now the built up of further structures which have also well defined surfaces. 
     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 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 10 
                 substrate 
               
               
                   
                 11 
                 narrow recess 
               
               
                   
                 12 
                 wide recess 
               
               
                   
                 13 
                 small area between recesses 
               
               
                   
                 14 
                 large area between recesses 
               
               
                   
                 15 
                 first layer 
               
               
                   
                 20 
                 blanket conformal fill layer 
               
               
                   
                 21 
                 planarized filled narrow recess 
               
               
                   
                 22 
                 planarized filled wide recess 
               
               
                   
                 24 
                 fill residue layer 
               
               
                   
                 26 
                 a first layer 
               
               
                   
                 28 
                 substrate 
               
               
                   
                 30 
                 first recess 
               
               
                   
                 32 
                 second recess 
               
               
                   
                 34 
                 second layer 
               
               
                   
                 34a 
                 remaining second layer 
               
               
                   
                 35 
                 conformed recess 
               
               
                   
                 35a 
                 ground level 
               
               
                   
                 36 
                 surface of the first layer 
               
               
                   
                 36a 
                 surface of the second layer in the recess 
               
               
                   
                 36b 
                 surface of the additional second layer in the recess 
               
               
                   
                 37a 
                 surface level 
               
               
                   
                 38 
                 additional second layer 
               
               
                   
                 38a 
                 additional remaining second layer 
               
               
                   
                 50 
                 base 
               
               
                   
                 50a 
                 top surface of base 
               
               
                   
                 52 
                 substrate 
               
               
                   
                 53 
                 surface of the base 
               
               
                   
                 54a 
                 top surface of standoffs 
               
               
                   
                 54b 
                 top surface of actuated ribbon elements 
               
               
                   
                 56 
                 thin bottom conductive layer 
               
               
                   
                 56b 
                 surface of conductive layer 
               
               
                   
                 58 
                 protective layer 
               
               
                   
                 60 
                 standoff layer 
               
               
                   
                 61 
                 standoff 
               
               
                   
                 64a 
                 coplanar surface 
               
               
                   
                 65 
                 spacer layer 
               
               
                   
                 66 
                 sacrificial layer 
               
               
                   
                 66a 
                 remaining sacrificial layer 
               
               
                   
                 67 
                 channel 
               
               
                   
                 67a 
                 first side wall 
               
               
                   
                 67b 
                 second side wall 
               
               
                   
                 67c 
                 bottom 
               
               
                   
                 68a 
                 conform recess 
               
               
                   
                 68b 
                 surface of material in the channel 
               
               
                   
                 70 
                 ribbon layer 
               
               
                   
                 70a 
                 top surface of the coplanar ribbon elements 
               
               
                   
                 70b 
                 bottom surface of the coplanar ribbon elements 
               
               
                   
                 72a 
                 first set of deformable ribbon elements 
               
               
                   
                 72b 
                 second set of deformable ribbon elements 
               
               
                   
                 74 
                 opening 
               
               
                   
                 75 
                 interconnection 
               
               
                   
                 76 
                 thick conducting layer 
               
               
                   
                 78a 
                 first conducting region 
               
               
                   
                 78b 
                 second conducting region 
               
               
                   
                 100 
                 mechanic grating device 
               
               
                   
                 A-A 
                 first line defining a view plane 
               
               
                   
                 B-B 
                 second line defining a view plane 
               
               
                   
                 L-L 
                 longitudinal direction of the substrate 
               
               
                   
                 H 
                 height of the recess 
               
               
                   
                 W 
                 width of the recess 
               
               
                   
                 D 
                 thickness of the ribbon layer