Abstract:
A micro mirror includes a hinge support post on the substrate, a hinge connection post on the hinge support post, wherein the hinge connection post comprises a bottom layer connected to the hinge support post and a side layer surrounding a cavity in the center of the hinge connection post, a hinge component connected to the side layer of the hinge connection post; and a mirror plate configured to tilt around the hinge component.

Description:
BACKGROUND 
       [0001]    The present disclosure relates to the fabrication of micro mirrors. 
         [0002]    A spatial light modulator (SLM) can be built with an array of tiltable mirror plates having reflective surfaces. Each mirror plate can be tilted about an axis by electrostatic forces to an “on” position and an “off” position. The electrostatic forces can be generated by electric potential differences between the mirror plate and an electrode underneath the mirror plate. In the “on” position, the micro mirror plate can reflect incident light to form an assigned pixel in a display image. In the “off” position, the micro mirror plate can direct incident light away from the display image. A mirror plate can be held by a mechanical stop at the “on” or the “off” position. 
       SUMMARY 
       [0003]    In one general aspect, the present invention relates to a micro mirror including a hinge connection post supported by the substrate, wherein the hinge connection post comprises a bottom layer connected to the hinge support post and a side layer surrounding a cavity in the center of the hinge connection post; a hinge component connected to the side layer of the hinge connection post; and a mirror plate configured to tilt around the hinge component. 
         [0004]    In another general aspect, the present invention relates to a method for fabricating a mirror plate over a substrate. The method includes forming a hinge support post on the substrate; simultaneously forming a hinge connection post on the hinge support post and a hinge layer connected to the hinge connection post; forming a reflective layer on the spacer layer; and selectively removing portions of the reflective layer and the hinge layer to form the mirror plate and a hinge component connected to the hinge connection post and the hinge layer, wherein the mirror plate is configured to tilt around the hinge component. 
         [0005]    In another general aspect, the present invention relates to a method for fabricating a mirror plate over a substrate. The method includes forming a hinge support post on the substrate; disposing a sacrificial material on the substrate and the hinge support post; forming a via in the sacrificial material to expose an upper surface of the hinge support post; depositing an electrically conductive material to simultaneously form a hinge connection post in the via and a hinge layer on the sacrificial material; selectively removing the electrically conductive material in the hinge layer to form openings in the hinge layer to define a hinge in the hinge layer and over the hinge connection post; forming a spacer layer on the hinge layer and the hinge; forming a reflective layer on the spacer layer; removing portions of the reflective layer, the spacer layer and the hinge layer to expose the sacrificial material; and removing the sacrificial material to form the mirror plate and the hinge connected to the hinge connection post and the hinge layer, wherein the mirror plate is configured to tilt around the hinge component. 
         [0006]    Implementations of the system may include one or more of the following. The side layer can be cone shaped. The side layer and the bottom layer can form a cup-like structure. The side layer, the bottom layer and the hinge component can form a unitary structure. The side layer, the bottom layer and the hinge component can be made of substantially the same material. The side layer can be substantially vertical to the substrate. The mirror plate can include a reflective layer and a hinge layer. The hinge connection post, the hinge component and the hinge layer can form a unitary structure. The hinge component and the hinge layer can form a co-planar structure. The hinge connection post, the hinge component and the hinge layer can be made of substantially the same material. The hinge connection post, the hinge component and the hinge layer can include an electrically conductive material. 
         [0007]    Implementations may include one or more of the following advantages. The disclosed system and methods can provide a simplified process for fabricating micro mirrors on a substrate and improved mechanical integrity and the strength of the micro mirrors. Several components of the mirror plate and support structure can be simultaneously formed in a unitary component and in a single step. 
         [0008]    Although the invention has been particularly shown and described with reference to multiple embodiments, it will be understood by persons skilled in the relevant art that various changes in form and details can be made therein without departing from the spirit and scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The following drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the present invention and, together with the description, serve to explain the principles of the invention. 
           [0010]      FIG. 1  illustrates an expanded view of a micro mirror. 
           [0011]      FIG. 2  is a bottom view of the mirror plate of the micro mirror of  FIG. 1 . 
           [0012]      FIG. 3  illustrates a detailed view of a hinge, a hinge connection post and a hinge support post in the micro mirror of  FIG. 1 . 
           [0013]      FIG. 4  illustrates a process flow diagram for fabricating the micro-mirror. 
           [0014]      FIGS. 5-8  are cross-sectional views along line A-A of  FIG. 2  showing several steps of fabricating the micro mirror on a substrate. 
           [0015]      FIGS. 9-12  are cross-sectional views along line B-B of  FIG. 2  showing several steps of fabricating the micro mirror on a substrate. 
           [0016]      FIGS. 13-14  are cross-sectional views along line A-A of  FIG. 2  showing several steps of fabricating the micro mirror on a substrate. 
           [0017]      FIGS. 15 ,  16 ,  17 A,  18 A,  19 A and  20 A are cross-sectional views along line C-C of  FIG. 2  showing several steps of fabricating the micro mirror on a substrate. 
           [0018]      FIGS. 17B ,  18 B,  19 B and  20 B are cross-sectional views along line A-A of  FIG. 2  showing several steps of fabricating the micro mirror on a substrate. 
           [0019]      FIGS. 21 and 22  are cross-sectional views along the lines C-C and A-A, respectively, of  FIG. 2  showing the micro mirror formed on the substrate. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Referring to  FIGS. 1-3 , a mirror plate  110  can include a reflective layer  111 , a spacer layer  113  and a hinge layer  114 . In some embodiments, the spacer layer  113  includes a pair of holes  112   a  and  112   b  and a pair of openings  108   a  and  108   b . In some embodiments the hinge layer  114  includes two hinge components  120   a  and  120   b . Each hinge component  120   a  or  120   b  includes a cavity  125   a  or  125   b  in the center. The hinge components  120   a  and  120   b  are respectively connected with the main portion of the hinge layer  114  by elongated hinges  163   a  and  163   b . The elongated hinges  163   a  and  163   b  are separated from the main portion of the hinge layer  114  by gaps  162   a ,  162   b . The hinge components  120   a  and  120   b  are separated from the main portion of the hinge layer  114  by gaps  161 . The mirror plate  110  can be tilted about an axis defined by the two hinge components  120   a  and  120   b . In some embodiments, the hinge layer  114  also include two pairs of holes  109   a  and  109   b , respectively, under the holes  112   a  and  112   b  in the spacer layer. Each pair of holes  109   a  or  109   b  define a bridge  107   a  or  107   b  in the hinge layer  114 . The bridge  107   a  or  107   b  is located under the hole  112   a  or  112   b  in the spacer layer  113 . As shown in  FIGS. 17-21 , each bridge  107   a  or  107   b  is positioned above a landing stop  140   a  and  140   b  on the substrate. Lines A-A, B-B and C-C in  FIG. 2  indicate the cross sections for the cross-sectional views in  FIG. 5-20 . 
         [0021]    The hinge component  120   a  (or  120   b ) is connected to a hinge connection post  122   a  under the hinge component  120   a . As also shown in  FIG. 22 , the hinge connection post  122   a  includes a bottom layer  312  and a side layer  315 , which define a cavity  125   a  in the center of the hinge connection post  122   a . The cavity  125  can have a circular opening as shown in the  FIG. 1-3  or a rectangular opening, such as a square opening. In some embodiment, the side layer  315  can be substantially vertical to the substrate. In embodiments, the side layer  315  has tapered walls. The side layer  315  can be form a cup-like structure in conjunction with the bottom layer  312 . In cavities that have a circular opening, the side layer  315  can be conical or have parallel walls. In cavities that have a rectangular opening, the side layer  315  can have tapered wall or walls that are parallel to one another. In embodiments, the hinge connection post has the same shape or cross section as the opening in the hinge component. 
         [0022]    The bottom of the hinge connection post  122   a  is connected to a hinge support post  121   a  on a substrate. The side layer  315  and the bottom layer  312  can be made of substantially the same material and form a unitary structure. The side layer  315  and the hinge layer  114  can have substantially the same thickness. In some embodiments, the side layer  315  is thinner than the bottom layer  312 . The hinge component  120   a ,  120   b  and the hinge layer can be formed by a same planar layer (the hinge layer  114 ). The hinge support post  121   a  can include an upper portion  123   a  and a lower portion  124   b  that can be formed in separate deposition steps. 
         [0023]    Referring to  FIGS. 1 ,  4  and  5 , the hinge support posts  121   a ,  121   b , step electrodes  130   a ,  130   b ,  131   a  and  131   b  and landing stops  140   a ,  140   b  are formed on a substrate  150  (steps  410 - 435 ). The substrate  150  can include electric circuits connecting to the hinge support posts  121   a ,  121   b , step electrodes  130   a ,  130   b ,  131   a  and  131   b  and landing stops  140   a ,  140   b . The hinge layer  114  and the hinge connection posts  122   a ,  122   b  and the support posts  121   a ,  121   b  are formed of an electrically conducting material. Thus, the hinge layer  114  is electrically connected with the hinge support posts  121   a ,  121   b  through the hinge connection posts  122   a ,  122   b . The electric potentials of the hinge layer  114  and the step electrodes  130   a ,  130   b ,  131   a  and  131   b  can be controlled to produce electric potential difference between the hinge layer  114  and the step electrodes  130   a ,  131   a  or the step electrodes  130   b ,  131   b . The resulting electrostatic forces can tilt the mirror plate  110  about an axis defined by the two hinge components  120   a  and  120   b . Details of the steps  410 - 435  are disclosed in U.S. patent application Ser. No. 11/382,630, entitled “Method for Fabricating a Micro Structure”, filed May 10, 2006, which is incorporated by reference herein for all purposes. 
         [0024]    Referring to  FIG. 6 , a sacrificial material  305  is disposed, for example, by spin-coating, over the substrate  150 , the hinge support posts  121   a ,  121   b  the step electrodes  130   a ,  130   b ,  131   a  and  131   b  and landing stops  140   a ,  140   b  (step  440 ). The sacrificial material can include a photo resist material, amorphous carbon, polyarylene, polyarylene ether (which can be referred to as SILK) and hydrogen silsesquioxane (HSQ). After hardening, if required, the sacrificial material  305  can be planarized by chemical mechanical polishing (CMP) to a predetermined height that defines the distance between the lower surface of the hinge layer  114  in the mirror plate  110  and the substrate  150  (see  FIGS. 8-22 ). A via  310  is formed in the sacrificial material  305  over the hinge support posts  121   a  to expose the upper surface of the hinge support posts  121   a  (shown in  FIG. 7A ). The via  310  can have a circular or a rectangular opening. 
         [0025]    The via  310  initially includes side walls  316  substantially perpendicular to the substrate  150 . The substrate  150  having the hinge support posts  121   a ,  121   b  and the sacrificial material  305  are then subject to a high temperature treatment to cause the photo resist to over flow to form side walls  317  that are sloped with respect to the substrate  150 , as shown in  FIG. 7B . In some embodiments, sloped side walls  317  can be formed in the via  310  by anisotropic etching. 
         [0026]    An electrically conductive material is next deposited, such as by physical vapor deposition, on the sacrificial material  305  and the upper surface of the hinge support posts  121   a  to form the hinge layer  114 , as shown in  FIG. 8 . The deposited electrically conductive material also simultaneously forms one or more side layers  315  and a bottom layer  312  in the via  310  (step  445 ). The side layers  315  and the bottom layer  312  define a cavity  125   a . The hinge connection post  122   a  is formed by the side layers  315  and the bottom layer  312 . Examples of the electrically conductive material include titanium, a titanium-aluminum alloy, a titanium-nickel alloy and an aluminum-copper alloy. The simultaneous formation of the hinge layer  114 , the side layers  315  and the bottom layer  312  combines several fabrication steps of other devices into one step and thus simplifies the fabrication of the micro mirror. The mechanical integrity and the strength of the mirror plate  110  are improved because the hinge layer  114 , the side layers  315  and the bottom layer  312  are formed in a unitary layer. 
         [0027]    A photo resist layer  318  is then introduced over the hinge layer  114 , the side layers  315  and the bottom layer  312 , as shown in  FIG. 9  (step  450 ). The photo resist layer  318  is patterned to form two openings  320  to expose the hinge layer  114 . The photo resist layer  318  also includes recesses for forming the two pairs of holes  109   a  and  109   b  (not shown in  FIG. 9 ). The hinge layer  114  is then etched to form the gaps  162   a  and the two pairs of holes  109   a  and  109   b  in the hinge layer  114  and under the openings  320 , as shown in  FIG. 11 . The sacrificial material  305  is thus exposed in the holes  109   a  and  109   b . The photo resist layer  318  is subsequently removed to define an elongated connection portion  163   a  in the hinge layer  114 , as shown in  FIG. 12 . 
         [0028]    Referring to  FIG. 13 , a sacrificial material  325  such as a photo resist is disposed to fill the cavity  125   a  (step  455 ). The sacrificial material  325  allows a spacer layer  113  to be formed on the cavity  125   a  and the hinge layer  114  in the subsequent step. The sacrificial material  325  is also disposed on the sacrificial material  305  through the holes  109   a  and  109   b  and fills the holes  109   a  and  109   b . The sacrificial material  325  can be spin-coated over the hinge layer and the via  310 . The sacrificial material  325  on the hinge layer  114  is subsequently removed. Since a single spin coating may not dispose enough sacrificial material  325  to fill the cavity  125   a , several spin coating of the sacrificial material  325  may be applied, each of which can be followed by a removal of the sacrificial material  325  from the top of the hinge layer  114 . The upper surface of the sacrificial material  325  is planarized to form a flat surface, that is, at substantially the same height as the upper surface of the hinge layer  114 . 
         [0029]    A spacer layer  113  is next deposited on the hinge layer  114 , as shown in  FIG. 14  (step  460 ). The spacer layer  113  can be formed for example of amorphous silicon material. A photo resist layer  127  is next spin coated over the spacer layer  113 , as shown in  FIG. 15  (step  465 ). The photo resist layer  127  is then patterned to form recesses  126   a  and  126   b  to expose the upper surface of the spacer layer  113  above the landing stops  140   a ,  140   b , as shown in  FIG. 16 . A recess is also formed the photo resist layer  127  over the hinge  113 . The spacer layer  113  is then etched in the exposed areas in the recesses  126   a  and  126   b  to form the cavities  112   a  and  112   b , as shown in  FIG. 17A . The spacer layer  113  is also etched to form a cavity  128  above the hinge component  120   a , as shown in  FIG. 17B . The cavities  112   a  and  112   b  and the two pairs of holes  109   a  and  109   b  are then filled with a sacrificial material  330 , as shown in  FIG. 18A . The cavity  128  is also filled by the sacrificial material  330 , as shown in  FIG. 18B . The sacrificial material  330  in the holes  109   a  and  109   b  contacts the sacrificial material  305  that is between the hinge layer  114  and the substrate  150 . 
         [0030]    A reflective layer  111  is next deposited on the spacer layer  113  and the sacrificial material  330 , as shown in  FIGS. 19A ,  19 B (step  470 ). Suitable materials for the reflective layer  112  can include gold, aluminum and gold/aluminum alloys. 
         [0031]    Openings  340  are next formed using photo-resist masking and etching to define the boundaries of each mirror plate  110 , as shown in  FIGS. 20A ,  20 B (step  475 ). That is, the openings  340  separate a mirror plate  110  from its adjacent mirror plates  110   a ,  110   b  and expose the sacrificial material  305 . 
         [0032]    The sacrificial materials  305 ,  325  and  330  are removed to separate the mirror plate  110  as shown in  FIGS. 21   a  and  22  (step  480 ). The mirror plate  100  includes the reflective layer  111 , the spacer layer  113  and the hinge layer  114 . The hinge connection posts  122   a  and  122   b , each of which includes one or more side layers  315 , a bottom layer  312  and a cavity  125   a  or  125   b  in the center. The hinge component  120   a  is connected to the side layer  315  of the hinge connection post  122   a . The hinge connection post  122   a  is further connected to the hinge support post  121   a  on the substrate  150 . The hinge layer  114 , the hinge connection posts  122   a ,  122   b  and the hinge support posts  121   a ,  121   b  are electrically conductive to allow the electric potential of the hinge layer  114  to be controlled by an electric circuit in the substrate  150 . 
         [0033]    The mirror plate  110  can tilt about an axis defined by the hinge components  120   a ,  120   b  under an electrostatic torque produced by an electric potential difference between the hinge layer  114  and the electrode  130   a - 131   b  on the substrate  150 . The tilt movement of the mirror plate  110  can be stopped when the bridge  107   a  or  107   b  comes to contact with a landing stop  140   a  or  140   b . The landing stops  140   a  and  140   b  can define the mirror plate  110  at precise tilt angels at which the reflective layer  111  can reflect an incident light in a predetermined direction. The electrostatic force can produce a distortion in the bridge  107   a  or  107   b . The stored elastic energy can be released to help the separation of the mirror plate  110  from the landing stop  107   a  or  107   b  when the electrostatic force is removed or reversed. 
         [0034]    In some embodiments, the dimensions of the micro mirrors are as follow. The hinge component  120   a ,  120   b  can be about 2-7 μm long, about 0.2-0.6 μm wide and about 0.04-0.1 μm thick. The hinge support posts  121   a ,  121   b  can be about 0.5-1.1 μm wide and 1-2 μm high. The landing stops  140   a ,  140   b  can be 0.5-2.0 μm high and 0.2-0.6 μm wide. The electrodes  130   a ,  130   b  can be 0.2-0.5 μm high. The step electrodes  131   a ,  131   b  can be 0.5-1.0 μm in height. The reflective layer  111  can be 500 angstroms or less in thickness. 
         [0035]    It is understood that the disclosed methods are compatible with other configurations of micro mirrors. Different material from described above can be used to form the different layers of the mirror plate, the hinge connection post, the hinge support post, the electrodes and the landing stops. The electrodes can include steps as shown in the figures, or an upper surface at a single height. The mirror plate can also have different shapes such as a hexagon, a diamond and an octagon.