Abstract:
This invention discloses a mirror device comprises a mirror array. The mirror array includes multiple mirror elements. Each element comprises a mirror supported on a hinge. The hinge is attached directly to the mirror and is substantially perpendicular to the mirror. The hinge penetrates a bottom surface of the mirror with a hinge-top buried in a layer of the mirror beneath a top surface of the mirror.

Description:
This application is a Non-provisional Application claiming a Priority date of Jul. 15, 2008 based on a previously filed application Ser. No. 12/009,389 filed on Jan. 17, 2008 for that has a Priority Date of May 12, 2007 according to a Provisional Patent Application 60/930,151. The application Ser. No. 12/009,389 is a Continuation in Part (CIP) Application of another U.S. patent application Ser. No. 10/918,677 filed on Aug. 14, 2004 and now issued into U.S. Pat. No. 7,183,618. The disclosures made in these patent applications filed by the same Applicant of this Non-Provisional Application are hereby incorporated by reference in this patent application. This application is further a Continuation-in-Part Application of two previously filed application Ser. No. 11/136,041 filed on May 23, 2005 (now issued into U.S. Pat. No. 7,304,783) and application Ser. No. 11/183,216 filed on Jul. 16, 2005 (now issued into U.S. Pat. No. 7,215,460). The disclosures made in these Applications as filed by the same Application of this Application are further incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to manufacturing process in applying the mechanical electrical micro-machining system (MEMS) technology and the improved device configurations by applying the manufacturing processes. More particularly, this invention relates to manufacturing processes in producing the Micromirror or Micro-window devices with flat mirrors with smooth mirror surface or windows without any protrusions or dips. This invention is particularly advantageous because the micromirrors may be implemented in a high performance image display system to achieve a high quality of image display with high contrast. 
     BACKGROUND ART 
     Even though there are significant advances made in recent years on the technologies of manufacturing and implementing the display devices with moving elements such as micro-mirrors (reflective device) or micro-windows (transmissive device) as spatial light modulator. There are still technical limitations and difficulties in the manufacturing process. There is a difficulty in a process of making flat mirrors or windows without any mark, protrusion or dip, because a hinge is attached to these moving elements. 
     MEMS devices have drawn considerable interest because of their application as sensors, actuators and display devices. MEMS devices often have a structure as shown in  FIG. 1  where an electronic circuit is formed on a substrate and the circuit provides voltage or current to electrodes or senses voltage or current from the electrodes. MEMS structures are often formed over the top or close to the electrodes with a gap between the electrodes and MEMS structure. The top view shown in  FIG. 1  illustrates a typical conventional micromirror device with each mirror formed with a hole in the middle of mirror. The uneven or non-uniform mirror surfaces of a mirror device implemented in the conventional image display system adversely affects the quality of display because of undesired reflection of incoming light by the holes, dips or protrusions on the non-uniform mirror surfaces. 
     Therefore a need still exists in the art of applying MEMS technologies for manufacturing electronic and optical components and devices to provide a method and material to produce flat mirrors and windows without leaving any hole, protrusion or dip. 
     SUMMARY OF THE INVENTION 
     An aspect of this invention is to provide new and improved structures for MEMS devices and manufacturing processes to produce mirror device comprises micromirror arrays with flat and smooth mirror surface such that the above discussed limitations and difficulties can be resolved. 
     Another aspect of this invention is to provide new and improved structures for MEMS devices and manufacturing processes to enable convenient manufacturing processes of hinges and flat and smooth mirror surfaces to reduce the production costs and to provide mirrors that can achieve high level of performance. 
     Another aspect of this invention is to provide new and improved structures for MEMS devices and manufacturing processes to enable convenient manufacturing processes and to provide stable structures by preventing metal migration to cause hinge deformation. 
     Another aspect of this invention is to provide new and improved structures for MEMS devices and manufacturing processes to manufacture hinges and mirrors with flat and smooth mirror surfaces wherein the hinge is supported on a hinge base higher than the electrode whereby the hinge base can serve the function as mirror stoppers and the potential problems of insulation layer breakdown on the electrodes are resolved. 
     Another aspect of this invention is to provide new and improved structures for MEMS devices and manufacturing processes to manufacture hinges and mirrors by etching the sidewall of semiconductor and polishing the surface after filing the hole with a sacrifice layer to form vertical hinges followed by etching the sacrificial layer with the hinge protruding over the sacrificial layer. Then the metal layer is deposited to form the mirror surface over the protruding hinge. A flat and smooth mirror surface is formed because the hinge is so thin compared with the thickness of the mirror and the hinge is buried in the mirror surface without leaving any noticeable marks on the surface of the mirror. 
     Another aspect of this invention is to provide new and improved structures for MEMS devices and manufacturing processes to enable convenient manufacturing processes and to provide stable structures by forming migration stop layer with Titanium or AL2O3 for preventing metal migration from the hinge base to the hinge and to the electrodes to prevent both the hinge deformation and electrode degradation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a top perspective view for illustrating a dip or hole at the center of the micromirrors produced by conventional MEMS manufacturing process. 
         FIG. 2  shows a side cross-section view of a micromirror element as an embodiment of this invention. 
         FIG. 3  shows a side cross section view of a micromirror element of this invention with a hinge foot and a metal mirror deposited on top of a semiconductor hinge forming a one-piece structure. 
         FIG. 4  shows a side cross section view of a micromirror element of this invention with a hinge-tab and a mirror-via formed with material of the mirror metal. 
         FIG. 5  shows a side cross section view of a micromirror element of this invention with a hinge-tab and a mirror-via formed with a different material than the mirror material and applying a polish process to planarize the surface. 
         FIGS. 6A and 6B  show the side cross section views of a micromirror element of this invention with a smooth and uniform mirror surface manufactured by a simplified manufacturing process. 
         FIG. 7  shows a side cross section view of a micromirror element of this invention with a migration stop layer to stop the migration of mirror metal into semiconductor hinge. 
         FIG. 8  shows a side cross section view of a micromirror element of this invention with a migration stop layer to stop the migration of mirror metal into semiconductor hinge and a hinge base to implement a shorter hinge. 
         FIG. 9  shows a side cross section view of a micromirror element of this invention with a shorter hinge extended from a hinge base that is higher than the electrodes accomplished by adding an additional via on top of the hinge-base that has the same height as the electrodes. 
         FIG. 10  is a cross sectional view for showing an alternate embodiment of this invention wherein the hinge base includes tow horns to serve the function as mirror stopper. 
         FIGS. 11A to 11C  are a series of cross sectional view to illustrate the manufacturing processes for making a mirror device of this invention. 
         FIGS. 12A to 12G  are cross sectional views and perspective views for showing the manufacturing processes to form the hinge on the sidewalls of a cavity. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 2  is a cross sectional view for illustrating a micromirror manufactured by applying a MEMS technology as exemplary embodiment of this invention. The micromirror includes a mirror  101  supported on a hinge  103 . The mirror  101  is formed as an aluminum surface has a flat and smooth top surface without a hole, dip or protrusion. The hinge  103  is formed as a semiconductor hinge, such as a silicon hinge. The hinge  103  has a foot, shown as a reversed L-shaped foot, supported on an insulation layer  104 . 
     The mirror element further includes two electrodes  102  disposed on two opposite sides of the hinge  103  underneath the mirror  101 . The electrodes  102  are connected to signal wires  105  and  109  through via connectors  110 ,  112 , and  115  penetrate through the inter-layer dielectric (ILD) layers  106 ,  107  and  108 . The micromirror element is supported and manufactured on a semiconductor substrate  111  such as a silicon substrate. There are also junction layers  113  and  114  formed during the COMS manufacturing processes. 
     The signal wires  105  and  109  may be configured as word lines and bit lines to transmit control signals for applying voltages to the electrodes  102  to control the deflection of the mirror  101 . The electrodes may also serve the function as the mirror stopper to contact and stop the mirror  101  at a predefined maximum deflection angles. As will be further described below, a top portion of the hinge  103  is embedded in a bottom layer of the mirror  101  through a special manufacturing process as illustrated and described in  FIGS. 11A to 11C . 
       FIG. 3  is a side cross sectional view of a micromirror element as another embodiment of this invention. The micromirror element includes a flat mirror  201  supported on a semiconductor hinge  202  includes a foot and a mirror platform supporting the mirror  201  thereon. The micromirror element further includes two electrodes  205  supported on two etch stop layers  204  and  206 . The electrodes  205  are connected to electric wires through via connectors  208  penetrated through the etch stop layers  204 ,  206  and the inter-layer dielectric (ILD) layer  203 . The ILD layer  203  is supported on a semiconductor substrate  210  and disposed on top of an insulting layer  207 . 
       FIG. 3A  is a photographic view of the micromirror device. Even though the configuration as shown in  FIG. 3  has the advantage of successfully sealing the holes in the mirror  201 , there is still a dip on the surface of the mirror and the surface of the mirror may be deformed to have warped shape as shown in  FIG. 3A . 
       FIG. 4  is a side cross sectional view of a micromirror element as another embodiment of this invention. The micromirror element includes a mirror  251  supported on a semiconductor hinge  254  includes a foot and a hinge tab  253 . The mirror tab  253  supports the mirror  251  through a mirror via  255  surrounding a mirror hole  252  to contact the hinge tab  253 . The mirror via  255  is composed of a mirror material such as aluminum and the mirror via  255  is placed on the hinge tab  253 . 
     The micromirror element shown in  FIG. 4  resolves the difficulties of mirror surface warping due to mirror surface deformation as that encountered in the micromirror element of  FIG. 3 . But the mirror  251  has a via-hole  252  and the light reflected from the edges and corners of the hole can degrade quality of the image display. 
       FIG. 5  is a side cross sectional view of a micromirror element as another embodiment of this invention. The micromirror element includes a mirror  241  supported on a semiconductor hinge  244  includes a foot and a hinge tab  243 . The hinge tab  243  supports the mirror  241  through a mirror via  242  formed by filling a via-hole, e.g., a mirror via-hole  242  as that shown in  FIG. 4 . The mirror via-hole  242  is filled with a material composed of a conductive material and planarized by applying a polishing process. This micromirror element has that benefits that the difficulties of surface warping and a hole on the surface of the mirror are resolved. However, the micromirror element shown in  FIG. 5  requires more manufacturing processing steps thus adversely affecting the production costs. 
       FIG. 6A  is a side cross sectional view of a micromirror element as another embodiment of this invention. The micromirror element includes a mirror  261  supported on a semiconductor hinge  262 . The hinge  262  attaches directly onto the mirror  261  to support the mirror  261  controlled by two electrodes  263  to deflect to different deflection angles when the electrodes  263  disposed on a semiconductor substrate are applied different voltages.  FIG. 6B  has a similar structure with  FIG. 6A  except that the hinge  264  in  FIG. 6B  penetrates through the bottom surface of the mirror  261  and attached to a buried layer in the mirror  261 . The bottom layer of the mirror may comprise an etch stop layer composed of a semiconductor material. According to the manufacturing processes as disclosed below in  FIGS. 11 and 12 , it is preferable that the mirror is protected by an etch stop layer composed of a semiconductor material. The depth of the penetration into the mirror may range from a depth below 100 Angstroms to approximately 5% and up to two-third (⅔) of the thickness of the mirror. The hinge  262  is attached directly to the bottom surface of the mirror  261  and not penetrating into the mirror  261  beyond the bottom surface of the mirror  261 . This micromirror element has the benefits that the difficulties of surface warping and a hole on the surface of the mirror are resolved. Furthermore, the micromirror element shown in  FIG. 6  can be manufactured by simplified manufacturing processing steps thus reducing the production costs. 
       FIG. 7  is a side cross sectional view of a micromirror element as another embodiment of this invention. The micromirror element includes a mirror  271  supported on a semiconductor hinge  273 . The hinge  273  supports the mirror  271  through a migration stop layer  272  formed between the mirror  271  and the hinge  273  to prevent the migration of the mirror material into the hinge. The migration stop layer thus prevents the deformation of the hinge  273  caused by migration of mirror material to the hinge. The migration layer may be a Ti (titanium) layer. Preferably, a migration layer is formed on all the interface areas between a semiconductor hinge and a metal layer. 
       FIG. 8  is a side cross sectional view of a micromirror element as another embodiment of this invention. The micromirror element includes a mirror  281  supported on a hinge  283 . The hinge  283  supports the mirror  281  through a migration stop layer  282  formed between the mirror  281  and the hinge  283  to prevent the migration of the mirror material into the hinge. The migration layer thus prevents the deformation of the hinge  283  caused by migration of mirror material to the hinge. 
     The hinge is supported on a hinge base  286  covered with a barrier metal layer  285  under a second migration stop layer  284  for contacting and supporting the foot of the hinge  283 . The second migration stop layer  284  prevents a migration of the material of the hinge base  286 , e.g., a hinge base composed of aluminum, to migrate to the hinge  283 . The hinge base  286  is placed on top of an inter-layer dielectric (ILD) layer  290  through a third migration layer  287  and an etch stop layer  288 . The third migration layer  287  prevents migration of the material of hinge base, e.g., a hinge base formed with aluminum, to adjacent layers thus affecting the electric conductivity as well causing mechanical deformation. A via-hole  289  is opened through the ILD layer  290  for electrically connecting the hinge-base to electrical wiring (not specifically shown). The migration layers, e.g., layer  282 ,  284  and  287 , may be a Ti (titanium) layer. Preferably, a migration layer is formed on all the interface areas between a semiconductor hinge and a metal layer and between the metallic hinge base  286  and the etch stop layer  288 . 
       FIG. 9  is a side cross sectional view of a micromirror element as another embodiment of this invention. The micromirror element includes a mirror  291  when operated in a horizontal state and  296  when tiled to a pull-in state. The mirror  291  is supported on a hinge  293  and the hinge is supported on a hinge base  294  placed upon one of three electrodes  295  on top of an inter-layer dielectric (ILD) layer  298 . The electrodes  295  have via connecters  297  opened through the ILD layer  298  connected to ground or power lines (not specifically shown here). 
     This embodiment is to provide a structure wherein the mirror  291  is prevented from contacting the electrodes with voltages applied thereon. Instead of contacting the electrode, the mirror  296  is tilted to contact the hinge base  294 . The mirror contacts the hinge-base  294  that is connected to a ground potential where no voltage is applied. This configuration prevents damage to the insulation layer covering the electrode when the mirror continuously deflects to a maximum angular position to contact the electrodes during multiple mirror oscillations to the fully-on or fully-off positions. The hinge base is connected to a ground potential and can be implemented to function as mirror stoppers to stop the mirror at the predefined maximum deflection angles on opposite side of mirror operations without concerns of the breakdown of the insulation layers. 
       FIG. 10  is a side cross sectional view of a micromirror element as another embodiment of this invention. The micromirror element includes a mirror  301  supported on a hinge  302 . The hinge  302  is supported on a hinge base  304  functions as an electrode with two adjacent electrodes  305  disposed on top of an inter-layer dielectric (ILD) layer (not specifically labeled). The hinge base  304  further includes two mirror-tilt-stoppers  303  on the top surface of the hinge base  304  on two opposite sides of the hinge  302 . The mirror-tilt-stoppers  303  stop the mirror when the mirror  301  is controlled to deflect to the maximum deflection angles that can be either fully-on or fully-off angular positions. This configuration also has the benefit of preventing a breakdown of the insulation layer insulating the electrodes  305  when these electrodes are also implemented as stopper to continuously contact and stop the mirror at the maximum deflection angles. 
       FIGS. 11A to 11C  are a series of cross sectional views to illustrate the processing steps for manufacturing a mirror device of this invention.  FIG. 11A  shows a supporting substrate  310  that comprises a semiconductor substrate and ILD layer supported thereon (not specifically shown) with via holes (not specifically shown). The supporting substrate  310  has a first and a second electrode  305  and a hinge base  304  with a first and a second horn  303  on two opposite sides of a hinge  302  formed thereon. The hinge  302 , the hinge base  304  and the electrode  305  are all covered by a sacrificial layer  306 . A polishing process is applied to ensure the flatness of the hinge  302  and the sacrificial layer  306 . In  FIG. 11B , a etching process is applied to the top surface of the sacrificial layer  306  to expose a top portion of the hinge  302  extending over and above the top surface of the polished top surface of the sacrificial layer  306 . In  FIG. 11C , a mirror layer  301  is deposited o top of the sacrificial layer  306 . The manufacturing steps proceed with an vapor etching process to remove the sacrificial layer  306  to form a flat and smooth top mirror surface without dip, holes or protrusion on the top surface of the mirror  301 . In an embodiment, the hinge  302  penetrates the bottom surface of the mirror  301  and buried in a layer of the mirror  301  below the top surface of the mirror. In a different embodiment, the hinge  302  is attached to the bottom surface of the mirror  301  without any penetration. 
     Therefore, this invention discloses a device configuration and manufacturing method to provide a flat mirror supported on a vertical hinge without any dip, mark, or hole on the top surface of the mirror. The vertical hinge is formed by the sidewall of a semiconductor and the top surface is polished back after filling the hole with a sacrificial layer. The hinge is not yet protruding above the top surface. Then a polishing etching process is carried out to etch only the top layer of the sacrificial layer, the top portion of the hinge protrudes above the sacrificial layer. Then, the mirror metal is deposited over the protruding vertical hinge. Because the hinge is very thin compared to the thickness of the mirror, the hinge is buried would not leave any noticeable mark on the surface of the mirror. 
       FIGS. 12A to 12F  are cross sectional views and perspective views for showing the processing steps to form the hinge of this invention.  FIG. 12A  is a cross sectional view of a sacrificial layer  405  has a cavity  401  with sidewalls surrounding the cavity  401 . In  FIGS. 12B and 12C , a layer of hinge material is deposited on the sidewalls  402  and over the top surface  403  of the cavity. In  FIGS. 12D and 12E , a vertical hinge  402 ′ is formed by etching the sidewall layer  402  of the hinge material deposited on the sidewalls of the cavity and a tab  403 ′ is formed by etching the layer deposited on the top surface surrounding the cavity  401 . In  FIG. 12F , a hinge foot  404 ′ is formed by etching and patterning the layer  404  of the hinge material deposited on the bottom surface of the cavity  401  and the bottom of the post. The hinge is then formed by etching off and completely removing the sacrificial layer  405  as that shown in  FIG. 12G . According to the manufacturing processes as disclosed in  FIGS. 11 and 12 , it is preferable that the mirror is protected by an etch stop layer composed of a semiconductor material. In an embodiment, a micromirror of this invention further comprises at least one etch stop layer of Al2O3. 
     Therefore, according to the manufacturing processes and configuration as disclosed in  FIGS. 2 to 12 , it is preferable that at least a vertical hinge may also serve the function as an electrode. Furthermore, in an embodiment, the hinge base has a same height as the address electrode. And, in an alternate embodiment, the hinge base has a different height from an address electrode. In this invention, the vertical hinge may be formed as part of a post composed of the same material. Furthermore, the vertical hinge may also have a foot composed with the same material as the vertical hinge. 
     Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.