MEMS Structure and Method of Forming Same

Abstract

A microelectromechanical system (MEMS) device includes a substrate and a movable element at least partially suspended above the substrate and having at least one degree of freedom. The MEMS device further includes a protrusion extending from the substrate and configured to contact the movable element when the movable element moves in the at least one degree of freedom, wherein the protrusion comprises a surface having a water contact angle of higher than about 15° measured in air.

What is claimed is: 
     
         1 . A method of forming a MEMS device, the method comprising:
 forming a cavity in a first substrate;   patterning a second substrate to form a series of interdigitated fingers, wherein each of the series of interdigitated fingers is fixed at one end and is free at another end;   mounting the second substrate atop the first substrate, wherein free ends of the series of interdigitated fingers extend over the cavity;   forming a plurality of protrusions extending from a floor of the cavity, wherein a first interdigitated finger of the series of interdigitated fingers will contact a first protrusion of the plurality of protrusions when the series of interdigitated fingers are deflected downwards towards the floor of the cavity;   electrically coupling the first protrusion of the plurality of protrusions to the series of interdigitated fingers; and   electrically coupling a second protrusion of the plurality of protrusions to a potential voltage node that provides a voltage of an opposite polarity to that of a voltage on the series of interdigitated fingers.   
     
     
         2 . The method of  claim 1 , wherein the plurality of protrusions have a lower surface energy than a surface energy of a material of the floor of the cavity. 
     
     
         3 . The method of  claim 1 , wherein mounting the second substrate atop the first substrate comprises bonding a silicon surface of the second substrate to a silicon oxide surface of the first substrate. 
     
     
         4 . The method of  claim 1 , further comprising electrically coupling the plurality of protrusions to a contact. 
     
     
         5 . The method of  claim 1 , wherein forming the plurality of protrusions extending from the floor of the cavity comprises:
 blanket etching first portions of the first substrate; and   after blanket etching the first portions of the first substrate, selectively etching second portions of the first substrate.   
     
     
         6 . The method of  claim 5 , wherein forming the plurality of protrusions further comprises:
 after selectively etching the second portions of the first substrate, depositing a conductive material over remaining portions of the first substrate, the conductive material having a water contact angle in a range from 20° to 50°.   
     
     
         7 . The method of  claim 6 , wherein the conductive material comprises TiN. 
     
     
         8 . A method of forming a MEMS device, the method comprising:
 etching a first cavity and a second cavity in a topmost dielectric layer of a first substrate, a portion of the topmost dielectric layer being disposed between the first cavity and the second cavity;   forming a first protrusion on a floor of the first cavity, and a second protrusion on a floor of the second cavity, wherein each of the first protrusion and the second protrusion have a low surface energy relative to the surface energy of a material of the topmost dielectric layer;   bonding a second substrate to the first substrate; and   after bonding the second substrate to the first substrate, patterning the second substrate to form a first movable element at least partially suspended above the first cavity, wherein the first protrusion is in a path of movement of the first movable element when the first movable element is deflected in a first direction.   
     
     
         9 . The method of  claim 8 , wherein after bonding the second substrate to the first substrate, patterning the second substrate to form a second movable element at least partially suspended above the second cavity, wherein the second protrusion is in a path of movement of the second movable element when the second movable element is deflected in the first direction. 
     
     
         10 . The method of  claim 8 , wherein the first substrate further comprises:
 a plurality of stacked dielectric layers beneath the topmost dielectric layer, the plurality of stacked dielectric layers having a plurality of interconnect layers formed therein.   
     
     
         11 . The method of  claim 8 , wherein forming the first protrusion on the floor of the first cavity comprises:
 patterning the floor of the first cavity to form a protrusion extending therefrom; and   depositing a first conductive film over a top surface and sidewalls of the protrusion, the first conductive film being electrically coupled to a first contact on the floor of the first cavity.   
     
     
         12 . The method of  claim 11 , wherein forming the first protrusion on the floor of the first cavity further comprises depositing a second conductive film over the first conductive film, wherein the first conductive film comprises TiN, and the second conductive film comprises AlCu. 
     
     
         13 . The method of  claim 11 , wherein the first protrusion comprises a surface that has a water contact angle that is higher than 15°, when measured in air. 
     
     
         14 . The method of  claim 11 , wherein the second protrusion on the floor of the second cavity is electrically coupled to a second contact on the floor of the second cavity. 
     
     
         15 . A method of forming a MEMS device, the method comprising:
 forming a cavity in a substrate;   forming a protrusion that extends from a floor of the cavity, the protrusion comprising:
 a dielectric layer; and 
 a conductive film over sidewalls and a top surface of the dielectric layer, wherein a first material of the conductive film has a low surface energy relative to the surface energy of a second material of the dielectric layer; and 
   positioning a movable element above the cavity such that the movable element is configured to contact the protrusion when the movable element is deflected vertically downwards into the cavity.   
     
     
         16 . The method of  claim 15 , further comprising:
 performing a wet process, wherein during the wet process, a liquid will occupy a space between the protrusion and the movable element, wherein a contact angle between the liquid and surfaces of the protrusion is in a range from 20° to 50°.   
     
     
         17 . The method of  claim 15 , wherein the conductive film comprises TiN. 
     
     
         18 . The method of  claim 15 , wherein the conductive film comprises amorphous carbon. 
     
     
         19 . The method of  claim 15 , wherein the movable element comprises a membrane, a cantilever beam, or a comb structure. 
     
     
         20 . The method of  claim 15 , wherein the protrusion is configured to be switchably coupled to a ground potential node or a potential voltage node.