Abstract:
In one embodiment, the invention provides a MEMS device. The MEMS device comprises a plurality of functional components including at least one moveable component; and a sacrificial component to at least reduce movement of the moveable component during shipping of the microelectromechanical systems device, wherein the sacrificial component can be removed after shipping.

Description:
FIELD OF THE INVENTION 
   This invention relates generally to fabrication processes for microelectromechanical systems (MEMS) devices and more specifically to the manufacture of interferometric modulators (iMoDs). 
   BACKGROUND OF THE INVENTION 
   An interferometric modulator is a class of MEMS (microelectromechanical) systems devices which have been described and documented in a variety of patents including U.S. Pat. Nos. 5,835,255, 5,986,796, 6,040,937, 6,055,090, and U.S. Pending patent application Ser. Nos. 09/966,843, 09/974,544,10/082,397,10/084,893, and 10/078,282, herein incorporated by reference. 
   One process for fabricating MEMS devices falls under the label of “surface micromachining” and comprises a sequence of deposition and etch steps that are repeated until a final step or release step. Such a process can often start with some kind of raw material in the form of films or thin film precursors which are deposited beforehand. These precursors may represent a definable component, which can be manufactured in high volumes in dedicated facilities. A more detailed description of this component is provided in patent application Ser. No. 10/606,001 herein incorporated by reference. 
   Surface micromachining includes monolithic semiconductor-like fabrication processes. Specifically, surface micromachining comprises a sequence of steps that combine film deposition, photolithography, and etching using a variety of techniques. Precursor films can be used as a starting point for the sequence which eventually results in a MEMS device with mechanical structures that can move. More detail on these processes is described in patent application Ser. No. 10/074,562 filed on Feb. 12, 2002 and herein incorporated by reference. 
   During shipping of the MEMS device, movement of the mechanical structures can occur and may result in damage to the MEMS device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a block diagram for a fully integrated MEMS processing facility as illustrated in the prior art. 
       FIG. 2  shows block diagram for a fully integrated MEMS processing facility incorporating precursor film deposition, structure processing, and backend processing. 
       FIG. 3  shows a block diagram for a non-integrated MEMS processing facility incorporating structure processing and backend processing. 
       FIG. 4  shows a MEMS device which is has been fabricated to the point of being ready to release 
       FIG. 5  shows a MEMS device which is has been released 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following detailed description of embodiments of the invention, numerous specific details are set forth such as examples of specific materials, machines, and methods in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that these specific details need not be employed to practice the present invention. In other instances, well known materials, machines, or methods have not been described in detail in order to avoid unnecessarily obscuring the present invention. 
   Broadly, in accordance with one embodiment of the invention, a MEMS device including a moveable component is fabricated, and the movement of the moveable component is inhibited using a sacrificial material, so that damage to the moveable component during shipping is at least reduced. In one embodiment, the sacrificial material is deposited during fabrication of the MEMS device, and the sacrificial material is removed during a release step after shipping. Removal of the sacrificial material may be by a chemical or related etch process, and results in the freeing of the moveable component. Thus, embodiments of the present invention disclose fabricating a MEMS device to the point of release but not beyond, and represent a component that may be readily manufactured in a high-volume dedicated facility. This component may then be conveniently removed to another factory where the release step and subsequent processing and packaging steps can be performed. One advantage of the present invention is that it allows entities that wish to fabricate MEMS devices, or perform post-fabrication operations on the MEMS device after shipping to operate in their respective spaces with the benefit of a low technological barrier-to-entry and reduced capital outlay since integrated facilities that fabricate the MEMS device and also perform the post-fabrication release and processing steps represent a higher technological barrier and require more capital outlay than separate facilities. Other advantages of the present invention will be apparent from the description below. 
   Patent application Ser. No. 10/606,001 filed on Jun. 24, 2003, describes a collection of deposited thin films, which can be used as precursor materials for the manufacture of iMoDs. Patent application Ser. No. 10/074,562 filed on Feb. 12, 2002 and, herein incorporated by reference, describes a prototypical fabrication sequence or structure process for building interferometric modulators, which can utilize the aforementioned precursor materials.  FIG. 1  represents a single factory,  100 , which contains two sections of manufacture,  102 , which generates the thin film precursor material, and  104 , which performs the structure processing that results in a finished MEMS structure or structures. 
     FIG. 2  is a more complete representation of the MEMS manufacturing chain. In  FIG. 2 , integrated factory  200 , includes section  202 , for precursor processing, section  204 , for structure processing, and section  206 , for backend processing. Backend processing generally refers to processes which interface a MEMS component to the outside world which can include device packaging, interconnection to external electronics and interfaces (i.e. drivers and touch screens for displays), interconnection to and integration with peripheral components (such as supplemental lighting for displays) and others. While these processes can be handled within a large integrated factory, they are often performed in dedicated facilities, which perform no other activities. For MEMS components and particularly for displays, this requires that there be a component which can be readily and easily transferred from the facility which defined it, the structure process section in this example, to the facility which will perform the backend process. 
     FIG. 3  illustrates this idea and its benefits conceptually. In  FIG. 3 , reference numeral  300  indicates a factory which performs only the structural processing on precursor films which have been supplied to it from another facility. It should be noted, of course, that if economics or other factors merit it this facility could perform both precursor processing and structural processing. In either case, economies of scale can be achieved by performing the structural processing or structural and precursor processing in a single facility  300 . The resulting component can then be supplied to one or more backend processing facilities,  304 , for further completion of the finished MEMS product. 
   For the structures and processes described in the aforementioned applications, a convenient point within the structural process to transfer the work product to backend processing is just before the release step.  FIG. 4  illustrates one kind of MEMS device, an iMoD, which resides at this point in the processing sequence. Referring to  FIG. 4 , reference numeral  400  indicates a substrate upon which optical thin films,  402 , have been deposited and patterned. Sacrificial film,  404 , has been deposited and patterned and resides above optical films  402 , and mechanical film,  406 , resides on and is mechanically coupled to sacrificial film  404 , and support posts  408 . 
   In  FIG. 5 , the release step has occurred. Specifically, the sacrificial film has been removed leaving an airgap,  504 , in its place. Support posts,  508 , remain to mechanically couple the mechanical membrane,  506 , to the substrate. However, the mechanical membrane is now free to move according to the function of its design. This release step is the result of a chemical etch process which utilizes an etchant to convert the sacrificial material into a byproduct which can be easily extracted in the form of a gas or a liquid. It is at this point that the device is ready to be packaged and interconnected as part of the backend process, though in some cases some backend processes may occur before release. 
   Regardless, transferring the MEMS component from one facility to another in the unreleased state is the preferred state for at least several reasons. First, no matter how well crafted the shipping containers are, there is always the possibility that the components to be shipped may be exposed to contaminants or other undesired particles or materials. Maintaining the component in the unreleased state minimizes the risk that such contaminants will be incorporated into the structure, and makes it easier to clean the component when it arrives a the backend facility. The MEMS component is also more stable from a mechanical standpoint. Thus, it is more resistant to extremes in environment such as temperature and mechanical shock which may occur during transport. Additionally, these components are more amenable to storage or stockpiling which might be beneficial under certain manufacturing scenarios or situations. Finally, the process tools required for performing the release step are relatively simple and inexpensive to acquire. Facilities and associated staff may, while expert in the tools and techniques required for backend processing may not be so facile with those that occur upstream in the structural processing section. Making the transfer at the unreleased stage lowers the technology and skill set barriers and speeds the manufacturing learning curves these teams have to deal with in preparing to manufacture iMoDs and other MEMS components. For components in the display arena, which usually involve large substrates with many displays, this component is referred to as a “ready-to-release-plate”.