Abstract:
A method of improving the robustness of microcomponents formed of silicon by armor coating the microcomponent with a ductile material, such as a metal. The armored coating may comprise either partial armored coating or total armored coating. Providing the microcomponent with an armored coating reduces chipping and breaking, and likewise reduces contamination problems which arise from chips and breaks.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority from provisional application serial No. 60/325,829, filed on Sep. 27, 2001, and entitled “ARMOR COATED MEMS DEVICES” by Zine-Eddine Boutaghou, Roger Lee Hipwell Jr., and Wayne Allen Bonin, which is herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method of increasing the robustness of microcomponents formed of silicon. In particular, the present invention relates to coating the microcomponents with a ductile metal to increase their robustness. 
     Many micro-electro-mechanical systems (MEMS) devices and other microcomponents are formed of silicon or other brittle materials. Though extremely brittle, silicon has become the industry standard for several reasons. First off, because of modem etching techniques, it is possible to form very precise microcomponents by etching them from silicon. As a result, much of the equipment and processing in many microcomponents facilities are configured for working with silicon. 
     In addition, the MEMS industry is influenced by and follows the semiconductor industry. The semiconductor industry has used silicon in making its components, and as a result, has perfected techniques for working with silicon. Furthermore, if the MEMS device has electrical connections or is to be integrated into other electrical components, it is preferable that the MEMS device be made of silicon. 
     Though silicon is a relatively strong material, it is also very brittle. When handling a MEMS device made of silicon, the MEMS device will typically come into contact with such traditional tools as tweezers, robot pick and place tools, and pin contacts. Any time the silicon MEMS device is contacted by one of these tools, stress concentrations at the location of contact may be created. These locations are very susceptible to chipping, cracking, or even breaking due to the increased stress concentrations. 
     When a silicon component is chipped during handling, the small amounts of silicon which chip off may contaminate nearby electrical components. Should the silicon device crack during handling, there is an increased likelihood that the entire device will break. This is because MEMS devices are often formed of a single silicon crystal. Once the single crystal is cracked, the crack may easily develop into a major break. Contamination can also result from cracks and breaks. Further, should the silicon MEMS device crack, chip, or break, the device may no longer be useful. 
     Therefore, there is a need in the art to form silicon microcomponents and MEMS devices in such a way that their robustness can be increased so that there is less breakage and less contamination caused due to chipping, cracking, or breaking. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a silicon microcomponents or MEMS device which is coated with a ductile metal at a contact interface. The silicon microcomponents or MEMS devices having this armored coating are much more robust, less prone to breakage, and less likely to chip. The armored coating of the MEMS device may comprise either partial armored coating or total armored coating. Total armored coating comprises coating the entire device with the metal, while partial armored coating involves coating the MEMS device with metal at only desired locations, such as the locations which will be contacted most often by a tooling mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of one example of a MEMS device which benefits from the present invention. 
     FIGS. 2A-2B are simplified cross-sectional views of the process flow involved in total armored coating of a wafer or component. 
     FIGS. 3A-3F are simplified cross-sectional views of the process flow involved in partial armored coating of a wafer or component. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a top plan view of a silicon MEMS device useful in testing sliders. Shown in FIG. 1 is a MEMS device  10  comprising an outer frame  12 , several inner springs  14 , two circular pin holes  16 , a tab  18 , and a pedestal  20 . The MEMS device  10  functions as a clamp for holding a slider during testing. The slider can be temporarily clamped into the MEMS device  10  on pedestal  20  so that the slider can be flown above a disc, tested, unclamped, and then removed from the MEMS device  10 . 
     The pin holes  16  on the MEMS device  10  align and hold the device  10  on a suspension or fixture (not shown in FIG.  1 ). The tab  18  provides a location at which pressure can be applied to the MEMS device  10 . When pressure is exerted on tab  18 , the springs  14  deform to open the clamp and allow the slider to be inserted or removed from pedestal  20  of the MEMS device  10 . 
     Clamping the slider  20  in the MEMS device  10  for testing is preferable to gluing the slider to a fixture for testing. When a slider is glued to a fixture for testing, the slider is typically no longer useable. Using a clamping device, such as the MEMS device  10 , allows each slider to be tested, yet remain useful once removed from the clamp. As a result, the MEMS device  10  is repeatedly opened and closed to allow for insertion and removal of the sliders before and after testing of each slider. 
     MEMS devices such as device  10  are typically formed of silicon using wafer level processing. Once the individual devices  10  are removed from the wafer, the MEMS device  10  must be handled. It is typical for the MEMS device  10  to be contacted by tweezers or similar tooling devices at its outer edge  12 , such as when installing the MEMS device  10  on a suspension. When so handled, it is not uncommon for the silicon to chip or crack at the locations where the tweezers contacts the MEMS device  10  outer surface  12 . 
     In addition, the MEMS device  10  is designed so that when installed on a suspension, pins on the suspension extend through the pin holes  16  on the device  10 . Each time the MEMS device  10  is opened and closed, the pin holes  16  experience certain stresses. As such, it is also common for the silicon to chip or break near the pin hole  16 . Similarly, in opening and closing the clamp  10  to allow a slider to be inserted into the MEMS device  10 , pressure is exerted on the tab  18  to deform the springs  14 . As a result, the tab  18  is another location on the MEMS device which receives repeated contact and which may chip or otherwise crack. 
     Any time the MEMS device  10  is chipped or cracked, small amounts of silicon may contaminate the slider held in the MEMS device  10  or may contaminate the disc or other electrical components near the device MEMS  10 . Furthermore, cracks in the MEMS device  10  can develop into more serious structural flaws or even breaks. To overcome the chipping and breakage problem, the present invention involves coating the MEMS device  10  with a ductile material, such as a metal, to prevent and reduce chipping and breakage. This armored coating serves to absorb the stress of repeated contact and prevents the stress from being transferred through the ductile material to the silicon crystals so that the silicon neither fractures, breaks, or chips. 
     There are two options for providing an armored coating on a MEMS device; total armored coating, and partial armored coating. The first option is to coat the entire surface of a MEMS device with the ductile metal. The second option involves only partially coating selected areas of the device. Providing the MEMS device with an armored coating can be performed at either an individual component level, or more preferably, at the wafer level. 
     FIGS. 2A-2B are simplified cross-sectional views of a wafer illustrating the process flow for providing micro components with a total armored coating. Shown in FIG. 2A is a wafer substrate  30 . In the first step of providing the wafer  30  with armored coating, a conformal coating of a seed layer  32  is deposited on the wafer substrate  30 . Any suitable seed layer material may be used, such as Tantalum. In depositing the seed layer  32 , it is desirable for the seed layer  32  to be very thin. Typically, the seed layer  32  is sputtered on and is about a few thousand Angstroms thick. The seed layer provides a surface onto which a ductile metal can be deposited. 
     FIG. 2B shows the step of depositing a soft metal  34  on the wafer  30  over the seed layer  32 . Any suitable metal, such as copper, aluminum, or nickel cobalt may be used. Most preferably, suitable metals are ductile and adhere well to silicon. In contrast to the seed layer  32 , the armor coating layer  34  is desired to be much thicker, and may be up to 10 microns or even 20 microns thick. However, the thickness of the armor coating  34  may be limited by the amount of stress the coating  34  puts on the features of the MEMS device or on the microcomponents itself. If the metal layer  34  is deposited too thickly, particularly when the layer  34  comprises ductile materials having high tensile or compressive stress, the layer  34  may fail or may rip off of the wafer  30 . 
     Any suitable method may be used to deposit the metal armored coating  34  on the wafer  30 . For instance, it is possible to deposit the metal layer  34  using chemical vapor deposition (CVD). In addition, it is possible to sputter the metal coating  34  onto the wafer  30 , or to deposit the metal coating  34  using an electroplating process. In coating the wafer  30  with the ductile material  34 , it may be possible to coat one surface of the wafer  30 , flip the wafer  30  over, and coat the other side of the wafer  30 . 
     The type of metal chosen as well as the method of depositing it on the wafer  30  may depend on the geometric factors of the features on the wafer  30 . In particular, for a MEMS device having intricate or fine geometric features. CVD may provide the best deposition method. A CVD process is particularly suited for instances where the coating  34  must evenly coat very small areas, deep recesses, and other features found in connection with intricate geometries. For devices having more coarse features, electroplating or sputtering may be suitable. 
     The type of metal chosen may also depend on the desired wear characteristics for the device. For instance, surfaces that will receive heavy and repeated contact may benefit from an armored coating  34  comprising a stronger metal such as nickel. In contrast, using a softer metal, such as copper, may be less suitable because when subjected to such repeated contact, the copper may smear or leave residue. 
     FIGS. 3A-3F are simplified cross-sectional views illustrating the process flow for providing a wafer with partial armored coating. In some instances, the microcomponent or MEMS device does not require a full armor coating due to either space requirements or other electromechanical requirements. In such a situation, only a partial armored coating may be applied. 
     FIG. 3A shows a wafer  40  and an area  42  of the wafer  40  to which it is desired that the armored coating be applied. The first step of applying a partial armored coating to the wafer  40  is shown in FIG.  3 B. FIG. 3B illustrates applying photo resist  44  to the wafer  40  on all areas of the wafer  40  but the area  42  which is to be armor coated. Next, as shown in FIG. 3C, a seed layer  46  is deposited on the wafer  40 . The seed layer  46  covers both the photo resist  44  as well as the area  42  to be armor coated. 
     Once again, any suitable seed layer material may be used, such as Tantalum. Also, it is preferable for the seed layer  46  be deposited in a very thin layer, so that it is about a few thousand Angstroms thick. 
     In the next step, as illustrated in FIG. 3D, the photoresist layer  44  is removed, such as by using a wet chemical strip or other suitable means for removing photoresist. Once the photoresist layer  44  is removed, the seed layer  46  remains on the wafer  40  at only the area of interest  42 . 
     Once the seed layer  46  is deposited on the wafer  40  at only the area of interest  42 , further processing may be performed on the wafer  40 . For instance, the wafer  40  may undergo additional processes of patterning and etching to form any other required features of the microcomponents. As shown in FIG. 3E, one example of a patterning or etching process that may be performed on the wafer  40  is the formation of a beam  48  using deep trench reactive ion etching. Because the seed layer  46  is so thin, the seed layer  46  does not interfere with any such remaining patterning operations. 
     In a final step illustrated in FIG. 3F, a ductile material  50  is applied to the wafer  40 . Because the seed layer  46  remains only at the area of interest  42 , the ductile material  50  is deposited only at the area of interest  42  as well. As a result, wafer  40  has a partial armored coating at the area of interest  42 . 
     Though disclosed in terms of a clamping device, the present invention is suitable for use on any microcomponent or MEMS device. Furthermore, though disclosed in terms of a wafer level process, the method can likewise suitably be performed on individual components or devices. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.