Abstract:
A micro-electro-mechanical system (MEMS) seek-scan probe (SSP) memory device utilizes a protective layer over the delicate media layer to protect the media during harsh processing steps that may otherwise damage the media layer. The protective layer may comprise a layer of germanium and a layer of silicon dioxide.

Description:
FIELD OF THE INVENTION 
       [0001]    Embodiments of the present invention are directed to micro-electro-mechanical system (MEMS) fabrication and, more particularly, to a protecting the media film of a MEMS probe memory device during the fabrication process. 
       BACKGROUND INFORMATION 
       [0002]    Seek-scan probe (SSP) memories are a type of memory that uses non-volatile storage media as the data storage mechanism and offers significant advantages in both cost and performance over conventional charge-storage memories. Typical SSP memories include storage media made of materials that can be electrically switched between two or more states having different electrical characteristics such as resistance, polarization dipole direction, or some other characteristic. 
         [0003]    SSP memories are written to by passing an electric current through the storage media or applying an electric field to the storage media. Passing a current through the storage media, or applying an electric field to the media, is typically accomplished by applying a voltage between a sharp probe tip on one side of the storage media and an electrode on the other side of the storage media. Current SSP memories use probe tips positioned on a free end of one or more MEMS probes. In an idle state each MEMS probe maintains the probe tip at a certain distance from the storage media, but before the electric field or current can be applied to the storage media the probe tip must usually be brought dose to, or in some cases in direct contact with, the storage media. 
         [0004]    In order to fabricate an SSP memory device based on ferroelectric media, a high-quality media film must be deposited on virgin silicon wafers. These wafers must subsequently be subjected to many steps to create the mechanical and electrical functionality to enable the memory device. This processing may include multiple film depositions, lithography, etching, electroplating, and wafer bonding processes for example. These steps can cause significant damage to the media film by mechanical abrasion, chemical exposure, thermal treatment, etc. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The foregoing and a better understanding of the present invention may become apparent from the following detailed description of arrangements and example embodiments and the claims when read in connection with the accompanying drawings, all forming a part of the disclosure of this invention. While the foregoing and following written and illustrated disclosure focuses on disclosing arrangements and example embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and the invention is not limited thereto. 
           [0006]      FIGS. 1A-1C  are diagrams showing an illustrative SSP memory device and its basic operation; 
           [0007]      FIG. 2A-2B  are diagrams showing a mover wafer including a protective layer added prior to processing to protect the media layer according to one embodiment; 
           [0008]      FIGS. 3A-3D  are diagrams illustrating the steps taken to fabricate drive and sense circuitry on the mover wafer using a carrier wafer; 
           [0009]      FIGS. 4A-B  are diagrams illustrating the steps taken to fabricate drive and sense circuitry on the mover wafer without a carrier wafer; 
           [0010]      FIGS. 5A-5D  are diagrams illustrating attachment of a cap assembly and releasing the mover from the mover wafer; and 
           [0011]      FIG. 6  is a diagram illustrating the completed SSP memory device. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
         [0013]      FIGS. 1A-1C  illustrate tracking in a common SSP memory configuration.  FIG. 1A  illustrates an SSP memory configuration in which a cantilever probe is anchored to a substrate (the cantilever wafer), and can be actuated to contact or de-contact the storage media on a mover that carries a storage media and is positioned over the cantilever wafer. The data tracks are stored in the storage media in one of two ways, depending on how the media mover scans relative to the cantilever tips. 
         [0014]      FIG. 1B  illustrates axial scanning, where data is stored in the storage media in-line with the cantilever direction, such that the mover scans in the direction parallel to a longitudinal axis of the cantilever to read/write/erase (R/W/E) each data track. 
         [0015]      FIG. 1C  illustrates transverse scanning, where the media mover scans in a direction perpendicular to the longitudinal axis of the cantilever probe to R/W/E each data track; data is consequently stored in lines that are transverse to the cantilever&#39;s longitudinal axis. To maximize the amount of data that can be written in the storage media the data density should be very high. During the fabrication process the media is easily damaged and therefore according to embodiments, a protection layer is herein used to protect the media throughout the process. 
         [0016]      FIG. 2A  shows a mover wafer  200  including the media layer  202 . The media layer may comprise a dielectric layer, such as a layer of Lead Zirconate Titanate (PZT), for example. According to embodiments, a media protection layer is added over the media layer  202 . The protection layer comprises a germanium film  204  that is deposited on the media  202 , followed by a capping layer of silicon dioxide  206 . The Ge can be deposited by evaporation, sputtering, or chemical vapor deposition (CVD) for example. It is stable to high temperatures expected during mover processing (up to 400° C.) and can be removed selectively to the media film  202  once the mover process is completed. 
         [0017]    The germanium-based protection layer  202  provides many advantages. First, the germanium film  202  can be deposited using a variety of gentle processes such as electron beam evaporation or chemical vapor deposition that does not damage the media  202 . 
         [0018]    Second, the Ge may be removed by gentle chemical cleaning after mover processing. This can be done using hydrogen peroxide, or even hot water saturated with ozone or dissolved oxygen. 
         [0019]    Third, since Ge is a semiconductor, it is extremely stable across the range of temperatures required for mover processing (up to 400 C), Since Ge can be etched relatively easily, a cap layer of silicon dioxide  206  is proposed for protecting the Ge throughout the wet cleaning steps in the mover process. The SiO 2    204  can be dry-etched selectively to Ge prior to Ge removal at the end of the process. The Ge—SiO 2  protection layer is also very resistant to abrasion or mechanical damage due to its high hardness. 
         [0020]    Alternatives to the Ge—SiO 2  protection layer include polymers, metals, other semiconductors, glassy materials such as oxides or nitrides; however, these have various drawbacks. Fabricating the mover without using a protection layer exposes the media to extensive processes that may cause mechanical (abrasion) or chemical attack. Materials such as oxides and nitrides can be ruled out because they are typically etched using aggressive acids including Hydrofluoric acid (HF), which are not selective to the media film. Polymers normally cure or harden upon exposure to high temperature steps, and may be very difficult to remove. Metals are expected to diffuse into the media film at high temperatures, which may degrade or destroy the media properties. 
         [0021]    The Ge—SiO 2  layer,  204  and  206 , is capable of surviving the entire mover process, which significantly simplifies the process compared to having different protection layers for different steps. 
         [0022]    Still referring to  FIGS. 2A and 2B , the Ge—SiO 2  protection layer,  204  and  206  is integrated into the SSP process as follows. First, the media film  202  is deposited on virgin silicon wafers  200 . The media film  202  may then be patterned (not shown), and the Ge layer  204  and SiO 2  protection layer  206  is deposited. 
         [0023]    Referring now to  FIGS. 3A-3D , the process of creating the mover is performed using a wafer support system. As shown in  FIG. 3A , a carrier wafer  300  is bonded to the protective layer,  206  of the mover wafer  200 . In  FIG. 3B , the mover wafer  200  may be thinned using known techniques. In  FIG. 3C , mover drive/sense circuitry  302  is defined on the mover wafer  200 . In  FIG. 3D , the carrier wafer  300  (shown in the previous Figures) is removed. This processing described above may include multiple film depositions, lithography, etching, electroplating, and wafer bonding processes for example. The media film  202  is protected according to embodiments from the potentially damaging steps processes by the protective layers  204  and  206 . 
         [0024]      FIGS. 4A and 4B  show an alternative method of forming the mover without the wafer support system where the wafer is simply thinned, as shown in  4 A, and thereafter the drive/sense circuitry  302  is defined directly on the thinned wafer  200 . 
         [0025]    Referring to  FIGS. 5A-5D , a Mover-Cap assembly  500  is attached. The cap wafer  500  and mover wafer  200  are bonded together. Bond rings  502  are defined on the bottom of the mover  200  on the protective layer  204  and  206  as shown in  FIG. 5B . In  FIG. 5C , the protection layer  202  and  204  is removed. Finally, the mover  504  is released by forming a suspension by deep reactive ion etching, for example. Contacts between the media electrode and bond metal may also be formed (not shown). 
         [0026]      FIG. 6  show the completed Seek-scan probe (SSP) memory device wherein a cantilever wafer  600  including a plurality of MEMS probes  602  is attached to the mover wafer  500  and cap assembly  500 . The above process can significantly improve the yield of a probe-based memory device by ensuring the quality of the media  202  throughout the processing of the mover  504 . This can improve the manufacturability and reduce the cost, as well as reducing the time-to-market by simplifying the development cycle. 
         [0027]    The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. 
         [0028]    These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.