Patent Application
20070090479
Microelectromechanical systems (MEMS) are micron-size devices widely used in many electronic applications, such as televisions, projection systems, and other optical applications. MEMS devices are created using micro machining processes like those used to produce integrated circuits. This allows two or three dimensional mechanical systems to be created in the same small area typical of an integrated circuit. Because the manufacturing processes are similar to an integrated circuit, MEMS devices are most often created on semiconductor wafers. In this way, thousands of MEMS devices can be fabricated onto a single wafer.
Semiconductor wafers are often fabricated (i.e., packaged) using a bonding technique known as plasma-enhanced bonding. During plasma-enhancement, the mating surfaces of the semiconductor wafers are subjected to a brief plasma treatment and then further processed prior to being assembled. Semiconductor substrates joined by plasma-enhancement are bonded directly at the atomic level with robust covalent bonds. In the case of MEMS packaging for optical applications, a glass substrate is bonded directly to an MEMS optical wafer to hermetically seal all MEMS devices contained therein. The plasma bonding process begins at the point of contact between the two substrates. In other words, a bond front that seals the substrates together propagates from the point of contact between the glass and the optical MEMS wafer until the entire area between the glass and optical wafer is bonded. Therefore, for purposes of this application, a bond front refers to the leading edge of the bonding process as it propagates to join two substrates.
A known approach to wafer bonding includes a wafer bonding machine that assembles the glass substrate to the optical wafer using a generally planar pressure plate. Generally, the bonding machine bows the center of the glass substrate so that when the glass and the optical wafer are assembled together by the pressure plate, the initial point of contact between them is at the center. In this way, the propagation of the bond front starts at the center of the wafer and propagates outward. This method works well for some bonding techniques; however, for pre-trenched glass substrates that are often used in optical MEMS applications, the trenches in the glass interrupt the bond front making the bond front propagation chaotic and unpredictable. In other words, when a portion of a propagating bond front reaches a trench, the trench tends to form a barrier that prevents further propagation of that portion of the bond front. Further, when a bond front stalls at a trench, but continues to propagate in other sections of the wafer, the bond front begins to propagate in multiple directions causing uncontrolled propagation. In many cases, the uncontrolled bond front results in trapped air pockets between the MEMS optical wafer and the glass substrate. The air pockets can cause hermeticity or optical issues and ultimately degrade the optical interface quality of the resulting MEMS device.
The embodiments described hereinafter were developed in light of these and other drawbacks associated with bond front propagation in wafer-scale packaging.
The present embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:
A generally planar bonder pressure plate having protruded structures for controlling bond fronts in wafer-scale packaging is provided. Wafer-scale packaging generally involves initiating a point of contact between two substrates using a bonder pressure plate. In an exemplary embodiment, the protruded structures on the bonder pressure plate are configured to selectively initiate bond fronts in selected areas of the wafer to control the bond front propagation. By selectively initiating the points of contact and controlling the bond fronts, air pockets due to uncontrolled multiple bond fronts are reduced.
The bonder pressure plates disclosed herein are used in conjunction with a variety of bonding techniques, including, but not limited to plasma-enhanced and hydrophilic bonding. However, for purposes of illustration, the bonder pressure plates disclosed herein are explained with reference to a plasma-enhanced bonding application.
Unfortunately, as shown in
Referring to
Further, the bonder pressure plate 46 of
Alternatively, the protruded structures that establish the points of contact between two substrates may be selectively positioned on one of the substrates themselves, rather than on the bonder pressure plate. In this case, the protruded structures may be positioned according to the bonder pressure plate configurations described above, or may be arranged according to other design criteria.
While the present invention has been particularly shown and described with reference to the foregoing preferred embodiment, it should be understood by those skilled in the art that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention without departing from the spirit and scope of the invention as defined in the following claims. It is intended that the following claims define the scope of the invention and that the method and system within the scope of these claims and their equivalents be covered thereby. This description of the invention should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. The foregoing embodiment is illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application. Where the claims recite “a” or “a first” element of the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.
