Hermetic chip scale packaging means and method including self test

[0002] The present invention relates to integrated circuit (IC) chips, and more particularly relates to such chips having micro-electro-mechanical-systems (MEMS) included thereon, and even more particularly relates to hermetic packaging of such MEMS.

[0003] In the past, MEMS have been included on chips for numerous reasons, and MEMS have provided much functionality.

[0004] While use of the MEMS on chips has some beneficial aspects, it does have serious drawbacks. The MEMS become damaged during conventional wafer processing steps and as a result, they are typically bonded to a chip individually at the chip level. This chip level processing of MEMS is time consuming and relatively expensive.

[0005] Consequently, there exists a need for improved IC chips having MEMS thereon and for improved methods of manufacturing the same.

[0006] It is an object of the present invention to provide an improved hermetic MEMS chip package.

[0007] It is a feature of the present invention to include a hermetic cap bonded to a wafer containing numerous chips with MEMS thereon.

[0008] It is an advantage of the present invention to eliminate the need for capping of MEMS individually at the chip level.

[0009] It is another object of the present invention to provide for self-test capability of MEMS.

[0010] It is another feature of the present invention to include piezo-resistive pressure sensor for sensing pressure around the MEMS.

[0011] It is another advantage of the present invention to sense a pressure change as a result of a hermetic packaging failure.

[0012] The present invention is a hermetic MEMS chip package and method for processing the same, which is designed to satisfy the aforementioned needs, provide the previously stated objects, include the above-listed features and achieve the already articulated advantages.

[0013] Accordingly, the present invention is a hermetic MEMS chip package and method which includes providing a hermetic cap over a wafer containing numerous MEMS chips thereon.

[0014] The invention may be more fully understood by reading the foregoing description of the preferred embodiments of the invention in conjunction with the appended drawings wherein:

[0015] FIG. 1 is a simplified cross-sectional diagram of a hermetic MEMS chip level package of the present invention, which includes an enlarged MEMS cavity in which MEMS may be disposed.

[0016] FIG. 2 is a simplified cross-sectional diagram of a hermetic MEMS chip level package of the present invention, which does not include an enlarged MEMS cavity in which MEMS may be disposed.

[0017] FIG. 3 is a top view of a MEMS chip, of the present invention, which shows piezo-resistive elements disposed thereon.

[0018] Now referring to the drawings, wherein like numerals refer to like matter throughout, and more particularly to FIG. 1, there is shown a MEMS chip package 100, of the present invention, which includes a MEMS chip base die 102, which is any type of die which is well known in the art. Disposed on top of MEMS chip base die 102 is MEMS hermetic cap 104, which is a portion of a wafer cap which is milled or etched or otherwise made to have cavities therein for enclosing MEMS disposed on a wafer having many chips thereon. MEMS hermetic cap 104 is coupled to MEMS chip base die 102 by a glass bond or other known technique. Disposed between MEMS chip base die 102 and MEMS hermetic cap 104 is enlarged MEMS cavity 106 which is enlarged by cavities or depressions in MEMS hermetic cap 104 to facilitate coverage of MEMS. MEMS hermetic cap 104 has a thick region 112 and a thin region 114. The thin region 114 corresponds to a depression or cavity in MEMS hermetic cap 104 and is preferably disposed over a high profile MEMS 118.

[0019] Now referring to FIG. 2, there is shown an alternate MEMS chip package 200, of the present invention which includes a MEMS chip base die 102 and a flat MEMS hermetic cap 204, which does not have any depressions or cavities therein. Flat MEMS hermetic cap 204 is coupled to MEMS chip base die 102 by bonding material 108. Flat MEMS cavity 206 does not have an enlarged area therein for covering larger MEMS. Low profile MEMS 218 is shown disposed in flat MEMS cavity 206.

[0020] Now referring to FIG. 3, there is shown a Self test MEMS chip package 300, of the present invention, which includes a MEMS chip base die 102, a MEMS hermetic cap 104 and several piezo-resistive elements 310. Piezo-resistive elements 310 are shown disposed over the MEMS hermetic cap 104 and are capable of measuring deflections in MEMS hermetic cap 104 which are result of failures of the Self test MEMS chip package 300 to maintain a hermetic seal and bond. Piezo-resistive elements 310 are known in the art and have been used for various sensing needs, including use as an accelerometer, such as that described in U.S. Pat. No. 4,430,895, entitled Piezoresistive Accelerometer, by Russell F. Colton.

[0021] In operation, the method of the present invention includes the steps of providing a wafer having numerous integrated circuits thereon. The integrated circuits having MEMS devices incorporated therein. Providing a MEMS hermetic cap 104 with depressions therein for location over the MEMS devices. Bonding the MEMS hermetic cap 104 to the wafer using low temperature glass bonding or other known techniques. The bonding process will include creating an independent hermetic bond around the various MEMS devices. Sawing the wafer into numerous individual MEMS chip packages 100. The MEMS hermetic cap 104 may have disposed thereon piezo-resistive elements 310. Alternatively, piezo-resistive elements 310 may be added after MEMS hermetic cap 104 is bound to the wafer and before or after the wafer is cut into individual integrated circuits.

[0022] It is thought that the method and apparatus of the present invention will be understood from the foregoing description and that it will be apparent that various changes may be made in the form, construction, steps and arrangements of the parts and steps thereof, without departing from the spirit and scope of the invention or sacrificing all of their material advantages. The form herein described is merely a preferred or exemplary embodiment thereof.