BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1-5 are schematic diagrams illustrating a method of fabricating flow channels capable of balancing air pressure according to a preferred embodiment of the present invention.
FIGS. 6-11 are schematic diagrams illustrating a method of fabricating flow channels capable of balancing air pressure according to another embodiment of the present invention.
DETAILED DESCRIPTION
Please refer to FIGS. 1-5. FIGS. 1-5 are schematic diagrams illustrating a method of fabricating flow channels capable of balancing air pressure according to a preferred embodiment of the present invention, where FIGS. 1 and 3 are top views, and FIGS. 2, 4 and 5 are cross-sectional views. As shown in FIGS. 1-2, a device wafer 30 e.g. a silicon wafer is provided. The device wafer 30 has a front surface 32. Subsequently, a front surface process is performed upon the front surface 32 of the device wafer 30. The front surface process can be various semiconductor or MEMS processes, such as deposition, photolithography, etching and implantation processes wherever necessary. In this embodiment, the front surface process includes forming a plurality of chambers 34 on the front surface 32 of the device wafer 30. The chambers 34 may be formed by either a dry etching processes such as reactive ion etching or a wet etching process which uses an etching solution e.g. potassium hydroxide (KOH) solution or Tetramethylammonium hydroxide (TMAH) solution. It is appreciated that the chambers 34 are not conducting to each other after the etching process.
As shown in FIG. 3, a cutting process is performed using a cutter to form a plurality of flow channels 36 on the front surface 32 of the device wafer 30. The function of the flow channels 36 is to conduct the chambers 34 without influencing the structures of the chambers 34, and thus the depth of the flow channels 36 is smaller than the depth of the chambers 34. In this embodiment, the flow channels 36 are arranged longitudinally and in stripes, but not limited. The flow channels 36 can be arranged in other ways such as latitudinally, diagonally, or in matrix as long as the chambers 34 can conduct to the environment there through.
As shown in FIG. 4, a carrier wafer 40 is provided, and a bonding layer 42 is formed on the surface of the carrier wafer 40. The material of the bonding layer can be photoresist, benzocyclobutene (BCB), polyimide, wax, dry film, thermal release tape, UV tape, or any other suitable materials that can be removed subsequently by etching, heating, irradiating, etc.
As shown in FIG. 5, the front surface 32 of the device wafer 30 is adhered to the carrier wafer 40 with the bonding layer 42, and a back surface process is performed upon the device wafer 30. The bonding layer 42 is then removed to separate the carrier wafer 40 from the device wafer 30. By virtue of the flow channels 36, the chambers 34 are not sealed by the bonding layer 42 and the carrier wafer 40 in the back surface process so that the chambers 34 can conduct to the environment. The flow channels 36 keep the pressure inside the chambers 34 and the pressure outside the chambers 34 equal so that the structures of MEMS devices are not damaged in the back surface process.
Please refer to FIGS. 6-11. FIGS. 6-11 are schematic diagrams illustrating a method of fabricating flow channels capable of balancing air pressure according to another embodiment of the present invention, where FIGS. 6 and 9 are top views, and FIGS. 7, 8, 10 and 11 are cross-sectional views. As shown in FIGS. 6-7, a device wafer 50 is provided. The device wafer 50 has a front surface 52. Subsequently, a front surface process is performed upon the front surface 52 of the device wafer 50. The front surface process includes forming a plurality of chambers 54, which do not conduct to each other, on the front surface 52 of the device wafer 50.
As shown in FIGS. 8-9, a sacrificial layer 56 is formed on the front surface 52 of the device wafer 50. The sacrificial layer 56 can be a photosensitive sacrificial layer, which can be partially removed by a photolithography process to form a plurality of flow channels 58. The sacrificial layer 54 can also be non-photosensitive. In such a case, a photoresist layer (not shown) is required to dispose on the sacrificial layer 56, and photolithography and etching techniques must be used to define the flow channels 58. The flow channels 58 are formed to make the chambers 54 conduct to each other. In this embodiment, the flow channels 58 are arranged in matrix but not limited. The flow channels 58 may also be arranged in other ways such as longitudinally, latitudinally or diagonally in stripes.
As shown in FIG. 10, a carrier wafer 60 is provided, and a bonding layer 62 is formed on the surface of the carrier wafer 60. The material of the bonding layer 62 can be any adhesive materials that may be removed by etching, heating, irradiating, or other ways without damaging the device wafer 50.
As shown in FIG. 11, the front surface 52 of the device wafer 50 is adhered to the carrier wafer 60 with the bonding layer 62, and a back surface process is performed upon the device wafer 50. The bonding layer 62 is removed subsequent to the back surface process to separate the carrier wafer 60 from the device wafer 50. By virtue of the flow channels 58, the chambers 54 are not sealed by the bonding layer 62 and the carrier wafer 60 in the back surface process so that the chambers 54 can lead to the environment. The flow channels 58 keep the pressure inside the chambers 54 and the pressure outside the chambers 54 equal so that the structures of MEMS devices are not damaged in the back surface process.
The method of the present invention forms the flow channels able to release the air pressure inside the chambers, and therefore the structures of MEMS devices will not be damaged due to pressure difference in the back surface process. Consequently, the method of the present invention can improve the yield of double side process, and particularly for the double side process which uses a thin wafer of a thickness less than 200 micrometers. In addition, the method of the present invention used a carrier wafer to support the device wafer. The carrier wafer is compatible with current wafer delivery configurations, and therefore the delivery configurations do not have to be redesigned.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Patent Application
20080096137
