A Micro-Electro-Mechanical (“MEMS”) device defines the integration of electromechanical elements on a common silicon substrate through micro-fabrication technology. The electrical elements such as complementary metal oxide semiconductor (“CMOS”) or bipolar devices are fabricated on an underlying silicon substrate using integrated circuit (“IC”) processes while the micro-mechanical components are fabricated by micro-machining processes that selectively etch away regions of the silicon substrate. The machining of the mechanical devices on the same silicon substrate results in a complete system-on-a-chip technology.
The process steps and sequences needed for MEMS can present possible vulnerabilities for the semiconductor device components of MEMS. Such problems do not arise in traditional semiconductor fabrications. For example, amorphous silicon is used for the sacrificial layer in MEMS devices. The sacrificial amorphous silicon material may directly interface with material such as aluminum which is used for the mechanical or conductive components of MEMS.
When the structure is subjected to heat treatment processes, extrusion occurs along the sidewalls of the metal line structure. Extrusion (or spiking) is the migration of metal atoms, molecules or ions into an adjacent layer such as silicon. Extrusion is a defect and can have adverse affects on the underlying device. Thus, there is a need for a method and apparatus configured to prevent spiking or extrusion of aluminum into adjacent silicon regions.
In one embodiment, the disclosure relates to a method for eliminating extrusion from a metallic atom of a MEMS device to a silicon layer of an IC wafer by providing a substrate having a MEMS structure thereon. The MEMS structure may include a metallization layer interposed between a first barrier layer and a second barrier layer. The MEMS structure may also include at least two exposed sidewalls. The method according to one embodiment of the disclosure includes depositing an oxide layer over the spacer structure to form a spacer covering each of the two sidewalls; selectively etching to remove the oxide layer while not affecting the spacers; forming a silicon layer to substantially cover the spacer structure, the metallization layer being separated from the silicon layer at each side by at least one of the spacer or the barrier layer.
In another embodiment, the disclosure relates to a method for preventing extrusion of metal along the contact walls of a MEMS device formed on a silicon wafer. The method includes providing a substrate having the MEMS structure thereon, the MEMS structure defined by a metallization layer interposed between a first barrier layer and a second barrier layer, the first barrier layer interfacing the substrate and a bottom surface of the metallization layer and the second barrier layer interfacing a top surface of the metallization layer, the MEMS structure having a top surface and at least two sidewalls; forming one or more spacer layers to conceal each of the sidewalls; and depositing a silicon layer to substantially cover the spacer structure, the metallization layer being separated from the silicon layer at each side by at least one of the spacers or the barrier layers.
In still another embodiment, the disclosure relates to a Micro-Electro-Mechanical device having electrical components formed on an integrated circuit wafer. A method for eliminating extrusion of metallic atoms of the MEMS device onto a silicon layer of the IC wafer includes providing a substrate having the MEMS structure thereon, the MEMS structure defined by a metallization layer interposed between a first barrier layer and a second barrier layer, the first barrier layer interfacing the substrate and a bottom surface of the metallization layer and the second barrier layer interfacing a top surface of the metallization layer, the MEMS structure having a top surface and at least two sidewalls; using oxygen plasma to form a plurality of spacers to cover the at least two side walls of the MEMS structure; growing amorphous silicon over the substrate to substantially cover the spacer structure, the metallization layer being separated from the amorphous silicon layer by at least one of the spacers or the barrier layers.
In yet another embodiment, the disclosure relates to preventing spiking between metallic portions of a MEMS device and an IC wafer by providing a substrate having the MEMS structure thereon, the MEMS structure defined by a metallization layer interposed between a first barrier layer and a second barrier layer, the first barrier layer interfacing the substrate and a bottom surface of the metallization layer and the second barrier layer interfacing a top surface of the metallization layer, the MEMS structure having a top surface and at least two sidewalls; using thermal oxidation to form a plurality of spacers to cover the at least two side walls of the MEMS structure; growing amorphous silicon over the substrate to substantially cover the spacer structure, the metallization layer being separated from the amorphous silicon layer by at least one of the spacers or the barrier layers.
FIGS. 1A-D illustrate a method for preventing extrusion according to one embodiment of the disclosure;
FIGS. 2A-C illustrate a method for preventing extrusion by using oxygen plasma coating; and
FIGS. 3A-C illustrate a method for preventing extrusion by using thermal oxidation to form a spacer structure.
The metallization layer 14 can be formed from aluminum, copper and alloys thereof. In one embodiment, the metallization layer comprises an alloy of AlSiCu. The metallization layer may also comprise one or more MEMS device fabricated by micro-machining processes and selectively positioned on substrate 10. The exemplary embodiment shown in
In the embodiment of
Referring now to
In
Finally, in step 1D silicon layer 20 can be deposited to substantially cover substrate 10, sidewalls 18 and barrier layers 12. The barrier layers prevent extrusion of metal atoms from the top surface of metallization layers 14 while spacers 18 protect extrusion from the sidewalls. While
FIGS. 2A-C schematically illustrate a method for preventing extrusion by using oxygen plasma coating in accordance with another embodiment of the disclosure.
According to one embodiment of the disclosure, spacers 18 are formed on the sides exposed of the MEMS device through oxygen plasma. The oxygen plasma step can be performed in situ to form a barrier layer between the MEMS device and the subsequently-deposited semiconductor wafer. The barrier can be an aluminum/oxide barrier layer. Thereafter, a silicon layer can be deposited to cover the entire structure including the MEMS device and the wafer. In one embodiment, the silicon layer is an amourphous silicon layer. In another embodiment, the amorphous silicon layer is grown on the substrate using a seed layer (not shown).
FIGS. 3A-C illustrate a method for preventing extrusion by using thermal oxidation to form a spacer structure. Specifically,
Referring to
While the principles of the disclosure have been described in relation to specific embodiments illustrated herein, it should be noted that the disclosure is not limited thereto. Accordingly, the principles of the disclosure include all permutations and variations to the embodiments presented herein and any modification thereof.