Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
1994-06-06
2001-04-17
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S758000, C257S764000, C257S771000
Reexamination Certificate
active
06218733
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of semiconductor devices, and in particular, to processes for forming an intermetallic by reacting a metal with a gas and devices formed by the process.
BACKGROUND OF THE INVENTION
An intermetallic material is a material that comprises a plurality of metallic elements. Intermetallic materials, in which one of the metallic elements is a refractory metal, are used in the aviation and aerospace industries. Refractory-metal intermetallics are sometimes used in aircraft parts because of their light weight and durability compared to other metals. In the aviation and aerospace industry, refractory-metal intermetallics are usually formed at temperatures of at least 800 degrees Celsius. Such a high temperature of formation is unacceptable for the semiconductor industry. The intermetallics are usually part of a contact, interconnect, or via and are formed relatively late in a semiconductor process flow (after a silicide layer or doped regions, such as emitter or source/drain regions, have been formed). Heating a substrate to a temperature higher than about 700 degrees Celsius is generally undesired.
Within the semiconductor industry, intermetallic materials are being investigated to examine their ability to reduce electromigration and oxidation of metals within contacts or interconnects. An example of an intermetallic used in the semiconductor industry is titanium aluminide (TiAl
3
). Titanium aluminide may be formed by sputtering or evaporating a layer of aluminum, sputtering or evaporating a layer of titanium, and reacting the layers to form titanium aluminide. This method of forming titanium aluminide is actually a type of solid-solid reaction because one solid reacts with another solid.
Although the solid-solid reaction that forms titanium aluminide is typically performed at a temperature less than 700 degrees Celsius, the process suffers from several detriments. As used in this specification, intermetallic step coverage is defined as the thickness of the intermetallic layer at its thinnest point along the side of a patterned metal layer divided by the thickness of the intermetallic layer formed on the top of the patterned metal layer. The intermetallic step coverage is expressed as a percentage. Using the solid-solid reaction that forms titanium aluminide, the intermetallic step coverage is typically no more than 10 percent and may even reach 0 percent in which case, the titanium aluminide is not formed along all of the sides of the aluminum layer. Electromigration, oxidation, and hillock formation may not be sufficiently reduced in a lateral direction because of the lower intermetallic step coverage. The unreacted titanium may: 1) form undesired electrical connections because of etch complications, 2) have undesired reactions before forming or with subsequently formed layers that contact the unreacted titanium, or 3) complicated a subsequent patterning step during the formation of interconnects.
SUMMARY OF THE INVENTION
The present invention includes a process for forming an intermetallic layer by reacting a metal layer over a substrate with a metal-containing gas, wherein the metals in the layer and the gas are different. The present invention also includes a device formed using the process. In one embodiment, a titanium aluminide layer is formed by reacting an aluminum-containing layer with titanium tetrachloride, which is a gas during the reaction. The gas allows the titanium aluminide layer to be formed on exposed sidewalls of a patterned aluminum-containing layer. Different embodiments of the invention may use a furnace, a rapid thermal processor, a plasma etcher, or a sputter deposition machine for a reactor. An embodiment of the present invention forms an intermetallic layer formed while the substrate is at a temperature no higher than 700 degrees Celsius during the reaction.
Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows.
REFERENCES:
patent: 4884123 (1989-11-01), Dixit et al.
patent: 5306952 (1994-04-01), Matsuura et al.
patent: 5312775 (1994-05-01), Fujii et al.
patent: 5313101 (1994-05-01), Harada et al.
patent: 5360995 (1994-11-01), Graas
patent: 03256362 (1991-11-01), None
Filipiak Stanley M.
Fiordalice Robert W.
Kawasaki Hisao
Olowolafe Johnson Olufemi
Meyer George R.
Motorola Inc.
Potter Roy
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