Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1996-12-04
2001-10-23
Quach, T. N. (Department: 2814)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S653000, C438S656000
Reexamination Certificate
active
06306762
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor device having a metalized multi-layer interconnect and a method for manufacturing the semiconductor device.
2. Description of Related Art
Interconnection metalizations for interconnects of semiconductor devices, are typically formed by a single layer of an aluminum alloy, or are multi-layer metalizations. Known multilayer metalizations are composed of a bottom, refractory metal layer, such as TiN, TiW, or the like, serving as a diffusion barrier layer, and a top aluminum alloy layer. Reductions in the size of semiconductor devices has led to the use of a further metal nitride layer as a top layer of an aluminum alloy interconnect. Use of a top metal nitride layer in this manner can serve, among other purposes, to prevent irregular reflection from the aluminum alloy layer in photolithographic processes, and to prevent the occurrence of hillocks. A metal nitride layer may be formed on an aluminum alloy layer by a reactive sputtering process.
In such interconnection metalizations for semiconductor devices, a lower resistance at the boundary of the aluminum alloy layer and the metal nitride layer is desirable. However, if the surface of an aluminum alloy layer is exposed to an atmosphere containing oxygen, while the metal nitride of the top layer is being formed by reactive sputtering, an oxide layer will form on the surface of the aluminum alloy layer. Such an oxide layer serves to electrically insulate the metal nitride from the aluminum alloy. Even when the interconnection metalization is formed in a vacuum chamber, the surface of the aluminum alloy layer is nitrided by exposure to a nitrogen plasma during the reactive sputtering, which increases the electrical resistance of the boundary between the metal nitride and aluminum alloy layers.
Tests have been performed on a triple layer interconnect composed of respective layers of titanium nitride, aluminum alloy, and titanium nitride (TiN/Al alloy/TiN), to measure the effect of the bottom nitride layer on electrical resistance and electromigration. In a double layer interconnect, formed of a bottom aluminum alloy layer and a top titanium nitride layer (TiN/Al alloy), a discontinuity in the aluminum alloy layer, such as would be caused by electromigration, results in a sudden failure of the interconnect (an open circuit).
When the triple layer interconnect was tested, a sudden failure of the interconnect did not result, because the lower titanium nitride layer served as a current path. However, the bottom nitride layer serves not only as an alternate current path, but also as a diffusion barrier into which atoms diffuse from the substrate below. As a result of such diffusion, the electrical resistance of the bottom nitride layer, and thus of the current path, gradually increased until the interconnect failed.
SUMMARY OF THE INVENTION
An object of the invention is to provide a semiconductor device having a conductive multi-layer metalization, that includes an aluminum alloy layer, and that continues to conduct even if the alloy layer is severed or is otherwise nonconducting.
Another object of the invention is to provide a semiconductor device having a multi-layer interconnection metalization, wherein the metalization layer has low electrical resistivity at an interface between an aluminum alloy layer and a metal nitride layer formed thereon.
A further object of the invention is to provide a semiconductor device with a multi-layer interconnection metalization highly resistant to failure due to electromigration.
Yet another object of the present invention is to provide a method of manufacturing a semiconductor device that meets the above objects, without increasing the number of required process steps.
To achieve the above objects, there is provided a semiconductor having multi-layer metalization, the multi-layer metalization including (a) an aluminum alloy layer; (b) a metal layer formed on the alloy layer; and (c) a metal nitride layer formed on the metal layer. In a one embodiment, the metal of the metal layer and the metal of the nitride layer are both formed of the same metal, such as titanium.
Tests performed by the inventors have shown that the metal layer prevents failure of interconnects when electromigration causes a discontinuity in the aluminum alloy layer, by assuring a low resistance boundary between the metal nitride layer and the alloy layer. Greater reliability can be obtained also with interconnects formed in two or more metal nitride/metal/aluminum alloy metalization levels, with an intervening insulation layer between successive levels, wherein the aluminum alloy layers of the successive levels are in direct contact through vias in the insulation layers.
The above objects of the invention can be further achieved, by a method of manufacturing a semiconductor device having multi-layer metalization, wherein an insulating layer is formed on a surface of a semiconductor substrate, and an aluminum alloy layer is formed on the insulating layer in a first vacuum chamber, a metal layer is formed on the alloy layer in a second vacuum chamber, and a metal nitride layer is formed on the metal layer in an nitrogen atmosphere within a third vacuum chamber. Sputter methods, such as RF-bias sputtering, or other physical vapor deposition methods such as evaporation, may be used to apply the respective nitride, metal and alloy layers.
According to another aspect of the invention, wherein the same metal is used for both the metal layer and the metal nitride layer, both of these layers are applied within the same vacuum chamber. First, the metal layer is applied in an atmosphere of inert gas such as argon gas, within a vacuum chamber. Then, the vacuum chamber is evacuated and a nitrogen gas atmosphere is provided. The nitride layer then is applied in this nitrogen gas atmosphere within the same vacuum chamber.
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Fukuda Yasuhiro
Harada Yusuke
Nakamura Makiko
Onoda Hiroshi
Tatara Yasuyuki
Electric Industry Co. Ltd.
Quach T. N.
Rabin & Berdo P.C.
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