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
1997-12-16
2001-01-16
Everhart, Caridad (Department: 2825)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C438S688000, C438S653000
Reexamination Certificate
active
06175154
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a fully encapsulated metal lead for multi-level interconnects for semiconductor applications and to the metal lead.
2. Brief Description of the Prior Art
In the fabrication of semiconductor devices, typical cross-sectional profiles of advanced multi-level metallization leads have been in the shape of an I-beam. In general, the lead is formed over an oxide layer and is connected to silicon or the like beneath the oxide layer through a via extending through the oxide layer which is filled with tungsten. This is accomplished by depositing a layer of titanium nitride into the via and over the oxide followed by a layer of chemically vapor deposited (CVD) tungsten (W) which fills the via and may extend over the titanium nitride. The tungsten is etched back in standard manner to leave tungsten only within the via as well as a layer of titanium nitride within the via and over the oxide. A layer of titanium nitride is then deposited, followed by a layer of aluminum alloy (about 0.5% copper (Cu) and then followed by a layer of titanium nitride. The upper layer of titanium nitride is then masked and an etchant is used to etch through the layers of titanium nitride, aluminum and the titanium nitride. Since the aluminum etches more rapidly than the titanium nitride, there is provided an I-shaped lead with exposed outer aluminum surfaces having an upper anti-reflective titanium nitride layer, etc., an intermediate aluminum alloy layer and a lower barrier metal layer of titanium nitride, titanium tungsten, etc.
A problem with leads having exposed surfaces is that of electromigration, though other properties of such leads can also be improved as will be discussed hereinbelow.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a fully encapsulated metal lead for multi-level interconnect for semiconductor applications. This is achieved by a chemical vapor deposition (CVD) film formed after metal etch followed by an isotropic etch to leave the encapsulating film on the edges or sidewalls of the lead. The top and bottom encapsulation layers are deposited by physical vapor deposition (PVD) as a three layer stack film such as, for example, TiN—Al alloy-TiN. By fully encapsulating metal leads, electromigration properties are enhanced, stress induced notching is reduced and the encapsulant also can act as a diffusion barrier.
The lead is fabricated over an oxide layer and is connected to silicon or the like beneath the oxide layer through a via extending through the oxide layer which is filled with tungsten as in the prior art. This is accomplished by depositing a layer of a barrier metal, preferably titanium nitride, titanium tungsten, as well as other well known barrier metals, into the via and over the oxide followed by a layer of chemically vapor deposited (CVD) tungsten (W), aluminum-filled vias and the like which fills the via and may extend over the barrier metal. The tungsten is etched back in standard manner to leave tungsten only within the via as well as a layer of barrier metal within the via which is optionally removed and over the oxide. A layer of titanium nitride is then deposited over the existing layer of titanium nitride (any aluminum alloy with current carrying capability can also be used), followed by a layer of aluminum alloy (preferably about 0.5% copper (Cu)) (any aluminum alloy with current carrying capability can also be used) and then followed by a blanket deposition of a conformal CVD film which encapsulates the entire structure fabricated up to that point. The CVD film is preferably one of titanium nitride, tungsten, titanium, silicon nitride, etc. CVD film is then isotropically etched. The resulting structure is as in the prior art, but with a sidewall encapsulating film of the CVD material. Since the material being etch is entirely the CVD material, the I-shaped structure of the prior art is avoided and the sidewalls are essentially straight along their entire length.
The benefits derived from the above described lead are: (1) improvement in electromigration due to the stress of the encapsulating film inhibiting extrusions or accumulation of metal transported from the voided region, (2) stress induced notching is reduced due to reduced surface diffusion and (3) the encapsulation film can act as a diffusion barrier.
REFERENCES:
patent: 5332693 (1994-07-01), Kim
patent: 5909635 (1999-06-01), Manieb et al.
Donald S. Gardner, et al. “Encapsulated Copper Interconnection Devices Using Sidewall Barriers”, 8th International VMIC Conf. pp. 99-108, Jun. 1991.
Brady III W. James
Everhart Caridad
Garner Jacqueline J.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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