Si-rich surface layer capped diffusion barriers

Details Si-rich surface layer capped diffusion barriers Si-rich surface layer capped diffusion barriers

2002-06-28

2004-01-20

Picardat, Kevin M. (Department: 2822)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S654000, C438S685000, C438S786000

Reexamination Certificate

active

06680249

ABSTRACT:

FIELD OF THE INVENTION
The invention is generally related to the field of interconnect layers in semiconductor devices and more specifically to diffusion barriers for copper interconnect layers.
BACKGROUND OF THE INVENTION
As the density of semiconductor devices increases, the demands on interconnect layers for connecting the semiconductor devices to each other also increases. Therefore, there is a desire to switch from the traditional aluminum metal interconnects to copper interconnects. Unfortunately, suitable copper etches for a semiconductor fabrication environment are not readily available. To overcome the copper etch problem, damascene processes have been developed.
In a damascene process, the IMD is formed first. The IMD is then patterned and etched. The barrier layer
14
and a copper seed layer are then deposited over the structure. The barrier layer
14
is typically tantalum nitride or some other binary transition metal nitride. The copper layer is then formed using the seed layer over the entire structure. The copper is then chemically-mechanically polished (CMP'd) to remove the copper from over the IMD
16
, leaving copper interconnect lines
18
as shown in
FIG. 1. A
metal etch is thereby avoided.
Barrier layer
14
is required because copper has high diffusivity into dielectrics. Unfortunately, conventional diffusion barriers have limited wettability (adhesion) with copper. This causes voids in the copper during the via fill and negatively impacts the electromigration performance. Metal-silicon-nitrides have better wetting properties. Unfortunately, current methods of forming these metal-silicon-nitrides are difficult to perform and result in a film having high resistivity.
Another approach is to combine a layer of TaN with a layer of Ta. TaN provides good adhesion to FSG (fluorine-doped silicate glass) but poor adhesion to copper. Ta provides a good adhesion to copper but poor adhesion to FSG. Unfortunately, when the TaN/Ta stack is used, fluorine dopants diffuse through the TaN to react with the Ta to form TaF. TaF is volatile and tends to peel off. Thus, an improved barrier for copper interconnects is desired.
SUMMARY OF THE INVENTION
The invention is a copper interconnect having a transition metal-nitride barrier with a thin metal-silicon-nitride cap. A transition metal-nitride barrier is formed over the structure. Then the barrier is annealed in a Si-containing ambient to form a silicon-rich capping layer at the surface of the barrier. The copper is then deposited over the silicon-rich capping layer.
An advantage of the invention is providing a diffusion barrier with improved adhesion with copper with low resistance.
This and other advantages will be apparent to those of ordinary skill in the art having reference to the specification in conjunction with the drawings.


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Wolf, Stanley, “Silicon Processing for the VLSI Era,” vol. 2, Lattice Press 1990, p. 132.

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