Researchers
at Advanced Micro Devices (AMD, Sunnyvale, CA) have developed
a copper damascene process for sub.0.5 pm technologies, using
a novel electroplating method. The work, presented in June
at the VLSI Multilevel Interconnect Conference (VMIC), resulted
in in-laid copper lines with an effective resistivity below
2 cm after low-temperature annealing.
In
addition to deposition techniques based on CVD and PVD,
electroplating and electro less plating have been used to
deposit copper. The advantage of plating techniques is their
low cost, high throughput, high quality of deposited copper
film and excellent via/trench filling capability. The AMD
researchers - V.M. Dublin, C.H. Ting and R. Cheung - say
electroplating has some added advantages compared in electro
less plating in that it provides higher deposition rates,
and the electroplating solutions used for copper are more
stable and easier to control.
The
AMD work was based on a electro-chemical deposition (ECD)
process, followed by Cu chemical mechanical polishing (CMP).
Sputtered Ta was used as a barrier and adhesion promotion
layer. A Cu seed layer was sputtered with the thickness
in the range of 50-100nm. Pulse plating conditions were
used to fill trenches down to 0.25 m in width, with up to
a 4:1 aspect ratio.
Electroplated
copper lines had a very low effective resistivity of <
8 cm, and this was further decreased by about 10-15% after
low-temperature annealing. The electrical uniformity of
the film was about 2-5%, 1 sigma.
The
deposited Cu films, which largely had a <111> orientation,
were also quite pure. The contamination of various elements,
such as K, Na, C, H, O, S, N, Cl, etc, did not exceed a
few ppm for each analyzed element. The total impurity level
was below 60 ppm, about the same as that observed in PVD
Cu films.
By
manipulating the deposition conditions, the researchers
were able to achieve enhanced copper deposition at the bottom
of trenches. They were also able to change the grain structure
and grain orientation.
*Semiconductor
International August 1997 issue.
