Introduction
Chemical mechanical polishing (CMP) is a widely used technique for the planarization of metal and dielectric films to accomplish multilevel
metallization. The fabrication of these layers without defects requires significant improvements in the CMP process. The success of CMP operations
depends on the rate of material removal and the quality of the surface finish. The need to study copper inhibitors for CMP slurries is essential in
order to achieve better performance of Cu CMP in future technology nodes.
K-SORBATE AS A PASSIVATOR IN COPPER CHEMICAL
MECHANICAL PLANARIZATION (CMP) SLURRIES M. Nagar 1, J. Vaes 2, Y. Ein-Eli1
1. Corrosion & Applied Electrochemistry Laboratory (CAE), Department of Materials Engineering, Technion , Israel Institute of Technology, Haifa 32000, Israel 2. IMEC, Kapeldreef 75, B-3001 Leuven, Belgium
This study examines an application of a new inhibitor, potassium sorbate K[CH3CH=CHCH=CHCO2] in copper CMP slurries. CMP slurry
composition was engineered in order to have a substantial copper removal, without compromising the capability to produce enhanced copper
passivity. CMP results obtained on patterned wafers are presented illustrating the effect of sorbate concentration on CMP performance.
Sorbate characteristics
The interesting ability of sorbate ion to protect copper surface is ascribed mainly to the
primer encoring carboxylate group. After absorption, this would cause alignment of the
dissolved short chain, normal to the copper surface, thus producing a thin, compact and
protective layer. Figure 1 presents anodic polarizations of copper with and without sorbate.
The constant current density over wide potential range implies an impressive stability of
sorbate protective film. Comparable anodic polarization without sorbate is presented as well, exhibiting an active dissolution of copper and higher current densities at E(OCP) .
O
O
Results
Copper CMP performance with patterned wafers is presented, showing
the importance in having a good passivator during CMP process: Figure 2
shows a decrease in dishing values with an increase in sorbate
concentration. Figure 3 presents SEM images of 90nm Meander fork,
showing dissolution of copper along lines with low sorbate concentration.
Figure 4 shows optic microscope images of copper bonpads, illustrating
higher polishing uniformity in high sorbate concentration.
Sorbate solution shift to
noble region
Constant current density
over wide potential range
Complexing
agent
Without
sorbate
Figure 1 :Anodic polarizations of copper with and without sorbate.
wafer performance
0.03M sorbate 1.7M sorbateFigure 3
HRP Scan of VDP80µm2 structure
Dishing vs K-sorbate concentration
Figure 2
polishing Uniformity
0.03M sorbate 1.7M sorbate
Figure 4
Cen
ter
die
Ed
ge d
ie
Cu lossCu dished out
Summary and conclusions
CMP results obtained on blanket and patterned wafers illustrate the effect of sorbate concentration on CMP performance: an increased sorbate
concentration in model Cu slurries provides lower dishing values of copper in patterned wafers.
The high solubility of sorbate in water (up to 9Molar) is a major advantage for CMP processing. A further reduction of the dishing values can be
expected when using higher concentrations of dissolved sorbate in the slurry.
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