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.