Effect Of Trapping On Dielectric Conduction Mechanisms Of ULK/Cu Interconnects

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1156-D01-04

Effect of trapping on dielectric conduction mechanisms of ULK/Cu interconnects V. Verrière1,2, C. Guedj2, D. Roy1, S. Blonkowski1, A. Sylvestre3 STMicroelectronics 850 rue J. Monnet 38926 Crolles Cedex France 2 CEA-Leti MINATEC 17 avenue des Martyrs 38054 Grenoble Cedex France 3 Grenoble Electrical Engineering Lab. (G2ELab) CNRS 25 avenue des Martyrs BP166 38042 Grenoble Cedex 9 France 1

ABSTRACT Trapping in low-κ dielectric for interconnects was highlighted by voltage shift in IV current-voltage measurements. It is shown that effects of trapping can impact the extraction of conduction mechanisms. Capacitance measurements made on these materials reveal that trapping is at the origin in the increase of capacitance. The creation of dipoles because of this trapping explains this increase in the value of capacitance. INTRODUCTION The drastic reduction of intra-level Metal-Metal spacing in advanced interconnects poses concern for reliability linked to the dielectric integrity. The Low-κ dielectric materials which compose the dielectric stack are the site of leakage currents under electric stress. These leakage currents damage the materials to the breakdown. The knowledge of the mechanisms linked to the leakage currents is a key to explain the damaging. Nevertheless the dielectric materials are composed of many defects, which can be active for conduction or just have a role of traps. Characterization of all these defects is an issue to establish the good diagnose of defectivity. Trapping had been already put in evidence in such structures [1]. We propose an analysis of trapping impact through leakage currents and capacitance measurements. EXPERIMENT Test structures were fabricated with an advanced Cu/ Low-κ process with 45 nm node processes (Figure 1). Measurements were performed on comb-comb test structures (Figure 2). Leakage currents against field are measured by sweep IV with different speeds of voltage. Dynamical behavior is studied by impedance spectroscopy for frequencies between 10-2 Hz and 103Hz. A sinusoidal voltage Vrms=0.5 V is applied. Measurements have been performed against temperature (between 100°C and 200°C).

Cu

SiCN εr=5

s

SiCOH εr=2,5

Ta/TaN

SiCN εr=5

Figure 1. TEM cross sectional view of structures. SiCOH is porous with a porosity of about 30%.

Figure 2. Test structures are interdigited combs structures. Space s between lines is 70 nm.

RESULTS AND DISCUSSION Measurement of leakage current against applied field and effect of trapping Trapping takes place in virgin structures from the application of an electric stress. In this part its impact is studied during measurement of leakage currents. If two successive sweeps are performed, a voltage shift to high fields is observed between the two curves (Figure 3). On the other hand, the voltage speed has no influence on the value of the current. 1E-4 1E-5

st

1 sweep

2

J (A/cm )

1E-6 1E-7

nd

2 sweep Shift ∆E

1E-8

0,1V/s 1V/s

1E-9 1E-10 0

1

2

3

E (MV/cm)

Figure 3. Leakage current measured by two successive sweeps at 125°C

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