Structural and Electrical Characterization of Si-Implanted TiN as a Diffusion Barrier for Cu Metallization
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increase in the leakage current of a reverse biased diode. This is one of the most sensitive techniques for evaluating the effectiveness of Cu diffusion barriers. Pn-diodes were fabricated in Si and metallized with unimplanted or Si28 implanted TiN and Cu. The diode junction areas were approximately 25p.m2 with 2ptm diameter contacts. TiN was formed by PVD of 45nm Ti followed by rapid thermal processing (RTP) at 800°C/30s in NH 3 . Samples were exposed to air between PVD-Ti and RTP. Samples were then implanted with Si 28, 10keV, 0.5-5xl0 16 ions/cm 2 at 00 tilt. Implantation was performed on a Varian/Extrion E220 implanter which uses a parallel beam scan. This allowed the contact bottom to be implanted without shadowing from the sidewalls. The barrier was patterned with standard lithography/etch techniques in preparation for selective CVD-Cu deposition. Non-patterned areas were used for composition analysis by Auger electron spectroscopy (AES) and for the determination of barrier crystallinity by plan view transmission electron microscopy (TEM). Patterned diodes were metallized with CVD-Cu from CupraSelect, a Cu+ 1 precursor,
provided by Schumacher, a division of Air Products Inc.. AES depth profile analysis was performed using a 3keV argon sputtering beam and a 5keV primary electron beam. TEM analysis was carried out using an accelerating voltage of 300keV. Results and Discussion Figure 1 shows current-voltage characteristics of Cu/TiN (unimplanted) diodes after a 15 minute anneal at 500'C. The reverse leakage current of unannealed diodes was less then 20nA at -1.0V for both implanted and unimplanted samples. The reverse leakage current of the Cu/TiN/Si increased to greater than IltA after 15minutes at 5000 C indicating failure of the barrier. However, samples of Cu/TiN implanted with Si, 5xl0 16 ions/cm 2 did not show an increase in leakage current until after 2 hours at 500'C (Figure 2). The onset of failure was followed by rapid degradation of the diodes rectifying behavior independent of the barrier preperation method.
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Figure 1. I-V curve of pn-/ diode metallized with Cu/TiN (unimplanted) after a 15 minute anneal at 500 0 C. The reverse leakage current has increased from less than 20nA to greater than I 2A at -I.OV.
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Plan view TEM bright field images and selected area diffraction patterns of unimplanted and Si-implanted TiN are shown in Figure 3a) and b) respectively. The unimplanted TiN is a cubic polycrystalline film with an average grain diameter of 40nm. After ion implantation of the same film with Si (5xl0 16 ions/cm 2 ) the layer amorphized. Th
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