Modification of low dielectric constant materials for ULSI multilevel interconnection by ion implantation

As integrated circuit (IC) dimensions continue to decrease, RC delay, cross-talk noise, and power dissipation of the interconnect structure become limiting factors for ultra-large-scale integration of integrated circuits. Low dielectric constant materials are being introduced and developed to replace silicon dioxide as inter level dielectrics into current interconnect technologies to meet RC delay goals and minimize cross-talk.; These low κ films generally have dielectric constants less than 3 (vs. 4 for silicon dioxide) and very poor mechanical strength. The elastic modulus (E) of the low κ film is typically less than 10Gpa, compared with 70Gpa for SiO₂. The poor mechanical strength of the low κ dielectric films increases the risk of thermo-mechanical failures within the Cu/low κ interconnect structure; e.g. thin film delamination and cracking. Maintaining the mechanical integrity of the low κ films with the stresses of fab processing, packaging and reliability testing has proven challenging. Therefore, surface hardening is necessary to withstand processing (e.g. CMP). This research work will address the methods to enhance the mechanical strength of low dielectric films. Results of two classes of material (i.e. Xerogel (porous) and methyl silsesquioxane (MSQ (organic)) are discussed.; Thin films of Ultra-Low κ materials such as Xerogel (κ = 1.76) and porous MSQ (κ = 2.2) were implanted with argon, neon, nitrogen, carbon and helium with 2 × 1015 cm−2 and 1 × 1016 cm−2 dose at energies varying from 20 to 150 keV at room temperature. In this work we showed that the surface hardness of the porous films can be improved five times as compared to the as-deposited porous films by implanting Ar with 1 × 10 16 cm−2 doses at 50 keV, sacrificing only a slight increase (∼15%) in dielectric constant (e.g., from 1.76 to 2.0). The hardness persists after 450°C annealing. The ion implantation process suppressed the moisture uptake in the porous low κ films. Surface chemical modification made the films hydrophobic.; The results also reveal one possible route to attain the “zero thickness” requirement for interconnect systems. It is shown that ion implantation can prevent the penetration of chemical gases such as CVD precursors into the Ultra-Low κ dielectrics during a CVD process. Surface modification of MSQ by converting its surface to a thin intrinsic barrier resembling SiO ₂ dramatically reduced Cu ion penetration into the film. Surface modification by ion implantation is therefore a powerful strategy to realize the future requirement of ultra-thin barriers. Ion implantation improved the adhesion property of Cu/Low-κ, interface.