Dielectric and Barrier Properties of Spin-On Organic Aromatic Low Dielectric Constant Polymers FLARE and SiLK

Abstract

This work investigates the dielectric and barrier properties of two species of organic aromatic low dielectric constant ͑low-k͒ polymers, namely, FLARE and SiLK. Experimental results indicate that both of the low-k polymers exhibit acceptable thermal stability with respect to a thermal annealing at 400°C for 8 h in an N 2 ambient. Moreover, they show a good dielectric barrier property against Cu penetration under bias-temperature stressing ͑BTS͒ at 150°C with an applied effective field of 0.8 MV/cm. Nevertheless, an anomalous instability of the capacitance-voltage curve was observed for the first time under BTS. This finding is explained by the proposed model of stress induced dielectric polarization charges within these organic aromatic polymers. The polarization instability may seriously degrade the long term reliability of circuit operations.Interconnect wire parasitics ͑wire resistance R and intra/interlevel capacitance C͒ at 0.18 m begins to dominate not only the overall device delay but also the packing density, reliability, and manufacturing cost of integrated circuits ͑ICs͒. 1 The RC time delay must be reduced by using new materials to alleviate the problem of achieving high performance ultralarge-scale integrated ͑ULSI͒ circuits without compromising the requirements of driving speed, crosstalk tolerance, and dynamic power dissipation imposed by the small feature sizes. 2 The substitution of Cu for Al and its alloys leads to lower electrical resistivity and superior electro/stressmigration resistance, as compared to the conventional Al-based metallization scheme. However, dielectrics with low dielectric constants ͑low-k͒ must be used to reduce the parasitic capacitance, which is dominated by the interline capacitance component in long parallel lines. 3 Therefore, the process integration of Cu-based metallization and low-k dielectrics has been eagerly pursued in the prevalent Cu dual damascene architecture.Although Cu interconnects originally offered the promise of 30% faster devices with fewer metal levels and a lower cost of production, attaining high device yields on chips with Cu interconnects remains the greatest challenge, making low-k the key enabler for high performance. 4 Low-k (kϽ3.0) dielectrics are currently being actively developed and present substantial challenges on both organic ͑carbon-based͒ and inorganic (SiO 2 -based͒ materials using either spin-on ͑SO͒ or chemically vapor deposited techniques. Among various organic polymers, such as fluorinated amorphous carbon, fluorinated polyimides, poly͑arylene ether͒, and benzocyclobutene, aromatic polyether polymers have recently attracted much attention. 1,4,5 These polymers are known to possess a better thermal and mechanical stability than aliphatic polymers, resulting in improved compositional, dimensional, and topographical integrity over continuous high temperature thermal cycles. Moreover, although the integration issues concerning Cu and various low-k dielectrics have been widely addressed, most of those investigations focused on the pure...