Shun-ichi Fukuyama

45 nm-node BEOL integration featuring porous-ultra-low-k/Cu multilevel interconnects

45 nm-node multilevel Cu interconnects with porous-ultra-low-k have successfully been integrated. Key features to realize 45 nm-node interconnects are as follows: 1) porous ultra-low-k material NCS (nano-clustering silica) has been applied to both wire-level and via-level dielectrics (what we call full-NCS structure), and its sufficient robustness has been demonstrated; 2) 70-nm vias have been formed by high-NA 193 nm lithography with fine-tuned model-based OPC and multi-hard-mask dual-damascene process - more than 90% yields of 1 M via chains have been obtained; 3) good TDDB (time-dependent dielectric breakdown) characteristics of 70 nm wire spacing filled with NCS has been achieved. Because it is considered that the applied-voltage (Vdd) of a 45 nm-node technology will be almost the same as that of the previous technology, the dielectrics have to endure the high electrical field. NCS in Cu wiring has excellent insulating properties without any pore sealing materials which cause either the k/sub eff/ value or actual wire width to be worse.

Advanced BEOL integration using porous low-k (k=2.25) material with charge damage-less electron beam cure technique

As a practical curing technique of low-k material for 32-nm BEOL technology node, we demonstrated that electron beam (e-beam) irradiation was effective to improve film properties of nano-clustering silica (NCS). We confirmed that by using optimized e-beam cure condition, NCS was successfully hardened without degradation of dielectric constant and the Youngs modulus increased by 1.7 times compared with that of thermally cured NCS. We fabricated two-level Cu wirings layers with NCS cured by optimized e-beam cure technique. The e-beam cure dramatically enhanced the lifetime of time-dependent dielectric breakdown (TDDB) of interlayer dielectrics. We also examined the influence of the charge damage to the MOSFETs under e-beam cured NCS layer and confirmed that there was no e-beam charge damage to the Ion-Ioff characteristics and reliability of MOSFETs with the optimized e-beam cure.

A highly reliable nano-clustering silica with low dielectric constant (k<2.3) and high elastic modulus (E=10 GPa) for copper damascene process

A highly reliable nano-clustering silica (NCS) with low dielectric constant(k<2.3) and high elastic modulus (E=10 Gpa) for copper damascene process has been developed by controlling the size and distribution of pores in the NCS precursor. Using this material in a process compatible with the 90 nm technology node, we successfully demonstrated Cu wiring in NCS dielectrics.

Plasma-Developable Electron-Beam Resists

Plasma-developable positive and negative resists with a high etching rate ratio between exposed and unexposed areas have been developed for electron-beam lithography. The negative resist systems are composed of radiation-degradation polymers such as poly-alkylmethacrylate and low molecular weight phenylsilane compounds such as triphenylsilane and diphenylsilandiol. Electron-beam exposure induces the formation of nonvolatile silicone compounds through chemical reaction between decomposition products of polyalkylmethacrylate and added silicone compound. The negative resist patterns are obtained by RIE 02 plasma development after removing the added silicone compound from unexposed areas by a relief treatment. Since the surface of the exposed area is covered with a plasma resistant layer produced from the nonvolatile silicone compound, the etching rate ratio between exposed and unexposed area is very high. The sensitivity of these resist systems depends on the glass transition temperature (Tg) of polyalkylmethacrylate and species of silicone compound. The range of sensitivity is 7 to 70 μC/cm2 and the resolution is better than 1.0 μm. These resist systems are applicable to bi-level or tri-level resist processes, and high aspect ratio patterns are obtainable. The positive resist systems comprise crosslinking polymers such as chloromethylatedpoly-styrene and the same silicone compounds. Positive resist patterns are obtained by electron-beam exposure and subsequent RIE 02 plasma development. Electron-beam exposure reduces resist film thickness by a few percent as a result of the crosslinking of polymer, then, the added silicone compound is separated as minute particles from uniformly mixed resist film. The exposed areas show less resistance to RIE 02 plasma than unexposed areas. The sensitivity of the typical resist system is about 60 μC/cm2, and resolution is 0.4 μm for 1.0 μm original resist film thickness.